气固两相流90°弯管抗冲蚀结构优化

为了提高天然气输送管道90°弯管的耐磨性能,提出了1种三段弯曲式弯管,通过对弯管弯曲段进行三段式改进来减小弯管中二次流的大小,优化弯管内的流场,改善弯管的冲蚀磨损状况。利用COMSOL仿真软件建立三段式弯管模型,并以弯管弯曲段和出口段二次流平均值之和最小为优化目标,在约束条件下凭借COMSOL中的COBYLA优化算法得到了最优管形;用Fluent对优化后的三段式弯管进行冲蚀数值模拟并与一段式弯管的模拟结果进行对比分析。研究结果表明:与一段式90°弯管相比,优化后的三段式弯管流场更加平稳,其弯曲段的二次流强度大幅降低,弯管壁面的冲蚀磨损程度得到较大的改善。     

草莓有机与无机种植系统能流和经济流的比较研究

通过３年田间试验，比较分析了草莓有机与无机种植系统的能流、经济流及对土壤环境的影响。结果表明，有机系统草莓产量、经济效益均高于无机系统；有机系统能量产投比仅为无机系统的２５％，但投入的绝大部分为可再生能源；有机系统土壤有机质、微生物量高于无机系统，具有更好的土壤条件     

The performance of RAMS in representing the convective boundary layer structure in a very steep valley

Data from a comprehensive field study in the Riviera Valley of Southern Switzerland are used to investigate convective boundary layer structure in a steep valley and to evaluate wind and temperature fields, convective boundary layer height, and surface sensible heat fluxes as predicted by the mesoscale model RAMS. Current parameterizations of surface and boundary layer processes in RAMS, as well as in other mesoscale models, are based on scaling laws strictly valid only for flat topography and uniform land cover. Model evaluation is required to investigate whether this limits the applicability of RAMS in steep, inhomogeneous terrain. One clear-sky day with light synoptic winds is selected from the field study. Observed temperature structure across and along the valley is nearly homogeneous while wind structure is complex with a wind speed maximum on one side of the valley. Upvalley flows are not purely thermally driven and mechanical effects near the valley entrance also affect the wind structure. RAMS captured many of the observed boundary layer characteristics within the steep valley. The wind field, temperature structure, and convective boundary layer height in the valley are qualitatively simulated by RAMS, but the horizontal temperature structure across and along the valley is less homogeneous in the model than in the observations. The model reproduced the observed net radiation, except around sunset and sunrise when RAMS does not take into account the shadows cast by the surrounding topography. The observed sensible heat fluxes fall within the range of simulated values at grid points surrounding the measurement sites. Some of the scatter between observed and simulated turbulent sensible heat fluxes are due to sub-grid scale effects related to local topography.     

长江上游典型区域丰枯转换期水资源变化分析

针对长江上游金沙江下游区域近几年6月和10月出现的较剧烈的水资源丰枯转换现象,以2018年金沙江下游来水过程作为研究案例,考虑金沙江下游流域来水组成及水利工程建设情况,从区间流量分析及上游水库群调蓄影响分析两方面开展了研究工作。研究结果表明:金沙江下游流域丰枯转换主要影响因素为三堆子流量变化,三堆子至溪洛渡区间流量变化影响较小。在6月,上游水库群调蓄对金沙江下游流域丰枯转换影响较大,10月影响相对较小。相关研究成果可为溪洛渡-向家坝梯级水库调度计划制订及实际调度工作提供参考。     

Clustering of aerosols in atmospheric turbulent flow

A mechanism of formation of small-scale inhomogeneities in spatial distributions of aerosols and droplets associated with clustering instability in the atmospheric turbulent flow is discussed. The particle clustering is a consequence of a spontaneous breakdown of their homogeneous space distribution due to the clustering instability, and is caused by a combined effect of the particle inertia and a finite correlation time of the turbulent velocity field. In this paper a theoretical approach proposed in Elperin et al. (2002) Phys Rev E 66:036302 is further developed and applied to investigate the mechanisms of formation of small-scale aerosol inhomogeneities in the atmospheric turbulent flow. The theory of the particle clustering instability is extended to the case when the particle Stokes time is larger than the Kolmogorov time scale, but is much smaller than the correlation time at the integral scale of turbulence. We determined the criterion of the clustering instability for the Stokes number larger than 1. We discussed applications of the analyzed effects to the dynamics of aerosols and droplets in the atmospheric turbulent flow.     

