一种适用于颗粒非规则分布的阻止SPH数值断裂的方法

 〖HT5”H〗摘〓要〖HTSS〗: 光滑粒子流体动力学(SPH)方法已广泛应用于航空航天领域中大变形的碰撞计算。数值断裂是SPH计算中一种常见问题,可严重影响计算结果。把适用于颗粒规则分布的阻止SPH数值断裂的方法推广到颗粒非规则分布的情形,得到了一种适用于颗粒非规则分布的阻止数值断裂的加颗粒方法。然后将该方法应用于存在数值断裂的悬臂梁弯曲仿真计算,验证了其有效性。最后把该方法应用于弹丸撞击飞机蒙皮的非规则颗粒模型计算,并和规则颗粒模型得到的结果及试验结果进行比较。对比结果表明：对于非规则分布的颗粒模型,该加颗粒方法可有效地阻止数值断裂,提高计算精度,并可较为普遍使用。     

基于光滑粒子流体动力学方法的液滴蒸发问题数值模拟研究

基于光滑粒子流体动力学方法（Smoothed Particle Hydrodynamics，SPH），开展了SPH新算法在蒸发燃烧领域的研究。建立了适用于SPH方法的蒸发数值模型，推导了基于傅立叶热传导公式和菲克扩散定律的SPH离散方程；借鉴VOF方法（Volume of Fluid）的思想，提出了SPH粒子的液相质量分数的概念，以有效表征蒸发过程中的相变问题。采用SPH方法对高温环境中单个液滴的蒸发过程进行数值模拟，结果符合D2定律，与理论模型相一致；在强迫对流环境中，液滴的蒸发过程受到对流作用及表面张力的影响，蒸发速率加快；进一步对双液滴在静止、对流环境中的蒸发过程进行数值模拟研究。结果表明，液滴的间距、滴径对多个液滴的蒸发过程影响至关重要，液滴间距至少在两倍的液滴直径以上，相互之间的影响才可以近似忽略。通过本文研究，拓宽了SPH方法在蒸发相变领域的应用范围，研究结果也能够为进一步的燃烧问题研究奠定基础。     

Numerical simulation of a rotary engine primary compressor impacted by bird

In order to examine the process of a rotary engine primary compressor impacted by bird, a finite element model of a bird impacted on plate is developed with the explicit code PAM-CRASH. The smooth particles hydrodynamic (SPH) method is used to simulate the bird because of the SPH method showing no signs of instability and correctly modeling the breaking-up of the bird into particles. Good agreement between the simulation results and experimental results indicates that the numerical method of bird strike used in the present paper is reasonable. Then a rotary engine primary compressor impacted by three different configurations bird named straight-ended cylinder bird, quadrangular bird, hemispherical-ended bird are investigated using the numerical simulation method. It is found that the whole process of bird strike sustained about 3.5 ms and the bird is slashed by blade during the strike. The geometry configuration of bird affected the displacement and von Mises stress of some blades severely, just because the breaking bird’s mass is affected by the bird’s configuration. In the event of bird striking on the site of"up"some blades may develop plastic deformation and it is very adverse for the safety work of the engine.     

Design of aircraft structures against threat of bird strikes

In this paper, a method to design bird-strike-resistant aircraft structures is presented and illustrated through examples. The focus is on bird strike experiments and simulations. The explicit finite element software PAM-CRASH is employed to conduct bird strike simulations, and a coupled Smooth Particles Hydrodynamic (SPH) and Finite Element (FE) method is used to simulate the interaction between a bird and a target structure. The SPH method is explained, and an SPH bird model is established. Constitutive models for various structural materials, such as aluminum alloys, composite materials, honeycomb, and foam materials that are used in aircraft structures, are presented, and model parameters are identified by conducting various material tests. Good agreements between simulation results and experimental data suggest that the numerical model is capable of predicting the dynamic responses of various aircraft structures under a bird strike, and numerical simulation can be used as a tool to design bird-strike-resistant aircraft structures.     

用SPH和有限元方法研究鸟撞飞机风挡问题

鸟与飞行中的飞机相撞是飞机结构损坏的重要因素,严重时会引发机毁人亡的灾难性事故。对高速低空飞行的军用飞机而言,风挡部分抗鸟撞的研究对保证飞行安全尤其重要。基于飞机圆弧风挡受鸟体撞击的实验观察,建立了国产某型军用飞机圆弧风挡及鸟体的计算模型,采用LS-DYNA3D中有限元和光滑粒子流体动力学(SPH)耦合的数值分析方法,对某飞机圆弧风挡受鸟体撞击的过程进行了数值模拟。计算结果得到了风挡结构的变形、位移和应变等几方面的数据,与实验结果基本吻合。同时,给出了500～650km/h速度范围内的撞击力和应力时程曲线、风挡发生破坏的临界撞速、圆弧风挡经受鸟体撞击时发生破坏的可能位置及其破坏方式。最后,与鸟体采用任意拉格朗日(ALE)和无网格伽辽金方法(EFG)进行了对比,验证了SPH方法在分析鸟撞问题中的优越性。研究结果为风挡的安全设计和研制新机型提供了有价值的数据。     

