Table of Content

30 March 1991, Volume 12 Issue 1

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Paper

Model-Reference Adaptive Autopilots

Zhang Yun、 Chen Desong

1991, 12(1):  1-6.  doi:10.3969/j.issn.1000-1093.1991.01.001

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A design method for autopilots has been developed using the direct model-reference adaptive algorithm. A new model~reference adaptive control law is derived. Advantages of the method lie in： no parameter identi?fication needed， simple controller implementation, good tracking perfor mance and fine robustness.

A Study on the Calculation of the Engraving Process on Projectiles

Jin Zhiming、 Zeng Simin

1991, 12(1):  7-13.  doi:10.3969/j.issn.1000-1093.1991.01.002

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Based on an analysis of the strain characteristics of the band material under conditions of strong impact, this paper puts forward a calculation method for the modeling of the projectile engraving process taken as a second-order dynamic system,Variation of the engraving drag with the pressure in gun barrel is obtained through experiments and linear analogy system theory. It is seen that the mathematica-phsical model established can be used to model quite closely the engraving process， as judged from a com-parison between the results of theoretical calculation and experiments.

Application of the Quaternion Method in Flight Trajectory Simulation of Tactical Missiles

Zheng Xiaoyu、 Qian Xingfang

1991, 12(1):  14-20.  doi:10.3969/j.issn.1000-1093.1991.01.003

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This paper discusses the application of quaternion method in the simulation of vertically launched tactical missiles and rocket-throwing submissiles. Equation derivation,computations and analysis for in-flight tra?jectory simulation of an anti-tank missile and a ship-to-air missile are also given

Robust Estimation for the Coefficient of Resistance CD

Wan Jianwei、 Xiong Dongliang、 Huang Fukan

1991, 12(1):  21-28.  doi:10.3969/j.issn.1000-1093.1991.01.004

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The coefficient of resistance CD is important for the esta?blishment of the characteristics and shooting-table of a shell. Traditionally the shooting tables are based on a large number of distance—shootings, and would Inevitably cost large sums, This paper discusses the application of Robust estimation in computing the coefficient CD defines the Robust estimation and investigates its (asymptotic) properties The paper also gives a flow chart for programming and experimental results., The results show that the computation of CD requires only a few distance-shootings.

Laminar Boundary Layer Calculation in the Symmetry-Plane of a Prolate Spheroid

Xm Wencan

1991, 12(1):  29-39.  doi:10.3969/j.issn.1000-1093.1991.01.005

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Steady and impulsiyely-started unsteady laminar boundary layer flows along the symmetry-plane of a prolate spheroid with ratio of 0.25 are calculated at incidence angles of 6°，30°，45° and 50° respectively Numerical experiments about the effect of steps on the steady calculation are carried out and appropriate steps selected.lt is found that marginal se?paration occurs near the nose at an incidence of 47° .Numerical experiments on the effects of spatial initial profiles on the unsteady calculation are also carried out and it is confirmed that the effect of the errors of spatial initial profiles are temporal and local， and that the nose singularity can be treated by the method of local similarity. Results of calculated skin friction and displacement thickness are given.

Contour Equations for Extended Range Projectiles Leading to Smallest Wave Drag

Wang Zhongyuan

1991, 12(1):  40-45.  doi:10.3969/j.issn.1000-1093.1991.01.006

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The aerodynamic shape of projectiles strongly influences their performance on ballistic trajectory. Reduction of drag is very helpful in shortening the flight time and increasing the range or to slow down the reduction in velocity. According to the present status of the extended ran?ge projectiles,the paper is devoted to a study of their aerodynamic shape and deduces contour equations leading to smallest wave drag. It is useful in the design of aerodynamic shapes for such a kind of projectiles.

Disturbance on an Armor-Piercing Jet Caused by an Explosive Armor

Zhu Dingbo、 Li Jingyun、 Li Dejun

1991, 12(1):  46-53.  doi:10.3969/j.issn.1000-1093.1991.01.007

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The paper aims to studvy the mechanism of interaction between an explosive armor and an incoming jet. Two dynamic models of the jet having respectively continuous and discontinuous disturbances caused by plates of the explosive armor have been set up. The formula for an expand?ing hole in a thin moving plate due to the jet is derived. Finally, the concept of degree of interference for the jet has been proposed. A compa?rison between the experimental results and computational ones is given.

Adaptive Noise Cancellation in Hydrodynamically Activated Mines

Ma Ning、 Liu Yuanheng

1991, 12(1):  54-59.  doi:10.3969/j.issn.1000-1093.1991.01.008

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By analysing the measures taken to counteract interferences on existing hydrodynamically activated fuzes, this paper points out that in some circumstances fuzes with these anti-mtarference methods still cannot meet all the requirements and suggests that the adaptive noise cancellation concept can be used to eliminate oceac wave interference. Computer simulation results show that the signal-to-noise ratio can be enhanced conside?rably The problem of strong ocean wave interference is solved, ft seems that the use of adaptive technology in mine fuzes has not been reported so far. This paper presents a new method with which the anti-interfereacfe performance can be obviously improved.

Crystal Structure and Piezoelectricity of Poly(vinylidene Fluoride）

Yan Fuming

1991, 12(1):  60-67.  doi:10.3969/j.issn.1000-1093.1991.01.009

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The piezoelectricity of PYDF originates from the oriented β cry?stal phase. Crystalline structure and morphologic transformation of orient?ed PVDF film have been studied by Laser Small Angle Light Scattering (SALS) and X-ray diffraction (WAXD). A piezoelectric plastic has been developed possessing excellent properties.

Experimental Techniques and Analysis

An Electronic Crusher Gauge

Zu Jing、 Zhang Wendong

1991, 12(1):  68-71.  doi:10.3969/j.issn.1000-1093.1991.01.010

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In this paper the principles of operation constructional features of a new pressure-measuring device—the Electronic Crusher Gauge are given. A bore pressure curve as obtained on a howitzer is given, and measurement data are compared with those obtained with a conventional copper crusher gauge

Dynamic Calibration of High-Pressure Transducers by a Quasi-6 Function Excitation source

Pan Deheng、 Lu Hongnian、 Wang Shuguang

1991, 12(1):  72-77.  doi:10.3969/j.issn.1000-1093.1991.01.011

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In this paper a dynamic calibration method using a finite duration impulse excitation source is presented , which can be used to calibrate the frequency response of high-pressure transducers(HPT). Some useful formulas are derived to arrive at the difference between the frequency spectrum of finite duration impulse and that of theδfunction or semi-sine impulse. With them the frequency range and crror of calibration can be assessed.In the conclusion, it is pointed out that the dynamic calibration method sets upan effective measure to calibrate the dynamic sensitivity of HPT (or the measuring system )by static ca-libration ,because the frequency response of HPT (or the measuring system )can be calibrated at 0 Hz by the method,and within the frequency range of 0-20 kHz the dynamic calibration method using this technique can solve the problem of dynamic calibration of pressure measuring systems under the pressure of lOOOMPa with an error of calibration of modulus o,r phase spectrum not exceeding 2% - 5% or 0.1°

Research Notes

Boundary Element Method in Two-Dimensional Incompressible Flow

Liu Xiyun

1991, 12(1):  78-81.  doi:10.3969/j.issn.1000-1093.1991.01.012

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The paper discusses applications of boundary element method in the solution of problems involving 2D incompressible flow. The continuity equation is translated into an integral equation by the vector Green formula. For potential flow, vorticity only distributes in the interior of boundary layer, then the tangential velocity at the outer edge of the boundary layer equals —X, where X is the strength of the vortex. If no-slip condition on the solid surface is assumed, the tangential velocity on the middle line of the boundary layer equals 一0.5X, The intergral equation is numerically solved, the strength of the vortex obtained, and distribution of the velocity is found.

An Analysis of the Dispersion of Base Bled Projectiles

Guo Xifu

1991, 12(1):  82-85.  doi:10.3969/j.issn.1000-1093.1991.01.013

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In this paper the dispersion of base bled projectiles is estimated，and the effects of various factors on the dispersion of the projectile analyzed. Factors that affect the dispersion of base drag with base bleeding are discussed, and methods of reducing the dispersion are given. Firing tests have verified the theory and method given in this paper.

Dynamic Fracture of Explosion Rings

Lu Yu、 Zhou Lanting

1991, 12(1):  86-80.  doi:10.3969/j.issn.1000-1093.1991.01.014

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Rapidly expanding rings loaded by explosives are ana-lyzed in this paper. Their fracture process and rupture characteristics as related to the behavior of materials are studied, A modified Kipp- Grady model for fracture energy is presented. Expressions are obtained for the nominal fragment size which are in good agreement with the experimental results.

Stress-Intensity Factors for Shallow Surface Cracks inside a Thick-Walled Cylinder

Huang Shizhen、 Lu Jingyu、Shen Peihui

1991, 12(1):  91-96.  doi:10.3969/j.issn.1000-1093.1991.01.015

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This paper presents the stress-intensity factors KI for axial shallow cracks on the inside of a pressurized thick-walled (RO/ Ri = 125/60) cylinder. The cracks are of semi-elliptical shape, having depth to crack length (a/c) ratios 0.35 and 0.15 respectively. The ra?tio of crack depth to wall thickness (a/ t) ranges from 0.05 to 0,35. stress-intensity factors are calculated by the boundarj-element method. The boundary-element models employ 8-node quarter point singular elements along the crack front and 8-node isoparameter elements else?where. The stress-intensity factors are evaluated from nodal point dis?placements at the crack surface. Effects of the shape and depth of cracks and that of the cylinder length on the stress-intensity factors are investigated. To estimate the accuracy of the solutions，benchmark problem involving similar mesh schemes are calculated，with fairly sa-tisfactory results.