基于Vortex模型分析金沙江水电开发对圆口铜鱼种群生存力的影响

圆口铜鱼(Coreius guichenoti)是长江上游特有鱼类,研究金沙江梯级水电开发背景下圆口铜鱼种群生存力变化对该物种的保护具有重要意义。Vortex模型在传统种群评估方法的基础上,引入种群年龄结构、繁殖体制、性比等因素,并考虑了环境、灾害、遗传等随机性对种群的影响,可模拟种群数量和生存力变化特征,是一种应用广泛的种群生存力分析模型。基于1981—2021年金沙江圆口铜鱼资源调查数据,采用Vortex模型构建了金沙江中下游干流大规模水电开发前、后两个时期圆口铜鱼种群生存力分析模型,考虑了水电开发下,水温、流速等环境变化对圆口铜鱼种群的影响,对比了两个时期圆口铜鱼种群数量、结构及生存力等。结果表明:水电开发前,严重过度捕捞对圆口铜鱼种群产生了显著威胁,10年内种群数量下降了12.5%,百年内种群内禀增长率为0.085,种群的生存和繁殖能力较稳定,灭绝概率为1%;水电开发后,10年内种群数量下降了42%,百年内种群内禀增长率降至-0.087,灭绝概率增大至36.1%,种群平均灭绝时间为83.7年,圆口铜鱼抵抗环境干扰的种群恢复能力降低,种群生存力受到影响。

Nonlinear tight formation control of multiple UAVs based on model predictive control

A tight formation of unmanned aerial vehicles(UAVs) has many advantages, such as fuel saving and deceiving enemy radar during battlefield entry. As a result, research on UAVs in close formation has received much attention, and the controller design for formation holding has become a popular research topic in the control field. However, there are many unknown disturbances in tight formation, and the tail aircraft is disturbed by the wake. This paper establishes a mathematical model of wake vortices for tail aircraft that considers uncertainty and strong interference. Two UAVs are simulated by Computational Fluid Dynamics software, followed by the design of a semiphysical simulation model predictive control(MPC) scheme that suppresses uncertainty and interference sufficiently to enable the tail aircraft to accurately track the lead aircraft and maintain a stable, tight formation. The tight formation controller is verified by numerical simulation and semiphysical simulation. The results show that the designed controller has an excellent control effect in the case of disturbance caused by the wake vortex.

Vortex Channel Modelling for the Radio Vortex System

In this paper, a free-space vortex channel model of the radio vortex system is proposed to describe the propagation characteristics of vortex signals over the vortex channel. The key idea is to combine the Laguerre-Gaussian(LG) modes in the optical field with the free-space propagation model in the radio field. The proposed free-space vortex channel model is derived from the electric field expression of the LG modes and the freespace channel transfer function of the freespace propagation model theoretically. Simulation results verify that the proposed model could reflect the vortex channel characteristics better than the currently used free-space propagation model.

A PREDICTION OF THE VORTEX-RING STATE BOUNDARY BASED ON MODEL TESTS

To understand the vortex-ring state and to develop an approach for predicting its boundary, a series of model rotor tests of vertical descent and oblique descent have been conducted on a newly-built test apparatus - the Whirling Beam. The test results showed some unsteady aerodynamic behavior of the model rotor operating in the vortex-ring state. A very irregular variation of the rotortorque at low rate-of-descent was observed here for the first time. We considered it to be the start of the 'power settling' and determined the critical descent velocity according to this observation. A previous criterion for the vortex-ring state was modified to give a semi-empirical method for predicting the entire vortex-ring state boundary. The computed boundary shows a good correlation with the model test results and the flight experiences.

Applicability of the vortex-glass model for the single crystal Tl_(0.4)K_(0.41)Fe_(1.71)Se_2

We measure the current–voltage（I–V） characteristics for the single crystal of Tl0.4K0.41Fe1.71Se2 with the superconducting transition temperature（TC） around 30.5 K, under a 10 T magnetic field applied perpendicular and parallel to the ab plane. We find that the shapes of the I–V isotherms are very different from the description by the vortex-glass（VG） model.Combining theoretical calculations and analysis of the ρH⊥ab–T and ρH ab–T data, we give an explicit discussion over the suitability of the VG model for the A0.8Fe2Se2 superconductors, and point out the possibility of the material acting as a convenient platform for re-examination and further study of the complex vortex behaviors in the layered superconductors.

