Table of Content

31 March 2011, Volume 32 Issue 3

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Paper

Coherent Target Direction-of-Arrival Estimation Based on Aperture Expansion of Acoustic Vector Array UnderColored Noise

LIU Zhao-ting, RUAN Xie-yong₂, LIU Zhong₁

2011, 32(3):  257-263.  doi:10.3969/j.issn.1000-1093.2011.03.001

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An array with larger aperture generally offers enhanced resolution and direction-of-arrival (DOA) accuracy. However, in the presence of spatially colored noise or coherent sources, the performances of the subspace-based estimators degrade critically. A computationally efficient coherent sources direction finding method in colored noise using two uniform linear vector sensor sub-arrays far separated but orthogonally oriented is proposed. It is based on the forward-backward average covariance matrix of the observations between two sub-arrays, the matrix is used to eliminate the effect of the spatially colored noise and de-correlate the sources coherency. Then, a so-called propagator method (PM) is employed to obtain the azimuth-elevation angle estimates without eigen-decomposition and 2D iterative searching. The proposed method combined with the disambiguation processing can improve the resolution and DOA accuracy by increasing the sensor spacing in a certain range without the computational expensive derivation of coarse reference estimates. Monte-Carlo simulations are presented to verify its effectiveness.

Range Estimation of Air Target Using Cylinder Array

XIAO Hui， YUAN Jun

2011, 32(3):  264-267.  doi:10.3969/j.issn.1000-1093.2011.03.002

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To improve the ranging accuracy for air target, an approximately time delay method using cylinder array is presented. According to different time delay expressions for different elements in cylinder array, the formula of range estimation is derived. Based on bearing estimation results, the algorithm's performance is analyzed. An experiment is carried out to validate the algorithm's performance. The experiment and simulation results show that the relative error of range estimation drops with the increase of SNR rapidly. The error is about 6.4% under higher SNR.

A Fractionally Spaced Blind Equalization Algorithm Based on Orthogonal Wavelet Transform and Genetic Optimization

LIAO Juan， GUO Ye-cai， LIU Zhen-xing， JI Juan-juan

2011, 32(3):  268-273.  doi:10.3969/j.issn.1000-1093.2011.03.003

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Aimed at some disadvantages of traditional constant modulus blind equa

Waveguide Invariant and Passive Ranging Using Double Elements

YU Yun₁, HUI Jun-ying₁, ZHAO An-bang₁, LIN Fang₂

2011, 32(3):  274-280.  doi:10.3969/j.issn.1000-1093.2011.03.004

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Sea-trial results indicate that a stable interference structure can be observed in low frequency continuous spectra sound field. The equation of the interference striation is derived by using the concept of waveguide invariant and shows that the striations are a set of quasi hyperbolas. Some parameters, such as heading angle φ, waveguide invariant β and r₀/v (r₀ is the range of the closest point of approach and v is the target velocity) can be estimated after image processing of the LOFAR gram and bearing-time history using Hough transform. Furthermore, four methods of passive ranging based on double elements model are proposed. The simulation results show that the first algorithm should be adopted in the target heading angle less than 10°; otherwise, the latter three algorithms have to be used to range, and the larger the heading angle is, the higher the ranging accuracy is. The relative ranging errors of four methods are all less than 10%.

Beam Forming Method Based on Modal Decomposition

GAN Tian, WANG Ying-min, ZHAO Jun-wei

2011, 32(3):  281-285.  doi:10.3969/j.issn.1000-1093.2011.03.005

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For the high side-lobe defeats of conventional beam applied to actual sensor array, a new beam forming method based on modal decomposition for circular sensor array is proposed, which expands the desired beam using orthogonal series, obtains the orthogonal series coefficients by optimization method, gets array element weights according to the physical mechanism, and then composes its direction. The simulation results show that the beam designed by using this method, compared with the second-order cone methods, obtains a lower side-lobe level under the same main lobe width situation and a narrower main lobe width with the same side-lobe level. The experiment results show that the method is feasible and effective.

