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  • 301.
    Ahlström, Johan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Björklund, Jacob
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Reglering av energikostnader med hjälp av energilagring i Danmark2014Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Energilagring med hjälp av tryckluft (CAES) innebär att luft komprimeras och lagras för att expanderas vid ett senare tillfälle. Tillsammans med pumpkraftverk (pumpning av vatten till en högre liggande vattenreservoar) är komprimerad luft (CAES) de enda kommersiellt gångbara storskaliga energilagringsteknologierna i dagsläget. Utifrån de geologiska förutsättningarna i Danmark utvärderades lönsamheten för två olika typer av CAES-teknologier mer specifikt som teknologi för energihandel.

    Danmark medverkar i den nordiska elmarknaden och elhandeln sker genom Nord Pool Spot (Elspot) där elpriset fastställs för var timme, dagen innan. Den dagliga prisvariationen år 2013 kunde, utifrån en empirisk analys av max- och minelpris, analyseras där elpriset var särskilt högt respektive särskilt lågt. Huvudmålet med denna rapport var därför att undersöka intäktsmöjligheter genom att med vald energilagringsteknik lagra energi vid lågt elpris för att senare sälja denna energi vid ett högt elpris.

    I dagsläget finns två CAES-anläggningar; en i Huntorf, Tyskland samt en i Alabama, USA. Ett antal olika fall undersöktes i rapporten. Fyra stycken fall, H1, H2, H3 och H4 ingår i ”Dagens scenario” med liknande och modifierad prestanda som den konventionella CAES-kraftanläggningen i Huntorf. Konventionella CAES-anläggningar använder naturgas i förbränningskammaren för att värma upp luften innan expansionsfasen för att förhindra frysning av turbinerna. Två ytterligare fall, A1 och A2 ingår “Framtidens scenario” som baseras på information från ett projekt kring en planerad avancerad adiabatisk anläggning vid namn ADELE, av energiföretaget RWE i Tyskland.

    Lönsamheten för Fall H1 beräknades utifrån anläggningen i Huntorfs ursprungliga prestanda med en kompressorkapacitet på 60 MW och en total uteffekt på 290 MW och upp-och urladdningstid på 4 respektive 2 timmar. Fall H2 liknar fall H1 med enda skillnaden att naturgaskonsumtionen antas vara 25 % lägre med införandet av en rekuperator. Fall H3 har en antagen kompressorkapacitet på 480 MW och uteffekt på 580 MW vilket ger en upp-urladdningstid på 1 respektive 1 timme. Fall H4 liknar H3 förutom att naturgaskonsumtionen är 25 % lägre med en med hjälp av en rekuperator. Fall A1 utgår från en upp- och urladdningstid på 8 respektive 4 timmar med en kompressorkapacitet på 200 MW och uteffekt på 260 MW. Fall A2 antas ha en kompressorkapacitet på 1600 MW och uteffekt på 1040 MW vilket ger en upp- och urladdningstid på en respektive en timme.

    Den ekonomiska beräkningsmodellen utgjörs av två olika investeringskalkyleringar, nuvärdes- och paybackmetoden. Genomförda beräkningar ger att investeringar enligt de betraktade CAES-fallen utifrån givna antaganden inte är lönsamma utifrån de estimerade ekonomiska och tekniska livslängderna. Nettonuvärdeskvoten för de olika fallen sträckte sig från -1 för fall H1 till -0,88 för fall A1. Återbetalningstiden sträckte sig från ingen återbetalningstid alls (fall H1) till 113 år för fall A1.

    De ekonomiska beräkningarna bör anses som grovt uppskattade och bör endast fungera som en antydan kring den framtida potentialen för CAES som medel för energihandel. Känslighetsanalysen påvisade för de fall som utgick från den konventionella CAES-anläggningen i Huntorf att en sänkning av naturgaspriset gav en stor positiv inverkan på lönsamheten. Generellt för alla de olika fallen var att en minskning av grundinvestering, drifts- och underhållskostnader och fler dagar med större prisvariation gjorde CAES-fallen mer lönsamma.

    Avancerade adiabatiska CAES-anläggningar, med nödvändiga tekniska framsteg, kan potentiellt bli en del i en framtida hållbar utveckling. 

  • 302.
    Ahlström, Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell ekonomi och organisation (Inst.), Entreprenörskap och Innovation.
    Framtiden för Svensk TV: Hur hanteraran den förändring av marknaden för TVsom följer med internet2013Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [sv]

    Marknaden för TV håller på att förändras. Mer och mer tittande flyttar från den traditionella TV-rutan till mobila plattformar och online tittande. De svenska kanalhusen så som TV4-gruppen, SBS, SVT och MTG har följt med i denna trend och levererar TV direkt till tittarna genom sina respektive  Play  tjänster.  Denna  underökning  tittar  på  hur  denna  tekniska  förändring  påverka marknaden från både ett konsument och affärsperspektiv.

    Studien grundar sig på ett teoretiskt ramverk samt empiriska studier hos aktörer på marknaden. De huvudsakliga teorierna som har använts för denna studie är affärsmodellers roll i att plocka upp nedärvda värden i ny teknologi, hur man hanterar teknologisk förändring i organisationer samt dominant design.

    Denna undersökning visar på att de tidigare distributörerna redan idag hotas av att ersättas antingen direkt av kanalhusen eller nya distributörer då man inte längre har ett naturligt monopol på sina konsumenter. Vidare visar studien att hur man ska implementera framgångsrika affärsmodeller kring  rättigheter  då  tittare  potentiellt  konsumerar  innehåll  på  ett   annorlunda  vis   genom online-tjänster är en mycket komplex fråga.

  • 303.
    Ahmad, Aftab
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Effective development of haptic devices using a model-based and simulation-driven design approach2014Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Virtual reality (VR)-based surgical simulators using haptic devices can increase the effectiveness of surgical training for surgeons when performing surgical procedures in hard tissues such as bones or teeth milling. The realism of virtual surgery through a surgical simulator depends largely on the precision and reliability of the haptic device, which reflects the interaction with the virtual model. The quality of perceptiveness (sensation, force/torque) depends on the design of the haptic device, which presents a complex design space due to its multi-criteria and conflicting character of functional and performance requirements. These requirements include high stiffness, large workspace, high manipulability, small inertia, low friction, high transparency, and cost constraints.

    This thesis proposes a design methodology to improve the realism of force/torque feedback from the VR-based surgical simulator while fulfilling end-user requirements.

    The main contributions of this thesis are:

    1. The development of a model-based and simulation-driven design methodology, where one starts from an abstract, top-level model that is extended via stepwise refinements and design space exploration into a detailed and integrated systems model that can be physically realized.

    2. A methodology for creating an analytical and compact model of the quasi-static stiffness of a haptic device, which considers the stiffness of actuation systems, flexible links and passive joints.

    3. A robust design optimization approach to find the optimal numerical values for a set of design parameters to maximize the kinematic, dynamic and kinetostatic performances of a 6-degrees of freedom (DOF) haptic device, while minimizing its sensitivity to variations in manufacturing tolerances and cost, and also satisfying the allowed variations in the performance indices.

    4. A cost-effective approach for force/torque feedback control using force/torque estimated through a recursive least squares estimation.

    5. A model-based control strategy to increase transparency and fidelity of force/torque feedback from the device by compensating for the natural dynamics of the device, friction in joints, gravity of platform, and elastic deformations.

     

  • 304.
    Ahmad, Aftab
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Kinematisk och dynamisk modellering av den haptiska enheten TAU i sex frihetsgrader2009Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The thesis presents an optimally designed kinematic structure for a new 6-DOF haptic device

    based on TAU configuration. The configuration of the TAU-2 proposed by Suleman Khan and

    Kjell Andersson [1] was modified and its mobility was verified by using Grübler criterion to

    have a 6 DOF. Analytical kinematic models for the inverse and forward kinematics were

    developed for the haptic TAU configuration to determine a set of optimal design parameters.

    Kinematic performance indices such as volume of the workspace, kinematic isotropy and pay

    load index, were defined based on the singular values of the Jacobian matrix. The Jacobian

    matrix was scaled to homogenize the physical units. The Jacobian matrix dependent on the

    position and orientation of the end-effector gives local isotropy and pay load index, so global

    design indices were defined, which represent the performance of the mechanism in the whole

    workspace. A multi-objective function was defined based on the minimum of the global design

    indices in order to find a set of optimal design parameters. Genetic algorithm (GA) was used for

    optimization due to the nonlinearity of the multi-objective function. The optimal design

    parameters were obtained by minimizing the payload index while maximizing the volume index

    and isotropy indices.

