Change search
Refine search result
565758596061 2901 - 2950 of 3049
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 2901.
    Xu, Johanna
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Material models development of damage formation in thin ply carbon/epoxy textile composites2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis work was carried out as a part of the Up in the Blue-project, which aims at introducing Oxeon´s TeXtreme ® fabrics into the aerospace industry. The purpose of this study was to assess the mechanical performance of the TeXtreme composite material, focused on the micro and meso level.On the micro level a method for determining the fibre volume fraction using image analysis was developed, with satisfactory accuracy.On the meso level the weave geometry of the TeXtreme fabric was modelled using finite element methods to investigate stiffness and strength. The predicted initial damage formation for the TeXtreme fabric loaded in tension is matrix cracks in the 90°-fibre bundle. In compression the predicted failure mode is fibre kinking in the 0°-fibre tow.Tensile and compressive properties (stiffness and strength) of both TeXtreme unidirectional and TeXtreme fabric composites were tested according to composite standards, and the measured properties were used in the numerical modelling. The tested specimens were studied in an optical microscope to investigate the damage formation.

  • 2902. Yalchiner, Fikri Bashar
    et al.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Life Extension of Welded Structures Using HFMI Techniques - Potential Application to Offshore Structures2017In: 2nd International Conference on Structural Integrity, ICSI 2017 / [ed] Iacoviello, F Moreira, PMGP Tavares, PJS, Elsevier, 2017, Vol. 5, p. 377-384Conference paper (Refereed)
    Abstract [en]

    Fatigue damage development in welded structures is a local phenomenon and if one need to achieve an extension of the life for the structure local post weld improvements need to be use in order to reduce/remove local features which contribute to the fatigue damage. In order to enhance the life time of load carrying welded structures without large amount of cost investments, e.g. redesign and replacement of existing structures, post weld improvement techniques need to be more applied. New High Frequency Mechanical Impact (HFMI) technologies have been developed in the last 10 years which enables cost-effective life extension and reparation of welded structures. The use improvement techniques for technical life enhancement upgrade and repair of welded structures within various industries, e.g. oil and gas, have been an accepted practice. HFMI treatment techniques are based on localized peening process of the welded joints and the devices are portable. The impacting results in a local cold plastic deformation which remove weld defects reduce stress concentration and induce compressive residual stresses which eventually will enhance the fatigue life of the welded structure. An overview of existing improvement techniques for welded structures is given followed by description of new technologies (HFMI). A brief description of the new international guideline and design recommendations within the International Institute of Welding (IIW) is given. Several validation studies on the fatigue performance of HFMI techniques are presented and onsite potential applications of the techniques for joints in fixed offshore structures are outlined.

  • 2903.
    Yan, Jack
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Simulation Method Development of Ultra Thick Laminates:: with Cohesive Zone Method and Empirical Arcan Tests2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    To reduce the product life cost of aircrafts, the conversion of major load bearing components from aluminium to carbon fibre reinforced plastics have been proposed. Large load bearing components require significantly thicker composite laminates than conventional. These ‘Ultra-Thick Laminates’ require studies into the out-of-plane behavioural and material properties before it can be used commercially. Cohesive Zone Modelling and Arcan empirical testing are chosen to help investigate these properties and behaviour of Ultra Thick Laminates. The Cohesive Zone Modelling method in the commercial FE-software, MSC.Marc Mentat, is validated by comparing results with standardized thin coupon tests prior to further simulation. Arcan tests are to provide material properties to improve accuracy of simulations. However, Arcan test rigs designed prior to the start of this thesis was not suitable for providing correct data and adjustments to the test rigs are needed. Alternatives to the Arcan test have been proposed and considerations of these tests are underway. Nevertheless, Cohesive Zone Modelling is applied to a realistic Ultra Thick Laminates component with the available material properties to provide context. The Cohesive Zone Modelling has shown to be accurate at predicting the behaviour of delamination onset, but the load-displacement predictions were not as accurate in the Ultra Thick Laminates component as in the Cohesive Zone Modelling validations. The sources of discrepancies in results are conceptualized and the Cohesive Zone Modelling remains a viable and potentially powerful method in delamination analysis. However, more development is required in the implementation of Cohesive Zone Modelling for larger components, such as Ultra Thick Laminates components, for Cohesive Zone Modelling to become a robust and standard analytical practice.

  • 2904. Yang, D.
    et al.
    Jacobson, B.
    Jonasson, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Gordon, T. J.
    Minimizing Vehicle Post Impact Path Lateral Deviation Using Optimized Braking And Steering Sequences2014In: International Journal of Automotive Technology, ISSN 1229-9138, E-ISSN 1976-3832, Vol. 15, no 1, p. 7-17Article in journal (Refereed)
    Abstract [en]

    This paper investigates the optimal control of a vehicle, after a light impact during a traffic accident. To reduce the risk of secondary events, the control target is set: to minimize the maximum lateral deviation from the initial path. In previous analysis path control was achieved by the active control of individual wheel braking. The present paper examines potential benefits from the additional control of front steering angles. Numerical optimization is used to determine optimal control sequences for both actuator configurations. It is found that steering provides significant control benefits, though not for all post-impact kinematics. For all cases considered, the optimal control operates at the boundary of the control domain of available forces and moments. This domain is expanded when steering is available, and there exists an expanded range of conditions for which coupled control of yaw moments and lateral forces is the most effective control strategy. The sensitivity of vehicle response to the individual actuator controls is studied; it reveals this sensitivity is related to the actuator bandwidth and the lack of any dynamic cost in the longitudinal direction. This motivates a further analysis which includes longitudinal and lateral dynamics in the cost function. This is broadly related to real-world crash risks. Further, different versions of such cost functions are compared as a basis for implementation in a closed-loop controller.

  • 2905. Yang, D.
    et al.
    Jonasson, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics. Volvo Cars, Sweden.
    Halleröd, T.
    Johansson, R.
    Evaluation of an evasive manoeuvre assistance system at imminent side collisions2017In: Advanced Vehicle Control AVEC’16 - Proceedings of the 13th International Symposium on Advanced Vehicle Control AVEC’16, CRC Press/Balkema , 2017, p. 55-60Conference paper (Refereed)
    Abstract [en]

    In this paper, the performance of an Evasive Manoeuvre Assistance System is evaluated on the test track, where an imminent half-overlapping side collision scenario is reconstructed. The control function here aims to reduce the steering effort for an emergency swerve in front of obstacle and to ease the following recovery into the driver perceived safe zone. This is realized by combined differential braking and steering torque overlay, which improves the agreement between steering input and vehicle response. Preliminary test results have shown that the function has a great potential to reduce collision risk at the presence of suddenly appeared obstacle in front.

  • 2906.
    Yezeguelian, Axel
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Modelling and Simulation of a Propulsive Hybridisation for a Light Fixed-wing Aircraft2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Propulsive hybridisation fits in with the sustainable development policies of many companies which are part of the transportation industry. Actually, it makes it possible either to reduce fuel consumption or to improve the aircraft performance at a fixed fuel burn. However, the current technologies of batteries restrain a more regular use in light aviation. For this project this issue is confirmed as both the quasi-static performance assessment and the dynamic studies show that the endurance objective cannot be improved with Li/Ion batteries. However, it is possible to act directly on the engine performance by placing a thermal energy recovery system on exhaust gas pipes to take advantage of their high temperatures, greatly boosting the aircraft performance in cruise.

