飞机投外挂时的动态响应及其地面飞行模拟

本文推导了飞机正常投放及故障投放外挂时的动态响应中各参数在时域内的解析表达式并以歼七飞机为例进行计算,计算结果与地面飞机模拟和飞行实际结果基本一致,从而证明计算是正确的,所进行的地面飞行模拟试验也是可靠的。     

计算液体晃动ALE网格速度的高精度方法

利用自由液面曲率参量,在传统求解方法基础上对相应结点网格速度引入修正,以提高计算精度.域内网格速度计算,由传统线性关系改用分段函数表达,以保证网格剖分的质量. 将二维矩形贮箱内流体晃动问题作为算例,求解激励响应结果并与已有物理实验进行对比,二者符合较好.     

成型充填过程的ALE有限元模拟

在ALE框架中提出了一个用于成型充填过程有限元数值模拟的模型。应用ALE参考构形及ALE参考粒子速度描写充填过程中的熔体质量运动。摒弃了Hele-Shaw近似假定,因而所提出的模型能用于非薄壁型腔中高分子材料充填过程的数值模拟。应用基于时域分步算法的Taylor-Galerkin方法,对控制成型充填过程的守恒方程建立了弱形式。对移动自由面附近的充填材料区构造了网格生成算法与网格重划分方案。给出了在几种不同形状的典型腔体中充填过程的数值模拟结果,表明了所提出的ALE有限元模型模拟充填过程的有效性。     

基于ALE方法的3D充填流动模拟

基于任意拉格朗日-欧拉方法发展了三维充填流动的数值模拟方案.该方案采用ALE方法准确地追踪移动自由面的位置并避免了网格扭曲;基于移动最小二乘曲面拟合方法提出了移动自由面上网格节点重定位方法,将充填流动的网格更新过程简化为自由面附近的局部网格重划分过程,并通过分级多面体三角剖分实现,减小了网格划分的计算量,实现了实时网格生成.给出的数值算例结果表明了该数值模型对三维充填流动模拟的有效性.     

基于ALE,CEL和SPH方法的球形破片高速冲击充液结构对比研究

为研究ALE,CEL和SPH方法在高速冲击流固耦合动力学数值分析中的差异性,开展球形破片高速冲击充液结构数值模拟研究。建立经文献资料验证的ALE,CEL和SPH三种动力学模型,研究了流体压力变化、形成的空腔尺寸、破片速度衰减变化和充液结构变形等模拟精度,并分析相应的计算成本。结果表明,ALE,CEL和SPH三种方法均能有效模拟破片高速冲击充液结构的流固耦合动力学过程;ALE方法预测的空腔尺寸精度较高;CEL方法预测的流体压力、破片速度衰减和充液结构变形精度较高;SPH方法预测的空腔尺寸、破片速度衰减精度较高;当网格尺寸一致时,SPH方法计算时长约为ALE和CEL方法的两倍,但SPH方法前后处理更加简便。     

正交异性复合材料储液容器入水过程数值分析

采用多物质ALE流固耦合算法,对柔性储液容器的入水问题进行了仿真研究。该方法可以方便地考虑多种流体同时与结构耦合。首先,通过模拟平板恒速入水试验,验证了该方法的有效性,并确定了空气的影响。进而,仿真分析了复合材料柔性容器入水时的动态响应行为,结果表明,底部"空气垫"及容器内空气对冲击载荷具有一定的缓冲作用,容器底部形状、储液量等因素也具有较大影响。仿真得到的响应规律为容器的优化设计提供了重要的理论参考。     

轴对称几何下耦合MOF界面重构的多介质ALE方法

推导了轴对称几何下的MOF(Moment of Fluid)界面重构,将其与多介质ALE方法相耦合,形成MOFMMALE方法,并应用于多介质大变形流动问题的数值模拟研究。数值算例表明,耦合MOF界面重构的多介质ALE方法是求解多介质大变形流动问题的有效手段,并且具有很好的界面精度和分辨率。     

基于结构拓扑随机变异的水平集优化方法

基于结构拓扑导数的水平集优化方法,利用结构拓扑导数信息和通过不断减少结构体积的方式来确定需开孔的结构位置,需选用最大设计区域结构作为初始优化结构.该方法不适合求解结构体积等式约束的优化问题.为了解决上述问题和克服水平集方法不能在结构内产生新孔洞的困难,提出了一种基于结构拓扑随机变异的水平集优化方法.引进了以小概率随机方式进行结构拓扑变异的结构优化方案.设计了变异算子,讨论了提出方法的收敛性情况.最后,结合考虑结构最大设计区域限制的结构拓扑优化的水平集方法,建立了一套新的涉及结构柔顺度作为目标函数,体积作约束条件的水平集演化算法.给出的算例验证了该方法的正确性和有效性.     

