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  • 101.
    Mallol, Pau
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Explicit dynamics simulations of the deployment of a composite boom for small satellitesManuscript (preprint) (Other academic)
  • 102.
    Manda, Krishnagoud
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Finite Element Simulations of Biphasic Articular Cartilages With Localized Metal Implants2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Articular cartilage is a specialized connective soft tissue that resides onthe ends of long-bones, transfers the load smoothly between the bones in diarthrodialjoints by providing almost frictionless, wear resistant sliding surfacesduring joint articulation. Focal chondral or osteochondral defects in articularcartilage are common and show limited capacity for biological repair. Furthermore,changes in the bio-mechanical forces at the defect site may makethe tissue more susceptible to continued degeneration. Alternatively, the contouredfocal resurfacing metal implant can be used to treat such full thicknesscartilage defects. Physiological and biomechanical studies on animal modelswith metal implant have shown good clinical outcomes. However, the mechanicalbehavior of cartilage surrounding the implant is not clearly known withrespect to the joint function after treating such defects with metal implantsand also to improve the implant design. We developed a simple 3-dimensionalfinite element model by approximating one of the condyles of the sheep kneejoint. Parametric study was conducted in the simulations to verify differentprofiles for the implant, positioning of the implant with respect to cartilagesurface, defect size and to show the mechanical sealing effect due to the wedgeshape of the implant. We found the maximal deformations, contact pressuresand stresses which constitute the mechanical behavior of cartilages. We alsoconfirmed that using a metal implant to fill the full thickness chondral defectsis more beneficial than to leave the defect untreated from mechanical point ofview. The implant should be positioned slightly sunk into the cartilage basedon the defect size, in order to avoid damage to the opposing surface. The largerthe defect size, the closer the implant should be to the flush. We also simulatedthe time dependent behavior of the cartilages. In all the simulations, a staticaxial loading was considered. The wedge shape of the implant provided themechanical sealing of the cartilage surrounding the implant. The determineddeformations in the cartilages immediately surrounding the implant are instrumentalin predicting the sticking-up of the implant into the joint cavity whichmay damage opposing soft tissues.

  • 103.
    Manda, Krishnagoud
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Modeling of articular cartilage growth around localized defect-filling metal implantIn: Journal of Biomechanical Engineering, ISSN 0148-0731, E-ISSN 1528-8951Article in journal (Other academic)
  • 104.
    Manda, Krishnagoud
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Simulating metal implants in full thickness cartilage defects2011In: ASME 2011 Summer Bioengineering Conference, SBC 2011, 2011, no PARTS A AND B, p. 1265-1266Conference paper (Refereed)
  • 105.
    Manda, Krishnagoud
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Time-dependent behavior of cartilage surrounding a metal implant for full-thickness cartilage defects of various sizes: a finite element study2012In: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 11, no 5, p. 731-742Article in journal (Refereed)
    Abstract [en]

    Recently, physiological and biomechanical studies on animal models with metal implants filling full-thickness cartilage defects have resulted in good clinical outcomes. The knowledge of the time-dependent macroscopic behavior of cartilage surrounding the metal implant is essential for understanding the joint function after treating such defects. We developed a model to investigate the in vivo time-dependent behavior of the tibiofemoral cartilages surrounding the metal implant, when the joint is subjected to an axial load for various defect sizes. Results show that time-dependent effects on cartilage behavior are significant, and can be simulated. These effects should be considered when evaluating the results from an implant. In particular, the depth into the cartilage where an implant is positioned and the mechanical sealing due to solidification of the poroelastic material need a time aspect. We found the maximal deformations, contact pressures and contact forces in the joint with time for the implant positioned in flush and sunk 0.3 mm into the cartilage. The latter position gives the better joint performance. The results after 60 s may be treated as the primary results, reflecting the effect of accumulation in the joint due to repeated short-time loadings. The wedge-shaped implant showed beneficial in providing mechanical sealing of cartilages surrounding the implant with time.

  • 106.
    Manda, Krishnagoud
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Ryd, Leif
    Department of Orthopaedics, Karolinska University Hospital/Huddinge and Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Sweden.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Finite element simulations of a focal knee resurfacing implant applied to localized cartilage defects in a sheep model2011In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 44, no 5, p. 794-801Article in journal (Refereed)
    Abstract [en]

    Articular resurfacing metal implants have recently been tested in animal models to treat full thickness localized articular cartilage defects, showing promising results. However, the mechanical behavior of cartilage surrounding the metal implant has not been studied yet as it is technically challenging to measure in vivo contact areas, pressures, stresses and deformations from the metal implant. Therefore, we implemented a detailed numerical finite element model by approximating one of the condyles of the sheep tibiofemoral joint and created a defect of specific size to accommodate the implant. Using this model, the mechanical behavior of the surrounding of metal implant was studied. The model showed that the metal implant plays a significant role in the force transmission. Two types of profiles were investigated for metal implant. An implant with a double-curved profile, i.e., a profile fully congruent with the articular surfaces in the knee, gives lower contact pressures and stresses at the rim of the defect than the implant with unicurved spherical profile. The implant should be placed at a certain distance into the cartilage to avoid damage to opposing biological surface. Too deep positions, however, lead to high shear stresses in the cartilage edges around the implant. Mechanical sealing was achieved with a wedge shape of the implant, also useful for biochemical sealing of cartilage edges at the defect.

  • 107.
    Martinsson Achi, Lina
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Architecture, Architectural Technologies.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    A graph theoretical methodology for conceptual design2012In: IASS-APCS 2012: Proceedings of the International Symposium on Shell and Spatial Structures, 2012Conference paper (Refereed)
  • 108. Murans, Girts
    et al.
    Gutierrez-Farewik, Elena M.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Saraste, Helena
    Kinematic and kinetic analysis of static sitting of patients with neuropathic spine deformity2011In: Gait & Posture, ISSN 0966-6362, E-ISSN 1879-2219, Vol. 34, no 4, p. 533-538Article in journal (Refereed)
    Abstract [en]

    Wheelchair dependent children with neuropathic and neuromuscular diseases have up to 90% risk for progressive spine deformities. An unbalanced sitting can induce progression of spinal and pelvic deformities. Many current clinical assessment methods of sitting of such patients are semi-quantitative, or questionnaire-based. A 3D movement analysis offers quantitative and objective biomechanical analysis of sitting. The aim was to validate a method to describe quiet sitting and differences between patients and controls as well as to apply the methodology for pre- and post-operative comparison. The analysis was performed on 14 patients and 10 controls. Four patients were retested after spine surgery. Seat load asymmetry was up to 30% in the patient group comparing to maximum 7% in the control group. The asymmetric position of Ground Reaction Force vector between left and right sides was significant. Plumb line of cervical 7th vertebra over sacral 1st was different only in rotation. The location of Common Center of Pressure relative to inter-trochanteric midpoint was more anterior in controls than in patients. Pelvic inclination in patients was smaller, the obliquity and rotation was similar. There were no significant differences between patients and controls of the thorax position. Results with more changes in the seat-loading domain in comparison with posture indicate good postural control compensation of spinal deformity induced disequilibrium despite neuromuscular disease in the background. The comparison of the pelvic obliquity data from kinematics and X-ray showed good correlation. The four patients tested postoperatively improved after surgery.