  • 2907. Yildirim, H. C.
    et al.
    Marquis, Gary
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Notch stress analyses of high-frequency mechanical impact-improved welds by using rho(f) = 1 mm and rho(f) = rho + 1 mm approaches2014In: Fatigue & Fracture of Engineering Materials & Structures, ISSN 8756-758X, E-ISSN 1460-2695, Vol. 37, no 5, p. 561-569Article in journal (Refereed)
    Abstract [en]

    This paper presents further assessments of the previously reported round-robin fatigue data obtained from high-frequency mechanical impact (HFMI)-improved longitudinal welds. A detailed statistical analyses of geometry measurements of HFMI-treated weld toe profiles are presented. The fatigue analyses based on notch stress as defined by the International Institute of Welding are performed using the finite element method. Notch stresses are assessed based on both the fictitious weld toe radius and the addition of measured actual notch radius to the fictitious radius. While no large differences are observed between the results of methods, the former one is found to be more practical and faster to implement from the end-user point of view.

  • 2908. Yildirim, H. C.
    et al.
    Marquis, Gary
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. Aalto University, Finland .
    Sonsino, C. M.
    Lightweight potential of welded high-strength steel joints from S700 under constant and variable amplitude loading by high-frequency mechanical impact (HFMI) treatment2015In: Procedia Engineering, 2015, no C, p. 467-475Conference paper (Refereed)
    Abstract [en]

    Investigations with longitudinal stiffeners of the steel grade S700 under fully-reversed, constant amplitude loading and under variable amplitude loading with a straight-line spectrum show impressive fatigue strength improvement by high-frequency mechanical impact (HFMI) treatment. However, the degree of improvement was for variable amplitude loading lower when compared to constant amplitude loading due to local plasticity which occurs during larger load levels and consequently reduces the beneficial compressive residual stresses. Apart from the HFMI-treatment, the exceedance of constant amplitude loading (Woehler-lines) by variable amplitude loading (Gassner-lines) offers further lightweight potential, despite the lower degree of improvement by HFMI under spectrum loading.

  • 2909. Yildirim, Halid Can
    et al.
    Leitner, Martin
    Marquis, Gary B.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. Department of Applied Mechanics, School of Engineering, Aalto University, Aalto, Finland.
    Stoschka, Michael
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. Department of Aerospace Engineering, Khalifa University of Science, Technology and Research (KUSTAR), P.O. Box: 127788, Abu Dhabi, United Arab Emirates.
    Application studies for fatigue strength improvement of welded structures by high-frequency mechanical impact (HFMI) treatment2016In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 106, p. 422-435Article in journal (Refereed)
    Abstract [en]

    In 2013, a new guideline for the design of high-frequency mechanical impact (HFMI) treatment was drafted. The proposed design curves were made based on the fatigue data of axially-loaded welded joints which were manufactured from high-strength steels. All the S-N curves were shown to be conservative with respect to the existing fatigue data for laboratory-scale specimens of longitudinal, transverse, and butt welds. In reality, structures in civil, offshore, mechanical engineering and ship industries generally include large-scale and more complicated components rather than laboratory-scale specimens. Therefore, this paper firstly presents the validation of design proposals by considering fatigue data sets for large-scale welded structures. In total, 62 fatigue data points for bridge, crane and beam-like components are reported, in which the yield strength varies from 250 to 725 MPa, and stress ratio varies from -1 to 0.56. Validations are then extended also for cover plates by performing fatigue tests of 23 weld details both in as-welded and HFMI-treated cases for the use of crane industry. Both the extracted and obtained fatigue data are found to be in good agreement with the previously-proposed design guidelines for nominal and effective notch stress assessment.

  • 2910. Yildirim, Halid Can
    et al.
    Marquis, Gary B.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    A round robin study of high-frequency mechanical impact (HFMI)-treated welded joints subjected to variable amplitude loading2013In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 57, no 3, p. 437-447Article in journal (Refereed)
    Abstract [en]

    High-frequency mechanical impact (HFMI) treatment has been significantly developed as a reliable, effective and user-friendly method for post-weld fatigue strength improvement technique for welded structures. The development of an International Institute of Welding best practice guideline for implementing HFMI has been hindered by the lack of directly comparable experimental data for numerous HFMI methods. In this study, nominally identical longitudinal attachments in high-strength steel were manufactured in one welding workshop and distributed to four HFMI equipment manufacturers for treatment. Specimens were fatigue tested on a machine using identical variable amplitude loading histories. HFMI groove measurements were done for each specimen and X-ray diffraction-based residual stress measurements were performed on 10 specimens. The HFMI groove dimensions and the residual stress states showed similarity in general, however small changes were observed. Experimental results indicate that all of the HFMI-improved welds from the HFMI equipment manufacturers satisfied the previously proposed characteristic S-N line based on both the yield strength and the specimen geometry. Results of the study are valuable and promising with respect to the development of a future guideline. The goal of the study has not been to compare treatments, so specific data points are not associated specific HFMI equipment manufacturers.

  • 2911. Yildirim, Halid Can
    et al.
    Marquis, Gary B.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Fatigue design of axially-loaded high frequency mechanical impact treated welds by the effective notch stress method2014In: Materials and Design, ISSN 0261-3069, Vol. 58, p. 543-550Article in journal (Refereed)
    Abstract [en]

    The effective notch stress method (ENS) as defined by the International Institute of Welding is widely used by design engineers to assess the fatigue strength of welded components. This paper provides a comprehensive evaluation of published data for welded joints improved by high frequency mechanical impact (HFMI) treatment. The goal is to verify already-known fatigue classes for the ENS with the available axially-loaded fatigue data. In total, 280 experimental test results obtained from longitudinal, cruciform and butt welds subject to stress ratio of R = 0.1 axial loading are evaluated. Notch stress concentration factors (K-n) for each joint geometry are analysed based on the finite element method. Calculated K-n and reported nominal stress values are used to determine local stresses. Fatigue strength assessment of the all available data is performed by the previously-proposed and verified correction procedure for yield strength (f(y)). A formerly-defined minimum K-n values as a function of f(y) is used for butt welds. The already-known fatigue classes are found to be conservative with respect to available fatigue test data.

  • 2912. Yildirim, Halid Can
    et al.
    Marquis, Gary B.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. Aalto University, Finland.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Fatigue assessment of high frequency mechanical impact (HFMI)-improved fillet welds by local approaches2013In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 52, p. 57-67Article in journal (Refereed)
    Abstract [en]

    Local fatigue assessment methods like the structural hot spot stress and effective notch stress methods as defined by the International Institute of Welding are widely used by design engineers and researchers to assess the fatigue strength of welded components. This paper provides a comprehensive evaluation of published data for welded joints which had been improved using high frequency mechanical impact (HFMI) treatment. All of the published data for HFMI-treated welds are presented in terms of nominal stress. The goal of the current paper is to establish local fatigue assessment procedures for improved fillet welds. In total, 160 published experimental results for longitudinal and cruciform welds subjected to R = 0.1 axial loading are evaluated. Local stress quantities for each joint were assessed based on the finite element analyses and reported nominal stress values. A correction procedure for yield strength that was previously verified for nominal stress-based fatigue assessment is also applied to the local stress methods studied in this paper. For both the structural hot spot stress and effective notch stress methods, sets of characteristic fatigue strength curves as functions of yield strength are proposed and verified. The structural hot spot stress method includes one set of fatigue strength curves for load-carrying welds and a second set for non-load carrying welds. The effective notch stress method includes a single set of curves for all welds. All of the design curves proposed in this study are conservative with respect to available fatigue test data.

