[Lonja]

Hi,
Modeling a hydraulic motor with moving pistons.

I am unsure of how mesh stiffness works with regard to mesh deformation.
Below is an image of what I am getting, when I am expecting an even stretch/compression of elements along the piston bore.
deformation is given in X and y components relative to initial position and is multiplied by an interpolation function to interpolate between 1 at the piston face and 0 towards the piston top (2).



I have tried increasing stiffness near small volumes and a value as below (1).


So my question is: as I have defined the movement of each node relative to its initial position, including interpolating between maximum movement and no movement, can I disable the mesh stiffness or change it to have no noticeable effect.



movement defined as below: P1MMX and P1MMY are the final movement equations.

Interpolator1 = if(P1ND >= Piston1Initial, if(P1ND <=(TDCD+MovingRegion),-(P1ND-Piston1Initial)/(TDCD+MovingRegion-Piston1Initial) +1 ,0),1)

P1MMX = Piston1X * Interpolator1
P1MMY = Piston1Y * Interpolator1
P1MMZ = Piston1Z * Interpolator1
P1ND = abs(P1NVX * Initial X + P1NVY * Initial Y + P1NVZ * Initial Z+P1NPD)
P1NPD = - PNPX * P1NVX - PNPY * P1NVY - PNPZ * P1NVZ
P1NVX = sin(Piston1Offset)
P1NVY = cos(Piston1Offset)
P1NVZ = sin(0)

[Opaque]

You cannot disable mesh stiffness since it is a required parameter of the model.

However, you can make its influence disappear by using a uniform value throughout the domain, say 1

[ghorrocks]

I have modelled a lot of piston compression things and I can tell you that the CFX mesh motion stuff works well if you start the mesh at top-dead-centre and expand it to bottom-dead-centre. If you try the other way around the mesh always ties itself in knots.