一种新型旋风气幕式排风罩数值模拟研究

利用Fluent计算流体力学软件对新型旋风气幕式排风罩工作流场及有害物分布进行了数值模拟,并与传统排风罩进行了对比。结果表明:旋转射流屏蔽作用下的抽吸流场具有中部压力较低和提高抽吸能力的作用;新型旋风气幕式排风罩不仅能有效地控制有害物扩散,而且可以实现远距离捕集有害物及以较小的排风速度排放有害物。     

EcoTroph: Modelling marine ecosystem functioning and impact of fishing

EcoTroph (ET) is a model articulated around the idea that the functioning of aquatic ecosystems may be viewed as a biomass flow moving from lower to higher trophic levels, due to predation and ontogenetic processes. Thus, we show that the ecosystem biomass present at a given trophic level may be estimated from two simple equations, one describing biomass flow, the other their kinetics (which quantifies the velocity of biomass transfers towards top predators). The flow kinetic of prey partly depends on the abundance of their predators, and a top-down equation expressing this is included in the model. Based on these relationships, we simulated the impact on a virtual ecosystem of various exploitation patterns. Specifically, we show that the EcoTroph approach is able to mimic the effects of increased fishing effort on ecosystem biomass expected from theory. Particularly, the model exhibits complex patterns observed in field data, notably cascading effects and ‘fishing down the food web’. EcoTroph also provides diagnostic tools for examining the relationships between catch and fishing effort at the ecosystem scale and the effects of strong top-down controls and fast-flow kinetics on ecosystems resilience. Finally, a dynamic version of the model is derived from the steady-state version, thus allowing simulations of time series of ecosystem biomass and catches. Using this dynamic model, we explore the propagation of environmental variability in the food web, and illustrated how exploitation can induce a decrease of ecosystem stability. The potential for applying EcoTroph to specific ecosystems, based on field data, and similarities between EcoTroph and Ecopath with Ecosim (EwE) are finally discussed.     

Neutral modelling of agricultural landscapes by tessellation methods—Application for gene flow simulation

Neutral landscape models are not frequently used in the agronomical domain, whereas they would be very useful for studying given agro-ecological or physical processes. Contrary to ecological neutral landscape models, agricultural models have to represent and manage geometrical patches and thus should rely on tessellation methods. We present a three steps approach that aimed at simulating such landscapes. Firstly, we characterized the geometry of three real field patterns; secondly, we generated simulated field patterns with two tessellation methods attempting to control the value of some of the observed characteristics and, thirdly, we evaluated the simulated field patterns. For this evaluation, we considered that good simulated field patterns should capture characteristics of real landscapes that are important for the targeted agro-ecological process. Real landscapes and landscapes simulated using either a Voronoi or a rectangular tessellation were thus compared when used as input data within a gene flow model. The results showed that neither tessellation method captured field shapes correctly, thus leading to over or (small) under estimation of gene flow. The Voronoi tessellation, though, performed better than the rectangular tessellation. Possible research directions are proposed to improve the simulated patterns, including the use of post-processing, the control of cell orientation or the implementation of other tessellation techniques.     

Techno-economic evaluation of ultrasound and thermal pretreatments for enhanced anaerobic digestion of municipal waste activated sludge

To enhance the anaerobic digestion of municipal waste-activated sludge (WAS), ultrasound, thermal, and ultrasound + thermal (combined) pretreatments were conducted using three ultrasound specific energy inputs (1000, 5000, and 10,000 kJ/kg TSS) and three thermal pretreatment temperatures (50, 70 and 90 °C). Prior to anaerobic digestion, combined pretreatments significantly improved volatile suspended solid (VSS) reduction by 29-38%. The largest increase in methane production (30%) was observed after 30 min of 90 °C pretreatment followed by 10,000 kJ/kg TSS ultrasound pretreatment. Combined pretreatments improved the dimethyl sulfide (DMS) removal efficiency by 42-72% but did not show any further improvement in hydrogen sulfide (H₂S) removal when compared with ultrasound and thermal pretreatments alone. Economic analysis showed that combined pretreatments with 1000 kJ/kg TSS specific energy and differing thermal pretreatments (50-90 °C) can reduce operating costs by $44-66/ton dry solid when compared to conventional anaerobic digestion without pretreatments.     

