Gravity and Base Excitation
Gravity is a global feature that applies forces to all features in the physics interface having a density, mass, or mass distribution. The gravitational force acts in a fixed spatial direction eg. Consider a domain feature having a density of ρ, the gravitational force is
where g is the acceleration of gravity. The default value of g is the earth’s standard acceleration of gravity, having the value of g_const = 9.8066 m/s2.
Base excitation is similar to gravity, but has two distinct properties: The sign is reversed (the acceleration of the foundation is given) and it defines variables for the global, room fixed, accelerations.