New Method for Sum and Difference Beam Pattern Synthesis of Low Side-lobe Using Phase Taper

XU Zhen-hua, HUANG Jian-guo, WANG Qiu-hong, PEI Xuan

2011, 32(3):  286-291.  doi:10.3969/j.issn.1000-1093.2011.03.006

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A new method for sum and difference beam forming pattern synthesis of

Cooperative Navigation for Multiple Autonomous Underwater Vehicles with Single Leader in Unknown Ocean Current

LI Wen-bai, LIU Ming-yong, LEI Xiao-kang, PEI Xuan

2011, 32(3):  292-297.  doi:10.3969/j.issn.1000-1093.2011.03.007

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Ocean current estimation is one of the major difficulties to the cooperative navigation for multiple autonomous underwater vehicles(AUVs). Aiming at the unknown current, a navigation method for multiple AUVs based on single leader vehicle is presented. By designing the relative motion trajectory between the leader and the follower vehicles, the initial positioning of the flower vehicle, the initial estimation of the current and speed error are transformed into solving a non-linear least squares optimization problem, which effectively improves the initial positioning accuracy. Furthermore, the current disturbance is considered as state variables to participate the filtering process of the cooperative navigation to obtain the real-time estimation of the ocean current and the follower vehicle's position. Simulation results show that this navigation method realizes the online estimation of the unknown current and offers good convergence and positioning accuracy.

Geoacoustic Inversion of Towed Line Array in Range-dependent Environment

QIU Hai-bin, YANG Kun-de

2011, 32(3):  298-304.  doi:10.3969/j.issn.1000-1093.2011.03.008

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Matched-field inversion (MFI) is an effective method which can infer the seabed parameters quickly. Much previous works on MFI uses a vertical line array (VLA). But, it can not be carried out in large area due to the poor mobility. Moreover, in the range-dependent environments, especially, with the increase of range between source and receiver, variation in the environment can reduce the prediction capability of the matched-field processor due to inaccuracies in the modeling. The horizontal line array (HLA) offers an advantage in terms of system mobility. The source can be towed together with the HLA, and kept at short range separations. MFI degradation due to environmental variability will be minimized or eliminated. This paper investigates the geoacoustic inversion with a towed HLA. Low frequency broad-band source signal and linear matched-field processor for geoacoustic inversion are applied, and the Bayesian and Monte Carlo methods are introduced to analyze the posterior probability density (PPD). The PPD results indicate that the geoacoustic inversions are performed well using the towed line array, and the inversion results tend to be more convergent and credible as the number of frequencies and length of HLA increase. The transmission loss is also calculated. Compared with the true transmission loss, the result indicates that the acoustic field performance prediction by using inverted parameters has small error.

New Wideband Beamforming Method Used in Underwater Communication System

SU Wei, CHENG En, YUAN Fei, SUN Hai-xin

2011, 32(3):  305-308.  doi:10.3969/j.issn.1000-1093.2011.03.009

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A novel wideband beam forming structure with constant width based on finite impulse response (FIR) digital filter with complex coefficients used in underwater acoustic communication is proposed. First, the complex envelopes of the received signal are calculated by using frequency shift method. Then, they are weighted by FIR digital filters with complex coefficients. The coefficients of these filters are obtained by using second order optimization method. The simulation results show that, in the communication band, the maximum difference between the wideband beams obtained by the proposed beam forming structure and the expected value is less than 0.3 dB when the ratio of communication band to the carrier frequency is 0.85.