  • 2913. Yildirim, H.C.
    et al.
    Marquis, Gary
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. Department of Applied Mechanics, Aalto University, Finland.
    Fatigue data of High-Frequency Mechanical Impact (HFMI) improved welded joints subjected to overloads2015In: Analysis and Design of Marine Structures: Proceedings of the 5th International Conference on Marine Structures, MARSTRUCT 2015, 2015, p. 317-322Conference paper (Refereed)
    Abstract [en]

    In the past decade, High Frequency Mechanical Impact (HFMI) has significantly developed as a reliable, effective and user-friendly method for post-weld fatigue strength improvement technique for welded steel structures. The evaluation and features of developing guideline within the International Institute of Welding (IIW) for the design of structures improved using HFMI is briefly discussed. So far, the extra fatigue strength benefit for HFMI-treated high strength steels has been mostly shown for constant amplitude loading. This paper reports 68 available HFMI-improved welds subjected to overloads or pre-fatigue loads at various loading conditions prior to fatigue testing. These loading conditions are often seen for marine structures.

  • 2914. Yin, Binglun
    et al.
    Mao, Huina
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Qu, Shaoxing
    A phase-field study of the scaling law in free-standing ferroelectric thin films2015In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 26, no 50, article id 505701Article in journal (Refereed)
    Abstract [en]

    The scaling law for ferroelectric stripe domains is investigated in free-standing BaTiO3 and PbTiO3 thin films via phase-field simulations. The results agree with the Kittel law, where the square of the domain width is found to be proportional to the thin film thickness. After being rescaled by the corresponding domain wall thickness, the generalized scaling law is also demonstrated, with the dimensionless scaling constant M estimated to be similar to 3.3 in two ferroelectric materials. Moreover, we predict the effect of the exchange constant which is incorporated in Ginzburg-Landau theory on the equilibrium domain width and the critical thickness of the ferroelectric thin films.

  • 2915. Yoshimura, Kimiyasu
    et al.
    Davari, Mohammad Mehdi
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Drugge, Lars
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Jerrelind, Jenny
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Stensson Trigell, Annika
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Studying Road Roughness Effect on Rolling Resistance Using Brush Tyre Model and Self-Affine Fractal Surfaces2016In: The Dynamics of Vehicles on Roads and Tracks - Proceedings of the 24th Symposium of the International Association for Vehicle System Dynamics, IAVSD 2015, CRC Press, 2016, p. 273-280Conference paper (Refereed)
    Abstract [en]

    While there are many tyre and vehicle dependent factors that affect the rollingresistance, the road properties play also an influential role in the overall resistance on the vehicle.The aim of this study is to develop amodel that can estimate the effect of road roughness on rollingresistance of tyres where both the texture-dependent and independent factors are contributing tooverall rolling resistance. In this paper, a method based on the self-affine fractal surfaces is usedto model realistic road characteristics in order to couple it with a brush based tyre model to beable to study the influence of road roughness on tyre rolling resistance. The simulation resultssuggest that the rolling resistance increases with increased RMS-value and both the macro- andthe micro-texture have an influence on the rolling resistance while the macro-texture effect is moreinfluential. The results of this paper can be related to the estimation of fuel economy on differentroad textures, from macro-texture to micro-texture and further optimisation of road surfaces.

  • 2916.
    Young, Pete Y
    et al.
    Massachusetts Institute of Technology.
    Malmqvist, Johan
    Chalmers University of Technology.
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Kuttenkeuler, Jakob
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Naval Systems.
    Svensson, Thomas
    Linköping university.
    Cunningham, Goeffrey
    Queen's University Belfast.
    Design and development of CDIO student workspaces - Lessons learned2005In: 2005 ASEE Annual Conference and Exposition: The Changing Landscape of Engineering and Technology Education in a Global World, 2005, p. 2867-2880Conference paper (Refereed)
    Abstract [en]

    CDIO project, which is an initiative that aims to develop a new model for engineering education, was discussed. A prominent attribute of the CDIO initiative has been the design and implementation of a new class of student workspaces that enable students to design, build and test project-based courses. A large number of factors were considered for the proper set-up of a student workspace that supports design-build-test education experiences. The factors are ownership, functionality, staff competence, costs, safety, security and sustainability.

  • 2917.
    Yuan, Yunxia
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ivchenko, Nickolay
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Schlatter, Nicola
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    RECONSTRUCTION OF ATTITUDE DYNAMICS OF FREE FALLING UNITS2015In: EUROPEAN ROCKET AND BALLOON: PROGRAMMES AND RELATED RESEARCH, 2015, p. 107-113Conference paper (Refereed)
    Abstract [en]

    Attitude reconstruction of a free falling sphere for the experiment Multiple Spheres for Characterization of Atmosphere Temperatures (MUSCAT) is studied in this paper. The attitude dynamics is modeled through Euler's rotational equations of motion. To estimate uncertain parameters in this model such as the matrix of inertia and the lever arm for the dynamic pressure with respect to the center of mass, the dynamics reconstruction can be formulated as an optimization problem. The goal is to minimize the deviation between the measurements and the propagation from the system equations. This approach was tested against a couple of flight data sets which correspond to different periods of time. The result is very reasonable compared to the laboratory test. The estimate can be improved further through allowing drag coefficients variable and taking advantage of measurements from a magnetometer in numerical calculation.

  • 2918.
    Yuan, Yunxia
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Ivchenko, Mykola
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Precession and nutation of a free flying and axi-symmetric sphere2017In: Acta Astronautica, ISSN 0094-5765, E-ISSN 1879-2030Article in journal (Other academic)
    Abstract [en]

    Attitude motion of small suborbital probes is closely related to scientic measurements performed on these probes. Attitude dynamics of a free ying and axi-symmetric sphere is studied in this paper. The sphere is exposed to aerodynamic torques due to the deviation between the center of mass and the geometric center. For some system parameters and initial motion conditions, the attitude motion can be thought of as regular precession, as well as superposition of precession and nutation. These motion phenomena were modeled and some physical quantities were formulated to describe them. For regular precession to occur, the aerodynamic torque must be perpendicular to the total angular momentum, and the angular momentum of non-precession must be aligned with the axis of symmetry. For superposition motion, the aerodynamic torque must be perpendicular to the total angular momentum,and the angular momentum of non-precession must not be aligned with the axis of symmetry. Numerical simulations verify these analysis. Eventually, these models are used to analyze flight data.

