MATHEMATICAL MODELING OF OSCILLATORY MHD COUETTE FLOW IN A ROTATING HIGHLY PERMEABLE MEDIUM PERMEATED BY AN OBLIQUE MAGNETIC FIELD

We study theoretically the incompressible, viscous, oscillatory hydromagnetic Couette flow in a horizontal fluid-saturated highly permeable porous medium parallel-plate channel rotating about an axis perpendicular to the plane of the plates under the action of a uniform magnetic field, B₀, inclined at an angle θ to the axis of rotation. The flow is generated by the non-torsional oscillation of the lower plate of the channel. The reduced unsteady momentum equations are nondimensionalized with appropriate variables. Exact solutions under specified boundary conditions are obtained using the Laplace transform method (LTM). The flow regime is found to be controlled by a rotational parameter (K²), which is the reciprocal of the Ekman number (Ek), the square of the Hartmann magnetohydrodynamic number (M²), a porous medium permeability parameter (K_p), which is the inverse of the Darcy number (Da), oscillation frequency (ω), dimensionless time (T), and magnetic field inclination (θ). The influence of these parameters on the primary (u₁) and secondary (v₁) velocity field is presented graphically and studied in detail. Asymptotic behavior of the solutions is also examined for several cases of the square of the Hartmann number, rotation parameter, and oscillation angular frequency. The existence of modified Hartmann boundary layers is also identified. The present study has important applications in MHD (magnetohydrodynamic) energy generator flows, chemical engineering magnetic materials processing, conducting blood flows, and process fluid dynamics.     

容器斜接管区应力状态的研究

以直径６００ｍｍ、具有两个斜接管的容器为模型，进行了内压作用下的应力测试，并用高精度壳单元的柱壳相贯程序进行了详细计算，得到了容器斜接管区的应力分布规律。同时，从实验数据和ＳＡＰ程序的计算对比中验证了柱壳相贯程序，可用于工程计算     

解读柏林犹太人博物馆中霍夫曼花园

建筑师丹尼尔·里伯斯金的建筑以其独特的形态学方法、晦涩难懂的建筑内涵、打破常规的大胆构思而被冠以解构主义、观念建筑等“标签”。该文认为只有对建筑师操作手法进行分析，找到隐藏在建筑背后的意图，加以总结归纳，方可运用自如，从而在建筑学习过程中避免复制现有模型和单纯照搬里伯斯金式样，创作出既富内涵和独创性又具可建造性的作品。     

无人机倾斜摄影测绘技术在某项目土石方算量中的应用

本文以研究无人机倾斜摄影测绘在土石方工程算量中的应用为目的,以丽水秀山公园基坑开挖阶段的土石方算量为研究对象,系统阐述了无人机倾斜摄影测绘技术在土石方算量中的应用实践及内外业关键流程。通过倾斜摄影测绘技术结合方格网土方算量方法快速高效完成了本项目的土石方算量,为相应的验工提供了准确的参考和依据,同时为类似项目的土石方算量提供了新思路和解决方案,具有创新意义。     

Busemann diffuser for supersonic ramjet engine with detonation combustion of hydrogen-air mixture

The expediency of using a Busemann diffuser in a scramjet engine with detonation combustion of hydrogen-air mixtures is studied. A method is developed for calculating an air intake that provides spontaneous initiation of oblique detonation in a hydrogen-air mixture under conditions of rarefied atmosphere at hypersonic freestream Mach numbers. The geometry of the Laval nozzle (convergent-expanding) with the Busemann diffuser for the free flow Mach number 9 is determined. It is shown that at an altitude of about 40 km, the detonation combustion of the hydrogen-air mixture in this nozzle can provide more than 0.4 tons of thrust and more than 35% efficiency. The mathematical model is based on unsteady two-dimensional Euler equations for axisymmetric multicomponent reacting gas flow. To simulate chemical transformations, the detailed kinetic scheme is used that takes into account 33 non-equilibrium reactions for nine components of the mixture. The heat capacity, enthalpy, and entropy of a mixture are calculated using the reduced Gibbs energy of the gas components. Numerical modeling is carried out according to the modified Godunov scheme of the second order of approximation in spatial variables.     

