What's New

View new features for OptiStruct 2021.1.

Altair OptiStruct 2021.1 Release Notes

Highlights

Aeroelasticity Flutter
Combined Hardening Material
Threaded Bolt
MPC TIE for Large Displacement Nonlinear Analysis
1D Fluid for Thermal analysis (CAFLUID)
Forced Convection Heat Transfer analysis for Topology optimization

New Features

Stiffness, Strength and Stability

Preloaded Cyclic Symmetry

Preloaded linear and normal mode analysis are supported. Preloading subcase is limited to linear subcase and can only include cyclic loading (Harmonic # 0).

Shear and Volumetric test data for viscoelasticity

Shear and Volumetric test data are supported for viscoelasticity (MATVE) and frequency domain viscoelasticity (MATFVE). For both entries, the MODEL field can be set to:

RTEST: Provides Shear and Volumetric test data for Relaxation.
CTEST: Provides Shear and Volumetric test data for Creep.

In each case, the SHEAR and/or BULK continuation lines can be used to define the shear and volumetric test data for viscoelasticity. The COMB continuation line is also available to specify both shear and volumetric data together.

TOTALFORCE output

TOTALFORCE is the sum of the applied force and the reaction force at any given grid points. This output is supported for linear and nonlinear static subcase in the .h3d file through the TOTALFORCE output request.

Support preloaded dynamic analysis when preloading subcase is NLSTAT with INISTRS from forming simulation

Preloaded normal mode analysis is now supported, even if the preloading subcase is nonlinear static and using initial stress input through INISTRS Subcase/Bulk Data pair.

Hyperfoam

Hyperfoam material type is supported with TYPE=FOAM in the MATHE Bulk Data Entry. Hyperfoam is supported for solid elements and axisymmetry, plane strain elements. Both direct parameter input and curve fitting through test data are supported for both implicit and explicit nonlinear analyses.

Adaptive Penalty

Adaptive Penalty for Nonlinear Contact analysis is supported and can be turned on by CONTPRM,TUNESTF,1 (“0” is the default and adaptive penalty is off by default). Adaptive penalty approach will adjust the contact penalty during Newton-Rapson iterations, while keeping the penetration within the user specified value. The maximum allowed penetration is chosen as MAXPNTRL*L, where L is the characteristic edge length (the average edge length on the main surface) of the contact. MAXPNTRL is defined through CONTPRM. Adaptive penalty approach can be tried in case the convergence difficulty is met with default linear penalty.

New convergence criteria

Maximum residual grid point force-based convergence criteria available with NLADAPT,ERRFINF,MAX. This is currently supported for Large Displacement nonlinear static and nonlinear transient analysis. This parameter supports input of two values: PARAM,ERRFINF,MAX,<FTOL>.

If NLADAPT,ERRFINF,MAX is set, then the maximum residual grid point force of any grids should be smaller than FTOL * Maximum grid point force. FTOL is the optional second value allowed for this parameter and the default is FTOL=0.005.

If NLADAPT,ERRFINF is defined, then nonlinear convergence criteria from NLPARM, as well as NLADAPT, ERRFINF should be satisfied.

Temperature-Dependent Hyperelasticity

Temperature-dependent hyperelastic material are available via the new MATTHE Bulk Data Entry. All material models currently supported with MATHE are also supported on the new MATTHE entry which adds temperature-dependency. Currently, only direct parameter input is supported for MATTHE and table input for curve-fitting is not supported.

MODCHG when the elements are attached to MPC or RBODY

MODCHG is now supported when the elements to be changed are attached to MPC or RBODY.

Contact interference

Contact interference fit control is available with CNTITF Bulk and Subcase Entry. When there is an overclosure of contact surface, the contact interference fit is triggered automatically to resolve the overclosure. For this case, the overclosure will be resolved gradually over the subcase.

With CNTITF, the following options are available:

Contact interference fit can be optionally resolved in just one loading increment instead of over multiple loading increments.
Contact interference fit can be resolved through a user-defined TABLE (time versus the multiplier to the initial penetration). This option allows the interference fit on different contact interfaces to be resolved at different times or subcases.
Amount of allowable penetration can be specified.
CNTITF can be specified for different contact interfaces.

Pressure-overclosure TABLE

Pressure-overclosure relationship can be specified through TABLEG/TABLES1 and defined in PCONT.

Threaded Bolt

Threaded bolts can be defined as part of a CONTACT interface by setting the CLEARANCE field to reference a CLRNC Bulk Data Entry.

