Table of Content

25 March 2014, Volume 35 Issue 3

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Paper

Design of Folded-cranktrain of Opposed-piston Two-stroke Internal Combustion Engine

ZHANG Fu-jun, GUO Shun-hong, WANG Bin, ZHANG Zhen-yu, WU Tao-tao, DONG Xue-fei

2014, 35(3):  289-297.  doi:10.3969/j.issn.1000-1093.2014.03.001

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Four design solutions are proposed for the folded-cranktrain of an advanced opposed-piston internal combustion engine. The kinematics and dynamics models of the proposed folded-cranktrains are established using Matlab/Simulink and ADAMS, and the best solution is obtained by analyzing the numerical simulation results. The results show that the piston kinematics characteristics of these four solutions are asymmetrical with respect to TDC, and the intake duration and compression duration are different compared with traditional internal combustion engine, which influences the turbulence intensity, scavenging quality and combustion isovolumetric degree. In view of dynamics, the lateral pressure of piston is much lower than that of traditional two-stroke internal combustion engine, which helps to reduce the abrasion of cylinder wall. Since Solution 4 has better spatial structure layout flexibility and system balance, the piston motion is conducive to the improvement in the charging efficiency of engine and the mixing rate of fuel and air; moreover, it also can shorten the ignition delay period, so Solution 4 is the optimal solution.

Study on the Contamination Wear Failure of Hydraulic Valve and the Influencing Factors

GE Peng-fei, ZHENG Chang-song, MA Biao

2014, 35(3):  298-304.  doi:10.3969/j.issn.1000-1093.2014.03.002

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The contamination wear failure of hydraulic valve is one of the common faults of tracked vehicle. The contamination wear process of hydraulic valve is analyzed from a micro point of view. A model of contamination wear process is established using the theory of three-body abrasion and oil analysis, and then the model is verified by an example. At last, the influencing factors of the hydraulic valve contamination wear are analyzed. Results show that the model is reliable. A lower hardness difference between the spool and the body, a shorter spool contact length and a smaller spool diameter lead to a longer contamination wear life; a higher oil contamination level, a larger proportion of big particles, a higher operating pressure and a higher operating temperature cause a shorter contamination life.

Accurate Calculation for Deformation of Multi-bearing Shafting System

LIU Yue, ZHOU Guang-ming, ZHANG Zu-zhi, DU Wan-li, MA Gui-ye

2014, 35(3):  305-311.  doi:10.3969/j.issn.1000-1093.2014.03.003

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A new modeling method of shaft-bearing stiffness coupling and an iterative method for calculating the deformation of multi-bearing shafting system are presented for the typical complex multi-bearing shafting system used in driving system. The bearing stiffness matrix is created by Newton-Raphson method through the following steps: calculation of contact stress and deformation, calculation of internal load distribution, and solution of rolling elements mechanics equilibrium equations, which is based on the theory of bearing geometry and contact mechanics. The shafting system stiffness matrix is constructed by coupling the Timoshenko beam and bearings. The deformation of system can be solved by iterative matrix displacement method of variable bearing stiffness, which is applied to SSOR iterative matrix. It is proven that the method has better convergence, lower demand to initial data, and higher accuracy, which is more convenient to use for engineering design.

Active Control Technology of Engine for Powertrain Plant During Upshifting

SUN Yong-gang， ZHAO Chang-lu， LIU Bo-lan， ZHANG Fu-jun

2014, 35(3):  312-317.  doi:10.3969/j.issn.1000-1093.2014.03.004

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Active control technology of engine is an important means to improve shift quality. For a powertrain plant of light tracked vehicle, the upshift dynamic process of the tracked vehicle is simulated and studied, and the effect of active control strategy on riding comfort and acceleration is discussed. The results show that the active control strategy can be used to improve the riding comfort of vehicle during upshifting, but the increase in reducing the fuel quantity and the shortening in the time of fuel reduction can improve the shift-feel and increase the power loss during upshifting.

