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Comsol multiphysics

  1. Aug 14, 2008 #1
    Hello everyone,
    Does anybody use Comsol multiphysics here?
    I am trying to model the electric double layer. If you have experience, please share with me.
  2. jcsd
  3. Aug 15, 2008 #2


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    yep, one of the foremost FE software packages our group is using nowadays (or well, the last 5-6 years think). What you've in mind?
  4. Sep 1, 2008 #3
    Hi PerennialII and everyone in the forum,
    Sorry for not getting back for so long 'cause I got the answer that I wanted. Now here's my new question. In Comsol, at the bottom corner on the right, there's a memory indicator. For example 145/172. What I know is that this is the virtual memory number. 145 is the current virtual memory usage, and 172 is the peak virtual memory usage.
    The situation is that I often run out of memory, which I think is this kind of memory i.e. virtual memory. Is there anyway to tell Comsol to increase the allowed maximum memory?. My PC has 4MB of memory.
    Thanks for your time.
  5. Sep 5, 2008 #4


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    Hi hoangpd,

    are you sure about those system specs ... 4 Mb? Increasing virtual memory otherwise (assuming you're running win) is something done by adjusting the settings & workings of the operating system (in win control panel -> system and from thereon). Comsol otherwise should just swallow everything available.
  6. Sep 5, 2008 #5
    HI Perennial,
    My RAM is 4GB instead of 4MB. It was a bad typo. Sorry!. Anyway, why is virtual memory being used when Comsol still has the physical memory to use? Or is Comsol that memory intensive that it uses all the physical memory the moment it runs?
    Also, my operating system is 32bit if that helps you answer my question.
  7. Sep 5, 2008 #6


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    If you're running windows it's probably easiest 1st to check the amount of virtual memory and increase it a somewhat if feasible (control panel -> system props -> advanced and virtual memory in there). If you're running linux or some related unix system you probably wouldn't have these issues at all :wink: (or well .... :biggrin: ). If that doesn't help, then the next thing could do is to start decreasing the amount of memory comsol is using to solve your model & problem (which means primarily solver parameters, and choosing as memory efficient solver as possible for the problem you're studying). Naturally, can try to modify the model trying to decrease the number of dofs and so on, but surely would be nice to find an another solution which would enable solving the model as is.

    The memory "spill" to virtual memory likely has to do with the memory management of your OS (when talking win this is fairly common although have physical memory remaining). Also, could check if your system can allocate the whole 4 Gb (i.e. does it "show" at the OS, in win for example under system properties). In principle would think so, but sometimes other limitations come into play (like weird BIOS behavior).
  8. Sep 17, 2008 #7
    I had solve this problem increasing the mesh size on the areas that are not of significance on the model. Also, maybe is due to the time step you are using, if it is a transient analysis.
  9. Feb 1, 2009 #8
    Hi All,

    I am trying to solve a problem where the solutions are expected to be zero for a very long time.

    I have refined the mesh with the maximum element size of 0.002 and am using the GMRES method with preconditioning quality of 0.01.

    However, inspite of it, the system is unable to process the solution and gives an error for residual computation citing singular matrix as the problem.

    Can anyone please suggest some ways to solve the problem?

  10. Apr 3, 2009 #9
    I guess you are using Nernst planck without electroneutrality and poisson equation.

    I set the solver to linear and then it worked, otherwise convergence was bumping up and down
  11. Apr 14, 2009 #10
    Hi All
    I'm trying to model the boundary layer created by a heated plate due to bouyancy effect. and I want to find the velocity boundary layer data points along the vertical plate at u=0.99u(infinity). Does anyone know how to define this criteria in Comsol and get the data points?
  12. May 10, 2009 #11
    i am a student of electrical engineering, and i am about to start working in comsol
    (ac/dc module), can anybody tell me from where to start kinda like abc.... when you
    start learning english
  13. May 22, 2009 #12
    Hi everyone.
    I'm a beginner COMSOl mph user.
    How can I implement the Landau-Lifgarbagez-Gilbert equation/model on
    COMSOL mph??(for time dipendent micromagnetic modeling).
    Is there any .pdf-tutorial/links etc. for this topic??

    Every suggestion will be good!

  14. May 31, 2009 #13
    Hi All:

    I'm trying to model barrier properties in flexible materials for food packaging specifically oxygen transmission rate, water vapor transmission rate & permeability. I'm using Comsol 3.5. Can anybody point me in the right direction to do this and select/import the materials in www.MATWEB.com.

  15. Jan 19, 2010 #14
    hi all!

    I have problems with .dxf import in COMSOL..

    even with the simplest 3d objects like sphere comsol import it as 2d image

    .dxf file I've created in Maple13
    does anybody know any other CAD program that can draw 3d surface by giving equation?

    please help,
  16. Oct 8, 2010 #15
    Hi everyone!
    I have a problem in Comsol, whenever I run "compute" option in the program, komsol goes out. why ?.... I have about 1GB of RAM ,аlso, my operating system is 32bit ...

    I need help

  17. Nov 17, 2011 #16
    Hi all!
    I working in Comsol for the Structural Mechanics Modeling, particularly the Solid Mechanics problem. I need your help to solve a problem concerning the boundary condition. For exemple, i have a cube, in a face of this cube (e.x face // yz) i want to apply a boundary condition of type: Two shear stress equal to zero (sigma xy et sigma xz = 0) and the normal displacement equal to a number predefide (ex: 5e-3m). Note that i don't know the normal stress. I've searched in comsol but i didn't find the constraint in stress. Anyone can help me?

    Thanks much!
  18. Jan 12, 2012 #17


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    Hello everyone!
    I need to solve a time dependant one-dimentional diffusion equation on a finite interval. Is it possible to alter comsol's internal diffusion equation to add one more term to it in order for a value of the concentration gradient, that is calculated on one of the interval's edges, to be added to it at every point during calculation process?

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  19. Mar 15, 2012 #18
    Hello Everyone,

    I am a Mechanical undergraduate currently working on Heat transfer in microchannels. I am using COMSOL 3.4 for simulating the flow.

    I am able to individually simulate the laminar flow and heat transfer modules and the results are encouraging.

    I am facing problems in coupling the modules. The solution is not converging, Please guide me regarding the same

    Thanks !
  20. Mar 19, 2012 #19
    I'm working on a project on comsol, so I have been trying to simulate the movement of a nanoparticle inside a phantom using acoustic pressure but I couldn't manage to do it... does anyone have any idea how to start?
  21. Apr 9, 2012 #20
    lol this thread obvious comes up on Google.
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