Search Results

You are looking at 1 - 10 of 10 items for :

  • Author: Xu Zhao x
  • Engineering x
Clear All Modify Search
Open access

Michael Danikas, Xu Zhao and Yong-hong Cheng

Experimental Data on Epoxy Resin Samples: Small Partial Discharges at Inception Voltage and Some Thoughts on the Possibility of the Existence of Charging Phenomena Below Inception Voltage

In this paper, some results are presented on experiments concerning partial discharges (PD) behavior of epoxy resin samples. The main idea is to see whether a sample with PD at its inception voltage, still presents some tendency to charging effects below inception. An effort is being made to relate the present work with previous publications on the same main idea. The experiment arrangement is three layers of epoxy resin with a void in middle layer. Different level voltages under inception voltage are applied to the arrangement and different PD waves are registered under different level voltages. To make sure that the tendency to charging effects below inception, infrared spectrum analysis is also conducted and the result is content to clarify our objective.

Open access

Yuan Zhang, Michael Danikas, Xu Zhao and Yonghong Cheng

Preliminary Experimental Work on Nanocomposite Polymers: Small Partial Discharges at Inception Voltage, The Existence of Possible Charging Mechanisms Below Inception Voltage and the Problem of Definitions

In this paper, some results are presented from experiments concerning partial discharge (PD) behaviour of epoxy resin samples having 3 wt% nano- and 3 wt% micro-fillers, as well as epoxy samples having 3 wt%and1 wt% nanoparticles. The nano- and micro-fillers were TiO2 (titania). The main idea is to see whether a sample with PD at its inception voltage, still presents some tendency to charging effects below inception. An effort is being made to relate the present work with previous publications on the same main idea, as well as to previous research performed recently at Xian Jiaotong University, State Key Laboratory of Electrical Insulation and Power Equipment. It is indicated that with the samples investigated, although on some occasions random charging phenomena were observed below the inception voltage, it was not noted the same behaviour as with pure epoxy samples. Finally, a discussion ensues as to the definitions of the phenomena taking place below inception voltage.

Open access

Qiming Zhao, Hao Xu and S. Jagannathan

Abstract

In this paper, the fixed final time adaptive optimal regulation of discrete-time linear systems with unknown system dynamics is addressed. First, by transforming the linear systems into the input/output form, the adaptive optimal control design depends only on the measured outputs and past inputs instead of state measurements. Next, due to the time-varying nature of finite-horizon, a novel online adaptive estimator is proposed by utilizing an online approximator to relax the requirement on the system dynamics. An additional error term corresponding to the terminal constraint is defined and minimized overtime. No policy/value iteration is performed by the novel parameter update law which is updated once a sampling interval. The proposed control design yields an online and forward-in-time solution which enjoys great practical advantages. Stability of the system is demonstrated by Lyapunov analysis while simulation results verify the effectiveness of the propose approach

Open access

Yonghong Cheng, Xu Zhao, Michael Danikas, Despoina Christantoni and Pavlos Zairis

A Study of the Behaviour of Water Droplets Under the Influence of Uniform Electric Field in Epoxy Resin Samples

Water droplets on the surface of epoxy resin samples were investigated under the influence of uniform electric fields. Several parameters of water droplets were investigated wrt the flashover voltage of the epoxy resin samples, such as water conductivity, droplet volume, number of droplets as well as the positioning of the droplets regarding the electrodes. The droplet behavior is affected by the above mentioned parameters. Perhaps the most striking conclusion is that the flashover voltage depends more on the positioning of the droplets wrt the electrodes than on the droplet volume and/or number of droplets.

Open access

Zhi Tao, He-ming Zhao, Jun Wu, Ji-hua Gu, Yi-shen Xu and Di Wu

Abstract

In this paper, a new lifting wavelet domain audio watermarking algorithm based on the statistical characteristics of sub-band coefficients is proposed. First of all, an original audio signal was segmented and each segment was divided into two sections. Then, the Barker code was used for synchronization, the LWT (lifting wavelet transform) was performed on each section, a synchronization code and a watermark were embedded into the first section and the second section, respectively, by modifying the statistical average value of the sub-band coefficients. The embed strength was determined adaptively according to the auditory masking property. Experiments show that the embedded watermark has better robustness against common signal processing attacks than present algorithms based on LWT and can resist random cropping in particular.

