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  • 2901.
    Zhou, Lin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Effect of viscosity on impedance eduction and validationManuscript (preprint) (Other academic)
  • 2902.
    Zhou, Lin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Experimental investigation of an in-duct orifice with bias flow under medium and high level acoustic excitation2014In: International Journal of Spray and Combustion Dynamics, ISSN 1756-8277, Vol. 6, no 3, p. 267-292Article in journal (Refereed)
    Abstract [en]

    This paper experimentally investigates the acoustic properties of an orifice with bias flow under medium and high sound level excitation. Orifices with two different edge configurations were tested. The study includes a wide range of bias flow velocities, various acoustic excitation levels and different frequencies. The nonlinear acoustic scattering matrix was identified by a finely controled two-source method. Aeroacoustic modal analysis was introduced based on eigenvalue-decomposition. Acoustic properties, such as impedance, nonlinear scattering matrix and the eigenvalues were compared and discussed. Experimental results also show that bias flow makes the acoustic properties more complex compared to the no bias flow case, especially when the velocity ratio between acoustic particle velocity and mean flow velocity is near unity.

  • 2903.
    Zhou, Lin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    The effect of combined high level acoustic excitation and bias flow on the acoustic properties of an in-duct orifice (AIAA 2013-2128)2013In: 19th AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2013, p. 1-13Conference paper (Refereed)
    Abstract [en]

    This paper investigates the acoustic properties of an orifice with bias flow under medium and high sound level excitation. Orifices with two different edge configurations were tested experimentally.The study includes a wide range of bias flow velocities, various acoustic excitation levels and different frequencies. The so-called Cummings equation was the starting point for the theoretical modelling. It was modified and a novel orifce acoustic discharge coefficient model was developed both for cases with and without bias flow. The model was experimentally validated. With this model the acoustic resistance is obtained by the harmonic balance method, and the results agree fairly well with the experimental results for low frequencies. Experimental results also show that bias flow makes the acoustic properties much more complex compared to the no bias flow case, especially when the velocity ratio between acoustic particle velocity and mean flow velocity is near unity.  

  • 2904.
    Zhou, Lin
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lahiri, Claus
    Bake, Fredrich
    Enghardt, Lars
    Comparison of impedance eduction results using different methods and test rigs2014In: 20th AIAA/CEAS Aeroacoustics Conference, 2014Conference paper (Refereed)
    Abstract [en]

    The last twenty years has seen a large development in inverse techniques for the determination of liner impedance under grazing flow conditions, so called impedance eduction techniques. This paper contribute to a continuing effort to gain confidence in results obtained using different test rigs as well as different impedance eduction techniques. The latter includes the use of different equations for solving for the sound field in the lined section. The DLR reference liner sample HR-S2 studied is a locally reacting single degree of freedom Helmholtz resonator liner which has previously been tested at DLR and NASA Langley. In this study it is tested in a smaller scale facility at KTH, but under similar mean flow and sound pressure level conditions as in the previous studies. A good agreement has been obtained for different method under the same plug flow assumption. The same trend but not identical effects of nonlinearity have been obtained with high levels of acoustic excitation. The effect of different flow Mach number assumptions are discussed in connection with the use of the Ingard-Myers boundary condition.

  • 2905.
    Zhu, Anlin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Railway Infrastructure Management - System Engineering and Requirement Management2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Rail Control Solutions (RCS) is one division of Bombardier Transportation, aimed at optimising flow of trains. OPTIFLO is a new solution package within RCS, providing services and solutions to address challenges in modern railway infrastructures worldwide. Infrastructure Management (IM) Service is a significant sub-module under OPTIFLO, performing monitoring and diagnostic functionalities for each impacted system or component in railway signalling systems to continuously improve safety, reliability and availability.

    Requirement management is a significant stage while dealing with engineering problems. In this master thesis project, three modules in railway signalling scope are focused, including system level Infrastructure Management, sub-system level Maintenance and Diagnostic Centre (MDC) and sub-system level Remote Sensor Unit (RSU). For each part, requirement managements have been implemented, referring to CENELEC standards where necessary. The work starts with the draft Requirement Specification for IM and then identify the requirements related to diagnostics and performance in each sub-system. Both links between the requirements in different modules and links between the requirements and their test cases are built from the requirement management tool DOORS to realize verification and validation following the system engineering process. Finally, the standard documentations "System Requirement Specification" for each impacted module that are mostly concerned in the thesis have been released.

  • 2906. Zhu, B.
    et al.
    Fan, L.
    Deng, H.
    He, Y.
    Afzal, M.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Dong, W.
    Yaqub, A.
    Janjua, N. K.
    Erratum: Corrigendum to “LiNiFe-based layered structure oxide and composite for advanced single layer fuel cells” (J. Power Sources (2016) 316 (37–43))2016In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 324Article in journal (Refereed)
    Abstract [en]

    The authors regret that the name of author Yunjuan He was misspelled as ‘Yunjune He’ in the original article. The authors would like to apologise for any inconvenience caused.

  • 2907.
    Zhu, Jinchao
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Computational Weld Mechanics - estimation of angular distortion and residual stresses2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The present study estimates the angular distortion and the residual stresses using the following methodologies: Thermo-elastic-plastic, Inherent strain (local-global) and Substructuring on two types of welded joints: T-type fillet weld and butt weld. The numerical results are compared with the experimental measurements and these methodologies are evaluated in terms of accuracy and computational time. The influence of welding sequence towards distortion and transverse residual stresses has been studied numerically by implementing Thermo-elastic-plastic and Inherent strain (local-global) methods on T-type fillet weld. It shows that the welding position and welding direction have almost the same influence on angular distortions from Thermo-elastic-plastic method. The Inherent strain (local-global) method can estimate the angular distortion caused by different weld position in good agreement with Thermo-elastic-plastic method. To have a better understanding of where the underestimation of angular distortion in Inherent strain (local-global) method comes from, the study discusses the influence of block length and welding speed towards angular distortion. It is found that for long weld length or slow welding speed, activating the plastic strain gradually by dividing the weld bead into an appropriate number of blocks can reduce the level of underestimation of angular distortion.