A High Resolution DOA Estimation Algorithm Based on Modified Inverse Beam-forming

CHEN Li-gang₁, YUAN Bing-cheng₂, LIU Jian-guo₂

2011, 32(3):  309-314.  doi:10.3969/j.issn.1000-1093.2011.03.010

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Aimed at some inherent shortcomings, such as high sidelobe level and limited resolution, of common inverse beam-forming (IBF), a new solution for the IBF integral equation based on an auto-regressive (AR) model is presented. By regarding the received data of each element as a spatial sequence satisfying a certain AR model, the method introduces the parametric model into the solution of the IBF integral equation and makes full use of the information received by the array to estimate the spatial spectrum of the acoustic field. The method also uses the sliding average to suppress the sidelobe, and it is beneficial to the DOA estimation for the weak target signal. The pre-estimate for number of source is not required, which makes it has a robust performance than the high resolution methods based on subspace decomposition in low SNR. The feasibility and superiority of the method are confirmed by the numerical simulations and the lake experiment results.

Numerical Calculation of Ship Wake and Its Bubble Number Density Distribution

ZHU Dong-hua₁, ZHANG Xiao-hui₁, GU Jian-nong₂, RAO Jiong-hui₁

2011, 32(3):  315-320.  doi:10.3969/j.issn.1000-1093.2011.03.011

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As the detective object for an underwater weapon platform, the ship wake and its bubble number density (BND) distribution are studied. The modified Reynolds-averaged Navier-Stokes fluid dynamical model and the bubble transport theory are taken to establish a numerical model to calculate the wake BND distribution, and the model is verified by measurement data. The study results show that the wake flow expands along the wake in a small angle while its depth increases greatly, by about 2 times at location of 3 000 m behind the stern. And the total BND decreases along the wake flow with the increase of distance from the stern. However, in near field, the total BND attenuates rapidly while slowly in far field. The total BND in the eddy flow area behind propellers of the ship is much higher than those in other locations. The bubbles with radius between 10 μm and 200 μm survive for the longest time in the ship wake.

Evaluation Approach for Anti-radiation Weapon's Effectiveness

LIU Yi, ZHAO Chun-na, WANG Xue-song, WANG Guo-yu , FENG De-jun

2011, 32(3):  321-326.  doi:10.3969/j.issn.1000-1093.2011.03.012

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The combat effectiveness evaluation is the necessary step in the anti-radiation weapon development, introduction, service process. With the development of anti-radiation weapons, their effectiveness evaluation has been transferred from simple accuracy assess to check comprehensive confrontation ability. Consequentially, the combat effectiveness evaluation for the anti-radiation weapons in the complex confronted environment becomes a research focal point. Considered the present situation of firing field test, an assessment model is proposed on the basis of non-linear index aggregation. And the corresponding index system model, aggregation methods, scoring methods and weight determination are given also. Finally, the simulation results verify the efficiency and feasibility of the proposed method.

Research on Small Sample Maintainability Experimentation and Evaluation of Weapon System

DONG Bo-chao, SONG Bao-wei, LIANG Qing-wei, MAO Zhao-yong

2011, 32(3):  327-330.  doi:10.3969/j.issn.1000-1093.2011.03.013

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In order to verify the index of small sample maintainability experimentation reasonably and save experimentation costs, it analyzes deficiency in common maintainability evaluation method, based on small sample maintainability experimentation features of weapon system, from an engineering perspective, and by using Bayesian theory and prior information. It provides a sequential posterior odd test method (SPOT) and a truncated SPOT to verify maintainability index. Taking the maintainability experimentation and evaluation of a torpedo launcher as example, the method’s effectiveness and feasibility are proved.

Reliability Modeling and Analysis for Cold Standby System with Monitor Mechanism Failures

WANG Xue, GAO Pu-yun, FENG Zhi-gang, ZHANG Lang, HU Jing

2011, 32(3):  331-336.  doi:10.3969/j.issn.1000-1093.2011.03.014

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For modeling and evaluating the reliability of cold standby system, the existing formulas only take the mission of monitoring failure status into account and assume that the mission of monitoring normal status is absolutely reliable. It may cause errors for reliability evaluation. This paper analyzes the defect of the existing formulas, and derives new reliability evaluation formulas for cold standby system in two types of failure of monitor mechanism. An event tree method and decomposition method are used. The monitor and switching mechanisms are treated as two independent components, and the cold standby systems are classified as two categories I and II according to the type of switching mechanism. This paper improves the reliability evaluation for cold standby system. The formulas obtained are more flexible than the existing formulas, and may degenerate into the later one on condition of the assumption mentioned above. Two examples indicate that the new formulas are more exact.