    A close form dynamic model was developed using Lagrange mechanics to describe the dynamic

    behavior of the configuration. A trigonometric helical trajectory was developed in Cartesian

    space for each degree of freedom for the moving platform while moving along the trajectory

  • 305.
    Ahmad, Aftab
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Andersson, Kjell
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Sellgren, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    A comparative study of friction estimation and compensation using extended, iterated, hybrid, and unscented kalman filters2013Inngår i: Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference - 2013, ASME Press, 2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Transparency is a key performance evaluation criterion for haptic devices, which describes how realistically the haptic force/torque feedback is mimicked from a virtual environment or in case of master-slave haptic device. Transparency in haptic devices is affected by disturbance forces like friction between moving parts. An accurate estimate of friction forces for observer based compensation requires estimation techniques, which are computationally efficient and gives reduced error between measured and estimated friction. In this work different estimation techniques based on Kalman filter, such as Extended Kalman filter (EKF), Iterated Extended Kalman filter (IEKF), Hybrid extended Kalman filter (HEKF) and Unscented Kalman filter (UKF) are investigated with the purpose to find which estimation technique that gives the most efficient and realistic compensation using online estimation. The friction observer is based on a newly developed friction smooth generalized Maxwell slip model (S-GMS). Each studied estimation technique is demonstrated by numerical and experimental simulation of sinusoidal position tracking experiments. The performances of the system are quantified with the normalized root mean-square error (NRMSE) and the computation time. The results from comparative analyses suggest that friction estimation and compensation based on Iterated Extended Kalman filter both gives a reduced tracking error and computational advantages compared to EKF, HEKF, UKF, as well as with no friction compensation.

  • 306.
    Ahmad, Aftab
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Andersson, Kjell
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Sellgren, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    A deterministic and probabilistic approach for robust optimal design of a 6-DOF haptic device2014Inngår i: Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference--2013: Volume 3 B, 2013, ASME Press, 2014, s. V03BT03A032-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This work suggests a two-stage approach for robust optimal design of 6-DOF haptic devices based on a sequence of deterministic and probabilistic analyses with a multi-objective genetic algorithm and the Monte-Carlo method. The presented model-based design robust optimization approach consider simultaneously the kinematic, dynamic, and kinetostatic characteristics of the device in both a constant and a dexterous workspace in order to find a set of optimal design parameter values for structural configuration and dimensioning. Design evaluation is carried out based on local and global indices, like workspace volume, quasi-static torque requirements for the actuators, kinematic isotropy, dynamic isotropy, stiffness isotropy, and natural frequencies of the device. These indices were defined based on focused kinematic, dynamic, and stiffness models. A novel procedure to evaluate local indices at a singularity-free point in the dexterous workspace is presented. The deterministic optimization approach neglects the effects from variations of design variables, e.g. due to tolerances. A Monte-Carlo simulation was carried out to obtain the response variation of the design indices when independent design parameters are simultaneously regarded as uncertain variables. It has been observed that numerical evaluation of performance indices depends of the type of workspace used during optimization. To verify the effectiveness of the proposed procedure, the performance indices were evaluated and compared in constant orientation and in dexterous workspace.

  • 307.
    Ahmad, Aftab
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Andersson, Kjell
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Sellgren, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    A model-based and simulation driven design approach for haptic devices2013Inngår i: Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference--2013, ASME Press, 2013, s. V02BT02A014-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The output from a design process of high precision and reliable haptic devices for surgical training like bones and teeth is a complex design. The complexity is largely due to the multi-criteria and conflicting character of the functional requirements. These requirements include high stiffness, large workspace, high manipulability, small inertia, low friction, and high transparency. The requirements are a basis for generating design concepts. The concept evaluation relies to a large extent on a systematic usage of kinematic, dynamic, stiffness, and friction models. The design process can benefit from a model-based and simulation driven approach, where one starts from an abstract top-level model that is extended via stepwise refinements and design space exploration into a complete realization of the system. Such an approach is presented and evaluated through a test case where a haptic device, based on a Stewart platform, has been designed and realized. It can be concluded, based on simulation and experimental results that the performance of this optimally designed haptic device satisfies the stated user requirements. This indicates that the methodology can support the development of an optimal haptic device. However, more test cases are needed to further verify the presented methodology.

  • 308.
    Ahmad, Aftab
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Andersson, Kjell
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinelement.
    Sellgren, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinelement.
    An approach to stiffness analysis methodology for haptic devices2011Inngår i: 2011 3rd International Congress on Ultra Modern Telecommunications and Control Systems and Workshops (ICUMT), IEEE conference proceedings, 2011, , s. 8s. 1-8Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this work a new methodology is proposed to model the static stiffness of a haptic device. This methodology can be used for other parallel, serial and hybrid manipulators. The stiffness model considers the stiffness of; actuation system; flexible links and passive joints. For the modeling of the passive joints a Hertzian contact model is introduced for both spherical and universal joints and a simply supported beam model for universal joints. For validation of the stiffness model a modified JP Merlet kinematic structure has been used as a test case. A parametric Ansys FEM model was developed for this test case and used to validate the resulting stiffness model. The findings in this paper can provide an additional index to use for multi-objective structural optimization to find an optimum compromise between a lightweight design and the stiffness performance for high precision motion within a larger workspace.

  • 309.
    Ahmad, Aftab
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Andersson, Kjell
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Sellgren, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    An Optimization Approach Toward a Robust Design of Six Degrees of Freedom Haptic Devices2015Inngår i: Journal of mechanical design (1990), ISSN 1050-0472, E-ISSN 1528-9001, Vol. 137, nr 4, artikkel-id 042301Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work presents an optimization approach for the robust design of six degrees of freedom (DOF) haptic devices. Our objective is to find the optimal values for a set of design parameters that maximize the kinematic, dynamic, and kinetostatic performances of a 6-DOF haptic device while minimizing its sensitivity to variations in manufacturing tolerances. Because performance indices differ in magnitude, the formulation of an objective function for multicriteria performance requirements is complex. A new approach based on Monte Carlo simulation (MCS) was used to find the extreme values (minimum and maximum) of the performance indices to enable normalization of these indices. The optimization approach presented here is formulated as a methodology in which a hybrid design-optimization approach, combining genetic algorithm (GA) and MCS, is first used. This new approach can find the numerical values of the design parameters that are both optimal and robust (i.e., less sensitive to variation and thus to uncertainties in the design parameters). In the following step, with design optimization, a set of optimum tolerances is determined that minimizes manufacturing cost and also satisfies the allowed variations in the performance indices. The presented approach can thus enable the designer to evaluate trade-offs between allowed performance variations and tolerances cost.

  • 310.
    Ahmad, Aftab
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Kjell, Andersson
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Sellgren, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    A model-based and simulation-driven methodology for design of haptic devices2014Inngår i: Mechatronics (Oxford), ISSN 0957-4158, E-ISSN 1873-4006, Vol. 24, nr 7, s. 805-818Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High precision and reliable haptic devices are highly complex products. The complexity that has to be carefully treated in the design process is largely due to the multi-criteria and conflicting character of the functional and performance requirements. These requirements include high stiffness, large work-space, high manipulability, small inertia, low friction, high transparency, as well as cost constraints. The requirements are a basis for creating and assessing design concepts. Concept evaluation relies to a large extent on a systematic usage of kinematic, dynamic, stiffness, friction, and control models. The design process can benefit from a model-based and simulation-driven approach, where one starts from an abstract top-level model that is extended via stepwise refinements and design space exploration into a detailed and integrated systems model that can be physically realized. Such an approach is presented, put in context of the V-model, and evaluated through a test case where a haptic device, based on a Stewart platform, is designed and realized. It can be concluded, based on simulation and experimental results that the performance of this deterministically optimized haptic device satisfies the stated user requirements. Experiences from this case indicate that the methodology is capable of supporting effective and efficient development of high performing haptic devices. However, more test cases are needed to further validate the presented methodology.

  • 311.
    Ahmad, Aftab
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Kjell, Andersson
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Sellgren, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    An optimization approach towards a robust design of 6-DOF haptic devicesManuskript (preprint) (Annet vitenskapelig)
  • 312.
    Ahmad, Aftab
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Kjell, Andersson
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Sellgren, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Model-based control strategy for 6-DOF haptic devicesManuskript (preprint) (Annet vitenskapelig)
  • 313.
    Ahmad, Aftab
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Kjell, Andersson
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Sellgren, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Boegli, Max
    Evaluation of friction models for haptic devices2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this work different friction models are evaluated to determine how well these models are suited for performance simulation and control of a 6-DOF haptic device. The studied models include, Dahl model, LuGre model, Generalized Maxwell slip model (GMS), smooth Generalized Maxwell slip model (S-GMS) and Differential Algebraic Multistate (DAM) friction model. These models are evaluated both numerically and experimentally with an existing 6-DOF haptic device that is based on a Stewart platform. In order to evaluate how well these models compensate friction, a model-based feedback friction compensation strategy along with a PID controller were used for position fracking accuracy The accuracies of the friction compensation models are examined separately for both low-velocity and high-velocity motions of the system. To evaluate these models, we use criteria based on fidelity to predict realistic friction phenomena, easiness to implement, computational efficiency and easiness to estimate the model parameters. Experimental results show that friction compensated with GMS, S-GMS and DAA4 models give better accuracy in terms of standard deviation, Root Mean Squared Error, and maximum error between a reference and measured trajectory. Based on the criteria of fidelity, ease of implementation and ease to estimate model parameters, the S-GMS model, which represents a smooth transition between sliding and pre-sliding regime through an analytical set of differential equations, is suggested.

