08 July 2014, Volume 32 Issue 19

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  • WANG Xinmin, WAN Xiaoheng, ZHU Yangya, JIANG Zhiliang, LIU Jixiang
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    Aimed at the complicated nonlinear relation between the factors influencing the blasting vibration velocity, a blasting vibration velocity prediction model is built by using the particle swarm optimization (PSO) global search optimal solution principle and extreme learning machine (ELM) ability which can deal with the nonlinear relationship. Taking blasting vibration measured data in a certain area as an example, the total dose, the explosive charge, the distance between shot and monitoring point, the ground vibration velocity and the height of the monitoring point are selected as input variables and the building vibration velocity is chosen as the output variable. The result shows that the mean square errors between training value and predicted value and between test value and predicted value are 0.18 and 2.56, respectively, and the average relative error is controlled within 6%. It is proved that the model has good precision and generalization ability. Compared with the traditional ELM model, the PSO-ELM model not only improves the accuracy and generalization ability, but also reduces the influence on the result of training when the numbers of training samples and the hidden layer nodes change, thus the fitting ability of the model is improved. This model has great a promotional value in similar predictive engineering.
  • DOU Shiqing, LIU Chengjun, LIN Yawen, DING Wei
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    In order to compress the huge amount of multi-beam echo sounding data, this paper puts forward a new method of multibeam sounding data thinning based on the 3D Douglas-Peucker algorithm. Firstly, determination of the initial base plane in the 3D Douglas-Peucker algorithm is improved, and the algorithm efficiency is increased by dozens of times. Then this algorithm is used for the data thinning experiment using the multi-beam sounding data of a sea area in the north of China, and good experimental results are achieved. Through comparison and analysis of the data thinning experimental results, it is shown that the feature points of the seabed terrain can well be extracted by the 3D Douglas-Peucker algorithm and this method is suitable for multi-beam echo sounding data thinning. It also fits the surface measurement model of a multi-beam sounding system, and can realize global data thinning in the three dimensional space. The way of progressive data selection can provide various required accuracies for LOD of underwater terrain. Therefore, it has a good prospect of application.
  • ZHENG Xiongbo, ZHANG Liang, MA Yong
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    Wave energy is a kind of clean renewable energy. Power generation is a main form of wave energy utilization. The double floalter WEC is a kind of wave energy converter which has features of simple structure and low cost. To improve its conversion efficiency and reliability, this paper studies the hydrodynamic performance and energy conversion property. Based on the linear wave theory, the equations of motion are established, and the response amplitude operator (RAO) functions of different structures and power function are obtained. At the same time, a hydrodynamic numerical method in the frequency domain is used to calculate the hydrodynamic coefficients for different structures, and the curves of displacement amplitude and output power changing with wave frequency under different conditions are given. Through calculating and analyzing, the laws that describe the performances of movement and energy conversion influenced by the power take-off (PTO) system damping coefficient, device size, quality and wave frequency.
  • WAN Xiaofeng, KANG Liping, YU Yunjun, LIN Weicai
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    The attitude angle measurement is not accurate in the process of four-rotor aircraft attitude solving for the field information collection. To deal with this problem, we choose the inertial measurement system based on accelerometer, electronic compass and gyro, and combine the plurality of sensor measurement by a Kalman filter algorithm to get the precision attitude angle. We set up an actual four-rotor attitude detection platform to verify the effectiveness and practicality of the Kalman filter algorithm. The results show that the dynamic response and the precision of the attitude angle are better and the maximum tracking error can be controlled within ±1.5°. The application of the Kalman filter algorithm in attitude solver can not only eliminate the white noise caused by the accelerometer and electronic compass but also inhibit the temperature drift of the gyro effectively. The attitude angle can meet the accuracy requirement of the attitude solution of the four-rotor.