非均质结构PBX炸药的动态压缩过程模拟

采用离散元方法,构建了考虑PBX炸药晶体颗粒与黏结剂非均匀性的计算模型,通过在炸药试样两端采用相向飞片加载、将原SHPB实验的应力边界替代为速度边界的方法,开展了PBX炸药的动态压缩数值模拟研究,再现了考虑PBX炸药非均质特性的SHPB实验过程,获得了不同加-卸载路径下炸药应力应变曲线以及相应的损伤破坏图像。模拟结果表明:在动态压缩过程中,虽然PBX炸药处于整体应力平衡,由于PBX高度非均质性,内部应力分布并不均匀,晶体间应力以应力桥形式传递;应力曲线为试样整体平均,试样内局部所受真实应力可能高于曲线峰值应力;出现卸载回滞曲线的试样发生局部损伤破坏,而完全软化曲线的试样发生整体失稳破坏。     

舱段结构在气泡射流作用下的毁伤效果

为研究水下爆炸气泡载荷对船舶局部结构的毁伤效果,设计建造了实尺度舱段模型,并进行水下爆炸实验,测量了水中压力、气泡脉动周期、舱段外板结构的动应变与塑性变形。分析了不同冲击因子作用下舱段结构的动态响应,并结合水中压力测量结果,探讨了气泡射流的成因。在此基础之上,分析了气泡射流载荷的影响范围以及外板在不同载荷作用下的毁伤模式。实验结果表明,相比冲击波载荷,在某些情况下射流冲击载荷引起的结构响应更剧烈,毁伤效果更严重,因此在中近场水下爆炸作用下,气泡射流冲击载荷对船体结构的影响不能忽视。     

Soil stress and deformation determination under a landing airplane on an unsurfaced airfield

This paper presents a multidisciplinary approach to a problem of soil–wheel interaction during the landing of an airplane on a grass airfield, with terramechanical analysis of the forces acting between a wheel and the surface. The experiment on stress and deformation state in soil under a wheel on touchdown was performed in the field. The soil stress state (major stress S1, minor stresses S2 and S3, stress invariant in an octahedral system, MNS and OCTSS) was determined with the use of an SST (stress state transducer), which was installed at 15 cm depth. Soil deformation was determined with an inertial measuring system, integrated with the SST. These soil data were captured exactly at the moment touchdown. In the experiment, a four-passenger, STOL multirole airplane was used and pilots performed two landing patterns: normal landing and emergency landing (without propeller thrust).     

On dimensionless numbers for dynamic plastic response of structural members

Summary A dimensional analysis is reported for the dynamic plastic response and failure of structural members, which includes material strain hardening, strain rate and temperature effects. Critical shear failure conditions are also discussed based on the dimensional analysis results. It is shown that the response number R _n proposed in [3], is an important independent dimensionless number for the dynamic plastic bending and membrane response of structural members. However, additional dimensionless numbers are necessary when transverse shear, strain hardening, strain rate, and temperature effects are important. Received 22 February 1999; accepted for publication 15 June 1999     

On the dynamic response of viscoelastic fluids

Summary To define the dynamic shear behaviour of a viscoelastic fluid we require two functions — one elastic and one viscous. There are two simple alternatives based on the Voigt and Maxwell concepts which are mathematically interrelated. Current practice interprets the dynamic response of fluids as a function of angular frequency () in terms of the storage (G) and loss (G) moduli: the loss function is commonly converted to a viscosity = G/. As is well known the parameters andG are the elements of a Voigt model whereas it is near universal practice to interpret steady flow in terms of the Maxwell model. This paper shows how the interpretation of dynamic experiments on fluids in terms of the apparent Maxwell parameters is more simple, more sensitive, more consistent with steady flow behaviour, and physically more realistic.

---

Zusammenfassung Zur Festlegung des dynamischen Scherverhaltens einer viskoelastischen Flüssigkeit benötigt man zwei Funktionen, eine für das elastische und eine für das viskose Verhalten. Dafür gibt es zwei einfache, mathematisch miteinander verknüpfte Alternativen, die entweder auf dem Voigtschen oder dem Maxwellschen Konzept gründen. Die übliche Praxis beschreibt das dynamische Verhalten der Flüssigkeiten als Funktion der Winkelgeschwindigkeit durch den SpeichermodulG und den VerlustmodulG bzw. die zugeordnete Viskosität = G/. Die Parameter undG sind bekanntlich die Elemente eines Voigt-Modells, wohingegen es nahezu allgemein üblich ist, das stationäre Fließen durch ein Maxwell-Modell zu beschreiben. Diese Arbeit zeigt nun, daß die Beschreibung dynamischer Versuche mit Hilfe von apparenten Maxwell-Parametern einfacher, empfindlicher, mit dem stationären Verhalten konsistenter und in physikalischer Hinsicht realistischer ist.

---

---

Paper presented at British Society of Rheology conference. Rheometry: Methods of measurement and analysis of results, Shrivenham, April 8–11, 1975.

