Issues with Proportional Damping

Analytical derivation of damping is extremely difficult and in most cases not possible. As a result, damping properties are typically specified on a mode-by-mode basis because of the availability of test data that can be used either directly, or can be used as a guide for similar systems for which data are not yet available. Occasionally there is need to develop from the modal damping properties damping matrices that correspond to the physical coordinate sets in which the finite element model mass and stiffness matrices were developed. Proportional damping, in which combinations of mass and stiffness matrices are used to develop the physical coordinate damping matrix, has been used extensively. It is the purpose of this work to discuss the appropriateness of including a mass proportional term. It is concluded that damping formulations that include a scaled mass term are fundamentally flawed and should not be used.