  • JIANG Liubing, WEI Honglang, YANG Changyu, XU Tengfei, GUAN Sihai
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    Ultra-wideband (UWB) life detection radar has found wide applications in anti-riot, rescue, and anti-terrorism actions due to its many advantages, such as strong penetrating ability, high distance resolution, and strong anti-interference ability. Therefore, research on human micro-tremor signal detection using UWB through-wall radar has much significance. As the echo signal of through-wall life detection radar is interfered by background noise clutter, the conventional method using the digital filter cannot effectively detect human micro-tremor signal. To solve this problem, this paper presents a human body micro-tremor signal detection algorithm. First, the frequency domain cumulation is used to increase the signal-to-noise ratio (SNR) of the echo signal, and then EMD is used for de-noising. This algorithm not only has the advantages of frequency domain cumulation, but also has the ability of EMD method for adaptive decomposition. Under low SNR, it overcomes the disadvantages of frequency domain cumulation and EMD method, the former being not real-time and the latter having ineffective clutter remove. The simulation results show that the algorithm not only improves the SNR of the radar echo signal, but also overcomes the disadvantage of frequency domain cumulation. The frequency of human respiration can be rapidly and accurately detected by processing the echo signal using this algorithm, which is a novel method for through-wall radar detection of weak signals.
  • ZHU Leiping, ZHU Liming, YU Xuetao, JIANG Wan, CHEN Weilin
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    In order to show radar echoes efficiently, this paper states the reflectivity storage format after analyzing the basic data of a kind of new weather radar CINRAD/CB. Then the CB radar's basic reflectivity data, this paper describes two visualization methods depending on the characteristics of vector data and raster data. Moreover, this paper also studies the conversion of reflectivity data from the polar coordinate system to the Cartesian system, and designs a method to show the radar echoes with vector data format and raster data format. Finally, the basic reflectivity data of the CINRAD/CB weather radar in Ordos City are taken as an example, and the result shows that the two methods both can accurately display the reflectivity echo, and that the raster method has a higher efficiency while the vector method is more analytic, each being applicable to its appropriate applications.
  • LIU Zhiqiang, ZHANG Zhang, WANG Peng
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    In order to reduce the false alarm rate of the lane departure warning system based on machine vision, a new lane departure warning system considering the driver's intention of changing lanes is put forward. In the proposed system, the collected road image information is filtered with Steerable Filter method, the road parameters are extracted using the local search algorithm, and the speed of motor vehicle, turning signal, lane departure situation as well as the driver's head movement are detected to judge the driver's lane departure intention. A lane departure warning decision algorithm is develped. Verification of the algorithm and simulation experiment are done using Matlab, with videos collected from vehicles. The results show that the proposed lane departure warning system is feasible. The system is more reliable, which can distinguish an intentional lane departure from unintentional lane departure and effectively avoid false alarm when the driver intends to change lanes.
  • XIONG Jian, LIANG Lixi, LIU Xiangjun
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    The fractal dimensions of pore structure of shale in the southeast Chongqing are calculated using the FHH model based on measured results of the pore structure by nitrogen adsorption. The result shows that the fractal dimensions of pore structure of shale in the southeast Chongqing obviously have the aperture boundary point, that is to say, have the dual fractal feature. The fractal dimension values of the big pore structure are 2.3559-2.6577, with an average of 2.488, and the fractal dimension values of the small pore structure are 2.5971-2.8746, with an average of 2.7631. The small pore structure, with a larger fractal dimension value, shows a higher degree of complexity than the large pore structure. There is a positive correlation among the fractal dimension values of shale pore structure and TOC content, gas adsorption, specific surface area and pore volume. Especially, it is found that the fractal dimension values show a significantly positive correlation with the specific surface area and pore volume. Whereas, there is a negative correlation between the fractal dimension values of shale pore structure and clay mineral content.
  • YI Xiangyi, ZHANG Ziwei, XIA Tao, DAI Yating, WU Yuanqin
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    The emulsion of crude oil and spent acid after acid fracturing treatment brings many troubles to production, such as increasing the loads of pump and pipe, causing corrosion and wax precipitation of pipe, and so on. Therefore, before trial-production we should find a way to break the emulsion which is made of residual acid and crude oil and then dehydrate it. In order to measure the demulsification effect and time of the mixed emulsion, demulsification experiments of emulsion of crude oil and three different spent acids with different concentrations are conducted in the laboratory. The spent acids include gelled acids, cross-linked acids, insitu gelled acids which are widely used in the field. Through analyzing all the impact factors, the results show that the demulsification efficiency of gelled acid is the best, followed by cross-linked acid, and the efficiency of in-situ acid is the worst. At the simulated bottom hole temperature of 90℃, the dehydration rate after demulsification of emulsion of crude oil and spent gelled acids is over 98%. The lower the acid concentration is, the better the demulsification efficiency will be. This feature is most obvious when in-situ acids are used. The longer the time taken, the better the demulsification efficiency will be. But the demulsification ends after 90 min.The demulsification is fast and the dehydration rate is high at high temperatures. However, with the production of the well, crude oil flows to the bottom hole from the reservoir and the temperature declines, so the dehydration rate may decrease.
