Table of Content

28 February 2017, Volume 23 Issue 1

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Dynamic obstacle avoidance for USV based on velocity obstacle and dynamic window method

ZHANG Yangyang, QU Dong, KE Jun, LI Xiaomao

2017, 23(1):  1-16.  doi:10.3969/j.issn.1007-2861.2016.07.021

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Velocity obstacle is a dynamic obstacle avoidance algorithm widely used on an unmanned surface vehicle (USV). However, traditional velocity obstacle does not consider the effect of USV’s kinematics and obstacle’s motion information error, and does not know when to start and terminate avoidance. Based on velocity obstacle, USV and obstacle are represented by an ellipse. A method for solving ellipse tangent is proposed. Considering the kinematics performance of USV, a dynamic window method and velocity obstacle are combined. Only the speed and course that the USV can reach in a given time are used in calculation. By comparing the collision time and the time required for the USV to finish avoidance to determine when to start avoidance, a method to terminate obstacle avoidance is proposed. A virtual obstacle method is then proposed to reduce influence of obstacle’s motion information error. Feasibility and effectiveness of the method are verified by simulation.

Complete coverage path planning of USV used for mapping round island

ZHONG Yuxuan, GE Lei, ZHANG Xin, PENG Yan, YANG Yi, LI Xiaomao

2017, 23(1):  17-26.  doi:10.3969/j.issn.1007-2861.2016.07.020

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When mapping the seabed around islands independently, there are difficulties like large amount of calculation and complex task scene for mapping with an unmanned surface vehicle (USV). To solve the problems, an algorithm composed of a dynamic grids algorithm for main motion direction and a heuristic search algorithm is proposed. This algorithm establishes an environmental model based on the dynamic grids algorithm. The heuristic algorithm based on priority is used to choose an appropriate path point to travel. When the USV getting into a deadlock, an optimal path is generated with the heuristic search algorithm to get out. Simulation results show that performance of path planning is improved with the proposed algorithm. The planned path is more reasonable and effective to meet the needs when using USV to map the seabed around an island.

3D Lidar-based marine object detection for USV

LI Xiaomao, ZHANG Xin, WANG Wentao, QU Dong, ZHU Chuan

2017, 23(1):  27-36.  doi:10.3969/j.issn.1007-2861.2016.07.022

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To realize autonomous navigation and avoidance, it is necessary for an unmanned surface vehicle (USV) to perceive the surrounding environment in real time, and detect obstacles threatening its sailing. Three dimensional Lidar plays an important role in unmanned system obstacle detection. In this paper, an obstacle detection algorithm based on 3D Lidar is proposed. The 3D laser point cloud is projected onto a 2.5D grid map in one period. The obstacles are clustered and segmented. The elliptical feature of obstacles is extracted from the raw laser point. Dynamic obstacles are found and tracked using the
nearest neighbor data association and a Kalman filter. The simulation data based on the electronic chart verifies effectiveness of the method in USV obstacle detection.

Design of a seawater sampling and docking ransmission device

YANG Chao1, GUO Weiqi2, JIN Zuowen3, YANG Yi4, LI Xiaomao4, LIU Mingque4, PENG Yan4

2017, 23(1):  37-46.  doi:10.3969/j.issn.1007-2861.2016.07.008

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To solve the docking problem of seawater sampling from lifting multi-bottle ampling arrays to storage and distribution, a set of design schemes for seawater transfer ocking device according to seawater sampling requirements is proposed. The docking ransmission device is composed of an upper fixed joint and a lower docking seat, where compressed guide claws surrounding the upper joint contact the lower cone, making a ough claws-cone docking mechanism and compensating rod and cone docking of the second ine docking of the positioning error to lessen the positioning accuracy requirements. The echanical structure ensures to meet the requirements of O-ring assembly in the seawater eccentric flow channel from the samplers to the distribution system. To eliminate the influence f variations in the docking process, the axial displacement and radial eccentricity are ompensated by the flexible connection of the orrugated pipe. The purpose is to prolong he service life of the device. Based on the SolidWorks Motion simulation, the centering rocess of the whole docking system is simulated to reveal influence of various kinds of ariations on the docking mechanism. The stress state of the guide claw in the docking rocess is simulated with SolidWorks Simulation, showing rationality of the structure design.

