cfx-fsi 14.5 lect-05 two way solving post
TRANSCRIPT
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© 2011 ANSYS, Inc. July 26, 20131 Release 14.5
14. 5 Release
Solving FSI Applications Using
ANSYS Mechanical and ANSYS CFX
Lecture 5
Two-way FSI Solving and PostProcessing
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Outline
Solution ProcessHere we discuss starting and monitoring the FSI solution in serial and
parallel. The various log and output files are also discussed.
Post Processing
This section will discuss common post-processing in CFD-Post and how
to post-process FSI results in the Mechanical post-processor.
Appendix A: Restarting FSI Simulations
This section covers restarting FSI simulations from completed runs and
backup points. Making physics changes to the CFD and Mechanical
setups when restarting is also discussed.
Appendix B: Multifield APDL Commands
This appendix provides some useful APDL commands relevant to MFX
simulations.
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Starting the Run
Write the Definition file and proceedto the CFX Solver Manager
• WB writes the def file in the background
Run Definition panel:
• Use Double Precision for FSI runs, since
the mesh deformations are often very
small compared to the size of the
domain
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Starting the Run
MultiField panel:
• MFX Run Mode:• Start ANSYS and CFX
• Both solvers started automatically
• Start ANSYS only / Start CFX only
• If running on different machine – see
parallel discussion later
• Process Input File only
• Produces a .mf file
• Used for physics changes; discussed later
• Mechanical Input File
• As set in CFX-Pre, but can be changed here
• Process ANSYS Input File
• Uncheck if the Mechanical Input File is a .mf
file (i.e. has already been processed)
• See restarts discussion later
… then Start Run
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Running in Parallel
CFX can use all the usual parallel methods
• Set up as for any non-FSI run
MAPDL solver is limited to local parallel
To run MAPDL in local parallel specify,for example, -np 4 in the Additional
Arguments field
• Will run on the local machine
• MAPDL can run on two cores without any
additional licenses
From the Command Line:
> cfx5solve -def CFX_Setup.def -double -mfx-run-mode "Start ANSYSand CFX" -ansys-input ds.dat -ansys-arguments "-np 2"
Start both solvers using the files specified, run CFX in double precision, run MAPDL solver
on two partitions. Note that on some systems spaces in the argument strings will need tobe escaped, e.g. “Start\ ANSYS\ and\ CFX” and “-np\ 2”
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Running on Two Different Hosts
To run on different machines:• Start ANSYS first on machine A
• MFX Run Mode = Start ANSYS only
• CFX out file will show a port and
hostname that ANSYS is listening on
• Start CFX on machine B• Other machines can be used as slaves
• Provide the port and hostname output
by ANSYS
...
...+--------------------------------------+| || Starting ANSYS Solver || |+--------------------------------------+ ANSYS solver listening on 1971@MACHINE1
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Running on Two Different Hosts
From the command line:
> cfx5solve -def CFX_Setup.def -mfx-run- mode “Start ANSYS only" -ansys-input ds.dat
• Starts the ANSYS solver using the input file specified
> cfx5solve -def CFX_Setup.def -double -mfx-run-mode"Start CFX only" -cplg-host 2249@MACHINE1
• Starts the CFX solver using the specified def file in double precision,
connects to the ANSYS solver already running on MACHINE1 using
the specified port
Run ‘cfx5solve –help’ or see doc for all command options
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Running in Parallel
Slave processes/threads must be on different cores• Otherwise things will run VERY slow
• The codes are (usually) running sequentially, it would seem logical
that they can share cores
• However, a slave process pulls 100% of the available CPU while it’s in
‘waiting’ mode
• The other code is starved of CPU
• OK for CFX and MAPDL to share a master processor
Example: single quad-core machine
• CFX: 4 partitions, MAPDL serial
• OK – only the master is shared
• CFX: 3 partitions, MAPDL 2 partitions (cores)
• OK – when MAPDL is ‘waiting’ 1 core will be in use, leaving 3 for CFX
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Another Look at the Workflow