Joint Target Tracking and Classification Based on Aerodynamic Model and RCS Observation

GUO Peng₁， BAI Liang₂， WU Meng-jie₂， JIANG Hong₁

2014, 35(3):  318-325.  doi:10.3969/j.issn.1000-1093.2014.03.005

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An effective joint target tracking and classification technology, which uses the radio frequency modulation (FM) signals transmitted by the commercial broadcast stations on ground, based on the aerodynamic model and RCS observation is proposed for the ground-based passive warning radars for monitoring the low altitude penetration incoming targets. The aerodynamic model is used to describe the translation and rotation of target, and the specific parameters of a particular type of aircraft are transferred to the tracker to realize the aerodynamic model-based tracking; at the same time, the radar cross section (RCS) is included in the observation to provide the main classification featuers, and the outputs of the tracker are used to predict the RCS value. Therefore, tracking and classification are coupled tightly to give full play to the advantage of joint tracking and classification, effectively improving the tracking performance and classification probability. In the implementation of this technology, the electromagnetic simulation software FEKO is applied to obtain the target’s real-time RCS observation; this joint tracking and classification is realized by particle filtering. A simulation platform for the FM signal-based target tracking and classification by passive radar is built. The simulation results show that the interacting multiple model regularized particle filter works better than the interacting multiple model particle filter in tracking accuracy and classification probability.

Three-dimensional Passive Localization of Near-field Source in a Multipath Environment

LIANG Guo-long， HAN Bo， SUN Xiang-qian

2014, 35(3):  326-332.  doi:10.3969/j.issn.1000-1093.2014.03.006

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A localization method based on the horizontal array in a multipath environment is presented for three-dimensional passive localization of near-field source. The result of underwater acoustic image measurement is obtained in an arbitrary scanning depth, and then the focal points of the signal source and the virtual source formed by surface reflection could be located by spectral peak searching. The three-dimensional coordinate is corrected by the geometric relationship of the focal points. The simulation shows that the different scanning depths have little impact on localizaton accuracy, the localization error increases with further distance between the source and the array, and the method is invalid when the source is much closer to the array because of aliasing in the two focal points. The method could three-dimensionally localize the near-field passive source within a certain region in a multipath environment.

Experimental Study on Unsteady Ventilated Cavitating Flows around an Axisymmetric Body with Cavitator

WANG Fu-feng, WANG Guo-yu, HUANG Biao, HU Chang-li, LIU Tao-tao

2014, 35(3):  333-339.  doi:10.3969/j.issn.1000-1093.2014.03.007

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The unsteady characteristics of ventilated cavitating flows around axisymmetric body with a cavitator are addressed by using experimental methods. Cavities around the body are observed by means of a high-speed video camera in the different conditions. The results show that the shapes of the cavities increase with the increase in ventilation rate at the same Froude number, and they develops from the free cavities to the supercavities. In the supercavitating flow stage, a smooth and clear interface exists between main stream and supercavitating region. The cavity shapes decrease with the increase in Froude number at the same ventilation rate. The ventilated air doesn’t form a big bubble because the air flows to downstream of flow field with the high speed flow. The unsteady characteristics can be observed in ventilated cavitating flow field. The velocity of re-entrant jet increases with the increase in ventilation rate.

Optimization of Direction-of-arrival Estimation of Single Pressure Gradient Vector Hydrophone

WANG Xu-hu， CHEN Jian-feng， HAN Jing， ZHANG Qun-fei

2014, 35(3):  340-346.  doi:10.3969/j.issn.1000-1093.2014.03.008

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The performance of direction-of-arrival (DOA) estimation of single pressure gradient vector hydrophone degrades rapidly when the diameter-wavelength ratio is more than 0.2. A modified MUSIC algorithm for single pressure gradient vector hydrophone is presented, which improves DOA estimation performance by optimizing the steering vector of the pressure gradient vector hydrophone. Simulation results indicate that the estimation performance of the MUSIC algorithm is better than that of the sound intensity method, and the modified MUSIC algorithm for single pressure gradient vector hydrophone has better estimation performance and robustness compared with MUSIC algorithm when the diameter-wavelength ratio is more than 0.2. The results of the lake trial powerfully testify the validity of the modified MUSIC algorithm for single pressure gradient vector hydrophone.

