Improvement of wind field hindcasts for tropical cyclones

This paper presents a study on the improvement of wind field hindcasts for two typical tropical cyclones, i.e., Fanapi and Meranti, which occurred in 2010. The performance of the three existing models for the hindcasting of cyclone wind fields is first examined, and then two modification methods are proposed to improve the hindcasted results. The first one is the superposition method, which superposes the wind field calculated from the parametric cyclone model on that obtained from the cross-calibrated multi-platform(CCMP) reanalysis data. The radius used for the superposition is based on an analysis of the minimum difference between the two wind fields. The other one is the direct modification method, which directly modifies the CCMP reanalysis data according to the ratio of the measured maximum wind speed to the reanalyzed value as well as the distance from the cyclone center. Using these two methods, the problem of underestimation of strong winds in reanalysis data can be overcome. Both methods show considerable improvements in the hindcasting of tropical cyclone wind fields,compared with the cyclone wind model and the reanalysis data.     

立轴漩涡多圈螺旋流速度分布的研究

本文引入分离变量法,研究了立轴旋涡的速度随径向、轴向的变化规律,并给出切向、径向和轴向速度的表达式。对立轴旋涡的多圈螺旋流现象,通过试验测量和速度分布计算两种方法进行了描述,二者定性一致。结果表明,立轴旋涡流场的切向速度占优,在流体质点从水面向下运动的过程中,围绕涡轴旋转十余圈,在进水口附近转为轴向流动。旋涡水面线的计算结果与实测值吻合较好。     

影响我国热带气旋的频数与强度预测研究及其在海洋工程中的应对

应用滑动平均的方法,对近58年影响我国的热带气旋频数,强度和年极值强度进行趋势分析,并应用Spearman非参数趋势检验法进行了显著性检验。在此基础上应用基于分形理论的R/S方法对未来的热带气旋频数、强度和年极值强度进行了趋势预测。分析表明:未来影响我国的热带气旋频数、强度、年极值强度都是呈增加增强趋势的。最后,给出了面对热带气旋强度增强的海洋工程的应对方法。     

EXPLICIT SIMULATION ON THE TRACK AND INTENSITY OF TROPICAL CYCLONE WINNIE （1997）

1. INTRODUCTION The Tropical Cyclone (TC) is a localized vortex characterized by strong multiscale interactions. Its horizontal extent is typically several hundred to a thousand kilometers, but the energy responsible for the whole system is mainly release…     

二维浅水流动的旋涡动力学问题探讨

导出了二维浅水流动的涡动议程与速度环量的随体导数表达式，以此为基础，分析了二维浅水流动中旋涡的动力学性质；阐明了离散涡方法（DVM）发展中的前沿问题，并对DVM在二维浅水流动数值模拟中的应用前景进行了展望。     

波浪对蘑菇头式取水口吸气漩涡流态影响的试验研究

滨海蘑菇头式取水口进口流态受波浪影响明显,但波浪作用下的取水口吸气漩涡规律尚缺乏系统研究,如何防止进水口前产生有害吸气漩涡是进水口设计中急需解决的问题。以某滨海电厂取水口为例,采用物理模型试验方法,研究了波浪作用下的取水蘑菇头进水流态和吸气漩涡特征,分析了波浪影响下取水口防进气所需的最小淹没深度。试验结果表明,波浪会抑制取水口周缘形成稳定的吸气漩涡。取水蘑菇头在淹没深度不足时会随着波浪周期产生间歇式吸气,但进气量要比持续波谷水位时小。在预防有害吸气漩涡方面,波浪的存在可降低临界淹没深度值,设计实践中可对淹没深度规范公式(Gordon公式)加以修正使用,而修正系数的取值应根据波浪要素和取水口结构形式确定。研究结果可为类似工程设计提供参考。     

湖泊风浪特性及风浪要素的计算

对太湖风浪观测资料的分析，得到了浅水湖泊中波高、波周期的统计分布，以及特征波要素之间的关系。采用自相关涵数法和最大熵法进行谱分析，得出了相应的无因次谱。文中的湖泊风波计算方法可供计算水库风浪参考。     

A numerical study on dispersion of particles from the surface of a circular cylinder placed in a gas flow using discrete vortex method

The dispersion of particles emitted from the surface of a circular cylinder placed in a gas flow at the Reynolds number of 200 000 is numerically investigated using the discrete vortex method coupled with a Lagrangian approach for solid particle tracking. The wake vortex patterns, the temporal-spatial distributions and trajectories as well as the dispersion functions for particles with various Stokes numbers（St） ranging from 0.001 to 1.0 are obtained. The numerical results reveal that：（1） Solid particles on the cylinder surface are picked up and then transported away from the cylinder by the wake vortex flow.（2） Solid particles emitted from the cylinder surface always follow the vortices in the cylinder wake, and the response of particles to wake vortices is directly related to their Stokes numbers（particles with St= 0.001, 0.0038, 0.01 can distribute both in the vortex core and around the vortex periphery, whereas those with St= 0.1, 1.0 can not enter the vortex core and congregate mainly around the vortex periphery）.（3） The particles move in rolling state in the wake region, and the dispersion intensity of particles in the lateral direction decreases remarkably as the Stokes number of particles is increased from 0.001 to 1.0.     

