Table of Content

25 December 2015, Volume 43 Issue 12

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Power & Electrical Engineering

A Differential Setting Method for Reactive Power Interval of 110 kV Substation Gateway

Zhang Yong-jun Yi Ying-qi Chen Yan

2015, 43(12):  1-8.  doi:10.3969/j.issn.1000-565X.2015.12.001

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As the reactive power control range of gateway in the traditional nine-zone automatic voltage control (AVC) strategy cannot adapt to the changes of operation modes,the correlation characteristic between the active loss and the reactive power of gateway in a 110 kV power grid is analyzed,and an optimization-oriented control strategy of the reactive power of gateway and a setting basis of the optimization-oriented network loss increment ΔP are proposed.Then,the reactive optimization interval of a 110 kV power grid gateway is discussed by using the boundary conditioned parameter,and a differential reactive power control range of gateway,which can adapt to dif- ferent operation modes,is obtained.Moreover,the relevant control range is quantitatively assessed by using an e- valuation model.Case analysis shows that the proposed method can improve the economy and safety of power sys- tems and is easy to implement.

Reinforcement Learning Method Applied to Multiobjective Emergency Control of Transient Voltage Security

Deng Zhuo-ming Liu Ming-bo

2015, 43(12):  9-17.  doi:10.3969/j.issn.1000-565X.2015.12.002

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Transient voltage collapse poses a serious threat to the security of power grid,which results in an urgent need for emergency control.In this paper,first,by taking the reference value increments of generator terminal volt- ages and the reactive power outputs of capacitors/reactors as the control variables,a multiobjective emergency con- trol model for ensuring transient voltage security is constructed by using trajectory sensitivity.In the model,the de- viation of voltages at key load nodes,the control cost and the variance of the reactive power output ratio of genera- tors are minimized respectively in two stages.Next,the proposed model is solved by means of the reduced rein- forcement learning method which resets the state functions of solution space and adjusts the magnitude of actions,and the state sensitivity is introduced to solve the conflicts between exploration and application.Then,the feasible region is divided into small zones,so that the probability that there may be optimal solutions in each zone can be judged alone and the search range is thus narrowed.Moreover,the quality of pareto frontier is further improved by optimizing the searching strategies,and the weights corresponding to the objective functions are determined accord- ing to the actual operating status,with the compromise optimal solution being given.Finally,the time-domain sim- ulation is performed on a provincial power grid.It is found that the proposed method can restore the transient volt- age security and is superior to the normal boundary intersection method in terms of the solution efficiency and the quality of PF.

Input Side Current Control of Matrix Converter Based on Back-Stepping Method

Pan Yue-dou Guo Kai Chen Ji-yi Xu Jie

2015, 43(12):  18-24,47.  doi:10.3969/j.issn.1000-565X.2015.12.003

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Aiming at the problem that the input side current of matrix converters can be easily affected by the power supply voltage fluctuation and the load change,a new back-stepping control strategy is proposed and implemented on a matrix converter.The matrix converter is converted into a mathematical model under the dq coordinate through the PARK transformation,and the controller for the input side current of the matrix converter is designed by adop- ting the proposed back-stepping control strategy and it is compared with that of the matrix converter with a PI con- troller by tests.Simulation results show that the controller using the proposed back-stepping control strategy can quickly follow the input currents under the conditions of both the change of load and the descent of three-phase power.Harmonic analysis indicates that the back-stepping control causes a low total harmonic distortion.Finally,the proposed back-stepping control strategy is encoded on the digital signal processor TMS320F2812,with an exper- iment involving resistance-inductance load being conducted.The results show that the input side current waveform of the matrix converter keeps a good sinusoidal characteristic.Simulation and experimental results demonstrate that the proposed back-stepping control strategy is both effective and feasible.

