Added-Mass and Viscous-Damping Forces Acting on Various Oscillating 3D Objects

In many fluid-structure-interaction problems, the “added mass”, “inertial mass”, “virtual mass”, “carried mass” or “induced mass” is one of important interests. In the present study, the authors propose a simple and efficient method to specify fluid-force coefficients of an oscillating object in stationary fluid. In this method, the authors consider incompressible-and-viscous fluid under the assumption of an infinitesimal oscillation amplitude of a three-dimensional object, and properly modify the Navier-Stokes equations into linear equations, namely, the Brinkman equations. The solving method is based on a discrete singularity method, one of the boundary methods. Furthermore, the authors conduct experiments, in addition to computations. In order to confirm the method’s effectivity and validity, the authors compute a sphere, comparing our computations to theories and experiments which show good agreement.

A New Computational Method for Dynamic Behaviour of Two-Dimensional Free Surface

A new method is proposed in order to compute dynamic behaviours of a liquid free surface. The method is based on a discrete singularity method, and enables us to simulate sloshing problems very easily and efficiently. The authors consider the free surface in a two-dimensional rectangular container that is vibrated vertically. It was found that there is the optimum clearance of singularity from a boundary, which makes surface error minimum. Furthermore, the authors conducted some experiments, and have observed three sloshing modes, and their stability regions. Then, we confirm that for the method is effective for 2D-sloshing problems.

An Approximate Method for the Drags of Two-Dimensional Obstacles at Low Reynolds Numbers

We propose a new simple method of computing the drag coefficients of two-dimensional obstacles symmetrical to the main-flow axis at Reynolds numbers less than 100. The governing equations employed in this method are the modified Oseen’s linearized equation of motion and continuity equation, and the computation is based on a discrete singularity method. As examples, simple obstacles such as circular cylinders, rectangular prisms, and symmetrical Zhukovskii aerofoils are considered. And it was confirmed that the computed drags agree well with experimental values. Besides optimum shapes of these geometries, which minimize the drag coefficients, are also determined at each Reynolds number.