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  • 251.
    Berquand, Audrey
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Aerodynamik.
    Relative Close Navigation for Non cooperative Rendezvous2014Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

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

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

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

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

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

  • 252.
    Bessman, Alexander
    et al.
    KTH.
    Soares, Rúdi
    KTH.
    Wallmark, Oskar
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Svens, Pontus
    KTH.
    Lindbergh, Göran
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemiteknik.
    Aging effects of AC harmonics on lithium-ion cellsManuskript (preprint) (Annet vitenskapelig)
  • 253.
    Bharath, G.
    et al.
    Trinity College Dublin, Department of Mechanical and Manufacturing Engineering, Ireland .
    O'Reilly, Ciarán J.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. Trinity College Dublin, Department of Mechanical and Manufacturing Engineering, Ireland.
    Barrera Rolla, Leandro
    Trinity College Dublin, Department of Mechanical and Manufacturing Engineering, Ireland.
    Rice, Henry J.
    Trinity College Dublin, Department of Mechanical and Manufacturing Engineering, Ireland .
    Iterative solutions of the three-dimensional Helmholtz equation using the wave expansion method for high frequency acoustic scattering problems2007Inngår i: 36th International Congress and Exposition on Noise Control Engineering, INTER-NOISE, 2007, Vol. 7, s. 4788-4795Konferansepaper (Annet vitenskapelig)
    Abstract [en]

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

  • 254.
    Bhat, Sriharsha
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Fordonsdynamik. KTH, Skolan för industriell teknik och management (ITM), Centra, Integrated Transport Research Lab, ITRL.
    An Investigation into the Optimal Control Methods in Over-actuated Vehicles: With focus on energy loss in electric vehicles2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

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

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

  • 255.
    Bhat, Sriharsha
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Fordonsdynamik.
    Davari, Mohammad Mehdi
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Fordonsdynamik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Nybacka, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Fordonsdynamik. KTH, Skolan för industriell teknik och management (ITM), Centra, Integrated Transport Research Lab, ITRL.
    Study on energy loss due to cornering resistance in over-actuated electric vehicles using optimal control2017Inngår i: SAE International Journal of Vehicle Dynamics, Stability, and NVH - V126-10, 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 256.
    Bhatti, Ayjwat A.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Development of efficient three-dimensional welding simulation approach for residual stress estimation in different welded joints2012Inngår i: Journal of Strain Analysis for Engineering Design, ISSN 0309-3247, E-ISSN 2041-3130, Vol. 47, nr 8, s. 539-552Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 257.
    Bhatti, Ayjwat A.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. Osaka University, Japan.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. Khalifa University of Science, United Arab Emirates.
    Murakawa, Hidekazu
    Barsoum, Imad
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. The Petroleum Institute, United Arab Emirates.
    Influence of thermo-mechanical material properties of different steel grades on welding residual stresses and angular distortion2015Inngår i: Materials & Design, ISSN 0261-3069, Vol. 65, s. 878-889Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 258.
    Bhatti, Ayjwat Awais
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    3D Fracture Analysis of Cold Lap WeldDefect in Welded Structures2011Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

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

  • 259.
    Bhatti, Ayjwat Awais
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Computational weld mechanics: Towards simplified and cost effective FE simulations2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

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

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

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

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

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

  • 260.
    Bhatti, Ayjwat Awais
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Khurshid, Mansoor
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Development of a finite element simulation framework for the prediction of residual stresses in large welded structures2014Inngår i: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 133, s. 1-11Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 261.
    Bhatti, Ayjwat Awais
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Van Der Mee, V.
    Kromm, A.
    Kannengiesser, T.
    Fatigue strength improvement of welded structures using new low transformation temperature filler materials2013Inngår i: Fatigue Design 2013, International Conference Proceedings, Elsevier, 2013, s. 192-201Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

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

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

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

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

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

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

  • 266.
    Bilen Oytun, Peksel
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Advanced Model of Acoustic Trim; Effect on NTF Accuracy2011Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 267. Birgersson, F.
    et al.
    Finnveden, Svante
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    A spectral super element for modelling of plate vibration. Part 2: turbulence excitation2005Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 287, nr 02-jan, s. 315-328Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

