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  • 101. Hedberg, Claes
    Multifrequency plane, nonlinear, and dissipative waves at arbitrary distances1999In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 106, no 6, p. 3150-3155Article in journal (Refereed)
    Abstract [en]

    A solution for multifrequency plane waves propagating through a dissipative and nonlinear medium is presented. It originates from the well-known Bessel function series ratio for a pure sinusiodal wave, introduced by Cole and Mendousse. The solution is exact. The only limitation, inherited from the single-frequency solution, is the slow convergence of the series when the nonlinearity is very large compared to the dissipation. Otherwise any frequencies, amplitudes and phases can be introduced in the original wave and the solution is valid for any propagated distance.

  • 102. Hedberg, Claes
    Nonlinear Dynamics of Grains in a Liquid-Saturated Soil2002Conference paper (Refereed)
    Abstract [en]

    Known models with huge nonlinear response of grainy media are based on nonlinear stress-strain relationships typical for solids containing mesoscopic inhomogeneities or defects in their structure. Such nonlinear behaviour is well-defined at significant local deformation caused by high applied load, even if the load does not vary in time. However, there exist a different type of nonlinearity which manifests itself due to inertial forces between grains. Such forces appear in a moving noninertial frame of reference, in particular, if a small system of interacting particles is placed into a vibrating fluid. High spatial gradients of internal forces are determined by the non-uniform distribution of mass. These gradients varying in time can excite the internal degrees of freedom. So, even at harmonic vibration of the fluid caused by sound, the nonlinear internal dynamics can be responsible for generation of higher harmonics. As an example of nonlinearity of inertial type, a model of grainy medium is developed where the grains are immersed into a vibrating fluid. The inertial attractive forces have hydrodynamic origin, and the repulsive forces are caused by deformation of colliding grains. Dynamic and stochastic motion is studied, resonances are discovered and nonlinear response is evaluated.

  • 103. Hedberg, Claes
    Parameter sensitivity in nonlinear and dissipative time-reversed acoustics1998Conference paper (Refereed)
    Abstract [en]

    Time-reversed nonlinear acoustics has shown that a propagated signal retains information about the original signal after shock formation and even after merging of shocks. This information is dependent on the accuracy of the measured or calculated data . Presented here is a more detailed analysis of the estimation of dimensionless and real parameters in the problem - the original amplitude, the distance traveled and the dissipation over non- linearity ratio. It is shown that the methods are fairly insensitive to noise.

  • 104.
    Hedberg, Claes
    Blekinge Institute of Technology, Department of Telecommunications and Mathematics.
    The multi-frequency solution for periodic nonlinear and dissipative waves1999Conference paper (Refereed)
    Abstract [en]

    The solution for multi-frequency plane waves propagating through a dissipative and nonlinear medium is shown for some examples of periodic conditions. The expression may for any given condition be expressed analytically as a ratio of Fourier series with Bessel function coefficients. In the examples are shown how the final appearance of any initial wave always is a pure periodic wave in the lowest frequency existing in the problem - the period of the condition.

  • 105. Hedberg, Claes
    et al.
    Arnoldsson, Sven
    Gunnarsson, Rikard
    TWO UTILIZATIONS OF OPEN RESONATOR CONCEPT IN NONDESTRUCTIVE TESTING2003Conference paper (Refereed)
    Abstract [en]

    Two ways in which the concept of open resonator can be used in connection with nondestructive evaluation will be described. In the first, a non-contact transducer's efficiency of transferring energy into an object can be increased by utilizing the resonance of the gap between the transducer and object. By choosing the gap distance, frequency and transducer width a resonant wave appears which will have a considerably larger amplitude at the object surface. Secondly, by fitting the critical parameters of open resonators for thin objects, like extended plates, the wave field inside the object can be localized. Thus some Nonlinear Elastic Wave Spectroscopy methods may be used to determine the location of damage.

  • 106. Hedberg, Claes
    et al.
    Enflo, Bengt
    Rudenko, Oleg
    Standing Waves In Quadratic And Cubic Nonlinear Resonators: Q-Factor And Frequency Response2005Conference paper (Refereed)
    Abstract [en]

    High-Q acoustic resonators are used to significantly increase the wave energy volume density. For high-intensity waves the magnitude of Q-factor is determined not only by the design of the resonator, but by the strength of internal field as well. Methods to calculate the Q-factor and both the spatio-temporal and spectral structure of this field are described. Results are given for quadratic and cubic nonlinear resonators demonstrating quite different physical properties.

  • 107. Hedberg, Claes
    et al.
    Enflo, Bengt
    Rudenko, Oleg
    Wave motion in a medium with a cubic nonlinearity2006Conference paper (Refereed)
    Abstract [en]

    An example of wave motion in a medium with a cubic nonlinearity is a transverse finite amplitude wave in an isotropic solid. The corresponding cubically nonlinear wave equation is derived with the nonlinearity expressed in terms of elastic constants. This nonlinear wave equation with dissipation is studied for standing and propagating waves. For standing waves in a resonator a simplified approach results in functional equations, from which frequency response curves are derived. These curves show the dependence of the amplitude on the difference between one of the resonator's ekgenfrequencies and the driving frequency. The frequency response curves are plotted for different values of the dissipation and are very different for quadratic and cubic nonlinearities. In the propagating wave case an N-wave evolution is studied, described by a modified Burgers' equation with a cubic nonlinearity. Approximate solutions to this equation are found for parts of the wave profile not studied in detail before.

  • 108. Hedberg, Claes
    et al.
    Ghazisaeidi, Hamid
    Variation of High Power Air Transducer2006Conference paper (Refereed)
    Abstract [en]

    High power ultrasonic transducers are widely used for detecting objects and measuring distances, etc. In actual applications, for the air coupling ones the impedance mismatch between the transducer surface and air is large, so there is only a small amount of energy transmitted. Most of the energy loss occurs during the transformation of energy from the transducer radial cone to the air. The purpose of this study is to investigate different designs of the radial cone of the transducer and analyze their vibration in order to suggest design variations for improved vibration amplitudes. Concerning a piezoelectric ceramic transducer, we focus on two parameters of the transducer radial cone. This report presents schemes for increasing pressure levels.

