Quantification of Freshwater Pearl Mussel Entrainment Velocities and Controlling Factors; a Flume Study

Increased flood frequency and magnitude are predicted for Scotland, and the country contains several of the world's largest recruiting populations of freshwater pearl mussel (Margaritifera margaritifera). This study provides a unique flume experiment to measure the near‐bed velocities required for freshwater pearl mussel entrainment and factors affecting their movement. It represents the first quantitative attempt at examining the precise water velocities at which freshwater pearl mussel become vulnerable to displacement during high flow events. Measurement of the near‐bed velocities at which the mussels moved was undertaken using an indoor recirculating flume. The effect of the different parameters (bed substrate, mussel burial depth, mussel curvature, mussel alignment, shell curvature and the presence of a simulated foot) on entrainment velocity was tested in the flume and their significance was verified using Kruskal–Wallis and Mann Whitney tests. Bed substrate was found to have the biggest influence on mussel entrainment velocities with averages of 0.86 ms^?1, 0.95 ms^?1, 1.01 ms^?1 and 1.42 ms^?1 for sand, gravel, mixed bed and boulder beds respectively. Stepwise logistic regression showed that bed substrate, foot presence, mussel length, mussel burial depth and shell curvature were sufficient to explain mussel entrainment velocity. These findings provide valuable information for the modelling of freshwater pearl mussel dynamics in streams systems and assessing the vulnerability of endangered mussel populations to higher flows associated with climate change in Scotland. Copyright © 2015 John Wiley & Sons, Ltd.     

铅芯橡胶隔震双槽渡槽设计与动力分析

结合南水北调中线工程,利用铅芯橡胶隔震技术对双洎河大型双槽渡槽进行隔震设计,采用Housner模型考虑水体与槽身流固耦合作用对其进行有限元动力分析。与非隔震渡槽相比,隔震渡槽的频率大幅降低;随隔震周期的增加,隔震渡槽振型保持不变;槽身底部剪力减小,支座位移增大。等效线性模型计算的地震响应极值大于双线性模型,偏安全。结果表明,铅芯橡胶隔震技术可显著降低渡槽结构的地震响应,且隔震周期越大,降幅亦越大。     

超大拱式变截面渡槽收缩徐变影响研究

以跨径200m的超大跨径变截面拱式渡槽的结构设计为例,通过建立有限元模型,对渡槽主拱圈的分段分环施工全过程进行了收缩徐变分析。结果表明,徐变收缩可引起较大的后期变形,对渡槽竖向位移影响显著。建议在超大跨拱式渡槽预拱度设计时,应充分考虑混凝土的收缩徐变对变形的影响,采取分段分环施工并在拱脚处使用微膨胀混凝土以减小收缩徐变的影响,并采取相应措施控制渡槽线形。     

Low flow regime measurements with an automatic pulse tracer velocimeter (APTV) in heterogeneous aquatic environments

Cost-effective velocity measurements at lab and field scales are required for understanding and modeling the flow characteristics in aquatic environments such as constructed wetlands, coastal marshes, lakes and reservoirs. This paper presents a new measurement device—the automatic pulse tracer velocimeter (APTV) that is designed to measure water velocities for low flow regimes (0.2–5.0 cm s⁻¹) in heterogeneous aquatic environments using NaCl pulse tracer measurements. Hydraulic data collected in a laboratory-scale flume and field-scale constructed wetland were analyzed to determine velocity, directional flow and dispersion coefficients measured by using a cross-type and arc-type APTV. Acoustic Doppler velocimeters (ADVs) were used to collect calibration measurements in a hydraulic flume to gain fundamental understanding in support of field experiments. To test the effects of vegetation, four scenarios of laboratory-scale tests having both submerged and emergent artificial vegetation were conducted in a flume including; (1) no artificial vegetation (NAV), (2) submerged artificial vegetation (SAV) (3) emergent artificial vegetation (EAV), and (4) mix artificial vegetation (MAV). Directional flow detection and simulated storm event flow tests were conducted using an arc-type APTV data in the flume to gain perspectives of APTV performance in variable flow conditions. Cross-type APTV pulse data were eventually analyzed to determine dispersion coefficients based on the tracer curves. Finally APTVs were tested alongside an ADV for a three-day duration in a constructed wetland nearby the Everglades, Florida. Operating advantages of the APTV compared to other similar sensors were summarized in the end to enhance the application potential. Results indicate that APTVs are ideal device for affordable measurements of velocities in a 0.2–4.5 cm s⁻¹ range with the prediction of both velocity field, direction and dispersion coefficients, and capable of autonomous deployment and control in a sensor network.     

