Change search
Refine search result
1234 1 - 50 of 179
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.
  • 1.
    Ajdén, Per
    et al.
    Linköping University, Department of Management and Engineering, Mechanics .
    Backlund, Carl
    Linköping University, Department of Management and Engineering, Mechanics .
    Pilotmodeller till flygmekanisk simulator för JAS 39 Gripen2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Abstract

    SAAB has for a long time used user controlled pilot models in ARES. ARES is a simulation tool used in the desktop environment for simulations and calculations of the JAS 39 Gripen fighter and other aircraft. ARES stands for ”Aircraft Rigid body Engineering Simulation”. To work with these pilot models has been both time-consuming and inefficient. In this master thesis, new pilot models are developed, where parameters are automatically generated, this will result in that the user doesn’t have to put a lot of work into adjusting the gains for different manoeuvres. This is called gain scheduling.

    To make this possible, simple models of the aircraft were created at different points in the envelope. These models were then used to calculate optimal controllers using LQ-control and pole placement techniques. These models and controllers were then implemented in Simulink. Simulink was then used to test the controllers before they were implemented in ARES.

    Control in all modes except roll attitude and speed by throttle are based on LQ-control in pitch-, roll- and yaw-angular velocity. And through these angular velocities the other angles are controlled by simple controllers, who is generating a reference in angular velocity. The roll attitude controller is based on direct pole placement based upon desired damping and undamped natural frequency, and the speed controller is based upon a model of throttle positions in trimmed states.

    The new pilot models are usable to control:

    • Roll rate
    • Roll attitude
    • Pitch rate
    • Pitch attitude
    • Angle of attack
    • Load factor
    • Yaw attitude
    • Course angle
    • Climb angle
    • Mach number
    • Climb rate

    These controllers can be combined so that the aircraft can perform desired maneuvers.

  • 2.
    Andric, Jelena
    et al.
    Chalmers University of Technology.
    Fredriksson, Sam T.
    Chalmers University of Technology.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Sasic, Srdjan
    Chalmers University of Technology.
    Nilsson, Håkan
    Chalmers University of Technology.
    A study of a flexible fiber model and its behavior in DNS of turbulent channel flow2013In: Acta Mechanica, ISSN 0001-5970, E-ISSN 1619-6937, Vol. 224, no 10, p. 2359-2374Article in journal (Refereed)
    Abstract [en]

    The dynamics of individual flexible fibers in a turbulent flow field have been analyzed, varying their initial position, density and length. A particle-level fiber model has been integrated into a general-purpose, open source computational fluid dynamics code. The fibers are modeled as chains of cylindrical segments connected by ball and socket joints. The equations of motion of the fibers contain the inertia of the segments, the contributions from hydrodynamic forces and torques, and the connectivity forces at the joints. Direct numerical simulation of the incompressible Navier-Stokes equations is used to describe the fluid flow in a plane channel, and a one-way coupling is considered between the fibers and the fluid phase. We investigate the translational motion of fibers by considering the mean square displacement of their trajectories. We find that the fiber motion is primarily governed by velocity correlations of the flow fluctuations. In addition, we show that there is a clear tendency of the thread-like fibers to evolve into complex geometrical configurations in a turbulent flow field, in fashion similar to random conformations of polymer strands subjected to thermal fluctuations in a suspension. Finally, we show that fiber inertia has a significant impact on reorientation timescales of fibers suspended in a turbulent flow field.

  • 3.
    Andric, Jelena
    et al.
    Chalmers University of Technology.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Sasic, Srdjan
    Chalmers University of Technology.
    Nilsson, Håkan
    Chalmers University of Technology.
    A particle-level fiber model, implemented in a general-purpose CFD code2013In: Svenska mekanikdagar, 2013, p. 113-Conference paper (Other academic)
  • 4.
    Andric, Jelena
    et al.
    Chalmers University of Technology.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Sasic, Srdjan
    Chalmers University of Technology.
    Nilsson, Håkan
    Chalmers University of Technology.
    A particle-level fiber model, implemented in OpenFOAM(R)2013In: 8th Int. OpenFOAM(R) Workshop, 2013Conference paper (Other academic)
  • 5.
    Andric, Jelena
    et al.
    Chalmers University of Technology.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Sasic, Srdjan
    Chalmers University of Technology.
    Nilsson, Håkan
    Chalmers University of Technology.
    A particle-level rigid fiber model for high-Reynolds number flow, implemented in a general-purpose CFD code2013In: 8th International Conference on Multiphase Flow ICMF 2013, Korea, 2013Conference paper (Refereed)
    Abstract [en]

    A particle-level rigid fiber model has been integrated into a general-purpose, open source computational fluid dynamics code to carry out detailed studies of fiber--flow interactions in realistic flow fields. The fibers are modeled as chains of cylindrical segments, and their translational and rotational degrees of freedom are considered. The equations of motion contain the contributions from hydrodynamic forces and torques, and the segment inertia is taken into account. The model is validated for the rotational motion of isolated fibers in simple shear flow, and the computed period of rotation is in good agreement with the one computed using Jeffery's equation for a prolate spheroid with an equivalent aspect ratio. The model is applied by suspending a number of fibers in the swirling flow of a conical diffuser, resembling one stage in the dry-forming of pulp mats. The Reynolds-averaged Navier--Stokes equations with an eddy-viscosity turbulence model are employed to describe the fluid motion, and a one-way coupling between the fibers and the fluid phase is included. The dependence of the fiber motion on initial position and density is analyzed.

  • 6.
    Andric, Jelena
    et al.
    Chalmers University of Technology.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Sasic, Srdjan
    Chalmers University of Technology.
    Nilsson, Håkan
    Chalmers University of Technology.
    Description and validation of a flexible fiber model, implemented in a general purpose CFD code2013In: 8th Int. Conf. Multiphase Flow ICMF 2013, 2013Conference paper (Refereed)
    Abstract [en]

    A flexible fiber model has been implemented in a general purpose open-source Computational Fluid Dynamics code. The fibers are modeled as chains of cylindrical segments, and all the degrees of freedom necessary to realistically reproduce the dynamics of real fibers, are taken into account. Each segment is tracked individually and their equations of motion account for the hydrodynamic forces and torques from the interaction with the fluid, the elastic bending and twisting torques, and the connectivity forces and moments that ensure the fiber integrity. The segment inertia is taken into account and a one-way coupling with the fluid phase is considered. The model is applied to simulate the rotational motion of an isolated fiber in a low segment Reynolds number shear flow. In the case of a stiff fiber, the computed period of rotation is in good agreement with the one computed using Jeffery's equation for an equivalent spheroid aspect ratio. A qualitative comparison is made with experimental data for flexible fibers. Further, a generic test case is described and used to validate the energy conservation and the response time of the fiber model concept. These results show that the implemented model can reproduce the known dynamical behavior of rigid and flexible fibers successfully.

