International Journal of Modeling, Simulation, and Scientific Computing

From the beginning, the GEANT4 Visualization System was designed to support several simultaneous graphics systems written to common abstract interfaces. Today, it has matured into a powerful diagnostic and presentational tool. It comes with a library of models that may be added to the current scene and which include the representation of the GEANT4 geometry hierarchy, simulated trajectories and user-written hits and digitizations. The workhorse is the OpenGL suite of drivers for X, Xm, Qt, and Win32. There is an Open Inventor driver. Scenes can be exported in special graphics formats for offline viewing in the DAWN, VRML, HepRApp and gMocren browsers. PostScript can be generated through OpenGL, Open Inventor, DAWN and HepRApp. GEANT4's own tracking algorithms are used by the Ray Tracer. Not all drivers support all features but all drivers bring added functionality of some sort. This paper describes the interfaces and details the individual drivers.

We present our recent research results regarding the designing and implementation of real-time physics simulation engines, which aim at developing physics-inspired e-entertainment such as computer games, mobile applications, interactive TV and other smart media in Korea. Our real-time physics engine consists of three functional components: rigid body dynamics simulation, deformable body simulation, and data-driven physics simulation. The core simulation techniques to realize these simulation components include real-time collision detection and response, large-scale model simulation, and character model control. In this paper, we highlight these features and demonstrate their performances. We also showcase some of the gaming applications that we have integrated our physics engine into.

We have been developing a visualization application for CAVE-type virtual reality (VR) systems for more than a decade. This application, VFIVE, is currently used in several CAVE systems in Japan for routine visualizations. It is also used as a base system of further developments of advanced visualizations. The development of VFIVE is summarized.

VFIVE is a scientific visualization application for CAVE-type immersive virtual reality (VR) systems. The source codes are freely available. VFIVE is used as a research tool in various VR systems. It also lays the groundwork for developments of new visualization software for CAVEs. In this paper, we pick up five CAVE systems in four different institutions in Japan. Applications of VFIVE in each CAVE system are summarized. Special emphases will be placed on scientific and technical achievements made possible by VFIVE.

Direct numerical simulation (DNS) of turbulent planar jet with a second-order chemical reaction (A + B → R) is performed to investigate the processes of mixing and chemical reactions in spatially developing turbulent free shear flows. Reactant A is premixed into the jet flow, and reactant B is premixed into the ambient flow. DNS is performed at three different Damköhler numbers (Da = 0.1,1, and 10). Damköhler number is a ratio of a time scale of a flow to that of chemical reactions, and in this study, the large Da means a fast chemical reaction, and the small Da means a slow chemical reaction. The visualization of velocity field shows that the jet flow is developed by entraining the ambient fluid. The visualization of concentration of reactant A shows that concentration of reactant A for Da = 1 and 10 becomes very small in the downstream region because the chemical reaction consumes the reactants and reactant A is diffused with the jet development. By comparison of the profiles of chemical reaction rate and concentration of product R, it is found that product R for Da = 10 is produced by the chemical reaction at the interface between the jet and the ambient fluids and is diffused into the jet flow, whereas product R for Da = 0.1 is produced in the jet flow after reactants A and B are well mixed.

Recent studies are focusing on the distribution of water mass because the mixture region of water mass is highly related to the rich fishing grounds [Yasuda I., Watanabe Y., Fish. Oceanogr.3(3):172–181, 1994]. Due to the large data size and time-varying property, efficient exploration and visualization of the ocean data is always extremely challenging. To extract the dynamic behaviors of the water mass and its mixture from a large-scale simulated ocean dataset, we developed an efficient visualization system by applying our volume compression method and our volume rendering method. This system allows us to investigate the time-varying distributions of ocean physical properties, additionally from the user's perspective and requirements. In the experiments, we show the generality and expressiveness by applying our system for single- and multi-property visualizations to find some significant ocean water mass. Consequently, we could obtain a clear visualization result to show the dynamic behaviors of the mixture of water mass for simulation data regarding a location in the northwestern Pacific near Japan.

This paper proposes a method to create 3D fusion images, such as volume–volume, volume–surface, and surface–surface fusion. Our method is based on the particle-based rendering, which uses tiny particles as rendering primitives. The method can create natural and comprehensible 3D fusion images simply by merging particles prepared for each element to be fused. Moreover, the method does not require particle sorting along the line of sight to realize right depth feel. We apply our method to realize comprehensible visualization of medical volume data.

The paper presents an approach to fast approximate estimation of conditions for space-time structures appearing in the flows. The approach is based on combination of optimization problem computation with methods of data visual presentation. The visual presentation methods are applied for analysis of multidimensional array containing discrete result data. Optimization problem solution is implemented by parallel computation in a multitask form. For some cases, the approach allows to obtain for control parameter of considered problem the sought-for approximate dependence on characteristic parameters in a quasi-analytical form.

In the process of interpreting simulation results, new post-processing techniques are developed. This work presents a post-processing method that analyzes the solidification pattern formed by simulation of the solidification process of molten metal in a mold to produce shaped castings. Simulations generally involve numerical solutions of differential equations which are discretized by dividing the three-dimensional computational domain into small finite volume elements using a 3D grid. The locations of the grid points and values of the solidification time at these locations are used to divide the spatial data into 3D sections such that starting from a hotspot location within the section that has high solidification time, there is a gradient outwards with lower values of solidification time. Each section is assumed to be fed by one or more feeders that must freeze only after the section has solidified completely. The volume of a feeder can be determined from the volume of the section it is supposed to feed. The volume and surface area of sections are determined approximately to calculate feeder size and dimensions. The post-processing algorithm is a simulation-based quantitative approach to feeder design which in conventional foundry practice has been more of an art than science. It is also general enough for use in other 3D segmentation applications.