NONLINEAR MODELING AND PREDICTION OF A RIVER FLOW SYSTEM1

ABSTRACT: Model estimation and prediction of a river flow system are investigated using nonlinear system identification techniques. We demonstrate how the dynamics of the system, rainfall, and river flow can be modeled using NARMAX (Nonlinear Autoregressive Moving Average with eXogenuous input) models. The parameters of the model are estimated using an orthogonal least squares algorithm with intelligent structure detection. The identification of the nonlinear model is described to represent the relationship between local rainfall and river flow at Enoree station (inputs) and river flow at Whitmire (output) for a river flow system in South Carolina.     

RUNOFF RESPONSE FROM TWO RECLAIMED WATERSHEDS1

ABSTRACT: Detailed studies of the surface hydrology of reclaimed surface-mined watersheds for both rainfall and snowmelt events are non-existent for central Alberta yet this information is crucial for design of runoff conveyance and storage structures. A study was initiated in 1992 with principal objectives of quantifying surface runoff for both summer rainfall and spring snowmelt events and identifying the dominant flow processes occurring in two reclaimed watersheds. Snowmelt accounted for 86 and 100% of annual watershed runoff in 1993 and 1994, respectively. The highest instantaneous peak flow was recorded during a summer rainfall event with a return period of greater than 50 years. Infiltration-excess overland flow was identified as the dominant flow process occurring within the Sandy Subsoil Watershed, whereas saturation overland flow was the principal runoff process occurring within the West Watershed.     

ESTIMATING THE Q100 IN BRITISH COLUMBIA: A PRACTICAL PROBLEM IN FOREST HYDROLOGY1

ABSTRACT. Estimates of peak flows, with specified return periods, are needed in practice for the design of works that affect streams in forested areas. In the province of British Columbia (B.C.), Canada, the new Forest Practices Code specifies the 100-year instantaneous peak flow (Q100) for the design of bridges and culverts for stream crossings under forest roads; and many practitioners are engaged in making such estimates. The state of the art is still quite primitive, very similar to the state of urban hydrology 30 years ago, when popular estimating techniques were used with little consideration given to their applicability. Urban hydrology then evolved on a much more scientific basis, such that within about a 10-year period, standard approaches to design were developed. Forest hydrology should follow the same pattern, at least as far as estimating design flows is concerned. Popular present day design procedures include the rational method and other empirical approaches based on rainfall data, as use of the standard flood frequency approach is limited by the paucity of relevant flow data. Estimating procedures based on peak streamflow measurements and statistics are likely to evolve, and these will include distinctions for rain, snowmelt, and rain on snow floods. Guidelines will also be developed for selecting and applying appropriate procedures for particular areas.     

复杂环境下洞室开挖的爆破震动监测与控制

钻爆开挖法洞室的施工点临近新完成结构体．爆破地震波必须严格控制在安全范围之内。根据爆破试验中的监测结果和经验公式确定最大单响药量。结合二次减振和微差爆破技术的控制爆破方案．密集钻孔形成的孔排有效地削弱了穿越的地震波，单发单响的导爆管微差爆破方案在保证施工进度的同时．避免了地震波的叠加。根据施工中的爆破震动监测结果调整施工参数．提高了施工效率并确定爆破震动控制在安全范围内。工程的实践表明结合爆破实验、控制爆破震动的施工方案和震动监测能保证保护目标的安全。     

世界煤炭资源流动的时空格局及成因分析

基于1990-2016年的统计数据,采用场理论研究世界煤炭资源流动的时空格局变化及其成因,揭示近30年来世界煤炭资源的流动状态及其演变过程。研究结果显示：（1）2016年世界煤炭的输出总量达12.25亿t,比1990年增加了10.13亿t,年均增长6.98%,其中澳大利亚、印尼和俄罗斯等是主要的煤炭输出国,印度、日本、中国和韩国是主要的煤炭输入国;（2）以场理论的位势、流场分布、流动迹线角度分析,世界煤炭资源的流动以北美洲、中南美洲和非洲为源流场,以欧洲及欧亚大陆、中东和亚太为汇流场,在澳大利亚—东亚、印尼—东亚/印度之间形成主要运输航线;（3）资源空间分布、供需匹配程度、空间距离、市场因素和国家政策等是煤炭资源流动的主要动因。研究发现：虽然中国煤炭储量丰富,但是煤炭消费数量庞大,仅可维持72年,必须重视煤炭的进口和储备工作。该研究对于中国科学制定产业政策具有重要价值。