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  • 51.
    Alenius, Emma
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    LES of Acoustic-Flow Interaction at an Orifice Plate2012Inngår i: 18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference), 2012Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    The scattering of plane waves by a thick orifice plate, placed in a circular or square duct with flow, is studied through Large Eddy Simulation. The scattering matrix is computed and compared to measurements, showing reasonably good agreement except around one frequency ($St \approx 0.4$). Here a stronger amplification of acoustic energy is observed in the circular duct simulations than in the measurements and the square duct simulations. In order to improve the understanding of the interaction between an incoming wave, the flow, and the plate, a few frequencies are studied in more detail. A Dynamic Mode Decomposition is performed to identify flow structures at significant frequencies. This shows that the amplification of acoustic energy occurs at the frequency where the jet in the circular duct has an axisymmetric instability. Furthermore, the incoming wave slightly amplifies this instability, and suppresses background flow fluctuations.

  • 52.
    Alenius, Emma
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Scattering of Plane Waves by a Constriction2011Inngår i: Proceedings of ASME Turbo Expo 2011, Vol 7, Parts A-C, American Society Of Mechanical Engineers , 2011, s. 1043-1052Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Liner scattering of low frequency waves by an orifice plate has been studied using Large Eddy Simulation and an acoustic two-port model. The results have been compared to measurements with good agreement for waves coming from the downstream side. For waves coming from the upstream side the reflection is over-predicted, indicating that not enough of the acoustic energy is converted to vorticity at the upstream edge of the plate. Furthermore, the sensitivity to the amplitude of the acoustic waves has been studied, showing difficulties to simultaneously keep the amplitude low enough for linearity and high enough to suppress flow noise with the relatively short times series available in LES.

  • 53. Alkhagen, M.
    et al.
    Toll, Staffan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    A triaxial rheometer for soft compressible solids2002Inngår i: Journal of Rheology, ISSN 01486055 (ISSN), Vol. 46, nr 1, s. 31-47Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The compression and the shear of soft compressible solids were studied using the triaxial rheometer. The sample was fixed between two parallel plates and the deformation was controlled by an x, y, z displacement on one plate while the stress was measured on the other. The triaxial stress transducer eliminates the edge effects by only measuring the stress on an interior region of the plate. The edge effects and the associated measurement errors were analyzed by the simple isotropic elastic theory and were compared to the measurements done on the chloroprene rubber foam.

  • 54.
    Al-Khalili Szigyarto, Cristina
    et al.
    KTH, Skolan för bioteknologi (BIO), Proteomik.
    Garme, Karl
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Marina system.
    Högfeldt, Anna-Karin
    KTH, Skolan för teknikvetenskaplig kommunikation och lärande (ECE), Lärande.
    Magnell, Marie
    KTH, Skolan för teknikvetenskaplig kommunikation och lärande (ECE), Lärande.
    Vägen från student till ingenjör: exempel från två kandidatexamenskurser och ett förslag om en programsammanhållande byggnadsställning2011Konferansepaper (Annet vitenskapelig)
  • 55. Alkmim, M. H.
    et al.
    Cuenca, J.
    De Ryck, L.
    Göransson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Model-based acoustic characterisation of muffler components and extrapolation to inhomogeneous thermal conditions2018Inngår i: Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics, KU Leuven - Departement Werktuigkunde , 2018, s. 3009-3020Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A methodology for evaluating the acoustic behaviour of two-port inhomogeneous media in experimentally unavailable thermal conditions is proposed. The method consists of an inverse estimation of the geometrical and material properties of the object at room temperature followed by a forced thermal input. The properties of interest for the inverse estimation are the spatially-varying cross-section and/or bulk properties. The underlying model relies on a transfer matrix approach, allowing for a representation of spatially inhomogeneous objects as piece-wise equivalent homogeneous fluids, while ensuring continuity conditions between successive elements. A model of non-stationary thermal conduction is used as a first approximation, where an integral formulation accounts for the cumulative effect of multiple homogeneous elements. In order to evaluate the validity of the extrapolation, a validation against a fully numerical simulation is presented in two cases, namely a simple expansion chamber and a complex muffler. 

  • 56.
    Alkmim, Mansour
    et al.
    Siemens Industry Software.
    Cuenca, Jacques
    Siemens Industry Software, Leuven Belgium.
    de Ryck, Laurent
    Siemens Industry Software, Leuven Belgium.
    Göransson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. Centre for ECO2 Vehicle Design.
    Model-based acoustic characterisation of muffler components and extrapolation to inhomogeneous thermal conditions2018Konferansepaper (Fagfellevurdert)
  • 57.
    Allam, S.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Cooling fan noise control using micro-perforates2012Inngår i: Int. Congr. Expos. Noise Control Eng., INTER-NOISE, 2012, s. 10434-10445Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Baffle or split silencers are commonly used, e.g., in HVAC systems and as inlet/outlet silencers on gas turbines. Another application is to reduce noise from the cooling fan inlet for large IC-engines. A baffle silencer can be seen as a periodic arrangement of parallel rectangular absorbers which can be placed in a rectangular duct. The noise reduction afforded by parallel baffles depends not only on the physical properties of the lining, but also upon the angle of incidence of the sound waves impinging and the baffle length. In this paper the potential of using baffles made of Micro-Perforated Panels is investigated in particular with the cooling fan inlet application in mind. Theoretical models for the damping is derived and used to design optimum configurations. The models are based on the wave propagation in a periodic array of baffles so that only one period can be investigated in order to find the different modes. In particular the least attenuated mode is important to find in order to optimize the behavior. An important aspect is the inner structure of the MPP baffle, i.e., can it just be an empty air volume or to what extent must internal waves be prevented by putting in walls. From a stiffness point of view some inner walls might also be needed to avoid vibration problems. Due to these complexities the theoretical models are only presented for the simplest cases. In order to validate the models and to get a more complete test of different designs experiments were also carried out. During these experiments the effect of flow was also tested.

  • 58. Allam, S.
    et al.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Investigation of aerodynamic installation effects for an axial fan2013Inngår i: 19th AIAA/CEAS Aeroacoustics Conference, 2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The aim of the work reported in this paper is to investigate the aerodynamic installation effects for a generic cooling fan system. This is done by treating the ducted fan as a multi-port source and performing a source characterization, i.e., determining the source strength and source reflection matrix. From the source strength, which represents the sound radiated by the fan in a reflexion free (infinite) duct, the effect of various inflow distortions can be studied. The work is part of the EU-project ECOQUEST where the data will be used to validate the acoustic prediction tools.

