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  • 1.
    Ashwear, Nasseradeen
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Influence of Temperature on the Vibration Properties of Tensegrity Structures2015In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 99, p. 237-250Article in journal (Refereed)
    Abstract [en]

    Vibration health monitoring methods use the sensitivity of the natural frequencies to structural damage. Natural frequencies are sensitive to damage, but are also affected by environmental conditions like temperature changes. It is important to be able to distinguish between the effects of these different factors when using the vibration properties as a monitoring tool. This paper discusses the impact of damage and environment temperature changes on the natural frequencies of tensegrity ("tensile-integrity") structures, in particular noting that component bending is a prominent vibration mode, which motivates a use of non-linear beam elements with axial-bending coupling. The model considers not only thermal expansion effects, but also the change of the elastic modulus with temperature. Changes in natural frequencies produced by environment temperature changes are shown to be similar to the ones produced by damage. The geometry of tensegrity structures, the support conditions and the materials are found to be important factors. The sensitivity of the natural frequency to temperature changes is found to be dependent on pre-stress level.

  • 2.
    Ashwear, Nasseradeen
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Natural frequencies describe the pre-stress in tensegrity structures2014In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 136, p. 162-171Article in journal (Refereed)
    Abstract [en]

    This paper investigates the effect of pre-stress level on the natural frequencies of tensegrity structures. This has been established by using Euler–Bernoulli beam elements which include the effect of the axial force on the transversal stiffness. The axial-bending coupling emphasizes the non-linear dependence of the natural frequencies on the pre-stress state. Pre-stress is seen as either synchronous, considering a variable final pre-stress design or as tuning, when increasing pre-stress is followed in a planned construction sequence. It is shown that for a certain tensegrity structure, increasing the level of pre-stress may cause the natural frequencies to rise or fall. This effect is related to whether the structural behavior can be seen as compression or tension dominant. Vanishing of the lowest natural frequency of the system is shown to be related to the critical buckling load of one or several compressed components. Modes of vibration show that when the force in the compressed components approaches any type of critical buckling load, this results in lower vibration frequencies. The methods in this study can be used to plan the tuning of the considered tensegrity structure towards the design level of pre-stress, and as health monitoring tools.

  • 3.
    Ashwear, Nasseradeen
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Reducing effects from environmental temperature on the natural frequencies of tensegrity structuresIn: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568Article in journal (Other (popular science, discussion, etc.))
    Abstract [en]

    n vibration health monitoring, dynamic properties such as natural frequencies and mode shapes are used as tools for assessing the structures health condition.~They are, however, also affected by environmental conditions like wind, humidity and temperature changes. Of particular importance is the change of the environmental temperature, and it is the most commonly considered environmental variable that influences the vibration health monitoring algorithms.~This paper discusses how the tensegrity structures can be designed such that some of their lowest natural frequencies are less sensitive to the temperature changes. A genetic algorithm is used to solve the optimization problem. In the form-finding stage, an asymmetric self-stress vector can be chosen so that the criterion is fulfilled as well as possible. The level of pre-stress can also be regulated to achieve the solution, particularly when a symmetric self-stress vector is chosen.

  • 4.
    Ashwear, Nasseradeen
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Vibration health monitoring for tensegrity structures2017In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 85, p. 625-637Article in journal (Refereed)
    Abstract [en]

    Tensegrities are assembly structures, getting their equilibrium from the interaction between tension in cables and compression in bars. During their service life, slacking'in their cables and nearness to buckling in their bars need to be monitored to avoid a sudden collapse. This paper discusses how to design the tensegrities to make them feasible for vibrational health monitoring methods. Four topics are discussed; suitable finite elements formulation, pre-measurements analysis to find the locations of excitation and sensors for the interesting modes, the effects from some environmental conditions, and the pre-understanding of the effects from different slacking scenarios.

  • 5.
    Ashwear, Nasseradeen
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Tamadapu, Ganesh
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Optimization of modular tensegrity structures for high stiffness and frequency separation requirements2016In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 80, p. 297-309Article in journal (Refereed)
    Abstract [en]

    Tensegrities are cable-strut assemblies which find their stiffness and self-equilibrium states from the integrity between tension and compression. Low stiffness and coinciding natural frequencies are known issues. Their stiffness can be regulated and improved by changing the level of pre-stress. In vibration health monitoring, the first natural frequency is used as an indicator of better stiffness, but coinciding natural frequencies will be an obstacle in measuring and analysing the correct resonance. In this paper, the above two issues have been considered for modular tensegrity structures. The finite element model used considers not only the axial vibration of the components, but also the transversal vibration where non-linear Euler-Bernoulli beam elements are used for simulations. A genetic algorithm is used to solve the optimization problem, with a multi-objective criterion combination. The optimum self-stress of the tensegrity structures can be chosen such that their lowest natural frequency is high, and separated from others. Two approaches are used to find the optimal self-stress vector: scaling from a base module or considering all modules at once. Both approaches give the same optimum solutions.

