Mechanical multiphase vibratory phenomena at very low mass ratios

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Flow-induced vibrations occur inevitably when fluid flow interacts with structures or other fluids. Cables and plant leaves excited by winds, two-phase flows in pipes and boilers and water waves are just but a few examples of self-excited vibrations or instabilities. Flow-induced vibrations can be harmful leading to structural failures or can be used wisely to extract energy. Undoubtedly, it is important to study, characterize and even find models to better understand and control their effects. Our research will provide theory and tools to solve fundamental aspects of flow-induced vibrations. The proposed research program focuses on essential unanswered problems that are not handled adequately by present commercial numerical solutions and difficult to apprehend experimentally only. We will develop and use innovative numerical methods to study multiphase mechanical problems with very low mass ratios and highly deformable boundaries. The proposed research program aims at studying the physics of three unanswered mechanical problems that are both fundamental and vital for the industry. A first axis on bubble rise in stagnant water will provide answers about what makes equal volume bubbles rise slow or fast (by a factor of 3!). We will characterize the modal content of bubble deformations and bubble-wake interaction dynamics. A second axis on the universal cap of vortex-induced vibration amplitude will further reinforce design guidelines especially for the low mass ratio encountered in subsea applications. A third axis on rotational and torsional galloping of non-circular cylinders in crossflow will contribute to improve rotational galloping modeling and design practice. These fundamental vibrational phenomena are characterized by large displacements and deformations induced by boundary dynamics in 3D. To achieve these goals, we will develop new algorithms and improve our fully coupled monolithic Arbitrary Lagrangian-Eulerian computational strategies based on finite and spectral elements. We will perform specific experiments to define initial conditions in simulations and validate theories or numerical observations. Our research will thus result in new tools for engineering, design guidelines and scientific knowledge. It offers excellent chances of success because it will fill needs in understanding, modeling and existing procedure improvement engineers need.