Learning Forum

[mrel]

Hello,

I have been running some simulations in Ansys 2021 R2 with the Hydrodynamic Diffraction module. I have made a simple box which is elevated a bit from the seabed, and for the current test, I am only having diffracting panels on the bottom of my box.

My problem is that I get an phase lag of 180 degrees for the vertical loads (Global Z) and when I look at that timestep I see the negative pressure which is correct in my opinion. My question is then, why do I not get a 0 degree phase shift as a results since this is the timestep where there should be positive pressure at the bottom of my box? Is there a known bug in the software specifically for this direction? For all other forces and moments I do follow the calculated phase lag but not for the vertical loads (Global Z).

Below is a picture that shows negative pressures on the bottom of my box when showing the timestep corresponding to 180 degrees phase shift and positive pressure for 0 degrees phase shift. For your information, the center of gravity in the middle of the box.

Br,

Mads

[Yu Bi]

Hi, for incident wave pressure, it has zero phase angle compared to the wave elevation. Regarding phase angle, I mean the one explained in Aqaw Theory Manual Section 1.3. From Equation (2.1), (2.2) and (4.4) in Aqwa Theory Manual, you can see there is no phase difference between the incident wave pressure and wave surface elevation. So, in your first graph, the incident pressure is the smallest while the wave elevation reaches the trough, and in your second graph, the incident pressure is the largest while the wave elevation reaches the crest.