  • 59. Allam, S.
    et al.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Noise reduction for automotive radiator cooling fans2015Inngår i: FAN 2015 - International Conference on Fan Noise, Technology and Numerical Methods, Institution of Mechanical Engineers , 2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Engine cooling fans have long been recognized as one of the major noise sources in a vehicle. As the engine and other vehicle components are made quieter, the need to reduce fan noise has become more and more urgent. To reduce fan noise in a cost-effective manner, it is necessary to incorporate the component of noise reduction into an early design stage. In this paper a detailed experimental study on an automotive vehicle cooling system is presented. The aim is to investigate the flow generated noise, characterize the heat exchanger damping properties and investigate the use of near-field noise control by micro-perforated (MPP) shrouds and tuned MPP dampers. For the tested standard automotive cooling fan system the MPP shroud gave a reduction in the range 1.5 to 4.5 dB(A) depending on the fan speed. Also the absorption on the back-side is significantly increased which can reduce the noise further. The near-field tuned MPP damper concept is also promising and gives a reduction around 3 dB(A) at the operating points. 

  • 60.
    Allam, Sabry
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. Helwan University, Egypt.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Methods for Accurate Determination of Acoustic Two-Port Data in Flow Ducts2005Inngår i: 12th International Congress on Sound and Vibration 2005: ICSV 2005, 2005Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Measurement of plane wave acoustic transmission properties, so called two-port data, of flow duct components is important in many applications. It is an important tool for instance in the development of mufflers for IC-engines. Accurate measurement of the acoustic two port data can be used not only to determine the transmission loss but also to determine physical properties like flow resistivty as well as speed of sound and impedance. Measurement of two-port data is difficult when the flow velocity in the measurement duct is high because of the flow noise contamination of the measured pressure signals. Techniques to improve the acoustic two-port determination have been tested in this paper. A number of possible configurations for connecting loudspeakers to the flow duct have been investigated. It was found that using a perforate pipe section with about 50% porosity between the loudspeaker side branch and the duct gave the best signal-to-noise ratio out of the studied configurations. Different signal processing techniques have been tested for reducing the adverse effects of flow noise at the microphones. The most successful techniques require a reference signal which can be either the electric signal being input to the loudspeakers or one of the microphone signals. As a reference technique stepped sine excitation with cross-spectrum based frequency domain averaging was used. This technique could give good results for most cases. Using a periodic signal (saw-tooth) and synchronised time domain averaging good results could be obtained if a sufficient number of averages was used. At flow velocities higher than M=0.2 about 10000 averages were needed. Random excitation together with cross-spectrum based frequency domain averaging also gave good result if the same number of averages was used. Ordinary frequency domain averaging is not sufficient at high flow velocities. It was also shown that using cross-spectrum based frequency domain averaging an improvement could be obtained if the microphone with the highest signal-to-noise ratio at each frequency was used as the reference microphone rather than a fixed microphone.

  • 61.
    Allam, Sabry
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Over-determination in acoustic two-port data measurement2006Inngår i: ICSV13-Vienna / [ed] J. Eberhardsteiner, H.A. Mang, H. Waubke, 2006Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Measurement of plane wave acoustic transmission properties, so called two-port data, of flow duct components is important in many applications. It is an important tool for instance in the development of mufflers for IC-engines. Measurement of two-port data is difficult when the flow velocity in the measurement duct is high because of the flow noise contamination of the measured pressure signals. The plane wave acoustic two-port is a 2x2 matrix containing 4 complex quantities at each frequency. To experimentally determine these unknowns the acoustic state variables on the inlet and outlet side must be measured for two independent test cases. The two independent test cases can be created by: changing the acoustic load on the outlet side leading to the so-called two-load technique or by using one acoustic source on the inlet side and one acoustic source on the outlet side leading to the so-called two-source technique. In the latter case the independent test cases are created by first using the source on the inlet side and then the source on the outlet side. As pointed out by Åbom it is also possible to run both sources simultaneously to create more than two independent test cases. This over-determination could be used to improve the measurement results for instance if the data is contaminated by flow-noise. In this paper over-determination is tested by applying up to 5 different test cases. This procedure has been applied to a single orifice test object.

  • 62.
    Allam, Sabry
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Knutsson, M.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Development of acoustic models for high frequency resonators for turbocharged IC-engines2012Inngår i: SAE Technical Paper 2012-01-1559, 2012, 2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Automotive turbo compressors generate high frequency noise in the air intake system. This sound generation is of importance for the perceived sound quality of luxury cars and may need to be controlled by the use of silencers. The silencers usually contain resonators with slits, perforates and cavities. The purpose of the present work is to develop acoustic models for these resonators where relevant effects such as the effect of a realistic mean flow on losses and 3D effects are considered. An experimental campaign has been performed where the two-port matrices and transmission loss of sample resonators have been measured without flow and for two different mean flow speeds. Models for two resonators have been developed using 1D linear acoustic theory and a FEM code (COMSOL Multi-physics). For some resonators a separate linear 1D Matlab code has also been developed. Different models, from the literature, for including the effect of mean flow on the acoustic losses at slits and perforates have been implemented in the codes and compared to the experimental data. Correct modeling of acoustic losses for resonators with complicated geometry is important for the simulation and development of new and improved silencers, and the present work contributes to this understanding. The developed models give acceptable agreement with the measured results even with flow but can be improved for 3D FEM if correct CAD data is available. The 1D linear theory can be used for simple geometries and to get a general overview related to the resonance frequencies and damping level.

  • 63. Allam, Sabry
    et al.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    A New Type of Muffler Based on Microperforated Tubes2011Inngår i: Journal of Vibration and Acoustics-Transactions of the ASME, ISSN 1048-9002, E-ISSN 1528-8927, Vol. 133, nr 3, s. 031005-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Microperforated plate (MPP) absorbers are perforated plates with holes typically in the submillimeter range and perforation ratios around 1%. The values are typical for applications in air at standard temperature and pressure (STP). The underlying acoustic principle is simple: It is to create a surface with a built in damping, which effectively absorbs sound waves. To achieve this, the specific acoustic impedance of a MPP absorber is normally tuned to be of the order of the characteristic wave impedance in the medium (similar to 400 Pa s/m in air at STP). The traditional application for MPP absorbers has been building acoustics often combined with a so called panel absorber to create an absorption peak at a selected frequency. However, MPP absorbers made of metal could also be used for noise control close to or at the source for noise control in ducts. In this paper, the possibility to build dissipative silencers, e. g., for use in automotive exhaust or ventilation systems, is investigated.

  • 64.
    Allam, Sabry
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Acoustic modeling and testing of a complex car muffler2006Inngår i: International Congress on Sound and Vibration 2006, 2006, s. 1119-1126Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Perforated mufflers are used by exhaust system manufacturers to improve the broadband attenuation at low frequencies, with the drawback that this normally also implies an increased pressure drop. The detailed modelling of this type of muffler depends on knowledge of the perforate impedance which is influenced by hole geometry as well as the details of the flow distribution. The existing formulas for calculation of perforate impedance are semi-empirical and a number of alternatives have been published. One motivation behind this work was to review the existing formulas for perforate impedance using accurate measured data for perforated mufflers. A modified model presented by Bauer 1977 was found to be the best. A second motivation was to show that for a detailed analysis, using 3D acoustic FEM, the mean flow can be neglected except for calculating the perforate impedances.

