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  • 51.
    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.

  • 52.
    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.

  • 53.
    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)
  • 54.
    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)
  • 55.
    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)
  • 56.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Instability of hyper-elastic balloon-shaped space membranes under pressure loads2012In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 237, p. 118-129Article in journal (Refereed)
    Abstract [en]

    This paper discusses the evaluation of quasi-static equilibrium solutions for inflatable space membrane structures. A Mooney-Rivlin hyper-elastic material model, with variable constitutive constants, is considered. A compressible weightless medium is used to introduce within the membrane a one-parametric over-pressure loading compared to an ambient pressure. Analytical instability results are shown for a spherical and derived for a cylindrical case. These are compared to numerical simulations based on a flat linearly interpolated triangular space membrane element. 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 membranes, but that the medium and means for introducing the internal pressure are of importance for the interpretation of stability.

  • 57.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Instability of thin hyper-elastic space membranes under pressure loads2011In: Proceedings of TCCM-2011, 2011Conference paper (Refereed)
  • 58.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Non-unique response of Mooney-Rivlin model in bi-axial membrane stress2014In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 144, p. 12-22Article in journal (Refereed)
    Abstract [en]

    The commonly used two-parameter Mooney-Rivlin incompressible hyper-elastic material model can show non-intuitive responses under certain conditions. This paper shows that critical states with non-unique responses occur at least at very specific bi-axial stress states. This can happen for cases where the constant related to the second invariant of strain is positive, but not for the case with this constant equal to zero (the Neo-Hookean case). The dependence of the instabilities on the ratio between the two constitutive constants is shown by evaluated fold lines. The instability is shown to be related to the imposed boundary conditions. An analytical treatment of the problem shows that dynamic edge effects correspond to the static instability.

  • 59.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Symmetry aspects in stability investigations for thin membranes2016In: Computational Mechanics, ISSN 0178-7675, E-ISSN 1432-0924, Vol. 58, no 5, p. 747-767Article in journal (Refereed)
    Abstract [en]

    Modelling of structural instability problems is considered for thin square membranes subjected to hydrostatic pressure, with a focus on the effects from symmetry conditions considered or neglected in the model. An analysis is performed through group-theoretical concepts of the symmetry aspects present in a flat membrane with one-sided pressure loading. The response of the membrane is described by its inherent differential eigensolutions, which are shown to be of five different types with respect to symmetry. A discussion is given on how boundary conditions must be introduced in order to catch all types of eigensolutions when modelling only a subdomain of the whole. Lacking symmetry in a FEM model of the whole domain is seen as a perturbation to the problem, and is shown to affect the calculated instability response, hiding or modifying instability modes. Numerical simulations verify and illustrate the analytical results, and further show the convergence with mesh fineness of different aspects of instability results.

  • 60.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Temporal finite element formulation of optimal control in mechanisms2010In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 199, no 25-28, p. 1783-1792Article in journal (Refereed)
    Abstract [en]

    A temporal finite element discretization of a boundary value problem has several advantages compared to a time-integrating evolution form for optimized target movement simulations. The paper gives some basic aspects on how such a finite element form can be stated, with both displacements and controls discretized and seen as unknowns. Aspects on the resulting formulations are discussed. Important issues are the order, continuity and fineness of the discretizations. When the formulation is seen in an optimization context, minimizing the effort for a prescribed movement, the discretization affects the results obtained in several manners, where some aspects of results are artifacts. The paper discusses these effects from basic principles, but also verifies them in numerical simulations.

  • 61.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Patil, Amit
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Zhou, Yang
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Parametric stability investigations for hydro-statically loaded membranes2016In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 174, p. 33-41Article in journal (Refereed)
    Abstract [en]

    This paper discusses instabilities occurring 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. A hydro-static pressurization can give instabilities in the form 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. Numerical examples considering the pressurization of a flat and a cylindrical pre-stressed membrane illustrate some aspects of instability.

  • 62.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Pacoste, C.
    Zdunek, A.
    Numerical analysis of complex instability behaviour using incremental-iterative strategies1999In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 179, no 3-4, p. 265-305Article in journal (Refereed)
    Abstract [en]

    The paper describes how quasi-static, conservative instability problems can be analysed in a multi-parametric space, using generalised path-following procedures for augmented equilibrium problems. The general formulation of such augmented equilibrium problems is discussed in some detail. The focus is set on two classes of generalised 1D paths: basic equilibrium paths and fold lines, i.e. critical subset paths. The solution methods are seen as extensions to common incremental-iterative strategies, allowing the computation of subsets of equilibrium states which also fulfil some auxiliary conditions, e.g. criticality. In this context, some emphasis is also given to the evaluation of the properties of the problem, at a certain state; the tangential stiffness is here used to evaluate - possibly multidimensional - tangent spaces, and in the isolation of special states, i.e. vanishing variables, turning points and exchanges of stability, being important aspects of instability analyses. A set of carefully chosen numerical examples demonstrate on one hand the ability of the numerical procedures to deal with complex instability phenomena, including coincident or near coincident buckling modes, modal interaction, secondary bifurcations, and, on the other hand, their versatility in performing parameter sensitivity analyses. Finally, comparisons with alternative techniques, based on asymptotic strategies, are also put forth. © 1999 Elsevier Science S.A.