Simplified Prediction Model for Vortex-Induced Vibrations of Top Tensioned Risers

According to the characteristics of deepwater top tensioned risers, a simplified model is presented to predict the multi-modal response of vortex-induced vibration （VIV） in non-uniform flow based on energy equilibrium theory and the exporimental data from VIV self-excited and forced oscillations of rigid cylinders. The response amplitude of each mode is determined by a balance between the energy fed into the riser over the lock-in regions and the energy dissipated by the fluid damping over the remainders. Compared with the previous prediction models, this method can take fully account of the intrinsic nature of VIV for low mass ratio structures on lock-in regions, added mass and nonlinear fluid damping effect, etc. Moreover, it is the first time to propose the accurate calculating procedure for VIV amplitude correction factor by solving energy equilibrium equation and a closed form solution is presented for the case of a riser of uniform mass and cross-section oscillating in a uniform flow. The predicted values show a reasonable agreement with VIV experiments of riser models in stepped and sheared currents.

A Novel Wake Oscillator Model for Vortex-Induced Vibrations Prediction of A Cylinder Considering the Influence of Reynolds Number

It is well known that the Reynolds number has a significant effect on the vortex-induced vibrations(VIV) of cylinders. In this paper, a novel in-line(IL) and cross-flow(CF) coupling VIV prediction model for circular cylinders has been proposed, in which the influence of the Reynolds number was comprehensively considered. The Strouhal number linked with the vortex shedding frequency was calculated through a function of the Reynolds number. The coefficient of the mean drag force was fitted as a new piecewise function of the Reynolds number, and its amplification resulted from the CF VIV was also taken into account. The oscillating drag and lift forces were modelled with classical van der Pol wake oscillators and their empirical parameters were determined based on the lock-in boundaries and the peak-amplitude formulas. A new peak-amplitude formula for the IL VIV was developed under the resonance condition with respect to the mass-damping ratio and the Reynolds number. When compared with the results from the experiments and some other prediction models, the present model could give good estimations on the vibration amplitudes and frequencies of the VIV both for elastically-mounted rigid and long flexible cylinders. The present model considering the influence of the Reynolds number could generally provide better results than that neglecting the effect of the Reynolds number.

Topological Structure of Vortex Solution in Jackiw-Pi Model

By using φ-mapping method,we discuss the topological structure of the self-duality solution in Jackiw-Pimodel in terms of gauge potential decomposition.We set up relationship between Chern-Simons vortex solution andtopological number,which is determined by Hopf index and Brouwer degree.We also give the quantization of flux inthis ease.Then,we study the angular momentum of the vortex,which can be expressed in terms of,the flux.

A Nonlinear Vortex Induced Vibration Model of Marine Risers

With the exploitation of oil and gas in deep water, the traditional vortex induced vibration (VIV) theory is challenged by the unprecedented flexibility of risers. A nonlinear time-dependent VIV model is developed in this paper based on a VIV lift force model and the Morison equation. Both the inline vibration induced by the flow due to vortex shedding and the fluid-structure interaction in the transverse direction are included in the model. One of the characteristics of the model is the response-dependent lift force with nonlinear damping, which is different from other VIV models. The calculations show that the model can well describe the VIV of deepwater risers with the results agreeing with those calculated by other models.

THE SEPARATION OF LARGE VORTEXES AND THE CLOSED EQUATIONS OF TURBULENCE MODEL

This paper presents a new kind of everage for the loeally-generated large vortexes so that the physieal quantities of the locally-generated large vortexes and the external large vortexes canberigorously separated from the equal ions for the large vortexes proposed in a previous paper[1] To the equations for the two kinds of large vortexes, some auxiliary relations are introduced, and the value, of the length-scale lN of energy dissipation of the external large vortexes may he determined according to the actual circumstances of the disturbance of external sources. Thus the resulting equations of the second moments of turbulent velocity fluctuations for the two kinds of large vortexes can be made closed. Meanwhile, the corresponding coefficients of diffusion in the previous paper[1] are improved,Finally, a closed set of numerically-solvable equations of turbulence model are obtained.