  • 65.
    Allam, Sabry
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Acoustic modelling and characterization of plate heat exchangers2012Inngår i: SAE Technical Paper 2012-01-1562, Society of Automotive Engineers, 2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    There is increased concern about the noise emission from cooling systems. This is mainly due to an increased need for cooling needs due to turbo-charging and EGR systems, which tend to increase the fan power and thereby the noise. An important issue in this context is the behavior of the heat-exchanger and its acoustic transmission and absorption properties. In this paper an acoustic model to evaluate such data for a common type of heat exchanger, the parallel plate type, is presented. The basic configuration is assumed to be a matrix of parallel, narrow channels. The developed model is based on a so called equivalent fluid for an anisotropic medium. It is mainly dependent on the heat exchanger geometry combined with the Kirchhoff model for thermo-viscous wave propagation in narrow tubes. The proposed model can be used to predict the sound transmission and absorption for an entire heat exchanger for incident plane waves. This model is validated by comparison with measurement results for seven different heat exchangers used in vehicle and train cooling units at different flow speeds

  • 66. Allam, Sabry
    et al.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Acoustic modelling and testing of diesel particulate filters2005Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 288, nr 02-jan, s. 255-273Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The use of Diesel Particulate Filters (DPFs) on automobiles to reduce the harmful effects of diesel exhaust gases is becoming a standard in many countries. Although the main purpose of a DPF is to reduce harmful emission of soot particles it also affects the acoustic emission. This paper presents a first attempt to describe the acoustic behavior of DPFs and to present models which allow the acoustic two-port to be calculated. The simplest model neglects wave propagation and treats the filter as an equivalent acoustic resistance modeled via a lumped impedance element. This simple model gives a constant frequency-independent transmission loss and agrees within I dB with measured data on a typical filter (length 250 mm) up to 200-300 Hz (at 20 degrees C). In the second model, the ceramic filter monolith is described as a system of coupled porous channels carrying plane waves. The coupling between the channels through the porous walls is described via Darcy's law. This model gives a frequency-dependent transmission loss and agrees well with measured data in the entire plane wave range.

  • 67.
    Allam, Sabry
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Advanced experimental procedure for in-duct aero-acoustics2006Inngår i: 13th International Congress on Sound and Vibration 2006, ICSV 2006, 2006, s. 1185-1192Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The purpose of this paper is to present a method for characterization of in-duct aero-acoustic sources that can be described as active acoustic two-ports. The method is applied to investigate the sound produced from an orifice plate. The motivation is to obtain better data for the development of improved prediction methods for noise from flow singularities, e.g., in HVAC systems on aircrafts. Most of the earlier works fall into two categories; papers modeling the scattering of acoustic waves and papers modeling the sound generation. Concerning the scattering it is possible to obtain estimates of the low frequency behavior from linear perturbations of the steady state equations for the flow. Concerning the sound generation most of the presented work is experimental and follows a paper by Nelson&Morfey, which present a scaling law procedure for the in-duct sound power based on a dipole model of the source. One limitation with the earlier works is that the sound power only was measured on the downstream side. Also data was only obtained in 1/3-octave bands, by measuring the sound radiated from an open duct termination. Assuming plane waves and linear acoustics the flow duct singularity can be completely modeled as an active 2-port. The experimental determination of its properties is done in a two steps procedure. In the first step the passive data, i.e., the scattering matrix S, is determined using external (independent) sources. In the second step the S matrix is used and the source vector is determined by testing the system with known acoustic terminations.

  • 68.
    Allam, Sabry
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Aeroacoustic investigation of diaphragm orifices in ducts2007Inngår i: Turkish Acoustical Society - 36th International Congress and Exhibition on Noise Control Engineering, INTER-NOISE 2007 ISTANBUL, 2007, s. 292-301Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Diaphragm orifices are used in duct systems to control or measure the flow rate. Such components generate complex flows and aeroacoustic phenomena, e.g., dissipation via forced vortex shedding, sound generation from eddy structures (broadband noise) and non-linear whistling. In this paper the acoustic properties (passive and active) of single and double diaphragm orifices are investigated experimentally for small Mach-numbers and low frequencies (plane waves). Using microphone arrays and wave decomposition the induct sound fields are resolved and used as input to determine the active acoustic 2-port. The work represents one of the first efforts to apply 2-port methods to characterize flow generated noise in-ducts. The motivation of this work is to obtain better understanding for noise from flow singularities in ducts, e.g., in HVAC systems on vehicles, develop and improve prediction methods and produce data for validation of CFD and other models. First the single orifice case is investigated and the 2-port data is obtained. The active (source) strength part represents a dipole type of source for which a scaling law is derived. For the passive part (the scattering matrix) a simple quasi-stationary model is tested and works well up to a few hundred Hz. Secondly the double orifice configuration is investigated and again the 2-port data is measured. To investigate the presence of orifice interaction and non-linear aeroacoustic effects, such as whistling, the double orifice data is reduced to two identical single orifices. The equivalent source data for this reduced case is then compared with the single orifice scaling law. It is found that if the separation is larger than 10 orifice diameters then orifice interaction can be neglected. Non-linear effects and tendencies for whistling were found for separations less than 3-4 duct diameters.

  • 69.
    Allam, Sabry
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Diesel engines after treatment devices: Acoustic modeling2005Inngår i: 12th International Congress on Sound and Vibration 2005: ICSV 2005, 2005, s. 2358-2365Konferansepaper (Fagfellevurdert)
    Abstract [en]

    To reduce exhaust pollutants from diesel engines a Diesel Particulate Filter (DPF) is normally fixed after a Catalytic Converter (CC) in an expansion chamber to create a complete After-Treatment Device (ATD). As part of the work in the EC-project ARTEMIS the authors have published a series of papers on the modeling of DPF units. Here the final and complete DPF model is presented. The model calculates the acoustic 2-port by solving the convective acoustic wave equations for two neighboring cells simplified in the manner of the Zwikker and Kosten theory. A segmentation approach has been employed to handle the actual flow, density, pressure, and temperature distribution inside the monoliths at each frequency. The theoretical results were compared with measured transmission loss data at different flow speeds and the agreement is excellent. The new complete model has also been compared with the 1-D model earlier suggested by the authors. It turns out that by using a wave number based on the Kirchhoff solution for plane waves in narrow pipes, the simple 1-D model works almost as well as the complete model. Another conclusion is that the effect of mean flow on the sound transmission through a filter is very small. Using the new model and existing models for standard pipe elements and the CC, the acoustic 2-port for a car ATD unit has been calculated and used to predict the transmission loss. The agreement between the predictions and the measured data for various flow speeds is good.

