Intermarine (Italy)

The topic of this paper is the modeling, parameter identification, and analysis of the heave and pitch dynamics in a remote operated vehicle (ROV). The work presented here is motivated by an unusual dynamic behavior experienced on the Gaymarine Pluto-Gigas ROV: if the depth is regulated using a proportional controller, the ROV exhibits permanent oscillations at high forward speed. The purpose of this paper is to gain insight into ROV dynamics, so as to explain the reason for the oscillations. To this end, a dynamic gray-box model is developed and its uncertain parameters are identified from real data. The analysis of such a model shows that the nonlinear dynamics of the ROV contains a limit cycle. This discovery explains the observed oscillatory behavior. An interesting aspect of this limit-cycling behavior is that it is not due (as usual) to saturation effects of the actuators, but is intrinsic in the ROV dynamics.

Improvement in river transport requires adopting more efficient towboat propellers. This paper summarizes the design and towboat trials of a new semi-Kaplan propeller with an unconventional pitch distribution. A comparison of towboat trip records shows that operation with semi-Kaplan propellers resulted in improvements over operations with conventionally designed propellers. These improvements included a 13.5 percent increase in barge mpg of fuel and a 10 percent increase in tow speed. The trials with the semi-Kaplan propeller indicated only a small increase in towboat vibration levels. The adoption of this new propeller has potential for improving present river transport.