Preoperational ocean forecasting in the southeastern Mediterranean Sea: Implementation and evaluation of the models and selection of the atmospheric forcing

Within the framework of several local and international programs, a quasi-operational ocean-forecasting system for the Southeastern Mediterranean Sea has been established and evaluated through a series of preoperational tests. The Princeton Ocean Model (POM) is used for simulating and predicting the hydrodynamics while the Wave Model (WAM) is used for predicting surface waves. Both models were set up to allow varying resolution and multiple nesting. In addition, POM was set up to be easily relocatable to allow rapid deployment of the model for any region of interest within the Mediterranean Sea. A common requirement for both models is the need for atmospheric forcing. Both models require time varying wind or wind stress. In addition, the hydrodynamic model requires initial conditions as well as time dependent surface heat fluxes, fresh water flux, and lateral boundary conditions at the open boundaries. Several sources of atmospheric forcing have been assessed based on their availability and their impact on the quality of the ocean models' forecasts. The various sources include operational forecast centers, other research centers, as well as running an in-house regional atmospheric model. For surface waves, higher spatial and temporal resolution of the winds plays a central role in improving the forecasts in terms of significant wave height and the timing of various high wave events. For the hydrodynamics, using the predicted wind stress and heat fluxes directly from an atmospheric model can potentially produce short range ocean forecasts that are nearly as good as hindcasts forced with gridded atmospheric analyses. Finally, a high-resolution, nested version of the model has shown to be stable under a variety of forcing conditions and time scales, thus indicating the robustness of the selected nesting strategy. For the southeastern corner of the Mediterranean, at forecast lead times of up to 4 days the high-resolution model shows improved skill over the coarser resolution driving model when compared to satellite derived sea surface temperatures. Most of the error appears to be due to the analysis error inherent in the initial conditions.     

An idealized model of interaction between fronds of the large seaweed Durvillaea antarctica

The effect of interactions between individual fronds in a bed of the large intertidal seaweed Durvillaea antarctica, when forced by breaking waves, is studied using a computational model. The model simulates the response of a seaweed bed using a sequence of connected oscillators which are excited by a propagating forcing function representing a breaking ocean wave. Two new facets of the interplay between seaweeds and hydrodynamics are considered: (i) wave forcing due to breaking waves is often not sinusoidal in the rocky intertidal zone and (ii) a frond interaction term is included. The addition of frond interaction reduces the maximum loading on individuals within the bed by around 30% using estimated biomechanical parameters. The rate of change of the loading on the holdfast (equivalent to the “jerk”) is affected in a similar or greater fashion.     

穿浪多体船运动性能研究

在穿浪双体船基础上，加装半潜体或带被动式减纵摇鳍的半潜体使其成为消波穿浪多体船，航行性能大大提高。半潜体不仅对耐波性能有利，对静水阻力和船体结构强度都有利。试验表明半潜体使经济航速阻力减小１８－２３％，设计航速阻力减小５－７％。耐波性综合指标比穿波双体船有提高，特别是纵摇明显减小。     

两道瑞雷波法在路基密实度检测中的应用

基于瑞雷波在层状介质中的传播理论,可以对地表实测瑞雷波进行频散分析,从而对地下岩土介质的物性差异给予判断分析。这种方法在岩土工程勘察检测领域得到了越来越多的应用。本文将两道瑞雷波应用于路基压实度检测问题。利用Matlab软件中的绝对相位展开技术,提取了两道瑞雷波之间的相位差信息,进而提取频散曲线。再根据半波长理论以及瑞雷波相速度与路基土的干密度关系,给出了干密度随深度变化的曲线,最后将多个测点的干密度曲线排列在一起,为检测路基的压实程度提供了很好的参照。另外,基于Matlab和Vc 开发了一套界面友好的两道瑞雷波路基密实度检测软件。本文的研究说明两道瑞雷波法用于检测路基压实度是行之有效的。     

Numerical study on breaking phenomena of ships’ waves in narrow and shallow waterways

The environmental impact of a ships waves, such as the risk of erosion of coasts and riverbanks, and unacceptable ship movements in a restricted waterway, is now a significant ship design criterion. Therefore, it is necessary to predict ship-wave phenomena accurately in a restricted waterway. In this study, a numerical investigation of the breaking phenomena of a ships waves in restricted waterways was carried out. Incompressible Navier–Stokes and continuity equations were employed. The equations are discretized by a finite-difference method in a curvilinear coordinate system. The interface capturing method was applied to simulation of a ships waves, including wave-breaking. A modification of the level-set method is proposed to find the free surface shape clearly and without difficulty of the implemation of the boundary conditions for the distance function. In order to obtain a high resolution of wave height, a constrained interpolated profile (CIP) algorithm is adopted. In order to check the advantage of the CIP method, computations by two numerical methods, the CIP and the 3rd-order up-wind scheme, were compared. The computations for a Wigley hull in restricted waterways were performed and compared with experiments. The phenomena of ships waves in restricted waterways are discussed in order to understand the mechanism of wave-breaking in relation to the change in water depth along a waterway.     

Numerical modeling of breaking waves generated by a ship’s hull

A new model for the simulation of spilling breaking waves in naval flows is presented. The hydrostatic pressure is used in order to mimic the weight of the breaker on the underlying flow, as in the model of Cointe and Tulin, whereas the algorithm for detecting the breaking inception and the definition of its geometry are completely new and are suitable for the simulation of three–dimensional flows around ships hulls. The model has been implemented in a finite-volume code developed for naval flows, and its performances have been validated against experimental data for a submerged profile, an S60 hull in drift motion, and the US Combatant DTMB 5415 model on a straight course.     

A 2D+T VOF fully coupled formulation for the calculation of breaking free-surface flow

We present the results of simulations obtained with a free-surface flow solver based on the following method. The free surface is simulated by the volume-of-fluid interface capturing method. This code solves the Navier–Stokes equations using a finite-volume method adapted to a structured or unstructured mesh. The system is constructed using a fully coupled approach. This global approach allows the simulation of complex flow as a breaking or merging wave. Moreover, with the use of a 2D+T decomposition, it is possible to simulate three-dimensional steady flow.     

地震动空间变异性对大跨刚构桥地震反应的影响

导致地震动空间变异性的原因主要包括几何不相干性效应和行波效应。文章首先根据O.Ramadan等人提出的方法合成地震位移波,然后对沪蓉国道上龙潭河大桥进行了抗震时程计算,对地震动空间变异性各个主要因素的单独影响、综合影响分别进行了系统分析。计算结果表明,与一致激励相比较,地震动的空间变异性对龙潭河大桥在地震作用下的动力反应具有较大的影响。     

参变管道系统在随机交通载荷下响应特征分析

研究了参变管道在随机交通荷载作用下的振动响应问题。利用摄动法表示了管道系统各参数的随机性，推导了管道在随机载荷下响应特性的计算表达式，并提出了一种简化求解算法；通过实例分析考察了管道系、统参数变化以及交通荷载的随机性特征对管道响应的影响，从而证明了该方法对这类问题的适用性。     

在方波电压作用下理想磁放大器的理论分析

本文详细分析了在方波电压作用下的理想磁放大器的磁化特性,得到了理想磁放大器的特性与参数,并同正弦波电压作用下理想磁放大器的磁化特性进行了对比.