WEIS hydroelastic

[hymdrj]

Hello,

I would like to ask whether elastic model can be considered within WEIS.

From what I understand, RAFT supports elastic models as shown below.

  - name      :  pontoon                   # [-]    an identifier (no longer has to be number)       
    type      :  beam                      # [-]    
    rA        :  [  5  , 0, -16.5]         # [m]    end A coordinates
    rB        :  [ 45.5, 0, -16.5]         # [m]    and B coordinates
    heading   :  [ 60, 180, 300]           # [deg]  heading rotation of column about z axis (for repeated members)
    shape     :  rect                      # [-]    circular or rectangular
    gamma     :  0.0                       # [deg]  twist angle about the member's z-axis
    potMod    :  False                     # [bool] Whether to model the member with potential flow (BEM model) plus viscous drag or purely strip theory
    E         :  210e9                     # [Pa]   Young's modulus
    G         :  80e9                      # [Pa]   shear modulus
    # --- outer shell including hydro---
    stations  :  [0, 40.5]                    # [-]    location of stations along axis. Will be normalized such that start value maps to rA and end value to rB
    d         :  [12.4, 7.0]               # [m]    diameters if circular or side lengths if rectangular (can be pairs)
    t         :  0.05                      # [m]    wall thicknesses (scalar or list of same length as stations)
    Cd        :  [1.5, 2.2 ]               # [-]    transverse drag coefficient       (optional, scalar or list of same length as stations)
    Ca        :  [2.2, 0.2 ]               # [-]    transverse added mass coefficient (optional, scalar or list of same length as stations)
    CdEnd     :  0.0                       # [-]    end axial drag coefficient        (optional, scalar or list of same length as stations)
    CaEnd     :  0.0                       # [-]    end axial added mass coefficient  (optional, scalar or list of same length as stations)
    rho_shell :  7850                      # [kg/m3]
    l_fill    :  40.5                      # [m]
    rho_fill  :  1025.0                    # [kg/m3]

However, in WEIS, the input file format does not match exactly. Therefore, I would appreciate your guidance on how the input file should be configured in order to implement an elastic model within WEIS.
In addition, could you please clarify what the "type" specifically represents in the input format shown below?

   -  name: platform_member8_
      type: 9
      rA: [-5.0, 1.794896514920806e-08, -16.5]
      rB: [-45.5, 1.6333558285779333e-07, -16.5]
      shape: rect
      gamma: 0.0
      potMod: false

Thank you very much for your time and assistance. Best regards,

[dzalkind]

Hi, good question. This is a recent change in RAFT that may not yet be fully reflected in WEIS. However, the RAFT developers made the models backwards compatible, so substructures should be rigid when no additional elastic information is provided.

@lucas-carmo, what needs to change on the WEIS side in the type entry of RAFT? Is there anything to correct/expand upon my response here?

Best, Dan

[lucas-carmo]

Hi! In RAFT, type now needs to be either rigid or beam, and it will yell at you if you provide something else. If that would be helpful in WEIS, we could change that behavior and make RAFT default to rigid if something other than beam is specified.

If you want to model a flexible tower atop a rigid floater, you could change the tower type to beam and provide elastic properties (E and G) like shown in the example you shared and set platform member types to rigid. But if you want to model a floater with flexible members, you would also need to define joints so that RAFT knows how to connect those members. This is exemplified in https://github.com/WISDEM/RAFT/blob/main/examples/VolturnUS-S-flexible_example.yaml

[hymdrj]

Thank you very much for your valuable response despite your busy schedule.
In that case, would it be correct to modify the WEIS input in this way?
I would appreciate it if you could confirm.
Best regards,

• Rigid

  • name: platform_member8_
    type: 9
    rA: [-5.0, 1.794896514920806e-08, -16.5]
    rB: [-45.5, 1.6333558285779333e-07, -16.5]
    shape: rect
    gamma: 0.0
    potMod: false

• Elastic

  • name: platform_member8_
    type: beam
    rA: [-5.0, 1.794896514920806e-08, -16.5]
    rB: [-45.5, 1.6333558285779333e-07, -16.5]
    shape: rect
    gamma: 0.0
    potMod: false
    E : 210e9 # [Pa] Young's modulus
    G : 80e9 # [Pa] shear modulus