---

With 13 figures and 2 tables     

Free-field dynamic response of an inhomogeneous half-space

In this work, elastic wave propagation in the inhomogeneous half-space is solved by an analytical approach based on plane wave decomposition in conjunction with appropriate functional transformations for the displacement vector. Specifically, free-field motions are recovered at the surface of a half-space with either quadratic or exponential type of depth-dependent material parameters. The incident wave is a time harmonic, planar pressure wave and the resulting free-field motions are obtained in closed form, first for the full-space and then for the half-space by adding the reflected waves. Parametric studies show marked differences in the results when compared against the corresponding ones for a homogeneous background. Finally, sensitivities of the free-field waves on the basic characteristics of the underlying inhomogeneous material and of the incoming wave are investigated.     

On the motion stability of an airplane on a runway under wind loading

A nonlinear mathematical model is constructed for an airplane in high-speed plane-parallel motion along a runway when the airplane's weight exceeds slightly the lift of its wings in the presence of a cross wind. The airplane is considered a two-weight mechanical object. A system of second-order equations is obtained that describes the airplane's behavior. A system of three phase variables is suggested in which the dynamics of transverse motion is described by a set of three second-order equations. A stationary solution of this system is obtained. A stability criterion for the plane-parallel motion of the airplane is established using the Routh-Hurwitz criterion. Analysis of the data of other authors indicates that the mathematical model is adequate for some objects of aviation technology. Translated from Prikladnaya Mekhanika, Vol. 35, No. 10, pp. 101–107, October, 1999.     

一种Birkhoff形式下结构动响应问题的保辛中点格式

结构动响应预测是结构设计的基础,是结构振动控制、载荷识别的前提。本文在辛体系下针对结构动响应问题,提出了一种Birkhoff形式下的保辛中点格式。首先引入状态变量,并基于摄动方法将结构动响应方程转化为线性自治Birkhoff方程的形式,进一步利用中心差分推导出线性自治Birkhoff方程的中点格式,其证明是保辛的。该格式不要求Birkhoff方程系数矩阵非奇异,因此适用于奇数维系统。两个不同数值算例的结果充分验证了本文方法的卓越性,也凸显了相对于传统算法在计算精确度和稳定性方面的明显优势。     

ANALYSIS OF DYNAMIC RESPONSE OF AN IMPACTED ELASTIC PLATE

ＡＮＡＬＹＳＩＳＯＦＤＹＮＡＭＩＣＲＥＳＰＯＮＳＥＯＦＡＮＩＭＰＡＣＴＥＤＥＬＡＳＴＩＣＰＬＡＴＥ￥(尹邦信)ＹｉｎＢａｎｇｘｉｎ（ＤｅｐａｒｔｍｅｎｔｏｆＣｉｖｉｌＥｎｇｉｎｅｅｒｉｎｇ，ＳｏｕｔｈｗｅｓｔｉｎｓｔｉｔｕｔｅｏｆＴｅｃｈｎｏｌｏｇｙ，...     

结构动力响应精细时程法的一种并行算法

结构动力响应精细时程法的并行算法分为两类：基于特解的并行算法和基于直接积分法的并行算法;后者因为不需知道荷载的具体形式而更具应用价值。精细时程法的时程积分由齐次方程的通解和非齐次项的积分构成,基于直接积分法的并行算法很好地并行了非齐次项的积分,而对通解项采用串行计算。设计了一种不均衡步数的负载分配策略,能够减少处理器等待自身初值的时间,相对均衡步数的分配策略,能够获得更高的加速比,给出了相应的证明和算例验证。     

Reservoir water level effects on nonlinear dynamic response of arch dams

In this study, reservoir water level effects on nonlinear dynamic response of arch dams are investigated. For this purpose, the nonlinear behaviour of the dam concrete is idealized as elasto-plastic using the Drucker–Prager model based on the associated flow rule assumption. Water in the reservoir is represented by the Lagrangian (displacement-based) fluid finite elements. The program NONSAP is modified for elasto-plastic analysis of fluid–structure systems and employed in the response calculations. Nonlinear dynamic analysis of an arch dam subjected to earthquake ground motion is performed for five different water levels. The El-Centro N–S component of the Imperial Valley earthquake, on May 18, 1940, has been used as the ground motion. The crest displacements, the maximum tensile stresses on the upstream and downstream faces of the dam and the time history of the yield function of an element in the dam body are presented. The results obtained from nonlinear analyses for different water levels are compared with each other. It is apparent that the reservoir water level effects must be considered in the elasto-plastic analyses of arch dams to earthquake ground motion.     

轻型飞机机翼气动/结构协同优化研究

探讨用协同优化方法能否有效地解决机翼气动／结构一体化设计优化问题。首先对基本的协同优化和基于响应面协同优化两种方法的特点进行了探讨,然后以轻型飞机机翼气动／结构一体化设计为例,着重研究如何用协同优化方法建立机翼气动／结构一体化设计的优化模型。研究结果表明,基本的协同优化算法不能有效地解决该机翼气动／结构一体化优化问题,而基于响应面的协同优化方法在求解这一问题时具有较好的鲁棒性。