[lalatuobu]

Hi All,
I was doing a 3d FSI on a cantilever column in uniform flow. I used the following configuration files: Sorry about putting them all here in the end of this thread.

The issue is that when I check the solution, it seems that the cantilever beam did not bend as expected. The coupling seems to work because I can still see small deformation on the surface of the column at high pressure but there was no bending.

I thought the reason is that the fluid mesh did not deform as expected. I wonder why this could happen. There must be something wrong with my mesh deformation in my configuration file. Could someone please help me to look in the configuration file>?

Thank you !!!!!

My output for the last iteration goes like this:

+-----------------------------------------------------------------------------+
| Zone 0 (Incomp. Fluid) |
+-----------------------------------------------------------------------------+
| Inner_Iter| Time(sec)| rms[P]| CL| CD| Avg CFL|
+-----------------------------------------------------------------------------+
| 0| 1.4844e+02| -8.057513| -0.000001| 0.000069| 2.0000e+04|
| 10| 9.3722e+01| -8.105184| -0.000004| 0.000066| 2.0000e+04|
+-----------------------------------------------------------------------------+
| Zone 1 (Structure) |
+-----------------------------------------------------------------------------+
| Inner_Iter| Load[%]| rms[U]| rms[R]| rms[E]| VonMises|
+-----------------------------------------------------------------------------+
| 0| 100.00%| -8.207325| -3.791529| -15.592381| 1.4176e+01|
| 99| 100.00%| -8.655378| -3.792181| -16.394546| 1.4176e+01|
+----------------------------------------------------------------+
| Multizone Summary |
+----------------------------------------------------------------+
| Outer_Iter| avg[bgs][0]| avg[bgs][1]|MinVolume[0]|DeformIter[0|
+----------------------------------------------------------------+
| 59| 0.102389| -10.135375| 3.7766e-14| 286|

# CG residual history
# Residual tolerance target = 1e-10
# Initial residual norm = 1.1249e-06
0 0.228422
100 5.94382e-08
270 1.09e-10
# CG final (true) residual:
# Iteration = 270: |res|/|res0| = 9.67159e-11.


----------------------------- Solver Exit -------------------------------

Maximum number of iterations reached (OUTER_ITER = 60) before convergence.
+-----------------------------------------------------------------------+
| Convergence Field | Value | Criterion | Converged |
+-----------------------------------------------------------------------+
| avg[bgs][0]| 0.102389| < -7| No|
| avg[bgs][1]| -10.1354| < -7| Yes|
+-----------------------------------------------------------------------
------------------------- Exit Success (SU2_CFD) ------------------------


Here is the configuration file I used:



%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%. MAIN CONFIG FILE %%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%

%%%%%%%%%%%%%%%%%%%%%%%
% SOLVER TYPE
%%%%%%%%%%%%%%%%%%%%%%%

SOLVER = MULTIPHYSICS

%%%%%%%%%%%%%%%%%%%%%%%
% INPUT
%%%%%%%%%%%%%%%%%%%%%%%

%MULTIZONE = YES
CONFIG_LIST = (hair_m_v0.cfg.cfg, config_hair_str.cfg)
MULTIZONE_MESH = NO


%%%%%%%%%%%%%%%%%%%%%%%
% COUPLING CONDITIONS
%%%%%%%%%%%%%%%%%%%%%%%

MARKER_ZONE_INTERFACE = (cyl-wet, structuralwet)

%%%%%%%%%%%%%%%%%%%%%%%
% SOLUTION STRATEGY
%%%%%%%%%%%%%%%%%%%%%%%

MULTIZONE_SOLVER = BLOCK_GAUSS_SEIDEL
OUTER_ITER = 60


%%%%%%%%%%%%%%%%%%%%%%%
% CONVERGENCE CRITERIA
%%%%%%%%%%%%%%%%%%%%%%%

CONV_FIELD = AVG_BGS_RES[0], AVG_BGS_RES[1]
CONV_RESIDUAL_MINVAL = -7

%%%%%%%%%%%%%%%%%%%%%%%
% OUTPUT
%%%%%%%%%%%%%%%%%%%%%%%

SCREEN_OUTPUT = (OUTER_ITER, AVG_BGS_RES[0], AVG_BGS_RES[1], DEFORM_MIN_VOLUME[0], DEFORM_ITER[0])
WRT_ZONE_CONV = YES

OUTPUT_FILES = (RESTART, PARAVIEW)
SOLUTION_FILENAME = solution_hair_m0_r1n_fsi_steady
RESTART_FILENAME = restart_hair_m0_r1n_fsi_steady
VOLUME_FILENAME = hair_m0_r1n_fsi_steady

