Body Motion (body + motion)

Distribution by Scientific Domains

Kinds of Body Motion

  • rigid body motion


  • Selected Abstracts


    Capturing human motion using body-fixed sensors: outdoor measurement and clinical applications

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 2 2004
    Kamiar Aminian
    Abstract Motion capture is mainly based on standard systems using optic, magnetic or sonic technologies. In this paper, the possibility to detect useful human motion based on new techniques using different types of body-fixed sensors is shown. In particular, a combination of accelerometers and angular rate sensors (gyroscopes) showed a promising design for a hybrid kinematic sensor measuring the 2D kinematics of a body segment. These sensors together with a portable datalogger, and using simple biomechanical models, allow capture of outdoor and long-term movements and overcome some limitations of the standard motion capture systems. Significant parameters of body motion, such as nature of motion (postural transitions, trunk rotation, sitting, standing, lying, walking, jumping) and its spatio-temporal features (velocity, displacement, angular rotation, cadence and duration) have been evaluated and compared to the camera-based system. Based on these parameters, the paper outlines the possibility to monitor physical activity and to perform gait analysis in the daily environment, and reviews several clinical investigations related to fall risk in the elderly, quality of life, orthopaedic outcome and sport performance. Taking advantage of all the potential of these body-fixed sensors should be promising for motion capture and particularly in environments not suitable for standard technology such as in any field activity. Copyright 2004 John Wiley & Sons, Ltd. [source]


    Performance-driven muscle-based facial animation

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 2 2001
    Byoungwon Choe
    Abstract We describe a system to synthesize facial expressions by editing captured performances. For this purpose, we use the actuation of expression muscles to control facial expressions. We note that there have been numerous algorithms already developed for editing gross body motion. While the joint angle has direct effect on the configuration of the gross body, the muscle actuation has to go through a complicated mechanism to produce facial expressions. Therefore,we devote a significant part of this paper to establishing the relationship between muscle actuation and facial surface deformation. We model the skin surface using the finite element method to simulate the deformation caused by expression muscles. Then, we implement the inverse relationship, muscle actuation parameter estimation, to find the muscle actuation values from the trajectories of the markers on the performer's face. Once the forward and inverse relationships are established, retargeting or editing a performance becomes an easy job. We apply the original performance data to different facial models with equivalent muscle structures, to produce similar expressions. We also produce novel expressions by deforming the original data curves of muscle actuation to satisfy the key-frame constraints imposed by animators.Copyright 2001 John Wiley & Sons, Ltd. [source]


    A method for representing boundaries in discrete element modelling,part II: Kinematics

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2001
    M. Kremmer
    Abstract The application of the DEM to engineering problems involving the dynamic behaviour of discontinuous media has necessitated the introduction of moving boundary surfaces. In this paper a method is presented for modelling three-dimensional moving boundary surfaces within the discrete element framework. The surfaces of boundary objects are discretized into triangular planar surfaces using the finite wall method. Wall elements are grouped and each group is associated with a single discrete boundary object which may move independently. Movement comprises any combination of translation and rotation of wall element groups, subject to a given acceleration and velocity during a calculation cycle. The scheme is explicit due to rigidity of the wall elements which are stationary fixed in position and orientation over a time step. Any in-plane velocity is handled as a contact point velocity within a calculation cycle. The kinematic conditions at each calculation cycle may be pre-defined or returned from a separate calculation of rigid body motion of the boundary object. The method provides a means for coupling sphere-based particle dynamics with rigid body dynamics and structural analysis of boundary components. Copyright 2001 John Wiley & Sons, Ltd. [source]


    Novel interleaved spiral imaging motion correction technique using orbital navigators

    MAGNETIC RESONANCE IN MEDICINE, Issue 2 2003
    Hisamoto Moriguchi
    Abstract Although spiral imaging seldom produces apparent artifacts related to flow, it remains sensitive to rapid object motion. In this article, a new correction method is presented for rapid rigid body motion in interleaved spiral imaging. With this technique, an identical circular navigator k -space trajectory is linked to each spiral trajectory. Data inconsistency due to both rotation and translation among spiral interleaves can be corrected by evaluating the magnitudes and phases of the data contained in the navigator "ring." Further, it is difficult to create a frequency field map for off-resonance correction when an object moves during a scan, because there is motion-dependent misregistration between the two images acquired with different TEs. However, this difficulty can be overcome by combining the motion-correction method with a recently proposed technique (off-resonance correction using variable-density spirals (ORC-VDS)), thereby enabling both motion compensation and off-resonance correction with no additional scanning. Magn Reson Med 50:423,428, 2003. 2003 Wiley-Liss, Inc. [source]


    The LGL (Lighthill,Gueron,Liron) Theorem,historical perspective and critique

    MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 17-18 2001
    Nadav Liron
    The 1970s saw a series of works on the modelling of slender bodies moving in slow flow (Re=0), instigated by the interest to understand the principles underlying the swimming of ciliates and flagellates. It was Lighthill in 1975, who wrote down the first theorem connecting slender body motion and singularities distributions along the centre line. This paper will describe the historical development from the early results through Lighthill's theorem to the Gueron,Liron Theorem, which enables discrete-cilia modelling, i.e., modelling of a multitude of slender bodies attached to a surface. Copyright 2001 John Wiley & Sons, Ltd. [source]