  • 63.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Svanberg, Krister
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Optimization in simulations of human movement planning2011In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 87, no 12, p. 1127-1147Article in journal (Refereed)
    Abstract [en]

    This paper discusses optimization algorithms in movement simulations for models of humans, humanoid robots or other mechanisms. Targeted movements between two configurations define a dynamically redundant system, for which there is freedom in the choice of control force time variations. A previously developed formulation for the treatment of targeted dynamics for mechanisms was used as a basis. The paper describes the development of an algorithm related to the method of moving asymptotes for the necessary optimization. The algorithm is specifically adapted to problems which are large and non-linear but sparse, and which include very high numbers of design variables as well as constraints. In particular, non-linear equality constraints from dynamic equilibrium equations are important. The optimization algorithm was developed to include these, but also in order to allow successively increasing penalty factors for constraint violations. The resulting setting was shown to be able to handle the systems established, robustly giving convergence to at least a local minimum also for very distant start iterates. The existence of very closely situated local optima, representing very similar movements, was discovered for the problem formulation, calling for an ad hoc method for finding the best of these local optima.

  • 64.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Thomasson, Per-Olof
    (KTH).
    On the behaviour of clamped plates loaded in comrpession. Some results from computer calculations.1987In: Proc. ECCS Int. Colloquium on stability of plates and shells, Ghent, 1987Conference paper (Refereed)
  • 65.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, GunnarKTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Proceedings of NSCM-23: the 23rd Nordic seminar on computational mechanics2010Conference proceedings (editor) (Other academic)
  • 66.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Redundant and force-differentiated systems in engineering and nature2006In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 195, no 41-43, p. 5437-5453Article in journal (Refereed)
    Abstract [en]

    Sophisticated load-carrying structures, in nature as well as man-made, share some common properties. A clear differentiation of tension, compression and shear is in nature primarily manifested in the properties of materials adapted to the efforts, whereas they in engineering are distributed on different components. For stability and failure safety, redundancy on different levels is also commonly used. The paper aims at collecting and expanding previous methods for the computational treatment of redundant and force-differentiated systems. A common notation is sought, giving and developing criteria for describing the diverse problems from a common structural mechanical viewpoint. From this, new criteria for the existence of solutions, and a method for treatment of targeted dynamic solutions are developed. Added aspects to previously described examples aim at emphasizing similarities and differences between engineering and nature, in the forms of a tension truss structure and the human musculoskeletal system.

  • 67.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Ölme, Rasmus
    KTH, School of Computer Science and Communication (CSC), Media technology and interaction design, MID.
    Functional movements2012In: (What´s) the matter with method, Kortrijk, Belgium, 2012Conference paper (Other academic)
  • 68.
    Eriksson, Marie
    et al.
    Karolinska Institutet, Dept. of Women's and Children's Health.
    Gutierrez-Farewik, Elena
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics. Karolinska Institutet.
    Broström, Eva
    Karolinska Institutet, Dept. of Women's and Children's Health.
    Bartonek, Åsa
    Karolinska Institutet, Dept. of Women's and Child's Health.
    Gait pattern in children with arthrogryposis multiplex congenita2010In: Journal of Children's Orthopaedics, ISSN 1863-2521, E-ISSN 1863-2548, Vol. 4, no 1, p. 21-31Article in journal (Refereed)
    Abstract [en]

    Purpose: Lower limb contractures and muscle weakness are common in children with arthrogryposis multiplex congenita (AMC). To enhance or facilitate ambulation, orthoses may be used. The aim of this study was to describe gait pattern among individuals wearing their habitual orthotic devices. Methods: Fifteen children with AMC, mean age 12. 4 (4. 3) years, with some lower limb involvement underwent 3-D gait analysis. Three groups were defined based on orthosis use; Group 1 used knee-ankle-foot orthoses with locked knee joints, Group 2 used ankle-foot orthoses or knee-ankle-foot orthoses with open knee joints and Group 3 used no orthoses. Results: The greatest trunk and pelvis movements in all planes and the greatest hip abduction were observed in Group 1, compared to Groups 2 and 3, as well as to the gait laboratory control group. Maximum hip extension was similar in Groups 1 and 2, but in Group 3, there was less hip extension and large deviations from the control data. Lower cadence and walking speed were observed in Group 1 than in Groups 2 and 3. The step length was similar in all groups and also with respect to the gait laboratory reference values. Conclusions: Children with AMC were subdivided according to orthoses use. Kinematic data as recorded with 3-D gait analysis showed differences among the groups in trunk, pelvis and knee kinematics, and in cadence and walking speed. The step length was similar in all groups and to the gait laboratory reference values, which may be attributable to good hip extension strength in all participants.

  • 69.
    Essén, Hanno
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Theoretical and Applied Mechanics.
    Sten, J. C. -E
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Magnetic energy of surface currents on a torus2013In: Progress in Electromagnetics Research B, ISSN 1937-6472, E-ISSN 1937-6472, no 46, p. 357-378Article in journal (Refereed)
    Abstract [en]

    The magnetic energy and inductance of current distribu-tions on the surface of a torus are considered. Specifically, we investigate the influence of the aspect ratio of the torus, and of the pitch angle for helical current densities, on the energy. We show that, for a fixed surface area of the torus, the energy experiences a minimum for a certain pitch angle. New analytical relationships are presented as well as a review of results scattered in the literature. Results for the ideally conducting torus, as well as for thin rings are given.