  • 2919.
    Yuan, Yunxia
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Ivchenko, Nickolay
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Attitude reconstruction of suborbital small spacecrafts using a global optimization method2017In: Acta Astronautica, ISSN 0094-5765, E-ISSN 1879-2030Article in journal (Other academic)
    Abstract [en]

    Attitude motion of suborbital payloads is closely related to the quality of scientic measurements. In this paper, attitude reconstruction of suborbital payloads in terms of yaw-pitch-roll Euler angle is studied, according to measurements of magnetic fields from a magnetometer and angular velocities from a gyro sensor. To avoid complex dynamical modelling, the kinematic equations were used. The Euler angles were established by using an global optimization method. Moreover, the Euler angles were estimated by employing Unscented Kalman Filter (UKF) technique. The comparison of the optimized results to the ones from the UKF shows that the global optimization method provides higher accuracy than the UKF.

  • 2920. Yurindatama, D.
    et al.
    Barsoum, Imad
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. The Petroleum Institute, United Arab Emirates.
    Constitutive model and failure locus of a polypropylene grade used in offshore intake pipes2017In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 57, p. 245-259Article in journal (Refereed)
    Abstract [en]

    BorECO®™ BA212E is a polypropylene block co-polymer which has become a common material in the manufacturing of large diameter non-pressurized gravity offshore intake pipelines. These lines are used for transportation of sea water for cooling of petrochemical process plants. The pipe sections are joined by butt heat fusion welding to create the pipeline. Recently a few premature failures of such pipelines have been reported in the field. Hence, there is a need to characterize the constitutive behavior of the pipe and weld material in order to properly design these pipes. The aim of this work is to determine the material constitutive behaviors of the pipe material and the welded joint material. Uniaxial tensile tests of both the pipe and weld joint material are conducted at various strain rates. Both the pipe and weld material show a rather high strain rate dependency, with the weld material having about half the yield strength than that of the pipe material. An analytical constitutive material model is developed for both the pipe and weld material, incorporating the effect of strain rate. The failure locus, expressed in terms of the equivalent plastic strain at failure vs. the stress triaxiality, for both materials is also determined as part of the constitutive model using notched dumbbell specimens. The constitutive model and failure loci for the pipe and weld material are implemented in a finite element model (FEM) and are validated by conducting a series of independent four-point bend experiments on both material types. The validation is carried out by comparing the FEM results of the four-point bend model with the experimental results, which show a rather good agreement.

  • 2921.
    Zachrisson, Daniel
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Naval Systems.
    Manoeuvrability model for a Pure Car and Truck Carrier2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This is a master thesis conducted during the autumn and winter 2010-2011 at KTH Centre for Naval Architecture in collaboration with Wallenius Marine AB.

    Traditionally the hull lines of typical Pure Car and Truck Carriers have been optimized for minimum resistance when going on a straight path and for maximum cargo capacity. This has resulted in vessels with slender underwater body, very high vertical centre of gravity and large flares in the waterlines of the aft body to provide form stability. Dynamic behaviour, such as manoeuvrability, has not been in main focus while designing the hulls.

    To create a tool for assessing the manoeuvrability, a model describing the motions in four degrees of freedom of a vessel have been developed. The equations of motion in surge, sway, yaw and roll are set up and solved numerically in Matlab. The code has been validated against available benchmark results and calibrated using trial data from a number of vessels from the Wallenius fleet. Good compliance to trial results is achieved for the initial part of a turn but some problems occur in the later part.

    Both trials and simulations indicate on very good turning and yaw checking abilities among the investigated vessels but also a tendency of dynamic instability.

  • 2922. Zamanizadeh, E.
    et al.
    Gomes, J.
    Bioucas-Dias, J. M.
    Karasalo, Ilkka
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Performance analysis of model-based localization of high-frequency acoustic sources in 3D2013In: OCEANS 2013 MTS/IEEE Bergen: The Challenges of the Northern Dimension, 2013Conference paper (Refereed)
    Abstract [en]

    A robust model-based source localization (MBSL) scheme for 3D positioning of high-frequency underwater acoustic (UWA) transmitters, as well as performance assessment of 3D speed vector estimation of the acoustic source, deploying two linear receiver arrays, is developed and evaluated. In addition, this paper presents the sensitivity evaluation of MBSL to uncertainties involved in environmental parameters, including the effects of sound speed profile and bathymetry mismatches. The results presented here pertain to the general framework of inferring side information concerning an UWA link from the environmental signature imprinted on waveforms by the propagation medium. The presented algorithms directly operate on estimated linear time-varying UWA channel responses, represented as 3-dimensional delay-Doppler-depth functions (DDDF). Estimation of DDDF coefficients is achieved jointly for all receivers deployed at different depths using Basis-Pursuit (BP) tools, which can efficiently handle sparse unconstrained ℓ2 - ℓ1 minimization, and directly operate on the complex signals of baseband models. To extract delay/Doppler information related to each path from the DDDF representation, an efficient energy-based scheme is developed to detect and label wavefronts using clustering techniques inspired by image processing.

  • 2923.
    Zapka, Nils Maximilian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Acoustic absorption and reflection as traininterior design elements2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Acoustic comfort in train compartments is discussed in relation to speech intelligibility. Passive acoustic design solutions were developed, resulting in two screen prototypes that use absorption and reflection to lower the level of speech intelligibility. A method of evaluating these prototype's eect on speech intelligibility was developed based on Speech Intelligibility Index (SII) measurements. Measurements were carried out in a train compartment mockup that resembled a 3 m section of a train coach. A computer ray-tracing model of the measurement setup was created in the ODEON ray-tracing software and verifed against the mockup.

    Simulations were carried out and compared to the measurement results and the applicability of the ray-tracing model discussed. The measurements and subsequent evaluation according to the method developed here were able to predict the prototype's efect on speech intelligibility and are found to be applicable to other future setups.

  • 2924.
    Zea, Elias
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    An application of multi-scale directional dictionaries to RIR interpolation2019In: Proceedings of the 23rd International Congress on Acoustics, 2019, p. 4923-4930Conference paper (Refereed)
    Abstract [en]

    The spatio-temporal sparsity of room impulse responses (RIRs) degrades in the late part due to the stronger wave interference compared with the early part. Meanwhile, such an interference decays in amplitude as time progresses due to absorption in the room, resulting in a decreasing dynamic range of the measurement. Together these aspects pose challenging conditions for compressive sensing applications, such as the interpolation of RIRs measured at sparse microphone positions. In the search of sparse transformation spaces, this paper examines the application of a multi-scale directional dictionary (known as shearlets) to interpolate RIR measurements. These redundant dictionaries consist of multiple curved elementary functions, which offer a decomposition of the acoustic wavefronts into various wavelengths, propagation directions, and times of arrival. Results reported in this paper demonstrate the potential these dictionaries have to interpolate RIRs in both convex and nonconvex rooms, motivating further examination under experimental conditions and in broader frequency ranges.