  • 314. Ahmad, Muhammad Ashfaq
    et al.
    Akram, Nadeem
    Raza, Rizwan
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Structural and electrical characterisation of nanostructure electrodes for SOFCs2014Inngår i: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 39, nr 30, s. 17487-17491Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper reports the effects of sintering temperature on structure, particle size and conductivity of electrodes (Sn0.2Zn0.8Fe0.2O & Sn0.8Zn0.2Fe0.2O). The electrode material was prepared by the chemical method combining a solid state reaction. Structural analyses were performed using X-ray diffraction and scanning electron microscopy. The particle size of the material obtained using Scherrer's formula was 50-60 nm and the nanostructure's surface was studied using electrochemical characterisations tools. Electrical conductivity was determined using the 4-probe DC method, which was compared with the 4-probe AC method. These results suggest a promising substitute for the conventional electrodes of solid oxide fuel cells (SOFCs). It is known that a sintering temperature above 1000 degrees C causes an increase in density and a reduction of porosity. Therefore, we optimised the sintering temperature at 1000 degrees C and obtained electrical conductivity of about 5 S Thus, this electrode could play a vital role in the development of high performance SOFCs at intermediate temperatures.

  • 315.
    Ahmad, Nawaz
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi. KTH Royal Institute of Technology.
    Numerical Modeling and Analysis of Small Gas Turbine Engine: Part I: Analytical Model and Compressor CFD2009Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The thesis work aims at devising analytical thermodynamic model and numerical modeling of the compressor of a small gas turbine to be operated on producer gas with lower heating contents. The turbine will serve as a component of “EXPLORE-Biomass Based Polygeneration” project to meet the internal electrical power requirements of 2-5 KW. The gas turbine engine is of radial type (one stage radial compressor, one stage radial turbine). Small gas turbines give less electrical efficiencies especially when operated with lower heating contents fuels like producer gas. This necessitates for optimum designing of components of the entire machine.

    Detailed analytical thermodynamic modeling of the engine has been analyzed for both internally and externally fired gas turbine cycles. Efforts are put on optimum utilization of energy available in the cycle and to enhance the efficiency thereby including various components.

    Numerical modeling of compressor using CFX has been performed for both steady and unsteady states. First different mesh sizes have been investigated followed by study of RMS residual targets on the results. Compressor performance has been studied for various speed lines. Thereafter, detailed steady state and unsteady simulations are performed for various cases including compressor single blade passage, 360 degree complete compressor, compressor connected with straight inlet pipe and for the compressor connected with 90 degree bended pipe.

    The operating point of the entire engine is analyzed. The numerical results are compared with each other and then to the ones from the 1D modeling. A good agreement has been found between the numerical results. Compared to 1D modeling, CFD presents higher performance at higher mass flow rates. However, for lower mass flow rates both 1D model and CFD present a similar performance.  

  • 316.
    Ahmad, Toqeer
    KTH, Skolan för industriell teknik och management (ITM), Industriell ekologi (flyttat 20130630).
    Environmental Management in a Pakistani Textile Company with Focus on Trade2000Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The discussion on the relationship between trade and environment has always been aheated one particularly in the context of varying economic and environmental conditionsbetween developed and developing countries. The economies of developing countriesdepend on their export to the Western countries and they are sensitive about anydevelopment, which is likely to affect their export capacity.A study has been conducted to assess the strengths, weaknesses, opportunities and threatsof a textile company in Pakistan exporting textile products to E.U countries with specificfocus on the issue of current and emerging environmental trade barriers.The study is divided into four major sections. Chapter 1 opens the debate on the issue oftrade and environment, recent developments and perspectives of major actors involvedi.e. business, environmentalists and the third world countries. Chapter 2 defines thepremises, aim, objectives and methodology. Chapter 3 outlines the detailed companyprofile. Chapter 4 deals with identification of current and emerging environmental tradebarriers that the company is facing or will face in the future. They are five namely, theNational Environmental Laws of the country, International Environmental Standards,Eco-Labeling Schemes, Intellectual Property Rights and Environmental Tariff. Chapter 5discusses the availability of resources in the company in term of information, humancapital and technology. Chapter 6 analyses the relationship between the company and itsinternational buyers in term of demand from the Western world and the supply from thethird world.This study is an example of how a Pakistani company is underpinned with the lack offinancial, technical and human resources. It also presents a case that demandingenvironmental obligations from this company for trade purposes, may create adversetrade barriers. There might be some standards, which this company may not be able tomeet in a given situation, but it does not rule out the possible improvements in theenvironmental management that can be worked upon within the given financial, technicaland human resources of the company.The study shows that the textile products in Pakistan are not cheap but have deliberatelybeen made cheaper by the policy makers at the expense of people’s health and thephysical environment. The installation and operation of primary and secondary treatmentplant, which is considered the most costly option to improve environmental condition ofthe factory, increases the cost merely up to approximately USD 0.01per square meter ofprocessing fabric. Similarly, the presence of other measures such as emission controldevices, use of environment-friendly chemicals, the recycling of waste water, exercisingfresh water consumption etc as discussed in this study would have minimal effect on theprice of the product. Considering the affluence of the European society, even the increasein product price cannot be regarded too much when converted into European currencies.This company fears that due consideration of the environmental issues will affect theprice of products which is true to some extent. But this fear is often exaggerated. The lackof environmental provisions in the company is a result of the poor environmentalbehaviour, which is due to the absence of effective communication and co-ordinationbetween the parties concerned. If this study is projected on a major scale, covering anumber of textile companies in the third world, there is a possibility of similar nature of4findings and results. If trade is part of the problem causing environmental damages, it canalso be used as a part of the solution.

  • 317.
    Ahmad, Yousef
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Oxidation of Graphite and Metallurgical Coke: A Numerical Study with an Experimental Approach2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    At the royal institute of technology (KTH) in the department of applied process metallurgy, a novel modelling approach has been developed which allows a dynamic coupling between the commercial thermodynamic software Thermo-Calc and the commercial computational fluid dynamic (CFD) software Ansys Fluent, only referred to as Fluent in the study. The dynamic coupling approach is used to provide numerical CFD-models with thermodynamic data for the thermo-physical properties and for the fluid-fluid chemical reactions occurring in metallurgical processes. The main assumption forthe dynamic coupling approach is the existence of local equilibrium in each computational cell. By assuming local equilibrium in each computational cell it is possible to use thermodynamic data from thermodynamic databases instead of kinetic data to numerically simulate chemical reactions. The dynamic coupling approach has been used by previous studies to numerically simulate chemical reactions in metallurgical processes with good results. In order to validate the dynamic coupling approach further, experimental data is required regarding surface reactions. In this study, a graphiteand metallurgical coke oxidation experimental setup was suggested in order to provide the needed experimental data. With the experimental data, the ability of the dynamic couplings approach to numerically predict the outcome of surface reactions can be tested.By reviewing the literature, the main experimental apparatus suggested for the oxidationexperiments was a thermo-gravimetric analyzer (TGA). The TGA can provide experimental data regarding the reaction rate, kinetic parameters and mass loss as a function of both temperature and time. An experimental setup and procedure were also suggested.In order to test the ability of Fluent to numerically predict the outcome of surface reactions, without any implementation of thermodynamic data from Thermo-Calc, a benchmarking has been conducted. Fluent is benchmarked against graphite oxidation experiments conducted by Kim and No from the Korean advanced institute of science and technology (KAIST). The experimental graphite oxidation rates were compared with the numerically calculated graphite oxidation rates obtained from Fluent. A good match between the experimental graphite oxidation rates and the numerically calculated graphite oxidation rates were obtained. A parameter study was also conducted in order to study the effect of mass diffusion, gas flow rate and the kinetic parameters on the numerically calculated graphite oxidation rate. The results of the parameter study were partially supported by previous graphite oxidation studies. Thus, Fluent proved to be a sufficient numerical tool for numerically predicting the outcome of surface reactions regarding graphite oxidation at zero burn-off degree.

  • 318.
    Ahmadi Moghaddam, Elham
    KTH, Skolan för industriell teknik och management (ITM), Industriell ekologi.
    Comparison of Biogas and Bioethanol for Sweden Transportation Fleet2010Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Biofuels were recently seen as a solution for the predicaments of our age; the “energy crisis” and the” climate change”. Today biofuels derived from food crops are a subject of debate for food hunger of the world’s poor and one of the main reasons of increased food prices. Latest studies also show that biofuels have no significant reduction in energy consumption and emissions. Today many attentions have been focused on biofuels extracted from biomass of different residual material such as agriculture residuals. Sweden produces biogas from different sources and also is one of the main users of Brazil’s bioethanol.

    In this report we aim to study two biofuel alternatives for Sweden transportation fleet; biogas from sugar beet residues in Sweden and imported bioethanol from sugarcanes from Brazil. The study is based on a life-cycle assessment (LCA) of the two mentioned biofuels. Three main units of agriculture, industrial production process and transportation is studied in the life cycle of the mentioned fuels.

    Based on energy inputs and emissions biogas from sugar beets in Sweden is a better alternative for Sweden transportation fleet. Bioethanol from Brazil is a crop-based fuel and highly energy consuming in the agricultural operations and industrial production process. Biogas fuel production requires increase in production capacity and technological developments.

