October 25, 2023 at 1:21 pm
Here are my opinions. Please correct me if something is wrong:
- In the frequency domain calculation, constraints affect only the RAO of the floating bodies but have no effect on the radiation coefficients, because radiation coefficients are obtained by forced motions (ignoring any constraints).
- As for my studied floating platform, the gap between the platform and ring-shaped float is 1.25m, and an External Lid is attached on the outer torus, with a width of 0.75m and different Lid Damping Factors. Although the Lid Damping Factor is increased to 1, the strange peaks still appear around omega ~ 1.25-1.4 rad/s. I found the strange peak omega ~ 0.28 Hz is eliminated using Lid Damping Factor = 1, but it does not seem to work for my model. Therefore, I am worrying whether the strange peaks in the surge, sway, roll, pitch and yaw directions are caused by the narrow gap resonance? Or generated by the forced motions? If the strange peaks (in the surge, sway, roll, pitch and yaw directions) are caused by the relative motion of two floating bodies during the forced motions (they don’t actually exist because of the constraints), what should be done with it? In fact, I’m concerned about the radiation IRF results. The External Lid has little effect on the radiation coefficients in the heave direction but has a significant effect on the other five directions. So I hypothesized that the strange peaks might be due to forced motions but not the narrow gap resonance. Improper handling of radiation damping will directly affect the radiation IRF and ultimately the time-domain results. Could you please give me some suggestions on it. Many thanks !