  • 2925.
    Zea, Elias
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Compressed sensing of impulse responses in rooms of unknown properties and contents2019In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 459, article id 114871Article in journal (Refereed)
    Abstract [en]

    This paper introduces a method to recover unmeasured room impulse responses (RIRs) in acoustical spaces with unknown properties and contents, by means of a compressed sensing methodology. Methods published in the existing literature have been validated in empty, convex rooms; a limited subset of the many, diverse acoustical spaces one can encounter. It results a challenge to represent such diverse wave phenomena with a sparse set of plane waves or equivalent sources, given the coupling between the sparsity of such representations and hypotheses regarding the properties of the acoustical space and its contents, far-field measurement distances, and other parameters. In contrast to this philosophy, the method introduced in this paper exploits the sparsity inherent to the mathematical structure of the wavefronts present in the RIRs, which without further hypotheses carry themselves all the information about the wave propagation in the room. In essence, the measured RIRs are instead represented with a sparse set of curved elementary functions of various sizes, propagation directions and times of arrival, which are linked with the various shapes and locations of the unknown scatterers and boundaries in the room. The main contribution of this work is thus to enable the measurement of RIRs in more complex acoustical spaces, while keeping the number of microphones to a minimum with the use of compressed sensing. The method is formulated as a sparse optimization problem, and the solution is obtained with an iterative thresholding algorithm whose threshold value is determined from the measurements. An analysis of sensing coherence is included, and the performance of the method is experimentally evaluated with 1D microphone array measurements in two lecture rooms and one meet-ing room. For the sake of comparison, the RIRs are also linearly interpolated using a low-pass filter in the wavenumber-frequency domain. The experimental results demonstrate that the proposed method is superior than linear interpolation in all the cases investigated, motivating further development of the method to higher spatial dimensions. In terms of accuracy, the proposed method attains recovery errors in the same order of magnitude as those attained by methods in the literature, yet here the acoustical spaces have arbitrary contents and exhibit more complex geometries and boundary conditions.

  • 2926.
    Zea, Elias
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Modelling space-variant reflections in wavenumber array spectra2018Conference paper (Refereed)
    Abstract [en]

    This paper introduces and investigates a novel single-layer Fourier-based near-field acoustic holography (NAH) technique suited to measurements with a linear microphone array in the presence of a reflector that is perpendicular to the array. The general idea is to model the reflected plane waves as weighted versions of the incident waves. Numerical experiments are performed in order to test the reconstructions against the conventional (free-field) NAH technique and reference results obtained from theoretical calculations. The most important outcome of this paper is that the reconstruction errors decrease as the wavelength of the plane waves is an integer multiple of the array length, and this is attributed to spectral leakage and windowing artefacts introduced by the use of the spatial Fourier transform. In the case of greatest leakage, that is, the wavenumbers of the plane waves are exactly in the middle of two adjacent bins of the wavenumber domain, the errors can exceed 100%. In the case of no leakage, the errors are no greater than 25%. Overall, this study points towards further investigation of the method.

  • 2927.
    Zea, Elias
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Single layer near-field acoustic imaging in space-invariant reflective environments2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The visualization of optical fields, or widely known as photography, is a common practice that can also be applied to acoustic fields. No less than three decades of research in acoustic imaging demonstrate its potential and relevance in plenty applications such as sound source identification and localization, as well as characterization of noise generation mechanisms. In particular, the resolution of the acoustic images can be greatly enhanced by means of measuring the sound in the acoustic near-field. Nevertheless, it is often the case that the field is disturbed by the measurement environment, in the form of noise and reflections, and the source must then be transported to a much quieter place, for instance, an echo-free chamber. Current state-of-the-art methods tackle the aforesaid complications, at the cost, however, of measuring two images instead of one: resulting in twice as many measurement sensors. The contribution of this thesis is the introduction of a novel technique that only requires a single image to be captured, and is specially tailored for acoustic imaging in space-invariant reflective environments, that is, in the presence of reflecting surfaces that are parallel to the measurements.

  • 2928.
    Zea, Elias
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Sound field separation with microphone arrays2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Sound field analysis is a fundamental tool in the design, manufacturing, testing and diagnosis of machines and transportation means, as well as the legislations that regulate noise levels in order to minimize environmental pollution. Customary solutions to the problem of sound field analysis are microphone array technologies such as near-field acoustic holography (NAH) and beamforming. One of the challenges of using these technologies often lies in the difficulty for separating disturbing sounds from the target source, specially when these are correlated. For example, NAH requires that no reflecting surfaces are found in the vicinity of the array, which is in theory only possible in an echo-free chamber. On the other hand, beamforming is most suitably used to separate uncorrelated sound sources, which is not the case of, for instance, the noise generated by the contact between the wheel of a train and a railway track. The present thesis examines the research problems of separating a sound source from its reflections, and separating the rail noise from the total noise radiated by a passing train. The overall goal of the thesis is to push the limits of microphone array technologies in the context of sound field separation, to the end of minimizing the cost and complexity of measurements and analyses. The proposed separation methods are formulated in the wavenumber domain, and the measurements are done with uniform single layer microphone arrays. The problem of separating reflections is addressed in three different papers: (i) compact sources and a parallel reflector, (ii) planar source and a parallel reflector, and (iii) a perpendicular reflector with respect to the microphone array, and the common requirement is the knowledge of the reflector impedance. The problem of separating rail noise is studied in a fourth paper, and the proposed method is formulated such that it does not require prior knowledge of the rail properties. Upon the findings obtained in the papers, a comprehensive description of areas for future work, as well as strategies to approach them, is given at the end of the thesis. 

  • 2929.
    Zea, Elias
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Lopez Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Department of Mechanical Engineering, Eindhoven University of Technology, The Netherlands.
    A single-layer formulation of Fourier-based planar NAH for enclosed spaces2014In: Proceedings of EAA, European Acoustics Association (EAA), 2014Conference paper (Other academic)
    Abstract [en]

    One of the limitations of Fourier-based planar near-field acoustic holography (P-NAH) is that the wave-field extrapolation only holds for outgoing waves, making the study of certain vibro-acoustic sources in reverberant environments a costly and difficult procedure. The present paper is concerned with a single-layer formulation of Fourier-based P-NAH that accounts for the presence of partially absorbing surfaces. The underlying theory is based on the WRW model, which is a rather popular technique in the seismic processing community. Unlike P-NAH, the WRWmodel proposes a solution to the forward acoustic problem, by performing the spatial convolutions via matrix multiplications. The aim of this paper is to investigate the use of the WRW model for inverse acoustics, particularly in the context of P-NAH. Numerical reconstructions with baffled point sources are carried out, investigating a geometrical case with one reflector under noise-free conditions. Several combinations of frequencies, reflection coefficients, measurement apertures and reflector positions are explored. Opportune observations are made regarding the influence of the propagation distances on the numerical implementation of the Green’s functions. The source reconstructions are performed via free-field P-NAH and via the present formulation, aiming towards a quantitative and qualitative understanding of the influence of the partially absorbing surfaces.

  • 2930.
    Zea, Elias
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Lopez Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Experimental Assessment of a Single-layer Near-field Acoustic Holography Method in an Enclosed Space2015Conference paper (Other academic)
    Abstract [en]

    Planar near-field acoustic holography (PNAH) is preferably performed in anechoic spaces, since the wave-field extrapolation only holds for outgoing waves, which makes the study of certain vibro- acoustic sources a troublesome pursuit. To overcome this limitation, a number of imaging alternatives have been investigated in recent years with the use of double-layer pressure (or particle velocity) measurements, as well as of single-layer pressure and velocity measurements. Unlike these methods, our approach is to use single-layer pressure measurements and extend the PNAH method such that it is valid in the presence of a parallel reflector. In this paper we address the experimental validation of the extended PNAH formulation by means of reconstructing the pressure radiated by an omnidirectional source and exploring a few excitation frequencies. The reconstruction performance is investigated via both the free-field and the extended PNAH techniques.

