# OS-T: 8020 Divergence Analysis of an Aircraft

This tutorial demonstrates the divergence analysis of an aircraft.

Preprocessing is done using Altair HyperWorks in the OptiStruct user profile. A model with existing structural and aeroelastic data is used as a base model and this tutorial demonstrates the creation of entities specific to divergence analysis.

Divergence occurs in aeroelasticity when the deflection of lifting surfaces of an aircraft leads to additional lift that, in turn, leads to further deflection in the same direction. A divergence analysis determines divergence dynamic pressures which are square of eigenvalues from a direct complex eigenvalue analysis. The lowest eigenvalue correlates with the critical divergence dynamic pressure. Using the divergence dynamic pressures, the critical velocities are computed. Once determined, you can aim to avoid your system nearing this critical velocity and beyond.

- Create DIVERG entry
- Define complex eigenvalue related entries
- Submit the job
- View the results

## Launch HyperWorks and Import the Model

Refer to Access the Model Files for more details about obtaining the tutorial model file. The model file required for this tutorial is aeroelasticity_diverg.fem

## Open the Aeroelasticity Browser

The Aeroelasticity Browser is useful for upcoming tasks in this tutorial.

## Set Up the Model

### Create DIVERG Entry

### Create EIGC Entry

Divergence analysis determines the divergence dynamic pressures, which are the eigenvalues from a complex eigenvalue analysis. Hence, the EIGC Bulk Data Entry will be defined.

### Create Constraints

### Create Divergence Analysis Subcase

In this step, the previously created Bulk Data Entries will be referenced in the divergence analysis subcase.

## Export the Input File

In this step, the input file is exported to the working directory. This file is later solved using OptiStruct as the solver.

## Submit the Job

## View the Results

### View the Mode Shapes

### Review the Divergence Dynamic Pressures

The divergence dynamic pressures can be viewed from the aeroelasticity_diverg.out file.

By definition, divergence occurs when the roots of the Direct Complex Eigenvalue analysis have purely imaginary components.