Response Of Elastic Structures Research Articles

Recent Contributions Under the Bureau of Ships Fundamental Hydromechanics Research Program

The third main nautical objective, Seakeeping, refers to that aspect of ship performance in which the seaway enters in a dominant manner and affects fundamentally the character of the problem. In the section on Control [3],1 a pattern was introduced according to which seakeeping was related to the uncontrolled as well as the controlled oscillations which take place with reference to a ship's inertial system. But, more broadly speaking, seakeeping includes all of the following subjects:Description of the seaway.Determination of the forces imposed by the seaway on the vessel—the excitation (hydrodynamic loadings, wave bending moment, slamming forces, and so on).Determination of the response of the ship in her six degrees of freedom (ship motions).Prediction of the perils to which a ship may be exposed (capsizing, foundering, safety at sea).Prediction of the loss in speed she will sustain in heavy weather.Evaluation of the amount of stabilization necessary to prevent unacceptable or undesirable displacements and accelerations. The elastic response and strength of a vessel's structure, though not included under seakeeping, depend, nevertheless, in an essential manner thereon.

Dynamic Elasto-Plastic Response of Rigid Frames

The procedure for determining the elastic response of structures to transient loads in terms of the elastic normal modes is well known. Assuming ideal plasticity, Bleich and Salvadori recently proposed a method for obtaining the response beyond the elastic range in terms of elasto-plastic normal modes. They applied the method to free-free beams acted on by impulsive loads. In this paper, the method of Bleich and Salvadori is applied in general to two hinged and fixed rigid frames acted upon by a time dependent concentrated force at the knee and in particular to a two hinged frame (for which the elastic normal modes are known) and a linearly decaying forcing function.