  • 70.
    Allam, Sabry
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. Hellwan University, Egypt .
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Experimental characterization of acoustic liners with extended reaction2008Inngår i: 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference), 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Suppressing of jet engine noise by inlet and exhaust duct liners and internal combustion engine (ICE) noise by intake and exhaust systems is an important part of developing environmentally acceptable vehicles. The acoustic liner is designed to provide an impedance boundary condition in the engine duct that reduces the propagation of engine noise through the duct. An accurate impedance boundary condition is necessary to optimally suppress the noise at different conditions. The goal of the research presented in this paper is to present a new technique to Educe and characterize the acoustic liner impedance for cases with extended reaction. This technique is depending on comparing both the measured and predicted 2-port transfer matrices. The measurement of the transfer matrix is performed using the two microphone technique, while the prediction of the transfer matrix is obtained assuming plane waves in the inner pipe and outer chamber coupled by a perforated wall impedance. By using a regression process the unknown wall impedance is then educed. The method is applied to investigate the effect of flow on the impedance of so called Micro-perforated panels (MPP). A MPP consists of a panel (here a plate made of Al or steel) with small perforations distributed over its surface. When these perforations are of sub-millimeter size they provide by themselves enough acoustic resistance and low acoustic mass reactance necessary for a wideband absorber.

  • 71.
    Allam, Sabry
    et al.
    Helwan University, Cairo, Egypt.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Fan Noise Control Using Microperforated Splitter Silencers2014Inngår i: Journal of Vibration and Acoustics-Transactions of the ASME, ISSN 1048-9002, E-ISSN 1528-8927, Vol. 136, nr 3, s. 031017-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Splitter or baffle silencers are commonly used, for example, in heating ventilation and air conditioning (HVAC) systems and as inlet/outlet silencers on gas turbines. Another application is to reduce noise from the cooling fan inlet for large IC-engines. A splitter silencer can be seen as a periodic arrangement of parallel rectangular absorbers, which can be placed in a rectangular duct. The noise reduction afforded by parallel splitters depends not only on the physical properties of the lining but also upon the angle of incidence of the impinging sound waves, and the splitter and duct dimensions. In this paper, the potential of using splitters made of microperforated plates (MPPs) is investigated, with a particular focus on cooling fan inlet/outlet applications.

  • 72. Allam, Sabry
    et al.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Investigation of damping and radiation using full plane wave decomposition in ducts2006Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 292, nr 05-mar, s. 519-534Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A general plane wave decomposition procedure that determines both the wave amplitudes (or the reflection coefficient) and the wavenumbers is proposed for in-duct measurements. To improve the quality of the procedure, overdetermi nation and a nonlinear least-squares procedure is used. The procedure has been tested using a six microphone array, and used for accurate measurements of the radiation from an open unflanged pipe with flow. The experimental results for the reflection coefficient magnitude and the end correction have been compared with the theory of Munt. The agreement is very good if the maximum speed rather than the average is used to compare measurements and theory. This result is the first complete experimental validation of the theory of Munt [Acoustic transmission properties of a jet pipe with subsonic jet flow, 1: the cold jet reflection coefficient, Journal of Sound and Vibration 142(3) (1990) 413-436]. The damping of the plane wave (the imaginary part of the wavenumber) could also be obtained from the experimental data. It is found that the damping increases strongly, compared with the damping for a quiescent fluid.. when the acoustic boundary layer becomes thicker than the viscous sublayer. This finding is in agreement with a few earlier measurements and is also in agreement with a theoretical model proposed by Howe [The damping of sound by wall turbulent sheer layers, Journal of Acoustic Society, of America 98(3) (1995) 1723-17301. The results reported here are the first experimental verifications of Howe's model. It is found that the model works well typically up to a normalized acoustic boundary layer thickness delta(+)(A) of 30-40. For values of A a delta(+)(A) less than 10, corresponding to higher frequencies or lower flow speeds, the model proposed by Dokumaci [A note on A transmission of sound in a wide pipe with mean flow and viscothermal attenuation, Journal of Sound and Vibration 208(4) (1997) 653-655] is also in good agreement with the experimental data.

  • 73. Allam, Sabry
    et al.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Modeling and testing of after-treatment devices2006Inngår i: Journal of Vibration and Acoustics-Transactions of the ASME, ISSN 1048-9002, E-ISSN 1528-8927, Vol. 128, nr 3, s. 347-356Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Driven by emission regulations in the US and the EU exhaust systems on new diesel engines are equipped with both a catalytic converter (CC) and a diesel particulate filter (DPF). The CC and DPF are normally placed after each other in an expansion chamber to create a complete after-treatment device (ATD) to reduce the exhaust pollutants. The ATD unit can also affect the acoustical performance of an exhaust system. in this paper an acoustic model of a complete ATD for a passenger car is presented. The model is made up of four basic elements: (i) straight pipes; (ii) conical inlet/outlet; (iii) CC unit, and (iv) DPF unit. For each of these elements, a two-port model is used and, with the exception of the DPF unit, known models from the literature are available. For the DPF unit, a new model suggested by the authors has been used. Using the models, the complete acoustic two-port model for the investigated ATD unit has been calculated and used to predict the sound transmission loss. The predictions have been compared to experimental data taken at cold conditions for various flow speeds and show a good agreement.

  • 74.
    Allam, Sabry
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Noise control for cooling fans on heavy vehicles2012Inngår i: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 60, nr 6, s. 707-715Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper two different objects for fan passive noise control have been examined: heat exchangers and inlet/outlet parallel splitter silencers based on micro-perforated panels. The first object is theoretically and experimentally examined while the second is only examined experimentally. Throughout this paper two measurement methods were used. The ISO 15186-1:2000 to test the acoustic transmission for a diffuse field and plane wave testing in a duct of a sample cut from each heat exchanger type. Based on an anisotropic equivalent fluid model a theoretical model for the heat exchanger acoustic transmission is presented. A new type of splitter silencers based on micro-perforated plates, which can add damping up 10-20 dB in the frequency range of interest (<5 kHz), are also presented.

  • 75.
    Allam, Sabry
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    On optimal design of mufflers using micro-perforated panels2010Inngår i: 17th International Congress on Sound and Vibration 2010, ICSV 2010: Volume 2, 2010, s. 1158-1165Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Passive mufflers are widely employed to reduce industrial and domestic ventilation noise as well as vehicle exhaust noise. Their basic geometry is formed by a simple expansion chamber and the performance is controlled by using complex geometries or by adding porous materials inside the chamber. However, when a clean absorbent system is desirable or when the muffler must support high air flux, it is not possible to add those fibrous materials and the use of micro perforated panels (MPP) as another alternative to improve the acoustic performance become important. The purpose of this work is not only to optimize the acoustic performance of low cost simple geometry mufflers using micro perforated panels (MPP) absorbers but also to find the best shape design under a limited space constraint. In this paper, on the basis of plane wave theory, the four-port system matrix for two wave guides coupled via a MPP tube is derived and used to compute the two-port transfer matrix for a expansion chamber muffler with a MPP tube. Moreover, a simulated annealing (SA) algorithm searching for the global optimum by imitating the softening process of metal has been adopted during the muffler's optimization. To assure SA's correctness, the sound transmission loss (TL) maximization of one-chamber perforated mufflers at a targeted frequency of 1500 Hz is tested first. The result of the optimized muffler is compared with the measured results at room temperature. Furthermore, a numerical case in dealing with a broadband noise emitted from an I.C. Engine by using one-chamber micro perforated mufflers has been introduced and is discussed.