  • 2908.
    Zimmermann, Kristian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Ultra Thick Laminates for Compact Load Introduction Fittings2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Composites are increasingly often used for thick and compact structures with the clear aim to reduce the overall weight and cost of an aircraft. But classic applications of composites are thinner structures with limited out of plane loads. Analysis and test methods are therefore commonly developed and used for thinner structures and neglect the special challenges involved with thicker laminates. In addition composites are increasingly becoming interesting for fittings and joints since the surrounding structures are either built or being developed in composites a well. Using metallic fitting and joints can cause additional thermal stresses and /or corrosion due to the material mix of composites and metals. Due to the enlarged field of application for composites, there is an increasing demand for suitable analysis, test and manufacturing methods. Compact and highly loaded composite structures are prone to be subjected to high and multidirectional loads. This causes an atypical load situation for composites, which usually are subjected to plane loads to best exploit the strength of the fibers. Due to the orthotropic nature of the material a large amount of design variables are introduced. The design of any composite part is highly manufacturing driven, meaning that the final shape is determined by manufacturing capabilities. Thick composites provide a cost effective alternative and can generate a distinct weight benefit over standard metallic components and hence will a play a significant role in future aircraft developments. Analysis, testing and manufacturing methods have to be developed and adapted for that purpose. A reliable analysis is only possible if accurate 3D material properties are available. Analysis capabilities have to be assessed using empirical test data in order to judge the applicability. The presented work has its emphasis on the analysis and testing of structural components manufactured in thick composites. The generated data from a comprehensive manufacturing and test program is also used as basis for a cost and weight study under the assumption of a highly automized serial production. The results further underline the potential of thick composites.  In a first approach, standard 2D finite element methods are used for a topology investigation. In order to fully capture the behavior of the material 3D methods are quickly implemented. An extensive test program with full scale samples and coupons is used to improve and evolve the analysis. An open mold manufacturing cycle minimizes tooling costs and provides optimum flexibility for frequent design changes. A strong link between the analysis, the manufacturing and the design is maintained throughout the developments in order to generate a material suitable design solution. Although the ultimate goal is to manufacture a specific component, the topics are approached as generic as possible in order to provide a basis for future studies with similar boundary conditions. Despite the fact that the material creates countless design variables, an affordable approach for the analysis of thick composite structures is provided using standard 3D composite brick elements. The initial problem of missing reliable 3D material properties is counteracted with tests of full scale sub- components and modified short beam shear tests. A new cure cycle for thick laminates is presented and analyzed to assess process induced stresses and deformations. A large landing gear fitting component is designed and manufactured and can be regarded as an excellent demonstrator of ultra thick composites. With a maximum wall thickness of 90mm, the component provides a weight reduction of 18% and a cost benefit of approximately 20% compared to the metallic counterpart. The potential of composites applied to a compact and highly loaded fitting is demonstrated and suitable analysis methods are established. A need for future tests to provide reliable and generic 3D material properties is identified. To provide a weight and cost benefit it is crucial to find a design topology suitable for composites.

  • 2909. Zimmermann, Kristian
    et al.
    Siemetzki, Markus
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Analysis and Manufacturing of Ultra Thick Laminates for Future Aircraft Applications2008In: ECCM-13, 2008, 2008Conference paper (Other academic)
    Abstract [en]

    Compact and highly loaded composite components experience extensive transverse shear stress concentrations in areas of load introduction and curved sections. Standard 3D multilayered composite brick elements are employed to analyze UTL. For the purpose of validation several full-scale test components with T-cross section have been manufactured with thicknesses ranging from 60-90mm. In a first approach single non interactive failure criteria have been used due to the uncertainty of out of plane material properties. Despite the fact that the used element type provides a simple mean of modeling and analyzing UTL, it is found that the element formulation strictly limits the accuracy of transverse shear stress prediction. The quadratic or even linear approximation of in plane displacements does not account for the irregular distribution in thickness direction [1]. Global deformations of the geometry can however be calculated with good results. Most failure modes experienced, are found to be dominated by transverse shear or out of plane peeling stresses. Particularly in the region of load introduction. For the analysis of the final landing gear fitting material restricted correction factors are introduced. In addition to the T-Sections, large so called ‘Double Corners’ are tested in both in plane and out of plane direction to develop effective countermeasures for premature failure modes, such as throat washers and load distribution plates. The utilized modified VAP cycle has significant benefits compared to closed mould processes, such as reduced tooling costs and high flexibility. For curved UTL sections spring back effects and preform compression rates are considered to improve laminate quality.

  • 2910. Zimmermann, Kristian
    et al.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Siemetzki, M.
    Testing and analysis of ultra thick composites2010In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 41, no 4, p. 326-336Article in journal (Refereed)
    Abstract [en]

    For the development of a composite main landing gear fitting in carbon fiber reinforced plastics the behavior and performance of Ultra Thick Laminate components is investigated. Material thicknesses exceeds 60 mm. For the purpose of validation a test program is arranged using T-cross sections subjected to multiple load cases. The components are manufactured entirely with non crimped fabrics (NCF) using an adapted open mould manufacturing process. In addition to these T-Sections large full scale subcomponents of the entire fitting are manufactured and tested. As main topic of this paper standard FE methods are investigated and validated for thick structures using the generated test results. Due to the presence of transverse shear and normal stresses a 3D modeling approach is chosen. Transverse shear and normal stresses are indentified as main failure cause and failure is mainly initiated in the curved regions. Solid composite brick elements offer an efficient way to model thick structures. These are incapable of calculating accurate shear stresses on a ply level; usable results are however achieved by discretisation of the component with multiple elements over thickness. In addition stress gradients in the failure region are small; stress variations on a ply level are minimal. Out of plane material properties are not available and initial assumptions are made. Material correction factors (degradation) are introduced and discussed.

  • 2911.
    Zuleger, Stefan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Modeling Sheet Forming of CompositeAerospace Component2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aerospace industry becomes more and more accustomed with automated processing.Current manufacturing techniques are under development for higher automation. Within thiswork the behavior of prepreg material during forming is investigated, conducting simulationson previously performed experiments at SAAB AB. The aim is to implement materialbehavior in the AniForm Virtual Forming Tool simulation. The results of various experimentshave been combined to generate the basic material properties to assemble the materialbehavior and the experiment. With the use of investigated simplifications, the possibilities ofthe AniForm Virtual Forming Tool are used to compare two experiments conducted. Byrelating the simulations of wrinkled and non-wrinkled trials, the analysis of stresses andstrains within the simulation output is conducted. With the outcomes of these simulations,previously taken assumptions on fiber direction behavior are investigated. With the resultsshowing no geometrical wrinkling of the prepreg material itself, indicators for wrinkling areexamined on the output of the results. It can be seen that looking at various parametersexclusively does not necessarily explain the wrinkling of the prepreg material. Multiplefactors need to be taken into account at the same time. The results indicate that alignment ofstress- and strain behavior next to the fiber angle deviations play important parts in futureinvestigations regarding wrinkle development.Die Luftfahrtindustrie wird mehr und mehr mit automatisierten Prozessen vertraut.Fertigungstechnologien werden in Bezug auf einen höheren Automatisierungsgrad entwickelt.Innerhalb dieser Arbeit wird das Verhalten von Prepreg Material während des Formprozessesuntersucht, indem bereits durch die SAAB AB durchgeführte Experimente simuliert werden.Das Ziel ist, das Materialverhalten in die Simulationen mit dem AniForm Virtual FormingTool einzubinden. Die Resultate verschiedener Experimente werden zusammen geführt, umdie Materialeigenschaften für das Prepreg sowie die Simulation zusammen zu stellen. Durchdie Nutzung untersuchter Vereinfachungen werden die Möglichkeiten des AniForm VirtualForming Tools genutzt, um zwei durchgeführte Experimente zu prüfen. Durch dasvergleichen der Simulationsergebnisse von Experimenten mit und ohne Faltenbildung könnendie Resultate im Hinblick auf Spannungen und Dehnungen analysiert werden. Außerdem wirdIImit den Ergebnissen der Simulation das vorausgesagte Verhalten von Faserrichtungenuntersucht. Da die Ergebnisse keine geometrische Faltenbildung des Prepreg Materials selbstzeigen, werden andere Indikatoren für die Faltenbildung untersucht. Es lässt sich erkennen,dass das Betrachten von einzelnen Parametern ohne Verknüpfung mit anderen Resultaten eineeventuelle Faltenbildung im Prepreg Material nicht notwendiger weise erklären kann.Verschiedene Faktoren müssen gleichzeitig betrachtet werden. Die Resultate deuten daraufhin, dass die Ausrichtung von Stress- und Dehnungs-Verhalten sowie die Abweichungen derFaserwinkel eine wichtige Rolle bei zukünftigen Betrachtungen von Faltenbildung spielen.