  • 109. Hedberg, Claes
    et al.
    Ghazisaeidi, Hamid
    Haller, Kristian
    Mfoumou, Etienne
    Design Alterations of a High Power Air Transducer2007In: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 46, no 7, p. 4908-4911Article in journal (Refereed)
    Abstract [en]

    For certain resonant high-power air transducers exists a radiating cone which is in some way connected to a forcing piezoelectric ceramic. This study focuses purely on the cone structure itself, and the form of excitation that gives desired results on the vibration modes of the cone. In the new design three different parameters are changed from existing devices. They are: 1) the change of the round piezoelectric disc center position to a piezoelectric ring shape, while making the cone center fixed, 2) the cutting of the cone into leaves, and 3) the radial thickness decreasing with radius. In simulations, the new design yields considerably higher vibration amplitudes.

  • 110. Hedberg, Claes
    et al.
    Gurbatov, Sergey
    Nonlinear crosstransformation of amplitude-frequency modulation of quasi-monochromatic acoustic signals1998In: Acustica, ISSN 0001-7884, Vol. 84, no 3, p. 414-424Article in journal (Refereed)
    Abstract [en]

    This work is devoted to the investigation of evolution of intense quasi-harmonic signals in the case of infinite acoustic Reynolds numbers. The consideration is based on the zero viscocity limit solution of the Burgers equation, which reduces the Cole-Hopf solution to a "maximum" principle. This limit solution permits an easy way to get the profile of the waves, postition of shocks and their velocities at arbitrary times. The process of transformation of an initial quasi-monochromatic wave into s sawtooth wave is considered. It is shown that the nonlinearity leads to suppression of the initial amplitude modulation and to the transformation of the initial frequency modulation inot a shock amplitude modulation. The amplitude of the low frequency component generated by a quasi-mono-chromatic wave is found. It is shown that the interaction of this component with high frequency waves leads to phase modulation, which increases with distance. The amplitudes of the new components of the spectrum are found. Is is show n that when the value of phase modulation is small, the amplitudes of the satellites do not depend on the distance or the number of harmonics of the primary wave.

  • 111. Hedberg, Claes
    et al.
    Haller, Kristian
    Double open resonator for localized non-contact acoustic testing2004Conference paper (Refereed)
    Abstract [en]

    There exist two concepts of open resonators that can be combined into a device for acoustic non-destructive testing. The device is non-contact and based on the fact that an airgap between a transducer surface and the test object can be set into resonance. This occurs for the conditions that makes this an open resonator (open because the air volume is not closed), and the wave field is amplified so that a larger amplitude is reached at the object surface. Let us assume that the object is a plate. When the acoustic wave enters the plate, one can let the frequency be the resonant frequency for one of the modes for the plate thickness. A limited part of the plate may be seen as a resonator, open to the sides. When the conditions for an open resonator is fulfilled for the plate thickness, the wave field will be greatly amplified within a region close to the insonified plate surface, and thus the linear or nonlinear response from this excitation is local. The device may then be used to scan the plate for material parameter changes.

  • 112.
    Hedberg, Claes
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Haller, Kristian
    Method for Monitoring Slow Dynamics Recovery2012In: Acoustical Physics, ISSN 1063-7710, E-ISSN 1562-6865, Vol. 58, no 3, p. 713-717Article in journal (Refereed)
    Abstract [en]

    Slow Dynamics is a specific material property, which for example is connected to the degree of damage. It is therefore of importance to be able to attain proper measurements of it. Usually it has been monitored by acoustic resonance methods which have very high sensitivity as such. However, because the acoustic wave is acting both as conditioner and as probe, the measurement is affecting the result which leads to a mixing of the fast nonlinear response to the excitation and the slow dynamics material recovery. In this article a method is introduced which, for the first time, removes the fast dynamics from the process and allows the behavior of the slow dynamics to be monitored by itself. The new method has the ability to measure at the shortest possible recovery times, and at very small conditioning strains. For the lowest strains the sound speed increases with strain, while at higher strains a linear decreasing dependence is observed. This is the first method and test that has been able to monitor the true material state recovery process.

  • 113. Hedberg, Claes
    et al.
    Haller, Kristian
    Non-contact nonlinear acoustic damage localization in plates. Part 2: Localized resonance through dynamically trapped modes2008In: Acta Acustica united with Acustica , ISSN 1610-1928 , Vol. 94, no 1, p. 48-53Article in journal (Refereed)
    Abstract [en]

    This work is the second part of three that presents new tools to be used for damage localization in plates by nonlinear acoustical methods. It introduces an important in-plane localization technique, which is based on the existence of resonant spatially localized wave fields. The wave from the transducer is acting as a dynamic influence on the plate surface, making the waves reflect in a non-ideal way. The non-ideal reflections make the modes underneath the transducer have different resonant frequencies than the modes beside the insonified area. They appear both for contact and non-contact sources. In the nonlinear damage localization application, the trapped mode wave field interacts with another signal at lower frequency. This results in sidebands around the high frequency whose amplitudes are related to the amount of damage underneath the transducer.

  • 114. Hedberg, Claes
    et al.
    Haller, Kristian
    Arnoldsson, Sven
    Non-contact nonlinear acoustic damage localization in plates. Part 1: Resonance of air between plates2007In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 93, no 1, p. 13-21Article in journal (Refereed)
    Abstract [en]

    This is the first of three articles that deals with the goal of using non-contact nonlinear acoustic methods for the damage localization in plates. In this first part, the resonant air gap wave field between one active and one passive reflecting plate was investigated experimentally. Of particular interest is the wave field amplitude strength, and its distribution on the passive surface. The wave amplitude may be increased by choosing one plate to be concave, overcoming the nonlinear damping taking place for two flat plates. Applications are connected with an increased wave field having advantages for processes taking place under open conditions and for a non-contact transducers' efficiency of transferring energy into an object. A double resonance gives highest air pressure, while a triple provides most energy in the passive object. By choosing the gap distance, frequency and transducer width, the appearing resonant wave will have a considerably larger amplitude at the object surface. The work through the interface from air to object is investigated and the wave field in a resonant air-plate system is shown.

