基于CFD-PID方法的仿生鱼自推进运动研究

相较于传统的螺旋桨推进方式,水下仿生推进具有灵活、高效及对环境干扰小等优势。该文在求解不可压N-S方程和牛顿第二定律的基础上,嵌入PID控制算法,构建CFD-PID求解器,模拟主动控制下的仿生鱼自推进运动。通过PID算法动态调节仿生鱼摆幅,间接控制其速度,使仿生鱼可以达到任意特定的收敛速度。与常规方式自推进相比,PID控制自推进能更快地加速到预定速度,且在加速时期产生更大尺度的涡,最终的动态平衡状态则与常规方式自推进一致。     

仿生机器鱼鳍波动推进速度的理论分析和实验测试

为了提高仿鱼型推进器在水中运动的稳定性和机动性,该文选择了典型的依靠胸鳍波状运动产生推进力的蓝点魟为仿生对象,对胸鳍的结构进行简化,并基于这种简化模型设计了仿生波动鳍推进装置。详细介绍了该装置的机械结构和控制电路,通过理论计算和实验测试相结合的方法,全面分析了影响仿生机器鱼鳍推进器波动游动速度的各种因素,包括:波动频率及摆幅和波长等运动学参数、鳍面面积、流体介质密度及仿生鳍的重量等,揭示了各因素的影响规律。通过研究发现:仿生波动鳍推进速度基本上随着波动频率、摆幅和波长等运动学参数的增加而增大;随着鳍面面积或流体介质密度的增大,相同运动学参数下推进速度亦明显加快;此外,推进速度随着该仿生鳍的重量增加而略有降低。     

金枪鱼自主波动游动的数值模拟

鱼类游动问题蕴含着复杂的流体力学机理,其仿生问题同时又有着重要应用背景.该文运用人工伪压缩方法求解三维不可压缩非定常Navier-Stokes方程,计算分析金枪鱼从静止加速起动到巡游直至减速波动游动的全过程,得到鱼类游动时各状态的流场信息以及受力情况.同时结合计算结果,对鱼类游动过程进行了参数研究并且分析了鱼体推力产生的机理.计算结果分析表明:数值求解非定常Navier-Stokes方程能够模拟鱼体运动时的流场;鱼体摆动频率以及摆幅会影响鱼的游动;持续摆动产生的涡环形成反卡门涡街是鱼体游动时产生推力的重要因素.     

静水中长鳍扭波推进的水动力数值研究

长鳍扭波推进是一种典型的鱼类游动方式,具有高效、低噪、机动灵活等一系列优点。该文以"尼罗河魔鬼"鱼为仿生研究对象,采用弹性光顺法和局部网格重划法的动网格技术对大摆幅的长鳍扭波推进运动流场进行了数值计算研究,鳍条最大摆幅高达85°,对长鳍扭波推进在系泊状态下的水动力进行了研究,并与试验结果进行了比较验证。数值分析了鳍面压力分布及其随相位的变化,以及与推力产生的关联,并分析了长鳍扭波推力随扭波频率的变化,研究表明,系泊状态下,推力系数不随频率而改变。     

不同流速对鲫鱼推进效率影响的数值研究

鱼类趋流性的试验和鱼类游动的数值模拟是当前研究的两个热点,大多数鱼类不仅有趋流特性而且还能高效节能的向前推进,开展鱼类趋流性与推进效率关系的研究既能完善鱼类推进机理理论,也能在鱼道设计时提高其过鱼效率。本文以鲫鱼在不同恒定流速中的实测游泳数据为依据,利用计算流体力学软件flow-3d对鱼类波状摆动进行数值模拟,建立鲫鱼游动的数值计算模型,研究在不同流速下鲫鱼完成一个运动周期后所对应的推进效率。结果表明,随着流速的增大鱼的推进效率呈现出先增大后减小的变化趋势,当流速条件为0.5 m/s时对应的鱼类推进效率值最大,也是推进效率随流速变化的转折点。该研究获得了鲫鱼在顶流运动状态下鱼类推进效率与流速条件之间的相关关系。     

