Hydrostatic restoring matrix

6

Dear Jonkman

For the lastest version (v3.4.1), my explanation of the hydrostatic restorating matrix is as follows. Please correct me if something is wrong.

image
image833×676 28.8 KB

  1. Buoyancy and rotational buoyancy is considered in p%F_HS_Moment_Offset in WAMIT
  do iBody = 1, p%NBody     
        p%F_HS_Moment_Offset(1,iBody) = 0.0_ReKi
        p%F_HS_Moment_Offset(2,iBody) = 0.0_ReKi
        p%F_HS_Moment_Offset(3,iBody) =  InitInp%RhoXg*InitInp%PtfmVol0(iBody)                                            
        p%F_HS_Moment_Offset(4,iBody) =  InitInp%RhoXg*InitInp%PtfmVol0(iBody)*( InitInp%PtfmCOByt(iBody) - InitInp%PtfmRefyt(iBody)  ) 
        p%F_HS_Moment_Offset(5,iBody) = -InitInp%RhoXg*InitInp%PtfmVol0(iBody)*( InitInp%PtfmCOBxt(iBody) - InitInp%PtfmRefxt(iBody)  )  
        p%F_HS_Moment_Offset(6,iBody) = 0.0_ReKi
end do

Part of m·g (steel weight) is subtracted in ElastDyn, and another part (ballast weight) is considered in Morison Strip-Theory.

When VCG is specified as zero in frequency-domin WAMIT, moments caused by weight are considered in corresponding modules. And
image, where C(4,6) and C(5,6) are generally zero.

  1. According to Moment of inertia, data interpolation in OpenFast, linear added mass matrix, linear hydrostatic matrix - #2 by Jason.Jonkman, HydroDyn inputs PtfmRefxt , PtfmRefyt , and PtfmRefzt must be consistent with (0,0,VCG) in frequency-domain WAMIT because hydrostatic restoring matrix, exciting forces and added-mass and damping coefficients are related to (0,0,VCG).
    In conjunction with the above discussion, PtfmRefxt , PtfmRefyt , and PtfmRefzt are always zero.