  • 319.
    AHMADI ÅMAN, HEIDI
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    ANDERSSON, EFFIE
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Development of a Lightening System in the Village Lwengo Bassila2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [sv]

    Rapporten beskriver ett examensarbete utfört på Institutionen för maskinkonstruktion på Kungliga Tekniska högskolan (KTH). Projektet baserades på en fältstudie utförd i Demokratiska republiken Kongo (DR Kongo) och målet var att förse en by i Menikongo med belysning och el till att ladda mobiltelefoner. Ett viktigt syfte var att förbättra livet för invånarna i byn.Fältstudien utfördes som en Minor Field Study (MFS) under åtta veckor och finansierades av Sida och PIEp. Studien uträttades i byn Lwengo Bassila i området Menikongo, ungefär en tio timmar lång bilfärd från huvudstaden Kinshasa.DR Kongo ligger i centrala Afrika och är det näst största landet i Afrika. Det bor cirka 73,6 miljoner människor där, vilket placerar DR Kongo på plats nitton över världens högst befolkade länder. Landet blev självständigt år 1960 från belgiskt styre och de officiella språken är franska, lingala, kikwana, kikongo och tshibula. DR Kongo har en mycket låg mänsklig utveckling och landet ligger på en sista plats på skalan för Human Development Index (HDI) sammanställd av UN Development Program. Klimatet är tropiskt med två årstider, nämligen regn- och torrperiod.Fältstudien utgick från att installera ett ljussystem som så många bybor som möjligt kunde dra nytta av. Lamporna installerades i en paillote (hydda) som låg centralt på gården i byn Lwengo Bassila. Det installerades även gårdslampor utomhus och inomhusbelysning i hövdingens hus. Systemet hade en lystid på 5 timmar och kunde ladda upp till åtta telefoner på en dag.Det gjordes även observationer på det vardagliga livet i byn, vilket innefattade observationer av brödbakning, matlagning och införskaffandet av vatten. Vindstyrka mättes kontinuerligt, viktiga avstånd noterades och byarna dokumenterades. Syftet var att skapa en bred grund för och främja framtida utveckling av systemet och eventuella framtida projekt.Det upptäcktes stora behov av det mesta i byn. De flesta bodde i lerhyddor, maten lagades över öppen eld och brödbakningen skedde i en vedeldad lerugn. Vattnet hämtades från en vattenkälla belägen 50 höjdmeter ned från byn. Avståndet till den närmaste skolan var 2 km och den sträckan gick de barn som hade råd att gå i skola varje dag. Vindstyrkan bedömdes vara för låg för nyttjandet av ett vindkraftverk

  • 320. Ahmed, A.
    et al.
    Raza, Rizwan
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik. COMSATS Institute of Information Technology, Pakistan.
    Khalid, M. S.
    Saleem, M.
    Alvi, F.
    Javed, M. S.
    Sherazi, T. A.
    Akhtar, M. N.
    Akram, N.
    Ahmad, M. A.
    Rafique, A.
    Iqbal, J.
    Ali, A.
    Ullah, M. K.
    Imran, S. K.
    Shakir, I.
    Khan, M. A.
    Zhu, B.
    Highly efficient composite electrolyte for natural gas fed fuel cell2016Inngår i: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 41, nr 16, s. 6972-6979Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Solid oxide fuel cells (SOFCs) have the ability to operate with different variants of hydro carbon fuel such as biogas, natural gas, methane, ethane, syngas, methanol, ethanol, hydrogen and any other hydrogen rich gas. Utilization of these fuels in SOFC, especially the natural gas, would significantly reduce operating cost and would enhance the viability for commercialization of FC technology. In this paper, the performance of two indigenously manufactured nanocomposite electrolytes; barium and samarium doped ceria (BSDC-carbonate); and lanthanum and samarium doped ceria (co-precipitation method LSDC-carbonate) using natural gas as fuel is discussed. The nanocomposite electrolytes were synthesized using co-precipitation and wet chemical methods (here after referred to as nano electrolytes). The structure and morphology of the nano electrolytes were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The fuel cell performance (OCV) was tested at temperature (300-600 °C). The ionic conductivity of the nano electrolytes were measured by two probe DC method. The detailed composition analysis of nano electrolytes was performed with the help of Raman Spectroscopy. Electrochemical study has shown an ionic conductivity of 0.16 Scm-1 at 600 °C for BSDC-carbonate in hydrogen atmosphere, which is higher than conventional electrolytes SDC and GDC under same conditions. In this article reasonably good ionic conductivity of BSDC-carbonate, at 600 °C, has also been achieved in air atmosphere which is comparatively greater than the conventional SDC and GDC electrolytes.

  • 321.
    Ahmed, Hassan
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Energi och klimatstudier, ECS.
    Energy need assessment and preferential choice survey of rural people in Bangladesh2013Independent thesis Advanced level (degree of Master (One Year)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This study is a part of a poly generation project which will use animal waste or agricultural waste to produce biogas and will provide cooking gas, electricity and arsenic free clean water for drinking in rural areas of Bangladesh.  The study mainly analyzes the cooking and lighting energy demand of households across different income groups in a village named “Pani Para” in the Faridpur district in Bangladesh and also looks at the potential of biogas in the village. It has been done by adopting case study method and conducting a survey in the village using a questionnaire.

    Fuel mix across different income groups for meeting their cooking and lighting energy needs have also been studied along with socio-economic situation of the villagers and their preferences to change their current cooking fuel utilization patterns. Various scenarios like variation in fuel consumption patterns, priority of income expenditure and access to fuel with income level have been examined. The study also focuses to analyze the awareness of the villagers about biogas technology and their willingness to contribute for the poly generation project along with the willingness of households to pay for embracing change in current cooking and lighting fuels. Biomass potential i.e. cow dung and agricultural waste is also calculated in the surveyed village along with the production of biogas from the available biomass resources. The scenarios to provide the cooking gas, electricity and clean water through biogas poly generation project from the available resources are also investigated.

    Analysis reveals that the total energy consumption (cooking and lighting) increases with the increase in the income level among the households. Average household cooking and lighting energy demand by low, medium and high income groups is 8492 kWh/yr, 9789 kWh/yr and 14806 kWh/yr respectively. Cooking energy demand and agricultural waste consumption also show an increasing trend with the increase in land holding size. Among the income expenditure priorities food is one of the most important priorities and energy being less important due to availability of biomass at little or no cost. Awareness of biogas technology among the households and willingness to contribute for the poly generation plant shows an increasing trend with the increase in education level. The study shows that there is a positive response of the villagers for being willing to embrace the change in the current cooking patterns as well as welcoming new technologies that could support such a change.

    It was found that the cow dung resource in the village is not enough to produce sufficient biogas for the poly generation project. With the incorporation of the agricultural waste with the cow dung, biogas production comes quite close to requirement of the poly generation plant but however could not suffice it completely due to the lack of raw material in the studied village. In that case the scenario of providing electricity and clean water to all the villagers and providing all the three facilities to the 2/3rd of households is investigated. 1/3rd of the low income households then could meet their cooking demands by provision of improved cooking stoves as cooking gas could not be provided to them due to limited feedstock. The study shows that despite of the fact that cooking and lighting energy needs increase with income but there is not much variation in the fuel mix and almost everyone in the village rely on biomass to meet their energy demand. It is because there is very limited access to the modern fuel for cooking and no electricity access in the village, so the households have to rely on the traditional fuels. 

  • 322.
    Ahmed, Hesham M.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Investigations of the Kinetics of Reduction and Reduction/Carburization of NiO-WO3 Precursors.2010Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Kinetic studies of reduction of the mixtures of NiO and WO3 having different Ni/(Ni+W) molar ratios in flowing hydrogen gas were investigated by means of Thermo Gravimetric Analysis (TGA), Fluidized Bed (FB) technique as well as Thermal diffusivity measurements under isothermal conditions. In the case of TGA, the reaction progress was monitored by mass loss, while evolved gas analysis by a gas chromatograph was the indicator of the reaction progress in the case of FB. The results indicate that the reduction reaction proceeds through three consecutive steps, viz.

    NiO-WO3 Ni-WO3 Ni-WO2 Ni-W

    The present results show that the fluidized bed technique can be successfully utilized in bulk production of intermetallics containing W and a transition metal (or a composite material) wherein the process conditions would have a strong impact on the particle size of the end product.

    During the investigations, it was found that there was a delay in the reaction during the hydrogen reduction of NiO-WO3 mixed oxides in a fluidized bed reactor. In order to understand the same, a theoretical model was developed to estimate the apparent reaction rate constant for the reduction reaction from the intrinsic chemical reaction rate constant. Appropriate differential mass balance equations based on intrinsic chemical reaction rate constants and thermodynamic equilibria were developed. The proposed model was successfully applied in predicting the overall reaction kinetics of a fluidized bed reactor. This model is also suitable for scale-up calculations.

    SEM images showed that the particle size of the final product was dependent on the Ni/(Ni+W) molar ratio; smaller particles were formed at higher nickel contents. X-ray diffractions of the reduced precursors exhibited slight shift of Ni peaks from the standard one indicating the dissolution of W into Ni.

