一种考虑截面任意变形模式梁的有限元模型

提出了一种考虑截面完整变形的截面插值梁模型,并用于机翼结构的建模与分析。首先引入截面插值函数——拉格朗日函数描述截面形状,以位移向量为未知变量描述截面位移,在此基础上依据插值理论构造梁单元位移场。不同于传统梁单元通过假定的中性轴的挠度和转角来确定梁截面各点位移,该梁模型摒弃了中性轴假设与平截面假设,通过截面插值函数得到梁截面面内、面外变形;然后通过有限元理论推导了梁单元刚度矩阵与质量矩阵;最后利用截面插值梁单元对机翼各部件进行有限元建模,并展开典型工况下的静力学分析以及动力学分析,与Nastran实体单元计算结果进行了对比分析,验证了该梁模型的有效性,为机翼的结构设计和强度分析提供了一种新的简化建模方法。     

Special Technologies Related to Electron Beam Welding

In order to improve the manufacturing quality of electron beam welding,some technologies are developed by using the special features of electron beam.Comparing with the conventional electron beam welding,the usage of multi-beam technology and micro-beam technology are introduced.In addition.the development of beam diagnostic system is also presented.     

Vibrations of an elastic guide beam with a missile moving along it

Transverse nonstationary vibrations of a guide beam having the initial flexure are considered. An absolutely rigid missile moves under the propulsive force along this guide beam on two sliding supports. The beam displacements introduced by its vibrations are presented as an expansion with respect to the given functions according to the Ritz method. The equations of nonstationary vibration of the beam with the missile moving along it are obtained in the generalized coordinates, the expansion coefficients being chosen as them. The example is presented. Also studied is the effect of different beam and missile parameters on the beam displacement and transverse and angular velocity of the missile.     

Beam Area Determination for Multiple-Beam Satellite Communication Applications

An exact analytical model and a simple numerical solution are presented for determining the surface area of the Earth illuminated by a conical beam, with an elliptical cross section, emanating from a satellite. The model is used to generate sets of parametric curves for determination of the beam area as a function of the different satellite locations, beam locations, and beamwidths. Numerical results show that for a circular beam with a 0.25° beamwidth, the beam illuminating the northern Continental United States (CONUS) can cover an area about five times larger than the area covered by the same size beam illuminating the southern CONUS. Comparisons are also made with the available approximate methods.     

含胶层复合材料梁构件性能分析

复合材料剪切模量通常比弹性模量低1个数量级,这就导致复合材料梁结构剪切效应比普通梁结构显著得多,尤其是梁截面高度较大的情况。作为夹胶玻璃等结构的复合材料支撑框架,复合材料方管梁翼缘通常存在较弱的胶层,此时复合材料梁横截面包含不同剪切模量的材料层,这就导致梁横截面在剪切作用下发生复杂的翘曲。剪切翘曲效应对梁结构的性能有着极大的影响,本文在分段线性位移场假设基础上,推导了对称面内变形的方管梁结构静力以及自振周期计算模型,并同经典梁理论计算结果进行对比,分析了梁几何参数、胶层力学参数等因素对两个模型计算误差的影响。计算结果表明,当胶层较弱时,弱层带来的层间剪切效应对梁的性能有着决定性的影响,此时经典梁理论不再适用。     

定向通信系统天线波束指向误差分析

对影响定向通信系统天线波束指向误差的因素进行了分析,给出了一种特殊情形下波束指向误差与姿态角的关系式,同时给出了一般情形下基于最小二乘估计的波束指向误差与姿态角关系的推导方法.给出的关系式和方法对分析定向通信系统波束指向误差提供了理论依据,有助于评估定向通信系统的波束对准情况.     

