Altair OptiStruct 2020.1 Release Notes

Highlights

Energy output for Nonlinear Static Analysis
Explicit Dynamic Analysis - Additional Elements supported
Aeroelasticity – Static Trim solution
User subroutine for Heat Transfer Analysis
Thickness mapping from Forming simulation
Material and property Encryption

New Features

Stiffness, Strength and Stability

Energy output for Nonlinear Static and Nonlinear Transient Analysis

Various energy output is available for the entire model and/or the SET of elements or Contact.

Plastic Energy dissipation -> Entire model and/or SET of elements
Static Stabilization energy -> Entire model and/or SET of elements
Contact Stabilization energy -> Entire model and/or each CONTACT

NLENRG Bulk/Subcase Entry has been added which can be used to specify the SET of elements or CONTACT IDs for energy output request. _e.out file is the ASCII output and _e.nlm is for plotting the energy results in HyperGraph.

Damping option for JOINTG

"DAMP" has been added as new property type in PJOINTG Bulk Data to specify damping for JOINTG. Currently, hinge, axial, and cylindrical joints are supported for damping input.

ADJUST option on CONTACT now considers the shells thickness in searching zone

Prior to v2020.1, ADJUST did not consider the thickness of shells in search zone but the shell thickness is now considered for ADJUST. For example, the penetration could be considered by considering the thickness of shells so that ADJUST in v2020.1 will properly defect the penetration and adjust the grids.

Baseline correction

Some errors in measured acceleration input causes the divergence of transient analysis for results such as displacement even at the end of simulation. Baseline correction helps correct the acceleration input to avoid such phenomena. Baseline correction is supported for Nonlinear Transient Analysis and activated by the BASELIN Bulk Data Entry and Subcase Entry. Baseline correction is only applicable when the acceleration input is through SPCD with TLOAD# data.

CONROD element support in Large Displacement Nonlinear Analysis

CONROD elements are now available in Large Displacement Nonlinear Analysis.

Enhanced NLMON Bulk Data

Monitoring of displacement for user-specified grid and component is now available through the NLMON Bulk and Subcase Data Entries.

HyperBolic Sine Creep law

HyperBolic Sine Creep law is now available. For this material law, temperature is directly included in the formulation. CTYPE=HYPERB is available on the MATVP Bulk Data Entry.

The HYPERB hardening form is given by:(1)

{\dot{\bar{ε}}}^{c} = {Asinh}^{n} (B \bar{σ}) exp (- \frac{d H}{R (θ - θ^{z})})

New combination joints via JOINTG (Cartesian + Orientation)

CARTORIE JOINTG type is now available as a combination of Cartesian and Orientation joints.

Temperature loading support for Nonlinear Transient and Static Analysis

TEMP(D) Bulk Entry can now be referenced by TLOAD1/2 to specify temperature loading. Temperature-dependent material is also supported under this loading.

Centrifugal Softening for preloaded Normal mode analysis with Large Displacement Nonlinear Analysis

Centrifugal Softening for preloaded Normal Mode Analysis with Large Displacement Nonlinear Analysis has been considered by default.

Additional diagnostic data in _nl.out and _nl.h3d files

Grid IDs with Contact Status Change and distorted element IDs are available in _nl.out ASCII file, as well as the _nl.h3d file. NLPRINT Bulk/Subcase Entry should be used to request the grid IDs with contact status change output in _nl.out file. In _nl.h3d file, grid IDs with contact status change and the distorted element IDs are always output by default.

Model Change (MODCHG) support for RBE2/RBE3

Subcase-dependent model change for RBE2/RBE3 is now supported. The set of rigids should be defined through a SET of TYPE=RIGID. Both with-strain and without-strain activation option is supported.

Alternate shell formulation for 1^st order shells for Large Displacement Analysis

PARAM,SHELLLG,YES activates an alternate 1^st-order LGDISP shell element (CQUAD4 and CTRIA3). PARAM,SHELLLG,YES introduces numerous departures from the original element design (Total Lagrangian formulation, element interpolation spaces, drill DOFs treatment, and quadratures). It is recommended for sensitive models.

