Hydrodynamic numerical modelling of storm surges — Application to the Bay of Bengal

A hydrodynamic numerical model and a tide-surge interaction model are described for the evaluation of storm surges and their interaction with the tides in the Bay of Bengal. Numerical experiments are performed with the help of these models to simulate the surges generated by three recent severe cyclonic storms which struck the east coast of India and Bangladesh. The predicted peak sea-surface elevations compare well with the limited observed values.     

Storm surges in the Bay of Bengal

In this paper, the scaling of the shallow water equations in terms of the speed of a cyclone moving over a basin, and another velocity related to basin characteristics is reported. The zero-order equations for which numerical solutions were obtained earlier are described. For a basin of uniform depth, an analytical solution has been obtained for the zero-order equations. The solution suggests that, in the initial stages, the divergence of the wind stress is more important than the curl of the wind stress. In subsequent stages, the curl becomes more important. It is also shown that the basin does not respond to a cyclone until a certain time has elapsed. The adjustment time depends on the storm speed, and is inversely proportional to the square-root of the basin depth.     

杭州湾、浙江沿海一带风暴潮数值预报研究

分析了风暴潮的特点、成灾、危害,介绍了杭州湾风暴潮的重大影响,在Visual Studio 2010平台下,采用C++编程语言开发了二维并行数值预报的可视化软件.通过输入计算域的水深数据及每6h变化的台风参数实现风暴潮数值计算,在界面上直观地显示台风的移动路径和伴随着台风移动整个计算域的增水时历过程,同时同步显示所选验潮站的风暴潮增水时历曲线和移行台风风速大小、方向时历曲线.结合杭州湾的实际地形,将计算域进行了粗网格、二分之一网格细化和四分之一网格细化三种划分,选取5612号、7708号台风和2012年的Damrey、Haikui台风,分别对粗网格和两种细网格区域进行计算.还将5612号、7708号台风的计算结果与验潮站的实测数据进行比对.结果表明,网格的粗细对计算结果的影响不大,但对比实测数据后发现网格越粗计算结果与实测潮位数据的吻合性就越好.     

A Transformed Coordinates Shallow Water Model for the Head of the Bay of Bengal Using Boundary-Fitted Curvilinear Grids

The Bay of Bengal is surrounded by coastline except to the south, where there is open sea. The coastline bends most sharply along the coast of Bangladesh, and there are many small and large islands in the offshore region there. In order to incorporate the island boundaries and the curved coastline properly, in any numerical scheme it is often necessary to consider a very fine grid resolution along the coastal belts whereas this is unnecessary away from the coasts. However, a very fine resolution involves more memory and more CPU time in the numerical solution process, and invites numerical instability. On the other hand, boundary-fitted curvilinear grids in hydrodynamic models for coastal seas, bays and estuaries not only fit to the coastline but also render the finite difference schemes simpler and more accurate. In this article, the boundary-fitted curvilinear grids for the model represent the complete boundary of the area considered by four curves defined by four functions, and the four boundaries of two of the larger islands are then represented approximately by two general functions. An appropriate independent coordinate transformation maps the curvilinear physical area to a square domain, and each island boundary is transformed to a rectangle within this square domain. The vertically integrated shallow water equations are transformed to the new space domain, and solved by a regular explicit finite difference scheme. The model is applied to compute the water levels due to astronomical tides, and also the water levels due to surges associated with tropical storms that hit the coast of Bangladesh.     

The effects of climate change on storm surges around the United Kingdom

Coastal flooding is often caused by extreme events, such as storm surges. In this study, improved physical models have been used to simulate the climate system and storm surges, and to predict the effect of increased atmospheric concentrations of greenhouse gases on the surges. In agreement with previous studies, this work indicates that the changes in atmospheric storminess and the higher time-average sea-level predicted for the end of the twenty-first century will lead to changes in the height of water levels measured relative to the present day tide. However, the details of these projections differ somewhat from earlier assessments.Uncertainty in projections of future extreme water levels arise from uncertainty in the amount and timing of future greenhouse gas emissions, uncertainty in the physical models used to simulate the climate system and from the natural variability of the system. The total uncertainty has not yet been reliably quantified and achieving this should be a priority for future research.     

On Bayesian interval prediction of future records

Based on the one-sample scheme, Bayesian prediction bounds for the s ^th future record value are obtained. All of the informative and future observations are assumed to be obtained from a general class of distributions which includes the Weibull, compound Weibull, Pareto, beta, Gompertz, compound Gompertz among other distributions. The prior belief of the experimenter is measured by a proper general conjugate prior which was suggested by AL-Hussaini (1999b).     

SPLASH诺模图的修正及应用

介绍了采用SPLASH模式诺模图法预报登陆台风引起最大风暴潮增水的基本思路和方法,并对SPLASH模式诺模图作了一定的修正和完善,使对其的编程计算更加易于实现且结果更精确.在此基础上对SPLASH模式诺模图法进行二元插值计算编程,并用若干个算例验证,获得了较为精确的预报结果.     