Half pitch angle (ALPHA), pitch (PITCH), bolt thread diameter (DMAJOR and DMEAN), the number of starts (NSTART), handedness (HANDED), clearance (CLEARANCE), and the bolt axis (XA/YA/ZA,

XB/YB/ZB) can be defined on the CLRNC Bulk Entry.

Each CLRNC entry is used to define one type of bolt geometry and this geometry can also be applied to multiple contact interfaces, if required. Multiple GSET_i continuation lines can be defined on a single CLRNC entry. This allows modeling multiple bolts with a single threaded bolt geometry. As long as these multiple GSET_i individually contain grids belonging to secondary sides of separate contact interfaces, then all these contact interfaces are applied the same threaded bolt geometry.

Combined Hardening Material

Combining hardening material can be used for analysis with cyclic loading, to capture shakedown, ratcheting effect, and so on. It consists of two nonlinear hardening rules, the nonlinear kinematic (NLKIN) and nonlinear isotropic (NLISO) hardening methods. Generally, the isotropic part is closely related to the von Mises criteria, and the kinematic part is described by the evolution law of back stress.

Combined hardening can be activated by setting HR=6 on the MATS1 Bulk Data. Nonlinear kinematic hardening material data can be specified with the NLKIN continuation line and nonlinear isotropic hardening material can be specified with the NLISO continuation line in the MATS1 Bulk Entry.

For nonlinear kinematic hardening, the input material data can be either:

Parameter Input (TYPKIN=PARAM): Input of kinematic hardening parameters directly.
Test Data (TYPKIN=HALFCYCL): Specifies stress – plastic strain curve. Total stress is provided from experiment versus the equivalent plastic strain.

For nonlinear isotropic hardening, the input material data can be either:

Parameter Input (TYPISO=PARAM): Input of isotropic hardening parameters directly.
Test Data (TYPISO=TABLE): Specifies stress – plastic strain curve. Isotropic part of yield stress stress is provided from experiment versus the equivalent plastic strain.

Heat Transfer Analysis

1D FLUID (CAFLUID): CAFLUID Bulk Data Entry is an 1D element with the ability to conduct heat and transmit fluid between its two primary nodes (G1 and G2). Heat flow occurs both due to the conduction within the fluid and the mass transport of fluid.; Property (PAFLUID) of CAFLUID defines the associated material property (MID), hydraulic diameter (D) that defines the flow cross sectional area, the mass flow rate (W) and the type of shape function (SF - linear or exponential).; Convection may be accounted for either with ambient nodes (G3, G4) on the CAFLUID entry or by referencing CAFLUID primary grid(s) on corresponding TAi fields on the CONV Bulk Data Entry associated with CHBDYE surface elements.; The MAT4 Bulk Data can be referenced on the PAFLUID entry to provide fluid material properties.

Aeroelasticity

Flutter Analysis

Aeroelastic flutter is a dynamic instability of a structure associated with the interaction of aerodynamic, elastic, and inertial loads. Flutter analysis of aeroelastic systems involves determining the velocity (and hence Mach Number) of the system and the frequency of oscillation at which the system attains the state of flutter. In this phenomenon, the aerodynamic loads on a flexible body couple with its natural modes of vibration to produce oscillatory motions with increasing amplitude. This may lead to catastrophic structural failure. Therefore, structures exposed to aerodynamic loads must be carefully designed to avoid flutter.

In finite element analysis, the prediction of flutter involves a series of complex eigenvalue solutions. OptiStruct uses the modal approach where the structural-vibration modes in a selected frequency range are used as the degrees of freedom.

There are four different methods for flutter analysis supported in OptiStruct, K, KE, PK, and PKNL methods.

The following entries are relevant for flutter analysis in OptiStruct:

Bulk Data Entry: Description
AERO: Defines flight conditions.
MKAERO1/MKAERO2: Specifies the Mach number and reduced frequency pairs for the explicit computation of the aerodynamic matrix.
FLFACT: Specifies the values of flutter parameters (density ratios, velocities, and reduced frequencies) for flutter analysis.
FLUTTER: Selects the method (K/KE/PK/PKNL) and parameters for flutter analysis. This entry also references the definitions of FLFACT.
EIGC: Selects the complex eigenvalue method for the K method.
EIGRL/EIGRA: Selects how the structural modes are computed and the number of them. The number of structural modes can be changed with LMODES/LFREQ/HFREQ. NVALUE in FLUTTER entry can be used to limit the number of eigenvalues printed in the .flt file.
PARAM, VREF: Used to scale the output velocity: Vout = V/Vref.