  • 6.
    Battini, Jean-Marc
    et al.
    KTH, Superseded Departments, Structural Engineering.
    Pacoste, Costin
    KTH, Superseded Departments, Structural Engineering.
    Eriksson, Anders
    KTH, Superseded Departments, Structural Engineering.
    Improved minimal augmentation procedure for the direct computation of critical points2003In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 192, no 16-18, p. 2169-2185Article in journal (Refereed)
    Abstract [en]

    This paper presents a new numerical procedure for the direct computation of critical points for elastic beam structures undergoing large displacements and rotations. Compared to the approach described by Wriggers et al. [Comput. Methods Appl. Mech. Engrg. 70 (1988) 329; Int. J. Numer. Methods Engrg. 30 (1990) 1551, two main modifications are introduced. First, following Eriksson [Comput. Methods Appl. Mech. Engrg. 114 (1994) 77; Comput. Methods Appl. Mech. Engrg. 156 (1998) 45; Comput. Methods Appl. Mech. Engrg. 179 (1999) 265; Int. J. Struct. Stability Dynam. l(l) (2001)], the condition of criticality is expressed by a scalar equation instead of a vectorial one. Next, the present procedure does not use exclusively the extended system obtained from the equilibrium equations and the criticality condition, but also introduces intermediate iterations based purely on equilibrium equations under load or displacement control, Eight numerical examples, presenting bifurcation and limit points, are used in order to compare the performances of this new method and the one presented in [Comput. Methods Appl. Mech. Engrg. 70 (1988) 329; Int. J. Numer. Methods Engrg. 30 (1990) 155].

  • 7.
    Bissal, Ara
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Magnusson, Jesper
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Salinas, Ener
    ABB AB Corporate Research, Sweden.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    On the Design of Ultra-Fast Electromechanical Actuators: A Comprehensive Multi-Physical Simulation Model2012In: Sixth International Conference on Electromagnetic Field Problems and Applications (ICEF), 2012, IEEE conference proceedings, 2012, p. 1-4Conference paper (Refereed)
    Abstract [en]

    In this paper, a simulation of an ultra-fast electromechanical drive was performed by using a two-dimensional axi-symmetric multi-physical finite element model. The aim of this paper is to primarily show that the following model can be used to simulate and design those actuators with good accuracy, secondly, to study the behavior and sensitivity of the system and thirdly, to demonstrate the potential of the model for industrial applications. The simulation model is coupled to a circuit and solves for the electro-magnetic, thermal, and mechanical dynamics utilizing a moving mesh. The actuator under study is composed of a spiral-shaped coil and a disk-shaped 3mm thick copper armature on top. Two numerical studies of such an actuator powered by 2640 J capacitor banks were performed. It is shown that forces up to 38 kN can be achieved in the range of 200 μs. To add credibility, a benchmark prototype was built to validate this experimentally with the use of a high speed camera and image motion analysis.

  • 8.
    Bröchner, Jan
    et al.
    KTH.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Lundequist, Jerker
    Byggprjktet som dataförädling: Processaspekter på informationsstrukturer1990Book (Other academic)
  • 9.
    Dalil Safaei, Seif
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Optimum pre-stress design for frequency requirement of tensegrity structures2011In: Proceeding of 10th World Congress on Computational Mechanics, 2011Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    Structures composed of tension and compression elements in equilibrium are denoted tensegrity structures. Stability of tensegrity structures is achieved through introducing initial member forces (pre-stress). The pre-stress design can be seen consisting of three different stages: (i) finding the bases of possible pre-stress states, (ii) finding admissible distributions considering unilateral properties of the elements and stability of the structure, (iii) finding the optimum pre-stress pattern for certain magnitude from compatible pre-stress states. So far, no research has been carried out to connect the three steps, i.e. finding a suitable pre-stress pattern which also considers mechanical properties of the highly pre-stressed structure e.g. its natural frequencies. This paper aims at finding an optimum pre-stress pattern and level of pre-stress for the maximum frequency. The pre-stress problem is on a linear static level where no slackening is allowed. An optimization is performed to find the optimum pre-stress pattern fromthe self-stress modes obtained by a singular value decomposition (SVD) of the equilibrium matrix. The objective function is the first natural frequency of the structure. Finite element analysis is employed for the linear analysis of the structure and a genetic algorithm for optimization i.e., a non-gradient method. The example considered is a double layer tensegrity grid consisting of 29 independent self-stress states. The method is applicable to complex asymmetric three-dimensional structures. The new aspect of this work is a link between the SVD analysis, finite element analysis and genetic algorithm.

  • 10.
    Dalil Safaei, Seif
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Stiffness visualization for tensegrity structures2010In: Proc. NSCM-23, 2010Conference paper (Refereed)
  • 11.
    Dalilsafaei, Seif
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Micheletti, A.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Parametric study of various tensegrity modules asbuilding blocks for slender boomsArticle in journal (Other academic)
  • 12.
    Dalilsafaei, Seif
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Application of flexibility analysis for design of tensegrity structures2011In: Proceeding of the 4th Structural Engineering World Congress, 2011Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    Tensegrity structures have been the subject of research for many years, but very few of them have been built. One major disadvantage of tensegrities compared to typical trusses is their stiffness, which can be significantly reduced when a cable goes slack. This paper aims to introduce a method for stiffness characterization of tensegrity structures for the following purposes: (i) comparison of the stiffness of tensegrity structures with other truss structures, (ii) comparison of the stiffness of different form-found geometries, (iii) finding the most flexible nodes and the principal flexibility directions and (iv) finding stiffness effects of different pre-stress levels and patterns. The method is based on the flexibility analysis of tensegrity structures and the finite element method is used for the non-linear static analysis of the structure to obtain the flexibility figures which visualize the flexibility for different plane and spatial truss and slender boom tensegrity structures.

