How to float a wind turbine

Far-offshore wind turbines are attractive in view of harnessing high-speed winds and reducing impact on population. When the sea is hundreds of metres deep, drilling wind turbines down to the seabed is too expensive. Today??s bottom-mounted foundations could be replaced by floating platforms, which can minimise the lateral wave-loads acting on the wind turbine and reduce the foundation cost in deep water. Computer models capable of calculating the motion of a full floating wind turbine are at an early stage of development. An efficient strategy to minimise the computational cost is also lacking. This contribution highlights how the motion of a floating wind turbine, and its interaction with the ocean, can be predicted by means of computer-model simulations.     

Pigeon flight in a wind tunnel

Summary Core temperatureT _c, breast temperatureT _s–br and leg temperatureT _s–1 were measured simultaneously in pigeons during rest and flight in a wind tunnel, using thermistors.MeanT _c at rest is 39.8±0.7°C and is independent of ambient temperatureT _a (10–30°C). In the first minutes of flight,T _c increases to 1.5–3.0°C above resting level and remains at this higher level. This hyperthermia increases withT _a (v=const.). It is±constant in the lowT _a range (10.6–13.9°C) at flight speeds v ranging from 10–18 m s^–1 and normal body mass, but increases with v and elevated body mass in the highT _a range (23.7–28.8°C). T _s–1 is adapted toT _a at rest and increases in flight up to 3–4°C belowT _c. This increase inT _s–1 is linear toT _a. T _s–br is always lower thanT _c, in extreme cases reaching restingT _c in flight.Supported by the Deutsche Forschungsgemeinschaft     

A tree swaying in a turbulent wind: a scaling analysis

A tentative scaling theory is presented of a tree swaying in a turbulent wind. It is argued that the turbulence of the air within the crown is in the inertial regime. An eddy causes a dynamic bending response of the branches according to a time criterion. The resulting expression for the penetration depth of the wind yields an exponent which appears to be consistent with that pertaining to the morphology of the tree branches. An energy criterion shows that the dynamics of the branches is basically passive. The possibility of hydrodynamic screening by the leaves is discussed.     

Regional wind patterns likely shape a seasonal migration detour

Migrating animals should optimise time and energy use when migrating, travelling directly to their destination. Detours from the most direct route may arise however because of barriers and weather conditions. Identifying how such situations arise from variable weather conditions is crucial to understand population response in the light of increased anthropogenic climate change. Here we used light-level geolocators to follow Cyprus wheatears for their full annual cycle in two separate years migrating between Cyprus, over the Mediterranean and the Sahara to winter in north–east sub-Saharan Africa. We predicted that any route detours would be related to wind conditions experienced during migration. We found that spring migration for all birds included an eastern detour, whilst autumn migrations were direct across the Sahara. The direct autumn migration was likely a consequence of consistent tail-winds, whilst the eastern detour in spring is likely to be more efficient given the wind conditions which are against a direct route. Such variable migration routes shaped by coincidence with prevailing winds are probably common suggesting that some birds may be able to adapt to future changes in wind conditions.     

Ski jumping takeoff in a wind tunnel with skis

The effect of skis on the force-time characteristics of the simulated ski jumping takeoff was examined in a wind tunnel. Takeoff forces were recorded with a force plate installed under the tunnel floor. Signals from the front and rear parts of the force plate were collected separately to examine the anteroposterior balance of the jumpers during the takeoff. Two ski jumpers performed simulated takeoffs, first without skis in nonwind conditions and in various wind conditions. Thereafter, the same experiments were repeated with skis. The jumpers were able to perform very natural takeoff actions (similar to the actual takeoff) with skis in wind tunnel. According to the subjective feeling of the jumpers, the simulated ski jumping takeoff with skis was even easier to perform than the earlier trials without skis. Skis did not much influence the force levels produced during the takeoff but they still changed the force distribution under the feet. Contribution of the forces produced under the rear part of the feet was emphasized probably because the strong dorsiflexion is needed for lifting the skis to the proper flight position. The results presented in this experiment emphasize that research on ski jumping takeoff can be advanced by using wind tunnels.     

Flight speed of male spruce bud worm moths in a wind tunnel at different wind speeds and at different distances from a pheromone source

ABSTRACT. Flying male spruce budworm ( Choristoneura fumiferana [Clem.]) moths responding to virgin females and to synthetic pheromone in a wind tunnel maintained a constant rate of upwind progress when held by moving optomotor cues at a constant distance from the pheromone source. When allowed to progress upwind to the source, however, they slowed their upwind speed progressively as they approached it. They also adjusted their flight speed to maintain similar rates of upwind progress at different wind speeds.     

