过黄河渡槽的脉动风荷载模拟

根据脉动风压功率谱与脉动风速功率谱之间的关系,利用风压功率谱密度函数矩阵的分解,通过一组余弦函数的和对过黄河渡槽随机形式的脉动风荷载进行了计算机模拟。     

雷暴大风环境特征及其对风暴结构影响的对比研究

2009年6月3日,受冷涡后部次天气尺度横槽的影响,在相邻的两个区域先后出现雷暴大风天气,造成两地强风的风暴类型、地面大风分布及灾害程度差异显著。风暴结构分析表明:产生晋陕大风的雷暴类型为一般单体风暴和脉冲风暴,而产生商丘致灾大风的则为典型的弓形回波。结合观测和数值模拟资料分析产生上述两类雷暴大风的环境要素,并构建其环境温、湿度廓线,结果表明:(1)晋陕大风区环境探空温、湿度廓线呈倒V形,为典型的干下击暴流探空廓线,类似探空在中国西部高原地区夏季常见;(2)商丘雷暴大风区环境温、湿度廓线类似典型湿下击暴流探空。数值模拟给出了典型的一般单体特征结构,老雷暴单体出流在其前方触发新单体。在中低层相对干的环境下多个对流单体的冷下沉形成冷池,强风由对流单体下沉辐散气流叠加在冷池密度流上造成。两类雷暴大风环境风垂直切变特点为:深层环境风垂直切变较弱、强水平风垂直切变集中在中低层。数值模拟表明:在这种风垂直切变配置下,低层湿度成为风暴结构的决定因素:中-高湿度环境下形成高度组织化的飑线,且其单体具有较强中层旋转;低湿度环境下产生组织程度差的一般单体和脉冲风暴,并基于高分辨率数值模式模拟结果给出了环境影响风暴结构的物理图像。     

基于NCEP风向数据的中国夏季降水估算研究

提出一个基于NCEP风向数据估算全国夏季降水的模型。根据NCEP地面气压、经纬向风数据计算得到全国1971—2000年夏季各月盛行风向;并将盛行风向与宏观坡向夹角的余弦值作为降水的坡向因子,以此区分山体迎风坡和背风坡降水的空间分布。利用站点观测资料、数字高程模型数据、坡向、坡度因子,采用逐步回归分析法,建立估算夏季降水的回归方程,得到全国1971—2000年夏季各月及总降水量的空间分布图,并对模型结果进行检验与对比分析。结果表明,此方法估算夏季总降水量的平均绝对误差为27 mm,平均相对误差为11.8%。模型结果能体现迎风坡与背风坡的雨量差,符合客观规律,能够定性、定量地再现中国夏季降水的实际空间分布特征。     

Business case for mussel aquaculture in offshore wind farms in the North Sea

The European Blue Growth strategy aims to expand the new maritime sectors of aquaculture, energy, biotechnology, coastal tourism and mineral mining. Growth of these sectors will increases pressure on the seas, particularly on those areas that are densely used by traditional sectors such as fisheries and transport. This has triggered interest in developing multiuse of space and multiuse platforms at sea. This paper assesses the feasibility of offshore mussel production project in wind farms by design and ex-ante evaluation of a mussel aquaculture system in the North Sea. A system for mussel cultivation in the Dutch Borssele offshore wind farm was designed, producing both mussel seed and consumption-sized mussels with semi-submerged longlines. Based on the economic model and the risk assessment, this paper concludes that mussel aquaculture is an appealing commercial model for increased returns in offshore wind farms. The economic models shows that the internal rate of return and net present value are positive and based on the sensitivity analysis, it can be concluded that these results are robust.     

Kinetic energy budget and moisture flux convergence analysis during interaction between two cyclonic systems: Case study

An analysis of the kinetic energy budget during a case of interaction between middle latitude and extratropical cyclones has been made in this work. Horizontal flux convergence constitutes a major energy sink. Generation of kinetic energy via cross-contour flow is a persistent source throughout the growth and decay periods. Dissipation of kinetic energy from subgrid to grid scales is an important source during the pre-storm period; it acts as a sink during the growth and decay periods. The major contribution to kinetic energy comes from a persistent upper tropospheric jet stream activity throughout the period of the cyclone development. The characteristics of moisture-flux components (divergent and rotational) along with precipitable water content for different tropospheric layers throughout the life cycle of our cyclone are also studied in this work. It is found that most of required humidity for our cyclone are initiated from Arabian Sea and then to some extent are reinforced over Gulf of Aden and east of central Africa and then by passing over Red sea enter to the south and south east of Mediterranean Sea. The rotational component of the moisture transport brings moisture from two regions; the first which is considered the main region is the Indian Ocean, Arabian Sea, Gulf of Aden and north east of Sudan. The second source region is the Atlantic and Mediterranean Sea. In the middle troposphere, the primary moisture source is found over central Africa, which in turn is traced to the Atlantic Ocean, the Indian Ocean, and the Arabian Sea. The upper-level moisture fluxes are weak and play a minor role over the area of interaction between two cyclones.     