  • 109. Pacoste, C.
    et al.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Element behavior in post-critical plane frame analysis1995In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 125, no 1-4, p. 319-343Article in journal (Refereed)
    Abstract [en]

    Depending on the type of uni-modal (cuspoid) catastrophe which governs the local behavior of a structure at a simple critical point, correct prediction of the post-critical path requires an accurate estimation of a number of terms in the Taylor series expansion of the total potential function at the critical point. This imposes certain conditions on the accuracy of the adopted non-linear elements. These conditions are mainly related to the quality of the kinematic assumptions which underlie the strain definition used in the model. If these assumptions are not accurate enough, the fourth and higher order terms in the Taylor expansion of the total potential function will not be correctly represented. As a consequence, the model will fail to predict correctly even the initial post-buckling behavior whenever the criticality at hand is more complex than the fold (limit point, asymmetric bifurcation). This proves to be the case for the so-called 'technical' beam models. This inability is inherited by any constructed finite element model, regardless of the interpolation function used in its definition and of the number of elements used in the discretization. An improved non-linear model based on the treatment by Antman (Bifurcation problems in non-linearly elastic structures, in: P.H. Rabinowitz, ed., Application of Bifurcation Theory, Academic Press, NY, 1977), is adopted, and several finite elements are developed on the basis of this model. These elements are tested for a number of problems for which the critical behavior is governed by fold, cusp and butterfly singularities. The numerical results outline the importance of the 'small' kinematic terms, especially in conjunction with the occurrence of higher-order uni-modal singularities. Some risks for numerical locking are pointed out and remedied. The recommended element leads to a computational cost, which is comparable to an implemented 'shallow arch' element. © 1995.

  • 110. Pacoste, C.
    et al.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Element behavior in post-critical plane frame analysis1995In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 125, no 1-4, p. 319-343Article in journal (Refereed)
    Abstract [en]

    Depending on the type of uni-modal (cuspoid) catastrophe which governs the local behavior of a structure at a simple critical point, correct prediction of the post-critical path requires an accurate estimation of a number of terms in the Taylor series expansion of the total potential function at the critical point. This imposes certain conditions on the accuracy of the adopted non-linear elements. These conditions are mainly related to the quality of the kinematic assumptions which underlie the strain definition used in the model. If these assumptions are not accurate enough, the fourth and higher order terms in the Taylor expansion of the total potential function will not be correctly represented. As a consequence, the model will fail to predict correctly even the initial post-buckling behavior whenever the criticality at hand is more complex than the fold (limit point, asymmetric bifurcation). This proves to be the case for the so-called 'technical' beam models. This inability is inherited by any constructed finite element model, regardless of the interpolation function used in its definition and of the number of elements used in the discretization. An improved non-linear model based on the treatment by Antman (Bifurcation problems in non-linearly elastic structures, in: P.H. Rabinowitz, ed., Application of Bifurcation Theory, Academic Press, NY, 1977), is adopted, and several finite elements are developed on the basis of this model. These elements are tested for a number of problems for which the critical behavior is governed by fold, cusp and butterfly singularities. The numerical results outline the importance of the 'small' kinematic terms, especially in conjunction with the occurrence of higher-order uni-modal singularities. Some risks for numerical locking are pointed out and remedied. The recommended element leads to a computational cost, which is comparable to an implemented 'shallow arch' element. © 1995.

  • 111.
    Patil, Amit
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Inflation Mechanics of Hyperelastic Membranes2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The applications of inflatable membrane structures are increasing rapidly in the various fields of engineering and science. The geometric, material, force and contact non-linearities complicate this subject further, which in turn increases the demand for computationally efficient methods and interpretations of counter-intuitive behaviors noted by the  scientific community. To understand the complex behavior of membranes in biological and medical engineering contexts, it is necessary to understand the mechanical behavior of a membrane from a physics point of view. 

    The first part of the  present work studies the pre-stretched circular membrane in contact with a soft linear substrate. Adhesive and frictionless contact conditions are considered during inflation, while only adhesive contact conditions are considered during deflation. The peeling of membrane during deflation is studied, and a numerical formulation of the energy release rate is proposed. It is observed that the pre-stretch is having a considerable effect on the variation of the energy release rate.

    In the second part, free and constrained inflation of a cylindrical membrane is investigated. Adhesive and frictionless contact conditions are considered between the membrane and substrate. It is observed that the continuity of principal stretches and stresses depend on contact conditions and the inflation/deflation phase. The adhesive traction developed during inflation and deflation arrests the axial movement of material points, while an adhesive line force created at the contact boundary is responsible for a jump in stretches and stresses at the contact boundary. The pre-stretch produces a softening effect in free and constrained inflation of cylindrical membranes.

    The third part of the thesis discusses the instabilities observed for fluid containing cylindrical membranes. Both limit points and bifurcation points are observed on equilibrium branches. The secondary branches emerge from bifurcation points, with their directions determined by an eigen-mode injection method. The occurrence of critical points and the stability of equilibrium branches are determined by perturbation techniques. The relationship between eigenvalue analysis and symmetry is highlighted in this part of the thesis.

  • 112.
    Patil, Amit
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Dasgupta, A.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Contact mechanics of a circular membrane inflated against a deformable substrate2015In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 67-68, p. 250-262Article in journal (Refereed)
    Abstract [en]

    Finite inflation of a hyperelastic flat circular membrane against a deformable adhesive substrate and peeling upon deflation are analyzed. The membrane material is considered to be a homogeneous, isotropic and incompressible Mooney-Rivlin solid. The deformable substrate is assumed to be a distributed linear stiffness in the direction normal to the undeformed surface. The adhesive contact is considered to be perfectly sticking with no tangential slip between the dry surfaces of the membrane and the substrate. The inflation mechanics problem in the variational form yields the governing equations and boundary conditions, which are transformed to a nonlinear two-point boundary value problem by a careful choice of field variables for efficient computation. It is found that during inflation (deflation) with adhesive contact, the meridional stretch exhibits continuity up to C0 (C-1) at the contact junction, while the circumferential stretch remains continuous up to C1 (C0). Interestingly, stretch locking in an adhesive contact is found to give a higher indentation on the substrate than in a frictionless contact. Peeling at the contact junction has been studied, and numerical formulations for the energy release rate are proposed.

