基于伞载多体动力学的降落伞开伞过程研究

针对降落伞开伞过程中柔性大变形、强非线性和强耦合性的特点,采用伞载多体动力学方法,以充气时间为自变量,分别建立拉直、充气和稳降3个阶段的动力学模型。对降落伞开伞过程中物伞系统运动学和动力学进行数值分析,研究降落伞开伞过程,通过某型号降落伞飞行试验验证,表明：基于多体动力学的降落伞开伞过程计算简单方便,能够快速指导降落伞的设计迭代,计算结果可以很好地体现降落伞的开伞特性。     

降落伞初始充气阶段伞形变化的数值模拟

降落伞动力学现象是由降落伞结构与流场之间的相互作用而产生的。对于这种流构耦合问题的处理是一大难题。本文采用一种基于投影法（Projection Method）的浸没边界法。对降落伞开伞充气阶段的伞形变化进行数值模拟。研究表明：此类方法的模拟结果与以往的试验数据符合得较好。能够成为一种降落伞设计的辅助数值工具。     

有限质量情况下降落伞开伞过程数值仿真研究(英文)

为了模拟降落伞减速系统在有限质量情况下的三维动态开伞过程,以典型平面圆形伞C9伞为例,采用LS-DYNA基于有限元理论的ALE流固耦合方法对其充气至稳降过程进行研究,并用空投试验验证计算结果。计算获得了结构、流场动态变化,还获得了反映减速特性的载荷速度、加速度变化情况,分析了降落伞工作过程中危险截面、过载及外形之间的对应关系。研究结果表明:ALE法能够预测伞衣展开过程中减速特性以及危险截面,数值结果反映了实际工作过程的一般规律。     

锥形降落伞开伞过程流动结构相互作用的数值模拟

根据多结点开伞模型建立了锥形降落伞系统的变形动力学方程组来对充气过程中的伞衣柔性体变形过程进行模拟.结合多结点模型动力学方程结算代码和计算流体力学软件,对降落伞的充气过程进行流固耦合动态仿真,从而得到充气过程中伞衣外形和流场的变化,以及充气时间、下降速度变化和下降距离等相关数据,与国外研究成果相吻合.      

降落伞充气过程的数值模拟

 基于降落伞的重要应用与设计的实际需要，降落伞的数值模拟开始得到越来越多的重视，而充气过程是其中最为复杂的一个阶段。本文建立了平面圆形伞主充气过程中的CFD（Computational Fluid Dynamics）与结构动力学的MSD（Mass Spring Damper）之间的耦合模型。流场求解采用稳定性较高的标准k-ε模型，在多块贴体坐标下，获得某时间节点处的流场，并将该流场中的压力数据引入MSD模型，以获得下一时间节点的伞衣形状，最终获得主充气过程中伞衣形状和流场之间的动态关系。数值计算结果和实验结果及经验值比较，均有较好的一致性。充气过程的数值求解有助于提高对降落伞充气过程机理的理解。      

稳定状态下锥形伞结构分析

通过合理简化和假设确定轴对称锥形降落伞模型，建立了充满稳定状态下锥形伞受力平衡微分方程，然后根据空间几何关系和弹性力学，补充约束方程，通过数值方法求解方程，最终得到伞绳和伞衣的形状和应力。编成非线性迭代程序对锥形伞进行验证。算例表明，该模型可以用于锥形伞结构的初步分析和设计。     

降落伞主充气阶段的动态仿真及流场分析

建立了有顶孔的平面圆形降落伞的轴向和径向动量方程,使用数值方法计算出选定的降落伞在主充气过程中各种参数的变化,对降落伞的主充气过程进行了动态仿真.在使用动量方程计算出的的充气模型的基础上,利用降落伞在各个时间结点时的外形和下降速度等相关数据,采用计算流体力学的方法和准定常假设,对降落伞充气过程中的流场进行了模拟和分析,对降落伞充气过程的机理及流场衍变情况进行了探讨.      

