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  • 251.
    Berglund, Lars
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Ansari, Mohd Farhan
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Fiberteknologi.
    Cellulose nanocomposites with ductile mechanical behavior2015Inngår i: ICCM International Conferences on Composite Materials, International Committee on Composite Materials , 2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The limited ductility of plant fiber biocomposites is typically caused by interfacial debonding mechanisms at low strain. This leads to damage development and premature failure. The present paper discusses recent results on cellulose nanocomposites with thermoset and thermoplastic matrices, where substantial ductility is observed. The data are presented and reasons for the observed ductility are discussed. 

  • 252.
    Berglund, Lars
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi, Biokompositer. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center. KTH Royal Inst Technol, WWSC, Fibre & Polymer Technol, Stockholm, Sweden..
    Yang, Xuan
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center. KTH Royal Inst Technol, WWSC, Fibre & Polymer Technol, Stockholm, Sweden..
    Berthold, Fredrik
    RISE Bioecon, Stockholm, Sweden..
    Holocellulose fibers: combining mechanical performance and optical transmittance2019Inngår i: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 257Artikkel i tidsskrift (Annet vitenskapelig)
  • 253.
    Berglund, Per-Olof
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Feng, Leping
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    An application of the noise synthesis technology (NST) to a system with an axial fan2002Inngår i: Forum Acustica 2002, Seville, Spain, 2002Konferansepaper (Fagfellevurdert)
  • 254.
    Bergman, David
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Aerodynamik.
    Study of the coupled interaction between the wake’s transient behavior and pressure surfaces upstream using Detached Eddy Simulation2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The aerodynamic sub-discipline of flow control has for many years been, and still is today, a very prominent subject of research. This field encompasses devices that produce a beneficial change in wall-bounded or free shear flows that may lead to, among many possibilities, reduced drag of ground vehicles and airplanes. The end result could have a substantial improved impact on fuel economy and also introduce new possible design options.

    Creo Dynamics AB recently started to venture into the field of active flow control with huge interest for the technology and its possible applications. One such application includes a system that reduces drag on ground vehicles via the use of active flow control. The system is composed of three components: actuators, controller and sensors. The work carried out in this thesis deals with a study into the sensory placement and control approach related to the system on a very conceptual level.

    According to Creo’s vision of the project the sensor shall record the pressure distribution and characteristics up-stream of the actuators. In turn the algorithm shall be capable of translating and correlating this data to the flow state downstream

    and in the wake. This data is then to be relayed to a control system producing the correct actuation response to achieve desired flow characteristics. For this system to work knowledge about the coupling between wake behavior and pressure distribution on surfaces upstream of the separated flow is necessary. This thesis is an initial investigation into the possible couplings that can be found. The scope also includes investigation of the coupling during cross-winds and gusts.

    Simulations of a simplified car geometry were carried out using the CFD package OpenFOAM and the DDES turbulence model. The initial investigation yielded promising results, showing that a link between the wake behavior and pressure distribution up-stream exists. But further work has to be carried out, as is discussed in the last chapter, before the algorithm according to Creo’s specifications can be constructed.

  • 255.
    Bergsek, Mattias
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Marina system.
    THRUST PREDICTION PROGRAM FOR MARINE JET POWER2011Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Marine Jet Power, MJP wishes to investigate the possibility of transforming their current Thrust Prediction Program, TPP written in C++ source code into a more up to date tool for their sales staff. The old TPP, though an accurate and precise tool, is not documented and lacks commentaries in the source code. Therefore the beginning of this master thesis was about documenting and investigates what methods were used to calculate the performance of the water jet system.The next step was splitting the long C++ source code in to smaller functions, this was done using MatLab where several m-files were created with the different functions in. C++ syntax and structure differs from MatLab so the source code must be translated in to MatLab syntax. Once the new TPP was translated and the calculation results were identical with the old TPP a Graphical User Interface, GUI was created and presented to MJP. The current MatLab TPP is not finished, only two of four calculation modes have been translated and MJP wants modifications in the GUI. The additional work needed in order to have the sales tool MJP wishes is currently discussed.

  • 256.
    Bergstedt, Robin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Aerodynamik.
    Aero-Design of Aerodynamically Lifting Struts for Intermediate Compressor Ducts2014Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Increasing demands on the performance and sustainability of modern turbofan engines put high requirements on each system component, and the limit of what is possible is expected to continue to extend. This thesis focuses on studies on the so-called turning struts concept which aims to shorten the compressor module of a future turbofan engine by introducing aerodynamically modified struts in the compressor mid-frame. Through CFD analysis and low-speed experimental evaluations, this concept is further developed with promising results attained in its early design stages. Important aerodynamic aspects related to this concept are highlighted, and appropriate conceptual design approaches are discussed. It was found that the length of the intermediate compressor duct could be reduced by up to 20% by eliminating the need for the last stator row in the upstream compressor, whilst providing comparable or improved performance compared to conventional designs.

  • 257.
    Bergstedt, Robin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    The Rocket SLS System - A Self Launch sailplane System Concept Analysis.2012Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
  • 258.
    Bergström, Rasmus
    et al.
    KTH.
    Crimella, Matteo
    KTH.
    Ivchenko, Nickolay
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Karlsson, Alexander
    KTH.
    Lindberg, Hannah
    KTH.
    Persson, Linnea
    KTH.
    Schlatter, Nicola
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Tibert, Gunnar
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Westerlund, Simon
    KTH.
    SCATTERING OF RADAR WAVES ON AEROSOLS IN PLASMAS2015Inngår i: EUROPEAN ROCKET AND BALLOON: PROGRAMMES AND RELATED RESEARCH, 2015, s. 87-94Konferansepaper (Fagfellevurdert)
    Abstract [en]

    To study the physical mechanisms of phenomena such as polar mesospheric summer echoes, the SCRAP (Scattering of Radar waves on Aerosols in Plasmas) experiment aimed to validate theories on density fluctuations in dusty plasmas. The SCRAP team developed two identical free falling units (FFUs) designed to create a cloud of copper particles once they eject from the REXUS17 sounding rocket 124 seconds after launch. By using the EISCAT incoherent scatter radar system to observe the cloud, the SCRAP experiment proposed to relate theoretical predictions to a controlled object. The SCRAP experiment was launched from ESRANGE on March the 17th 2015. The FFUs GPS signal was lost during launch and the units were therefore not found. Moreover, no backscattering from the copper cloud was observed by the radar.

  • 259.
    Bergwall, Robert
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Sandwich design of a lift plate for tail lift platforms for cargo trucks2015Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This master thesis examines a sandwich lift plate for cargo trucks in order to propose an option for existing lift platforms in aluminium or steel. The wish is to make it lighter but not less stiff or weak. Two different cores in Divinycell with different density; H130 and H250 is examined. Calculations are made with respect to deflection and max stress in both core and faces for the whole plates. But also more local calculations are performed to see how the faces and core behaved on local point loads from pallet lift wheels.

