I'm currently trying to simulate a free decay test of a floating structure and I'm experiencing some problems after changing the timestep. The first simulation, which worked fine and had reasonable results, was run with the standard values:
CFL = 0.2
CoefDtMin = 0.05#DtIni
After this I just wanted to check, if the results are changed by using a different timestep. To do so, I changed the values to the following:
CFL = 0.0002 (factor 1/1000)
CoefDtMin = 0.05 (factor 1/1)#DtIni
= 0.00000001 (factor 1/10000)#DtMin
= 0.000000001 (factor 1/10000)
As you can see, the factor we used in comparison to the stable simulation is not the same for the four variables.
Simulating with these parameters led to errors that looked like numerical instabilities. After ca. 5 s there was a big increase in the fluid velocity and the floating body was moved to the right side by this accelerated fluid particles.
Has anyone ever experienced something similar? Or is there something wrong in the definition, mainly because I didn't use the same factor for all four variables?