航道整治对东流水道四大家鱼栖息地适宜度的影响

为探讨长江下游东流水道二期整治工程对河段内四大家鱼繁殖水流条件的影响,根据平面二维水流数学模型和四大家鱼适宜度曲线,建立了四大家鱼栖息地适宜度模型,并对东流水道不同时期的四大家鱼适宜度分布情况进行了数值模拟,初步评估了东流水道二期整治工程对四大家鱼适宜度的影响。结果表明:东流水道二期工程能增加四大家鱼产卵期理想的适宜性区域,有助于四大家鱼的产卵繁殖;对四大家鱼在生长期的影响因时期不同而有略有差异,在二期工程施工刚完成时不利于鱼群生长,但在施工完成较长一段时间后则有利于鱼群生长。建议在进行航道整治工程的整体布局和尺寸设计时考虑工程对目标鱼群栖息地适宜度的影响,使航道整治工程对目标鱼群栖息地适宜度的影响达到最小,甚至增加目标鱼群的理想适宜度和范围。     

仿飞鱼跨介质无人平台的探索研究

跨介质飞行器是一种既能在空中飞行,又能在水下潜航的新概念飞行器,它兼有飞行器的速度和潜航器的隐蔽性。该文以自然界的飞鱼为模仿对象,研究了一种仿飞鱼的跨水气介质无人平台。该仿生飞鱼的身体长度25 cm,排水重量约为0.191 kg。采用计算流体力学的手段,研究了仿生飞鱼水下游动与水面滑行阶段的水动力学特性。重点比较了飞鱼达到巡航状态所需功率,从而证实飞鱼可以通过水面滑跑过程进一步加速到起飞状态。首先,对于水下游动状态,当巡游速度为10 m/s,尾鳍摆动频率为145 Hz时,在小摆动幅度工况下,飞鱼达到巡游状态需要的输入功率约为350 W,此时通过身体重量计算出的肌肉功率密度为3 664 W/kg,该数值可以在生物学上找到合理解释。当飞鱼在水面滑跑时,同样输入功率为350 W时,滑飞速度可达到16.5 m/s。可见,飞鱼可通过水面滑跑进一步将自身加速到起飞状态。     

多关节鱼形机器人的动态特性的建模与仿真研究

本文以James LightHill的鱼类的细长体理论为基础,利用能量守恒、动量定理和波动理论来分析计算仿生机器鱼在运动中的受力。建立了转角、相位差、转动频率等重要参数的动态模型,在对模型进行仿真的基础上,对仿生机器鱼的效率进行了数值模拟和估算,分析了影响效率的一些因素,揭示了鱼类运动的高效的机理,为进一步展开对仿生机器鱼的研究提供了一个思路。     

基于自适应人工鱼群算法的含水层参数确定

水文地质参数是地下水数值模拟中重要的参数,通常通过抽水试验进行水文地质参数的反演,并用一个复杂的非线性优化问题来描述反演过程,然而传统方法如图解法等因人为因素造成计算结果精度低。提出利用自适应人工鱼群算法求解含水层参数的优化函数问题,即把某一条人工鱼与最优人工鱼的距离作为该人工鱼的视野并计算步长,步长和视野随着迭代次数的继续不断调整变化,加快了收敛速率并提高了计算结果的精度。实例分析结果表明:改进后的人工鱼群算法计算结果可靠、收敛快、精度高,是一种求解含水层参数的简单、有效的方法。     

蝌蚪模型并列游动的数值研究

该文通过数值求解雷诺平均N-S方程,对高雷诺数下蝌蚪模型同相位和反相位并排游动进行了数值研究,揭示了并列蝌蚪群游的流动机制。研究表明,非流线型的蝌蚪并列群游与流线型的鱼体不同。蝌蚪同相位并列游动时,总推力比单独游动时低,尽管能量消耗有所增加但推进效率更高;蝌蚪反相位并列游动时,总推力比单独游动时低,但比同相位并列游动时高,间距很近时消耗的能量会显著增加,而推进效率依然提高。蝌蚪的钝体头部产生的涡在群游时有利于增加推力。     

Call for Papers

正As the eldest and most distributed professional journal of water industry,Water Wastewater Engineering(W WE)gained very wide acceptance from the colleagues working in this field in this country since start publication in 1964.Now it is administrated by the Ministry of Construction of the People’s Republic of China and sponsored by the China Civil Engineering Society etc.     