    The analytical results successfully meet the deflection requirements causing only 30 mm deflection in the worst scenario with 33% overload on a lift plate built up by 3 mm aluminium faces and H130 Divinycell core measuring a total (incl. faces) 20 mm thickness in the top. Nor did the von Mises stresses exceed 50% of ultimate strength for the aluminium parts or the Divinycell core. The choice between the lighter (H130) and heavier (H250) core only appears to affect the deflection 1-2 mm and the von Mises face stress for point loads are in the order of 10 MPa.

    The objective regarding the mass of the lift plate was not met. This is however a matter of further optimisation and is considered to be solved.

  • 260.
    Berhane, Joel
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.).
    Emil, Godonou
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Analysis and modeling of child mortality.2014Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    Child mortality has always been a strong indicator on the general wealth of a country therefore was decreasing it in the world one of the millennium goals. Since child mortality is such an important measure we have decided to make a structural model of it. This is an investigation regarding the causes of child mortality.

    The definition of child mortality is the number of children that died before the age of five. Not to be mixed with infant mortality which is a measure of those who died before the age of one. In contrast to infant mortality we think that child mortality strongly depends on other factors than just sickness, that’s why we chose to investigate child mortality among the two of them.

    We emanated from the assumption that it was possible to describe child mortality with the model:

    Y=Xβ+e

     

    With that in mind we collected data from the UN and the World Bank for child mortality and all possible factors that could affect child mortality.

    The analysis is made with the method "multiple linear regression". At the end it all came down to a structural model consisting of six explanatory variables which are:

    • U-nation

    • GNI in PPP-terms

    • Improved sanitation

    • Average precipitation

    • Help organization

    • Colony

    All of these variables got a positive coefficient in their effect on child mortality except for "GNI in PPP-terms" and "improved sanitation" which rationally got a negative sign. We also made a model which could be used for predicting child mortality. The difference between the prediction model and the structural model is the variable birthrate which is included in the prediction model but not in the structural model. In the prediction model birthrate got a positive sign.

  • 261.
    Berhouni, Ilyès
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Flygdynamik.
    Flow transition prediction approaches evaluated on a single-aisle type aircraft2019Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Nowadays, as the demand for fuel efficiency is increasing and the manufacturing techniques improved to allow the design of laminar wings, the laminar concepts are being revived and studied, and seen as one of the most promising techniques to reduce skin friction and hence the overall drag of the airframe. In order to predict the kind of benefits that could be obtained from such concepts, computational fluid dynamics (CFD) computations can now be carried out but it is necessary to be able to predict flow transition from laminar to turbulent around the lifting surfaces of the aircraft, such as the wing and the horizontal tail plane. Such capability has been developed in the last years by the French Aerospace Laboratory (ONERA) with their CFD code elsA, and by the German Aerospace Center (DLR) with their CFD code Tau. These two codes are widely used in Airbus in their CFD campaigns, and this study aims to assess the capability of the different approaches to predict transition and the benefits from laminar flow in the overall drag. The methods used, the limitations and the suggestions for further improvement of the codes will be detailed in this paper.

  • 262.
    Bernebrant, Sarah
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Topologioptimering av skruvförband2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [sv]

    Mjukvaruutvecklingen inom strukturoptimering har de senaste decennierna varit under ständig utveckling och förbättring. Fördelarna med lättare och mer hållbara strukturer ökar efterfrågan på bra metoder och verktyg för simulering och analys i konstruktionsprocessen. Topologioptimering är en typ av strukturoptimering som fokuserar på att hitta den optimala formen given en viss volym och designutrymme. Detta examensarbete behandlar topologioptimering av skruvförband. Skruvarna tar ofta höga laster i en struktur och det är viktigt att de inte glider eller går sönder. På Scania finns redan metoder för att hantera topologioptimering av skruvförband i programmet SIMULIA Tosca Structure 8.1.0. I år har även Altair kommit ut med en ny applikation som hanterar skruvar i deras topologioptimeringsprogram solidThinking Inspire som också används på Scania.

    Denna nya funktion analyseras och utvärderas för att se hur den ställer sig mot det mer etablerade Tosca för ett cylinderfäste med två skruvar. Efter att topologi samt spänningar i struktur och skruvar har analyserats för de bägge fallen drogs slutsatsen att den nya funktionen i solidThinking Inspire 2016 gav ett tillförlitligt resultat.

    För att lösa kvarstående problem, som jämn kraftdistribuering, påbörjas den andra delen av examensarbetet. Här diskuteras en ny metod för att simulera skruvförband med bivillkor i solidThinking Inspire 2016. Studien visar att kraftdifferensen mellan skruvarna minskar samt att storleken på kraften reduceras. Metoden kan även användas för att få en indikation för hur skruvarna ska positioneras och vilka som ska tas med i designen och vilka som kan tas bort.

  • 263.
    Berquand, Audrey
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    EXPERIENCE FROM THE STUDENT PROGRAMME REXUS/BEXUS: A STEPPING STONE TO A SPACE CAREER2015Inngår i: EUROPEAN ROCKET AND BALLOON: PROGRAMMES AND RELATED RESEARCH, 2015, s. 63-67Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The aim of this paper is to give an inside view to the REXUS/BEXUS programme from the perspective of a student who has been involved in the project. Each year, the German Aerospace Center (DLR) and the Swedish National Space Board (SNSB), in cooperation with the European Space Agency (ESA), offer the opportunity to European University Students to fly an experiment on board sounding rockets or stratospheric balloons in the frame of the REXUS/BEXUS programme. From December 2012 to May 2014 a team of master students from KTH, the Royal Institute of Technology, worked on ISAAC project, an atmospheric experiment launched on board REXUS 15. The author was part of this student team and was involved in the whole process of the ISAAC project from design building and testing phases to the launch campaign and results analysis. The points raised in this article were presented on the occasion of a keynote speech during the 22nd ESA Symposium on European Rocket and Balloon Programmes and Related Research, in Tromso (Norway) from the 7th to the 12th of June 2015. The aim of this presentation was to demonstrate the benefits of hands-on Education programme at University level. In addition to the research opportunities, future space engineers and scientists can profit from a first practical experience under the supervision of experimented experts. The results of the ISAAC project were also presented in the frame of this conference [1].

  • 264.
    Berquand, Audrey
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Aerodynamik.
    Relative Close Navigation for Non cooperative Rendezvous2014Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This report presents the work done in the frame of a master thesis at Airbus Defence and Space, Les Mureaux on « Relative Close Navigation for Non cooperative Rendezvous » from the 3rd of March to the 29th of August 2014.

    The master thesis subject is the implementation of an initialization algorithm based on Infrared monovision sensors into a pose estimation simulator in the frame of a Non cooperative Rendezvous.

    The pose of a satellite represents its orientation in Euler angles and its relative position to the chaser.

    The initialization algorithm chosen to be implemented is a model-based method involving a Principal Component Analysis. A target template image of size (K, L) pxls is decomposed into a feature vector of size (1, r ). The feature vector contains all the main characteristics of the image. The matching is done via a comparison between a set of feature vectors representing several known target attitudes and the feature vector of the input attitude. The computation load is higly reduced compared to a omparison between images.