  • 115. Hedberg, Claes
    et al.
    Haller, Kristian
    Kamakura, Tomoo
    A Self-Silenced Sound Beam2010In: Acoustical Physics, ISSN 1063-7710, E-ISSN 1562-6865, Vol. 56, no 5, p. 637-639Article in journal (Refereed)
    Abstract [en]

    Parametric loudspeakers are transmitting two high power ultrasound frequencies. During propagation through the air, nonlinear interaction creates a narrow sound beam at the difference frequency, similar to a light beam from a torch. In this work is added the physical phenomenon of propagation cancellation, leaving a limited region within which the sound can be heard—a 1 meter long cylinder with diameter 8 cm. It is equivalent to a torch which would only illuminate objects within 1 meter. The concept is demonstrated both in simulation and in experiment.

  • 116.
    Hedberg, Claes
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Mathematics and Science.
    Martinet, Philippe
    Non-linear dynamics in granular materials2007In: The universality of nonclassical nonlinearity, with applications to / [ed] Paolo, Pier, New York: Springer , 2007, p. 327-336Chapter in book (Other academic)
    Abstract [en]

    This book comes as a result of the research work developed in the framework of two large international projects: the European Science Foundation (ESF) supported program NATEMIS (Nonlinear Acoustic Techniques for Micro-Scale Damage Diagnostics) (of which Professor Delsanto was the European coordinator, 2000-2004) and a Los Alamos-based network headed by Dr. P.A. Johnson. The main topic of both programs and of this book is the description of the phenomenology, theory and applications of nonclassical Nonlinearity (NCNL). In fact NCNL techniques have been found in recent years to be extremely powerful (up to more than 1000 times with respect to the corresponding linear techniques) in a wide range of applications, including Elasticity, Material Characterization, Ultrasonics, Geophysics to Maintenance and Restoration of artifacts (paintings, stone buildings, etc.). The book is divided into three parts: Part I - defines and describes the concept of NCNL and its universality and reviews several fields to which it may apply; Part II - describes the phenomenology, theory, modelling and virtual experiments (simulations); Part III -discusses some of the most relevant experimental techniques and applications.

  • 117. Hedberg, Claes
    et al.
    Rudenko, Oleg
    Interaction between low and high-frequency Modes in a Nonlinear System: Gas-Filled Cylinder Covered by a movable Piston2003In: Nonlinear dynamics, ISSN 0924-090X, E-ISSN 1573-269X, Vol. 32, no 4, p. 405-416Article in journal (Refereed)
    Abstract [en]

    A simple mechanical system containing a low-frequency vibration mode and set of high-frequency acoustic modes is considered. The frequency response is calculated. Nonlinear behaviour and interaction between modes is described by system of functional equations. Two types of nonlinearities are taken into account. The first one is caused by the finite displacement of a movable boundary, and the second one is the volume nonlinearity of gas. New mathematical models based on nonlinear equations are suggested. Some examples of nonlinear phenomena are discussed on the base of derived solutions.

  • 118. Hedberg, Claes
    et al.
    Rudenko, Oleg
    Pulse response of a nonlinear layer2001In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 110, no 5, p. 2340-2350Article in journal (Refereed)
    Abstract [en]

    A simple analytical theory is developed for the description of non-steady state response of a thin nonlinear layer, which differs markedly in its linear properties from the surrounding medium. Such a layer can model the behavior of real inhomogeneities like a cloud of gas bubbles in a liquid, a crack or split plane in a solid, or the contact between two slightly tighted rough surfaces. Both weakly nonlinear pulse and harmonic responses are calculated and the general properties of the spectral and temporal structure of the scattered field are discussed. The exact strongly nonlinear solutions are derived for a special type of stress-strain relationship corresponding to the behavior of real condensed media under strong load. Profiles and spectra shown are in conformity with experimental results. The pulse response on the short delta-pulse shaped incident wave is calculated for arbitrary nonlinear properties of the layer. The possibilities to apply the sets of data on measured characteristics of pulse response in the solution of inverse problems are briefly discussed.

  • 119. Huang, Yayu
    et al.
    Hu, Xiang Ping
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Shen, Yujie
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Liao, Taohong
    Method of obtaining dynamic stress intensity factor by measuring crack mouth opening displacement on a 3-point bending specimen2012In: Lecture Notes in Electrical Engineering, Jiaozuo, Henan: Springer , 2012, Vol. 138, p. 1269-1275Conference paper (Refereed)
    Abstract [en]

    This paper focuses on how to obtain the Dynamic Stress Intensity Factor by measuring Crack Mouth Opening Displacement on a pre-cracked 3-Point Bending Specimen. During the experiments, one uses impactor to hit on a pre-crack 3-Point Bending Specimen and at the same time uses a high-speed camera to take a set of photos of the crack. Crack Mouth Opening Displacement can then be measured from these photos. According to the relationship of J integral, Crack Open Mouth Displacement and the Dynamic Stress Intensity Factor, the Dynamic Stress Intensity Factor could be obtained. This result could be useful for guiding the practical engineering design.

  • 120. Huang, Yayu
    et al.
    Hu, Xiangping
    Fracture mechanics theoretical modelling and FEM analysis of 3-Point Bending Specimen suffering cyclic loads2011Conference paper (Refereed)
    Abstract [en]

    Fracture mechanics theoretical modelling and Finite Element Method analysis of a pre-cracked 3-Point Bending Specimen (3PBS) have been conducted in this paper. Using the equivalent system of the specimen, fracture mechanical characteristics have been analyzed and the theoretical Dynamic Stress Intensity Factor (DSIF) is obtained later and used together with the Pairs theorem to analyze the fatigue life time of the specimen. Based on the simulations from ABAQUS, dynamic characteristics of the pre-cracked 3PBS are obtained and verified. The results are further analyzed and discussed with special concern on fracture mechanics characteristics of the material and will provide a guideline for further research and practical design

  • 121. Huang, Yayu
    et al.
    Hu, XiangPing
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Liao, Taohong
    Fracture mechanics analysis of the Dynamic Stress Intensity Factor of 3-Point Bending Specimen suffering cyclic loads2012In: Applied Mechanics and Materials, Jiaozuo, 2012, Vol. 143-144, p. 503-507Conference paper (Refereed)
    Abstract [en]

    Fracture mechanics analysis of the Dynamic Stress Intensity Factor of a pre-cracked 3-Point Bending Specimen suffering cyclic loads has been studied. Using the theoretical equivalent system of the pre-cracked 3-Point Bending Specimen, the Dynamic Stress Intensity Factor could be obtained theoretically. The finite element method was then applied to study the dynamic behaviors of the Dynamic Stress Intensity Factor under different cyclic loads' conditions using the standard software ABAQUS. The results have also been analyzed and discussed, which provided a deeper view for the fracture characteristics of the materials and could be used to guide further researches and practical engineering design.

