Experimental study of unidirectional irregular wave slamming on the three-dimensional structure in the splash zone

The experimental investigation of unidirectional random wave slamming on the three-dimensional structure in the splash zone is presented. The experiment is conducted in the marine environment channel in the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology. The test wave is unidirectional irregular wave. The experiments are carried out with perpendicular random waves (β=0°) and oblique random waves (β=15°, 30°, 45°), the significant wave heights H_1/3 ranging from 7.5 to 20 cm with 2.5 cm increment, the peak wave periods T_p ranging from 0.75 to 2.0 s with 0.25 s increment, and the clearance of the model with respect to the significant wave height s/H_1/3 ranging from 0.0 to 0.5 with 0.1 increment. The statistical analysis results of different test cases are presented. The statistical distribution characteristics of the perpendicular irregular wave impact pressures are compared with that of the oblique irregular wave on the underside of the structure. The effect of the wave direction β on the wave impact forces on the underside of the structure is determined. The relation between the impact forces and the parameters such as the significant wave height, the relative structure width and the relative clearance of the structure is also discussed.     

Design weight of armour stone considering the effect of extreme waves

In this study, waves with the heights higher than H_1/3 in an irregular wave train are called as extreme waves and defined with the help of extreme wave parameter, α_extreme. In order to see the effect of extreme waves on the design weight of armour stone, stability analysis is carried out based on the hydraulic model test results. The test results of high α_extreme cases (HE) and low α_extreme cases (LE) are compared with currently used van der Meer's formulae with permeability factor P=0.4 and 0.45 and Hudson formula by using H_1/3 and H_1/10 in terms of the design weight of armour stone. As a result of the comparison, it is found that Hudson formula by using H_1/3 underestimates the necessary armour weight. Usage of H_1/10 instead of H_1/3 in Hudson formula doubles the weight which seems overestimated when Irribaren number is away from the transition zone in which both wave run-up and run-down forces become effective. However, it seems underestimated near the transition zone where experiment case HE gives higher armour weights. When the design weight of armour stone is calculated by van der Meer's formulae with P=0.4, it may be necessary to increase the weight up to 30% in the case of high extreme waves. On the other hand, van der Meer's formulae may overestimate the weight 14% when the extreme waves are low.     

Delaunay三角剖分的快速实现

主要探讨了以Delaunay三角剖分的逐点插入法为基础构建不规则三角网的方法,并在程序设计中对该算法进行了改进,极大地提高了Delaunay三角网的构建效率。     

三维随机波浪对桩柱的作用

试验研究了三维随机波浪作用于垂直圆柱上的作用力.采用二维波浪的方法计算三维波浪力,研究了各波力系数随ＫＣ数和波浪方向分布的变化规律,并对三维波力和二维波力进行了对比分析.     

The deepest Hubble Space Telescope far-ultraviolet observations in the Large Magellanic Cloud

We present a new analysis of the deepest pure-ultraviolet (UV) observations with the highest angular resolution ever performed. A set of 12 exposures with the Hubble Space Telescope ( HST ) WFPC2 and F160BW filter obtained in parallel observing mode, which cover ∼12 arcmin² in the Large Magellanic Cloud (LMC), north of the bar and in the 'general field' region of the LMC, contain stars with far-UV monochromatic magnitudes as faint as 22 mag. The 198 detected UV sources represent an accumulated exposure of  ≥ 2 × 10⁴ s  and reveal stars as faint as   m _UV≃ 20 mag  . We combine these observations with deep UBVI charge-coupled device (CCD) imaging of the same region reaching as faint as   V ≃ 26 mag  , and reselect probable optical counterparts for the UV sources. After a two-stage search-and-analysis process, we detect robust counterparts for 129 stars. These are mostly upper main-sequence stars, from early B to early A spectral classes, with several F stars. We point out the lack of blue supergiants, which could have been easily detected in our survey. We measure a foreground extinction   E ( B − V ) ≃ 0.08 mag  by Galactic dust and a surface density of star formation rate twice the average Galactic value. These observations indicate that relatively recent star formation took place even off the bar of the LMC.     