  • 2912.
    Zulu, Andrew Wisdom
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Thick Composite Properties and Testing Methods2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In most application to date reinforced carbon fiber composites have been used in relatively smaller thickness, less than 10mm thick and essentially for carrying in-plane loads. As a result, design and testing procedures were developed which reflected the need to understand the in-plane response of the material. recently, engineers and designers have begun to use reinforced carbon fiber composites in thicker sections, where an understanding of the through-thickness response is of para-mount importance in designing reliable structures, particularly where the through-thickness strength has a controlling influence on the overall structural strength of the component. In this thesis tests will be done on carbon fiber non-crimp fabric (NCF) which will be loaded in compression and shear and elastic moduli and strength will be evaluated. In characterizing the through-thickness mechanical properties of a composite, the objective is to produce a state of stress in the test specimen which is uniform and will repeatedly measure the true properties with accuracy. In this study, specimens were machined from two blocks of thick (~20 mm) laminates of glass/epoxy and NCF carbon fiber infused with vinylester and tested in compression, and shear.

  • 2913.
    Zöld, Thomas
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Performance assessment of a hybrid electric-powered long-range commercial airliner 2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Despite the recent increase in the amount of smaller electric general aviation aircrafts, a fully electric airliner is not likely to fly in the near future. Partially inspired by the automotive industry’s success with the hybrid car, this thesis investigated the feasibility of an electric-hybrid propulsion system for an Airbus A340-600 on a long-haul flight and its effect on the aircraft’s performance. First, an analysis was done of the reference aircraft, A340-600, using conventional propulsion. Second, a 5700 nautical miles flight was modelled to determine performance data such as the power and thrust requirements during the different flight phases. Third, the flight phases where electric propulsion would be implemented were identified and an optimum ratio between conventional and electric propulsion was calculated. Finally, a detailed performance analysis of the new hybrid electric aircraft comparing it to a conventional aircraft was conducted.

    The maximum available conventional thrust was reduced to a certain percentage of the maximum thrust. Primarily conventional thrust is used, however when it is no longer sufficient, additional thrust is gained through electric propulsion. Conventional thrust ratio of 69.5%, 63.5% and 59.5% of total thrust was investigated yielding 8680 kg, 10500kg and 8585kg of payload decrease respectively. Net energy of 6.70MWh, 11.71MWh and 31.06MWh is required and the electric engines need to provide 21.3 MW, 25.5 MW and 28.3 MW of net power respectively.

    Partial electric propulsion will result in increased weight; however, it will also give room for further performance optimisation and technical innovations. On the one hand, the conventional engines will run at a constant speed throughout the flight allowing for better optimisation at a specific design point. On the other hand, electric engines are more reliable and require less maintenance than conventional engines. Furthermore, lower fuel consumption means less carbon-dioxide emissions. An exemption from CO2-taxes, similar to measures implemented for hybrid cars in certain countries, could financially justify use of the aircraft by airlines and compensate for the decrease in payload. Since a fully electric propelled airliner is not likely to fly for several decades, a hybrid-airliner would be a suitable alternative for the transition period from fossil fuels to electric energy.

  • 2914.
    Ängeby, William
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Använding av geometrisk akustik för beräkning av efterklangstid i idrottshallar2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    When measures for acoustic improvements in sports halls, and other rooms, are to be implemented it is a great advantage to be able to predict how the action is going to affect for example the reverberation time even before it is done in reality. Since it costs money to install acoustic absorbers you want it to be right the first time around. Through the use of geometrical acoustic calculations digital models of the sports halls can be used to predict the results of a certain action. An often used method is to create a model with the existent absorbing materials and compare the calculated reverberation time to the measured reverberation time from the actual hall to check if the model is valid. Apart from calculations of the reverberation time the influence of the measured reverberation time to STI, a measure of speech intelligibility, is analyzed. A sports hall is often used as work places for sports teachers and it is therefore important to achieve a good acoustic environment in the hall.

    One of the aims of this project is to increase the knowledge of what gives a good model for acoustic calculations and how to choose absorption- and scattering coefficients. The goal is to make the calculated reverberation times to match the measured reverberation times. The other aim is to examine if there is a certain reverberation time curve which helps to achieve as good STI as possible.

    This project is part of the final examination in technical acoustics at KTH and has been carried out at Akustikbyrån T4p in Stockholm.

    The reverberation time for five sports halls has been measured. Models and geometrical acoustic calculations has been done for three of the halls. The absorption- and scattering coefficients used have been chosen from an absorption database as well as from analysis using the Eyring reverberation time model. The calculated reverberation times has been compared to the measured reverberation times. The measured STI for each of the five halls has been compared to the measured reverberation time for an analysis of if there is a certain reverberation curve which provides good speech intelligibility.

    The project resulted in recommendations for how detailed a model should be and also a procedure for estimating absorption- and scattering coefficients. Small details in the model usually don’t have a big impact on the calculated reverberation time at the same time as they do have a huge effect on the calculation times. The results also show that the scattering coefficients can have a huge impact on the calculated reverberation times and that they should not be neglected. It was found that both absorption- and scattering coefficients must often be overestimated for the 125 and 250 Hz octave bands for the calculated reverberation time to match the measured reverberation time in those bands. It turns out to be hard to give a specific reverberation time curve which provides for as good STI as possible since there are other parameters affecting the results. A requirement for reverberation times in sports halls used by school students is 1.2 seconds in all octave bands. The results shows that a reverberation time of 1.2 seconds in all octave bands is not necessary for good speech intelligibility.

    The procedure for estimation of absorption- and scattering coefficients hopefully leads to better understanding of how the coefficients can be chosen and how they affect the calculation results. The results could also give better understanding of the limitations when using software based on geometrical acoustics

  • 2915.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Acoustic multi-ports with application to duct acoustics2010In: 17th International Congress on Sound and Vibration 2010, ICSV 2010: Volume 5, 2010, p. 3930-3942Conference paper (Refereed)
    Abstract [en]

    In this paper the development of multi-port models to describe linear acoustic problems in ducts with flow is presented. From an engineering point of view this field covers many important applications ranging from ventilation ducts in vehicles or buildings to intake/exhaust ducts on ICengines and power plants. Historically the use of multi-port models for ducts started in the 1920's, when the four-pole (2-port) filter models used by electrical engineers were applied to analyse transmission of low frequency 1D (plane) waves with application to automotive mufflers. An important step was then taken in 1971, when Cremer presented the idea that such "black box" models can be applied to describe aerodynamically generated sound in ducts. This implies that any fluid machine or unsteady flow process can be modelled as a "black box", with a "passive part" that describes how incident waves are scattered and an "active part" that describes the sound generation. The active part is normally assumed independent of the acoustic state, which makes the "black box" or acoustic multi-port model consistent with Lighthills acoustic analogy.