HISTORY_OUTPUT = ITER, BGS_RES[0], AERO_COEFF[0], BGS_RES[1]

WRT_ZONE_HIST = YES
CONV_FILENAME= history



%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%Sub CONFIG FILE - FLUID%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% ------------- DIRECT, ADJOINT, AND LINEARIZED PROBLEM DEFINITION ------------%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% Physical governing equations (EULER, NAVIER_STOKES,
% WAVE_EQUATION, HEAT_EQUATION, FEM_ELASTICITY,
% POISSON_EQUATION)
SOLVER= INC_NAVIER_STOKES
%
% Specify turbulent model (NONE, SA, SA_NEG, SST)
KIND_TURB_MODEL= NONE
%
% Mathematical problem (DIRECT, CONTINUOUS_ADJOINT)
MATH_PROBLEM= DIRECT
%
% Restart solution (NO, YES)
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% --------------------------- VISCOSITY MODEL ---------------------------------%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Viscosity model (SUTHERLAND, CONSTANT_VISCOSITY).
VISCOSITY_MODEL= CONSTANT_VISCOSITY
%
% Molecular Viscosity that would be constant (1.716E-5 by default)
MU_CONSTANT= 1.716E-5
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% ---------------------- REFERENCE VALUE DEFINITION ---------------------------%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Reference origin for moment computation
REF_ORIGIN_MOMENT_X = 0.00
REF_ORIGIN_MOMENT_Y = 0.00
REF_ORIGIN_MOMENT_Z = 0.00
%
% Reference length for pitching, rolling, and yawing non-dimensional moment
REF_LENGTH= 1.0
%
% Reference area for force coefficients (0 implies automatic calculation)
REF_AREA= 1.0
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% ------------------------- UNSTEADY SIMULATION -------------------------------%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
TIME_DOMAIN = NO
%
% Numerical Method for UnsteadNOy simulation(NO, TIME_STEPPING, DUAL_TIME_STEPPING-1ST_ORDER, DUAL_TIME_STEPPING-2ND_ORDER, TIME_SPECTRAL)
%TIME_MARCHING= DUAL_TIME_STEPPING-2ND_ORDER
%
% Time Step for dual time stepping simulations (s)
%TIME_STEP= 5e-4
%
% Maximum Number of physical time steps.
%TIME_ITER= 10
%
% Number of internal iterations (dual time method)
INNER_ITER= 50
%
% Restart after the transient phase has passed
RESTART_SOL = NO
%
% Specify unsteady restart iter
RESTART_ITER = 0
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% ---------------- incompressible inlet setting ------------------%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% inlet
INC_INLET_TYPE = VELOCITY_INLET
INC_INLET_DAMPING= 0.1
% outlet
INC_OUTLET_TYPE= PRESSURE_OUTLET
INC_OUTLET_DAMPING= 0.1
% Density model within the incompressible flow solver.
% Options are CONSTANT (default), BOUSSINESQ, or VARIABLE. If VARIABLE,
% an appropriate fluid model must be selected.
INC_DENSITY_MODEL= CONSTANT
%
% Solve the energy equation in the incompressible flow solver
INC_ENERGY_EQUATION = NO
%
% Initial density for incompressible flows
% (1.2886 kg/m^3 by default (air), 998.2 Kg/m^3 (water))
INC_DENSITY_INIT= 1.2886
FREESTREAM_PRESSURE= 101325.0

