静态低应力无变形焊接技术的数值模拟与优化

针对静态低应力无变形技术(LSND)在铝合金薄板焊接上的应用,开展了其焊接过程应力应变分布特征的有限元数值模拟和优化研究.分别建立了常规钨惰性气体(TIG)焊接和静态低应力无变形技术焊接时温度场和应力应变场的有限元模型,计算了两种方法焊接时温度场、应力应变场的差异.根据数值模拟结果,优化了静态低应力无变形技术的两个重要工艺参数:加热温度和加热区域边缘到焊缝中心的距离,给出了针对具体材料和试件尺寸的工艺参数推荐值.     

钛合金薄板对接及锐角接电子束焊接

针对TC4钛合金薄板对接接头和TC1钛合金薄板锐角接头进行电子束焊接工艺研究,得到TC4及TC1钛合金薄板的电子束焊接工艺参数.通过常规力学性能测试和X射线检查,TC4钛合金对接焊缝的拉伸强度平均为1050MPa,达到了母材强度的95％以上.试验结果证明,上述工艺参数得到的焊缝,满足设计及相关文件的要求.     

随行辅助预热电子束薄板焊接的数值模拟

电子束焊接薄板过程中,由于局部加热过快,易产生焊接变形。因此,在电子束焊接的主热源两侧引入基于高频扫描技术的电子束辅助热源,进行焊前预热,以达到减小焊接变形的目的。建立了矩形均匀加热辅助热源模型,采用热弹塑性有限元分析方法对1.5mm厚不锈钢薄板随行辅助预热电子束焊接进行数值模拟,并且进行了试验验证。结果表明,焊后残余应力和变形的模拟结果与试验所得结论一致。电子束焊接随行辅助预热方法不仅可以改变熔池前方材料的应力状态,而且当熔池形成瞬间熔池时,还可以减小前方材料的压应力峰值,有利于减小薄板结构的焊接变形。     

一种针对局部结构的有限元模型修正方法

针对实际结构有限元模型（FEM）的建模误差通常仅存在于局部区域,提出了一种对局部结构单独进行模型修正的方法。首先,根据频响函数（FRF）解耦理论得到由残余结构频响函数与包含待修正参数的局部结构动刚度所重构的整体结构频响函数的拟合值,然后通过迭代优化使其与测量值的残差最小化,从而得到参数的极大似然估计。在此基础上,将残差关于参数的灵敏度以局部结构动力学矩阵表示,建立了模型修正的基本方程,利用整体结构的测试数据即可直接对分离出来的局部结构进行模型修正。最后,对喷气式飞机和三角机翼飞机分别进行了数值模拟和实验研究,验证了所提方法的可行性和有效性。结果表明,所提方法可以成功地用于仅局部区域含有建模误差的实际结构有限元模型的修正,修正后的有限元模型的动态特性与实际结构有较好的一致性。     

CP3薄壁焊管数控弯曲成形有限元分析

根据焊接管材的特点,通过母材试样和包含焊缝及焊缝热影响区的混合试样的单向拉伸试验以及混合试样横截面的显微硬度测试,基于拉伸过程的等应变假设和混合法则,得到了CP3焊管母材、焊缝以及焊缝热影响区的材料拉伸应力应变关系.进而建立了薄壁CP3钛管数控弯曲有限元模型,分析了弯曲参数对焊管弯曲结果的影响,比较了均质管模型和焊管模...     

Q235钢相变超塑性焊接试验及有限元分析

试验研究了Q2 35钢相变超塑性扩散焊接过程 ,从中得出工艺参数对焊接接头的影响规律 ,并利用有限元方法研究了焊接接头的变形、应力和应变。模拟结果表明 ,焊缝质量好坏主要取决于界面上拉应力出现的位置以及拉应力的数值大小 ,因而要求工艺参数的合理配合     

GARTEUR有限元模型修正与确认研究

待修正参数的选择以及修正后模型的质量评估是有限元模型修正的两个重要问题。以欧洲学术界广泛采用的GARTEUR飞机模型为例,利用基于灵敏度分析的模型修正方法,通过仿真算例研究参数选择对模型修正质量的影响,并以试验数据为目标值对有限元模型进行修正与确认。为全面评估模型的修正质量,引入三级标准对修正后有限元模型进行确认。     

2524铝合金的搅拌摩擦焊对接工艺

以2524-T3板材作为试验材料,研究了薄板的搅拌摩擦焊对接工艺,优化了对接焊的工艺参数,获得了焊接工艺窗口及最优工艺参数.在最优工艺参数下生产的对接焊件具有良好的质量外观,焊件的变形量和焊缝减薄量极小;焊件的X射线检测结果表明焊件内部质量良好,没有在照片上发现缺陷;金相组织分析显示,焊缝横截面组织均匀致密;焊接接头静力拉伸性能测试结果表明焊缝抗拉强度的平均为397 MPa,为母材抗拉强度的90.4％.     

