Ansys Aqwa Pitch Free Decay

- April 18, 2024 at 4:44 am
  
  Senthil Balamurugan Saravanan
  Subscriber
  
  Hi, Im doing my masters project using OC4 platform and in that I am trying to validate my surge, heave and pitch free decay with the NREL research derived results. In which I completed validating my hevae and surge but when coming to pitch free decay Im not getting the same values according to NREL paper they get a pitch free decay period of 25 sec but im getting only 19 sec and even with my hydrostatic result my roll and pitch stiffness values are not matching with the NREL values can anyone please help me its.
- April 18, 2024 at 11:01 am
  
  Shuangxing Du
  Ansys Employee
  
  Please check the definition position and orientation of your model in still water. If they are not the same as what NREL values, the hydrostatic results of pitch stiffness will not be the same.
  If they are the same, please check if all the normal directions of the submerged surafces are pointing towards the water.
- April 18, 2024 at 12:12 pm
  
  Senthil Balamurugan Saravanan
  Subscriber
  
  Hi I have checked the position but im not sure how to check the normal direction can you please help me out
- April 18, 2024 at 12:38 pm
  
  Senthil Balamurugan Saravanan
  Subscriber
- April 18, 2024 at 12:43 pm
  
  Senthil Balamurugan Saravanan
  Subscriber
  
  could that be because of the warnings shown in the image ? if so can you please help me to rectify it ?
- April 18, 2024 at 2:46 pm
  
  Shuangxing Du
  Ansys Employee
  
  It seems that these warning messages are not relevant. I noticed that the displayed unit of angle is in degree, so that the unit of the rotational motions' stiffness matrix diagonal elements is in [Nm/degree].
  The NREL's values could be in [ Nm/rad]. Could you please compare these values again by setting the unit as rad?
- April 18, 2024 at 2:48 pm
  
  Shuangxing Du
  Ansys Employee
  
  Normal directions of the surfaces can be displayed in SpaceClaim.
- April 22, 2024 at 3:02 am
  
  Senthil Balamurugan Saravanan
  Subscriber
  
  Hi even after that the values are not same... can you help me out
  So all the porcesses are same as to Heave and surge decay ? because Im getting exact values for heave and surge but not for pitch
- April 22, 2024 at 8:21 am
  
  Shuangxing Du
  Ansys Employee
  
  If the pitch/roll hydrostatic stiffness values are not the same, please check your geometry. Are there any moorings or current/wind drags in the model?