  • 76. Allam, Sabry
    et al.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Sound propagation in an array of narrow porous channels with application to diesel particulate filters2006Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 291, nr 05-mar, s. 882-901Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In an earlier work the authors have presented a 1-D acoustic model for diesel particulate filters (DPFs). One shortcoming of this first model is the approximate treatment of the viscous and thermal losses along the narrow channels. In the present paper this issue is analyzed in more detail, by solving the convective acoustic wave equations for two neighboring channels simplified in the manner of the Zwikker and Kosten theory. From the solution the acoustic two-port has been calculated to predict the sound transmission losses for an entire DPF unit. The theoretical results are compared with experimental data for clean filter units at room temperature and the agreement is very good and better, in particular for very small Mach numbers, than for the earlier presented 1-D model. A modified 1-D model using the classical (exact) Kirchhoff solution for a plane wave in a narrow tube is also presented. This modified 1-D model is in close agreement with the predictions of the new model. Furthermore, the earlier proposed 1-D model, which assumes isothermal sound propagation, works satisfactorily up to 800-1000Hz for a typical filter at operating (hot) conditions.

  • 77.
    Allam, Sabry
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Whistling potential for duct components2013Inngår i: SAE Technical Papers: Volume 4, 2013, S A E Inc , 2013, Vol. 4, s. 2013-01-1889-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Components in ducts systems that create flow separation can for certain conditions and frequencies amplify incident sound waves. This vortex-sound phenomena is the origin for whistling, i.e., the production of tonal sound at frequencies close to the resonances of a duct system. One way of predicting whistling potential is to compute the acoustic power balance, i.e., the difference between incident and scattered sound power. This can readily be obtained if the scattering matrix is known for the object. For the low frequency plane wave case this implies knowledge of the two-port data, which can be obtained by numerical and experimental methods. In this paper the procedure to experimentally determine whistling potential will be presented and some examples are given to show how this procedure can be used in some applications for automotive intake and exhaust system components.

  • 78. Allaoui, Aissa
    et al.
    Toll, Staffan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Evesque, Pierre
    Bai, JinBo
    On the compressive response of carbon nanotube tangles2009Inngår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 373, nr 35, s. 3169-3173Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The nonlinear bulk compressibility of entangled multiwalled carbon nanotubes is studied. The analogy with textile fibre assemblies is explored by means of the well established van Wyk model. In view of the small diameter of the nanotubes. the possible effect of adhesive van der Waals interactions at tube-tube contacts is analysed. It is found, however, that the contribution of adhesive contacts to the bulk stress should be negligible. Compression experiments are performed on multi-walled carbon nanotubes and show that van Wyk's model is able to describe the response, although the values of the dimensionless parameter k of van Wyk's model were lower than expected. There is indeed no indication that van der Waals interactions play any significant role.

  • 79. Allen, T.
    et al.
    Battley, M.
    Casari, P.
    Kerling, B.
    Stenius, Ivan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Marina system.
    Westlund, Joacim
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Marina system.
    Structural responses of high performance sailing yachts to slamming loads2011Inngår i: 11th International Conference on Fast Sea Transportation, FAST 2011 - Proceedings, 2011, s. 585-592Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Experimental measurements of transient strains, local accelerations and pressure were undertaken on the IMOCA Open 60' class sailing yacht Paprec-Virbac III, and on a replica hull panel section tested in a laboratory slam testing facility. The approximately 1m x 0.7m panel for laboratory testing was manufactured on a mould taken from the plug used for the vessel construction, ensuring that the panel had identical curved geometry to the vessel. The laboratory panel included two stringers as on the same region of the vessel. An instrumentation layout including arrays of resistance strain gauges, accelerometers and a transient pressure transducer was used. Linear displacement transducers were used to measure panel deformations during the laboratory tests. The laboratory testing was undertaken at a range of constant impact velocities from 0.5 to 3m/s using a Servohydraulic Slam Testing System. Sea-trials were undertaken in the Hauraki Gulf, Auckland New Zealand. There was good qualitative agreement between the field and laboratory measurements in regard to timing and relative magnitudes of strains at different positions on the structure. Results demonstrate that the hull structure undergoes very complex transient deformations during the slamming events.

  • 80.
    Allen, Tom
    et al.
    Centre for Advanced Composite Materials, University of Auckland, New Zealand.
    Battley, Mark
    Centre for Advanced Composite Materials, University of Auckland, New Zealand.
    Stenius, Ivan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Marina system.
    Experimental Methods For Determining Shear Loads In Sandwich Structures Subjected To Slam Loading2010Inngår i: 9th International Conference on Sandwich Structures, 2010Konferansepaper (Annet vitenskapelig)
  • 81. Almquist, Martin
    et al.
    Karasalo, Ilkka
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Mattsson, Ken
    Atmospheric Sound Propagation Over Large-Scale Irregular Terrain2014Inngår i: Journal of Scientific Computing, ISSN 0885-7474, E-ISSN 1573-7691, Vol. 61, nr 2, s. 369-397Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A benchmark problem on atmospheric sound propagation over irregular terrain has been solved using a stable fourth-order accurate finite difference approximation of a high-fidelity acoustic model. A comparison with the parabolic equation method and ray tracing methods is made. The results show that ray tracing methods can potentially be unreliable in the presence of irregular terrain.

  • 82.
    Alonso, Asier
    et al.
    CAF I+D.
    Casanueva, Carlos
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Perez, Javier
    CAF S.A..
    Stichel, Sebastian
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Physical damage mechanisms for uniform wear calculation2018Inngår i: Proceedings of the 11th International Conference on Contact Mechanics and Wear of Rail/wheel Systems, CM 2018, Delft, The Netherlands, 2018Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    This work presents the initial steps given in order to obtain a comprehensive physical model for the specific case of wheel rail contact, which would be able to relate contact conditions, material properties and wear rates. The main advantage of a physical damage wear model is that wheelset an rail manufacturers can perform simulations in order to improve and optimize material properties for different operational cases. The initial work has focused on delaminative wear, starting with the importance and modelling of rough contact, and a comparison against classic smooth contact models. 

  • 83.
    Alsharifi, Hussein
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Design och prestanda för höghastighetståg2011Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
  • 84.
    Altimira, Mireia
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Casanueva, Carlos
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    RAISING AWARENESS ON DIVERSITY AND EQUALITY IN STEM DEGREES IN HIGHER EDUCATION2017Inngår i: INTED2017: 11TH INTERNATIONAL TECHNOLOGY, EDUCATION AND DEVELOPMENT CONFERENCE / [ed] Chova, LG Martinez, AL Torres, IC, IATED-INT ASSOC TECHNOLOGY EDUCATION A& DEVELOPMENT , 2017, s. 1037-1041Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Higher education environments are becoming more and more diverse, regarding both gender and cultural background, which could pose significant challenges for both students and teachers. In order to raise the topic amongst STEM students, a lecture on Diversity has been implemented in the course Research Methodologies for Engineering Mechanics, where different concepts regarding equality have been introduced and unconscious bias have been explained to the students. The lecture was placed in the middle of the course so that students could reflect back on their previous evaluations and enable them to correct their biases in the second half of the course. Feedback of the whole course has also been compared between the 2016 and 2015 editions, where this lecture was not present. The results show that a lecture in Diversity and Equality is especially useful for female students, strongly supporting its inclusion in the course.