  • 70.
    Falk, Andreas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Architecture, Architectural Technologies.
    Samuelsson, Sture
    KTH, School of Architecture and the Built Environment (ABE), Architecture, Architectural Technologies.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Plate based tensegrity structures2005In: IASS 2005: Proceedings of the International Symposium on Shell and Spatial Structures, 2005Conference paper (Refereed)
  • 71. Faroughi, Shirko
    et al.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Co-rotational formulation for dynamic analysis of space membranes based on triangular elements2017In: International Journal of Mechanics and Materials in Design, ISSN 1569-1713, E-ISSN 1573-8841, Vol. 13, no 2, p. 229-241Article in journal (Refereed)
    Abstract [en]

    Nonlinear triangular space membrane elements are developed for the analysis of thin structures subjected to dynamic loading. By using a co-rotated framework, displacements are decomposed into rigid body motions and pure deformational displacements. The novelty of the formulation is that it employs the co-rotated framework to derive tangent dynamic matrix and an inertial force vector. Closed forms for the inertia force vector, the tangent dynamic matrix, the mass matrix and the gyroscopic matrix are derived directly from the current coordinate transformation matrix. Three numerical examples are presented to illustrate the robustness and efficiency of the new co-rotational formulation. The efficiency of the proposed approach is compared to the updated Lagrangian method, and savings in computation of up to 50 %, were achieved.

  • 72.
    Gärdsback, Mattias
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Deployment Control of Spinning Space Webs and Membranes2008Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Future solar sail and solar power satellite missions require deployment of large and lightweight flexible structures in space. One option is to spin the assembly and use the centrifugal force for deployment, stiffening and stabilization. Some of the main advantages with spin deployment are that the significant forces are in the plane of rotation, a relatively simple control can be used and the tension in the membrane or web can be adjusted by the spin rate to meet the mission requirements. However, a successful deployment requires careful development of new control schemes. The deployment rate can be controlled by a torque, applied either to a satellite in the center or by thrusters in the corners, or by deployment rate control, obtained by tether, spool braking or folding properties.

    Analytical models with only three degrees of freedom were here used to model the deployment of webs and membranes for various folding patterns and control schemes, with focus on space webs folded in star-like arms coiled around a center hub. The model was used to investigate control requirements and folding patterns and to obtain optimal control laws for centrifugal deployment. New control laws were derived from the optimal control results and previously presented control strategies. Analytical and finite element simulations indicate that the here developed control laws yield less oscillations, and most likely more robustness, than existing controls.

    Rotation-free (RF) shell elements can be used to model inflation or centrifugal deployment of flexible memebrane structures by the finite element method. RF elements approximate the rotational degrees of freedom from the out-of-plane displacements of a patch of elements, and thus avoid common singularity problems for very thin shells. The performance of RF shell elements on unstructured grids is investigated in the last article of this thesis, and it is shown that a combination of existing RF elements performs well even for unstructured grids.

  • 73.
    Gärdsback, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Deployment control of space webs2007In: Proceedings of the 20th Nordic Seminar on Computational Mechanics, 2007, p. 3.5-3.8Conference paper (Other academic)
  • 74.
    Gärdsback, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Deployment simulations of space webs2007In: Proceedings of the 6th European LS-DYNA Users' Conference, 2007, p. 1.111-1.120Conference paper (Other academic)
  • 75.
    Gärdsback, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Evaluation of triangular shell elements for thin membrane structures2005In: Proceedings of the 5th International Conference on Computation of Shell and Spatial Structures, 2005Conference paper (Other academic)
  • 76.
    Gärdsback, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Finding the most efficient rotation-free triangular shell element2005In: NSCM-18: Proceedings of the 18th Nordic Seminar on Computational Mechanics, 2005Conference paper (Other academic)
  • 77. Hernandez, Andres
    et al.
    Kosterina, Natalia
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Katz, Abe
    Westerblad, Håkan
    Oxidative stress restores force loss in skeletal muscle following eccentric contractions2010In: The FASEB Journal, ISSN 0892-6638, E-ISSN 1530-6860, Vol. 24Article in journal (Other academic)
  • 78. Hébert-Losier, K.
    et al.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Leg stiffness measures depend on computational method2014In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 47, no 1, p. 115-121Article in journal (Refereed)
    Abstract [en]

    Leg stiffness is often computed from ground reaction force (GRF) registrations of vertical hops to estimate the force-resisting capacity of the lower-extremity during ground contact, with leg stiffness values incorporated in a spring-mass model to describe human motion. Individual biomechanical characteristics, including leg stiffness, were investigated in 40 healthy males. Our aim is to report and discuss the use of 13 different computational methods for evaluating leg stiffness from a double-legged repetitive hopping task, using only GRF registrations. Four approximations for the velocity integration constant were combined with three mathematical expressions, giving 12 methods for computing stiffness using double integrations. One frequency-based method that considered ground contact times was also trialled. The 13 methods thus defined were used to compute stiffness in four extreme cases, which were the stiffest, and most compliant, consistent and variable subjects. All methods provided different stiffness measures for a given individual, but the between-method variations in stiffness were consistent across the four atypical subjects. The frequency-based method apparently overestimated the actual stiffness values, whereas double integrations' measures were more consistent. In double integrations, the choice of the integration constant and mathematical expression considerably affected stiffness values, as variations during hopping were more or less emphasized. Stating a zero centre of mass position at take-off gave more consistent results, and taking a weighted-average of the force or displacement curve was more forgiving to variations in performance. In any case, stiffness values should always be accompanied by a detailed description of their evaluation methods, as our results demonstrated that computational methods affect calculated stiffness.