Bernoulli-Euler梁振动的人工神经元网络控制方法

分析了Bernoulli-Euler梁的振动特性,从控制系统的角度得出梁振动控制系统的传递函数,并采用人工神经元网络的方法对其进行控制,辨识器及控制器均采用非线性神经元网络, 最后用matlab对振动控制系统进行仿真。     

基于MSC.Nastran优化梁元偏置的分析

在有限元结构设计分析中,对梁的受力形式以及在空间放置方式等的理解直接影响整个分析计算结果。文中将加筋板离散为板元和梁元,用大型通用有限元商业软件MSC.Nastran的SOL200优化了梁元考虑偏心和不偏心的4种工况,其结果满足位移和应力约束。对几种工况中优化后的加强筋的不同尺寸,表明存在巨大差异,且符合真实物理模型的有限元模型,即带梁元偏心的情况质量达到了最轻。将优化结果参数用于原模型,用MSC.M arc进行了模态分析,并比较了前三阶模态。最后,得出了结论,如设计中不考虑梁元偏心,会给梁元尺寸的优化结果带来极大的误差,并对刚度的影响也不可忽略。考虑梁元偏置的加筋板不仅具有最小质量,而且具有广泛的实用价值。     

Beam overlap impact on phased-array target detection

The impact of beam overlap on the probability of detection during a single scan of a phased-array volumetric scan radar is examined. Rectangular and triangular beam packing arrangements are considered. Beam positions near the beam most centered on the target are allowed to contribute to the detection process. The treatment of the impact of beam overlap on target detection for a phased array is consistent with the results that would be achieved by proper use of the search radar range equation     

A closed-form nonlinear model for spatial Timoshenko beam flexure hinge with circular cross-section

Beam flexure hinges can achieve accurate motion and force control through the elastic deformation. This paper presents a nonlinear model for uniform and circular cross-section spatial beam flexure hinges which are commonly employed in compliant parallel mechanisms. The proposed beam model takes shear deformations into consideration and hence is applicable to both slender and thick beam flexure hinges. Starting from the first principles, the nonlinear strain measure is derived using beam kinematics and expressed in terms of translational displacements and rotational angles. Second-order approximation is employed in order to make the nonlinear strain within acceptable accuracy. The natural boundary conditions and nonlinear governing equations are derived in terms of rotational Euler angles and subsequently solved for combined end loads. The resulting end load-displacement model, which is compact and closed-form, is proved to be accurate for both slender and thick beam flexure using nonlinear finite element analysis. This beam model can provide designers with more design insight of the spatial beam flexure and thus will benefit the structural design and optimization of compliant manipulators.     

Some properties of retrodirective beam of multiple sidelobecanceler

The retrodirective or perturbation beam concept is often used to aid in explaining the nulling of interference sources. The classical explanation for cancellation of a single-zero-bandwidth source is that of a perturbation beam steered to and peaking at that interferer angle. The subtraction of this perturbation beam from the main beam causes the nulling. It is shown that, for discrete point main and auxiliary antennas, this explanation can be generalized to non-zero bandwidth sources. It is demonstrated that if the main and auxiliary antennas are spatial points, then the retrodirective beam is nonuniformly weighted, steered to the interference source, and peaks at the interferer angle. For the more realistic assumption of a nonpoint main antenna, the retrodirective beam does not peak at the interferer angle for any bandwidth     

改善离子推力器束流均匀性的方法

离子推力器的束流分布,直接影响离子推力器离子光学系统（亦称栅极组件）的性能和寿命。通过对离子推力器离子光学系统的改进和放电室磁场的优化,使束流均匀性系数R值达到0.7左右。离子推力器束流分布均匀性的有效提高,有助于改善离子光学系统的受热分布,降低离子光学系统的温度,并能减小其温度差,使离子光学系统的热应力和热变形降低,进而延长离子推力器的寿命。     

Time-dependent stresses in a beam under a load moving along its surface

We studied the time-dependent processes in a beam under the action of the load that is normal to its surface and moves with the constant velocity. It was found that the maximum stresses are realized in the fixed beam section at different moments of time depending on the travel speed of external load. With increasing the load movement velocity, the maximum stresses in the region of beam clamping are reduced, while the levels of local normal and shear stresses in the limits of its action increase more significantly approaching to the limiting values in accordance to the known experimental fact that at high rates the beam failure is caused by shear stresses.     