  • 7.
    Andric, Jelena
    et al.
    Chalmers University of Technology, Göteborg, Sweden.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Sasic, Srdjan
    Chalmers University of Technology, Göteborg, Sweden.
    Nilsson, Håkan
    Chalmers University of Technology, Göteborg, Sweden.
    Rheological properties of dilute suspensions of rigid and flexible fibers2014In: Journal of Non-Newtonian Fluid Mechanics, ISSN 0377-0257, E-ISSN 1873-2631, Vol. 212, p. 36-46Article in journal (Refereed)
    Abstract [en]

    Particle-level simulations are used to study the rheology of monodispersed suspensions of rigid and flexible fibers in a creeping, simple shear flow of a Newtonian fluid. We also investigate the influence of different equilibrium shapes (straight and curved) of the fibers on the behavior of the suspension. A parametric study of the impacts of fiber flexural rigidity and morphology on rheology quantifies the effects of these realistic fiber features on the experimentally accessible rheological properties. A fiber is modeled as a chain of rigid cylindrical segments, interacting through a two-way coupling with the fluid described by the incompressible three-dimensional Navier–Stokes equations. The initial fiber configuration is in the flow–gradient plane. We show that, when the shear rate is increased, straight flexible fibers undergo a buckling transition, leading to the development of finite first and second normal stress differences and a reduction of the viscosity. These effects, triggered by shape fluctuations, are dissimilar to the effects induced by the curvature of stiff, curved fibers, for which the viscosity increases with the curvature of the fiber. An analysis of the orbital drift of fibers initially oriented at an angle to the flow–gradient plane provides an estimate for the time-scale within which the prediction of the rheological behavior is valid. The information obtained in this work can be used in the experimental characterization of fiber morphology and mechanics through rheology.

  • 8.
    Asghar, Raja Babar
    Linköping University, Department of Management and Engineering, Mechanics .
    Optimization as a Thermodynamic System2010Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
    Abstract [en]

    As we know that nature made the things optimized in all point of views, also it is supposed that nature works under some evolutionary process.

    Since there was no such Evolutionary Structural Optimization (ESO) method having strong mathematical background, that’s why these are not much reliable. The purpose of this thesis work is a little effort to introduce such an ESO method having a strong mathematical background.

    In this thesis work Optimization as a thermodynamic system, we are introducing a new method for topology optimization by using concept of Free Energy and Dissipation Potential from non-smooth thermodynamics system. For better understanding we may call it as Evolutionary Structural Topology Optimization (ESTO), and this project work is done in the following steps.

    An evolution problem is formulated in terms of free energy and dissipation potential for a non-smooth thermodynamical system. Free energy is taken as an objective function for a general structural optimization problem. Derivation of a well posed evolution problem for which evolution is such that objective function always decreases. An optimality criteria method is derived for given evolution problem and it is implemented in a FEM program TRINITAS. And the behaviour of the so called evolutionary parameters such as Forward and Backward plastic constants is analyzed.

  • 9.
    Bakker, Henriëtte E
    et al.
    Wageningen University.
    Lindström, Stefan
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Sprakel, Joris
    Wageningen University.
    Geometry- and rate-dependent adhesive failure of micropatterned surfaces2012In: Journal of Physics: Condensed Matter, ISSN 0953-8984, Vol. 24, no 6, p. 065103-Article in journal (Refereed)
    Abstract [en]

    The dynamic nature of adhesive interface failure remains poorly understood, especially when the contact between the two surfaces is localized in microscopic points of adhesion. Here, we explore the dynamic failure of adhesive interfaces composed of a large number of micron-sized pillars against glass. Surprisingly, we find a large influence of the microcontact geometry; ordered arrays of these pillars exhibit significantly stronger adhesive properties than equivalent surfaces in which the pillars are disordered. This can be understood with a simple geometric argument that accounts for the number of adhesive bonds that needs to be broken simultaneously to propagate the crack front. Moreover, the adhesive strength in both cases depends largely on the velocity with which the surfaces are separated. This rate dependence is explained on the basis of a semi-phenomenological model that describes macroscopic failure as a consequence of microscopic bond-rupture events. Our results suggest that the dynamics of adhesive failure, in the limit explored here, is predominantly stress-driven and highly sensitive to local geometry effects.

  • 10.
    Barber, James R.
    et al.
    Department of Mechanical Engineering University of Michigan.
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Mechanics . Linköping University, The Institute of Technology.
    Ciavarella, Michele
    CEMEC-PoliBA-Center of Excellence in Computational Mechanics.
    Shakedown in frictional contact problems for the continuum2008In: Comptes rendus. Mecanique, ISSN 1631-0721, E-ISSN 1873-7234, Vol. 336, p. 34-41Article in journal (Refereed)
  • 11. Barber, J.R.
    et al.
    Klarbring, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Mechanics.
    Ciavarella, M.
    Shakedown in frictional contact problems2007In: 2007 Proceedings of the ASME/STLE International Joint Tribology Conference, 2007, p. 517-519Conference paper (Other academic)
    Abstract [en]

    If a linear elastic system with frictional interfaces is subjected to periodic loading, any slip which occurs generally reduces the tendency to slip during subsequent cycles and in some circumstances the system ‘shakes down’ to a state without slip. It has often been conjectured that a frictional Melan’s theorem should apply to this problem — i.e. that the existence of a state of residual stress sufficient to prevent further slip is a sufficient condition for the system to shake down. Here we discuss recent proofs that this is indeed the case for ‘complete’ contact problems if there is no coupling between relative tangential displacements at the interface and the corresponding normal contact tractions. By contrast, when coupling is present, the theorem applies only for a few special two-dimensional discrete cases. Counter-examples can be generated for all other cases. These results apply both in the discrete and the continuum formulation.

