Altair OptiStruct 2026 Release Notes

New Features

Stiffness, Strength, and Stability

FASTCONT support for plane stress and plane strain elements: FASTCONT is now supported for plane stress (CQPSTS) and plane strain (CQPSTN) elements. Available for implicit analysis with PPLANE contacts.
New integrated beam section types available in PBEAML: L and TUBE sections are now available in integrated beam formulation via PBEAML. They are available in implicit (only nonlinear) and explicit analysis.
Retain deformed structure from enforced displacement with CNTNLSUB and apply additional load: The new Bulk Data Entry SPCF can be used to retain the deformed structure from a previous subcase. This feature also allows the application of additional load in a continuation subcase to degrees of freedom for which enforced displacement was applied in the preceding subcase. Similar to FORCE and SPCD, the set ID of SPCF can be specified in the subcase information section either directly using the LOAD entry, or indirectly through Bulk Data Entries such as LOADADD, TLOAD1/2. This feature is available only for nonlinear implicit analysis.
New CYCSET card available to define TIE-contact based cyclic symmetry: The CYCSET Bulk Data Entry is now available to define surface pairs for TIE-contact based cyclic symmetry boundary constraints. This is only supported for cyclic symmetry analysis and can be helpful when the secondary and main surfaces do not have the same number of nodes. Supported analysis types include linear static (STATIC), normal mode analysis (MODES) and implicit nonlinear (NLSTAT & NL-DTRAN) analyses. Prestressed analyses are supported with STATSUB(PRELOAD).
New option available in CFASTG to select all surfaces in a model: The new keyword ALL following the keyword SURF on CFASTG entry can be used to conduct a global search and automatically select the surfaces in a model to be connected with CFASTG elements.
Temperature-dependent CBUSH for implicit nonlinear analysis: The TIDs on KN continuation line on PBUSHT can now reference TABLEMD tables which provide temperature-dependent force-displacement (or temperature-dependent moment-rotation) data for Implicit Nonlinear Analysis.

Explicit Dynamics Analysis

Contact moment output now supported in explicit analysis: Contact moment output is now available for explicit analysis in the .cntf file. You can define the reference point (REFPOINT) field with Grid ID, CENTER, ORIGIN, or coordinate input options using the MNTREF continuation line on the CONTACT Bulk Data Entry. The coordinate system (CID) in which the resultant force/moments are output can also be defined. This is supported for both implicit and explicit analysis.
CELAS1/2 now supported in explicit analysis: CELAS1/2 elements defined along with PELAS or PELAST are now supported in explicit analysis.
New option for filtering explicit analysis results: Time history (THIST output) filtering can be applied to an explicit analysis output to remove any high frequency noise and possibly reduce the size of output files by only saving data below a specified cut-off frequency. On the new FILTER entry, an exponential filter and three types of Butterworth filters are currently available. Applicable only for explicit analysis.
MPCFORCE in explicit analysis: MPCFORCE result can now be requested for explicit analysis in H3D format.
Rigid analytical surface can now be defined for explicit analysis: Rigid analytical surfaces can now be defined for an explicit analysis using RSURF Bulk Data Entry. The TYPE on the RSURF entry can be defined as either a PLANE or a SPHERE. This rigid surface can be fixed in space or given a motion. It has many applications, such as representing the floor, impacting surface, and so on. This feature also simplifies the model setup. Applicable only for explicit analysis.
New Bulk Data Entry MATARU available to define advanced properties for adhesive materials: The new MATARU Bulk Data Entry can be used to define parameters required for modeling an elasto-plastic, rate-dependent failure in an adhesive material. The material model is similar to MCOHED until yield and then the behavior is different. MATARU should be referenced on the PCOHE entry which is referenced on the CIFHEX/CIFPEN elements. PCOHE defines the adhesive thickness. Applicable only for explicit analysis.
Initial and current nodal mass now available in HyperView: Initial nodal mass and current nodal mass contours are now available in HyperView by default for an explicit analysis.
PLASTIC strain results are now supported for explicit analysis: PLASTIC strain tensor results, that is, STRAIN(H3D,PLASTIC,PLASTIC=YES)=ALL, can now be requested for an explicit analysis. They are output to the H3D file.
STATSUB(PRETENS) can now refer to an explicit subcase: STATSUB(PRETENS) is now supported for explicit subcases, that is, it can refer to an explicit analysis subcase with pretensioning applied.

