Biologists study on the biological behavior of various marine creatures in situ using underwater observation systems. However, darkness in an underwater environment is always one of the most difficult problems to overcome in order to clearly monitor the life of underwater creatures. In this research, a light-following scheme is proposed with the lighting device installed on a separate Pan/Tilt platform as a slave while the main Pan/Tilt camera platform works as a master. A dynamic model of Pan/Tilt platform was developed using the Lagrange’s equation. In order to achieve high speed manipulation of the Pan/Tilt platforms in underwater environment, hydrodynamic forces have to be considered. Scientists had done a great deal of researches on the hydrodynamic forces of underwater motion bodies. Most of the researches employed the semi-empirical equation based on the experimental study. The coefficients (Cd Cm) of drag and added-mass which were solved by experimental study were the research point of hydrodynamic modeling in previous researches. However, these modeling methods can be employed for the underwater bodies with the simple geometry dimension. Two hydrodynamic torque models which represent the degree of freedoms (DOFs) of panning and tilting respectively had been developed employing CFD software. The selection of turbulence models, i.e., K-E, K-W, SST, RSM and LES, was firstly accomplished using the case of turbulence flow over flat plane. The hydrodynamic torque models are obtained with the simulations results for a certain range of position and velocity values for each of DOFs. The maximum velocity for simulation was set at 60 rpm for each axis. The geometry model which represents the space relationship between the master (camera) and slave (light) and the control algorithms would be elaborated in a separate paper.

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