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

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

  • 269.
    Birgersson, Fredrik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Ferguson, Neil S
    Application of the spectral finite element method to turbulent boundary layer induced vibrations of plates2003Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 259, s. 873-891Artikkel i tidsskrift (Fagfellevurdert)
  • 270. Bisping, R.
    et al.
    Dickson, Crispin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Khan, Shafiq
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Psychometric analysis of stationary aircraft sounds2006Inngår i: 13th International Congress on Sound and Vibration 2006, 2006, s. 3658-3664Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 271.
    Björkblad, Anders
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    A novel tool for crack modelling in finite element analysisArtikkel i tidsskrift (Annet vitenskapelig)
  • 272.
    Björkblad, Anders
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Conventional vs. closure free crack growth in nodular iron2005Inngår i: Competent Design by Castings: Improvements in a Nordic Project / [ed] Samuelsson J, Marquis G, Solin J, Valtion Teknillinen Tutkimuskeskus , 2005, s. 273-286Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 273.
    Björkblad, Anders
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Fatigue assessment of cast components2005Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 274.
    Björkblad, Anders
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Fatigue Assessment of Cast Components: Influence of Cast Defects2008Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

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

  • 275.
    Björkblad, Anders
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Fracture mechanics evaluation of a nodular cast iron component by 3d modelling2005Inngår i: Competent Design by Castings: Improvements in a Nordic Project / [ed] Samuelsson J; Marquis G; Solin J, 2005, Vol. 237, s. 351-374Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 276.
    Björkblad, Anders
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Fracture-mechanics-founded quality rules for defect classification in nodular cast ironArtikkel i tidsskrift (Annet vitenskapelig)
  • 277.
    Björkblad, Anders
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    On the prediction of crack propagation in cast steel specimens2005Inngår i: Competent Design by Castings: Improvements in a Nordic Project / [ed] Samuelsson, J; Marquis, G; Solin, J, ESPOO: TECHNICAL RESEARCH CENTRE FINLAND , 2005, Vol. 237, s. 251-272Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 278.
    Björkblad, Niklas
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    VERIFICATION METHOD FOR FLEXIBLE EXHAUST HOSE: A background study2015Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

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

  • 279.
    Björnholdt Böll, Signe
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    A study of SPEs ​and the consequences of radiation exposure2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

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

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

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

  • 281.
    Björnsson, Lars
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Marina system.
    Comparison of Idealized 1D and Forecast 2D Wave Spectra in Ship Response Predictions2013Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

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

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

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

  • 282.
    Blanco, Blas
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Development of new techniques for the numerical modelling of railway track dynamics. Application to rolling noise assessment2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

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

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

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

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

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

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

  • 283.
    Blanco, Blas
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Railway track dynamic modelling2017Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

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

  • 284.
    Blanco, Blas
    et al.
    KTH.
    Alonso, A.
    Gil-Negrete, N.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Giménez, J.G.
    Implementation of Timoshenko element local deflection for vertical track modellingInngår i: Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 285.
    Blanco, Blas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. University of Navarra, Spain.
    Alonso, A.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Gil-Negrete, N.
    Gimenez, J. G.
    Distributed support modelling for vertical track dynamic analysis2018Inngår i: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, Vol. 56, nr 4, s. 529-552Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 286.
    Blanco, Blas
    et al.
    KTH.
    Alonso, A.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Gil-Negrete, N.
    Giménez, J.G.
    Distributed support modelling for vertical track dynamic analysisInngår i: Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 287.
    Blanco, Blas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Gil-Negrete, Nere
    Alonso, Asier
    Modelling of the track supports with elements over elastic foundation together with dynamic internal degrees of freedom2018Inngår i: Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics2018, Pages 3255-326828th International Conference on Noise and Vibration Engineering, ISMA 2018 and 7th International Conference on Uncertainty in Structural Dynamics, USD 2018; Leuven; Belgium; 17 September 2018 through 19 September 2018 / [ed] W. Desmet, B. Pluymers, D. Moens, W. Rottiers, KU Leuven - Departement Werktuigkunde , 2018, s. 3255-3268Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Formulation of the Timoshenko elements is improved with the use of internal degrees of freedom (iDOF) representing the local displacements, leading to a new finite element approach specially devoted to the numeric analysis of the track dynamics. The dynamic formulation of the local displacement is proved to correct the frequency content of the track model. Regarding time domain studies, this approach avoids the displacement underestimation and shear discontinuity between elements, which are sources of inaccuracies and irregular behaviour.  Those rail sections located above the supports are modelled with Timoshenko element over elastic foundation (TEEF), and the rest with conventional Timoshenko elements (TIM4). By using TEEF prompt disruption of the contact force at support surpassing is avoided, and the frequency response of the track around the `pinned-pinned' frequency is corrected. Moreover the TEEF formulation is extended in order to account for the sleeper pitch rotation, and evaluation of its influence over the track dynamics is performed. 

