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## Re: [ff3d-users] Navier-Stokes problem

 From: Thomas B Subject: Re: [ff3d-users] Navier-Stokes problem Date: Sun, 10 Jun 2007 21:50:09 +0200 User-agent: Icedove 1.5.0.10 (X11/20070329)

```Hello,

thank you very much for your help.

```
Unfortunately the results are not quite the one I expect: F_z should at least be positive (a tilted plate in a flow should be experience a force upwards).
```
Is anything basically wrong to simulate such a case?

Regards,
Thomas

Stephane Del Pino wrote:
```
```Hello Tomas.

I noticed something wrong in your ff3d file:

double eps = 1000;
function P  = eps*one(<1,0,0>)+1
// ... then ...
double fx = int[M](ki/eps*u);
double fy = int[M](ki/eps*v);
double fz = int[M](ki/eps*w);

```
The problem is that in my mind, eps is something small and P is defined using 1/eps so the force here is not evaluated correctly. I suggest:
```
double eps = 1E-4;
function P  = 1/eps*one(<1,0,0>)+1
// ... then keep ...
double fx = int[M](ki/eps*u);
double fy = int[M](ki/eps*v);
double fz = int[M](ki/eps*w);

I have run you example for a few iterations, and I get for instance
<#i=8
<#Fx=-0.378171
<#Fy=2.7602e-05
<#Fz=-0.0644279

Is it more what you expect?

Best regards,
Stéphane.

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```