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41.
Suction buckets differ with their easy and cost-efficient installation technique from other foundation types for offshore wind turbines. For successful completion of their installation process, suction is essential, but the imposed seepage leads to the changes in states of the soil in and around the bucket. Especially, a loosening of soil inside the bucket affects the load carrying behaviour of bucket subjected to repetitive loading resulting from environmental conditions. In this study, the behaviour of buckets under cyclic axial compressive loads with considering a possible loosening and related changes in permeability of soil inside the bucket is investigated numerically. In the framework of finite element analysis, a fully coupled two-phase model and a hypoplastic constitutive model are used to describe the saturated sandy soil behaviour under repetitive loading. The porosity-permeability variation is taken into account by Kozeny–Carman relationship. Special attention is dedicated to load carrying behaviour of bucket top plate, inner and outer skirt as well as base and their changes resulting from a loosening of soil inside the bucket with variable aspect ratio. For this purpose, cyclic axial compressive loads which cause an attenuation and progressive failure of soil-bucket system response are considered. The main findings on the changes in load carrying behaviour of bucket are presented and discussed. 相似文献
42.
Large diameter monopiles are typical foundation solutions for offshore wind turbines. In design of the monopile foundations in sand, it is necessary to understand the drainage conditions of the foundation soil under the design loading conditions as the soil performance (strength and stiffness) is highly dependent on the drainage conditions. This paper presents a numerical investigation into this issue, with a purpose to develop a simple design criterion for assessing the soil drainage conditions around a monopile in sand. It is found that for typical monopile foundations in sand, the drainage condition during a single load cycle is generally expected to be undrained. However, the current state-of-practice uses p-y springs derived for drained soil responses for monopile design. The impact of this discrepancy on monopile foundation design was evaluated and found to be insignificant due to the relatively low level of loading as compared to the capacity of the soil. 相似文献
43.
Offshore pipelines are critical infrastructures and any possible damage may have devastating financial and environmental consequences. Earthquake-related geohazards (such as strong ground motion, active seismic faults, submarine landslides and debris flows) consist crucial threats that an offshore pipeline has to overcome. The main aim of the current study is to examine analytically a seabed-laid offshore pipeline subjected to a lateral kinematic distress due to a submarine landslide or a debris flow. Extra emphasis is given on the impact of pipe-soil interaction on the pipe response, by the realistic representation of the soil resistance via a tri-linear model. Firstly, the proposed analytical model is validated with a numerical model utilizing the finite-element method. Subsequently, various combinations of soil parameters and loading conditions that affect the examined problem are investigated with realistic input data taken from the offshore section of the high-pressure natural-gas pipeline TAP (Trans Adriatic Pipeline) in the Adriatic Sea. Finally, useful conclusions are drawn regarding the applicability and the efficiency of the proposed approach. 相似文献
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为研究雾和霾天气下VOCs时空变化特征,于2020年11月19日—2021年1月15日在江苏省东海国家气象观测站进行为期58 d的外场观测试验。利用自主研发的多旋翼无人机捕获2次辐射雾和2次霾天气过程,获得气温、气压、相对湿度、风向、风速、VOCs、O3等7种要素100多条垂直廓线。结果表明:时间上,霾过程夜间VOCs体积浓度(0.225~0.253 ppm(parts per million, 1 ppm=10-6))明显高于白天(0.191~0.205 ppm),雾形成前体积浓度(0.121~0.239 ppm)显著高于雾过程(0.056~0.209 ppm)。雾过程中VOCs体积浓度与雾强度变化相反,雾层高度与VOCs体积浓度剧烈变化高度一致,雾层(<200 m)中VOCs体积浓度(0.172~0.178 ppm)明显减小,显著低于雾形成前(0.195~0.240 ppm),雾层以上浓度变化大,雾结束后1 h内保持雾过程中分布特点。雾对逆温层中的水溶性污染物有清除作用,VOCs体积浓度和O3质量浓度均下降。 相似文献
46.
山东省近50年海洋气象灾害特征分析 总被引:3,自引:0,他引:3
本文通过大量的文献和资料查阅,系统的统计分析了近50a山东省沿海及责任海区海雾、风暴潮、风暴海浪、海冰等几种主要海洋气象灾害的海洋、气象及分布特征和灾害情况,进一步分析了它们的变化规律和产生原因,为海洋气象业务、服务、科研提供有益的参考。 相似文献
47.
在山东半岛北部近海海域进行了多条剖面的声波探测,初步查明了蓬莱-威海断裂带的基本活动特征.该断裂带由一系列北西走向的次级断层组成,主体在长岛至大竹岛之间的海域,多数断层以正断兼有走滑运动为主,部分断层具有逆冲运动性质.断裂带在第四纪活动明显,以北东向桃村-东陡山断裂在海域的延伸段为界,蓬莱-威海断裂带可分为两段:长岛-烟台段和烟台-威海段.西段长岛-烟台段为晚更新世活动段,多数次级断层上断点埋深位于海底以下30m,明显错断了中更新世地层,部分断层明显错断了晚更新世早期地层,有些断层达到晚更新世地层中部,但没有发现全新世地层错动现象.东段烟台-威海段为中更新世活动段,没有发现晚更新世地层错断现象.蓬莱-威海断裂带对历史地震和现代小震活动具有明显控制作用,其中1548年7级地震发生于断裂带西段,1948年6级地震发生于断裂带东段.蓬莱-威海断裂带与北东向断裂交汇区是中强地震发生的有利部位. 相似文献
48.
青岛地区海雾多发,观测表明海雾对沿海地区影响范围不尽相同,特别是海雾影响内陆的机理尚缺乏研究。本文利用观测资料及数值模式统计了青岛地区4月-7月海雾分布特征,并对不同影响范围海雾典型个例进行对比分析,结果表明:海雾发生日数自沿海向内陆递减。胶州湾沿岸雾日数比黄海沿岸明显减少,胶州湾东北部的雾日数要少于胶州湾西北部。海雾多发生于高空形势稳定,低层偏南流场的天气条件下。大气边界层内逆温层的的范围大致影响着海雾的分布。只影响沿海的海雾,地面为偏南风,风速在3~8 m/s之间,内陆风力减弱不明显。500 m以下大气边界层内风速切变大。湍流作用使海雾向内陆推进过程中倾斜抬升为低云,地面雾区减弱。能够影响内陆地区的海雾,多出现在地面风力较弱的情况之下,大部分在1~3 m/s之间。500 m以下大气边界层内风速切变小,大气边界层内湍流强度不强,使沿海到内陆的逆温层能够始终维持,沿海海雾在弱南风影响下延伸影响内陆地区。 相似文献
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50.
The synoptic analysis of sea fog in western Antarctic sea region is made based on the observation data in the Chinese Antarctic station, Great Wall Station, from December 1994 to November 1995, and the facsimile weather charts issued by Chile. It is found that more than 90% fog in this region is the advection cooling fog. Also, the synoptic mechanism of the fog creation and distinction is discussed by analyzing the pressure field, the temperature field and the upperlevel stratification. Finally, the focus of attention in forecasting fog is pointed out. 相似文献