孟氏浮游蓝丝藻在模拟水体中的垂直分布与浮力规律研究

采用大型室内湖泊模拟装置对孟氏浮游蓝丝藻在富营养化湖泊中的垂直分布与迁移特征进行了模拟,并通过10 L玻璃瓶实验对孟氏浮游蓝丝藻浮力对光的响应进行了分析.湖泊模拟实验结果表明,光照后,表层孟氏浮游蓝丝藻开始向下层迁移,光照8h后,藻丝在深2～3m左右水层形成稳定聚集层;藻丝容易集聚层在光照度为10μmol·(m2·s)-1左右水层,处于该水层上部的藻丝漂浮百分率<50%趋向于沉降,处于该水层下部的藻丝漂浮百分率>50%趋向于漂浮;无光照后,藻丝开始往水体表层聚集,无光照12h后,约20%的藻丝聚集在水体表层,无光照48h后,约50%的藻丝聚集在水体表层;说明浮游蓝丝藻白天主要分布在水体2～3m处,在早晨或连续的阴天后,可能在水体表层形成水华.10 L玻璃瓶实验结果表明,强光照[100μmol·(m2·s)-1]/无光照周期下藻丝漂浮百分率在30%-70%间变化,弱光照[25μmol·(m2·s)-1]/无光照周期下藻丝漂浮百分率在30%-50%间变化,说明强光照[100μmol·(m2·s)-1]/无光照周期下藻丝具有明显的沉降与漂浮特征.1昼夜内,藻细胞蛋白质和伪空胞的变化不明显,糖含量在14%-35%间变化,藻丝的浮力对光照的响应可能通过藻细胞的糖含量变化实现.     

多驱动力作用下高层建筑火灾烟气输运规律研究现状

高层建筑发生火灾后,火灾烟气会在多种驱动力的作用下从着火房间迅速蔓延扩散至整栋建筑,严重威胁建筑内人员的生命安全。因此,控制建筑内烟气蔓延是建筑消防安全的一项重要内容。该文对热浮力、烟囱效应和室外风作用下建筑内火灾烟气输运规律进行分析,较系统地总结了这三种驱动力作用下火灾烟气输运的国内外研究成果,指出了以往研究的一些不足之处。根据国内外相关工作的研究进展及当前需要,对今后高层建筑火灾烟气输运规律的主要研究内容提出了几点展望。     

海洋水下滑翔机浮力调节系统的设计与实验

目的提高海洋滑翔机浮力调节系统的可靠性,进一步降低系统功耗,设计气压与液压结合的低功耗浮力调节系统。方法基于理论分析确定系统的体积控制量,设计气压调节模块以保证高压油泵的正常工作与回油的顺利进行。利用有限元方法分析承压管路的可靠性,通过实验测试,验证浮力系统的响应性能。结果浮力系统的排油效率随着外压的增大而减小,2MPa的压力会使出油率降低3%左右,同时功耗增加50%左右。在大气压力环境下,依靠系统内负压,400 s即可完成回油600 mL,完成上浮到下潜的转换。结论设计的浮力调节系统的气压调节装置能以较低的功耗保障主泵的正常工作,同时保障回油过程的通畅,满足海洋滑翔机对浮力调节的要求,可以应用于一般海洋深度的水下滑翔机。     

藻类光竞争模型构建及水体紊动对竞争的影响

光是藻类进行光合作用的重要能量来源,决定藻类的初始生产力,当多种浮游藻类共同生存时,会一起竞争光强.光竞争能力强的浮游藻类浓度增加,光竞争能力较弱的则减少,从而完成水体中浮游藻类优势藻的替代.本文通过在以往建立的单藻模型的基础上,耦合入竞争模型,构建两种（多种）浮游藻类光竞争模型,尝试通过数值模拟,研究不同水体紊动中竞争藻属分别取得竞争优势的机理.模拟结果表明：稳态水体中,竞争藻属的自身垂向迁移决定藻浓度的垂向分布,具有浮力调节能力的微囊藻属占据上层水体优势地位,并取得竞争优势;动态水体中,竞争藻属垂向分布均较为均匀,生长速率决定藻的竞争优势,小球藻属生长速率快,最终易取得竞争优势.此外,考虑浮游藻属的动态自遮蔽,会加速稳态水体中微囊藻属取得竞争优势,并限制动态水体中小球藻属的无限制生长,使得模拟结果更加符合实际情况.     

半密闭空间油气爆炸初期火焰特性研究

为了研究半密闭空间内部油气着火爆炸初期火焰特性，进行了不同油气体积分数下的油气着火爆炸实验，通过高速摄影等技术手段对爆炸过程中火焰形态进行了捕捉，分析了不同油气体积分数下爆炸初期火焰着火模式、火焰形态、传播过程和火焰浮力稳定性的变化规律。结果表明:油气体积分数为决定容器内部着火模式的关键因素，随着油气体积分数的逐渐增大，着火模式呈现出燃烧-爆炸-爆燃后持续燃烧的转变；爆炸下的火焰具有明显的分区现象，而其他的着火模式则没有；随着油气体积分数的增加，越靠近化学当量比，纵向和横向火焰阵面速度越大；油气体积分数小于等于1.1%或大于等于2.6%时，火焰稳定性受浮力影响显著。     