  • 12. Bendsoe, MP
    et al.
    Klarbring, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Mechanics .
    Joakim Petersson 1968-2002 - Obituary2003In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 25, no 3, p. 151-152Other (Other academic)
  • 13.
    Borrvall, Thomas
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering.
    Petersson, Joakim
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Mechanics .
    Large-scale topology optimization in 3D using parallel computing2001In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 190, no 46-47, p. 6201-6229Article in journal (Refereed)
    Abstract [en]

    We consider large-scale topology optimization of elastic continua in 3D using the regularized intermediate density control introduced in [1]. The nested approach is used, i.e., equilibrium is solved at each iteration. To get a high-quality resolution of realistic designs in 3D, problems involving several hundreds of thousand finite elements are solved. In order to deal with problems of this size, parallel computing is used in combination with domain decomposition. The equilibrium equations are solved by a preconditioned conjugate gradient algorithm and the optimization part is solved using sequential convex programming. Several numerical results obtained from computations performed on a Cray parallel computer are presented. © 2001 Elsevier Science B.V. All rights reserved.

  • 14.
    Borrvall, Thomas
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering.
    Petersson, Joakim
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Mechanics .
    Topology optimization of fluids in Stokes flow2003In: International Journal for Numerical Methods in Fluids, ISSN 0271-2091, E-ISSN 1097-0363, Vol. 41, no 1, p. 77-107Article in journal (Refereed)
    Abstract [en]

    We consider topology optimization of fluids in Stokes flow. The design objective is to minimize a power function, which for the absence of body fluid forces is the dissipated power in the fluid, subject to a fluid volume constraint. A generalized Stokes problem is derived that is used as a base for introducing the design parameterization. Mathematical proofs of existence of optimal solutions and convergence of discretized solutions are given and it is concluded that no regularization of the optimization problem is needed. The discretized state problem is a mixed finite element problem that is solved by a preconditioned conjugate gradient method and the design optimization problem is solved using sequential separable and convex programming. Several numerical examples are presented that illustrate this new methodology and the results are compared to results obtained in the context of shape optimization of fluids. © 2003 John Wiley and Sons, Ltd.

  • 15.
    Borrvall, Thomas
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering.
    Petersson, Joakim
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Mechanics .
    Topology optimization using regularized intermediate density control2001In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 190, no 37-38, p. 4911-4928Article in journal (Refereed)
    Abstract [en]

    We consider topology optimization of elastic continua. The elasticity tensor is assumed to depend linearly on the design function (density) as in the variable thickness sheet problem. In order to get "black-white" design pictures, the intermediate density values are controlled by an explicit constraint. This constraint is regularized by including a compact and linear operator S to guarantee existence of solutions. A proof of convergence of the finite element (FE) discretized optimization problem's solutions to exact ones is also given, so the method is not prone to numerical anomalies such as mesh dependence or checkerboards. The procedure is illustrated in some minimum compliance examples where S is chosen to be a classical convolution-type operator. The FE-discretized optimization problems are solved by sequential convex approximations. © 2001 Elsevier Science B.V. All rights reserved.

  • 16.
    Carrick, Christopher
    et al.
    KTH Royal Institute of Technology, Stockholm, Sweden.
    Lindström, Stefan
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Larsson, Per Tomas
    KTH Royal Institute of Technology, Stockholm, Swede; Innventia AB, Stockholm Sweden .
    Wågberg, Lars
    KTH Royal Institute of Technology, Stockholm, Sweden .
    Lightweight, highly compressible, noncrystalline cellulose capsules2014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 26, p. 7635-7644Article in journal (Refereed)
    Abstract [en]

    We demonstrate how to prepare extraordinarily deformable, gas-filled, spherical capsules from nonmodified cellulose. These capsules have a low nominal density, ranging from 7.6 to 14.2 kg/m(3), and can be deformed elastically to 70% deformation at 50% relative humidity. No compressive strain-at-break could be detected for these dry cellulose capsules, since they did not rupture even when compressed into a disk with pockets of highly compressed air. A quantitative constitutive model for the large deformation compression of these capsules is derived, including their high-frequency mechanical response and their low-frequency force relaxation, where the latter is governed by the gas barrier properties of the dry capsule. Mechanical testing corroborated these models with good accuracy. Force relaxation measurements at a constant compression rendered an estimate for the gas permeability of air through the capsule wall, calculated to 0.4 mL mu m/m(2) days kPa at 50% relative humidity. These properties taken together open up a large application area for the capsules, and they could most likely be used for applications in compressible, lightweight materials and also constitute excellent model materials for adsorption and adhesion studies.

  • 17.
    Christensen, Peter
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Mechanics .
    A nonsmooth Newton method for elastoplastic problems2002In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 191, no 11-12, p. 1189-1219Article in journal (Refereed)
    Abstract [en]

    In this work we reformulate the incremental, small strain, J2-plasticity problem with linear kinematic and nonlinear isotropic hardening as a set of unconstrained, nonsmooth equations. The reformulation is done using the minimum function. The system of equations obtained is piecewise smooth which enables Pang's Newton method for B-differentiable equations to be used. The method proposed in this work is compared with the familiar radial return method. It is shown, for linear kinematic and isotropic hardening, that this method represents a piecewise smooth mapping as well. Thus, nonsmooth Newton methods with proven global convergence properties are applicable. In addition, local quadratic convergence (even to nondifferentiable points) of the standard implementation of the radial return method is established. Numerical tests indicate that our method is as efficient as the radial return method, albeit more sensitive to parameter changes. © 2002 Elsevier Science B.V. All rights reserved.

  • 18.
    Christensen, Peter
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Mechanics .
    A semi-smooth newton method for elasto-plastic contact problems2002In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 39, no 8, p. 2323-2341Article in journal (Refereed)
    Abstract [en]

    In this paper we reformulate the frictional contact problem for elasto-plastic bodies as a set of unconstrained, non-smooth equations. The equations are semi-smooth so that Pang's Newton method for B-differentiable equations can be applied. An algorithm based on this method is described in detail. An example demonstrating the efficiency of the algorithm is presented. © 2002 Elsevier Science Ltd. All rights reserved.