Noise and Vibration

MFLUID in response spectrum analysis now supported: MFLUID is now available for response spectrum analysis.
Rigid response and missing mass response are now available in response spectrum analysis: Rigid response can now be calculated in response spectrum analysis by setting the RIGRESP field on RSPEC Bulk Data Entry to GUPTA or LINDLEY. For the missing mass response, field 5 on the RSPEC entry should be set to MMASS.
Statistics output is now available for frequency response analysis: Statistics output is now available via STATIS/OSTATIS options for DISPLACEMENT, VELOCITY, ACCELERATION, STRESS, and STRAIN results in frequency response analysis.
Neuber correction is now supported for response spectrum analysis: Neuber correction output for stress and strain results is now supported for a response spectrum analysis.
EIGKE output support for complex eigenvalue analysis: EIGKE output can now be requested for a complex eigenvalue analysis. If the NORM field on the EIGC entry is set to a different option (except MASS), it is automatically reset to MASS if EIGKE output request is present and a corresponding WARNING is printed in the .out file.
MOTNJG for normal modes analysis: MOTNJG is now supported for normal modes (MODES) analysis with zero valued motion. If a non-zero value is specified on MOTNJG for normal modes analysis, it is automatically reset to zero. Multiple subcases can reference different MOTNJG but the motion should be applied on the same joint degrees of freedom.
Strain energy proportional damping output is now supported for CBUSH element: Damping coefficient for strain energy proportional damping output can be specified via the ESDAMP continuation line on PBUSH property for CBUSH elements. The strain energy proportional damping output is then output to the .esdamp file if OUTPUT,ESDAMP is specified in the input file.
Frequency dependent NSGE and MATF1 with FASTMATF: Frequency dependent NSGE (NSGEF entry) and MATF1 can now be defined on the same element along with the fast process for frequency-dependent material (via FASTMATF). FASTMATF can be used in the I/O Options section to control the fast process for frequency dependent materials in modal dynamic analysis.
Section force resultant for response spectrum analysis: Section forces are now available in OPTI format and are printed in the <filename>.secres file for response spectrum analysis.
Enhanced mode tracking for flutter can now be enabled via PARAM, MDTRKFLT: Enhanced mode tracking for flutter analysis can now be enabled via PARAM, MDTRKFLT. Various approaches are available for tracking, and these approaches can be selected through options 1 to 4 on the PARAM card. The available approaches are eigenvalue-extrapolation, Normalized Cross Complex Orthogonality (NC2O), Modal Assurance Criteria in modal space (MMAC), and Slope Continuity (SLCON) approach.
Interior fluid response recovery with PFPATH is now supported using CDS superelement: Fluid grid set is now supported as part of CSET for CDS superelements. This can be used for interior fluid response recovery with PFPATH. PEAKOUT is currently not supported for the internal fluid DOF.

Optimization

Advanced restart for level-set optimization: Advanced restart is now supported for level-set optimization. Similar to regular topology optimization, DOPTPRM, TOPDV, and DOPTPRM TOPRST, ADVNOR must be defined for advanced restart of level-set optimization. This allows also for the restart of level-set optimization with a finer mesh.
Plane stress and plane strain elements now supported in topology and free shape optimization: CTPSTS (plane stress) and CTPSTN (plane strain) elements are now supported in topology, free shape, and free size optimization. This support is particularly useful for testing mechanical reliability analyses of electric motors where the motors are modeled using plane stress and plane strain elements.
Element based responses can now be defined with PTYPE as SET in DRESP1: Various response types such as mass (fraction), volume (fraction), center of gravity, moment of inertia, and static compliance can now be defined with PTYPE = SET and ATTi referring to a SET ID on the DRESP1 Bulk Data Entry.
Energy result for each outer loop iteration now available for DiESL: Energy result for each outer loop iteration is now printed in individual files containing file extensions named with iteration numbers such as _iter01, _iter02 and so on; for example: xyz_expl_energy_iter01.mvw or xyz_s1_iter01_e.expl. Only applicable for DiESL runs.
Transient powerflow optimization via the ESL method: Transient powerflow optimization is now supported through the ESL method. A new response type TRFLOW is added to target the transient powerflow. This response applies to a SECTION and multiple TRFLOW responses can be defined. Multiple transient loadcases are supported, with their own TRFLOW responses. Additional loadcases can be used alongside the transient loadcases. TRFLOW responses can be referenced in DRESP1 and DRESP2 responses.
Contact clearance response: A new contact clearance response (normal distance between surfaces) is now available on the DRESP1 entry. It can be activated via the CNTC option for RTYPE. PTYPE should be set to CONTACT (similar to CNTP and CNTF responses). ATTI is the Contact ID number. The CONTACT Bulk Data Entry has a new TYPE option called GAUGE. This option allows gaps that are always open to only measure clearance without affecting the analysis when using the CNTC response.
Automatic mesh refinement for topology optimization: Automatic mesh refinement is now available for topology optimization. This allows the generation of more detailed results and also significant improvements in performance. Coarse meshes can be used at the beginning and they are automatically and iteratively refined based on the topology design progress. This is currently supported for CHEXA and CTETRA elements. It can be activated using the REMESH continuation line on the DTPL Bulk Data Entry. Additional control via the REFTYPE, LB and UB fields are available. Three parameters, namely DOPTPRM, REFMEMAX (number of refinement runs), DOPTPRM, REFMERST (control density source), and DOPTPRM, REFMEAUG (control of augmentation of automatically identified refinement regions) are available for additional user control.

General

MOTNJG to apply motion to a SET of JOINTGs

MOTNJG can now be used to apply motion on a set of JOINTGs instead of one JOINTG. This can be done using keyword SET, which indicates that the corresponding JID refers to an element set containing a set of JOINTG entries. MOTNJG with JID and SET is supported for both implicit and explicit analyses.

Linearized system of state-space matrices (ABCD matrices)

Linearized system of state-space matrices can now be directly generated from OptiStruct using the OUTPUT,STATESPACE,SET1,SET2,SET3 entry for a CMSMETH CBN superelement generation run. The SET1, SET2, and SET3 are GRID or GRIDC sets corresponding to the displacement, velocity, and acceleration output sets. Input degrees of freedom are based on ASET DOFs. A <filename>.oml file is generated from the run which contains the ABCD state-space matrices and can be subsequently used to conduct further analysis, such as control system analysis in tools such as Altair Activate.

Coordinate-based input now available for RELOC

Coordinates-based input is now supported for the RELOC Bulk Data Entry. This type of input can be provided using four new TYPEs of RELOC: MOVEC, ROTATEC, MIRRORC, and MATCHC. Supported for both implicit and explicit analysis.

New SET option to create a set of exterior elements/grids

A new SUBTYPE called EXTER on the SET Bulk Data Entry provides an option to create a set of elements/grids only on the exterior of a model. This keyword can be applied to TYPE of GRID or ELEM in SET. The following continuation line must contain IDs corresponding to existing SETs of grids/elements. This allows finer control of results contouring wherein results can be output only for exterior elements/grids. ISOL is another new keyword in the field OPTION1 used along with EXTER on the SET entry. ISOL can be used to indicate that the provided SETs need to be treated in isolation irrespective of the remainder of the model. In the case where both EXTER and ISOL are mentioned, the exterior surface is the exterior of the isolated component only. Applicable for both implicit and explicit analysis.

ACMFORCE can now be used to request force results at ACM elements

The new ACMFORCE Subcase Information Entry can now be used to request force results on the ACM elements in area contact method for spot weld analysis. Additionally, PARAM,ACMFOSYS,1/2 can be defined to output the results in the conventional OptiStruct beam coordinate system or in the local coordinate system. ACMFORCE output is available in OPTI format (.acmfrc file) for static analysis, direct transient response analysis, and modal transient response analysis.

Nonlinear restart run can now include GRAV, RFORCE, and PLOAD4 Bulk Data Entries

Traditional and enhanced nonlinear restart runs can now include GRAV, RFORCE, and PLOAD4 Bulk Data Entries. The restart functionality is currently supported for nonlinear implicit analysis.

Non-structural mass definition, LOADJG, and MOTNJG now available in Part and Instance (PI) modeling

Non-structural mass can now be defined via a number of non-structural mass Bulk Data Entries, that is, NSM, NSM1, NSML, NSML1 and NSMADD for a list of elements or properties in Part and Instance (PI) modeling. Non-structural damping for a list of elements or properties is also supported now via NSGE and NSGE1 in PI modeling. Additionally, load and motion application on joint connectors is now supported via LOADJG and MOTNJG respectively. For instance, JOINTG ID on MOTNJG entries can now reference fully-qualified IDs. Applicable to all types of analyses except optimization.

ASSIGN, HFILE for mapping density from Polyfoam .h3d file to current grid

ASSIGN, HFILE can be used to map elemental temperatures from a PolyFoam .h3d file to the current mesh grids using the TEMPT Bulk Data Entry in combination with the TEMP Subcase Information Entry.

ASSIGN, H3DRES for mapping density from Polyfoam .h3d file to current mesh.

