Discussion Forum

Hi

it's the other way around:

1) thermal stress is set up via temperature increase from the HT physics, that one feed into the Structural ST physics to adapt the resulting stress level, all via a stationary solver process
2) the Structural eigenfrequency solver is called upon, and being asked to start to linearise from the previous stationary solved (and stored) solution

This works OK in v4 (call up both solvers sequentially, and check that you apply the correct physics for the correct solvers. But in v3.5a you must still go via matlab to read in and load back the first stationary case to have a stressed starting point for the eigenfrequency analysis

--
Good luck
Ivar

Hi

Thanks for your reply.

In my model I start by calculating the thermal stress and strain, as you suggested. However, I do not know how to use the calculated stress and strain in the frequency simulation.

I have tried to find a tutorial that explains this, but without any success. Are you aware of one?

Best regards Tom

Hi

Store/save your stress calculation, add a new solver case eigenfrequency and tell the solver to start from the "stored solution", thenit will linearise the stress values.

Take a buckling axample there you ahve COMSOl setting up a stationary and an eigenfrequency calculation and be inspired ;)

--
Good luck
Ivar

Hi

Thanks for your help. I think I am making progress. Now I can change the temperature of the structure and then calculate the eigenfrequency. However, when I plot the deformed structure after calculating the stress and strain, it looks not right.
The idea it that a beam with a high coefficient of thermal expansion (AL) is support at both ends by a material which has a lower coefficient of thermal expansion (Si). When the temperature of the structure is lowered the beam will contract more then the supporting structure. The will generates a tensile stress in the beam. Due this I would expect a straight beam after the temperature has been lowered. This is not the case, see the attached model.

Do you know what I am doing wrong?

Best regards
Tom

Hi
in the model you sent there is no HT or HS so I do not see how you stresss the beam thermally.

I would propose that you start very simple, just with yut Al beam, add some prestress pulling it and make a first eigenfrequency scan with a parameter loop.

Thereafter you can make it with several materials

--
Good luck
Ivar

Hi

Thanks

I stress the structure thermally by setting the strain reference temperature and the temperature of the structure in Solid Mechanics (solid) -> Linear Elastic Material Model 1 -> Thermal Expansion.

I will try to get ther thermal deformation correct before I look at the eigenfrequency.

Best regards
Tom