等角圆锥投影法的误差分析

在电子对抗系统对空中目标定位时,为了简化复杂的计算,在目标不太高时,常用二维坐标。本文对较为广泛被人们接受的一种地图投影方法—等角圆锥投影法的误差进行了分析,给出在不同距离内采用等角圆锥投影方法的距离误差和方向角误差,以便在实际应用中有选择使用。

等比力法与等角位置法测试加速度计误差模型系数的比较

阐述了在重力场下分别用等比力法和等角位置法标定加速度计的方法,给出了加速度计误差模型系数的不确定度公式,比较了两种方法的加速度计误差模型系数的标定精度,对加速度计进行了实际测试和误差分析,实验结果表明两种方法的加速度计标定精度各有优劣,可针对不同误差系数的标定精度选择其一。

航海导航参数计算方法及应用

论文描述了航路点导航的基本原理,简要介绍了航海中常用的大圆航法和等角航法,分别推导了这两种航法下航程、航向角、偏航距这三种主要导航参数的计算公式,并通过算例验证了两种航法应用的正确性,这些公式可应用于海用导航仪中。

Die structure optimization of equal channel angular extrusion for AZ31 magnesium alloy based on finite element method

Three-dimensional（3D） geometric models with different comer angles （90° and 120°） and with or without inner round fillets in the bottom die were designed. Some important process parameters were regarded as the calculation conditions used in DEFORMTM-3D software, such as stress--strain data of compression test for AZ31 magnesium, temperatures of die and billet, and friction coefficient. Influence of friction coefficient on deformation process was discussed. The results show that reasonable lubrication condition is important to plastic deformation. The change characteristics for distributions of effective stress and strain during an equal channel angular extrusion （ECAE） process with inner angle of 90° and without fillets at outer comer were described. Inhomogeneity index （C） was defined and deformation heterogeneity of ECAE was analyzed from the simulation and experiment results. The deformation homogeneity caused by fillets at outer comer increased compared with the die without fillets. The cumulated maximum strains decrease with increasing the fillets of outer comer in ECAE die and the inner comer angle. The analysis results show that better structures of ECAE die including appropriate outer comer fillet and the inner comer angle of 90° for the die can improve the strain and ensure plastic deformation homogenization to a certain extent. The required extrusion force drops with increasing the fillet made at outer comer in ECAE die. It is demonstrated that the prediction results are in good agreement with experiments and the theoretical calculation and the research conclusions in literatures.

3D FEM simulations and experimental validation of plastic deformation of pure aluminum deformed by ECAP and combination of ECAP and direct extrusion

Rigid-viscoplastic3D finite element simulations(3D FEM)of the equal channel angular pressing(ECAP),thecombination of ECAP+extrusion with different extrusion ratios,and direct extrusion of pure aluminum were performed andanalyzed.The3D FEM simulations were carried out to investigate the load-displacement behavior,the plastic deformationcharacteristics and the effective plastic strain homogeneity of Al-1080deformed by different forming processes.The simulationresults were validated by microstructure observations,microhardness distribution maps and the correlation between the effectiveplastic strain and the microhardness values.The3D FEM simulations were performed successfully with a good agreement with theexperimental results.The load-displacement curves and the peak load values of the3D FEM simulations and the experimentalresults were close from each other.The microhardness distribution maps were in a good conformity with the effective plastic straincontours and verifying the3D FEM simulations results.The ECAP workpiece has a higher degree of deformation homogeneity thanthe other deformation processes.The microhardness values were calculated based on the average effective plastic strain.Thepredicted microhardness values fitted the experimental results well.The microstructure observations in the longitudinal andtransverse directions support the3D FEM effective plastic strain and microhardness distributions result in different formingprocesses.

Reheating and thixoforging of ZK60+RE alloy deformed by ECAE

The two-pass equal channel angular extrusion (ECAE) process was introduced into strain-induced melt activation (SIMA) to predeform a ZK60 alloy with rare earth (RE) addition. Microstructure evolution of ECAE-formed ZK60+RE alloy during reheating was investigated. Furthermore, tensile properties of thixoforged components were determined. The results show that the SIMA process can produce ideal microstructures, and spheroidized solid particles with little entrapped liquid can be obtained. With prolonging holding time, the size of solid particles increases and the degree of spheroidization is improved. The tensile properties of the thixoforged ZK60+RE samples are close to those of two-pass ECAE-formed samples.

Numerical and physical simulation of new SPD method combining extrusion and equal channel angular pressing for AZ31 magnesium alloy

A new serve plastic deformation(SPD) including initial forward extrusion and subsequent shearing process(ES) was proposed.The influence of the ES forming on the grain refinement of the microstructure was researched.The components of ES forming die were manufactured and installed to Gleeble1500D thermo-mechanical simulator.The microstructure observations were carried out on the as-extruded rods(as-received) and ES formed rods.From the simulation results,ES forming can increase the cumulative strain enormously and the volume fraction of dynamic recrystallization.From the physical modeling results,the microstructures can be refined.