     

  • 13.
    Dalilsafaei, Seif
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Flexibility-based pre-stress design of tensegrity structuresManuscript (preprint) (Other academic)
    Abstract [en]

    Tensegritiy structures have been subjects of research for many years, but very few of them have been built. One major disadvantage of tensegrities compare to regular truss structures is their low stiffness. This papers aims to have a new look at the stiffness problem of tensegrity structures. Here, it is assumed that the form-finding step has been completed and the axial stiffness of the elements is known. We introduce a tool for stiffness characterization of a given tensegrity structure for different pre-stress magnitudes. Since the pre-stress has a critical influence on the stability of the structure with a role to prevent or postpone slackening, the magnitude of pre-stress of the structure exposed to large external loads and disturbances are found. Finite elements are utilized in the solution for the non-linear static analysis. The method is based on geometrical interpretation of flexibility of unconstrained nodes. Suggested concept, flexibility analysis, shows promising properties in finding flexible nodes, weak directions of structure, detection of cable elements with higher risk of going slack and better knowledge of influence of various external loads. The authors believe results of this research could help the researchers and designer of better understanding the behavior of tensegrity structures.

     

  • 14.
    Dalilsafaei, Seif
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Improving bending stiffness of tensegrity booms2012In: International Journal of Space Structures, ISSN 0956-0599, Vol. 27, no 2-3, p. 117-129Article in journal (Refereed)
    Abstract [en]

    There is a high interest in employing lightweight, low-cost, deployable structures for space missions. Utilization of tensegrity structures in space application is limited, due to their low stiffness, while a number of high stiffness-to-mass truss booms have been launched. This paper aims to describe and improve the bending stiffness of tensegrity booms. Tensegrity booms of Snelson and triangular prism type are selected for the study. These structures are excellent samples of class 1 tensegrities, with a single state of self-stress and one mechanism, and class 2 tensegrities, with multiple states of self-stress and mechanisms. The stiffness modification procedure includes three steps: (Step 1) developing a strategy for a fair comparison of tensegrity booms with a high performance truss boom. A genetic algorithm is employed to find the optimum cross-section areas of the boom elements. Sources of low stiffness of tensegrities are discussed. (Step 2) an effort is made to find the optimum placement of actuators for improving the stiffness of the tensegrity booms. (Step 3) a genetic algorithm is utilized to calculate their optimum actuation. All three stages have been performed based on a link between non-linear finite element analysis and a genetic algorithm. The genetic algorithm shows high accuracy of searching non-structural space, and also dealing with above steps. Results indicate that the stiffness of tensegrity booms is highly improved by activating the structures.

  • 15.
    Dalilsafaei, Seif
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Sensitivity analysis of tensegrity booms due to member loss2011In: Proceedings NSCM-24, 2011Conference paper (Other academic)
  • 16.
    Dijkstra, Erik J.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH Engineering Sciences.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Gutierrez-Farewik, Elena M.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Sensitivity in prediction of human posture by constrained optimizationManuscript (preprint) (Other academic)
    Abstract [en]

    In a variety of activities of daily living, it is important to be able to stand still in one place. For persons with motion disorders, orthopaedic treatment, which changes geometric or biomechanical properties, can improve the individual's posture and walking ability. Such treatment requires insight into how posture and walking ability are affected. As this is very challenging to observe by the naked eye, engineering tools are increasingly employed to support clinical diagnostics and treatment planning. Because of their potential to help unravel the causal relation between treatment and its outcome, the number of predictive methods are increasing. This study addresses the complications in the creation and analysis of a posture prediction framework. The fmincon optimization function in MATLAB was used in conjunction with a musculoskeletal model in OpenSim. One clear local minimum was found in the form of a symmetric standing posture but perturbation analyses revealed the presence of many other postural congurations, each representing its own unique local minimum in the feasible parameter space. For human postural stance, this can translate to there being many different ways of standing without actually noticing a difference in the efforts required for these poses.

  • 17. Ekstrand, Vilhelm
    et al.
    Wiksell, Hans
    Schulz, I
    Sandstedt, B.
    Rotstein, S
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Influence of electrical and thermal properties on RF ablation of breast cancer: is the tumour preferentially heated?2005In: Biomedical engineering online, ISSN 1475-925X, E-ISSN 1475-925X, Vol. 4, p. 41-41Article in journal (Refereed)
    Abstract [en]

    Background: Techniques based on radio frequency (RF) energy have many applications in medicine, in particular tumour ablation. Today, mammography screening detects many breast cancers at an early stage, facilitating treatment by minimally invasive techniques such as radio frequency ablation (RFA). The breast cancer is mostly surrounded by fat, which during RFA-treatment could result in preferential heating of the tumour due to the substantial differences in electrical parameters. The object of this study was to investigate if this preferential heating existed during experimental in vitro protocols and during computer simulations. Methods: Excised breast material from four patients with morphologically diagnosed breast cancers were treated with our newly developed RFA equipment. Subsequently, two finite element method (FEM) models were developed; one with only fat and one with fat and an incorporated breast cancer of varying size. The FEM models were solved using temperature dependent electrical conductivity versus constant conductivity, and transient versus steady-state analyses. Results: Our experimental study performed on excised breast tissue showed a preferential heating of the tumour, even if associated with long tumour strands. The fat between these tumour strands was surprisingly unaffected. Furthermore, the computer simulations demonstrated that the difference in electrical and thermal parameters between fat and tumour tissue can cause preferential heating of the tumour. The specific absorption rate (SAR) distribution changed significantly when a tumour was present in fatty tissue. The degree of preferential heating depended on tissue properties, tumour shape, and placement relative to the electrode. Temperature dependent electrical conductivity increased the thermal lesion volume, but did not change the preferential heating. Transient solutions decreased the thermal lesion volume but increased the preferential heating of the tumour. Conclusions: Both the computer model and the in vitro study confirmed that preferential heating of the tumour during RFA exists in breast tissue. However, the observed preferential heating in the in vitro studies were more pronounced, indicating that additional effects other than the difference in tissue parameters might be involved. The existing septa layers between the cancer tissue and the fatty tissue could have an additional electrical or thermal insulating effect, explaining the discrepancy between the in vitro study and the computer model.

