Search

The six-degree-of-freedom (6 DOF) motion of the mother-ship, which is caused by wave fluctuation, makes offshore operations difficult. To solve this problem, various heave compensation systems were proposed, as well as the law of wave motion. These heave compensation systems included passive heave compensation system, semi-active heave compensation system, and active heave compensation (AHC) system. However, the empirical formula of wave motion is not suitable for practical offshore operations, and rare AHC systems take the characteristic of compensation into consideration. To study the compensation characteristic of the AHC system based on electric-driven marine winch in the actual sea condition and improve the accuracy of compensation, this work uses the measured data of wave motion, and deduces the motion equations of multi-axial driving system. By substituting the above elements into the AHC system and designing the sliding mode controller (SMC), the simulation results show the ideal compensation effect of the system. By comparing with experimental results, it is concluded that the driving system operates in according with the specified states, and the compensation performance of system is effective. The overall work is conductive to the research on AHC system, as well as the exploitation of marine resources. [ABSTRACT FROM AUTHOR]

When a high-power wind turbine runs in normal status, and if bearing current exists for a long time, multiple point corrosion would occur and gradually increase, eventually forming a ripple groove on the inner ring race, outer ring race and rolling body. It would lead to more vibration and shock, thereby causing fault in the equipment; the best way to prevent the this kind of fault is to find the effective fault characteristics and predict the damage's degree on the bearing. In this paper, an adaptive neural network prediction method based on the quadratic root mean square of sub-band manifold is proposed. The damage characteristics can be analyzed by following steps: firstly, the vibration signal is decomposed into multidimensional time frequency space by wavelet packet method. Secondly, the sub-band of the manifold is constructed. The third step is to extract the root mean square value. Finally, the damage characteristics of the bearing current of the two square root sub-band manifold are obtained. Based on the back propagation network, the adaptive prediction model is built, and the training speed could be adjusted automatically according to the prediction error and precision. According to the bearing's fault mechanism with current damage on the high-power wind turbine, one fault experiment platform has been built to simulate the current damage process of the bearing and verify the prediction method based on the quadratic root mean square of sub-band manifold. The experimental results show that the method can effectively predict the degree of bearing current damage, and the relative error of prediction is less than 5%. [ABSTRACT FROM AUTHOR]

This paper focuses on the problem of adaptive control for uncertain nonaffine nonlinear systems. The original nonaffine systems are transformed into the augmented affine systems via adding an auxiliary integrator, which makes the explicit control design possible. By introducing a modified sliding mode filter in each step, a novel adaptive dynamic surface controller is proposed, where the 'explosion of complexity' problem inherent in the backstepping design is avoided. It is proven rigorously that for any initial control condition, the proposed adaptive scheme is able to ensure the semiglobal uniformly ultimately boundedness of all signals in the closed loop. An illustrative example is carried out to verify the effectiveness of the proposed approach. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]