Dear @PoChuan.Mao,
Ah, OK; thanks for clarifying.
I was using the value of Cd = 2 from: IEA-15-240-RWT/IEA-15-240-RWT-UMaineSemi_MoorDyn.dat at master · IEAWindTask37/IEA-15-240-RWT · GitHub.
Unfortunately, I’m not sure why the difference between FEAMooring and MoorDyn remain. I don’t have much experience with FEAMooring; at NREL, we generally rely on the use of MoorDyn.
The following forum topic is likely of interest to you: FEAMooring Design. As mentioned in this topic, I would suggest reaching out to Prof. Yoon Hyeok Bae, the developer of FEAMooring and now a professor at Jeju National University in Korea for help with FEAMooring.
Best regards,