Recent ventifact development on the central Oregon coast,western USA

The unusual location of ventifacts, on a boulder‐built jetty at the mouth of the Siuslaw River, Oregon coast, western USA, allows ventifact age and wind abrasion rates to be estimated with some precision. The jetty was built mainly between 1892–1901 and extended throughout the twentieth century. Consideration of historical shoreline position and the history of jetty construction and repair suggests the ventifacts have formed since about 1930. Morphologically the ventifacts are aligned south‐to‐north reflecting winter winds and sediment transport from the adjacent beach. Wind‐parallel grooves and ridges with sharp, sinuous crests are developed on inclined boulder surfaces on top of the jetty and reflect suspended sand transport in wind vortices. Deeply pitted surfaces on steep boulder surfaces nearest the beach reflect impact by saltating sand grains. Based on present wind regimes (1992–2000) from three regional weather stations, southerly winds above the sand transport threshold occur for 21·9–29·6 per cent of the time. Based on estimated depth of loss from boulder surfaces, wind abrasion rates are calculated to be on the order of 0·24–1·63 mm a^?1. This is the first well‐constrained field estimate of ventifact age and ventifaction rate from a modern coastal environment. Copyright © 2003 John Wiley & Sons, Ltd.     

Coupled Dynamic Response Analysis of A Multi-Column Tension-Leg-Type Floating Wind Turbine

This paper presents a coupled dynamic response analysis of a multi-column tension-leg-type floating wind turbine (WindStar TLP system) under normal operation and parked conditions. Wind-only load cases, wave-only load cases and combined wind and wave load cases were analyzed separately for the WindStar TLP system to identify the dominant excitation loads. Comparisons between an NREL offshore 5-MW baseline wind turbine installed on land and the WindStar TLP system were performed. Statistics of selected response variables in specified design load cases (DLCs) were obtained and analyzed. It is found that the proposed WindStar TLP system has small dynamic responses to environmental loads and it thus has almost the same mean generator power output under operating conditions as the land-based system. The tension mooring system has a sufficient safety factor, and the minimum tendon tension is always positive in all selected DLCs. The ratio of ultimate load of the tower base fore-aft bending moment for the WindStar TLP system versus the land-based system can be as high as 1.9 in all of the DLCs considered. These results will help elucidate the dynamic characteristics of the proposed WindStar TLP system, identify the difference in load effect between it and land-based systems, and thus make relevant modifications to the initial design for the WindStar TLP system.     

Using meteorological observer data to compare wind erosion during two great droughts in eastern Australia; the World War II Drought (1937–1946) and the Millennium Drought (2001–2010)

Australian meteorological observers started using the World Meteorological Organization (WMO) weather coding system in the 1950s. This system is still in use around the world today. However, observing and recording the weather in an organized and systematic manner had been ongoing for over 100 years prior to the adoption of this coding system, and much like Australia, most countries will have historical meteorological records. In this paper we compare the wind erosion of two of the greatest droughts in Australian recorded history; the World War II (WWII) Drought (1937–1945) and the Millennium Drought (2001–2009). To do this we analysed previously unavailable meteorological observer records from the Australian Bureau of Meteorology (ABM). Wind erosion records, mostly in long‐hand written form, were translated to the modern WMO coding system for the WWII Drought and compared with the wind erosion of Australia's recently‐ended Millennium Drought, one of the longest and harshest on record. We quantify wind erosion using Dust Event Days (DED) and a modified version of a published Dust Storm Index (DSI) to show that wind erosion during the WWII Drought was up to 4.6 times higher than during the Millennium Drought. This study has international significance because it demonstrates a methodology for tracking changes in wind erosion over the past 75 years based on observer records available in every country with a history of organized weather observation. Copyright © 2014 John Wiley & Sons, Ltd.     

Performance of various similarity functions for nondimensional wind and temperature profiles in the surface layer in stable conditions

The linear functions for non-dimensional wind and temperature profiles are commonly used to describe the surface layer fluxes in atmospheric models. However, their applicability is limited to smaller values of the stability parameter z/L (where z is the height above ground and L is the Obukhov length) i.e. z/L < 1.0. These linear functions have been modified (Webb 1970, Quart. J. Roy. Meteor. Soc. 96, 67–90; Clarke 1970, Quart. J. Roy. Meteor. Soc. 96, 91–114; Hicks 1976, Quart. J. Roy. Meteor. Soc. 102, 535–551; Beljaars and Holtslag 1991, J. Appl. Meteorol. 30, 327–341; Cheng and Brutsaert 2005, Boundary-Layer Meteorol. 114, 519–538) over the years for calculating fluxes when z/L > 1.0 under strongly stable conditions. In view of this, the objective of the present study is to analyze the performance of these similarity functions to compute surface fluxes in stable conditions.The meteorological observations from the Cooperative Atmosphere-Surface Exchange Study (CASES-99) experiment are utilized for computing the surface fluxes in stable conditions. The computed fluxes are found to be reasonably close to those observed. The ratio of observed to computed fluxes reveals that the computed fluxes are close to the observations for all the similarity functions for z/L < 1.0 whereas the computed values show relatively a large scatter from observations for z/L > 1.0. The computed values of u and heat flux do not show significant differences from those observed at 99% confidence limit. The performance of all the similarity functions considered here is found to be comparable to each other in strongly stable conditions.