Subcase Entry: Description
FMETHOD: References the FLUTTER entry.
CMETHOD: References the EIGC entry, for complex eigenvalue extraction (K method only).

Composite

Strength Ratio output for PCOMPLS: Strength ratio output for PCOMPLS with PARAM,SRCOMPS is now available.
Max Stress Criteria with FT=STRS for PCOMP(G) and PCOMPP: Max stress criteria with FT=STRS is now available for PCOMP(G) and PCOMPP.

Optimization

Convection Topology Optimization with Darcy Flow

Forced Convection Heat Transfer is available via Darcy Flow analysis. Currently, this is supported for Linear steady-state heat transfer analysis only and both optimization and analysis only runs are supported.

Forced convection applications include cooling solutions for Electric motors, Machine tools (casting, forming), Heat Exchangers, HVAC systems, Cooling for electronic devices including PCBs. Additionally, Topology Optimization is available for steady-state heat transfer with Darcy flow analysis.

Topology optimization considers the effect of forced convection for cooling in conjunction with structural steady-state heat transfer analysis. Topology optimization can help optimize cooling channel structure and placement for a wide range of applications.

Boundary conditions are required for both thermal structural and fluid flow analysis. The typical structural thermal boundary conditions are available via the SPC Subcase/Bulk Data.

For flow analysis, there are two options to define the boundary conditions:

Nodal Pressure: Flow analysis is solved in the same subcase as thermal analysis. The SPCP Subcase Entry and SPCP Bulk Data are available to define flow pressure boundary conditions. Both inlet and outlet flow pressures can be defined using the SPCP entry.
Inlet Velocity: Inlet velocity via the INLETVEL Subcase Entry and INLETVEL Bulk Data are alternately available, instead of inlet pressure definition via SPCP entries. The outlet pressure still has to be defined using the SPCP entry.

Material Properties for both structure and fluid for forced convection heat transfer analysis can be defined via the MAT4 Bulk Data Entry. The structural material properties are typically defined using the first line which specify the fields, K (structural conductivity), CP (structural specific heat), RHO (structural density), and H (convection heat transfer coefficient). H is only used for free convection to ambient in the presence of CONV Bulk Data. For the fluid heat transfer properties, the DARCY continuation line can be used to define KAPPA (fluid permeability), MU (fluid dynamic viscosity), K (fluid conductivity), CP (fluid specific heat), and RHO (fluid density).

Darcy Flow analysis and Convection Topology Optimization is supported for shell and solid elements. The DTPL Bulk Data Entry can be used to turn on Topology Optimization.

VERTEXM Free-shape

The following enhancements have been added for VERTEXM free-shape optimization.

Pattern grouping (1, 2, and 3 plane symmetry are supported)
GRIDCON with FIXED, VECTOR and PLANAR

MMO for Global Fatigue response

Multi-Model Optimization (MMO) now supports fatigue optimization with global fatigue constraints defined in the DTPL and DSIZE Bulk Data Entries.

General

Modal damping based on mode ID

Modal damping input for each mode ID (instead of frequency with TABDMP1) is available through the newly added TABDMP2 entry.

Bolt Section output for 1D bolt

Section coordinate system and Section resultant force summary are available .out file and .secres file for 1D pretension bolt section. The same results for solid bolt section has already been available in previous releases.

Option to suppress mode output or adjust the printing frequency in .out file

OUTPUT,MODES is now available, so that the normal mode results printing in the .out file can be suppressed (OUTPUT,MODES,NO) or the printing frequency can be specified (OUTPUT,MODES,n).

AVL Excite support

Structural damping for .exb file
SET support for .exb file
PARAM,EXCOUT is now obsolete and disabled
PARAM,EXCOP2 is set to NO by default

Force output in OPTI format .force file for Normal Modes Analysis

Element force output for normal modes analysis in the .force file is available with OPTI output request.

HDF5

Available enhancements for HDF5 output (.h5 file) are:

Element force and stress for CBUSH elements
PSD/RMS and cumulative RMS (Displacement, Velocity, Acceleration, and SPCF)
Frequency response analysis results (Displacement, Velocity, Acceleration, and SPCF)
CORD1R and CORD2R support

MEFFMASS

Modal effective mass output with MEFFMASS I/O Option Entry is now available. Additional options available in MEFFMASS compared to PARAM,EFFMASS is that MEFFMASS allows to specify a grid point as reference for the calculation of the rigid body mass matrix. The default is the origin of the basic coordinate system. Also, MEFFMASS has an option to output the results in the units of weight.

