| 講演要旨： |
In nature, many phenomena involve interactions between flexible bodies and their surrounding viscous fluid, such as a swimming fish or a flapping flag. The intrinsic dynamics is complicate and not well understood. A flexible filament can be regarded as a one-dimensional flag model. Many similarities can be found between a flapping filament and a swimming fish, although different wake speed results in a drag force for the flapping filament and a propulsion force for the swimming fish. In the present study, we propose a new immersed boundary formulation for swimming filaments immersed in a viscous fluid flow. Fluid motion is governed by the Navier-Stokes equations and a momentum forcing is added in order to bring the fluid to move at the same velocity with the immersed surface. A flexible inextensible filament model is described by another set of equations with an additional momentum forcing which is a result of the fluid viscosity and the pressure difference across the filament. The momentum forcing is calculated by a feedback loop. Simulations of several numerical examples are carried out, including a hanging filament which starts moving under gravity without ambient fluid, a filament swimming within a uniform surrounding flow, and flow over two side-by-side filaments. The numerical results agree well with the theoretical analysis and previous experimental observations. The present numerical method is extended to simulate the locomotion of an elongate fishlike body. The motion of the centerline of body is governed by the same equations as the flexible filament. The positions of surface points are determined by the centerline. Swimming in the wake of a bluff body is simulated to compare with the experiment. It is found that the fishlike body flaps at the same frequency as the vortex shedding from the bluff body. The thrust force is obtained by exploiting the vortices without exerting any active muscle force. |