多级漏孔泄漏分析及其漏率预测方法研究

为了评估气体介质经多级漏孔的泄漏量,指导多道密封结构的安全设计,有必要研究气体经多级漏孔的泄漏特性。通过建立双级与多级漏孔的数学模型,在不同的初始条件下对多级漏孔的泄漏特性进行了计算分析。结果表明:多级漏孔的稳定漏率仅与各级独立漏孔漏率有关,与中间空腔体积无关,其倒数等于各级漏孔漏率的倒数之和。影响稳定时间的因素包括末级漏孔的漏率、其余各级漏孔组成的多级漏孔漏率以及中间空腔的容积。利用分析结果,提出了多级漏孔漏率的预测方法。     

On the nature of over-dispersion in motor vehicle crash prediction models

Statistical modeling of traffic crashes has been of interest to researchers for decades. Over the most recent decade many crash models have accounted for extra-variation in crash counts--variation over and above that accounted for by the Poisson density. The extra--variation--or dispersion--is theorized to capture unaccounted for variation in crashes across sites. The majority of studies have assumed fixed dispersion parameters in over-dispersed crash models--tantamount to assuming that unaccounted for variation is proportional to the expected crash count. Miaou and Lord [Miaou, S.P., Lord, D., 2003. Modeling traffic crash-flow relationships for intersections: dispersion parameter, functional form, and Bayes versus empirical Bayes methods. Transport. Res. Rec. 1840, 31-40] challenged the fixed dispersion parameter assumption, and examined various dispersion parameter relationships when modeling urban signalized intersection accidents in Toronto. They suggested that further work is needed to determine the appropriateness of the findings for rural as well as other intersection types, to corroborate their findings, and to explore alternative dispersion functions. This study builds upon the work of Miaou and Lord, with exploration of additional dispersion functions, the use of an independent data set, and presents an opportunity to corroborate their findings. Data from Georgia are used in this study. A Bayesian modeling approach with non-informative priors is adopted, using sampling-based estimation via Markov Chain Monte Carlo (MCMC) and the Gibbs sampler. A total of eight model specifications were developed; four of them employed traffic flows as explanatory factors in mean structure while the remainder of them included geometric factors in addition to major and minor road traffic flows. The models were compared and contrasted using the significance of coefficients, standard deviance, chi-square goodness-of-fit, and deviance information criteria (DIC) statistics. The findings indicate that the modeling of the dispersion parameter, which essentially explains the extra-variance structure, depends greatly on how the mean structure is modeled. In the presence of a well-defined mean function, the extra-variance structure generally becomes insignificant, i.e. the variance structure is a simple function of the mean. It appears that extra-variation is a function of covariates when the mean structure (expected crash count) is poorly specified and suffers from omitted variables. In contrast, when sufficient explanatory variables are used to model the mean (expected crash count), extra-Poisson variation is not significantly related to these variables. If these results are generalizable, they suggest that model specification may be improved by testing extra-variation functions for significance. They also suggest that known influences of expected crash counts are likely to be different than factors that might help to explain unaccounted for variation in crashes across sites.     

Windstorm and storm surges in Europe: loss trends and possible counter-actions from the viewpoint of an international reinsurer

Windstorm disasters (including storm surges) account for about one-third of all natural disasters throughout the world (by number, fatalities and economic losses), but for more than two-thirds of the corresponding insured losses. Trend analyses reveal that major windstorm disasters and the losses generated by them have increased drastically in recent decades. Risk partnership between the state, the affected population and the insurance industry assumes a key role with regard to the windstorm hazard. Scientists, engineers and insurers must work together in formulating their requirements and shaping them in such a way that politicians can derive clearly recognizable policy options (e.g. land-use, restrictions, design-code adjustments) from them. Another important aspect is stepping up the efforts being made towards curbing climate change, which will, otherwise, exacerbate the risk in the future.     

The rationale of reliability prediction

This paper is the first of what is intended to be a series of papers which investigate the foundations of reliability theory, particularly when applied to the prediction process. It will contrast current reliability practice against those practices common in normal science and engineering. The claim will be made that in general the prediction process as used in reliability, when stripped of the mathematical embellishments, is no more than simple enumeration: a method long held by the philosophers of science to be unreliable and in general a poor basis on which to make predictions. This initial paper rejects the statistical method as being an insufficient basis for making predictions and claims that it is incapable of logically supporting its conclusions. Although no evidence is provided to substantiate this claim, a number of scientific methods, both of historical and present day importance, are briefly reviewed with which one can contrast the statistical method.     

基于GRNN的粘弹材料阻尼性能的预测

考虑到粘弹性材料阻尼性能随环境的非线性变化，运用GRNN（广义回归网络）对粘弹阻尼材料动态力学性能函数进行逼近，并构建预测模型。结果证明，该模型具有良好的函数逼近效果，能够较准确的预测材料的动态力学性能，为阻尼材料的研究、开发和性能评定提出了一些指导性的建议。     

Strength prediction of sheet to tube single sided resistance spot welding

Single-Sided Spot Welding (SSSW) procedure is considered as a feasible method to join hydroformed or closed section parts to others in vehicle productions. A ‘doughnut’ shaped or ring nugget can be formed between the two workpieces during this process. The strengths of conventional button spot welds can be determined by the attributes of weldments and many functions that link weld diameter, sheet thickness and material properties to weld strength have been established. For welds of sheet to tube joining, the strength prediction model is greatly different from that of conventional welds for the completely different nugget form. In this study, computer experiments were conduced using the concept of design of experiments (DOE) and the method of finite element used to simulate the tensile-shear tests. The stress and strain distribution contour clouds during tensile-shear process were analyzed and quantitative relationship models were established to link a weld’s geometric and material properties to its tensile-shear strength. The results can give a simple judgment whether a ring spot weld was good only by its appearance.     