    Skipping flights in Ypthima butterflies (Lepidoptera: Nymphalidae)

    ENTOMOLOGICAL SCIENCE, Issue 2 2010
    Munenori SUGIURA
    Abstract The skipping flight patterns of three species of Ypthima (Lepidoptera: Nymphalidae) were analyzed using high-speed video recordings to clarify how wings move and how driving forces are produced. All three species showed a flight pattern that includes a pause that accounts for about 50% of a flap cycle when their wings completely close after each upstroke. The observed pause causes the "skipping" flight trajectory based on the clap,fling mechanism. Pause duration was correlated with upstroke wing motion, suggesting the contribution of the latter to a long pause duration. This is also supported by the temporal relationship between the wing and body motions. The aerodynamic power necessary for the pause flight was calculated for the three species. [source]


    An efficient hourglass control implementation for the uniform strain hexahedron using the Total Lagrangian formulation

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 11 2008
    Grand Roman Joldes
    Abstract The under-integrated hexahedron is one of the best candidates for use in real-time surgical simulations, because of its computational efficiency. This element requires a very efficient method of controlling the zero energy (hourglass) modes that arise from one-point integration. An efficient implementation of the perturbation hourglass control method proposed by Flanagan and Belytschko for the uniform strain hexahedron is presented. The implementation uses the Total Lagrangian formulation and takes into consideration large deformations and rigid body motions. By using the Total Lagrangian formulation most of the necessary components for calculating the hourglass forces can be pre-computed, leading to a significant reduction of the additional computation time required for hourglass control. The performance evaluation results show the very good accuracy and computational efficiency of the presented algorithm. Copyright 2007 John Wiley & Sons, Ltd. [source]


    A refined semi-analytic design sensitivity based on mode decomposition and Neumann series

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2005
    Maenghyo Cho
    Abstract Among various sensitivity evaluation techniques, semi-analytical method (SAM) is quite popular since this method is more advantageous than analytical method (AM) and global finite difference method (GFD). However, SAM reveals severe inaccuracy problem when relatively large rigid body motions are identified for individual elements. Such errors result from the pseudo load vector calculated by differentiation using the finite difference scheme. In the present study, an iterative refined semi-analytical method (IRSAM) combined with mode decomposition technique is proposed to compute reliable semi-analytical design sensitivities. The improvement of design sensitivities corresponding to the rigid body mode is evaluated by exact differentiation of the rigid body modes and the error of SAM caused by numerical difference scheme is alleviated by using a Von Neumann series approximation considering the higher order terms for the sensitivity derivatives. In eigenvalue problems, the tendency of eigenvalue sensitivity is similar to that of displacement sensitivity in static problems. Eigenvector is decomposed into rigid body mode and pure deformation mode. The present iterative SAM guarantees that the eigenvalue and eigenvector sensitivities converge to the reliable values for the wide range of perturbed size of the design variables. Accuracy and reliability of the shape design sensitivities in static problems and eigenvalue problems by the proposed method are assessed through the various numerical examples. Copyright 2004 John Wiley & Sons, Ltd. [source]


    Efficient mixed Timoshenko,Mindlin shell elements

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2002
    G. M. Kulikov
    Abstract The precise representation of rigid body motions in the displacement patterns of curved Timoshenko,Mindlin (TM) shell elements is considered. This consideration requires the development of the strain,displacement relationships of the TM shell theory with regard to their consistency with the rigid body motions. For this purpose a refined TM theory of multilayered anisotropic shells is elaborated. The effects of transverse shear deformation and bending-extension coupling are included. The fundamental unknowns consist of five displacements and eight strains of the face surfaces of the shell, and eight stress resultants. On the basis of this theory the simple and efficient mixed models are developed. The elemental arrays are derived using the Hu,Washizu mixed variational principle. Numerical results are presented to demonstrate the high accuracy and effectiveness of the developed 4-node shell elements and to compare their performance with other finite elements reported in the literature. Copyright 2002 John Wiley & Sons, Ltd. [source]


    An objective finite element approximation of the kinematics of geometrically exact rods and its use in the formulation of an energy,momentum conserving scheme in dynamics

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2002
    I. Romero
    Abstract We present in this paper a new finite element formulation of geometrically exact rod models in the three-dimensional dynamic elastic range. The proposed formulation leads to an objective (or frame-indifferent under superposed rigid body motions) approximation of the strain measures of the rod involving finite rotations of the director frame, in contrast with some existing formulations. This goal is accomplished through a direct finite element interpolation of the director fields defining the motion of the rod's cross-section. Furthermore, the proposed framework allows the development of time-stepping algorithms that preserve the conservation laws of the underlying continuum Hamiltonian system. The conservation laws of linear and angular momenta are inherited by construction, leading to an improved approximation of the rod's dynamics. Several numerical simulations are presented illustrating these properties. Copyright 2002 John Wiley & Sons, Ltd. [source]