Study on hydrodynamic characteristics of a towed vehicle

A depth, pitch and roll controllable towed vehicle `Flying Fish' is being developed to measure the ocean current, temperature, salinity, dissolved oxygen, pH, turbidity, chlorophyll and total inorganic hydrocarbon. Field experiments on the performance of Flying Fish began in 1994. The control system used in these field experiments is designed based on the PID controller theory because the parameters in the PID controller are easily modified to correspond with conditions of the hardware. The hardware of Flying Fish was decided on field experiments conducted in 1996, and an even more advanced control scheme will be designed to obtain more accurate motion control beginning in 1997. For this we need a more precise model for the dynamics of Flying Fish. A series of model tests were carried out in an experimental tank using a 1/5 scale model to obtain hydrodynamic coefficients for the numerical model. The hydrodynamic coefficients were estimated based on the wing theory and the slender body theory and a regression analysis was made using the data from field experiments. Numerical simulations using hydrodynamic coefficients obtained from these methods were compared with the results of field experiments.