    The simulations with simulated images of a basic target shape (a cube) led to accurate attitude and position estimations.The results with real Infrared images inputs give us reasons to believe that the estimations in real space conditions could be conclusive. However, the simulations were done for simplified cases, without, for instance, considering noise measurements. Further studies will have to be done to see if the initialization algorithm allows the simulator tracking algorithm to converge.

  • 265.
    Bessman, Alexander
    et al.
    KTH.
    Soares, Rúdi
    KTH.
    Wallmark, Oskar
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Svens, Pontus
    KTH.
    Lindbergh, Göran
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemiteknik.
    Aging effects of AC harmonics on lithium-ion cellsManuskript (preprint) (Annet vitenskapelig)
  • 266.
    Bharath, G.
    et al.
    Trinity College Dublin, Department of Mechanical and Manufacturing Engineering, Ireland .
    O'Reilly, Ciarán J.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. Trinity College Dublin, Department of Mechanical and Manufacturing Engineering, Ireland.
    Barrera Rolla, Leandro
    Trinity College Dublin, Department of Mechanical and Manufacturing Engineering, Ireland.
    Rice, Henry J.
    Trinity College Dublin, Department of Mechanical and Manufacturing Engineering, Ireland .
    Iterative solutions of the three-dimensional Helmholtz equation using the wave expansion method for high frequency acoustic scattering problems2007Inngår i: 36th International Congress and Exposition on Noise Control Engineering, INTER-NOISE, 2007, Vol. 7, s. 4788-4795Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Modelling sound propagation over large domains presents severe challenges with respect to computational requirements. In general, direct solutions of system equations resulting from the full field discretization of many three-dimensional problems of practical interest cannot be attempted. The present study investigates iterative solutions for solving a Three-Dimensional Helmholtz equation. The discretization of the Helmholtz equation is done by a Wave Based Finite Difference scheme known as the Wave Expansion Method (WEM). The WEM requires only 2-3 nodes per wavelength to obtain accurate solutions which offers a potential for major improvement in efficiency compares to conventional techniques such as the Finite Element/Finite Difference approaches which require around 8-10 nodes per wavelength. The solver employed here is the standard Bi-Conjugate Gradient Stabilized (Bi-CGSTAB) algorithm. Results are presented for high frequency acoustic scattering problems occurring in aircrafts. Investigations are also carried out to check the effectiveness of the standard preconditioning strategies such as the Incomplete LU decomposition with drop tolerance method. The influence of the scatterer is also studied in this paper.

  • 267.
    Bhat, Sriharsha
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Fordonsdynamik. KTH, Skolan för industriell teknik och management (ITM), Centra, Integrated Transport Research Lab, ITRL.
    An Investigation into the Optimal Control Methods in Over-actuated Vehicles: With focus on energy loss in electric vehicles2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    As vehicles become electrified and more intelligent in terms of sensing, actuation and processing; a number of interesting possibilities arise in controlling vehicle dynamics and driving behavior. Over-actuation with inwheel motors, all wheel steering and active camber is one such possibility, and can facilitate control combinations that push boundaries in energy consumption and safety. Optimal control can be used to investigate the best combinations of control inputs to an over-actuated system. In Part 1, a literature study is performed on the state of art in the field of optimal control, highlighting the strengths and weaknesses of different methods and their applicability to a vehicular system. Out of these methods, Dynamic Programming and Model Predictive Control are of particular interest. Prior work in overactuation, as well as control for reducing tire energy dissipation is studied, and utilized to frame the dynamics, constraints and objective of an optimal control problem. In Part 2, an optimal control problem representing the lateral dynamics of an over-actuated vehicle is formulated, and solved for different objectives using Dynamic Programming. Simulations are performed for standard driving maneuvers, performance parameters are defined, and a system design study is conducted. Objectives include minimizing tire cornering resistance (saving energy) and maintaining the reference vehicle trajectory (ensuring safety), and optimal combinations of input steering and camber angles are derived as a performance benchmark. Following this, Model Predictive Control is used to design an online controller that follows the optimal vehicle state, and studies are performed to assess the suitability of MPC to over-actuation. Simulation models are also expanded to include non-linear tires. Finally, vehicle implementation is considered on the KTH Research Concept Vehicle (RCV) and four vehicle-implementable control cases are presented.

    To conclude, this thesis project uses methods in optimal control to find candidate solutions to improve vehicle performance thanks to over-actuation. Extensive vehicle tests are needed for a clear indication of the energy saving achievable, but simulations show promising performance improvements for vehicles overactuated with all-wheel steering and active camber.

  • 268.
    Bhat, Sriharsha
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Fordonsdynamik.
    Davari, Mohammad Mehdi
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Fordonsdynamik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Nybacka, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Fordonsdynamik. KTH, Skolan för industriell teknik och management (ITM), Centra, Integrated Transport Research Lab, ITRL.
    Study on energy loss due to cornering resistance in over-actuated electric vehicles using optimal control2017Inngår i: SAE International Journal of Vehicle Dynamics, Stability, and NVH - V126-10, 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    As vehicles become electrified and more intelligent in terms of sensing, actuation and processing; a number of interesting possibilities arise in controlling vehicle dynamics and driving behavior. Over-actuation with in- wheel motors, all wheel steering and active camber is one such possibility, which facilitate the control strategies that push boundaries in energy consumption and safety. Optimal control can be used to investigate the best combinations of control inputs to an over-actuated system. This paper shows how an optimal control problem can be formulated and solved for an over-actuated vehicle case, and highlights the translation of this optimal solution to a real-world scenario, enabling intelligent means to improve vehicle efficiency. This paper gives an insight into the Dynamic Programming (DP) as an offline optimal control method that guarantees the global optimum. Therefore the optimal control allocation to minimize an objective function and simultaneously fulfill the defined constraints can be achieved. As a case study the effect of over-actuation on the cornering resistance were investigated in two different maneuvers i.e. step steer and sine with dwell, where in both cases the vehicle assumes to be in steady state situation. In this work the cornering resistance is the main objective function and maintaining the reference trajectory is the constraint which should be fulfilled. A parameter study is conducted on the benefits of over-actuation, and depending on the type of over-actuation about 15% and 50% reduction in cornering resistance were observed during step steer and sine with dwell maneuver respectively. From a second parameter study that focused on COG position from a safety perspective, it is more beneficial for the vehicle to be designed to under-steer than over-steer. Finally, a method is described to translate the offline optimal results to vehicle implementable controllers in the form of both feed-through lookup-tables and rule-based feed-forward control.

