The Experts below are selected from a list of 61944 Experts worldwide ranked by ideXlab platform
Steve Haake - One of the best experts on this subject based on the ideXlab platform.
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Experimental and finite element analysis of a tennis ball impact on a Rigid Surface
Sports Engineering, 2005Co-Authors: Simon Goodwill, R. Kirk, Steve HaakeAbstract:An explicit finite-element (FE) model of a pressurised tennis ball is presented. The FE model was used to model an oblique impact between a tennis ball and a Rigid tennis Surface, to further the understanding of this impact. Impacts were also conducted in the laboratory and the results from the FE model were in good agreement with this experimental data. The FE model was used to illustrate why a tennis ball rebounds with a higher vertical coefficient of restitution in an oblique impact compared to an equivalent impact perpendicular to the Surface; this equivalent perpendicular impact has the same inbound velocity as the vertical component of the oblique impact. The FE model was also used to illustrate that the structural compliance of the felt covering on a tennis ball was a contributing factor to the ball attaining more spin in the impact than would have been calculated using a conventional analytical model. Also, the spin values calculated in the FE simulation were in good agreement with experimental data.
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Modelling of tennis ball impacts on a Rigid Surface
Proceedings of the Institution of Mechanical Engineers Part C: Journal of Mechanical Engineering Science, 2004Co-Authors: Simon Goodwill, Steve HaakeAbstract:A viscoelastic model of a tennis ball impact at normal incidence on a Rigid Surface is presented in this study. The ball model has three discrete elements that account for the structural stiffness, material damping and momentum flux loading. Experiments using a force platform are performed to determine the force that acts on the ball during impact, for a range of ball inbound velocities. The inbound and rebound velocities of the ball are measured using speed gates. The contact time and coefficient of restitution for the impact are also determined in these experiments. The model parameters are determined such that the values of the coefficient of restitution and contact time that are calculated by the model are consistent with those values determined experimentally. The model can be used to calculate the force that acts on the ball during impact. Generally, the force-time plots calculated by the model were consistent with those determined experimentally. Furthermore, the model can be used to calculate the three components of the force that acts on the ball during impact. It is shown that the main component of the force during the first 0.6 ms of impact is that due to momentum flux loading. This is approximately equal in magnitude for each ball type and explains why the total force acting on each ball is very similar during this period.
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Impact of a non-homogeneous sphere on a Rigid Surface
Proceedings of the Institution of Mechanical Engineers Part C: Journal of Mechanical Engineering Science, 2004Co-Authors: Matt Carré, David James, Steve HaakeAbstract:This paper examines the impact behaviour of a non-homogenous sphere (in this case a cricket ball with a rolled core construction) with a Rigid Surface. Experiments were carried out to measure the force-deflection behaviour of a cricket ball during a normal impact in two orientations (impacting on the seam and perpendicular to the seam). For the two orientations of impact, a disparity was found in terms of the force-deflection behaviour. Greater deformation was found for impacts landing on the seam, compared to those landing perpendicular to the seam. Comparisons with quasi-static test data suggested that only the bottom third of the ball may have been compressed during impact. The dynamic force-deflection behaviour was modelled using a mass attached to a Hertzian spring in parallel with a damper whose damping coefficient varied with the contact area. The coefficients in the model could be described using the velocity before impact alone. The model was found to be in good agreement with the experimental data. The model was then extended to predict oblique impacts by incorporating a measured coefficient of friction. This performed well in predicting the rebound velocity, angle and spin of a cricket ball after oblique impact with a cricket pitch. Inconsistencies in the results were attributed to deformation in the pitch Surface.
Serge Belongie - One of the best experts on this subject based on the ideXlab platform.
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Non-Rigid Surface detection for gestural interaction with applicable Surfaces
2012 IEEE Workshop on the Applications of Computer Vision (WACV), 2012Co-Authors: Andrew Ziegler, Serge BelongieAbstract:In this work we present a novel application of non-Rigid Surface detection to enable gestural interaction with applicable Surfaces. This method can add interactivity to traditionally passive media such as books, newspapers, restaurant menus, or anything else printed on paper. We allow a user to interact with these Surfaces in a natural manner and present basic gestures based on pointing and touching. This technique was developed as part of an ongoing effort to create an assisted reading device for the visually impaired. However, it is suited to general applications and can be used as a practical mechanism for interaction with screen-less wearable devices. Our key contributions are a unique application of non-Rigid Surface detection, a basic gesturing paradigm, and a proof of concept system.
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WACV - Non-Rigid Surface detection for gestural interaction with applicable Surfaces
2012 IEEE Workshop on the Applications of Computer Vision (WACV), 2012Co-Authors: Andrew Ziegler, Serge BelongieAbstract:In this work we present a novel application of non-Rigid Surface detection to enable gestural interaction with applicable Surfaces. This method can add interactivity to traditionally passive media such as books, newspapers, restaurant menus, or anything else printed on paper. We allow a user to interact with these Surfaces in a natural manner and present basic gestures based on pointing and touching. This technique was developed as part of an ongoing effort to create an assisted reading device for the visually impaired. However, it is suited to general applications and can be used as a practical mechanism for interaction with screen-less wearable devices. Our key contributions are a unique application of non-Rigid Surface detection, a basic gesturing paradigm, and a proof of concept system.