    A new method for studying kinetics of the hydrogen reduction of NiO-WO3 precursors was developed in which the reaction progress was monitored by following the change of thermal diffusivity of the precursors. Activation energies of reduction as well as sintering were calculated. This method is considered unique as it provides information regarding the physical changes like sintering, change of porosity and agglomeration along with the chemical changes occurring during the gas/solid reaction.

    As a continuation of the kinetic studies, Ni-W-C ternary carbides were synthesized by simultaneous reduction–carburization of Ni-W-O system using H2-CH4 gas mixtures by TGA. The results showed that the reduction of the oxide mixture was complete before the carburization took place. The nascent particles of the metals formed by reduction could react with the gas mixture with well-defined carbon potential to form a uniform product of Ni-W-C. The above-mentioned experiments were conducted in such a way to ensure that the reaction was controlled by the chemical reaction. The activation energies of the reduction as well as carburization processes at different stages were calculated accordingly.

    The present dissertation demonstrates the potential of the investigations of gas/solid reactions towards tailoring the process towards materials with optimized properties as for example introduction of interstitials. The present process design is extremely environment-friendly with reduced number of unit processes and the product being H2O.

  • 323.
    Ahmed, Hesham M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    El-Geassy, A. H. A.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Kinetics of Reduction of NiO-WO3 Mixtures by Hydrogen2010Inngår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 41, nr 1, s. 161-172Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The kinetics of reduction of the oxide mixtures of Ni-W with different Ni/(Ni-W) molar ratios within the range of 923 K to 1173 K in flowing hydrogen gas was investigated by means of thermogravimetric analysis under isothermal conditions. The products were examined by X-ray diffraction, scanning electron microscope (SEM), and electron dispersion spectroscopy (EDS) analyses. Five different oxide mixtures apart from the pure oxides were studied in the present work. The results indicate that the reduction reaction proceeds through three consecutive steps that are as follows: NiO-WO3 -> Ni-WO3 -> Ni-WO2 -> Ni-W From the experimental results, the Arrhenius activation energies of the three steps were evaluated for all of the studied compositions. The activation energy for the first step was calculated to be approximately 18 kJ/mol. For the second and third stages, the activation energy values varied from 62 to 38 kJ/mol for the second stage and 51 to 34 kJ/mol for the third stage depending on the Ni/(Ni + W) molar ratio in the precursors; the activation energy increased with increasing ratios. SEM images showed that the grain size of the final product was dependent on the Ni/(Ni + W) molar ratio; smaller grains were formed at higher nickel contents.

  • 324.
    Ahmed, Hesham M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    El-Geassy, Abdel-Hady A.
    Viswanathan, Nurni Neelakantan
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Kinetics and Mathematical Modeling of Hydrogen Reduction of NiO-WO(3) Precursors in Fluidized Bed Reactor2011Inngår i: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 51, nr 9, s. 1383-1391Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present work, Fluidized bed reduction of NiO-WO(3) precursors was investigated isothermally at temperatures 973-1 273 K. The reaction progress was monitored by analysis of H(2)O evolved during the reaction process using a gas chromatograph instrument. A theoretical model based on intrinsic chemical reaction rate constants and thermodynamic equilibria was developed to estimate the apparent reaction rate constant for the reduction reaction. In developing the model, the particles are considered to be in a completely mixed condition and gas flow is described as plug flow. The proposed model is also suitable for scale-up calculations. The interfacial chemical reaction model was found to fit the experimental results. The apparent activation energy values of the reduction process at different stages were calculated accordingly. The present investigation proved that the fluidized bed technique can be successfully utilized in bulk production of intermetallics containing W and a transition metal (or a composite material) wherein the process conditions would have a strong impact on the particle size of the end product.

  • 325.
    Ahmed, Hesham M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    El-Geassy, Abdel-Hady
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Kinetic Studies of the Hydrogen Reduction of NiO-WO3 precursors in a Fluidized-bed reactorInngår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916Artikkel i tidsskrift (Annet vitenskapelig)
  • 326.
    Ahmed, Hesham M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Isothermal dynamic thermal diffusivity studies of the reduction of NiO and NiWO(4) precursors by hydrogen2011Inngår i: International Journal of Materials Research - Zeitschrift für Metallkunde, ISSN 1862-5282, E-ISSN 2195-8556, Vol. 102, nr 11, s. 1336-1344Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thermal diffusivity measurements of uniaxially cold pressed NiO and NiWO(4) were carried out in a dynamic mode in order to monitor the kinetics of hydrogen reduction of the above-mentioned materials using a laser flash unit. The calculated activation energy was found to be higher than that for chemically-controlled reaction obtained earlier by thermogravimetry. The difference has been attributed to physical changes occurring along with the chemical reaction. The activation energy of sintering of the products was evaluated to be 33 and 36 kJ.mol(-1) for NiO and NiWO(4), respectively. Thermal conductivities were calculated taking into consideration the change in heat capacity considering the compositional and the structural changes with the progress of the reaction. The potentiality of the laser-flash method as a complementary technique to thermogravimetry in understanding the mechanism of gas solid reactions is discussed.

  • 327.
    Ahmed, Hesham M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Reduction-Carburization of NiO-WO3 Under Isothermal Conditions Using H2-CH4 Gas Mixture2010Inngår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 41, nr 1, s. 173-181Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ni-W-C ternary carbides were synthesized by simultaneous reduction–carburization of NiO-WO3 oxide precursors using H2-CH4 gas mixtures in the temperature range of 973 to 1273 K. The kinetics of the gas–solid reaction were followed closely by monitoring the mass changes using the thermogravimetric method (TGA). As a thin bed of the precursors were used, each particle was in direct contact with the gas mixture. The results showed that the hydrogen reduction of the oxide mixture was complete before the carburization took place. The nascent particles of the metals formed by reduction could react with the gas mixture with well-defined carbon potential to form a uniform product of Ni-W-C. Consequently, the reaction rate could be conceived as being controlled by the chemical reaction. From the reaction rate, Arrhenius activation energies for reduction and carburization were evaluated. Characterization of the carbides produced was carried out using X-ray diffraction and a scanning electron microscope (SEM) combined with electron dispersion spectroscopy (SEM-EDS) analyses. The grain sizes also were determined. The process parameters, such as the temperature of the reduction–carburization reaction and the composition of the gas mixture, had a strong impact on the carbide composition as well as on the grain size. The results are discussed in light of the reduction kinetics of the oxides and the thermodynamic constraints.

  • 328.
    Ahmed, Hesham M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Viswanathan, N. N.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    On The Kinetics of Hydrogen Reduction of NiO-WO3 Precursors in Fluidized Bed- A Modeling Approach2011Inngår i: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 51, nr 9, s. 1383-1391Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present work, Fluidized bed reduction of NiO-WO3 precursors was investigated isothermally at temperatures 973-1 273 K. The reaction progress was monitored by analysis of H2O evolved during the reaction process using a gas chromatograph instrument. A theoretical model based on intrinsic chemical reaction rate constants and thermodynamic equilibria was developed to estimate the apparent reaction rate constant for the reduction reaction. In developing the model, the particles are considered to be in a completely mixed condition and gas flow is described as plug flow. The proposed model is also suitable for scale-up calculations. The interfacial chemical reaction model was found to fit the experimental results. The apparent activation energy values of the reduction process at different stages were calculated accordingly. The present investigation proved that the fluidized bed technique can be successfully utilized in bulk production of intermetallics containing W and a transition metal (or a composite material) wherein the process conditions would have a strong impact on the particle size of the end product.

  • 329.
    Ahmed, Hesham M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Viswanathan, Nurini N.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Dynamic Thermal Diffusivity Measurements - A Tool for Studying Gas-Solid Reactions2011Inngår i: DIFFUSION IN SOLIDS AND LIQUIDS VI, PTS 1 AND 2, 2011, s. 217-222Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In the present work, the thermal diffusivity measurements of uniaxially cold pressed NiWO(4) has been carried out. The measurements were performed isothermally at temperatures between 973 and 1273 K under H(2) gas using the laser flash technique. The experimental thermal diffusivity values were found to increase with the reduction progress as well as with increasing temperature. The calculated activation energy was found to be higher than that for chemically controlled reaction. The difference has been attributed to factors like agglomeration of the product as well as sintering of the precursor along with the chemical reaction. In order to sort out the sintering effect on the thermal diffusivity values, complementary experiments have been done on pressed NiWO(4) and Ni-W, produced by the reduction of NiWO(4) at 1123K, under Argon gas. The porosity change and its effect on thermal diffusivity values have been studied.