  • 122. Huang, Yayu
    et al.
    Hu, Xiangping
    Liao, Taohong
    Fracture mechanics mathematical modelling for Dynamic Stress Intensity Factor of 3-Point Bending Specimen2011Conference paper (Refereed)
    Abstract [en]

    This paper emphasizes on the analysis of fracture mechanical characteristics of 3-Point Bending Specimen suffering driving force. By analyzing the structural characteristics of the 3-Point Bending Specimen, the equivalent mathematical model mass-damping-spring system has been formulated. The variation of parameters method is then used to solve the corresponding second order differential equation and find the general analytical formula for the Dynamic Stress Intensity Factor. This analytical formula for Dynamic Stress Intensity Factor will be useful for the further researches and practical engineering design and applications in fracture mechanical field

  • 123.
    Håkansson, Lars
    Blekinge Institute of Technology, Faculty of Engineering, Department of Applied Signal Processing.
    The Fourier Transform in Sound and Vibration2015In: International Journal of Acoustics and Vibration, ISSN 1027-5851, ISSN 1027-5851, Vol. 20, no 4, p. 190-190Article in journal (Refereed)
  • 124. Håkansson, Lars
    et al.
    Brandt, Anders
    Lagö, Thomas L
    Claesson, Ingvar
    Modal Analysis and Operating Deflection Shapes of a Boring Bar2003Conference paper (Refereed)
    Abstract [en]

    In the manufacturing industry, the internal turning or boring operation is a common metal working process that is usually associated with vibration problems. Vibration in boring operations is usually inevitable. This necessitates extra care being taken in production planning and preparation. Thus, the vibration problems in internal turning considerably influence important factors such as productivity, production costs, etc. In order to gain further understanding of the dynamic behaviour of clamped boring bars in the metalcutting process experimental methods may be utilized. Two experimental methods have been used in order to investigate dynamic properties of a clamped boring bar: an experimental modal analysis and an operating deflection shape analysis. The results indicate a correlation between the shapes of the deflection shapes and/or mode shapes produced by the two different analysis methods. On the other hand, the orientation of the forced deflection shapes and/or mode shapes and the resonance frequencies demonstrates differences between the two methods. During continuous cutting, it is demonstrated that the bending motion of the first two resonance frequencies is to a large extent in the cutting speed direction.

  • 125. Håkansson, Lars
    et al.
    Johansson, Sven
    Claesson, Ingvar
    Chapter 78 Machine Tool Noise, Vibration and Chatter Prediction and Control2005In: HANDBOOK OF NOISE AND VIBRATION CONTROL / [ed] Crocker, Malcolm J., New York: To be published by by John Wiley & Sons , 2005Chapter in book (Other academic)
    Abstract [en]

    A frequent problem in the manufacturing industry today is the vibrations or chatter induced by metal cutting, e.g. turning, milling and boring operations. Vibrations in boring operations or internal turning operations, for example,are inevitable and constitute a major problem for the manufacturing industry. Tool vibrations in metal cutting affect the result of machining, particularly the surface finish. Furthermore, tool life is correlated with the degree of vibration and acoustic noise introduced. Generally, tool vibrations are related to a low-order bending mode of, for example, the tool holder shank in external turning, the boring bar in internal turning, spindle-cutter assembly in milling, etc. Tool chatter or vibration problems in internal turning or milling may be reduced, for example, by using boring bars and milling adapters with passive tuned dampers. These are usually manually tuned to increase the dynamic stiffness of the boring bar or milling adapter at one of the eigenfrequencies of its low-order bending modes. Active control approaches for the attenuation of the bending motion of boring bars, tool holder shanks and spindle-cutter assembly in milling have been developed; such approaches involve both adaptive and time-invariant feedback control. In addition, prediction and control methods for controlling cutting data to maintain stable cutting, i.e. to avoid cutting data resulting in chatter, have been developed.

  • 126.
    Ibragimov, Nail
    Blekinge Institute of Technology, School of Engineering, Department of Mathematics and Natural Sciences.
    Construction of Conservation Laws Using Symmetries2014Conference paper (Refereed)
    Abstract [en]

    The concept of nonlinear self-adjointness of differential equations, introduced by the author in 2010, is discussed in detail. All linear equations and systems are nonlinearly self-adjoint. Moreover, the class of nonlinearly self-adjoint equations includes all nonlinear equations and systems having at least one local conservation law. It follows, in particular, that the integrable systems possessing infinite set of Lie-Backlund symmetries (higher-order tangent transformations) are nonlinearly self-adjoint. An explicit formula for conserved vectors associated with symmetries is provided for all nonlinearly self-adjoint differential equations and systems. The number of equations contained in the systems under consideration can be different from the number of dependent variables. A utilization of conservation laws for constructing exact solutions is discussed and illustrated by computing non-invariant solutions of the Chaplygin equations in gas dynamics.

  • 127. Ibragimov, Nail H.
    Transformation groups and Lie algebras2009Book (Other academic)
    Abstract [en]

    These notes are designed for the graduate course on Transformation groups and Lie algebras that I have been teaching at Blekinge Institute of Technology since 2002. The course is aimed at augmenting a preliminary knowledge in this field obtained by students during the course on Differential equations based on my book "A practical course in differential equations and mathematical modelling".

  • 128.
    Ibragimov, Nail H.
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Gazizov, Rafail H.
    Approximate symmetries and solutions of the Kompaneets equation2014In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 55, no 2, p. 220-224Article in journal (Refereed)
    Abstract [en]

    Different approximations of the Kompaneets equation are studied using approximate symmetries, which allows consideration of the contributions of all terms of this equation previously neglected in the analysis of the limiting cases.

  • 129.
    Ibragimov, Nail H.
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Ibragimov, Ranis N.
    Galiakberova, L. R.
    Symmetries and Conservation Laws of a Spectral Nonlinear Model for Atmospheric Baroclinic Jets2014In: Mathematical Modelling of Natural Phenomena, ISSN 0973-5348, E-ISSN 1760-6101, Vol. 9, no 5, p. 111-118Article in journal (Refereed)
    Abstract [en]

    In this paper, we shall obtain the symmetries of the mathematical model describing spontaneous relaxation of eastward jets into a meandering state and use these symmetries for constructing the conservation laws. The basic eastward jet is a spectral parameter of the model, which is in geostrophic equilibrium with the basic density structure and which guarantees the existence of nontrivial conservation laws.

