ERCIM News No.26 - July 1996 - CNR

Numerical Grid Generation as a Basic Step in Computational Field Simulation

by Rosa Maria Spitaleri

Numerical grid generation is the crucial initial step of any computational simulation problem. Research activities at the Istituto per le Applicazioni del Calcolo (IAC) of the Italian National Research Council (CNR) have addressed the development of numerical methods and interactive graphics tools for this task. These studies have resulted in the implementation of advanced multiblock multigrid algorithms and an interactive prototype system called GENSY (GENeration SYstem).

The computational simulation of physical phenomena is a large research field, continuously requiring improved grid generation technology. Before using solver codes, application and numerical experts working in various scientific areas have to investigate a number of points if they are to achieve compu-tational success: what algorithm can generate a good-quality grid, whether the chosen algorithm could become heavily time consuming, and what efficient and easy-to-use implementations are available.

It is well known that the capability to carry out effective numerical processes for the approximation of Computational Fluid Dynamics (CFD) problems depends on the geometric modelling and grid generation phases which often consume up to 80% of the total simulation time. Advances in grid generation can remove difficulties from this computational phase and help to prevent gridding from becoming a dangerous bottleneck in complex simulations. For this reason, over the last years, IAC research projects have regarded grid generation and have concentrated on the development of numerical methods for the generation of structured and unstructured grids, the application of multigrid computation to obtain accelerated convergence histories and the design of multiblock decomposition to handle geometrically complex domains.

The growing complexity of simulation processes means that an increasingly large spectrum of methodologies are needed to handle them: on the one hand, high-level interactive pre-processing and, on the other, automatic techniques, such as the automatic generation of block structures and adaptive grids, can be both powerful in practical applications. Specialized interactive and graphics technologies are essential not only for the presentation of the results but also for the investigation of the overall simulation cycle. In addition to numerical algorithms, the research activity at IAC has included the design of an integrated grid generation system, called GENSY, which allows the interactive generation of grids to be easily carried out in two- and three-dimensional spaces. Moreover, appropriate visualizations of the computed grids and convergence histories of method executions are available for user investigation. This software module integrates visual techniques into numerical computing to offer straight manipulation of numerical gridding.

The GENSY Interface

The Graphical User Interface (GUI) of the system includes menus, graphical windows and icons1 in a consistent and effective screen layout. Using prototype icons1 and dialogue boxes, the users can control and optimize numerical processing; in particular, they can assign and update multigrid computation parameters and control function coefficients to easily modify the spacing of grid lines. By the interactive assignment of computational parameters, the user can control both the global fineness and the local interior spacing of the grid. The design of this integrated system has been partially supported by the Italian Space Agency (Agenzia Spaziale Italiana).

Researchers working at or co-operating with IAC on grid generation not only participate in but also promote and support initiatives to group together developers of grid generation techniques and user communities in order to diffuse results and exchange ideas. They contribute in national and international conferences as both speakers and minisymposia organizers in order to propose and disseminate advances in grid generation and debate new useful trends.

The last IAC participation was in the 5th International Conference on Numerical Grid Generation in Computational Field Simulation, April 1996, at Mississippi State University. This meeting confirmed the worldwide interest in grid generation as a basic step in Computational Field Simulation. CFS is recognized as a powerful tool in a large spectrum of application areas besides fluid dynamics, in atmospheric and ocean science, heat and mass transfer, geophysics, solid mechanics, and other physical field problems. The large number of participants and represented countries were a concrete sign that grid generation is extending its range of potential application from its initial area to a wide number of multidisciplinary field simulation problems.

Please contact:
Rosa Maria Spitaleri - IAC-CNR
Tel: +39 6 88470254

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