  • 85. Al-Zubaidy, M. N.
    et al.
    Chan, J. F. L.
    Gibson, A. G.
    Toll, Staffan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Properties of orthotropic glass-polypropylene composites manufactured by weaving of prepreg tapes and other routes2000Inngår i: Plastics, Rubber and Composites Processing and Applications, ISSN 09598111 (ISSN), Vol. 29, nr 10, s. 520-526Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper reports a study of the melt impregnation and weaving of glass-polypropylene prepreg tapes into sheet for use as a precursor for pressed thermoplastic composite products and a comparison of the properties attainable with those achievable by other comparable routes. Melt impregnation has been used successfully to manufacture well impregnated tapes, with and without internal coupling agent. It appears that weaving could be an economically viable process for converting unidirectional tape into a conformable, press formable prepreg. The properties of glass-polypropylene laminates manufactured by pressing the tape woven product were compared with those of other glass-polypropylene composites, including crossply laminate made from Plytron and samples prepared by film stacking. Quasi-static mechanical properties were found to be comparable with those of Plytron and superior to those of the other materials. In the coupled samples, coupling was somewhat less effective than in Plytron. The impact behaviour of the pressed, tape woven products was impressive and superior to any of the other materials tested. © 2000 IoM Communications Ltd.

  • 86.
    Ambre, Rombaut
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Flygdynamik.
    Landing the Propellant Stage of a launcher2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    To reduce the cost of launch, several aerospace companies are exploring the possibility of partly reusable launchers. In order to be reusable with minimum refurbishment cost the reusable part of the launcher has to suffer little damage and land in optimal conditions. In this paper, a guidance algorithm to achieve the return of the reusable vehicle on ground through a vertical landing is described. Different mission scenarios are taken into account and the performance of the guidance algorithm is assessed using a 6 Degrees Of Freedom simulator.

  • 87.
    Amlinger, Hanna
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Reduction of Audible Noise of a Traction Motor at PWM Operation2018Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    A dominating source for the radiated acoustic noise from a train at low speeds is the traction motor. This noise originates from electromagnetic forces acting on the structure resulting in vibrations on the surface and thus radiated noise. It is often perceived as annoying due to its tonal nature. To achieve a desirable acoustic behavior, and also to meet legal requirements, it is of great importance to thoroughly understand the generation of noise of electromagnetic origin in the motor and also to be able to control it to a low level.

    In this work, experimental tests have been performed on a traction motor operated from pulse width modulated (PWM) converter. A PWM converter outputs a quasi-sinusoidal voltage created from switched voltage pulses of different widths. The resulting main vibrations at PWM operation and their causes have been analyzed. It is concluded that an appropriate selection of the PWM switching frequency, that is the rate at which the voltage is switched, is a powerful tool to influence the noise of electromagnetic origin. Changing the switching frequency shifts the frequencies of the exciting electromagnetic forces. Further experimental investigations show that the trend is that the resulting sound power level decreases with increasing switching frequency and eventually the sound power level reaches an almost constant level. The underlying physical phenomena for the reduced sound power level is different for different frequency ranges. It is proposed that the traction motor, similar to a thin walled cylindrical structure, shows a constant vibration over force response above a certain frequency. This is investigated using numerical simulations of simplified models. Above this certain frequency, where the area of high modal density is dominating, the noise reducing effect of further increasing the switching frequency is limited.

  • 88.
    Amlinger, Hanna
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Botling, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Lopez Arteaga, Ines
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Leth, Siv
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Operational deflection shapes of a PWM-fed traction motor2016Inngår i: Conference Proceedings of the Society for Experimental Mechanics Series, Springer, 2016, s. 209-217Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Operational deflection shapes of an asynchronous traction motor for railway applications are investigated. The radiated noise from the tractionmotor on a train is, especially at low speeds, dominated by noise generated by electromagnetic forces. The tested motor is fed by a pulse-width-modulated (PWM) frequency converter for which the voltage is modulated as a series of pulses that are switched with a certain frequency. In this case, PWM force lines can be expected to influence the radiated noise. Therefore, detailed knowledge about the frequencies and deflection shapes of vibrations generated by PWM forces is of great importance for understanding and controlling the radiated noise and its spectral content. Vibration levels are measured on the stator shield and the operational deflection shapes are studied for several PWM switching frequencies and motor speeds. The deflection shapes with the largest vibration levels are determined. These are then compared to the expected excitation resulting from the pure PWM force lines. Changing the switching frequency, will shift the frequencies of the exciting forces. An appropriate selection of the PWM switching frequency is therefore important for the resulting acoustic radiation from the motor. © The Society for Experimental Mechanics, Inc. 2016.

  • 89.
    Amlinger, Hanna
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    Lopez Arteaga, Ines
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    Leth, Siv
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    Impact of PWM switching frequency on the radiated acoustic noise from a traction motor2017Inngår i: 2017 20th International Conference on Electrical Machines and Systems, ICEMS 2017, Institute of Electrical and Electronics Engineers Inc. , 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The radiated acoustic noise from a traction motor at low speeds is dominated by the noise of electromagnetic origin. For a motor operated from pulse width modulated (PWM) converters, the switching frequency of the converter will have a large impact on the noise. The total harmonic distortion of the motor phase currents and thus also the exciting forces, will decrease with increasing switching frequency. Furthermore, changing the switching frequency will shift the frequencies of the exciting forces, hence have an influence on the coincidence with structural resonances of the motor. Tests have been performed on a traction motor and a decrease in sound pressure level with increasing switching frequency has been quantified and analyzed.

  • 90.
    Amlinger, Hanna
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Lopez Arteaga, Ines
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Leth, Siv
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Reduction of radiated acoustic noise of a traction motor at PWM converter operationManuskript (preprint) (Annet vitenskapelig)
  • 91.
    Amundin, Eskil
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Marina system.
    Modeling of fatigue in RORO ships2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The largest modern Pure Car and Truck Carriers (PCTC’s) are typically 230 meters long and have 13 cargo decks. In order to facilitate rapid loading and unloading these ships have been subject to a development of reducing any obstructing structures in the cargo hold, meaning that the transversal shear preventing structures, i.e. the racking bulkheads, has been taken to a minimum. Previous studies have concluded that some points on the racking bulkheads, as a result of the stripped down design, are subject to high stresses resulting from wave induced accelerations of the ship.