Prediction Model for Vortex-Induced Vibration of Circular Cylinder with Data of Forced Vibration

A model based on the data from forced vibration experiments is developed for predicting the vortex-induced vibra- tions （VIV） of elastically mounted circular cylinders in flow. The assumptions for free and forced vibration tests are explored briefly. Energy equilibrium is taken into account to set up the relationship between the dynamic response of selfexcited oscillations and the force coemcients from forced vibration experiments. The gap between these two cases is bridged straightforwardly with careful treatment of key parameters. Given reduced mass m^# and material damping ratio of an elastically mounted circular cylinder in flow, the response characteristics such as amplitude, frequency, lock-in range, added mass coefficient, cross-flow fluid force and the corresponding phase angle can be predicted all at once. In- stances with different combination of reduced mass and material damping ratio are compared to investigate their effects on VIV. The hysteresis phenomenon can be interpreted reasonably. The predictions and the results from recent experiments carried out by Wifliamson＇ s group are in rather good agreement.

Numerical Modelling of Coal Combustion Processes in the Vortex Furnace with Dual-Port Loading

The work is devoted to numerical simulation of pulverized-coal combustion processes in the vortex furnace which is a prospective design of a boiler unit for thermal power plants. New modification of this design characterized by additional tangential-injection nozzle located at the bottom of combustion chamber has been studied. Numerical results for the case of Siberian brown coal combustion in this vortex furnace with dual-port loading are presented, including 3-D aerodynamic structure, the fields of temperatures, radiated heat fluxes, species and dispersed phase concentrations, and NOx emissions.

基于尾流振子模型的柔性悬挂立管涡激振动分析

为了分析深海采矿柔性立管涡激振动响应特性,提出了一种高效的针对特殊边界的处理方法.基于欧拉梁模型和尾流振子模型,结合有限差分方法,系统研究不同边界条件、中间仓质量和海流剪切参数对深海采矿立管涡激振动的影响规律.结果表明:悬挂立管底部会产生较大位移,与传统两端铰接立管相比,相同激励下悬挂立管会激发出更高阶的振动模态,从原本5阶模态升至6阶;随着中间仓质量增加,立管振动的主导模态会随之降低,在同一模态下,悬挂立管底部位移逐渐减小,从0.460降至0.405,当模态转换时,底部位移均方根会迅速增大,由0.405升至0.413;底部位移随着均匀流速的增加呈现出波动趋势,在一定流速范围内,位移随流速线性变化;随着剪切参数增大,在同一模态下,立管底部的位移逐渐减小,当模态转换时,底部位移会增加.

旋涡空化水动力学特性研究进展与展望

涡空化作为一种在推进器叶顶涡心处产生的空化现象,在推进器原型上往往最早出现,其一旦发生将会严重影响舰艇的声隐身性能(噪声增加10 dB以上),在很大程度上限制了舰艇临界航速的进一步提升,因而长期以来一直是空化水动力学领域研究的重点与难点课题之一.本文首先简要介绍了旋涡空化流动相较于其他形式空化流动的特点,并以梢涡空化为主要对象,系统阐述了旋涡空化初生、发展的演变行为与流动机理研究,从空化三要素的角度深入讨论了其影响因素与作用机制.在此基础上,本文分别对旋涡空化流动中尺度效应、流动控制等关键问题的相关研究进展进行了回顾,较为系统地梳理了旋涡空化尺度效应的内在原因以及旋涡空化流动控制方法与控制思路.最后,本文针对目前旋涡空化研究领域关注的重点与难点问题,对旋涡空化流动研究中采用的实验测量及数值模拟技术进行了总结与展望.

基于POD和DMD的60°交叉管绕流分析

本文利用本征正交分解(Proper Orthogonal Decomposition,POD)和动力学模态分解(Dynamic Mode Decom⁃position,DMD)分析雷诺数Re=200时三维60°交叉管在间隙比G=4下的涡量数据,并探究尾涡的演变规律。分析结果表明:尾流场中的涡流尺度及重要程度随频率增加而减小,少数低频模态便可主导大尺度流动现象,而高频模态主要丰富尾流场中的小尺度湍流细节;上下游圆柱的涡结构以0.19 Hz的频率从两圆柱脱落,并在相同的频率下以平行形态向下游演变;上游圆柱脱落涡与下游圆柱的相互作用导致下游圆柱涡激振动明显,并产生多个高频升力频谱峰值。

