Pressure induced phase transformations and band structure of different high pressure phases in tellurium

We report here high-pressure x-ray diffraction (XRD) studies on tellurium (Te) at room temperature up to 40 GPa in the diamond anvil cell (DAC). The XRD measurements clearly indicate a sequence of pressure-induced phase transitions with increasing pressure. The data obtained in the pressure range 1 bar to 40 GPa fit five different crystalline phases out of Te: hexagonal Te (I) → monoclinic Te(II) → orthorhombic Te (III) → Β-Po-type Te(IV) → body-centered-cubic Te(V) at 4, 6.2, 11 and 27 GPa, respectively. The volume changes across these transitions are 10%, 1.5%, 0.3% and 0.5%, respectively. Self consistent electronic band structure calculations both for ambient and high pressure phases have been carried out using the tight binding linear muffin tin orbital (TB-LMTO) method within the atomic-sphere approximation (ASA). Reported here apart from the energy band calculations are the density of states (DOS), Fermi energy (E _f) at various high-pressure phases. Our calculations show that the ambient pressure hexagonal phase has a band gap of 0.42 eV whereas high-pressure phases are found to be metallic. We also found that the pressure induced semiconducting to metallic transition occurs at about 4 GPa which corresponds to the hexagonal phase to monoclinic phase transition. Equation of state and bulk modulus of different high-pressure phases have also been discussed.     

Mechanism of proton anisotropic velocity distribution in the solar wind

Although it has been long that spacecraft observed the anisotropy of velocity protons in the solar wind, there is still not a reasonable explanation. In this paper we try to give an explanation from the diffusion plateau of protoncyclotron resonance predicted by the quasi-linear theory for the resonance between the protons and the parallel propagating waves. We consider the effect of dispersion relation on diffusion plateau and notice that the diffusion plateau we have got by using cold plasma dispersion relation accords with the density contours in the velocity phase space detected at 0.3 AU in fast solar wind. For explaining proton distributions obtained in the fast solar wind from 0.7 AU to 1 AU hot plasma dispersion relation should be considered. We also give a theoretical relation of proton thermal anisotropy A and plasma parameter β.     

定速风力发电机模型参考自适应控制

在对定速风力发电机建模的基础上,设计了模型参考自适应控制器,并进行了跟随性能和抗干扰性能仿真,仿真结果表明自适应控制器的自适应能力很好.     

Validation of adaptive unstructured hexahedral mesh computations of flow around a wind turbine airfoil

In this paper we investigate local adaptive refinement of unstructured hexahedral meshes for computations of the flow around the DU91 wind turbine airfoil. This is a 25% thick airfoil, found at the mid‐span section of a wind turbine blade. Wind turbine applications typically involve unsteady flows due to changes in the angle of attack and to unsteady flow separation at high angles of attack. In order to obtain reasonably accurate results for all these conditions one should use a mesh which is refined in many regions, which is not computationally efficient. Our solution is to apply an automated mesh adaptation technique. In this paper we test an adaptive refinement strategy developed for unstructured hexahedral meshes for steady flow conditions. The automated mesh adaptation is based on local flow sensors for pressure, velocity, density or a combination of these flow variables. This way the mesh is refined only in those regions necessary for high accuracy, retaining computational efficiency. A validation study is performed for two cases: attached flow at an angle of 6° and separated flow at 12°. The results obtained using our adaptive mesh strategy are compared with experimental data and with results obtained with an equally sized non‐adapted mesh. From these computations it can be concluded that for a given computing time, adapted meshes result in solutions closer to the experimental data compared to non‐adapted meshes for attached flow. Finally, we show results for unsteady computations. Copyright © 2005 John Wiley & Sons, Ltd.     

Solar wind in the near-Earth interplanetary space: 1964–1987 revisited

Summary Solar-wind data, as obtained in the near-Earth space, have been re-examined for the period 1964 to 1987. For each month, the maximum and minimum hourly values of the solar-wind bulk speed together with those for the interplanetary magnetic-field intensity have been selected. They are reported in a tabular form (available as readable ASCII text files on DOS-formatted floppy disks) to ease off further studies in the framework of the Solar-Terrestrial System.     

A Complex Mode Method for Wind-Induced Responses of 6-Parameter Practical Viscoelastic Damping Energy Dissipation Structures Based on the Davenport Wind Speed Spectrum北大核心CSCD

针对六参数实用黏弹性阻尼耗能结构,基于Davenport风速谱系列响应问题进行了系统的研究.首先,利用六参数黏弹性阻尼器的微分型本构关系,建立了耗能结构基于Davenport风速谱激励下的运动方程;然后,运用复模态法将耗能结构的运动方程由二阶微分方程转化为一阶方程,获得了耗能结构系统对风振激励响应的频域解和功率谱密度函数表达式;最后,利用数学恒等式,基于随机振动理论获得了耗能结构系统在Davenport风速谱激励下的响应和阻尼器受力的解析解.该文方法不仅考虑了结构系统在风振激励作用下全振型展开的结果,表达式较现有结果更为简便,效率及精度更高,且适用于非经典阻尼结构.     

低速风洞微机控制闭环调速

本文提出一种用于调节低速风洞流速的测量及控制系统。该系统以微计算机为核心,不断采集风洞实验段的流速数据,并根据测量结果与指定值的比较去调节和控制风洞的电机转速,使风洞能准确地按指定风速运行或按予定的程序升速或降速,实现了低速风洞的闭环自动调速。本文给出了该系统的构成原理和性能实验结果。测试结果表明,本系统的超调量小于5％,稳态误差小于0.3％,调节时间小于50秒。     

沟谷坡面风沙起动规律研究

根据坡面风沙受力情况,以滚动模式建立了坡面风沙起动的风速公式.计算分析了相同风向条件下不同坡度风沙的起动风速和相同坡度条件下不同风向风沙的起动风速,并与平面风沙起动计算风速和实测风速进行了比较.计算分析表明,在风向一定时,坡面风沙更容易起动,风沙起动速率随着坡度的变陡而变小.在坡度一定时,风沙起动风速受到风向的影响很大,起动风速随风力与水平面垂线夹角的增大而增大.与平面相比,当风力与水平面垂线夹角小于90°时,坡面风沙起动流速比平面为小.在当风力与水平面垂线夹角大于90°时,起动风速比平面为大.当坡面为平面时,风沙起动公式与平面拜格诺起动公式完全一致.     

建筑风压数值模拟的几种并行化策略

针对四个处理机的Ｔｒａｎｓｐｕｔｅｒ并行计算机系统，建立了建筑风压数值模拟问题基于ＳＩＭ－ＰＬＥＣ算法的几种并行化策略：分区并行策略、方程并行策略和双重并行策略。对各种策略的计算流程、数据通讯及并行效率等进行了分析和比较，并通过实例计算作了验证。     

翼型与风洞侧壁交接角区分离流动研究

运用Navier-Stokes数值模拟对翼型模型试验时风洞侧壁和翼型模型结合部拐角区黏型分离流动进行模拟,并将简单代数湍流模型扩展用于机翼/风洞侧壁拐角区流动.计算格式在空间上采用中心有限体积离散,在时间上采用多步Runge-Kutta时间步长格式进行积分.结果显示,在翼型模型风洞试验时,模型/侧壁拐角区、模型表面、侧壁表面和模型后形成复杂的黏性分离流动和二次分离,对实验结果产生很大的影响.