Local wind characteristics on bridge deck of twin-box girder considering wind barriers by large-scale wind tunnel tests

Natural Hazards - Traffic accidents on bridges occur occasionally and have attracted the wide attention of the whole society as well as world. Therefore, researching and exploring the wind...     

Katabatic glacier wind

Doklady Earth Sciences -     

On wind velocity profile measurements taken in wind tunnels with saltating grains

This paper reviews some aspects of wind tunnel experiments on sand-transporting winds. It follows previous papers that have discussed the influence of the outer region of the boundary layer on wind velocity measurements. This influence was quantified with the use Coles’Wake function. In this paper this correction is applied to six previously described wind velocity profiles. An attempt is made to calculate the profile parameter II from these measurements. The values found were not consistent with the expected II, which was determined by Coles for clean air flow. This value (II=0.55) was assumed to be valid in previous analyses for sand-transporting winds. Evidence for a mutual dependency of friction velocity and profile parameter is presented and the difficulty in determining u. is pointed out. It is suggested that the constant stress region of the boundary layer should be kept large enough for measurements when Coles’Wake function is not to be used in the data analysis.     

Experimental study on gyroscopic effect of rotating rotor and wind heading angle on floating wind turbine responses

Limited fossil resources, daily increasing rate of demand for energy and the environmental pollution fact have made people revert to renewable sources of energy as a solution. One type of renewable energy is offshore wind energy which has high potential without any sound and visual noises. Recently, a lot of researchers have carried out on the issue of offshore wind turbine. Because of incapability of most of software programs to simulate gyroscopic effect of rotating rotors, in this articles a significant effort has been made to fabricate and test an offshore wind turbine under different rotor rotation velocities and different heading angle of wind so as to obtain the effects of these parameters on structure responses. Study on the response of a wind turbine under environmental loads has had a notable importance due to the fact that structure behavior can strongly affect procedure of modeling and optimizing wind turbine structures. On the other hand, frequency-domain structural response of a wind turbine can also make engineers be informed about of appropriate mooring system for a special environmental condition. Consequently, it has been observed that increasing the rotor rotation velocity leads the peak of spectrums shift to a higher frequency due to the gyroscopic effect appeared as a damping term, and changing heading angle of wind may lead to a change in heave and pitch amplitudes in the time domain response, and heave, sway and surge motion in frequency response.     

Effect of protection against wind according to the variation porosity of wind fence

This study examines shelter effect against the wind by using wind fence with various porosities and distance. The shelter effect of wind fence was investigated by a wind tunnel test. Flow characteristics of velocities and turbulences behind wind fence were measured using a hot-wire anemometer. This was done by varying the porosity by 0, 20, and 40% of the wind fence. The wind fence distance ranged from 1H to 9H. In addition, the overall characterization of the wind fence was investigated by measuring a total of 28 points on the wind fence, which forms a lattice structure on it with 7 points in the lateral direction and 4 points in the vertical direction. The results indicate that the degree of the turbulence is lowered and the velocity of the wind is decreased when porosity of 40% is used at a distance of 4H–7H. The effectiveness of the wind fence depends on the porosity and distance. Porosity of 20% proved to be effective for the protection area of 1H–3H, while that of 40% was effective for the protection area of 4H–6H.     

The pressure-field characteristics around porous wind fences: results of a wind tunnel study

Using detailed measurements of the instantaneous velocity fields around fences with different heights and porosities, the pressure fields around the fences were calculated using the Reynolds equations. Based on the results of calculation, the relationships among the pressure field, fence porosity (i.e., the β coefficient), fence height, and free-stream wind velocity were examined. For all fences, a high-pressure region exists upwind of the fence, and a low-pressure region exists downwind of the fence, the change of mean pressure is gradually less to a long distance from the fence. The pressure value at the center of the low-pressure area downwind of the fence decreases with increasing fence height and free-stream wind velocity. The impact of the fence’s porosity on pressure is large, when β < 0.2, the mean pressure upwind of the fence is relatively small, and the center value of the low-pressure area downwind of the fence increases with increasing fence porosity; when β > 0.3, the mean pressure increases around the fence.     

