Quantifying the effects of wind, upwelling, curl, sea surface temperature and sea level height on growth and maturation of a California Chinook salmon (Oncorhynchus tshawytscha) population

We used retrospective scale growth chronologies and return size and age of female Chinook salmon (Oncorhynchus tshawytscha) from a northern California, USA, population collected over 22 run years and encompassing 18 complete cohorts to model the effects of oceanographic conditions on growth during ocean residence. Using path analyses and partial least squares regressive approaches, we related growth rate and maturation to seven environmental variables (sea level height, sea surface temperature, upwelling, curl, scalar wind, northerly pseudo‐wind stress and easterly pseudo‐wind stress). During the first year of life, growth was negatively related to summer sea surface temperature, curl and scalar winds, and was positively related to summer upwelling. During the second, third and fourth growth years growth rate was negatively related to sea level height and sea surface temperature, and was positively related to upwelling and curl. The age at maturation and the fork length at which three ocean‐winter fish returned were related to the environment experienced during the spring before the third winter at sea (the year prior return). Faster growth during the year before return led to earlier maturation and larger return size.     

The influence of environment and spawning distribution on the survival of anchovy (Engraulis encrasicolus) larvae in the Bay of Biscay (NE Atlantic) investigated by biophysical simulations

A growth and survival model of the early life stages was run along virtual drift trajectories tracked in a hydrodynamic model to simulate the annual recruitment process of anchovy (Engraulis encrasicolus) in the Bay of Biscay (NE Atlantic). These biophysical simulations concerning three different years were analysed in order to investigate the influence of environment and spawning dynamics on the survival of larvae and juveniles. The location of space–time survival windows suggested major environmental mechanisms involved in simulated recruitment variability at the different scales – retention of larvae and juveniles in favourable habitats over the shelf margins and turbulence effects. These small‐scale and meso‐scale mechanisms were related to the variations in wind direction and intensity during spring and summer. Survival was also variable according to the origin of the drift trajectories, that is spawning distribution in space and time. The observed spawning distribution (according to field surveys) was compared with the spawning distribution that would maximize survival (according to the biophysical model) on a seasonal scale, which revealed factors not considered in the biophysical model (e.g. spawning behaviour of the different age classes). The variation of simulated survival according to spawning distribution was examined on a multi‐annual scale and showed a coherent pattern with past and present stock structures. The interaction processes between the population (influence on spawning) and its environment (influence on survival) and its implications on recruitment and stock dynamics are discussed.     

林带透风系数与湍流度关系的风洞试验研究

林带降低风速最根本的问题是在林带背风面形成湍流,湍流的变化与透风系数紧密相关。所以探讨林带的透风系数与湍流度的变化是农田防护林网气象效应的一个重要方面。本文应用二次回归正交旋转组合设计的方法,通过风洞实验和计算建立了透风系数与湍流度之间的回归模型方程。利用该方程可对林带背风面不同高度的透风系数和湍流度相互进行预测,并揭示了两者之间内在的相关关系。同时利用本文的回归模型方程,用最篷透风系数可预测最适湍流度,并对了解林带背风面不同高度上湍流度的变化有重大意义。     

湍流模型在泵站进水池漩涡模拟中的适用性研究

泵站进水池表面漩涡、附底漩涡和附壁漩涡是影响水泵装置稳定运行的重要因素,为研究不同湍流模型在进水池漩涡模拟中的适用性,分别采用标准k-? 模型、RNG k-? 模型和Realizable k-? 模型3种湍流模型对进水池流场进行了数值计算,得到了进水池内漩涡位置及强度信息,并与试验进行了对比分析。结果表明,Realizable k-? 模型对进水池表面涡、附底涡和附壁涡的位置和形状预测比较准确,对漩涡的切线速度和环量的预测也与试验值更为接近。为泵站进水池的水力设计与结构优化具有指导作用。     

偏航状态下水平轴风力机尾迹偏移及湍流特征分析

为探索水平轴风力机偏航状态下尾迹变化情况,采用数值模拟结合理论分析的方法对不同风速、不同偏航角工况下的S翼型水平轴风力机尾迹流场进行数值分析.首先分析偏航与风力机输出功率之间关系,在此基础上分析不同偏航角工况尾迹中心的偏移情况以及尾迹处湍流强度的变化情况.结果表明:随着偏航角的增大,叶片表面的压强差减小,方位角每隔120°,叶片表面正压和负压在数值上均达到一次峰值,能造成风力机输出功率有明显损失的恶劣偏航角临界值为10°~15°;随着偏航角增大,沿轴向在1.0D之前尾迹速度中心向X轴的负方向偏移的程度增大,在此之后偏航角小于15°时尾迹中心的偏移程度增大,偏航角大于15°时减小;随着偏航角的增大,尾迹湍流强度的最大值增大,尾迹湍流强度恢复加快,尾迹缩短;偏航下风力机尾迹上下侧湍流强度分布不对称,湍流强度变化不同,使风力机尾迹湍流环境更复杂.     