  • 113.
    Patil, Amit
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    DasGupta, Anirvan
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Contact Mechanics of a Circular Membrane Inflated Against a Soft Adhesive Substrate2014In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146Article in journal (Other academic)
  • 114.
    Patil, Amit
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Free and constrained inflation of a pre-stretched cylindrical membrane2014In: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences, ISSN 1364-5021, E-ISSN 1471-2946, Vol. 470, no 2169, p. UNSP 20140282-Article in journal (Refereed)
    Abstract [en]

    This paper presents the free and constrained inflation of a pre-stretched hyperelastic cylindrical membrane and a subsequent constrained deflation. The membrane material is assumed as a homogeneous and isotropic Mooney-Rivlin solid. The constraining soft cylindrical substrate is assumed to be a distributed linear stiffness normal to the undeformed surface. Both frictionless and adhesive contact are modelled during the inflation as an interaction between the dry surfaces of the membrane and the substrate. An adhesive contact is modelled during deflation. The free and constrained inflation yields governing equations and boundary conditions, which are solved by a finite difference method in combination with a fictitious time integration method. Continuity in the principal stretches and stresses at the contact boundary is dependent on the contact conditions and inflation-deflation phase. The pre-stretch has a counterintuitive softening effect on free and constrained inflation. The variation of limit point pressures with pre-stretch and the occurrence of a cusp point is shown. Interesting trends are observed in the stretch and stress distributions after the interaction of the membrane with soft substrate, which underlines the effect of material parameters, pre-stretch and constraining properties.

  • 115.
    Patil, Amit
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Instability investigation on fluid-loaded pre-stretched cylindrical membranes2015In: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences, ISSN 1364-5021, E-ISSN 1471-2946, Vol. 471, no 2177, article id 20150016Article in journal (Refereed)
    Abstract [en]

    This paper discusses the evaluation of instabilities on the quasi-static equilibrium path of fluid-loaded pre-stretched cylindrical membranes and the switching to a secondary branch at a bifurcation point. The membrane is represented by only the in-plane stress components, for which an incompressible, isotropic hyperelastic material model is assumed. The free inflation problem yields governing equations and boundary conditions, which are discretized by finite differences and solved by a Newton-Raphson method. An incremental arclength-cubic extrapolation method is used to find generalized equilibrium paths, with different parametrizations. Limit points and bifurcation points are observed on the equilibrium path when fluid level is seen as the controlling parameter. An eigen-mode injection method is employed to switch to a secondary equilibrium branch at the bifurcation point. A limit point with respect to fluid level is observed for a partially filled membrane when the aspect ratio (length/radius) is high, whereas for smaller aspect ratios, the limit point with respect to fluid level is observed at over-filling. Pre-stretch is observed to have a stiffening effect in the pre-limit zone and a softening effect in the post-limit zone.

  • 116.
    Patil, Amit
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Wrinkling of cylindrical membranes with non-uniform thickness2015In: European journal of mechanics. A, Solids, ISSN 0997-7538, E-ISSN 1873-7285, Vol. 54, p. 1-10Article in journal (Refereed)
    Abstract [en]

    Thin membranes are prone to wrinkling under various loading, geometric and boundary conditions, affecting their functionality. We consider a hyperelastic cylindrical membrane with non-uniform thickness pressurized by internal gas or fluid. When pre-stretched and inflated, the wrinkles are generated in a certain portion of the membrane depending on the loading medium and boundary conditions. The wrinkling is determined through a criterion based on kinematic conditions obtained from non-negativity of Cauchy principal stresses. The equilibrium solution of a wrinkled membrane is obtained by a specified combination of standard and relaxed strain energy function. The governing equations are discretized by a finite difference approach and a Newton-Raphson method is used to obtain the solution. An interesting relationship between stretch induced softening/stiffening with the wrinkling phenomenon has been discovered. The effects of pre-stretch, inflating medium, thickness variations and boundary conditions on the wrinkling patterns are clearly delineated. (C) 2015 Elsevier Masson SAS. All rights reserved.

  • 117.
    Pettersson, Robert
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Simulation of Human Movements through Optimization2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Optimization has been used to simulate human neural control and resulting movement patterns. The short term aim was to develop the methodology required for solving the movement optimization problem often arising when modelling human movements. A long term aim is the contribution to increased knowledge about various human movements, wherein postures is one specific case. Simulation tools can give valuable information to improve orthopeadic treatments and technique for training and performance in sports. In one study a static 3D model with 30 muscle groups was used to analyse postures. The activation levels of these muscles are minimized in order to represent the individual’s choice of posture. Subject specific data in terms of anthropometry, strength and orthopedic aids serve as input. The specific aim of this part was to study effects from orthopedic treatment and altered abilities of the subject. Initial validation shows qualitative agreement of posture strategies but further details about passive stiffness and anthropometry are needed, especially to predict pelvis orientation. Four studies dealt with movement optimization. The main methodological advance was to introduce contact constraints to the movement optimization. A freetime multiple phase formulation was derived to be able to analyse movements where different constraints and degrees of freedom are present in subsequent phases of the movements. The athletic long jump, a two foot high jump, a backward somersault and rowing were used as applications with their different need of formulation. Maximum performance as well as least effort cost functions have been explored. Even though it has been a secondary aim in this work the results show reasonable agreement to expected movements in reality. Case specific subject properties and inclusion of muscle dynamics are required to draw conclusions about improvements in the sport activity, respectively.

  • 118.
    Pettersson, Robert
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Free-time optimization of targeted movements based on temporal FE approximation2010In: Proc. CST 2010, 2010Conference paper (Refereed)
  • 119.
    Pettersson, Robert
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Optimisation of multiple phase human movements2013In: Multibody system dynamics, ISSN 1384-5640, E-ISSN 1573-272X, Vol. 30, no 4, p. 461-484Article in journal (Refereed)
    Abstract [en]

    When simulating human movements it is frequently desirable to optimise multiple phase movements where the phases represent, e.g., different contact conditions. The different constraints are usually acting in parts of the movements and their time durations are in most cases unknown. Therefore a multiple phase free-time optimisation method is formulated in this work, with phase times included as variables. Through a temporal finite element approach, a discrete representation is derived and a nonlinear optimisation algorithm solves for the rather high number of variables (similar to 6000) and constraints (similar to 15000) in the presented numerical problem. A four degrees of freedom test problem, representing a standing high jump, is solved in order to test some basic aspects. A more realistic problem shows its performance in its intended applications, biomechanical simulations. This is a sagittal eight degrees of freedom model for a human backward somersault, including preparing movement, flight phase and landing. The numerical performance as well as some application specific results are discussed. The method description is general and applicable to other movements in its presented format.

  • 120.
    Pettersson, Robert
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Optimization of multiple phase human movementsIn: Multibody system dynamics, ISSN 1384-5640, E-ISSN 1573-272XArticle in journal (Other academic)
    Abstract [en]

    When simulating human movements it is frequently desirable to optimize multiple phase movements where the phases represent, e.g., different contact conditions. The different constraints are usually acting in parts of the movements and their time durations are in most cases unknown. Therefore a multiple phase free-time optimization method is formulated in this work, with phase times included as variables. Through a temporal finite element approach, a discrete representation is derived and a nonlinear optimization algorithm solves for the rather high number of variables (∼ 6000) and constraints (∼ 15000) in the presented numerical problem. The method is applied to a test problem and a more realistic problem in order to test some basic aspects as well as to see its performance in its intended applications, biomechanical simulations. First a four degrees of freedom test problem, representing a standing high jump, is solved. Then a sagittal eight degrees of freedom model is used with application to a human backward somersault, including preparing movement, flight phase and landing. The numerical performance as well as some application specific results are discussed. The method description is general and applicable to other movements in its presented format.