  • 79.
    Jackson, Miranda
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Pearce, Mark
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kiss, Mózsi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Klamra, Wlodzimierz
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Mallol, Pau
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Bettolo, Cecilia Marini
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Rydström, Stefan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Varner, G.
    Yoshida, H.
    PoGOLite: a balloon-borne soft gamma-ray polarimeter2009In: 2009 IEEE NUCLEAR SCIENCE SYMPOSIUM CONFERENCE RECORD, VOLS 1-5  / [ed] Yu B, 2009, p. 449-453Conference paper (Refereed)
    Abstract [en]

    PoGOLite is a balloon-borne X-ray polarimeter, designed to measure the polarization of 25-80 keV X-rays. It is scheduled for a pathfinder flight in August 2010. This paper outlines the scientific motivation and the status of preparations of the payload.

  • 80.
    Kaphle, Manindra
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Optimal simulations for human and robotic movements2006In: Proc. NSCM-19, Lund, Sweden, 2006Conference paper (Refereed)
  • 81. Katz, Abram
    et al.
    Hernandez, Andres
    Ramos Caballero, Diana Marcela
    Bonilla Briceno, Javier Fernando
    Rivera Amezquita, Laura Victoria
    Kosterina, Natalia
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Bruton, Joseph D.
    Westerblad, Håkan
    Effects of N-acetylcysteine on isolated mouse skeletal muscle: contractile properties, temperature dependence, and metabolism2014In: Pflügers Archiv: European Journal of Physiology, ISSN 0031-6768, E-ISSN 1432-2013, Vol. 466, no 3, p. 577-585Article in journal (Refereed)
    Abstract [en]

    The effects of the general antioxidant N-acetylcysteine (NAC) on muscle function and metabolism were examined. Isolated paired mouse extensor digitorum longus muscles were studied in the absence or presence of 20 mM NAC. Muscles were electrically stimulated to perform 100 isometric tetanic contractions (300 ms duration) at frequencies resulting in similar to 85 % of maximal force (70-150 Hz at 25-40 A degrees C). NAC did not significantly affect peak force in the unfatigued state at any temperature but significantly slowed tetanic force development in a temperature-dependent fashion (e.g., time to 50 % of peak tension averaged 35 A +/- 2 ms [control] and 37 A +/- 1 ms [NAC] at 25 A degrees C vs. 21 A +/- 1 ms [control] and 52 A +/- 6 ms [NAC, P < 0.01] at 40 A degrees C). During repeated contractions, NAC maximally enhanced peak force by the fifth tetanus at all temperatures (by similar to 30 %). Thereafter, the effect of NAC disappeared rapidly at high temperatures (35-40 A degrees C) and more slowly at the lower temperatures (25-30 A degrees C). At all temperatures, the enhancing effect of NAC on peak force was associated with a slowing of relaxation. NAC did not significantly affect myosin light chain phosphorylation at rest or after five contractions (similar to 50 % increase vs. rest). After five tetani, lactate and inorganic phosphate increased about 20-fold and 2-fold, respectively, both in control and NAC-treated muscles. Interestingly, after five tetani, the increase in glucose 6-P was similar to 2-fold greater, whereas the increase in malate was inhibited by similar to 75 % with NAC vs. control, illustrating the metabolic effects of NAC. NAC slightly decreased the maximum shortening velocity in early fatigue (five to seven repeated tetani). These data demonstrate that the antioxidant NAC transiently enhances muscle force generation by a mechanism that is independent of changes in myosin light chain phosphorylation and inorganic phosphate. The slowing of relaxation suggests that NAC enhances isometric force by facilitating fusion (i.e., delaying force decline between pulses). The initial slowing of tension development and subsequent slowing of relaxation suggest that NAC would result in impaired performance during a high-intensity dynamic exercise.

  • 82.
    Khoshparvar, Soheil
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Bylander, Lars
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ivchenko, Nickolay
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Random vibration stress analysis of the BepiColombo boom deployment system2010In: Proceedings of the 23rd Nordic Seminar on Computational Mechanics / [ed] Anders Eriksson and Gunnar Tibert, Stockholm, Sweden: KTH Royal Institute of Technology, 2010, p. 108-111Conference paper (Other academic)
  • 83.
    Klets, Olesya
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Subject-specific musculoskeletal modeling of the lower extremities in persons with unilateral cerebral palsy2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The computational musculoskeletal models that are used to study muscle moment-generating capacities of persons with movement disorders and planning treatment options must be accurate, and take into account the inter-individual variability of musculoskeletal geometry.

    In Paper I the methods of creating the subject-specific musculoskeletal model of the lower extremities from magnetic resonance images (MRIs) were developed. The subject-specific model was used to analyze hip, knee and ankle muscle moment arms (MALs) and muscle-tendon lengths (MTLs) during gait in a subject with unilateral cerebral palsy (CP), and to evaluate the accuracy of widespread and commonly-used scaled generic model.

    It was found that the scaled generic model delivered accurate values for changes in MTLs in most muscles. However, the scaled generic and the subject-specific lower extremity musculoskeletal models showed substantial differences in MALs calculated during gait.

    In Paper II subject-specific musculoskeletal models of nine subjects with unilateral CP were created to study muscles volumes, MTLs and MALs; and to examine the accuracy of MALs calculated by the scaled generic models.

