北京市企业景气波动的实证分析

根据北京市统计局提供的企业景气指数和企业家信心指数的历史数据,利用假设检验的统计方法,对北京市的经济景气状况进行分析,为经济发展的预测和宏观调控政策提供了有力的依据.     

双三角钻臂及其液压系统的建模与参数估计

双三角钻臂具有结构紧凑、运行平稳、凿岩无盲区等优点,被凿岩机器人所采用.为了控制钻臂,对轨迹进行跟踪和精确定位,要求建立钻臂及其液压系统的数学模型.然而,该系统十分复杂,具有非线性和快时变的特点,要建立其精确的模型很困难,也没有必要.作者从液压系统的流量方程、连续性方程和力平衡方程入手,对双三角钻臂及其液压驱动系统机理建模.在建模过程中,忽略一些对模型精度影响不大的次要因素,获得了系统的简化模型.通过对钻臂的结构和受力进行分析,导出了模型中的参数、液压缸负载力的估算公式和估算方法,为实现钻臂的轨迹跟踪和精确定位控制打下了基础.     

基于可持续发展的生态环境的问题与对策

探讨了与生态环境相关的几个问题：大气污染,水资源短缺和水污染,近年来多发的“水华”,“赤潮”等水的富营养化问题以及乡镇企业对环境的影响,并提出了基于可持续发展的防治对策。     

油莎豆及其栽培技术

针对油莎豆的生物学特性,经济价值和栽培技术进行了探讨,为引种栽培者提供理论指导。     

Deployable boom for Mars Orbiter Magnetometer onboard Tianwen-1

A more than 3 m-long deployable boom is an essential component of the Mars Orbiter Magnetometer (MOMAG) onboard the orbiter of Tianwen-1. The boom was developed to place fluxgate magnetometer (FGM) sensors away from the satellite to reduce the influence of the satellite magnetic field. It was designed as an articulated spring-driven deployable mechanism for single-shot deployment. Functionality, reliability and system constraints are fully considered in the boom design. Mechanical analyses and proof tests show that the boom has sufficient safety margin to withstand environmental conditions, even in the worst cases. After a long voyage from Earth to Mars, the boom was deployed successfully on May 25, 2021. A full deployment was performed in about 4.6 s, sending the two sensors to distances of 3.19 m and 2.29 m respectively, away from the orbiter. After deployment, the field from the orbiter decreased from 1250 nT to less than 6 nT at the sensor mounted at the tip of the boom. The MOMAG boom provides valuable engineering experience for the development of deployable structures stowed for long periods in cold temperatures in space missions.     

On the dynamics of deployment of an orbital structure with elastic elements

The object to be studied is a spacecraft with a deployable pantograph structure as a solar-battery carrier. The objective of research is to design a mathematical model of this structure taking the elasticity of pantograph elements into account. The Lagrangian formalism is followed. To model the dynamic processes in the system, a software package has been developed, which can be adapted, if necessary, to study deployable structures of other types. The behavior of the structure during deployment, collapse, and redeployment under the action of various perturbations is modeled numerically. Plots illustrating the variation of characteristic variables are presented __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 8, pp. 136–144, August 2006.     

Numerical and experimental investigation of wave dynamic processes in high-speed train/tunnels

Numerical and experimental investigation on wave dynamic processes induced by high-speed trains entering railway tunnels are presented. Experiments were conducted by using a 1:250 scaled train-tunnel simulator. Numerical simulations were carried out by solving the axisymmetric Euler equations with the dispersion-controlled scheme implemented with moving boundary conditions. Pressure histories at various positions inside the train-tunnel simulator at different distance measured from the entrance of the simulator are recorded both numerically and experimentally, and then compared with each other for two train speeds. After the validation of nonlinear wave phenomena, detailed numerical simulations were then conducted to account for the generation of compression waves near the entrance, the propagation of these waves along the train tunnel, and their gradual development into a weak shock wave. Four wave dynamic processes observed are interpreted by combining numerical results with experiments. They are: high-speed trains moving over a free terrain before entering railway tunnels; the abrupt-entering of high-speed trains into railway tunnels; the abrupt-entering of the tail of high-speed trains into railway tunnels; and the interaction of compression and expansion waves ahead of high-speed trains. The effects of train-tunnel configuration, such as the train length and the train-tunnel blockage ratio, on these wave processes have been investigated as well.     

在多重网格上同时计算的叠缩法

讨论一种多重网格叠缩并行计算方法。此方法在多重网格上同时执行对所有未知量的运算，它的全部工作渐近估计为Ｏ（２ｌｏｇＮ），与标准Ｖ周期多重网格方法的计算复杂性等同。     

Turbulent jet interaction with a long rise-time pressure signature

A sonic boom signature with a long rise time has the ability to reduce the sonic boom, but it does not necessarily minimize the sonic boom at the ground level because of the real atmospheric turbulence. In this study, an effect of the turbulence on a long rise-time pressure signature was experimentally investigated in a ballistic range facility. To compare the effects of the turbulence on the long and short rise-time pressure signatures, a cone-cylinder projectile that simultaneously produces these pressure signatures was designed. The pressure waves interacted with a turbulent field generated by a circular nozzle. The turbulence effects were evaluated using flow diagnostic techniques: high-speed schlieren photography, a point-diffraction interferometer, and a pressure measurement. In spite of the fact that the long and short rise-time pressure signatures simultaneously travel through the turbulent field, the turbulence effects do not give the same contribution to these overpressures. Regarding the long rise-time pressure signature, the overpressure fluctuation due to the turbulence interaction is almost uniform, and a standard deviation 1.5 times greater than that of the no-turbulence case is observed. By contrast, a short rise-time pressure signature which passed through the same turbulent field is strongly affected by the turbulence. A standard deviation increases by a factor of 14 because of the turbulence interaction. Additionally, there is a non-correlation between the overpressure fluctuations of the long and short rise-time pressure signatures. These results deduce that the length of the rise time is important to the turbulence effects such as the shock focusing/diffracting.     

基于Ogden公式的充压伸缩式水封非线性计算研究

考虑橡胶类止水材料性能对水封设计的重要作用,论文采用Mooney-Rivlin公式和Ogden公式对橡胶类止水材料的单向拉伸、单轴压缩和纯剪实验数据进行曲线拟合与研究.结合工程实例将该两种公式的拟合参数应用于充压伸缩式水封自由外伸量的非线性有限元计算中,并将计算结果与该水封自由外伸量模型实验进行对比研究.结果表明:Og...