Enhancements for Explicit Dynamic Analysis

BEAM/BAR: Beam/Bar element through CBEAM/CBAR has been added for Explicit Dynamic Analysis. The formulation is based on Belytschko-Schwer Beam theory. This formulation considers transverse shear deformation as in Timoshenko beam theory. PBEAM, PBAR, PBEAML, and PBARL properties are supported.
CBUSH with linear and nonlinear stiffness: CBUSH Bulk Entry has been added to represent the bushing modeling capabilities in explicit dynamic analysis. The stiffness can be linear (PBUSH) or nonlinear (PBUSHT) based on the properties chosen. Mass is required for CBUSH through “M” continuation line on PBUSH.
First Order Tetra with Nodal pressure average: First order tetra elements with nodal pressure average can alleviate volumetric locking and is the default for first order tetra elements. Regular first order tetra element can be activated thru ISOPE field on PSOLID continuation line.
RBE3: RBE3 is now supported for Explicit Dynamic Analysis.
Max time step limit on TSTEPE: DTMAX (Maximum allowed time increment) has been added in the TSTEPE Bulk Entry.
Bergstrom-Boyce Material Model: This material law represents the nonlinear viscoelastic characteristics of material and can be combined with any Hyperelastic materials that are supported. Currently, only solid elements are supported. MATVE Bulk Entry is used to define this type of material.
Frequency control for plotting of energy results: FREQ option on NLENRG Bulk Entry can be used to control the frequency of output for energy in _expl.mvw file.
External work as energy output: External work is now available as one of the energy outputs for plotting.

Aeroelasticity:

OptiStruct version 2020.1 supports Static Aeroelasticity capability for subsonic regime. Other aeroelasticity solution types, such as flutter, will be supported in the future release.

The Vortex Lattice Method (VLM) solves the aerodynamic equations for low-speed-linear potential flows by distributing elementary solutions of Laplace’s equation over the boundary surface.

Static aeroelasticity is the study of the deflection of flexible aircraft structures under aerodynamic loads, where the forces and acceleration are assumed to be independent of time. Stability and control derivatives are available for each unique flight condition (Mach number and dynamic pressure). Derivatives are printed for the rigid vehicle and for the restrained and unrestrained elastic vehicles.

A trim analysis is performed that determines unknown trim values. Aerodynamic forces and pressures on the aerodynamic elements may be obtained via the AEROF and APRES Case Control commands, respectively.

The results from TRIM analysis such as stability, control derivatives, the aerodynamic forces and pressures are available in the ASCII ouput file (.trim file).

Monitor points (MONPNT1, MONPN3 Bulk Entry) are available to understand the integrated loading or the force going thru the section of the models. The results of Monitor points are available in the .monpnt file.

The following table illustrates the reference guide entries supported for Aeroelastic Trim Analysis.

Aeroelastic Trim Analysis	Bulk Data	Case Control
Structural Model	GRID, Finite Elements, Properties, and so on
Aerodynamic Model	CAERO1, PAERO1, AERO, AEROS, AEFACT	AESYMXZ, AESYMXY
Splines (interpolation)	SPLINE1, SPLINE2, SPLINE4
Boundary Conditions	SUPORT, SPC, SPC1	SPC
Aerostatic Trim Analysis	TRIM, AELIST, AELINK, AESTAT, AESURF
MONITOR points	MONPNT1, MONPNT3
Structural Output		DISP, STRESS, STRAIN, and so on.
Aerodynamic Output		AEROF, AEPRESSURE, TRIMF
Aeroelastic Parameters	PARAM,AUNITS

Heat Transfer

MUMPS Solver for Nonlinear Steady-State and Transient Heat Transfer Analysis

MUMPS Solver for Nonlinear Steady-State and Transient Heat Transfer Analysis is now available and can be activated through the SOLVTYP Bulk/Subcase Entries (the default solver is BCS). Some test results have shown that MUMPS solver provided a better scalability with multiple processors (SMP) than BCS solver.

Radiation to Space in Transient Analysis

Radiation to Space for Transient Heat Transfer Analysis is supported.

Radiation boundary conditions can be specified with the RADBC Bulk Data where the radiation view factor is defined and the RADBC entry should be referenced by a CHBDYE entry. In addition, the RADBC entry points to a grid for ambient temperature definition and the ambient temperature can be specified with SPC.