An analysis of drag force on wind of shrubs simulated in a wind tunnel

Shrubs that exert drag force on the wind significantly affect the air–surface interaction in arid and semiarid regions, and some coastal regions where aeolian processes are active. An understanding of the drag force on wind of shrubs provides important information on the dynamics of shrubs in reducing wind erosion, and their geomorphological significances. Thus, we analyzed the drag force and drag coefficient for model shrubs using wind measurements obtained by particle image velocimetry in a scaled wind tunnel simulation. The drag force was found to be a function of wind velocity and shrub density. Both drag force and drag coefficient revealed a critical shrub density of around 0.08. The vertical drag force changed direction when the shrub density became greater or less than the critical density. The drag coefficient increased rapidly with shrub density when the density was below 0.08, but it increased very gently when the density was increased beyond the critical value. The results have an important theoretical significance for our understanding of the dynamics of vegetated dunes and the windbreak mechanism of shrubs.     

Hurricane wind risk in Louisiana

A statistical procedure for estimating the risk of strong winds from hurricanes, known as the Hurricane Risk Calculator, is demonstrated and applied to several major cities in Louisiana. The procedure provides an estimate of wind risk over different length periods and can be applied to any location experiencing this hazard. Results show that an area 100 km around the city of New Orleans can expect to see hurricane winds blowing at 49 ms^?1 (44.3–53.7) [90 % confidence interval (CI)] or stronger, on average, once every 20 years. In comparison, for the same time period, the capital city of Baton Rouge and the surrounding area can expect to see hurricane winds of 43 ms^?1 (38.2–47.8) (90 % CI) or stronger. Hurricane track direction is also analyzed at the cities of interest. For Morgan City, Lafayette, Lake Charles, and Alexandria, tropical cyclones with winds at least 18 ms^?1 travel from the southeast to northwest. New Orleans and Baton Rouge tropical cyclones have a greater tendency to turn toward the east while within 100 km of the city, historically giving them a southwesterly approach. Tropical cyclones within 350 km off the south-central Louisiana coast occur most often in September, and the most extreme of these events are becoming stronger through time as shown with quantile regression.     

Assessing the vegetation canopy influences on wind flow using wind tunnel experiments with artificial plants

Wind erosion causes serious problems and considerable threat in most regions of the world. Vegetation on the ground has an important role in controlling wind erosion by covering soil surface and absorbing wind momentum. A set of wind tunnel experiments was performed to quantitatively examine the effect of canopy structure on wind movement. Artificial plastic vegetations with different porosity and canopy shape were introduced as the model canopy. Normalized roughness length (Z ₀/H) and shear velocity ratio (R) were analyzed as a function of roughness density (λ). Experiments showed that Z ₀/H increases and R decreases as λ reaches a maximum value, λ _max, while the values of Z ₀/H and R showed little change with λ value beyond as λ _max.     

Origins and properties of the quasi-stationary slow solar wind

Comparisons of the brightness distributions of the white corona observed at distances of several solar radii with solar wind velocities derived from interplanetary-scintillation observations, as well as analyses of solar wind data obtained on spacecraft from December 1994 to June 1995, indicate that the fast solar wind can contain plasma with velocities V ≈ 300–450 km/s, approaching those typical for the slow solar wind that flows in the streamer belt and chains of streamers. At the same time, certain other parameters, first and foremost the plasma density N and ratio T/N ^0.5 (where T is the temperature), indicate that these two flows differ considerably. The slow solar wind flowing in the streamer belt and chains displays high densities N > 10 ± 2 cm^?3 and low T/N ^0.5 < 1.7 × 10⁴ K cm^3/2 at the Earth’s orbit. The number of slow solar-wind sources observed in chains can be comparable with the number observed in the belt. The fast solar wind flowing from coronal holes always displays low densities N≤ 8 cm^?3 and high T/N ^0.5 > 1.7 × 10⁴ K cm^3/2. These properties probably indicate different origins of the fast and slow solar winds.     

