Effect of wind on the vertical circulation and stratification in the Volkerak Estuary

In the partially mixed part of the Volkerak Estuary current speed and salt concentration are measured in several stations for periods of 13 hours on August 16 and 17, 1977. The freshwater discharge on those days and during the preceding six months is kept constant at a rate of 50 m³·s⁻¹. In spite of different wind conditions, the longitudunal distribution of the tidally- and cross-sectionally averaged salt concentration is the same for both days. The vertical structure of circulation and salt concentration differ significantly. A similar set of measurements is carried out on March 18, 1980 with a constant freshwater discharge of 100 m³·s⁻¹. The doubling of freshwater discharge leads to a relatively small increase in vertical circulation and stratification.In this study, the vertical circulation and stratification is examined in terms of the external forcings, freshwater discharge and wind, with special emphasis on wind. Tide conditions, for the three measurement days are similar. The estuary is schematized to a prismatic channel with a rectangular cross-section. In the schematized channel the tidally averaged salt concentration and velocity distribution are laterally uniform. To account for salt fluxes in the actual estuary associated with lateral and time-variations in current velocity and salt concentration, a diffusive salt flux is introduced. The effect of wind and longitudinal density gradients on the vertical circulation and stratification in the schematized channel is investigated using a simplified form of the two-dimensional conservation of momentum and salt equations. Using observed values along the axis of the estuary a scaling analysis shows that in the two-dimensional conservation of momentum equation the longitudinal pressure gradient and horizontal turbulent shear are the dominant terms, closely followed by the tidal stress. In the conservation of salt equation, the dominant terms are those associated with advective fluxes resulting from the horizontal and vertical tidal mean velocities, a horizontal flux associated with tidal variations in the longitudinal velocity and salt concentration and the vertical turbulent flux. Retaining only first order terms, the equations are solved using the similarity solution of Hansen and Rattray. Comparing calculated and observed vertical circulation and stratification it is shown that wind mixing significantly increases the vertical exchange of momentum, thereby reducing the density-driven vertical circulation (=gravitational circulation) and stratification. At the same time, through the wind surface stress, wind generates its own vertical circulation and, therefore, stratification. An expected increase in vertical exchange of mass with increasing wind speed and accompanying reduction in stratification could not be confirmed by the analysis. It is concluded that on the days of the measurements wind is as important as the longitudinal salt concentration gradient in forcing vertical circulation and stratification. Care should be taken in generalizing this conclusion as on the days of the measurements the axial component of the wind velocity is always in the down estuary direction.     

Mean currents and current variability in the iceland basin

Long-term (>6 months) current measurements from five moorings in the Iceland Basin have been analysed for the mean currents and the structure of the variable current components. The time-averaged flow at all five moorings had a strong baroclinic character. The mean circulation in the upper layers with relatively warm Sub-Polar Mode Water appears to have a general north-eastward direction with maximum mean velocities of 6 to 7 cm·s⁻¹. In the bottom layer south of Iceland, where the cold Iceland-Scotland Overflow Water flows westwards along the topography in a Deep Northern Boundary Current, mean velocities of the order of 10 to 20 cm·s⁻¹ have been observed. Over the deep slope of the Hatton Bank, water enters the Iceland Basin in a branch of the Deep Northern Boundary Current which has a cyclonic rotation sense in the Iceland Basin. The variable part of the current has been analysed by means of principal-component analysis. The current variations in the central Iceland Basin appear to have a mainly barotropic character while variations in the baroclinic flow of Iceland-Scotland Overflow Water contributed 10% or less to the total energy of the variable deep flow. Over the slope of the Hatton Bank the variable currents had a mainly baroclinic character with shear in both current speed and direction. Comparison of the geostrophic velocity with the mean Eulerian velocity has revealed that the σ_θ=27.725 kg·m⁻³ surface can be used adequately as level of non-motion for the geostrophic modelling of the flow along the Iceland and Hatton slopes. The mean westward geostrophic transport of ISOW south of Iceland relative to this reference surface amounted to 3.5 Sv, in agreement with existing independent estimates.     