应力比对不锈钢焊接接头疲劳寿命的影响研究

针对0Cr18Ni9不锈钢薄板焊接接头,开展了高周疲劳性能测试,研究了应力比对其疲劳极限和疲劳寿命S-N曲线的影响。结果表明应力比对疲劳寿命有较大的影响,在最大应力一定的情况下,应力比越大其疲劳寿命越大。基于试验结果,得到了反映应力比影响的0Cr18Ni9不锈钢薄板焊接接头Goodman修正和Walker修正的高周疲劳寿命预测模型。模型的预估寿命和试验数据对比表明,Walker修正模型对疲劳寿命的预测结果全部处于1.0倍分散带以内,其更能反映应力比对0Cr18Ni9不锈钢薄板焊接接头疲劳寿命的影响。     

液体火箭发动机喷管简化建模及模型修正

为了准确掌握喷管的动力学特性,提出了一种等效简化建模结合试验数据的模型修正方法。首先,将喷管的原始几何模型经过几何处理成简化模型,建立了喷管的有限元模型,对有限元模型在自由条件下进行模态计算,将得到的计算数据与测试数据对比分析,再利用测试数据对有限元模型的弹性模量参数进行修正,修正后的喷管有限元模型前9阶模态计算结果与测试结果频差在5%以内,MAC值(模态置信准则)在0.8以上。表明此方法是一种高效可行的喷管简化建模方法,既保证了精度又提高了计算效率,对其动力学特性分析、振动响应预测等方面具有重要应用价值,对于液体火箭发动机其他部件的动力学建模及分析也具有普适性。     

The effect of inlet conditions on the flow and heat transfer in multiple rotating cavity with axial throughflow

This paper discusses experimental results from two different build configurations of a heated multiple rotating cavity test rig.Measurements of heat transfer from the discs and tangential velocities are presented.The test rig is a 70% full scale version of a high pressure compressor stack of an axial gas turbine engine.Of particular interest are the internal cylindrical cavities formed by adjacent discs and the interaction of these with a central axial throughflow of cooling air.Tests were carried out for a range of non-dimensional parameters representative of high pressure compressor internal air system flows(Re up to 5×106 and Rez up to 2×105).Two different builds have been tested.The most significant difference between these two build configurations is the size of the annular gap between the(non-rotating) drive shaft and the bores of the discs.The heat transfer data were obtained from thermocouple measurements of surface temperature and a conduction solution method.The velocity measurements were made using a two component,LDA system.The heat transfer results from the discs show differences between the two builds.This is attributed to the wider annular gap allowing more of the throughflow to penetrate into the cavity.There are also significant differences between the radial distributions of tangential velocity in the two builds of the test rig.For the narrow annular gap,there is an increase of non-dimensional tangential velocity V/Ωr with radial location to solid body rotation V/Ωr=1.For the wider annular gap,the non-dimensional velocities show a decrease with radial location to solid body rotation.      

Research on Auto-detection for Remainder Particles of Aerospace Relay Based on Wavelet Analysis

Aerospace relay is one kind of electronic components which is used widely in national defense system and aerospace system. The existence of remainder particles induces the reliability declining, which has become a severe problem in the development of aerospace relay. Traditional particle impact noise detection (PIND) method for remainder detection is ineffective for small particles, due to its low precision and involvement of subjective factors. An auto-detection method for PIND output signals is proposed in this paper, which is based on direct wavelet de-noising (DWD), cross-correlation analysis (CCA) and homo-filtering (HF), the method enhances the affectiv-ity of PIND test about the small particles. In the end, some practical PIND output signals are analysed, and the validity of this new method is proved.     

Preparation of Highly Dispersed Antimony-doped Tin Oxide Nano-powder via Ion-exchange Hydrolysis of SnCl4 and SbCl3 and Azeotropic Drying

Antimony-doped tin hydroxide colloid precipitates have been synthesized by hydrolysis of SnCl4 and SbCl3 using: (1) an ion-exchange hydrolysis to remove chlorine ions, and (2) isoamyl acetate as an azeotropic solvent to obviate water. The obtained dried powder is of high dispersivity without any need for further grinding. The size and dispersivity of the final particles are investigated with the aid of TG-DTA, BET, XRD and TEM. After having calcined, the antimony-doped tin oxide nanopowder possesses a tetragonal rutile structure with high dispersivity, uniform particles and low hard agglomeration.     

Effects of Mo on the Microstructure and Hydrogen Sorption Properties of Ti-Mo Getters

The effects of Mo on the microstructure evolution, porosity and hydrogen sorption properties of Ti-Mo getters are investigated in this work. The results show that the addition of Mo prolongs the densification process of Ti-Mo getters and results in a significant amount of sintered pores. With the Mo content increasing, the porosity of getters firstly increases reaching the maximum value as it at- tains about 7.5wt.%, and then drops. At the room temperature, the hydrogen sorption property of getters increases progressively with the Mo content increasing, but the tendency is not very clear before its content lies below 2.5wt.%. When the Mo content achieves about 7.5wt.%, the hydrogen sorption property proves to be the best. The discussion is made about the above mentioned phenomena inclusive of hydrogen sorption properties of getters under different activation conditions (from 500-750 ℃).     

