热声载荷下薄壁开孔结构振动响应与寿命预估

金属薄壁开孔结构在强热声载荷下,表现出大挠度强非线性响应特性,疲劳寿命缩短。基于时域的基础上,利用有限元法(FEM)结合降阶模态法(ROM)获取4边固支开孔薄板在不同热、声载荷组合下的位移和应力的动态响应,并进行响应时间历程和功率谱(PSD)的统计分析。采用雨流计数法和Morrow平均应力模型,结合Miner线性累积损伤理论对结构进行疲劳寿命的预估和分析。结果表明:屈曲后的位移响应由热声载荷的相对强弱决定。此外,屈曲前结构随热、声载荷的增加,寿命缩短。屈曲后,持续跳变使得结构的寿命缩至最短;进入间歇跳变区域,间歇时间短的跳变要比间歇时间长的跳变造成的结构损伤大,即快频跳变引起的损伤更大。跳变结束后,随着温度的升高,寿命先延长后缩短。     

A partition of unity level set method with moving knot CS-RBFs for optimizing variable stiffness composites

A partition of unity level set method with moving knot Compactly Supported Radial Basis Functions (CS-RBFs) is proposed for optimizing variable stiffness composite structures. The iso-contours of a level set function are utilized to represent the curved fiber paths, and the tangent vector of the iso-contour defines the orientation of fiber. The level set function of the full design domain is constructed according to the Partition of Unity (POU) method by a set of local level set functions defined on an array of overlapping subdomains, and they are constructed by using the CS-RBFs. The positions of knots are iteratively changed during the optimization to improve the performance of composite structures. Several examples of compliance minimization are presented.     

多孔金属夹芯结构的抗爆性能研究

多孔金属夹芯结构已被广泛应用于航空航天等领域,研究其抗爆吸能性能具有十分重要的意义。分别对金属空心小球和泡沫铝两种夹芯壳结构在TNT爆炸载荷作用下的抗爆性能进行爆炸实验,并采用AN-SYS/LS-DYNA有限元软件进行数值模拟研究。结果表明:金属空心小球夹芯结构作为抗爆吸能结构是可行的;在结构框架尺寸与质量相同时,内面板厚外面板薄的夹芯结构具有更好的抗变形能力,内面板薄外面板厚的夹芯结构则具有更好的吸能特性;在结构框架尺寸与质量相同时,负梯度夹芯结构、并列型小球夹芯结构、小半径小球夹芯结构具有更好的抵抗爆炸载荷和吸收冲击能量的性能;在结构框架尺寸与质量相同时,金属空心小球夹芯结构的整体强度更高,而泡沫铝夹芯结构能更充分地发挥芯层的缓冲性能。     

A three-equation transition model with mechanical considerations

A three-equation transition model based on the transition V-model is proposed for subsonic flows in this study. Considering the mechanical approximation of the generation process of the pre-transitional vorticities, the value of laminar Reynolds shear stress related to the mean shear deformation was calculated in the original transition V-model. Then a new transition model, named V-SA model, was proposed, which considered the phenomenological process of transition and presented great results for flows with and without pressure gradient. It is well-known that the baseline Shear Stress Transport (SST) turbulence model shows excellent performance of accuracy and robustness in plentiful flow cases, but it is important to predict boundary layer transition. The current model (V-SST) successfully couples the V-model to the SST turbulence model by introducing the effective turbulent viscosity and additional correction terms into the transport equations. A thorough evaluation of its ability to predict transition features is performed versus the well-documented flat plate of ERCOFTAC, including T3A and T3B without pressure gradient, T3L2 and T3L3 with semi-circular leading edge, the three-dimensional 6:1 prolate-spheroid under two angles of attack, and the NLR-7301 airfoil under different Mach numbers. Numerical results show that the current model has an attractive and superior performance in the simulation of boundary layer transition processes     

Error modeling and compensating of a novel 6-DOF aeroengine rotor docking equipment

In the docking process of aeroengine rotor parts, docking accuracy that indicates the gaps between the end faces is strictly required. A key issue is improving docking accuracy using automated docking equipment. In this paper, a systematic study is carried out on the error modeling and compensation of a novel six-degrees-of-freedom(6-DOF) docking equipment for aeroengine rotors. First, a new model for indicating the main indexes of docking accuracy is proposed. Then, the error model of a special...     

Design and application of solar sailing: A review on key technologies

Solar sail technology has been proposed and developed for space explorations with advantages of low launch cost, no-propellant consumption, and continuous thrust, which has great potentials in earth polar detection, interstellar explorations and etc. The development of solar sail has made significant progress in structural design, manufacturing, materials, orbit transfer, and stability control in the past few decades, which makes meaningful contributions to astronomy, physics, and aerospace science. Technological breakthroughs of Solar Radiation Pressure (SRP) propulsion and interstellar transfer have been achieved in current solar sail missions. However, there are still many challenges and problems need to be solved. This paper attempts to summarize the research schemes and potential applications of solar sailing in space missions from the viewpoint of key technologies, so as to provide an overall perspective for researchers in this field. Analyses of the key technologies of solar sailing system design are provided. Finally, challenges and prospective development of solar sailing are discussed.     

刚性基体高应变复合材料在空间可展结构中的应用及发展

梳理了空间可展结构的分类及发展趋势，从铰接可展结构-带簧铰链、杆状可展结构、面状可展结构及体可展结构四个方面调研了刚性基体高应变复合材料在空间可展结构中的应用现状，从力学和黏弹性特性方面提出了其在可展结构中的应用优势及需要考虑的问题。高模量、低密度、低膨胀系数的刚性基体高应变复合材料是空间可展结构的应用方向，而刚性基体高应变复合材料可展结构的设计方法，以及将其用于大尺寸可展结构的低成本和高精度制造工艺仍有很大的探索空间。     

Hierarchical model updating strategy of complex assembled structures with uncorrelated dynamic modes

In structural simulation and design, an accurate computational model directly determines the effectiveness of performance evaluation. To establish a high-fidelity dynamic model of a complex assembled structure, a Hierarchical Model Updating Strategy(HMUS) is developed for Finite Element(FE) model updating with regard to uncorrelated modes. The principle of HMUS is first elaborated by integrating hierarchical modeling concept, model updating technology with proper uncorrelated mode treatment, and...     

低速长航时无人机垂直突风过载分析

低速中空长航时无人机的升力非线性较强,利用标准离散突风模型和连续紊流模型计算得到的突风过载差别较大.针对该问题,本文采用改进的离散突风模型求解突风载荷,即直接求解突风条件下原始的运动学方程,并在运动历程中考虑非线性升力的影响.结果表明:改进的离散突风模型计算得到的突风载荷明显低于标准离散突风模型所得的载荷,更贴近无人机的实际情况,且改进的离散突风模型与连续紊流模型的计算结果也相近.