The emissivity and absorptivity material surface properties are specified on the RADM Bulk Data Entry. The RADM entry is directly referenced by a surface element entry (CHBDYE).

PARAM,TABS defines the absolute temperature scale and PARAM,SIGMA defines Stefan-Boltzman constant.

User subroutine for Thermal Analysis

User subroutines can be programmed using Fortran or C/C++. A dynamic library built with user subroutine can be loaded with the LOADLIB entry.

The following use cases are currently supported with user subroutines for thermal analysis.

Function	Time Dependency	Temp Dependency	Solution type
Volumetric Heat Generation			Linear and Nonlinear Transient
Convection Coefficient			Nonlinear Transient
Ambient Temperature for convection			Linear and Nonlinear Transient
Heat Flux			Linear and Nonlinear Transient

Noise and Vibration

Modal participation output for Equivalent Radiated Power (ERP): Modal participation for Equivalent Radiated Power (ERP) is available and can be requested with “MPF” option in ERP output request. The participation results are available in punch and H3D file.; In addition, “MFILTER” as filtering option for the participation and “FREQUENCY/SOLUTION” as frequency set have been added, as well.

Composite

Mechanical and Thermal Strain output for continuum shells with PCOMPLS: In addition to the total strain output, mechanical and thermal strains are available with MECH and THRM options on the CSTRAIN output request for continuum shells.
Failure Criteria Enhancement for PCOMPLS: Prior to v2020.1, the failure criteria for PCOMPLS assumes the strength limit for thickness direction (local Z) is the same as the strength limit on local y direction thus V5 and V6 on MATF were ignored. The failure criteria has been enhanced such that the strength limit for thickness direction is correctly taken into account.
Corner option support for CSTRAIN and CFAILURE: Corner option support for CSTRAIN and CFAILURE is available in H3D file for linear and nonlinear static analysis.
Max Stress failure Criteria added to MATF: Max Stress failure Criteria “STRS3D” is now supported on the MATF Bulk Data Entry.
NDIV support for CSTRESS/CTRAIN in Transient and Frequency Response: NDIV is now supported for CSTRESS/CTRAIN output in Transient and Frequency Response.
Support of NU13 input, instead of NU31 for MAT9OR: SYSSETTING(MAT9ORT=NU31/NU13) has been added to select either NU31 or NU13 for the 8th field on MAT9ORT for Poisson’s ratio for uniaxial 3–direction.
Multiple Failure Criteria support on MATF: Multiple Failure Criteria are supported on the MATF Bulk Data by allowing multiple “CRI” lines with different failure criteria. Solid (PSOLID, PCOMPLS) and shells (PCOMP(G), PCOMPP) are supported.

Optimization

MMA Optimizer: MMA optimizer has been added as an additional optimization algorithm to choose from by using DOPTPRM,OPTMETH. MMA can be tried in case the default optimizer, DUAL2, does not provide satisfactory results for topology or topography design variables.
Improved sensitivity for Contact pressure/force response with Shape design variables: Accuracy of sensitivity has been improved for contact pressure/force responses with shape design variables. This is the case even when the shape design variables are defined in contact surface domain.
Flexible Initial thickness for free-size optimization: Flexible initial thickness can be defined for free-size optimization, based on nodal average thickness or property thickness. If nodal thickness on the element is available, the initial thickness of each element is based on the average nodal thickness for the given elements.; If you specify “T1” on DSIZE, T1 will be used for design space to determine the initial thickness (T1*MATINIT). If you want to start the initial thickness distribution based on nodal thickness or the thickness on PSHELL properties (if no nodal thickness is defined), add DOPTPRM,MATINIT,ANALYSIS. In this case, the initial thickness is “elemental thickness” or thickness from the properties (if no nodal thickness is defined).

General

Material and property Encryption

Encryption is now available for material and property data, as well as some table data that are referenced by material data.

HyperMesh support for encryption of the data is planned for a future release. Currently, the user can use the encryption tool available in $ALTAIR_HOME/hwsolvers/optistruct/bin/platform to encrypt the data.

On Windows, the os_encrypt_win.exe encryption tool can be used to encrypt lines using the following example command:

os_encrypt_win.exe original.txt encrypted.txt

On Linux, the os_encrypt_linux encryption tool can be used to encrypt lines using the following example command:

os_encrypt_linux original.txt encrypted.txt

After the encryption tool runs, the file encrypted.txt will contain both the encryption key and the encrypted lines.

