Stress recovery during FSI analysis

[neri alamanni]

Hi all
I am trying to run a FSI analysis with stress recovery during non linear elasticity solution. I did not notice any errors during the solution but stress values are all zero.
Is this kind of analysis supported? Am i doing some errors
Attached you can find . .sif file
thank you
best regards
neri alamanni

[mika]

Hi,

In principle I don't see any reason why stress computation shouldn't work in connection with FSI simulation. It anyhow appears that in your case definition the nonlinear elasticity equations are not really solved as the solver for linear elasticity is used. Therefore consider selecting Procedure = "ElasticSolve" "ElasticSolver" in stead of choosing the linear elasticity solver by the command Procedure = "StressSolve" "StressSolver". If you make this change, then note also that the nonlinear elasticity solver assumes that the command Calculate Stresses = Logical True is given in the solver section associated with the nonlinear elasticity solver.

- Mika

[neri alamanni]

Hi Mika
it does not work,if I remove from .sif file the statement
Procedure = "StressSolve" "StressSolver"
replacing it with the statement
Procedure = "ElasticSolve" "ElasticSolver"
no stress is calculated by the solver and, therefore, no stress components are written in .ep file
My model is bidimensional, could this be the problem?
Thank you
kind regards
neri alamanni

[mika]

Hi again,

As opposed to my previous advice you still give the command "Calculate Stresses = Logical True" in Equation section. This option is not supported in connection with the nonlinear elasticity solver, so try setting

Solver 2
...
Calculate Stresses = Logical True
...
End

- Mika

[neri alamanni]