Adaptation of a functional model of grassland to simulate the behaviour of irrigated grasslands under a Mediterranean climate: The Crau case

In order to take into account firstly the specificities of Mediterranean weather conditions on grass growth and secondly the effect of irrigation management on hay, we adapted an already published model of grassland growth. From literature new equations were added to account for water balance, botanical composition and the effect of wind. The modified model was parameterised based on new experimental data. An automatic and rigorous parameter estimation procedure was developed based on a criterion that combines the goodness-of-fit for dry matter (DM), leaf area index (LAI) and fraction of total transpirable soil water (FTSW). Mean squared error of prediction (MSEP) was estimated using cross-validation.Adding the three equations for water balance, botanical composition and wind effect improved the goodness-of-fit of the model. A sensitivity analysis showed that the model results were mainly sensitive to the parameter that controls the increase of leaf area index and to the radiation use efficiency coefficient. Both absolute values and dynamics of DM, LAI and FTSW were well simulated and satisfactory for future use of the model in a decision support tool. Estimated MSEP values for DM, LAI and FTSW were 0.145 T ha⁻¹, 0.092 m² m⁻² and 0.0155% respectively.     

Wind Loads Distribution on Typical Vaulted Shells

The distribution characteristics of shape factors and fluctuating wind pressure coefficients on two vaulted shells were investigated by simultaneous measurement of external and internal wind pressures on static models in wind tunnel. The effects of orifices on bottom and blocking at ends on wind loads distribution are discussed. It is shown that the wind pressure distribution is significantly affected by changes on orifices at bottom and blocking at ends. Wind pressure on ends decrease effectively and wind pressure on surface is distributed smoothly by blocking ends with highly curved surface shell. Small orifices at bottom not only contribute to degreasing negative pressure because of count acting effects of internal and external pressures, but also to extending the positive pressures region and increasing positive pressures. Wind loads suggestions on these structures are described at end.     

One-dimensional Steady-state Model for Gas Pressure Distribution in Municipal Solid Waste Landfills

Gas pressure distribution in landfills is of great importance to control hazards and improve recovery of landfill gas. An one-dimensional steady-state model and its solving approach are presented for gas pressure distribution in layered waste landfills. The model can be used to investigate the gas pressure distribution of the landfill with horizontal gas collection layers having specified pressure or flux. The influences of layered properties, horizontal permeable layer under final cover and horizontal gas collection layers and bottom leachate drainage systems dually serving as gas collection layers on gas pressure distribution are investigated. The results of parameter analyses using the presented model show that the assumption that homogenizations of gas generation rate and gas permeability through a landfill considerably overestimate gas pressure in landfill; horizontal permeable layer under final cover and horizontal gas collection layers can effectively reduce gas pressure in landfills; the bottom leachate drainage systems dually serving as gas collection layers can significantly reduce the gas pressure in the lower portion of landfills. The presented model provides a useful tool in the designing of landfill gas collection systems, such as, the positions and spacing of horizontal gas collection layers and pump section.     

Analysis of Buckling Bearing Capacity for Super-Large Cooling Towers Subjected to Random Wind Loading

Based on the formal solutions of the buckling eigen equation,the probability density evolution equation for the random buckling eigenvalue is derived considering the random wind loading.Taking the averaged wind speed at 10m height and roughness length as the random factors,the random buckling bearing capacity for a super-high cooling tower is then analyzed.Furthermore,both the mean and the standard deviations of the capacity are calculated.It is indicated that there exhibits a general shape for the probability density function of the random buckling capacity.And the mean of the random buckling bearing capacity is close to that one computed by the averaged parameter.However,the variation of the random buckling bearing capacity is between the corresponding values of averaged wind speed at 10m height and roughness length.     