  • 121.
    Pettersson, Robert
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Simulation of rowing in an optimization context2014In: Multibody system dynamics, ISSN 1384-5640, E-ISSN 1573-272X, Vol. 32, no 3, p. 337-356Article in journal (Refereed)
    Abstract [en]

    Competitive rowing requires efforts close to the physiological limits, where oxygen consumption is one main aspect. The rowing event also incorporates interactions between the rower, the boat and oars, and water. When the intention is to improve the performance, all these properties make the sport interesting from a scientific point of view, as the many variables influencing the performance form a complex optimization problem. Our aim was to formulate the rowing event as an optimization problem where the movement and forces are completely determined by the optimization, giving at least qualitative indications on good performance. A mechanical model of rigid links was used to represent rower, boat and oars. A multiple phase cyclic movement was simulated where catch slip, driving phase, release slip and recovery were modeled. For this simplified model, we demonstrate the influence of the stated mathematical cost function as well as a parameter study where the optimal performance is related to the planned average boat velocity. The results show qualitatively good resemblance to expected movements for the rowing event. An energy loss model in combination with case specific properties of rower capacities, boat properties, and rigging was required to draw qualitative practical conclusions about the rowing technique.

  • 122.
    Prigent, Yoann
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Mallol, Pau
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    A classical lamination model of bi-stable woven composite tape-springs2011In: Proceedings of the 24th Nordic Seminar on Computational Mechanics / [ed] Jouni Freund and Reijo Kouhia, Department of Civil and Structural Engineering, Aalto University , 2011, p. 51-54Conference paper (Refereed)
    Abstract [en]

    This extended abstract presents the work done so far on modeling woven composite materials, specifically two carbon fiber reinforced plastics materials: twill and plain weave. The material model has been initially verified against data available in a database.

  • 123.
    Reid, William
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Achtert, P.
    Ivchenko, Nickolay
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Magnusson, Patrick
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Kuremyr, Tobias
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Shepenkov, Valeriy
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Technical Note: A novel rocket-based in situ collection technique for mesospheric and stratospheric aerosol particles2013In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 6, no 3, p. 777-785Article in journal (Refereed)
    Abstract [en]

    A technique for collecting aerosol particles between altitudes of 17 and 85 km is described. Spin-stabilized collection probes are ejected from a sounding rocket allowing for multi-point measurements. Each probe is equipped with 110 collection samples that are 3 mm in diameter. The collection samples are one of three types: standard transmission electron microscopy carbon grids, glass fibre filter paper or silicone gel. Collection samples are exposed over a 50 m to 5 km height range with a total of 45 separate ranges. Post-flight electron microscopy will give size-resolved information on particle number, shape and elemental composition. Each collection probe is equipped with a suite of sensors to capture the probe's status during the fall. Parachute recovery systems along with GPS-based localization will ensure that each probe can be located and recovered for post-flight analysis.

  • 124.
    Riad, Jacques
    et al.
    Karolinska Institutet, Dept. of Women's and Children's Health.
    Modlesky, Christopher
    Gutierrez-Farewik, Elena
    KTH, School of Engineering Sciences (SCI), Mechanics, Biomechanics. KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Broström, Eva W.
    Karolinska Institutet, Dept. of Women's and Children's Health.
    Are Muscle Volume Differences Related to Concentric Muscle Work During Walking in Spastic Hemiplegic Cerebral Palsy?2012In: Clinical Orthopaedics and Related Research, ISSN 0009-921X, E-ISSN 1528-1132, Vol. 470, no 5, p. 1278-1285Article in journal (Refereed)
    Abstract [en]

    Background: Individuals with spastic hemiplegic cerebral palsy are typically high functioning and walk without assistive devices. The involved limb is usually smaller and shorter, although it is not clear whether the difference in muscle volume has an impact on walking capacity. Questions/purposes: We determined the volume of muscles important for propulsion and related that volume to concentric muscle work during walking on the hemiplegic and noninvolved sides in patients with cerebral palsy. Patients and Methods: We studied 46 patients (mean age, 17.6 years; range, 13-24 years) with spastic hemiplegic cerebral palsy. We assessed muscle volume using MRI and concentric muscle work in the sagittal plane from the hip, knee, and ankle using three-dimensional gait analysis. Patients were classified by Winters' criteria to assess the involvement of cerebral palsy and movement pattern during walking. Results: On the hemiplegic side, muscles were smaller, except for the gracilis muscle, and concentric muscle work from the ankle plantar flexors, knee extensors, and hip flexors and extensors was lower compared to the noninvolved side. Hip extensor work was higher on the hemiplegic and the noninvolved sides compared to a control group of 14 subjects without cerebral palsy. Hemiplegic to noninvolved volume ratios correlated with work ratios (r = 0.40-0.66). The Winters classification and previous calf muscle surgery predicted work ratios. Conclusions: Our observations of smaller muscles on the hemiplegic side and changes in muscle work on both sides can help us distinguish between primary deviations that may potentially be treatable and compensatory mechanisms that should not be treated.

  • 125.
    Rosen, Tomas
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Einarsson, J.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Aidun, C. K.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Mehlig, B.
    Numerical analysis of the angular motion of a neutrally buoyant spheroid in shear flow at small Reynolds numbers2015In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 92, no 6, article id 063022Article in journal (Refereed)
    Abstract [en]

    We numerically analyze the rotation of a neutrally buoyant spheroid in a shear flow at small shear Reynolds number. Using direct numerical stability analysis of the coupled nonlinear particle-flow problem, we compute the linear stability of the log-rolling orbit at small shear Reynolds number Re-a. As Re-a -> 0 and as the box size of the system tends to infinity, we find good agreement between the numerical results and earlier analytical predictions valid to linear order in Re-a for the case of an unbounded shear. The numerical stability analysis indicates that there are substantial finite-size corrections to the analytical results obtained for the unbounded system. We also compare the analytical results to results of lattice Boltzmann simulations to analyze the stability of the tumbling orbit at shear Reynolds numbers of order unity. Theory for an unbounded system at infinitesimal shear Reynolds number predicts a bifurcation of the tumbling orbit at aspect ratio lambda(c) approximate to 0.137 below which tumbling is stable (as well as log rolling). The simulation results show a bifurcation line in the lambda-Re-a plane that reaches lambda approximate to 0.1275 at the smallest shear Reynolds number (Re-a = 1) at which we could simulate with the lattice Boltzmann code, in qualitative agreement with the analytical results.