  • 288.
    Blanco, Blas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Gil-Negrete, Nere
    Giménez, José Germán
    Alonso, Asier
    Assessment of the influence of railway track periodicity, load speed and support modelling on the rolling noise emissionManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The presented methodology jointly accounts for the railway track periodicity and the moving load nature at noise predictions. This modelling approaches rail and sleepers employing the Timoshenko beam theory, and it is formulated to be directly implemented into noise software based on irregularity strip technique. By means of precalculated time domain responses with an analytical track model, the periodicity and moving track dynamics are addressed. In the same way, the propagative behaviour in moving conditions of waves along the rail is characterised by comparison of the responses at several positions.Regarding track support modelling, the usual point modelling is substituted by a distributed representation in order to explore the advantages of accounting for the support length. A numerical model fulfils this task and avoids boundary effects utilising infinite elements. Distributed modelling achieves a more realistic representation of the track geometry. It prevents exaggeration of the amplitude at the `pinned-pinned' frequencies without resorting to overestimation of the steel loss factors. This improvement is especially useful when overvalued rail damping leads to predicted track decay rate (TDR) higher than the one experimentally measured.Finally, the impact of periodicity, load speed and support modelling are assessed through the sound power level (SWL) results.  The predictions are performed with a software package, CRoNoS (CAF Rolling Noise Software), developed by CAF S.A. Moving conditions has a limited impact on the SWL, while modelling of the foundation as periodic is important at tracks with hard pad types, and distributed support modelling becomes significant when realistic values of the steel loss factor are used.

  • 289.
    Blandineau, Pauline
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Flygdynamik.
    Wake Vortex Encounter Detection and Severity Assessment from Flight Data2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Hazards associated to Wake Vortex Encounters (WVE) are increasing with the growing traffic and the appearance of super heavy aircrafts such as the A380. The project comes with the need from airports and airlines to clearly analyze the phenomenon by detecting WVE and quantifying their strength from Flight Data Recorder data. A tool is developed with this purpose using Roll Control Ratio as severity metric. Flight data from flight simulator are used for first analyses. The obtained results are encouraging and enable proposed improvements and consideration to further work.

  • 290.
    Blaszykowski, Sylvain
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Fordonsdynamik.
    Design, modeling and implementation of the power train of an electric racing car: Control of a permanent magnet machine and implementation of a torque vectoring process in a FSAE car2013Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This work emphasize the design, implementation and optimization of an electric power train for a Formula Student racing car.

    As a first part, theory and control of a PMSM machine, in an automotive context is investigated: a CAN bus communication system has been implemented and a field weakening strategy. Precise modeling of the car has then been performed using CarMaker, developed by IPG and making it possible to perform accurate tests and forecast regarding the performances of the vehicle. This model was then used to develop and test different launch control strategies together with a torque vectoring strategy and study the influence of different parameters on the vehicle performances.

  • 291.
    Blom, Peter
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Exploring the vibration control potential of magneto-sensitive rubber2005Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Two new aspects of the dynamic behaviour in the audible frequency range of magneto-sensitive (MS) rubber are highlighted: the existence of an amplitude dependence of the shear modulus—referred to as the Fletcher–Gent effect—for even small displacements, and the appearance of large MS effects. These results have been obtained experimentally and are subsequently used to model two examples of magneto-sensitive rubber isolators to show how by means of MS rubber they can be improved. The first model calculates the transfer stiffness of a torsionally excited isolator and the second one the energy flow into the foundation for a bushing inserted between a vibrating mass and an infinite plate. In both examples notable improvements in isolation can be obtained

