The Flow-induced Vibration Analysis Of Microstructure Turbulence Profiler

The micro-scale turbulence is responsible for dissipating the kinetic energy inthe ocean, and it is important to calculate the dissipation rate of turbulence kineticenergy and construct the ocean models. The freely falling microstructure profiler (i.e.vertical profiler) is the most common and effective platform for measuring themicro-scale turbulence. The flow-induced vibration (FIV), which is unavoidableduring the microstructure profiler freely falling, is the decisive factor for the low enddetection limit of the dissipation rate of the turbulence kinetic energy measured bythe profiler. The FIV is also critical for modifying the velocity spectra of verticalshear, and has bad influence on accuracy of the turbulence measurement. Therefore,the knowledge of the FIV is essential for designing and applying the vertical profiler,especially for deep-sea profiler.At present, studies on the FIV of the vertical profiler mainly depend on watertests, in which, the FIV of the profiler is obtained by analyzing the acceleration datameasured by the acceleration sensor mounted on the profiler. However, it costs muchtime, human and material resources through water tests to obtain the FIV. In order topromote the study of FIV of the profiler and, we try to find a convenient,unexpensive and effective method to calculate the FIV of the profiler. Using thismethod, the law of FIV of the profiler can then be obtained. The present studies willprovide theoretical guidance for designing of the profiler. Achievements of this paperare as follows:(1) Proper oscillation center is the prerequisite of calcalute the FIV of theprofiler accurately. In this thesis, combining rigid body dynamics with fluiddynamics, the oscillation center of the free falling microstructure profiler wasdetermined during its sinking in water.(2) Focused on the vertical microstructure profiler developed by TianjinUniversity, a fluid-solid interaction (FSI) model was constructed to calculate the FIVof the profiler by using the UDF (user defined function) in the soft platform ofANSYS–WORKBENCH. The vibration velocities and displacements of the profilercan be obtained through the constructed FSI model, and the vibration frequency and the vibration acceleration can then be calculated. Through sea tests, the FSI modelwas validated to be feasible and accuracy.(3) Using the proposed FSI method, the effects of moment of inertia, distancebetween center of gravity and center of buoyancy and sinking velocity of the profileron the FIV of the profiler were discussed. The frequency and acceleration of the FIVwere formulated by the influencing factors, such as moment of inertia, distancebetween center of gravity and center of buoyancy and sinking velocity of the profiler.The developed formula were proved to be accurate for predicting the FIV of theprofiler by sea tests.