In the computation of multiphase flow with mass transfer, the large disparity between the length and time scale of the mass transfer and the fluid flow demand excessive grid resolution for fully resolved simulation of such flow. We have developed a subscale description for the mass transfer in bubbly flow to alleviate the grid requirement needed at the interface where the mass gets transferred from one side to the other.In this fluid dynamics video, a simulation of the mass transfer from buoyant bubbles is done using a Front Tracking method for the tracking of interface and a subscale description for the transfer of mass from the bubble into the domain. After the mass is transferred from the bubble into the domain, mass is followed by solving an advection-diffusion equation on a relatively coarse Cartesian grid. More detail about the method can be found in our paper [1]. This simulation shows 13 moving bubbles in a periodic domain,

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The International Energy Agency Technology Collaboration Programme for Ocean Energy Systems (OES) initiated the OES Wave Energy Conversion Modelling Task, which focused on the verification and validation of numerical models for simulating wave energy converters (WECs). The long-term goal is to assess the accuracy of and establish confidence in the use of numerical models used in design as well as power performance assessment of WECs. To establish this confidence, the authors used different existing computational modelling tools to simulate given tasks to identify uncertainties related to simulation methodologies: (i) linear potential flow methods; (ii) weakly nonlinear Froude–Krylov methods; and (iii) fully nonlinear methods (fully nonlinear potential flow and Navier–Stokes models). This article summarizes the code-to-code task and code-to-experiment task that have been performed so far in this project, with a focus on investigating the impact of different levels of nonlinearities in the numerical models. Two different WECs were studied and simulated. The first was a heaving semi-submerged sphere, where free-decay tests and both regular and irregular wave cases were investigated in a code-to-code comparison. The second case was a heaving float corresponding to a physical model tested in a wave tank. We considered radiation, diffraction, and regular wave cases and compared quantities, such as the WEC motion, power output and hydrodynamic loading.

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