Wangqiang Niu

Exact Analysis of Frequency Splitting Phenomena of Contactless Power Transfer Systems

Frequency splitting phenomena are investigated systematically by circuit theory in a series-tuned contactless power transfer (CPT) system. First, in a symmetrical CPT system, the splitting equation is defined and the key frequency splitting characteristics are described by the trough and the ridge equations in a complete fashion. The even and the odd splitting frequencies are exactly two roots of the ridge equation; the splitting coupling is determined theoretically when the even and odd splitting frequencies merge together. Second, in an unsymmetrical CPT system, the idea of the trough and the ridge equation is exploited to find exactly the splitting coupling. Next, the relationship between frequency bifurcation and splitting is elucidated; and a zero-phase control method is suggested to track the splitting frequency when the coupling changes in the splitting region. Finally, the theoretical results are validated by a 10-W prototype with planar spiral coils.

Frequency splitting patterns in wireless power relay transfer

Frequency splitting patterns in low-order wireless power relay transfer systems are analysed by the coupled-mode theory. In addition to the V-type splitting pattern reported widely, two new patterns, I-type and W-type, are introduced. Specifically, it is found that a 0-relay system shows a V-type or I-type splitting; a symmetrical 1-relay system shows an I-type or W-type splitting; and a symmetrical 2-relay system usually shows a V-type or W-type splitting. The criteria for different frequency splitting patterns are given, and the theoretical results are validated finally by 1-relay and 2-relay wireless power transfer experimental systems.

Four Statistical Approaches for Multisensor Data Fusion under Non-Gaussian Noise

Multisensor data fusion methods for Gaussian noise are widely reported, while fusion approaches for non-Gaussian noise are seldom met in the literature. In this study, four statistical fusion methods are presented for a mixture of Gaussians noise. These four methods are the minimum variance approach, the maximum kurtosis approach, the minimum kurtosis approach, and the minimum mean absolute error approach. Preliminary numerical simulations demonstrate that the maximum kurtosis method shows the worst fusion performance, while the rest three methods shows equivalent better fusion performance.

The Integrated Ship Monitoring Systems: from Small Size to Large Size

The modern integrated monitoring system of ships plays an important role in the ship safety, reliability, and energy consumption level. This review article depicts in detail the characteristics of the monitoring systems of four ships in different sizes and types. These four ships are a small-sized unmanned surface vehicle, a medium-sized floating crane, a medium-sized geotextiles-laying vessel and a large-sized patrol ship. The joint features of these four monitoring systems are all showing a network topology of double layer structure, where the bottom layer consists of a field bus network, and the top layer is an Ethernet network. The bottom layer is usually responsible for real time ship data acquisition, and the top layer is mainly used for ship control and management. This double layer structure has good real time performance, high reliability, strong compatibility, and easy expansibility. A wide application of this structure will be expected in the future.

Anti-swing control of a new container crane with fuzzy uncertainties compensation

A class of new container cranes with eight-link lifting mechanics which can reduce sway efficiently as a result of improved lifting structure have been put to use recently, and both modeling and swing control of such a crane system attracts a lot attention in the field of control technology development. In this paper, dynamics model of the new container crane is investigated, an anti-swing control scheme with fuzzy uncertainty compensation is proposed to ensure the positioning control as well as overall closed-loop system stability. None of the system parameters is required for the controller design in a priori. In the proposed control laws, the position error can be driven to a bounded area while the swing angle can also be rapidly damped so as to achieve minimal sway of the crane system. Stability analysis of the controller is also given. Finally, simulation results show the performance successfully.

Robust Tension Control of the Anchor Chain of the Ship Windlass under Sea Wind

Constant tension control of anchor chains is important for safety of moored ships. The core driving component of an anchor windlass system is an induction motor which is a multi-variables, coupled nonlinear system, and is difficult to control. To surmount this problem, a control scheme based on the inverse system method is introduced to linearize an induction motor into a decoupled linear system, and linear controllers are then designed to complete the control task. In addition, theoretical analysis based on the Lyapnov method is carried out to investigate the influence of the time-varying rotor resistance to the control scheme suggested. Both theoretical analysis and numerical simulations show this control scheme is able to keep anchor chains at desired tension under sea wind at a time-varying rotor resistance.

Dynamic Tension Allocation of Ship Mobile Mooring System under Sea Wind

The mobile mooring system of ships usually consists of dozen of anchor windlasses, and it is an important question how these windlasses coordinate to fulfill the commanded tension input. The tension allocation of mobile mooring system with eight anchor windlasses is formulated in this study. The tension allocation problem is defined as an optimization problem and an active set method is adopted to find the optimized solutions. The simulation results show that the mobile mooring system is able to allocate dynamically the tension of each anchor windlass, and keep the ship at the desired position under sea wind.

Fault-Tolerant Tension Allocation of Ship Mobile Mooring System under Sea Wind

A fault-tolerant tension allocation framework is suggested for ship mobile system consisting of eight anchor windlasses. The fault-tolerant performance is evaluated under sea wind disturbance. The simulation results indicate that ship mobile mooring systems have certain fault-tolerant ability. When one windlass failed, the ship is able to completely counteract the sea wind disturbance. When two windlasses failed, the ship fault-tolerant ability becomes worse, and the remaining six windlasses are able to roughly balance the wind disturbance. When three windlasses failed, the ship fault-tolerant ability becomes even worse, and the remaining five windlasses are unable to counteract the lateral force from the sea wind. In summary, more windlasses failed, more performance degradation of the mooring system is resulted.

Estimation of the maintenance cycle from small sample based on a local fault interval model

Maintenance cycle is an important factor of a repairable system, and it is closely related to the safety operation and the level of energy consumption of the system. Two methods are presented to estimate the maintenance cycle from small sample based on a local fault interval model, one is the multi-point statistics method, and the other is the difference of Sigmoidals method. Both methods are tested by real sample data from a portal crane. It is found that both methods are able to estimate the maintenance cycle of a repairable system. Furthermore, these two methods have a smaller probability to invoke the false positive problem than the three-point statistics method, while the difference of Sigmoidals method is more robust than the multi-point statistics method.