  • 2931.
    Zea, Elias
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Lopez Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Eindhoven University of Technology, Department of Mechanical Engineering.
    Identification of rail contribution to pass-by noise by a modified wave signature extraction (WSE) method2018In: INTER-NOISE and NOISE-CON Congress and Conference Proceedings, Institute of Noise Control Engineering , 2018, p. 617-625Conference paper (Other academic)
    Abstract [en]

    The present paper explores a modified version the wave signature extraction (WSE) method [1], whose aim is to separate the rail contribution to the pass-by noise of railway vehicles. The method requires a line microphone array parallel to the rail, and two accelerometers on the rail in the ver- tical and lateral direction. The motivation for this work is the need to separate the rail contribution to the pass-by noise of railway vehicles. The WSE method [1] is based on the wavenumber domain filtering of pass-by data measured with a microphone array located in the near-field of the rail. The filter design does not require a priori information of the structural properties of the rail, since the required information is obtained from array pressure data and rail vibration data before and after the train passes in front of the array. The filter is such that it extracts the dispersion plot branches of the first family of horizontal and vertical bending waves (moving band-pass filter). Although the comparison with TWINS simulation data provides very promising results, there are discrepancies at the higher frequencies, possibly due to the onset of new bending wave families. Therefore in the present paper we propose a modified filtering procedure, where a bank of band-pass and low-pass filters are used instead, and the results are compared to the original WSE implementation and the TWINS simulation data. We show that the results in the higher frequency range are improved with respect to the original WSE implementation.

  • 2932.
    Zea, Elias
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Lopez Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Eindhoven University of Technology, Department of Mechanical Engineering.
    On modified wavenumber filters for rail contribution estimations2018In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 144, p. EL286-EL289Article in journal (Refereed)
    Abstract [en]

    This brief communication exposes an overview of various wavenumber filters to separate the rail contribution to pass-by noise via the wave signature extraction method [Zea, Manzari, Squicciarini, Feng, Thompson, and Lopez Arteaga, J. Sound Vib. 409, 24–42 (2017)]. It has been found that the originally proposed filters underesti- mate the rail noise at frequencies above 1.6 kHz due to the presence of higher-order wave families that is unaccounted for. The goal of this let- ter is thus to propose and examine different filter functions that can cap- ture such waves, and to assess whether the rail contribution estimations can be improved.

  • 2933.
    Zea, Elias
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Lopez Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Eindhoven University of Technology, Department of Mechanical Engineering.
    Simplified wave signature extraction method for rail contribution estimations2018Conference paper (Other academic)
    Abstract [en]

    The present paper investigates a modified implementation of the wave signature extraction (WSE) method [1], whose aim is to separate the rail contribution to the pass-by noise of railway vehicles. The method requires a line microphone array parallel to the rail, and two accelerometers on the rail in the vertical and lateral direction. The motivation for this work is the need to separate the rail contribution to the pass-by noise of railway vehicles. The WSE method [1] is based on the wavenumber domain filtering of pass-by data measured with a microphone array located in the near-field of the rail. The filter design does not require a priori information of the structural properties of the rail, since the required information is obtained from array pressure data and rail vibration data before and after the train passes in front of the array. The filter is such that it extracts the dispersion plot branches of the first family of horizontal and vertical bending waves (moving band-pass filter). Although the comparison with TWINS simulation data provides very promising results, there are discrepancies at the higher frequencies, possibly due to the onset of new bending wave families. Therefore in the present paper we assess the performance of a simplified WSE method, where a moving low-pass filter is used instead, and the results are compared to the original WSE implementation and the TWINS simulation data. We show that the results in the higher frequency range are improved with respect to the original WSE implementation.

    [1] Zea et al. Journal of Sound and Vibration 409, pp. 24–42, 2017

  • 2934.
    Zea, Elias
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Lopez Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Single layer planar near-field acoustic holography for compact sources and a parallel reflector2016In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 380, p. 129-145Article in journal (Refereed)
    Abstract [en]

    We consider the problem of planar near-field acoustic holography (PNAH) and introduce a new reconstruction method that can be used to process single layer pressure measurements performed in the presence of a reflective surface that is parallel to the measurement plane. The method is specially tailored for compact sources, or for problems in which the scattered field due to the source can be neglected. The approach consists in formulating a seismic model (WRW model) in wavenumber–space and employ it for sound source reconstructions. The proposed method is validated with numerical and experimental data, and, although the most accurate results are obtained when an estimate of the surface impedance is known beforehand, we show that it can substantially improve the reconstruction performance with respect to that of free-field PNAH.

  • 2935.
    Zea, Elias
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Lopez Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Single-layer array method to reconstruct extended sound sources facing a parallel reflector2017In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 141, no 5, p. 3984-3984Article in journal (Other academic)
    Abstract [en]

    The accuracy of sound field reconstruction methods with single-layer microphone arrays is subject to the room or enclosure in which the measurements take place. Thus, the authors recently introduced a single-layer method that can be employed to reconstruct compact sources in the presence of a reflecting surface that is parallel to the array. Now the authors propose a method conceived for extended planar sources such as baffled plates facing a parallel reflector. The method is based on a wavenumber-domain function describing the propagation paths between the source, the reflector and the array. The free-space sound field radiated by the source is then recovered by means of a regularized inversion of the propagation function. Numerical simulations are performed in order to assess the method's performance and potential for source reconstructions. The results are promising and point towards future experimental validation.

  • 2936.
    Zea, Elias
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Lopez Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Eindhoven University of Technology, Department of Mechanical Engineering.
    Sound field separation for planar sources facing a parallel reflector2019In: Applied Acoustics, ISSN 0003-682x, Vol. 149C, p. 181-191Article in journal (Refereed)
    Abstract [en]

    We consider the problem of separating and reconstructing the sound field radiated by a planar source, e.g. a vibrating plate, that faces a parallel reflector. For this purpose we propose a Fourier-based technique to process near-field microphone array measurements that are performed on a single plane between the plate and the reflector. A closed-form expression is derived in the wavenumber domain to recover the free-space sound field radiated by the plate. The fundamental assumption is that the plate scatters sound in a locally-reacting fashion. Overall, provided the admittances of the plate and the reflecting surface are known, the results demonstrate that it is possible to recover the free-field sound radiated by the plate with a reasonable accuracy.

  • 2937.
    Zea, Elias
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Lopez Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Eindhoven University of Technology, Department of Mechanical Engineering.
    Space-variant sound field separation with linear microphone arrayManuscript (preprint) (Other academic)
  • 2938.
    Zea, Elias
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Manzari, Luca
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Lopez Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Eindhoven University of Technology, Department of Mechanical Engineering, The Netherlands.
    Squicciarini, Giacomo
    University of Southampton, ISVR.
    Thompson, David
    University of Southampton, ISVR.
    Separation of track contribution to pass-by noise by near-field array techniques2016In: Proceedings of the 22nd International Congress on Acoustics, 2016Conference paper (Other academic)
    Abstract [en]

    A technique to separate the track noise contribution is proposed based on identifying and extracting the track signature from the pass-by noise information measured with a microphone array relatively close to the track. Separation of the contributions of the vehicle and the track in the pass-by noise spectra is a challenging task, which is currently addressed by a combination of direct and indirect measurements and model predictions. Due to the uncertainties in the separation of the track contribution, whether a vehicle will comply with regulations during certification tests is still very much track dependent. Therefore, accurate means to identify the track contribution to the pass-by noise are needed. In this paper we propose to make use of the fact that in a wide frequency range the track is a distributed source that radiates plane waves at a given angle with respect to the track. By measuring the sound field close to the track with a microphone array, the wavenumber spectrum of the radiated sound can be determined. For the track contribution this wavenumber spectrum is tonal and therefore sparse. We make use of this property to design filters that extract the track contribution to the total pass-by noise. This is illustrated with simulations and experiments. 