Maximum Power Point Tracking Based on Adaptive Variable Step-Size Incremental-Resistance Method

2015, 43(12):  25-32.  doi:10.3969/j.issn.1000-565X.2015.12.004

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In order to ensure that the photovoltaic system under a drastically-changing light can still output its maxi- mum power,an adaptive variable step-size incremental-resistance maximum power point (MPP) tracking (MPPT) algorithm is proposed.In the algorithm,a threshold function is adopted to automatically divide the operation area of the photovoltaic system into the fixed step-size region and the variable step-size region according to the changes of external environments.In the fixed step-size region,a method of tuning initial fixed step sizes is proposed based on the approximate linear relationship between the short-circuit current and the maximum power point current.In the variable step-size region,by drawing on the relationship between the step conversion function and the output power,a scaling factor of the variable step-size strategy is determined to ensure the convergence of the proposed al- gorithm.Finally,a Matlab/Simulink model of the photovoltaic system and a 5kW photovoltaic system controlled by DSP (TMS320F28035) are established to conduct a series of experiments.Simulation and experimental results in- dicate that the proposed algorithm can improve the dynamic response speed of the photovoltaic system under a dras- tically-changing light by 73%，and can achieve a steady-state tracking accuracy of 98. 9%.

TOPSIS Technique and Its Application to Reactive Compensation Evaluation for Low-Voltage Distribution Network Area

Ouyang Sen Geng Hong-jie Chen Xin-hui

2015, 43(12):  33-40.  doi:10.3969/j.issn.1000-565X.2015.12.005

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In the low voltage distribution network area,the current reactive compensation evaluation still remains mostly at the level of direct economic benefit and ignores the voltage characteristics.In order to solve this problem,a TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) technique is proposed to evaluate the comprehensive benefit of the reactive compensation scheme from the aspects of both the voltage characteristics and the direct economic benefit.First,a voltage characteristic index is set up from the perspective of the voltage charac- teristics along the line,and a direct economic benefit index is also set up.Next,the evaluation indexes are prepro- cessed according to their attributes,and the weight of each evaluation index is determined by means of the rank cor- relation analysis.Then,the positive and negative －ideal solutions of each evaluation index are obtained,and the rel- ative close degrees between the reactive compensation scheme and the ideal solution are calculated by means of the improved close degree method,thus achieving the good or bad order of the comprehensive benefit of the reactive com- pensation scheme.Finally,the proposed method is used to evaluate five kinds of reactive power schemes for several actual low voltage distribution network areas,and the result is compared with the result of the good or bad order only based on the direct economic benefit.It is found that the proposed method is both objective and effective.

Lifespan Assessment of 110kV XLPE Cable Based on Isothermal Relaxation Current Method and Stepwise Voltage Method

Liu Gang Jin Shang-er Zhao Lu Wu Liang Liang Zi-peng Huang Jia-sheng

2015, 43(12):  41-47.  doi:10.3969/j.issn.1000-565X.2015.12.006

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Short and long samples from the cables running for over twenty years were cut out． Then，the short samples as well as the long samples before and after the electric heating process were tested by means of the isothermal
relaxation current method． The results show that the long samples have a larger aging factor because they have cable
joints，which means that the cable joints constitute the weak link in the cables，and the joints under the electric
heating process are easier to get aging． After the electric heating process，the aging factor of the long samples increases due to the increase of their internal defects，which means that the electric heating process can aggravate the
aging degree of the cables． From the voltage-endurance tests，it is found from the voltage-endurance tests that the
residual life of the samples ranges from ten to twenty years，which is consistent with the expected life in their design． Thus，it comes to the conclusion that the XLPE cable can be more comprehensively judged by combining the
isothermal relaxation current method with the stepwise voltage-endurance method，which means that the aging degree and the residual life can be respectively assessed by using both methods．


A Load Transfer Method for Power Distribution Networks Based on Graph Theory and Improved Fuzzy Genetic Algorithm