  • 130. Ibragimov, Nail H.
    et al.
    Meleshko, Sergey
    Rudenko, Oleg
    Group analysis of evolutionary integro-differential equations describing nonlinear waves: General model2011In: Journal of Physics A: Mathematical and Theoretical, ISSN 1751-8113, E-ISSN 1751-8121, Vol. 44, no 31Article in journal (Refereed)
    Abstract [en]

    The paper deals with an evolutionary integro-differential equation describing nonlinear waves. Particular choice of the kernel in the integral leads to well-known equations such as the Khokhlov-Zabolotskaya equation, the Kadomtsev-Petviashvili equation and others. Since solutions of these equations describe many physical phenomena, analysis of the general model studied in the paper equation is important. One of the methods for obtaining solutions differential equations is provided by the Lie group analysis. However, this method is not applicable to integro-differential equations. Therefore we discuss new approaches developed in modern group analysis and apply them to the general model considered in the present paper. Reduced equations and exact solutions are also presented.

  • 131. Isaksson, Ola
    et al.
    Bertoni, Marco
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Hallstedt, Sophie
    Blekinge Institute of Technology, Faculty of Engineering, Department of Strategic Sustainable Development.
    Lavesson, Niklas
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Model Based Decision Support for Value and Sustainability in Product Development2015Conference paper (Refereed)
    Abstract [en]

    Decomposing and clarify “sustainability” implications in the same way as concrete targets on product functionality is challenging, mainly due to the problem of showing numbers and ‘hard facts’ related to the value generated by sustainability-oriented decisions. The answer lies in methods and tools that are able, already in a preliminary design stage, to highlight how sustainable design choice can create value for customers and stakeholders, generating market success in the long term. The paper objective is to propose a framework where Sustainable Product Development (SPD) and Value Driven Design (VDD) can be integrated to realize a model-driven approach to support early stage design decisions. Also, the paper discusses how methods and tools for Model-Based Decision Support (MBDS) (e.g., response surface methodology) can be used to increase the computational efficiency of sustainability- and value-based analysis of design concepts. The paper proposes a range of activities to guide a model-based evaluation of sustainability consequences in design, showing also that capabilities exist already today for combining research efforts into a multi disciplinary decision making environment.

  • 132. Isaksson, Ola
    et al.
    Kossman, Mario
    Bertoni, Marco
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Eres, Hakki
    Monceaux, Anne
    Bertoni, Alessandro
    Wiseall, Steve
    Zhang, Xinwei
    Value-­Driven Design -­ A methodology to Link Expectations to Technical Requirements in the Extended Enterprise2013Conference paper (Refereed)
    Abstract [en]

    Current systems engineering (SE) standards do not address ‘Value’ in much detail. Yet, understanding what drives the generation of stakeholder value in a given business context, is fundamental to promoting a common and clear vision throughout the extended enterprise, of what should be the focus of their early, conceptual work at all levels of development. This paper presents a Value-Driven Design (VDD) methodology designed to strengthen the value and requirements maturation process within an extended enterprise setting. The work presented is the result of a three and a half year European program (CRESCENDO) within the aerospace sector. The VDD methodology is introduced and explained in an industrial aircraft development context and a selection of enabling methods and tools associated to the VDD methodology is presented.

  • 133.
    Ising, Erik
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Falk, Mathias
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Konstruktion av kostnadseffektiv lyftvagn2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 134.
    Islam, Md Shafiqul
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering. Blekinge Institute of Technology.
    Fracture and Delamination in Packaging Materials: A Study of Experimental Methods and Simulation Techniques2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Packages are the means of preservation, distribution and convenience of use for food, medicine and other consumer products. The introduction of a new package-opening technique for a better opening experience requires additional prototype development and physical testing. In order for the design process to be more rapid and robust, finite element (FE) simulations are widely used in packaging industries to compliment and reduce the amount of physical testing.

    The goal of this work is to develop some building blocks for complete package-opening FE-simulation. To begin with, the study focuses on mechanical testing of packaging materials’ fracture and delamination; especially shear fracture. Use of tools like digital image correlation (DIC) and scanning electron microscope (SEM) greatly aided to the strain measuring technique and observation of fractured and delaminated surfaces respectively.

    A modified shear test specimen for polymer sheet testing was developed and its geometry was optimized by FE-simulation. A geometry correction factor of shear fracture toughness for the proposed specimen was derived based on linear elastic fracture mechanics (LEFM). It was found that the specimen ligament length should vary between twice the thickness and half the ligament width of the modified shear specimen to measure the essential work of fracture.

    Thin-flexible laminate of low-density polyethylene (LDPE) and aluminium (Al) is another key packaging material addressed in this study. The continuum and fracture testing of individual layers provided the base information and input for FE-modelling. The FE-simulation material parameters were calibrated from the physical test response through inverse analysis. Identification process of the laminate interface fracture energy (Gc) from peel tests was studied experimentally and theoretically. A successful FE-simulation optimization framework using artificial neural network and genetic algorithm was developed for the calibration of Gc. To address the challenge in quantifying shear Gc of laminate with very thin substrates, a convenient test technique was proposed. In a separate case, the tearing response of LDPE/PET (polyethylene terephthalate) laminate was studied to examine crack propagation, crack path deviation and delamination of the laminate in mode III fracture. Several tear EWF evaluation theories were proposed along with a cyclic tear test method.

