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Solvers in COMSOL

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Hello everyone!

I am a newbie who seeks help in COMSOL.
I have simulated a laminar flow in an annulus using direct solvers. The results match well with the problem (taken from Bird Stewart Lightfoot). I am trying to observe if changing the solver I have used will bring about any change in simulation time, easier convergence,etc. However, I am not sure where to look for these details.

Could you help me find where any changes, due to changing solvers, may be possible?
Also, I find a convergence plot laid out while using DIRECT solvers. It shouldn't be there, right? I have read that the solution is generated 'at once' using direct solvers using matrix method.

Thank you for your time.
--
Raja Barnwal

2 Replies Last Post 28.09.2016, 12:01 GMT-4
Niklas Rom COMSOL Employee

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Posted: 8 years ago 28.09.2016, 09:50 GMT-4
The COMSOL blogs is a good place to start, for example this:
www.comsol.com/blogs/solutions-linear-systems-equations-direct-iterative-solvers/

The direct solver is used as a linear system solver. Navier-Stokes is a nonlinear problem per se. As such a nonlinear method is used around each linear step. That is the convergence progress you see in the graph.

Niklas


Hello everyone!

I am a newbie who seeks help in COMSOL.
I have simulated a laminar flow in an annulus using direct solvers. The results match well with the problem (taken from Bird Stewart Lightfoot). I am trying to observe if changing the solver I have used will bring about any change in simulation time, easier convergence,etc. However, I am not sure where to look for these details.

Could you help me find where any changes, due to changing solvers, may be possible?
Also, I find a convergence plot laid out while using DIRECT solvers. It shouldn't be there, right? I have read that the solution is generated 'at once' using direct solvers using matrix method.

Thank you for your time.
--
Raja Barnwal


The COMSOL blogs is a good place to start, for example this: https://www.comsol.com/blogs/solutions-linear-systems-equations-direct-iterative-solvers/ The direct solver is used as a linear system solver. Navier-Stokes is a nonlinear problem per se. As such a nonlinear method is used around each linear step. That is the convergence progress you see in the graph. Niklas [QUOTE] Hello everyone! I am a newbie who seeks help in COMSOL. I have simulated a laminar flow in an annulus using direct solvers. The results match well with the problem (taken from Bird Stewart Lightfoot). I am trying to observe if changing the solver I have used will bring about any change in simulation time, easier convergence,etc. However, I am not sure where to look for these details. Could you help me find where any changes, due to changing solvers, may be possible? Also, I find a convergence plot laid out while using DIRECT solvers. It shouldn't be there, right? I have read that the solution is generated 'at once' using direct solvers using matrix method. Thank you for your time. -- Raja Barnwal [/QUOTE]

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Posted: 8 years ago 28.09.2016, 12:01 GMT-4
Thank you, Niklas.

You mentioned, "As such a nonlinear method is used around each linear step". This means linear and nonlinear step work together to generate the solution. Right? I have gone through the link you suggested. Could you throw some more light in this regard? Maybe some other comprehensive source?

--
Raja Barnwal
Thank you, Niklas. You mentioned, "As such a nonlinear method is used around each linear step". This means linear and nonlinear step work together to generate the solution. Right? I have gone through the link you suggested. Could you throw some more light in this regard? Maybe some other comprehensive source? -- Raja Barnwal

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