PSD/RMS results for beam/bar

Normal, shear and von Mises stress output on each evaluation point of beam/bar is supported for random response analysis in h3d.

CBEAM axial stress in OPTI format output (.strs file)

Axial stress/strain of beam is added at the end of line in .strs file for beam elements.

PART Superelements

The Bulk Data section in which CID is defined in GRAV/RFORCE entries can now be specified using the MB field. This feature is useful when loading needs to be defined in a fixed coordinate system, regardless of the orientation of the superelement, defined by a partitioned Bulk Data section.
Original user ID is retained in H3D and punch output files for each part/superelement.
In the H3D file:
- Each part/superelement has its own component/grid/element pool.
- Component labels are highlighted with its superelement SEID.
  For example, if original component name is PSHELL1 in superelement SEID=1, then in HyperView, the component label is displayed as (SE1) PSHELL1.
In the punch file, SEID is printed in title/label section.

String Label-based Input file definition

Entities can be identified by string labels in their corresponding ID field, in addition to the existing support of integer IDs. While integer-based IDs offer more flexibility when the input file is edited manually, string-based labels offer easier identification of entries in the input file, especially when many entries are defined. There are currently two types in which string-based labels can be used.

Type 1: String labels can be used to identify entries via their corresponding ID field. For example, a string label in the MID field of MAT1 entry can uniquely identify this material entry.
Type 2: Entries defined with string labels as IDs can then be referenced by other entries using their unique string labels. For example, the string label identifier of a MAT1 entry can be specified on the MID field of a PSOLID entry,

Support has been extended to more entities in this release, summarized as follows (only newly supported entities have been listed). *Support was available for certain entries in 2020 release.

Entity	Type 1 Support	Type 2 Support
Surfaces	String labels can be defined in the `SRFID` field of SURF entries.	String labels can be defined in the surface field of the following entries: CONTACT and TIE (`SSID` and `MSID` fields) PLOADSF (`SURF` field)
Sets	String labels can be defined in the `ID` field of element and grid-based SET entries.	String labels can be defined in the SET `ID` field of following entries: NSM1/NSML1 (element set in `ID` field) RBODY (grid and element set in `ID` field) TIE (`GSETID`) PLOADSF (`ELSET`)
Properties	String labels can be defined in the `PID` field of PCONT.	String labels can be defined in the `PID` field of CONTACT.
Tables	String labels can be defined in the `TID` field of TABLES1 entries.	String labels can be defined `TID` of MATS1 entry if it references a TABLES1 entry.
Coordinate systems	String labels can be defined in the `CID` field of all the coordinate system definitions.	String labels can be defined in the `CID` field of RFORCE.

High Performance Computing

Memory option for MPI runs

Memory option such as -minlen, -maxlen, -len, -fixlen are now per-host instead of per-MPI process which was the case until the previous release. -hostmem=no will revert to the per-MPI process memory allocation mechanism.

Example: mpirun -np 4 -fixlen=100

if all 4 MPI processes are allocated on 1 host, then each process will use -fixlen=100/4=25
if 2 hosts are used with 2 MPI processes each, then each process will use -fixlen=100/2=50
if host 1 has 1 MPI process and host 2 has 3 MPI processes, then the process on host 1 will use -fixlen=100 while each process on host 2 will use -fixlen=100/3=33