  • 2916.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Method for reducing noise of a high power combustion engine2003Patent (Other (popular science, discussion, etc.))
  • 2917.
    Åbom, Mats
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Allam, Sabry
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Dissipative silencers based on micro-perforated plates2013In: SAE Technical Papers, 2013, Vol. 6Conference paper (Refereed)
    Abstract [en]

    Micro-perforated plates (MPP:s) can be defined as a perforated plate where the hole impedance is dominated by viscous losses. This will always be true for sufficiently low frequencies or small holes. In addition for a standard MPP the perforation ratio is chosen so that the normalized acoustic resistance is between 1-2, which yields optimum damping for incident plane waves. Historically MPP:s have been used as panel absorbers to reduce reflections in rooms and enclosures. More recently the potential for machinery and vehicle applications has come into focus, e.g., dissipative exhaust silencers. Some advantages offered by a MPP solution, when compared to traditional dissipative silencers, are that it can reduce the weight and the problem with fibre breakout. In this paper the work on cylindrical MPP dissipative silencers at KTH is summarized. One important question being how an optimum damping is achieved, for a certain frequency band and for a given volume (length & area ratio) of the silencer.

  • 2918.
    Åbom, Mats
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Allam, Sabry
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Industrial Education College, Cairo, Egypt .
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Aero-acoustics of flow duct singularities at low mach numbers2006In: Collection of Technical Papers - 12th AIAA/CEAS Aeroacoustics Conference, 2006, p. 3708-3717Conference paper (Refereed)
    Abstract [en]

    This paper describes the application of an acoustic 2-port model to describe flow generated noise in ducts. An experimental procedure that enables determination of both the passive (the scattering matrix) as well as the active (source) 2-port data is described. The method is applied to investigate the aero-acoustics of an orifice plate in a duct. The passive data is compared with a simple quasi-stationary model and the active part is analyzed using a scaling law procedure, based on the assumption of a compact dipole source.

  • 2919.
    Åbom, Mats
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH-Centre for Sustainable Aviation.
    Bolin, Karl
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH-Centre for Sustainable Aviation.
    Ulfvengren, Pernilla
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Industrial Management. KTH-Centre for Sustainable Aviation.
    Air traffic management and noise2018In: INTER-NOISE 2018 - 47th International Congress and Exposition on Noise Control Engineering: Impact of Noise Control Engineering, Institute of Noise Control Engineering , 2018Conference paper (Refereed)
    Abstract [en]

    With the steady increase of air traffic the need for developing sustainable aviation increases as well. To meet this need, the Swedish Transport Administration and KTH Royal Institute of Technology have established a Centre for Sustainable Aviation. In a global perspective, aviation research focuses on meeting future capacity needs for increased travel and at the same time achieve sustainability with reduced environmental impact and sustained or increased safety. This paper describes four on-going projects, as examples of the variety of research that may contribute to a sustainable society in both shorter and longer terms as well as both in a local and in an international perspective. Initially the centre will apply and direct existing knowledge towards noise abatement initiatives in aviation. I the long-term perspective the research will contribute to knowledge on a broader spectrum of sustainability aspects of aviation.

  • 2920.
    Åbom, Mats
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Kabral, Raimo
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Turbocharger noise - Generation and control2014In: SAE technical paper series, ISSN 0148-7191, Vol. 2014Article in journal (Refereed)
    Abstract [en]

    An important part of modern engine design is the concept of downsizing where a key role is carried by the charging devices. These devices are effective aero-acoustic sources forming a coupled acoustic system with the connected flow-channel components. At KTH a unique test facility for determination of the complete acoustic Two-port for turbochargers has been built. Using this facility both the passive (transmission & reflection) as well as the active (sound generation) data for turbochargers can be measured at a given operating point. One important issue which has been studied in detail using this data is the coupling between the aerodynamic and acoustic fields close to "surge". In addition, the control of compressor noise is an increasing concern. For instance heavy duty diesels and light duty engines with screw (roots) compressors can create strong charging harmonics well below 10 kHz. The standard noise control solution for these cases is to build a series of resonators. As an alternative KTH has developed a novel compact and very efficient silencer in the form of an expansion chamber with locally reacting cavities. The cavities consists of a micro-perforated plate in front of a closed air volume. The micro-perforate and volume are then chosen so that the cavity impedance equals the so called Cremer impedance at a target frequency. This ensures a very high damping at one frequency (hundreds of dB/m) and using this concept compact silencers with a damping higher than 30 dB in octave around the target frequency can be designed.

  • 2921.
    Åbom, Mats
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Karlsson, Mikael
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Can acoustic multi-port models be used to predict whistling2010In: 16th AIAA/CEAS Aeroacoustics Conference (31st AIAA Aeroacoustics Conference), 2010, p. 2010-4009-Conference paper (Refereed)
    Abstract [en]

    In duct aeroacoustic problems can be described using so called acoustic multi-port models. Such models represent a linear and time-invariant aeroacoustic model, which split the problem in a passive part, a scattering matrix in the frequency domain, describing the reflection and transmission and an active part describing the source strength. In accordance with Lighthill one normally assumes in this kind of model that the source part is uncoupled from the acoustic field. However, this assumption can be relaxed and it is fully possible to assume that the source strength can be affected by incident sound waves via a linear and time-invariant mechanism. The most general frequency domain model for this is a matrix which formally can be added to the scattering matrix describing the passive part. This leads to a model that has the same structure as the traditional multi-port model, but where the scattering matrix also contains information about fluid-acoustic interaction effects which is the origin for creating fluid driven feedback loops or whistles. The implication of these ideas is that multi-port models can be used to analyze amplification of sound and whistling.

  • 2922.
    Åbom, Mats
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Karlsson, Mikael
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Kierkegaard, Axel
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    On the use of linear aero-acoustic methods to predict whistling2009In: 16th International Congress on Sound and Vibration 2009, ICSV 2009, 2009, p. 2406-2413Conference paper (Refereed)
    Abstract [en]

    In duct aero-acoustic problems can be described using so called acoustic multi-port models. Such models represent a linear and time-invariant aero-acoustic model, which split the problem in a passive part, a scattering matrix in the frequency domain, describing the reflection and transmission and an active part describing the source strength. In accordance with Lighthill one normally assumes in this type of model that the source part is uncoupled from the acoustic field. However, this assumption can be relaxed and it is fully possible to assume that the source strength can be affected by incident sound waves via a linear and time-invariant mechanism. The most general frequency domain model for this is a matrix which formally can be added to the scattering matrix describing the passive part. This leads to a model that has the same structure as the traditional multi-port model, but where the scattering matrix also contains information about fluid-acoustic interaction effects which is the origin for creating fluid driven feedback loops or whistles.

