Scanning currents in stokes flow and the efficient feeding of small organisms

The feeding behaviour of many small, free swimming organisms involves the creation of a scanning current by the coordinated movement of a group of appendages. In this paper, we study the generation of scanning currents in Stokes flow in a number of simple models, utilizing the movement of Stokeslets, spheres, or stalks to set up an average scanning drift in a suitable far field formulation. Various mechanisms may then be classified by the rate of decay at infinity of the mean scanning current. In addition, optimal scanning can be investigated by minimizing the mean power required to create a current of prescribed amplitude. The simple mechanisms for scanning described here provide a framework within which the appendage movements of small aquatic organisms can be analysed and the relative merits of scanning and swimming strategies can be investigated.