农畜产品虚拟水研究的背景、方法及意义

虚拟水是近年出现在水资源管理领域的新概念,随着全球贸易的增加,虚拟水已成为影响区域水资源管理的重要因素。分析了虚拟水概念出现的经济背景,总结介绍了与农作物和畜产品相关的虚拟水含量的计算方法,以及国际上虚拟水贸易的基本情况,揭示了虚拟水在提高水资源效率、制定水资源战略的作用,以及对社会经济、水资源管理等方面的重要影响。     

草地退化系统预测与畜种结构调整分析：以西藏聂荣县为例

利用灰色关联方法对聂荣县草地发展的相关因子进行了系统关联分析,得出由牧业人口和载畜量为主的人为因素是影响该县草地退化,沙化的最强因子,利用灰色系统预测方法对草爱化与强关联因素进行１０年的中期预报,并对牧业人口与牲畜结构进行了方案优化与比较。     

Morphological evolution of a barchan dune migrating past an offshore wind farm foundation

As the number of manmade structures installed on the seafloor is increasing rapidly, we seek to understand the impact of these immobile obstacles on marine geomorphological processes, such as the evolution of bedforms. A 5.8 m diameter monopile foundation was installed at the case study offshore windfarm approximately 30 m ahead of an approaching barchan (crescent-shaped) dune. The impact of the monopile on the dune's evolution was analysed using six multibeam bathymetry surveys spanning 20 years. To substantiate this analysis, coupled three-dimensional numerical modelling of flows and sediment was conducted in which the scour inducing bed shear stresses were calculated from the modelled turbulent kinetic energy. Following the installation of the monopile, the mid-section of the dune accelerated and stretched in the direction of the wake of the monopile. Four years after the monopile's installation the rest of the dune had caught up, flattening out the slip face within half the dune's length downstream of the monopile. Due to the modified flow field, the dune was scoured deeply at the base of the monopile to a depth of 6.8 m (supported by the model results that predicted a scour depth exceeding 2 m over a period of just a few days). The surveyed volume of material scoured amounted to 8% of the total dune volume. Whilst the process of scouring occurs at a timescale of days to weeks, the dune migrated on average by 25 m/yr. The difference in the timescale of the two processes allowed the scouring to occur through the full thickness of the dune. The scoured dune profile recovered rapidly once the dune migrated downstream of the monopile. This article demonstrates how large geomorphological features can intercept and migrate past a monopile foundation without long-lasting impacts on the integrity of the feature or the foundation. © 2020 John Wiley & Sons, Ltd.     

WRF/CALMET/BP预报系统对内陆山区风电场的一次滚动预报检验

利用以中尺度数值模式WRF/CALMET作为风电场预报系统的动力模块,及BP神经网络法(BP-ANN)作为风电场预报系统的统计订正方法,对重庆市齐跃山风电场进行了一次时间分辨率为5 min的24 h风速、风功率的滚动预报试验,探讨了适用于中国典型内陆山区的风电场预报系统。结果显示：以WRF/CALMET/BP组成的动力—统计预报系统能够较好地模拟出内陆山区的风场特征,系统对正午至傍晚时段的风速预报准确率较高。WRF/CALMET动力模式对于风速中心振幅的模拟能力较好,经过BP神经网络订正后,模拟结果会趋于均值。不同风速段中,模式对低风速段(3～8 m·s^-1)的预报效果较好,BP神经网络对中风速段(8～14 m·s^-1)预报结果的订正效果最明显。     

带偏航角串列式两风机复杂尾流场数值模拟

在多风机风电场中,通过主动调节上游风机的偏航角度,抑制上游风机尾流对下游风机的影响,减少风力机机组之间的尾流相互干扰,以达到提高整个风电场效率的目的。采用基于开源平台Open FOAM自主开发的FOWT-UALM-SJTU求解器中风电场求解模块ALMWindFarmFoam,将致动线模型与CFD方法相结合,利用大涡模拟(LES)计算研究当上游风机处于不同偏航角度时,两风机之间的复杂尾流干扰效应。对比分析偏航角度改变时,上下游风机气动功率的输出特性,尾流速度变化以及风机的尾涡结构。数值模拟结果表明:在上下游风机沿流向方向距离保持不变的情况下,随着上游风机偏航角度的变化,上下游风机的尾流干扰现象以及下游风机的入流条件会发生明显改变,并会对下游风机的气动功率输出以及两风机风电场的整体流场产生显著影响。     

Queer Farmland: Land Access Strategies for Small-Scale Agriculture

Farmers struggle to afford farmland because competing land uses raise prices higher than what farmers earn, especially in small-scale and sustainable agriculture. Farmers often depend on an intimate partner’s income or labor to access land, yet few studies investigate sexual relationships in farmland access. I interrogate how sexuality shapes land access for small-scale agriculture through participant observation and interviews with 25 queer farmers in New England. I find that queer farmers’ sexual identities and relationships influence where they farm, who they live and work with, how they afford the land, and how they learn to farm. I argue that finding land, labor, credit, and knowledge are intertwined, heteronormative processes of capital accumulation shaped by racism and sexism. Queer farmers’ experiences navigating heteronormativity suggest the relevance of sexuality to land conservation and food justice, limits of organizing land access through sexual relationships, and alternatives to the “family farm.”     

农用化学物质对环境的影响及对策

农用化学物质主要是指化肥、农药和农膜。农用化学物质在农业生产中对增加农产品产量起到了巨大的作用,但由于使用过量、不合理使用以及农用化学物质本身结构的原因引起了一系列环境问题,严重地影响了人类的生存环境和人类的健康。本文概述了农用化学物质的种类及农用化学物质对水体、土壤、大气及农产品的影响,并在借鉴国外先进经验的基础上,结合我国的实际情况,提出了6项防治措施。     

生产堤溃口展宽过程的概化模型试验研究

为研究生产堤溃口横向展宽过程的发展规律,以黄河下游生产堤土体为材料,开展概化模型试验,分析溃口处水深、流速、流量以及溃口宽度的变化。试验结果显示,溃口横向展宽的机理主要表现为水流冲刷堤身下层土体伴随上层悬臂土体发生绕轴崩塌;随着溃口展宽,堤前水深持续下降但下降速率逐渐减小,溃口流速呈先增大后减小的趋势,流速峰值约为1.1 m/s;随着主槽流量增加,溃口宽度发展至0.7 m时,溃口的水深、泄流流量、流速、展宽速率均有所增加。基于对溃口展宽的影响因素分析,提出溃口横向展宽速率的计算关系式,计算溃口展宽过程与实测值符合较好。研究结果不仅有助于生产堤展宽机理及发展规律的研究,还可为数学模型的建立与验证提供参考资料。