    It was shown that the scaled generic model significantly underestimated hip MALs discrepancies between the affected and the non-affected sides of the lower extremities. However, it significantly overestimated hip adduction/abduction of gluteus maximus, gluteus medius, gluteus minimus, tensor fascia latae and biceps femoris long head; and hip flexion of adductor longus and rectus femoris in the affected and the non-affected sides.

    It was also found that muscle volumes and hip abduction MALs in gluteus medius and gluteus minimus, hip flexion MALs in iliacus and hip rotation in gluteus maximus were smaller in the affected side of lower extremities. MTLs in the affected and the non-affected sides throughout the range of hip motion were similar.

    This thesis suggests the need for the subject-specific musculoskeletal models that can account for variability of muscle attachments and musculoskeletal geometry of persons with movement disorders. Based on inaccuracies of the scaled generic model reported here, the generic models that are used to guide treatment decisions must be tested, and interpreted with care.

  • 84.
    Klets, Olesya
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Riad, Jacques
    Department of Orthopaedics, Skaraborg Hospital, Skövde, Sweden.
    Broström, Eva W.
    Karolinska Intitutet, Dept. of Women's and Children's Health, Stockholm, Sweden.
    Gutierrez-Farewik, Elena
    KTH, School of Engineering Sciences (SCI), Mechanics, Biomechanics.
    Comparison between a subject-specific and a scaled generic musculoskeletal model of the lower extremities in a subject with unilateral cerebral palsy2011In: Clinical Biomechanics, ISSN 0268-0033, E-ISSN 1879-1271Article in journal (Other academic)
    Abstract [en]

    The purpose of this paper was to develop methods to build a subject-specific musculoskeletal model of the lower extremities based on MRIs of a subject with unilateral CP, and to determine whether a scaled generic musculoskeletal model is accurate enough to characterize MTLs and MALs of 70 muscles in both lower limbs during gait in a subject with unilateral cerebral palsy. We found, that the generic models produced accurate values for changes in MTL during gait for almost all muscles, except adductor longus, adductor magnus, adductor brevis, quadratus femoris, pectineus, extensor digitorum longus, soleus, lateral gastrocnemius, and medial gastrocnemius. MALs computed from the scaled generic model, however, differed considerably from those computed from the subject-specific model. Upon comparison of hip, knee and ankle MALs in affected and non-affected sides of the lower extremities, the scaled generic model generally failed to identify level arm dysfunction in the subject with unilateral CP

  • 85.
    Klets, Olesya
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Riad, Jacques
    Department of Orthopaedics, Skaraborg Hospital, Skövde, Sweden.
    Broström, Eva W.
    Karolinska Institutet, Dept. of Women's and Children's Health, Stockholm, Sweden.
    Gutierrez-Farewik, Elena
    KTH, School of Engineering Sciences (SCI), Mechanics, Biomechanics.
    Moment-generating biomechanical factors of hip muscles in persons with unilateral with subject-specific models2012In: Journal of Applied Biomechanics, ISSN 1065-8483, E-ISSN 1543-2688Article in journal (Other academic)
  • 86.
    Kosterina, Natalia
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Modelling of muscular force induced by non-isometric contraction2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The main objective of the study was to investigate and simulate skeletal muscleforce production during and after isometric contractions, active muscle lengtheningand active muscle shortening. The motivation behind this work was to improve thedominant model of muscle force generation based on the theories of Hill from 1938. Effects of residual force enhancement and force depression were observed after concentric and eccentric contractions, and also during stretch-shortening cycles. It wasshown that this force modification is not related to lengthening/shortening velocity, butinstead the steady-state force after non-isometric contractions can be well describedby an initial isometric force to which a modification is added. The modification isevaluated from the mechanical work performed by and on the muscle during lengthvariations. The time constants calculated for isometric force redevelopment appearedto be in certain relations with those for initial isometric force development, an observation which extended our basis for muscle modelling.

    A macroscopic muscular model consisting of a contractile element, and paralleland series elastic elements was supplemented with a history component and adoptedfor mouse soleus muscle experiments. The parameters from the experiment analysis, particularly the force modification after non-isometric contractions and the timeconstants, were reproduced by the simulations. In a step towards a general implementation, the history modification was introduced in the muscluloskeletal model ofOpenSim software, which was then used for simulations of full body movements.

  • 87.
    Kosterina, Natalia
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Wang, Ruoli
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Gutierrez Farewik, Lanie
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Force enhancement and force depression in a modified muscle model used for muscle activation prediction2013In: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 23, no 4, p. 759-765Article in journal (Refereed)
    Abstract [en]

    This article introduces history-dependent effects in a skeletal muscle model applied to dynamic simulations of musculoskeletal system motion. Force depression and force enhancement induced by active muscle shortening and lengthening, respectively, represent muscle history effects. A muscle model depending on the preceding contractile events together with the current parameters was developed for OpenSim software, and applied in simulations of standing heel-raise and squat movements. Muscle activations were computed using joint kinematics and ground reaction forces recorded from the motion capture of seven individuals. In the muscle-actuated simulations, a modification was applied to the computed activation, and was compared to the measured electromyography data. For the studied movements, the history gives a small but visible effect to the muscular force trace, but some parameter values must be identified before the exact magnitude can be analysed. The muscle model modification improves the existing muscle models and gives a more accurate description of underlying forces and activations in musculoskeletal system movement simulations.

