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Hi

I cannot interpreat your error messages, I do not know enough about COMSOL internals, but I was woundering, if you do not have any inlet nor outlet, and a incomresssble fluid in a given volume, arent you overconstraining your model ?

Ivar

Hello Mr. Kjelberg,

The fluid is contained by two rubber volumes and separated by a metal middle piece and I am trying to examine the damping and stiffness of the mount. Attached is a pic of a (quickly drawn) typical hydraulic mount. The black is rubber and the silver and purple are metal. The upper and lower chambers are filled with incompressible fluid. I am trying to examine how the rubber deforms partnered with the reaction forces back from the fluid. Thank you for your help, does this still seem over-constrained or do you have any additional ideas?

Walt

I had the same error but for a different variable, just check in your subdomain dialogue box under each material, there will be one variable that you forgot to set, for me it was T (temperature) so for you its the variable called T_x_ns not sure what it is but you wil l find it in BOLD in the subdomain settings where all the properties are defined probably under the physics tab. it will look like this :

my example:

sigma_solid_1(T[1/K])[S/m]

goes to k=293

sigma_solid_1(1/293)[S/m]

hope this helps! i spent an hour until i realised that it was the problem

I had the same error but for a different variable, just check in your subdomain dialogue box under each material, there will be one variable that you forgot to set

Excellent advice for the problem of "Failed to evaluate variable."

I thought because I used the material library, these values would be set for me, but "lo' and behold", mur (permeability) was not set for "Air" in ACDC physics, elec. and mag. fields.

Thanks!

Hi

there is a often forgotten rule with V4:
Always check your material AGAIN and once you have FINSIHED to set-up your model, just before you solve.

Because when you hange the phsics you might ask for new or other material properties and these might request some further variables. i.e. if you have no temperature nor any pressure in your model physics it is often useful to add the two Parameters:

T = 20[degC] and p=1[atm]

with his the internally defined material functions are mostly covered. But still some simple material properties are often missing by default, such as mur of air ;)

We could perhaps suggst to COMSOL that they add a little /!\ on the node icone of the material node image (far up so it's visible)


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Good luck
Ivar

I'm new to comsol, I opened subdomain to find variable T but couldn't find where I'm supposed to define it.

Any advice?

Hi

your question is a bit too short, you need to be more specific, tell which version, which physics, even which node or more about your issue. In the beginning its difficult to find all the places one need to adapt variables, fill in etc, just run systematically through the cases, but really START SIMPLE iyou will progress far quicker (FSI is already a complex multiphysics case)

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Good luck
Ivar

HI,

I have similar error as well as below:

Failed to evaluate variable.
-Variable: mod1.v1x
-Geometry:1
-Domain:2

Failed to evaluate expression.
-Expression: Y+mod1.v1x

I wonder what is v1x and the Y. Did anyone have the similar error? Could you please advice??

Hi

"Y" is the "material frame Y" coordinate of some selected Entity,
while "v1x" is probably the spatial frame space derivative long "x" of "v1", that could be the 2nd structural "v" = y direction dependent variable (if you have 2 structural physics)

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Good luck
Ivar

Can anyone tell me what's wrong with this:

(The funny thing is that it worked with version 3.5a, but its not working in 3.4....I also defined the rho and eta values for both the subdomains in the Incompressible Navier stokes equation)

Error: 6170
Failed to evaluate variable
- Variable: t
- Geometry: 1
- Dimension: 2
- Domains: {1}
Failed to evaluate variable
- Variable: V
- Defined as: ((cos((((x*6)/unit_m_cf)+((5*t)/unit_s_cf)))*y)/unit_s_cf)
Failed to evaluate variable
- Variable: f
- Defined as: (((unit_N_cf*(U-V))*unit_s_cf)/(unit_m_cf^4))
Failed to evaluate variable
- Variable: F_x_chns
- Defined as: (-f)
Failed to evaluate variable
- Variable: res_u_chns
- Defined as: (((px+(((uy*v)+(u*ux))*rho_chns))-F_x_chns)-((vxy+(uyy+(uxx*2)))*eta_chns))
Failed to evaluate expression
- Expression: diff(((+(-2*eta_chns*ux+p)*test(ux)+(-eta_chns*(uy+vx))*test(uy)+(F_x_chns-rho_chns*(u*ux+v*uy))*test(u)+(-test(nojac(rho_chns)*(nojac(u)*ux+nojac(v)*uy)+px-nojac(eta_chns)*(2*uxx+uyy+vxy))*taum_chns*res_u_chns))-(0))*(dvol),{test@4})