Why is M_A in 'Otter.m' a diagonal matrix？

[JasonWang2333]

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but in ur text book, 'the vehicle also has three planes of symmetry', when the M_A is a diagonal matrix. and i check the USV doesn't has three planes of symmetry: what's the reason of simplifying this matrix?

[cybergalactic]

The process of purchasing a hydrodynamic program and creating a 3D drawing for hydrodynamic computations is both time-consuming and costly. Alternatively, you could compute the 6x6 added mass matrix using these methods, or you might opt for simplified semi-empirical approaches. For surface vehicles like the Otter USV, there is port-starboard symmetry. The submerged hull exhibits nearly perfect fore-aft and top-bottom symmetry, except for appendages like propellers. Therefore, it's feasible to model this as having 3-plane symmetry implying a diagonal MA matrix by implicitly assuming that the off-diagonal elements are significantly smaller than the diagonal ones.

[JasonWang2333]

Thanks a lot. I get it.