# Discussion Forum

## Segregated Solver

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Patrick Kirby

March 22, 2013 2:35pm UTC

Segregated Solver

Hello,

I was wondering if someone could perhaps explain to me the nature of the segregated solver so that I may understand it a little more clearly. I have seen other threads discussing this in the past yet I still have some questions. In particularly I was wondering if when using this solver is each segregated step solved in an iterative manner. For example I am solving a system which incorporates several different chemical species. The transport of each of these species is coupled with one another and also fluid transport which I have also modeled.

So I have species 1 whose production is dependent upon the concentration of species 2. The transport of species 2 is meanwhile dependent upon chemical species 3. And the transport and in particularly the production of species 3 is dependent upon species 1 and 2.

The way that I have things set up right now is using a segregated solver I choose the first step to solve for laminar flow
The second segregated step I have aligned with Chemical species 1 and the third step solves for both species 2 and 3.

Will Comsol automatically iterate this in the segregated solver until convergence?

Appreciate any clarity which one could provide. Also good examples dealing with 3d mass transport and fluid dynamics would be useful as well.

Thanks

Pat

Ivar Kjelberg

March 22, 2013 8:38pm UTC in response to Patrick Kirby

Re: Segregated Solver

Hi

I have understood it's iterating, over the different steps, but in the specified order, until the convergence criteria is reached, but I do not have any definitive answer, the only way to find out is to once follow carefully what COMSOL does in the solver sequences, you have the log (also a detailed view but it does not bring much more), and you can follow in the solver sequence view during solving, there you should be able to see the segregated evels, one per line and how these loop around.

--
Good luck
Ivar

Patrick Kirby

March 22, 2013 10:52pm UTC in response to Ivar Kjelberg

Re: Segregated Solver

Thanks Ivar, I will do exactly what you recommend.

Mattia Montanari

March 23, 2013 9:15am UTC in response to Patrick Kirby

Re: Segregated Solver

Hi Patrick,

the idea of segregated solvers is to solve each governing equation separately. In Comsol (as is written in the Reference Manual) each substep uses a damped version of Newtonâ€™s method.So, Comsol iterates among the segregated steps (eventually even inside..) before giving you the solution of the whole system.

Hope it helps,
Mattia

Patrick Kirby

March 23, 2013 1:06pm UTC in response to Mattia Montanari

Re: Segregated Solver

Hey Mattia,
This does help, and it is what I had hoped that Comsol would do.
Much appreciated

Pat

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