Sea-sky line detection based on structured forests edge detection and Hough transform

XU Liangyu1, MA Lukun1, XIE Xie1, PENG Yan1, PENG Yanqing2, CUI Jianxiang1

2017, 23(1):  47-55.  doi:10.3969/j.issn.1007-2861.2016.07.018

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The sea-sky line is an important feature in the sea-surface environment image, and detection of the sea-sky line is essential in dividing the sea and sky, and detecting the coastline area and objects. This paper provides a method to detect the sea-sky line using structured forests edge detection and Hough transform. The method uses a Gaussian low-pass filter to reduce the influence of regional textures such as wave texture and light reflection. A trained structured random decision forest is then used to label each pixel, and binarize it to determine whether it belongs to an edge or not. Hough transform is used to fit the sea-sky line more accurately. Experimental results show that this method can neglect clutter edge, greatly improve edge detection, and effectively extract sea-sky lines from a complicated sea-sky background with high robustness and accuracy.

Design and implementation of USV simulation system

HU Xinming1, ZHANG Xin1, ZHONG Yuxuan1 PENG Yanqing2, YANG Yi1, YAO Junfeng1

2017, 23(1):  56-67.  doi:10.3969/j.issn.1007-2861.2016.07.019

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Offshore commissioning for unmanned surface vehicle (USV) is costly, difficult and inefficient. To reduce the workload of sea tests, a simulation system is designed for test and analysis of USV control systems, and a simulation process is programed. The simulation system includes five modules. The display and control module is used for global path planning and comprehensive information monitoring. The data simulation module simulates data of sensors for obstacle detection and positioning. The obstacle process module preprocesses, rasterizes, clusters and fits the detected data, and tracks moving obstacles. The navigation and obstacle avoidance module is made of line of sight (LOS) and an elliptical clustering-cone deduction algorithm. The cascaded generalized predictive control-proportion-integral-derivative (GPC-PID) method is used in the motion control module. Every simulation module is independent, and can be switched according to different requirements. The simulation results show that the described design of the simulation system for USV is accurate and reasonable.

A preconditioning iterative algorithm for eigenvalue problem of symmetric tensor

GU Chuanqing, LI Long

2017, 23(1):  68-72.  doi:10.3969/j.issn.1007-2861.2016.07.009

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Shifted symmetric high order power method (SS-HOPM) is a well-known iterative algorithm for solving tensor Z-eigenvalue. In this paper, the Newton method is used to deal with the initial condition of the algorithm. A Newton preconditioning SS-HOPM(PSS-HOPM) for the symmetric tensor eigenvalue problem is obtained. Two numerical examples are used to illustrate that, compared with the SS-HOPM algorithm, this algorithm can calculate more eigenvalues with little increase of computation time.

Determination of Ostwald coefficient in silicone oil

XU Yi1, XU Yanyan1, YUAN Bin2

2017, 23(1):  73-80.  doi:10.3969/j.issn.1007-2861.2015.04.011

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With eco-friendliness and excellent electrical insulation properties, silicone oil has attracted widespread attentions in industries, especially as China is currently increasing investments in power construction. In this paper, the Ostwald coefficient of dissolved gas in silicone oil treated as insulting oil for transformers based on well-developed gas chromatography techniques is tested. Multiple sets of paralleled Ostwald coefficients of silicone oil are obtained, and it is believed that it can be used for testing parameters of silicone oil for transformer insulation.

