# Basics : Strong FSI — Welcome to LS-DYNA Examples

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This LS-DYNA simulation shows a simple FSI coupling problem using strong FSI. Indeed, the density of the solid and the fluid are very close. Such cases are by definition unstable when using explicit coupling between solid mechanics and a CFD code (‘added mass effect’). In order to reduce those instabilities, strong fluid structure interaction is needed. In order for this to be possible, both solvers need to advance at the same time thus making the use of the implicit solver for solids mandatory.

## Animated Result

Fluid velocity fringes

## Keywords

```*BOUNDARY_PRESCRIBED_MOTION_RIGID
*CONTROL_IMPLICIT_DYNAMICS
*CONTROL_IMPLICIT_GENERAL
*CONTROL_IMPLICIT_SOLUTION
*CONTROL_TERMINATION
*DATABASE_BINARY_D3PLOT
*DEFINE_CURVE_FUNCTION
*DEFINE_CURVE_TITLE
*ELEMENT_SHELL
*END
*ICFD_BOUNDARY_FREESLIP
*ICFD_BOUNDARY_FSI
*ICFD_BOUNDARY_PRESCRIBED_VEL
*ICFD_BOUNDARY_PRESCRIBED_PRE
*ICFD_BOUNDARY_NONSLIP
*ICFD_CONTROL_FSI
*ICFD_CONTROL_TIME
*ICFD_DATABASE_DRAG
*ICFD_MAT
*ICFD_PART
*ICFD_PART_VOL
*ICFD_SECTION
*INCLUDE
*KEYWORD
*MAT
*MESH_BL
*MESH_SURFACE_ELEMENT
*MESH_SURFACE_NODE
*MESH_VOLUME
*NODE
*PARAMETER
*PART
*SECTION
*TITLE
```

## Reduced Input

```\$-----------------------------------------------------------------------------
\$
\$ Example provided by Iñaki (LSTC)
\$
\$ E-Mail: info@dynamore.de
\$ Web: http://www.dynamore.de
\$
\$ Copying for non-commercial usage allowed if
\$ copy bears this notice completely.
\$
\$X------------------------------------------------------------------------------
\$X
\$X 1. Run file as is.
\$X    Requires LS-DYNA MPP R8.0.0 (or higher) with double precision
\$X
\$X------------------------------------------------------------------------------
\$# UNITS: Dimensionless.
\$X------------------------------------------------------------------------------
\$X
*KEYWORD
*TITLE
ICFD Cylinder flow - Strong FSI
*INCLUDE
mesh.k
*INCLUDE
struc.k
*INCLUDE
implicit.k
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
\$                                                                              \$
\$                             PARAMETERS                                       \$
\$                                                                              \$
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
*PARAMETER
R    T_end      40.0
R  dt_plot      0.20
\$
\$--- Fluid
\$
R  v_inlet       1.0
Rrho_fluid       1.0
R mu_fluid     0.005
R dt_fluid     0.050
\$
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
\$                                                                              \$
\$                           ICFD CONTROL CARDS                                 \$
\$                                                                              \$
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
*ICFD_CONTROL_TIME
\$#     ttm        dt
&T_end &dt_fluid
*ICFD_CONTROL_FSI
\$#     owc
0
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
\$                                                                              \$
\$                       ICFD PARTS/ SECTION/ MATERIAL                          \$
\$                                                                              \$
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
*ICFD_SECTION
\$#     sid
1
*ICFD_MAT
\$#     mid       flg        ro       vis
1         1&rho_fluid &mu_fluid
*ICFD_PART
\$#     pid     secid       mid
1         1         1
*ICFD_PART
\$#     pid     secid       mid
2         1         1
*ICFD_PART
\$#     pid     secid       mid
3         1         1
*ICFD_PART
\$#     pid     secid       mid
4         1         1
*ICFD_PART_VOL
\$#     pid     secid       mid
10         1         1
\$#   spid1     spid2     spid3     spid4
1         2         3         4
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
\$                                                                              \$
\$                    ICFD BOUNDARY/INITIAL CONDITIONS                          \$
\$                                                                              \$
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
*ICFD_BOUNDARY_PRESCRIBED_VEL
1         1         1         1
*ICFD_BOUNDARY_PRESCRIBED_VEL
1         2         1         2
*ICFD_BOUNDARY_PRESCRIBED_PRE
\$#     pid      lcid        sf     death     birth
2         2
*ICFD_BOUNDARY_FREESLIP
\$#     pid
3
*ICFD_BOUNDARY_NONSLIP
\$#     pid
4
*ICFD_BOUNDARY_FSI
\$#     pid
4
*DEFINE_CURVE_TITLE
Velocity inlet
\$#    lcid      sidr       sfa       sfo      offa      offo    dattyp
1
\$#                a1                  o1
0.0                  0.
5.0                  0.
6.0            &v_inlet
10000.0            &v_inlet
*DEFINE_CURVE_TITLE
Pressure outlet
\$#    lcid      sidr       sfa       sfo      offa      offo    dattyp
2
\$#                a1                  o1
0.0                 0.0
10000.0                 0.0
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
\$                                                                              \$
\$                            ICFD MESH KEYWORDS                                \$
\$                                                                              \$
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
*MESH_VOLUME
\$#   volid
10
\$#    pid1      pid2      pid3      pid4
1         2         3         4
*MESH_BL
\$#     pid     nelth
4         2
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
\$                                                                              \$
\$                             DATABASE (OUTPUT)                                \$
\$                                                                              \$
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
*ICFD_DATABASE_DRAG
\$#     pid
4
*DATABASE_BINARY_D3PLOT
&dt_plot
*end```