重型货物空投系统过程仿真及特性分析

建立了货物空投系统仿真计算模型,包括货台在舱内和舱外全过程的运动特性、降落伞拉直和充气过程的轨迹特性计算等,提出了伞群模拟和多吊带系统分析的新方法。结合目前已有的降落伞性能计算模型和物伞系统运动模型,对重型货物空投全过程进行了完整计算,开发了空投过程三维动画仿真软件,通过与试验数据的对比,表明本模型能很好地满足应用的需要。分析了空投速度、伞包安装位置和牵引比等因素对空投过程的影响,指出了实际系统的改进方向。     

十字伞伞群的多节点静力学模型动力特性计算

为计算某型救灾专用空投系统十字伞伞群的气动特性,建立了多节点静力学模型来计算伞衣充满时的气动外形;对不同臂长比和伞绳比的十字伞进行数值模拟,并与文献中风洞实验结果对比验证;根据建立的模型得到十字伞伞群的气动外形并进行气动力特性研究.结果表明:计算结果和文献结果一致性较好,建立的多节点静力学模型合理可行;十字伞轴向力随臂长比和伞绳比的增大而增大;随攻角增大轴向力先减小后增大,而法向力则增大.建立的模型可用于伞群的气动外形计算,并为降落伞系统的设计提供参考.      

飞机层合风挡鸟撞击有限元数值模拟

建立了鸟撞击层合风挡三维有限元分析模型,对层合材料采用具有失效模型的率型本构模型,用非线性接触-碰撞有限元程序模拟了飞机层合风挡的鸟撞击动响应过程,给出了层合风挡鸟撞的计算实例,讨论了层合风挡结构被鸟冲击变形破坏的机理,数值模拟结果为层合风挡抗鸟撞击叠层设计提供了理论依据。     

Simulation of 3D parachute fluid–structure interaction based on nonlinear finite element method and preconditioning finite volume method

A fluid–structure interaction method combining a nonlinear finite element algorithm with a preconditioning finite volume method is proposed in this paper to simulate parachute transient dynamics. This method uses a three-dimensional membrane–cable fabric model to represent a parachute system at a highly folded configuration. The large shape change during parachute inflation is computed by the nonlinear Newton–Raphson iteration and the linear system equation is solved by the generalized minimal residual(GMRES) method. A membrane wrinkling algorithm is also utilized to evaluate the special uniaxial tension state of membrane elements on the parachute canopy. In order to avoid large time expenses during structural nonlinear iteration, the implicit Hilber–Hughes–Taylor(HHT) time integration method is employed. For the fluid dynamic simulations, the Roe and HLLC(Harten–Lax–van Leer contact) scheme has been modified and extended to compute flow problems at all speeds. The lower–upper symmetric Gauss–Seidel(LUSGS) approximate factorization is applied to accelerate the numerical convergence speed. Finally,the test model of a highly folded C-9 parachute is simulated at a prescribed speed and the results show similar characteristics compared with experimental results and previous literature.     

Fluid structure interaction simulation of supersonic parachute inflation by an interface tracking method

An Arbitrary Lagrangian–Eulerian (ALE) approach with interface tracking is developed in this paper to simulate the supersonic parachute inflation. A two-way interaction between a nonlinear finite element method and a finite volume method is accomplished. In order to apply this interface tracking method to problems with instantaneous large deformation and self-contact, a new virtual structure contact method is proposed to leave room for the body-fitted mesh between the contact structural surfaces. In addition, the breakpoint due to the fluid mesh with negative volume is losslessly restarted by the conservative interpolation method. Based on this method, fluid and structural dynamic behaviors of a highly folded disk-gap-band parachute are obtained. Numerical results such as maximum Root Mean Square (RMS) drag, general canopy shape and the smallest canopy projected areas in the terminal descent state are in accordance with the wind tunnel test results. This analysis reveals the inflation law of the disk-gap-band parachute and provides a new numerical method for supersonic parachute design.     

Study of parachute inflation process using fluid–structure interaction method

A direct numerical modeling method for parachute is proposed firstly, and a model for the star-shaped folded parachute with detailed structures is established. The simplified arbitrary Lagrangian–Eulerian fluid–structure interaction(SALE/FSI) method is used to simulate the inflation process of a folded parachute, and the flow field calculation is mainly based on operator splitting technique. By using this method, the dynamic variations of related parameters such as flow field and structure are obtained, and the load jump appearing at the end of initial inflation stage is captured. Numerical results including opening load, drag characteristics, swinging angle, etc. are well consistent with wind tunnel tests. In addition, this coupled method can get more space–time detailed information such as geometry shape, structure, motion, and flow field. Compared with previous inflation time method, this method is a completely theoretical analysis approach without relying on empirical coefficients, which can provide a reference for material selection, performance optimization during parachute design.     