  • 88.
    Kosterina, Natalia
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Westerblad, Håkan
    KI Fysiologi och farmakologi.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    History effect and timing of force production introduced in a skeletal muscle model2012In: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 11, no 7, p. 947-957Article in journal (Refereed)
    Abstract [en]

    Skeletal muscle modelling requires a detailed description of muscular force production. We have performed a series of experiments on mouse skeletal muscles to give a basis for an improved description of the muscular force production. Our previous work introduced a force modification in isometric phases, which was based on the work performed by or on the muscle during transient-length-varying contractions. Here, state-space diagrams were used to investigate the timing aspects of the force production. These show a dominant exponential nature of the force development in isometric phases of the contractions, reached after a non-exponential phase, assumed as an activation or deactivation stage and not further analysed here. The time constants of the exponential functions describing isometric force redevelopment after length variations appear to be related to the one for an initial isometric contraction, but depending on the previous history. The timing of force production calculated from the state-space diagrams was in agreement with the generally accepted muscle properties, thereby demonstrating the reliability of the method. A macroscopic muscular model consisting of a contractile element, parallel and series elastic elements was developed. The parameters from the experiment analysis, particularly the force modification after non-isometric contractions and the time constants, were reproduced by the simulations. The relationship between time constants introduced in a mechanistic model and the measured macroscale timings is discussed.

  • 89.
    Kosterina, Natalia
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Westerblad, Håkan
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Mechanical work as predictor of force enhancement and force depression2009In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 42, no 11, p. 1628-1634Article in journal (Refereed)
    Abstract [en]

    The steady-state force following active muscle shortening or stretch differs from the maximum isometric force associated with the final length. This phenomenon proves that the isometric force production is not only dependent on current muscle length and length time derivative, but depends on the preceding contraction history. Isolated extensor digitorum longus and soleus muscles from mice (NMRI strain) were used to investigate the force produced by a muscle, and some parameters hypothetically influencing this history-dependent force modification. The muscles were pre-stimulated at a fixed length, then different stretch/shortening episodes were introduced, whereafter changes of the active force were recorded while the muscles were held isometrically to approach a steady-state force before de-stimulation. The mechanical work during active stretch and shortening was evaluated by integrating the product of force and ramp velocity over the length-varying period. The results show a negative linear correlation between the force modification and the mechanical work produced on or by the muscle, continuous between shortening and stretch. A corresponding modification of the passive force component following each stimulation was also observed. The conclusion is that the isometric force attained after stretch or shortening is well described by an asymptotic force which is determined by the mechanical work.

  • 90.
    Kosterina, Natalia
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Westerblad, Håkan
    Lannergren, Jan
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Muscular force production after concentric contraction2008In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 41, no 11, p. 2422-2429Article in journal (Refereed)
    Abstract [en]

    The steady-state force following active shortening does not reach the maximum isometric force associated with the final length. Isolated extensor digitorum longus and soleus muscles from mice (NMRI strain) were used to investigate the force produced by a muscle, and some parameters hypothetically influencing this shortening-induced force depression. The muscles were pre-stimulated at fixed length, shortened and then held isometrically to give maximum post-shortening forces, before de-stimulation. The shortening magnitude was 0.18. 0.36 or 0.72 mm (about 2-7% of optimal length), time of shortening was chosen as 0.03, 0.06 and 0.12 s, and final length as +0.72. 0 and -0.72mm, related to optimal length. The mechanical work during active shortening was evaluated by integrating the product of force and shortening velocity over the shortening period. The results show a positive correlation between the force depression and the mechanical work. whereas the force depression was not correlated to the velocity of shortening. Depression of the passive force component was also observed following all stimulations. Experiments show that the fully stimulated redevelopment of isometric force following concentric contraction follows a time function similar to the creation of force when isometric muscle is initially stimulated. The conclusion is that the isometric force development after active shortening can be well described by an asymptotic force which is decided by the produced work, and the initial isometric time constant.

  • 91. Kullen, A.
    et al.
    Buchert, S.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Johansson, T.
    Lileo, S.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nilsson, H.
    Marchaudon, A.
    Fazakerley, A. N.
    Plasma transport along discrete auroral arcs and its contribution to the ionospheric plasma convection2008In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 26, no 11, p. 3279-3293Article in journal (Refereed)
    Abstract [en]

    The role of intense high-altitude electric field (E-field) peaks for large-scale plasma convection is investigated with the help of Cluster E-field, B-field and density data. The study covers 32 E-field events between 4 and 7 R-E geocentric distance, with E-field magnitudes in the range 500 1000 mV/m when mapped to ionospheric altitude. We focus on E-field structures above the ionosphere that are typically coupled to discrete auroral arcs and their return current region. Connected to such E-field peaks are rapid plasma flows directed along the discrete arcs in opposite directions on each side of the arc. Nearly all the E-field events occur during active times. A strong dependence on different substorm phases is found: a majority of intense E-field events appearing during substorm expansion or maximum phase are located on the night-side oval, while most recovery events occur on the dusk-to-dayside part of the oval. For most expansion and maximum phase cases, the average background plasma flow is in the sunward direction. For a majority of recovery events, the flow is in the anti-sunward direction. The net plasma flux connected to a strong E-field peak is in two thirds of the cases in the same direction as the background plasma flow. However, in only one third of the cases the strong flux caused by an E-field peak makes an important contribution to the plasma transport within the boundary plasma sheet. For a majority of events, the area covered by rapid plasma flows above discrete arcs is too small to have an effect on the global convection. This questions the role of discrete auroral arcs as major driver of plasma convection.

