I’m currently thinking about (weakly) coupling BeamDyn with an external fluid dynamics solver to compute fluid structure interaction problems. I am currently digging through documentation and source code of BeamDyn and maybe some of you can help me with open questions.
Since BeamDyn uses an implicit time integration, it needs the loads at t+dt to advance in time. In the BeamDyn standalone version these loads can be calculated since they are constant (or maybe a function of time only), however this is of curse not the case for coupled calculations. There would be several coupling strategies for that, like assuming a constant aerodynamic load during one structural time step or extrapolating the load at t+dt using information from t, t-dt and t-2*dt (I believe in the coupled FAST computation this is done). Or as a last resort subiterations. My question would be if anyone has experiences with using BeamDyn in a weakly coupled setting and can talk about what is maybe sufficient or can point out references for that.
Another question is regarding the output of displacements etc. I found the appropriate array BD_ContinuousState%q in the code which gives me displacements and rotation-parameters as well as BD_ContinuousState%dqdt which gives velocities and rotational velocities. But I could not quite figure out in which coordinate system these quantities are represented. Does anyone have information on that?