Hi
I am still having problems. Using these statements in Solver 2 definition the solution diverges immediately
Solver 2
Equation = Nonlinear elasticity
Variable = -dofs 2 Displacement
Procedure = "ElasticSolve" "ElasticSolver"
Calculate Stresses = Logical True
Exec Solver = Always
...
End
The log of the solution is the following
ELMER SOLVER (v 7.0) STARTED AT: 2012/11/13 11:04:58
MAIN:
MAIN: =============================================================
MAIN: ElmerSolver finite element software, Welcome!
MAIN: This program is free software licensed under (L)GPL
MAIN: Copyright 1st April 1995 - , CSC - IT Center for Science Ltd.
MAIN: Webpage http://www.csc.fi/elmer, Email elmeradm@csc.fi
MAIN: Library version: 7.0 (Rev: )
MAIN: =============================================================
MAIN:
MAIN:
MAIN: -------------------------------------
MAIN: Reading Model: case_fsi.sif
Loading user function library: [FlowSolve]...[FlowSolver_Init0]
Loading user function library: [ElasticSolve]...[ElasticSolver_Init0]
Loading user function library: [MeshSolve]...[MeshSolver_Init0]
Loading user function library: [ShearRateSolver]...[ShearRateSolver_Init0]
Loading user function library: [SaveData]...[SaveScalars_Init0]
Loading user function library: [ResultOutputSolve]...[ResultOutputSolver_Init0]
MAIN: -------------------------------------
Loading user function library: [FlowSolve]...[FlowSolver_Init]
Loading user function library: [FlowSolve]...[FlowSolver]
OptimizeBandwidth: ---------------------------------------------------------
OptimizeBandwidth: Computing matrix structure for: navier-stokes...done.
OptimizeBandwidth: Half bandwidth without optimization: 2027
OptimizeBandwidth:
OptimizeBandwidth: Bandwidth Optimization ...done.
OptimizeBandwidth: Half bandwidth after optimization: 38
OptimizeBandwidth: ---------------------------------------------------------
Loading user function library: [ElasticSolve]...[ElasticSolver_Init]
Loading user function library: [ElasticSolve]...[ElasticSolver]
OptimizeBandwidth: ---------------------------------------------------------
OptimizeBandwidth: Computing matrix structure for: nonlinear elasticity...done.
OptimizeBandwidth: Half bandwidth without optimization: 1474
OptimizeBandwidth:
OptimizeBandwidth: Bandwidth Optimization ...done.
OptimizeBandwidth: Half bandwidth after optimization: 87
OptimizeBandwidth: ---------------------------------------------------------
Loading user function library: [MeshSolve]...[MeshSolver_Init]
Loading user function library: [MeshSolve]...[MeshSolver]
OptimizeBandwidth: ---------------------------------------------------------
OptimizeBandwidth: Computing matrix structure for: mesh update...done.
OptimizeBandwidth: Half bandwidth without optimization: 2027
OptimizeBandwidth:
OptimizeBandwidth: Bandwidth Optimization ...done.
OptimizeBandwidth: Half bandwidth after optimization: 38
OptimizeBandwidth: ---------------------------------------------------------
Loading user function library: [ShearRateSolver]...[ShearRateSolver_Init]
Loading user function library: [ShearRateSolver]...[ShearRateSolver]
OptimizeBandwidth: ---------------------------------------------------------
OptimizeBandwidth: Computing matrix structure for: wss...done.
OptimizeBandwidth: Half bandwidth without optimization: 2027
OptimizeBandwidth:
OptimizeBandwidth: Bandwidth Optimization ...done.
OptimizeBandwidth: Half bandwidth after optimization: 38
OptimizeBandwidth: ---------------------------------------------------------
Loading user function library: [SaveData]...[SaveScalars_Init]
Loading user function library: [SaveData]...[SaveScalars]
Loading user function library: [ResultOutputSolve]...[ResultOutputSolver_Init]
Loading user function library: [ResultOutputSolve]...[ResultOutputSolver]
MAIN:
MAIN: -------------------------------------
MAIN: Time: 1/70 1.00000000000000002E-002
MAIN: -------------------------------------
MAIN:
SolveEquations: -------------------------------------
SolveEquations: Coupled system iteration: 1
SolveEquations: -------------------------------------
FlowSolve:
FlowSolve:
FlowSolve: -------------------------------------
FlowSolve: NAVIER-STOKES ITERATION 1
FlowSolve: -------------------------------------
FlowSolve:
FlowSolve: Starting Assembly...
FlowSolve: Assembly done
FlowSolve: Dirichlet conditions done
1 0.1100E+02
2 0.8368E+01
3 0.5173E+01
4 0.1788E+01
5 0.2730E-01
6 0.4209E-01
7 0.5302E-03
8 0.8372E-05
8 0.8372E-05
FlowSolve: iter: 1 Assembly: (s) 0.17 0.17
FlowSolve: iter: 1 Solve: (s) 0.14 0.14
ComputeChange: NS (ITER=1) (NRM,RELC): ( 0.97080906E-03 2.0000000 ) :: navier-stokes
FlowSolve: Result Norm : 9.70809058345948077E-004
FlowSolve: Relative Change : 2.0000000000000000
ComputeChange: SS (ITER=1) (NRM,RELC): ( 0.97080906E-03 2.0000000 ) :: navier-stokes
ElasticSolve:
ElasticSolve:
ElasticSolve: -------------------------------------
ElasticSolve: ELASTICITY ITERATION 1
ElasticSolve: -------------------------------------
ElasticSolve:
ElasticSolve: Starting assembly...
ElasticSolve: Assembly done
ElasticSolve: BCs are now set
1 0.4477E+00
2 0.4025E+00
3 0.1609E+01
4 0.5371E+01
5 0.1286E+01
6 0.1984E+00
7 0.1870E+00
8 0.2941E+00
9 0.2170E+00
10 0.3739E-01
11 0.2571E-01
12 0.1294E+00
13 0.2016E-01
14 0.1867E-01
15 0.1974E-01
16 0.1900E-01
17 0.1344E-01
18 0.7095E-01
19 0.7267E-02
20 0.1284E-01
21 0.8307E+00
22 0.4386E-02
23 0.4394E-02
24 0.4247E-02
25 0.5398E-02
26 0.3235E-02
27 0.2769E-02
28 0.2746E-02
29 0.4755E-02
30 0.8943E-03
31 0.3897E-02
32 0.3788E-03
33 0.3319E-03
34 0.3308E-03
35 0.2638E-03
36 0.1324E-03
37 0.1135E-03
38 0.1010E-03
39 0.1247E-03
40 0.6443E-04
41 0.6041E-04
42 0.4175E-04
43 0.2977E-04
44 0.2905E-04
45 0.4428E-04
46 0.1304E-04
47 0.9574E-05
48 0.7629E-05
49 0.3210E-04
50 0.7603E-05
51 0.5112E-05
52 0.5071E-05
53 0.5233E-05
54 0.4861E-05
55 0.4704E-05
56 0.4766E-05
57 0.2823E-05
58 0.2224E-05
59 0.2539E-05
60 0.2542E-05
61 0.2543E-05
62 0.2295E-05
63 0.2398E-05
64 0.1513E-05
65 0.1518E-05
66 0.1109E-05
67 0.8461E-06
68 0.8394E-06
69 0.7842E-06
70 0.7880E-06
71 0.4944E-06
72 0.5890E-06
73 0.3914E-06
74 0.2576E-06
75 0.2642E-06
76 0.2133E-06
77 0.1737E-06
78 0.2364E-06
79 0.4576E-06
80 0.1179E-06
81 0.1013E-06
82 0.4468E-07
83 0.3653E-06
84 0.1344E-06
85 0.5003E-07
86 0.5752E-07
87 0.1499E-07
88 0.1450E-07
89 0.1937E-08
89 0.1937E-08
ComputeChange: NS (ITER=1) (NRM,RELC): ( 0.28085104E-07 2.0000000 ) :: nonlinear elasticity
ElasticSolve: Result Norm : 2.80851036106565112E-008
ElasticSolve: Relative Change : 2.0000000000000000
OptimizeBandwidth: ---------------------------------------------------------
OptimizeBandwidth: Computing matrix structure for: ...done.
OptimizeBandwidth: Half bandwidth without optimization: 3393
OptimizeBandwidth:
OptimizeBandwidth: Bandwidth Optimization ...done.
OptimizeBandwidth: Half bandwidth after optimization: 128
OptimizeBandwidth: ---------------------------------------------------------
1 0.1409E-03
2 0.1254E-03
3 0.1254E-03
4 0.1254E-03
5 0.1254E-03
6 0.1254E-03
7 0.1254E-03
8 0.1254E-03
9 0.1254E-03
10 0.1254E-03
11 0.1254E-03
12 0.1254E-03
13 0.1254E-03
14 0.1254E-03
15 0.1254E-03
16 0.1254E-03
17 0.1254E-03
18 0.1255E-03
19 0.1267E-03
20 0.1281E-03
21 0.1292E-03
22 0.1873E-03
23 0.5548E-03
24 0.1426E-02
25 0.2955E-02
26 0.4111E-02
27 0.2439E-02
28 0.4112E-01
29 0.7730E-03
30 0.8262E-03
31 0.2030E-02
32 0.1560E-02
33 0.5955E-03
34 0.2222E-02
35 0.3265E-03
36 0.2030E-03
37 0.9364E-03
38 0.1654E-02
39 0.7142E-03
40 0.7131E-03
41 0.4484E-03
42 0.4215E-03
43 0.5355E-03
44 0.2215E-03
45 0.1345E-03
46 0.1349E-03
47 0.2626E-03
48 0.2125E-03
49 0.1312E-03
50 0.1300E-03
51 0.1727E-03
52 0.1543E-03
53 0.1375E-03
54 0.1410E-03
55 0.1273E-03
56 0.1265E-03
57 0.1282E-03
58 0.1333E-03
59 0.1334E-03
60 0.1288E-03
61 0.1807E-03
62 0.1279E-03
63 0.1270E-03
64 0.1308E-03
65 0.1263E-03
66 0.1259E-03
67 0.1283E-03
68 0.1260E-03
69 0.1256E-03
70 0.1325E-03
71 0.1261E-03
72 0.1264E-03
73 0.1264E-03
74 0.1258E-03
75 0.1268E-03
76 0.1355E-03
77 0.1319E-03
78 0.1297E-03
79 0.1303E-03
80 0.1214E-02
81 0.1694E-03
82 0.1762E-03
83 0.1325E-03
84 0.1281E-03
85 0.1892E-03
86 0.2595E-03
87 0.1475E-03
88 0.1699E-03
89 0.1807E-03
90 0.1897E-03
91 0.2441E-03
92 0.1273E-03
93 0.1261E-03
94 0.1264E-03
95 0.1277E-03
96 0.1318E-03
97 0.1993E-03
98 0.2273E-03
99 0.1421E-03
100 0.1363E-03
101 0.7255E-03
102 0.1935E-03
103 0.1862E-03
104 0.1790E-03
105 0.1054E-02
106 0.1324E-03
107 NaN
108 NaN

