基于分数阶时间导数的黏弹性衰减VTI介质中平面波传播

目前在地震勘探频带范围内通常假设品质因子Q与频率无关,且呈衰减各向同性.事实上,相比较速度各向异性,介质的衰减各向异性同样不可忽视.本文将衰减各向异性和速度各向异性二者与常Q模型相结合,建立了黏弹性衰减VTI介质模型,并基于分数阶时间导数理论,给出了对应的本构关系和波动方程.利用均匀平面波分析和Poynting定理,推导出准压缩波qP、准剪切波qSV和纯剪切波SH的复速度、相速度、能量速度以及品质因子的解析表达式.对模型的正确性进行了数值验证,并分析了qP,qSV和SH波在介质中的传播特性.数值试验结果表明：本模型能够实现理想的恒定Q行为,表现了品质因子和速度的各向异性特征,显示出黏弹性增强将导致能量速度和相速度的频散曲线变化剧烈;速度和衰减各向异性参数与传播角度之间的耦合效应对qP,qSV和SH波的速度和能量影响明显;qP,qSV和SH波的频散曲线和波前面随着衰减各向异性强度的改变发生显著变化,其中耦合在一起的qP和qSV波变化趋势相同,而SH波与它们呈现相反的变化规律.本研究为从常Q模型角度分析地震波在衰减各向异性黏弹性介质中的传播特征奠定了理论基础.

     

第三系砂岩波速特性探讨及统计分析

波速测试技术作为一种简便、快捷的测试技术被广泛应用于各种工程实践中, 第三系砂岩是非常具有代表性的软岩, 对第三系砂岩波速测试的研究具有重要意义。本文以吉阳核电厂址的第三系砂岩为研究对象, 通过整理单孔波速、跨孔波速方法获得的参数, 分析半成岩岩体波速的空间分布规律及特性, 寻找波速与埋深深度、标贯动探参数之间的关系。结果表明单孔、跨孔波速测试波速值随深度增加而增加, 埋深5m以上增加幅度明显, 埋深5m以下增加趋势减缓, 平面上不同位置各孔的波速值基本一致, 说明第三系半成砂岩岩体分布较均匀。剪切波速与埋置深度线性回归拟合效果较好, 对数拟合优度在0.95以上, 精度最高, 相对可靠, 剪切波速与标贯击数之间相关性不明显, 与动探击数之间基本不相关。     

两参量的海面阻力系数模式的探讨

从风浪的能量平衡方程出发，引进若干风要素与波要素以及波要素之间的定性关系，经演算可导出海面阻力系数（Ｃｐ）或是风速（Ｕ）和波龄（β）或是Ｕ和波高（Ｈ）的函数，然后沿用最小二乘法，终将得出４组１２个回归方程。当β（或β）或Ｈ为某一给定值，惟有Ｕ为唯一参量时，所提各式均可简化为非线性方程：ＣＤ＝ａ＋ｂ，Ｕ＋ｃ．Ｕ＾２；式中ａ，ｂ和ｃ为三个经验系数，就所检验的例子而言，本文的结果与实际的符合前人的为好。     

层化流体中半板造波的内波解

为了形象地说明内波的传播模式,研究给出了内波水槽中由半板造波所形成的内波解。结合Ｖａｅｉｓａｅｌａｅ频率Ｎ（ｚ）＝ｃｏｎｓｔ和简化Ｈｏｌｍｂｏｅ两种密度剖面模式讨论了内波场的传播图案。在内波水槽中成功地形成了上述两种密度剖面,相应的实验印证了本文分析的正确性。     

An empirical formula for friction coefficient of a perforated wall with vertical slits

The friction coefficient in the permeability parameter of a perforated wall has been estimated on the basis of a best fit between measured and predicted values of such hydrodynamic coefficients as reflection and transmission coefficients. In the present study, an empirical formula for the friction coefficient is proposed in terms of known variables, i.e., the porosity and thickness of the perforated wall and the water depth. This enables direct estimation of the friction coefficient without invoking a best fit procedure. To obtain the empirical formula, hydraulic experiments are carried out, the results of which are used along with other researchers' results. The proposed formula is used to predict the reflection and transmission coefficients of various types of structures including a perforated wall. The concurrence between the experimental data and calculated results is good, verifying the appropriateness of the proposed formula. It is also shown that the proposed formula can be used for irregular waves as well.     