  • 126.
    Rosén, Tomas
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Mechanics. KTH Royal Institute of Technology.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Aidun, Cyrus K.
    Do-Quang, Minh
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Mechanics.
    Quantitative analysis of the angular dynamics of a single spheroid in simple shear flow at moderate Reynolds numbers2016In: Physical Review Fluids, ISSN 2469-990X, Vol. 1, no 4, p. 044201-1-044201-21Article in journal (Refereed)
    Abstract [en]

    A spheroidal particle in simple shear flow shows surprisingly complicated angular dynamics; caused by effects of fluid inertia (characterized by the particle Reynolds number Rep) and particle inertia (characterized by the Stokes number St). Understanding this behavior can provide important fundamental knowledge of suspension flows with spheroidal particles. Up to now only qualitative analysis has been available at moderate Rep. Rigorous analytical methods apply only to very small Rep and numerical results lack accuracy due to the difficulty in treating the moving boundary of the particle. Here we show that the dynamics of the rotational motion of a prolate spheroidal particle in a linear shear flow can be quantitatively analyzed through the eigenvalues of the log-rolling particle (particle aligned with vorticity). This analysis provides an accurate description of stable rotational states in terms of Rep,St, and particle aspect ratio (rp). Furthermore we find that the effect on the orientational dynamics from fluid inertia can be modeled with a Duffing-Van der Pol oscillator. This opens up the possibility of developing a reduced-order model that takes into account effects from both fluid and particle inertia.

  • 127.
    Russell, Colin
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Deployment of tensegrity frameworks using inflatable tubes2005In: Structural Membranes 2005: Proceedings of the International Conference on Textile Composites and Inflatable Structures, 2005Conference paper (Other academic)
  • 128.
    Russell, Colin
    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 inflatable tensegrity structures2008In: International Journal of Space Structures, ISSN 0956-0599, Vol. 23, no 2, p. 63-77Article in journal (Refereed)
    Abstract [en]

    nsegrity structures are attractive as deployable space structures since they are composed mainly of flexible tension members and can thus easily be folded. To automatically deploy such structures it is proposed that the tension members are replaced or enclosed by thin-film tubes, which form a continuous volume. The structure deploys when this volume is pressurised. This concept was studied by numerical simulations of the deployment process in a zero-gravity environment using the control volume method for the fluid-structure interaction. First, single z-folded and coiled tubes were analysed to determine suitable element size, number of control volumes and gas flow rate. Then one- and three-stage tensegrity masts were modelled, folded and finally deployed. The study showed that the deployment concept is feasible.

  • 129.
    safaei, Seif
    et al.
    KTH, School of Engineering Sciences (SCI), 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.
    Study of various tensegrity modules as building blocks for slender booms2013In: International Journal of Space Structures, ISSN 0956-0599, Vol. 28, no 1, p. 41-52Article in journal (Refereed)
    Abstract [en]

    This study investigates the structural performance of long and slender tensegrity booms. Previous studies show that tensegrity structures are generally more flexible than conventional trusses or space frames. The aims here were (i) to quantify how much more flexible eleven different tensegrity booms are, when compared to state-of-the-art truss booms, (ii) to find a general explanation for this. The performance criterion used for the comparison was the first natural frequency of the boom. A finite element program with truss elements was used to compute the natural frequencies around the initial prestressed configurations. The results show that tensegrity booms have between one and three orders of magnitude lower natural frequencies than truss booms. It is concluded that for the best performing tensegrity booms, the bending stiffness is independent of the level of pre-stress and the number of infinitesimal mechanisms as the bending stiffness is given mainly by the material stiffness of the tension elements and not the geometric stiffness as the infinitesimal mechanisms are not activated by bending. Thus, whereas the level of pre-stress and the presence of infinitesimal mechanisms play major roles for the stiffness of some tensegrity structures, the axial stiffness and orientation of tension elements are most important for the studied slender booms.

  • 130.
    Shepenkov, Valeriy
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Vibration Modal Analysis of a Deployable Boom Integrated to a CubeSat2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    CubeSat or Cubic Satellite is an effective method to study the space aroundthe Earth thanks to its low cost, easy maintenance and short lead time. However, a great challenge of small satellites lies in achieving technicaland scientific requirements during the design stage. In the present workprimary focus is given to dynamic characterization of the deployable tapespringboom in order to verify and study the boom deployment dynamiceffects on the satellite. The deployed boom dynamic characteristics werestudied through simulations and experimental testing. The gravity offloadingsystem was used to simulate weightlessness environment in theexperimental testing and simulations showed that the deployment of thesystem influence the results in a different way depending on the vibrationmode shape.

  • 131. Sinn, T.
    et al.
    Brown, R.
    McRobb, M.
    Wujek, Adam
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Lowe, C.
    Weppler, J.
    Parry, T.
    Yarnoz, D. G.
    Brownlie, F.
    Skogby, Jerker
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Dolan, I.
    De Franca Queiroz, T.
    Rogberg, Fredrik
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Donaldson, N.
    Clark, R.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Lessons learned from three university experiments onboard the REXUS/BEXUS sounding rockets and stratospheric balloons2013In: 64th International Astronautical Congress 2013, International Astronautical Federation, 2013, p. 7965-7976Conference paper (Refereed)
    Abstract [en]

    Over the last three years the authors have been involved in three experiments that were or will be launched on sounding rockets and high altitude balloons with the REXUS/BEXUS program (Rocket-borne / Balloon-borne Experiments for University Students). The first experiment, called Suaineadh was launched from Esrange (Kiruna, Sweden) onboard REXUS 12 in March 2012. Suaineadh had the purpose of deploying a web in space by using centrifugal forces. The payload was lost during re-entry but was recovered 18 month later in early September 2013. StrathSat-R is the second experiment, which had the purpose of deploying two cube satellites with inflatable structures from the REXUS 13 sounding rocket, was launched first in May 2013 and will be launched a second time in spring 2014. The last experiment is the iSEDE experiment which has the goal of deploying an inflatable structure with disaggregated electronics from the high altitude balloon BEXUS15/16 in October 2013. All these experiments have been designed, built and flown in a timeframe of one and a half to two years. This paper will present the lessons learned in project management, outreach, experiment design, fabrication and manufacturing, software design and implementation, testing and validation as well as launch, flight and post-flight. Furthermore, the lessons learned during the recovery mission of Suaineadh will be discussed as well. All these experiments were designed, built and tested by a large group of university students of various disciplines and different nationalities. StrathSat-R and iSEDE were built completely at Strathclyde but the Suaineadh experiment was a joint project between Glasgow and Stockholm which was especially tricky during integration while approaching the experiment delivery deadline. This paper should help students and professionals across various disciplines to build and organise these kinds of projects more efficiently without making the same, sometimes expensive, mistakes all over again.