  • 2939.
    Zea, Elias
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Manzari, Luca
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Squicciarini, Giacomo
    University of Southampton, Institute of Sound and Vibration Research.
    Feng, Leping
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Thompson, David
    University of Southampton, Institute of Sound and Vibration Research.
    Lopez Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Eindhoven University of Technology, Department of Mechanical Engineering.
    Wavenumber-domain separation of rail contribution to pass-by noise2017In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 409, p. 24-42Article in journal (Refereed)
    Abstract [en]

    In order to counteract the problem of railway noise and its environmental impact, passing trains in Europe must be tested in accordance to a noise legislation that demands the quantification of the noise generated by the vehicle alone. However, for frequencies between about 500 Hz and 1600 Hz, it has been found that a significant part of the measured noise is generated by the rail, which behaves like a distributed source and radiates plane waves as a result of the contact with the train's wheels. Thus the need arises for separating the rail contribution to the pass-by noise in that particular frequency range. To this end, the present paper introduces a wavenumber–domain filtering technique, referred to as wave signature extraction, which requires a line microphone array parallel to the rail, and two accelerometers on the rail in the vertical and lateral direction. The novel contributions of this research are: (i) the introduction and application of wavenumber (or plane–wave) filters to pass-by data measured with a microphone array located in the near-field of the rail, and (ii) the design of such filters without prior information of the structural properties of the rail. The latter is achieved by recording the array pressure, as well as the rail vibrations with the accelerometers, before and after the train pass-by. The performance of the proposed method is investigated with a set of pass-by measurements performed in Germany. The results seem to be promising when compared to reference data from TWINS, and the largest discrepancies occur above 1600 Hz and are attributed to plane waves radiated by the rail that so far have not been accounted for in the design of the filters.

  • 2940.
    Zeeshan, Muhammad
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Tensile Strength of Bonded Lap-mitered Butt-Joints between Layered CFRP Bands: -In collaboration with RUAG Space AB2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Joints in structures always cause strength reduction. The percentage of strength reduction depends upon the selection of several factors such as: type of joint (i.e. adhesive or mechanical), technique of joint (i.e. lap joint, butt joint etc.), geometry of joint, mode of load application etc. Here in this research, the strength of adhesively bonded butt joints with several geometries, later referred as joint angles, is investigated under uniaxial tension loading.

    Adhesively bonded simple butt joints, where joints are placed perpendicular to the loading direction are in common practice mainly because of ease in manufacturing process. But when the joint is fabricated with an angle respective to the loading direction, the geometry of the joint itself affects the strength of the joint significantly. Without going too deep into other factors that affects the joint strength such as manufacturing techniques, manufacturing defects, material behavior etc. only the geometry of the joint is considered and it is evaluated whether it is worth to change the joint geometry or not.

    The significant issue in adhesive joint technology is the prediction of joint strength. However, an approach similar to plastic yield criterion later referred as elastic limit offset method (attempted for 0.025% offset) is considered to estimate the linear elastic limit. Since RUAG Space AB (the industry for which this project is performed) is only interested in the linear elastic regime of the stress-strain curve, therefore the elastic limit offset method is considered to be the suitable one.

    The present work is concerned with the study of adhesively bonded angled butt joint vs. strength behavior. The strength of adhesively bonded butt joints is examined for several butt joint angles under uniaxial tensile loading. The employed butt joint angles are: 0°, 30°, 45°, 60° and 75°. The main objective of the current investigation is to find the joint angle that has the highest strength or the highest capability of load transfer.

    In addition to the above, the influence of the joint on the stress field, joint strength and type of failure is also evaluated using DSP (Digital Speckle Photography) technique and simulated using well known finite element tool, ABAQUS. It is observed that specific strength of the joint is greatly influenced with joint angle. The 45° joint showed the highest elasticity and failed like ductile behavior whereas 75° joint showed the lowest elasticity and failure was purely brittle. Moreover, post-failure inspection of fractured surfaces showed cohesive failure (failure within adhesive layers) for 0°, 30°, 45° and 60°whereas 75° showed composite or adherend failure.

    The simulation is performed for each joint angle. However to validate the model only 45° and 75° joints results are compared with experimental results and plotted in the report. The simulation results of these angles showed good agreement with the experimental ones. Moreover, the stress fields for each joint angle are captured (from ABAQUS), showing that all joints are susceptible to inter-laminar shear. Besides, the relative slip between the top and middle adherends is also calculated, the results show that, the 45° joint has higher tendency of relative slip than others.

  • 2941.
    Zeidler, Jacob
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Conceptual Design Study of a Foil-Trailer to AUV 62-AT2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The Swedish Navy has been using the AUV62-AT for submarine hunting training successfully for a while and it has been found that the biggest drawback is the transport which is very resource draining. The Swedish Defence Materiel Administration was given the task to solve this and a hydrofoiling-trailer was seen as a potential solution. This thesis will present the design process of the foil-trailer as well as issues found and how theses were mitigated, to produce a viable design. To develop the final design both current use of hydrofoil vessels and further adaptions needed for this applications were investigated. The project was done in collaboration with Simon Källerfelt Korall, who has during the project investigated in detail the foil-trailer’s roll stability, presents this in "The development of a foiling trailer for transport of the AUV62-AT"[1], which deals with how the experimental- and model results lines up. The result is a final design of a foil-trailer which is constituted of several sub-systems that has been found to improve the overall concept. It was concluded that the concept was viable and if further developed it can be used as a great method of saving time when deploying the AUV62-AT.

  • 2942. Zein, A.
    et al.
    Elnady, T.
    Elsabbagh, A.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    E-laboratories for sound and vibration education2015In: 22nd International Congress on Sound and Vibration, ICSV 2015, International Institute of Acoustics and Vibrations , 2015Conference paper (Refereed)
    Abstract [en]

    Several universities face the problem of overcrowded classes and laboratories; hence, there is a difficulty of delivering high quality education, which will affect the quality of graduating engineers. It is needed to introduce the missing experimental part in teaching of the courses without the burden of building new labs. This is done by making these experiments available virtually over the internet, available to the students 24 hours to repeat the experiment as many times as necessary to meet the learning objectives of the experiment. Several elearning programs exist nowadays with regards to courses and teaching material but there are very few e-laboratories available worldwide. Some of the e-laboratories are fully simulated and some are real hardware at the university lab and controlled over the internet. There are a number of technical challenges to realize these e-laboratories; the learning management system to handle this virtual campus, the communication between the client machines and the hardware experiments, and the transfer of data to the client machine for further postprocessing. This paper introduces some of the e-laboratories in Sound and Vibration Education, which were developed and implemented within a project funded by the European Commission through the Tempus Program.