%
% Initial velocity for incompressible flows (1.0,0,0 m/s by default)
INC_VELOCITY_INIT= ( 10.0, 0.0, 0.0 )
%
% Initial temperature for incompressible flows that include the
% energy equation (288.15 K by default). Value is ignored if
% INC_ENERGY_EQUATION is false.
INC_TEMPERATURE_INIT= 288.15
%
% Non-dimensionalization scheme for incompressible flows. Options are
% INITIAL_VALUES (default), REFERENCE_VALUES, or DIMENSIONAL.
% INC_*_REF values are ignored unless REFERENCE_VALUES is chosen.
INC_NONDIM= DIMENSIONAL
%
% Reference density for incompressible flows (1.0 kg/m^3 by default)
INC_DENSITY_REF= 1.0
%
% Reference velocity for incompressible flows (1.0 m/s by default)
INC_VELOCITY_REF= 1.0
%
% Reference temperature for incompressible flows that include the
% energy equation (1.0 K by default)
INC_TEMPERATURE_REF = 1.0
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% -------------------- BOUNDARY CONDITION DEFINITION -------------------------- %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Navier-Stokes wall boundary marker(s) (NONE = no marker)
MARKER_HEATFLUX= ( cyl-wet, 0.0, wall, 0.0 )
%
% Farfield boundary marker(s) (NONE = no marker)
MARKER_FAR= ( top )
%
% inlet
% Inc. Velocity: (inlet marker, temperature, velocity magnitude, flow_direction_x,
% flow_direction_y, flow_direction_z, ... ) where flow_direction is
% a unit vector.
MARKER_INLET = (inlet, 288.15, 10, 1, 0, 0 )
%
% Outlet boundary marker(s) (NONE = no marker)
% Compressible: ( outlet marker, back pressure (static thermodynamic), ... )
% Inc. Pressure: ( outlet marker, back pressure (static gauge in Pa), ... )
% Inc. Mass Flow: ( outlet marker, mass flow target (kg/s), ... )
MARKER_OUTLET= ( outlet, 0 )
%
%
% Marker(s) of the surface to be plotted or designed
MARKER_PLOTTING= ( cyl-wet )
%
% Marker(s) of the surface where the functional (Cd, Cl, etc.) will be evaluated
MARKER_MONITORING= ( cyl-wet )

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%---------- COUPLING CONDITIONS----------------%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

MARKER_FLUID_LOAD = ( cyl-wet )

DEFORM_MESH = YES
MARKER_DEFORM_MESH = ( cyl-wet )

DEFORM_STIFFNESS_TYPE = WALL_DISTANCE
DEFORM_LINEAR_SOLVER = CONJUGATE_GRADIENT
DEFORM_LINEAR_SOLVER_PREC = ILU
DEFORM_LINEAR_SOLVER_ERROR = 1E-10
DEFORM_LINEAR_SOLVER_ITER = 500
DEFORM_CONSOLE_OUTPUT = YES

