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Problems encountered in COMSOL 4.1(Out-of-core; Java heap space; parameterized geometry)

Posted 2011/04/15 22:29 GMT-4 Low-Frequency Electromagnetics, Heat Transfer & Phase Change, Geometry, Results & Visualization, Studies & Solvers Version 4.1 2 Replies

Yang Yulong
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Hi All

I have used Comsol for a short time, and the following questions or errors puzzled me.

Descriptions:
Version: 4.1.0.185
Memory:3.25G
Platform: Windows XP

Questions:

1, Out-of-core
what do this mean in the direct solver setting? Will it be useful for saving memory if I turn on the option?

2,Parameterized geometry
We want to simulate the mobile induction heating process, and by now it's known that sweeping Parameterized geometry and ALE(moving mesh) can deal with the issue. So could you please make comparison between the two methods, especially on the reliability, precision, and convergence difficulty? And how to add to the precision of the solution by sweeping Parameterized geometry

3, Error in sweep: Java heap space
when a parametric sweep was conducted to move the position of a sub-domain, the first several position values got the solution successfully. And then the solver stopped and warned "Error in sweep: Java heap space".
How to get through this problem? I have about 100 position values to sweep, but it can only solve the first several ones.

Hoping for your advice,
Best regards
Yulong Yang
2 Replies Last Post 2011/04/16 8:53 GMT-4
Drake Mith
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Posted: 1 decade ago 2011/04/16 3:29 GMT-4
First off, do a google search for a computer core, and cpu core memory. I don't know much, but I do know that memmory gets stored in different places in the computer hardware depending on how close it is to being calculated on. Hard drives store the most memory, then RAM, and then different levels of memory in the CPU, and each is subsequently faster than the rest. Because memory in the core is fastest, it uses that memory to calculate on during runtime. If your core memory is too small for a single "chunk" of computations, then you can store part of it in, say, RAM, during runtime. The downside is it is slower, and perhaps MUCH slower, especially if you're using hard drive space. That may be related to your java heap space error. I don't have COMSOL documentation with me now, but that is my understanding. I'll see in the morning if I am totally wrong.
First off, do a google search for a computer core, and cpu core memory. I don't know much, but I do know that memmory gets stored in different places in the computer hardware depending on how close it is to being calculated on. Hard drives store the most memory, then RAM, and then different levels of memory in the CPU, and each is subsequently faster than the rest. Because memory in the core is fastest, it uses that memory to calculate on during runtime. If your core memory is too small for a single "chunk" of computations, then you can store part of it in, say, RAM, during runtime. The downside is it is slower, and perhaps MUCH slower, especially if you're using hard drive space. That may be related to your java heap space error. I don't have COMSOL documentation with me now, but that is my understanding. I'll see in the morning if I am totally wrong.
Yang Yulong
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Posted: 1 decade ago 2011/04/16 8:53 GMT-4

First off, do a google search for a computer core, and cpu core memory. I don't know much, but I do know that memmory gets stored in different places in the computer hardware depending on how close it is to being calculated on. Hard drives store the most memory, then RAM, and then different levels of memory in the CPU, and each is subsequently faster than the rest. Because memory in the core is fastest, it uses that memory to calculate on during runtime. If your core memory is too small for a single "chunk" of computations, then you can store part of it in, say, RAM, during runtime. The downside is it is slower, and perhaps MUCH slower, especially if you're using hard drive space. That may be related to your java heap space error. I don't have COMSOL documentation with me now, but that is my understanding. I'll see in the morning if I am totally wrong.


Hi,

Thanks for your prompt reply, and after a search I found a solution to this " Java heap space" problem, which said changing the default value after "-Xmx" in \comsol41\bin\win32\comsol.ini and comsol server.ini.
I changed from default 256m to 512m, and this works well for my problem.

But another problem follows.My RAM is about 3.25G and the issue contains about 80k DoF, the memory usage will increase with the process of parametric sweeping. That is every time only about 5 values can be solved , and then the solver stop with error " Out of memory during LU factorization".

I find that some guys also come across the same problem, what they did was just to save and close the file when the solver stopped and then open and solve again.

And how to combine the solutions obtained by the parametric sweep solver, because they are stored as seperated solutions in the model. What i want is a continual solution to a transient issue.

Do you have any suggestions?
Thanks a lot for your reply
Best regards!
[QUOTE] First off, do a google search for a computer core, and cpu core memory. I don't know much, but I do know that memmory gets stored in different places in the computer hardware depending on how close it is to being calculated on. Hard drives store the most memory, then RAM, and then different levels of memory in the CPU, and each is subsequently faster than the rest. Because memory in the core is fastest, it uses that memory to calculate on during runtime. If your core memory is too small for a single "chunk" of computations, then you can store part of it in, say, RAM, during runtime. The downside is it is slower, and perhaps MUCH slower, especially if you're using hard drive space. That may be related to your java heap space error. I don't have COMSOL documentation with me now, but that is my understanding. I'll see in the morning if I am totally wrong. [/QUOTE] Hi, Thanks for your prompt reply, and after a search I found a solution to this " Java heap space" problem, which said changing the default value after "-Xmx" in \comsol41\bin\win32\comsol.ini and comsol server.ini. I changed from default 256m to 512m, and this works well for my problem. But another problem follows.My RAM is about 3.25G and the issue contains about 80k DoF, the memory usage will increase with the process of parametric sweeping. That is every time only about 5 values can be solved , and then the solver stop with error " Out of memory during LU factorization". I find that some guys also come across the same problem, what they did was just to save and close the file when the solver stopped and then open and solve again. And how to combine the solutions obtained by the parametric sweep solver, because they are stored as seperated solutions in the model. What i want is a continual solution to a transient issue. Do you have any suggestions? Thanks a lot for your reply Best regards!

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