  • 2943.
    Zemovski, Mikael
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Interval Based Integer Ambiguity Resolution Using Multiple Antennas: Applied to airplane attitude determination2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Finding the correct integers is the key to high precision range measurements. This has been an issue of investigation since the early 1980’s and many different techniques have been developed, none of them can guarantee to resolve the correct integers in 100% of the cases(Kim & Langley, 2000) though. This thesis focuses on a new approach for Integer Ambiguity Resolution (IAR), using a geometric approach and Interval Analysis (IA). The new method can guarantee that if all measurement errors are bounded by the interval bands the correct integers will always be found. Depending on the width of the interval bands though, there may be more than one solution. The research objective of the thesis is to determine if the Interval Based Integer Am-biguity Resolution (IBIAR) method can be used for accurate attitude determination with only one remaining (correct) solution. Earlier results using the Bounded integer ambiguity resolution using interval analysis (BOUNDS) algorithm (van Kampen, 2010) have shown that one solution can not be obtained for all epochs when applied to flight data from a Cessna Citation II research airplane equipped with three antennas. The analysis did not make use of two frequencies, comparing the baseline orientations and adding an extra antenna though. These aspects are added to the BOUNDS algorithm in order to potentially reduce the number of solutions. Further the effects of the noise on both the carrier phase measurements and baseline lengths are investigated. All simulations are done off line as no real flight data is available for the test configurations. The simulations are loosely based on the Cessna Citation II research airplane belonging to the Dutch National Aerospace Laboratory (NLR) and Delft University of Technology (DUT). For all simulations the correct solution is bounded by the noise levels, which means that the BOUNDS algorithm theoretically always finds the correct solution. Further it is assumed that there are no multipath effects, no restrictions on the attitude angles the airplane can fly with, that the antennas always have a clear view of the satellites and the cut off angle is zero degrees.

    The conclusion of the thesis is that the IBIAR method can be used for attitude determination where one (correct) solution remains but the accuracy of the solution is low. The thesis gives recommendations on how to improve the accuracy of the attitude angles.

  • 2944.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Damage Tolerance of Naval Sandwich Panels2009In: Major Accomplishments in Composite Materials and Sandwich Structures: An Anthology of ONR Sponsored Research / [ed] I.M. Daniel, E.E. Gdoutos, Y.D.S. Rajapakse, Springer Publishing Company, 2009, p. 279-303Chapter in book (Refereed)
    Abstract [en]

    This paper is a review of activities concerning various damage tolerance modelling and testing aspects of sandwich panels for typical Naval applications. It starts with a review of testing methods for primarily core materials and how to extract properties and data required for damage tolerance assessment. Next some typical damage types are defined and how they are modelled with the aim of predicting their effect on load bearing capacity. The paper then describes in brief how such models can used in the context of providing a systematic damage assessment scheme for composite sandwich ship structures.

  • 2945.
    Zenkert, Dan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Burman, Magnus
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Failure mode shifts during constant amplitude fatigue loading of GFRP/foam core sandwich beams2011In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 33, no 2, p. 217-222Article in journal (Refereed)
    Abstract [en]

    This paper presents fatigue results for sandwich beams that exhibit a transition in failure mode, from core shear failure to face laminate tensile failure, as function of load amplitude only. The basis of this are fatigue tests of foam cores in shear and tensile tests on composite laminates. These results show that the slopes of the stress-life (S-N) relation are different for the core and laminates. By using the obtained stress-life relations, a simple design scheme is given for sandwich beams which are anticipated to have a transition of failure mode for a particular load level. Two designs are manufactured and tested in fatigue under constant amplitude loading. The results clearly show the aim of investigation with transitions in failure modes giving a structural stress-life diagram a bi-linear shape. For high load and small number of cycles to failure, the beams fail by core shear fracture while for lower loads, and large number of cycles to failure the beams fail by face sheet tensile failure.

  • 2946.
    Zenkert, Dan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Burman, Magnus
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Failure Mode Shifts in Fatigue of Sandwich Beams2009Conference paper (Other academic)
    Abstract [en]

    Sandwich beams are designed and tested in fatigue, and it is found that for high load and small number of cycles to failure, the beams fail by face tensile fracture. For lower loads, and large number of cycles to failure, the beams fail by core shear.

  • 2947.
    Zenkert, Dan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Burman, Magnus
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Fatigue of closed-cell foams in compression2011In: Journal of Sandwich Structures and Materials, ISSN 1099-6362, E-ISSN 1530-7972, Vol. 13, no 4, p. 467-478Article in journal (Refereed)
    Abstract [en]

    This article deals with fatigue of closed-cell foams under compression loading. Testing is performed on three densities of Divinycell H-grade and three densities of Rohacell WF-grade foam under cyclic compression loading. The fatigue failure is in all cases described as localized crushing of cell layers. The two main observations from this are that the slopes of the stress-life curves are almost all different, both between the foam types and relative density. Secondly, the stress-life relation slopes are considerably flatter than corresponding data in tension. For one particular foam grade, the stress-life relation is almost flat.

  • 2948.
    Zenkert, Dan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Burman, Magnus
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Tension, compression and shear fatigue of a closed cell foam2007In: 16th International Conference on Composite Materials, ICCM-16, 2007Conference paper (Refereed)
    Abstract [en]

    A closed cell foam of Polymetacrylimide (Rohacell) with three different densities is studied. The foam is tested quasistatically in tension, compression and shear. The tensile properties scale very well with the relative density of the foam, but the compression and shear properties do not. It is believed to be due to cell edge and cell wall buckling being the dominated deformation mechanism in compression and shear for lower densities that does not occur for higher densities. Fatigue testing is then performed in tension, compression and shear. It is seen that for all load cases and densities, the fatigue life can be plotted using Basquin's law. The results also show that the different failure mechanisms found in the static tests are the same in fatigue. This means that the fatigue life for different load types exhibit different failure mechanisms. This shows not only as a clear difference in the stress levels for fatigue failure, but also on the slope in the fatigue life relation.

  • 2949.
    Zenkert, Dan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Burman, Magnus
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Tension, compression and shear fatigue of a closed cell polymer foam2009In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, p. 785-792Article in journal (Refereed)
    Abstract [en]

    A closed cell foam of Polymetacrylimide (Rohacell) with three different densities is studied. The foam is tested quasistatically in tension, compression and shear. The tensile properties scale very well with the relative density of the foam, but the compression and shear properties do not. It is believed to be due to cell edge and cell wall buckling being the dominated deformation mechanism in compression and shear for lower densities that does not occur for higher densities. Fatigue testing is then performed in tension, compression and shear. It is seen that for all load cases and densities, the fatigue life can be plotted using Basquin’s law. The results also show that the different failure mechanisms found in the static tests are the same in fatigue. This means that the fatigue life for different load types exhibit different failure mechanisms. This shows not only as a clear difference in the stress levels for fatigue failure, but also on the slope in the fatigue life relation.

  • 2950.
    Zenkert, Dan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Carlsson, Leif A
    KTH.
    Prof. Karl-Axel Olsson (1933-2018) Obituary2018In: Journal of Sandwich Structures and Materials, ISSN 1099-6362, E-ISSN 1530-7972, Vol. 20, no 4, p. 512-513Article in journal (Refereed)
565758596061 2901 - 2950 of 3049
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf