# Analysis Techniques

The Analysis Techniques section provides an overview of the following:

The Analysis Techniques section provides an overview of the following:

**Parts and Instances**

The Parts and Instances functionality can be used to combine independently created substructures (or, parts) into a single model.**Subcase Specific Modeling**

Subcase specific modeling allows analyzing multiple structures in a single solver run.**Global-Local Analysis (Submodeling)**

Global-local analysis is a technique in which a full model is solved using two (or more) submodels; one submodel represents the full structure but at a lower accuracy (for example, a larger mesh size) and the second submodel represents only a part of the structure (for example, using a smaller mesh size).**Internal Superelements**

Superelement or DMIG (Direct Matrix Input) approach is a known industry standard to efficiently reduce out the user-defined components to the specified interface grids and this method helps improve the performance of finite element analysis when used properly.**Direct Matrix Input (Superelements)**

The Direct Matrix Input (Superelements) section provides an overview of the following:**Flexible Body Generation**

**Poroelastic Materials (Biot theory)**

Poroelastic materials can be used to model coupled fluid-structure systems where the fluid exists within the interstitial spaces of a porous solid.**Prestressed Linear Analysis**

Preloaded or Prestressed Linear Analysis is any type of structural linear analysis performed on a structure under prior loading (also termed preloading or prestressing).**Pretensioned Bolt Analysis**

Many engineering assemblies are put together using bolts, which are usually pretensioned before application of working loads.**Imperfection**

Imperfection is used in large displacement nonlinear static analysis, for example, to solve post-buckling problems combined with the arc-length method, among other techniques.**Cohesive Zone Modeling**

Cohesive zone modeling can be used to model adhesive and bonded interfaces and corresponding crack initiation and propagation.**Symbolic Substitution**

Symbolic substitution provides flexibility to modify the input file to use parameterized input to define various data fields across the model.**Cyclic Symmetry Analysis**

Cyclic symmetry is a type of symmetry in which a representative (or basic) segment, if patterned circularly about an axis of symmetry would result in the full model.**Thickness Mapping**

The thickness mapping feature allows the user to map the thickness data from an external forming result file to the corresponding model in OptiStruct.**Modeling Errors**