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Kinematic Models (kinematic + models)
Selected AbstractsKinematic models for non-coaxial granular materials.INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 7 2005Part I: theory Abstract The purpose of this paper is to present a physically based plasticity model for non-coaxial granular materials. The model, which we shall call the double slip and rotation rate model (DSR2 model), is a pair of kinematic equations governing the velocity field. The model is based on a discrete micro-analysis of the kinematics of particles in contact, and is formulated by introducing a quantity called the averaged micro-pure rotation rate (APR) into the unified plasticity model which was proposed by one of the authors. Our macro,micro mechanical analysis shows that the APR is a non-linear function of, among other quantities, the macro-rotation rate of the major principal axis of stress taken in the opposite sense. The requirement of energy dissipation used in the double-sliding free-rotating model appears to be unduly restrictive as a constitutive assumption in continuum models. In the DSR2 model the APR tensor and the spin tensor are directly linked with non-coaxiality of the stress and deformation rate tensors. We also propose a simplified plasticity model based on the DSR2 model for a class of dilatant materials, and analyse its material stability. Copyright © 2005 John Wiley & Sons, Ltd. [source] Kinematic models for non-coaxial granular materials.INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 7 2005Part II: evaluation Abstract In this paper we present results of numerical simulations for the evaluation of kinematic models for non-coaxial granular materials by the distinct element method (DEM). Strain-rate controlled monotonic and cyclic un-drained simple shear tests were specifically designed and evaluation criteria established for this purpose. The models examined are the double-shearing model, the double-sliding free-rotating model, and the double slip and rotation rate model (DSR2 model) proposed by the authors (see the accompanying paper). It is shown that the assumption used in the double-shearing model appears to not be in agreement with the DEM data. It is also shown that in the double-sliding free-rotating model the energy dissipation requirements appear to be unduly restrictive as a constitutive assumption. The DSR2 model, which is a hybrid of discrete micro-mechanics and continuum modelling, gives better agreement with the results of our DEM simulations, than either the double-shearing model or the double-sliding free-rotating model. Copyright © 2005 John Wiley & Sons, Ltd. [source] Animating Quadrupeds: Methods and ApplicationsCOMPUTER GRAPHICS FORUM, Issue 6 2009Ljiljana Skrba I.3.7 [Computer Graphics]: 3D Graphics and Realism , Animation Abstract Films like Shrek, Madagascar, The Chronicles of Narnia and Charlotte's web all have something in common: realistic quadruped animations. While the animation of animals has been popular for a long time, the technical challenges associated with creating highly realistic, computer generated creatures have been receiving increasing attention recently. The entertainment, education and medical industries have increased the demand for simulation of realistic animals in the computer graphics area. In order to achieve this, several challenges need to be overcome: gathering and processing data that embodies the natural motion of an animal , which is made more difficult by the fact that most animals cannot be easily motion-captured; building accurate kinematic models for animals, with adapted animation skeletons in particular; and developing either kinematic or physically-based animation methods, either by embedding some a priori knowledge about the way that quadrupeds locomote and/or adopting examples of real motion. In this paper, we present an overview of the common techniques used to date for realistic quadruped animation. This includes an outline of the various ways that realistic quadruped motion can be achieved, through video-based acquisition, physics based models, inverse kinematics or some combination of the above. [source] Contribution of different kinematic models and a complex Jurassic stratigraphy in the construction of a forward model for the Montagna dei Fiori fault-related fold (Central Apennines, Italy)GEOLOGICAL JOURNAL, Issue 5-6 2010L. Di Francesco Abstract The Montagna dei Fiori has received attention from geologists over the past decades because of both its Jurassic stratigraphy and its complex present-day structure. The latter is the result of multiple phases of deformation, from the Early Jurassic, during the opening of the Tethyan Ocean, to Neogene evolution of the Apennines fold-and-thrust belt. In this paper, we present a new stratigraphic interpretation of the Jurassic palaeogeography, based on a new geological mapping project in the area. Using this new stratigraphy, we constructed two forward models, using a combination of different fault/fold interactions, in order to unravel the kinematic evolution of the Montagna dei Fiori fault-related fold. The first model was constructed manually using the fault-bend and fault-propagation theories from an initial configuration which included previous extensional features, whereas the second model was constructed using the software 2DMove (Midland Valley) using the fault-bend and trishear fault-propagation folding theories and starting from a layer-cake stratigraphy. Both forward models involved the same main steps and provided a reasonable geological simulation of the geometry of the Montagna dei Fiori structure. Copyright © 2010 John Wiley & Sons, Ltd. [source] Kinematic models for non-coaxial granular materials.INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 