Wu Zhi-gang Ma Yi-song

2015, 43(12):  48-54,70.  doi:10.3969/j.issn.1000-565X.2015.12.007

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In view of the fault recovery of complicated power distribution networks，a load transfer method for power distribution networks is proposed based on the graph theory and the improved fuzzy genetic algorithm． First，the to-pological structure and component parameters of feeders are integrated together by means of the JGraphT － based da-ta modeling of power distribution networks，and by taking advantage of the topological structure of power distribution networks explicitly，the tedious node encoding rules and the storage modes in the form of miscellaneous adjacency lists or matrices are avoided． Next，with the help of the graph theory algorithms integrated in JGraphT，different types of fault sections are quickly distinguished and the topological constraint is rapidly determined． Then，a for-ward － backward sweep method based on the recursive graph theory is developed． Finally，an improved fuzzy genet-ic algorithm is proposed according to the characteristics of power distribution networks． In the proposed algorithm，the initial solutions and genetic operators of the genetic algorithm are dynamically adjusted so as to improve the opti-mizing performance of the proposed algorithm，and the fuzzy inputs and fuzzy rules are revised reasonably to im-prove the convergence rate of the genetic algorithm and avoid the premature convergence． Simulation results show that the proposed algorithm is superior to the other methods in terms of power flow calculation and optimization effi-ciency．


Power Grid Loss and Its Conducting Model Based on Life Cycle Cost Theory

Jiang Li-min Han Yong-xia Huang Wei Yan Hua-guang Dai Dong Li Li-cheng

2015, 43(12):  55-62.  doi:10.3969/j.issn.1000-565X.2015.12.008

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The analysis of life cycle costs (LCC) plays a key role in the concept of life cycle management． In or-der to develop a more precise LCC model for the power grid and its main equipment，the inflation rate prediction method and the loss conducting model are introduced into the LCC model． Based on the power grid characteristics that the increase of total loss will cause the cost of generation side to increase and the loss of subordinate power grid will lead to the raise of the comprehensive investment of above grid，a power grid loss conducting model is pro-posed，and a method to calculate the loss conducting cost-to-LCC ratio is put forward． In addition，the inflation rate is predicted by using the autoregressive integrated moving average (ARIMA) model． Then，the loss distribution in each part of a typical power grid is analyzed based on the above LCC model，and the necessity and importance of the energy conservation in the power distribution grid are pointed out． Finally，a case study on the influence of the loss conducting cost on the LCC is performed，which proves that the proposed loss conducting model is of practical value．


Estimation Method of Residual Capacity of Battery in Hybrid Devices

Feng Zhi-jun Zhou De-jian

2015, 43(12):  63-70.  doi:10.3969/j.issn.1000-565X.2015.12.009

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First，a definition of the residual capacity of the battery with variable current and its modified formula under the actual working condition are proposed in this paper． Next，the power curve of the battery of a parallel hybrid excavator is scaled down to the range of a single battery，and the scaled curve is taken as the input signals of the tested battery． Then，the data samples of the residual capacity are obtained from the input signals，and they are analyzed by using several grey prediction algorithms． On this basis，a fragmentation prediction scheme is proposed，which adopts the direct grey prediction model of the cumulative-average operator at the charge stage and the grey prediction model of the variable weight buffer factor at the discharge stage． The results show that the proposed method can fully and effectively improve the accuracy of estimating the residual capacity of the battery in hybrid devices．


Numerical Simulation for the Downward Smoke Displacement under the Effect of Water Droplets

Numerical Simulation of Downward Smoke Displacement in Fire Under the Effect of Water Droplets

2015, 43(12):  71-76,84.  doi:10.3969/j.issn.1000-565X.2015.12.010

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Based on the basic physic laws and the idea of two-zone model of fire，a mathematical model of the downward smoke displacement in fire under the effect of water droplets is constructed by analyzing the interaction between a single droplet and hot air flow and by investigating the impact of water droplets on the smoke layer of fire． Then，the constructed model is compared with the measured data，finding that the error of the constructed model is ±0. 3 m． The modeling results show that (1) increasing the flow rate of nozzles and decreasing the size and spray angle of water droplets can increase the downward smoke displacement; (2) under the same spray condition，the downward smoke displacement is easy to occur in a thin and low-temperature fire smoke layer; (3) when the thick-ness of the smoke layer is less than a critical value，the downward smoke displacement distance will greatly increase;and (4) the operation pressure of the commonly-used sprinkler nozzle with a 12. 7 mm orifice should not be larger than 20 m，so that the impact of the water droplets on the downward smoke displacement can be effectively reduced．