  • 19.
    Christensen, Peter
    et al.
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    An introduction to structural optimization2009 (ed. 1)Book (Other academic)
    Abstract [en]

    Mechanical and structural engineers have always strived to make as efficient use of material as possible, e.g. by making structures as light as possible yet able to carry the loads subjected to them. In the past, the search for more efficient structures was a trial-and-error process. However, in the last two decades computational tools based on optimization theory have been developed that make it possible to find optimal structures more or less automatically. Due to the high cost savings and performance gains that may be achieved, such tools are finding increasing industrial use.This textbook gives an introduction to all three classes of geometry optimization problems of mechanical structures: sizing, shape and topology optimization. The style is explicit and concrete, focusing on problem formulations and numerical solution methods. The treatment is detailed enough to enable readers to write their own implementations. On the book's homepage, programs may be downloaded that further facilitate the learning of the material covered.The mathematical prerequisites are kept to a bare minimum, making the book suitable for undergraduate, or beginning graduate, students of mechanical or structural engineering. Practicing engineers working with structural optimization software would also benefit from reading this book."--Publisher's website.

  • 20.
    Ciavarella, M.
    et al.
    CEMEC-PoliBA-Ctr.ExcellenceComputat., Politecnico di Bari, V.le Japigia 182, Bari 70125, Italy.
    Johansson, Lars
    Linköping University, Department of Management and Engineering, Mechanics . Linköping University, The Institute of Technology.
    Afferrante, L.
    CEMEC-PoliBA-Ctr.ExcellenceComputat., Politecnico di Bari, V.le Japigia 182, Bari 70125, Italy.
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Mechanics . Linköping University, The Institute of Technology.
    Barber, J.R.
    Department of Mechanical Engineering, University of Michigan, 2350 Hayward Street, Ann Arbor, MI 48109-2125, United States.
    Interaction of thermal contact resistance and frictional heating in thermoelastic instability2003In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 40, no 21, p. 5583-5597Article in journal (Refereed)
    Abstract [en]

    Thermoelastic contact problems can posess non-unique and/or unstable steady-state solutions if there is frictional heating or if there is a pressure-dependent thermal contact resistance at the interface. These two effects have been extensively studied in isolation, but their possible interaction has never been investigated. In this paper, we consider an idealized problem in which a thermoelastic rod slides against a rigid plane with both frictional heating and a contact resistance. For sufficiently low sliding speeds, the results are qualitatively similar to those with no sliding. In particular, there is always an odd number of steady-state solutions, if the steady-state is unique it is stable and if it is non-unique, stable and unstable solutions alternate, with the outlying solutions being stable. However, we identify a sliding speed V0 above which the number of steady states is always even (including zero, implying possible non-existence of a steady-state) and again stable and unstable states alternate. A parallel numerical study shows that for V > V0 there are some initial conditions from which the contact pressure grows without limit in time, whereas for V < V0 the system will always tend to one of the stable steady states. © 2003 Elsevier Ltd. All rights reserved.

  • 21.
    Denoyelle, Thibaud
    et al.
    Solid Mechanics, KTH.
    Kulachenko, Artem
    Solid Mechanics, KTH.
    Galland, Sylvain
    Wallenberg Wood Science Center, KTH.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Elastic properties of cellulose nanopaper versus conventional paper2011In: / [ed] Ulrich Hirn, Graz, Austria: TU , 2011, p. 131-134Conference paper (Other academic)
  • 22.
    Dervisic, Admir
    Linköping University, Department of Management and Engineering, Mechanics.
    Kraftberäkning på transportsystemet Gripper TGG 32002011Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Schur AB is a company that specializes on post and paper management, they offer their clients a wide selection of solutions in these areas. One of these areas is a conveyor system called Gripper TGG 3200 which transports newspapers from the press to different packing units. The system is driven by a couple of asynchronous motors, the amount of motors used varies with the length of the complete system. Because the motors and the stations they are placed in are some of the most expensive parts in the system. There is a big interest of minimizing the amount of these units.

    The system is composed of aluminum profiles which makes the system modifiable for the customers’ needs. It’s in these profiles that the chain of units that transport the newspaper transfers from the press to packing machines throughout the customers’ factory floor. To be able to place a motor with a given power on the most efficient place in the system you need to obtain how much power is required to overcome all the different losses in the profile. Once you have obtained the power needed from the motor to overcome the losses in every profile you can easily place the motor.

    this master thesis the motor power has been calculated for all the common used profiles in the system. To simplify the calculations a template has been developed for each of the profiles and a summary for the complete system. With this template the user can easily overlook the entire system and see where the optimal place for the motor is.

  • 23.
    Edlund, Ulf
    et al.
    Linköping University, Department of Management and Engineering, Mechanics . Linköping University, The Institute of Technology.
    Schmidt, Peter
    Linköping University, Department of Management and Engineering, Mechanics . Linköping University, The Institute of Technology.
    Roguet , E
    ENSMA, France.
    A model of an adhesively bonded joint with elastic-plastic adherends and a softening adhesive2009In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 198, no 5-8, p. 740-752Article in journal (Refereed)
    Abstract [en]

    This paper deals with the generalization of a model of an adhesively bonded joint with the aim to allow elastic-plastic adherends. In the model of the joint that we extend, the thinness of the bodies and the low Youngs modulus of the adhesive were used to obtain a simplified model where the parts are described as material surfaces. We formulate an elastic-plastic material model with isotropic hardening expressed in the generalized stress and strain measures used for the surface description of the joint. The finite element formulation and the numerical treatment of the constitutive law are discussed. Numerical results showing the accuracy of the proposed treatment of the adherends are presented. Two failure load computations, using a softening material model for the adhesive, are presented and compared with experiments. The results show the importance of taking into account potential plastic deformations in the adherends in failure load computations.