超声速燃烧数值模拟中的湍流与化学反应相互作用模型

高精度数值模拟有助于理解超声速湍流燃烧中湍流与化学反应的相互作用,可为发动机燃烧室等工程应用设计提供可靠的预测模型。除直接数值模拟外,目前在湍流燃烧应用中使用的大涡模拟和雷诺平均Navier-Stokes模拟均需要借助模型模化发生在湍流小尺度上的流动与化学反应过程对湍流大尺度运动的影响。现有的湍流与化学反应相互作用模型大致可分为:火焰面类模型和概率密度函数类模型,2类模型在不同的应用中各自具有优势和局限性。此外,现有模型大都基于低马赫数燃烧,而超声速燃烧中通常会伴随快速混合、局部熄火和再着火以及激波等复杂过程,这为发展其中的湍流与化学反应相互作用模型提出了更多的挑战。     

适于低轨卫星IP网络的单核共享树组播算法(英文)

为了解决低轨卫星IP网络中现有典型源组播算法的信道资源浪费问题,本文提出了一套单核共享树组播算法,即核心群合并共享树(CCST)和加权核心群合并共享树(w-CCST)算法。CCST 算法包括动态近似中心(DAC)选核方法和核心群合并组播路径构建方法。DAC方法专为周期、规律运动的低轨卫星网络提出,不需要复杂的星上计算。在核心群合并方法中,以核节点作为初始核心群,通过核心群和剩余组成员的最短路径方法逐步扩展直至整棵组播树构建完成,从而使得组播树的树代价最小,大大提高了网络的带宽利用率和组播传输效率。w-CCST 算法中所提出的加权因子可以调整树代价和端到端传播时延之间的折衷程度,因此,可以通过调整加权因子来适度增大树代价、降低端到端传播时延以支持某些端到端时延要求苛刻的实时组播业务。最后,与低轨卫星 IP 网络中典型算法进行了性能比较,仿真结果说明,CCST 算法的平均树代价比其它算法显著降低,w-CCST 算法的平均端到端传播时延小于 CCST 算法。     

Jet Vectoring Control Using a Novel Synthetic Jet Actuator

A primary air jet vectoring control system with a novel synthetic jet actuator (SJA) is presented and simulated numerically. The results show that, in comparison with an existing traditional synthetic jet actuator, which is able to perform the duty of either “push” or “pull”, one novel synthetic jet actuator can fulfill both “push” and “pull” functions to vector the primary jet by shifting a slide block inside it. Therefore, because the new actuator possesses greater efficiency, it has potentiality to replace the existing one in various appli- cations, such as thrust vectoring and the reduction of thermal signature. Moreover, as the novel actuator can fulfill those functions that the existing one can not, it may well be expected to popularize it into more flow control systems.     

Nonlinear Adaptive Slewing Motion Control of Spacecraft Truss Driven by Synchronous V-gimbaled CMG Precession

The slewing motion control of a truss arm driven by a V-gimbaled control-moment-gyro (CMG) is a nonlinear control problem. The V-gimbaled CMG consists of a pair of gyros that must precess synchronously. The moment of inertia of the system, the angular momentum of the gyros and the external disturbances are not exactly known. With the help of feedback linearization and recursive Lyapunov design method, an adaptive nonlinear controller is designed to deal with the unknown items. Performance of the proposed controller is verified by simulation.     

An SOR Implicit Time-accurate Scheme in Calculating Unsteady Flows

A new time-accurate marching scheme for unsteady flow calculations is proposed in the present work. This method is the combination of classical Successive Over-Relaxation (SOR) iteration method and Jacobian matrix diagonally dominant splitting method of LUSGS. One advantage of this algorithm is the second-order accuracy because of no factorization error. Another advantage is the low computational cost because the Jacobian matrices and fluxes are only calculated once in each physical time step. And, the SOR algorithm has better convergence property than Gauss-Seidel. To investigate its accuracy and convergency, several unsteady flow computa- tional tests are carried out by using the proposed SOR algorithm. Roe’s FDS scheme is used to discritize the inviscid flux terms. Un- steady computational results of SOR are compared with the experiment results and those of Gauss-Seidel. Results reveal that the numerical results agree well with the experimental data and the second-order accuracy can be obtained as the Gauss-Seidel for unsteady flow computations. The impact of SOR factor is investigated for unsteady computations by using different SOR factors in this algorithm to simulate each computational test. Different numbers of inner iterations are needed to converge to the same criterion for different SOR factors and optimal choice of SOR factor can improve the computational efficiency greatly.