Narrow Results

This paper proposes a novel tube model predictive control approach for dynamic positioning of autonomous underwater vehicles with state and input constraints. The cost function is selected as a mixture of weighted 1-norms and $\infty$-norms of states and inputs, which can be reconstructed into linear summation form. Specially, a method is presented to calculate the weighted matrix of the terminal cost so that closed-loop stability is achieved. The proposed control problem can be solved by linear programming, which provides high computational efficiency. Experimental results on “UVIC-I” AUV are conducted to validate the viability and validity of the presented method.

Based on the experimentally detected forces induced by internal solitary waves (ISWs), an analysis on capability of dynamic positioning (DP) for the semi-submersible platform model under the influence of different ISW-amplitudes with three kinds of ocean stratified conditions is carried out. The environmental forces acting on the semi-submersible platform arise due to the following two main components: the measurements of ISW-forces and calculations of the wind, currents and waves. Combined with quadratic programming (QP) methods, extreme safe amplitudes under different upper layer depths and the DP strategy are proposed. It is obvious from the experimental results that both the maximum and minimum horizontal ISW-forces increase linearly with the wave amplitudes under different layer thickness ratios, and the upper layer depth has a significant effect on the ISW-forces. Reference to the obtained results from the DP capability simulation reveals that the maximum thrust, with overloading, appears at heading angles of 90${}^{\circ }$ and 270${}^{\circ }$ under different upper layer depths, whilst the minimum thrust is under angles of 0${}^{\circ }$ and 180${}^{\circ }$.

This article presents a unified state-space model for ship maneuvering, station-keeping, and control in a seaway. The frequency-dependent potential and viscous damping terms, which in classic theory results in a convolution integral not suited for real-time simulation, is compactly represented by using a state-space formulation. The separation of the vessel model into a low-frequency model (represented by zero-frequency added mass and damping) and a wave-frequency model (represented by motion transfer functions or RAOs), which is commonly used for simulation, is hence made superfluous.

The traditional GNSS relative positioning precision test is unitary, so it is applied in limited scope. On the basis of analyzing linear combination of dual-frequency wide lane observation method of ambiguity solution and the traditional method of relative positioning precision test, the paper discusses the method based on the comparison of the real-time relative baseline-length between two vehicles. Precision test methods are proposed respectively in the conditions of static positioning and dynamic positioning. In addition, the characteristics of each method is compared. For validity, some experimental data is provided and analyzed, in which the dual frequency wide-lane observation for ambiguity solution is used in dual dynamic positioning.

The thrust allocation of Dynamic Positioning system allocates the control force to thrusters by calculating thrust and angle of each thruster. The whole thrust optimization allocation goal is to minimize energy consumption of the propulsion system, taking account of the amplitude and rate saturation of thrusters, the rate of change of the angle of azimuth thrusters, prohibited area of thrust of thrusters and so on. Under extreme sea environment such as gust, the output value of control force is beyond the ability of thrusters. It is proposed to reduce all the generalized forces with the same percent. The reducing percent is obtained based on Multiobjective optimization method. Then augmented Lagrange method is adopted to solve general thrust optimization allocation. This approach reserves the desired generalized force direction. Simulation results show that the proposed thrust allocation scheme is applicable and reliable without specified requirements on storage of memory and the control performance is satisfied with the proposed thrust allocation scheme. There is more extensive application prospect.