鸟撞飞机风挡动态响应数值模拟方法研究现状

总结了目前用于鸟撞飞机风挡动态响应的数值模拟方法,主要有解耦解法、耦合解法和光滑质点动力学法,其中耦合解法涉及接触-碰撞耦合解法和流固耦合解法。各种方法围绕鸟体（鸟撞载荷）的模拟和风挡的模拟,部分内容针对鸟撞击发动机叶片、雷达罩和垂直尾翼等,但其方法同样适用于飞机风挡,最后指出应进一步深入研究的内容。     

Fragment Identification and Statistics Method of Hypervelocity Impact SPH Simulation

A comprehensive treatment to the fragment identification and statistics for the smoothed particle hydrodynamics (SPH) simulation of hypervelocity impact is presented. Based on SPH method, combined with finite element method (FEM), the computation is performed. The fragments are identified by a new pre- and post-processing algorithm and then converted into a binary graph. The number of fragments and the attached SPH particles are determined by counting the quantity of connected domains on the binary graph. The size, velocity vector and mass of each fragment are calculated by the particles’ summation and weighted average. The dependence of this method on finite element edge length and simulation terminal time is discussed. An example of tungsten rods impacting steel plates is given for calibration. The computation results match experiments well and demonstrate the effectiveness of this method.     

A numerical model for bird strike on sidewall structure of an aircraft nose

In order to examine the potential of using the coupled smooth particles hydrodynamic(SPH) and finite element(FE) method to predict the dynamic responses of aircraft structures in bird strike events, bird-strike tests on the sidewall structure of an aircraft nose are carried out and numerically simulated. The bird is modeled with SPH and described by the Murnaghan equation of state, while the structure is modeled with finite elements. A coupled SPH–FE method is developed to simulate the bird-strike tests and a numerical model is established using a commercial software PAM-CRASH. The bird model shows no signs of instability and correctly modeled the break-up of the bird into particles. Finally the dynamic response such as strains in the skin is simulated and compared with test results, and the simulated deformation and fracture process of the sidewall structure is compared with images recorded by a high speed camera. Good agreement between the simulation results and test data indicates that the coupled SPH–FE method can provide a very powerful tool in predicting the dynamic responses of aircraft structures in events of bird strike.     

非均匀来流下三维激波反问题的微元密切轴对称解法

传统的密切轴对称理论被广泛应用于均匀来流下的三维密切曲面激波反设计，为解决非均匀来流条件下的三维曲面激波反问题，提出了一种微元密切轴对称流场（MOA）求解方法。该方法沿激波面的周向和流向构建一系列微元密切面，在每个微元面内进行三维向二维流动的等效转换，从而突破了传统密切方法中不能有横向波后流动的限制。利用该方法编写设计程序，分别基于带攻角来流条件和外锥型流来流条件重构了标准内锥曲面激波，并与数值仿真结果进行了比较。结果表明，非均匀来流下激波曲面的三维形状均与预设形状完全一致，实现了非均匀来流下曲面激波形状可控。MOA方法在吸气式高超声速推进领域中前体/进气道一体化设计方面有重要应用前景。     

基于SPH方法的射流撞击仿真

为了研究液体推进剂的撞击雾化问题,采取光滑粒子流体动力学方法 (SPH)进行了射流撞击形成液膜过程的数值模拟。修正了基于连续表面力模型的表面张力算法,推导了考虑粘性与表面张力作用的SPH形式的控制方程,对撞击雾化模型进行了合理简化,采用水作为推进剂模拟液。得到了不同撞击速度、角度下的液膜图像及液膜的形成过程图像。证明了SPH方法适于解决存在自由表面及大变形的射流撞击问题。     

边界层分离流边值问题的算法研究

本文给出了边界层方法边值问题的一种快速求解方法,该方法可用于二维与三维问题,它是在正方法边界层算法的基础之上增加了一个矩阵算法,该矩阵很容易逆,总的ＣＰＵ时间仅增加约２０％,使用该算法对反方法问题求解和进行数值稳定性分析都将十分方便。     

现代自然层流翼型的设计方法

本文介绍一种设计跨声速自然层流翼型的计算流体力学(CFD)方法。本方法采用“正反迭代、余量修正”设计原理,通过将跨声速翼型设计软件NPU-TD2D中的反设计程序进行改进,并与含有层、湍流混合边界层修正的跨声速层流翼型计算程序DLRBGKWALZ耦合,实现了在跨声速粘性流动条件下直接设计层流翼型。亚、超临界的设计实例和风洞验证表明,本方法可以在几个设计迭代内设计出压力分布、转捩位置及气动参数均准确收敛于设计目标的新翼型,是一种设计现代自然层流翼型的有效而实用的CFD方法。     

Double-decoupled inverse design of natural laminar flow nacelle under transonic conditions

The inverse design based on the pressure distribution is an essential approach to realize the improvement of Natural Laminar Flow(NLF) performance for nacelles. However, the direct definition of target pressure distribution at design point is challenging for the dilemma to consider the constraints of shock wave and laminar flow at the same time. In addition, the universality of method will be limited when the inverse design is strongly coupled with the solver. Thus, a double-decoupled methodolog...     