  • 269.
    Bhattacharyya, Shounak
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Fordonsdynamik.
    Sivaramakrishnan, Suraj
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Fordonsdynamik.
    Parameter Optimisation of EPAS Using CAE2019Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    To keep up with technological as well as logistical challenges of the modern automobile market, major car manufacturing firms have resorted to virtual simulation tools. This enables the development as well as validation of vehicular models much before resources are invested into a new physical prototype.This project focuses on the development of a tool that would help in optimising the handling parameters of a vehicle. This is achieved by creating an optimization routine for tuning the various parameters of the Electronic Power Steering (EPAS). This process is usually done manually, by on-track testing, due to the difficulties in correlating Subjective Assessments (SA) with Objective Metrics (OM). Automating this process would help to reduce the overall research and development time, by providing a baseline tune for the EPAS parameters which could then be finely tweaked by manual track testing.The tool is built by interfacing various software in a multi-objective optimisation environment known as ModeFrontier. The modelling and simulations are performed in IPG CarMaker, with the post processing of the results taken care of by Sympathy for Data. Multiple optimization algorithms were tested to achieve the best optimisation routine. The EPAS parameters, namely the Basic Steering Torque, Active Return and Active Damping, act as the input to the optimization routine. The outputs of the model are the Objective Metrics, which provide a clear indication of the dynamic performance of a component. These metrics are optimized to _t the Steering DNA structure, which uniquely describes the attributes of a vehicle. The final optimised vehicle is manually tested at the track, to determine the real driving feel.

  • 270.
    Bhatti, Ayjwat A.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Development of efficient three-dimensional welding simulation approach for residual stress estimation in different welded joints2012Inngår i: Journal of Strain Analysis for Engineering Design, ISSN 0309-3247, E-ISSN 2041-3130, Vol. 47, nr 8, s. 539-552Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Based on the available welding simulation approaches found in the literature, an alternative and simplified welding simulation approach is developed, called rapid dumping. It is a sequential thermomechanical approach, which makes use of the moving heat source in thermal analysis and the block-dumping approach in mechanical analysis for prediction of welding residual stresses in three dimensions. It is first developed for longitudinal stiffener joint and then validated by applying on a butt-welded, T-fillet, and multipass tube-flange joints. The temperature-dependent material properties were obtained using JMat Pro software, a java-based material property simulation software. The material properties were validated with experimentally determined material properties found in the literature. The predicted residual stresses were validated by X-ray diffraction measurements on the longitudinal stiffener fillet-welded joint. Using the rapid-dumping approach, the residual stresses obtained at the weld toe were in qualitatively good agreement with the measured residual stresses. The rapid-dumping approach showed to capture the effects of moving heat source and weld start/stop location. In addition, it has reduced the computational time significantly with a preserved accuracy of the estimated welding residual stresses.

  • 271.
    Bhatti, Ayjwat A.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. Osaka University, Japan.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. Khalifa University of Science, United Arab Emirates.
    Murakawa, Hidekazu
    Barsoum, Imad
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. The Petroleum Institute, United Arab Emirates.
    Influence of thermo-mechanical material properties of different steel grades on welding residual stresses and angular distortion2015Inngår i: Materials & Design, ISSN 0261-3069, Vol. 65, s. 878-889Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The present study investigates the influence of thermo-mechanical material properties of different steel grades (S355-S960) on welding residual stresses and angular distortion in T-fillet joints. Different cases in which temperature dependent thermo-mechanical material properties are considered as constant, linear, and as a function of temperature are simulated by using finite element (FE) method. Experiments are carried out to evaluate temperature dependent yield stress and Young's modulus for S700 and S960 steel grades. Furthermore, JMat Pro software is used to obtain the remaining thermo-mechanical material properties. The numerical predictions of angular distortion and transverse residual stresses are validated with experimental measurements. It is observed that for assessment of residual stresses, except yield stress, all of the thermo-mechanical properties can be considered as constant. For the prediction of angular distortions with acceptable accuracy, heat capacity, yield stress and thermal expansion should be employed as temperature dependent in the welding simulations.

  • 272.
    Bhatti, Ayjwat Awais
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    3D Fracture Analysis of Cold Lap WeldDefect in Welded Structures2011Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This thesis is concerned with the classification and effect of cold lap weld defect onthe fatigue strength of a welded structure. Cold lap is a type of weld defect whichoccurs when molten metal does not completely fuse with the cold plate surface. Thisproduces a crack like defect, often very small, which is parallel to the plate. The coldlap weld defect has been classified into three types namely spatter, overlap andspatter-overlap cold lap. Study showed that all three types of cold lap defects have thecorresponded lack of fusion in the interface, which could be considered as initialmacro cracks in different shapes where a possible fatigue crack growth could start.Fatigue life assessment of the above mentioned three types of cold lap defects wascarried out using finite element and crack growth analysis in 2D and 3D. In the 2Danalysis the cold lap defects were modeled as line crack (assuming a/c=0). Based onthe experiments the cold lap defects were visualized as having two probable crackshapes; penny shaped and part through, which required 3D crack growth analysis.Results showed that in 2D analysis the three types of cold lap defects have sameinfluence on fatigue life of the weld. In 3D analysis, the shape of the cold lap defectsdid not show any difference in fatigue life. Overall penny shaped and part throughcracks in 3D analysis predicted 1.75 times longer fatigue life as compared to line crackin 2D analysis.

  • 273.
    Bhatti, Ayjwat Awais
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Computational weld mechanics: Towards simplified and cost effective FE simulations2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    It is the demand of the world’s ever increasing energy crisis to reduce fuel consumption wherever possible. One way of meeting this demand is by reducing the weight of a structure by replacing thick plates of low strength steel with thin plates of high strength steel in the structure. Fusion welding process is extensively used in the manufacturing industry, however, despite many advantages different problems such as weld defects, residual stresses and permanent distortions are associated with this process.

    Finite element (FE) method has proved itself as an alternative and acceptable tool for prediction of welding residual stresses and distortions. However, the highly nonlinear and transient nature of the welding process makes the FE simulation computationally intensive and complex. Thus, simplified and efficient welding simulations are required so that they can be applied to industrial scale problems.

    In this research work an alternative FE simulation approach for the assessment of welding residual stresses, called rapid dumping is developed. This approach proved to be efficient and predicted the residual stress with acceptable accuracy for different small scale welded joints. This approach was further implemented on a large scale welded structures along with other available approaches. It was found that the computational time involved in the welding simulations for large structures using rapid dumping approach can be reduced but at the cost of accuracy of the results.

    Furthermore, influence of thermo-mechanical material properties of different steel grades (S355-S960) on welding residual stresses and angular distortion in T-fillet joints is investigated. It is observed that for assessment of residual stresses, except yield stress, all of the thermo-mechanical properties can be considered as constant. For the prediction of angular distortions with acceptable accuracy, heat capacity, yield stress and thermal expansion should be employed as temperature dependent in the welding simulations.

    Finally, the influence of two different LTT (Low Transformation Temperature) weld filler material on residual stress state and fatigue strength was investigated. It was observed that a reduction in tensile residual stresses at the weld toe of the joint was observed. Furthermore, at higher R-ratio no significant increase in the fatigue strength was observed . However, at low R-ratio significant  increase in fatigue strength was observed.