A Time-variant Curve Model-based Automatic Equalization Method for Synthetic Aperture Sonar Images

LIU Wei, JIANG Ze-lin, LIU Ji-yuan, HUANG Hai-ning

2014, 35(3):  347-354.  doi:10.3969/j.issn.1000-1093.2014.03.009

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A time-variant curve (TVC) model-based automatic equalization method is proposed for the intensity variation problem of synthetic aperture sonar (SAS) images. A theoretical expression of TVC is deduced based on sound transmission model, underwater backscattering strength model and SAS image model. A method to calculate the TVC observations is established based on the statistical model of SAS images. An estimation method based on non-linear least square fitting model (NL-LSFM) is used to acquire the optimized parameter of TVC. At last, the SAS images are automatically equalized and enhanced based on the optimized TVC. The method proposed has been validated by lake and sea trials. The test results show that the result calculated by the TVC expression is consistent with the experimental data, and the automatic equalization method can remove the intensity variation of SAS images properly.

Effect of Wave Phase on Hydrodynamic Characteristics of Underwater Vehicle out of Water

ZHU Kun， CHEN Huan-long， LIU Le-hua， YANG Xiao-guang， ZHANG Ji-hua

2014, 35(3):  355-361.  doi:10.3969/j.issn.1000-1093.2014.03.010

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To explore how wave and cavity affect the mechanic property of underwater launched vehicle, the hydrodynamic characteristics of vehicles are researched through numerical simulation, the physical mechanism is analyzed for the development of cavitation-geometrical features near the water level with changeable launching wave phase, and the related flow field data is presented. The results show that the variation of phase leads to the shearing motion of particles close to the free surface, of which intensity and direction are the important factors to cause the asymmetrical structure of cavity on the vehicle shoulder. The asymmetrical feature contributes to an apparent diversity of mechanical load between the upstream and downstream faces, which has an adverse effect on the vehicle attitude during launching, consequently influencing the hit accuracy.

The Lagrangian Coherent Structure-based Investigation of Cavitating Flows around a Disc

BAI Ze-yu, WANG Guo-yu, WU Qin, HUANG Biao

2014, 35(3):  362-370.  doi:10.3969/j.issn.1000-1093.2014.03.011

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The cavitating flows around a disc is analyzed based on finite-time Lyapunov exponents (FTLE) and Lagrangian coherent structure (LCS). The inhomogeneous model is utilized to predict the interaction between vapour and water flows in the simulation. The simulation results are confirmed by the experimental data. The analytical result shows that LCS defined by the ridges of FTLE can be divided into straight and circular LCSs. The straight LCS reflects that the disc hinders the motion of fluid, and the circular LCS distinguishes the large-scale vortex and identifies the center of vortex accurately. The vortex is intensified and the distribution is concentrated with the development of cavity. It is the periodic change in the intensity of re-entrant flow that causes the periodic expansion and contraction of cavity. A low FTLE region emerges near the support-rod with the increase in re-entrant flow, and there exists a corresponding relationship between the region and the start point of streamline.

Computational Analysis and Prediction of Wave Forces on Portable Underwater Vehicle

PAN Guang，LIU Ya-nan，DU Xiao-xu，Saeed Akram Malik

2014, 35(3):  371-378.  doi:10.3969/j.issn.1000-1093.2014.03.012

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The wave forces on portable underwater vehicle during sailing close to water surface are calculated based on panel method. Hydrodynamic forces acting on the underwater vehicle under the desired sea wave condition is calculated when it floats and submerges as well as operates at a constant velocity in a constant depth beneath the free surface waves. The effects of various factors, such as wave frequency, vehicle depth, direction, etc., on surge, heave and pitch are analyzed. A real time lognitudinal position is used instead of encounter frequency. The results are then used to derive the analytical formulae for wave forces and moment by curve fitting approach. The results are satisfactory by comparing the prediction and the real-time simulation. The proposed method can be used to assess the maneuverability of underwater vehicle when it operates in the ocean wave environment. The accuracy of the numerical simulation is ensured by verifying the difference between numerical simulation and experimental results.

Robust Adaptive Beamforming of Acoustic Vector-sensor Array Based on Least Squares Estimation

WANG Yan，WU Wen-feng，LIANG Guo-long

2014, 35(3):  379-384.  doi:10.3969/j.issn.1000-1093.2014.03.013

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The performance of Capon beamformer of acoustic vector-sensor array degrades sharply in the presence of array steering vector mismatch. A robust beamforming algorithm based on least squares estimation is proposed to solve this problem. Several generalized sidelobe cancellers are designed for acoustic pressure channel and vibration velocity channel in consideration of the different error sources of their steering vectors.The Capon beamformer of acoustic vector-sensor array is converted to a robust least-squares estimation problem based on the principle of worst-case performance optimization. The second-order cone programing is adopted to obtain the optimal solution. The simulation results show the efficiency of the proposed algorithm in the cases of steering vector mismatch, snapshot deficiency and sensor attitude error.