  • 135.
    Islam, Md. Shafiqul
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Simulation of Laminates and a Modified Shear Test Specimen2015Other (Other academic)
  • 136.
    Islam, Md. Shafiqul Islam
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Zhang, Defeng
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Mehmood, Nasir
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Study of Shear Dominant Delamination in Thin Brittle-High Ductile Interface2015In: National Agency for Finite Element Methods and Standards (NAFEMS), 2015Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    Thin laminates of Aluminum (Al) and Low Density Polyethylene (LDPE) is an essential constituent of food packages where these two substrates are bonded together with a thin layer of LDPE acting as adhesive. Noticeably, Al is a low ductile/quasi brittle material whereas, LDPE is highly ductile.  The mechanism of delamination and strength of bond between the interfaces dictates the continuum and damage behaviour of this composite. However, measuring the shear delamination is challenging as conventional test methods have limitations when the substrates are very thin. This study explains a method that uses uniaxial tensile testing on the pre-cracked specimen of this composite to find energy dissipation due to shear delamination and successfully use it in Finite Element Simulation in Abaqus. The delamination was observed in a narrow strip region close to fracture surfaces and measured with special visualization aid. Similar response was found in FEM simulation. Scanning Electron Microscopic (SEM) study of delaminated interface confirms the domination of shearing. In a cohesive zone modelling in Finite Element Simulation software, the shear delamination energy was used as input parameter along with an arbitrary bi-linear cohesive law. The substrates’ constitutive response was modelled considering non linear plasticity and softening. Finally proposed delamination energy separation method was validated with comparison between the physical tests and FEM simulations.

  • 137.
    Islam, Md. Shafiqul
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Chen, Xin
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Deng, Hong Yu
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Innovation for and by the People with Disabilities: A Case Study in Improvement of the Manual Wheelchair2013Conference paper (Refereed)
    Abstract [en]

    This paper focuses on information-driven engineering, where information is gathered by means of innovation for people and by the people. This case study was carried out on innovation of a manual wheelchair. Through active participation of person with disability (direct users) and their carers (indirect user), knowledge awareness of the early design was increased. Computer aided engineering tools were used for the development of virtual prototype (VP) and after further feedback from direct and indirect users design was adjusted. Additionally, Physical prototype was built to practically demonstrate the new features to users and finally the prototype was readjusted to bridge user requirement even more. This innovation process identifies additional improvement aspects and contributes beyond fundamental personal needs and increases well being.

  • 138.
    Islam, Md. Shafiqul
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Jian, Li
    Mehmood, Nasir
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Study of Shear Property of HDPE by Experiment and Simulation2014Conference paper (Refereed)
    Abstract [en]

    The aim of this work is to evaluate the effect of different specimen dimension and crack length on the mechanical properties of HDPE (High Density Polyethylene) which is often used in the packaging industry. In the experimental part, two main specimens are chosen. One is dog-bone shaped tensile specimen for finding the tensile material properties. The other one is modified shear specimen for studying the shear damage. A corresponding numerical simulation is done by applying a commercial Finite Element Analysis (FEA) program ABAQUS. In addition, the microscopic analysis was performed to observe the fracture surface of specimen after the test with scanning electron microscope (SEM). A series of experiments and simulation were processed and results show that fracture initiation and propagation behavior in the shear specimen is sensitive to the size of the pre-crack (notch) and shear strain at failure.

  • 139.
    Islam, Md. Shafiqul
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering. Shanghai Second Polytechnic Univ., Faculty of Mech. & El. Eng., 201209, Shanghai, China.
    Yang, Geng
    Kungliga Tekniska högskolan, SWE.
    Study of Ligament Length Effect on Mode Mix of a Modified In-Plane Shear Test Specimen2016In: Materials Performance and Characterization, E-ISSN 2165-3992, ISSN 2165-3992, Vol. 5, no 3, p. 249-259Article in journal (Refereed)
    Abstract [en]

    Shear fracture toughness is an important material behavior that needs to be determined and considered in many industrial fields. At the same time, shear testing is one of the complex material testing areas where available methods are few, often need special arrangements, and most of the methods do not strictly satisfy the definition of pure shear. In this study, a modified shear test specimen was proposed to measure the shear fracture toughness by uniaxial loading in a tensile testing machine. High density polyethylene (HDPE) was used as test material for the experiments. The specimen was created in order to suit the most common used tensile test machine. The specimen was then optimized by using finite element analysis (FEA) to find the geometry and the size of the pre-notch to avoid the mixed mode loading and minimize effects of normal stresses. For the specimen in discussion, an upper and lower limit of usable ligament length can be found. A method for determining the fracture toughness was discussed according to the essential work of fracture. Finally, an example of a special application of the proposed specimen was presented where the variation of shear strength of controlled delamination material (CDM) was measured.

  • 140.
    Islam, Md. Shafiqul
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Zhang, Defeng
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Mehmood, Nasir
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Study of Shear Dominant Delamination in Thin Brittle-High Ductile Interface2016In: 21ST EUROPEAN CONFERENCE ON FRACTURE, (ECF21) / [ed] Francesco Iacoviello, Elsevier, 2016, Vol. 2, p. 152-157Conference paper (Refereed)
    Abstract [en]

    Thin laminates of Aluminum (Al) foil and Low Density Polyethylene (LDPE) film are essential constituents of food packages where these two substrates are bonded together with a thin layer of LDPE acting as adhesive. Noticeably, Al is a low ductile/quasi brittle material, whereas LDPE is highly ductile. The mechanism of delamination and strength of bond between the interfaces dictates the continuum and damage behavior of this composite. However, measuring the shear delamination properties is challenging as conventional test methods have limitations when the substrates are very thin and flexible. This study explains a tentative method that uses uniaxial tensile testing on the pre-cracked specimen of this composite to find energy dissipation due to shear delamination and successfully uses it in Finite Element Simulation in Abaqus. The delamination was observed in a narrow strip-like region close to fracture surfaces and measured with special visualization aid. A similar response was found in FEM simulation. Scanning Electron Microscopic (SEM) study of delaminated interface confirms the delamination to be shear in nature. In a cohesive zone modeling in Abaqus, the measured shear delamination energy was used as input parameter along with an arbitrary bi-linear cohesive law for validation of the experimental measurement.

  • 141.
    Islam, Shafiqul
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Yang, Geng
    Measuring Shear Fracture Toughness with a Modified Shear Test Specimen2015Conference paper (Refereed)
    Abstract [en]

    Shear fracture toughness is an important material behavior that needs to be determined and considered in many industrial fields. At the same time, shear testing is one of the complex material testing areas where available methods are few and often need special arrangements. In this study, a modified shear test specimen was proposed to measure the shear fracture toughness by uniaxial loading in a tensile testing machine. High Density Polyethylene (HDPE) was used as test material for the experiments. The specimen was created in order to suit the most common used tensile test machine. The specimen was than optimized by using Finite Element Analysis (FEA) to find the geometry and the size of the pre-crack to avoid the mixed mode loading and minimize effect of normal stresses. For the specimen in discussion, an upper and lower limit of useable ligament length can be found. Finally, a method for determining the fracture toughness was discussed according to essential work of fracture.

