Project No. 20161

Open Interface for Coupling of Industrial Simulation Codes on Parallel Systems

Most industrial simulation codes are not able to handle fluid flow and structural deformation simultaneously, but deal only with either fluid dynamics or structural mechanics separately. However, there are several practical applications that require the solution of fluid-structure-interaction and other multi-physics problems. The CISPAR project (ESPRIT no. 20161), funded by the European Commission, addresses this particular problem. One of its main goals is to develop a communication library COCOLIB to support the exchange of data between existing simulation programmes for structure mechanics and fluid dynamics. Germanischer Lloyd, being among the project partners, provide an industrial test case in which a finite element model of a ship hull interacts with a fluid dynamic model of the surrounding water. Coupling both models defines a numerical problem, which is then solved by coupling two corresponding solvers, in this case STAR-CD for the fluid dynamic part and codes PERMAS and PAM-solid for the structural mechanics part of the problem. The project partners provide all codes.
The project results are of primary concern to Germanischer Lloyd and improve the technical safety of the international maritime industry and for waterborne transport in general.

Slamming Induced Loads

An animation showing the wave induced movement of a ship.

To certity safety of ships, ship classification societies such as Germanischer Lloyd consider effects of various kinds of loads. Imagine a ship sailing in bad weather conditions, encountering heavy seas. The resulting wave induced movement of the ship will be very large. Eventually, the ship's bow area emerges out of the water and the hull slams down a few seconds later. This typical situation - called slamming - is characterised by high impact of pressures, resulting in highly loaded ship structures. Therefore, it has to be verified by, e.g., simulation during the design phase that slamming will not damage the ship.

Numerical Simulation of Slamming Impacts

Germanischer Lloyd apply numerical simulation methods to obtain reliable estimates for slamming induced pressures. State-of-the-art methods of Computational Fluid Dynamics are used to predict external and internal impact loads. The current German research program Life Cycle Design deals with the determination of impact pressures on ship structures. The following figure shows a typical pressure distribution for a hull cross section during slamming. The color table at the side of the figure applies to the pressure below the free surface only.

Fluid Structure Interaction

High impact pressure values occuring during the slamming event may cause elastic or plastic deformation of the ship structure. To simulate this deformation, Germanischer Lloyd generate a finite element model of the structural elements of the ship. To capture all deformation effects due to slamming, a simulation program has to account for the interaction between ship hull and fluid flow simultaneously. Structural response is calculated by assigning loads resulting from fluid flow (red arrows) onto the nodes of the finite element model.

The figure shows a finite element model of a typical hull cross section of a container ship.

Simulation of a ship entering the water

Software developed for the CISPAR project has not yet been applied to the industrial test case provided by Germanischer Lloyd. However, an animation of the simulated water entry, of a ship hull cross section produced for the German research program Life Cycle Design, provides a much better understanding of the situation. The animation shows the evolution of the free surface. The computation solved the momentum and mass equations for a two-fluid flow. The free surface was captured by an equation for the volume fraction (VOF) of the two media. (VOF=1 stands for water, and VOF=0 indicates air).

Partnership

Pallas GmbH, Hermülheimer Straße 10, D-50321 Brühl, Germany
Computational Dynamics Ltd., 317 Latimer Road, W10 6RA, GB-London, England
Imperial College, Exhibition Road, SW7 2BX, GB-London, England
Engineering Systems International, 20 Rue Saarinen - Silic 270 -, F-94578 Rungis (Cedex), France
INTES GmbH, Schulze-Delitzsch-Str. 16, D-70565 Stuttgart, Germany
GMD/SCAI, Postfach 1316, D-53731 Sankt Augustin, Germany
Aerospatiale-Missiles, Beranger 2, BP 84, F-92322 Chatillon Cedex, France
Germanischer Lloyd AG, Vorsetzen 32, D-20459 Hamburg, Germany
Daimler-Benz AG, HPC C404, D-70546 Stuttgart, Germany
Sulzer lnnotec Ltd., P.O. Box, CH-8401 Winterthur, Switzerland
C&C Research Laboratories, NEC Europe Ltd., Rathausallee 10, D-53757 Sankt Augustin, Germany

Germanischer Lloyd - Certified Safety

Germanischer Lloyd were established in 1867 in Hamburg as a classification society to supervise safety and reliability of ships and ship operations from design to decommissioning on the basis of their own rules and regulations. Germanischer Lloyd are an independent, impartial non-profit organisation, offering technical expertise to the maritime industry through the use of their own technical experts and a world-wide network of surveyors in the field of certification of ships and offshore structures, industrial units, and quality management systems. Design approval, as well as inspection planning and evaluation, are activities of Germanischer Lloyd that are continuously accompanied and improved by research and development projects.