Lecture 5 Two-way FSI Solving and Post Processing. Solving FSI Applications Using ANSYS Mechanical and ANSYS CFX Release. Release 14.

Transcription

1 Lecture 5 Two-way FSI Solving and Post Processing Release Solving FSI Applications Using ANSYS Mechanical and ANSYS CFX ANSYS, Inc. July 26, 2013

2 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 ANSYS, Inc. July 26, 2013

3 Starting the Run Write the Definition file and proceed to 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 ANSYS, Inc. July 26, 2013

4 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 ANSYS, Inc. July 26, 2013

5 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 ANSYS and 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 to be escaped, e.g. Start\ ANSYS\ and\ CFX and -np\ ANSYS, Inc. July 26, 2013

6 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@MACHINE ANSYS, Inc. July 26, 2013

7 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 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 ANSYS, Inc. July 26, 2013

8 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 ANSYS, Inc. July 26, 2013

9 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 CFX-Pre Definition File Contains CCL definition of fluid model and interface / coupling settings Mechanical Input File Contains APDL definition of structural model 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 Solver Settings from the Definition file Process Input File CFX adds APDL commands for interface / coupling settings MAPDL Solver Input File + appended APDL commands from CFX ANSYS, Inc. July 26, 2013

10 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 and combines 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 File Contains CCL definition of fluid model and interface / coupling settings CFX Solver Settings from the Definition file Process Input File CFX adds APDL commands for interface / coupling settings Mechanical Input File Contains APDL definition of structural model MAPDL Solver Input File + appended APDL commands from CFX ANSYS, Inc. July 26, 2013

11 MAPDL Commands Inserted by CFX You can view the commands generated by CFX in the MAPDL Solver output, following the end of the Input File End of Input File from Mechanical CFX generated these commands ANSYS, Inc. July 26, 2013

12 Process Input File If you disable Process ANSYS Input File then CFX does not generate any 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 File Contains CCL definition of fluid model Mechanical Input File Contains APDL definition of structural model and interface / coupling settings CFX Solver Settings from the Definition file ANSYS Solver Settings from Input File ANSYS, Inc. July 26, 2013

13 Solver Files Generated CFX The working directory will contain the CFX Output and 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 and contains all the MAPDL Solver files All results are stored in the.rst file The auto-generated ANSYS.mf file can be viewed in this subdirectory ANSYS.stdout is the ANSYS Solver output as displayed in the CFX Solver Manager Workbench The working directory is: /<ProjectName>_files/dp0/CFX/CFX ANSYS, Inc. July 26, 2013

14 CFX Solver Output Start 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 ANSYS, Inc. July 26, 2013

15 CFX Solver Output ANSYS Field Solver and Interface Loads plot also shown X-axis values do not correspond to each other or to CFX Cumulative ANSYS Iterations Cumulative Coupling Iteration L2 normalized values should be less than corresponding convergence criteria (CRIT) Interface loads should be negative at the end of each timestep ANSYS, Inc. July 26, 2013

16 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 ANSYS, Inc. July 26, 2013

17 MAPDL Solver Output Time 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 Field Solvers are Converged Check Interface Load Convergence ANSYS, Inc. July 26, 2013

18 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 runtime 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 ANSYS, Inc. July 26, 2013

19 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 ANSYS, Inc. July 26, 2013

20 Combined Post-Processing Editing the CFX Results cell for a 2-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 ANSYS, Inc. July 26, 2013

21 Combined Post-Processing In CFD-Post CFX and structural results entries and regions are shown in the outline tree When creating objects they can be scoped to all or selected domains ANSYS, Inc. July 26, 2013

22 Combined Post-Processing Use the Timestep Selector to load different time steps as usual Tab panels show the available results from each solver Sync Cases allows both sets of data to be updated when a time step from one set is selected Animations can show both fluid and structural results simultaneously ANSYS, Inc. July 26, 2013

23 Combined Post-Processing Animations Transient blood flow through a three-leaf valve Symmetry used with 1/6 th 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 and anisotropic (non-linear) materials ANSYS, Inc. July 26, 2013

24 Combined Post-Processing Animations Transient free surface flow in a 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 (oneway only) via co-simulation to determine the stresses acting on the baffles Determine the integrity and viability of the adhesive bonding ANSYS, Inc. July 26, 2013

25 Combined Post-Processing 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 specified Undefined Color Some variables apply to both fluid and structural regions, e.g.: Total Mesh Displacement (X/Y/Z) Velocity (u/v/w) Mesh metrics (Area, Edge Length Ratio, X, Y, Z, etc) ANSYS, Inc. July 26, 2013

26 Combined Post-Processing CFD-Post read components from a.cm file written 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 containing shell 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 ANSYS, Inc. July 26, 2013

27 Post-Processing in Mechanical Structural results are associated with the CFX Solution and Results cells To post-process in Mechanical: Edit the Mechanical Solution cell Select the Solution entry from the Outline tree Select Tools > Read Results Files and browse for the.rst/.rth file associated with the CFX FSI system ANSYS, Inc. July 26, 2013

28 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 ANSYS, Inc. July 26, 2013

29 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 be specified 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 ANSYS, Inc. July 26, 2013

30 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 the CFX 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 Typical Restart Commands Generated by CFX 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,cm KBC,1 /GST,ON,ON SOLVE SAVE CMWRITE,ANSYS,cm FINISH /EXIT ANSYS, Inc. July 26, 2013

31 Restarts from a Backup Point A failed run can be restarted using a CFX backup file and MAPDL files produced using 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, with Continue History From enabled Same MultiField settings as restarting from 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 not used and CFX re-creates the MF commands ANSYS, Inc. July 26, 2013

32 Restarts from a Backup Point Only the first FSI run will contain a rdb file. For multiple restarts copy 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 ANSYS, Inc. July 26, 2013

33 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 in CFX 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? ANSYS, Inc. July 26, 2013

34 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 ANSYS, Inc. July 26, 2013

35 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 the Mechanical 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 ANSYS, Inc. July 26, 2013

36 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 ANSYS Multi-field Run ANSYS, Inc. July 26, 2013

37 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 ANSYS, Inc. July 26, 2013

38 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 ANSYS, Inc. July 26, 2013

39 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 ANSYS, Inc. July 26, 2013

40 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 ANSYS, Inc. July 26, 2013

41 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, ERASE OUTRES, ALL, NONE OUTRES, NSOL, LAST Structural Solution Only OR OUTRES, ERASE OUTRES, ALL, NONE OUTRES, NSOL, LAST OUTRES, ESOL, LAST Structural + Thermal or Thermal Solution ANSYS, Inc. July 26, 2013

42 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 ANSYS, Inc. July 26, 2013