结合抛物型缓坡方程计算波浪辐射应力

将波浪辐射应力与抛物型缓坡方程中的待求变量联系起来,提出了一种计算辐射应力的新方法,并用有限差分法对控制方程进行了数值求解。数值结果表明这种方法精度高、编程简单、求解快速,可用于实际大区域波浪辐射应力的计算。     

MetroIn在大尺寸天线罩安装测量中的应用

阐述大尺寸天线罩的高精度安装测量方案,基于MetroIn工业测量软件平台对测量数据进行处理和分析,全方位实时指导天线罩的现场安装.通过对一台口径为5m的天线进行防护罩安装测量,验证方案的正确性,表明其理论和技术成功可行.     

具非线性扩散系数的中立抛物型方程的振动结果

研究一类具非线性扩散系数的中立抛物型方程的振动性,利用Green定理和时滞微分不等式,获得了该类方程在Robin边值条件下所有解振动的若干充分性判据。结论充分表明振动是由时滞量引起的。     

3S技术在抛物线沙丘形态特征研究中的应用

3S技术的发展为风沙地貌研究提供了新的方法和强有力的技术支持。基于GIS平台,利用差分GPS实测数据,通过空间插值生成DEM,可有效提取地形因子和形态参数,实现风沙地貌三维形态特征的定量化研究;结合高分辨率遥感影像,不但可以提取风沙地貌二维形态特征,还可以提取植被覆盖信息。该文以内蒙古库布齐沙漠典型抛物线沙丘为研究对象,探讨3S技术在沙丘形态特征研究中的应用,结果表明:该区沙丘平面形态呈U型,丘臂指向W;纵剖面上迎风坡较缓、背风坡较陡,横剖面不对称;沙脊线所夹中轴线走向为WNW-ESE,反映了盛行风或合成输沙方向;油蒿灌丛分布在背风坡、两翼及其间平坦地;在长期合成风的作用下,沙丘向前移动,丘臂间的油蒿灌丛发生阶段性的弧带状自然恢复。     

The Square Kilometre Array: An International Engineering Perspective

The pace of the international Square Kilometre Array (SKA) project is accelerating, with major concept reviews recently completed and a number of technology demonstrators well underway. First-round submissions to host the telescope were lodged by six countries. The SKA timeline currently shows a site decision in 2006, and one or more technology concepts chosen in 2008. The telescope is expected to be operational, in various phases, in the period 2015–2020. This paper gives a status review of the project, and outlines engineering concept development and demonstration projects.     

Analytical inversion of specific energy–depth relationship in channels with parabolic cross-sections

Abstract

The specific energy–depth relationship in open channels with parabolic cross-sections is analytically inverted. Two nondimensional expressions of the specific energy are considered, depending on the prescribed quantity (specific energy or alternate depth). The inversion of such functions consists of finding the roots of cubic and quartic equations. By solving a quartic equation for a given discharge and for each value of the specific energy, a subcritical depth and a supercritical depth are found analytically. In this case, two acceptable roots are recognized and two other roots are discarded, on the basis of their physical meaning. Moreover, by solving a cubic equation for a given discharge and for each value of the depth, the other corresponding alternate depth is found analytically. Then, one acceptable root is recognized and two other complex conjugate roots are discarded. Finally, different examples are presented, to show the efficiency of the proposed solutions. Such analytical solutions can be easily used in natural rivers and parabolic channels.

Citation Vatankhah, A. R. & Valiani, A. (2011) Analytical inversion of specific energy–depth relationship in channels with parabolic cross-sections. Hydrol. Sci. J. 56(5), 834–840.     

A process‐based hypothesis for the barchan–parabolic transformation and implications for dune activity modelling

The introduction of vegetation to bare barchan dunes can result in a morphological transformation to vegetated parabolic dunes. Models can mimic this planform inversion, but little is known about the specific processes and mechanisms responsible. Here we outline a minimalist, quantitative, and process‐based hypothesis to explain the barchan–parabolic transformation. The process is described in terms of variations in the stabilization of wind‐parallel cross‐sectional dune slices. We hypothesize that stabilization of individual ‘dune slices’ is the predictable result of feedbacks initiated from colonization of vegetation on the slipface, which can only occur when slipface deposition rates are less than the deposition tolerance of vegetation. Under a constant vegetation growth regime the transformation of a barchan dune into a parabolic dune is a geometric response to spanwise gradients in deposition rates. Initial vegetation colonization of barchan horns causes shear between the anchored sides and the advancing centre of the dune, which rotates the planform brinkline angle from concave‐ to convex‐downwind. This reduces slipface deposition rate and allows vegetation to expand inward from the arms to the dune centre. The planform inversion of bare barchans dunes into vegetated parabolic dunes ultimately leads to complete stabilization. Our hypothesis raises several important questions for future study: (i) are parabolic dunes transitional landforms between active and vegetation‐stabilized dune states? (ii) should stabilization modelling of parabolic dune fields be treated differently than linear dunes? and (iii) are stabilized parabolic dune fields ‘armoured’ against re‐activation? Copyright © 2012 John Wiley & Sons, Ltd.     

Resolution of GPR bowtie antennas: An experimental approach

Since target reflections directly depend on the emitted pulse characteristics, a key factor for carrying out a successful GPR survey is to know as much as possible about the transmission features of the antennas used. This information is very important in order to choose the right antennas and set the appropriate configuration parameters for a specific survey. With this in mind this paper deals with the development of a set of laboratory experiments on the resolution capabilities of three bowtie antennas at frequencies of 500, 800 and 1000 MHz. Results from these measurements give a first estimation of the resolution of the antennas under test, showing the advantage of performing experiments rather than relying only on theoretical assumptions. The results are also expressed in terms of the central wavelength for each antenna and compared with some theoretical estimations proposed in the specialized bibliography.     

逆散射级数法去除自由表面多次波

压制多次波是地震资料处理过程中的重要环节之一,多次波去除的效果直接影响到最后成像的质量．本文研究的逆散射级数法以波动方程和Born级数为基础,构造一个与自由表面多次波相关的子序列来预测并消除多次波,该方法不需要知道地下的速度结构信息,适用于各种复杂的地下情况．在逆散射级数法的实现过程中,地震子波和近道波场是必不可少的信息,本文采用能量最低法则和带限抛物Radon变换法来弥补原始地震资料中所缺失的这些信息．合成资料和实际地震资料的处理结果表明,逆散射级数法能够在去除自由表面多次波的同时保留有效波的信息,对于地下复杂结构的情况同样有效．     

定向电磁波传播随钻测量基本理论及其在地层界面预测中的应用

采用水平层状各向异性介质中的磁流源并矢Green函数计算定向电磁波传播随钻测量的幅度衰减和相位移.分析了定向电磁测量的探测范围和对地层界面的灵敏性,研究了地层各向异性、地层相对倾角和接收天线倾角对定向测量的影响.计算结果表明,频率越低、线圈距越大、目的层和围岩层电阻率对比度越大,定向电磁测量的探测范围越大.随着接收天线倾角的增加,定向幅度衰减在接近地层界面时的变化更加明显,对地层界面的灵敏性增加.采用对称天线结构可消除定向测量信号在远离地层界面处对地层各向异性和地层相对倾角的依赖,实现对地层界面的准确预测.