Learning Forum

[HOANGPHONG96]

I have studied Ansys Fluent recently. Now I conduct simulation of ROV's motion under water. 

"When a body accelerates in a flow field, fluid surrounding the body also accelerates, and pressure forces on the body must increase to push the fluid out of the way. Energy is required to accelerate the fluid to a higher level of total kinetic energy, and this energy is felt on the accelerating body as an additional drag force. It is common to express this additional force in terms of added mass. "

So, how to find added mass (virtual mass) in ansys fluent. Thank you 

[Amine Ben Hadj Ali]

Are you modeling a two phase flow? If yes the added mass force is as interfacial force.

[HOANGPHONG96]

I think I have modeled a one phase flow, because i have subtract the enclose for the object, so my model is only water.
This is the picture of my model.

[Amine Ben Hadj Ali]

And so why are you interested in virtual mass force? You just need to study the motion and either let it be calculated (six degrees of freedom) or assign the motion explicitly (via CG Motion).

[HOANGPHONG96]

 

I want to find the time from when the ROV starts moving until a certain speed is reached. So I applied Newton's second law.

So, I find added mass to caculate acceleration and time to certain speed is reached. 

 

[Amine Ben Hadj Ali]

Okay. Happy for you.

[Amine Ben Hadj Ali]

What is now the question related to Fluent?

[Yasinmasumi1992]

I have the same problem with Ansys about added mass. Are you find the solution? nFSI in Ansys automatically calculate the added mass and use it?n we should separately calculate this parameter and add it to our simulation? nhow we should add it?n

[YasserSelima]

nFluent accounts for the virtual mass of a particle or droplet (Discrete Phase), the equations are in the theory guide under equation of motion of a particle.nWhen you have a dynamic mesh model and a moving body, Fluent theory guide did not mention anything about the virtual mass (according to my knowledge). However, I believe that this term is included in the fluid forces as the acceleration of the fluid contacting the wall will results in higher pressure and higher shear stress at the wall.nFluent calculate the force at the wall as a sum of the pressure forces and the shear stress forces.nn

[YasserSelima]

If you still want to add this term to your simulation, you can do this in your UDF.nAdd the virtual mass to the mass if you are using SDOF , or add the virtual mass to your equation of motion if you are using CG_MOTION n