果园风送喷雾机出风口风场CFD建模与试验

塔式果园风送喷雾机是目前普遍使用的果园喷雾机,塔式结构易产生旋转和不规则的垂直气流,导致喷雾机出风口两侧风场分布不对称,且分布规律不易预测。为探究适用塔式果园风送喷雾机出风口风场建模方法,本研究基于喷雾机出风口风场计算流体动力学（Computational Fluid Dynamics,CFD）建模方法,提出了用户定义函数（User-Defined Function,UDF）分段式三维风速入口边界条件设置方法,并研究了湍流模型和计算域尺寸对喷雾机CFD风场模拟结果的影响特性。采用Fluent软件,建立了三种CFD模型：模型一以11个区域的平均风速作为边界条件;模型二采用UDF分段式三维风速入口作为边界条件;为进一步研究计算域尺寸对风场模拟的影响,建立了小计算域尺寸的模型三。三种模型均采用基于雷诺时均控制（Reynolds-Averaged Navier-Stokes,RANS）方程的k-\epsilon湍流模型和k-\omega湍流模型进行风场计算。为了验证模型的可靠性,设计了空间风场立体测量系统,实现了精确快速空间风速测量。验证结果表明,Standard k-\epsilon、Realizable k-\epsilon、BSL k-\omega和SST k-\omega湍流模型较适合风场CFD建模,其中Standard\text{?}k-\epsilon湍流模型运算结果最优,模型决定系数R²为0.81。基于UDF分段式三维风速入口边界条件设置方法不仅提高了仿真结果的准确性（提高了5%）,而且降低了计算的复杂性。在其他参数设置相同的情况下,大尺寸计算域模型的性能略优于小尺寸计算域。实际建模过程中建议根据计算机计算能力、仿真的实际要求设置合适的计算域尺寸。本研究结果可为喷雾机出风口风场CFD建模方法提供参考。     

建筑数值风洞的基础研究

假设计算区域的上空面和二侧面为自由边界，地面和建筑物的各面为壁函数的边界，计算网格为３６×３０×２７，构造１０ｍ×１０ｍ×１０ｍ建筑数值风洞，采用ｋ－ε湍流模型，对该数值风洞进行了风绕流数值计算。得到了建筑表面压力分布及建筑周围速度矢量图，与实验结果比较表明，该数值风洞是可行的。     

温室结构风振效应的数值模拟

根据大气边界层风的特性,利用CFD方法,采用N-S方程、湍流κ-ε模型及壁面函数法对空气湍流进行了数值模拟;采用有限元方法对温室结构模型进行离散,利用大型通用有限元分析软件ANSYS,对脉动风下考虑流-固耦合的温室结构进行了数值模拟计算和分析。结果表明,脉动风作用下,结构最大位移为0.21 m,与平均风压作用下的结构最大位移0.007 4 m相比显著增大。认为进行温室结构设计时,应考虑流-固耦合作用下的脉动风效应。     

幂律流体管内紊流摩阻系数计算式评价

幂律流体是最常见的非牛顿流体,其管内紊流摩阻系数的计算方法较多,但远没有牛顿流体的成熟.对搜集的国内外已公开报道的14个幂律流体管内紊流摩阻系数的计算式,通过计算机程序计算了Fanning摩阻系数f,对计算结果以图表形式进行了相对偏差评价.结果表明,相对于其他计算公式,Dodge-Metzner式计算结果的总平均相对偏差最小,因而该公式适用于幂律流体管内紊流摩阻系数的计算.     

高转速轴流泵性能及叶轮内湍流流场分析

为了探索高转速轴流泵的性能及内部流场特性,自行设计一转速为2 900 r/min的轴流式模型泵,并基于ANSYS CFX 11.0商用软件,采用κ-ε模型对模型泵多个工况点进行了三维湍流数值计算,计算得到了叶片表面的速度、压力分布.基于数值计算结果对高转速轴流式模型泵性能进行预估和叶轮内部流场分析,结果表明:高转速轴流泵最高效率较低,但效率曲线平坦,高效区较宽;叶片压力面存在小范围的径向流动.最后,提出对叶片进行优化设计的思路,为研发性能优良的高转速轴流泵提供一定的参考.