[FEM] Elmer: use direct solving as default for stresses

- direct solving is sometimes even 10 times faster (as fast as CCX) and as accurate as CCX

src/Mod/Fem/femsolver/elmer/equations/elasticity.py

@@ -83,6 +83,10 @@ class Proxy(linear.Proxy, equationbase.ElasticityProxy):
         obj.EigenmodesCount = 5
         obj.Priority = 10
         obj.CalculatePrincipal = True
+        # according to the Elmer tutorial and forum, for stresses direct solving
+        # is recommended -> test showed 10 times faster and even more accurate
+        obj.LinearSolverType = "Direct"
+        obj.LinearDirectMethod = "Umfpack"
 
 
 class ViewProxy(linear.ViewProxy, equationbase.ElasticityViewProxy):

src/Mod/Fem/femtest/data/elmer/box_static_0_mm.sif

@@ -15,13 +15,10 @@ Solver 1
   Equation = String "Stress Solver"
   Exec Solver = String "Always"
   Linear System Abort Not Converged = Logical False
-  Linear System Convergence Tolerance = Real 1e-08
-  Linear System Iterative Method = String "BiCGStab"
-  Linear System Max Iterations = Integer 500
+  Linear System Direct Method = String "Umfpack"
   Linear System Precondition Recompute = Integer 1
-  Linear System Preconditioning = String "ILU0"
   Linear System Residual Output = Integer 1
-  Linear System Solver = String "Iterative"
+  Linear System Solver = String "Direct"
   Optimize Bandwidth = Logical True
   Procedure = File "StressSolve" "StressSolver"
   Steady State Convergence Tolerance = Real 1e-05

src/Mod/Fem/femtest/data/elmer/ccxcantilever_faceload_0_mm.sif

@@ -15,13 +15,10 @@ Solver 1
   Equation = String "Stress Solver"
   Exec Solver = String "Always"
   Linear System Abort Not Converged = Logical False
-  Linear System Convergence Tolerance = Real 1e-08
-  Linear System Iterative Method = String "BiCGStab"
-  Linear System Max Iterations = Integer 500
+  Linear System Direct Method = String "Umfpack"
   Linear System Precondition Recompute = Integer 1
-  Linear System Preconditioning = String "ILU0"
   Linear System Residual Output = Integer 1
-  Linear System Solver = String "Iterative"
+  Linear System Solver = String "Direct"
   Optimize Bandwidth = Logical True
   Procedure = File "StressSolve" "StressSolver"
   Steady State Convergence Tolerance = Real 1e-05

src/Mod/Fem/femtest/data/elmer/ccxcantilever_faceload_1_si.sif

@@ -15,13 +15,10 @@ Solver 1
   Equation = String "Stress Solver"
   Exec Solver = String "Always"
   Linear System Abort Not Converged = Logical False
-  Linear System Convergence Tolerance = Real 1e-08
-  Linear System Iterative Method = String "BiCGStab"
-  Linear System Max Iterations = Integer 500
+  Linear System Direct Method = String "Umfpack"
   Linear System Precondition Recompute = Integer 1
-  Linear System Preconditioning = String "ILU0"
   Linear System Residual Output = Integer 1
-  Linear System Solver = String "Iterative"
+  Linear System Solver = String "Direct"
   Optimize Bandwidth = Logical True
   Procedure = File "StressSolve" "StressSolver"
   Steady State Convergence Tolerance = Real 1e-05

src/Mod/Fem/femtest/data/elmer/ccxcantilever_nodeload_0_mm.sif

@@ -15,13 +15,10 @@ Solver 1
   Equation = String "Stress Solver"
   Exec Solver = String "Always"
   Linear System Abort Not Converged = Logical False
-  Linear System Convergence Tolerance = Real 1e-08
-  Linear System Iterative Method = String "BiCGStab"
-  Linear System Max Iterations = Integer 500
+  Linear System Direct Method = String "Umfpack"
   Linear System Precondition Recompute = Integer 1
-  Linear System Preconditioning = String "ILU0"
   Linear System Residual Output = Integer 1
-  Linear System Solver = String "Iterative"
+  Linear System Solver = String "Direct"
   Optimize Bandwidth = Logical True
   Procedure = File "StressSolve" "StressSolver"
   Steady State Convergence Tolerance = Real 1e-05

src/Mod/Fem/femtest/data/elmer/ccxcantilever_prescribeddisplacement_0_mm.sif

@@ -15,13 +15,10 @@ Solver 1
   Equation = String "Stress Solver"
   Exec Solver = String "Always"
   Linear System Abort Not Converged = Logical False
-  Linear System Convergence Tolerance = Real 1e-08
-  Linear System Iterative Method = String "BiCGStab"
-  Linear System Max Iterations = Integer 500
+  Linear System Direct Method = String "Umfpack"
   Linear System Precondition Recompute = Integer 1
-  Linear System Preconditioning = String "ILU0"
   Linear System Residual Output = Integer 1
-  Linear System Solver = String "Iterative"
+  Linear System Solver = String "Direct"
   Optimize Bandwidth = Logical True
   Procedure = File "StressSolve" "StressSolver"
   Steady State Convergence Tolerance = Real 1e-05