A Geomagnetic Navigation Algorithm for Miniature Unmanned Helicopter

XU Yu， REN Qin-yuan， SUN Wen-da， LI Ping

2011, 32(3):  337-342.  doi:10.3969/j.issn.1000-1093.2011.03.015

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A geomagnetic navigation algorithm for miniature unmanned helicopter is presented. On the basis of the analysis of strapdown magnetometer output model, an ellipsoid hypothesis correction algorithm is introduced to compensate the zero bias and scale factor error based on recursive least square. The corrected geomagnetic measurements are then fused with the measurements of strapdown gyros using complementary filter. The yaw angle is finally calculated from the tilt compensated geomagnetic measurements. The experiment results show that the static yaw angle estimation error derived from the proposed algorithm is less than 1.5°, and in the autonomous hovering, trajectory tracking and landing flight modals of miniature autonomous helicopter, the algorithm can well realize the yaw angle control and the decoupling of longitudinal and lateral velocity. Thus, the proposed geomagnetic navigation algorithm can meet the requirements of miniature autonomous helicopter.

Reliability Sensitivity Analysis Using Variable Environment Test Data

HONG Dong-pao, MA Xiao-bing, ZHAO Yu

2011, 32(3):  343-347.  doi:10.3969/j.issn.1000-1093.2011.03.016

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Many products always operate under various complex environment conditions. To describe the dynamic influence of environment factors on their reliability, a method of reliability sensitivity analysis using variable environment test data is proposed. In this method, a location scale model is introduced to relate the reliability to environment factors. And the location parameter is assumed as a function of relevant environment variables while the scale parameter is assumed as an unknown positive constant. Then, the location parameter function is constructed by using the method of radial basis function. Using the varied environment test data, the log-likelihood function is transformed to a generalized linear expression by describing the indicator as Poisson variable. With the generalized linear model, the maximum likelihood estimations of the model coefficients are obtained. Thus, the influences of environment factors on the reliability of the product are measured quantitatively, especially the interaction of varied environment factors. With the reliability model, the reliability sensitivity is obtained. An instance analysis shows that the method can be used to analysis the dynamic variety character of reliability along with environment factors and is straightforward for engineering application.

Experimental Technique and Analysis

Reliability Analysis on Stiffened Panel Structure with Crack Defects

AN Hai， AN Wei-guang， ZHAO Wei-tao

2011, 32(3):  348-354.  doi:10.3969/j.issn.1000-1093.2011.03.017

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The influence of crack flaw on ultimate strength of stiffened panel is analyzed, and the reliability calculation and sensitivity analysis expressions of stiffened panel element are given also. The reliability analysis calculation method of integrity reliability index and reliability index sensitivity expressions of structure system which consists of the stiffened panel elements with crack defect are presented. The calculation formula of reverse node forces applied on residual structure after failure of stiffened panel element with crack flaw is deduced. It guarantees the calculation precision and reasonableness of reliability analysis. Finally, taken a cabin section of ship structure as an example, the reliability of structure with and without crack flaw are both analyzed comparatively. The method provides a reference for the safety design and maintenance of the structure system.