Performance analysis of a horizontal axis 3-bladed Savonius type wave turbine in an experimental wave flume (EWF)

The present experimental study investigates the generation and propagation of regular water waves and their interactions with an in-house fabricated horizontal-axis 3-bladed Savonius rotor in an experimental wave flume (EWF) equipped with a piston-type wave maker with active absorption capability to assess the rotor performance for different parametric conditions namely, wave height, wave period and submergence level in intermediate-to-shallow water depths. The motion of the wave particles around the Savonius rotor is observed during the experiments as well as measuring the power and torque performance of the rotor to make a reliable assessment of the water movement with the rotor positioning for different inflow wave boundary conditions. The wave-to-mechanical energy conversion efficiency (ECE) of the present device is determined for each case to suggest a possible optimum positioning accompanied with optimum wave heights and frequencies for the manufactured small scale prototype. The present results suggest that experimental solutions within the wave flume can provide a proper guideline for performance analysis of such devices in intermediate-to-shallow water depths for further studies of optimization of design of Savonius rotor type sea and/or ocean wave energy conversion devices for different operating conditions provided that optimum physical flow conditions are satisfied.     

边界层理论在三角形长喉道量水槽流量计算中的应用

三角形长喉道量水槽是一种明渠量水设施。目前的流量计算主要是经验公式,经验公式的应用受试验条件的限制较大。本文根据边界层位移厚度和临界水深理论,推导了该量水槽流量的理论设计方法,该方法可以根据渠道的比降、糙率和设计流量灵活的调整量水槽的几何尺寸,喉道底部也可以根据量水范围的要求设计成平底或底部拱起。用文献[1]的实验结果进行了比较,计算与实测值一致。在此基础上,还提出了三种复合三角形断面长喉道量水槽的理论计算方法。     

大型U型渡槽正常运行期寒潮降温影响分析

重点分析了不同降温幅度及降温速率对大型U型混凝土渡槽温度场影响,计算结果表明,秋冬季寒潮降温可能导致槽身出现较大的内外温差及温度梯度,导致出现裂缝,影响渡槽正常使用,应采取必要的保温措施以抵御寒潮袭击。     

大型混凝土渡槽的预应力施加程序优化

采用三维有限元技术对南水北调中线工程中大型预应力混凝土渡槽的预应力施加程序进行了优化研究，提出了合理的预应力施加方案，该方案使渡槽结构在施工期能更好地满足应力、变形的要求。     

樟洋U型薄壳渡槽环向无粘结预应力施工技术

无粘结预应力混凝土是在浇灌混凝土之前，把预先加工好的无粘结钢绞线与普通钢绞线一样直接放置在模板内，然后浇筑混凝土，待混凝土达到设计强度时，即可进行张拉。介绍樟洋U型薄壳渡槽横向无粘结预应力的施工工艺、技术要点等。     

Behaviour of two small pelagic and demersal fish species in diverse hydraulic environments

Increased hydraulic diversity could be a means to promote fish diversity in rivers, but little is known of the behaviour of fish in hydraulic environments. This study concerns the behaviour of two species of small native Australian freshwater fish in variable hydraulic environments and ecological habit, with regard for (a) whether the apparent differences in swimming ability are reflected in the behaviour of the species and (b) the influence of changing hydraulic conditions on their patterns of use. An artificial channel was constructed with three levels of discharge, and fish were allowed to swim freely for 3 h without human interference. Their movements and habitat choices reflected their swimming ability and ecological habit, in that the stronger swimming, pelagic common galaxias (Galaxias maculatus) spent most time cruising in the open channel, preferring the turbulent inflow, and the demersal flat‐headed gudgeon (Philypnodon grandiceps) remained in the shelter of boulders. In effect, the galaxias changed their behaviour with changes in hydraulic conditions, while the gudgeons continued to use their preferred habitat. This study, therefore, provides support for the use of hydraulic diversity as a tool to foster fish diversity. Copyright © 2010 John Wiley & Sons, Ltd.