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%
% ------------- COMMON PARAMETERS DEFINING THE NUMERICAL METHOD ---------------%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%
% Numerical method for spatial gradients (GREEN_GAUSS, WEIGHTED_LEAST_SQUARES)
NUM_METHOD_GRAD= GREEN_GAUSS
%
% Courant-Friedrichs-Lewy condition of the finest grid
CFL_NUMBER= 100.0
%
% Adaptive CFL number (NO, YES)
CFL_ADAPT= YES
%
% Parameters of the adaptive CFL number (factor down, factor up, CFL min value,
% CFL max value )
CFL_ADAPT_PARAM= ( 0.1, 2.0, 0.01, 20000 )
%
% Runge-Kutta alpha coefficients
RK_ALPHA_COEFF= ( 0.66667, 0.66667, 1.000000 )
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% ------------------------ LINEAR SOLVER DEFINITION ---------------------------%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Linear solver for implicit formulations (BCGSTAB, FGMRES)
LINEAR_SOLVER= FGMRES
%
% Preconditioner of the Krylov linear solver (JACOBI, LINELET, LU_SGS)
LINEAR_SOLVER_PREC= ILU
%
% Minimum error of the linear solver for implicit formulations
LINEAR_SOLVER_ERROR= 1E-10
%
% Max number of iterations of the linear solver for the implicit formulation
LINEAR_SOLVER_ITER= 100
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% ----------------------- SLOPE LIMITER DEFINITION ----------------------------%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Coefficient for the limiter
VENKAT_LIMITER_COEFF= 0.1
%
% Coefficient for the sharp edges limiter
ADJ_SHARP_LIMITER_COEFF= 3.0
%
% Reference coefficient (sensitivity) for detecting sharp edges.
REF_SHARP_EDGES= 3.0
%
% Remove sharp edges from the sensitivity evaluation (NO, YES)
SENS_REMOVE_SHARP= NO
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% -------------------------- MULTIGRID PARAMETERS -----------------------------%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Multi-Grid Levels (0 = no multi-grid)
MGLEVEL= 2
%
% Multi-grid cycle (V_CYCLE, W_CYCLE, FULLMG_CYCLE)
MGCYCLE= V_CYCLE
%
% Multi-grid pre-smoothing level
MG_PRE_SMOOTH= ( 1, 2, 3, 3 )
%
% Multi-grid post-smoothing level
MG_POST_SMOOTH= ( 0, 0, 0, 0 )
%
% Jacobi implicit smoothing of the correction
MG_CORRECTION_SMOOTH= ( 0, 0, 0, 0 )
%
% Damping factor for the residual restriction
MG_DAMP_RESTRICTION= 0.8
%
% Damping factor for the correction prolongation
MG_DAMP_PROLONGATION= 0.8
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% -------------------- FLOW NUMERICAL METHOD DEFINITION -----------------------%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Convective numerical method (JST, LAX-FRIEDRICH, CUSP, ROE, AUSM, HLLC,
% TURKEL_PREC, MSW)
CONV_NUM_METHOD_FLOW= FDS
%
% Monotonic Upwind Scheme for Conservation Laws (TVD) in the flow equations.
% Required for 2nd order upwind schemes (NO, YES)
MUSCL_FLOW= YES
%
% Slope limiter (NONE, VENKATAKRISHNAN, VENKATAKRISHNAN_WANG,
% BARTH_JESPERSEN, VAN_ALBADA_EDGE)
SLOPE_LIMITER_FLOW= VENKATAKRISHNAN
%
%
% Time discretization (RUNGE-KUTTA_EXPLICIT, EULER_IMPLICIT, EULER_EXPLICIT)
TIME_DISCRE_FLOW= EULER_IMPLICIT
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% -------------------- TURBULENT NUMERICAL METHOD DEFINITION ------------------%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Convective numerical method (SCALAR_UPWIND)
CONV_NUM_METHOD_TURB= SCALAR_UPWIND
%
% Monotonic Upwind Scheme for Conservation Laws (TVD) in the turbulence equations.
% Required for 2nd order upwind schemes (NO, YES)
MUSCL_TURB= NO
%
% Slope limiter (VENKATAKRISHNAN, MINMOD)
SLOPE_LIMITER_TURB= VENKATAKRISHNAN
%
% Time discretization (EULER_IMPLICIT)
TIME_DISCRE_TURB= EULER_IMPLICIT
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% --------------------------- CONVERGENCE PARAMETERS --------------------------%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Convergence criteria (CAUCHY, RESIDUAL)
CONV_FIELD= RMS_PRESSURE
%
% Min value of the residual (log10 of the residual)
CONV_RESIDUAL_MINVAL= -8
%
% Start convergence criteria at iteration number
CONV_STARTITER= 10
%
% Number of elements to apply the criteria
CONV_CAUCHY_ELEMS= 100
%
% Epsilon to control the series convergence
CONV_CAUCHY_EPS= 1E-6
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% ------------------------- INPUT/OUTPUT INFORMATION --------------------------%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Mesh input file
MESH_FILENAME= hair-m-fluid-r2n.su2
%
% Mesh input file format (SU2, CGNS, NETCDF_ASCII)
MESH_FORMAT= SU2
%
% Mesh output file
MESH_OUT_FILENAME= hair-m-fluid-r2n.su2
%
% Restart flow input file
SOLUTION_FILENAME= hair-m-fluid-r2n.dat
%
% Restart adjoint input file
SOLUTION_ADJ_FILENAME= hair-m-fluid-r2n.dat
%
% Output file format (PARAVIEW, TECPLOT, STL)
TABULAR_FORMAT= CSV
%
% output file
%
% Output file convergence history (w/o extension)
CONV_FILENAME= hair-m-fluid-r2n_history