  • 18.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Analysis methodology based on temporal FEM for bio-mechanical simulations2005In: Modelling in Medicine and Biology VI / [ed] Ursino, M; Brebbia, CA; Pontrelli, G; Magosso, E, SOUTHAMPTON: WIT PRESS/COMPUTATIONAL MECHANICS PUBLICATIONS , 2005, Vol. 8, p. 295-304Conference paper (Refereed)
    Abstract [en]

    This paper deals with the analysis of optimal path forward dynamics of mechanical systems. The primary applications considered are bio-mechanical simulations of musculoskeletal systems. The focus is put on problems of controlled movements from one configuration to another. Different criteria for this movement are allowed in the formulation. Formulations, examples and conclusions are given.

  • 19.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Constraint paths in non-linear structural optimization2014In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 140, p. 39-47Article in journal (Refereed)
    Abstract [en]

    Optimization of significantly non-linear structures is a demanding task. The paper discusses how boundaries of the feasible region can be followed as generalized equilibrium paths in parametric space, reflecting engineering demands on stiffness, strains and stability. Solutions on the constraint paths are then evaluated with respect to any chosen objective function. For few design parameters, this approach is efficient and robust. This is demonstrated for a pre-stressed pressurized membrane of three parameters, showing several constraint paths for the problem, and indicating how these are used in optimization. The view is often closer to engineering design analyses than the mathematical optimization settings, which often has problems in handling stability constraints.

  • 20.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Criteria for optimality in movements2006In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 39, no s1, p. S54-S54Article in journal (Refereed)
  • 21.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Derivatives of tangential stiffness matrices for equilibrium path descriptions1991In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 32, no 5, p. 1093-1113Article in journal (Refereed)
    Abstract [en]

    The paper describes how several procedures, based on expressions from analytical elastic stability theory, are introduced as numerical tools in a general Finite Element program for geometrically non-linear structural analysis. Especially is discussed how derivatives of the tangential stiffness matrix can be utilized in several contexts in the solution algorithm. These include improved predictions for the step-wise solution of equilibrium states, identification of critical points and accurate descriptions of initial post-bifurcation behaviour. For two plane beam and bar elements, formulations have been developed giving analytical expressions for these derivatives. The corresponding numerical approximations, needed in other element types, are also discussed. The paper discusses the relative efficiency of higher order predictions in relation to these different element types and different solution strategies. Some numerical examples, showing different types of behaviour, are analysed and discussed.

  • 22.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Fold lines for sensitivity analyses in structural instability1994In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 114, no 1-2, p. 77-101Article in journal (Refereed)
    Abstract [en]

    The paper describes how a two-parameter formulation of a structural equilibrium problem can be used for a more accurate description of the occurring critical states. A fold line concept is used to evaluate the dependence of these states on an added variable, describing a disturbing load case or a disturbed geometry. The concept describes the local behaviour for small disturbances, but can also be used for parameter dependence analyses, e.g. in connection with optimization algorithms. Two different augmentations of the equilibrium relations are discussed; they describe the criticality of a solution state in different ways. Numerical adoption for a general equilibrium path following algorithm is discussed. A postponed factorization method for solution of the augmented sets of equations is proposed. Two simple examples are used to show the properties and the possibilities of the fold line concept. It is concluded that the suggested numerical procedure can give a better description of critical structural behaviour, especially with respect to imperfections in the structure and idealizations in the model. © 1994.

  • 23.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Instabilities in pressurized membranes2014In: Civil-Comp Proceedings, ISSN 1759-3433, Vol. 106Article in journal (Refereed)
    Abstract [en]

    This paper discusses instabilities occuring in thin pressurized membranes, important in biological as well as in engineering contexts. The membranes are represented by only their in-plane stress components, for which an incompressible isotropic hyper-elastic behavior can be assumed. The inherently non-linear response to pressurization can give instabilities in the forms of limit points with respect to a loading parameter, but also bifurcations and wrinkling. The hyper-elastic material model itself can also, under some circumstances, lead to a bifurcation situation. The instability situations can be included as constraints in a structural optimization. The paper discusses the formulation, the solution methods and some relevant instability situations. A numerical example considering the internal pressurization of a cylindrical pre-stressed membrane illustrates some aspects of instability.

  • 24.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Multi-parametric constraint paths in optimization of pre-stressed membraneArticle in journal (Refereed)
    Abstract [en]

    Optimization of significantly non-linear structures is a demanding task. The paper discusses how boundaries of the feasible region are followed as generalized equilibrium paths in parametric space. As the optimum normally activates one or more inequalities, solutions on the constraint paths are evaluated with respect to the cost function. For few design parameters, this method is efficient and robust. The method is demonstrated for a pre-stressed pressurized membrane of three parameters, with displacement and instability constraints, and with strain limits. Numerical examples show several constraint paths for theproblem, and indicate how these are used in optimization.