  • 24.
    Evgrafov, A.
    et al.
    Chalmers University of Technology, Göteborg University, Department of Mathematics, 412 96 Goteborg, Sweden.
    Patriksson, M.
    Chalmers University of Technology, Göteborg University, Department of Mathematics, 412 96 Goteborg, Sweden.
    Petersson, Joakim
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Mechanics .
    Stochastic structural topology optimization: Existence of solutions and sensitivity analyses2003In: Zeitschrift für angewandte Mathematik und Mechanik, ISSN 0044-2267, E-ISSN 1521-4001, Vol. 83, no 7, p. 479-492Article in journal (Refereed)
    Abstract [en]

    We consider structural topology optimization problems including unilateral constraints arising from, for example, non-penetration conditions in contact mechanics or non-compression conditions for elastic ropes. To construct more realistic models and to hedge off possible failures or an inefficient behaviour of optimal structures, we allow parameters (for example, loads) defining the problem to be stochastic. The resulting nonsmooth stochastic optimization problem is an instance of stochastic mathematical programs with equilibrium constraints (SMPEC), or stochastic bilevel programs. The existence as well as the continuity of optimal solutions with respect to the lower bounds on the design variables are established. The question of continuity of the optimal solutions with respect to small changes in the probability measure is analysed. For a subclass of the problems considered the answer is affirmative, thus establishing the robustness of optimal solutions. © 2003 WILEY-VCH Verlag GmbH & Co. KGaA.

  • 25.
    Fahlgren, Anna
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Orthopaedics and Sports Medicine. Linköping University, Faculty of Health Sciences.
    Bostrom, Mathias Pg
    Hospital for Special Surgery, New York, NY, USA.
    Yang, Xu
    Hospital for Special Surgery, New York, NY, USA.
    Johansson, Lars
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Edlund, Ulf
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Agholme, Fredrik
    Linköping University, Department of Clinical and Experimental Medicine, Orthopaedics and Sports Medicine. Linköping University, Faculty of Health Sciences.
    Aspenberg, Per
    Linköping University, Department of Clinical and Experimental Medicine, Orthopaedics and Sports Medicine. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Orthopaedic Centre, Department of Orthopaedics Linköping.
    Fluid pressure and flow as a cause of bone resorption2010In: Acta Orthopaedica, ISSN 1745-3674, E-ISSN 1745-3682, Vol. 81, no 4, p. 508-516Article in journal (Refereed)
    Abstract [en]

    Background Unstable implants in bone become surrounded by an osteolytic zone. This is seen around loose screws, for example, but may also contribute to prosthetic loosening. Previous animal studies have shown that such zones can be induced by fluctuations in fluid pressure or flow, caused by implant instability. Method To understand the roles of pressure and flow, we describe the 3-dimensional distribution of osteolytic lesions in response to fluid pressure and flow in a previously reported rat model of aseptic loosening. 50 rats had a piston inserted in the proximal tibia, designed to produce 20 local spikes in fluid pressure of a clinically relevant magnitude (700 mmHg) twice a day. The spikes lasted for about 0.3 seconds. After 2 weeks, the pressure was measured in vivo, and the osteolytic lesions induced were studied using micro-CT scans. Results Most bone resorption occurred at pre-existing cavities within the bone in the periphery around the pressurized region, and not under the piston. This region is likely to have a higher fluid flow and less pressure than the area just beneath the piston. The velocity of fluid flow was estimated to be very high (roughly 20 mm/s). Interpretation The localization of the resorptive lesions suggests that high-velocity fluid flow is important for bone resorption induced by instability.

  • 26.
    Fahlgren, Anna
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Division of Inflammation Medicine. Linköping University, Faculty of Health Sciences.
    Johansson, Lars
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Edlund, Ulf
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Aspenberg, Per
    Linköping University, Department of Clinical and Experimental Medicine, Division of Inflammation Medicine. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center for Surgery, Orthopaedics and Cancer Treatment, Department of Orthopaedics in Linköping.
    Direct ex vivo measurement of the fluid permeability of loose scar tissue2012In: Acta of Bioengineering and Biomechanics, ISSN 1509-409X, Vol. 14, no 2, p. 47-51Article in journal (Refereed)
    Abstract [en]

    Fluid flow is important in many biomechanical models, but there is a lack of experimental data that quantifies soft tissue permeability. We measured the tissue permeability in fibrous soft tissue, using a novel technique to obtain specimens by allowing soft tissue to grow into coralline hydroxyapatite scaffoldings implanted between the abdominal muscle layers of rats.

  • 27.
    Fall, Andreas
    et al.
    Department of Fiber Technology, KTH.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Sprakel, Joris
    Wågberg, Lars
    Department of Fiber Technology, KTH.
    A physical cross-linking process of cellulose nanofibril gels with shear-controlled fibril orientation2013In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 9, p. 1852-1863Article in journal (Refereed)
    Abstract [en]

    Cellulose nanofibrils constitute the smallest fibrous components of wood, with a width of approximately 4 nm and a length in the micrometer range. They consist of aligned linear cellulose chains with crystallinity exceeding 60%, rendering stiff, high-aspect-ratio rods. These properties are advantageous in the reinforcement components of composites. Cross-linked networks of fibrils can be used as templates into which a polymer enters. In the semi-concentrated regime (i.e. slightly above the overlap concentration), carboxy methylated fibrils dispersed in water have been physically cross-linked to form a volume-spanning network (a gel) by reducing the pH or adding salt, which diminishes the electrostatic repulsion between fibrils. By applying shear during or after this gelation process, we can orient the fibrils in a preferred direction within the gel, for the purpose of fully utilizing the high stiffness and strength of the fibrils as reinforcement components. Using these gels as templates enables precise control of the spatial distribution and orientation of the dispersed phase of the composites, optimizing the potentially very large reinforcement capacity of the nanofibrils.

  • 28.
    Fors, Fredrik
    Linköping University, Department of Management and Engineering, Mechanics .
    Analysis of Metal to Composite Adhesive Joins in Space Applications2010Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Within the European space programme, a new upper stage engine (Vinci) for the Ariane 5 launcher is being developed, and the Volvo Aero Corporation (VAC) is contributing with tur-bines for the fuel turbopumps. This MSc thesis investigates the possibility of designing the Turbine Exhaust Duct (TED) of the Vinci-engine in a carbon fibre composite material with adhesively attached titanium flanges. The focus of the project has been on stress analyses of the adhesive joints using Finite Element Methods (FEM), more specifically by using a cohe-sive zone material (CZM) to model the adhesive layer. Analysing adhesive joints is complex and an important part of the work has been to develop and concretise analysis methods for future use within VAC.