Enhanced EIGVSAVE and EIGVRETRIEVE for Modal Transient Analysis

Partial degrees of freedom are now allowed for EIGVSAVE run if the corresponding retrieve run is Modal Transient analysis. Solver should be AMSES or AMLS in this case.

Mass and Damping for GENEL

Prior to 2020.1, only stiffness matrix input has been available on the GENEL Bulk Data. Now mass and damping are also available for matrix input on the GENEL entry.

The field to indicate the type of matrix now supports “M” for mass and “B” for viscous and “K4” for structural damping matrix.

Thickness mapping from Forming Solvers

Thickness results from the forming solvers available in Nastran (.nas) or LS-DYNA (.k) file can be directly mapped to the OptiStruct model without using any pre-processor. Such mapping capability is available even if the mesh between the forming and OptiStruct model is different. Newly introduced MAP Bulk Entry is used to select several options.

Thickness results from forming solver will be read via ASSIGN,MAP entry.

THICK: Thickness mapping
SID: Set of element to be mapped
ASID: External file to be used for map, defined by ASSIGN
SCALE: Used to convert from different unit system
RELOC: Assemble the component with 3 pairs of grids matched in case the configuration of model between Forming solver and OptiStruct is different.

Additional Statistics Results for Transient Analysis

Mean, RMS, Variance, Standard Deviation are added for statistics output from Transient analysis with STATIS or OSTATIS option on respective output requests. Displacement, Velocity, Acceleration, SPCF and ELFORCE support these additional statistics output.

Enhanced Stress results calculation for 2^nd order shells

PARAM,CURVSHL2,THICK activates an alternative stress recovery calculation in curved, 2^nd-order shell elements (CQUAD8 and CTRIA6). It is recommended for very thick shells.

HDF5 Enhancements

The output file format for Hierarchical Data Format, version 5, has been switched from .hdf5 to .h5. The new .h5 file replaces the old .hdf5 file. The .h5 file is now output whenever HDF5 output is requested.

This format contains both model and result information and hence can be used for post-processing directly.
The old format (.hdf5) does not contain finite element model information and hence requires importing the model file in addition to importing the result file in a post-processor.
PARAM,HDF5 can be used to switch between the old and new formats or output both formats. The options for this parameter are:
- FORM1: Switches to old format (.hdf5)
- FORM2: Switches to new format (.h5). This is the default option.
- BOTH: Both old and new formats are output

The .h5 file output is supported for Linear Static, Nonlinear Static, Normal Modes, and Linear Buckling Analysis.

The supported output requests with the new format (.h5) are summarized as:

Result Type	Result	Comments
Grid-based	DISPLACEMENT	Grid-based results mentioned in the Result column are supported.
	OLOAD
	GPFORCE
	SPCFORCE
	MPCFORCE
Element-based	Stress/Strain	Elements supported: CROD, CBAR, CBEAM, CONROD, CELAS1, CELAS2, CBUSH, CTRIA3, CTRIA6, CQUAD4#, CQUAD8, CTETRA, CHEXA, CPENTA
	ELFORCE	Elements supported: CBAR, CBEAM, CONROD, CTRIA3, CTRIA6, CQUAD4#, CQUAD8
	CSTRESS/CSTRAIN	Properties supported: PCOMP, PCOMPP/STACK

* - Supported with PSHELL and PCOMP, # - Corner results are also available

Adaptive time step for Linear Transient

Adaptive time step schema has been added for Linear Direct Transient Analysis with the Newmark beta time integration method. MREF continuation option on TSTEP controls adaptive time stepping (default is ON), similar to Nonlinear Transient analysis. TMTD continuation option on TSTEP Bulk should be used in case Newmark Beta time integration method is to be used for Linear Direct Transient analysis.

Remote Job submission using the Solver Run manager

Remote Job submission is now available using the HWSolver Run Manager. This allows you to submit a job to a remote machine. The actual run will be performed on the remote machine and the results are copied back to the client machine (where the job was initiated using the Run Manager). The remote machine may be a single host or a cluster. The client machine can be Linux or Windows; however, the remote machine should be Linux. Client machines using Windows are currently not supported.