基于“风感”的紧凑型城市开放空间风环境实测和CFD模拟比对研究

城市开放空间的风场不仅影响微环境的"风感"舒适度还影响宏观尺度的城市气候。从景感生态学的角度出发,首先阐述"风感"的定义,总结了街道峡谷空间风场的基本规律和特点。运用Kestrel NK4500手持气象站对城市开放空间的风环境进行实测,采用CFD(Computational Fluid Dynamics)模拟软件Fluent 14.0对不含绿地的同一空间进行风环境模拟,通过两者的数据比对来研究紧凑型城市开放空间内绿地对行人高度风场的实际干扰程度。结果发现,紧凑型城市开放空间的"风感"受建筑和绿地空间布局的共同影响。当建筑高于绿地时,风场受建筑的控制;当林带高于建筑时,林带对风环境的影响程度受其疏密度影响。疏密度较高的常绿林带对风向和风速影响很大,而疏密度较低的林带会影响风速,对风向影响不大。影响风速的主要因素是空间围合所形成的空气域,相比实体、多孔介质,空气域对风的阻力要小的多。如铺装、草坪上方的通风廊道是影响行人高度层通风、导风的关键因素。紧凑型空间内的绿地在行人高度应保持通畅以保证通风,并通过建立平面和竖向上的通风、导风廊道体系,促进空气循环。     

Barotrauma is a significant cause of bat fatalities at wind turbines

Bird fatalities at some wind energy facilities around the world have been documented for decades, but the issue of bat fatalities at such facilities — primarily involving migratory species during autumn migration — has been raised relatively recently [1] and [2]. Given that echolocating bats detect moving objects better than stationary ones [3], their relatively high fatality rate is perplexing, and numerous explanations have been proposed [1]. The decompression hypothesis proposes that bats are killed by barotrauma caused by rapid air-pressure reduction near moving turbine blades [1], [4] and [5]. Barotrauma involves tissue damage to air-containing structures caused by rapid or excessive pressure change; pulmonary barotrauma is lung damage due to expansion of air in the lungs that is not accommodated by exhalation. We report here the first evidence that barotrauma is the cause of death in a high proportion of bats found at wind energy facilities. We found that 90% of bat fatalities involved internal haemorrhaging consistent with barotrauma, and that direct contact with turbine blades only accounted for about half of the fatalities. Air pressure change at turbine blades is an undetectable hazard and helps explain high bat fatality rates. We suggest that one reason why there are fewer bird than bat fatalities is that the unique respiratory anatomy of birds is less susceptible to barotrauma than that of mammals.     

Differential wind dispersal of cladoceran ephippia in a rock pool metacommunity

Dispersal connects patches within metapopulations and is crucial to the persistence of many species, particularly those living in discontinuous habitat. Rock pools are excellent habitats in which to study dispersal in time as well as space, because many of the organisms that live within them make resistant long-lived dormant stages, they are often abundant, and they are easy to sample. The rock pools on Appledore Island, Gulf of Maine, USA, are home to several cladocerans, including Moina macrocopa and Daphnia pulex × pulicaria hybrids. Both taxa exist in extremely high abundances in some pools and make diapausing eggs enclosed in ephippia that are dispersed in time by hatching long after they are produced, and are also known to spatially disperse via pool overflows and by adhering to gulls. I hypothesized that ephippia of both taxa would also be spatially dispersed by wind. I found that while Moina are present in more pools, more abundant in those pools, and produce more ephippia, many more Daphnia ephippia dispersed into traps placed around the island. This may be explained, in part, by differences in the buoyancy of ephippia between the two species. A higher propensity to disperse may result in Daphnia relying more heavily on the spatial context of rock pools than Moina.     

Carbon footprint and embodied energy of a wind turbine blade—a case study

Purpose

The main goal of this work is to evaluate the environmental impact of a 63-m blade for wind generators. The embodied energy and the carbon footprint are used as supporting tools for material selection in the initial project stages.

Methods

Real industrial data regarding the most used materials for wind turbine blade construction are used. Two eco-parameters, embodied energy and carbon footprint, were calculated from each selected material together with values of manufacture, transport, use, and final disposal. The blades must be built to have a mechanical strength high enough to withstand vibrations caused by manufacturing flaws, turbulence, or irregular loading. In this sense, Young’s modulus, yield strength, and density were compared to the environmental footprint data to support the final material choice. This evaluation process of the possible materials to be used in the blade manufacture was carried out in the initial stages of the project.

