Diffraction of a directionally spread wave group by a cylinder

The problem of diffraction of a directionally spread focused wave group by a bottom-seated circular cylinder is considered from the viewpoint of second-order perturbation theory. After applying the time Fourier transform and separation of vertical variable the resulting two-dimensional non-homogeneous Helmholtz equations are solved numerically using finite differences. The detailed formulation of the second-order radiation condition is presented. Numerical solutions of the problem are obtained for JONSWAP amplitude spectra for the incoming wave group with various types of directional spreading. The results are compared with the corresponding results for a unidirectional wave group of the same amplitude spectrum. Finally we discuss the applicability of the averaged spreading angle concept for practical applications.     

分析海浪方向谱的EEV方法的一种迭代形式

将Pawka为改进最大似然方法（MLM）而提出的迭代方案应用于扩展本征关方法（EEV），作为EEV的一种迭代形式（IEEV）。用模拟数据检验了IEEV的合理性，并与EEV作了比较。计算结果表明，IEEV的估计性状较EEV有改善。最后将IEEV及EEV用于分析仪器阵列的外海观测数据。     

Caisson breakwaters embodying an OWC with a small opening—Part II: A small-scale field experiment

A common and intuitive idea is that, before an absorbing breakwater, waves are smaller than before a conventional reflecting breakwater. The theory of Part I has shown that, on the contrary, before a breakwater converter, in some cases, the wave height may be greater than before a conventional reflecting breakwater. Now, an experiment off the eastern coast of the Straits of Messina provides a confirmation of the theory: some huge amplifications of swells are common at a breakwater converter, and as a consequence the energy absorption gets very large. Here, we show the results of the experiment, and, basing ourselves on these results and on the theory of Part I, we suggest some practical way of calculation.     

水平分量磁变仪的定向与定向检查

水平分量磁变仪定向与定向检查是保证记录质量的一项重要工作。本文研究表明，失磁下影响的的一般条件下，定向与定向检查均可用”扭头带动镜面法进行，日常可根据定向记录位置ｎ。监 状态。已有精确定向结果的标度线圈用于定向检查与校正操作简便，如果度盘进一步改进，检查精度也可以达到较高水平。     

BOREAS中北部针叶林的短波辐射传输测量结果及建模(英文)

通过ＢＯＲＥＡＳ实验，我们研究了北部森林植物群落对气候变化所起的作用。对针叶林地带太阳辐射通量的测量表明在辐射场中有重要的方向效应。这些效应主要与树林的分布及树冠结构有关。一个简单的方向传输模型可以解释在观测结果中的一个重要的角度特征。     

全张量磁梯度数据解释的均衡边界识别及深度成像技术

全张量磁梯度数据具有高精度、高分辨率、多参量的优点,能更加清晰地刻画地质体的分布特征,综合利用磁张量梯度数据准确地获得地质体水平位置和深度信息是解释的主要目的.磁张量数据的方向解析信号具有减小倾斜磁化干扰的优点,常被用来圈定磁源体的水平位置,但解析信号强度随着地质体埋深的增加急剧衰减,难以有效识别较深的地质体.张量数据均衡边界识别技术,利用不同方向解析信号的比值函数,能有效地均衡不同深度地质体的响应,同时显示不同深度地质体的边界,提高了对较深地质体的分辨率.磁张量数据深度成像技术根据实测张量数据与假定模型张量数据的相关系数来给定地质体的深度,综合利用多参量数据联合反演提高了反演结果的准确性,且无需进行复杂的反演运算,是大数据量张量数据解释的有效方法.理论模型试验证明：磁张量数据均衡边界识别技术可清晰和准确地识别地质体的水平范围,受倾斜磁化干扰小;磁张量数据深度成像技术可准确地获得地质体的深度信息,具有较强的抗噪性.将上述方法应用于铁矿区实测航磁张量梯度数据解释,获得了铁矿体水平分布与埋深,深度结果与张量欧拉反褶积法计算结果一致.     

Nearshore directional wave measurements by surface-following buoy and acoustic Doppler current profiler

Directional energy spectra of nearshore surface waves were measured for a 3-year period (2004–2007) at a site with mean depth 14 m and mean tidal range 2.1 m. Triaxys surface-following wave buoys reported hourly directional wave energy spectra and wave parameters near the offshore end of the Savannah River Entrance Channel, Georgia, USA. An acoustic Doppler current profiler (ADCP) was located beside the wave buoy for 3 months. Directional and non-directional surface wave energy spectra and the corresponding bulk wave parameters (height, period, and direction) are compared for the two systems. Most parameters derived from the spectra agree closely; the most significant differences were found at the upper and lower frequency measurement limits, where signal-to-noise ratios were lower. The wave buoy consistently reports a small amount of energy below 0.05 Hz that does not appear in the ADCP-derived spectra and does not appear to be related to the mooring system. This leads to larger mean and peak periods reported by the buoy. All directional spectra were computed using the Maximum Entropy Method for both instruments, but the buoy, with spectra derived from six independent time series, provides lower directional resolving power than the ADCP, which utilizes twelve time series. Both systems gave similar results defining mean and peak wave directions, with the primary difference being that the ADCP indicates energy to be more tightly concentrated around the peak direction.     

On the accurate and efficient calibration of a 3D wave basin

This paper describes the calibration procedure adopted for the new 3D wave basin located in the Hydrodynamics Laboratory at Imperial College London. Unlike traditional calibrations, based on observations of regular wave trains, the method described herein uses a focused wave approach. Such waves, produced by the constructive interference of freely propagating wave components, have led to a number of recent advances in theoretical wave modelling in which it was essential to know the underlying linear components. In the context of a laboratory study, similar advantages can be realised provided the linear wave components generated by the wave paddles are well defined. This, in turn, can only be achieved if the calibration is sufficiently accurate. The current study provides a calibration based upon a realistic JONSWAP spectrum, describes the details of the methodology employed, and highlights how the application of focused wave techniques eliminates spurious calibration effects due to unwanted reflections from the boundaries of the basin. The final calibration is verified through the generation of test cases, involving linear and nonlinear, unidirectional and directionally spread waves. These confirm both the accuracy of the calibration and the suitability of the methods employed.     

Directional measurements of wave growth in a short and narrow fetch geometry

The growth of young waves along a narrow bay and their directional spectra were studied. The fetch geometry was found to affect the shape of the spectrum already when the waves were young. When compared to the growth from a straight shoreline, the dimensionless energy was reduced, but the change in dimensionless peak frequency was smaller. The behaviour of the young waves was similar to that of the mature waves but the differences between narrow and broad fetch geometries were smaller, which suggests that due to a stronger nonlinear transfer the young waves are less sensitive to the fetch geometry. The directional spectrum of the young waves in the narrow fetch geometry was narrower at all energy containing frequencies than the spectra from broad fetch geometry, which further supports the conclusion that the shape of the spectrum is not independent of the fetch geometry.