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Applied Force (applied + force)
Selected AbstractsThe response of an elastic half-space under a momentary shear line impulseINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2003Moche Ziv Abstract The response of an ideal elastic half-space to a line-concentrated impulsive vector shear force applied momentarily is obtained by an analytical,numerical computational method based on the theory of characteristics in conjunction with kinematical relations derived across surfaces of strong discontinuities. The shear force is concentrated along an infinite line, drawn on the surface of the half-space, while being normal to that line as well as to the axis of symmetry of the half-space. An exact loading model is introduced and built into the computational method for this shear force. With this model, a compatibility exists among the prescribed applied force, the geometric decay of the shear stress component at the precursor shear wave, and the boundary conditions of the half-space; in this sense, the source configuration is exact. For the transient boundary-value problem described above, a wave characteristics formulation is presented, where its differential equations are extended to allow for strong discontinuities which occur in the material motion of the half-space. A numerical integration of these extended differential equations is then carried out in a three-dimensional spatiotemporal wavegrid formed by the Cartesian bicharacteristic curves of the wave characteristics formulation. This work is devoted to the construction of the computational method and to the concepts involved therein, whereas the interpretation of the resultant transient deformation of the half-space is presented in a subsequent paper. Copyright © 2003 John Wiley & Sons, Ltd. [source] Dynamic stiffness for piecewise non-uniform Timoshenko column by power series,part II: Follower forceINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2001A. Y. T. Leung Abstract A follower force is an applied force whose direction changes according to the deformed shape during the course of deformation. The dynamic stiffness matrix of a non-uniform Timoshenko column under follower force is formed by the power-series method. The dynamic stiffness matrix is unsymmetrical due to the non-conservative nature of the follower force. The frequency-dependent mass matrix is still symmetrical and positive definite according to the extended Leung theorem. An arc length continuation method is introduced to find the influence of a concentrated follower force, distributed follower force, end mass and stiffness, slenderness, and taper ratio on the natural frequency and stability. It is found that the power-series method can handle a very wide class of dynamic stiffness problem. Copyright © 2001 John Wiley & Sons, Ltd. [source] Auxetic lattice of multipodsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2009Peter V. Pikhitsa Abstract Auxetics are novel counterintuitive materials that grow thicker perpendicularly to the applied force when stretched and therefore are described by a negative Poisson's ratio. We show that a regular lattice of individual multipods properly assembled in three dimensions has the ultimate negative Poisson's ratio ,1: the lattice expands or contracts uniformly in all directions. Our ball-and-stick working model verifies the mathematical construction. Application of the model to real materials is discussed. Our result is important for understanding the ways to create entangled materials with interesting mechanical properties. [source] Single-molecule pair studies of the interactions of the ,-GalNAc (Tn-antigen) form of porcine submaxillary mucin with soybean agglutininBIOPOLYMERS, Issue 9 2009Marit Sletmoen Abstract Mucins form a group of heavily O -glycosylated biologically important glycoproteins that are involved in a variety of biological functions, including modulating immune response, inflammation, and adhesion. Mucins are also involved in cancer and metastasis and often express diagnostic cancer antigens. Recently, a modified porcine submaxillary mucin (Tn-PSM) containing GalNAc,1- O -Ser/Thr residues was shown to bind to soybean agglutinin (SBA) with ,106 -fold enhanced affinity relative to GalNAc,1- O -Ser, the pancarcinoma carbohydrate antigen. In this study, dynamic force spectroscopy is used to investigate molecular pairs of SBA and Tn-PSM. A number of force jumps that demonstrate unbinding or rebinding events were observed up to a distance equal to 2.0 ,m, consistent with the length of the mucin chain. The unbinding force increased from 103 to 402 pN with increasing force loading rate. The position of the activation barrier in the energy landscape of the interaction was 0.1 nm. The lifetime of the SBA,TnPSM complex in the absence of applied force was determined to be in the range 1.3,1.9 s. Kinetic parameters describing the rate of dissociation of other sugar lectin interactions are in the range 3.3 × 10,3,2.5 × 10,3 s. The long lifetime of the SBA-TnPSM complex is compatible with a binding model in which lectin molecules "bind and jump" from ,-GalNAc residue to ,-GalNAc residue along the polypeptide chain of Tn-PSM before dissociating. These findings have important implications for the molecular recognition properties of mucins. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 719,728, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Improving realism of a surgery simulator: linear anisotropic elasticity, complex interactions and force extrapolationCOMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3 2002Guillaume Picinbono Abstract In this article, we describe the latest developments of the minimally invasive hepatic surgery simulator prototype developed at INRIA. The goal of this simulator is to provide a realistic training test bed to perform laparoscopic procedures. Therefore, its main functionality is to simulate the action of virtual laparoscopic surgical instruments for deforming and cutting tridimensional anatomical models. Throughout this paper, we present the general features of this simulator including the implementation of several biomechanical models and the integration of two force-feedback devices in the simulation platform. More precisely, we describe three new important developments that improve the overall realism of our simulator. First, we have developed biomechanical models, based on linear elasticity and finite element theory, that include the notion of anisotropic deformation. Indeed, we have generalized the linear elastic behaviour of anatomical models to ,transversally isotropic' materials, i.e. materials having a different behaviour in a given direction. We have also added to the volumetric model an external elastic membrane representing the ,liver capsule', a rather stiff skin surrounding the liver, which creates a kind of ,surface anisotropy'. Second, we have developed new contact models between surgical instruments and soft tissue models. For instance, after detecting a contact with an instrument, we define specific boundary constraints on deformable models to represent various forms of interactions with a surgical tool, such as sliding, gripping, cutting or burning. In addition, we compute the reaction forces that should be felt by the user manipulating the force-feedback devices. The last improvement is related to the problem of haptic rendering. Currently, we are able to achieve a simulation frequency of 25,Hz (visual real time) with anatomical models of complex geometry and behaviour. But to achieve a good haptic feedback requires a frequency update of applied forces typically above 300,Hz (haptic real time). Thus, we propose a force extrapolation algorithm in order to reach haptic real time. Copyright © 2002 John Wiley & Sons, Ltd. [source] Axial Rotation of the Lower Human Spine by Rhythmic Torques Automatically Generated at the Resonant FrequencyEXPERIMENTAL PHYSIOLOGY, Issue 3 2003E. Geoffrey Walsh Subjects sat on a ,Balans' chair supported by the shaft of a large torque generator. The lower but not the upper part of the body was free to make to/fro movements maintained by feeding back a modified velocity signal to the generator. The stiffness could be increased by the use of a position signal. Using the equations for a torsion pendulum the good linearity observed in relationship to the applied forces allowed stiffness, inertia, damping, critical damping and the damping factor to be determined in absolute terms. The method enables parameters relevant to back function and problems to be evaluated. Eleven adults acted as subjects. [source] On computing the forces from the noisy displacement data of an elastic bodyINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2008A. Narayana Reddy Abstract This study is concerned with the accurate computation of the unknown forces applied on the boundary of an elastic body using its measured displacement data with noise. Vision-based minimally intrusive force-sensing using elastically deformable grasping tools is the motivation for undertaking this problem. Since this problem involves incomplete and inconsistent displacement/force of an elastic body, it leads to an ill-posed problem known as Cauchy's problem in elasticity. Vision-based displacement measurement necessitates large displacements of the elastic body for reasonable accuracy. Therefore, we use geometrically non-linear modelling of the elastic body, which was not considered by others who attempted to solve Cauchy's elasticity problem before. We present two methods to solve the problem. The first method uses the pseudo-inverse of an over-constrained system of equations. This method is shown to be not effective when the noise in the measured displacement data is high. We attribute this to the appearance of spurious forces at regions where there should not be any forces. The second method focuses on minimizing the spurious forces by varying the measured displacements within the known accuracy of the measurement technique. Both continuum and frame elements are used in the finite element modelling of the elastic bodies considered in the numerical examples. The performance of the two methods is compared using seven numerical examples, all of which show that the second method estimates the forces with an error that is not more than the noise in the measured displacements. An experiment was also conducted to demonstrate the effectiveness of the second method in accurately estimating the applied forces. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||