How to simulate changing CG/CB

VinayKS · February 11, 2013, 04:57

Hi,

I am trying to simulate the motion of an underwater vehicle that has a varying Center of Gravity and a varying Center of Buoyancy. The variation occurs when the vehicle reaches a particular depth (for ex, at 0.5m depth, the CG moves forward, and CB moves back). As a consequence of these changes, the vehicle moves in a roughly sinusoidal pattern.

Does anyone if this can be modeled in Star CCM+? Specifically, how to model a varying CG/CB, and the consequential motion? Would be deeply grateful for any help.

VKS

ryancoe · February 11, 2013, 08:36

You would need to use the rigid body "6-DOF Model" to do this. You could vary the model's CoG with time using a field function or a user macro.

To change the CoB you'll need to omit the gravity model (no hydrostatic pressure variation in the water column) and instead have user-defined external force that changes with time to reflect the desired CoB location and the proper orientation (always up in the inertial frame).

February 11, 2013, 04:57	How to simulate changing CG/CB	#1
VinayKS New Member VKS Join Date: Jan 2013 Posts: 6 Rep Power: 13	Hi, I am trying to simulate the motion of an underwater vehicle that has a varying Center of Gravity and a varying Center of Buoyancy. The variation occurs when the vehicle reaches a particular depth (for ex, at 0.5m depth, the CG moves forward, and CB moves back). As a consequence of these changes, the vehicle moves in a roughly sinusoidal pattern. Does anyone if this can be modeled in Star CCM+? Specifically, how to model a varying CG/CB, and the consequential motion? Would be deeply grateful for any help. VKS

February 11, 2013, 08:36		#2
ryancoe Member Ryan Coe Join Date: Jun 2010 Location: Albuquerque, NM Posts: 98 Rep Power: 16	You would need to use the rigid body "6-DOF Model" to do this. You could vary the model's CoG with time using a field function or a user macro. To change the CoB you'll need to omit the gravity model (no hydrostatic pressure variation in the water column) and instead have user-defined external force that changes with time to reflect the desired CoB location and the proper orientation (always up in the inertial frame). __________________ Ryan

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