MAPDL is the master process• MAPDL controls the transient
timestep, interface mapping,
interface convergence checks,
load transfer, etc
But all these settings are defined in
CFX-Pre
We have an input file from
Mechanical that contains the
structural model with the FSI
surfaces tagged
• Workbench writes this input file
into the project directory
CFX-Pre
Definition FileContains CCL definition of
fluid model and interface /
coupling settings
Mechanical
Input FileContains APDL definition
of structural model
MAPDL SolverInput File + appended APDL
commands from CFX
Process Input FileCFX adds APDL commands for
interface / coupling settings
CFX SolverSettings from the Definition
file
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Another Look at the Workflow
CFX-Pre writes a Definition File(.def) containing the CFD model
and the interface / MFX controls
When the run is started, CFX
creates APDL commands for the
interface / coupling settings andcombines them with the contents
of the input file from Mechanical
• Important to understand what’s
happening here when
performing restarts
• See Appendix A for restart
details
CFX-Pre
Definition FileContains CCL definition of
fluid model and interface /
coupling settings
Mechanical
Input FileContains APDL definition
of structural model
MAPDL SolverInput File + appended APDL
commands from CFX
Process Input FileCFX adds APDL commands for
interface / coupling settings
CFX SolverSettings from the Definition
file
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MAPDL Commands Inserted by CFX
You can view the commandsgenerated by CFX in the
MAPDL Solver output,
following the end of the Input
File
CFX generated these
commands
End of Input File from
Mechanical
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“Process Input File”
If you disable Process ANSYS Input
File then CFX does not generateany APDL commands
• Therefore the Input File for
MAPDL must already contain the
interface and coupling settings
• Occurs in some restart workflow
Also see CFX documentation:
• ANSYS CFX Solver Manager User’s
Guide >> Working with Solver
Manager >> ANSYS Multi-field Run
>> Processing the ANSYS Input File
CFX-Pre
Definition FileContains CCL definition of
fluid model
Mechanical
Input FileContains APDL definition
of structural model and
interface / coupling
settings
ANSYS SolverSettings from Input File
CFX SolverSettings from the Definition
file
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Solver Files Generated
CFX
• The working directory will contain the CFX Outputand Results files as usual
• The transient (.trn) and backup (.bak) results files
are stored in the <name>_001 directory
MAPDL Solver
• The subdirectory <name>_001.ansys is created andcontains all the MAPDL Solver files
• All results are stored in the .rst file
• The auto-generated ANSYS.mf file can be viewed inthis subdirectory
• ANSYS.stdout is the ANSYS Solver output asdisplayed in the CFX Solver Manager
Workbench
• The working directory is:…/<ProjectName>_files/dp0/CFX/CFX
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CFX Solver OutputStart of Time Step
First Coupling Iteration
Solve Mesh Displacement
- Should be fully converged
CFX Coefficient Iterations
- Should be converging
Second Coupling Iteration
Solve Mesh Displacement
- Should be fully converged
CFX Coefficient Iterations
- Should be converged by the
end of the last Coupling Iteration
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CFX Solver Output
ANSYS Field Solver and Interface Loads plot also shown
L2 norm al ized values should b e less than
correspo nding conv ergence cr i ter ia (CRIT) Interface loads sho uld be negat ive
at the end of each t imestep
X-axis values do not
correspon d to each
other or to CFX
Cumulat ive
ANSYS
Iterat ions
Cumulat ive
Coupl ing
Iterat ion
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MAPDL Output – Check Interface Mapping
In the MAPDL output, ALWAYS check the interface mapping
Scroll to the top of the output file (ANSYS.stdout)
Right-click in the window and select Find…
Search for the following – make sure Match case is enabled:
This section provides information on the mapping
between the CFX and ANSYS meshes. If the
Non-Matching Area Fraction or the No. of Un-Mapped Nodes is non-zero, then some parts of
the FSI interface will not be passing loads
between the field solvers. In this case check that
the two side physically match and completely
overlap.