Resolved Issues

Models with frequency-dependent materials previously showed sensitivity in results for repeated runs. That is, the same model running multiple times previously produced different results.
ROMAX output through PARAM,ROMAX,YES no longer ends with a programming error.
An MMO job no longer hangs after detecting an element distortion error.
A plane strain N2S/S2S CONSLI model no longer fails with a programming error.
H3D file from nonlinear analysis was not written out after the loss of license. Now the .h3d file will be written out, even if the loss of license occurs during the analysis.
A Modal FRF model with EIGVSAVE/EIGVRETIREVE resulted in ERROR # 3478 in OptiStruct v2021 and v2020.1 while the same model ran in older versions.
A nonlinear contact model with optimization encountered a programming error in igapst datablock.
PARAM,AMSE4EFM no longer produces wrong results if there is viscous “B” option on PBUSH, with no value specified in that line (blank line).
A programming error could occur if MFLUID Bulk Data is defined, but not referenced.
With DOPTPRM,TOPDISC,YES, optimization restart run showed different density results at initial iteration than the last iteration in the original run.
The thickness of RBODY influenced nonlinear analysis results, even if the thickness padding is “NONE” for contact.
When there are multiple VABS cross-sections in a single deck, the VABS-OS run errored out with the ERROR # 5863. This has been fixed in the latest VABS code that is available on the APA download site.
Preloading subcase with temperature-dependent material with TEMP(LOAD) through SYSSETTING,TLOADMAT updates the material properties properly.
Translational JOINTG with MOTNJG(FIXED) in multiple subcases is respected.
Mass from CBUSH is available in mass printing.
The curve fitting process no longer fails for some models with Ogden hyperelastic material with ERROR #4905.
Incorrect “HyperMesh Component weight table” in the .out file with DDM mode.
The .mvw file is written out for modal analysis.

Altair OptiStruct 2021 Release Notes

HIghlights

PART superelements
Divergence
Frequency domain viscoelasticity
Cyclic symmetry
Auto-Contact for Explicit Analysis (Beta feature)
Altair Compute Console (ACC) GUI to submit jobs

New Features

Stiffness, Strength and Stability

Continuous Sliding (CONSLI) support for Preloaded Linear Analysis

Continuous Sliding (CONSLI) is supported for Preloaded Linear Analysis

MODULUS (Long or Instantaneous) option added in MAT1, MAT9 and MATHE

Modulus specified in MAT1, MAT9 and MATHE can either be based on Long term or Instantaneous. Default is Long term and this option is only relevant when MAT1/MAT9/MATHE are used with viscoelasticity material (MATVE). For the frequency- domain viscoelasticity (MATFVE), the MODULUS option is irrelevant because the specified elastic modulus is always considered as Long-term modulus. Prior to v2021, the modulus was assumed to be instantaneous.

RESTARTR when multiple nonlinear subcases continued from the same subcase

RESTARTR is now supported for the case where each new subcase in restart model will be continued from the same subcase which had already been solved in the original run (before the restart run). This means that all new subcases in the restart run can be independent to each other. Typical use case is all the independent subcases in restart run is continued from the pretension subcase which is solved in the original run (before the restart).

Cast Iron Plasticity

Cast Iron Plasticity is used to model gray cast iron. It allows elastic-plastic behavior with different yield strengths, flow, and hardening in tension and compression.

Cast Iron Plasticity material data can be specified by using the MCIRON Bulk Data Entry which has the same Identification Number as an existing MAT1 Bulk Data Entry. The tensile and compressive stress-strain curves can be defined using the TABLE_T and TABLE_C fields on the MCIRON entry.

Cast Iron material via MCIRON is supported for Small and Large Displacement Nonlinear Static Analysis. It is supported for CHEXA, CTETRA, CPENTA, and CPYRA elements (both first and second order).

Static Stabilization for Axisymmetry and Plane Strain

Static Stabilization is available for axisymmery and plane strain elements. Static Stabilization is activated by STABILIZ on NLADAPT Bulk Data Entry.

2nd order element support for Axisymmetry and Plane Strain

Higher order elements (2nd order) are now supported for axisymmetry and plane strain.

Contact Results for both sides (Positive or Negative) of shell elements

Contact related results such as Contact pressure, status and so on are now available for both sides of shells. The positive or negative sides are determined based on the normal direction of shells.

Contact Status output for Stick and Slip

Closed contact status in h3d file has “Close-Stick” and “Close-Slip” as new status outputs.

Frequency Domain Viscoelasticity (MATFVE)

Frequency domain viscoelasticity material is available with MATFVE Bulk Data Entry. There are several ways to specify the material properties in MATFVE.

FORMULA
TABLE
PRONY
PRELOAD

PRELOAD option allows the input of storage and loss modulus from uniaxial and volumetric tests. For information regarding each option, refer to MATFVE Bulk Data Entry. MATFVE can be combined with MAT1, MAT9 or MATHE.

Enhancements

Enhanced Cohesive element output: Additional outputs such as Cohesive energy by mode and Cohesive energy per area by modes are now available.

