杭州湾南部主水道内温度、盐度、潮流的变化特征

本文基于船载及锚定ADCP、CTD观测,获得了大、小潮时的温度、盐度、浊度、潮位、流速等观测数据,研究杭州湾南部的一个主要弯曲航道——螺头水道内的潮流动力学特性。螺头水道水深超过100 m、最大潮差大于2.5 m。涨潮时,强潮流速出现在水道北岸,落潮时,强潮流速出现在水道南岸,最大流速值分别为约2 m/s和1.8 m/s。受压强梯度、密度梯度、科氏力和离心力影响,涨落潮过渡时在水道的横断面产生较为明显的环流。夏季存在较弱的层化现象,深水处受环流的影响,盐度、温度的混合较强。锚定观测数据表明,温度、盐度的变化频率与潮流的变化频率相似,但存在高于M2分潮频率的谱峰值。因此,笔者认为潮流与横向环流的相互作用,可能导致更高频率的盐度和温度变化。     

Response of Static and Cyclic Laterally Loaded Rigid Piles in Sand

An experimental investigation was made into the response of piles in sand subjected to lateral cyclic loading. Seven instrumented model piles tests were conducted. Five tests were conducted under typical magnitude and number of cyclic loading, and two were under static loading. The results were used to deduce modulus of subgrade reaction k and the profile of limiting lateral resistance force per unit length (LFP, p_u profile) in light of closed-form solutions. The study demonstrates a large impact of lateral (cyclic) load level than the number of cycles, a 1.5–2.8 times increase in the modulus k, and a 10% reduction in the p_u due to cyclic loading. The tests confirm the linear correlation between maximum bending moment and the applied lateral load, regardless of the number of cycles.     

Analysis and Design of Monopile Foundations for Offshore Wind-Turbine Structures

Offshore wind turbines (OWTs) are generally supported by large-diameter monopiles, with the combination of axial forces, lateral forces, bending moments, and torsional moments generated by the OWT structure and various environmental factors resisted by earth pressures mobilized in the soil foundation. The lateral loading on the monopile foundation is essentially cyclic in nature and typically of low amplitude. This state-of-the-art review paper presents details on the geometric design, nominal size, and structural and environmental loading for existing and planned OWT structures supported by monopile foundations. Pertinent ocean-environment loading conditions, including methods of calculation using site-specific data, are described along with wave particle kinematics, focusing on correlations between the loading frequency and natural vibration frequency of the OWT structure. Existing methods for modeling soil under cyclic loading are reviewed, focusing in particular on strain accumulation models that consider pile–soil interaction under cyclic lateral loading. Inherent limitations/shortcomings of these models for the analysis and design of existing and planned OWT monopile foundations are discussed. A design example of an OWT support structure having a monopile foundation system is presented. Target areas for further research by the wind-energy sector, which would facilitate the development of improved analyses/design methods for offshore monopiles, are identified.     

北黄海獐子岛邻近海域大型底栖动物群落结构和季节变化

本文以2009年8月-2010年6月在北黄海獐子岛海域4个季度航次调查的大型底栖动物资料为基础,分析了该海域大型底栖动物群落的结构和季节变化。结果表明,4个航次共采集了211种底栖动物,调查海域主要优势种为薄索足蛤(Thyasira tokunagai)、斑角吻沙蚕(Goniada maculata)、紫蛇尾(Ophiopholis mirabilis)、博氏双眼钩虾(Ampelisca bocki)和短角双眼钩虾(Ampelisca brevicornis),各季节的优势种组成有明显变化;运用聚类分析和MDS研究了其群落结构,将该区域大型底栖动物分为3个群落,即,群落I--位于调查区北部的美原双眼钩虾(Ampelisca miharaensis)-短角双眼钩虾(Ampelisca brevicornis)-斑角吻沙蚕群落,群落II--位于獐子岛邻近的紫蛇尾(Ophiopholis mirabilis)-日本倍棘蛇尾群落(Amphioplus japonicus),群落III--位于南部区域的薄索足蛤-浅水萨氏真蛇尾(Ophiura sarsii vadicola)群落,各群落有一定的季节变化;运用ABC曲线分析了4个季节群落受扰动情况,表明该海域环境良好,受扰动较小,夏季受扰动略大于其它季节。     

Contribution of baseflow during dry spells in irregular channel cross section

The discharge and water level of a gaining stream are known to be maintained during dry spells by baseflow, which is defined as discharge from underground storage. However, the effect of baseflow on a real river is not well known because direct measurements of baseflow in field are difficult to conduct. Therefore, this study attempts to clarify the contribution of baseflow to streamflow and the extent to which the water level is maintained even during dry spells. A digital filter technique is applied to the records of daily mean streamflow in order to estimate the amount of baseflow, and the lateral distribution method is applied to irregular cross sections at observational sites to obtain the stage–discharge rate curve. Through a comparison of the observed data and calculation results, the amount of baseflow is estimated across the channel, in addition to the maximum water level retained during dry spells in relation to the baseflow. Finally, based on the results of an energy conservation model, this study proposes that the source of the amount of baseflow estimated across a channel section may be different from that of the water level maintained during dry spells.     