蒲绒-芦苇机械混合复合材料的吸油性能

2010年本实验室开始生物质对柴油的吸附实验,和前人的结论一致,生物质热改性后其吸油和漂浮性能提高,但成本增加很多。受到前人复合吸油材料的启发,2012年开展了蒲绒-芦苇机械混合复合材料吸油和漂浮性能的研究,并采用正交实验对影响除油效果的因素进行优化。结果表明,蒲绒-芦苇复合材料较之芦苇吸油性能提高,且比各组分的叠加饱和吸油量还高。震荡使芦苇的漂浮率明显降低,但对蒲绒及复合材料的影响较小。正交实验结果显示,投加量0.7g,油膜厚度0.55 mm,不震荡时,蒲绒除油最佳;在相同条件下,粒径为380~500μm的芦苇除油最佳,蒲绒和该粒径的芦苇按质量比为1∶4混合成的复合材料的除油效果最佳。     

Stratification and Tidal Current Effects on Larval Transport in the Eastern English Channel: Observations and 3D Modeling

We study how the combination of tides and freshwater buoyancy affects the marine organisms accumulation and horizontal transport in the ROFI system of the eastern English Channel. The Princeton Ocean Model coupled with a particle-tracking module is used to study the migration of fish eggs and larvae under different forcing conditions. Results of modeling are validated against observed concentrations of Flounder (Pleuronectes flesus) larvae. Numerical Lagrangian tracking experiments are performed with passive and active particles, representing sea-water organisms. Passive particles are neutrally buoyant whereas active particles are able to exercise light dependent vertical migrations equating to the swimming behavior of larvae. The experiments reveal that the strongest accumulation of particles occurs along the French coast on the margin of the ROFI. This happens because the interaction between the turbulence, the freshwater buoyancy input, and tidal dynamics, produces particle trapping and vertical spreading within the frontal convergence zone. Tides and freshwater input induce net alongshore horizontal transport toward the North. Tidal currents modulate the magnitude of horizontal transport whereas the fresh water input controls more the location of accumulation zones. Tracking experiments with active particles indicate that the vertical migration leads to a significant departure from the passive particle transport pattern. Differences lie in the shape of the particle transport pattern and the rate of the northward migration. In particular, vertically migrating particles travel slower. To find possible Flounder migration pathways, particles are released within the assumed spawning area of Flounder. The model predicts larvae drift routes and demonstrates that throughout the entire particle-tracking period the horizontal structure of the particle distribution is consistent with the larvae concentrations observed during the field experiments.     

On the estimation of overwater buoyancy length from routine measurements

The stability parameter (z/L, where z is the height and L the buoyancy length) is an essential parameter in atmospheric boundary layer studies. From routine measurements, the bulk Richardson number (R_b) is usually computed. On the basis of appropriate field measurements at sea, it is shown that z/L = A R_b where A = 10.2 (with R ² = 0.97) for unstable and 6.3 (with R ² = 0.97) for stable conditions, respectively. It is also demonstrated that the proposed simplified equations are in excellent agreement with those more complicated formulations.     

厂房内H_2连续泄漏扩散的模拟分析

利用计算流体动力学软件Fluent对厂房内易燃易爆气体H2泄漏扩散过程进行了数值模拟,研究H2连续泄漏扩散规律。计算结果表明,厂房内H2泄漏一定时间后扩散将达到稳定,室内H2浓度将不再变化;根据室内H2浓度分布规律,得出H2泄漏报警装置应设在泄漏口正对墙壁上,且厂房的排风口应开设在H2钢瓶喷射方向上的屋顶处;结合H2的毒性级别和爆炸极限,划分该厂房为紧急防爆疏散区,必须在泄漏初期进行紧急人员疏散并做好防火防爆措施。研究结果为厂房内H2泄漏事故应急救援、泄漏报警装置及排风口的位置设置提供重要技术支持和理论依据。     

A Wind Tunnel Investigation of the Influence of Solar-Induced Wall-Heating on the Flow Regime within a Simulated Urban Street Canyon

A wind tunnel study has been undertaken to assess theinfluence of solar-induced wall heating on the airflowpattern within a street canyon under low-speed windconditions. This flow is normally dominated by large-scalevortical motion, such that the wind moves downwards at thedownstream wall. In the present work the aim has been toexamine whether the buoyancy forces generated at this wallby solar-induced heating are of sufficient strength tooppose the downward inertial forces and, thereby, changethe canyon flow pattern. Such changes will also influencethe dispersion of pollutants within the street. In theexperiments the windward-facing wall of a canyon has beenuniformly heated to simulate the effect of solar radiation.Four different test cases, representing different degreesof buoyancy (defined by a test Froude number, Fr), havebeen examined using a simple, 2-D, square-section canyonmodel in a wind tunnel. For reference purposes, the neutralcase (no wall heating), has also been studied. The approachflow boundary layer conditions have been well defined, withthe wind normal to the main canyon axis, and measurementshave been taken of canyon wall and air temperatures andprofiles of mean velocities and turbulence intensities.Analysis of the results shows clear differences in the flowpatterns. As Fr decreases from the neutral case there arereductions of up to 50% in the magnitudes of the reverseflow velocities near the ground and in the upward motionnear the upstream wall. A marked transition occurs at Fr 1, where the single dominant vortex, existing at higher Fr values, weakens and moves upwards whilst a lower region of relatively stagnant flow appears. This transition hadpreviously been observed in numerical model predictions butat a Fr at least an order of magnitude higher.