山区桥址处CFD计算域的选取方法

山区桥址处风场具有较强的随机性与不确定性,在选取其CFD计算域时,盲目参考已有的工程可能会造成较大的模型误差,或增加大量的计算开销。为解决该问题,提出了山区复杂地形CFD计算域选取的方法与步骤,验证了其准确性。具体方法为：设置一个大范围的基准计算域进行初算,通过后处理软件绘制平均风压系数极差随高度的变化曲线、壁面附近水平面上的静压偏差等值云图以及横风向各平面静压值与对应边界面的均方根差值曲线,分别筛选出基准计算域在高度方向、顺风向及横风向上对整体风场贡献可忽略的区域,余下部分则可用于该区风场的求解。     

玉米雌穗分化与籽粒发育及败育的关系

以郑单958 (ZD958)和登海661 (DH661)为试材,比较研究了4.5、7.5、10.5万株hm^-2三个种植密度下,雌穗分化与籽粒发育及败育的关系。结果表明,密度对玉米雌穗原基开始分化的时间无影响(不同密度下,穗原基均在播后28~29 d左右开始分化),对吐丝期分化的小花总数影响很小。但是高密度推迟了雌穗的分化进程,增加了败育花和未受精花的数目,导致正常成熟小花数目的降低。与低密度相比,高密度下DH661正常小花数减少了100.0个,ZD958减少了76.4个。高密度加大了雌雄穗吐丝开花间隔,降低了吐丝植株的比例(DH661吐丝植株占93.64%;ZD958的占81.80%),推迟了吐丝时间,使单株吐丝量减少,散粉持续时间缩短,导致败育增加。正常受精的小花在灌浆期也会发生籽粒败育,尤其是在花后10 d左右败育严重。相关分析表明,玉米最终的穗粒数与开花期以及花后10 d、20 d的冠层底部透光率相关性显著,花败育率与开花前冠层底部透光率显著负相关。     

Dynamic optimization design of gear transmission system for wind turbine

The differential equation which governs the behavior of the gear transmission system of 1.5 MW wind turbine is established. The external excitation caused by wind speed fluctuation is discussed and the internal excitation due to time varying mesh stiffness and comprehensive error is also analyzed. The calculating formulations of the harmonic balance method of nonlinear dynamic equations are presented. Then, the multi objective dynamic optimization model is developed to minimize the value of vibration acceleration and the overall volume. The optimization of a practical example using mixed discrete combined programming is performed. The result shows that the proposed method of modeling and optimization design can effectively reduce the wind turbines gearbox vibration levels and weight.     

Wind effects on prey availability: How northward migrating waders use brackish and hypersaline lagoons in the sivash,Ukraine

Large numbers of waders migrating northward in spring use the Sivash, a large system of shallow, brackish and hypersaline lagoons in the Black Sea and Azov Sea region (Ukraine). The bottoms of these lagoons are often uncovered by the wind. Hence, for waders the time and space available for feeding depend on wind conditions. In hypersaline lagoons the benthic and pelagic fauna was very poor, consisting mainly of chironomid larvae (0.19 g AFDM·m⁻²) and brine shrimps Artemia salina, respectively. Brine shrimp abundance was correlated with salinity, wind force, wind direction and water depth. Dunlin Calidris alpina and curlew sandpiper Calidris ferruginea were the only species feeding on brine shrimp. As brine shrimp densities are higher in deeper water, smaller waders such as broad-billed sandpipers Limicola falcinellus are too short-legged to reach exploitable densities of brine shrimp. In brackish lagoons the benthic and pelagic fauna was rich, consisting of polychaetes, bivalves, gastropods, chironomid larvae, isopods and amphipods (8.9 to 30.5 g AFDM·m⁻²), but there were no brine shrimps. Prey biomass increased with the distance from the coast, being highest on the site that was most frequently inundated. Dunlin, broad-billed sandpiper and grey plover Pluvialis squatarola were the most abundant birds in the brackish lagoon. Due to the effects of wind-tides only a small area was usually available as a feeding site. Gammarus insensibilis was the alternative prey resource in the water layer, and their density varied with wind direction in the same way as brine shrimp. Curlew sandpipers and dunlins in the hypersaline lagoons and broad-billed sandpipers in the brackish lagoons often changed feeding sites, probably following the variation in prey availability. Only because of the large size and variety of lagoons are waders in the Sivash always able to find good feeding sites.     