  • 92. Lidbeck, Cecilia M.
    et al.
    Gutierrez-Farewik, Elena
    KTH, School of Engineering Sciences (SCI), Mechanics, Biomechanics. KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Broström, Eva
    Karolinska Institutet, Stockholm, Sweden .
    Bartonek, Åsa
    Karolinska Institutet, Stockholm, Sweden .
    Postural Orientation During Standing in Children With Bilateral Cerebral Palsy2014In: Pediatric Physical Therapy, ISSN 0898-5669, E-ISSN 1538-005X, Vol. 26, no 2, p. 223-229Article in journal (Refereed)
    Abstract [en]

    Purpose: To investigate postural orientation and maintenance of joint position during standing in children with bilateral spastic cerebral palsy (BSCP). Methods: Standing was examined with 3-D motion analysis in 26 children with BSCP, and 19 children typically developing (TD). Two groups of children with cerebral palsy (CP) were analyzed: 15 who were able to maintain standing without support and 11 who needed support. Results: Children with CP stood with more flexion than children TD. In the CP groups, children standing without support stood more asymmetrically with less hip and knee flexion and less movement than those who required support. Conclusion: Children with CP had varying abilities to stand and maintain standing posture with or without support. Both CP groups stood with more flexion than their potential passive joint angle, more obvious in children requiring support. Investigations on how muscle strength and spatial perception influence posture remains to be explored.

  • 93.
    Ljubimova, Darja
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Biomechanics of the Human Eye and Intraocular Pressure Measurements2009Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis addresses the reliability of Goldmann-type applanation tonometers (GAT). It deals with the investigation of the relation between predicted intraocular pressure, IOPG and true pressure, IOPT. The problem of the accuracy of GAT readings has acquired special importance over the last two decades as new types of surgical procedures to correct vision disorders are being explored and gain universal acceptance. The overall aim of the present study is to assess the effects of individual variations in the corneal central thickness (CCT), material properties of the involved tissues and paracentral applanation on the accuracy of IOPG.

    Two finite element models have been constructed: a two-dimensional axisymmetric model of the cornea and a three-dimensional model of the whole corneoscleral envelope. Various material descriptions were adopted for the cornea in 2D, whereas the 3D model accounted for collagen microstructure and represented a hyperelastic ber reinforced material. Nonlinear analyses were carried out using the commercial general-purpose finite element software ABAQUS. An extensive literature survey and consultations with ophthalmologists and clinicians were the platform for establishing relevant modelling procedures.

    The results reveal a clear association between all considered parameters and measured IOPG. The effect of assumed CCT is highly dependent on the corneal material properties. Material model alone has a profound effect on predicted IOPG. Variations in tonometer tip application produce clinically signi cant errors to IOPG measurements. Potential effects of corneal stiffness and paracentral applanation on GAT readings are larger than the impact of CCT. The behaviour of the models is broadly in agreement with published observations. The proposed procedures can be a useful tools for suggesting the magnitudes of corrections for corneal biomechanics and possible human errors. The present modelling exercise has an ability to reproduce the behaviour of human cornea and trace it under IOP and GAT, providing potentially useful information on the distribution of stresses and strains. Some recommendations can be drawn in pursuit of the clinical imperatives of ophthalmologists.

  • 94.
    Ljubimova, Darja
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Numerical modelling of the human eye accommodation2005Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis addresses the biomechanics of the human eye accommodation. It deals with the development of numerical model of a 29-year-old eye, incorporating the vitreous body as a part of accommodative apparatus. A more complete understanding of the mechanism of accommodation becomes increasingly important as new types of lens implants and surgical procedures to correct both accommodative loss in aphakia as well as in the aging process are being explored. It is necessary to conduct the experimental and analytical studies to gain a better comprehension on ophthalmologic processes. The accommodation has been investigated through numerical simulations based on finite element analysis. The extensive literature survey was the platform for establishing relevant modelling procedures. The calculations were carried out using the commercial general-purpose finite element software ABAQUS. All materials were modelled as being linearly elastic and the interiors on the lens and vitreous were assumed to be incompressible. Present research seeks to investigate the validity of some fundamental assumptions about the construction and functioning of human accommodation system. The model is rather general and involves the synthesis of disparate sets of geometric and mechanical data from a variety of published sources. Different configurations of the structural model can easily be simulated by appropriate adjustments of parameters. The results of this study are broadly in agreement with published observations. The model behaviour is consistent with classical Helmholtz theory. It is shown that such a modelling exercise captures at least some physiological aspects of human accommodation. The proposed procedures and developed inverse methodology can be a useful tool to derive previously not documented parameters and test the consistency of different sets of experimental measurements. The obtained results can be used to draw some recommendations in pursuit of the clinical imperatives of ophthalmologists.

  • 95.
    Ljubimova, Darja
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Bauer, Svetlana
    Aspects of eye accommodation evaluated by finite elements2008In: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 7, no 2, p. 139-150Article in journal (Refereed)
    Abstract [en]

    Axisymmetric nonlinear finite models of accommodation incorporating the posteriorly sloped force and vitreous effects have been studied by means of their effectiveness in mechanical and optical performances. All materials were assumed to be linearly elastic, vitreous and lens matrices were incompressible. The present model is subjected to certain indicated shortcomings, however, the behavior of the model is predictable, reasonable and favourably consistent with different published data, supporting the Helmholtz theory of accommodation.