  • WANG Tao, ZHANG Junjing, SHI Hailei
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    Bottom water coning is a critical issue in the development of oil reservoirs containing bottom water. A numerical model is built in this study for a bottom-water reservoir using realistic reservoir parameters. In consideration of the individual factors that impact bottom-water coning, clusters of the dimensionless indices are designed. The Yu Qitai water flooding type curves are generated by regression analysis using the cumulative oil, water and liquid productions from numerical simulation; The index b (slope of the water flooding type curve) that reflects the water breakthrough characteristics in the vertical well is calculated. Factors that influence b are then investigated in details using the Box-Behnken experimental design and the responsive surface method. The severity, order, and trend of the influence by each factor are finally examined.
  • ZHU Peike, DENG Jingen, HUANG Kaiwen, LUO Yuwei, ZHU Jianglin, WU Shan
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    In optimizing the selection of corrosion-resistant materials and safe and economic casing and tubing materials for oil & gas fields with high content of CO2 and H2S, the oilfield coupon corrosion test plays an important role. The weakness of the current detecting devices of corrosion is shown and the structural features that a detecting device of corrosion should have for the assessment of the steel corrosion under oilfield conditions are analyzed. Based on these analyses, an on-line detecting device of corrosion is designed and manufactured. During the design phase, the strength of the on-line detecting device of corrosion is checked and a PTFE (polytetrafluoroethylene) holder and the coupons with the trapezoidal cross sectional shape are specially designed. After the device is manufactured, the pressure test is carried out to check the device for the maximum working pressure and the specific operation method. The corrosion detecting devices are installed in wells of the Missan oilfield. The device is in the wellhead and before the injection point of the corrosion inhibitor and can meet the requirement of the oilfield. The oilfield test covers the scheduled amount for different materials of coupons during 3 months. The results show that 13Cr martensitic stainless steel can work under the condition of 0.2 MPa CO2 and under the condition of 1.3 MPa CO2, 0.8 MPa H2S, the 13Cr super-martensitic stainless steel shows no local corrosion with a very low corrosion rate.
  • DENG Jun, XIE Changchun, WANG Qiuhong, QU Jiao
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    Using the device for the HY16429 dust cloud minimum ignition temperature experiment, the minimum ignition temperatures for different kinds of coal dust clouds and different particle sizes are measured. The following results are obtained: The coal dust cloud minimum ignition temperature for a given kind of coal decreases with the decrease of the particle size; For different kinds of coal and with the coal dust particle size ≥250 μm, the temperature for the coal dust clouds to generate sparks is not very much affected by the volatile content, and for the different kinds of coal, that temperature takes a value close to each other; when the coal dust particle size is small, the coal dust cloud minimum ignition temperature is reduced with the increase of the content of volatile content. Through analyzing the received coal dust cloud minimum ignition temperature characteristics, their relationship with the characteristics of coal dust and volatile is obtained.
  • Reviews
  • LI Ke, ZHANG Hongxun
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    Phototrophic organisms play an important role in biogeochemical cycles of elements in desert soil ecosystems, where the ecological environment is fragile. Algae and moss are ubiquitous and can take photosynthesis in desert ecosystems. They can improve the physical properties of soil to protect the soil, and some of them have the ability of nitrogen fixation to increase soil nitrogen storage. More importantly, these phototrophic organisms are the main contributors of soil carbon storage, because they can fix carbon dioxide. The study of carbon dioxide fixation ability of desert ecosystem is an important part of the study of global climate change. The amount of fixed carbon is not only affected by the natural conditions but also closely related to the composition and abundance of phototrophic microorganisms (mainly algae and moss). The photosynthesis rate is usually low when there are only filamentous cyanobacteria in the topsoils, and the photosynthesis rate will increase when green algae and moss inhabit the topsoils. This article is to summarize the composition of phototrophic organisms in desert topsoils and the influencing factors and review and forecast the analysis methods of carbon fixation.