湖州大气扩散能力变化特征及其原因探讨

为大气环境治理提供理论参考,利用1980-2013年湖州大气混合层高度、大气扩散参数和平均风速等资料,分析其多时间尺度变化特征及可能原因。结果表明：(1)湖州大气混合层高度呈现缓慢增长趋势,水平风速和大气扩散参数总体趋于减弱,风速与大气扩散参数有显著的正相关关系。(2)大气混合层高度、扩散参数和水平风速的月变化呈双峰型,3月与8月为波峰,7月和10月为波谷,且三者存在显著正相关关系,其季节变化呈现春高秋低特征。(3)城市化建设、城市热岛和干岛效应等增加了大气的垂直运动能力,使得大气混合层高度增加,而地表粗糙度的增加使得水平风速减小,导致大气的水平运动能力减弱,大气扩散能力减弱。(4)紧邻太湖水体使得湖州大气扩散能力与沿海相似,水陆热力差异、风速变化、梅雨、晴热高温等对大气混合层厚度和扩散参数的季节变化都有明显影响。     

Density responses and spatial distribution of cotton yield and yield components in jujube (Zizyphus jujube)/cotton (Gossypium hirsutum) agroforestry

Trees are the dominant species in agroforestry systems, profoundly affecting the performance of understory crops. Proximity to trees is a key factor in crop performance, but rather little information is available on the spatial distribution of yield and yield components of crop species under the influence of trees in agroforestry systems. Also, little information is available on how crop density may be exploited to optimize the yield in such systems. Here we studied the performance of cotton in jujube/cotton agroforestry. Field experiments were conducted in 2012 and 2013 in Hetian, Xinjiang, China. Cotton was grown at a row distance of 60 cm in three densities, 13.5, 18.0 and 22.5 plants m⁻² in six m wide paths between tree lines in a jujube plantation. Plant density affected both cotton aboveground dry matter and yield significantly. The highest yield was attained at the intermediate density of 18.0 plants m⁻² (20.0 plants m⁻² corresponding in sole cotton), lower than the optimal density in sole cotton (25.0 plants m⁻²). Yield at the lower density was constrained by the low number of bolls per m² as a direct consequence of the low density, whereas at the high plant density yield was constrained by a lower allocation of assimilates to cotton seed and lint, as a consequence of intraspecific and interspecific competitions. There were strong gradients in yield and yield components in relation to the distance from the tree rows. Leaf area and total dry matter of cotton in rows close to the tree lines were reduced, especially in the rows next to the trees. Moreover, biomass allocation to cotton fruits was reduced in these rows. Competitive influences from the trees on cotton performance extended two rows deep in a six-year old jujube stand, and even three rows deep in a seven-year old stand. Shading effects on cotton yield were compensated by increasing plant density as a result of greater boll numbers per unit ground area. Data from this study help guide the design of optimal plant density of cotton in jujube plantations and give insight in the spatial distribution and dynamics of competitive effects in agroforestry systems in general.     