Traffic & Transportation Engineering

Investigation into Prestress Loss of Short Straight Tendons in Pylon Anchorage Zone of Cable-Stayed Bridge

Cui Nan-nan Jia Bu-yu Yu Xiao-lin Yang Zheng Yan Quan-sheng

2015, 43(12):  77-84.  doi:10.3969/j.issn.1000-565X.2015.12.011

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As the way of arranging circular prestress tendons in the PC (Prestressed Concrete) pylon anchorage zones of cable-stayed bridges has its disadvantages in terms of mechanical performance and construction，a new arrangement of prestress tendons by the name of one-way straight tendons is put forward． Under this kind of arrangement，the prestress tendons are relatively short，and their prestress loss laws and construction control are different from the tendons with common length． In order to investigate the loss characteristic of this kind of short straight prestress tendons，the friction loss (the duck friction and the anchorage friction) and the loss due to anchorage set as well as the elongation control are emphatically analyzed by a full-scale model test． Moreover，the prestress tendons under anchor are observed for a short time． The results show that (1) the average total loss of prestress is 26%;(2) in the total loss，the loss due to anchorage set，the duct friction loss and the anchorage head friction loss respectively account for more than 50%，about 12% and 20%，and the latter two types of loss should not be ignored as most articles and codes have recommended; and (3) the elongation control is still applicable in the construction of short prestress tendons，but in view of its exquisite sensitivity to the construction error，the construction quality must be guaranteed and the permissible error should be extended to ±9%．


Investigation into Minimum Vertical Curve Ｒadius and Length of Highway in Mountainous Wind Farm

Yang Yong-hong Hou Huang Chen Xing-guang Zhou Xiang-yang

2015, 43(12):  85-90.  doi:10.3969/j.issn.1000-565X.2015.12.012

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As the wind power equipment is heavy and its blades are long，it requires a special highway to transport，which belongs to special equipment transportation． As there is no specification for the highway alignment design of large-scale wind farms in the mountainous areas in China，the relevant indexes of large blade transportation vehicles，which influence the highway profile design，are systematically investigated in this paper． From the four aspects of mitigating the impact in the vertical curve of vehicles，ensuring an adequately long travel time，keeping the blade tail from scraping the ground and restricting the pitch angle，the minimum radius and length of vertical curves are analyzed，and the models to calculate the minimum radii and lengths of concave and convex vertical curves are constructed under different constraint conditions． Finally，the minimum radii and lengths of vertical curves are recommended for the large aerogenerator transportation with various design speeds and scopes of algebraic difference in grades． The results can provide guidance for the highway design and construction of the aerogenerator transportation，and can also be used to formulate the standards relevant to the aerogenerator transportation highway．


Stopping Schedule Optimization of Express/Local Trains in Urban Ｒail Transit

Wang Zhi-peng Luo Xia

2015, 43(12):  91-98.  doi:10.3969/j.issn.1000-565X.2015.12.013

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In view of the high complexity and unreasonable station classification of the existing stopping schedule optimization models of express/local trains，by utilizing the grey variable weight clustering model to preliminarily cluster stations so as to achieve the decision attributes and by taking the clustering results of each index as the condition attributes，the attribute reduction of the factors influencing the station classification is conducted． Then，the advantage analysis of the reduced attributes is performed to determine the relative grey correlation degree between the condition attributes and the decision ones，and the grey fixed weight clustering model is adopted to classify stations． By setting the principle that express trains must stop at the stations in the first level and they may stop in the second level if it is required but do not stop in the third level，a nonlinear 0 －1 programming model of the stopping schedule optimization of express/ local trains is constructed according to the classification results，and the constructed model is solved by using the genetic-annealing algorithm． The results show that the proposed method can eliminate a large number of invalid solutions and greatly narrow the solution space，thus greatly improving the solution efficiency，which is of great significance in quickly establishing the operation scheme of trains．


Investigation into Travel Time of Management Unit of Expressway in Disastrous Events