  • 132. Sinn, T.
    et al.
    McRobb, M.
    Wujek, Adam
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Skogby, Jerker
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Rogberg, Fredrik
    KTH, School of Electrical Engineering (EES).
    Wang, Junyi
    KTH, School of Electrical Engineering (EES).
    Vasile, M.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Results of rexus12's suaineadh experiment: Deployment of a spinning space web in micro gravity conditions2012In: Proceedings of the International Astronautical Congress, IAC: Volume 2, 2012, International Astronautical Federation, 2012, p. 803-810Conference paper (Refereed)
    Abstract [en]

    On the 19th of March 2012, the Suaineadh experiment was launched onboard the sounding rocket REXUS12 (Rocket Experiments for University Students) from the Swedish launch base ESRANGE in Kiruna. The Suaineadh experiment served as a technology demonstrator for a space web deployed by a spinning assembly. The deployment of this web is a stepping stone for the development of ever larger structures in space. Such a structure could serve as a substructure for solar arrays, transmitters and/or antennas. The team was comprised of students from the University of Strathclyde (Glasgow, UK), the University of Glasgow (Glasgow, UK) and the Royal Institute of Technology (Stockholm, Sweden), designing, manufacturing and testing the experiment over the past 24 months. Following launch, the experiment was ejected from the ejection barrel located within the nosecone of the rocket. Centrifugal forces acting upon the space webs spinning assembly were used to stabilise the experiment's platform. A specifically designed spinning reaction wheel, with an active control method, was used. Once the experiment's motion was controlled, a 2 m by 2 m space web is released. Four daughter sections situated in the corners of the square web served as masses to stabilise the web due to the centrifugal forces acting on them. The four daughter sections contained inertial measurement units (IMUs). Each IMU provided acceleration and velocity measurements in all three directions. Through this, the positions of the four corners could be found through integration with respect to known time of the accelerations and rotations. Furthermore, four cameras mounted on the central hub section captured high resolution imagery of the deployment process. After the launch of REXUS12, the recovery helicopter was unable to locate the ejected experiment, but 22 pictures were received over the wireless connection between the experiment and the rocket. The last received picture was taken at the commencement of web deployment. Inspection of these pictures allowed the assumption that the experiment was fully functional after ejection, but perhaps through tumbling of either the experiment or the rocket, the wireless connection was interrupted. A recovery mission in the middle of August was only able to find the REXUS12 motor and the payload impact location.

  • 133. Sinn, T.
    et al.
    Vasile, M.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Design and development of deployable Self-inflating Adaptive Membrane2012In: 53rd Structures, Structural Dynamics, and Materials Conference (SDM) 2012, American Institute of Aeronautics and Astronautics, 2012, p. AIAA 2012-1517-Conference paper (Refereed)
    Abstract [en]

    Space structures nowadays are often designed to serve just one objective during their mission life, examples include truss structures that are used as support structures, solar sails for propulsion or antennas for communication. Each and every single one of these structures is optimized to serve just their distinct purpose and are more or less useless for the rest of the mission and therefore dead weight. By developing a smart structure that can change its shape and therefore adapt to different mission requirements in a single structure, the flexibility of the spacecraft can be increased by greatly decreasing the mass of the entire system. This paper will introduce such an adaptive structure called the Self-inflating Adaptive Membrane (SAM) concept which is being developed at the Advanced Space Concepts Laboratory of the University of Strathclyde. An idea presented in this paper is to adapt these basic changeable elements from nature's heliotropism. Heliotropism describes a movement of a plant towards the sun during a day; the movement is initiated by turgor pressure change between adjacent cells. The shape change of the global structure can be significant by adding up these local changes induced by local elements, for example the cell's length. To imitate the turgor pressure change between the motor cells in plants to space structures, piezoelectric micro pumps are added between two neighboring cells. A passive inflation technique is used for deploying the membrane at its destination in space. The trapped air in the spheres will inflate the spheres when subjected to vacuum, therefore no pump or secondary active deployment methods are needed. The paper will present the idea behind the adaption of nature's heliotropism principle to space structures. The feasibility of the residual air inflation method is verified by LS-DYNA simulations and prototype bench tests under vacuum conditions. Additionally, manufacturing techniques and folding patterns are presented to optimize the actual bench test structure and to minimize the required storage volume. It is shown that through a bio-inspired concept, a high ratio of adaptability of the membrane can be obtained. The paper concludes with the design of a technology demonstrator for a sounding rocket experiment to be launched in March 2013 from the Swedish launch side Esrange.

  • 134.
    Sinn, Thomas
    et al.
    University of Strathclyde.
    McRobb, Malcolm
    University of Strathclyde.
    Wujek, Adam
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Skogby, Jerker
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Rogberg, Fredrik
    KTH, School of Electrical Engineering (EES).
    Wang, Junyi
    KTH, School of Electrical Engineering (EES).
    Vasile, Massimiliano
    University of Strathclyde.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Lessons learned from REXUS12'S suaineadh experiment: Spinning deployment of a space Web in milli gravity2013In: 21st ESA Symposium: European Rocket & Balloon Programmes and Related Research / [ed] L. Ouwehand, ESA Communications , 2013, p. 329-338Conference paper (Refereed)
    Abstract [en]

    On the 19th of March 2012, the Suaineadh experiment was launched onboard the sounding rocket REXUS 12 (Rocket Experiments for University Students) from the Swedish launch base ESRANGE in Kiruna. The Suaineadh experiment served as a technology demonstrator for a space web deployed by a spinning assembly. Following launch, the experiment was ejected from the ejection barrel located within the nosecone of the rocket. Centrifugal forces acting upon the space web spinning assembly were used to stabilise the experiment's platform. A specifically designed spinning reaction wheel, with an active control method, was used. Once the experiment's motion was controlled, a 2 m by 2 m space web is released. Four daughter sections situated in the corners of the square web served as masses to stabilise the web due to the centrifugal forces acting on them. The four daughter sections contained inertial measurement units (IMUs). After the launch of REXUS 12, the recovery helicopter was unable to locate the ejected experiment, but 22 pictures were received over the wireless connection between the experiment and the rocket. The last received picture was taken at the commencement of web deployment. Inspection of these pictures allowed the assumption that the experiment was fully functional after ejection, but probably through tumbling of either the experiment or the rocket, the wireless connection was interrupted. A recovery mission in the middle of August was only able to find the REXUS 12 motor and the payload impact location.

  • 135. Sinn, Thomas
    et al.
    McRobb, Malcolm
    Wujek, Adam
    KTH, School of Information and Communication Technology (ICT).
    Skogby, Jerker
    KTH, School of Information and Communication Technology (ICT).
    Rogberg, Fredrik
    KTH, School of Electrical Engineering (EES).
    Wang, Junyi
    KTH, School of Electrical Engineering (EES).
    Vasile, Massimiliano
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Mao, Huina
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    THE EXPERIMENT THAT CAME FROM THE COLD: RESULTS FROM THE RECOVERED REXUS12 SUAINEADH SPINNING WEB EXPERIMENT2015In: EUROPEAN ROCKET AND BALLOON: PROGRAMMES AND RELATED RESEARCH, 2015, p. 449-459Conference paper (Refereed)
    Abstract [en]