  • 2923. Ågren, Jan
    et al.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Railway Technology.
    Flash Temperature in Wheel/Rail contact and Martensite Formation: A Review2006In: Proc. of the 7th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems (CM2006), 2006Conference paper (Refereed)
  • 2924.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Thermoforming of closed cell polymer foam and its residual compressive mechanical properties2008In: 8th International Conference on Sandwich Structures, FEUP edições (Faculdade de Engenharia da Universidade do Porto Edicoes), 2008Conference paper (Refereed)
  • 2925.
    Åkermo, Malin
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Larberg, Ylva
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Hallander, Per
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Forming of advanced components out of pre-stacked crossplied UD prepreg2011In: 18th International Conference on Composite Materials, ICCM-18, 2011Conference paper (Refereed)
  • 2926.
    Åkermo, Malin
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Larberg, Ylva
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Sjölander, Jens
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Hallnader, Per
    Saab.
    Influence of interply friction on the forming of stacked prepreg2013In: Proceedings of 19th International Conference on Composite Materials (ICCM19), Curran Associates, Inc., 2013, p. 919-928Conference paper (Refereed)
  • 2927.
    Åstrand, Erik
    et al.
    Volvo Construction Equipment AB.
    Stenberg, Thomas
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Jonsson, Bertil
    Volvo Construction Equipment AB.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Welding procedures for fatigue life improvement of the weld toe2016In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 60, no 3, p. 573-580Article in journal (Refereed)
    Abstract [en]

    This paper presents the results of an experimental study of gas metal arc welded, GMAW, cruciform joints made of common construction steel S355. The hypothesis is that smooth undercuts in as welded conditions can give enhanced fatigue properties similarly as post treated welds. Undercuts are generally seen as a defect or imperfection. Welders try to avoid these and repair them when they occur, which result in increased production lead time. Post weld improvement methods i.e. grinding or high-frequency-impact treatment (HFMI) as fatigue-enhancing post-treatment methods enforce amongst other effects a certain smooth undercut-shaped groove in the treated weld toe region. The obtained shallower weld toe transition reduces the geometrical notch effect and increases fatigue strength. This paper presents a study whereas welded specimens with a weld toe geometry similar to what is obtained by weld toe grinding or HFMI-treatment, has been produced, fatigue tested and analyzed. The improvement of the fatigue strength is comparable to post-weld treated specimens. It has proven to be an efficient way to achieve high-quality welds without introducing any additional operations in production, thus enabling weight reduction using cost-effective methods.

  • 2928.
    Çinar, O.Y.
    et al.
    Linnæus University, International Centre of Mathematical Modelling, School of Computer Science, Physics and Mathematics, Sweden. Gebze Institute of Technology, Department of Mathematics, Turkey.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Çinar, G.
    Linnæus University, International Centre of Mathematical Modelling, School of Computer Science, Physics and Mathematics, Sweden. Gebze Institute of Technology, Department of Mathematics, Turkey.
    Nilsson, B.
    Linnæus University, International Centre of Mathematical Modelling, School of Computer Science, Physics and Mathematics, Sweden.
    Jet pipe reflections - Influence of geometrical and flow exit conditions2010In: 16th AIAA/CEAS Aeroacoustics Conference (31st AIAA Aeroacoustics Conference), 2010, p. 2010-4013-Conference paper (Refereed)
    Abstract [en]

    In this paper, we study the influence of the exit conditions on the acoustic reflections at a jet pipe opening. For the flow exit conditions, the model of Munt assuming a vortex sheet at the exit of a semi-infinite jet pipe is improved by considering more general coupling conditions. We focus on modelling the acoustic properties at the shear layer in general and the stability properties in particular. Experimental methods are used for studying primarily the geometric exit conditions. Both theoretical and experimental results are presented and discussed. Numerical results related to the theory show that the thickness of the shear layer causes an expected increase in the magnitude of the reflection coefficient compared to the original infinitely thin shear layer in the Munt model. The experimental results, on the other hand, show that there are additional effects due to the presence of thick walls at the exit of the straight pipes used in the experiments. These effects are observed to be more dominant than the effects due to the shape of the edges. Based on the discussions, further theoretical and experimental investigations are proposed.

  • 2929.
    Öhnander, Fred
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    An Attempt Towards FE-Modelling of Fracture Propagation in Railway Wheels2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The demand for higher velocities and heavier axle loads for freight trains leads to higher forces on the railway wheels which in turn lead to an increase in stresses on and below the surface of the wheel-rail contact. By time, this induces wear on the wheels which consequently lead to higher maintenance costs and in some cases accidents. The ability to predict the evolution of wheel profiles due to uniform wear has been demonstrated with a rather accurate precision in most operational conditions. These wear models are based on wear coefficients and since they are not usually valid for real operational conditions, the models are generally calibrated against real-life scenarios in order to adjust the coefficients from test conditions to real-life lubrication conditions. This engineering approach can be useful in prediction of wear in systems where the materials and contact conditions do not vary. However, when addressing material development focused on reducing specific damage modes, the approach is of limited use because the obtained wear coefficients are not directly related to material properties. Therefore, attempts towards developing physical fracture propagation models that relates to the contact conditions and material properties have been made. The purpose has been to retrieve vital information about where a fracture initiates and how it propagates. In the long run, it is of great interest to be able to attain information about how a material particle is removed from the contact surface. Studies for this type of model was done in the 70’s and 80’s mainly with pin-disk experiments but has not been utilized in the specific field of wheel-rail contact. The thesis is part of the FR8RAIL project arranged by the European rail initiative Shift2Rail. Literature studies have been the basis for the thesis in order to gain vital insights into fracture mechanics and other related fields. The physical fracture propagation models have been constructed in the FE software Abaqus with the implementation of the XFEM. For the 2D model, the fracture initiates at the top of the implanted inclusion when the friction coefficient is  and propagates upwards a few elements. For , the fracture initiates at the right surface boundary where the pressure distribution and traction is applied. The fracture propagation angle increases relative to the surface as the friction coefficient value is increased. The fracture for the 3D model extends broader compared to the 2D model at the top of the inclusion in the case of . The fracture initiates at the same surface location as for the 2D model for . The fracture propagation is however non-existent due to convergence problems. The FE-models constructed are initial steps towards analysing the fracture propagation and closely related phenomena for a railway freight wheel in detail. At the end of the thesis, the simplified models give mainly information about the fracture initiation, propagation and its patterns. From this first phase, further adjustments and improvements can take place in order to eliminate the margins of error. In the long run, fully integrated models with further implementations such as detailed microstructure for the contact conditions, plastic behaviour for the material, and complete three-dimensional models can finally be employed.

  • 2930.
    Öhnander, Fred
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Höghastighetståg på rätt spår?: EN HISTORISK OCH TEKNISK ANALYS AV HÖGHASTIGHETSTÅG I VÄRLDEN2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    There is a large demand on increasing the mobility and efficiency for high speed rail in the world. Travellers request flexible train journeys and want to be able to get to their destinations as fast as possible. An improvement of the travelling times between stations is a must to be able to meet these claims. This can be achieved if speeds on high speed rail networks increase but more specifically if the average speed between stations increases.

    It is therefore of interest to explore the development of higher speeds and how it has proceeded over the years. The goal is to increase the understanding of a number of technical fields and innovations that have an impact on the average speed of a train. Specifically, the technical areas that will be treated because of their impact on average speed is tilting technology of trains, aerodynamics and eddy current brake.