  • 274.
    Bhatti, Ayjwat Awais
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Khurshid, Mansoor
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Development of a finite element simulation framework for the prediction of residual stresses in large welded structures2014Inngår i: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 133, s. 1-11Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study a framework for efficient prediction of residual stresses in large welded structure is proposed. For this purpose different finite element simulation approaches available in literature are implemented on a large bogie beam structure. Among all approaches rapid dumping approach used minimum computational time and also it showed qualitatively good agreement with X-ray diffraction measurements for welding residual stresses. Moreover, gradual weld bead deposition approach predicted more accurate results when compared with the experimental measurements and other approaches. Also, by using substructuring approach the computational time is significantly reduced with an acceptable accuracy of predicted welding residual stresses.

  • 275.
    Bhatti, Ayjwat Awais
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Van Der Mee, V.
    Kromm, A.
    Kannengiesser, T.
    Fatigue strength improvement of welded structures using new low transformation temperature filler materials2013Inngår i: Fatigue Design 2013, International Conference Proceedings, Elsevier, 2013, s. 192-201Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The results reported in this research study are part of a larger EU RFCS (Research Fund for Coal and Steel) project where the aim is to study the fatigue behavior of improved welds in high strength steels by utilizing different improvement techniques. In this particular study LTT (Low Transformation Temperature) weld filler material have been investigated and their possibility to improve the fatigue strength. The characteristic of these filler material is that they undergo phase transformation at temperature close to room temperature which will reduce the tensile residual stress in the weld and in some cases result in compressive residual stresses. Two different LTT alloy compositions have been developed, with different Ms (Martensite Start) temperatures in order to study the amount of tensile/compressive residual stresses produced by these wires. Welding residual stress measurements were carried out by X-ray diffraction technique. Plates with welded longitudinal attachments were fabricated in 700 MPa and 960 MPa steel grades using different LTT filler materials. These specimens were fatigue tested in constant and variable amplitude loading and the fatigue test results were compared with results from specimen welded with conventional weld filler material.

  • 276. Bhatti, Ayjwat Awais
    et al.
    Li, Peigang
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Svensson, Lars Erik
    Samuelsson, Jack
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Classification and crackgrowth modeling of cold lap defects in tandem GMAW welding2011Inngår i: International Symposium onFatigue Design & Material Defects, 2011Konferansepaper (Fagfellevurdert)
  • 277. Bhiwapurkar, M. K.
    et al.
    Saran, V. H.
    Goel, V. K.
    Mansfield, N.
    Berg, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Study of human comfort under thermal and vibratory environment using physiological indices2009Inngår i: 16th International Congress on Sound and Vibration 2009, ICSV 2009, 2009, s. 4376-4383Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Besides the vibrations, passenger discomfort is influenced by various other factors such as, the environmental factors of noise, temperature, humidity and visual stimuli, etc. The discomfort can be measured both subjectively and objectively. Rammohan25 studied the influence of backrest support and handgrip contractions on acute metabolic, respiratory, and cardiovascular responses during exposure to whole-body vibration (WBV). In the present work, discomfort of passengers subjected to whole body random vibrations, environmental factors such as temperature, humidity and noise level variations by assessing their effect on various physiological parameters like, Pulse Rate, Respiration Rate, Galvanic Skin Response, Skin Temperature, Heart Rate, Heart Rate Variability and ECG values has been studied. The study was conducted on the three axes vibration simulator developed in the Laboratory, IIT Roorkee, India as a mock-up of a railway vehicle. The simulator room has a controlled temperature and humidity environment and its noise level can also be controlled. A BIOPAC system was used for data acquisition along with various modules for measuring physiological parameters. The mean and standard deviation of physiological parameters, possibly indicating the human comfort or discomforts for the 12 subject is found out. The design of experiment (ANOVA) was employed to quantify the relationships between measured responses and the input factors. The results show that some physiological parameters viz, pulse rate, SKT and HR show variation in vibration condition at 0.6 m/s2. It is also found that all the parameters affected by noise level and temperature show significant variation between no vibration condition and vibration condition.

  • 278. Bhiwapurkar, M. K.
    et al.
    Saran, V. H.
    Harsha, S. P.
    Goel, V. K.
    Berg, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Spårfordon. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    Effect of magnitudes and directions (mono-axis and multi-axis) of whole body-vibration exposures and subjects postures on the sketching performance2011Inngår i: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 225, nr F1, s. 71-83Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Whole-body vibrations in trains are known to affect the performance of sedentary activities such as reading, writing, sketching, working on a computer, etc. The objective of the study was to investigate the extent of disturbance perceived in sketching task by seated subjects in two postures under mono-and multi-axis Gaussian random vibration environment. The study involved 21 healthy male subjects in the age group of 23-32 years. Random vibrations were generated both in mono-and multi-axial directions in the frequency range of 1-10 Hz at 0.5, 1.0, and 1.5 m/s(2) rms (root mean square) amplitude. The subjects were required to sketch given geometric figures such as a circle, triangle, rectangle, and square with the help of ball-point pen under given vibration stimuli in two postures (sketch pad on lap and sketch pad on table). The deviation in distortion with respect to the given figure is represented in terms of percentage distortion. The influence of vibrations on the sketching activity was investigated both subjectively and by two specifically designed objective methods, namely, RMS (root mean square methodology) and area methods. The judgements of perceived difficulty to sketch were rated using seven-point semantic judgement scale. The percentage distortion and difficulty in sketching activity increased with an increase in vibration magnitude. Both subjective evaluation and the RMS method revealed that the task was affected more while sketching on the table. The percentage distortion was affected similarly and maximum in all the vibration directions except for the vertical, while sketching difficulty was found to be higher only with longitudinal and multi-axis vibration direction. The subjective evaluation also revealed that there was no effect of the type of entity chosen on the sketching difficulty.

  • 279. Bhiwapurkar, M. K.
    et al.
    Saran, V. H.
    Harsha, S. P.
    Goel, V. K.
    Berg, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Spårfordon. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    Influence of Mono-axis Random Vibration on Reading Activity2010Inngår i: Industrial Health, ISSN 0019-8366, E-ISSN 1880-8026, Vol. 48, nr 5, s. 675-681Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent studies on train passengers' activities found that many passengers were engaged in some form of work, e.g., reading and writing, while traveling by train. A majority of the passengers reported that their activities were disturbed by vibrations or motions during traveling. A laboratory study was therefore set up to study how low-frequency random vibrations influence the difficulty to read. The study involved 18 healthy male subjects of 23 to 32 yr of age group. Random vibrations were applied in the frequency range (1-10 Hz) at 0.5, 1.0 and 1.5 m/s(2) rms amplitude along three directions (longitudinal, lateral and vertical). The effect of vibration on reading activity was investigated by giving a word chain in two different font types (Times New Roman and Anal) and three different sizes (10, 12 and 14 points) of font for each type. Subjects performed reading tasks under two sitting positions (with backrest support and leaning over a table). The judgments of perceived difficulty to read were rated using 7-point discomfort judging scale. The result shows that reading difficulty increases with increasing vibration magnitudes and found to be maximum in longitudinal direction, but with leaning over a table position. In comparison with Times New Roman type and sizes of font, subjects perceived less difficulty with Anal type for all font sizes under all vibration magnitude.