受限通道中三维激波与侧壁面作用的数值模拟研究

为了了解超燃冲压发动机中三维斜激波与壁面的相交情况,以冷态模拟为基础,对两种不同形状的斜劈结构产生的斜激波进行数值模拟。当斜劈展向与气流方向成45.0°时,激波和膨胀波结构呈现三维特性,并且激波在两侧壁面处的反射现象不同。以激波面上游为视角,当激波与壁面相交成锐角时会产生马赫反射;而激波与壁面相交成钝角则会以叠加膨胀波的形式减弱激波,并且使激波面的法线方向与壁面的法线方向垂直。由于两侧壁面的影响,随着高度的增加激波强度减弱,同时气体经过斜激波后偏转角度也减小。对于构型Ⅱ,有斜劈的区域产生三维斜激波会延伸到无斜劈区域,此时下壁面与斜激波相交成钝角,同样会以叠加膨胀波的形式减弱斜激波。     

The total energy and the total entropy of force signals — new parameters for monitoring oblique turning operations

In unmanned CNC turning operations, the accuracy of tool wear predictions is very important for accurate tool replacement policies and avoiding unnecessary tool insert changes. This paper introduces two new parameters, namely the total energy and the total entropy of force signals, for tool condition monitoring. The correlation between the new parameters, tool wear and a wide range of cutting conditions is examined. The experimental results show that the energy of force signal can be reliably used to monitor tool flank and crater wear over a wide range of cutting conditions. However, the total entropy of forces does not appear to be sensitive to feed rate, rake angle and tool wear. The experimental results also indicate that crater wear causes an increase in the effective rake angle resulting in lower total energy of forces. For some particular shapes of worn tool, however, the crater wear results in a decreased rake angle which increases the total energy of forces. The influence of crater wear on forces and the root mean square of acoustic emission (AErms) signals is also observed in this research.     

Experiments to study turbulence and flow past a low-rise building at oblique incidence

It is now well-known that high suction pressures develop along the leading edges of the building due to the formation of corner vortices when the wind is incident at oblique angles. These high suction pressures can damage the roof surface, which may even result in total failure. This paper gives the results from experiments carried out on 1:100 scale models of the Texas Tech University Test Building in a wind tunnel under different flow conditions. Both sharp-edged models and round-edged models were used to conduct flow and turbulence experiments. The results from flow visualization experiments reveal that there exists a separation and recirculation region on roof top at normal incidence and corner vortices form at oblique incidence with different magnitudes of rounding of roof edges influencing the turbulence levels and flow differently.     

超宽带宽角极化不敏感的电路模拟吸波材料设计

传统的电路模拟吸波材料设计只考虑正入射时的吸波性能,当入射角较大,尤其是大于30°时,雷达吸波器的吸波效果明显恶化。随着现代双站雷达探测技术的发展,雷达探测电磁波可能来自不同的空间方向,这就要求雷达吸波材料不仅在电磁波正入射时具有较高的吸波性能,在斜入射时同样实现良好的隐身特性。为此,该文提出了一种新型的宽带吸波材料。...     

Influence of deposition regime on physical properties of gallium doped zinc oxide films

Zinc oxide films doped by gallium were deposited using RF diode sputtering from a ceramic ZnO + 2% Ga₂O₃ target on Corning glass in argon atmosphere. Samples were supported in three different positions against a substrate holder - horizontal, and at 60 and 80° to the horizontal position. Two series of samples 700-1000 nm in thickness were prepared: one at room temperature (RT) and the second at 200 °C. XRD, optical and electrical experiments indicated that the films are polycrystalline having average crystallite sizes from 30 to 80 nm, integrated transmittances in the range of 400-1000 nm increased from 85 to 90 per cent and optical band-gap values increased from 3 to 3.2 eV with higher deposition temperature. The resistivity of the obliquely sputtered samples positioned at 80° to the substrate holder was one order lower than the horizontally positioned samples. No significant changes were observed in case of optical properties of the films in dependence on the tilt-angle.