空间充气管展开动力学研究进展

最近空间充气展开结构引起了人们的广泛关注, 这是因为空间充气展开结构具有折叠体积小, 重量轻和展开可靠性高等优点, 于是一些空间计划也开始考虑利用充气展开结构的优势.然而, 在空间充气展开结构应用到太空之前还有一些重要的问题需解决, 其中之一就是控制和掌握充气展开结构的充气展开动力学特性.充气管用于驱动展开并支撑空间结构是一种重要的构件. 围绕充气管在展开过程中的动力学问题, 详细地综述了近20年来国际上的研究进展情况. 首先讨论了有关的充气展开模型, 包括非线性铰链模型、卷曲折叠管展开模型、控制体积模型、能量法模型和流-固耦合模型等.然后介绍了有限元模拟研究进展, 并分别评述了$Z$形、卷曲、多边形以及变直径伸缩等折叠管的充气展开实验研究. 文章最后指出了充气管的充气展开的理论、有限元模拟以及实验在今后值得关注的研究方向.     

空间折叠薄膜管的充气展开动力学实验研究

空间折叠薄膜管是空间充气展开结构的基本支撑部件, Z形折叠是充气展开管的基本折叠方式之一. 针对空间微重力环境, 建立了折叠薄膜管的充气展开实验系统, 采用气浮导轨, 解决了地面重力对充气展开过程的影响; 采用非接触式的光电测量方式, 有效地避免了接触式传感器对充气展开过程的干扰. 针对V形折叠薄膜管, 研究了不同的充气流量、薄膜管尺寸效应以及展开端有无有效载荷对充气展开动力学特性的影响; 通过实验研究, 选择充气流量、管子直径和载荷质量为主定参量, 对充气展开过程进行量纲分析和实验误差分析, 结果表明, 折叠薄膜管的充气展开最大速度与充气的体积流量成正比, 与管直径的立方成反比.      

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为了研究爆炸及燃烧产生的“蘑菇状”烟云,采用中尺度气象模式RAMS(Regional Atmospheric Modeling System)模拟计算了冲击波过后的爆炸烟云运动过程。对于稳定层结大气条件,模拟结果显示爆炸烟云造成的流动是一个多层次涡-波运动的过程。爆炸烟云在浮力作用下会形成浮力涡环结构,在到达最大高度以后,其烟云外侧边缘部分涡度变号,形成了环套环的多涡结构。随时间增加,涡能量的逐步衰减,涡运动转变为重力内波运动。通过模拟不同爆炸当量和不同稳定度烟云的上升最大高度,得到了与目前常用的爆炸烟云上升公式一致的形式。     

Development of flexible telescopic boom model using absolute nodal coordinate formulation sliding joint constraints with LuGre friction

In this investigation, a modeling procedure of a telescopic boom of cranes is developed using the absolute nodal coordinate formulation together with the sliding joint constraints. Since telescopic booms are extracted and retracted under various operating conditions, the overall length of the boom changes dynamically, leading to the time-variant vibration characteristics. For modeling the telescopic structure of booms, a special care needs to be exercised since the location of the sliding contact point moves along the deformable axis of the flexible boom and the solution to a moving boundary problem is required. This issue indeed makes the modeling of the telescopic boom difficult, despite the significant needs for the analysis. It is, therefore, the objective of this investigation to develop a modeling procedure for the flexible telescopic boom by considering the sliding contact condition with the dynamic frictional effect. To this end, the sliding joint constraint developed for the absolute nodal coordinate formulation is employed for describing relative sliding motion between flexible booms, while flexible booms are modeled using the beam element of the absolute nodal coordinate formulation, which allows for modeling the large rotation and deformation of the structure.     