Yan Ying Wang Xiao-Fei

2015, 43(12):  99-105,113.  doi:10.3969/j.issn.1000-565X.2015.12.014

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In order to effectively serve the route guidance and control management of the expressway corridor network in disastrous events，a method to divide the management unit of road networks is put forward． For the management unit with no disastrous events involved，a travel time characteristic function is established by taking into account the influences of the management unit length，the average speed and the real-time traffic density． By combining the queuing and dissipating characteristics of the management units involving disastrous events and by using the flow and density relationship model，the duration time and dissipation time of incidents are determined，and a travel time calculation model of incident management units is constructed based on the wave theory． Then，the proposed model is modified by taking the real-time safety reliability as a road resistance function． Finally，the effectiveness of the constructed model is verified by an example．


Coordinated Signal Timing Optimization at Closely-Spaced Split Midblock Crosswalks

Xu Hong-feng He Long Zhang Kun

2015, 43(12):  106-113.  doi:10.3969/j.issn.1000-565X.2015.12.015

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Crosswalks are a kind of important pedestrian crossing facility． It is proper to implement the simultaneous signalization at integrated crosswalks and the separate signalization at split crosswalks． Regarding isolated split midblock crosswalks，a method to calculate the maximum pedestrian-crossing time is proposed according to the time-space diagram of pedestrian movements． Regarding closely-spaced split midblock crosswalks along an arterial，a coordinated signal timing optimization model is constructed by means of the integer nonlinear programming method according to the time-space diagram of vehicular movements． In the constructed model，the maximum of the maximum pedestrian-crossing time in any crosswalk and in any movement direction is minimized without any negative effect on the two-way green waves for vehicular movements． Case studies indicate that the constructed model is of practical value and can be widely applied．


A Distance-Based Weighted Pattern Recognition Algorithm for Traffic Flow Forecasting

Liu Shu-qing Xu Jian-min Lu Kai Ma Ying-ying

2015, 43(12):  114-118,126.  doi:10.3969/j.issn.1000-565X.2015.12.016

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In the short-term traffic flow forecasting based on the weighted traffic pattern recognition algorithm(WPRA)，the weights of different historical state values are distinguished according to the time-interval characteristics of historical traffic patterns，but in practical application，the subjective setting of the weight values reduces the reliability of this method． In this paper，by analyzing the core principle of the data-driven non-parametric-regression traffic flow forecasting algorithm and by improving the forecasting algorithm aiming at the uncertainty of the time-interval-characteristic weights of WPRA，a distance-based weighted pattern recognition algorithm (DWPRA) is proposed to forecast the short-term traffic flow． Finally，the root mean square error between real traffic flows and predicted ones is introduced to verify the proposed algorithm． The results show that，at the same neighbor number K，the root mean square error of DWPRA is 4.8% ～7.1% lower than that of WPRA，which proves the effectiveness of DWPRA．


Delay Models for Two Kinds of Left-Turn Traffic Flow Organizations at Intersection

Lin Pei-qun Gu Yu-mu Zhuo Fu-qing Ran Bin Xu Jian-min

2015, 43(12):  119-126.  doi:10.3969/j.issn.1000-565X.2015.12.017

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In order to provide theoretical basis for the traffic organization design of intersections，the whole delay characteristics of intersections under two kinds of left-turn traffic flow organizations，namely，the direct left-turn plan and the right-turn-straight-U-turn (Ｒ-S-U) plan，are analyzed in this paper． Based on the Webster delay model and the gap acceptance theory，the vehicle average delay models for the two kinds of traffic flow organizations and a discriminant model of the left-turn traffic flow organization are constructed by means of mathematical derivation． It is found that，with the whole intersection delay as the optimization objective，the R-S-U plan has more advantages when the left-turn traffic flow volume is smaller than a certain threshold; otherwise，the direct left-turn plan is more reasonable． The threshold of flow discriminant is related to the relationship between the left-turn traffic flow volume and the opposite direction traffic flow volume． Finally，the theoretical delay parameter of a typical intersection is calculated，and the simulation delay parameter is obtained through VISSIM． The results show that the theoretical calculation results are consistent with the simulation ones，which means that the constructed models are of higher accurate and reliable．