Open access

Li Bing-jie, Zhao Jia-hong, Wang Xu, Mohamode Amuer and Wang Zhi-liang

Abstract

As the air flow control system has the characteristics of delay and uncertainty, this research designed and achieved a practical air flow control system by using the hydrodynamic theory and the modern control theory. Firstly, the mathematical model of the air flow distribution of the system is analyzed from the hydrodynamics perspective. Then the model of the system is transformed into a lumped parameter state space expression by using the Galerkin method. Finally, the air flow is distributed more evenly through the estimation of the system state and optimal control. The simulation results show that this algorithm has good robustness and anti-interference ability

Open access

Lei Su, Zongqiang Xie, Wenting Xu and Changming Zhao

Abstract

Mixed evergreen-deciduous broadleaved forest is the transitional type of evergreen broadleaved forest and deciduous broadleaved forest, and plays a unique eco-hydrologic role in terrestrial ecosystem. We investigated the spatio-temporal patterns of throughfall volume of the forest type in Shennongjia, central China. The results indicated that throughfall represented 84.8% of gross rainfall in the forest. The mean CV (coefficient of variation) of throughfall was 27.27%. Inter-event variability in stand-scale throughfall generation can be substantially altered due to changes in rainfall characteristics, throughfall CV decreased with increasing rainfall amount and intensity, and reached a quasi-constant level when rainfall amount reached 25 mm or rainfall intensity reached 2 mm h−1. During the leafed period, the spatial pattern of throughfall was highly temporal stable, which may result in spatial heterogeneity of soil moisture.

Open access

Zhonglin Xu, Zhaodong Feng, Chuanyan Zhao, Jianghua Zheng, Jianjun Yang, Fengxia Tian, Huanhua Peng, Chao Wang, Shouzhang Peng and Hassan Sher

Abstract

Interception is one of the most underestimated processes in hydrological cycle in arid and semiarid regions. In Qilian Mountains of northwestern arid and semiarid China, the Qinghai spruce (Picea crassifolia) forest plays an important role in the hydrological cycle of the inland Heihe River basin. The historical disturbance of Qinghai spruce forest has resulted in various ecological problems. In order to realize the sustainable development of Heihe River basin, the Chinese government implemented restoration practices for Qinghai spruce in the past three decades. In this study, we estimated the rainfall interception in the actual and potential distribution of Qinghai spruce forest. Some of the important findings include: (1) The interception ratio of rainfall events ranged from 11-51% with a mean value of 27.02%; (2) Totally, 147 Mt of rainfall is intercepted by canopy of actual Qinghai spruce forest, in the projected potential distribution of the forest, totally 407 Mt of rainfall will be intercepted.

Open access

Xu Zhao, Yong-Hong Cheng, Yong-Peng Meng and Michael G. Danikas

Partial discharge (PD) current is an impulse signal at nanosecond level, which can generate electromagnetic (EM) wave containing broadband frequency information. The frequency band of EM signal is from MHz up to GHz. Due to different PD patterns, impulse currents with different shapes induce different EM waves containing different frequency information. Therefore, using the features extracted from frequency domain of EM signals, the classification of PD patterns can be effectively got. It is good to use wavelet or wavelet packet decomposition to select features. However, if the decomposition level is too shallow to find enough effective features, it cannot group the EM signals to the right pattern. On the contrary, although it is easier to find features to distinguish the PD pattern if the decomposition level is deep, there will be a lot of redundancy variables and it is hard to select features among so many variables. In this paper, a method is presented, which selected features in the whole decomposition tree instead of selecting among the leaf node of the tree, because more potential features can be found in the whole tree. With the present method, it is possible not only to get enough features, but also to eliminate the redundancy variables effectively. In order to validate the method, large EM signals from four PD patterns in a power transformer are acquired as the training data and testing data for feature selection and classification, and three common classification methods are introduced to classify the PD patterns using the features selected by the method. Most of the classification results are satisfactory indicating that the proposed method is effective.

Open access

Peiqi Liu, Liming Zhang, Siyuan Xu, Zhixiang Duan, Zuzhi Chen and Wenjing Zhao

Abstract

The structure of wellbore and coupling is connected by thread, it is the position where fatigue failure accidents are happened in gas storage well, and the make-up torque of thread is the key factor that influences the mechanical properties of this structure. In this pa- per, a finite element method was established to discuss the calculation method of make-up torque and the influence law on the stress of coupling in the gas storage well. Results show that the make-up torque cannot be simply ignored due to its great impact on internal stress distribution of gas storage well. Experimental results showed the correctness of the model. Under the action of the make-up torque, the overall stress level inside the wellbore is higher than the external coupling. However the maximum stress exists in the external coupling. The overall stress grad- ually increases with the increase of interference rotation number (abbr. RN) between coupling and wellbore, but the overall distribution trend is almost the same. The first thread on the left of the connection part is the area where fatigue failure is most likely to occur. The make-up torque between threads increases linearly with the increase of RN between cou- pling and wellbore.