7 2005Part II: evaluation Abstract In this paper we present results of numerical simulations for the evaluation of kinematic models for non-coaxial granular materials by the distinct element method (DEM). Strain-rate controlled monotonic and cyclic un-drained simple shear tests were specifically designed and evaluation criteria established for this purpose. The models examined are the double-shearing model, the double-sliding free-rotating model, and the double slip and rotation rate model (DSR2 model) proposed by the authors (see the accompanying paper). It is shown that the assumption used in the double-shearing model appears to not be in agreement with the DEM data. It is also shown that in the double-sliding free-rotating model the energy dissipation requirements appear to be unduly restrictive as a constitutive assumption. The DSR2 model, which is a hybrid of discrete micro-mechanics and continuum modelling, gives better agreement with the results of our DEM simulations, than either the double-shearing model or the double-sliding free-rotating model. Copyright © 2005 John Wiley & Sons, Ltd. [source] Kinematic modeling of mobile robots by transfer method of augmented generalized coordinatesJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 6 2004Wheekuk Kim A kinematic modeling method, which is directly applicable to any type of planar mobile robots, is proposed in this work. Since holonomic constraints have the same differential form as nonholonomic constraints, the instantaneous motion of the mobile robot at current configuration can be modeled as that of a parallel manipulator. A pseudo joint model denoting the interface between the wheel and the ground (i.e., the position of base of the mobile robot) enables the derivation of this equivalent kinematic model. The instantaneous kinematic structures of four different wheels are modeled as multiple pseudo joints. Then, the transfer method of augmented generalized coordinates, which has been popularly employed in modeling of parallel manipulators, is applied to obtain the instantaneous kinematic models of mobile robots. The kinematic models of six different types of planar mobile robots are derived to show the effectiveness of the proposed modeling method. Lastly, for the mobile robot equipped with four conventional wheels, an algorithm estimating a sensed forward solution for the given information of the rotational velocities of the four wheels is discussed. © 2004 Wiley Periodicals, Inc. [source] Discrete-element modelling of detachment foldingBASIN RESEARCH, Issue 4 2005Stuart Hardy ABSTRACT A two-dimensional, discrete-element modelling technique is used to investigate the initiation and growth of detachment folds in sedimentary rocks above a weak décollement level. The model depicts the sedimentary rocks as an assemblage of spheres that obey Newton's equations of motion and that interact with elastic forces under the influence of gravity. Faulting or fracturing between neighbouring elements is represented by a transition from repulsive,attractive forces to solely repulsive forces. The sedimentary sequence is mechanically heterogeneous, consisting of intercalated layers of markedly different strengths and thicknesses. The interlayering of weak and strong layers within the sedimentary rocks promotes the localization of flexural flow deformation within the weak layers. Even with simple displacement boundary conditions, and straightforward interlayering of weak and strong layers, the structural geometries that develop are complex, with a combination of box, lift-off and disharmonic detachment fold styles forming above the décollement. In detail, it is found that the modelled folds grow by both limb rotation and limb lengthening. The combination of these two mechanisms results in uplift patterns above the folds that are difficult, or misleading, to interpret in terms of simple kinematic models. Comparison of modelling results with natural examples and with kinematic models highlights the complexities of structural interpretation in such settings. [source] Modelling detrital cooling-age populations: insights from two Himalayan catchmentsBASIN RESEARCH, Issue 3 2003I. D. Brewer The distribution of detrital mineral cooling ages in river sediment provides a proxy record for the erosional history of mountain ranges. We have developed a numerical model that predicts detrital mineral age distributions for individual catchments in which particle paths move vertically toward the surface. Despite a restrictive set of assumptions, the model permits theoretical exploration of the effects of thermal structure, erosion rate, and topography on cooling ages. Hypsometry of the source-area catchment is shown to exert a fundamental control on the frequency distribution of bedrock and detrital ages. We illustrate this approach by generating synthetic 40Ar/39Ar muscovite age distributions for two catchments with contrasting erosion rates in central Nepal and then by comparing actual measured cooling-age distributions with the synthetic ones. Monte Carlo sampling is used to assess the mismatch between observed and synthetic age distributions and to explore the dependence of that mismatch on the complexity of the synthetic age signal and on the number of grains analysed. Observed detrital cooling ages are well matched by predicted ages for a more slowly eroding Himalayan catchment. A poorer match for a rapidly eroding catchment may result from some combination of large analytical uncertainties in the detrital ages and inhomogeneous erosion rates within the basin. Such mismatches emphasize the need for more accurate thermal and kinematic models and for sampling strategies that are adapted to catchment-specific geologic and geomorphic conditions. [source] | |||||||||||||