考虑剪切效应的旋转FGM楔形梁刚柔耦合动力学建模与仿真

本文对一类中心刚体-柔性梁系统在大范围转动下的刚柔耦合动力学问题进行了研究. 柔性梁为功能梯度材料(functionally graded materials, FGM)楔形变截面梁,材料体积分数在梁轴向呈幂律分布变化. 以弧长坐标来描述柔性FGM梁的几何位移关系,分别使用倾角和拉伸应变变量描述柔性梁的横向弯曲和纵向拉伸变形,并计及剪切效应. 采用假设模态法离散变形场,运用第二类拉格朗日方程进行方程推导,得到系统考虑剪切效应的刚柔耦合动力学模型. 基于全新的刚柔耦合动力学建模理论,研究不同轴向材料梯度分布的FGM楔形梁,通过数值仿真计算,分析讨论不同的转速、梯度分布规律以及变截面参数对系统动力学特性的影响. 结果表明,剪切效应对大高跨比的FGM楔形梁的变形影响较为明显,不容忽略;材料梯度分布规律和截面参数的选取均会对旋转FGM楔形梁的动力学响应和频率产生较大影响. 本文提出的考虑剪切效应的倾角刚柔耦合动力学模型是对以往非剪切模型的进一步完善,可应用于工程中的 Timoshenko梁结构的动力学问题求解.      

Study of γ‐Fast Neutron Attenuation and Mechanical Characteristics of Modified Concretes for Shielding and Sheltering Purposes

The study of γ‐neutrons attenuation and mechanical characteristics of modified concrete are vital and crucial parameters for the construction of civilian radiological, nuclear shielding, and/or shelters. In this work, fifteen samples of ordinary concretes with five different additives; steel fibers, polypropylene, silica fume, and fly ash, with variation of cement percentages, were prepared and used for performing the mechanical and radiation attenuation investigations. The compressive strength, tensile strength, slump test, bulk density, and water permeability were also carried out for the prepared concrete mixes. Collimated coherent beams from ⁶⁰Co and Pu‐Be fast neutron sources were used to check the radiation penetrability through the syntheized mixed concrete‐additives. Very sensitive and well calibrated gamma‐neutron pulse shape discriminating spectrometer with its electronic componenets and stilbene organic detector and 3′′ × 3′′ NaI scintillation crystal was used to measure the radiation before and after attenuation and transmission. The integrated fast neutron removal macroscopic cross section (Σ_r) and linear attenuation coefficient of total gamma rays (μ) were calculated for all the analysed concrete mixes. The results of measurements, tests, analyses and calculations are given and explained. The investigated modified concrete mixes show good workability and properties from the view point of mechanical loads and γ‐fast neutrons penetrability and resistance. These results can be used for shielding and sheltering design.     

Crossed Beam Study on the F+D2→DF+D Reaction at Hyperthermal Collision Energy of 23.84 kJ/mol

We presented an experimental apparatus combining the H-atom Rydberg tagging time-of-flight technique and the laser detonation source for studying crossed beam reactions athyperthermal collision energies. The preliminary study of the F+D₂→DF+D reaction at hyperthermal collision energy of 23.84 kJ/mol was performed. Two beam sources were used in this study: one is the hyperthermal F beam source produced by a laser detonation process, and the other is D₂ beam source generated by liquid-N₂ cooled pulsed valve. Vibrational state-resolved di erential cross sections (DCSs) of product for the title reaction were determined. From the product vibrational state-resolved DCS, it can be concluded that products DF(v'=0, 1, 2, 3) are predominantly distributed in the sideway and backward scattering directions at this collision energy. However, the highest vibrational excited product DF(v'=4), is clearly peaked in the forward direction. The probable dynamical origins for these forward scattering products were analyzed and discussed.     

