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Verification of results

Posted 29.01.2010, 14:53 GMT-5 2 Replies

David Smith
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Hi,

Sorry if this is a pointless question but I am a fairly basic user of Comsol.

I have modelled a tee piece pipe section and applied an internal pressure of 3 MPa while fixing it at each end. I have computed all my results and my simulation matches up quite similarly to that of the same test I did in Autodesk Inventors stress analysis.

I am not sure how to verify the results I have found by hand. Is it possible to calculate manually what Comsol has done, to manually write down the process the programme has gone through.

This is for a university project, I feel I need to go into as much detail as possible.

I apologise if this question is hard to answer, if not impossible. I don't really know myself.

Thanks

Dave
2 Replies Last Post 03.03.2020, 15:24 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 31.01.2010, 12:21 GMT-5
Hi

This should always be done to verify your model, at least to the extend of a simplified model.
To get closer to the formulas COMSOL applies you could :
1) generate a report and study that one,
2) save the model as a m file or just look into the "history" file (do a "reset model" to clean it up a little)
3) look at the physics equations ... tabs where you have the formulas, variables and the PDE coefficients

Then use the documentation extensively (I suggest to index it as the info is somewhat scattered in several volumes).

Quite a programme, but it's absolutely worth it, to be able to play efficiently with COMSOL and to do thing you never could do with your Autodesk, as is today.

Good luck
Ivar
Hi This should always be done to verify your model, at least to the extend of a simplified model. To get closer to the formulas COMSOL applies you could : 1) generate a report and study that one, 2) save the model as a m file or just look into the "history" file (do a "reset model" to clean it up a little) 3) look at the physics equations ... tabs where you have the formulas, variables and the PDE coefficients Then use the documentation extensively (I suggest to index it as the info is somewhat scattered in several volumes). Quite a programme, but it's absolutely worth it, to be able to play efficiently with COMSOL and to do thing you never could do with your Autodesk, as is today. Good luck Ivar
Jeff Hiller COMSOL Employee

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Posted: 4 years ago 03.03.2020, 15:24 GMT-5
Updated: 4 years ago 10.03.2020, 16:24 GMT-4

Hello David,

COMSOL uses the finite element method to solve the structural mechanics equations. Any university library will give you your pick of textbooks that explain what a finite element package does behind the scene (i.e. how to compute elemental stiffness matrices, how to assemble them into the global stiffness matrix, how to assemble the load vector, and how to invert the system). The one I used as a grad student is Bathe's Finite Element Procedures, but like I said there are many others that cover that same topic. In practice, as soon as there are more than one or two elements in your mesh performing the operations by hand becomes a major pain in the neck (particularly the matrix inversion)... which is why we use computers.

I'll just add that COMSOL recently added to our website this page that gathers well over a hundred verification and validation models and their documentation. Models can be filtered by discipline or by module, as well as searched through via a free word search. This is a great way to check that COMSOL indeed solves the equations implemented in its physics interfaces accurately, without performing manually the same steps as the software performs for you.

Best,

Jeff

-------------------
Jeff Hiller
Hello David, COMSOL uses the finite element method to solve the structural mechanics equations. Any university library will give you your pick of textbooks that explain what a finite element package does behind the scene (i.e. how to compute elemental stiffness matrices, how to assemble them into the global stiffness matrix, how to assemble the load vector, and how to invert the system). The one I used as a grad student is Bathe's Finite Element Procedures, but like I said there are many others that cover that same topic. In practice, as soon as there are more than one or two elements in your mesh performing the operations by hand becomes a major pain in the neck (particularly the matrix inversion)... which is why we use computers. I'll just add that COMSOL recently added to our website [this page](https://www.comsol.com/verification-models) that gathers well over a hundred verification and validation models and their documentation. Models can be filtered by discipline or by module, as well as searched through via a free word search. This is a great way to check that COMSOL indeed solves the equations implemented in its physics interfaces accurately, without performing manually the same steps as the software performs for you. Best, Jeff

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