  • 292.
    Blom, Peter
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Magneto-sensitive rubber in the audible frequency range2006Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The dynamic behaviour in the audible frequency range of magneto-sensitive (MS) rubber is the focus of this thesis consisting of five papers A-E. Paper A presents results drawn from experiments on samples subjected to different constant shear strains over varying frequencies and magnetic fields. Main features observed are the existence of an amplitude dependence of the shear modulus referred to as the Fletcher-Gent effect for even small displacements, and the appearance of large MS effects. These results are subsequently used in Paper B and C to model two magneto-sensitive rubber isolators, serving to demonstrate how, effectively, by means of MS rubber, these can be readily improved. The first model calculates the transfer stiffness of a torsionally excited isolator, and the second one, the energy flow into the foundation for a bushing inserted between a vibrating mass and an infinite plate. In both examples, notable improvements in isolation are obtainable. Paper D presents a non-linear constitutive model of MS rubber in the audible frequency range. Characteristics inherent to magneto-sensitive rubber within this dynamic regime are defined: magnetic sensitivity, amplitude dependence, elasticity and viscoelasticity. A very good agreement with experimental values is obtained. In Paper E, the magneto-sensitive rubber bushing stiffness for varying degrees of magnetization is predicted by incorporating the non-linear magneto-sensitive audio frequency rubber model developed in Paper D, into an effective engineering formula for the torsional stiffness of a rubber bushing. The results predict, and clearly display, the possibility of controlling over a large range through the application of a magnetic field, the magneto-sensitive rubber bushing stiffness.

  • 293.
    Blom, Peter
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    A non-linear constitutive audio frequency magneto-sensitive rubber model including amplitude, frequency and magnetic field dependence.2011Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 330, nr 5, s. 947-954Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A novel constitutive model of magneto-sensitive rubber in the audible frequency range is presented. Characteristics inherent to magneto-sensitive rubber within this dynamic regime are defined: magnetic sensitivity, amplitude dependence, elasticity and viscoelasticity. Prior to creating the model assumptions based on experimental observations concerning these components are formulated. The first observation is that not only does the rubber display a strong amplitude dependence even for small strains, but also the magnetic sensitivity is strongly amplitude dependent. The second and third are, respectively, that the elastic component is magneto-sensitive, whereas the viscoelastic dependence on magnetic induction appears to be small. Thus, the model is developed from these assumptions and parameters are optimized with respect to experimental values for one case and subsequently validated for others; a very good agreement is obtained.

  • 294.
    Blom, Peter
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Amplitude and frequency dependence of magneto-sensitive rubber in a wide frequency range2005Inngår i: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 24, nr 5, s. 656-662Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two new aspects of the dynamic behaviour in the audible frequency range of magneto-sensitive (MS) rubber are highlighted: the existence of an amplitude dependence of the shear modulus - referred to as the Fletcher-Gent effect - for even small displacements, and the appearance of large MS effects. In order to illustrate these two features, results are presented of measurements performed in the audible frequency range on two different kinds of rubber: silicone and natural rubber with a respective iron particle volume concentration of 33%. The particles used are of irregular shape and randomly distributed within the rubber. An external magnetic field of 0-0.8 T is applied. Both kinds of rubber are found to be strongly amplitude dependent and, furthermore, displaying large responses to externally applied magnetic fields - a maximum of 115%. Also included are graphs of measurements on silicone and natural rubber devoid of iron particles. Those results support the conclusion that introducing iron particles in the rubber gives rise to a strong, non-negligible, amplitude dependence in the entire frequency range.

  • 295.
    Blom, Peter
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Magneto-sensitive rubber in the audible frequency range2005Inngår i: CONSTITUTIVE MODELS FOR RUBBER IV / [ed] Per-Erik Austrell, Leif Kari, London: Taylor & Francis, 2005Konferansepaper (Fagfellevurdert)
  • 296.
    Blom, Peter
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Smart audio frequency energy flow control by magneto-sensitive rubber isolators2008Inngår i: Smart materials and structures (Print), ISSN 0964-1726, E-ISSN 1361-665X, Vol. 17, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A magneto-sensitive rubber isolator inserted between a source and an infinite plate is modelled in the audible frequency range, and the energy flow into the plate with the rubber subjected to a magnetic field applied perpendicular to the axial displacement is calculated. Subsequently the result is compared to the corresponding energy flow for zero magnetic induction; upon the application of an external magnetic field the rubber becomes stiffer, thus shifting the internal resonances of the isolator. This is a fast and reversible process enabling adaption of the isolator to rapidly changing audio frequency conditions by simply turning on and off a magnetic field. In the application example considered, the energy flow into the plate at the first internal dynamic peak stiffness frequency is reduced by approximately 7 dB-a large difference in a sound and vibration context-by inducing magnetic saturation of the rubber.