    In this M.Sc. Thesis the fatigue life of a corner of a transverse bulkhead opening in a 230 meter long PCTC with a capacity of 7200 cars is calculated with different methods.

    •Fatigue life is calculated from recorded ship motion data with the notch stress method in conjunction with rain flow counting and the cumulative damage principal.

    • Fatigue life is calculated according to (DNV CN. 30.7, 2010), based on a Lloyd’s Register FE model load case.

    • Actual findings on the ship are compared to the calculated results. Due to the lack of inspection data this comparison is not very extensive and only more briefly discussed.

    It is concluded that the fatigue life of the examined point, calculated from recorded motion data is 9.6 years and the fatigue life according to DNV is 8.0 years. It is also found that the fatigue damage is cumulated in almost discrete portions and thus the calculated fatigue life can be inaccurate when a short period of time is evaluated as is done in this thesis.

    A modification to the racking bulkhead with respect to fatigue life is also analyzed and it is concluded that the fatigue life in the examined point could be extended significantly by some simple modifications to the geometry.

  • 92.
    Anandito, Akhsanto
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Dynamic Analysis of Sinusoidal, Random and Shock Vibration according to Launch Environment for Small Spacecraft Development to Asteroid 2016-HO32019Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The investment of space commerce is skyrocketing and it is predicted to be a nascent business in the future. The spacecraft demand has been growing not only for NASA and other space agency’s mission but also collaboration business between small space industries, academia, and scientific community. This glimpse brought an interest to a new investor, government, military, and manufacturing company to deliver their objectives efficiently. Nowadays, many startups compete embracing innovation and pioneering the novelty of space project beyond prodigious vision in an unprecedented way. Many players foresee that decreasing size of the rocket is an important key to survive and succeed in the space business. One of the efficient acts is lowering the launch cost. This can be achieved by designing a small size, lightweight and affordable spacecraft. Within this context, a Beyond Atlas Spacecraft which will be sent to Asteroid 2016-HO3, has achieved a wet mass of 20.85 kg with the size of 24.7 x 42.2 x 40.8 cm in stowed mode and 84 x 399 x 40.8 cm in unstowed mode. However, the drawback being light and small may lead to catastrophic failure due to resonance frequency events. According to past experience, the gyro of the Swedish national satellite was damaged during ground testing and it was suspected due to high amplification when the natural frequency coincides to the main structure resonance. Therefore, this work is focusing on a spacecraft development and a non-destructive structural analysis. The coupled-load analysis of a preliminary spacecraft design including sinusoidal, random vibration and shock analysis are calculated using FEM. This effort can reduce the risk of component destruction before laboratory testing as well as understand better the dynamic behavior of the spacecraft. The critical frequency in each orthogonal axis with base input from launch environment of the LM-3A Launch Vehicle was devised. The maximum stress, amplitude, and acceleration in accordance of qualification test criteria were evaluated and discussed.

  • 93.
    Ananthasubramanian, Srikanth
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Gupta, Priyank
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Early assessment of composite structures: Framework to analyse the potential of fibre reinforced composites in a structure subjected to multiple load case2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    To meet the need of lightweight chassis in the near future, a technological step of introducing anisotropic materials like Carbon Fibre Reinforced Plastics (CFRP) in structural parts of cars is a possible way ahead. Though there are commercially available tools to find suitability of Fibre Reinforced Plastics (FRPs) and their orientations, they depend on numerical optimization and complexity increases with the size of the model. Nevertheless, the user has a very limited control of intermediate steps. To understand the type of material system that can be used in different regions for a lightweight chassis, especially during the initial concept phase, a more simplified, yet reliable tool is desirable.The thesis aims to provide a framework for determining fibre orientations according to the most-ideal loading path to achieve maximum advantage from FRP-materials. This has been achieved by developing algorithms to find best-fit material orientations analytically, which uses principal stresses and their orientations in a finite element originating from multiple load cases. This thesis takes inspiration from the Durst criteria (2008) which upon implementation provides information on how individual elements must be modelled in a component subjected to multiple load cases. This analysis pre-evaluates the potential of FRP-suitable parts. Few modifications have been made to the existing formulations by the authors which have been explained in relevant sections.The study has been extended to develop additional MATLAB subroutines which finds the type of laminate design (uni-directional, bi-axial or quasi-isotropic) that is suitable for individual elements.Several test cases have been run to check the validity of the developed algorithm. Finally, the algorithm has been implemented on a Body-In-White subjected to two load cases. The thesis gives an idea of how to divide the structure into sub-components along with the local fibre directions based on the fibre orientations and an appropriate laminate design based on classical laminate theory.

  • 94. Andersson, B. L.
    et al.
    Bolin, Karl
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Cederholm, A.
    Karasalo, Ilkka
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. FOI - Swedish Defence Research Agency, Sweden .
    Assessment of sound propagation modelling from a wind turbine site at sea2009Inngår i: 16th International Congress on Sound and Vibration 2009, ICSV 2009, 2009, s. 896-903Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We present results from numerical modelling of sound propagation from Utgrunden lighthouse in Kalmarsund to a receiver at Hammarby on the island Ö land east of Sweden in the Baltic. The propagation distances from source to shore and from shore to receiver are ca 9 km and 0.7 km, respectively. Our purpose is to assess prediction of atmospheric sound propagation by methods that use detailed knowledge of the local geometry and meteorology, by comparing model predictions of the transmission loss with experimental data. The experimental data, collected several times daily during a one-week campaign in June 2005, consist of (i) data on the transmission loss of narrow band signals from controlled sources with frequencies 80 Hz, 200 Hz and 400 Hz, (ii) atmospheric parameters as function of height from radio-soundings and balloon-tracking at the receiver location and (iii) atmospheric parameters from sensors mounted on a meteorological mast at the source location. Model-predicted soundfields were computed once per hour during the one-week period, with a windfield composed of a laminar field determined from data at the receiver, superimposed by a turbulent field determined by data from the meteorological mast. Comparisons of the experimentally observed transmission loss with predictions by the Green's Function Parabolic Equation (GFPE) method by Gilbert and Di are presented. A reasonably good fit of the model predicted transmission loss as function of time to experimental data at all frequencies is observed.