  • 280.
    Bilen Oytun, Peksel
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Advanced Model of Acoustic Trim; Effect on NTF Accuracy2011Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 281. Birgersson, F.
    et al.
    Finnveden, Svante
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    A spectral super element for modelling of plate vibration. Part 2: turbulence excitation2005Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 287, nr 02-jan, s. 315-328Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the accompanying paper, the suitability of a spectral super element to predict the response to point force excitation, was demonstrated. This paper expands the element formulation to also include distributed forces, which is useful when studying distributed excitation. First the sensitivity function, i.e. the structural response to a travelling pressure wave, is found. This sensitivity function and a wavenumber frequency description of the wall pressure are then used to predict the response of a turbulence excited panel in a numerically efficient way. The predictions were validated by a conventional finite element method and also compared to measurements.

  • 282. Birgersson, F.
    et al.
    Finnveden, Svante
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Nilsson, C. M.
    A spectral super element for modelling of plate vibration. Part 1: general theory2005Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 287, nr 02-jan, s. 297-314Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dynamic response of vibrating structures is studied with a proposed merger of the standard finite element method with the more computationally efficient spectral finite element method. First a plate structure is modelled with a newly developed spectral super element. Then this element is coupled to other parts that can have a more complex geometry and are modelled entirely with conventional finite elements. Some numerical examples are given to illustrate and validate the developed method and studies of numerical stability are also presented. In an accompanying paper the predicted and measured response of a turbulence excited aircraft panel are compared.

  • 283.
    Birgersson, Fredrik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Ferguson, Neil S
    Application of the spectral finite element method to turbulent boundary layer induced vibrations of plates2003Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 259, s. 873-891Artikkel i tidsskrift (Fagfellevurdert)
  • 284. Bisping, R.
    et al.
    Dickson, Crispin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Khan, Shafiq
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Psychometric analysis of stationary aircraft sounds2006Inngår i: 13th International Congress on Sound and Vibration 2006, 2006, s. 3658-3664Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The acoustical properties of aircraft sounds dynamically change during the time-history of the fly-over. It is therefore difficult to determine the relationship between the human perception of aircraft sounds and these acoustical changes. One option could be to use time continuous judgment to find relationships between acoustical and perceptual data, e.g. by applying cross-correlation methods. Since aircraft sounds comprise many acoustical features which might change simultaneously this method has a limited range of validity. To overcome such problem in the present study synthesized stationary aircraft sounds were used instead of the natural aircraft sounds. This allows the experimental variation of just one feature of interest at a given time. The sounds were generated to represent three different angles of the aircrafts flyover position relative to the observer at 78, 7°, 90° and 101, 3°. These three positions were found to cover a significant part of the acoustical phenomena which may occur during flyover, e.g. tonal components, fan noise, low-versus high frequency broadband effects, etc. Synthesis was performed based on the measurements of six different aircrafts and two flight conditions (take-off & arrival). All the sounds were equalized to have the same EPNL-level. The sounds were judged by 25 subjects using a multidimensional scale having five different attributes: loudness, annoyance, hardness, power and pitch. The statistical analysis of the data showed highly significant differences between the acoustical phenomena and all chosen perceptual attributes. The paper will present the applied methods and the results.

  • 285.
    Björkblad, Anders
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    A novel tool for crack modelling in finite element analysisArtikkel i tidsskrift (Annet vitenskapelig)
  • 286.
    Björkblad, Anders
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Conventional vs. closure free crack growth in nodular iron2005Inngår i: Competent Design by Castings: Improvements in a Nordic Project / [ed] Samuelsson J, Marquis G, Solin J, Valtion Teknillinen Tutkimuskeskus , 2005, s. 273-286Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This investigation deals with the fatigue properties and material parameters for a silicon alloyed nodular cast iron. The material follows the Swedish standard SS 140725. The objectives for this investigation where to evaluate properties of the material in a fracture mechanic sense of view. In this part, the attention was paid to the basic fracture mechanic properties, i.e. da/dN-curves and Pan's law parameters. It also include R-dependence behaviour evaluated for R-values from R= 0 and R= 0.8. The main incitement for using the closure free approach is that it produces the fastest crack propagation rate that can be found at given conditions and load levels. This investigation of nodular iron will be followed by subsequent parts. The investigation in total is a part of the nordic project "Cast Design 2005".

  • 287.
    Björkblad, Anders
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Fatigue assessment of cast components2005Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 288.
    Björkblad, Anders
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Fatigue Assessment of Cast Components: Influence of Cast Defects2008Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

     This thesis is on the fatigue assessment of cast components with special attention to defects. The primary material in view is nodular cast iron, but also cast steel is considered. However, the fatigue behaviour is in principle valid for general use on other cast metals.The first two papers is about general cast material behaviour in fatigue loading. The materials considered are a high strength alloyed cast steel and a medium strength nodular cast iron. It is concluded that cast defects is the main fatigue initiation cause and it is only in exception that the fatigue life is not ruled by fracture mechanics. The third paper is a fracture mechanics evaluation of a nodular iron cast sleeve. The analysis of the component is based on crack initiation from cast defects and low-cycle fatigue. Fracture mechanics material parameters for Paris law, c and m, are extracted for the materials considered. In paper D design quality rules for nodular cast iron based on the Swedish standard SS 11 40 60 is presented. The quality rules regard cast defects in fatigue assessments and facilitate defect-based component design. In paper E, a finite element tool that is capable to predict and calculate 3D crack propagation for embedded cracks and defects is presented. The tool is an add-on for ANSYS finite element program. In paper F, closure equations for nodular cast iron are proposed in parallel to refined fracture mechanics material data. The paper includes crack propagation at different load ratios and in different microstructures.Summarized, the thesis composes a further development of the fatigue assessment of cast components. The central role of defects in fatigue is clarified and tools are provided for fracture mechanics evaluations of defects as well as for defect based design. The quality rules are also fit for application in manufacturing and for acceptance tests, hence covering the span from design to complete product.

  • 289.
    Björkblad, Anders
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Fracture mechanics evaluation of a nodular cast iron component by 3d modelling2005Inngår i: Competent Design by Castings: Improvements in a Nordic Project / [ed] Samuelsson J; Marquis G; Solin J, 2005, Vol. 237, s. 351-374Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The object of this paper was fracture mechanic modelling of solids using finite element (FEM). The main tool that has been utilized was the software Mcrack which is a group of macros intended for use jointly with ANSYS finite element program. One major advantage of the Mcrack software is that it supports solid modelling with a crack located at an arbitrary location. This implies that it is possible to calculate also torsion and mixed mode cases within a most reasonable work effort. However, Mcrack was developed to cover complex weld geometries. Utilizing Mcrack for general solid modelling requires an analysis of the possibility of development for arbitrary crack paths. As test object a cast sleeve made of nodular iron has been used. Previous to this investigation the component was submitted to a test program and a subsequent evaluation according to S/N criteria's at ABB, Sweden. This paper is thus a continuation of the ABB work, and at the same time an extension of the field of application for the Mcrack software. For validation purposes the software AF-Grow as well as elementary cases has been used in parallel. The investigation is a part of the nordic project "Cast Design 2005".