On the controls of preferential flow in soils of different hillslope position and lithological origin

Soils derived from different lithologies and their controls on preferential flow remain underexplored in forested landscapes. In the same lithology, the propensity for preferential flow occurrence at different hillslope positions also remains largely elusive. By utilizing a soil moisture response time method, we compared preferential flow occurrence between a shale site (Shale Hills, silt loam soils) and a sandstone site (Garner Run, sandy loam soils) at four hillslope positions: ridge-top, North- and South-facing mid-slopes and toe slope, for over 2 years. The catchments are neighbouring and covered by temperate forest. For the four hillslope positions, Shale Hills had higher preferential flow frequencies compared to Garner Run. Between these two catchments, the South-facing mid-slope sites showed the highest contrasts in preferential flow frequency (33.5% of events at Shale Hills vs. 8.8% at Garner Run) while the ridge-top sites showed the lowest contrasts (18.7 vs. 13.2%). Additionally, over the unfrozen period, for seven out of eight monitoring sites, drier antecedent conditions tended to be more favourable for preferential flows to occur, with significant (p < .01) relationships at two sites. Except for the South-facing mid-slope sites, both Shale Hills and Garner Run had two preferential flow pathways. The characteristic preferential flow pathways at Shale Hills were the B_w and C horizons, and for Garner Run, preferential flow moved from the E/AE horizon to the B_w horizon. This study shows that shale-derived soils tended to have higher preferential flow occurrence than sandstone soils, but hillslope positions exhibit different levels of contrasts. More effort should be paid to study the impact of lithology on preferential flows in the context of land surface modelling and biogeochemical reactions to improve ecosystem services of headwater catchments.     

Dynamic responses of a pile embedded in a layered poroelastic half‐space to harmonic lateral loads

A single pile embedded in a layered poroelastic half‐space subjected to a harmonic lateral load is investigated in this study. Based on Biot's theory, the frequency domain fundamental solution for a horizontal circular patch load applied in the layered poroelastic half‐space is derived via the transmission and reflection matrices method. Utilizing Muki and Sternberg's method, the second kind of Fredholm integral equation describing the dynamic interaction between the layered half‐space and the pile subjected to a top harmonic lateral load is constructed. The proposed methodology is validated by comparing results of this paper with some existing results. Numerical results show that for a two‐layered half‐space, the thickness of the upper softer layer has pronounced influences on the dynamic response of the pile and the half‐space. For a three‐layered half‐space, the presence of a softer middle layer in the layered half‐space will enhance the compliance for the pile significantly, while a stiffer middle layer will diminish the dynamic compliance of the pile considerably. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of strong lateral discontinuity on ground motion characteristics and aggravation factor

This paper presents the effects of strong lateral discontinuity (SLD) in basins on the ground motion characteristics, differential ground motion (DGM) and aggravation factor (aggravation factor is simply the extra spectral amplification due to complex 2D site effects over the 1D response of the soil column). The seismic responses of open- and closed-basin models with SLD were simulated using SH-wave finite difference algorithm with fourth-order spatial accuracy. Simulated seismic responses, DGM and its spectra revealed that SLD induces Love waves, and the lower cutoff frequency for the same is equal to the fundamental frequency (f₀) of the soil layer. The maximum average aggravation factor (AAF) and DGM were obtained near the edge of open basin and at the centre of closed basin. A decrease of amplitude of Love wave, DGM level and AAF with offset from SLD was observed in an open basin. On the other hand, in closed basin, spatial variation of AAF and DGM level was highly variable. Duration of shaking, AAF and DGM level was more in the closed basin than in an open basin. Increase of DGM level and AAF with decrease of the width of basin was observed.     

两侧铰接地下连续墙的试验研究及数值分析

地下连续墙用于平面不规则形状基坑支护时,对任意直线段墙体,其受力与变形实际上是三维的,而不是一般经验简化方法假设的二维变形与受力,并应考虑相邻墙体之间的相互作用。采用考虑墙土相互影响的地下连续墙与土共同作用的三维有限元方法,研究了墙端铰接和墙端自由两种边界条件对等刚度及变刚度墙体内力与变形的影响,计算结果表明,建议的理论计算方法与模型试验结果吻合较好。通过与模型试验实测值的对比,指出了以往采用平面有限元进行分析的方法的不足,并重点分析了墙端铰接对墙体横向弯矩的影响,研究结果表明,三维变形产生的横向弯矩是可观的,必须加以考虑。     

STUDY ON CLIMATIC CHARACTERISTICS OF CHINA-INFLUENCING TYPHOONS AND THE INTERRELATIONS BETWEEN THEM AND THEIR ENVIRONMENTAL FACTORS

Climatic characteristics of China-influencing typhoons (CIT) were analyzed in this paper. Main characteristics include: (1) CIT season is May-November, especially from July to September. (2) Frequency of the CIT shows a decreasing trend during 1951-2004, especially after the late period of the 1960s. (3)Strong CIT also shows an obvious decreasing trend. Meanwhile, there exist obvious interdecadal variations in the CIT genesis, being more southward and eastward than normal in 1960s-1970s, and more northward and westward than normal in the 1980s. In addition, the interrelations between CIT and its environmental factors show that CIT has close relationships with sea surface temperature and East Asian summer monsoon; the structure of the circulations in frequent CIT years is much different from that in infrequent CIT years.