Thank you
kind regards
neri alamanni

[mika]

Well, this appears to be a linear solver issue which is unrelated to the stress computation that should happen after the displacement solution has been found. Therefore try using other linear solvers, for example GCR iteration or even direct solve.

- Mika

[neri alamanni]

Hi
using GCR I have a crash in Solver. The solver is configured as follows
Solver 2
Equation = Nonlinear elasticity
Variable = -dofs 2 Displacement
Procedure = "ElasticSolve" "ElasticSolver"
Calculate Stresses = Logical True
Exec Solver = Always
Stabilize = True
Bubbles = False
Lumped Mass Matrix = False
Optimize Bandwidth = True
Steady State Convergence Tolerance = 1.0e-5
Nonlinear System Convergence Tolerance = 1.0e-6
Nonlinear System Max Iterations = 1
Nonlinear System Newton After Iterations = 3
Nonlinear System Newton After Tolerance = 1.0e-3
Nonlinear System Relaxation Factor = 1.0
Linear System Solver = Iterative
Linear System Iterative Method = GCR
Linear System Max Iterations = 1000
Linear System Convergence Tolerance = 1.0e-6
Linear System Preconditioning = ILU1
Linear System ILUT Tolerance = 1.0e-3
Linear System Abort Not Converged = False
Linear System Residual Output = 1
Linear System Precondition Recompute = 1
End
Attached you can find the log generated during the solution
Thank you
best regards
neri alamanni