    The work is primarily a literature survey of already known knowledge. Information about the historic development in certain countries has been obtained mainly from internet sources. Research material and doctoral theses have been studied where technical knowledge has been needed.

    Tilting technologies are suited for trains that run on older railway lines where a significant amount of horizontal curves are common. Passive tilting technology works effectively by reducing lateral accelerations. The safety is however impaired since the centre of gravity of the train shifts sideways. The active tilting technology compensates for the lateral acceleration and the centre of gravity shifts marginally. A running speed benefit of around 15% and a running time benefit of around 10% are achievable for a train with active tilting technology.

    The underneath components for a train have a big impact on the aerodynamic drag if the resistance area of the car body is relatively large. The surface roughness of the train has a big impact on the aerodynamic drag if the resistance area of the car body is relatively small. The length of the nose shape has a small impact on the aerodynamic drag if a length/width-ratio of at least 1.0 is used. The optimal shape for the purpose of reducing the drag for a train-tail should be long and pointed.

    The eddy current brake is effective when applied at high speeds but should be supplemented with other braking systems at low to medium speeds. The brake is wear-free and independent of the weather. A large amount of heat is however dissipated onto the rail when the brake is applied which can lead to track buckling.

  • 2931.
    Öman Lundin, Gustav
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    G.E.T.O.U.T.   - Group Evacuation Transport at the Occurence of Unexpected Trauma.2012Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
  • 2932.
    Östberg, Martin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Modelling tools for quieter vehicles: Waves in poro– and visco–elastic continua2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    New modelling tools intended to contribute to the development of components for quieter vehicles are developed. The tools are based on continuum models for wave propagation in poro– and visco–elastic media. By using geometric attributes of the studied components, the computational cost may be radically decreased compared to traditional methods. By assigning known analytical functions for one or two of the spatial directions, the spatial dimension of the remaining numerical problem is reduced. This reduction of spatial dimensions is performed in two di↵erent ways. The first one treats wave propagation in infinitely extended homogeneous and hollowed cylindrical rods, or wave guides, consisting of visco–elastic media. The wave solutions obtained are then used to model rubber vibration isolators of finite length by mode–matching the fields to the radial boundary conditions of interest. The second one is a method for modelling rotationally symmetric multilayered structures consisting of poro–elastic, elastic and fluid domains. By using a harmonic expansion for the azimuthal spatial dependence, the original three–dimensional problem is split up into several, much smaller, two– dimensional ones, radically decreasing the computational load.

    Moreover, using a mixed measurement/modelling approach, the audible frequency range characteristics of a viscous damper from a truck is studied, illustrating the influence of the rubber bushings by which it is attached to surrounding structures.

    The modelling approaches presented in this thesis are intended as tools aiding the design process of new vehicles, enabling new technology striving for more sustainable vehicle concepts. More specifically, the tools aim to improve the modelling of sound and vibration properties which are often penalised when seeking new, more sustainable vehicle designs.

  • 2933.
    Östberg, Martin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Waves in elastic and poro-elastic cylinders with spatially varying anisotropy2012In: Proceedings Of International Conference On Noise And Vibration Engineering (ISMA2012) / International Conference On Uncertainty In Structural Dynamics (USD2012), 2012, p. 4193-4200Conference paper (Refereed)
    Abstract [en]

    A modelling approach for studying waves in elastic and poro-elastic cylinders with spatially varying anisotropy is proposed. The formulation utilizes a spatial Fourier expansion for the azimuthal angle is used for the Hooke's tensor and the dependent variables. This causes the orthogonality of the modes to break down, and the modes will, sometimes to a very high degree, spread. The special case of anisotropic media having principal directions coinciding with a Cartesian coordinate system is studied, and the degree of mode spreading is discussed.

  • 2934.
    Östberg, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Coja, Michael
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Dynamic stiffness of hollowed cylindrical rubber vibration isolators - The wave-guide solution2013In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 50, no 10, p. 1791-1811Article in journal (Refereed)
    Abstract [en]

    The dynamic stiffness of hollowed cylindrical vibration isolators using a wave-guide modelling approach is given. The isolators consist of rubber and metal elements in series. The boundary conditions at the lateral and radial surfaces of each rubber component are locally non-mixed and simultaneously satisfied by using the modes corresponding to the dispersion relation for axial waves in infinite hollow cylinders while the metal plates are assumed rigid, following Newton's second law. The modes of the rubber elements exactly satisfy the stress free boundary conditions at the curved radial boundaries, while the displacement conditions on the flat cylinder ends are satisfied in mean by a mode matching approach. The rubber is modelled as nearly incompressible with deviatoric visco-elasticity based on a fractional derivative, standard linear solid. The stiffness is found to depend strongly on frequency, displaying resonances and anti-resonances. Further, results indicate a great potential for optimising vibration isolators of the studied kind. By choosing appropriate combinations of metal plates and rubber elements, the dynamic transfer stiffness in higher frequency bands can be suppressed to be magnitudes lower than the static stiffness, a highly sought feature in vibration isolators. Finally, simplified models including mass-spring systems and the long rod theory are implemented and compared to the derived formulation.

  • 2935.
    Östberg, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Numerical acoustics.
    Göransson, Peter
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Numerical acoustics.
    On cylindrical waves in anisotropic Cartesian materials and its implications on the harmonic mode separability assumption2011Conference paper (Other academic)
  • 2936.
    Östberg, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Numerical acoustics.
    Göransson, Peter
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Numerical acoustics.
    Prediction of noise transmission through anisotropic multilayered aircraft fuselage, using finite element models including porous, elastic and fluid domains2010Conference paper (Refereed)
    Abstract [en]

    Prediction of noise transmission through anisotropic multilayered aircraft fuselage, using finite element models including porous, elastic and fluid domains is carried out. A passenger aircraft carrier is modelled using a novel finite element formulation, utilising the rotationally symmetric geometry in order to greatly reduce the computational cost. The model consists of anisotropic porous, elastic and fluid domains. The axi-symmetry of the structure allows for the use of analytical functions describing the wave propagation in the circumferential spatial directions, and thus reducing the number of required finite elements considerably. It is found that a fairly limited number of modes are required to satisfactorily describe the sound fields.

  • 2937.
    Östberg, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Göransson, Peter
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Hörlin, Nils
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Weak forms for modelling of rotationally symmetric, multilayered structures, including anisotropic poro-elastic media2012In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 90, no 8, p. 1035-1052Article in journal (Refereed)
    Abstract [en]

    A weak form of the anisotropic Biot's equation represented in a cylindrical coordinate system using a spatial Fourier expansion in the circumferential direction is presented. The original three dimensional Cartesian anisotropic weak formulation is rewritten in an arbitrary orthogonal curvilinear basis. Introducing a cylindrical coordinate system and expanding the circumferential wave propagation in terms of orthogonal harmonic functions, the original, geometrically rotationally symmetric three dimensional boundary value problem, is decomposed into independent two-dimensional problems, one for each harmonic function. Using a minimum number of dependent variables, pore pressure and frame displacement, a computationally efficient procedure for vibro-acoustic finite element modelling of rotationally symmetric three-dimensional multilayered structures including anisotropic porous elastic materials is thus obtained. By numerical simulations, this method is compared with, and the correctness is verified against, a full three-dimensional Cartesian coordinate system finite element model.