Difference beam aided target detection in monopulse radar

The classical detection step in a monopulse radar system is based on the sum beam only,the performance of which is not optimal when target is not at the beam center. Target detection aided by the difference beam can improve the performance at this case. However, the existing difference beam aided target detectors have the problem of performance deterioration at the beam center, which has limited their application in real systems. To solve this problem, two detectors are proposed in this paper. Assuming the monopulse ratio is known, a generalized likelihood ratio test(GLRT) detector is derived, which can be used when targeting information on target direction is available. A practical dual-stage detector is proposed for the case that the monopulse ratio is unknown. Simulation results show that performances of the proposed detectors are superior to that of the classical detector.     

飞机整体翼梁结构断裂特性分析研究

研究飞机整体翼梁结构的损伤容限特性,采用ANSYS有限元分析软件,计算不同结构参数下应力强度因子,并根据最大拉应力理论确定裂纹扩展轨迹.分别讨论裂纹按照直线轨迹扩展和按照最大拉应力理论确定的轨迹扩展对应力强度因子的影响,并进行了分析比较.研究了整体翼梁结构腹板厚度及止裂筋条结构参数变化对应力强度因子及裂纹扩展轨迹的影响.     

小束斑电子束脉冲轰击偏压电源的研制

为了获得一种性价比较高的电子束表面处理技术,采用定频调压电路,研制出一种新型偏压脉冲电源。这种电源由偏压主电路拓扑、偏压变压器和偏压整流滤波电路组成,其中偏压主电路由偏压基值发生电路和偏压脉冲发生电路组成。偏压基值发生电路控制偏压脉冲基值,偏压脉冲发生电路控制偏压脉冲频率和占空比。脉冲偏压电源的脉冲基值、脉冲频率、占空比均连续可调,相应实现脉冲束流的幅值、束流频率和占空比的调节。检测分析了脉冲偏压电源的输出电压波形,带载时的输出束流波形,并观察分析了电子束轰击后钨合金组织变化规律。结果表明所研制的脉冲偏压电源输出电压稳定、可调性好,能满足小束斑脉冲电子束轰击工艺的要求。     

含裂纹梁的动力特性

 本文研究了含裂纹梁的动力特性。首先,由应力强度因子积分得到含裂纹单元体的刚阵,继而提出了一种有限元方法。将该方法应用于单边裂纹悬臂梁,计算出不同裂纹长度与位置时梁的固有频率,结果与实验值吻合良好。最后,给出了一种确定裂纹位置的简捷方法。     

电子枪束源部件结构尺寸对束流品质影响的CST仿真

在直热式电子枪中,电子枪束源部件结构尺寸的改变会改变静电场对电子束的初次汇聚,从而影响束流品质。针对电子枪中静电场以及电子运动轨迹难以用常规方法直接测量的问题,通过建立1∶1三维模型,并利用CST电磁仿真粒子工作室对整个束流产生过程进行模拟。利用控制单一变量的方法,结合模拟所得数据,得到了在不同条件下,静电场分布、电子的运动轨迹以及各个变量与最终焦点处束流电流密度关系曲线,最终得到了束流品质最优的束源部件结构尺寸。用优化了阴阳极结构及阴阳极距离后的电子枪在铝合金板材上进行实际焊接试验,所得焊缝形貌优于原有电子枪焊接所得焊缝,证明了模拟结果的正确性。此种模拟方法为改善现有电子枪束流品质以及未来电子枪设计提供了参考依据。     

轴向力作用两端支承梁的固有特性和稳定性分析

推导了轴向力作用下的两端支承梁的运动微分方程,以两端支承梁的振型函数为假设振型函数,分析了不同扭转弹簧刚度下轴向力变化对梁固有频率的影响,导出了两端支承梁在临界轴向力作用下的解析表达式,讨论了扭转弹簧刚度对梁临界轴向力的影响特性.     

Structurally coupled characteristics of rotor blade using new rigid-flexible dynamic model based on geometrically exact formulation

In rotor dynamics, blades are normally modelled as a slender beam, in which elastic deformations are coupled with each other. To identify these coupling effects, new rigid-flexible structural model for helicopter rotor system is proposed in this paper. Finite rotations of the whole blade(on flapwise, lagwise, and torsional) are described as three global rigid degrees of freedom.The nonlinear deformation geometrics of the beam is built on geometrically exact beam theory.New expressions for blade ...