Design and Testing of a Turbulence Probe for Harsh Flows

The force of wind on the ground created by turbulent eddies is commonly used to describe the horizontal flux of material during wind erosion. Here we present the Murdoch Turbulence Probe, an instrument for use in both clean and eroding flows which uses pressure differences to measure the three components of wind velocity. Correlation techniques calculate the forces near the ground and turbulence statistics in nearly real time, including turbulent velocity fluctuations from less than 0.1 Hz to 200 Hz, mean flow velocities, Reynolds stresses as well as the integral length and time scales. In the portable wind-tunnel used by Agriculture Western Australia, turbulence statistics were recorded over stable surfaces and in blowing sand from the initiation of erosion up to the time the sand supply was exhausted. Estimates of the friction velocity derived from the turbulence probe were compared with estimates obtained from the wind speed profile measured with a rake of pitot and static tubes. The Murdoch Turbulence Probe appears to work well in sandblasting conditions. Relative turbulence intensities ranged from 0.11 to 0.2 and are in close agreement with values in the literature. The ratio of the turbulence to the friction velocity (3 to 3.2) is at the high end of the reported range. The Reynolds stress measurements agree closely with predictions of the threshold friction velocities of the sand and estimates from the wind speed profile with a von Kármán constant of about 0.3, lower than the commonly accepted value of 0.4. We suggest that the wind-tunnel profile represents the `outer layer' of the boundary-layer that may best be described by a `Wake Law' or `Defect Law'. At about 54 mm above the surface, the friction velocity decreases from 0.64 m/s to 0.39 m/s and the mean velocity increases from 9.6 m/s to 11.6 m/s as the supply of sand is depleted. In addition to the friction velocity, other scales may be necessary to characterise the overriding effect of the wind and in extending wind-tunnel results to the field.     

考虑指标协调性的湖泊富营养化评价模型

湖泊富营养化程度评价标准中同一评价指标的分级界点值差异很大,近似地呈现指数变化.基于该认识,提出了1个基于指标协调性的湖泊富营养化综合评价模型.对评价标准及待评湖泊监测值进行对数变换,改善了评价指标值的协调性,降低了评价系统的非线性化程度;在定义待评湖泊各监测指标与富营养化标准各级别之间距离测度的基础上,按评价指标协调性要求构造评价函数;鉴于评价标准为区问教的实际情况,采用区间数计算待评湖泊与各级标准的相对距离测度,并按距离测度值的大小进行湖泊富营养化状态分类.该模型建模思路清晰,物理意义明确,计算过程简捷,一组由5个湖泊组成的富营养化综合评价案例计算结果表明,评价结果符合实际.     

能源足迹变化的多因素影响效应研究——以吉林省为例

采用对数平均迪氏指数法构建能源足迹因素分解模型,定量分析1994—2008年吉林省能源足迹变化的主要影响因素及其效应特征。结果表明,1994—2008年,吉林省人均能源足迹从0.228 hm2增至0.524 hm2。在能源足迹增长的抑制因素中,能源强度效应占84.54%,排放因子效应占15.46%;在能源足迹增长的促进因素中,经济产出效应占91.39%,能源结构效应占4.30%,人口规模效应占3.73%,土地固碳效应占0.57%。以经济产出因素为主导的正效应明显大于以能源强度因素为主导的负效应,两者之比为1.73∶1,叠加表现为对能源足迹增长的促进作用,导致其总体呈递增趋势。此外,在正、负效应的双变量格局下,能源足迹呈复合曲面分布。目前减缓吉林省能源足迹增长的重点在于通过技术进步促进能源强度下降,同时需调整能源结构以发挥其应有的抑制作用。