液体火箭发动机推力室内壁寿命预估

为了分析推力室内壁失效机理及准确预估推力室内壁寿命,对推力室进行流-热-固耦合计算.流-热耦合为热-固耦合提供准确的热和机械载荷,热-固耦合模型对推力室内壁在循环加载下的变形进行非线性平面应变有限元分析.通过计算,得到了推力室内壁在单循环各阶段的应力-应变分布和循环加载下的变形过程,并进行了寿命预估.结果表明:采用的流-固耦合策略能准确地实现流-热耦合模块向热-固耦合模块的载荷传递,能为结构分析提供准确的边界条件.在预冷、后冷和松弛阶段,内壁承受拉应力;在工作阶段,内壁承受压应力.随着循环次数的增加,内壁残余应力和应变不断增大,内壁向燃烧室内鼓起和不断变薄,冷却通道中心最先失效.所采用的分析模型能够模拟内壁在循环热和机械载荷下的变形过程,用于预估推力室内壁的循环寿命.      

Gust response analysis and wind tunnel test for a high-aspect ratio wing

A theoretical nonlinear aeroelastic response analysis for a flexible high-aspect ratio wing excited by harmonic gust load is presented along with a companion wind tunnel test. A multidisci-plinary coupled numerical calculation is developed to simulate the flexible model wing undergoing gust load in the time domain via discrete nonlinear finite element structural dynamic analysis and nonplanar unsteady vortex lattice aerodynamic computation. A dynamic perturbation analysis about a nonlinear static equilibrium is also used to determine the small perturbation flutter bound-ary. A novel noncontact 3-D camera measurement analysis system is firstly used in the wind tunnel test to obtain the spatial large deformation and responses. The responses of the flexible wing under different static equilibrium states and frequency gust loads are discussed. The fair to good quanti-tative agreements between the theoretical and experimental results demonstrate that the presented analysis method is an acceptable way to predict the geometrically nonlinear gust response for flex-ible wings.     

Parachute dynamics and perturbation analysis of precision airdrop system

To analyze the parachute dynamics and stability characteristics of precision airdrop system,the fluid–structure interaction(FSI) dynamics coupling with the flight trajectory of a parachute–payload system is comprehensively predicted by numerical methods.The inflation behavior of a disk-gap-band parachute is specifically investigated using the arbitrary Lagrangian–Euler(ALE) penalty coupling method.With the available aerodynamic data obtained from the FSI simulation,a nine-degree-of-freedom(9DOF) dynamic model of a parachute–payload system is built and solved to simulate the descent trajectory of the multi-body dynamic system.Finally,a linear five-degree-of-freedom(5DOF) dynamic model is developed,the perturbation characteristics and the motion laws of the parachute and payload under a wind gust are analyzed by the linearization method and verified by a comparison with flight test data.The results of airdrop test demonstrate that our method can be further applied to the guidance and control of precision airdrop systems.     

夹层板精密成形的数值模拟

为了实现基于“点阵钉模、真空负压、蜂窝夹层”的双曲度面板精密成形过程的有限元数值模拟,分析了成形 2个阶段的变形过程,建立了简化的力学模形,以一种广义协调薄板弯曲四边形位移单元为基础构造了具有公共横向位移自由度的几何非线性四边形四节点分别考虑和不考虑横向剪切的多层板单元,通过牛顿 -拉斐逊法结合载荷、位移约束量的增量法求解几何非线性方程,较好地再现了真实成形过程     

降落伞充气过程中伞衣外形及流场变化研究

根据降落伞的结构和其在充气过程中的受力特性,以某平面圆形伞为原型,建立了伞衣充气过程中的计算流体力学与结构动力学耦合模型。并采用七孔探针对充满状态的绕流流场进行了定量测量,将该状态的试验结果和计算结果进行对比分析,二者的拓扑结构非常相似,压差系数也相差不大,因此所采用的数学模型是可靠的。在此基础上,对整个充气阶段的流场进行了数值模拟和分析,以详细了解降落伞整个开伞过程中伞衣外形变化及伞衣内外流场的变化情况。研究结果表明:①在初始充气阶段,伞衣展开部分外形基本保持较光滑的直筒形状,而非喇叭形。在主充气阶段:空气首先在伞衣顶部聚集,使伞衣顶部膨胀,然后膨胀部分向伞衣底边扩展,直到伞衣完全张满。②当伞顶孔被气流冲开后,伞衣的结构透气性对流场会产生显著影响。但从内外压力系数的变化来看,透气性对伞衣内滞止压力的影响较小,对伞衣外流场结构的影响较大,从而对伞衣外表面的压力影响较大。③对于此类有伞顶孔的平面圆形伞,当伞衣充气张开后,伞衣尾部出现气流分离,在一个漩涡区内形成两个相反旋转方向的漩涡。且随着伞衣直径扩张,分离区扩大,主流对漩涡区的剪切面积增大,因此漩涡区两个漩涡中外侧的一个漩涡增大,内侧漩涡被挤压至离伞顶更近的区...