Explicit Dynamic Analysis:

Auto-Contact (Beta Feature): Auto-Contact for Explicit Dynamic Analysis is now available. TYPE field on CONTACT Bulk Data Entry should be “AUTO” to activate auto-contact. Using ACTIVA/DEACTIVA continuation line, the particular surfaces specified on that line will be only considered (ACTIVA) or excluded (DEACTIVA) from auto-contact generation. Edge-to-Edge contact can be considered with PSURF entry.
Enhanced 2nd order Tetra elements (10-noded CTETRA): Enhanced 10-noded CTETRA allows the same time step as first-order tetra (4-noded CTETRA). This enhanced 10-noded CTETRA is now turned on by default for explicit analysis. Regular 2nd order tetra can be activated through HGHOR=REGULAR on the EXPLICIT continuation line on PSOLID.
Pin Flag support for Beam and Bar elements: Pin Flag (releasing the dofs) is supported for CBEAM and CBAR elements for explicit analysis.
Force output for CBUSH: CBUSH force output is now available in h3d file for explicit analysis.
MAT2 and MAT8 support: MAT2 and MAT8 material properties are now supported for explicit analysis.
Composite Support: PCOMP(G), PCOMPP/STACK are now supported for Explicit Dynamic Analysis.

Aeroelasticity:

Static Aeroelastic Divergence Analysis: Divergence can occur when deflection of lifting surfaces of an aircraft leads to additional lift, which in turn leads to further deflection in the same direction. A Divergence analysis determines divergence dynamic pressures using a direct complex eigenvalue analysis. The lowest eigenvalue correlates with the critical divergence dynamic pressure.
Aeroelastic Divergence Analysis Input: Divergence analysis determines the divergence dynamic pressures which are the eigenvalues from a complex eigenvalue analysis. The analysis is activated by a DIVERG Subcase Entry pointing to a corresponding DIVERG Bulk Data Entry. The DIVERG Bulk Data Entry contains information regarding the number of eigenvalues to be extracted and the Mach numbers for which these eigenvalues are to be extracted. A CMETHOD case-control entry referencing a EIGC Bulk Data Entry should be specified to activate complex eigenvalue extraction.

Heat Transfer:

DM support for Nonlinear Steady-State and Nonlinear Transient: Domain Decomposition Method (DDM) is supported for parallelization of Nonlinear Steady-State and Nonlinear Transient Heat Transfer analysis.
MUMPS as default for Nonlinear Steady-State: MUMPS is now the default solver for Nonlinear Steady-State Heat Transfer analysis.
User Material for Nonlinear Transient Thermal Analysis: The MATUSHT Bulk Data Entry, in combination with the LOADLIB I/O Option Entry, allows for the definition of thermal material through user-defined external functions. The external functions may be written in Fortran or C. MATUSHT is currently supported only for Nonlinear Transient Thermal analysis.

Fatigue:

Surface Damage: Since fatigue is a surface phenomenon, it is a common practice to assess damage only at the surface of a structure. Damage is assessed on the surface of a structure modeled with solid elements. Two options are available to assess surface damage of a structure (surface damage using the membrane stress or grid point stress). The surface damage calculation is automatically turned on when multiaxial fatigue analysis is carried out.
Surface damage using membrane stress: When requested in FATPARM, OptiStruct automatically creates membrane elements on the surface of the structure to assess surface damage.; The membrane fatigue method is available in fatigue analysis with linear static analysis, linear transient analysis, random response analysis, and frequency response analysis. It is supported for SN and EN Fatigue.
Surface damage using grid point stress: When requested in FATPARM, OptiStruct uses grid point stress to calculate damage on the surface of the structure.; Grid-point stress fatigue method is available in fatigue analysis with linear static analysis and nonlinear static analysis. It is supported for SN, EN, and FOS. Pseudo damage is not supported with grid point stress-based damage. Grid-point stress-based Fatigue is not supported for Weld Fatigue, Solder Fatigue, Vibration/Dynamic fatigue, Transient Fatigue, or Pseudo Damage analysis.
Input: The SURFSTS field can be set to MBRN (membrane stress) or GP (grid point stress) for surface stress after sub-keyword STRESS in FATPARM Bulk Data Entry. Membrane stress is calculated in multiaxial fatigue analysis by default, unless grid point stress is chosen.
Output: No additional output request is required. Damage/Life/FOS output of an element set will automatically output surface damage. If membrane stress is chosen, the worst damage caused by the membrane stress will assigned to the original solid element. If grid point stress is chosen, damage of surface nodes will be output.
Stress Gradient Effect: Stress gradient effect can be taken into consideration through either FKM guideline method or Critical Distance method. It is supported for both shells and solid elements. For solid elements, the stress gradient effect is only available with grid point stress in fatigue analysis using results of static analysis. For solid elements, SURFSTS field on FATPARM is automatically set to GP when Stress Gradient effect is activated.; The Stress Gradient method is supported for Uniaxial and Multiaxial SN, EN and FOS Fatigue. It is not supported for Weld, Vibration, and Transient Fatigue analyses.
Nonlinear Analysis with EN: Small Displacement Nonlinear Static Analysis results can be used to assess the fatigue characteristics for both SN and EN fatigue. PARAM,NLFAT,YES should be turned on for this situation.; When EN fatigue analysis is carried out with nonlinear analysis results, cyclic strength coefficient (K’) and cyclic strain hardening exponent (n’) are not required. No plasticity correction such as Neuber correction, Hoffmann-Seeger correction, and Jiang-Sehitoglu plasticity model is involved in damage calculation as stresses and strains are already elasto-plastic stresses and strains.