ASSIGN, H3DRES can be used to map elemental density from Inspire Polyfoam .h3d result file to the current mesh through the MATUSR Bulk Data Entry via the FIELD continuation line. Inclusion of the FIELD continuation line indicates that the “nprops” variable in the usermaterial subroutine includes the total number of properties defined via the PROPi fields, and, additionally, it includes the number of thermal expansion parameters and the density. So with the FIELD continuation line on MATUSR, both the thermal expansion and density (from PolyFoam .h3d file) are accessible to the user-defined material subroutine.

SCALE and OFFSET for curve definition

Scaling a curve or defining an offset for a curve is now supported via SCALE and OFFSET continuation lines on multiple curve defining table entries such as TABLEG, TABLEM1, TABLED1, TABLES1 and TABDMP1. Applicable for the analysis types for which the table entries are supported.

Property/material ID search control in Parts and Instances

Property or material ID searching option for local part or global part is now available via SYSSETTING(PIRENUM=LOCAL/GLOBAL). When the option is set to LOCAL, the search starts from local part first and, if not successful, the search continues to the global model. This is most useful when same material or property ID are used in local part and also in the global model.

Input file list now printed by default

By default, the complete list of input files is now printed in ASCII format in the <file_name>.files file and in HDF5 format in <file_name>.h5 file. This list includes input files assigned via INCLUDE and ASSIGN entries. The output file contains the file name, file size, a checksum string, and the timestamp.

Assign multiple temperatures from multiple external H3D files on multiple components

The ASSIGN keyword (referring to an ASSIGN,H3DRES entry) on the TEMP Bulk Data Entry can now be used to assign multiple temperatures to multiple components/parts. Each component can have a SET defined, containing all grid points related to that component and the temperatures from the external H3D file can be assigned to these grid points. Multiple TEMPs can be defined with multiple ASSIGN IDs and the TEMPADD entry can be used to combine temperatures of all grids together.

Plastic strain CORNER results are now available on-the-fly

Plastic strain CORNER results for shell, solid, plane stress, plane strain and axisymmetric elements are now available in on-the-fly H3D format. Plastic strain CORNER results can be requested in VON, TENSOR and DIRECT formats.

GPFORCE output now supported for frequency response analysis with preloaded LGDISP analysis

GPFORCE results, including force calculations from preloaded LGDISP, are now supported for frequency response analysis.

Mid-plane strain and curvature output

A new option STRAIN(STRCUR) is now available which outputs mid-plane strains and curvatures, instead of the default top (Z1) and bottom (Z2) strain for shell elements. The default is now identified via STRAIN(FIBER). This is currently supported for linear static analysis and random response analysis.

CONVG free convection enhancement

For transient heat transfer analysis, the following data precedence now applies in CONVG input:

Ambient temperature: If both TEMP_AMB and TID_AMB are specified, the time-dependent TID_AMB values are used.
Heat Transfer Coefficient (HTC): If both a constant HTC and a temperature- or time-dependent table (TID_HTEMP/TID_HTIME) are defined, the table data is used.

Resolved Issues

PSD/RMS Stress filtering for random response analysis is now correct.
Internal force is now properly recovered when nonlinear transient subcase is continued from nonlinear static analysis.
Correct results are now generated when multiple MATMDS material definitions are specified in the model.
A modal analysis preloaded with nonlinear large displacement analysis no longer crashes.
MFREQ with random response analysis with SPCD loading no longer shows degraded runtime performance in SPCDLCAL module.
An MMO model with DRESPM and DRESP2 both being referenced on a DRESP2 response no longer fails with an internal programming error. Various combinations of DRESPM, DRESP1, DRESP2, DRESP1L, and DRESP2L are now also supported.
The table headers in the .out and .effmass files no longer show REFERENCE POINT at ORIGIN of BASIC COORDINATE SYSTEM when a different Grid ID is defined as reference point on the MEFFMASS entry.
Non-zero SPCs defined via the SPCADD entry are now respected in cyclic symmetry analysis.
Zero or incorrect contact results (CONTF) are no longer output for TIE/FREEZE contact interfaces in explicit analysis.
A model no longer shows non-zero Contact Force/Traction for nodes belonging to open contact for S2S.
A model no longer fails with programming error for CMS generation analysis subcase preloaded with nonlinear static analysis with pretension.
ESDAMP results are now correct when AMSES is used and rotational displacements are required.
RBE3 in nonlinear large displacement analysis no longer shows non-zero SPCF for components that are not active.
Contact area for N2S CONSLI contact is no longer only calculated initially, it is also subsequently updated during the course of the analysis.