    The Suaineadh experiment had the purpose to deploy a 2m x 2m web in milli gravity conditions by using the centrifugal forces acting on corner sections of a web that is spinning around a central hub. Continuous exploration of our solar system and beyond requires ever larger structures in space. But the biggest problem nowadays is the transport of these structures into space due to launch vehicle payload volume constrains. By making the space structures deployable with minimum storage properties, this constrain may be bypassed. Deployable concepts range from inflatables, foldables, electrostatic to spinning web deployment. The advantage of the web deployment is the very low storage volume and the simple deployment mechanism. These webs can act as lightweight platforms for the construction of large structures in space without the huge expense of launching heavy structures from Earth. The Suaineadh experiment was launched onboard the sounding rocket REXUS12 in March 2012. After achieving the required altidue, the Suaineadh experiment was ejected from the rocket in order to be fully free flying. A specially designed spinning wheel in the ejected section was then used to spin up the experiment until the required rate is achieved for web deployment to commence. Unfortunately during re-entry, the probe was lost and also a recovery mission in August 2012 was only able to find minor components of the experiment. After 18 month, in September 2013, the experiment was found in the wilderness of Northern Sweden. In the following months all data from the experiment could be recovered. The images and accelerometer data that has been analysed showed the deployment of the web and a very interesting three dimensional behaviour that differs greatly from on ground two dimensional prototype tests. This paper will give an overview on the recovered data and it will present the analysed results of the Suaineadh spinning web experiment.

  • 136.
    Sinn, Thomas
    et al.
    University of Strathclyde.
    McRobb, Malcolm
    University of Glasgow.
    Wujek, Adam
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Skogby, Jerker
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Zhang, Mengqi
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Vasile, Massimiliano
    University of Strathclyde.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Weppler, Johannes
    University of Stuttgart.
    Feeney, Andrew
    University of Glasgow.
    Russell, John
    University of Glasgow.
    Rogberg, Fredrik
    KTH, School of Electrical Engineering (EES).
    Wang, Junyi
    KTH, School of Electrical Engineering (EES).
    REXUS 12 Suaineadh experiment: deployment of a web in microgravity conditions using centrifugal forces2011In: IAC 2011: Proceedings of the 62nd International Astronautical Congress, 2011, p. IAC-11-A2.3.7-Conference paper (Refereed)
  • 137. Suleman, A.
    et al.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Topping, B.H.V.
    Mota-Soares, C.A.
    Computational structures technology2007In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 85, no 17-18, p. 1281-1283Article in journal (Other academic)
  • 138.
    Summerer, Leopold
    et al.
    ESA Advanced Concepts Team.
    Purcell, Oisin
    ESA Advanced Concepts Team.
    Vasile, Massimiliano
    University of Glasgow.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Kaya, Nobuyuki
    Kobe University.
    Making the first steps towards solar power from space - microgravity experiments testing the deployment of large antennas2009In: IAC 2009: Proceedings of the 60th International Astronautical Congress, 2009, p. IAC-09.C3.4.4-Conference paper (Refereed)
    Abstract [en]

    Concepts for solar power from space have received renewed attention over the past year. High costs for fossil fuel during most of 2007 and 2008 have contributed to increasing the interest not only in traditional renewable energy sources but also in options usually considered as rather "exotic". Solar power from space is one of these. Given the potential size of such an endeavour, it is particularly important to demonstrate its feasibility and convince energy sector representatives and critics via concrete demonstrator projects targeting key technologies. The construction of a light-weight, very large structure as needed for transmitting antennas and the demonstration of wireless power transmission over very large distances are two of these key technologies. The present paper presents two experiments Furoshiki-2 and Suaineadh addressing these key technologies.

  • 139.
    Swarén, Mikael
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Experimental test setups and simulations in skiing mechanics2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Product testing and development are essential parts in sports and for the athletes in their quest to reach the podium. Manufacturers of sports equipment often use basic test methods which do not test the equipment in a sports specific way. Much of the equipment used by world-class athletes is chosen based only on subjective tests and the athletes’ feelings. One short term aim was therefore to develop test methods for objective tests of sports equipment that also tested the equipment in a sports  specific  way.  Another  aim  was  to  integrate  mechanics  and  simulations  to  enhance  the understanding of the test results. The more long term aims are to contribute to increased theoretical knowledge regarding test methods for sports equipment and to contribute to the development of test  methods  to  create  new  and  better  sports  equipment.  Experimental  tests  combined  with simulations  can  give  valuable  information  to  improve  the  performance  and  safety  of  sports equipment. Three studies dealt with the issue of objective yet sport specific test methods for sports equipment. The main methodological advancement is the modification of established test methods together  with  conventional  mechanics  calculations.  New  test  devices  and  methodologies  are proposed for alpine ski helmets and cross-country ski poles. Suggestions are given for improved test setups as well as theoretical simulation are introduced for glide tests of skis. The results show how sport   specific   test   methodologies   together   with   theoretical   calculations   can   improve   the objectiveness and relevance when testing sports equipment. However, the collected and used data require high precision to obtain high accuracy in the simulations. High data accuracy can be an issue in field measurements but also due to manufacturers not disclosing key material data. Still, the used methods  and  calculations  in  this  thesis  produce  relevant  and  reliable  results  which  can  be implemented to accurate evaluations of different sports equipment. Even though it has not been a first priority aim in this work, the results from the alpine helmet study have been used by helmet manufacturers to design new helmets with increased safety properties. This further show how an objective and sport specific test approach together with theoretical simulation can improve sports equipment and in the longer perspective, also the athletes’ performances.

     

  • 140.
    Swarén, Mikael
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Holmberg, H.-C.
    Swedish Winter Sports Research Center, MiUn.
    Treadmill simulation of olympic cross country ski track2012In: Proceedings of 2nd International Congress on Science and Nordic Skiing 2012, Vuokatti: ICSNS 2012 , 2012Conference paper (Refereed)
  • 141.
    Swarén, Mikael
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Holmberg, H.-C.
    Swedish Winter Sports Research Center, MiUn.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Repeated low impacts in alpine ski helmets2013In: Sports Technology, ISSN 1934-6190, Vol. 6, no 1, p. 43-52Article in journal (Refereed)
    Abstract [en]

    Alpine ski race helmets are subjected to multiple impacts during a race caused by the skiers hitting the gates on their way down the course. This study investigated the difference between expanded polystyrene (EPS) and expanded polypropylene (EPP) cores in alpine ski race helmets when subjected to repetitive violence, caused by alpine slalom gates. A special test rig was developed where a rotating slalom pole impacted the helmets with a velocity of 13.3 m·s- 1. All helmets (six EPS and six EPP) were attached to a headform, monitored with a triaxial accelerometer at the center of mass. Each helmet sustained 1000 impacts and acceleration data were collected around every 200 impacts. No significant differences were observed between the first hit and after 1000 hits for either the EPS or the EPP helmets. However, the total group mean acceleration and mean peak acceleration were 15% and 16% higher, respectively, for the EPS series compared with the EPP series. Also, all EPS helmets showed cracked cores after 1000 impacts compared with 1 cracked EPP core. Findings suggest that EPP cores might be more suitable for absorbing multiple low impacts caused by alpine gates and that repeated violence is a relevant parameter to consider when constructing alpine ski race helmets.

