# Modal Prestressed

Prestressed eigenvalue analysis is governed by:

$$\left(\overline{\text{K}}\text{\hspace{0.17em}}\text{+}\text{\hspace{0.17em}}\text{\lambda M}\right)\text{A}\text{\hspace{0.17em}}\text{=}\text{\hspace{0.17em}}\text{0}$$

Where,

- $\overline{\text{K}}$
- Prestress stiffness matrix
- $\text{M}$
- Mass matrix
- $\text{A}$
- Eigenvector
- $\text{\lambda}$
- Eigenvalues

Prestressed loadcases can be either linear or non-linear. All non-linearity types are supported.

Depending on preloading conditions, the resulting effect could be a weakened or
stiffened structure.

- If the preloading is compressive, it typically has a weakening effect on the structure (for example, column or pillar under compressive preloading).
- If the preloading is tensile, it typically has a stiffening effect (for example, rotorcraft blade under centrifugal preloading).