Simon Goodwill - One of the best experts on this subject based on the ideXlab platform.
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Experimental and finite element analysis of a tennis ball impact on a Rigid Surface
Sports Engineering, 2005Co-Authors: Simon Goodwill, R. Kirk, Steve HaakeAbstract:An explicit finite-element (FE) model of a pressurised tennis ball is presented. The FE model was used to model an oblique impact between a tennis ball and a Rigid tennis Surface, to further the understanding of this impact. Impacts were also conducted in the laboratory and the results from the FE model were in good agreement with this experimental data. The FE model was used to illustrate why a tennis ball rebounds with a higher vertical coefficient of restitution in an oblique impact compared to an equivalent impact perpendicular to the Surface; this equivalent perpendicular impact has the same inbound velocity as the vertical component of the oblique impact. The FE model was also used to illustrate that the structural compliance of the felt covering on a tennis ball was a contributing factor to the ball attaining more spin in the impact than would have been calculated using a conventional analytical model. Also, the spin values calculated in the FE simulation were in good agreement with experimental data.
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Modelling of tennis ball impacts on a Rigid Surface
Proceedings of the Institution of Mechanical Engineers Part C: Journal of Mechanical Engineering Science, 2004Co-Authors: Simon Goodwill, Steve HaakeAbstract:A viscoelastic model of a tennis ball impact at normal incidence on a Rigid Surface is presented in this study. The ball model has three discrete elements that account for the structural stiffness, material damping and momentum flux loading. Experiments using a force platform are performed to determine the force that acts on the ball during impact, for a range of ball inbound velocities. The inbound and rebound velocities of the ball are measured using speed gates. The contact time and coefficient of restitution for the impact are also determined in these experiments. The model parameters are determined such that the values of the coefficient of restitution and contact time that are calculated by the model are consistent with those values determined experimentally. The model can be used to calculate the force that acts on the ball during impact. Generally, the force-time plots calculated by the model were consistent with those determined experimentally. Furthermore, the model can be used to calculate the three components of the force that acts on the ball during impact. It is shown that the main component of the force during the first 0.6 ms of impact is that due to momentum flux loading. This is approximately equal in magnitude for each ball type and explains why the total force acting on each ball is very similar during this period.
Andrew J Szeri - One of the best experts on this subject based on the ideXlab platform.
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dynamics of bubbles near a Rigid Surface subjected to a lithotripter shock wave part 2 reflected shock intensifies non spherical cavitation collapse
Journal of Fluid Mechanics, 2008Co-Authors: Michael L Calvisi, Jonathan Iloreta, Andrew J SzeriAbstract:In this paper we use the boundary integral method to model the non-spherical collapse of bubbles excited by lithotripter shock waves near a Rigid boundary. The waves we consider are representative of those developed by shock wave lithotripsy or shock wave therapy devices, and the Rigid boundaries we consider are representative of kidney stones and reflective bony tissue. This study differs from previous studies in that we account for the reflection of the incident wave and also the asymmetry of the collapse caused by the presence of the Rigid Surface. The presence of the boundary causes interference between reflected and incident waves. Quantities such as kinetic energy, Kelvin impulse and centroid translation are calculated in order to illuminate the physics of the collapse process. The main finding is that the dynamics of the bubble collapse depend strongly on the distance of the bubble relative to the wall when reflection is taken into account, but much less so when reflection is omitted from the model. The reflection enhances the expansion and subsequent collapse of bubbles located near the boundary owing to constructive interference between incident and reflected waves; however, further from the boundary, the dynamics of collapse are suppressed owing to destructive interference of these two waves. This result holds regardless of the initial radius of the bubble or its initial state at the time of impact with the lithotripter shock wave. Also, the work done by the lithotripter shock wave on the bubble is shown to predict strongly the maximum bubble volume regardless of the standoff distance and the presence or absence of reflection; furthermore, allowing for non-sphericity, these predictions match almost exactly those of a previously developed spherical model.
Pascal Fua - One of the best experts on this subject based on the ideXlab platform.
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fast non Rigid Surface detection registration and realistic augmentation
International Journal of Computer Vision, 2008Co-Authors: Julien Pilet, Vincent Lepetit, Pascal FuaAbstract:We present a real-time method for detecting deformable Surfaces, with no need whatsoever for a priori pose knowledge. Our method starts from a set of wide baseline point matches between an undeformed image of the object and the image in which it is to be detected. The matches are used not only to detect but also to compute a precise mapping from one to the other. The algorithm is robust to large deformations, lighting changes, motion blur, and occlusions. It runs at 10 frames per second on a 2.8 GHz PC.We demonstrate its applicability by using it to realistically modify the texture of a deforming Surface and to handle complex illumination effects. Combining deformable meshes with a well designed robust estimator is key to dealing with the large number of parameters involved in modeling deformable Surfaces and rejecting erroneous matches for error rates of more than 90%, which is considerably more than what is required in practice.