Combined system for biogas production using kitchen wastes and recycled water

MA Zhen1, WAN Hao2, ZHANG Meng2

2017, 23(1):  81-90.  doi:10.3969/j.issn.1007-2861.2015.04.010

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Regarding the current situation of treatment of kitchen wastes and sewage in colleges, constructing a combined energy-saving system to produce biogas using kitchen wastes and recycled water is proposed. The two recycling systems have a complementary relation. It can provide a new mode of energy-saving work in general, and for colleges in particular. Different mixing ratios of kitchen wastes and sludge are considered in the experiment of biogas production. With the ratio of 1:1, the cumulative yield of biogas reaches a maximum value. The cumulative biogas yield for 40 days is 621 mL/(g·VS), the removal rate of volatile solid (VS) is up to 67.5% and efficiency of methane production is 78.6%. The removal efficiencies of solluted chemical oxygen demand (SCOD), soluble carbohydrate and protein after the reaction by mixed substrate of 1:1 are 55.7%, 68.7%, and 22.7%, respectively. The pH values of the substrate is between 6.8 and 7.2. According to an estimation of energy saving in the South Campus of Shanghai University, the program can save energy costing 260 000 RMB every year after reconstruction, making a good economic benefit.

Target-screening of eight organic chloride compounds in chemical agents of liquid oil fields using gas chromatography and mass spectrometry

HU Zhimeng1, XIA Lingyan2, SHAO Hongyun2, JIANG Shaohui2, ZHAO Junqiao2, ZHENG Kewen1, CHEN Zheng1, REN Guofa1

2017, 23(1):  91-100.  doi:10.3969/j.issn.1007-2861.2015.03.015

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A method is proposed to target-screen the eight organic chloride compounds in chemical agents of liquid oil fields using gas chromatography and mass spectrometry(GC/MS). Parameters affecting both extraction and instrumental analysis are studied. Under optimal conditions, the linear range is from 2 to 100 ng/μL for the target compounds. The correlation coefficient R is above 0.99 for the analytes with the 1imit of detection(LOD) ranging from 10 to 120 ng/mL. Good recovery, ranging from 77.2% to 93.5% with relative standard deviation (RSD) less than 7%, has been achieved in the matric spiking experiments. The established method is applied to target-screen the eight organic chloride compounds in a mixed sample of chemical agents of liquid oil fields provided by the Shengli Oilfield Corporation. However, no target compound is detected in the sample. Reasons for such result are given in the paper.

Pollution characteristics, source identification and health risk assessment of PAHs in road dust

LI Hong, SHEN Xinhao, WANG Yujie, TANG Liang, WU Minghong, MA Jing

2017, 23(1):  101-111.  doi:10.3969/j.issn.1007-2861.2015.03.017

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A total of 112 road dust samples from Shanghai urban areas were collected with a mesh point method to investigate road dust in Shanghai. Levels of polycyclic aromatic hydrocarbons (PAHs) and their potential risks to human health were assessed, and source contributions to road dust PAHs were identified. This paper is focused on 16 the United States Environmental Protection Agency priority PAHs, concentrations of  PAHs in summer samples ranging from 0.817 ng/g to 21.800 μg/g with a mean of 10.400 μg/g, and in winter samples ranging from 4.08 μg/g to 59.90 μg/g with a mean of 23.70 μg/g.
Difference of PAHs in road dust samples taken from functional areas between summer and winter shows that the total PAH concentrations at transportation hubs, construction areas  and commercial districts are high, while offshore region , green areas and open territory have a low level. Differences exist in main sources of road dust in summer and winter using a characteristic ratio method. However, the health risk assessment for both children and adults exposed to road dust in summer and winter indicates that  Cancer risk is less than 10⁻⁶, without posing a potential cancer threat. In addition, the incremental lifetime cancer risk (ILCR) of PAHs in road dust in winter is significantly higher than that in summer, and ILCR of PAHs in road dust for adults is higher than for children.

