Zero pressure in 3D-calculation

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Zero pressure in 3D-calculation

I have a problem with the 3D calculation of SPHysics.
I modeled my problem in 2D (SPHYSICS_2D_v2.2.001) and it worked very well. I get a plausible pressure distribution and path of motions of the particles. Afterwards I generated an 3D geometry and tried SPHysics 3D (SPHYSICS_3D_2.2.001).
In this setup all particles had the pressure value zero. The particles move only with their initial velocity (no changing of the velocity (they also pass the boundary particles without any interaction). So I thought, maybe I have to change some parameters. So I wrote a script that tries all possible combinations of kernel, algorithm, density filter and so on. But there are to much possibilities. So I checked only some combinations. The result is the same (zero pressure).
After this I tried to figure out where it comes from. Its causes of the EoS. If rho0 is equal rho, the pressure is zero (it’s the same for all EoS). If I change rho0 the pressure is not zero, but the pressure of all particles is the same, so there is no force depending on the pressure.
It seems to me, that there is no search for neighbor particles. But “h” is big enough to have same neighbors. Is there a common mistake.
The test cases form SPHysics work fine.

Regards
Seb
sebastian.koch

Posts: 5
Joined: Wed Jan 27, 2016 8:46 am

Re: Zero pressure in 3D-calculation

A few more background information:
I use matlab to generate the initial particle informations (IPART file).
In 2D it worked well. I added the z-position and z-velocity for 3D calculations. In 3D exists an *.out file. The last line says “EXTERNAL GEOMETRY FOR 3D Not yet activated in code please input the tmax and out”. How can I activate the external geometry? tmax and out are stated via INDAT at line 31 and 32.
sebastian.koch

Posts: 5
Joined: Wed Jan 27, 2016 8:46 am 