条带式太阳帆的结构动力学分析

依靠光压推进,太阳帆被认为是最可行的星际探测航天器,太阳帆结构总体方案主要有两类:桅杆式和旋转式,其中,帆膜被分割成窄条的条带式太阳帆在桅杆式太阳帆中具有较为理想的结构效率,如何准确计算条带式太阳帆的结构动力学特性值得研究.本文对条带式太阳帆结构的振动特性和结构稳定性进行研究,将太阳帆看作是由若干个桅杆-膜带组件依次连接而成的整体结构,桅杆-膜带组件由4根桅杆段和4条薄膜条带组成,分段轴压作用下的桅杆与薄膜条带耦合振动.考虑帆面薄膜条带与支撑桅杆之间的耦合振动,采用分布传递函数法建立了的条带式太阳帆的结构动力学模型,推导了条带式太阳帆结构自由振动和失稳载荷的求解方法.研究表明:条带式太阳帆构型有利于提高太阳帆结构的整体刚度和结构稳定性,随着帆面薄膜条带数目的增加,太阳帆结构的振动频率和失稳载荷增大;随着帆面薄膜预应力的增大,太阳帆结构振动的基频减小,稳定性变差;随着支撑桅杆刚度的提高,太阳帆结构整体的振动频率和失稳载荷增大.本文建立的解析求解方法具有求解效率快和精度高的特点,为条带式太阳帆的结构设计和姿态控制提供了有力的分析工具.      

INTERACTION MODEL OF THE ENCLOSED AIR AND THE OUTER MEMBRANE

将充气膜结构内充气体假定为势流,推导得到速度势表示的内充气体小幅波动方程,并采用Galerkin法离散得到内充气体的有限元动力学方程。引入界面协调条件,建立了内充气体结点速度势与外部膜材结点位移的关系,然后联立薄膜动力方程和气体动力学方程得到充气膜系统内充气体与外部膜材的共同作用理论模型。在该理论模型基础上,建立了两类典型充气结构的数值模型进行分析,通过将数值结果与试验结果对比,验证了共同作用理论模型的准确性和合理性。     

充气结构与流场的耦合求解方法

针对一种充气前缘(inflatable leading edge, ILE)增升技术,建立了其充气结构与流场耦合作用的运动方程. 将方程写成状态空间形式,采用时域推进方法求解. 对使用了变前缘增升技术的NACA63-212翼型进行了充气结构静变形的数值计算,结果表明充气结构的刚度对翼型的气动特性有明显影响. 与原翼型相比,在不考虑充气结构变形时, 该增升技术大约能使翼型的失速迎角增加30{\%},最大升力系数增加22{\%};考虑结构变形后增升效果有所降低. 刚度较低的薄膜在前缘吸力峰的作用下会隆起形成鼓包,容易引起流动分离.      

Dynamic analysis of a rigid-flexible inflatable space structure coupled with control moment gyroscopes

The vibration generated by the inflatable structure after deployment has a great impact on the performance of the payloads. In this paper, the influence of the control moment gyroscopes (CMGs) on the dynamic responses and characteristics of an inflatable space structure is studied, based on the flexible multibody dynamics in a combination of the absolute nodal coordinate formulation (ANCF) and the natural coordinate formulation (NCF). Firstly, the ANCF and NCF are used to accurately describe the large deformations and large overall motions of flexible inflatable tubes and rigid satellites, respectively. Then, instead of modeling gyroscopic flexible bodies, this paper pioneers a rigid body dynamic model of the CMG in detail by using the NCF modeling scheme, which can be attached to and coupled with any flexible bodies without any assumptions. Then, the orbital dynamic equations of the inflatable space structure coupled with distributed CMGs are obtained by considering the effects of Coriolis force, centrifugal force, and gravity gradient through coordinate transformation. The dynamic characteristics of the inflatable space structure are also analyzed by deriving the eigenvalue problem of a flexible multibody system. Finally, the accuracy of the CMG dynamic model is verified via a classic heavy top example. Several numerical examples are presented to study the influence of the magnitudes and directions of the rotor angular momentum of the CMGs on the dynamic responses and characteristics of the inflatable space structure.

     

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。     

Reduction of the sonic boom level by heating the flow in front of the body

A numerical study of the possibility of reducing the sonic boom level in the case of local heat release to a supersonic gas flow at Mach number equal to 2 ahead of a body is described. The computations are performed for a spherical heat supply zone located on the flight trajectory ahead of the tip of an axisymmetric thin body. For the numerical study the combined method of “phantom bodies” is used. Different magnitudes of heat supply to the incoming flow are tested. These calculations are performed with allowance for interaction of shock waves emanating from the heated gas region and from the body in the far field. The computational results show that the local heat supply to a supersonic gas flow ahead of a body can reduce the sonic boom level by more than 20 %. The reduction of the sonic boom level is ensured by changing the free-stream parameters ahead of the body and by preventing the coalescence of shock waves from the heat supply zone and from the body in the far field.     

