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Boundary problem

Posted Jul 22, 2021, 6:30 a.m. EDT 1 Reply

Malgorzata Wojcik, PhD The CHEMKOP Company
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Hello, I have a problem with the solution. Can you check the boundary conditions for me? Calculations do not give a solution. Sincerely, Małgorzata

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1 Reply Last Post Jul 23, 2021, 4:59 a.m. EDT
Henrik Sönnerlind COMSOL Employee

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Posted: 3 years ago Jul 23, 2021, 4:59 a.m. EDT

Hi,

It is not a problem with boundary conditions, but with initial conditions. There is a stored bad solution which is used as initial condition. You can fix this in two ways:

  • Clear the solution: Solution 1 -> Solution -> Clear
  • Explicitly use a zero solution as initial value: in Step 1: Time Dependent, set Initial values of variables solved for to User controlled

I took a quick look at the model and noted two other issues (there may be more):

  • The max number of iterations is set to 1000. If there are convergence problems so that the time step needs to be decreased, it will take forever until all 1000 unsuccessful iterations have run out. I would use something like 5 to 20.
  • The initial stress depends on the deformed coordinate 'z'. If this is not intentional, use 'Z' instead in order to avoid this source of nonlinearity.
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Henrik Sönnerlind
COMSOL
Hi, It is not a problem with boundary conditions, but with initial conditions. There is a stored bad solution which is used as initial condition. You can fix this in two ways: * Clear the solution: *Solution 1* -> *Solution* -> *Clear* * Explicitly use a zero solution as initial value: in *Step 1: Time Dependent*, set *Initial values of variables solved for* to *User controlled* I took a quick look at the model and noted two other issues (there may be more): * The max number of iterations is set to 1000. If there are convergence problems so that the time step needs to be decreased, it will take forever until all 1000 unsuccessful iterations have run out. I would use something like 5 to 20. * The initial stress depends on the deformed coordinate 'z'. If this is not intentional, use 'Z' instead in order to avoid this source of nonlinearity.

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