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Adding Collision Modeling to FLOW-3D

In version 9.0 of FLOW-3D, a fixed-mesh method for modeling interactions between solid objects and fluid flow, called the General Moving Objects model, was introduced. With the GMO model, the solid objects can have motion which is either user-prescribed or dynamically coupled to the fluid flow, with full six degrees of freedom, a fixed axis or a fixed point. The model allows users to model multiple moving objects in a single simulation, and each of the objects can be independently assigned prescribed or coupled motion.

This CFD simulation is demonstrating the capability of the new collision model to handle fully-coupled interaction, including collision dynamics of solid bodies and fluid motion.

In this spillway simulation, floating logs are seen to collide with each other and with the walls of the dam.

This fixed-mesh method has proven superior to conventional moving mesh, deforming mesh or re-meshing methods because it is more efficient. No adjustment or regeneration of the mesh is required, repeated flow field interpolation (which can accumulate computational error) is not required, and no limitation on distances between moving objects is imposed. In Flow Science's release of Version 9.1 earlier this year, heat transfer and mass sources to moving objects were added to the GMO model. One more limitation has now been taken on: the ability to model collisions between moving objects and collisions of moving objects with fixed objects.

Many cases can require simulation of collisions between objects, e.g., a berthing ship impacting a dock, flooding waters causing debris to hit structures, or a valve contacting its seating as it closes. The GMO model in Version 9.1 possesses no collision capability. When moving bodies collide with each other or hit a non-moving object, nothing in the code as presently implemented prevents the two objects from overlapping. Thus, the bodies will pass through each other or penetrate into the solid walls.