Goals| Partners: |
Institute for Algorithms and Scientific Computing |
|---|---|
| Contact Persons: | Klaus Wolf, Karl Solchenbach |
GoalsHeart valves, torque converters as well as ships are subject to enormous stresses during their daily operation. The permanent interaction between the fluid they are sited in (blood, oil, or water) and their own structure might result in a machine fatigue or in the worst case in a fracture. The risk of such an accident could be minimized if at the design stage of the structural components, the fluid/structure interaction could be simulated on parallel computers. In future such multidisciplinary simulations will be possible by the help of the coupling library developed in the CISPAR project (January 1996 - December 1998).
Although a lot of high quality tools for (mono-disciplinary) simulations are available today, it is not possible to do multi-disciplinary computations as described above. During the EU funded project CISPAR, researchers, software-engineers, and end users cooperate to specify, implement, and use an open interface (COCOLIB = Coupling Communication Library) for the coupling of arbitrary simulation codes.
Such simulations often require extremely high computing resources that can only be matched by coupling several supercomputers. The typical communication patterns are also well suited for a metacomputing environment: only 2-D (surface) data has to be exchanged between the different simulation codes. The expected bandwidth requirements are still in the range of several hundred megabits per second.
Fluid-Structure
Interaction: A Multidisciplinary ProblemA demonstration of a 'Bending Flap Test Case' might be very helpful to understand the problem area we are currently working on. The bending flap test case describes a tube where a bending flap and two fluid streams are interacting with each other. The flap is installed inside a tube and fixed only at the left end. Flow is coming in from the left side at the upper and the lower side of the flap with different velocities. Because of the narrowing tube at the end of the flap this causes a downward force. The flap deforms and changes the flow field. This change of the flow field again has a direct influence on the forces.
The testcase was computed during the CISPAR project by a coupled computation between PAM-SOLID and STAR-CD and PERMAS and STAR-CD resp. coupled by the help of GMD's COCOLIB. Both demos are in GIF-format
Bending Flap Demo PAM-SOLID & STAR-CD (Gif ~ 210 Kbytes)
Bending Flap Demo PERMAS & STAR-CD (Gif ~ 440 Kbytes)
Technical
ApproachEach code has its own internal data representation for the physical problems to be computed. The space where the fluid moves or where structure is deformed will be represented by different mesh types. In the example of the artificial heart valve the fluid space has the form of a regular grid mesh, whereas the flaps of the heart valve itself are defined by irregular triangles (finite elements). Each point in the grid or cell has several attributes: e.g. pressure or velocity for the fluid or force and deformation coefficient for the structure. Those values will be updated during the simulation run. To investigate the interaction between both parts the structure deformation has to be derived directly from the pressure value of the fluid, i.e. values (e.g. pressure) from one part have to be transformed into those of the other side (e.g. force).
In order to transport values across the coupling border, first the neighborhood between grid points and triangle elements has to be computed. If they match exactly, the values can be transported without any change. Otherwise they have to be interpolated according to the geometric distance between point and triangle. All tasks - neighborhood computation, interpolation and communication - will be supported by COCOLIB. Additionally, neighborhood information has to be kept up to date all the time: in case of the opening heart valve former separated fluid grids (closed flap) have to be combined into one, if the flaps are totally open.
StatusThe design and implementation of the coupling library COCOLIB is under way. A first public version will be available in january 1999 after the end of the CISPAR project.