%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%% Sub-Config SOLID PART%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%


%%%%%%%%%%%%%%%%%%%%%%%
% SOLVER TYPE
%%%%%%%%%%%%%%%%%%%%%%%

SOLVER = ELASTICITY

%%%%%%%%%%%%%%%%%%%%%%%
% STRUCTURAL PROPERTIES
%%%%%%%%%%%%%%%%%%%%%%%

GEOMETRIC_CONDITIONS = LARGE_DEFORMATIONS
MATERIAL_MODEL = NEO_HOOKEAN
%ELASTICITY_MODULUS = (0.5E6, 1.6E11)
%POISSON_RATIO = (0.49, 0.0)
%MATERIAL_DENSITY = (960,7500)

ELASTICITY_MODULUS = (0.5E5)
POISSON_RATIO = (0.49)
%MATERIAL_DENSITY = (960)
% FORMULATION_ELASTICITY_2D = PLANE_STRAIN

%%%%%%%%%%%%%%%%%%%%%%%
% INPUT
%%%%%%%%%%%%%%%%%%%%%%%

MESH_FORMAT = SU2
MESH_FILENAME = hair-m-structural-r2n.su2

%FEA_FILENAME = element_prop.dat

%%%%%%%%%%%%%%%%%%%%%%%
% BOUNDARY CONDITIONS
%%%%%%%%%%%%%%%%%%%%%%%

MARKER_CLAMPED = ( clamped )
MARKER_PRESSURE = ( structuralwet, 0)

%%%%%%%%%%%%%%%%%%%%%%%
%% BODY FORCE
%%%%%%%%%%%%%%%%%%%%%%%
%


%BODY_FORCE = YES
%BODY_FORCE_VECTOR = (0.0, -9.81, 0.0)


%%%%%%%%%%%%%%%%%%%%%%%
% COUPLING CONDITIONS
%%%%%%%%%%%%%%%%%%%%%%%

MARKER_FLUID_LOAD = ( structuralwet )

%%%%%%%%%%%%%%%%%%%%%%%
% SOLUTION METHOD
%%%%%%%%%%%%%%%%%%%%%%%

NONLINEAR_FEM_SOLUTION_METHOD = NEWTON_RAPHSON
INNER_ITER = 100

INCREMENTAL_LOAD = YES
NUMBER_INCREMENTS = 5
INCREMENTAL_CRITERIA = (-1.0, -1.0, -1.0)

%%%%%%%%%%%%%%%%%%%%%%%
% CONVERGENCE CRITERIA METHOD
%%%%%%%%%%%%%%%%%%%%%%%

CONV_FIELD = RMS_UTOL, RMS_RTOL, RMS_ETOL
CONV_RESIDUAL_MINVAL = -7

%%%%%%%%%%%%%%%%%%%%%%%
% LINEAR SOLVER
%%%%%%%%%%%%%%%%%%%%%%%

LINEAR_SOLVER = CONJUGATE_GRADIENT
LINEAR_SOLVER_PREC = ILU
LINEAR_SOLVER_ERROR = 1E-8
LINEAR_SOLVER_ITER = 400

%%%%%%%%%%%%%%%%%%%%%%%
% OUTPUT
%%%%%%%%%%%%%%%%%%%%%%%

SCREEN_OUTPUT = (INNER_ITER, LOAD_INCREMENT, RMS_UTOL, RMS_RTOL, RMS_ETOL, VMS)
SCREEN_WRT_FREQ_INNER = 1

[pcg]

At first glance all looks ok.

Can you post some pictures? Keep in mind that the structural result is always undeformed, you need to apply the deformation (displacements) in postprocessing if you want. In Paraview this is done with the "warp" function.

Also, what version of SU2 are you using?

[lalatuobu]

Originally Posted by pcg

At first glance all looks ok.

Can you post some pictures? Keep in mind that the structural result is always undeformed, you need to apply the deformation (displacements) in postprocessing if you want. In Paraview this is done with the "warp" function.

Also, what version of SU2 are you using?