    To obtain the specialised material parameters needed for a CZM analysis, FE-models of ten-sile test specimens were analysed and the results compared to those of equivalent experimen-tal tensile tests. These parameters were then used when analysing the TED geometry with load cases specified to simulate the actual operation conditions of the Vinci engine. Both two-dimensional axisymmetric and fully three-dimensional models were analysed and, addition-ally, a study was performed to evaluate the effect of cryogenic temperatures on the strength of the joint.

    The results show that the applied thermal and structural loading causes local stress concentra-tions on the adhesive surface, but the stresses are not high enough to cause damage to the joint if a suitable joint design is used. Cryogenic temperatures (-150 °C) caused a significant strength reduction in the tensile specimens, partially through altered adhesive properties, but no such severe effects were seen in the temperature-dependent FE-analyses of the TED. It should be pointed out however, that some uncertainties about the material parameters exist, since these were obtained in a rather unconventional way. There are also several other impor-tant questions, beside the strength of the adhesive joint, that need to be answered before a metal-composite TED can be realised.

  • 29.
    Ginebre, Emmanuel
    Linköping University, Department of Management and Engineering, Mechanics.
    Geometry-dependence of the adhesive strength of biomimetic, micropatterned surfaces2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Pressure sensitive adhesive surfaces are often inspired by nature. Miming the toe-surface of gecko, engineered surfaces made of thousands of micro-pillars show promising adhesive properties. This surfaces, covered with cylindrical pillars arranged into a pattern have adhesive properties greatly dependent on the geometrical characteristics. In this thesis, have been studied successively two models of micro-patterned surfaces, one two-dimensional, the other in three-dimensional using a FEM tool. Varying geometry parameters, has been determined optimal geometries to improve adhesive strength on these biomimetic, micropatterned surfaces. This study concludes to the non-adaptability of one-level scale micropatterned surface to large area of adhesion, to the strong advantage from the point of adhesion per contact area for high aspect ratio at each level of the geometry and study the opportunity of hierarchical structures. Some further suggestions of improvements to adhesion properties are discussed in the final chapter.

  • 30.
    Gunnarsson, Svante
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Krus, Petter
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Adaptive Control of a Hydraulic Crane using On-Line Identification1993In: Proceedings of the Third Scandinavian International Conference on Fluid Power, 1993, Vol. 2, p. 363-388Conference paper (Other academic)
    Abstract [en]

    In this paper we present an approach to adaptive control of hydraulic actuators with flexible mechanical loads. The approach is based on recursive identification of low order models of the dynamics from valve input to actuator position and effective load pressure respectively. The model parameters are used to compute a regulator that gives a well damped system with good servo properties. The identification is carried out on-line in closed loop with no other signals than those present in normal operation. Here RLS with variable forgetting factor is used. The method does not, however, need not more paramters to be set a priori than ordinary RLS with fix forgetting factor. In this way an easily tuned and robust identification algorithm is obtained. Results from experiments carried out on a lorry crane are presented.

  • 31.
    Gunnarsson, Svante
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Krus, Petter
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    LQG Control of a Hydraulic Actuator with a Flexible Mechanical Load1993In: Proceedings of the 12th IFAC World Congress, 1993, p. 469-472Conference paper (Refereed)
    Abstract [en]

    This paper presents a control system based on linear quadratic state feedback and state estimation for an hydraulic actuator with a flexible mechanical load. The purpose of the control system is to improve the dynamic properties by reducing the oscillatory behavior of the load and to eliminate the steady state error in the load position caused by external disturbances. Using a simplified linear model a control system is developed and evaluated using simulations and experiments.

  • 32.
    Gunnarsson, Svante
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Krus, Petter
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    LQG Control of a Hydraulic Actuator with a Flexible Mechanical Load1993Report (Other academic)
    Abstract [en]

    This paper presents a control system based on linear quadratic state feedback and state estimation for an hydraulic actuator with a flexible mechanical load. The purpose of the control system is to improve the dynamic properties by reducing the oscillatory behavior of the load and to eliminate the steady state error in the load position caused by external disturbances. Using a simplified linear model a control system is developed and evaluated using simulations and experiments.

  • 33.
    Gunnarsson, Svante
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Krus, Petter
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, Department of Electrical Engineering, Automatic Control.
    LQG Control of an Hydraulic Actuator with a Flexible Mechanical Load1991Report (Other academic)
    Abstract [en]

    This paper presents a control system based on linear quadratic state feedback and state estimation for an hydraulic actuator with a flexible mechanical load. The purpose of the control system is to improve the dynamic properties by reducing the oscillatory behavior of the load and to eliminate the steady state error in the load position caused by external disturbances. Using a simplified linear model a control system is developed and evaluated using simulations and experiments.

  • 34.
    Habbal, Abderrahmane
    et al.
    Laboratoire J.A.Dieudonné, Université de Nice Sophia-Antipolis, France.
    Petersson, Joakim
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Thellner, Mikael
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Multidisciplinary topology optimization solved as a Nash game2004In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 61, no 7, p. 949-963Article in journal (Refereed)
    Abstract [en]

    In the present work, multidisciplinary optimization is formulated in the game theory framework. We choose a coupled heat transfer—thermoelastic system as the case study for which a topology design approach is developed. The multidisciplinary optimization problem is solved as a non-cooperative game and we determine a Nash equilibrium. The game has two players and the parameterization of the design domain is such that the design variables describe the material density and a parameter which influences the heat flow by convection to the surrounding fluid. The first player controls the structure and the second player controls the temperature distribution in the structure. For the second player, we present mathematical proof of existence of a discrete valued optimal solution and it is concluded that no regularization of the suboptimization problem is needed. We present two numerical examples which illustrate the proposed methodology. One of the examples is also solved by weighting the objectives to a scalar valued objective function and the result is compared with the Nash game solution.