Client Machine	Remote Machine	Support
Linux/Windows	Linux	Supported
Linux/Windows	Windows	Not Supported
Linux/Windows	PBS (Linux)	Supported
Linux/Windows	PBS (Windows)	Not Supported

Brief overview of steps to initiate Remote Job submission

Install HWSolvers on both the client machine and remote machine. The HWSolver Run Manager version should be the same on both the client and remote machines.
Establish password-less connection from the client machine to the remote machine using SSH keys.
Configure a remote server by adding the remote machine to the HWSolvers Run Manager GUI.
1. Go to Edit > Remote Servers.
2. Choose Add and enter the remote server information in the Remote Server Details dialog.
3. Click Save.
Submit the remote job from the HWSolver Run Manager GUI.
1. Under the Remote drop-down menu, choose the newly added remote machine.
2. Uncheck the Use solver control checkbox (use solver control is not supported for remote jobs).
3. Click Run.
4. If a PBS server is selected as a remote machine, then an additional dialog named PBS settings appears. You can enter the Number of cpu’s: and the Memory in GB: for the job and click OK.

High Performance Computing

Multi-Level DDM support for Nonlinear Static Analysis: DDM is now supported for the case where there is a main Pretension bolt subcase then the rest of the subcases are all independent but each of those subcases are continued from the main pretension bolt subcase.
AVX2 compiler option enabled: Advanced Vector Extensions 2 (AVX2) instruction set is suitable for floating point-intensive calculation and would help improve the robustness of such calculations. Due to this change, there could be some difference in the results if the model setup is not robust. If the model is setup properly, there should not be noticeable difference in results.

Known Issues

MPI multi-node cluster runs on Linux may error out due to an SSH error

For example, the following error may occur:

Error :/bin/ssh: 
$ALTAIR_HOME/altair/hwsolvers/common/python/python3.5/linux64/lib/libcrypto.so.10: 
version OPENSSL_1.0.2 not found (required by /bin/ssh).

This can occur when the libcrypto library from Python conflicts with the one required by MPI. To resolve this, copy libcrypto from the system to the location mentioned in the error above. In the system, this library is typically in /usr/lib64.

For more information, refer to the Knowledge Base article available at the following link: https://support.altair.com/csm?id=kb_article_view&sysparm_article=KB0037367

Resolved Issues

No separation was not respected for CONSLI type of contact and this has now been fixed.
Body force such as gravity for Explicit Dynamic Analysis is now handled properly.
GPFORCE is correct for Nonlinear Analysis with temperature loading.
FLAT table option for plasticity is now properly implemented.
Stress combination “Signed Max Shear” results for Fatigue is corrected for shells.
ASSIGN entry used for MMO runs now supports up to 600-character length.
DRESP3 with COMPOSE jobs no longer show some issues with older versions.
Complex DMIG input no longer causes some issues when the imaginary part is zero.
MFLUID is now properly supported even for optimization runs.
OptiStruct runs finish properly when OUTPUT,FSTOSZ is defined and the design space includes STACK and PSHELLs.
Preloading analysis with centrifugal force applied in static analysis produces results when the centrifugal force is applied on element SET.
GPKE results no longer are incorrect if the job runs with DDM mode.
Design Sensitivity Analysis (DSA) no longer ends with programing error when the model has material sizing design variables.
PFMODE results are available when DSA was performed at the same time.
Initial velocity is interpreted properly in Explicit Dynamic Analysis when applied on the same DOFs as enforced acceleration.
When a single SN curve is defined with (SNCM flag on MATFAT card) TABLEXN, the fatigue damage results are now correct.
Shell thickness is considered properly for ADJUST with CONSLI.
Stress responses in topology/free-size design space are printed in the main .out file in Multiple Model Optimization (MMO).
The input file generated with OUTPUT,FSTOSZ is formatted properly, if the free-size model is in long format.
NSM with error 2359 (NSM=n control cards allowed only in static subcases) occurred even if there was only a single subcase in the model and this is now fixed. With single subcase in the model, the error 2359 will not occur regardless of where NSM entry is defined (subcase level or global level).
Thickness output from large displacement nonlinear analysis is accurate with DDM mode.