Analysis of Ｒoute Choice of Risk-Prone Drivers in a Stochastic Road Network

Yu Li-jun Yang Can-jie

2015, 43(12):  127-132,140.  doi:10.3969/j.issn.1000-565X.2015.12.018

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In order to reveal the relationship between the road congestion and the risk-prone drivers' route choice and risk tendency，a stochastic road network-based Weibull stochastic user equilibrium (SUE) model is constructed by combining the equivalent link disutility function and the Weibull stochastic user equilibrium of the risk-prone drivers，and an algorithm to solve the constructed model is designed by taking the minimization of the equivalent link disutility as the route choice criterion． By adopting a test case and the risk-prone coefficient obtained from the questionnaire survey data gathered in Guangzhou and by taking the equivalent link disutility function and the Bureau of Public Ｒoads function as the road performance function，both the stochastic road network-based Weibull stochastic user equilibrium traffic assignments and the Logit stochastic user equilibrium traffic assignments are performed and are then compared． Case analysis shows that the route choice behaviors of the risk-prone drivers can aggravate the congestion of some roads． Finally，the sensitivity of the constructed model is analyzed by a case study． It is found that the risk-prone coefficient significantly influences the traffic flow of some roads． This study helps to describe the traffic flow distributions of the risk-prone drivers in real road networks and deepen the understanding of travel behaviors．


Occurrence Probability Model of Bridge Fires Caused by Vehicles

Ma Ming-lei Ma Ｒu-jin Chen Ai-rong

2015, 43(12):  133-140.  doi:10.3969/j.issn.1000-565X.2015.12.019

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In view of the fact that bridge fires have posed an increasingly serious problem，the fuzzy comprehensive evaluation method is adopted to analyze the occurrence probability of vehicle fires in bridges in this paper． First，the risk evaluation index system of bridge fires is set up by taking into account all kinds of factors influencing the occurrence probability of vehicle fires． Then，the weight of each index is determined by combining the analytic hierarchy process (AHP) and the entropy weight，and the initial evaluation matrixes are also processed based on the gray fuzzy theory． Thus，an occurrence probability model of bridge fires is constructed． Because of the great similarity between bridge fires and tunnel fires，a frequency classification criterion of vehicle fires in bridges is set up by collecting the data of tunnel fires as the reference． Finally，the case analysis of a bridge is carried out，and the occurrence probability of a truck fire is obtained． The results show that the proposed model is feasible and applicable，so it can provide the decision-making basis for the fire-resistance design and safety maintenance of bridges．


Analysis of Thrust Characteristics of Ducted Propeller in Underwater Vehicle with Yawing Motion

Wu Jia-ming Ye Zhi-jian Jin Xiao-dong Zhang Cheng-wei Xu Ying

2015, 43(12):  141-148.  doi:10.3969/j.issn.1000-565X.2015.12.020

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In the investigation，the CFD approach and the multi sliding mesh technique are used to numerically simulate the thrust characteristics of a ducted propeller in an underwater vehicle with a yawing motion，in which the ducted propeller is utilized as the major control mechanism to manipulate the vehicle and the propeller running motion is influenced by the fluid field of the components of the vehicle． Then，the effect of the underwater vehicle assembly on the thrust of the ducted propeller is discussed，and the law of issuing thrust of the ducted propeller in the vehicle with a yawing motion is examined． Moreover，the hydrodynamic interaction between the ducted propeller and the vehicle assembly is analyzed． Simulation results indicate that (1) the fluid field of the underwater vehicle assembly has a non-ignorable effect on the thrust characteristics of the ducted propeller，of which the torpedoshaped buoyant hull on the front of the ducted propeller is the major factor affecting its thrust characteristics; (2)within the hydrodynamic interaction region，the smaller the axial distance between the buoyant hull and the ducted propeller，the greater the thrust issued by the ducted propeller will be; and (3) the effect of the torpedo-shaped buoyant hull on the thrust characteristics of the ducted propeller is mainly exhibited by altering the rate of advance on the ducted propeller disk． When the thrust characteristics of the ducted propeller in the underwater vehicle system is discussed，only by taking the vehicle and the ducted propeller as an integrated assembly and by incorporating such an integrated assembly with the specific environment of the underwater vehicle system to conduct relevant computation，can the results in accordance with engineering application be achieved．