  • 35.
    Hamache, Violette
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Dynamic Ground Clearance2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The purpose of this work is to develop a test method which will consider the variation of the ground clearance when driving, the so-called dynamic ground clearance. This has been done through the analysis of a specific application: the tractors in grain used in Brazil.

    Series of real life tests are run in order to obtain data on the tire compressions and the suspension travels. The tractor used is a 6x4 and is loaded with a trailer.

    When investigating critical cases, the minimum dynamic ground clearance is found to be as small as 123 mm at the axle 1, 78 mm at the exhaust outlet, 137 mm at the fuel tank, 35 mm at the bumper and 213 mm at the axle 2.

    These data will be transmitted to the engineer responsible for the chassis design in order for him to get a better understanding of the motion of the truck relative to ground.

  • 36. Hilding, D.
    et al.
    Torstenfelt, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics .
    Klarbring, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Mechanics .
    A computational methodology for shape optimization of structures in frictionless contact2001In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 190, no 31, p. 4043-4060Article in journal (Refereed)
    Abstract [en]

    This paper presents a computational methodology for shape optimization of structures in frictionless contact, which provides a basis for developing user-friendly and efficient shape optimization software. For evaluation it has been implemented as a subsystem of a general finite element software. The overall design and main principles of operation of this software are outlined. The parts connected to shape optimization are described in more detail. The key building blocks are: analytic sensitivity analysis, an adaptive finite element method, an accurate contact solver, and a sequential convex programing optimization algorithm. Results for three model application examples are presented, in which the contact pressure and the effective stress are optimized. cr 2001 Elsevier Science B.V. All rights reserved.

  • 37.
    Hilding, Daniel
    et al.
    DYNAmore Nordic AB, Linköping.
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Optimization of structures in frictional contact2012In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 205-208, no S1, p. 83-90Article in journal (Refereed)
    Abstract [en]

    This paper describes a new approach to optimization of linear elastic structures in frictional contact. It uses a novel method to determine an, in a specified sense, likely equilibrium state of the structure, using only the static equilibrium conditions. That is, no complex dynamic/quasi-static analyses have to be performed. The approach has the advantage that it is not necessary to know the complete load history, which is most often unknown for practical problems. To illustrate the theory, numerical results are given for the optimal design problem of sizing a truss to attain a more uniform normal contact force distribution.

  • 38.
    Holmberg, Erik
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Stress and fatigue constrained topology optimization2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis concerns structural optimization in conceptual design stages, for which constraints that are adapted to industrial requirements have been developed for topology optimization problems. The objective of the project has been to identify and solve problems that today prevent structural optimization from being used in a broader sense in the avionic industry; the main focus has been on stress and fatigue constraints in topology optimization.

    The thesis consists of two parts. The rst part gives an introduction to topology optimization and describes the developed methods for stress and fatigue constraints. In the second part, two papers are included, where the stress and fatigue constraints are evaluated, respectively.

    In the rst paper, a clustered approach is presented, where stress constraints are applied to stress clusters, rather than points on the structure. This allows for a trade-o between computational time and accuracy, as the number of clusters and thus constraints can be varied. Dierent approaches for how to sort stress evaluation points into clusters and how to update the clusters, such that the results are suciently accurate for conceptual designs, are developed and evaluated. The two-dimensional examples conrm the theoretical discussions and the designs that are obtained have managed to avoid large stress concentrations, even for problems with an initial stress singularity. Compared to the traditional stiness based designs, the stress constrained designs are considered to be closer to a nal design, which will decrease the total product development time.

    The second paper uses the methodology developed in the rst paper and applies it to high-cycle fatigue constraints. Using loads described by a variable load spectrum and material data from fatigue tests, the tensile principal stresses are constrained by a limit that is determined such that fatigue failure will not occur. In the examples, where the mass is minimized subjected to fatigue and static stress constraints, simple topologies are obtained and the structural parts are sized with respect to the critical fatigue stress and the yield limit. Stress concentrations are again avoided, for example by the creation of a radius around an internal corner. A comparison between static stress constraints based on the von Mises criterion and the highest tensile principal stresses is given and the examples clearly show the characteristics of the two formulations.

  • 39.
    Holmberg, Erik
    et al.
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Torstenfelt, Bo
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Fatigue constrained topology optimization2014In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 50, no 2, p. 207-219Article in journal (Refereed)
    Abstract [en]

    We present a contribution to a relatively unexplored application of topology optimization: structural topology optimization with fatigue constraints. A probability based high-cycle fatigue analysis is combined with principal stress calculations in order to find the topology with minimal mass that can withstand prescribed loading conditions for a specific life time. This allows us to generate optimal conceptual designs of structural components where fatigue life is the dimensioning factor.

    We describe the fatigue analysis and present ideas that makes it possible to separate the fatigue analysis from the topology optimization. The number of constraints is kept low as they are applied to stress clusters, which are created such that they give adequate representations of the local stresses. Optimized designs constrained by fatigue and static stresses are shown and a comparison is also made between stress constraints based on the von Mises criterion and the highest tensile principal stresses.

  • 40.
    Holmberg, Erik
    et al.
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology. Saab AB, Linköping, Sweden.
    Torstenfelt, Bo
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Global and clustered approaches for stress constrained topology optimization and deactivation of design variables2013Conference paper (Other academic)
    Abstract [en]

    We present a global (one constraint) version of the clustered approach previously developed for stress constraints, and also applied to fatigue constraints, in topology optimization. The global approach gives designs without large stress concentrations or geometric shapes that would cause stress singularities. For example, we solve the well known L-beam problem and obtain a radius at the internal corner.

    The main reason for using a global stress constraint in topology optimization is to reduce the computational cost that a high number of constraints impose. In this paper we compare the computational cost and the results obtained using a global stress constraint versus using a number of clustered stress constraints.

    We also present a method for deactivating those design variables that are not expected to change in the current iteration. The deactivation of design variables provides a considerable decrease of the computational cost and it is made in such a way that approximately the same final design is obtained as if all design variables are active.

