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The stability characteristics of a hinged beam subjected to a dynamic moment is investigated. The moment is proportional to the curvature of the beam at some point along its length. The stability investigations are carried out using a Galerkin approximation, both in the presence and absence of external flow. In the absence of external flow, stability is lost through divergence and flutter depending on the location of the point of measurement of curvature and the sign of the applied moment. In the presence of external flow, additional terms are introduced in the dynamic model. This alters the mechanism of flutter, reduces the value of the parameter at the critical point, and changes the nature of oscillations from standing waves to traveling waves.

Aquatic animals commonly oscillate their fins, tails, or other structures to propel and control themselves in water. These elements are not perfectly rigid, so the interplay between their stiffness and the fluid loading dictates their dynamics. We examine the propulsive qualities of a tail-like flexible beam actuated by a dynamic moment over a range of frequencies and flow speeds. This is accomplished using the equations of fluid-immersed beams in combination with a set of tractable expressions for thrust and efficiency. We solve these expressions over the velocity-frequency plane and show that the flexible propulsor has regions of both positive and negative thrust. We also show the behavior of a sample underwater vehicle with fixed drag characteristics as an illustration of a realizable system.