  • 290.
    Björkblad, Anders
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Fracture-mechanics-founded quality rules for defect classification in nodular cast ironArtikkel i tidsskrift (Annet vitenskapelig)
  • 291.
    Björkblad, Anders
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    On the prediction of crack propagation in cast steel specimens2005Inngår i: Competent Design by Castings: Improvements in a Nordic Project / [ed] Samuelsson, J; Marquis, G; Solin, J, ESPOO: TECHNICAL RESEARCH CENTRE FINLAND , 2005, Vol. 237, s. 251-272Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This investigation deals with the fatigue behaviour of cast steel with respect to defects, crack initiation, crack growth and material parameters. It constitutes the initial part of a larger work in cast materials. The main objectives have been to validate calculations made by FEM and Paris law with data from fatigue tests and to confirm material parameters for Pan's law. Furthermore, the results where put against calculations obtained from the fracture mechanic software AF-GROW. During the accomplishment some difficulties was experienced concerning the initiation of the crack, with result that there where just a few specimens suitable for evaluation by LEFM. However, some conclusions concerning the crack growth behaviour could yet be done. The results in general showed good correspondence, the results from AF-GROW included. Most divergences could be explained by residual stresses and, to some extent, the initiation problems.

  • 292.
    Björkblad, Niklas
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    VERIFICATION METHOD FOR FLEXIBLE EXHAUST HOSE: A background study2015Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    On Scania trucks of today a flexible exhaust hose is used to decouple the motions of components in the exhaust system. This flexible hose section experiences premature and unpredictable failures. To gain control over the situation a lifetime assessment is required, in which the ultimate verification is to be confirmed in a test rig. In order to build this rig and perform adequate tests, background information is needed. This report is aimed at collecting and analysing information on the underlying problem, such as material characteristics, working conditions and failure modes for the flexible hose. This is done by a literature study, measurements and investigations and an FE-model. The results show that the major failure mechanism is wear. The wear is concentrated to a small portion of the hose due to the unstable nature of the construction, aggravating the working conditions for the material. In addition, heating to working temperature seems to bring with it much increased wear rates and a significant increased friction coefficient for the interaction between the metal sheets constituting the hose. Because of the working mode of the hose, the material used should be replaced with a more suitable alternative. To start out, a change from the current EN 1.4301 (AISI 304) to the, from the manufacturer instantly available, EN 1.4571 (AISI 316 Ti) should be made. There are other material alternatives offered as direct replacements, these should be evaluated along with suitable surface treatments.

  • 293.
    Björnholdt Böll, Signe
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    A study of SPEs ​and the consequences of radiation exposure2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    With thorough literature studies as well as simulations, a way to minimize the exposure to radiationthat astronauts are at risk of encountering during a solar proton event is sought. The understanding ofwhere these particles come from, as well as the random nature of solar particle events is of importancein order to predict their occurrence. Different models used for predicting solar particle events based on aPoisson possibility distribution are presented, as well as real-time forecasts which give a warning of anapproaching event. Although the models used for real-time forecasts have a high accuracy rate, the averagewarning time is only approximately one hour. The downside with the predicted possible occurrence isthat this only gives a statistical probability of events that could possibly occur. For the real-time forecaststhe downside is that with an average warning time of only one hour, they do not give a lot of time forseeking shelter during the onset of an event. With simulations it is shown that the best way to minimizethe radiation dose obtained by astronauts is to use different materials of shielding. It is also shown that alower shielding thickness when encountering SPEs, for example when in a space suit, is useful as longas the total amount of time spent in this suit during the duration of a mission is planned thoroughly inorder to stay below the radiation dose limits. If an astronaut would be caught in an event with the samemagnitude and intensity as the solar particle event of August 1972, it is shown that the astronaut onlyhas nine minutes to seek shelter before exceeding the radiation dose limits and thereby risking radiationinduced sickness.

  • 294. Björnsson, A.
    et al.
    Jonsson, M.
    Lindbäck, J. E.
    Åkermo, Malin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Johansen, K.
    Robot-forming of prepreg stacks - Development of equipment and methods2016Inngår i: ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials, European Conference on Composite Materials, ECCM , 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Within the aerospace industry the manufacturing of composite components with complex shapes, such as spars, ribs and beams are often manufactured using manual layup and forming of prepreg material. Automated processes for prepreg layup and efficient forming techniques like vacuum forming are sometimes difficult to employ to these type of products due to technical limitations. This paper describes the development of tools and the forming sequence needed to automate sequential forming of a complex shape using an industrial robot. Plane prepreg stacks are formed to the final shape using a dual-arm industrial robot equipped with rolling tools. Tests show that the developed tools and the employed sequence can be used to form stacks to the desired shape with acceptable quality. 

  • 295.
    Björnsson, Lars
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Marina system.
    Comparison of Idealized 1D and Forecast 2D Wave Spectra in Ship Response Predictions2013Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Commonly, when calculating ship responses one uses idealized wave spectra to represent the sea. In the idealized model, the sea is frequently assumed to consist of swell and windwaves, which are usually represented by idealized 1D wave spectra, and the directionality of wind-waves is accounted for by multiplication with a standard spreading function. In operational response predictions these idealized spectra are typically generated by extracted parameters from real directional 2D wave spectra obtained from a weather forecast, i.e. spectra that reflects the sea state conditions for the particular place and time. It is generally not known in a statistical sense how large the errors become when idealized wave spectra are used to represent 2D wave spectra, especially not regarding the directionality. The objective with the study is hence to assess the errors that arise when adopting this simplification.

    The analysis compares three ship types that cover different combinations of hull form, load condition and operational conditions: a 153m RORO ship, a 219 m PCTC and a 240m bulk carrier. Chosen response parameters are roll motion, vertical acceleration and wave added resistance, which were calculated in 12240 sea states, for 10 speeds and 36 courses for each ship. The sea states are forecast 2D spectra from the North Atlantic 25th of September 2012. Transfer functions were generated from the hull geometry and realistic load conditions at speeds 2-20 knots. For each sea state-speed-course combination, responses were calculated for 2D wave spectra and corresponding generalized spectra. The error is taken as the difference in response between results obtained with 2D and idealized spectra, using 2D-results as reference. Several statistical measures were used to represent the errors for one sea state with only one number, and among them the root-mean-square error (RMSE) and the worst possible error (WPE) are regarded most relevant.

    The results show that the relative error decreases with increasing share of wind waves and decreasing share of swell. Multi-directionality of wind waves causes large errors only for small waves, and it is concluded that for higher sea states (for which the wind waves are predominant) the Bretschneider representation with spreading function leads to small relative errors. Absolute errors are considered the only relevant for investigating the effect of the error on seakeeping calculations. In general, the RMS acceleration levels are in the order of percentages of one g for all ships. For the bulker, WPE and RMSE for wave added resistance was found to be 8.3% and 3.8% of the total calm-water hull resistance in general, and almost 50% in worst case. The roll angle bias could reach up to 15. Also, the effect of ship speed was investigated, and it shows that the error increases in general with higher speed. It is concluded that it is necessary to use 2D spectra in order to avoid large errors, and to keep performance predictions correct on average.