An accelerated scheme with high quality mesh based on Lloyd iteration

High quality mesh plays an important role for finite element methods in science computation and numerical simulation.Whether the mesh quality is good or not,to some extent,it determines the calculation results of the accuracy and efficiency.Different from classic Lloyd iteration algorithm which is convergent slowly,a novel accelerated scheme was presented,which consists of two core parts:mesh points replacement and local edges Delaunay swapping.By using it,almost all the equilateral triangular meshes can be generated based on centroidal Voronoi tessellation(CVT).Numerical tests show that it is significantly effective with time consuming decreasing by 40%.Compared with other two types of regular mesh generation methods,CVT mesh demonstrates that higher geometric average quality increases over 0.99.

Triangulation Approach to Costing in Higher Education Institutions

This study presents a triangulation approach to the investigation of costing possibilities in Greek higher education institutions. The historical data contained in the financial statements of universities provide the expenditures of the latter. These expenditures are then re-determined with the use of independent variables （Jacobian determinants）, as well as with activity-based costing （ABC） and interviews, in order to obtain certainty of accuracy of the calculations and an indication of the cost of educational services, which can help determine magnitudes and improve the long-term planning of university resources. The above process can be used to create cost drivers and cost pools for the new financial burden of academic departments （cost centres） and to calculate the cost per student for each department. This information does not function at variance with or as a substitute for traditional accounting systems but in parallel （or supplementally）, providing administrators with more comparative data and a clearer picture of a university＇s economic operations which will facilitate its decision planning. Thus, it can provide higher education institutions with a decision-making tool for the following tasks： （1） allocation of national and community funds to university departments; （2） financing of textbooks, food, and accommodation; and （3） determining the optimum number of new enrolments.

Lattice Boltzmann simulation of flow around two,three and four circular cylinders in close proximity

Cross-flows around two,three and four circular cylinders in tandem,side-by-side,isosceles triangle and square arrangements are simulated using the incompressible lattice Boltzmann method with a second-order accurate curved boundary condition at Reynolds number 200 and the cylinder center-to-center transverse or/and longitudinal spacing 1.5D,where D is the identical circular cylinder diameter.The wake patterns,pressure and force distributions on the cylinders and mechanism of flow dynamics are investigated and compared among the four cases.The results also show that flows around the three or four cylinders significantly differ from those of the two cylinders in the tandem and side-by-side arrangements although there are some common features among the four cases due to their similarity of structures,which are interesting,complex and useful for practical applications.This study provides a useful database to validate the simplicity,accuracy and robustness of the Lattice Boltzmann method.

Study on intelligent control technology for forming steel pipe of pipeline with JCO process

Based on plastic bending engineering theory and machine vision technology, the intelligent control technology for forming steel pipe with JCO process is presented in this paper. By ‘twice pre-bending method’ in the first forming step, the springback law can be obtained. With the springback law and the target angle, the exact punch displacement which determines the formed angle in each bending step is predicted. In the succedent forming steps, the bending process is carried out with the exact punch displacement by real-time revising the springback law. And the angle error in each forming step is calculated by comparing the actual formed angle with the target angle. By conducting compensation for the last angle error in the next forming step, each precise bending process step is realized. A system of intelligent control technology for forming the steel pipe was developed. A calibration method is proposed to calculate the exterior parameters of the CCD camera, in which the equilateral triangle is em-ployed as the calibrating board and only one image needs to be captured. A mathematical model, which converts the angle in the image into the actual formed angle, is derived. The experimental results showed that the ellipticity of the formed pipes was less than 1.5% and the high-quality pipes can be manufactured without the worker's operating experience by employing the in-telligent control technology.

Samuel multiplicity and the structure of essentially semi-regular operators: A note on a paper of Fang

Motivated by a paper of Fang (2009), we study the Samuel multiplicity and the structure of essentially semi-regular operators on an infinite-dimensional complex Banach space. First, we generalize Fang's results concerning Samuel multiplicity from semi-Fredholm operators to essentially semi-regular operators by elementary methods in operator theory. Second, we study the structure of essentially semi-regular operators. More precisely, we present a revised version of Fang's 4 × 4 upper triangular model with a little modification, and prove it in detail after providing numerous preliminary results, some of which are inspired by Fang's paper. At last, as some applications, we get the structure of semi-Fredholm operators which revised Fang's 4 × 4 upper triangular model, from a different viewpoint, and characterize a semi-regular point λ∈ C in an essentially semi-regular domain.