海上风电勘探装备研发与应用

配置合理的海上风电勘探装备,对海上风电地质钻探至关重要,而配置合理、功能齐备的海上风电勘探平台更是重中之重。为了提升35 m以上水深海上风电勘探作业工效、安全、精度,本文主要从平台运维功能和勘探功能设计为切入点,针对性地开展了平台主要技术规格、升降操控系统、场区设计、现场土工试验室等方面的海上风电勘探自升式勘探平台装备的功能设计与研究,研发了具备双孔勘探能力的自升式勘探平台,并在投产运营2年中,取得了良好的使用效果,勘探工效、安全性大大提升,达到了研发的目标,为海上风电勘探提供了有力的装备支撑。     

Observing the atmospheric wind from space

Among the basic variables that characterize the thermodynamic state of the atmosphere, wind is relatively poorly observed. Surface measurements by in situ sensors are numerous, but irregularly distributed over the globe. Upper level winds are characterized by radiosoundings that are reliable and accurate, but in a very limited number due to their expensive cost. They are complemented by wind measurements performed by commercial aircrafts, but these data are mostly acquired along the major flight routes at a cruising altitude of ～10 km. Radio sondes and aircrafts leave large gaps in the observation network that have been partly complemented for 10 years by an increasing amount of wind information derived from cloud tracking in satellite images, and more recently, surface winds by scatterometers. However, the observation capacity still suffers deficiencies as there is still no information in cloud-free parts of the atmosphere, and no complete vertical profiles except for the radiosoundings. They should be overcome with the launch in 2011 of the European satellite ADM-Aeolus, a space-based Doppler lidar currently under development at the European Space Agency.     

Thermal and wind structure of the monsoon trough boundary layer

Radiosonde data from Jodhpur, taken at 0530, 1730 and around 1100 hr IST during MONTBLEX 1990, reveal that the distribution of virtual potential temperature0 _v below about 500 hPa has a structure characterized by up to three layers each of approximately constant gradient. We are thus led to introduce a characterization of the observed thermal structure through a sequence of the symbolsN, S andU, standing respectively for neutral, stable or unstable conditions in the different layers, beginning with the one closest to the ground. It is found that, of the 29 combinations possible, only the seven classes,S, SS′, SNS′, NS, NSS′, USS′ andUNS are observed, whereS′ stands for a stable layer with a different gradient of0 _r. than in the layerS. It is also found that, in 90% of the launches at 0530 hr, 48% of the launches at 1730 hr and 69% of the launches around 1100 hr, the first radiosonde layer near the ground is stable; the classical mixed layer was found in only 11 % of the data set analysed, and, if present on other occasions, must have been less than 250 m in height, the first level at which radiosonde data are available. Supplementing the above data, sodar echograms, available during 82% of the time between June and August 1990, suggest a stable layer up to a few tens of metres 48% of the time. A comparative study of the radiosonde data at Ranchi shows that the frequent prevalence of stability near the surface at Jodhpur cannot be attributed entirely to the large scale subsidence known to be characteristic of the Rajasthan area. Further, data at Jodhpur reveal a weak low level jet at heights generally ranging from 400 to 900 m with wind speeds of 6 to 15 m/s. Based on these results, it is conjectured that the lowest layers in the atmosphere during the monsoons, especially with heavy clouding or rain, may frequently be closer to the classical nocturnal boundary layer than to the standard convective mixed layer, although often with shallow plumes that penetrate such a stable layer during daytime.     

Energy cycle of wind generated surface waves

Doklady Earth Sciences -     

风荷载在地质灾害中的作用

采用效果测度分析方法，分析风荷载在长白山天池地区地质灾害中的作用及其影响因素的排序。计算表明，天池地区地质灾害形成的11个影响因素中，风荷载列首位，说明风荷载因素对地质灾害的影响是不可忽视的；天池地区山高坡陡，有利于风荷载发挥破坏作用。环天池分布的崩塌崖地势高，相对高差大，风荷载在岩体迎风面上产生压力，岩体背风面上则产生吸力。天池地区变化不定的风向，使岩体常年处于气流压力与吸力交替变换作用下，更易使岩体发生破坏。     

Auto-correlation analysis of ocean surface wind vectors

The nature of the inherent temporal variability of surface winds is analyzed by comparison of winds obtained through different measurement methods. In this work, an auto-correlation analysis of a time series data of surface winds measuredin situ by a deep water buoy in the Indian Ocean has been carried out. Hourly time series data available for 240 hours in the month of May, 1999 were subjected to an auto-correlation analysis. The analysis indicates an exponential fall of the autocorrelation in the first few hours with a decorrelation time scale of about 6 hours. For a meaningful comparison between satellite derived products andin situ data, satellite data acquired at different time intervals should be used with appropriate ‘weights’, rather than treating the data as concurrent in time. This paper presents a scheme for temporal weighting using the auto-correlation analysis. These temporal ‘weights’ can potentially improve the root mean square (rms) deviation between satellite andin situ measurements. A case study using the TRMM Microwave Imager (TMI) and Indian Ocean buoy wind speed data resulted in an improvement of about 10%.     