Results

Composite materials such as glass fiber-reinforced polymer (GFRP) and carbon fiber-reinforced polymer (CFRP), bonded together with an adhesive material, are used to build modern wind turbine blades. Those composites comprise a considerable number of different materials that can be mixed to reach adequate performance. Comparisons were made with 46 pre-selected materials, considering the mechanical behavior and environmental impacts. The final selected materials have better properties than the reference material. Finally, two materials with the desired mechanical properties and with a potential lower negative environmental impact than the reference material were selected.

Conclusions

Replacing the reference resin—epoxy/E-glass fiber—with the epoxy resin with the lowest environmental impact—epoxy/S-glass fiber—will reduce the total value of the environmental load to 102 GJ of energy and 3.4 t of CO₂. As important as the material selection in the early stages of product development is the end of life (EoL) choice. In this case, the glass fiber has an EoL potential of 370 GJ of energy and 460 t of CO₂ in the remanufacturing option, against zero for the landfill. This work shows that carefully selected raw materials and EoL alternatives for WTB can significantly reduce the environmental impact of this component.

     

设施塑料大棚风洞试验及风压分布规律

风洞试验是研究建筑结构表面风压分布规律的最重要且有效的技术手段.利用NH-2型风洞研究设施塑料大棚表面风压分布规律,风洞为串置双试验段闭口回流风洞,风速连续可调,最高风速为90 m/s.试验模型的几何缩尺比为1:6,模型表面共布置192个测点,其中端面布置3排测压点,共63个测点,模型固定在风洞转盘上,试验风向角从0°到180°,间隔15°,共13个风向角.测量和分析不同风向角下设施大棚表面的风压系数和分布规律,并推导出了设施大棚各区域发生风灾的临界风速.结果表明:设施大棚迎风面以风压力为主,迎风边缘等值线密集,风力梯度大;背风面则受风吸力影响,风力变化平缓.在不同风向角下,设施大棚各迎风区域风压系数均由正压向负压过渡,在此过程中出现了零压区;而一直背风的区域风压系数均为负值.在45°风向角下,大棚顶端迎风边缘最高点处的负压达到最大.根据公式推导出各区域的临界风速,设施大棚顶部两侧区域受风吸力影响最大,最小临界风速为14.5 m/s,研究为设施大棚的风灾防御提供科学依据.     

Impact of wind farms on soaring bird populations at a migratory bottleneck

Collision with turbines at wind farms is expected to have a greater impact on birds at particular sites where high concentrations of individuals occur, such as migration bottleneck areas. The Strait of Gibraltar (southern Spain) has long been recognized as the most important bottleneck in western Europe for soaring bird migration. Moreover, this area is within one of the most important potential areas for wind energy generation in Spain. Here, we examine monthly migratory soaring bird abundance in relation to long-term avian mortality rates at 21 wind farms located near the Strait of Gibraltar using zero-inflated hurdle negative binomial and gamma models. Best fit models included an effect of season in the collision mortality rates and in the proportion of adult individuals within the total deaths. However, monthly bird abundance was not directly related to the number of fatalities over the year. The accumulated fatalities during autumn migration constitute a small percentage (1%) of the total migrating population size. Moreover, mortality peak during autumn migration is largely attributable to juvenile birds. In contrast, the number of fatalities coinciding with the breeding period constitutes a substantial proportion (6%) of the local population, and it involved substantial losses among adult birds. Our results show that wind farms probably have an individually low impact on the migratory population of soaring birds. On the contrary, annual losses among adult local birds are remarkably high considering the small size of the local populations, and they may have population level effects.     

Gone with the wind — a second blow against spontaneous generation

Christian Gottfried Ehrenberg can be considered to be the founder of the science of air-borne micro-organisms and thus aerobiology. The bicentennial of his birth (he was born on Easter Sunday, April 19th, 1795), however marks the beginning of several sciences and fields of science. He is the founder of geomicrobiology, protistology, co-founder of microbiology, scientific microscopy, neurobiology, and last not least of the theory of the Earth as a living entity, including rocks and rock deposits. The number of genera and species of bacteria, spirochaetes, fungi, diatoms, radiolaria, protozoa, and rotifera which were first described by him is in the hundreds. He is known as the discoverer and detailed describer of some of the most common bioluminescent marine organisms (Noctiluca miliaris andPeridinium), as well as the person who first deciphered the secret of the bloody hostia (Monas orBacterium prodigiosum, or more correctlySerratia marcescens), of the red snow and of the ‘meteor paper’ or ‘paper meteorites’. In this commemorative paper his work on air-borne dust and air-borne micro-organisms is reviewed.