Research Notes

Classical Exact Limits of Structural Reliability for Normal Stress and Normal Strength

SUN Zhu-ling

2011, 32(3):  355-358.  doi:10.3969/j.issn.1000-1093.2011.03.018

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The estimation of structural reliability is one of main problems in mechanical reliability. The structural model whose strength and stress are all normal variables is known commonly. The interval estimation of structural reliability of this model is studied, a new method to deal with the interval estimation by using the variation coefficient of normal distribution is proposed, and a classical, precise confidence lower limit expression of structural reliability, when the parameters of the distribution for normal stress and strength are unknown, is given. It makes an important progress for the parameter estimation of this model.

Target Passive Location by Time-reversal Mirror Based on Vertical Array

SHENG Xue-li₁, LUO Fang-fang₁, GUO Yong₁, LIU Lei₂

2011, 32(3):  359-364.  doi:10.3969/j.issn.1000-1093.2011.03.019

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The passive localization technology based on the time-reversal mirror is a signal processing technology to implement spatial and temporal self-adaptation focusing for coherent sources and passive target location in the shallow sea, which can also position non-cooperative target. Four implementations for array passive time reversal mirror (APTRM) localization technology are proposed and the improved algorithms used to increase the processing gain, precision and robust of location are studied. The pool experiments and sea trials are carried out. The results validate the feasibility and practicability of this technology and show that the environment noise can be depressed effectively by using synthetic cross-correlation method, and the pseudo focus coursed by environment mismatch can be cut down by the using improved algorithms. The results also prove that the improved implementations for APTRM have good robustness and better anti-isotropic interfere ability.

A Target Location Algorithm Based on Single Direction Finding and Ranging Sonobuoy

TAO Lin-wei, WANG Ying-min

2011, 32(3):  365-369.  doi:10.3969/j.issn.1000-1093.2011.03.020

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In order to solve the problem of target location using single direction finding and ranging(DIFAR) sonobuoy, a new targets location algorithm is proposed. The algorithm based on new generation sonobuoy signal processing system makes full use of the target's Dopper information and direction estimation, and can detect, locate and track targets by using only one DIFAR sonobuoy. Furthermore, it increases calculation accuracy remarkably by using multiple test results based on the least square method. Simulation results show its correctness. And, the algorithm is simple, stable and easy to be implemented in engineering and can overcome the disadvantages of other classical algorithm which needs two DIFAR sonobuoys at least.

Position Deviation Calculation and Optimal Design of Magnetic Probes Subjected to Ocean Current

LIU Da-ming, GAO Jun-ji, ZHOU Guo-hua, LIU Sheng-dao

2011, 32(3):  370-377.  doi:10.3969/j.issn.1000-1093.2011.03.021

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In order to solve the influence of the position deviation of hanging magnetic probe subjected to ocean current on the ship's magnetic field measurement accuracy and design the magnetic probes with optimal shape and structure, a calculation method for the position deviation of magnetic probes and a optimal design method for the probe shape and structure are proposed. Firstly, the equivalent mathematical model of hanging probes is established. Based on the hydromechanics method, the total resistance applying on the cables and the different shapes probes in ocean current are calculated. Then, by using finite element method, the position deviations of magnetic probes are calculated. The rule of the probe deviation varying with its mass is analyzed. Therefore, the probe with optimal shape and structure can be determined. These methods can be used to guide the design and manufacture of magnetic probes in ship degaussing service.

Modeling and Simulation of Complex Repairable System with Built-in Test Equipment

LV Xue-zhi, YU Yong-li₁, ZHANG Han-feng₁, REN Fan₁

2011, 32(3):  378-384.  doi:10.3969/j.issn.1000-1093.2011.03.022

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In order to research the effects of built-in test (BIT) on the system and select BIT and test strategy, the modeling and simulation methods for complex system based on Simulink are put forth. The influences of the different types built-in test equipment (BITE), maintenance time and error rate on the system usability are simulated and evaluated by using the model. The simulation results show that the different types of BITE, maintenance time and error rate have different effects on the system. The simulation method for complex system based on Simulink provides a technique approach to research the effects of BIT on the system, select BIT and evaluate the test strategy.