# Constant Stiffness Model

The linear stiffness force is computed according to Hooke’s Law of Elasticity:

Where:

${k}_{i}$ is the constant stiffness value found in corresponding [CONSTANT_STIFFNESS_xx] block for the ${i}^{th}$ direction in the property file.

${q}_{i}$ is the displacement of Body-I relative to Body-J in the ${i}^{th}$ direction after offset, scaling and coupling effects have been considered.

The default value for ${k}_{i}$ is the slope of the experimentally measured static spline at (0,0).