Composite:

Max Stress Criteria, STRS, for Composite Shells: New composite failure type, Max Stress, is now available for Composite shells. This is activated by setting the CRITERIA field to STRS on the MATF Bulk Data Entry.
Support of Direct Coupling input for Tsai-Wu Failure Criterion: For TSAI3D and TSAI.
Transverse Shear Stress for PCOMPLS: Redistribution of transverse shear stress with PARAM,COMPSHST is now also supported for PCOMPLS.

Optimization:

Nodal thickness as design variables with DVCLRE1/2

In case the nodal thickness is defined on the shell element, the average nodal thickness of the element can be defined as design variables using DVCREL1/2. If the nodal thickness is not uniform within the element, the ratio of nodal thickness will be maintained during the optimization. Item code for DVCRLE1/2 is “T”.

Loading frequencies as arguments for DRESP2/DRESP3

Loading frequencies associated with DRESP1 response will be passed down to DRESP2/DRESP3 through DFREQ1, DFREQ1L, DFREQ1V, and DFREQ1LV.

GRID ID input for GRIDCON (GRID-based Free-Shape)

Direct input of GRID IDs are supported for GRIDCON continuation line for Grid-based free-shape optimization (TYPE = VERTEXM on DSHAPE Bulk Data.

Enhanced LEVELSET

LEVELSET Topology Optimization has been enhanced to improve its robustness. LEVELSET Topology optimization can be activated by LEVELSET continuation line on DTPL Bulk Data Entry.

Minimum member size and Draw direction constraints are supported.
Maximum Member size control is currently not supported with Levelset Topology Optimization. If present, then the setting will be ignored and a message is printed in the .out file.
Pattern Grouping, Pattern Repetition, and Extrusion Constraints are not supported by Levelset Optimization. If present, the run will error out.
PARAM,TOPDISC,YES is not supported in conjunction with Levelset Topology Optimization. If present, then this parameter is ignored and a message is printed in the .out file.
Multi-Model Optimization (MMO) and Fail Safe Optimization (FSO) are not supported with Levelset Topology and the run will error out if present.
Draw Direction constraint is supported. SINGLE and/or SPLIT constraint types are only supported. All DTPL entries in the model should have or should not have the Draw direction constraint defined, if Levelset Topology is specified. If some DTPL entries in the model have draw direction and others do not, then the run will error out.

General

PART Superelement

PART Superelement allows the definition of each PART by its own partitioned bulk entries. PART can be defined, not only by a superelement but also by FE data. Each PART is self-contained and consists of grids, elements, properties, materials and loading specific to that PART. Supported Superelement format for PART superelement is op4 and punch.

Each PART can have its own ids for grids, elements and properties and so on.
A PART can consist of Superelements (op4, punch) or FE data (Grids, elements, properties, materials).
A PART can be moved and connected to the residual part.
A PART can be repeated (REPEAT).

New Bulk Data and I/O Options for PART superelements.

SEBULK

Definition of the type of superelement (TYPE field) and the superelement boundary search options.

SECONCT

Definition of GRIDs/SPOINTs that are used to connect the PART.

SELOC

Defines a partitioned superelement relocation by listing three non-collinear points in the superelement and three corresponding points not belonging to the superelement.

BEGIN SUPER

Definition of PART (Superelement or FE data).

ASSIGN,INPUTT4

Assignment of .op4 for the analysis with PART superelement.

