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Thermoelastic damping - nonlinear geometry - Jacobian variable problem
Posted Apr 19, 2012, 3:20 a.m. EDT 3 Replies
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Dear all,
I try to do a modal analysis thermoelastic damping in 4.2 within a membrane spring. I adapted the model
www.comsol.com/showroom/gallery/1439/
and it worked quite well with the equation for the thermal source (even though I thought in 4.x it should be different variables)
-smsld.iomega*(rho*Cp*T+T0*smsld.Ent)
My problem now is that I need to include nonlinear geometry and I always get the error that the Jacobian variable cannot be evaluated.
- Modal analysis including nonlinear geometry but without the thermal source does work.
- Modal analysis including the thermal source but just linear geometry does work.
Does anybody have an idea what the issue might be?
Thanks a lot!
c
I try to do a modal analysis thermoelastic damping in 4.2 within a membrane spring. I adapted the model
www.comsol.com/showroom/gallery/1439/
and it worked quite well with the equation for the thermal source (even though I thought in 4.x it should be different variables)
-smsld.iomega*(rho*Cp*T+T0*smsld.Ent)
My problem now is that I need to include nonlinear geometry and I always get the error that the Jacobian variable cannot be evaluated.
- Modal analysis including nonlinear geometry but without the thermal source does work.
- Modal analysis including the thermal source but just linear geometry does work.
Does anybody have an idea what the issue might be?
Thanks a lot!
c
3 Replies Last Post May 21, 2012, 3:11 p.m. EDT
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Posted:
1 decade ago
No idea?
I tried the analysis with solid - same result
I tried it using two steps (first static with nonlinear geometry, second eigenfrequency with linear geometry) - no impact of the prestress.
The error message I get is
Failed to evaluate variable Jacobian.
- Variable: solid2.Ent
- Geometry: 1
- Domain: 1 2 3 4
I don't understand why entropy cannot be evaluated...
I'm running out of ideas what I could change... :(
I tried the analysis with solid - same result
I tried it using two steps (first static with nonlinear geometry, second eigenfrequency with linear geometry) - no impact of the prestress.
The error message I get is
Failed to evaluate variable Jacobian.
- Variable: solid2.Ent
- Geometry: 1
- Domain: 1 2 3 4
I don't understand why entropy cannot be evaluated...
I'm running out of ideas what I could change... :(
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Posted:
1 decade ago
Update: I get a result when I just use
-solid2.iomega*(rho*Cp*T)
as heat source, all reference temperatures =20K and T0 is 0K. Although, this cannot give the correct value, it suggests that the error is within solid2.Ent which cannot be evaluated, I guess.
Btw: the thermoelastic damping from the equation above is too low.
-solid2.iomega*(rho*Cp*T)
as heat source, all reference temperatures =20K and T0 is 0K. Although, this cannot give the correct value, it suggests that the error is within solid2.Ent which cannot be evaluated, I guess.
Btw: the thermoelastic damping from the equation above is too low.
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Posted:
1 decade ago
Hi,
I want to give you an update. My supervisor got help from the support:
In
-solid2.iomega*(rho*Cp*T+T0*solid2.Ent)
the variables solid2.iomega and solid2.Ent are unknown. Replace it by
-solid2.iomega=-2*pi*i*freq
solid2.Ent=solid2.alpha11*solid2.sx+solid2.alpha12*solid2.sxy+solid2.alpha13*solid2.sxz+solid2.alpha12*solid2.sxy+solid2.alpha22*solid2.sy+2*solid2.alpha23*solid2.syz+solid2.alpha13*solid2.sxz+solid2.alpha33*solid2.sz
and it should work. In fact, the eigenfrequency still does not consider the nonlinear stiffness of the spring. At least, it computes the thermoelastic damping..
I want to give you an update. My supervisor got help from the support:
In
-solid2.iomega*(rho*Cp*T+T0*solid2.Ent)
the variables solid2.iomega and solid2.Ent are unknown. Replace it by
-solid2.iomega=-2*pi*i*freq
solid2.Ent=solid2.alpha11*solid2.sx+solid2.alpha12*solid2.sxy+solid2.alpha13*solid2.sxz+solid2.alpha12*solid2.sxy+solid2.alpha22*solid2.sy+2*solid2.alpha23*solid2.syz+solid2.alpha13*solid2.sxz+solid2.alpha33*solid2.sz
and it should work. In fact, the eigenfrequency still does not consider the nonlinear stiffness of the spring. At least, it computes the thermoelastic damping..