Three-dimensional current structure in the Dutch coastal zone

As part of a more comprehensive programme on the hydrography in the Netherlands coastal zone its complex current structure is investigated. One of the aims is to identify the various dominant factors that control the patterns of the coastal flow. To that end field observations covering a one year period were taken at strategic locations in the Dutch coastal area.One of the main results reported here concerns the long term (i.e. one year) average residual currents. Near the bottom these appear to have a significant onshore directed component, with values of the order 2.5 to 3.5 cm/s. In the upper layer typical average values are between 7 and 11 cm/s. The near surface residual flow is mostly in longshore direction with an onshore component increasing with distance from shore, due to the prevailing southwesterly winds (i.e. close to longshore) over the area.The observed large variability of the three-dimensional current structure on different time-scales is largely induced by variations in wind conditions. If strong winds are accompanied by a high river discharge, a distinct two layer system results with very high residual current speeds in the upper-layer, up to 40 cm/s. The observations also produce evidence for the outflow of Rhine river water to be at least partly responsible for the significant onshore component of residual currents near the bottom, as it determines the density structure in this area.Tidal current ellipses show a marked vertical structure both with respect to shape and sense of rotation. For the region considered the spatial distribution of these parameters clearly illustrates the large influence of bottom friction and coastal boundaries, in combination with earth's rotation. Furthermore the data show that variations due to the spring-neap tidal cycle are substantial.     

Deep-water transit times in the eastern Indonesian basins,calculated from dissolved silica in deep and interstitial waters

The flushing of the deep basins in the eastern Indonesian archipelago is studied by means of the dissolved silica (Si) distribution, using water column data from the Snellius-II Expedition as well as from the Indopac Expedition. The linear θ-Si relationships below 500 to 1000 m permit the use of Si as a water-mass tracer. The main outflow of deep water from the Banda Sea into the Timor Trench is found east of Timor, above 1250 m depth, and the deeper parts of this outflow are partly recirculated through the Aru Basin and the Seram Sea into the north Banda Sea. Below the sill depth of the various basins, θ remains about constant while Si gradually increases towards the bottom. The time needed to create this Si-excess is obtained with the Si-flux out of sediments, calculated from pore-water gradients. Deep-water transit times are 20 years for the Banda Sea, 2 to 15 years for smaller basins and 60 years for the intermittently flushed Weber Deep. Modelling the Si-excess with error functions in some small basins gives high diffusion coefficients of 45 to 150 cm²·s⁻¹. The flux of Si from the sediments, 0.5 to 2 mol·m⁻²·a⁻¹, is higher than in other deep-sea basins, it amounts to roughly 30% of the biogenic silica production in the euphotic zone. Dissolved Si at 20–40 cm depth in the sediments ranges from 450 to 590 mmol·m⁻³; about 2% of Al in biogenic silica from sediments might cause this apparently low solubility for sediments rich in biogenic silica.     

Effect of Phosphorus Fertilizer on Soya Bean Residue Turnover in the Tropical Moist Savanna

The contributions of soya bean (Glycine max) to the maintenance of soil N, organic matter and physical properties in any cropping system is dependent on the amount of the crop residue returned after grain harvest. This amount of residue is a function of the dry matter accumulated during growth. In the topical moist savanna (MS) of West Africa where soya bean production has increased especially due to the cultivation of more hectarage of land, increase in soya bean dry matter with the resulting residue is limited by P deficiencies. In this study, the effect of P application on residue turnover by soya bean varieties of different maturity classes was evaluated across the MS. The amount of root residue in the late varieties was double that of the early and medium varieties. The effect of P application on root residue was also greater in the late varieties. Although root residue was 0.35–0.72 Mg ha^?1, this was about 17–21 % of total dry matter at harvest. Among the varieties, litter residue averaged less than 1 Mg ha^?1 in the early and medium varieties, and was 32 % higher in the late varieties. Litter residue increased by 42–46 % with P application. The total amount of soya bean residue that is a potential source of organic material in a cropping system after the export of grain is small and averaged 2.88 Mg ha^?1 . Of this, root residue constituted 18 %, litter residue 41 % and stover residue 40 %. In this study C/N ratio averaged 17.1, 34.8 and 32.2 for root, litter and stover, respectively. The amount of total residue obtained in this study shows that the benefit of the effect of soya beans on soil organic matter and physical properties derivable from a single soya bean crop is small.     

