[mztcu]

Hi,

I simulate porous air bearing. I use rotor shaft motion via rigid body option. It works. But when I try change boundary condition like input pressure, temperature etc. shaft motion increase and shaft crash to porous wall. When this happen CFX gives negative element errror. I want to write motion equation for rotor shaft via expression without rigid body. I use general newton's first law F:m.a. I wrote expression but cfx give error when calculating mesh velocity x and y component.

My expression,
ax = fxnet/1 [kg]
ay = fynet/1 [kg]
dx = if(locR>14.9[micron],0[micron],velox*ts+(0.5*ts^2*ax))
dy = if(locR>14.9[micron],0[micron],veloy*ts+(0.5*ts^2*ay))
fxnet = force_x()@ROTORTOGAP Side 1-50 [N]
fynet = force_y()@ROTORTOGAP Side 1
locR = (locX^2+locY^2)^0.5
locX = ave(x)@ROTORTOGAP Side 1
locY = ave(y)@ROTORTOGAP Side 1
rev = 10000 [rev min^-1]
ts = 0.00005[s]
velox = areaAve(Mesh Velocity X)@ROTORSHAFT Side 1
veloy = areaAve(Mesh Velocity Y)@ROTORSHAFT Side 1

And the error,
The function 'ave' referenced by parameter 'Displacement X Component' in object '/Flow:Flow Analysis 1/DOMAIN:ROTORDOLID/BOUNDARY:ROTORSHAFT Side 1 /BOUNDARY CONDITION/MESH MOTION/DISPLACEMENT' has a disallowed argument, 'x'. The solver does not support the use of this variable in this context.

I need your advice and helps.
Thanks.

[Opaque]

You should read the documentation for the CEL functions, such as ave(Variable)@location, to understand the limitation and suggested workaround.

If your intention is using the global mesh coordinates (not the local coordinates), you can get away by using xGlobal/yGlobal/zGlobal.

Hope the above helps

[mztcu]

Originally Posted by Opaque

You should read the documentation for the CEL functions, such as ave(Variable)@location, to understand the limitation and suggested workaround.

If your intention is using the global mesh coordinates (not the local coordinates), you can get away by using xGlobal/yGlobal/zGlobal.

Hope the above helps

Actually this expressions works clearly at CFX-Post I tried. The problem is solver and pre dont accept velox and veloy expressions while calculating mesh displacement. They depends X and Y axis. Mesh displacement option's does not allow any variable depends on X/Y/Z. I think, I need to change rule file in cfx root.
I had lived same problem with angular velocity, I changed dependency option at the rule file in the cfx root problem was solved.
I tried add a new veriable for mesh velocity and created but it did not work.
I tried xGlobal/yGlobal as you say but it does not work. -(areaAve_xGlobal(Mesh Velocity)@location and areaAve@(Mesh Velocity xGlobal)@location)-
There must be a way for the program to allow to use mesh velocity in mesh displacement.