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cybergalactic / MSS

The Marine Systems Simulator (MSS) is software that supplements the textbook "Handbook of Marine Craft Hydrodynamics and Motion Control," 2nd Edition, by T. I. Fossen, published in 2021 by John Wiley & Sons Ltd.
https://mss.fossen.biz
MIT License
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Why is M_A in 'Otter.m' a diagonal matrix？ #59

Closed JasonWang2333 closed 5 months ago

JasonWang2333 commented 6 months ago

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

cybergalactic commented 6 months ago

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 commented 5 months ago

Thanks a lot. I get it.