  • 25.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Multi-parametric stability investigations for pressurized thin membranes2012In: ECCOMAS 2012 - European Congress on Computational Methods in Applied Sciences and Engineering, e-Book Full Papers / [ed] J. Eberhardsteiner et al., ECCOMAS , 2012, p. 7357-7371Conference paper (Refereed)
    Abstract [en]

    The contribution describes how the quasi-static, conservative problem of pressurized space membranes, i.e., balloons, can be seen in a multi-dimensional context, and how one- and two-dimensional solution manifolds can reveal further information on the structural response. The discussed viewpoint can be seen as the natural extension of the common one-dimensional path-following methods for load-displacement traces, when additional variables are introduced to describe the parameter dependence in structural response, and in instability analyses. The paper describes the general setting of the balloon problem, and the generalized equilibrium form, with some aspects of its treatment. Numerical examples show applications of these models.

  • 26.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Multi-parametric stability investigations for pressurized thin membranes2012In: Proceedings NSCM-25 / [ed] K. Persson, J. Revstedt, G. Sandberg & M. Wallin, Lund: Lund University , 2012Conference paper (Refereed)
    Abstract [en]

    Pressurized thin membranes are frequently encountered in engineering and medical con-texts. Membranes subjected to pneumatic pressurization respond by changing volume and internal over-pressure, and can exhibit different instability conditions.  The response is significantly dependent onparameters for the loading, geometry and material. We used generalized equilibrium path and surfaceevaluation algorithms to describe and investigate the parameter dependence in different response aspects.We describe the algorithmic setting, but also give some aspects of quasi-static instability for pneumaticallypressurized thin membranes. Two examples are used to illustrate the methodology and the obtainableresults

  • 27.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Numerical modeling of thin pressurized membranes2012In: Proc CST-2012 / [ed] BHV Topping, Stirling, U.K.: Civil-Comp , 2012Chapter in book (Refereed)
    Abstract [en]

    The contribution describes how thequasi-static, conservative  problem of pressurized space membranes, i.e., balloons, can be seen in amulti-dimensional context, and how one- and two-dimensionalsolution manifolds can reveal further information on thestructural response. The discussed viewpoint can be seen as thenatural extension of the common one-dimensional path-followingmethods  for load-displacement traces, when additional variables are introduced to describe theparameter dependence in structural response, and in instabilityanalyses. The paper describes the generalsetting of the balloon problem, and the generalized equilibrium form, with some aspects of itstreatment.  Numerical examples showapplications of these models.

  • 28.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Numerical simulations of skeletal muscle mechanics2006In: Innovation in Engineering Computational Technology / [ed] Topping, BHV; Montero, G; Montenegro, R, 2006, p. 107-126Conference paper (Refereed)
    Abstract [en]

    This paper discusses the simulation of forces in a musculoskeletal system. The main focus is on the treatment of static and dynamic equilibria for a redundant force system, where the distribution of the required force for maintaining a posture or performing a movement is not unique. Reference is made to some general aspects of redundancy, and a brief discussion of the static optimisation method follows. This leads to a general framework for static optimisation, where different performance criteria can be introduced. Also dynamic equilibrium during movement is discussed, and a temporal finite element viewpoint is introduced for the treatment of target-controlled movements. This also leads to a rather general framework, where different criteria for optimal movement can be introduced. From both static and dynamic optimisation algorithms it can be concluded that existing numerical descriptions of muscular behaviour are missing some important elements, primarily related to memory aspects of the function. Finally we discuss some ideas around the types of research required in the area of muscular force production.

  • 29.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    On a thin shell element for non-linear analysis, based on the isoparametric concept1992In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 42, no 6, p. 927-939Article in journal (Refereed)
    Abstract [en]

    This paper discusses a finite element method model for the large displacement, moderate strain analysis of thin shells. The model is based on an 'adapted' reference configuration for a displaced element, separating the displacements into rigid body displacements and strain-producing deformations. A strategy is developed, making use of the isoparametric concept for both the choice of reference configuration and in the element formulation. This makes the use of arbitrarily shaped elements possible. The model is shown to give accurate results for a range of relevant problems. Some problems in the general application of this type of model are discussed. © 1992.

  • 30.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    On accurate descriptions for primary and secondary paths in equilibrium problems1992In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 44, no 1-2, p. 229-242Article in journal (Refereed)
    Abstract [en]

    The paper describes how several procedures, based on ideas and expressions from the analytical elastic stability theory, have been introduced as numerical tools in a general finite element program for geometrically non-linear structural analysis. Derivatives of the tangential stiffness matrix are utilized for improved predictions in the step-wise solution of equilibrium states, for identification of critical points and for accurate descriptions of initial post-bifurcation behaviour. The methods are used in a general solution algorithm, based on a parameterizing component formulation. For some element types, analytical expressions for these derivatives can be developed. The corresponding numerical approximations, needed in other element types, are also discussed. Other practical details in the numerical implementation are given. Two numerical frame examples, showing different types of limit and bifurcation behaviours, are used to discuss the numerical properties of the methods. © 1992.

  • 31.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    On improved predictions for structural equilibrium path evaluations1993In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 36, no 2, p. 201-220Article in journal (Refereed)
    Abstract [en]

    The paper describes how several procedures for higher-order predictions have been introduced in order to improve the convergence speed in a general finite element program for non-linear structural analysis. In addition to higher-order Taylor expansions earlier discussed, Lagrangian extrapolations and some methods commonly used for the integration of initial value problems have been introduced. The methods are used for improved predictions in the stepwise solution of equilibrium states and for accurate descriptions of the initial post-bifurcation behaviour. They are used in a general solution algorithm, based on a parameter formulation. The methods are discussed in the light of the strategies for re-creation of the tangential stiffness matrix, used for equilibrium iterations. Numerical examples, exhibiting different limit and bifurcation behaviours for trusses, frames and shells, are used to evaluate the numerical properties and efficiencies of the methods. The paper concludes that the overall efficiency in the algorithm can be improved by introduction of more accurate predictions than the standard Euler prediction. In terms of reliability combined with efficiency, an implicit generalized Simpson method is the preferred method.