  • 142.
    Islam, Shafiqul
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Khan, Abdullah
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Jian, Li
    A Study of Shear Stress Intensity Factor of PP and HDPE by a Modified Experimental Method together with FEM2013In: International Journal of Mechanical, Aerospace, Industrial and Mechatronics Engineering, ISSN 2010-376X, Vol. 7, no 11Article in journal (Refereed)
    Abstract [en]

    Shear testing is one of the most complex testing areas where available methods and specimen geometries are different from each other. Therefore, a modified shear test specimen (MSTS) combining the simple uniaxial test with a zone of interest (ZOI) is tested which gives almost the pure shear. In this study, material parameters of polypropylene (PP) and high density polyethylene (HDPE) are first measured by tensile tests with a dogbone shaped specimen. These parameters are then used as an input for the finite element analysis. Secondly, a specially designed specimen (MSTS) is used to perform the shear stress tests in a tensile testing machine to get the results in terms of forces and extension, crack initiation etc. Scanning Electron Microscopy (SEM) is also performed on the shear fracture surface to find material behavior. These experiments are then simulated by finite element method and compared with the experimental results in order to confirm the simulation model. Shear stress state is inspected to find the usability of the proposed shear specimen. Finally, a geometry correction factor can be established for these two materials in this specific loading and geometry with notch using Linear Elastic Fracture Mechanics (LEFM). By these results, strain energy of shear failure and stress intensity factor (SIF) of shear of these two polymers are discussed in the special application of the screw cap opening of the medical or food packages with a temper evidence safety solution.

  • 143.
    Johansson, Christian
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Managing Uncertainty and Ambiguity in Gates: Decision Making in Aerospace Product Development2014In: International Journal of Innovation and Technology Management (IJITM), ISSN 0219-8770, Vol. 11, no 2Article in journal (Refereed)
    Abstract [en]

    This paper investigates decision making in the stage-gate process used by an aerospace manufacturer. More specifically, it focuses on the way decision makers deal with uncertainties and ambiguities when making decisions. The stage-gate model was found to be a discussion trigger - a boundary negotiating artefact - through which stakeholders bring issues to the table, reflect on uncertainties, and decide in what areas more knowledge is needed. Managers should be aware that the knowledge base might not always be perfect and should make use of the sensemaking capabilities of the stage-gate model and the gate meeting to mitigate and improve the knowledge base. This paper elaborates on formalized knowledge-based criteria so as to support this evaluation of the knowledge base.

  • 144. Josefsson, Andreas
    Identification and Simulation Methods for Nonlinear Mechanical Systems Subjected to Stochastic Excitation2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    With an ongoing desire to improve product performance, in combination with the continuously growing complexity of engineering structures, there is a need for well-tested and reliable engineering tools that can aid the decision making and facilitate an efficient and effective product development. The technical assessment of the dynamic characteristics of mechanical systems often relies on linear analysis techniques which are well developed and generally accepted. However, sometimes the errors due to linearization are too large to be acceptable, making it necessary to take nonlinear effects into account. Many existing analysis techniques for nonlinear mechanical systems build on the assumption that the input excitation of the system is periodic and deterministic. This often results in highly inefficient analysis procedures when nonlinear mechanical systems are studied in a non-deterministic environment where the excitation of the system is stochastic. The aim of this thesis is to develop and validate new efficient analysis methods for the theoretical and experimental study of nonlinear mechanical systems under stochastic excitation, with emphasis on two specific problem areas; forced response simulation and system identification from measurement data. A fundamental concept in the presented methodology is to model the nonlinearities as external forces acting on an underlying linear system, and thereby making it possible to use much of the linear theories for simulation and identification. The developed simulation methods utilize a digital filter to achieve a stable and condensed representation of the linear subparts of the system which is then solved recursively at each time step together with the counteracting nonlinear forces. The result is computationally efficient simulation routines, which are particularly suitable for performance predictions when the input excitation consist of long segments of discrete data representing a realization of the stochastic excitation of the system. Similarly, the presented identification methods take advantage of linear Multiple-Input-Multiple-Output theories for random data by using the measured responses to create artificial inputs which can separate the linear system from the nonlinear parameters. The developed methods have been tested with extensive numerical simulations and with experimental test rigs with promising results. Furthermore, an industrial case study of a wave energy converter, with nonlinear characteristics, has been carried out and an analysis procedure capable of evaluating the performance of the system in non-deterministic ocean waves is presented.

  • 145.
    Josefsson, Andreas
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Ahlin, Kjell
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Broman, Göran
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Bias errors due to leakage effects when estimating frequency response functions2012In: Shock and Vibration, ISSN 1070-9622, E-ISSN 1875-9203, Vol. 19, no 6, p. 1257-1266Article in journal (Refereed)
    Abstract [en]

    Frequency response functions are often utilized to characterize a system's dynamic response. For a wide range of engineering applications, it is desirable to determine frequency response functions for a system under stochastic excitation. In practice, the measurement data is contaminated by noise and some form of averaging is needed in order to obtain a consistent estimator. With Welch's method, the discrete Fourier transform is used and the data is segmented into smaller blocks so that averaging can be performed when estimating the spectrum. However, this segmentation introduces leakage effects. As a result, the estimated frequency response function suffers from both systematic (bias) and random errors due to leakage. In this paper the bias error in the H_1 and H_2-estimate is studied and a new method is proposed to derive an approximate expression for the relative bias error at the resonance frequency with different window functions. The method is based on using a sum of real exponentials to describe the window's deterministic autocorrelation function. Simple expressions are derived for a rectangular window and a Hanning window. The theoretical expressions are verified with numerical simulations and a very good agreement is found between the results from the proposed bias expressions and the empirical results.

