RNG Rigid Body Motion

This note outlines how the coupling between the motion of rigid bodies immersed in a fluid and the motion of this fluid is handled in XNS. For a rigid body one has a group of nodes which define the surface of the rigid body called “reference node group” (RNG). For each RNG we save the properties of motion in arrays which in the following we will call “RNG arrays”. They contain the bottom and top level values for each spatial dimension and for each RNG. Here is a list of all currently used RNG arrays containing information on the linear motion of the center of mass of the respective RNG: rnglinpos(2,nsd,rng) rnglinvel(2,nsd,rng) rnglinacc(2,nsd,rng) rnglinfor(2,nsd,rng). The information about angular motion is stored in the following RNG arrays: rngangpos(2,nsd,rng) rngangvel(2,nsd,rng) rngangacc(2,nsd,rng) rngangfor(2,nsd,rng). Here, the information stored in the first array is redundant in the case of rigid body motion. The abbreviations are as follows: • pos: position vector • vel: velocity/angular velocity vector • acc: acceleration/angular acceleration vector • for: force/moment vector. In the initialization routine all entries of the RNG arrays are set to zero. The RNG arrays carry the information of position and motion of the rigid bodies. The parts of XNS touched by the rigid body motion which is described in this technote are shown in figure 1. RNG Rigid Body Motion E. Schlauch Time Step Loop updatex(): transfer RNG arrays to bottom level of new time step Iteration Loop genbc(): set boundary conditions “g” from RNG arrays setd(): transfer boundary contitions “g” to solution “d” . . . newd(): checkd(): new top level forces and moments (checkforce()) new top level RNG arrays . . .