  • 41.
    Holmberg, Erik
    et al.
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Torstenfelt, Bo
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Stress constrained topology optimization2013In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 48, no 1, p. 33-47Article in journal (Refereed)
    Abstract [en]

    This paper develops and evaluates a method for handling stress constraints in topology optimization. The stress constraints are used together with an objective function that minimizes mass or maximizes stiffness, and in addition, the traditional stiffness based formulation is discussed for comparison. We use a clustering technique, where stresses for several stress evaluation points are clustered into groups using a modified P-norm to decrease the number of stress constraints and thus the computational cost. We give a detailed description of the formulations and the sensitivity analysis. This is done in a general manner, so that different element types and 2D as well as 3D structures can be treated. However, we restrict the numerical examples to 2D structures with bilinear quadrilateral elements. The three formulations and different approaches to stress constraints are compared using two well known test examples in topology optimization: the L-shaped beam and the MBB-beam. In contrast to some other papers on stress constrained topology optimization, we find that our formulation gives topologies that are significantly different from traditionally optimized designs, in that it actually manage to avoid stress concentrations. It can therefore be used to generate conceptual designs for industrial applications.

  • 42.
    Holmberg, Joakim
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Cross-country Skiing Biomechanics using the AnyBody Modeling System2007Conference paper (Other academic)
  • 43.
    Holmberg, Joakim
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Simulera med mera2008In: CAD & ritnytt, ISSN 0282-5708, no 4, p. 27-28Article in journal (Other (popular science, discussion, etc.))
    Abstract [sv]

    Varför tillverkar man produkter utan att ta hänsyn till människan som ska använda dem? Är det inte konstigt att det nästan inte finns någon egenskap hos tekniska produkter som inte går att simulera, men ingen vet belastningen på din ryggrad när du sitter i din kontorsstol?

  • 44.
    Holmberg, Joakim L.
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Computational Biomechanics in Cross-country Skiing2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Traditionally, research on cross‐country skiing biomechanics is based mainly on experimental testing alone. Trying a different approach, this thesis explores the possibilities of using computational musculoskeletal biomechanics for cross‐country skiing. As far as the author knows, this has not been done before.

    Cross‐country skiing is both fast and powerful, and the whole body is used to generate movement. Consequently, the computational method used needs to be able to handle a full‐body model with lots of muscles. This thesis presents several simulation models created in the AnyBody Modeling System, which is based on inverse dynamics and static optimization. This method allows for measurementdriven full‐body models with hundreds of muscles and rigid body segments of all major body parts.

    A major result shown in the thesis is that with a good simulation model it is possible to predict muscle activation. Even though there is no claim of full validity of the simulation models, this result opens up a wide range of possibilities for computational musculoskeletal biomechanics in cross‐country skiing. Two example of new possibilities are shown in the thesis, finding antagonistic muscle pairs and muscle load distribution differences in different skiing styles. Being able to perform optimization studies and asking and answering “what if”‐questions really gives computational methods an edge compared to traditional testing.

    To conclude, a combination of computational and experimental methods seems to be the next logical step to increase the understanding of the biomechanics of crosscountry skiing.

  • 45.
    Holmberg, Joakim
    et al.
    Linköping University, Department of Management and Engineering, Mechanics . Linköping University, The Institute of Technology.
    Lund Ohlsson, Marie
    MittUniversitet.
    Biomekaniska simuleringar adderar insikt om längdskidåkning2010In: Svensk Idrottsforskning: Organ för Centrum för Idrottsforskning, ISSN 1103-4629, Vol. 19, no 1, p. 38-40Article in journal (Other (popular science, discussion, etc.))
    Abstract [sv]

    Varför ska man kopiera de som är bäst? När man väl lärt sig deras teknik så har de bästa kanske redan gått vidare och utvecklat ännu bättre tekniker? Med biomekaniska simuleringar adderas insikt så att man kan utveckla sin teknik och ligga i framkant, istället för i svallvågorna.

  • 46.
    Holmberg, Joakim
    et al.
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Lund Ohlsson, Marie
    Department of Engineering and Sustainable Development, Mid Sweden University, Sweden .
    Danvind, Jonas
    Department of Engineering and Sustainable Development, Mid Sweden University, Sweden .
    Letter: Musculoskeletal simulations: a complementary tool for classification of athletes with physical impairments2012In: Prosthetics and orthotics international, ISSN 0309-3646, E-ISSN 1746-1553, Vol. 36, no 3, p. 396-397Article in journal (Other academic)
    Abstract [en]

    n/a

  • 47.
    Holmberg, Joakim
    et al.
    Linköping University, Department of Management and Engineering, Mechanics . Linköping University, The Institute of Technology.
    Rännar, L-E
    Mid Sweden University.
    Versatile Optimization2001In: Nordic MATLAB Conference Proceedings Oslo, Norway, October 17‐18, 2001, p. 207‐212-Conference paper (Refereed)
  • 48.
    Holmberg, Joakim
    et al.
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Wagenius, P.
    Mid Sweden University.
    A biomechanical model of a double‐poling skier2003In: In International Society of Biomechanics XIXth Congress on The human body in motion, CD Rom Abstracts and Proceedings, Milburn, P. (Ed.), University of Otago, Dunedin, New Zealand, 6‐11 July, 2003Conference paper (Other academic)
  • 49.
    Holmberg, L. Joakim
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    A simulation study on the necessity of muscle contraction dynamics in cross-country skiingManuscript (preprint) (Other academic)
    Abstract [en]

    Competitive cross-country skiing is considered to be a fast and powerful dynamic movement. It is unknown what level of complexity that is needed in a musculoskeletal model of a skiing movement, e.g. double-poling. Therefore, a simulation study is carried out to explore the influence of muscle model choice. The theoretical framework of two types of muscle models and their respective implementations are given. These models are a Hill-type model with contraction dynamics and a constant force model, respectively. Results show that it is necessary to incorporate muscle contraction dynamics to estimate individual muscle behaviour in double-poling. Moreover, it may be bad practice to model different body parts with different muscle models; the musculoskeletal system is not a collection of discrete uncoupled body parts and kinetic effects will propagate through the system.

  • 50.
    Holmberg, L. Joakim
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Biomekanisk simulering av längdskidåkning2012In: Svensk idrottsmedicin, ISSN 1103-7652, Vol. 31, no 3, p. 11-13Article in journal (Other (popular science, discussion, etc.))
1234 1 - 50 of 179
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