不同结构林带防风效能风洞模拟     

李晓烨  王克俭  谷建才  刘启国  崔严 《中国沙漠》2019,39(6):118-125

防风林带结构是影响防风效能的主要因素。建立不同宽度、不同株行距林带防风效能与林带后距离之间的统计模型，可以为防风林建设提供指导性意见。通过风洞实验，在11 m·s^-1风速下，对4种宽度、5种株行距林带的背风面0~10H（H为林带高度）的风速进行测定，采用曲线参数估计法、傅立叶模型、SSF模型（Sum of Sin Functions），构建了不同结构林带防风效能与林带后距离间的统计模型。结果表明：傅立叶模型拟合不同宽度林带的防风效能与林带后距离的关系效果最优，可决系数（R²）均在98%以上；SSF模型拟合不同株行距林带的防风效能与林带后距离的关系效果最优（R²>0.98）。根据构建的统计模型，风速为11 m·s^-1左右时，林带宽度8 m（两行一带）的防风林的防风效能存在明显优势；5种株行距的林带中，株行距为8 m×8 m的防风林带本试验条件下防风效果最好。  相似文献   

湍流度随高度的变化及其对城市宏观地形的依赖     

李大全  孙武  欧阳睿康  黄盛  高梦媛  李庆祥  黄启明 《热带地理》2019,39(3):365-376

分别构建广州主建成区垂直比例尺为1﹕2 000、1﹕1 000和1﹕500的3个建筑物模型，利用大型边界层风洞，在西北和东南两风向下，基于中性流模拟分析了复杂城市地形下湍流度随高度的变化及其对宏观地形的依赖。结果表明：风廓线指数α与不同高度的湍流度之间的关系密切，利用现有模型，根据4类粗糙度边界层和不同垂直比例尺，可确定相应的湍流度随高度变化模型的主要系数，预测精度高。城市地形下最大湍流度面发育在0~0.2 h之间狭窄的范围内。用湍流度形态指数β来表征湍流度随高度的变化，无论城市屋脊还是平坦地形，随着风程区的延伸，廓线的指数α升高，湍流度形态指数β降低。表明同一高度湍流度值具有由迎风区、丘顶区向背风区增高，沿风程逐渐增大的规律，对地形部位和风程的依赖性强，与来流翻越简单地形时的特征一致。  相似文献   

海气动量通量研究综述   总被引：1，自引：0，他引：1  

冯兴如  李水清  尹宝树 《海洋科学》2018,42(10):103-109

海气界面动量通量也称为风应力,是海流和表面海浪的主要驱动力,是海洋从大气获得动量的重要途径。因此,合理可靠的海洋表面风应力的参数化对于海洋、大气和波浪以及气候模式的准确预报都具有非常重要的科学意义和实用价值。对风应力拖曳系数的参数化是风应力参数化的主要内容。近来的观测发现,风应力拖曳系数随着风速的增加出现了先增后减的趋势,同时还与海面的波浪状态以及海流有关。基于观测或理论分析,目前已经得到了一系列的风应力拖曳系数计算方法或公式,有的考虑了海浪的作用,有的没有,但这些方案大都是适合中低风速,在高风速下的适用性还有待检验。本文回顾了目前在海气动量通量观测和参数化方面的研究进展,并建议应增加高风速下风速、海流以及海浪等的同步观测,以进一步完善风应力参数化方案。  相似文献   

Global Statistical Assessment and Cross-Calibration with Jason-2 for Reprocessed HY-2 A Altimeter Data     

Maofei Jiang  Ke Xu  Yalong Liu 《Marine Geodesy》2018,41(3):289-312

HY-2 A (Haiyang-2 A) satellite was launched on August 16, 2011 and radar altimeter is one of its main payloads. We reprocessed two years of HY-2 A altimeter sensor geophysical dataset records (SGDR) data. This paper presents the main results in terms of reprocessed HY-2 A altimeter data quality: verification of data availability and validity, monitoring several relevant altimeter parameters, and assessment of the HY-2 A altimeter system performances. A cross-calibration analysis of reprocessed HY-2 A altimeter data with Jason-2 was conducted. The reprocessed HY-2 A altimeter data show good quality and have a low level of noise with respect to Jason-2. The same geophysical correction methods were used to calculate the sea surface height (SSH) for the two missions. The mean standard deviations of the crossover differences for HY-2 A and Jason-2 are 5.24 cm and 5.34 cm, respectively. The mean standard deviation of the crossover differences between HY-2 A and Jason-2 is 5.37 cm. These show that HY-2 A can provide SSH measurements at almost the same level of accuracy as Jason-2. The relative SSH bias between HY-2 A and Jason-2 due to the Ultra Stable Oscillator (USO) drift is obviously observed, and it can affect the calculation of mean sea level and should be further studied and corrected.  相似文献   