A framework for the prediction and management of environmental cracking problems

The complexity of engineering systems is growing steadily with the introduction of advanced materials and modern protective methods. This increasing technical complexity is paralleled by an increasing awareness of the risks, hazards and liabilities related to the operation of engineering systems. Environmental cracking (EC) is, in the context of lifetime prediction, one of the most important forms of damage because of its insidious and catastrophic character. EC and particularly stress corrosion cracking (SCC) can affect a wide variety of metals and alloys exposed to specific environments. After briefly reviewing some of the tests and simple models used to evaluate and represent the susceptibility of materials to SCC, this paper proposes the adoption of a top-down approach, used in the aircraft industry for the development of its maintenance programmes, as an information model for the integration of lifetime data. Such an approach can provide the ability to accommodate different sources of information into a single information system while keeping the specific details in a managerial context.     

The prediction of the viscosity of dense gas mixtures

An extension of an earlier procedure for the evaluation of the viscosity of very dense gas mixtures is proposed. The scheme is based upon the rigid-sphere theory of dense fluids, which is modified to take into account the behavior of real gases in a self-consistent manner. In particular, it is shown that a pseudoradial distribution function for each pure gas constructed from pure component viscosity data is a smooth function of density and is well behaved in limits of both high and low density. The method proposed removes the restrictions on the range of applicability of earlier methods. Comparisons with the limited amount of experimental information available indicate that the procedure allows evaluation of the viscosity of gas mixtures to within a few percent.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Sensitivity analysis of an accident prediction model by the fractional factorial method

Sensitivity analysis of a model can help us determine relative effects of model parameters on model results. In this study, the sensitivity of the accident prediction model proposed by Zegeer et al. [Zegeer, C.V., Reinfurt, D., Hummer, J., Herf, L., Hunter, W., 1987. Safety Effect of Cross-section Design for Two-lane Roads, vols. 1-2. Report FHWA-RD-87/008 and 009 Federal Highway Administration, Department of Transportation, USA] to its parameters was investigated by the fractional factorial analysis method. The reason for selecting this particular model is that it incorporates both traffic and road geometry parameters besides terrain characteristics. The evaluation of sensitivity analysis indicated that average daily traffic (ADT), lane width (W), width of paved shoulder (PA), median (H) and their interactions (i.e., ADT-W, ADT-PA and ADT-H) have significant effects on number of accidents. Based on the absolute value of parameter effects at the three- and two-standard deviation thresholds ADT was found to be of primary importance, while the remaining identified parameters seemed to be of secondary importance. This agrees with the fact that ADT is among the most effective parameters to determine road geometry and therefore, it is directly related to number of accidents. Overall, the fractional factorial method was found to be an efficient tool to examine the relative importance of the selected accident prediction model parameters.     

A strain energy model for the prediction of the effective coefficient of thermal expansion of composite materials

In this paper, a strain energy model is developed for the prediction of the effective coefficient of thermal expansion (CTE) of composite materials. This model is based on the relationship established between the strain energy of the microstructure and that of the homogenized equivalent model under specific thermo-elastic boundary conditions. Expressions in closed-form are derived for the effective CTE in terms of the strain energy and effective elastic tensor. Different kinds of composites are tested to validate the model. Representative unit cells with specific boundary conditions are used to evaluate effective CTEs that are compared with available results obtained numerically and experimentally.     

New model for reliability prediction of telecommunication hardware

A new simplified model has been developed for making reliability evaluations of radio base stations and enclosed equipment. Components are grouped into families since individual component types are difficult to study in the field due to a low failure rate. A failure rate interval is assigned to each component family based on operational field data from Ericsson telephone equipment. Critical families can be pointed out as a base for reliability improvement programmes.     

船舶上层建筑舱室振动灰色预测

基于灰色系统理论，以5618箱集装箱船为母型船，利用灰关联分析法．分别确定了影响船舶上层建筑甲板平均振动和各甲板舱室振动的主要因素，采用非等间隔GM（1，1）建模的方法，分别建立上层建筑甲板平均振动模型和各甲板舱室相对于甲板平均振动的差值的模型，通过将两个模型的预测值求和来得到最终的上层建筑舱室振动预测值。应用此模型对4100箱集装箱船上层建筑舱室振动进行了预测，预测结果显示：用灰色预测方法对复杂的船舶上层建筑舱室的振动进行预测是可行的，不仅能考虑多个因素的影响．而且具有要求的样本少、预测快、精度较高等优点．尤其是在船舶开发设计的初期，较其它方法具有明显的优越性。