Learning Forum

[floatingstones]

Hello there,nI'm modelling a floating body in AQWA.nWhen inputting the mass moments of inertia Ixx, Iyy and Izz [kg.m^2] of a Point Mass, should I consider the values with respect to the center of mass?nOr should I use the Parallel Axis Theorem to obtain moments of inertia with respect to the Fixed Reference Axes (origin in the water level)? nI cannot seem to find this information in any part of the user's/reference/theory manuals from AQWA.nThank youn

[Mike Pettit]

Hello,nYou should enter inertia values with respect to the centre of mass.nCheers, Miken

[Yu Bi]

Hi, the moments of inertia for a point mass is with respect to the point where you defined for the point mass, and the orientation of the axis is parallel to the Fixed Reference Axes. n

[floatingstones]

and nThanks for your answers.nThe thing is, when setting up my point mass, I set its Z as the vertical location of my mass' CoG with respect to the FRA. (It's a negative value, naturally, since Z=0 is in the water level).nI understand that I want my inertia values with respect to the center of mass, but the software understands the center of mass as being at my negative Z location.nSo, my question would be: In this case, should I apply the parallel axis theorem when calculating inertia moment to consider that shift on Z?n

[Yu Bi]

Hi, the program will think the moment of inertia you define in the point mass detail panel is with respect to the point mass defined position, and the program will automatically transfer those values to the real centre of gravity or anywhere needed.n