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Secondary flows in statistically unstable turbulent boundary layers with spanwise heterogeneous roughness

Theoretical & Applied Mechanics Letters 2022年第2期12卷 65-71页

作者： Ali Amarloo Pourya Forooghi mahdi abkar Department of Mechanical and Production Engineering Aarhus UniversityAarhus C8000Denmark

Large-scale secondary motions are known to occur in turbulent flows over surfaces with spanwise roughness heterogeneity.Numerical studies often use adjacent high-and low-roughness longitudinal strips to investigate these secondary rolls in boundary layers without any thermal stratification.In the present study,the effect of unstable thermal stratification on secondary rolls in a very high-Reynolds-number turbulent flow with spanwise-heterogeneous roughness is investigated by means of large-eddy simulation.The strength of the unstable stratification is systematically changed from L/h=−20 to L/h=−1,where L and h are Monin-Obukhov length and boundary-layer height,respectively.This range covers the transition from neutral stratification to unstable stratification.The results show that the positive buoyancy associated with the unstable thermal stratification acts against the roughness-induced secondary rolls.In the case of unstable stratification,secondary rolls are completely canceled out by buoyancy and replaced by new stronger convection-induced rolls rotating in opposite directions.

关键词： Secondary flows Roughness heterogeneity Unstable/convective boundary layer Large-eddy simulation

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Reinforcement learning for wind-farm flow control:Current state and future actions

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Theoretical & Applied Mechanics Letters 2023年第6期13卷 455-464页

作者： mahdi abkar Navid Zehtabiyan-Rezaie Alexandros Iosifidis Department of Mechanical and Production Engineering Aarhus UniversityAarhus N8200Denmark Department of Electrical and Computer Engineering Aarhus UniversityAarhus N8200Denmark Centre for Digitalization Big Dataand Data AnalyticsAarhus UniversityAarhus N8200Denmark

Wind-farm flow control stands at the forefront of grand challenges in wind-energy science.The central issue is that current algorithms are based on simplified models and,thus,fall short of capturing the complex physics of wind farms associated with the high-dimensional nature of turbulence and multiscale wind-farm-atmosphere interactions.Reinforcement learning(RL),as a subset of machine learning,has demonstrated its effectiveness in solving high-dimensional problems in various domains,and the studies performed in the last decade prove that it can be exploited in the development of the next generation of algorithms for wind-farm flow control.This review has two main objectives.Firstly,it aims to provide an up-to-date overview of works focusing on the development of wind-farm flow control schemes utilizing RL methods.By examining the latest research in this area,the review seeks to offer a comprehensive understanding of the advancements made in wind-farm flow control through the application of RL techniques.Secondly,it aims to shed light on the obstacles that researchers face when implementing wind-farm flow control based on RL.By highlighting these challenges,the review aims to identify areas requiring further exploration and potential opportunities for future research.

关键词： Wind-farm flow control Turbine wakes Power losses Reinforcement learning Machine learning

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MEAN APPROXIMATION BY DILATATIONS IN BERGMAN SPACES ON THE UPPER HALF-PLANE

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数学物理学报:B辑英文版 2023年第5期43卷 2204-2214页

作者： Ali abkar Department of Pure Mathematics Faculty of ScienceImam Khomeini International UniversityQazvin 34149Iran

We study sufficient conditions on radial and non-radial weight functions on the upper half-plane that guarantee norm approximation of functions in weighted Bergman,weighted Dirichlet,and weighted Besov spaces on the u... 详细信息

关键词： mean approximation dilatation non-radial weight angular weight weighted Bergman space weighted Besov space

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高原低氧对DSS诱导小鼠溃疡性结肠炎免疫功能的影响

高原低氧对DSS诱导小鼠溃疡性结肠炎免疫功能的影响

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作者： Mohammed Salem Yahya abkar Gamah 青海大学

学位级别：硕士

目的:本实验研究高原低氧对硫酸右旋糖酐钠（DSS）诱导的溃疡性结肠炎小鼠免疫功能的影响。方法:40只Balb/c小鼠随机分为四组,分别为:常氧对照组、DSS诱导产生溃疡性结肠炎的常氧DSS组、低氧对照组和低氧DSS组,常氧组饲养于西宁（海拔22... 详细信息

目的:本实验研究高原低氧对硫酸右旋糖酐钠（DSS）诱导的溃疡性结肠炎小鼠免疫功能的影响。方法:40只Balb/c小鼠随机分为四组,分别为:常氧对照组、DSS诱导产生溃疡性结肠炎的常氧DSS组、低氧对照组和低氧DSS组,常氧组饲养于西宁（海拔2260 m,大气压582 mm Hg）;低氧组饲养于模拟海拔5000 m的实验动物低压舱中,低氧处理7天。通过流式细胞术、ELISA和RT-PCR分别检测IL-4、IL-10、1L-17、TNF-α和INF-γ的含量及表达水平;结肠组织H.E.染色后观察其形态和病理变化。结果:成功建立了低压低氧条件下的溃疡性结肠炎小鼠模型。实验结果表明,小鼠暴露于低压低氧条件下时,其溃疡性结肠炎的表现明显加重,包括体重减轻、结肠长度缩短、同时伴随着血便和腹泻。低氧DSS组的小鼠脾脏和肠系膜淋巴结中炎症因子TNF-α、IFN-γ、IL-17和IL-10的浓度显著高于常氧对照组,并且结肠中上述细胞因子m RNA的表达量也明显高于对照组。此外,结肠组织髓过氧化物酶活性显着增加,组织病理学分析表明,与常氧对照组相比低氧增强了DSS诱导的小鼠溃疡性结肠炎的严重程度。结论:高海拔低氧会通过扩大炎症细胞浸润和活化中性粒细胞加重溃疡性结肠炎。

关键词：高原缺氧溃疡性结肠炎细胞因子 Th细胞硫酸右旋糖酐钠

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Stability Analysis and Hopf Bifurcation for ODE System of Predator-Prey Model with Mutual Interference

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Applied Mathematics 2021年第9期12卷 793-802页

作者： Khalid Ahmed Abbakar Yafei Yang Alhussein Mohamed Songchen Xia Mogahid Mamoon abkar Omer Bushra Elfadil Hassan College of Mathematics and Statistics Northwest Normal University Lanzhou China Department of Mathematics and Physics Faculty of Education University of Gadarif Gadarif Sudan School of Mathematics and Statistics Northeast Normal University Changchun China Department of Mathematics School of Mathematics University of Witwatersrand Johannesburg South Africa

In this paper, the temporal and spatial patterns of a diffusive predator-prey model with mutual interference under homogeneous Neumann boundary conditions were studied. Specifically, first, taking the intrinsic growth rate of the predator as the parameter, we give a computational and theoretical analysis of Hopf bifurcation on the positive equilibrium for the ODE system. As well, we have discussed the conditions for determining the bifurcation direction and the stability of the bifurcating periodic solutions.

关键词： Predator-Prey Model Mutual Interference Hopf Bifurcation Functional Response

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