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MAPDL Solver OutputTime Step and Coupling Iteration #
Start and End Time for this Time Step
Actual Force Loads Received
(and/or Thermal Loads)
Start and End Time for this Load Step – 1:1 correspondence to Time Step
ANSYS Field Solver
convergence and iterations
Check if CFX & ANSYS FieldSolvers are Converged
Check Interface Load
Convergence
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Summary
• The CFX Solver Manager or CFX Solver command line is used to
launch 2-way FSI simulations
• Mapping is performed by the MAPDL solver. Mapping
diagnostics are provided in the MAPDL solver output file and
should always be checked.
• FSI settings defined in CFX-Pre are passed to MAPDL at run-time by generating APDL commands
• Understanding this workflow is important for restarts
• Restarts can be made from completed runs, interrupted runs
and from backup points. Physics changes can be made when
restarting. See Appendix A.
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Outline
Solution ProcessHere we discuss starting and monitoring the FSI solution in serial and
parallel. The various log and output files are also discussed.
Post Processing
This section will discuss common post-processing in CFD-Post and how
to post-process FSI results in the Mechanical post-processor.
Appendix A: Restarting FSI Simulations
This section covers restarting FSI simulations from completed runs and
backup points. Making physics changes to the CFD and Mechanical
setups when restarting is also discussed.
Appendix B: Multifield APDL Commands
This appendix provides some useful APDL commands relevant to MFX
simulations.
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Combined Post-Processing
Editing the CFX Results cell for a2-way FSI case will automatically
load both the CFX and structural
results into CFD-Post
Can also use File > Load Results
and browse for .rst (structural)or .rth (thermal) results
• Enable Keep Current Case
Loaded to post-process
multiple sets of results
• Disable Open in new view to
have CFX and Mechanical
results in a single window
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In CFD-Post CFX and structural resultsentries and regions are shown in the
outline tree
When creating objects they can be scopedto all or selected domains
Combined Post-Processing
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Use the Timestep Selector to loaddifferent time steps as usual
• Tab panels show the availableresults from each solver
• Sync Cases allows both sets ofdata to be updated when a timestep from one set is selected
Animations can show both fluid and
structural results simultaneously
Combined Post-Processing
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Combined Post-Processing Animations
• Transient blood flow through athree-leaf valve
• Symmetry used with 1/6th
of fluid domain
• Non-Newtonian fluid (i.e.
blood) defined in Fluent• Non-Linear contact in Transient
Structural to cater for closure of
valve leaflets
• Blood vessel wall has
combination of isotropic andanisotropic (non-linear)
materials
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Combined Post-Processing Animations
• Transient free surface flow ina liquid storage tank with
baffles
• Tank is excited by a time
varying gravitational load for
a duration of 10s• Baffles are “non-metallic”
and fixed to the tank with an
adhesive
• Forces are transferred (one-
way only) via co-simulationto determine the stresses
acting on the baffles
• Determine the integrityand viability of the
adhesive bonding
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When selecting Variables to plot,the variables list shows all variables
from CFD and structural results
• If a variable is not available (e.g.
Pressure on a slice plane in a structural
region) is it plotted in the specifiedUndefined Color
Some variables apply to both fluidand structural regions, e.g.:
• Total Mesh Displacement (X/Y/Z)
• Velocity (u/v/w)
• Mesh metrics (Area, Edge Length Ratio,
X, Y, Z, etc)
Combined Post-Processing
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CFD-Post read components from a .cm filewritten out by the MAPDL solver
• This is created by default for FSI cases using the
command CMWRITE,file,cm
• You’ll see a Mesh Regions branch in CFD-Post
containing the components
When load structural results containingshell elements, CFD-Post reads and
displays data from the top side of the
shells
• To read and display results from the bottom
side set the system environment variable
CFDPOST_RST_READ_BOTTOM_SHELL_DATA
to any value
Combined Post-Processing
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Post-Processing in Mechanical
Structural results are associated with theCFX Solution and Results cells
To post-process in Mechanical:
• Edit the Mechanical Solution cell
• Select the Solution entry from the Outlinetree
• Select Tools > Read Results Files… and
browse for the .rst/.rth file
associated with the CFX FSI
system
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Outline
Solution Process
Here we discuss starting and monitoring the FSI solution in serial and
parallel. The various log and output files are also discussed.