  • 296.
    Blanco, Blas
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Development of new techniques for the numerical modelling of railway track dynamics. Application to rolling noise assessment2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The numerical modelling is widely employed for the prediction of the railway track dynamic behaviour, which is of utmost importance for the characterisation of the undesired medium-high frequency phenomena, such as corrugation, wheel-out-of-roundness and noise emission. This study is devoted to the improvement of railway track numerical modelling, the efficient resolution of the problem in the time domain and the assessment of rolling noise for different approaches of the track modelling.

    Regarding the enhancement of the railway track numerical modelling, two main core ideas have led the development of this task. On the one hand, the rail modelling, and on the other hand, the characterisation of the finite length nature of track supports. The proposals of this work include two basic premises, accuracy and computational efficiency.

    Firstly, the study makes use of Timoshenko beam theory for the numerical description of the rail. However, the conventional Timoshenko finite element involves drawbacks for the description of the rail dynamic behaviour and the calculation of the wheel-rail interaction in the time domain. These problems are addressed by improving the finite element formulation, which is based on the description of its local displacements.

    Secondly, the versatility of numerical methods is exploited to develop a distributed model of support. It substitutes the usual concentrated model, which entails overestimation of the periodicity effects and disruption of the wheel-rail interaction in the time domain.

    Thirdly, the advantages of the formulation of numerical models in the frequency domain are explored focusing on the ability to fairly describe the sleeper dynamics, the enhancement of the model boundaries and the realistic modelling of the track components dissipative behaviour. Moreover, the frequency domain response can be used to obtain the wheel-rail interaction in the time domain efficiently, by means of the moving Green's function.

    Lastly, this work deals with the assessment of rolling noise, in which particular emphasis is made on the influence of track dynamics in the noise prediction. At this regard, a methodology is proposed to account for the track periodicity, load speed and finite length of supports.

  • 297.
    Blanco, Blas
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Railway track dynamic modelling2017Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The railway vehicles are an increasing mean of transportation due to, its reduced impact on environment and high level of comfort provided. These reasons have contributed to settle a positive perception of railway traffic into the European society. In this upward context, the railway industrial sector tackles some important challenges; maintaining low operational costs and controlling the nuisance by-products of trains operation, the most important being railway noise. Track dynamic plays a main role for both issues, since a significant part of the operational costs are associated with the track maintenance tasks and, the noise generated by the track can be dominant in many operational situations. This explains why prediction tools are highly valued by railway companies. The work presented in this licentiate thesis proposes methodologies for accurate and efficient modelling of railway track dynamics. Two core axes have led the development of this task, on one hand, the rail modelling and, on the other hand, the characterisation of the finite length nature of track supports. Firstly, concerning the rail modelling technique, it has evolved under two major premises. On one hand, regarding the frequency domain, it should describe high frequency behaviour of the rail. In order to accomplish with this first premise, a model based on Timoshenko beam theory is used, which can accurately account for the vertical rail behaviour up to 2500 Hz. On the other hand, with respect to the time domain, the response should be smooth and free of discontinuities. This last condition is fulfilled by implementation of the Timoshenko local deformation. Secondly, a model of support that considers its finite length nature is sought. For this purpose, a Timoshenko element over elastic foundation is formulated. Thus, the common model of support, which is based on a concentrated connection, is substituted by a distributed model of support. In this way, several enhancements are achieved; the temporal contact force response is smoothed and a more realistic shape is obtained, the amplitude of the displacement due to the parametric excitation is reduced and the magnitude associated to the ‘pin-pin’ frequency is not overestimated.

  • 298.
    Blanco, Blas
    et al.
    KTH.
    Alonso, A.
    Gil-Negrete, N.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Giménez, J.G.
    Implementation of Timoshenko element local deflection for vertical track modellingInngår i: Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A vertical track model suitable for the study of the dynamic response and the interaction between wheel and rail in the time domain is developed by using Timoshenko beam elements, and its performance is optimized by accounting for the local deflection of these type of elements. Implementation of the local system enables to obtain an accurate description of the contact force in a more computational efficient way than other numerical methods, and it leads to an almost total elimination of the discontinuities caused by the moving nature of the load and the shear incompatibilities introduced by the conventional formulation with Timoshenko beam elements. The work presented here describes both static and dynamic approaches of the local system directly obtained through the resolution of the beam governing equations. Two resolution strategies for the timedomain response are proposed, along with the local system formulation. The first is based on numerical integration of the whole system by introducing a Newmark scheme followed by a Newton–Raphson iterative process. The second resolution strategy is based on a numerical convolution integration, which is able to reduce significantly the computational cost of the simulation. This last resolution methodology together with implementation of the local system approach, join a computationally efficient routine and an accurate description of the track dynamic, which are valuable features for dynamics simulations. The results are validated by comparison with those from previous works.

  • 299.
    Blanco, Blas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. University of Navarra, Spain.
    Alonso, A.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Gil-Negrete, N.
    Gimenez, J. G.
    Distributed support modelling for vertical track dynamic analysis2018Inngår i: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, Vol. 56, nr 4, s. 529-552Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The finite length nature of rail-pad supports is characterised by a Timoshenko beam element formulation over an elastic foundation, giving rise to the distributed support element. The new element is integrated into a vertical track model, which is solved in frequency and time domain. The developed formulation is obtained by solving the governing equations of a Timoshenko beam for this particular case. The interaction between sleeper and rail via the elastic connection is considered in an analytical, compact and efficient way. The modelling technique results in realistic amplitudes of the pinned-pinned' vibration mode and, additionally, it leads to a smooth evolution of the contact force temporal response and to reduced amplitudes of the rail vertical oscillation, as compared to the results from concentrated support models. Simulations are performed for both parametric and sinusoidal roughness excitation. The model of support proposed here is compared with a previous finite length model developed by other authors, coming to the conclusion that the proposed model gives accurate results at a reduced computational cost.

  • 300.
    Blanco, Blas
    et al.
    KTH.
    Alonso, A.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Gil-Negrete, N.
    Giménez, J.G.
    Distributed support modelling for vertical track dynamic analysisInngår i: Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The finite length nature of rail-pad supports is characterised by a Timoshenko beam element formulation over an elastic foundation, giving rise to the distributed support element (TEEF). The new element is integrated into a vertical track model, which is solved in frequency and time domain. The developed formulation is obtained by solving the governing equations of a Timoshenko beam for this particular case. The interaction between sleeper and rail via the elastic connection is considered in an analytical, compact and efficient way. The modelling technique results in realistic amplitudes of the ‘pin-pin’ vibration mode and, additionally, it leads to a smooth evolution of the contact force temporal response and to reduced amplitudes of the rail vertical oscillation, as compared to the results from concentrated connection support models. Simulations are performed for both parametric and sinusoidal roughness excitation. The model of support proposed here is compared with a previous finite length model developed by other authors, coming to the conclusion that the proposed model gives accurate results at a reduced computational cost.

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