A GPU-implemented physics-based haptic simulator of tooth drilling.

BACKGROUND: Restorative dentistry simulation is one of the most challenging applications involving virtual reality and haptics. This paper presents a haptics-based tooth drilling simulator for dental education. METHODS: Unlike the existing methods, the force model is based on physical properties which consider the geometrical model of the tool. In order to provide uniform force feedback from tooth layers, a new approach is suggested in which the physical properties of each tooth voxel are subsequently used in calculating the feedback force. We implement a hashing algorithm for collision detection due to its reduced time complexity. The haptics algorithm has been implemented on a graphics processing unit using the CUDA toolbox. RESULTS: In parallel processing, the speed of haptic loop execution is increased almost 8 times. CONCLUSION: The proposed idea for force calculation leads to a uniform sensation of force. An important feature of the designed system is the capability to run in a real-time fashion.

A numerical and experimental study of periodic flow in a model of a corrugated vessel with application to stented arteries.

The investigation presented in this paper has attempted to study, from a fluid dynamics point of view, the consequences of the presence of a stent on the flow of blood. The method adopted is mainly by numerical simulation using a finite element technique, but visualization experiments and an analytical study have also been carried out. The flow of blood is treated as being transient, laminar and Newtonian within a rigid section of the stented vessel. The flow is driven by an imposed pressure gradient in the form of a physiological waveform. A periodic boundary condition has been applied. Particle trajectories, fluid shear rate contours and wall shear stress maps, together with the use of a simplified form of particle image velocimetry in the experimental work, have been used to interpret the results. It was found that the vessel wall experienced oscillating levels of wall shear stress, in particular extensive exposure to low shear stress. Regions of flow recirculation, points of flow separation and reattachment constantly move in regions of low shear stress. Vortices form and then are destroyed rapidly by reversing flow. Their potential physiological significance to stented arteries is discussed.

Comparison of flow in numerical and physical models of a ventricular assist device using low- and high-viscosity fluids.

The flows in a model of a ventricular assist device (VAD) were investigated numerically and experimentally for two different Newtonian test fluids. These were a blood analogue fluid and a much higher viscosity fluid. A finite volume method was employed to solve the governing equations for a three-dimensional unsteady laminar flow on a transient grid. The numerical solutions were compared with experimental results from an identical physical model. The experimental flows were investigated by flow visualization and by laser Doppler velocity measurements at selected points in the flow field. The validation was based on comparisons of flow patterns and of non-component velocity-time histories. The maximum Reynolds numbers in the inflow tube of the model VAD were approximately 460 and 3300 using the high- and low-viscosity fluids respectively. The investigation showed that the flow patterns were better predicted for the high-viscosity fluid. However, the agreement between the velocity-time histories was found to be slightly better for the low-viscosity fluid. The discrepancies in the flow patterns may be due to intermittent turbulence with a further contribution from numerical diffusion.

Investigation of unsteady flow in a model of a ventricular assist device by numerical modelling and comparison with experiment.

Prior to this study, a clinical prototype of a sac-type ventricular assist device (VAD) was investigated experimentally, using both flow visualisation and Laser Doppler anemometry (LDA), in order to optimise its geometry. As poor optical access precluded the experimental investigation of the flow in some areas of the prototype VAD, computational fluid dynamics (CFD) was used in the present work. Flow patterns during one full pumping cycle were investigated in a simplified model of the VAD. The numerical solutions were compared with experimental results from an identical physical model. The model consists of the hemispherical cylinder and two attached tubes for the inflow and outflow. Instead of a diaphragm in the clinical device, which deforms non-uniformly during pumping, a piston with a matching hemispherical crown was used. A finite volume method was employed to solve the governing equations for the three-dimensional, unsteady, laminar flow of an incompressible, Newtonian fluid. The general flow features were predicted very well by the simulation, with some differences in the details of the flow structures. This allows the conclusion that CFD can be used to facilitate improvement of the design of the clinical device. The comparison of one-component velocity time histories at selected points showed that the predicted velocities were approximately 20-50% lower than those measured by LDA. Such underprediction would lead to erroneous results for particle residence times and may result in an underestimation of wall shear stresses.