Post Processing
This section will discuss common post-processing in CFD-Post and how
to post-process FSI results in the Mechanical post-processor.
Appendix A: Restarting FSI Simulations
This section covers restarting FSI simulations from completed runs and
backup points. Making physics changes to the CFD and Mechanical
setups when restarting is also discussed.
Appendix B: Multifield APDL Commands
This appendix provides some useful APDL commands relevant to MFX
simulations.
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Restarts from a Completed Run
This includes runs that were manually
stopped before reaching the End Time
On the CFX side restart as usual
• If manually specifying a previous res file,
Continue History From must be enabled for
FSI restarts
MAPDL always resumes from a previous
database
• Select the db file from the previous *.ansys
run directory
• The Mechanical Input File must bespecified but is not used in this case
• Enable Process ANSYS Input File:
– APDL commands are created again from the
CFX Solver Input File and a RESUME command
is also inserted
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Restarts from a Completed Run
Example of the commands generated by CFX
shown
Note that there’s no reference to the
Mechanical Input File
• Any changes made there are not used
The MF commands are recreated from theCFX Solver Input File
• The MF commands stored in the db file are not
used
If Process ANSYS Input File is disabled, the
Mechanical Input File is used and is run “as is”
• The Restart ANSYS Run toggle is ignored because
CFX doesn’t generate a RESUME command
• No MF commands generated
resume,ANSYS,db/SOLU
MFAN,ON
MFCLEAR,MFLC
MFRS,-1,SING
MFTI,1
MFDT,1,1,1,OFF
MFLC,SURF,ANSYS,1, …
MFLC,SURF,CFX,'Wall', …MFIT,20,1,20
MFCO,ALL,1e-3
MFRE,ALL,0.75,RELX
MFPS,group1,ANSYS
MFPS,group2,CFX
MFSO,group2,group1
CMWRITE,ANSYS,cmKBC,1
/GST,ON,ON
SOLVE
SAVE
CMWRITE,ANSYS,cm
FINISH
/EXIT
Typical Restar t Command s
Generated b y CFX
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Restarts from a Backup Point
A failed run can be restarted using a CFX
backup file and MAPDL files producedusing the MFRC command
• Must be from a consistent time point
Pick the CFX .def file and use the CFX
backup file as the Initial Values File, withContinue History From enabled
Same MultiField settings as restartingfrom a completed run, except the rdb
(restart database) file is used
• This file is created by the MFRC command
Again, the Mechanical Input File is notused and CFX re-creates the MF
commands
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Restarts from a Backup Point
Only the first FSI run will contain a rdb file. For multiple restartscopy the rdb file to the most recent run directory
• Any previous changes you have manually made in a .mf file must be
re-applied to every restart from a rdb file, since the rdb file
represents the structural setup from the first FSI run
• The correct nodal displacements, velocities, etc are still used, since
the rdb file will read the .r00# file corresponding to the restart time
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Restarts with Physics Changes
Changes to CFX physics can be made as usual
• In Workbench edit the Setup cell
• Or create a new .def file and use the previous res file as the Initial Values
File, with Continue History From enabled
Changes to coupling, interface or time settings specified inCFX can use the same procedure as a CFX physics change
• Since CFX re-creates the MF commands each time, these changes will be
passed to MAPDL
• Example: Extending a run by increasing the Coupling Time Duration
Changes to Mechanical settings are less straight-forward
since the Mechanical Input File is not used when restarting
• Where should be changes be made?