  • 330.
    Ahmed, Hesham
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Mis, Michal
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    El-Geassy, Abdel-Hady
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Seethararnan, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Reduction-Carburization of the Oxides of Ni and W Towards the Synthesis of Ni-W-C Carbides2010Inngår i: ADVANCED MATERIALS FORUM V, PT 1 AND 2  / [ed] Rosa LG; Margarido F, 2010, Vol. 636-637, s. 952-962Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Ternary Ni-W-C cemented carbides were synthesized directly from mixture powder of NiO-WO3 by simultaneous reduction-carburization in mixed H-2-CH4 gas environment in a thin bed reactor in the temperature range 973-1273K. The kinetics of the reaction was closely followed by monitoring the mass change using thermogravimetric method (TGA). The nascent particles of the metals formed by reduction could react with the gas mixture with well-defined carbon potential to form a uniform product of Ni-W-C. The gas mixture ratio was adjusted in such a way that the Ni-W-C formed was close to the two phase tie line. In view of the fact that each particle was in direct contact with the gas mixture, the reaction rate could be conceived as being controlled by the combined reduction-carburization reaction. From the reaction rate, the Arrhenius activation energies were evaluated. Characterization of the carbides produced was carried out by using X-ray diffraction, SEM-EDS as well as high resolution electron microscope (HREM). The grain sizes were also determined. Correlations were found between the carbide composition as well as grain size and the process parameters such as temperature of the reduction-carburization reaction as well as the composition of the gas mixture. The results are discussed in the light of the kinetics of the reduction of oxides and the thermodynamic constraints.

  • 331. Ahmed, Hesham
    et al.
    Morales-Estrella, R.
    Viswanathan, Nurin
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Gas-Solid Reaction Route toward the Production of Intermetallics from Their Corresponding Oxide Mixtures2016Inngår i: METALS, ISSN 2075-4701, Vol. 6, nr 8, artikkel-id 190Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Near-net shape forming of metallic components from metallic powders produced in situ from reduction of corresponding pure metal oxides has not been explored to a large extent. Such a process can be probably termed in short as the "Reduction-Sintering" process. This methodology can be especially effective in producing components containing refractory metals. Additionally, in situ production of metallic powder from complex oxides containing more than one metallic element may result in in situ alloying during reduction, possibly at lower temperatures. With this motivation, in situ reduction of complex oxides mixtures containing more than one metallic element has been investigated intensively over a period of years in the department of materials science, KTH, Sweden. This review highlights the most important features of that investigation. The investigation includes not only synthesis of intermetallics and refractory metals using the gas solid reaction route but also study the reaction kinetics and mechanism. Environmentally friendly gases like H-2, CH4 and N-2 were used for simultaneous reduction, carburization and nitridation, respectively. Different techniques have been utilized. A thermogravimetric analyzer was used to accurately control the process conditions and obtain reaction kinetics. The fluidized bed technique has been utilized to study the possibility of bulk production of intermetallics compared to milligrams in TGA. Carburization and nitridation of nascent formed intermetallics were successfully carried out. A novel method based on material thermal property was explored to track the reaction progress and estimate the reaction kinetics. This method implies the dynamic measure of thermal diffusivity using laser flash method. These efforts end up with a successful preparation of nanograined intermetallics like Fe-Mo and Ni-W. In addition, it ends up with simultaneous reduction and synthesis of Ni-WN and Ni-WC from their oxide mixtures in single step.

  • 332.
    Ahmed, Rabbu
    et al.
    KTH, Skolan för industriell teknik och management (ITM).
    Gopi Sripathy, Arun
    KTH, Skolan för industriell teknik och management (ITM).
    Kvantifiering av den samlade miljöbelastningen av tomgångskörning i Sverige samt förslag till beteendepåverkande åtgärder2019Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Den accelererande klimatförändringen idag kommer huvudsakligen från mänskliga aktiviteter. Utsläppen från människor rubbar naturens balans idag och ännu mer i framtiden. Den största boven är koldioxid, som bland annat släpps ut från bilar med förbränningsmotor. Statistik påvisar att koldioxidutsläppen minskar för nyare bilar, dessvärre ökar antalet bilar med tiden. En del av problemet ligger i tomgångskörning. Tomgång kallas det låga varvtalet en förbränningsmotor ligger vid då den är igång men inte används. I Sverige är det endast tillåtet att ha bilen på i tomgång max en minut i de flesta kommunerna, med undantag för fordon som får ha motorn igång längre för att driva en anläggning. Mängden av tomgångskörning i Sverige fastställdes med hjälp av beräkningar baserad på litteraturstudie och statistik. Orsaker till att tomgångskörning förekommer och förares attityd till tomgångskörning hos olika befolkningsgrupper undersöktes med hjälp av en enkätundersökning. Slutsatsen som kunde dras är att tomgångskörning utgör ca 25 % av all koldioxidutsläpp från personbilar. De vanligaste situationerna då bilister hade bilen i tomgång var vid stilla trafik, kö på drivethrough, värma bilen och när de väntade på någon. Majoriteten hade bilen på tomgång i längre än två minuter vilket överskrider de lokala hälsoskyddsföreskrifterna. Enkätundersökningen visade att brist på kunskap angående tomgångskörningens hälso- och miljöpåverkan är en avgörande orsak till att tomgångskörning sker.

  • 333.
    Ahmed, Sabih Zeb
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Reduction of vibrations during horizontal milling of aluminum parts: An Experimental and Numerical Study 2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This thesis aims at vibration problem during milling operation. Vibration sets in at tool- workpiece interface if certain conditions are achieved. Research has been carried out try to reduce or eliminate chatter. Chatter decreases the dimensional accuracy and surface finish of workpiece.

    Main objective is to examine the source of vibration and provide as solution to problem based on the findings. CAD Model of workpiece and clamping has been developed as close to real system as possible. Experimental modal analysis and Finite Element analysis is done to obtain system behaviour during vibration. Natural frequencies are determined and then compared with possible sources of excitation.

    Modal testing and computer simulations are done before and after Final cutting operations to map out complete behaviour of system. Both forced excitation and self-excited vibrations are taken in consideration during measurements. Finally calculations are done to determine the solution and give recommendations. Suggestions for future work in this area are also provided that could enable SAAB to analyse and improve machining of all parts.

  • 334.
    Ahmed, Sunny
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Olsson, Linnéa
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Urbanears Ugglan - Studying Usercentered Designin Product Development2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This report describes the master’s thesis conducted by Sunny Ahmed and Linnéa Olssonat KTH Royal Institute of Technology for the client Zound Industries. By exploringemerging technologies and user needs, the project members developed a design proposal forheadphones for active users that can be released in three to five years’ time.Urbanears Ugglan is the headphone solution that allows you to take control of your physicalactivities and experience true freedom. It consists of two parts: true wireless earphonesand a wearable wrist accessory that stores and charges the earphones on the go, while alsofunctioning as a fitness tracker.Aside from the first purpose of creating the design proposal, the second purpose of the thesiswas to investigate the impact of involving the intended user in the design process duringproduct development when adopting a user-centered design approach.Different methods were used to gather relevant information. Both market research and atechnical trend analysis were done as background research, and complemented the userstudies. The insights discovered from these phases were used to generate concepts, fromwhich one was selected for further development after discussion with the client company. Thisconcept evolved into the final design proposal, Urbanears Ugglan.The project team found a positive impact from using user-centered design and involving theuser in several stages of the project. Including the intended user in the development led toa better understanding of their needs and values, which in turn allowed the project team toquickly verify the potential of product ideas.

  • 335.
    Ahmed, Yahye
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Tillämpad maskinteknik (KTH Södertälje).
    Carlsson, Ossian
    KTH, Skolan för industriell teknik och management (ITM), Tillämpad maskinteknik (KTH Södertälje).
    Analys: Olyckor och tillbud vid pappersmassabruk2016Independent thesis Basic level (university diploma), 10 poäng / 15 hpOppgave
  • 336.
    Ahmned, Sragadin
    KTH, Skolan för industriell teknik och management (ITM), Industriell ekologi.
    Reningsmetoder för minskning av oljelukt från bergrummen i Oxelösunds Hamn AB2009Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [sv]

    Föreliggande sammanställning av teknik och kostnader för att begränsa utsläpp av flyktiga organiska ämnen som har orsakat oljeluktproblem med olika förfaranden har gjorts på uppdrag av Oxelösund Hamn AB. I Oxelösunds Hamn AB hanteras tjockolja och VGO- olja. Oljan lossas från fartyg till bergrum och återlastas från bergrum till fartyg. Hamnen har sju bergrum, sex stycken av dem är i drift medan den sjunde inte är verksam.

    Bergrummen har ett gemensamt ventilationssystem för andning. När oljan lossas från fartygen till bergrummen kommer motsvarande volym kolvätebemängd luft som överpumpats att pressas ut från bergrummen och detta skapar ett oljeluktproblem. Oljeluktproblemet uppkommer även vid temperatur ändring, det vill säga när ute temperaturen stiger ökar oljelukten och vise versa. Det finns även andra faktorer som påverkar luktproblemet och dessa är tryckändring, dvs. vid andning av bergrummen och korsdrag.

    För att kunna identifiera vad lukten vid Oxelösund Hamn består av har en luftprovtagning gjorts både i bergrummen och utomhus, vid skorstenen(bergrummens gemensamma avluftningsrör). Luftproverna har visat höga halter av olika VOC- er 13000 ppm.

    Enligt 8 a § Till skydd för människors hälsa i miljöskyddslagen får bensen som tillhör flyktiga organiska ämnen(VOC) efter den 1 januari 2010 inte förekomma i utomhusluft med mer än i genomsnitt 5 μg/m3 luft som årsmedelvärde. Förordning (2003:112). Utsläppen av flyktiga organiska ämnen i Europa är reglerat i direktivet (2001/81/EG), det så kallade takdirektivet. Takdirektivet för VOC innebär att Sverige förbinder sig att nå en utsläppsnivå på 241 000 ton/år till år 2010.