基于量子衍生涡流算法和T⁃S模糊推理模型的储层岩性识别

鉴于梯度下降法易陷入局部极值、普通群智能优化算法易早熟收敛,提出一种基于量子衍生涡流算法(Quantum Vortex Search Algorithm,QVSA)和T⁃S模糊推理模型的岩性识别方法,QVSA具有操作简单、收敛速度快、寻优能力强等优点,有助于T⁃S模糊推理模型获得最优参数配置,从而实现储层岩性的准确识别。首先利用具有全局搜索能力的QVSA优化T⁃S模糊推理模型的各种参数;然后利用主成分分析方法降低获取的地震属性维度;再利用优化的T⁃S模糊推理模型识别储层岩性。实验结果表明,利用反映储层特征的8个地震属性识别储层岩性时,所提方法的识别正确率达到92%,比普通BP网络方法高5.1%,同时查准率、查全率、F1分数等指标也较BP网络方法提升明显。

基于LES方法的新型涡激振动风能采集器俘能特性分析

以所研制的涡激振动能量收集器(VIVPEHS)为研究对象,联合开源软件OpenFOAM和Matlab对大涡模拟(LES)方程、二阶范德波尔(Van der Pol’s)方程和高斯定律(Gauss’law)进行涡街振动俘能耦合计算,建立流机电耦合VIVPEHS数值模型,同时搭建并列双圆柱VIVPEHS俘能测试平台对数值模型开展实验验证。结果表明:升/阻力、压电梁位移、机电转换效率和尾流形态的预测值与实验数据符合良好。实验和计算结果表明,当圆柱直径(D)不变时,随着俘能距离(Sn)的增加,输出电压先增大后减小,在S_(n)=8D时输出电压最大;随着负载阻抗的增大,输出功率先增大后减小,存在最优负载阻抗(25000Ω),此时并列双圆柱VIVPEHS的输出功率可达72 mW,且直接点亮21只商用LED。

基于种群生存力分析的陕西铜川朱鹮再引入种群的可持续性及保护对策

种群生存力分析(population viability analysis,PVA)虽然已经在濒危物种的保护管理中得到广泛应用,但目前面临的严峻挑战是如何采用PVA分析影响濒危物种种群长期维持的内外因子。经过数十年的保护,朱鹮(Nipponia nippon)野生种群的数量已经从7只增长到约4 400只,若干再引入计划也分别在中国、日本和韩国相继实施。过去的研究表明,种群统计随机性、灾害和种群性比等因素是影响朱鹮野生种群稳定增长的主要因素,然而,对影响朱鹮再引入种群长期稳定维持的因素却知之甚少,这严重阻碍了在释放地开展具有针对性的优先保护计划。本研究在野外收集了2014—2023年铜川朱鹮再引入种群的生活史监测数据,利用基于个体的Vortex模型(Version 10.0),将朱鹮移动的适应模式与环境容纳量、死亡率、扩散、性比和灾害频率相结合,预测该种群的未来生存能力。结果发现,铜川朱鹮种群在未来100年内的存活概率为99.10%,种群规模估计值为508只,种群遗传多样性估计值为0.930 4。敏感性分析表明,种群大小和灭绝概率主要取决于环境容纳量、幼鸟死亡率和扩散存活率。因此,后续的保护措施应优先考虑如何提高与栖息地质量密切相关的环境容纳量、降低死亡率和提高扩散存活率。

密度分层介质中水下航行体绕流涡演化特性

在真实海洋环境中,海水存在密度分层。当水下航行体在密度分层界面附近航行时,其尾流会破坏初始密度分层界面,形成分层尾迹。分层尾迹是非声目标特征之一,分层尾迹探测已成为水下航行体探测的新兴技术。为建立分层环境水下航行体尾迹探测的理论基础和方法,应先探明水下航行体绕流涡系在密度分层介质中的发展演化特性。本文以缩比SUBOFF模型为研究对象,开展了实验测试和大涡模拟,得到了水下航行体绕流涡系在密度分层介质中的精细流场,大涡模拟和实验测试结果与相关文献测试结果基本吻合。研究发现:由于模型尾部分离涡存在强非定常性,尾流中盐水与淡水的掺混表现出多尺度特征;较强的孤立涡结构在掺混分层流体的过程中,逐渐演化为规则结构并脱离分层主界面,分层界面在一定宽度范围内整体呈现出离散特征。研究表明,基于密度梯度的尾迹探测手段可以对水下航行体尾流场进行有效探测。