FluidStructure Problem

FluidStructureProblem nsteps #(in) deltaT #(rn)
prob1 #(s) prob2 #(s)
[maxiter #(in)]
[rtolv #(rn)]
[rtolp #(rn)]

Represents a fluid-structure analysis based on StaggeredProblem but providing iterative synchronization of sub-problems. The implementation uses the the PFEM model 3.3.3 for the fluid part. For the structural part a full dynamic analysis using implicit direct integration DIIDynamic3.1.7 is considered.

The coupling of both phases is based on the idea of enforcing compatibility on the interface. Special fluid particle are attached to every structural node on the interface that can be hit by the fluid. These special particles have no degrees of freedom associated, so no equations are solved on them. However, their movement is fully determined by associated structural nodes. Their velocities governed by the solid part affect the fluid equation naturally.

This iterative procedure is based on the so-called Dirichlet-Neumann approach. Dirichlet boundary conditions are the prescribed velocities on the fluid side of the interface, whereas applied forces on the structural side represent the Neumann boundary conditions.

The convergence criterion is based on the difference of the pressure and velocity values on the interface from the subsequent iterative steps. Once they are smaller than prescribed tolerance, the iteration is terminated and solution can proceed to the next step.

The subproblem input files are described using prob1 and prob2 parameters, which are strings containing a path to sub-problem input files, the prob1 contains input file path of the first sub-problem, which runs first for each solution step, the prob2 contains input file path of the second sub-problem. The time step sequence is controlled by the number of steps nsteps and the time step length deltaT.

Optional parameters rtolv and rtolp allow to specify relative norms for velocity and pressure differnce of two subsequent iteration step. Default values are 1.e-3. By default maximal 50 iterations are performed, if not specified by maxiter.

Note: This problem type is included in PFEM module and it can be used only when this module is configured.

Borek Patzak