Hi PCG,
Thank you for your respond. The flow field and the corresponding pressure distribution on the surface, along with y+, are all what I expected. However, the force seems not to be transmitted into the solid calculation as only a few mesh nodes were shifted to cause stress on the cantilever. In addition, there was no bending observed.

Fluid domain, notice that no mesh movement>
13265327.png

surface pressure:
922624236.jpg

Von-mises stress on column
1479390492.jpg

To verify the problem is not due to structural mesh. I did a separate simulation using same mesh file but in steady loading of uniform 100 Pa in +x direction from 1 side of the column for the solid only. The deformation met my expectation.

999.jpg

I do think there is something wrong within my coupling or mesh deformation for fluid domain. I don't know what that is however. I was using Release 7.0.4. I was using a standard OH grid for this fluid domain.

[pcg]

I don't see anything major in your config.
There are some options that are not necessary or slightly misplaced but I don't think they would cause issues.

Anyway, I modified one of the 2D examples to use the incompressible NS solver (attached), it runs and deforms try to adapt the configs to your grid and see if it works.

[lalatuobu]

Originally Posted by pcg

I don't see anything major in your config.
There are some options that are not necessary or slightly misplaced but I don't think they would cause issues.

Anyway, I modified one of the 2D examples to use the incompressible NS solver (attached), it runs and deforms try to adapt the configs to your grid and see if it works.

Hi PCG,

Thank you for your reply. I had done a 2D case before using modified tutorial file and it works great. However, in my 3d case, it seems that the coupling went wrong. As you pointed out, my config file looks okay. So I wonder if the convergence is the reason that the pressure coupling seems to failed. I wonder what should be the convergence criteria for the mesh deformation, solid as well as fluid. I was aiming at E(-6) for fluid and solid, but not sure what should be the minimum residual error for mesh deformation solver.


In addition, by looking at the output from my last iteration:

+-----------------------------------------------------------------------------+
| Zone 0 (Incomp. Fluid) |
+-----------------------------------------------------------------------------+
| Inner_Iter| Time(sec)| rms[P]| CL| CD| Avg CFL|
+-----------------------------------------------------------------------------+
| 0| 1.4844e+02| -8.057513| -0.000001| 0.000069| 2.0000e+04|
| 10| 9.3722e+01| -8.105184| -0.000004| 0.000066| 2.0000e+04|
+-----------------------------------------------------------------------------+
| Zone 1 (Structure) |
+-----------------------------------------------------------------------------+
| Inner_Iter| Load[%]| rms[U]| rms[R]| rms[E]| VonMises|
+-----------------------------------------------------------------------------+
| 0| 100.00%| -8.207325| -3.791529| -15.592381| 1.4176e+01|
| 99| 100.00%| -8.655378| -3.792181| -16.394546| 1.4176e+01|
+----------------------------------------------------------------+
| Multizone Summary |
+----------------------------------------------------------------+
| Outer_Iter| avg[bgs][0]| avg[bgs][1]|MinVolume[0]|DeformIter[0|
+----------------------------------------------------------------+
| 59| 0.102389| -10.135375| 3.7766e-14| 286|

# CG residual history
# Residual tolerance target = 1e-10
# Initial residual norm = 1.1249e-06
0 0.228422
100 5.94382e-08
270 1.09e-10
# CG final (true) residual:
# Iteration = 270: |res|/|res0| = 9.67159e-11.


----------------------------- Solver Exit -------------------------------

Maximum number of iterations reached (OUTER_ITER = 60) before convergence.
+-----------------------------------------------------------------------+
| Convergence Field | Value | Criterion | Converged |
+-----------------------------------------------------------------------+
| avg[bgs][0]| 0.102389| < -7| No|
| avg[bgs][1]| -10.1354| < -7| Yes|


does these convergence raise red flag? To me it is. Is the "failed coupling" actually due to poor convergence?


Thank you again.

[pcg]

The example I provided follows what I consider to be best practices for FSI, 2D or 3D.

There is no mesh deformation on the solid side.

You specified a Poison ratio of 0.49 for the structure, this makes the equations very ill-conditioned, especially in 3D.
You should never need more than 10 inner iterations on the structure, if with 100 iterations the residuals do not drop it means the linear solver is not able to solve the systems.