Question about Lid Driven Cavity Flow modeled by FEM

msalamih · February 28, 2014, 16:54

Dear All,
I have written a FEM code in MATLAB to analyse Lid Driven Cavity flow . But I have a big problem with that. When I run the code, MATLAB tells me that the stiffness matrix is singular and there is some irrelevant results for velocity and nonsense for pressure. I'm attaching the all codes and required file here. Just execute mixed.m and view the results in GiD 11 (*.res and *.msh file should be copied to fem22.gid folder).
I tried to find the problem but I couldn't.... I check every routine but everything seems correct.....

PS: I have checked my code for flow in a duct... it is not working

Jonas Holdeman · March 1, 2014, 10:43

I opened your main code with MATLAB version 2013b and it gave dozens of warnings. You might try to eliminate these before continuing to examine the code for logic or implementation errors.

Earlier versions of MATLAB did not have this capability to analyze the code in the editor before execution. I was surprised to find so many warnings (and errors) in my working codes when I first upgraded to a current version, though many of these were due to changes in the MATLAB language. It is important to know that your program is free from syntax errors before spending a lot of time following and analyzing the flow of the computation. The most difficult error to find is the conceptual error, where you think the program is doing one thing but it is doing something else.

msalamih · March 1, 2014, 15:41

Thanks for your comment. I will try to check it with a newer version of MATLAB (I'm currently using R2011).

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March 1, 2014, 10:43		#2
Jonas Holdeman Senior Member Jonas T. Holdeman, Jr. Join Date: Mar 2009 Location: Knoxville, Tennessee Posts: 128 Rep Power: 18	I opened your main code with MATLAB version 2013b and it gave dozens of warnings. You might try to eliminate these before continuing to examine the code for logic or implementation errors. Earlier versions of MATLAB did not have this capability to analyze the code in the editor before execution. I was surprised to find so many warnings (and errors) in my working codes when I first upgraded to a current version, though many of these were due to changes in the MATLAB language. It is important to know that your program is free from syntax errors before spending a lot of time following and analyzing the flow of the computation. The most difficult error to find is the conceptual error, where you think the program is doing one thing but it is doing something else.

March 1, 2014, 15:41		#3
msalamih New Member Mahdi Salami Join Date: Feb 2014 Posts: 6 Rep Power: 12	Thanks for your comment. I will try to check it with a newer version of MATLAB (I'm currently using R2011).