Numerical investigations on dynamic process of muzzle flow

The integrative process of a quiescent projectile accelerated by high-pressure gas to shoot out at a supersonic speed and beyond the range of a precursor flow field was simulated numerically. The calculation was based on ALE equations and a second-order precision Roe method that adopted chimera grids and a dynamic mesh. From the predicted results, the coupling and interaction among the precursor flow field, propellant gas flow field and high-speed projectile were discussed in detail. The shock-vortex interaction, shockwave reflection, shock-projectile interaction with shock diffraction, and shock focus were clearly demonstrated to explain the effect on the acceleration of the projectile.     

Calculation of capillary jet

The Arbitrary Lagrangian Eulerian (ALE) framework coupled with some boundary tracking techniques is proven to be an effective method for simulation of free‐surface flows. In this paper, a special ALE framework is derived with clarification of three velocities, the notion of mesh‐frozen and field‐frozen, and the notion of tentatively inertial coordinates. A weighted integral ALE governing equations are formulated on generic coordinates and discretized with a finite element method and linear implicit time scheme. The system is solved with a discrete operator splitting technique and superposition‐based logistic parallelization. The formulation and implementation are verified through several fixed‐geometry problems and a reasonably good parallel performance is observed. Capillary jet flow is the main problem of the paper and the numerical techniques for boundary tracking are elaborated, which include an indirect boundary tracking of flux method and an iterative direct boundary tracking method. Also, a high‐order compact scheme for dynamic boundary condition and a squeeze technique for kinematic boundary condition are adopted. The axisymmetric jet breakup is studied in detail and numerical results match with the published data very well. Numerical accuracy and sensitivity are studied, including effects of element type, time scheme, compact scheme, and boundary tracking techniques. Copyright © 2010 John Wiley & Sons, Ltd.     

Pseudo-beam method for compressive buckling characteristics analysis of space inflatable load-carrying structures

This paper extends Le van＇s work to the case of nonlinear problem and the complicated configuration. The wrinkling stress distribution and the pressure effects are also included in our analysis. Pseudo-beam method is presented based on the inflatable beam theory to model the inflatable structures as a set of inflatable beam elements with a prestressed state. In this method, the discretized nonlinear equations are given based upon the virtual work principle with a 3-node Timoshenko＇s beam model. Finite element simulation is performed by using a 3-node BEAM189 element incorporating ANSYS nonlinear program. The pressure effect is equivalent included in our method by modifying beam element cross-section parameters related to pressure. A benchmark example, the bending case of an inflatable cantilever beam, is performed to verify the accuracy of our proposed method. The comparisons reveal that the numerical results obtained with our method are close to open published analytical and membrane finite element results. The method is then used to evaluate the whole buckling and the loadcarrying characteristics of an inflatable support frame subjected to a compression force. The wrinkling stress and region characteristics are also shown in the end. This method gives better convergence characteristics, and requires much less computation time. It is very effective to deal with the whole load-carrying ability analytical problems for large scale inflatable structures with complex configuration.     

流固耦合分析的一种改进CBS有限元算法

针对流固耦合问题, 发展了一种基于任意拉格朗日-欧拉(ALE)描述有限元法的弱耦合分区算法. 运用半隐式特征线分裂算法求解Navier-Stokes方程, 在压力Poisson 方程中引入质量源项以满足几何守恒律; 运用子块移动技术更新动态网格, 并配以光滑处理防止网格质量下降; 采用Newmark-β 法求解结构运动方程. 为保持流体-结构界面处速度和动量守恒, 利用修正结合界面边界条件方法求解界面处速度通量和动量通量. 运用本方法分别模拟了不同雷诺数下单圆柱横向和两向流致振动、串列双圆柱两向流致振动. 计算表明, 本文方法计算效率高, 计算结果与已有实验和数值计算数据吻合.     

Controlling the sonic boom from a thin body by means of local heating of the incoming flow

The problem of reduction of the sonic boom level by heating the flow in front of the body is solved numerically. A combined method of “phantom bodies” is used for calculations. The sonic boom generated by an axisymmetric thin body for the flight Mach number of 2 with different levels of energy supply to the incoming flow is calculated. The calculation results show that the sonic boom can be reduced by means of local heat supply to a supersonic gas flow. Reduction of the sonic boom level is provided by specific gas-dynamic features of the flow behind the heat supply zone.     