  • 32.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    On linear constraints for Newton-Raphson corrections and critical point searches in structural F.E. problems1989In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 28, no 6, p. 1317-1334Article in journal (Refereed)
    Abstract [en]

    The paper discusses the introduction of constraining equations in the tangential stiffness relation used to calculate the responses to different load cases in solution algorithms for non-linear mechanical Finite Element (F.E.) problems. An alternative to the normal two-phase solution method is discussed. This method is used to represent different iteration constraints, and in conjunction with the search for critical solution points. Numerical tests are presented, evaluating the efficiency of different iteration constraints for a model problem. Practically useful criteria for critical points are discussed. The basic methods for search of such points and some numerical aspects are discussed and evaluated for three different problems.

  • 33.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    ON SOME PATH-RELATED MEASURES FOR NON-LINEAR STRUCTURAL F. E. PROBLEMS.1988In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 26, no 8, p. 1791-1803Article in journal (Refereed)
    Abstract [en]

    In the paper, the solution of a non-linear structural mechanical problem is seen as a set of points along a curve in the displacement space, resulting from a continuous variation of a load parameter. The state of the structure at a specified point on the path is described by a tangent vector describing the response to a small load factor increment. For a completed, finite step, the deviation from this tangent response is described by a suggested measure. From this measure, some conclusions can be drawn concerning the iteration behavior, guiding the iteration strategy in coming steps. Two path-related stiffness measures are derived, giving information concerning the behavior of the structure. Some conclusions concerning limit load points, bifurcations, etc. can be drawn from these measures.

  • 34.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Optimal simulations in musculoskeletal posture and movement2008In: Computer and experimental simulations in engineering and science, Vol. 1, p. 39-56Article in journal (Refereed)
  • 35.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Optimization for targeted movements2006In: Proc. III Eur. Conf. Comp. Mech.: Solids, structures and coupled problems in engineering / [ed] CA Mota-Soares, 2006Conference paper (Refereed)
  • 36.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Optimization in target movement simulations2008In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 197, no 49-50, p. 4207-4215Article in journal (Refereed)
    Abstract [en]

    This paper discusses a methodology for fixed-time simulations of optimal movements of a mechanical system, between specified initial and target configurations, without any a priori knowledge on the trajectory between those. It is primarily aimed at human movement simulations with muscular controls. The basic formulation considers both displacements and forces as unknowns during the movement, connects them, and utilizes a finite element time discretization for solving the whole fixed-time interval simultaneously. Through a consistent interpolation of all kinetic and kinematic variables, the formulation becomes general, needing only minimal input for description of a particular problem, but also eliminating errors inherent in many forms of time-integration. The same consistency allows systematic formulations of a large class of optimization cost functions, primarily focussing on the mechanical behavior of the system rather than on the matching of previously measured movements. It thereby allows the use of robust and efficient general optimization algorithms. Kinetic and kinematic constraints can restrict the movement. As an example of the general setting, a simplified human movement is studied, with different choices of controls (joint moments or muscular tensions), and with different optimization criteria. The example shows that the simulation results are strongly dependent on these choices, in particular that smoothness of movement demands forces considerably higher than the strictly minimum ones. A larger example shows that more complex constraints can be handled within the setting proposed, but also the effects from the fixed-time assumption.

  • 37.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Optimization of power input in simulated cross-country skiingManuscript (preprint) (Other academic)
    Abstract [en]

    Optimal simulations for a simplified skier in a cross-country track are considered.  The skier is modeled considering air resistance drag, friction and normal forces when following a track of cubic splines in a vertical plane. The race is modeled as a time-evolution problem, where the acting forces give the movement. Based on an assumption on how the driving  power variation along the track is limited by capacity measures, a mathematical optimization problem is formulated. This  minimizes the race time under a constraint of maximum integrated cost of the mechanical work rate. The paper discusses the mathematical and numerical formulations of the problem, and shows some aspects of discretization and accuracy. It is obvious from the simulations, that significant reductions in race time can be reached by strategically using the available power resources, rather than using a uniform work rate. With the fatigue criterion used, the conclusion from simulations is that it is advantageous  for the skier to input extra power in parts of the track where resistance is high, i.e., in up-slopes, in parts where friction is locally higher, and in parts where a head-wind is affecting the performance. Although the criterion used catches some aspects of how power production causes fatigue, it is concluded that better descriptions are needed for fatigue accumulation and reduction during a regime with different work rates.

  • 38.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Optimization Techniques in Human Movement Analysis2008In: Trends In Engineering Computational Technology / [ed] Papadrakakis, M; Topping, BHZ, 2008, p. 127-150Conference paper (Refereed)
    Abstract [en]

    This paper discusses a few aspects of human movements when seen as an optimal control problem for a mechanism. In particular, the redundancy of the muscle force actuators in simplified models of a body or body part is a main concern. The criteria governing the control of human movement planning are far from fully known, but a general optimization setting allows investigation of alternatives. The numerical description of muscular force production is complex, and its history dependence only partially known. The paper discusses a setting of the dynamic optimization problem, which is reliable and efficient compared to shooting-type methods, and which allows several criteria for optimal performance. The method is demonstrated by a few aspects of a weight-lifting problem. The need for muscular models compatible with the basic formulation, and accurately representing the history dependence in force production is emphasized.

