Fluid structure interaction

In this work, we use the immersed boundary method with four extensions to simulate a moving liquid–gas interface on a solid surface. We first define a moving contact line model and implements a static-dynamic friction condition at the immersed solid boundary. The dynamic contact angle is endogenous instead of prescribed, and the solid boundary can be non-stationary with respect to time. Second, we simulate both a surface tension force and a Young’s force with one general equation that does not involve estimating local curvature. In the third extension, we splice liquid–gas interfaces to handle topological changes, such as the coalescence and separation of liquid droplets or gas bubbles. Finally, we resample liquid–gas interface markers to ensure a near-uniform distribution without exerting artificial forces. We demontrate empirical convergence of our methods on non-trivial examples and apply them to several benchmark cases, including a slipping droplet on a wall and a rising bubble.

Flow in the inverted U-shaped tube of a conventional siphon can be established and maintained only if the tube is filled and closed, so that air does not enter. We report on siphons that operate entirely open to the atmosphere by exploiting surface tension effects. Such capillary siphoning is demonstrated by paper tissue that bridges two containers and conveys water from the upper to the lower. We introduce a more controlled system consisting of grooves in a wetting solid, formed here by pressing together hook-shaped metallic rods. The dependence of flux on siphon geometry is systematically measured, revealing behaviour different from the conventional siphon. The flux saturates when the height difference between the two container’s free surfaces is large; it also has a strong dependence on the climbing height from the source container’s free surface to the apex. A one-dimensional theoretical model is developed, taking into account the capillary pressure due to surface tension, pressure loss due to viscous friction, and driving by gravity. Numerical solutions are in good agreement with experiments, and the model suggests hydraulic interpretations for the observed flux dependence on geometrical parameters. The operating principle and characteristics of capillary siphoning revealed here can inform biological phenomena and engineering applications related to directional fluid transport.

In this work a finite arrays of bottom hinged flap-type wave energy converters are modeled using a numerical approach. The converters are similar to the ones from Aquamarine Power, which is called Oyster and we use ANSYS-AQWA as a software for numerical simulation. The goal of this study is to optimize the annual energy absorption of a farm depending on the lateral and vertical spacing between converters based on a wave-spectrum case study. By design of some tests, the ability of ANSYS-AQWA is probed for modeling the hydrodynamic interactions of wave energy converters (WEC) in a farm. In order to obtain the acceptable results from the tests and validate the software abilities, three different layouts are presented for the farm. The performances of converters are studied in each layout and later on the layout with appropriate spacing and power-take-off systems (PTO) is chosen in order to maximize the farm annual energy absorption. Our results show that variation in the lateral spacing (perpendicular to the wave direction) of the converters changes the energy absorption slightly and the shape of energy diagram and its peak period remain the same. However, changing the vertical spacing (parallel to the wave direction) of the converters dramatically affects the energy absorption as well as the peak period of energy diagram.