AQWA Hydrodynamic Diffraction / Non-symmetry in the ship added mass matrix

- August 30, 2024 at 5:14 pm
  
  pohigor
  Subscriber
  
  I modeled a symmetrical ship hull in the xz plane using Aqwa to determine the hydrodynamic coefficients for added mass and potential damping. I imported the geometry into Design Modeler and aligned the xy plane with the waterline, setting the plane's origin at the ship's centerline. I divided the hull geometry into two sections—dry and wet—and successfully created a mirrored mesh, ensuring that the port side mesh was symmetrical to the starboard side. After reimporting the geometry into Aqwa, I added a mass point. As well explained in Faltinsen's book, for the case without forward speed, the relations Aij = Aji and Bij = Bji must be respected. However, in my model, this is not observed for all terms. As examples are the terms A35 and A53:
  
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  Does anyone know why the symmetry of the matrix is not respected?
  Thanks in advance.
  
  Wave directions: -180 to 180 / number of directions: 9
  Wave periods: 180s to 2s / number of periods: 21
  Ship length: 55m
  Mesh size: 0.4m
- September 16, 2024 at 11:37 am
  
  Shuangxing Du
  Ansys Employee
  
  Could you please set the unit of degree as [rad] in your Aqwa Workbench project? A35 and A53 should be very close if the unit of A53 is in [kg.m/rad].
- October 15, 2024 at 5:49 pm
  
  pohigor
  Subscriber
  
  converting to radians the values become close. thanks for your help.