徽州传统民居室内水体蒸发实测研究

徽州传统民居室内水体蒸发对室内环境的营造起到了积极作用。根据水体蒸发热平衡,建立民居室内水体蒸发模型,用实地连续测试的蒸发数据对该模型进行验证。结果表明,该模型能有效的计算徽州传统民居室内水体蒸发过程,计算和测试的水体蒸发量之间的均方根误差和平均相对误差分别为41.5 g/（m²·h）和4.2%。环境参数中地面温度、太阳辐射、风速、相对湿度和气温对水体蒸发的影响程度逐渐降低,蒸发量和环境参数之间的相关系数分别为0.909、0.779、0.736、-0.654和0.622。     

Numerical Modeling of Ice Slurry Flow Pressure Drop in Horizontal Pipes

To predict pressure drop of ice slurry flow in horizontal pipes, a mixture CFD model was applied to simulate the two-phase flow without considering ice melting. Based on the specific flow features, the Newtonian and non-Newtonian rheological expressions were employed respectively. It is found that in high speed the Thomas viscosity equation behaves well in representing the mixture fluid viscosity; whereas in low speed the Bingham model is more suitable for describing the mixture fluid rheology. Compared with the published pressure drop correlations, the current numerical model can involve with various factors and has a good balance between precision and suitability. The results of numerical model are in excellent agreement with the experimental data and the relative errors are limited to ±15%.     

Estimating the fatty acid composition of the oil in intact-seed rapeseed (Brassica napus L.) by near-infrared reflectance spectroscopy

The objective of this work was to evaluate the potential of near-infrared reflectance spectroscopy (NIRS) as a rapid method to estimate the fatty acid composition of the oil in intact-seed samples of rapeseed. A total of 549 samples (3 g intact seed) from selected mutant and breeding lines were scanned by NIRS, and 220 of them were selected and scanned again by using two different adapters, which reduced the sample size to 300 and 60 mg, respectively. Selected samples were analysed by gas liquid chromatography and calibration equations for individual fatty acids were developed. Calibrations for oleic, linoleic, linolenic, and erucic acid were highly accurate, with values of r² in cross validation from 0.95 to 0.98 (samples of 3 g), from 0.93 to 0.97 (300 mg), and from 0.84 to 0.96 (60 mg). Calibrations for palmitic and stearic acid were less accurate, with values of r² in cross validation always lower than 0.8, probably because of the narrow range available for these fatty acids. The accuracy of the calibration equations for eicosenoic acid was very low (r² = 0.69 in 3 g samples), although improved equations were developed (r² from 0.78 to 0.91) when the relationship between erucic and eicosenoic acid was taken into account. We conclude that NIRS is a powerful technique to estimate the fatty acid composition of the oil in rapeseed, provided that samples covering a wide range of fatty acid levels are available, with the advantage that such estimation is possible with few additional costs when NIRS is used for the determination of other seed quality traits. This revised version was published online in July 2006 with corrections to the Cover Date.     

化学打顶对棉花群体容量的拓展效应

以常规人工打顶为对照,在大田条件下设置不同种植密度(18万、22.5万和27万株·hm-2),研究化学打顶对棉株形态、群体器官数量和经济产量等的影响.结果表明,化学打顶棉花株高显著高于人工打顶,平均高出17％,中上部果枝显著变短,尤其是上部果枝平均比人工打顶短75％.冠层中部透光率平均提高约13％.在相同密度条件下,化...     

通辽市固日班花风电场风能储量分析

为了开发科尔沁沙地的风能资源,为其治理提供便捷、安全的能源,利用科尔沁沙地最典型地区奈曼旗固日班花风电场测风塔和奈曼气象站的风向、风速资料,对固日班花风电场的风能储量进行分析。结果表明,固日班花风电场塔高10、60、65、70、80 m处的年平均风速订正后分别为4.9、6.8、7.0、7.2、7.3 m/s;相应风功率密度分别为136.5、315.4、341.3、365.6、382.1 W/m2。逐月风速与逐月风功率密度年内变化规律基本一致。风电场风能资源较为丰富,达到了建设大型风电厂的要求。