  • 95.
    Andersson, Emil
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Marina system.
    Application of the open sourcecode Nemoh for modelling ofadded mass and damping in shipmotion simulations2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Two different numerical tools were considered, the first one is a seakeeping method developed by KTH Ship Dynamics Research Program. It utilizes strip theory and Lewis forms and is further addressed as SMS. The second one, Nemoh is an open source code utilizing three-dimensional panel method for calculating first order hydrodynamic coefficients in the frequency domain.A comprehensive revision of Nemoh and SMS has been performed on behalf of the KTH Ship Dynamics Research Program. The background to the revision was the high interest in accurately capturing a ships dynamic response. The aim was to explore the prospect of making use of the open source code Nemoh for modelling of added mass and damping in terms of modelling, computational efforts and ship motion prediction improvements. Further, the thesis includes a well-described method on how to operate and pre-process data for Nemoh together with a validation study including results from commercial software´s and experimental studies. An approach with the aim to capture the speed-dependency of the hydrodynamic coefficients together with further potential development of Nemoh is addressed.The validation of Nemoh is showing diverse result. For two cases, the Response Amplitude in Heave is insufficiently modelled. In consequence it’s stated that further studies are required in order to establish whether it’s the case of inadequate input from the authors’ side or lack of robustness in Nemoh that is the cause. The approach to capture speed effects in the hydrodynamic coefficients is proven to be fairly accurate and is considered to be of further use for future development of Nemoh.With respect to identified computational efforts, it’s concluded that Nemoh requires much more computational time than SMS while the accuracy of result is lower. No major improvements may therefore be achieved by substituting or implementing parts of Nemoh into SMS. Nemoh is however of use for the KTH Ship Dynamics Research Program and of other users of Lewis Method when establishing whether a hull-geometry is considered to be “too” unconventional for a two-parameter mapping technique or not. The capability to calculate the RAO in surge is also of interest for KTH Ship Dynamics Research Program since it’s not a feature in SMS.

  • 96.
    Andersson, Evert
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Spårfordon. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    Berg, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Spårfordon. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    Greenhouse gas emissions from rail services: Present and future2010Inngår i: Proceedings of Railways and Environment, 2010Konferansepaper (Fagfellevurdert)
  • 97.
    Andersson, Evert
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Spårfordon. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    Berg, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Spårfordon. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    Nelldal, Bo-Lennart
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Trafik och logistik. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    Fröidh, Oskar
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Trafik och logistik. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    TOSCA. Rail freight transport: Techno-economic analysis of energy and greenhouse gas reductions2011Rapport (Annet vitenskapelig)
    Abstract [en]

    In Stage 1 of the EU/FP7-funded project TOSCA (Technology Opportunities and Strategies toward Climate-friendly trAnsport) the techno-economical feasibility of different technolo-gies and means to reduce greenhouse gas (GHG) emissions is being analysed for different modes of transport. This is made over the long-term perspective until 2050, with 2009 as the reference year. This is the report on the rail freight transport market, applicable to the European Union (EU-27).The analysis presented in this report estimates that a number of efficient technologies and means are available, individually and in combination, to significantly reduce energy use and the resulting GHG emissions on the rail freight market until 2050. The analysis has considered the following technologies and means:

    – heavy freight trains (high payload capacity per metre of train as well as longer trains)

    – eco-driving, including traffic flow management

    – energy recovery

    – high-efficiency machinery in locomotives and electric supply

    – low air drag

    – incremental improvements, in particular reduced tare mass of wagons.

    Despite anticipated higher train speeds in most future train operations the above-mentioned technologies and means have, according to the analysis, the potential to reduce the average energy use per net-tonne-km (tkm) of payload by 40–50 % until 2050. As a consequence also the direct and indirect GHG emissions will be reduced. Energy use and GHG emissions are measured per net-tonne-km, assuming representative load factors in different operations.

  • 98.
    Andersson, Evert
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Spårfordon. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    Berg, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Spårfordon. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    Nelldal, Bo-Lennart
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Trafik och logistik. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    Fröidh, Oskar
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Trafik och logistik. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    TOSCA. Rail passenger transport: Techno-economic analysis of energy and greenhouse gas reductions2011Rapport (Annet vitenskapelig)
    Abstract [en]

    In Stage 1 of the EU/FP7-funded project TOSCA (Technology Opportunities and Strategies toward Climate-friendly trAnsport) the techno-economical feasibility of different technologies and means to reduce greenhouse gas (GHG) emissions is being analysed for the different modes of transport. This is made in the long-term perspective until 2050, with 2009 as the reference year. This is the report on rail passenger transport, applicable to the European Union (EU-27).The present report has been subject to review among railway experts, representing train suppliers, railway operators as well as academia. They have also responded to a questionnaire. Further, a workshop was held, where the report with assumptions and results was discussed.In the analysis presented in this report it is estimated that a number of efficient improvements that, individually and in combination, are available in order to significantly reduce energy use and the resulting GHG emissions on the rail passenger market until 2050. The analysis has considered different technologies and means:

    – low air drag

    – low train mass

    – energy recovery

    – eco-driving, including traffic flow management

    – space efficiency in trains (increasing payload per metre of train)

    – incremental improvements of energy efficiency, in particular reduced losses.

    Despite anticipated higher average train speeds in the future these combined approaches will, according to the analysis, have the potential to reduce the average specific energy use per passenger-km (pkm) in the order of 45–50 % in the very long term until 2050. As a consequ-ence also the direct and indirect GHG emissions will be reduced. The highest reductions are possible in city and regional rail operations. Reductions are more limited in high-speed opera-tions, because of the advanced technologies already applied. However, high-speed rail has today a comparatively low energy use per passenger-km, partly due to its high average load factor. To be consistent with other work packages of TOSCA, energy use and GHG emissions are measured per passenger-km, assuming representative load factors in different operations.

  • 99.
    Andersson, Evert
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Spårfordon. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    Berg, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Spårfordon. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    Stichel, Sebastian
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Spårfordon. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    Casanueva, Carlos
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Spårfordon. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    Rail Systems and Rail Vehicles: Part 2: Rail Vehicles2016 (oppl. 1)Bok (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    This compendium is mainly intended for MSc education in rail vehicle engineering at KTH Royal Institute of Technology, Stockholm, Sweden. The objective is to give an overview and fundamental knowledge of different rail systems, followed by a more thorough introduction to rail vehicles. In this way most rail aspects are covered. The compendium consists of 20 chapters.

  • 100.
    Andersson, Evert
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Carlsson, U.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Lukaszewicz, Piotr
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Leth, Siv
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    On the environmental performance of a high-speed train2014Inngår i: International Journal of Rail transportation, ISSN 2324-8378, E-ISSN 2324-8386, Vol. 2, nr 1, s. 59-66Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Environmental performance is one of the major considerations of future high-speed trains. Two main issues have been closely investigated in the Green Train programme, namely (1) energy use and (2) external noise. Analysis, development and testing in the Green Train programme have focused primarily on speeds up to 250 km/h, although the energy issues have also been studied at top speeds up to 320 km/h. The energy use is estimated for both long-distance trains with few stops and for fast regional services with relatively tight underway stops. These estimations result in an energy use of 46–62 Wh per passenger-km – or 30–40 Wh per seat-km – accounted as electricity taken from the public electric power grid. Improved aerodynamic performance, efficient space utilization, electric regenerative brakes, eco-driving advice and improved energy efficiency in the propulsion system make this possible. Trackside noise has also been analysed and tested in the programme. In order to maintain the same or lower noise level at 250 km/h as at lower speeds with current trains, a number of measures are proposed. These include bogie skirts, wheel absorbers and careful aerodynamic design of the front area and of all protruding objects. In sensitive residential areas, further improvement may be achieved with rail absorbers or low trackside screens.

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