  • 142.
    Swarén, Mikael
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics. Mid Sweden University, Sweden.
    Karlöf, L.
    Holmberg, Hans-Christer
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics. Mid Sweden University, Sweden.
    Validation of test setup to evaluate glide performance in skis2014In: Sports Technology, ISSN 1934-6182, E-ISSN 1934-6190, Vol. 7, no 1-2, p. 89-97Article in journal (Refereed)
    Abstract [en]

    Although today's ski waxing chemicals and micro-machining techniques of the ski base are highly sophisticated, objective procedures for testing and verification of the results have not yet been developed and evaluation is based on comparison of subjective experience. The purpose of the present study was thus to compare different setups for testing the glide of cross-country skis. Two differently waxed ski pairs were tested for glide inside a ski tunnel. Inertial measurement units (IMUs) were attached to each ski; instantaneous velocities monitored by three different speed-traps; the velocities during the acceleration phase determined by Doppler radar. Kinetic, potential and total energy, giving the energy dissipation, were calculated for four representative trials during the acceleration phase. No reliable data were obtained from the IMUs due to high drift. The mean maximal velocity for the two ski pairs were 6.97, s = 0.09 and 6.70, s = 0.09 m·s − 1, respectively. Higher differences between the skis were identified during the retardation phase compared to the acceleration phase. The mean difference between the velocities determined by the speed-trap and Doppler radar was 0.6, s = 1%, demonstrating that the latter provides accurate data for evaluation of gliding characteristics and performance. However, theoretical confirmation of the friction coefficient, on the basis of data provided by Doppler radar and energy calculations requires exact measurements of the inclination and topography of the track in question.

  • 143.
    Swarén, Mikael
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Karlöf, Lars
    Holmberg, H.-C.
    Mittuniversitetet.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Validation of test setups to evaluate glide performance in skisManuscript (preprint) (Other academic)
  • 144.
    Swarén, Mikael
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Therell, M.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Holmberg, H. -C
    Testing method for objective evaluation of cross-country ski poles2013In: Sports Engineering, ISSN 1369-7072, E-ISSN 1460-2687, Vol. 16, no 4, p. 255-264Article in journal (Refereed)
    Abstract [en]

    The aim of the study was to develop an objective classification method for cross-country ski poles. A test device was designed to expose different pole models to maximal loading and impact tests. A load cell measured the axial forces in the pole shafts, and a laser distance meter measured shaft deflection when a load was applied via the wrist strap. In the loading tests, each shaft reached a plateau where no more force could be transferred. This maximal force transfer (MFT) value was a characteristic measure for flexural rigidity and thereby also strength. The developed test method enables a loading that is more similar to real-life skiing than a standard three-point bending test. Results show that the introduction of shaft indices for buckling strength is beneficial for comparison purposes. The MFT is a relevant parameter used in the characterization of poles.

  • 145.
    Swarén, Mikael
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Therell, Mikael
    Swedish Winter Sports Research Center, MiUn.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Holmberg, H.-C.
    Swedish Winter Sports Research Center, MiUn.
    Cross-country ski poles: Introduction of a shaft strength index2012In: Proceedings of the 2nd International Congress on Science and Nordic Skiing 2012, ICSNS , 2012Conference paper (Refereed)
  • 146.
    Tamadapu, Ganesh
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Resonances of a submerged fluid-filled spherically isotropic microsphere with partial-slip interface condition2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, no 4, article id 044903Article in journal (Refereed)
    Abstract [en]

    Motivated by the numerous applications of spherical shell models in micro and nano scales (such as microbubbles, bacterial cells, and viral capsids), we have considered the axisymmetric free vibrations of a spherically isotropic fluid-filled thick microspherical shell suspended in another unbounded fluid. A partial-slip condition is considered at the solid-fluid interface(s). Three-dimensional linear elasticity equations for the spherically isotropic shell dynamics and linearized Navier-Stokes equations for the two compressible viscous fluids are used in the analysis. The eigenvalue problem is discretized and solved to find the resonances and quality factors. A perfectly matched layer technique is used to separate the solid driven spectrum from the boundary reflecting spectrum. An example of air filled polymer shell suspended in water is presented. The added mass effect and partial-slip condition from water (air) on the frequencies and quality factors are found to be significant (negligible). Spherical isotropy is found to have major influence on the low frequency and large meridional wave number region of the resonance spectrum. High quality eigenmodes are observed due to very small viscous penetration depth compared to the shell size. In the thin-shell limit, the eigenvalue problem can have only two modes of vibration for any meridional wave number greater than or equal to two. This explains the reason for the second resonance frequency found for the quadrupole shape oscillations of various bacterium cells in the earlier work. The partial-slip condition is found to have very small influence on the first few modes of vibration. Surface tension is found to have significant influence only on the lowest frequency trend of the eigenspectrum. Perfectly matched layer technique used in the present analysis is found to be very effective in handling the boundary truncated problems.

  • 147. Tedroff, K.
    et al.
    Lowing, K.
    Haglund-Akerlind, Y.
    Gutierrez-Farewik, Elena
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Forssberg, H.
    Botulinumtoxin A treatment in toddlers with cerebral palsy2010In: Acta Paediatrica, ISSN 0803-5253, E-ISSN 1651-2227, Vol. 99, no 8, p. 1156-1162Article in journal (Refereed)
    Abstract [en]

    Aims: In this study the aim was to evaluate the effect of botulinum toxin A (BoNT-A) treatment on muscle tone, contracture development and gait pattern in young children with cerebral palsy (CP). Method: Fifteen children with spastic CP (mean age = 16 months) were included in a randomized control study. All received a daily stretching programme and children in the BoNT-A group additionally received two injections, 6 months apart in the gastrocnemius muscle. Outcomes were assessed at baseline, and after 1 and 3.5 years. A 3D gait-analysis was performed at 5 years of age. Results: Plantarflexor muscle tone in the BoNT-A group was significantly reduced after 3.5 years, while the muscle tone at the ankle and knee in the control group remained unchanged. The change-score in knee-flexion muscle tone between the groups was significantly different after 3.5 years. The knee joint ROM was significantly increased at 1 year in the BoNT-A group but reduced at the knee and ankle joints in the control group after 3.5 years. No group differences were found for gait analysis, GMFM-66 or PEDI. Conclusion: Early treatment of BoNT-A in children with spastic CP may decrease muscle tone and decelerate contracture development after 3.5 years. The effect on gait development remains inconclusive.

  • 148.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Bending-stiff tensegrity masts: do they exist?2008In: Proceedings of the 6th International Conference of Shell and Spatial Structures, 2008Conference paper (Refereed)
  • 149.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Computational challenges for highly flexible space structures2008In: Proceedings of the 21st Nordic Seminar on Computational Mechanics, 2008, p. 43-46Conference paper (Other academic)
  • 150.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Design and form-finding analysis of tensegrity power lines2011In: Proceeding of the 4th Structural Engineering World Congress, 2011Conference paper (Other academic)
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