  • 146. Josefsson, Andreas
    et al.
    Berghuvud, Ansel
    Ahlin, Kjell
    Broman, Göran
    Performance of a Wave Energy Converter with Mechanical Energy Smoothing2011Conference paper (Refereed)
    Abstract [en]

    A wave energy converter which uses a power balancing mechanism for turning intermittent and irregular wave motion input to smoothed continuous electrical power output is studied by combined scale-model testing and numerical simulation. The studied concept consists of a moored floating device together with a moving mass which is used to store instantaneous incoming power and deliver a controllable load to an electric generator over a unidirectional rotating shaft. A mathematical model describing the vertical dynamics of the wave energy converter is presented. The wave-body interaction is modelled with linear potential theory and a nonlinear rigid-body model describes the power take-off system. Experimental data from a scale-model test is utilized to validate and update the linear hydrodynamic model. A simulation study is then carried out in order to investigate the performance characteristics of the coupled hydrodynamic and mechanical system. An efficient time-domain algorithm is developed in order to simulate the discontinuous nonlinear characteristics of the combined system in non-deterministic wave situations. The simulation result provides a prediction of the absorbed power and capture ratio which can be used to evaluate the performance in different wave situations. The developed analysis procedure demonstrates its capability to produce computationally efficient performance predictions suitable for design evaluation and optimisation.

  • 147. Josefsson, Andreas
    et al.
    Magnevall, Martin
    Ahlin, Kjell
    Control Algorithm For Sine Excitation On Nonlinear Systems2006Conference paper (Other academic)
    Abstract [en]

    When using electrodynamic vibration exciters to excite structures, the actual force applied to the structure under test is the reaction force between the exciter and the structure. The magnitude and phase of the reaction force is dependent upon the characteristics of the structure and exciter. Therefore the quality of the reaction force i.e. the force applied on the structure depends on the relationship between the exciter and structure under test. Looking at the signal from the force transducer when exciting a structure with a sine wave, the signal will appear harmonically distorted within the regions of the resonance frequencies. This phenomenon is easily observed when performing tests on lightly damped structures. The harmonic distortion is a result of nonlinearities produced by the shaker when undergoing large amplitude vibrations, at resonances. When dealing with non-linear structures, it is of great importance to be able to keep a constant force level as well as a non-distorted sine wave in order to get reliable results within the regions of the resonance frequencies. This paper presents theoretical methods that can be used to create a non-distorted sinusoidal excitation signal with constant force level.

  • 148. Josefsson, Andreas
    et al.
    Magnevall, Martin
    Ahlin, Kjell
    On Nonlinear Parameter Estimation with Random Noise Signals2007Conference paper (Refereed)
    Abstract [en]

    In the field of nonlinear dynamics it is essential to have well tested and reliable tools for estimating the nonlinear parameters from measurement data. This paper presents an identification technique based on using random noise signals, as initially developed by Julius S. Bendat. With this method the nonlinearity is treated as a feedback forcing term acting on an underlying linear system. The parameter estimation is then performed in the frequency domain by using conventional MISO/MIMO techniques. To apply this method successfully it is necessary to have some pre-information about the model structure and thus methods for nonlinear characterization and localization are studied. The paper also demonstrates the various ways the method can be formulated for multiple-degree-of-freedoms. The implementation of the method is illustrated with simulated data as well as a practical application, where the method is used to create a dynamic model of a test-rig with a significant nonlinearity.

  • 149.
    Josefsson, Andreas
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Magnevall, Martin
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Ahlin, Kjell
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Broman, Göran
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Spatial location identification of structural nonlinearities from random data2012In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 27, no 1, p. 410-418Article in journal (Refereed)
    Abstract [en]

    With growing demands on product performance and growing complexity of engineering structures, efficient tools for analyzing their dynamic behavior are essential. Linear techniques are well developed and often utilized. However, sometimes the errors due to linearization are too large to be acceptable, making it necessary to take nonlinear effects into account. In many practical applications it is common and reasonable to assume that the nonlinearities are highly local and thus only affect a limited set of spatial coordinates. The purpose of this paper is to present an approach to finding the spatial location of nonlinearities from measurement data, as this may not always be known beforehand. This information can be used to separate the underlying linear system from the nonlinear parts and create mathematical models for efficient parameter estimation and simulation. The presented approach builds on the reverse-path methodology and utilizes the coherence functions to determine the location of nonlinear elements. A systematic search with Multiple Input/Single Output models is conducted in order to find the nonlinear functions that best describe the nonlinear restoring forces. The obtained results indicate that the presented approach works well for identifying the location of local nonlinearities in structures. It is verified by simulation data from a cantilever beam model with two local nonlinearities and experimental data from a T-beam experimental set-up with a single local nonlinearity. A possible drawback is that a relatively large amount of data is needed. Advantages of the approach are that it only needs a single excitation point that response data at varying force amplitudes is not needed and that no prior information about the underlying linear system is needed.

  • 150. Jönsson, Anders
    Lean Prototyping of Multi-body and Mechatronic Systems2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Major drivers behind increased efforts in product development are the increased competition due to globalisation and the urgent transformation of society towards sustainability. Furthermore, the average product lifetime has been compressed significantly over the last decade. Due to these trends, there is increasing demand for an efficient product development process. Cutting time-to-market, reducing costs and increasing quality are widely accepted as key factors to successful product development. Consideration of sustainability aspects in product development is also becoming increasingly important. Methods and tools that are useful also for small and medium sized enterprises are of particular importance for the Swedish industry. This thesis suggests a definition of lean prototyping and points to its potential for supporting efficient product development. This is done through two case studies: a soil compactor machine treated as a multi-body system and a water jet cutting machine treated as a mechatronic system. Lean prototyping is defined as a coordinated approach to experimentation with the purpose of achieving cost-efficient and accurate enough prediction of product characteristics to support optimisation and well-informed design decisions during product development, especially in the early stages. This often involves an iterative search for and use of a suitable combination of virtual and limited physical prototypes as well as the reuse of knowledge from previous projects. The case studies are performed in cooperation with one small and one medium sized company, indicating the usefulness of the approach for different product types as well as for different company sizes. More specifically, the validated multi-body model of the soil compactor machine describes the dynamics of the machine satisfactorily and the optimisation study shows a significant potential for improved compaction capacity. This potential would not likely been found through traditional physical prototyping. The related comparative study of contact transition conditions is a contribution to consistent impact modelling in multi-body dynamics in general. The real-time virtual machine concept for simulation of the water jet cutting machine, including detailed mechanical component models, is unique. The fully automated concept implementation makes it a promising base for multidisciplinary design optimisation of the water jet cutting machine, and probably of mechatronic products in general.

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