Seems Rayleigh damping beta is killing the initial conditions. I can’t find any reference in the manual warning about this effect. Only reference to Explicit.
“in explicit dynamic calculations without massless contact the damping is only
allowed to be mass proportional: the coefficient beta of the stiffness proportional term must be zero”
I guess if that limitation also applies to implicit dynamic.?¿. Maybe we should report on Github.
this seems to work:
*STEP, NLGEOM, INC=10000
*DYNAMIC, ALPHA=-0.05, DIRECT
1E-7, 0.001
*OUTPUT, frequency=100
*INITIAL CONDITIONS,TYPE=VELOCITY
Nall, 1, 40.
Nall, 2, -1.5
*AMPLITUDE, NAME=RAMP_X
0.0, 0.0
1.0, 40.
*AMPLITUDE, NAME=RAMP_Y
0.0, 0.0
1.0, -1.5
*BOUNDARY, AMPLITUDE=RAMP_X
Nlrmoving, 1, 1, 1.
*BOUNDARY, AMPLITUDE=RAMP_Y
Nlrmoving, 2, 2, 1.
*BOUNDARY
Nall, 3
*CLOAD
Nsurface, 1, 0.0
Nsurface, 2, 0.0
Nsurface, 3, 0.0
*NODE FILE
U,V
*EL FILE
S, E
*END STEP
Velocity magnitude is decreasing with time so it looks like the ICs are working but beta is damping it away. If you make beta smaller, the problem gets less. I wouldn’t expect beta to have any effect on rigid body motion though.
Probably a foolish question but what is the deeper meaning with the “amplitude” card, except for less significant digits in stress & strain, the outcome seems identical.
*STEP, NLGEOM, INC=10000
*DYNAMIC, ALPHA=-0.05, DIRECT
1E-7, 0.001
*OUTPUT, frequency=100
*INITIAL CONDITIONS,TYPE=VELOCITY
Nall, 1, 40.
Nall, 2, -1.5
*BOUNDARY
Nall, 3
*CLOAD
Nsurface, 1, 0.0
Nsurface, 2, 0.0
Nsurface, 3, 0.0
*NODE FILE
U,V
*EL FILE
S, E
*END STEP
Amplitude and BC is needed to keep Constant velocity of the plate.
Edited: Why this particlar aproach instead of fixing the plate and performing a CFD or FSI is a different question but one never knows…
Thank you very much for your thoughts and help. I have found a solution to this problem. It may be that I am missing the gravity load. After I applied the gravity acceleration, this phenomenon disappeared and the program can run normally. I didn’t care about the gravity acceleration before, and I didn’t expect it to cause such a serious problem.
@Disla , thanks, for the good illustration 
, and my apologize for not reading the fully thread.
I am using a Linux system and I am calculating an FSI problem. PrePomax is usually installed in a Windows system. Therefore, I may need to install a virtual machine or similar software. This may not be very convenient. So I am using Paraview. Can Calculix directly extract the stress and strain information of the surface probes (not necessarily the nodes) of the structure? For example, can it directly generate a .csv file?
Your aircraft is very cool. Are you working on this kind of water aircraft?
No. Just came to my mind some days ago when trying to understand your problem and why constant velocity.
Glad you fix your problem.
Thanks, this is mainly because of the help from you and other users. Also do you have experience with “Can Calculix directly extract the stress and strain information of the surface probes (not necessarily the nodes) of the structure? For example, can it directly generate a .csv file?”