基于分解策略的涡轮叶片可靠性及多学科设计优化

将反一阶可靠性分析方法与多学科可行方法相结合,提出了一种适用于涡轮叶片复杂结构的可靠性及多学科设计优化方法.在优化过程中使用Kriging近似模型并不断提高模型精度,解决了多学科可行方法反复调用仿真程序进行多学科分析,计算量较大的问题.该方法将可靠性分析与多学科优化过程分离,提高了优化计算效率.以某型涡轮叶片的设计优化为例,对该方法进行了验证并与传统双循环方法进行了对比.结果表明,优化结果满足可靠性的要求,与双循环方法相比优化效率提高63.8%,证明了该方法在工程应用中的可行性和有效性.      

Numerical simulation method of surge experiments on gas turbine engines

In order to obtain the surge margin of an aero-engine during its operation, an engine surge experiment is required. A multi-dimensional simulation method for an aero-engine is established in this paper. The simulation of a surge experiment using high-pressure air-injection is then carried out on a turbo-shaft engine to obtain the surge boundary using this method. More specifically, firstly, a body-force model is employed to calculate the compressor performance owing to its capability of capturin...     

Singularity analysis for single gimbal control moment gyroscope system using space expansion method

Control Moment Gyroscope (CMG) is an effective candidate for agile satellites and large spacecraft attitude control because of its powerful torque amplification capability. The most serious situation, however, in using CMG is the inherent geometric singularity problem, where there’s no torque output along a particular direction. Space expansion method has been proposed in this work for the singularity analysis. Based on inverse mapping transformation, an expanded Jacobian matrix which is a full rank square matrix is obtained. The singular angle sets of the 3-parallel cluster and pyramid cluster are distinguished using space expansion method. An effective hybrid steering strategy, able to deal with the elliptic singularity, is further proposed. Simulation results demonstrate the excellent performance of the proposed steering logic compared to the generalized singular robust logic and pseudo inverse logic in terms of energy consumption and torque error.     

Low Velocity Collisions and the Growth of Planetesimals

The physics of low velocity collisions (5 m/s to 40 m/s) between basalt bodies ranging in size from 1 m to 10 km is studied in an effort to investigate the early phases of planetesimal accretions. To assess the importance of the internal structure of planetesimals on the outcome of the collisions, we model them either as solid spheres or as rubble piles with a filling factor of 0.5. The collisions are simulated using a three dimensional Smooth Particle Hydrodynamics (SPH) code that incorporates the combined effects of material strength and a brittle fragmentation model. This approach allows the determination not only of the mass of the largest fragments surviving the collisions but also their dynamical characteristics. We find that low velocity collisions are for equal incoming kinetic energy per gram of target material considerably more efficient in destroying and dispersing bodies than their high velocity counterparts. Furthermore, planetesimals modeled as rubble piles are found to be characterized by a disruption threshold about 5 times smaller than solid bodies. Both results are a consequence of a more efficient momentum transfer between projectile and fragments in collisions involving bodies of comparable sizes. Size and shape dependent gas drag is shown to provide relative collision velocities between similar meter-sized objects well in excess of the critical disruption threshold of either rubble piles or solid bodies. Unless accretion can proceed avoiding collisions between bodies of similar masses, the relative weakness of bodies in this size range creates a serious bottleneck for planetesimal growth. This revised version was published online in June 2006 with corrections to the Cover Date.     

翼型的气动最优化设计方法和反设计方法＊

本文将数值优化方法同计算流体动力学（ＣＦＤ）相结合,形成两种跨声速翼型的气动设计方法,即：最优化方法和反设计方法。采用求解Ｅｕｌｅｒ方程的有限体积法计算流场,通过结合优化算法,从正反两个方向对跨声速翼型进行气动优化设计。实例证明它们是翼型气动设计的有效方法,有较高的工程应用价值。     

粘性三维流动计算的任意拉格朗日—欧拉法

推导了旋转叶轮内流三维粘性流动计算的ALE格式。以网格的虚拟运动计算对流作用;采用粘性子循环时步、拉格朗日子循环时步加速收敛;改进上风格式为部分施主单元格式来减小扩散同时实现良好的计算性能;由通量限制控制耗散截断误差;计算中引入短波长阻尼以消除不规则性;以亚网格(SGS)湍流模式模拟湍流运动。      

HIERARCHICAL ITERATION METHOD TO SOLVE DYNAMIC DIFFERENTIAL EQUATION

1CauseoftheProblemTherearemultitalysystemsindynamicanalysswherethemassandinertiaOfthemaintheyaremuchbiggerthanthoseoftheappendagds,buttheactionofasmallapPendagecanchangethecharacterofmOionofthemaintalydramaticallylforexample,amultitheysystemlike8pin-stdssateiliteanditspassivenutatindamPer.ThesmalldamPerhastheabili-tytochangethesateilitenutationmotbofromanunstablestatustoastableone.Generally,theenergydissipationmethodcanbeusedtoanalyzethiskindOfdampersys-tem.Unfortunately,ifthesystemdynamicr…