地下厂房施工过程的三维非线性数值模拟分析

根据冗各电站地下厂房开挖支护的施工顺序,以隐式杆单元模拟锚杆,以壳单元模拟混凝土喷层,采用三维非线性有限元技术,对洞室群的开挖支护动态过程进行了模拟计算。通过三维非线性有限元计算分析得到:洞室群动态开挖过程中围岩应力变形的分布规律,围岩塑性区的发展规律,锚杆受力变化情况。计算结果表明:整个开挖过程中,洞周围岩位移变化规律正常,量值较小,塑性区主要分布在洞室周边,围岩稳定性较好;但在洞室交叉口处围岩的变形较大,出现较大范围的塑性区,在此基础上提出了支护措施优化方案,并对优化方案的效果进行了评价。     

Evaluation of freshwater mussel relocation as a conservation and management strategy

The relocation of unionacean mussels is commonly used as a conservation and management tool in large rivers and streams. Relocation has been used to recolonize areas where mussel populations have been eliminated by prior pollution events, to remove mussels from construction zones and to re-establish populations of endangered species. More recently, relocation has been used to protect native freshwater mussels from colonization by the exotic zebra mussel Dreissena polymorpha. We conducted a literature review of mussel relocations and evaluated their relative success as a conservation and management strategy. We found that 43% of all relocations were conducted because of construction projects that were forced to comply with the Endangered Species Act 1973 and that only 16% were monitored for five or more consecutive years. Most (43%) relocation projects were conducted from July to September, presumably a period when reproductive stress is relatively low for most species and the metabolic rate is sufficient for reburrowing in the substrate. The mortality of relocated mussels was unreported in 27% of projects; reported mortality varied widely among projects and species and was difficult to assess. The mean mortality of relocated mussels was 49% based on an average recovery rate of 43%. There is little guidance on the methods for relocation or for monitoring the subsequent long-term status of relocated mussels. Based on this evaluation, research is needed to develop criteria for selecting a suitable relocation site and to establish appropriate methods and guidelines for conducting relocation projects.     

基于模型试验的河床砂砾石层基本特性研究

为了经济可靠地确定深厚覆盖层的基本特性参数,以大渡河双江口水电站坝基河床砂砾石层基本特性研究为工程背景,进行大尺寸模型试验,研究河床砂砾石层的旁压模量和动探击数随密度、级配以及上覆压力的变化规律。根据室内模型试验结果,结合现场旁压试验及钻孔试验成果,推断出坝址区河床砂砾石相关层位的密度,并依此进行砂砾石室内力学试验,获得设计所需力学参数。研究成果可为深厚覆盖层基本特性测试提供新的方法。     

库水波动下库岸边坡地下水浸润线解析解及误差分析

解析法是库岸边坡地下水浸润线计算中便于实际应用的方法,但该方法须基于若干假定并对潜水运动基本方程线性化后才能求解。针对各假定和线性化过程建立不同的地下水渗流数学模型,用解析法和有限元法解答上述数学模型,分析各误差大小及其规律。结果表明：库岸垂直处理带来的误差要小于方程线性化处理和不考虑非饱和渗流带来的误差,而且它们都随渗透系数变大而减小;在三峡库区库水调度情况下,假定库水位等速变化带来的误差对大多岸坡而言可以忽略;计算库岸边坡地下水浸润线时,解析法只适用于水位变化幅度相比含水层厚度较小,且几何边界规则、岩土结构简单、岩土体渗透性较好时的情况。     

SPATIAL AND TEMPORAL WATER QUALITY VARIABILITY IN AQUATIC HABITATS OF A CULTIVATED FLOODPLAIN

The floodplains of lowland rivers contain diverse aquatic habitats that provide valuable ecosystem services but are perturbed when intensively cultivated. Hydrologic, water chemistry and biological (fish) conditions in five aquatic habitats along the Coldwater River, Mississippi, were measured for more than 4 years: the river, two severed meanders that functioned as backwaters, a managed wetland and an ephemeral channel draining cultivated fields. Off‐channel habitats were connected to downstream regions 0.10% to 32% of the dry season and 24% to 67% of the wet season. The median temperatures for the five monitored sites ranged from 18°C to 23°C, the median total solids concentration for all sites was 135 mg L^?1, the median total phosphorus was 0.29 mg L^?1 and the median total nitrogen was 1.56 mg L^?1. Chemical and physical water quality displayed strong seasonal differences between the wet winter/spring and the dry summer/fall periods so that temporal variation consisted of gradual seasonal trends superimposed on strong diurnal variations. All off‐channel habitats exhibited periods of hypoxia and temperatures >30°C during the dry season. Between‐site gradients of water and habitat quality were strongly coupled to water depth and runoff loading. The rehabilitation of one backwater by increasing water depth and diverting agricultural runoff was associated with improved water quality and fish species richness relative to an adjacent untreated backwater. The diversion of polluted runoff and the use of water control structures to maintain greater water depth were observed to be effective management tools, but the former reduces the water supply to habitats that tend to dry up and the latter reduces connectivity. Published in 2011 by John Wiley & Sons, Ltd.     

