## Support #89

### Density difference for fluid and solid in FSI solver

Status: | New | Start date: | 07/08/2013 | |
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Priority: | Normal | Due date: | ||

Assignee: | - | % Done: | 0% | |

Category: | - | |||

Target version: | - |

**Description**

Hi all,

Beside stress force difference for fluid and solid, there is also density difference. Since this quantity is involved into the momentum conservation equation. Theoretically, for incompressible flow and elastic body, the momentum conservation equation becomes:

For FLUID:`\rho^f(\dot u + u \cdot \boldsymbol{\nabla} u) = f + \boldsymbol{\nabla} \cdot \sigma^f`

For SOLID: `\rho^s(\dot u + u \cdot \boldsymbol{\nabla} u) = f + \boldsymbol{\nabla} \cdot \sigma^s`

In the fsi solver, if I'm not mistaken, the density is set to 1.0 for both phases.

My questions are:

1. Is the solver implemented that way (density = 1.0) or this density is considered somewhere else?

2. If it's one-const density, how does it effect the physical meaning and result of the simulation?

Best,

Truc