  • 2938.
    Östberg, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Hörlin, Nils-Erik
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Numerical acoustics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Göransson, Peter
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Numerical acoustics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Weak formulation of Biot's equations in cylindrical coordinates with harmonic expansion in the circumferential direction2010In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 81, no 11, p. 1439-1454Article in journal (Refereed)
    Abstract [en]

    A weak symmetric form of Biot's equation in cylindrical coordinates with a spatial Fourier expansion in the circumferential direction is presented. The solid phase displacement and the pore pressure are used as the dependent variables. The original three-dimensional boundary value problem is here, due to the orthogonality of the harmonic functions and the rotationally symmetric geometry, decomposed into independent two-dimensional problems, one for each harmonic function. This formulation provides a computationally efficient procedure for vibroacoustic finite element modelling of rotationally symmetric three-dimensional multilayered structures including porous elastic materials. By numerical Simulations, this method is compared with, and verified against, full three-dimensional Cartesian coordinate system finite element models.

  • 2939.
    Östberg, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Jerrelind, Jenny
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    A study of the influence of rubber bushings on the audible frequency behaviour of a truck damper2014In: International Journal of Heavy Vehicle Systems, ISSN 1744-232X, Vol. 21, no 4, p. 281-294Article in journal (Refereed)
    Abstract [en]

    The audible frequency range behaviour of a truck damper element, connected to surrounding structures by means of rubber bushings, is investigated, applying a mixed measurement/modelling procedure. The damper element properties are retrieved through an experimental procedure, while the rubber bushings are modelled using a finite element formulation including a realistic fractional derivative visco-elastic rubber model. Focus is on the influence of the subpart properties on the overall dynamic behaviour. It is found that, in the audible frequency range studied, similar to 100-1000 Hz, an accurate model of the rubber bushings plays an important role, while the level of detail in the description of the dynamical behaviour of the damper element itself is less crucial, contributing mainly with its lumped mass; these results aid in the development of new, quiet vehicles.

  • 2940.
    Östberg, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    A study of tilting and radial stiffness of elastomer bushes in the audible frequency range2009Conference paper (Other academic)
  • 2941.
    Östberg, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Dynamic stiffness of hollowed cylindrical rubber vibrationisolators: The wave-guide solutionArticle in journal (Other academic)
  • 2942.
    Östberg, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Transverse, tilting and cross-coupling stiffness of cylindrical rubber isolators in the audible frequency range-The wave-guide solution2011In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 330, no 13, p. 3222-3244Article in journal (Refereed)
    Abstract [en]

    Audio-frequency wave-guide models for antisymmetric dynamic stiffness of arbitrary long elastomer cylinders are presented. The locally non-mixed boundary conditions at the lateral and radial surfaces are simultaneously satisfied by using the modes corresponding to the dispersion relation for axial waves in cylinders satisfying the stress free boundary conditions at the curved radial boundaries, while the displacement conditions on the flat cylinder ends are satisfied by mode matching. The elastomer is modelled as nearly incompressible with deviatoric visco-elasticity based on a fractional derivative, standard linear solid embodying a Mittag-Leffler relaxation kernel, the main advantage being the minimum parameter number required to successfully model the material properties over a broad frequency band. The stiffness is found to depend strongly on frequency: displaying resonances and anti-resonances. The method is compared with and verified against finite element models. In addition, comparison to thin beam theories, i.e. Euler and Timoschenko theory and a simple shear model, is presented, illustrating the limitations of these models.

  • 2943.
    Österlind, Tomas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Machine and Process Technology.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Nicolescu, Cornel-Mihai
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Machine and Process Technology.
    Analysis of stationary displacement patterns in rotating machinery subject to local harmonic excitation2017In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 389, p. 224-235Article in journal (Refereed)
    Abstract [en]

    Rotor vibration and stationary displacement patterns observed in rotating machineries subject to local harmonic excitation are analysed for improved understanding and dynamic characterization. The analysis stresses the importance of coordinate transformation between rotating and stationary frame of reference for accurate results and estimation of dynamic properties. A generic method which can be used for various rotor applications such as machine tool spindle and turbo machinery vibration is presented. The phenomenon shares similarities with stationary waves in rotating disks though focuses on vibration in shafts. The paper further proposes a graphical tool, the displacement map, which can be used for selection of stable rotational speed for rotating machinery. The results are validated through simulation of dynamic response of a milling cutter, which is a typical example of a variable speed rotor operating under different load conditions.

  • 2944. Österlöf, R.
    et al.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Wentzel, Henrik
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Temperature dependency of a viscoplastic constitutive model for rubber with reinforcing fillers2015In: Constitutive Models for Rubber IX - Proceedings of the 9th European Conference on Constitutive Models for Rubbers, ECCMR, CRC Press/Balkema , 2015, p. 149-156Conference paper (Refereed)
    Abstract [en]

    A material model is presented that captures the amplitude and frequency dependency of rubber with reinforcing fillers at temperatures between 23 to 85°C. It is a modification of the authors previous work and the basic principle is a smooth elastoplastic element in series with a viscoelastic network, implemented in the time domain. The rheological equivalence is based on the observation in literature that the frequency dependency of filled rubber is stronger for smaller strain amplitudes than for large amplitudes. Finally, the assumption that rubber with reinforcing fillers is thermo-rheologically simple is not always true for higher filler concentrations, resulting in discontinuous master curves for the temperature- frequency dependency. There as on for this discontinuity is that the amplitude dependency is temperature dependent. Therefore, material characterizations evaluated at a low strain amplitude could lead to erroneous results when a higher strain amplitude is of interest. Instead, it is suggested that a material model is fitted to a wide range of experimental data in order to enable realistic calculations of an actual component under operational conditions. To test the constitutive model, a double shear test specimen of natural rubber with 50 phr of carbon black filler is subjected to sinusoidal strains. The amplitudes are varied between 0.2 and 50% shear strain for frequencies between 0.5 and 20 Hz at 23, 60 and 85°C. The derived model needs only 5 material parameters to be fitted to experimental data and captures the storage and loss modulus for the entire range of strain amplitudes and frequencies, as well as non-sinusoidal loading conditions. Moreover, with the proposed modelling technique, it is expected that frequencies well above the available experimental data can be simulated. This is important, since the purpose of every model should be to make predictions outside of the range of available experimental data.

  • 2945.
    Österlöf, Richard
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Wentzel, Henrik
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    A finite strain viscoplastic constitutive model for filled rubber2015In: 22nd International Congress on Sound and Vibration, ICSV 2015, International Institute of Acoustics and Vibrations , 2015Conference paper (Refereed)
    Abstract [en]

    A phenomenological material model for carbon black filled natural rubber based on the multiplicative split of the deformation gradient is implemented for finite strains in three dimensions. This is a generalising of the authors previous work, where the uniaxial rheological equivalent is a smooth friction element in series with a generalized Maxwell chain. The aim of the paper is to demonstrate the advantage of this viscoplastic modelling approach. With only 5 material parameters, the storage and loss modulus is calculated for strain amplitudes between 0.2-50% strain and 0.5-20 Hz, with very encouraging results. These are reasonable ranges of interest when designing the reliability of load bearing components, such as vibration isolators for drivelines in the automotive industry. The Fletcher-Gent effect is well captured, where the strain rate dependency on the storage modulus is higher at smaller strain amplitudes. In addition, the storage and loss modulus are similar to measurements in literature, both in value and shape over the entire range of amplitudes and frequencies. It should be emphasized that capturing both the storage and loss modulus of a material is essential for a material model's capability to describe more complex loading situations than sinusoidal loading. A future implication of the developed model is that it enables realistic simulation of vibration isolators early in the design process whereby extensive physical testing can be reduced, saving both time and money.