Changes in Summer Irrigated Crop Area and Water Use in Southeastern Turkey from 1993 to 2002: Implications for Current and Future Water Resources

Changes in summer irrigated cropland acreage and related water use are estimated from satellite remote sensing and ancillary data in semi-arid Southeastern Turkey where traditionally dry agricultural lands are being rapidly transformed into irrigated fields with the help of water from the Euphrates-Tigris Rivers. An image classification methodology based on thresholding of Landsat NDVI images from the peak summer period reveals that the total area of summer irrigated crops has increased three-fold (from 35,000 ha to over 100,000) in the Harran Plain between 1993 and 2002. Coupled analysis of annual irrigated crop area from remote sensing and potential evapotranspiration based estimates of irrigation water requirements for cotton indicate a corresponding increase in agricultural water use from about 370 million cubic meters to over one billion cubic meters, a volume in accordance with the state estimates. These estimates have important implications for understanding the rapid changes in current agricultural withdrawals in Southeastern Turkey and form a quantitative basis for exploring the changes in future water demands in the region. For example, expansion of irrigated lands have led to a steady decrease in potential evaporation due to increased roughness and decreased humidity deficit in the Harran Plain. Assuming that the changes in future evaporation conditions will be of similar nature, water use for irrigation is expected to decrease over 40 percent in future irrigation sites. Incorporating this decrease in overall planning of the irrigation projects currently under construction should lead to improved management, and by extension, sustainability of water resources in the region.     

基于BP神经网络-马尔科夫链模型的隧道围岩位移预测

在隧道工程施工中,围岩位移预测起着很重要的作用。将BP神经网络-马尔科夫链模型引入到隧道围岩位移预测中来,通过对训练样本的学习,利用BP神经网络实现了对位移时间序列的滚动预测,同时得到了实测值与预测值的相对误差;在此基础上利用马尔科夫链对相对误差进行修正,有效地提高了预测结果的精度。并将该模型应用于某公路隧道拱顶下沉位移时序预测中,结果表明该模型具有精度高、科学可靠的特点,为隧道围岩变形的预测提供了新的途径。     

Spatio‐temporal variation of gross CO2 and CH4 diffusive emissions from Australian reservoirs and natural aquatic ecosystems,and estimation of net reservoir emissions

Carbon dioxide (CO₂) and methane (CH₄) diffusive emissions were measured during two field surveys in Queensland and Tasmania, Australia, using the floating chamber method. Bubbling and degassing emissions in 2010 were estimated in Koombooloomba Dam reservoir using only inverted funnels and gas concentrations, respectively. A total of 14 reservoirs and 16 rivers and lakes were sampled from 2006 to 2010. Spatial variation was substantial within each water body, as well as between them. The main drivers of diffusive emission variation were physiographic region and climate, with a clear demarcation being observed between diffusive emissions from tropical Queensland and temperate Tasmania, and between the humid West Coast Range (Tasmania) and dry Central Plateau (Tasmania). Higher CO₂ and CH₄ diffusive emissions were observed during the dry season, when long water residence times would promote organic matter degradation. Estimated total gross emissions, including diffusive, bubbling and degassing emissions, for Koombooloomba Dam reservoir were about 1.5 × 10⁶ t CO₂eq km² per year, or 24 × 10⁶ t CO₂eq per year. This corresponds to a plant emission factor of 3.18 kg CO₂eq MWh^?1. Using an estimate of terrestrial emissions derived from literature data for the Tully River catchment area, rough estimated net emissions from the catchment area are about 44 kt CO₂eq per year, or 5.83 kg CO₂eq MWh^?1, which is in the lower range of the studied reservoirs.     

Short communication. Pipelines as a refuge for freshwater snails

In the lower River Murray, Australia, populations of gastropods have declined markedly over the past 40 years. Of the native fauna of about 18 species, only the ancylid Ferrissia petterdi remains common (but in patches), and another five species feature in sporadic local resurgences. Until recently the viviparid Notopala was thought to be extinct. The introduced physid Physa acuta is widespread, but in low numbers. The decline probably is associated with flow regulation, high turbidity and the introduction of common carp. Snail populations have persisted, however, in irrigation pipelines fed from the river, where they periodically cause blockages. This paper reports the discovery of the only known populaion of Notopala hanleyi in a pipeline where the inner wall accumulates microbial and other organic matter, providing high quality food for snails. In the Murray before regulation most of the periphytic biomass was probably microbial, as fluctuating water levels would have maintained littoral communities in a highly productive, early state of succession his postulated that, by stabilizing seasonal water levels, regulation has promoted the production of filamentous green algae, an inferior food source, and so displaced snail populations from the open aquatic environment.