Hyper Beam Amplitude Weight-based Blind Space Spectrum Subtraction for Interference Cancellation

ZHOU Hong-jin, ZHONG Yun-hai, YI Cheng-tao, LI Wei

2014, 35(3):  385-391.  doi:10.3969/j.issn.1000-1093.2014.03.014

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A blind space spectrum subtraction(BSSS) method based on hyper beam forming for interference cancellation is proposed for two typical near-field strong interference sources (towed-ship self noise and friendly neighbor ship noise) which affect the target detection performance of towed array sonar. The hyper beam technology is used to form multi-beams to cover a strong interference area. The amplitude spectrum of interfering beams is computed, and the multi-beam amplitude spectrum is subtracted from the basic element field amplitude spectrum by using an appropriate spectrum subtraction strategy. The frequency signal of basic element field is get from the cancelled amplitude spectrum signal, and the target azimuth is estimated using the frequency field block adaptive filtering algorithm. The simulation and sea test results show that BSSS method can improve the array gain by about 10 dB compared to the minimal variance distortionless response(MVDR) method under the conditions of high interference-to-noise ratio and low signal-to-noise ratio. BSSS method can be used simultaneously to cancel the towed-ship self noise and the friendly neighbor ship noise, and effectively reduce the fluctuation of detected background.

Multi-objective Optimal Design of Automatic Underwater Vehicle Shell Structure

DONG Hua-chao, SONG Bao-wei, WANG Peng

2014, 35(3):  392-397.  doi:10.3969/j.issn.1000-1093.2014.03.015

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A multi-objective optimal method based on adaptive response surface is proposed for the multi-objective optimization of deep-sea AUV (automatic underwater vehicle) shell structure. The original samples are obtained by the experimental design, the response surface methodology is used to create an approximate model, and the Pareto solution set is obtained after optimization. A spatial sampling method is introduced to get the equally distributed samples from Pareto solution set.

Measurement of Interface Bond Quality of Composite Structure Using Nonlinear Ultrasound

JIANG Nian， WANG Zhao-ba， JIN Yong， CHEN You-xing

2014, 35(3):  398-402.  doi:10.3969/j.issn.1000-1093.2014.03.016

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A nonlinear ultrasonic test system is established to meet the needs of evaluating the interface bond quality of composite structure. Epoxy resin is chosen as adhesive to make three sets of specimens which are made up of synthetic glass/adhesive/steel so as to simulate the different bond strengths with three different rations of epoxy resin to curing agent. For the problem of the complexity to determine the mode of lamb using lamb wave approach and the situation of that bond states cant not be evaluated based on second harmonic exciting efficiency using pulse-echo ultrasonic techniques, a method is developed, in which the specimen is excited by a single-frequency ultrasound, and A₂/A₂₁ (the ratio of second harmonic A₂ to fundamental wave A₂₁) is used to characterize the degree of nonlinear ultrasonic response. The experimental results indicate that the interface bond quality reduces with the increase in the degree of nonlinearity, and thus it can effectively evaluate the interface bond quality.

Research Notes

Comparative Analysis of Combustion and Emissions of DI Engine Operating on Diesel/Methanol by Different Methods

LI Ren-chun₁, WANG Zhong, YUAN Yin-nan, ZHANG Deng-pan, LI Ming-di

2014, 35(3):  403-408.  doi:10.3969/j.issn.1000-1093.2014.03.017

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The combustion process and emissions of diesel with 10% of diesel/methanol blend or 10% of port-injected methanol are studied. 4B26 turbo-charge DI engine without any change in its original structure is test at a constant speed of 2 200 r/min under the conditions of four different engine loads, which is equipped with an electrically-controlled port injection system. The result shows that the in-cylinder pressure of DI engine has no great difference in the use of diesel/methanol blend and port-injected methanol. Compared with diesel/methanol blend, the port-injected methanol gives a lower intake air temperature, contributing to a further lower exhaust temperature. The ignition delay period becomes longer at low load, and NOx and soot emissions are reduced significantly, meanwhile, HC and CO emissions are high. In both cases, compared with diesel, the maximum pressure hardly changes, the in-cylinder temperature decreases, and the ignition delay postpones at low load; NOx and soot emissions are reduced, and HC and CO emissions are increased.