  • 2946.
    Österlöf, Rickard
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Modelling of the Fletcher-Gent effect and obtaining hyperelastic parameters for filled elastomers2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The strain amplitude dependency , i.e. the Fletcher-Gent effect and Payne effect, and the strain rate dependency of rubber with reinforcing fillers is modelled using a modified boundary surface model and implemented uniaxially. In this thesis, a split of strain instead of stress is utilized, and the storage and loss modulus are captured over two decades of both strain amplitudes and frequencies. In addition, experimental results from bimodal excitation are replicated well, even though material parameters were obtained solely from harmonic excitation. These results are encouraging since the superposition principle is not valid for filled rubber, and real-life operational conditions in general contain several harmonics. This means that formulating constitutive equations in the frequency domain is a cumbersome task, and therefore the derived model is implemented in the time domain. Filled rubber is used irreplaceable in several engineering solutions, such as tires, bushings, vibrations isolators, seals and tread belts, to name just a few. In certain applications, it is sufficient to model the elastic properties of a component during finite strains. However, Hooke’s law is inadequate for this task. Instead, hyperelastic material models are used. Finally, the thesis presents a methodology for obtaining the required material parameters utilizing experiments in pure shear, uniaxial tension and the inflation of a rubber membrane. It is argued that the unloading curve rather than the loading curve is more suitable for obtaining these parameters, even at very low strain rates.

  • 2947.
    Österlöf, Rickard
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Scania.
    Modelling the viscoplastic properties of carbon black filled rubber: A finite strain material model suitable for Finite Element Analysis2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    An increased environmental awareness, legal demands and the large part of total costs attributable to fuel cost are all incentives for the automotive industry to reduce fuel consumption. The optimal driveline to enable this reduction depends on the operational conditions and the available infrastructure. Moreover, special care is needed when developing the driveline isolators, since the demands on noise, vibration and harshness (NVH) are the same regardless of driveline. To this end, computer aided calculations can be used in order to evaluate a large number of configurations. However, these calculations are only, at best, as good as the material models employed. In the foreseeable future, rubber with reinforcing fillers will be used in vibration isolators in order to obtain the desired properties of these components. However, the stiffness and damping of rubber with reinforcing fillers are highly non-linear functions, and the available material models in commercial software and in the literature are often insufficient. Therefore, a finite strain viscoplastic material model is derived in the time domain and implemented as a user defined material model in Abaqus Explicit. The model captures the strain amplitude and frequency dependency of the storage and loss modulus for a carbon black filled natural rubber. The model is accurate over a wide range of shear strain amplitudes and frequencies, 0.2-50 % and 0.5-20 Hz, respectively, using only 5 material parameters. In addition, the model correctly captures the response from bimodal excitations. The implementation in Abaqus Explicit enables component characteristics to be evaluated early in the development phase, with material parameters derived from simple test specimens. The improved accuracy of simulations of these components can aid engineers develop more optimized solutions faster than with conventional methods.

  • 2948.
    Österlöf, Rickard
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Scania CV AB, Sweden.
    Wentzel, Henrik
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). Scania CV AB, Sweden.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    A finite strain viscoplastic constitutive model for rubber with reinforcing fillers2016In: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 87, p. 1-14Article in journal (Refereed)
    Abstract [en]

    A three dimensional viscoplastic constitutive model for finite strains in a co-rotational explicit scheme is developed and implemented using finite elements that captures the amplitude dependency, commonly referred to as the Fletcher-Gent effect, and frequency dependency of rubber with reinforcing fillers. The multiplicative split of the deformation gradient is utilized and the plastic flow rule stems from an extension to finite strains of a boundary surface model with a vanishing elastic region. The storage and loss modulus for a 50 phr carbon black filled natural rubber are captured over a large range of strain amplitudes, 0.2-50% shear strain, and frequencies, 0.2-20 Hz. In addition, bimodal excitation is replicated accurately, even though this measurement data is not included when obtaining material parameters. This capability is essential when non-sinusoidal loading conditions are to be replicated. By separating the material and geometrical influence on the properties of a component, the design engineers have the capability to evaluate more concepts early in the design phase. This also reduces the need of complex prototypes for physical testing, thereby saving both time and money.

  • 2949.
    Österlöf, Rickard
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Scania.
    Wentzel, Henrik
    Scania.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    A finite strain viscoplastic constitutive model for rubberwith reinforcing fillersManuscript (preprint) (Other academic)
    Abstract [en]

    A three dimensional viscoplastic constitutive model for finite strains in aco-rotational explicit scheme is developed and implemented using finite elementsthat captures the amplitude dependency, commonly referred to as theFletcher-Gent effect, and frequency dependency of rubber with reinforcingfillers. The multiplicative split of the deformation gradient is utilized andthe plastic flow rule stems from an extension to finite strains of a boundarysurface model with a vanishing elastic region. The storage and loss modulusfor a 50 phr carbon black filled natural rubber are captured over a largerange of strain amplitudes, 0.2 − 50% shear strain, and frequencies, 0.2 − 20Hz. In addition, bimodal excitation is replicated accurately, even though thismeasurement data is not included when obtaining material parameters. Thiscapability is essential when non-sinusoidal loading conditions are to be replicated.By separating the material and geometrical influence on the propertiesof a component, the design engineers have the capability to evaluate more concepts early in the design phase. This also reduces the need of complexprototypes for physical testing, thereby saving both time and money.

  • 2950.
    Österlöf, Rickard
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. Scania, Södertälje, Sweden .
    Wentzel, Henrik
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    An efficient method for obtaining the hyperelastic properties of filled elastomers in finite strain applications2015In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 41, p. 44-54Article in journal (Refereed)
    Abstract [en]

    An efficient methodology for obtaining hyperelastic material parameters for filled elastomers utilizing unloading curves in uniaxial tension, pure shear and the inflation of a rubber membrane is presented. Experimental results from biaxial extension are crucial when fitting hyperelastic material parameters, and the bubble inflation technique is an excellent method of obtaining this data when specialized test equipment is unavailable. Moreover, filled elastomers have considerable hysteresis, and the hysteresis grows with increasing strain amplitudes. Therefore, the loading curve is in general comprised of both elastic and inelastic contributions, even at very low strain rates. Consequently, it is deemed more accurate to use experimental data from the unloading curve to describe the elastic behavior of the material. The presented methodology enables obtainment of parameters related to both the first and second strain invariant, which is required for a good fit between measurement and simulation results. Finally, it is essential that a chosen material model is accurate in all deformation modes when designing components subjected to a complex, multi-axial load history. An accurate material model enables more concepts and geometries of a component to be studied before a physical prototype is available.

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