综采工作面粉尘运移和粉尘浓度三维分布的数值模拟研究

分析了综采工作面流场及粉尘分布的特点 ,视工作面含尘风流为气 粒两相流 ,建立了描述综采工作面风流中粉尘运动和浓度分布的数学模型。采用计算流体力学的有限容积法求解 ,编制了模拟计算综采工作面三维空间内风速和粉尘浓度分布的计算机程序     

调节风阀与风量的测量

根据玻璃熔窑助燃风系统 ,分析了工业炉燃烧自动控制过程中 ,调节风阀结构和流量计及其相对安装位置对风量测量及自控的影响 ,对通风自控系统设计、选型及安装具有一定的参考价值     

金川公司二矿区通风系统风流非定常流动规律研究

实际上 ,矿井的风流状态受多种因素影响 ,金川公司二矿区井下风流就处于非定常状态 ,为了保证生产安全 ,控制风流状态 ,采取相应的通风措施 ,开设课题研究 ,建立了井巷内空气非定常流动能量方程和通风网络中非定常流动的数学模型。根据该模型可以模拟出矿井通风系统内非定常状态下任意时刻、任意位置通过风量。通过对金川公司二矿区井下机站风机开停和风门开关引起通风系统风流的非定常流动过程的数值模拟 ,得出了受其影响区域内风流状态的变化规律 ,并为其采取通风措施和控制风流状态 ,提供了科学依据     

LONG‐TERM CHANGES IN REGIONAL HYDROLOGIC REGIME FOLLOWING IMPOUNDMENT IN A HUMID‐CLIMATE WATERSHED1

ABSTRACT: We analyzed the type of hydrologic adjustments resulting from flow regulation across a range of dam types, distributed throughout the Connecticut River watershed, using two approaches: (1) the Index of Hydrologic Alteration (IHA) and (2) log‐Pearson Type III flood frequency analysis. We applied these analyses to seven rivers that have extensive pre‐and post‐disturbance flow records and to six rivers that have only long post‐regulation flow records. Lastly, we analyzed six unregulated streams to establish the regional natural flow regime and to test whether it has changed significantly over time in the context of an increase in forest cover from less than 20 percent historically to greater than 80 percent at present. We found significant hydrologic adjustments associated with both impoundments and land use change. On average, maximum peak flows decrease by 32 percent in impounded rivers, but the effect decreases with increasing flow duration. One‐day minimum low flows increase following regulation, except for the hydro‐electric facility on the mainstem. Hydrograph reversals occur more commonly now on the mainstem, but the tributary flood control structures experience diminished reversals. Major shifts in flood frequency occur with the largest effect occurring downstream of tributary flood control impoundments and less so downstream of the mainstem's hydroelectric facility. These overall results indicate that the hydrologic impacts of dams in humid environments can be as significant as those for large, multiple‐purpose reservoirs in more arid environments.     

TEN YEARS OF VEGETATION SUCCESSION ON A DEBRIS‐FLOW DEPOSIT IN OREGON1

ABSTRACT: We tracked vegetation succession on a debris‐flow deposit in Oregon's Coast Range to examine factors influencing the development of riparian plant communities following disturbance. Plots were stratified across five areas of the deposit (bank slump, seep, upper and lower sediment wedge, log jam) the first growing season after debris flow. At six times during the next ten years we estimated cover of vascular plants and tallied density of woody plants. Plant colonization occurred within two years. Total cover increased two‐to seven‐fold on the five areas within three years. Red alder and salmonberry were the dominant species, although weedy herbs persisted where woody species were lacking. Ordination of cover data showed that the five areas remained floristically distinct over time, while undergoing similar shifts related to the increasing dominance of alder and salmonberry. Rapid height growth of alder allowed it to outcompete salmonberry and effectively capture most areas by the tenth year, even where sprouts from transported rhizomes gave salmonberry an early advantage. Our results suggest that successional patterns were influenced by substrate variability, species composition of initial colonizers, propagule sources and their distribution, and species life‐history traits such as growth rate, competitive ability, and shade tolerance.     

A SIMPLE METHOD FOR ESTIMATING BASEFLOW AT UNGAGED LOCATIONS1

ABSTRACT: Baseflow, or water that enters a stream from slowly varying sources such as ground water, can be critical to humans and ecosystems. We evaluate a simple method for estimating base‐flow parameters at ungaged sites. The method uses one or more baseflow discharge measurements at the ungaged site and longterm streamflow data from a nearby gaged site. A given baseflow parameter, such as the median, is estimated as the product of the corresponding gage site parameter and the geometric mean of the ratios of the measured baseflow discharges and the concurrent discharges at the gage site. If baseflows at gaged and ungaged sites have a bivariate lognormal distribution with high correlation and nearly equal log variances, the estimated baseflow parameters are very accurate. We tested the proposed method using long‐term streamflow data from two watershed pairs in the Driftless Area of southwestern Wisconsin. For one watershed pair, the theoretical assumptions are well met; for the other the log‐variances are substantially different. In the first case, the method performs well for estimating both annual and long‐term baseflow parameters. In the second, the method performs remarkably well for estimating annual mean and annual median baseflow discharge, but less well for estimating the annual lower decile and the long‐term mean, median, and lower decile. In general, the use of four measurements in a year is not substantially better than the use of two.