MEGN 537 – Probabilistic Biomechanics Applying the AMV Method with a Finite Element Model Anthony J Petrella, PhD

The Model Can be analytical or computational MATLAB for analytical Finite elements for computational ABAQUS ANSYS SolidWorks Simulation (COSMOS)

Parameterization The most challenging step for an FE model Some variables are easy Material properties Loading Already parametric Some variables are more difficult Dimensional parameters Affect the mesh

Typical Steps for Prob FE 1.Setup model in usual way → model database 2.Add or confirm parameters in FE model 3.Script(s) to update model parameters and regenerate FE mesh 4.Run FE solution 5.Script to extract scalar result(s) of interest 6.Encapsulate above in NESSUS to automate

Example Syringe Sealing Pressure 1.Setup model in usual way → model database

Example Syringe Sealing Pressure 1.Setup model in usual way → model database Axisymmetric Rigid barrel, plunger rod Rubber stopper Note initial interference! First, resolve interference Second, apply fluid pressure Rigid Barrel Rigid Plunger Rod

Example Syringe Sealing Pressure 2.Add or confirm parameters in FE model rib1_od rib2_od rib2_width rib1_width rib1_rad rib2_rad plunger_od

Example Syringe Sealing Pressure 2.Add or confirm parameters in FE model a. rib1_od, rib2_od = ± b. rib1_rad, rib2_rad = ± c. rib1_width = ± d. rib2_width = ± e. plunger_od = ±

Example Syringe Sealing Pressure 3.Script(s) to update model parameters and regenerate FE mesh All good FE codes have a scripting language… For ABAQUS it is Python ANSYS Parametric Design Language (ADPL) SolidWorks Simulation uses VB scripting The script simply automates mouse clicks There is typically a “replay” file from which you can extract the needed commands

Try This… Download ABAQUS files Double-click CAE file Change rib1_od to Close CAE file and save changes Now open abaqus.rpy file in a text editor These are the Python commands that perform the task you executed above with mouse clicks

Typical Steps for Prob FE 4.Run FE solution Use command-line 5.Script to extract scalar result(s) of interest Created in the same way as before using the replay file One may extract multiple results of interest, but each must be a scalar – this is how prob analysis works

Typical Steps for Prob FE 6.Encapsulate in NESSUS to automate… » copy..\..\axi_10ml_syringe.cae » copy..\..\script_extract.py » abaqus cae nogui=script_update » abaqus j=temp inp=axi_10ml interactive » abaqus cae nogui=script_extract » del *.rpy.* Note: script_update is your input file, so it’s automatically copied to each trial folder by NESSUS 1 2 3

Typical Steps for Prob FE 6.Encapsulate in NESSUS to automate » copy..\..\axi_10ml_syringe.cae » copy..\..\script_extract.py » abaqus cae nogui=script_update » abaqus j=temp inp=axi_10ml interactive » abaqus cae nogui=script_extract » del *.rpy.* Model Database – allows for re-meshing; must be copied to the working directory to be operated on by script_update.py 1 2 3

Typical Steps for Prob FE 6.Encapsulate in NESSUS to automate » copy..\..\axi_10ml_syringe.cae » copy..\..\script_extract.py » abaqus cae nogui=script_update » abaqus j=temp inp=axi_10ml interactive » abaqus cae nogui=script_extract » del *.rpy.* Extraction script – the default ABAQUS output is a binary results database, so this script is needed to extract scalar results to a text file; this will be a similar situation for any FE code 1 2 3

Typical Steps for Prob FE 6.Encapsulate in NESSUS to automate » copy..\..\axi_10ml_syringe.cae » copy..\..\script_extract.py » abaqus cae nogui=script_update » abaqus j=temp inp=axi_10ml interactive » abaqus cae nogui=script_extract » del *.rpy.* Update script – changing dimensions changes the mesh, so you need a script to operate on the model database and regenerate the mesh after all dims are updated; this file contains all the parameters that are prob variables modified by NESSUS, so it is copied to the working directory automatically 1 2 3

Typical Steps for Prob FE 6.Encapsulate in NESSUS to automate » copy..\..\axi_10ml_syringe.cae » copy..\..\script_extract.py » abaqus cae nogui=script_update » abaqus j=temp inp=axi_10ml interactive » abaqus cae nogui=script_extract » del *.rpy.* FE solution – this is the ABAQUS command to run the solution for a single trial 1 2 3

Typical Steps for Prob FE 6.Encapsulate in NESSUS to automate » copy..\..\axi_10ml_syringe.cae » copy..\..\script_extract.py » abaqus cae nogui=script_update » abaqus j=temp inp=axi_10ml interactive » abaqus cae nogui=script_extract » del *.rpy.* Extract results – run the extraction script to read the binary results file from ABAQUS and write scalar output to a text file 1 2 3

Output There are two output files of interest… cpress.out – this is the peak contact pressure on the 1 st rib cfn1_initial.out – radial component of contact force after assembly Line 1: force on 1 st rib Line 2: force on 2 nd rib Line 3: total force on both ribs

Typical Steps for Prob FE 6.Encapsulate in NESSUS to automate » copy..\..\axi_10ml_syringe.cae » copy..\..\script_extract.py » abaqus cae nogui=script_update » abaqus j=temp inp=axi_10ml interactive » abaqus cae nogui=script_extract » del *.rpy.* Clean up any unnecessary files 1 2 3

Files Summary axi_10ml_syringe.cae (model database, need to copy) script_update.py (input for NESSUS, copied automatically) script_extract.py (extraction script, need to copy) axi_10ml.inp (ABAQUS input created when update script is run) temp.odb (ABAQUS binary output created when FE solution is run) cpress.out (text output file created by extraction script) cfn1_initial.out (text output file created by extraction script) These first three files are the only ones you need to begin the analysis… the others below are created automatically