# Iges vs box volume

Hi,

I have just finished the rans tutorials. I wish to make some exercises.

I imported an iges file (a ship hull) from rhino. I created a box (i wish to simulate a towing tank test which we had done it last year) and used "translate" command to move the box like "wheel in a box" tutorial. I wish to substract the hull from the box so i'll use the wall condition on my iges form, and the box volume will be the water.

But when i use the subtract command Caedium crashes. I tried with a .step import but nothing changed.

Also i tried to import a subtracted box too but Caedium doesn't see it as a volume.

Can you help me to figure it out? If this is possible i will have a couple of questions like:

Can Caedium solve a free surface problem?

Can Caedium solve this problem with a free surface condition?

## No Free Surface Modeling

No Caedium can not yet model a free surface between water and air.

In terms of the crashes you are seeing - I would guess it is because you are trying to subtract faces from a volume. Your ship hull needs to be a water-tight volume like the cylinder prior to subtraction from the box in the tutorial "Wheel in a Box".

The best geometry exchange format is STEP (.stp) as it preserves accuracy and topology much better than IGES. If you have only faces after importing geometry then you will need to use the

Volumes->Stitchtool on theGeometryTool Palette to make a closed volume. Keep an eye on the Log for warnings and errors, e.g., that the faces don't form a closed volume. Then subtract the new stitched volume from your box.## it worked but...

Thanks for your answer. When i closed the model at rhino and exported as .step, i subtracted it easly.

But now i am having an other problem. i tried it for 3 different models. I did all the steps (except angular velocity) as shown as in the wheel tutorial. when i try to run the solver this error occures;

Warning:

volume_2 [www.1787.5] Tetulator: Failed: Face already in front

Warning:

volume_2 [www.1787.5] RANS Flow: Failed

Unexpected process exit.

--> FOAM FATAL ERROR:

Illegal cell label -1 in neighbour addressing for face 353878

From function polyMesh::initMesh()

in file meshes/polyMesh/polyMeshInitMesh.C at line 78.

FOAM exiting

## Diagnose Meshing Problems

Good to hear you are making progress with the geometry exchange using STEP.

Now you'll need to diagnose the meshing problems according to "How do I fix mesh and solver failures?"