  • 39.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Quasi-static simulations of thin membranes, aiming at stability analyses of balloon-like structures.2011In: Proc. Compdyn 2011 ECCOMAS Thematic Conference, 2011Conference paper (Refereed)
  • 40.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Quasi-static simulations of thin space membranes, aiming at stability analyses of balloon-like structures2011In: ECCOMAS Thematic Conference - COMPDYN 2011, 2011Conference paper (Refereed)
    Abstract [en]

    This paper discusses the evaluation of quasi-static equilibrium solutions for inflatable space membrane structures, such as balloons. A flat linearly interpolated triangular element is used for simulations, with a Mooney-Rivlin hyper-elastic material model, with variable constitutive constants. A compressible medium is used to introduce a one-parametric over-pressure loading within the membrane. Complex path-following procedures are used to find generalized equilibrium paths, with different parameterizations. Numerical examples show that the methods developed can give information on the stability of the structures, but that the medium and means for introducing the internal pressure is of importance for the interpretation of stability.

  • 41.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Structural instability analyses based on generalised path-following1998In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 156, no 1-4, p. 45-74Article in journal (Refereed)
    Abstract [en]

    This paper describes how quasi-static, conservative instability problems can be completely described, using generalised path-following procedures for augmented equilibrium formulations. In particular, methods for treatment of compound critical states are discussed. The numerical methods are seen as extensions to common equilibrium path methods, allowing the solution of subsets of equilibrium states, also fulfilling auxiliary relations, e.g. criticality. These formulations are in general used to describe the parameter dependence in structural response, in instability analyses and in optimisation. The paper describes the general setting of these generalised equilibrium problems, and discusses some details in their numerical treatment. Emphasis is given to the evaluation of path tangent vectors, in the presence of critical eigenvectors for the structural tangential stiffness matrix. Also, the isolation of special states, i.e. vanishing variables, turning points and exchanges of stability, is discussed. Numerical examples are used to show the possibilities and properties of the obtained solution paths, together with some aspects of the numerical procedures.

  • 42.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Temporal finite element descriptions in structural dynamics2004In: Proceedings of the Seventh International Conference on Computational Structures Technology / [ed] B.H.V. Topping, C.A. Mota Soares, Civil-Comp , 2004Conference paper (Refereed)
    Abstract [en]

    This paper discusses a temporal finite element approximation in the analysis of dynamics of mechanical systems, with a special emphasis on problems where a targeted control is desired. This is defined as a situation where forces are to be introduced for the movement of a structure from an initial to one or more target states, but where the behavior between these states is arbitrary. The primary applications are related to bio-mechanical simulations of skeleto-muscular systems, or to robotic analyses. By interpolating simultaneously displacements and velocities in the discrete degrees of freedom, a collocation over the time interval can be used to decide the necessary control variations. As a second step, the control can be optimized for chosen criteria on the integrated force components. By the introduced interpolation of control forces and discrete displacements, a degree of continuity is introduced in the obtained results.

    The presentation focusses on the similarity in computational formulations between several types of dynamic simulations, and sets them in a common algorithmic context. The temporal descriptions of all discrete displacement components are thereby based on a Hermitian finite element form, where each variable is represented by its value and its time differential at a set of discrete time stations. All displacement variables are thereby represented as piecewise cubic polynomials.

    Using the basic equilibrium for the stated problem, and introducing the temporal interpolation of the variables, a finite element form of the problem can be established, with elements in the time dimension, supplementing the discrete or discretized description at each time instance. A set of equations is then established by using a two-point collocation within each time element. This view allows equilibrium equations of any complexity, but is primarily suited for problems of low to moderate numbers of degrees of freedom. The acting forces consist of prescribed external forces and a priori unknown control forces. Prescribed boundary conditions add equations to the system to be solved.

    Dependent on the formulation of the problem, the solution method handles three basic classes of problems. These are distinguished by the number of boundary conditions on the displacements and velocities, and the number of free control force values. For the evolution problem, without control forces, the problem formulation must specify two values for each displacement component. For the fixed control problem, where a target state is desired, the number of free control force values is equal to the number of excessive boundary conditions, and their values can be determined. For an optimal control problem, the number of free control force values is higher than the number of excessive displacement conditions, allowing the optimization of their values.

    For all the three classes of problems, a set of equation is established. In the optimal control problem, the set will add equations of optimality, increasing the size of the problem; a general algorithm can, however, be easily established, where only the number of prescribed displacement values and the number of free control force components decide the used method.

    Performed tests indicate that the developed viewpoint and algorithm can be efficient in the study of complex, but primarily small to moderate size problems, with an improved continuity in the description of motion, and a good stability in dynamic solution. Comparing accuracy and computational effort, the method is efficient for a small problem, compared to Euler and Newmark methods, [1], and comparable to a Runge-Kutta 4th order method.

    The method avoids the common shooting procedure to find a target displacement state, by solving for all discrete time stations at once. For a target controlled non-linear mechanism problem, the convergence with discretization is studied, and shown to be quick, given that a reasonably good initial approximation can be introduced. The method also allows full Newton iterations, leading to high accuracy in results. Alternative local optima in control force cost are discussed, starting from a well-known problem, [2].

    With a sparse matrix for the established system, the efficiency of the method can in many cases be improved. Ongoing work expands the method to allow redundant force systems, limits in control force values, and interpolation of activation measures in the muscular system, rather than in forces themselves.