The characteristic‐based split (CBS) meshfree method for free surface flow problems in ALE formulation

A semi‐implicit characteristic‐based split (CBS) meshfree algorithm in the arbitrary Lagrangian Eulerian (ALE) framework is proposed for the numerical solution of incompressible free surface flow problem in the paper. The algorithm is the extension of general CBS method which was initially introduced in finite element framework, this is due to the fact that CBS method not only can enhance the stability, but also avoid LBB condition when equal order basis function is used to approximate velocity and pressure variables. Meanwhile, a simple way for node update and node speed calculation is developed which is used to capture the free surface exactly. The numerical solutions are compared with available analytical and numerical solutions, which shows that the proposed method has better ability to simulate the free surface incompressible flow problem. Copyright © 2009 John Wiley & Sons, Ltd.     

空间充气展开结构动态分析研究进展

空间充气展开结构是一种以薄膜材料为主构建而成的新型结构, 可用于构建大型的天线、太阳能集中器、太阳帆等空间结构, 为空间结构的大型化提供了一条有效的解决途径.其动态特性是充气展开结构设计过程中必须考虑的问题, 动态分析测试技术一直是充气展开结构研究过程中的关键问题, 由于充气展开结构在材料、结构形式及工作环境等方面的特殊性, 使得其动态分析和测试技术出现了很多新的问题.目前充气展开结构动态分析的研究方法主要集中在两个方面:实验研究和数值模拟.实验研究主要是针对充气薄膜结构的特点, 由接触式的测试手段向非接触式的测试手段发展, 但实验研究在真空和微重力环境的模拟上面临着很大的问题.数值模拟研究可以有效的模拟结构在真空和微重力环境下的动态行为, 并可分析重力、空气和褶皱等因素对结构振动特性的耦合影响.本文综述了空间充气展开结构动态分析的实验研究和数值研究的发展和现状, 并讨论了其中存在的问题, 在此基础上指出了该项研究的发展趋势.      

Numerical predictions of bubble growth in viscoelastic stretching filaments

In this study, we investigate the growth of bubbles within predominately extensional-deformation flows of thin film stretching form. This involves more than one free-surface to the flow (multiple surfaces), typically as inner (bubble) and outer (filament) boundaries that introduces fluid–gas interfacial treatment. Various bubble initial states and locations may be considered. The problem is discretised in space–time through a hybrid-finite element/volume pressure-correction formulation, coupled with an arbitrary Lagrangian–Eulerian (ALE) coupled with VOF scheme to track domain-mesh and free-surface movement. We contrast these results against the results from a complete ALE algorithm. Various fluid-filament materials have been considered, covering such properties as constant viscosity fluids (Newtonian), low-polymeric/high-solvent viscosity Boger-type (Oldroyd-B) fluids and high-polymeric/low-solvent viscosity elastic-type fluids (Oldroyd-B and Phan-Thien/Tanner). Numerical solutions are presented in terms of comparison between algorithms (ALE versus hybrid ALE/VOF), shapes (bubble shapes, filament shapes), contours of extra-stress (magnitude and location), mid-filament radius and extensional viscosity.     

流体-结构耦合问题的有限元并行计算研究

流体-结构耦合问题广泛存在于各种工程领域,本文采用ALE显式有限元法求解该类问题,并对该方法的并行性进行讨论。同时根据流体-结构耦合问题与ALE显式有限元的计算特点,在坐标递归分区方法的基础上设计并程序实现了基于流体-结构耦合均衡的分区算法。通过与坐标递归分区方法的计算结果相比较,对于流体-结构耦合问题的求解,耦合均衡并行分区方法具有更好的加速比和并行效率。     

An arbitrary Lagrangian Eulerian (ALE) formulation for free surface flows using the characteristic‐based split (CBS) scheme

An arbitrary Lagrangian Eulerian (ALE) method for non‐breaking free surface flow problems is presented. The characteristic‐based split (CBS) scheme has been employed to solve the ALE equations. A simple mesh smoothing procedure based on coordinate averaging (Laplacian smoothing) is employed in the calculations. The mesh velocity is calculated at each time step and incorporated as part of the scheme. Results presented show an excellent agreement with the available experimental data. Copyright © 2005 John Wiley & Sons, Ltd.