Adaptive analysis of infinite beams dynamics problems using the periodic configuration update method in the time domain          下载免费PDF全文

Reda Mezeh  Marwan Sadek  Fadi Hage Chehade  Isam Shahrour 《国际地质力学数值与分析法杂志》2018,42(4):618-635

This paper proposes a new approach for the assessment of the dynamic response of continuously supported infinite beams under high‐speed moving loads. A change in the representation of equations of motion in the dynamics of discrete structures is proposed to obtain an improved accuracy of the numerical integration in the time domain. The proposed numerical method called the “periodic configuration update” or “PCU method” is applied to solve the problem of a vertical moving harmonic load on an infinite classical Euler‐Bernoulli beam resting on a continuous viscoelastic foundation. This study shows the superiority of the proposed method in comparison with other methods presented in the literature that suffer from the material time derivative, i.e., convective terms, that arises from the Galilean transformation. To confront this numerical problem, the PCU method retains the principle of the spatial follow of loads while zeroing the relative velocity with the traversed beam via a step‐by‐step adaptive integration of the equation of structural dynamics. The dynamic load is modeled with high theoretical velocities that can reach the critical velocity of the studied beam with different angular frequencies belonging to moderate frequency range. A parametric study is carried out to analyze the influence of key parameters on the convergence. The obtained results show a high efficiency of the PCU method for solving these types of problems relative to the dynamics of high speed trains/tracks.  相似文献   

In situ measurements of wind‐driven salt fluxes through constructed channels in a coastal wetland ecosystem          下载免费PDF全文

Alex K. Manda  Enrique Reyes  James M. Pitt 《水文研究》2018,32(5):636-643

A suite of instruments was deployed in a coastal wetland ecosystem in the Albemarle estuarine system, North Carolina (USA), to characterize wind‐driven transport of saltwater through a constructed (man‐made) channel. Flow velocity, electrical conductivity, and stage were measured in a representative channel over a 2‐month period from May to July 2014, during which 4 wind tides were observed. Collected data show that thousands of metric tons of salt were advected through the channel into coastal wetlands during each event, which lasted up to 4 days. The results reveal that as much as 36% of advected salts accumulated in the wetlands, suggesting that the cumulative effects of these events on the health of coastal wetlands in the Albemarle system may be substantial due to the abundance of constructed channels and the frequency of wind‐driven tidal events. This study is the first to quantify wind‐driven salt fluxes through constructed channels in coastal wetland settings.  相似文献   

乌兰布和沙漠典型植物群落土壤风蚀可蚀性研究   总被引：1，自引：0，他引：1       下载免费PDF全文

王佳庭  于明含  杨海龙  吴其淦  刘泰含 《干旱区地理》2020,43(6):1543-1550

为探明植被恢复对乌兰布和沙漠土壤风蚀可蚀性的影响，以乌兰布和沙漠内不同沙地固 定阶段的 8 种典型植物群落及群落内表土作为研究对象，对土壤物理因子（可蚀性颗粒含量、土壤 含水量、有机质含量）、土壤结皮因子、植被因子 3 类土壤风蚀可蚀性因子指标进行监测，分析土壤 风蚀可蚀性因子在不同植物群落类型间、沙地固定阶段间的差异。结果表明：（1）在乌兰布和沙漠 典型植物群落中，沙蓬、沙生针茅、盐爪爪等草本植物群落的土壤风蚀可蚀性最强，白刺、梭梭、沙 冬青等灌木植物群落土壤风蚀可蚀性弱于草本植物群落，说明灌木林能显著降低土壤风蚀作用。 （2）随着沙地的不断固定，土壤结构不断发育，土壤可蚀性不断降低，土壤风蚀可蚀性强弱表现为 固定沙地<半固定沙地<流动沙地。（3）土壤可蚀性颗粒含量、土壤有机质含量、土壤含水量、土壤结 皮、植被因子与植被类型及沙地固定阶段具有显著相关关系。因此，在沙区生态建设工程中，为了 减少土壤风蚀量，不仅要考虑物种的选择，还要促进人工生态系统的演替和恢复，从而有效降低土 壤风蚀可蚀性。研究结果可为乌兰布和沙区植被生态系统服务功能的科学评价、防沙治沙工程的 建设与管理提供一定参考。  相似文献   

