Hi guys, I'm using libmesh to solve a basic structural mechanics problem: Just using 1 element (QUAD4) for now. - 1 side (Node 0 -1) is constrained, 3 other frees, - 1 force (0,-20) (x-y coordinate) acting down face 3 (Node 3-0).
0----------------force down y------------------------------------3 - - -constrained - -constrained - - constrained - -- - --- - 1-----------------------------------------2 Long story short, after assembling, I've got a matrix look like this: *3.34825e+09** **3.32591e+09** **1.66e+09** ** 1.66832e+09* -9.77308e+06 6.6e+06 1.52308e+06 -825000 3*.32591e+09** **3.36083e+09** **1.66914e+09** **1.64206e+09* 6.6e+06 -1.67856e+07 -1.65e+06 1.38981e+07 *1.66e+09** ** 1.66914e+09** **3.34412e+09** **3.33663e+09* 1.52308e+06 -1.65e+06 -5.64808e+06 -4.125e+06 *1.66832e+09** **1.64206e+09** **3.33663e+09** **3.35938e+09* -825000 1.38981e+07 -4.125e+06 -1.53418e+07 -9.77308e+06 6.6e+06 1.52308e+06 -825000 2.00538e+07 -8.25e+06 -1.18038e+07 2.475e+06 6.6e+06 -1.67856e+07 -1.65e+06 1.38981e+07 -8.25e+06 3.82038e+07 3.3e+06 -3.53163e+07 1.52308e+06 -1.65e+06 -5.64808e+06 -4.125e+06 -1.18038e+07 3.3e+06 1.59288e+07 2.475e+06 -825000 1.38981e+07 -4.125e+06 -1.53418e+07 2.475e+06 -3.53163e+07 2.475e+06 3.67601e+07 AND the following RHS # Value 0 0 1 -20 2 0 3 0 4 0 5 0 6 0 7 -20 -----Solve for the following u1x u1y u2x u2y u3x u3y u4x u4y ---------------------------------(x-y) displacements at 4 nodes The matrix is correct because I used the example from the book First Course to Finite Elements and coefficients are correct. Only the *LARGE* numbers (i.e. 10^9) are not sure - because I use penalty method - not like in the book. My question is: - Does the matrix looks right in term of penalty method? Because node 0 and 1 is constrained, so the large numbers are on these, therefore node 0 and 1 should be ZERO? Libmesh gave me very weird answers though! - I use "u" and "v" ( 2 variables) in a LinearImplicitSystem with FIRST order appx, to make the DOF became "8" (because eventhough it's 2D, libmesh still provide DOF of 4 !!!! (for a QUAD4 element)). I think this might be a problem! Does system->solve() just simply inverse the matrix and multiply to the RHS?? Does the "2 variables" affect the "solve()" in any way? Many thanks guys. I really appreciate this if you could help. Regards, Ha Le --------------------------------------------------------------------------------------------- Intern at University of Nebraska - Lincoln COHESIVE project Lincoln, NE Phone: 402 - 613 - 9268 --------------------------------------------------------------------------------------------- Undergraduate B.E. Robotics and Mechatronics B.S. Computer Science (Software Engineering) Swinburne University of Technology, Melbourne, Australia PH 0433 595 307 ------------------------------------------------------------------------------ This SF.Net email is sponsored by the Verizon Developer Community Take advantage of Verizon's best-in-class app development support A streamlined, 14 day to market process makes app distribution fast and easy Join now and get one step closer to millions of Verizon customers http://p.sf.net/sfu/verizon-dev2dev _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