  • 96.
    Ljubimova, Darja
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Bauer, Svetlana
    Numerical study of the effect of vitreous support on eye accommodation2005In: Acta of Bioengineering and Biomechanics, ISSN 1509-409X, Vol. 7, no 2, p. 3-15Article in journal (Refereed)
    Abstract [en]

    The aim of the current work was to extend previously created finite element models of accommodation such as the one by BURD [2] by addition of vitreous. The zonule consisted of anterior and central sets and vitreous was modelled as a linear clastic incompressible body. An inverse method was used to find some important, previously not documented, aspects. The model was found to behave according to the expectations, with results consistent with classical Helmholtz theory.

  • 97.
    Magnusson, Patrick
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Reid, William
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Achert, Peggy
    Stockholm University.
    Ivchenko, Nickolay
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lindén, Erik
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Shepenkov, Valeriy
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Preliminary results from the RAIN mesospheric and stratospheric aerosol particle collection experiment launched on REXUS-112013In: 21st ESA Symposium: European Rocket & Balloon Programmes and Related Research / [ed] L. Ouwehand, ESTEC, Noordwijk, The Netherlands: ESA Communications , 2013, p. 511-517Conference paper (Refereed)
    Abstract [en]

    The RAIN (Rocket deployed Atmospheric probes conducting Independent measurements in Northern Sweden) experiment demonstrates a technique for collecting aerosol particles in the middle atmosphere using multiple probes ejected from a sounding rocket. Collection samples on each probe are exposed over varying height ranges between 80 and 22 km giving an altitude distribution profile of aerosol particles. The experiment was launched on board the REXUS-11 sounding rocket on November 16, 2012 from Esrange Space Centre. The experiment operated nominally and was recovered. Initial scanning electron microscopy analysis of the collection samples indicates that aerosols were collected during the fall, however detailed analysis over all height ranges is ongoing.

  • 98.
    Mallol Parera, Pau
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Deployment Simulations of a Composite Boom for Small Satellites2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The use of small satellites is rapidly growing, especially satellites with masses between 1 and 10 kg and few litres of volume. The main reasons are due to the low development time and cost. Electronics miniaturization and high density integration is enabling the small satellites class to perform more and better tasks and at a lower cost. When deployable structures are required for the missions, the actual paradigm is that there are very few that have been successfully developed and flown. It is usually not possible to scale down existing deployable structures from larger satellites. Power and attitude control is also very limited in small satellites thus, completely new deployable structures, low mass and with high packaging ratio (yet large and with adequate mechanical properties when deployed) must be developed. Furthermore, such new structures are usually made of very thin and light materials which complicates the on-ground tests prior the launch. Therefore, advances in modelling and simulation deployable structures such as booms are also of great interest for the scientific community.

    This thesis and the papers included herein focus on the finite element modelling of a meter-class passively deployable boom – based on the SIMPLE boom by Thomas W. Murphey – and deployment simulations. Experimental tests were also carried on a boom prototype suspended from a gravity off-loading system. An analytical model produced certain parameters which are used for validation of the finite element model. The strain energy stored in the boom prior to deployment and spacecraft displacements during deployment agreed well. The deployment time, however, have discrepancies: the models predicted a deployment time six times faster than the experimental tests. For that reason the deployment simulations cannot be compared with the tests. The reason of the discrepancies are believed to be due to the actual material model and the contacts formulation used in the finite element model. The finite element simulations, however, shows a reasonable behaviour given the nature of the deployment thus, despite the necessary improvements, we believe that future improvements in the material and friction models will provide us more realistic results.

  • 99.
    Mallol, Pau
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Deployment modeling and experimental testing of a Bi-stable composite boom for small satellites2013In: 54th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, American Institute of Aeronautics and Astronautics, 2013Conference paper (Refereed)
    Abstract [en]

    The rapidly growing use of nano- and pico-satellites for space missions requires deployable systems to be highly storable yet large and with adequate mechanical properties when deployed. This paper focuses on the modeling and simulation of a meter-class passively deployable boom - based on the SIMPLE boom by Thomas W. Murphey - exploiting the bi-stable nature of composite shells. Experimental tests were also carried on a boom prototype suspended in a gravity off-loading system. The strain energy level, deployment time and spacecraft displacements of the models agree well with analytical analyses, confirming the theoretical accuracy of the finite element model. However, the simulations show that the boom deploys six times faster than the real prototype. The quick deployment and violent end-of-deployment shock provokes the boom deployment dynamics to be unrealistic but still shows a reasonable behavior given the nature of the deployment. Future improvements in the material and friction models will, most likely, provide us with a more realistic finite element model.

  • 100.
    Mallol, Pau
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, GunnarKTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Deployment modelling and experimental testing of a bi-stable composite boom for small satellites2013Conference proceedings (editor) (Other academic)
    Abstract [en]

    The rapidly growing use of nano- and pico-satellites for space missions requires deployable systems to be highly storable yet large and with adequate mechanical properties when deployed. This paper focuses on the modelling and simulation of a meter-class passively deployable boom – based on the SIMPLE boom by Thomas W. Murphey – exploiting the bi-stable nature of composite shells. Experimental tests were also carried on a boom prototype suspended in a gravity off-loading system. The strain energy level, deployment time and spacecraft displacements of the models agree well with analytical analyses, confirming the theoretical accuracy of the finite element model. However, the simulations show that the boom deploys six times faster than the real prototype. The quick deployment and violent end-of-deployment shock provokes the boom deployment dynamics to be unrealistic but still shows a reasonable behaviour given the nature of the deployment. Future improvements in the material and friction models will, most likely, provide us with a more realistic finite element model.

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