Improvements in height datum transfer expected from the GOCE mission

 One of the aims of the Earth Explorer Gravity Field and Steady-State Ocean Circulation (GOCE) mission is to provide global and regional models of the Earth's gravity field and of the geoid with high spatial resolution and accuracy. Using the GOCE error model, simulation studies were performed in order to estimate the accuracy of datum transfer in different areas of the Earth. The results showed that with the GOCE error model, the standard deviation of the height anomaly differences is about one order of magnitude better than the corresponding value with the EGM96 error model. As an example, the accuracy of the vertical datum transfer from the tide gauge of Amsterdam to New York was estimated equal to 57 cm when the EGM96 error model was used, while in the case of GOCE error model this accuracy was increased to 6 cm. The geoid undulation difference between the two places is about 76.5 m. Scaling the GOCE errors to the local gravity variance, the estimated accuracy varied between 3 and 7 cm, depending on the scaling model. Received: 1 March 2000 / Accepted: 21 February 2001     

辽,金,元测绘史考（下）

概述辽、金、元三代有关测绘的管理和机构,职官设置,各类测绘状况及成果,着重介绍了元代的测绘技术,发明创造及著述。     

Rainfall on the Sea: Surface Renewals and Wave Damping

Rainfall on the sea surface causes a variety of effects on the molecular boundary layers. Two such effects are the reduction of the surface renewal time period and the damping of short gravity waves being responsible for wave breaking at higher wave frequencies. The effects described recently by Schlüssel et al. are revaluated in order to fully include the varying raindrop velocity. New parameterizations are derived, which differ from the previous ones, and a substantially higher kinetic energy flux due to rain is found. The general conclusions about the impact on the thermal molecular boundary do not change, although we point to several minor errors in the calculations of Schlüssel et al. (1997).     

Wave energy conversion under constrained wave-by-wave impedance matching with amplitude and phase-match limits

This paper investigates an approach to limit the fullness of ‘tuning’ provided by wave-by-wave impedance matching control of wave energy devices in irregular waves. A single analytical formulation based on the Lagrange multiplier approach of Evans [1] is used to limit the velocity amplitude while also limiting the closeness of the phase match between velocity and exciting force. The paper studies the effect of the present technique in concurrently limiting the device velocity and the required control/actuation force. Time domain application requires wave-profile prediction, which here is based on a deterministic propagation model. Also examined in the time domain is the effect of possible violation of the displacement constraint, which for many designs implies impacts at hard stops within the power take-off mechanism. Time domain simulations are carried out for a 2-body axisymmetric converter (with physical end-stops) in sea states reported for a site off the US east coast. It is found that the approach leads to effective power conversion in the less energetic sea states, while as desired, considerable muting of the optimal response is found in the larger sea states. Under the assumptions of this work, the end-stop collisions are found to have a minor effect on the power conversion. The present approach could be used to guide the design of power take-off systems so that their displacement stroke, maximum force, and resistive and reactive power limits are well-matched to the achievable performance of a given controlled primary energy converter.     

Sediment transport patterns at Trafalgar offshore windfarm

A simple analytical model of wave propagation has been developed in order to study the potential sediment transport patterns due to the action of currents and waves in the neighborhood of cylindrical structures as well inside a group of these structures. The attention is focused on the study of Trafalgar offshore windfarm, a case in which it has been necessary to analyze the flow trough porous structures in order to model fish growing-cages planned to be installed at each aerogenerator structure. The results are obtained by averaging over one period of wave in order to evaluate the net potential sediment transport. The analysis of the results reveals how the processes of wave diffraction and reflection give rise to periodic patterns of sediment transport around and between the structures.