Cyclic Symmetry

Cyclic symmetry is available for Linear static Analysis and Normal mode analysis. New Bulk Data Entries for cyclic symmetry.

CYJOIN: Defines grids on the segment boundaries.
CYAX: This entry is used to list the grids that lie on the axis of symmetry.
CYSYM: Specifies the number of segments.
LOADCYN: This entry is used to define the loading.
LOADCYH: This entry is used to define the harmonic coefficients of loading New Case Control entries for cyclic symmetry.
HARMONIC: This option is used to specify the solution harmonics to be used.
NOUTPUT: This entry is used to specify the segments for which results must be recovered and output.

Skip Case Control Section entries

SKIPON, SKIPOFF can be used to skip entries defined in case control section. SKIPON turns on the skipping of lines. SKIPOFF turns off the skipping of lines. If SKIPON is defined but there is no SKIPOFF, the all the entries after SKIPON and until BEING BULK will be skipped.

SKIPON, SKIPOFF are only relevant for case control section of data. They will be ignored, if defined in BULK entry.

Monitor Point Output - MONPNTi

MONPNT1, MONPNT2 and MONPNT3 are supported for Static analysis, as well as Aeroelasticity.

MONPNT1: Defines an integrated load monitor point at a point (x,y,z) in a user defined coordinate system. The integrated loads about this point over the associated nodes will be computed and printed.
MONPNT2: Element output monitor. Stress, Strain and Forces are supported. CBAR, CBEAM, CELAS1,CONROD, CBUSH, CWELD, CQUAD4, CSHEAR, CHEXA, and CTAXI elements are supported.
MONPNT3: Sum of grid point forces with respect to a user-defined point for a user-defined section.

Skip Degrees-of-freedom from AUTOSPC SPCOFF/SPCOFF1

SPCOFF/SPCOFF1 defines degrees of freedom which will be skipped from AUTOSPC.

HDF5 Enhancements:

CSHEAR force output: CSHEAR element force output is now available.
Frequency Response and Random response: Complex displacement and SPCFORCE, PFPANEL results are supported for Frequency Response. PSD/RMS Disp/Velo/Accel/SPCF and RCROSS results are supported for Random Response.

Graphical User Interface (GUI):

Altair Compute Console (ACC) GUI to submit jobs: With this release, a new utility is included called Altair Compute Console (ACC). It replaces individual menu entries for a group of Altair solvers (including OptiStruct, Radioss, MotionSolve, AcuSolve, HyperXtrude and several more). It is the easiest way to launch a solver on a local host or submit simple job to a remote Linux server/cluster or PBS system. It includes an interactive GUI for selecting input files, defining run options, submit multiple solver runs using a queue, schedule a delay, monitor solution progress, kill/pause a job, and provides easy way to execute Fluid-Structure Interaction (FSI) solution sequence for AcuSolve with OptiStruct and MotionSolve.

Resolved Issues

Applied Power calculation for Thermal convection is corrected.
MPC force output with LGDISP is inaccurate in text file output such as .pch or .mpcf.
Some Nonlinear Analysis restart job no longer fails with programing error when temperature loading is present.
Interlaminate Shear Stress for continuum shells (PCOMPLS) is correct.
GROUP option in DSIZE for MMO job no longer fails with programing error.
Stress results for normal modes analysis is correct when JOINTG is present in input file.
Sliding distance no longer is output as zero for continuous sliding (CONSLI).
.dens file no longer is created for topology optimization (even without user’s request).
Pretension force output in .pret file is corrected for DDM runs.
For asynchronous rotordynamics model with modal complex eigenvalue analysis, a programming error does not occur when there is more than one rotor speed and the number of desired complex eigenvalues (ND0 in the EIGC card) is left blank.
When there are multiple MATMDS Bulk Data Entries and dynamic analysis is performed (i.e. normal mode analysis), density was only used from the first MATMDS.
Reading issue no longer occurs when using op4 DMIG in residual run.
Slow performance of nonlinear transient calculation has been improved.
SPCF output is no longer incorrect, if CNTNLSUB points to the subcase ID.
The accuracy of Node-to-Surface (N2S) TIE/FREEZE for Linear analysis and the small displacement Nonlinear Analysis has been improved.
Advanced restart with overhang constraints or extraction constraints are enhanced to handle such use cases properly.
A programing error may occur when advanced restart with mode tracking is performed. This has been fixed.