Numerical Simulation of Rotary Self-cleaning Air Pre-filter Based on CFD

TAN Ye-fa， DONG Gui-yang， TAN Hao-guang， TAN Hua， WANG Xiao-long

2014, 35(3):  409-414.  doi:10.3969/j.issn.1000-1093.2014.03.018

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An effective computational method is provided for the design and performance optimization of new efficient air pre-filter. The method can be used for the numerical simulation of transient turbulent flow in air pre-filter. A 3D geometric model of rotary self-cleaning air pre-filter flow channel is established by FARO-LDI 3D laser scanning measurement system which is used for reverse modeling. The hybrid grid of flow channel is generated by ANSYS ICEM CFD. The passive rotation of the rotating impeller is achieved by the user-defined function and the sliding mesh model of the multi-flow region coupling algorithm in Fluent. The RNG k-ε turbulence model and PRESTO pressure discrete format are used in the simulation, SIMPLE algorithm with first order upwind format is used for pressure-velocity coupling, and the central difference scheme is also used in the diffusion and pressure terms of the momentum equation. The results show that this method can be used accurately to calculate the flow field of air pre-filter and simulate the passive rotation state of rotating impeller.

Simulation of Hydrogen-Oxygen Combustion of Combustion Light Gas Gun Using Detailed Chemical Kinetics Model

DENG Fei， ZHANG Xiang-yan

2014, 35(3):  415-420.  doi:10.3969/j.issn.1000-1093.2014.03.019

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The hydrogen-oxygen combustion single-zone model of a combustion light gas gun is given based on the 19-step detailed chemical reaction mechanism of burning hydrogen-oxygen. The combustion process of hydrogen-oxygen mixed gas in projectile is simulated by this model. The numerical simulation results are in good agreement with the test results in Ref.［1］, and reflect the thermodynamic process of hydrogen-oxygen combustion in a combustion light gas gun. On this basis, the combustion processes of hydrogen-oxygen gases with different conditional parameters are also calculated. The influences of initial temperature, initial pressure, diluents composition and its ratio on the interior ballistic performance of combustion light gas gun and the changes of each chemical composition in hydrogen-oxygen combustion process are analyzed. The results show that initial temperature, initial pressure, diluents composition and its ratio significantly affect the interior ballistic performance of combustion light gas gun.

DOA Estimation of Wideband Linear Frequency Modulated Pulse Signals Based on Fractional Fourier Transform

WANG Rui, MA Yan

2014, 35(3):  421-427.  doi:10.3969/j.issn.1000-1093.2014.03.020

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A new method for a center frequency estimation based on fractional Fourier transform (FRFT) is proposed for the case that the time width of wideband linear frequency modulated pulse signals is not equal to the width of observation time. The MUSIC algorithm for direction of arrival (DOA) estimation in the fractional Fourier domain is improved. Based on the energy-concentrated properties of linear frequency modulated signal in the fractional Fourier domain, the proposed approach is used to analyze the change of center frequency with the position variation of pulse signal in observation time. And the array manifold vector of fractional Fourier domain is constructed using the MUSIC algorithm for DOA estimation. Numerical simulation shows the effectiveness of the algorithm for DOA estimation. Then the influence of the SNR and time width in observation time on DOA estimated results is analyzed.

Acoustic Attenuation Modeling of Buried Mines in Different Sediments and Depths

LI Tong-xu, ZHANG Xiao-min , HAN Chong， CHEN Yu

2014, 35(3):  428-432.  doi:10.3969/j.issn.1000-1093.2014.03.021

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Biot-Stoll model is used to predict the attenuation and transmission coefficients of sound in coarse sand, sandy clay and clay mud. A sound attenuation model for buried mines in different sediments and depths is established by studying the acoustic propagation characteristics of various sediments, and the effect of burial on buried mine is analyzed. The result shows that the different sediments，the buried depth and the operating frequency of fuze have different impacts on the functions of mine fuze. In the same depth and the frequency range of 10 Hz~5 kHz, the coarse sand has the greatest influence on the acoustic fuze, and the clay mud has the least influence on the acoustic fuze. The effect of burial on acoustic fuze is decreased with the increase in porosity and the decrease in average particle diameter.