Thermo-electro-hydrodynamic instabilities in a dielectric liquid under microgravity

Linear stability analysis of a dielectric fluid confined in a cylindrical annulus of infinite length is performed under microgravity conditions. A radial temperature gradient and a high alternating electric field imposed over the gap induce an effective gravity that can lead to a thermal convection even in the absence of the terrestrial gravity. The linearized governing equations are discretized using a spectral collocation method on Chebyshev polynomials to compute marginal stability curves and the critical parameters of instability. The critical parameters are independent of the Prandtl number, but they depend on the curvature of the system. The critical modes are non-axisymmetric and are made of stationary helices.     

火箭整流罩声振环境缩比特性研究

针对火箭整流罩全尺寸声振环境试验过程中难度大、成本高的问题，通过量纲分析的方法建立了缩比模型的相似准则，研究并获得了缩比模型与原模型之间内部声场、壁面振动加速度的关系，并使用声学有限元方法(FEM)进行了仿真计算。仿真结果表明，缩比模型与原模型场点处声压级相吻合，壁面振动加速度成一定的比例关系，符合缩比准则结果。该方法为火箭整流罩的声振环境预示和试验提供了理论依据。     

Detached-Eddy Simulation of the vortical flow field about the VFE-2 delta wing

The numerical simulation of the flow for the VFE-2 delta wing configuration with rounded leading edges is presented using the Cobalt Navier–Stokes solver. Cobalt uses a cell-centered unstructured hybrid mesh approach, and several numerical results are presented for the steady RANS equations as well as for the unsteady DES and DDES hybrid approaches. Within this paper the focus is related to the dual primary vortex flow topology, especially the sensitivity of the flow to angle of attack and Reynolds number effects. Reasonable results are obtained with both steady RANS and SA-DDES simulations. The results are compared and verified by experimental data, including surface pressure and pressure sensitive paint results, and recommendations for improving future simulations are made.     

Attitude and orbit control systems for the LISA Pathfinder mission

The main purpose of the LISA Pathfinder mission is to provide in-orbit validation of the critical technologies necessary for LISA (Laser Interferometer Space Antenna), aiming at detecting gravitational waves generated by very massive objects such as black holes. The spacecraft consists of a Science Module (SCM) and a Propulsion Module (PRM). The former performs the science experiment, and the later provides the propulsive capability to raise the spacecraft from the injection orbit to the operational orbit at around L1 and is then separated from the former. The Spacecraft Attitude and Orbit Control System (AOCS) is actually composed of three distinct systems to fulfill the needs of the whole mission: – Composite AOCS, used to reach L1, aims at raising the Perigee through a succession of about 10 boosts performed with high thrust chemical propulsion; – Micro-propulsion AOCS takes over once the separation of the SCM from PRM has occurred and is based on micro-propulsion systems (micro-Newton electrical thrusters); – Drag-Free Attitude Control System (DFACS) is then used to perform science experiments. This article provides a comprehensive overview of the AOCS architecture, requirements, selected sensors and actuators, system design & evolution, and achieved performances. It focuses in particular on the Composite AOCS and the Micro-propulsion AOCS and will analyze the challenges of using micro-Newton electric propulsion.     

The International Vortex Flow Experiment 2 (VFE-2): Background,objectives and organization

In this paper the background and the objectives for the International Vortex Flow Experiment (VFE-2) as well as its organization within the RTO Task Group AVT-113 are described. The available test facilities and wind tunnel models, the applied experimental techniques and the program of work are outlined. Concerning the realization the close cooperation between the measurements and CFD is emphasized.     

Particle swarm optimization applied to impulsive orbital transfers

The particle swarm optimization (PSO) technique is a population-based stochastic method developed in recent years and successfully applied in several fields of research. It mimics the unpredictable motion of bird flocks while searching for food, with the intent of determining the optimal values of the unknown parameters of the problem under consideration. At the end of the process, the best particle (i.e. the best solution with reference to the objective function) is expected to contain the globally optimal values of the unknown parameters. The central idea underlying the method is contained in the formula for velocity updating. This formula includes three terms with stochastic weights. This research applies the particle swarm optimization algorithm to the problem of optimizing impulsive orbital transfers. More specifically, the following problems are considered and solved with the PSO algorithm: (i) determination of the globally optimal two- and three-impulse transfer trajectories between two coplanar circular orbits; (ii) determination of the optimal transfer between two coplanar, elliptic orbits with arbitrary orientation; (iii) determination of the optimal two-impulse transfer between two circular, non-coplanar orbits; (iv) determination of the globally optimal two-impulse transfer between two non-coplanar elliptic orbits. Despite its intuitiveness and simplicity, the particle swarm optimization method proves to be capable of effectively solving the orbital transfer problems of interest with great numerical accuracy.     

Mechanical wear debris feature,detection, and diagnosis: A review

Mechanical debris is an important product of friction wear, which is also a crucial approach to know the running status of a machine. Many studies have been conducted on mechanical debris in related fields such as tribology, instrument, and diagnosis. This paper presents a comprehensive review of these studies, which summarizes wear mechanisms (e.g., abrasive wear, fatigue wear, and adhesive wear) and debris features (e.g., concentration (number), size, morphology, and composition), analyzes detection methods principles (e.g., offline: spectrograph and ferrograph, and online: optical method, inductive method, resistive-capacitive method, and acoustic method), reviews developments of online inductive methods, and investigates the progress of debris-based diagnosis. Finally, several notable problems are discussed for further studies.     

The effect of climber transit on the space elevator dynamics

The space elevator offers an alternate and efficient method for space travel. It will have two main components. The first component is the tether (or the ribbon), which extends from the Earth to an equatorial satellite at an altitude beyond the geostationary orbit, and is fixed to a base on the surface of the Earth at its lower end. The second component is the climber, which scales the ribbon, transporting payloads to space. An important issue for effective operation of the space elevator will be to understand its dynamics. This paper attempts to develop a realistic and yet simple planar model for this purpose. The basic response of the ribbon to climber transit is determined. Both analytical and numerical results are presented. Specific climbing procedures are devised based on these results so as to minimize the adverse effects of climber transit on the ribbon.     

星间光通信中压电偏转系统控制算法研究

针对星间光通信中压电偏转系统通道间强耦合和系统状态量无法得到的问题，提出了分散式李亚普诺夫自适应控制系统。该系统采用分散式控制技术，引入非线性和参数漂移误差项，使通道间耦合作用动力学模型更加精确，增加自适应反馈和自适应前馈控制项，以提高控制自适应性和跟踪精度，并结合李亚普诺夫稳定性理论确定各自适应参数以保证系统的稳定性。仿真结果表明了该控制器可有效提高跟踪精度，抑制通道间耦合和卫星平台振动，从而证明了本文所提出控制方案的有效性和可靠性。     

有机小分子杂化阻尼材料研究进展

从组成、制备工艺、阻尼机理讨论了有机小分子杂化阻尼材料的研究现状，并给出了一些该类阻尼材料的实例及其阻尼性能数据，提出了有机小分子杂化阻尼材料目前存在的问题，指出该类阻尼材料阻尼性能突出、Tg可设计，是一种颇有前景的材料。