Determination of 30 halogenated hydrocarbon compounds in soil with head space solid phase micro-extraction and gas chromatography

PEI Yongqiang, FAN Zhanchun, ZHAO Jing, YUE Jianwei, LI Yongqing, LI Huanfeng

2017, 23(1):  112-120.  doi:10.3969/j.issn.1007-2861.2015.03.012

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This paper studies an analytical technique of 30 halogenated hydrocarbon compounds in soil using a method of head space solid phase micro-extraction (HS-SPME), and analyzes influencing factors of target extraction efficiency. As a result, optimum extraction conditions are determined within 0.25~50.0×10³ ng/L, with good linearity. The detection limit is 0.04~3.58×10³ ng/kg. Blank standard addition recovery is 62.7%~122.0%, and relative standard deviation (RSD) is 0.7%~14.9%.

Shear strength of unsaturated Nanyang expansive soil and its prediction

SUN Hongyun, SUN Dean

2017, 23(1):  121-127.  doi:10.3969/j.issn.1007-2861.2015.01.018

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Expansive soil is a problematic soil with swelling and shrinkage. Compared with ordinary clay, the strength is clearly affected by water content. To investigate the effect of water content on the strength of expansive soil, a series of direct shear tests on Nanyang expansive soil with different water contents were carried out. Relationship between shear strength and water content at the same dry density was obtained. Test results show that the shear strength and cohesion decrease with increasing water content, and the internal friction angle changes little. In addition, by introducing macro saturation into the Bishop’s equation for unsaturated soil, the results show that the modified strength equation can well predict strength of unsaturated expansive soil.

Biaxial bending of rectangular plates with different modulus

ZHANG Liangfei, YAO Wenjuan

2017, 23(1):  128-137.  doi:10.3969/j.issn.1007-2861.2015.02.003

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An eutral axis can be considered from two bending directions to solve the biaxial bending problem of rectangular plates with different modulus. Based on the different modulus theories, an equation of the neutral axis location is derived using the static equilibrium equation of rectangular plates with different modulus. The deflection curve equation is solved with the Kantorovich method. Its solution agrees well with the finite element solution. The result shows that the classical shell theory is not applicable in calculating deflection of a rectangular plate when tensile and compressive modulus are quite different. The proposed method provides an approach to analyze the bending problem of other structure forms of plate with different modulus, and theoretical reference for engineering applications.

Estimation algorithm of sampling clock frequency offset for OOFDM system based on training sequence

ZHANG Zhen, SONG Yingxiong, ZHANG Junjie, DUN Han, GUO Songlin, XUE Ziwei

2017, 23(1):  138-146.  doi:10.3969/j.issn.1007-2861.2015.02.011

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This paper studies sampling clock synchronization for optical orthogonal frequency division multiplex (OOFDM) systems, and proposes a simple sampling clock frequency offset (SCFO) estimation algorithm for hardware implementation based on crosscorrelation properties of the training sequence. The main idea is as follows. First, correlation between the received training sequence and the known training sequence is obtained, and then sampling clock frequency offset found with a few adders and one divider based on the property that an additional sampling point is introduced when the cross-correlation
value periodically changes a cycle. An optical OFDM system with intensity-modulation and direct-detection (IMDD-OFDM) is set up to show performance of the algorithm. Experimental and simulated results indicate that the algorithm has good accuracy and noise immunity.

A novel tri-section SIR dual-band filter with high stopband rejection

JIANG Yifei1,2, MENG Lingqin1,2, YANG Guangli1

2017, 23(1):  147-154.  doi:10.3969/j.issn.1007-2861.2015.01.019

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A dual-band filter with high stopband rejection is designed using a tri-section signal to interference ratio (SIR) resonator. The center frequencies and first spurious frequencies of resonators can be controlled independently to design aspecific dual-band filter. The tri-section coupling structure is aimed at transmission zeros and high stopbands rejection. To get a high external quality factor, an inter-digital finger coupling structure is introduced. The filter has dual passband center frequencies of 1.57 GHz (GPS) and 2.5 GHz (4G), with 3 dB fractional bandwidths of 4.0% and 2.4%, respectively. Measured results well agree with simulations.