Searching for water ice on 47171 1999 TC36, 1998 SG35, and 2000 QC243: ESO large program on TNOs and centaurs

Transneptunian objects and Centaurs are supposed to be among the most pristine bodies of the Solar System. To investigate their physical properties and their surface composition, an ESO large program at the Very Large Telescope was carried out. In this paper we present photometric and spectroscopic near-infrared data of two Centaurs (1998 SG35 and 2000 QC243) and one transneptunian object (47171 1999 TC36). For 47171 1999 TC36 and 1998 SG35 visible photometry is also presented. Models of the surface composition of these objects are presented and discussed. By including a small percentage of water ice in our geographical mixtures, we obtain a better agreement with the observations in the H and K bands.     

Origin of scattered disk resonant TNOs: Evidence for an ancient excited Kuiper belt of 50 AU radius

Resonance occupation of trans-neptunian objects (TNOs) in the scattered disk (>48 AU) was investigated by integrating the orbits of 85 observed members for 4 Gyr. Twenty seven TNOs were locked in the 9:4, 16:7, 7:3, 12:5, 5:2, 8:3, 3:1, 4:1, 11:2, and 27:4 resonances. We then explored mechanisms for the origin of the resonant structure in the scattered disk, in particular the long-term 9:4, 5:2, and 8:3 resonant TNOs (median 4 Gyr), by performing large scale simulations involving Neptune scattering and planetary migration over an initially excited planetesimals disk (wide range of eccentricities and inclinations). To explain the formation of Gyr-resident populations in such distant resonances, our results suggest the existence of a primordial planetesimal disk of at least 45-50 AU radius that suffered a dynamical perturbation leading to 0.1-0.3 or greater eccentricities and a range of inclinations up to ∼20° during early stages of the Solar System history, before planetary migration.     

The edge of the Kuiper belt: the Planet X scenario

Our goal is to determine whether or not the observed sudden termination of the Edgeworth-Kuiper belt can be the result of perturbations from a hypothetical planet. We investigate the effects that such an object would produce on the primordial orbital distribution if the trans-neptunian objects, for a range of masses and orbital parameters of the hypothetical planet. In this numerical investigation, the motion of the hypothetical planet was influenced by the existing planets but not by its interaction with the disk. We find that no set of parameters produce results that match the observed data. Dynamical interaction with the disk is likely to be important so that the orbit of the hypothetical planet changes significantly during the integration interval. This is also discussed. The overall conclusion is that none of the models for the hypothetical planet that were investigated can reproduce the observed features of the Edgeworth-Kuiper belt starting from any probable primordial distribution.     

面向对象空间数据组织与管理的初步实现

通过分析3种传统数据模型的特点，得出它们在管理地理复杂对象方面的局限性，从而引出了面向对象数据模型。本文利用面向对象数据模型中的各种操作，以基本地理对象为基础构建复杂地理对象，并且在VC＋＋6．0平台上实现了面向对象几何数据模型。     

Simulating the hydraulic characteristics of the lower Yellow River by the finite‐volume technique

The finite‐volume technique is used to solve the two‐dimensional shallow‐water equations on unstructured mesh consisting of quadrilateral elements. In this paper the algorithm of the finite‐volume method is discussed in detail and particular attention is paid to accurately representing the complex irregular computational domain. The lower Yellow River reach from Huayuankou to Jiahetan is a typical meandering river. The generation of the computational mesh, which is used to simulate the flood, is affected by the distribution of water works in the river channel. The spatial information about the two Yellow River levee, the protecting dykes, and those roads that are obviously higher than the ground, need to be used to generate the computational mesh. As a result these dykes and roads locate the element interfaces of the computational mesh. In the model the finite‐volume method is used to solve the shallow‐wave equations, and the Osher scheme of the empirical function is used to calculate the flux through the interface between the neighbouring elements. The finite‐volume method has the advantage of using computational domain with complex geometry, and the Osher scheme is a method based on characteristic theory and is a monotone upwind numerical scheme with high resolution. The flood event with peak discharge of 15 300 m³/s, occurring in the period from 30 July to 10 August 1982, is simulated. The estimated result indicates that the simulation method is good for routing the flood in a region with complex geometry. Copyright © 2002 John Wiley & Sons, Ltd.