    I detta examens arbete redovisas de olika lösningsteknikerna som finns till förfogande för att minska oljeluktproblemet. Etablerade gasbehandlingstekniker utgörs av katalytisk eller termisk förbränning, adsorption, absorption, kondensation samt biologisk reningsteknik. Efter en teknisk utvärdering av olika alternativ har förbränningsteknik och adsorption befunnits vara lämpliga som reningsteknik i det här aktuella fallet. För att vara säker på att vald reningsteknik är lämplig för utsläppssituationen förbränningsteknik i form av katalytisk förbränning rekommenderas som reningsteknik för minskning av oljeluktproblemet och VOC: erna.

    Som förbränningsteknik har man olika tekniker att välja emellan exempelvis katalytisk- respektive konventionell termisk förbränning eller förbränning i förbränningsvärmeväxlare. Både katalytisk- och termiskförbränning har sina för- och nackdelar. Den katalytiska förbränningen blir autoterm vid mycket lägre VOC- halter än den termiska förbränningen och kräver därmed mindre av stödbränsle tillförsel behövs. Ju mindre behov av stödbränsle desto mindre utsläpp av koldioxid. Utifrån ekonomi och miljö föredrar man således vid låga VOC- halter katalytisk förbränning framför termisk förbränning.

    Vid användning av adsorption behöver man i det här aktuella fallet torka gasen från fukten eftersom den relativa fukthalten uppgår till 95 %. Om man inte torkar luften från fukten så begränsar denna fukt kolbäddens adsorptionskapacitet. När kolbädden börjar blir mättad regenereras den på plats och desorbat (VOC- erna och vattnet) behöver då tas om hand. Desorbat är i det här fallet är litet och kan föras tillbaka till bergrummen, men kan även behandlas med lämplig behandlingsteknik.

  • 337.
    Aho, Aziz Sebastian
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Tillämpad maskinteknik (KTH Södertälje).
    Ikzir, Nawar
    KTH, Skolan för industriell teknik och management (ITM), Tillämpad maskinteknik (KTH Södertälje).
    Krockskydd av chassimonterade komponenter2017Independent thesis Basic level (university diploma), 10 poäng / 15 hpOppgave
  • 338.
    Aho, Isa
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Tillämpad maskinteknik (KTH Södertälje).
    Halef, Madeleine
    KTH, Skolan för industriell teknik och management (ITM), Tillämpad maskinteknik (KTH Södertälje).
    Flödeskartläggning avbilflödenpå Södertälje Hamn2013Independent thesis Advanced level (degree of Master (One Year)), 10 poäng / 15 hpOppgave
  • 339.
    Aho, Isa
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Tillämpad maskinteknik (KTH Södertälje).
    Halef, Madeleine Halef
    KTH, Skolan för industriell teknik och management (ITM), Tillämpad maskinteknik (KTH Södertälje).
    Flödeskartläggning avbilflödenpå Södertälje Hamn(Car-flow mapping at the Port of Södertälje)2013Independent thesis Advanced level (degree of Master (One Year)), 10 poäng / 15 hpOppgave
  • 340.
    Aho, Isa
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Tillämpad maskinteknik (KTH Södertälje).
    Karlsson, Daniel
    KTH, Skolan för industriell teknik och management (ITM), Tillämpad maskinteknik (KTH Södertälje).
    Säkra förband - kvalitetssäkring av differentialförbandet2011Independent thesis Basic level (university diploma), 10 poäng / 15 hpOppgave
  • 341. Ahola-Tuomi, M.
    et al.
    Punkkinen, Marko Patrick John
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Laukkanen, P.
    Kuzmin, M.
    Lang, J.
    Schulte, K.
    Pietzsch, A.
    Perala, R. E.
    Rasanen, N.
    Vayrynen, I. J.
    Properties of self-assembled Bi nanolines on InAs(100) studied by core-level and valence-band photoemission, and first-principles calculations2011Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, nr 24, s. 245401-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have studied self-assembled bismuth (Bi) nanolines on the Bi-terminated InAs(100) surface by core-level and valence-band photoelectron spectroscopy, and ab initio first-principles calculations. A structural model for this intriguing surface is suggested based on the comparison of the measured and calculated core-level shifts. Also, the atomic origins for the core-level shifts are proposed based on the calculations. A clear peak related to this surface was observed in the valence band 0.34 eV below the Fermi level, which can be used as a "fingerprint" of a well-ordered Bi/InAs(100) nanoline surface.

  • 342.
    Ahrnstein, Lina
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Dahlberg, Johanna
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    En jämförelse av RDF och avfall som förbränningsbränsle2012Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    In the EU the amount of waste increased by 14 percent during the years 2000 to 2010. EU’s target to reduce waste generation runs parallel with the aim of increasing the efficiency and profitability aligned with energy recovery. In Sweden the energy recovery through incineration is increasing steadily, and 46 percent of the municipal solid waste (MSW) is treated by combustion. This report aims to examine the profitability of processing MSW into Refuse Derived Fuel (RDF) from an economic-, energy- and environmental perspective. In order to obtain a comparison with incineration of MSW the starting point of the feasibility study is one ton of combustible MSW incinerated directly in a stocker grate type incinerator, compared to the same ton of MSW processed to RDF and incinerated in a fluidized bed.The proportion of MSW processed to RDF varies between 23-85 percent, which leads to an average of 540 kg, 54 percent, processed RDF from a ton of MSW. One ton of RDF has a calorific value between 18.5-23 MJ/kg. The calorific value of combustible MSW is calculated to 10.38 MJ/kg. The two different boilers for combustion of the fuels have the same power of 28 MW. The comparison shows the total energy recovery, of heat and electricity, for the combustible MSW in the stocker grate to 2.51 MWh, and for the 540 kg RDF incinerated in a fluidized bed to be 2,56 MWh. As long as the proportion of RDF processed from a ton of MSW is greater than 51 percent, the energy recovery is higher for the RDF.A cost-benefit analysis, calculated from the combustion of 70 000 tons of MSW, and 54 percent of the amount processed to RDF, shows a higher net present value for RDF, 1042 million. However, the net present value of the combusted MSW was also positive, 1024 million, which indicates that both investments are profitable. The payback method showed the same result, with a payback time of 3.17 years for RDF-combustion and 4.24 years for combustion of MSW.Emissions of carbon dioxide and nitrogen oxide are both higher when incineration of 540 kg RDF takes place in a fluidized bed, than of a ton of MSW in a stocker grate incinerator. Emission of carbon dioxide is 17,7 percent higher and for nitrogen oxide 23 percent higher.

  • 343.
    Ahrén, Jesper
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Bühlman, Carl
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Lean Production: Redogörelse av Lean och jämförelse med Scanias produktionssystem2015Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Sammanfattning

    Syftet med denna rapport är att täcka och förklara grunderna för Lean Production, hur det implementeras i industrin samt att jämföra Lean i teori och praktik.Vi vill ta reda på vad som kännetecknar en lyckad tillämpning av Lean och vad det kan medföra för resultat. Lean Production är en vidareutveckling av TPS (Toyota Production System), en filosofi om hur man gör ett företag mer resurseffektivt. TPS är ett resultat av Toyotas arbete att eliminera slöseri och kombinerar massproduktion med stor valfrihet.

    För att inte välja ett för brett område valde vi att titta specifikt på Lean i fordonsindustrin och för att bättre förstå industrin i dag har vi intervjuat en anställd på Scania. Den teoretiska delen av vårt arbete genomfördes av litteraturstudier, KTH databassökning och hemsidor. Scania har utvecklat sina egen Lean filosofi, SPS (Scania Production System) som är ett resultat av ett samarbete med Toyota.

    Det finns flera olika strategier ett företag kan vidta för att identifiera och förbättra sina svagheter. Lean fokuserar på eliminering av slöseri men också hur man använder resurserna på ett effektivt sätt. Toyota Production System är baserat på 14 principer, medan Lean Production har fem principer som bas, men det finns dock flera tolkningar.

    Under arbetet har vi funnit att en nyckelfaktor för en lyckad Lean-­‐implementering är att få hela organisationen att se och att tro på konceptet, men man måste även ganska snabbt kunna påvisa resultat och förbättringar. För att nå detta mål är en tydlig presentation av resultat och goda ledare nyckelfaktorer. För att inte falla tillbaka i gamla vanor har vi funnit att ett standardiserat arbetssätt där man skapar förutsättningar för de anställda att ständigt förbättra sin situation är avgörande.

    För Scanias del har Lean-­‐implementeringen inneburit ökad kvalitet och produktivitet, högre närvaro, lägre energikonsumtion samt bättre lönsamhet än konkurrenter. Man har skapat en god organisation för både samhället, kunderna och sina anställda, vilket har varit nödvändigt för Scanias överlevnad.