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Restarts with Physics Changes
First, create the .mf file
• This is what CFX is doing in the
background when Process ANSYS Input
File is checked
• Use Process Input File only option
• Select the Mechanical Input File and the
previous db file
• Provide the CFX def file and Start Run
Run will complete in a few seconds
Inside the *.ansys/ run directory an ANSYS.mf file is created
…/RunName_002.ansys/ANSYS.mf
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Restarts with Physics Changes
Manually edit the ANSYS.mf file, inserting
APDL commands to make any changes
Start the run using the edited .mf file as theMechanical Input File
Disable Process ANSYS Input File
Select the previous db file
Can also use this approach to change
interface / coupling settings (MF commands)instead of making a new .def file in CFX-Pre
You need to use this approach to restart a
steady-state 2-way FSI case as transient
• Add TIMINT,ON to the .mf file to switch
Mechanical from steady-state to transient
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Restarts - General
MAPDL results are appended to the rst file• Old rst is copied into new run directory
• Can be a very large file!
• You can move the old rst file to a new directory before restarting to
prevent it being copied
• A new rst file will be created for the new run
For all restarts also see the CFX documentation:
• ANSYS CFX Solver Manager User’s Guide >> Working with Solver
Manager >> ANSYS Multi-field Run >> Restart Procedure for ANSYSMulti-field Run
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Outline
Solution Process
Here we discuss starting and monitoring the FSI solution in serial and
parallel. The various log and output files are also discussed.
Post Processing
This section will discuss common post-processing in CFD-Post and how
to post-process FSI results in the Mechanical post-processor.
Appendix A: Restarting FSI Simulations
This section covers restarting FSI simulations from completed runs and
backup points. Making physics changes to the CFD and Mechanical
setups when restarting is also discussed.
Appendix B: Multifield APDL Commands
This appendix provides some useful APDL commands relevant to MFX
simulations.
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Multi-Field Commands - Background
• Note: the Command Reference section in the Mechanical APDL
documentation provide details on all MAPDL commands
• MF commands are APDL commands that control Multifield parameters
• They are created by CFX-Pre and appended to the MAPDL input at run-time
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Basic MF Commands
MFRS
• Multifield restart time (for restarts only)
• Usually has a value of -1, meaning restart from end of previous solution
MFAN
• Turns on Multifield solver
MFTI
• End time for the Multifield analysis
MFIT
• Controls the number of Coupling Iterations
MFDT
• Control the transient time step size
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Basic MF Commands
MFOU
• Controls how often results are stored
MFRC
• Control how often restart files are written
MFCO
• Controls Field Convergence Criteria
MFRE
• Field Relaxation Factors
MFLC,SURF,CFX,'Interface','Total Force', ANSYS, 1,FORC,CPP• Load transfer command
MFPS and MFSO
• Which field goes first, sequential or parallel
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Other Relevant APDL Commands
BCSOPTION,,INCORE
• For the sparse solver tries to retain the entire factorized matrix in memory
• Runs faster, but significantly increases memory usage
KBC,1
• Sets stepped loads - CFX will always append this command to the ANSYS input
• If using Prep7 make sure you set it manually
OUTRES
• Minimum data you can write and still restart
• Note that you may need more data for post-processing (e.g Stress data)
OUTRES, ERASEOUTRES, ALL, NONE
OUTRES, NSOL, LAST
OUTRES, ERASEOUTRES, ALL, NONE
OUTRES, NSOL, LAST
OUTRES, ESOL, LAST
OR
Structural Solution OnlyStructural + Thermal
or Thermal Solution
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Other Relevant APDL Commands
NEQIT
• Sets the maximum number of equilibrium iterations
NCNV
• The ANSYS solver will continue when convergence has not been achieved
Note that MAPDL runs until convergence or max. number of equilibrium
iterations, but the calculation will stop if max. number of equilibrium iterations is
reached. You can set NCNV so that MAPDL will continue if convergence is not
achieved and this can be combined with NEQIT to limit the number of
equilibrium iterations. However, you need to be careful when doing this – you
must make sure MAPDL is converged by the end of the last Coupling Iteration.
If you are reaching the maximum number of Coupling Iterations then
something hasn’t converged – CFX, interface loads, or MAPDL – this needs to
be corrected. If one of the field solvers is very poorly converged, it may pass
spurious loads to the other which could cause failure.