新疆S214公路台特玛湖干涸湖盆段风沙危害及防治     

蔡东旭  李生宇  王海峰  俞祥祥  王世杰  徐新文 《中国沙漠》2020,40(1):1-11

新疆S214（考干-米兰，考米线）公路位于库鲁克塔格沙漠东南缘，穿越台特玛湖干涸湖盆。由于该区气候干旱，风力强劲，沙源丰富，流动沙丘广布且快速移动，风沙危害对公路运输构成严重威胁。通过对风沙环境和风沙危害定位观测和土壤水盐特征系统调查，确定了风沙危害极为严重的公路区段，提出了合理的风沙防护措施及防沙体系结构。结果表明：该区具有明显的单风向风况，主要盛行ENE和NE风，偶有反向风沙活动，起沙风频率、输沙势、输沙率极高，属于高能-大比率风能环境；受土壤水分、盐分含量影响，地表紧实度差异较大，部分地段为极疏松的沙层，部分地段为紧实的盐壳；S214公路风沙危害防护区段为K4+900~K18+200，设计建造的阻-固-输相结合的机械-植物复合防沙体系，防沙效果明显，保障了道路安全运营。这一强风沙、高盐区公路防沙体系建设模式可为类似环境地区工程防沙提供借鉴。  相似文献   

青藏铁路沿线不同类型挡沙墙阻沙率     

杨印海  薛春晓  石龙  李凯崇  孔令伟  张芳 《中国沙漠》2020,40(1):173-178

基于风洞试验对青藏铁路沿线不同类型防沙措施防沙效果进行模拟研究，探讨了不同类型挡沙墙的防沙效果。结果表明：挂板式、轨枕式和箱式挡沙墙输沙率随高度基本呈递增缓变型趋势，最大输沙率低于20%；铃铛式和高立式聚乙烯（PE）网挡沙墙随高度呈递减陡降型趋势，距地表6~8 cm处为转折点，转折点以上输沙率随高度增大急剧减小，转折点以下输沙率随高度变化较为平缓，最大输沙率低于50%。随着风速的增大，各挡沙墙的阻沙率呈递减趋势：挂板式和轨枕式挡沙墙对风速的敏感性最弱，整体阻沙效果较优，可大范围推广；箱式挡沙墙对风速的敏感性较弱，建议在风速18 m·s^-1以下的地区使用；PE网挡沙墙防沙效果对风速的敏感性最强，建议在风速10 m·s^-1以下的地区使用。  相似文献   

The variation and controls of mean transit times in Australian headwater catchments     

Ian Cartwright  Uwe Morgenstern  William Howcroft  Harald Hofmann  Robin Armit  Michael Stewart  Chad Burton  Dylan Irvine 《水文研究》2020,34(21):4034-4048

Determining mean transit times in headwater catchments is critical for understanding catchment functioning and understanding their responses to changes in landuse or climate. Determining whether mean transit times (MTTs) correlate with drainage density, slope angle, area, or land cover permits a better understanding of the controls on water flow through catchments and allows first-order predictions of MTTs in other catchments to be made. This study assesses whether there are identifiable controls on MTTs determined using ³H in headwater catchments of southeast Australia. Despite MTTs at baseflow varying from a few years to >100 years, it was difficult to predict MTTs using single or groups of readily-measured catchment attributes. The lack of readily-identifiable correlations hampers the prediction of MTTs in adjacent catchments even where these have similar geology, land use, and topography. The long MTTs of the Australian headwater catchments are probably in part due to the catchments having high storage volumes in deeply-weathered regolith, combined with low recharge rates due to high evapotranspiration. However, the difficulty in estimating storage volumes at the catchment scale hampers the use of this parameter to estimate MTTs. The runoff coefficient (the fraction of rainfall exported via the stream) is probably also controlled by evapotranspiration and recharge rates. Correlations between the runoff coefficient and MTTs in individual catchments allow predictions of MTTs in nearby catchments to be made. MTTs are shorter in high rainfall periods as the catchments wet up and shallow water stores are mobilized. Despite the contribution of younger water, the major ion geochemistry in individual catchments commonly does not correlate with MTTs, probably reflecting heterogeneous reactions and varying degrees of evapotranspiration. Documenting MTTs in catchments with high storage volumes and/or low recharge rates elsewhere is important for understanding MTTs in diverse environments.  相似文献