The effect of directionality on extreme wave design criteria

Sea state design criteria for offshore facilities are frequently provided by direction. For example, it is typical for return-period values of the significant wave height to be specified for each of eight 45° sectors in addition to the omni-directional case. However, it is important that these criteria be consistent so that the probability of exceedance of a given wave height from any direction derived from the directional values is the same as for the omni-directional value. As recently demonstrated by Forristall it is not sufficient simply to scale the directional values so that the value of the wave height from the most severe sector is the same as the omni-directional value.We develop an approach for establishing appropriate directional criteria and an associated omni-directional criterion for a specific location. The inherent directionality of sea states is used to develop a model for the directional dependence of distributions of storm maxima. The directional model is applied to the GOMOS data, and the distributional properties of the 100-year significant wave height are estimated and the implications for design discussed. An objective risk-cost approach is proposed for optimising directional criteria, while preserving overall reliability. Simulation studies are performed, using realistic extreme value assumptions, to quantify the uncertainties.     

Refractive optical systems for astronomical instruments using infrared arrays in the 0.8 to 2.5 micron bands

As modern infrared arrays evolve towards larger formats and smaller pixel sizes, their use in instruments requires optics of increasingly higher performance. Refractive systems are attractive for many applications because they can accommodate wide fields of view or fast focal ratios while permitting a compact, unobscured layout. We examine design considerations for lenses which can address the entire near-infrared spectral region of 0.8 to 2.5 m. Achromatization over this broad range is a particular challenge. We discuss a systematic study of candidate materials and combinations of materials having useful chromatic properties, with particular emphasis on alkaline earth halides and metallic oxides. We present an example of a practical design being incorporated into an instrument currently under construction.     

基于智能遗传算法和Otsu法的多目标图像分割方法

为了克服传统遗传算法在优化多目标图像分割参数时易陷入局部收敛和搜索效率低的缺陷,本文提出一种基于智能遗传算法和Otsu法的多目标图像分割方法,并将它应用于航空影像的分割。实验结果表明,本文提出的算法比传统遗传算法可以更加快速、更稳定地获取图像分割的最优阈值。     

伸臂式结构地震剪力图和弯矩图的理论包络线

本文以人工工振型作为理论工具、推演出伸臂式结构地震剪力地震弯矩的主、次上界的简练公式。不难理解,上界地震剪力图和弯矩图就分别相当于无数地震剪力图的弯矩图的包络线。文中还推演出主、次上界与等效静力解之间的一个十分简明的理论关系。     

Determination of first mode ground period and site-dependent design response spectrum for Taiwan High Speed Rail

The objective of this paper is to identify the first mode ground period T_g, at each interesting site along Taiwan High Speed Rail (THSR) route, and further, to determine the site-dependent design response spectrum for particular sites with T_g larger than 1 s. In this paper, a linear model of shear wave propagating in a multi-layered half-space is developed to identify the first mode ground period T_g of an interesting site on the basis of the field bore hole data. Furthermore, for each one of the strong ground motion observation stations within the Chiayi-Tainan area, the first mode ground period T_g was identified by either coda waves or pre-event ambient vibrations from the seismograms. In addition, the site-specific parameter C_v in defining the normalized response spectrum was also determined based on the observed strong ground motions at the specified observation station, and hence the empirical function between T_g and C_v can be regressed for this interesting area. Therefore, for a particular site along THSR route within the Chiayi-Tainan area, the site-specific parameter C_v can be determined from the regressed empirical function by the identified first mode ground period T_g, and further, used to develop the site-dependent design response spectrum.     

县级农业气象常规业务软件设计

介绍了县级农业气象常规业务软件的总体设计思路及具体功能模块的实现方法，并对现行的业务运作模式进行了思考。     

关于基坑设计计算中若干问题的榷商

结合近年来笔者在审核基坑设计时遇到的计算上存在的问题,就土锚和土钉(墙)的概念异同点、设计计算的异同点作了分析,对土钉(墙)的设计深度、土锚锚固段或土钉被动粘结段摩阻力的长度衰减问题提出了初步的想法.对采用m法计算桩内力和桩顶位移时m值取值的限制条件及桩顶位移的计算作了梳理,并提出在基坑设计中慎用m法的主张.     

地图数据库管理系统设计与实现

文中分析了地图空间信息的基本特征,探讨了关系数据库管理系统管理属性信息,专门的管理软件管理定位信息的技术和方法,提出了扩充关系数据库管理系统建立地图数据库管理系统的具体实施方案,并且进行了初步的研究实践;最后对系统的用户界面和数据库保护作了简要的介绍。     

Design sensitivity analysis for vertical free vibration of hull girder

This paper presents a calculation method of derivatives of natural frequencies and mode shapes to parameters affecting vertical hull girder vibration based on design sensitivity analysis. The method premises free vibration analysis of hull girder using the transfer matrix method. Governing sensitivity equation is derived from the direct differentiation of state vector and transfer matrix to design variables. Derivatives of natural frequencies and mode shapes are determined after two trial calculations of the equation. By using the obtained derivatives, the changes of natural frequencies can be rationally and efficiently predicted in case of ship design modification and loading variation.     

Prediction of design wave loads of the ocean structure by equivalent irregular wave approach

The present study is employing the equivalent irregular wave approach to predict the wave loads for a ship encountering the worst sea state with respect to the critical dynamic loading parameter. Two different hydrodynamic numerical models, i.e. 3D pulsating source technique and 3D translating pulsating source technique, are applied to calculate the corresponding RAO of the ship moving in waves. Incorporating the RAO of the related physical properties, we can calculate the extreme value for the corresponding ship loading factor, which can be regarded as the worst sea state in the service lifetime of the ship. With the time and period of the occurrence of the corresponding extreme value, we can simulate the time history of the wave load in this period, which is so-called equivalent irregular wave approach. Comparing with the results calculated by the traditional equivalent regular wave approach, we find that the equivalent irregular wave approach can simulate the corresponding wave load more realistic, especially for dynamic pressure. Using the equivalent irregular wave approach can offer the effective and practical base for the ship structural analysis.