  • 43.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Temporal finite elements for target control dynamics of mechanisms2007In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 85, no 17-18, p. 1399-1408Article in journal (Refereed)
    Abstract [en]

    This paper discusses a temporal finite element description in the analysis of dynamics of mechanical systems, with a special emphasis on problems where target control is desired. This is defined as a situation where forces are sought for the movement of a structure from an initial to one or more specified target states. The primary applications lie in robotics and in bio-mechanical forward simulations of musculoskeletal systems. A temporal discretization of the movement and forces is introduced. By interpolating simultaneously displacements and velocities in the spatial discrete degrees of freedom, a collocation over the time interval can be used to decide the necessary system. The needed control can be optimized for chosen criteria on the integrated force components. The temporal interpolation of control forces and discrete displacements introduces a degree of continuity in the obtained results. The viewpoint allows variation of many aspects of problem formulation, and leads to efficient solutions for systems of high complexity but moderate size.

  • 44.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    USING EIGENVECTOR PROJECTIONS TO IMPROVE CONVERGENCE IN NON-LINEAR FINITE ELEMENT EQUILIBRIUM ITERATIONS.1987In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 24, no 3, p. 497-512Article in journal (Refereed)
    Abstract [en]

    In an earlier paper a method for calculation of non-linear structural response was described. A method for selective damping of solution components parallel to critical eigenvectors was proposed, reducing the risk for diverging equilibrium iterations. This method is, in the present paper, shown to be related to the 'dynamic relaxation' approach. The method has been further studied for practical problems, and especially adapted for the analysis of plate buckling. A method for variable damping is proposed, and compared to existing methods. The conclusions are that damping, based on eigenvector projection, is an efficient way to improve the stability in the iterations, and in this an alternative to other methods for choice of optimum corrections in N-R schemes. In the paper, suitable criteria for reformulation of the tangential relation during iterations in a step are also discussed.

  • 45.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Faroughi, Shirko
    Quasi-static inflation simulations based on a co-rotational triangular space membrane element2013In: International Journal of Structural Stability and Dynamics, ISSN 0219-4554, Vol. 13, no 3, p. 1250067-Article in journal (Refereed)
    Abstract [en]

    Co-rotational triangular space membrane elements are developed for the quasi-static analysis of very thin structures subjected to pressure loadings from compressible media, aiming primarily at simulations of inflation processes. By separating rigid body motion and deformational displacement, the major part of geometric nonlinearity is treated by a co-rotational filter. With the formulation, hyper-elastic and linear elastic material models are used in the local plane element expressions. Numerical experiments show that either material model can be used in the present context, but that the linearly elastic model demands an optimal reference system. The hyper-elastic form is useful also for very large expansions, but the neo-Hookean expression chosen has some limitations for large strains. Simulations are parameterized by internal over-pressure, but an amount of injected gas can be calculated from pressure and enclosed volume. The uniqueness and stability in the response of the structures must be seen as a function of either pressure or amount of gas, dependent on the precise mechanism for inflation.

  • 46.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics. Mid Sweden University, Sweden.
    Holmberg, H. -C
    Westerblad, H.
    A numerical model for fatigue effects in whole-body human exercise2015In: Mathematical and Computer Modelling of Dynamical Systems, ISSN 1387-3954, E-ISSN 1744-5051Article in journal (Refereed)
    Abstract [en]

    A physiology-based fatigue model was developed and tested, with the long-term objective to study optimal pacing strategies in cross-country skiing. The model considers both aerobic and anaerobic power contributions, with different demands for carbohydrate fuel. The fatigue model accumulates traces from anaerobic efforts, and dissipates fatigue exponentially. The current fatigue value affects the effective work rate output. A limited reservoir of fuel is considered. This paper discusses the numerical formulations. Examples show the relevance of the model for basic regimes of power output, and give qualitatively relevant results, but demonstrate the need for individual physiological parameters. Further examples study the model’s predictions with respect to interval training strategies, with conclusions on work rates and interval lengths.

  • 47.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Kouhia, R.
    On step size adjustments in structural continuation problems1995In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 55, no 3, p. 495-506Article in journal (Refereed)
    Abstract [en]

    Procedures for automatic step size control in non-linear structural equilibrium analyses are discussed. Some algorithms found in the literature are briefly described and compared. The main emphasis is given to the development of criteria for detecting the need for a change of the step size as early as possible. Hence, the size of the increment is controlled during the corrector phase. Two possible procedures for this are developed and compared. Both reduce the step size in highly curved parts of an equilibrium path. The performance of the proposed algorithm is demonstrated in some numerical examples, including both geometrical and material non-linearities. The conclusions are that a procedure for reduction of the step size within the step can give improved possibilities for convergence in the iterations. The need for suitable scaling of used variables in any continuation algorithm is also emphasized. © 1995.

  • 48.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Ludvigsson, Jan
    KTH.
    Datorn för byggnadskonstruktionarbete - metoder, möjligheter och risker1983Book (Other academic)
  • 49.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Marti, K.
    Müller-Hannemann, M.
    Topping, BHV.
    Mota-Soares, CA.
    Engineering computational technology2007In: Advances in Engineering Software, ISSN 0965-9978, E-ISSN 1873-5339, Vol. 38, no 11-12, p. 723-725Article in journal (Refereed)
  • 50.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Månsson, JohanKTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.Tibert, GunnarKTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    NSCM-17: Proceedings of the 17th Nordic Seminar on Computational Mechanics2004Conference proceedings (editor) (Refereed)
123 1 - 50 of 117
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