RAFM钢TIG焊和电子束焊疲劳性能实验和分析模拟

利用ANSYS 对低活化铁素体马氏体(RAFM)钢进行非熔化极气体保护焊(TIG 焊)与电子束焊的抗疲劳模拟分析，再利用SDS200 电液伺服疲劳试验机对TIG 焊和电子束焊的两种RAFM 钢试件进行实验。通过施加相同梯度负荷对TIG 焊和电子束焊试件进行焊缝的疲劳性能实验。与实验结果对比分析，结果显示电子束焊优于 TIG 焊，但在一定负载下可以用TIG 焊代替电子束焊。     

Self‐focusing of a cosh‐Gaussian laser beam in magnetized plasma under relativistic‐ponderomotive regime

The combined effect of relativistic and ponderomotive nonlinearities on the self‐focusing of an intense cosh‐Gaussian laser beam (CGLB) in magnetized plasma have been investigated. Higher‐order paraxial‐ray approximation has been used to set up the self‐focusing equations, where higher‐order terms in the expansion of the dielectric function and the eikonal are taken into account. The effects of various lasers and plasma parameters viz. laser intensity (a₀), decentred parameter (b), and magnetic field (ω_c) on the self‐focusing of CGLB have been explored. The results are compared with the Gaussian profile of laser beams and relativistic nonlinearity. Self‐focusing can be enhanced by optimizing and selecting the appropriate laser‐plasma parameters. It is observed that the focusing of CGLB is fast in a nonparaxial region in comparison with that of a Gaussian laser beam and in a paraxial region in magnetized plasma. In addition, strong self‐focusing of CGLB is observed at higher values of a₀, b, and ω_c. Numerical results show that CGLB can produce ultrahigh laser irradiance over distances much greater than the Rayleigh length, which can be used for various applications.     

混凝土重力坝爆炸荷载数值分析及抗爆性能研究

利用LS-DYNA非线性有限元程序，基于Eulerian和Lagrangian耦合的方法，研究了RHT本构模型模拟的混凝土板在爆炸荷载下的动力反应，并且将数值结果与现场实验结果进行比较，由此说明了RHT本构模型模拟爆炸荷载下混凝土动力反应的有效性。研究了2 t TNT炸药在距离坝体上游面10 m不同起爆深度的情况下，有泡沫混凝土保护层和无泡沫混凝土保护层的坝体动力响应及其损伤状况。计算结果表明，无泡沫混凝土保护层时，坝体上游面主要损伤区域位置总是随起爆深度的增加向坝体底部移动；当上游表面有泡沫混凝土保护层时，坝体上游表面的损伤明显变小，下游面的损伤较无保护层情况也明显减小。表明泡沫混凝土能够有效减小混凝土大坝在爆炸荷载下的损伤，在提高混凝土大坝的抗爆性能方面起到很好的保护作用。     

Aeroelastic analysis of cantilever plates using Peters’ aerodynamic model,and the influence of choosing beam or plate theories as the structural model

In this paper, the aeroelastic analyses of a rectangular cantilever plate of varying aspect ratio is presented. The classical plate theory has been selected as the structural model. The main point that distinguishes this study from previously reported research is employing Peters’ theory to model aerodynamic effect which is not straightforward. The Peters’ aerodynamic model was originally developed to provide lift and moment, which is only applicable to the structural model based on the beam theories. In this study, using the basic concept of the Peters’ aerodynamic model in addition to utilizing the Fourier series, the pressure distribution is derived, which makes Peters’ model applicable to structural models based on plate theory. This combination provides a much simpler state–space aeroelastic model for plates in comparison to the prevalent panel methods, which could lead to a significant reduction in computational time. In addition, the aeroelastic response of the plate with respect to changes in the structural model from the beam theory to the plate theory is evaluated. By using data from an experiment carried out at Duke University, the theoretical results are evaluated. Furthermore, the differences in structural models obtained from the plate and beam theories can be divided into two distinct parts, which are responsible for differences in bending and torsional behaviors of the structure, separately. This approach enables us to measure the effects of differences of each behavior separately, which could provide with a new insight into the problem. It has been determined that the flutter speeds obtained from the beam and plate aeroelastic models are little affected by the difference in bending behavior, but rather is mainly caused by the difference in torsional frequencies.