波浪模拟系统中规则波特征参数的提取方法研究

主动吸波技术是波浪模拟系统中的新技术，其中入射流特征参数的及时提取是一个关键问题。本文从基本的离散Fourier变换出发，建立了规则波特征参数的快速识别方法，并讨论了该方法的适用范围。大量仿真及实验表明，该方法是有效、可行的。     

Sensitivity of water quality indicators in a large tropical reservoir to selected climate and land‐use changes

This study compared the sensitivity of water quality in tropical Aguamilpa Reservoir, as represented by normalized algae mass and dissolved oxygen, to selected projected changes from global climate change and development. The sensitivity of reservoir stratification as an indicator of reservoir sensitivity also was analysed. Model simulations indicated the reservoir was more sensitive to changes during the warm‐dry season than at other times. Both indexes (normalized algal mass and dissolved oxygen mass) were more sensitive to changes in air temperature (climate change) and nitrogen loading (development) than to changes in flow. The sensitivity to air temperature was similar to, but generally less than, the sensitivity to nutrient inflow. At the bounding values for change (3 °C for temperature; 50% increase in nitrogen loading), the algae mass sensitivities were 0.15 mg L^?1 per 3 °C and 0.2 mg L^?1 per 50% nitrogen load increase, and the dissolved oxygen mass sensitivities were 0.7 mg L^?1 per 3 °C and 2.0 mg L^?1 per 50% load increase. Changes in air temperature and nitrogen loadings affect the reservoir in different ways, air temperature mostly changing the timing of the algal growth with little change in peak values, while nutrient loadings change the peak values with little change in the timing. While the sensitivities are similar, the total algal mass change is significantly larger for nitrogen loading, compared to air temperature changes. These results imply global climate change effects can be partially mitigated by implementing management measures in the surrounding watersheds to minimize nutrient inflows, especially nitrogen in the case of Aguamilpa Reservoir.     

Application of signal processing techniques to the detection of tip vortex cavitation noise in marine propeller

The tip vortex cavitation and its relevant noise has been the subject of extensive researches up to now. In most cases of experimental approaches, the accurate and objective decision of cavitation inception is primary, which is the main topic of this paper. Although the conventional power spectrum is normally adopted as a signal processing tool for the analysis of cavitation noise, a faithful exploration cannot be made especially for the cavitation inception. Alternatively, the periodic occurrence of bursting noise induced from tip vortex cavitation gives a diagnostic proof that the repeating frequency of the bursting contents can be exploited as an indication of the inception. This study, hence, employed the Short-Time Fourier Transform (STFT) analysis and the Detection of Envelope Modulation On Noise (DEMON) spectrum analysis, both which are appropriate for finding such a repeating frequency. Through the acoustical measurement in a water tunnel, the two signal processing techniques show a satisfactory result in detecting the inception of tip vortex cavitation.     

探地雷达和浅层地震波法在海堤抛石层探测中的应用

介绍探地雷达、瑞雷波法和地震映像法的基本原理及特点,针对海堤抛石断面结构分层及其物性特征,以浙江东部某海堤为例,综合运用探地雷达、瑞雷波法和地震映像法,高效、可靠、准确地探明了抛石层的分布范围及深度。探测实践表明,探地雷达具有快速、连续和整体性的优势,瑞雷波法具有较强的纵向分辨能力,地震映像法具有较强的横向分辨能力,这3种方法分别从浅层人工地震波场和电磁场方面反映探测对象和目标,起到了较好的互补和综合作用。     

采用纵向翼形管模拟水击波速

在水击模型实验中，采用纵向翼形管是模拟水击波速的有效途径之一。为了便于确定翼缘长度，满足模型设计，本文应用结构力学方法和平面有限元方法研究了翼级长度，管壁厚度，管道半径，管材的弹模等关键参数对水击波速的影响，揭示了该结构型式的管道在内水压力作用下变形量与水击波速间的内丰规律，并将理论计算与实验结果进行了对比，两者十分吻合。