  • 297.
    Blom, Peter
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    The frequency, amplitude and magnetic field dependent torsional stiffness of a magneto-sensitive rubber bushing2011Inngår i: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 60, nr 1, s. 54-58Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A dynamic torsional stiffness model of a magneto-sensitive circular annular rubber bushing is presented where influences of frequency, amplitude and magnetic field dependence are included. This is achieved by employing a newly developed non-linear magneto-sensitive audio frequency constitutive equation in an engineering formula for the torsional stiffness of a rubber bushing. The engineering stiffness formula predicts the frequency and amplitude dependent stiffness in a simple way, based on geometric dimensions and the shear modulus. The shear modulus is provided by the rubber model. The results from these calculations predict and clearly display the possibility of controlling over a large frequency range, through the application of a magnetic field, the magneto-sensitive rubber bushing stiffness.

  • 298.
    Blomberg, Karl
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Marina system.
    Gross, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Marina system.
    Conceptual Study of a USV for theSwedish Navy2014Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This thesis is an initial conceptual study of an unmanned surface vehicle (USV) for the

    Swedish Navy. The purpose is to highlight challenges and possibilities connected to

    unmanning a vessel and to suggest one specific concept.

    Generating one concept meant weighing characteristics of different hull types against one

    another to derive a valuable compromise. The generated concept includes a feature of

    longitudinal bulkheads separating an inner, dry volume from outer ballast volumes. The

    latter fill with seawater at low velocities, causing the hull to partly submerge which in turn

    decreases signature and increases ballistic protection within the semi-submerged speed

    range. The!concept!measures 6.2 by 2.3 meters, weigh, approximately 1800 kg and may

    reach a calm water top speed of 44 knots. Investigating needs and potentials of an

    unmanned vessel within the Swedish Navy resulted in a set of requirements, including the

    possibility to arm the USV. This study investigates feasibility of carrying the SAAB Trackfire

    remote weapon platform aboard.

    Development of the initial USV concept was focused on aspects of naval architecture,

    including the making of a!general arrangement, evaluating materials, a structural design,

    stability and power need analysis. Although unmanned vessels are likely to be subject to

    lessened structural safety factors as opposed to manned, scantling determination is based

    on DNV rules for classification of High Speed, Light Craft and Naval Surface Craft.

     

  • 299.
    Boden, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    IC-Engine Exhaust and Intake System Acoustic Source Characterization2014Inngår i: SAE International Journal of Engines, ISSN 1946-3936, E-ISSN 1946-3944, Vol. 7, nr 3, s. 1579-1584Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The paper gives an overview of techniques used for characterization of IC-engines as acoustic sources of exhaust and intake system noise. Some recent advances regarding nonlinear source models are introduced and discussed. To calculate insertion loss of mufflers or the level of radiated sound information about the engine as an acoustic source is needed. The source model used in the low frequency plane wave range is often the linear time invariant one-port model. The acoustic source data is obtained from experimental tests or from 1-D CFD codes describing the engine gas exchange process. The IC-engine is a high level acoustic source and in most cases not completely linear. It is therefore of interest to have models taking weak non-linearity into account while still maintaining a simple method for interfacing the source model with a linear frequency domain model for the attached exhaust or intake system. The use of source characterization in acoustic design of mufflers is also briefly discussed.

  • 300.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Acoustic characterisation of perforates using non-linear system identification techniques2007Inngår i: 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), American Institute of Aeronautics and Astronautics, 2007Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper discusses the use of nonlinear system identification techniques for determination of linear acoustic impedance and non-linear acoustic properties of perforates and other facing sheets used in aircraft engine liners.

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