Assessment of wind speeds that damage buildings

A method to determine the wind speed to cause damage to buildings is described. The method is based on engineering calculations of wind loads generated on the weakest links of buildings such as the roof-to-wall joints of a wood-frame house. Data needed for the calculation include wind direction, building geometry, conditions of windows, doors and other exterior openings immediately before the occurrence of wind damage, and details of the weakest links that initiated the failure. The method can be used for estimating the maximum wind speed of a storm from an in-depth post-disaster investigation. Results of this study indicate that it takes no more than the wind speed of a F-2 tornado to completely destroy either a wood-frame house or a nonreinforced masonry building. The study supports the belief that the wind speed associated with F-3, F-4 and F-5 tornadoes are grossly overrated.     

The initiation of particle movement by wind

When air blows across the surface of dry, loose sand, a critical shear velocity (fluid threshold, ut), must be achieved to initiate motion. However, since most natural sediments consist of a range of grain sizes, fluid threshold for any sediment cannot be defined by a finite value but should be viewed as a threshold range which is a function of the size, shape, sorting and packing of the surface sediment. In order to investigate the initiation of particle movement by wind a series of wind-tunnel tests was carried out on a range of pre-screened fluvial sands and commercially available glass beads with differing mean sizes and sorting characteristics. A sensitive laser-monitoring system was used in conjunction with a high speed counter to detect initial grain motion and to count individual grain movements. Test results indicate that when velocity is slowly increased over the sediment surface the smaller or more exposed grains are first entrained by the fluid drag and lift forces either in surface creep (rolling) or in saltation (bouncing or hopping downwind). As velocity continues to rise, larger or less exposed grains may also be moved by fluid drag. On striking the surface saltating grains impart momentum to stationary grains. This impact may result in the rebound of the original grain as well as the ejection of one or more stationary grains into the air stream at shear velocities lower than that required to entrain a stationary particle by direct fluid pressure. As a result, there is a cascade effect with a few grains of varying size initially moving over a range of shear velocities (the fluid threshold range) and setting in motion a rapidly increasing number of grains. Results of the tests showed that the progression from fluid to dynamic threshold, based on grain movement, can be characterized by a power function, the coefficients of which are directly related to the mean size and sorting characteristics of the sediment.     

Quantifying initial and wind forcing uncertainties in the Gulf of Mexico

This study aims at analyzing the combined impact of uncertainties in initial conditions and wind forcing fields in ocean general circulation models (OGCM) using polynomial chaos (PC) expansions. Empirical orthogonal functions (EOF) are used to formulate both spatial perturbations to initial conditions and space-time wind forcing perturbations, namely in the form of a superposition of modal components with uniformly distributed random amplitudes. The forward deterministic HYbrid Coordinate Ocean Model (HYCOM) is used to propagate input uncertainties in the Gulf of Mexico (GoM) in spring 2010, during the Deepwater Horizon oil spill, and to generate the ensemble of model realizations based on which PC surrogate models are constructed for both localized and field quantities of interest (QoIs), focusing specifically on sea surface height (SSH) and mixed layer depth (MLD). These PC surrogate models are constructed using basis pursuit denoising methodology, and their performance is assessed through various statistical measures. A global sensitivity analysis is then performed to quantify the impact of individual modes as well as their interactions. It shows that the local SSH at the edge of the GoM main current—the Loop Current—is mostly sensitive to perturbations of the initial conditions affecting the current front, whereas the local MLD in the area of the Deepwater Horizon oil spill is more sensitive to wind forcing perturbations. At the basin scale, the SSH in the deep GoM is mostly sensitive to initial condition perturbations, while over the shelf it is sensitive to wind forcing perturbations. On the other hand, the basin MLD is almost exclusively sensitive to wind perturbations. For both quantities, the two sources of uncertainty have limited interactions. Finally, the computations indicate that whereas local quantities can exhibit complex behavior that necessitates a large number of realizations, the modal analysis of field sensitivities can be suitably achieved with a moderate size ensemble.