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Loads and Dynamics 77
Loads and structural dynamics is a specialty branch of structural and mechanical engineering that deals with the determination of the vibration response of a structure subjected to dynamic (time varying) forces in its operational environment. In aerospace applications dynamic loads include applied forces such as wind forces, mechanical and pyrotechnic shock, acoustic pressures, engine or rocket thrust, plume impingement forces, aerodynamic fluctuating pressures, control system forces, and contact forces. In dynamic analysis the structural response may be determined as the frequencies and mode shapes of vibration, and the time histories or frequency response spectra of displacement, velocity, acceleration, internal force, or stress. Dynamic analysis can be performed by classical methods (closed-form solutions or formulae, and hand calculations) or by a number of modern numerical methods such as Finite Element Analysis (FEA), Boundary Element Analysis (BEA), and Statistical Energy Analysis (SEA). The magnitude of the responses of concern may span from millions of pounds as in a launch vehicle internal load to micro-g''s as in an on-orbit experiment vibration environment.