THE DECAY OF SLOW VISCOUS-FLOW

A weak force acts within a viscous fluid for a finite time leading to a slow flow with negligible viscous effects; the force then ceases so that the fluid returns steadily to a state of rest under the action of diffusion. In the model developed, the force is equivalent in time to a delta function mathematically, having the form of a pulse physicall y; singular solutions such as rotlets and stokeslets are introduced to simplify the calculations and their use can be justified as represent ing solid bodies. Here we solve the transient Stokes flow equations to find the behaviour in a number of different situations, the rates of decay are computed, and the nature of the final motion described. A nu mber of general conclusions are deduced from these examples.