  • 344.
    Ahuja, Rajeev
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Sa
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje Örje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    High pressure structural transitions in Cm metal2006Inngår i: Mater Res Soc Symp Proc, 2006, s. 247-254Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The high pressure behaviour of Cm metal is investigated theoretically using ab initio electronic structure methods. Our calculations reproduce the structural phase transitions which are obsereved in recent experiment performed by Heatman et al. [Science 309, 110 (2005)]. Calculated transition pressures are in reasonable agreement with the experimental values. Calculations performed for an antiferromagnetic state is essential to reproduce the stability of Cm-III phase. Thus, the stability of the Cm-III phase is related to the spin polarization of its 5f electrons.

  • 345.
    Ahuja, Rajeev
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Sa
    Luo, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    High-pressure structural transitions in Cm and Am0.5Cm0.5 binary alloy2006Inngår i: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 26, nr 4, s. 377-381Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The high-pressure behaviour of Cm and Am0.5Cm0.5 binary alloy is investigated theoretically using ab initio electronic structure methods. Our calculations reproduce the structural phase transitions, which are observed in recent experiment performed by Heathman et al. [S. Heathman, R.G. Haire, I Le Bihan et al., Science 309 110 (2005)] and Lindbaum et al. [A. Lindbaum, S. Heathman, T. Le Bihan et al., J. Phys: Condens. Matter 15 S2297 (2003)]. Calculated transition pressures are in reasonable agreement with the experimental values. Calculations performed for an antiferromagnetic state are essential to reproduce the stability of Cm-III phase.

  • 346.
    Aichmayer, Lukas
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Solar Receiver Design and Verification for Small Scale Polygeneration Unit2011Independent thesis Advanced level (degree of Master (Two Years)), 30 poäng / 45 hpOppgave
    Abstract [en]

    Against a backdrop of our world’s changing climate solar thermal power generation shows great potential to move global energy production away from fossil fuels to non-polluting sources. The Department of Energy Technology at the Royal Institute of Technology Stockholm is contributing to the development and research of solar thermal power by building a solar driven small scale polygeneration unit based on an externally fired micro gas turbine.

    This project focused on the design, analysis and verification of a high temperature solar receiver for integration into this planned solar polygeneration unit. Mean irradiance levels at the focal spot of the solar receiver of 5.5 MW/m² and peak levels of 14 MW/m² were identified as major design challenges. A preliminary heat transfer analysis found volumetric receivers to be the only applicable receiver type capable of withstanding these expected high irradiance levels.

    With volumetric receivers selected as the receiver type, a basic volumetric receiver model was evaluated using a multi-objective optimization tool based on advanced evolutionist algorithms and a numerical heat transfer model. The results were a set of Pareto-optimal solutions showing a tradeoff between a pressure drop in the receiver and material temperature especially at the window of the receiver.

    A parameter study was conducted based on the previous analysis to improve specific aspects of the initial design using a value of benefit analysis to evaluate the different designs. Of all the investigated receiver parameters, the absorber properties and shape had the biggest positive influence on material temperature and thermal stresses without significantly increasing the pressure drop. External cooling of the receiver window with ambient air was found to beneficial influence the window temperature without greatly decreasing the thermal efficiency. For non-uniform high irradiance levels ceramic absorber materials were found to be most suitable. Furthermore, mechanically decoupling the window and the absorber from their surrounding parts was found to be very important; enabling them to expand more or less independently with changing temperature minimizing thermal stresses.

    It can be concluded, when properly designed, volumetric solar receivers for small scale solar polygeneration units are feasible as designs with material temperature, thermal stresses and pressure drop below acceptable limit were found within this work.

  • 347.
    Aichmayer, Lukas
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Solar receiver development for gas-turbine based solar dish systems2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Small-scale concentrating solar power plants such as micro gas-turbine based solar dish systems have the potential to harness solar energy in an effective way and supply electricity to customers in remote areas. In such systems, the solar receiver transfers the power of concentrated solar radiation to the working fluid of the power conversion cycle. It is one of the key components as it needs to operate at high temperatures to ensure a high power cycle efficiency and under high flux densities to ensure a high receiver efficiency. In order to address these challenges and to ensure efficient and reliable operation innovative designs are needed.

    This research work focuses on the complete development of a novel solar receiver applying a new systematic design and analysis methodology. Therefore, a comprehensive receiver design and experimental evaluation process were developed and implemented. The design process includes the identification of technical specifications and requirements, the development of receiver design tools of different investigation levels coupled with multi-objective optimization tools, the evaluation of scaling effects between tests in the KTH high-flux solar simulator and the full-scale solar dish system. As a result of the design process a representative final receiver was established with material temperatures and stresses below critical limits while respecting the design specification.

    The experimental evaluation includes the enhancement of the KTH high-flux solar simulator to provide stable and reliable operating conditions, the precise characterization of the radiative boundary conditions, the design of a receiver test bed recreating the operating behavior of a gas-turbine, and the final receiver testing for multiple operating points. It was shown that the prototype reaches an efficiency of 69.3% for an air outlet temperature of 800°C and a mass flow of 29.5 g/s. For a larger mass flow of 38.4 g/s a receiver efficiency of 84.8% was achieved with an air outlet temperature of 749°C.

    The measurement results obtained were then used for a multi-point validation of the receiver design tools, resulting in a high level of confidence in the accuracy of the tools. The validated models were then harnessed to calculate the performance of a full-scale solar receiver integrated into the OMSoP solar dish system. It was shown that a solar receiver can be designed, which delivers air at 800°C with a receiver efficiency of 82.2%.

    Finally, the economic potential of micro gas-turbine based solar systems was investigated and it was shown that they are ideally suited for small-scale stand-alone and off-grid applications.

    The results of the receiver development highlight the feasibility of using volumetric solar receivers to provide heat input to micro gas-turbine based solar dish systems and no major hurdles were found.

  • 348.
    Aichmayer, Lukas
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Garrido, Jorge
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Laumert, Björn
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Performance Improvements of the KTH High-Flux Solar Simulator2017Inngår i: AIP Conference Proceedings 1850, American Institute of Physics (AIP), 2017, Vol. 1850, artikkel-id 150001Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents the performance improvements implemented in the KTH high-flux solar simulator to deliver a total power on target closer to the working conditions of real CSP systems. Therefore, additional rectifiers were installed in the power conversion unit of the high-power lamps as well as the back reflector was coated providing more favorable spectral reflectance properties. The results of a single lamp/lens-combination show that the power on target in an aperture of 280mm in diameter was increased from 831W to 1446W while the peak flux was increased from 675kW/m² to 905kW/m².

  • 349.
    Aichmayer, Lukas
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Garrido, Jorge
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Laumert, Björn
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Scaling effects of a novel solar receiver for a micro gas-turbine based solar dish system2018Inngår i: International Journal of Solar Energy, ISSN 0142-5919, E-ISSN 1477-2752, Vol. 162, s. 248-264Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Laboratory-scale component testing in dedicated high-flux solar simulators is a crucial step in the developmentand scale-up of concentrating solar power plants. Due to different radiative boundary conditions available inhigh-flux solar simulators and full-scale power plants the temperature and stress profiles inside the investigatedreceivers differ between these two testing platforms. The main objective of this work is to present a systematicscaling methodology for solar receivers to guarantee that experiments performed in the controlled environmentof high-flux solar simulators yield representative results when compared to full-scale tests. In this work theeffects of scaling a solar air receiver from the integration into the OMSoP full-scale micro gas-turbine based solardish system to the KTH high-flux solar simulator are investigated. Therefore, Monte Carlo ray-tracing routines ofthe solar dish concentrator and the solar simulator are developed and validated against experimental characterizationresults. The thermo-mechanical analysis of the solar receiver is based around a coupled CFD/FEManalysislinked with stochastic heat source calculations in combination with ray-tracing routines. A geneticmulti-objective optimization is performed to identify suitable receiver configurations for testing in the solarsimulator which yield representative results compared to full-scale tests. The scaling quality is evaluated using aset of performance and scaling indicators. Based on the results a suitable receiver configuration is selected forfurther investigation and experimental evaluation in the KTH high-flux solar simulator.

  • 350.
    Aichmayer, Lukas
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Spelling, James
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Laumert, Björn
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Preliminary design and analysis of a novel solar receiver for a micro gas-turbine based solar dish system2015Inngår i: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 114, nr 4, s. 378-396Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The solar receiver is one of the key components of hybrid solar micro gas-turbine systems, which would seem to present a number of advantages when compared with Stirling engine based systems and photovoltaic panels. In this study a solar receiver meeting the specific requirements for integration into a small-scale (10 kWel) dish-mounted hybrid solar micro gas-turbine system has been designed with a special focus on the trade-offs between efficiency, pressure drop, material utilization and economic design. A situation analysis, performed using a multi-objective optimizer, has shown that a pressurized configuration, where the solar receiver is placed before the turbine, is superior to an atmospheric configuration with the solar receiver placed after the turbine. Based on these initial design results, coupled CFD/FEM simulations have been performed, allowing detailed analysis of the designs under the expected operating conditions. The results show that the use of volumetric solar receivers to provide heat input to micro gas-turbine based solar dish systems appears to be a promising solution; with material temperatures and material stresses well below permissible limits.

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