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CFD Visualization in Virtual Reality: the Titanic Resurrected

By Jos Roerdink

Nowadays, we have to deal with floods of data in many branches of science. One of these areas is Computational Fluid Dynamics (CFD), i.e. computerized fluid flow simulation. The dynamics of liquids or gases are computed in two or three spatial dimensions.

The grand challenge equations, with the Navier-Stokes equation as used in CFD calculations
The grand challenge equations, with the Navier-Stokes equation as used in the CFD calculations

For this purpose, millions of computational cells are used at any given time step, where each cell can contain several values, such as fluid pressure or velocity. Visualization can be a powerful tool to obtain an overview of all the relevant aspects of the data in the computational domain. From autumn 2002 to summer 2003, a project ran to combine 3D fluid flow simulations with visualization in the Virtual Reality (VR) facilities of the Reality Centre of the University of Groningen. The project was conducted by the Master's student Michael ten Caat, under the joint supervision of Prof. Arthur Veldman (Computational Mechanics and Numerical Mathematics), Prof. Jos Roerdink (Scientific Visualization and Computer Graphics) and Jan Kraak (Center for Information Technology).

The project’s goal was to set up a simple framework for CFD visualizations in VR.
Computer model of the Titanic hitting a gigantic wave
Computer model of the Titanic hitting a gigantic wave

So-called green water simulations were selected as the topic for this pilot project. These simulate the crashing of water that is coloured green by phytoplankton onto the deck of a ship. These simulations are referred to as Titanic simulations. The most important aspects of this particular water flow, i.e. its surface shape and the pressure it exerts on the ship, were to be shown in the VR facilities.

The data generated by the simulation program were transferred in a format that could be used in both the Reality Theatre and the Reality Cube. We used the freely available Visualization Toolkit (VTK) to transform the computed data to the widely used Virtual Reality Modelling Language (VRML) format. After the data conversion, the VRML files were read and projected in stereo on the screens in the Cube and the Theatre via a VRML viewer called VRMLview, which runs both on a Linux desktop and on the Onyx. With this viewer it is possible to navigate smoothly through the virtual world.

Pressure distribution over the ship
Pressure distribution over the ship 

A very fancy result was obtained by using the recent feature of reflection maps in VRML, which accounted for the reflective property of the water surface. Also, a computer model of the real Titanic was incorporated in a final version, which can be used for demonstration purposes. In addition, the sounds of roaring waves and howling wind were included. (Some people with an apparent interest in ornithology even suggested adding the sounds of gulls and albatrosses).

It was found that for this application, the performance of the Onyx was insufficient to visualize the large amount of CFD data with a reasonable frame rate. This problem seems likely to remain since progressive developments in computing and visualization hardware will always be accompanied by an increase in computational demands from the user.

Last modified:24 January 2017 1.08 p.m.
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