[Sunny Chitti]

Can anyone tell me how to calculate added body mass in water using CFX? Thank you.

[ghorrocks]

I do not know what added body mass in water is. Please explain what you are talking about.

[Sunny Chitti]

Originally Posted by ghorrocks

I do not know what added body mass in water is. Please explain what you are talking about.

When you place a body in fluid, there will be a certain amount of mass added to body due to surrounding fluid. It is called added body mass.

[ghorrocks]

I still do not understand what you are talking about. If I have a brick which is 4kg mass and I put it in water then the brick is still 4kg mass. So what is added body mass?

[BlnPhoenix]

Originally Posted by Sunny Chitti

When you place a body in fluid, there will be a certain amount of mass added to body due to surrounding fluid. It is called added body mass.

Do you mean Virtual Mass Force? It's for accelerated masses and only significant under certain conditions.

[urosgrivc]

I must say that I also dont undestand vhat you meen.
Are you simulating some kind of porous solid or vhat?

[Sunny Chitti]

Originally Posted by urosgrivc

I must say that I also dont undestand vhat you meen.
Are you simulating some kind of porous solid or vhat?

https://en.wikipedia.org/wiki/Added_mass

[Sunny Chitti]

Originally Posted by BlnPhoenix

Do you mean Virtual Mass Force? It's for accelerated masses and only significant under certain conditions.

Yes, virtual mass and added mass are same. I am working on a accelerating body.

[Sunny Chitti]

Originally Posted by ghorrocks

I do not know what added body mass in water is. Please explain what you are talking about.

https://ocw.mit.edu/courses/mechanic...05reading6.pdf

[urosgrivc]

Yes but this only aplies if you are calculating it by hand, a simplification to vhat a real CFD simulation is capable of. As I undarstand this shouldnt even be caled added mass but apparent (or virtual yes) added mass and in a transient fluid simulation all this is calculated with the simulation as this doesent exist. Only mass flow, energy conservation and pressure and others matter beacause this ˝vitrual mass˝ is derived from flow properties on or near the wals of an object like velocity, pressure, density and others which are calculated betven milions of nodes you are just not capable to compute by hand.

Just put an empty void in the fluid (where solid is located) accelerate the walls of this ˝apparent solid˝ make it a transient and monitor the force on the wals it is actualy that simple let the computer do the rest of the computational work for you. Make sure that your timesteps are not too long as force walues will than be wrong because of incorect flow properties.

[karachun]

It is not CFD but FEA problem, in many FEA packages you can mark some faces of elements as 'underwater', set water free surface position and program will include virtual mass at dynamic analysis. It is widely used in shipbuilding, the difference in eigenvalues can be more than 100%.