Institute Of Mechanics,Chinese Academy of Sciences
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Generalized Similarity Laws for Unstart Phenomenon of Contraction Ducts in Supersonic Flow
No full textThe prediction of hypersonic inlet unstart has been a difficult aerodynamic problem over the past half century. Different from inviscid unstart theories, this study develops empirical and theoretical prediction methods for viscous flow. By proposing a corrected contraction angle and contraction ratio, a generalized similarity law for unstart boundary is established and validated by sufficient numerical and experimental results, describing the effects of aerodynamic and geometric parameters simultaneously. To explain the physical implications of the generalized unstart similarity law, two-dimensional flow-based theoretical models are established for three unstart modes using oblique shock relations, free interaction theory, and scaling laws for separation length. For the short-cowl and long-cowl modes, the self-similarity of the unstart boundary is attributed to the separation scale relative to the effective throat height and the mass-averaged throat Mach number accompanied by shock reflections, respectively. The transitional unstart is triggered by the decrease of the shock-impingement distance relative to the separation scale, and the self-similarity is broken by the wedge length independence and Reynolds number dependence. Moreover, to facilitate unstart detection in wind tunnel or flight tests, the corrected dimensionless pressure rise is proposed, correlating the critical wall pressure characteristics with the incident shock pressure rise and dimensionless wedge length
Intracellular pressure: Regulation, characterization and implication
No full textIntracellular pressure is one of the most fundamental mechanical factors, influencing cellular homeostasis and functions. Gaining insight into the intracellular pressure is essential for understanding fundamental cellular processes and developing therapeutic strategies. In this review, we provide an overview of the intracellular pressure, focusing on three key aspects including its regulation, characterization, as well as biological implications. We summarize representative experimental and modeling methods, highlighting their principles, strengths, and weaknesses. Meanwhile, we discuss how the intracellular pressure is generated and how it shapes the biological processes, particularly exemplified by cell division and migration. We highlight the necessity and significance of developing non-invasive and precise techniques and methods to characterize in vivo intracellular pressure under different circumstances. More light should be shed on intranuclear pressure and nuclear response to the intracellular pressure dynamics. In addition, further efforts should also be directed toward exploring the intrinsic relationship between intracellular pressure and other cellular activities
Self-consistent model for active control of wind turbine wakes
No full textActive wake control (AWC) has emerged as a promising strategy for enhancing wind turbine wake recovery, but accurately modelling its underlying fluid mechanisms remains challenging. This study presents a computationally efficient wake model that provides end-to-end prediction capability from rotor actuation to wake recovery enhancement by capturing the coupled dynamics of wake meandering and mean flow modification, requiring only two inputs: a reference wake without control and a user-defined AWC strategy. The model combines physics-based resolvent modelling for large-scale coherent structures and an eddy viscosity modelling for small-scale turbulence. A Reynolds stress model is introduced to account for the influence of both coherent and incoherent wake fluctuations, so that the time-averaged wake recovery enhanced by the AWC can be quantitatively predicted. Validation against large-eddy simulations (LES) across various AWC approaches and actuating frequencies demonstrates the model's predictive capability, accurately capturing AWC-specific and frequency-dependent mean wake recovery with less than 8 % error from LES while reducing computational time from thousands of central-processing-unit hours to minutes. The efficiency and accuracy of the model makes it a promising tool for practical AWC design and optimization of large-scale wind farms
Distribution of Flow Characteristics and Productivity Evaluation of Herringbone Wells in Bottom-Water Reservoirs
No full textWith the characteristics of large drainage area and low drilling cost, the herringbone wells are becoming a significant way to boost the well production, improve the dynamic flow profile, delay the coning of bottom water, and enhance the development effect. Due to the complex flow characteristics of herringbone wells, result in a disparity between expected and actual production, therefore, it is crucial to investigate the productivity and flow characteristics of herringbone wells. In this paper, taking into account the interference between branch wellbores and perforations, the herringbone wells productivity model in bottom-water reservoirs is derived, the flow characteristics and the productivity sensitivity factors are analyzed. The results indicate that the transient flow time in reservoir is brief and that pressure changes increase with proximity to the wellbore, the productivity declines as the production time increases and subsequently tends to a certain value, reaching a quasi-steady-state. The per unit length radial inflow of wellbore decreases as the branch length, branch angle, and the number of branches increase, however, the rate of decrease slows down when exceeding three branches. The phase angle has a larger effect on production in high anisotropy reservoirs, and the production is the highest at 180 deg phase angle. When the perforation density rises above 16 shots/m, the production increasing trend slows down. This study provides significant guidance for practical application in the oil fields, including optimizing the shape of herringbone wells, allocating production in a rational manner, defining appropriate work systems, and improving oil recovery in bottom-water reservoirs
Physics-informed neural network approach to randomly rough surface contact mechanics
No full textIn this study, we employed the Green's function molecular dynamics (GFMD) to simulate the non-adhesive contact between an elastic half-space and a rough counter face in (1+1)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}\end{document} dimensions, obtaining the contact stress distribution under varying length scales and Hurst exponents. Subsequently, based on the dataset generated by GFMD and adopting the diffusion equation form from Persson's theory, we obtained the stress distribution as well as the relative contact area using Physics-informed neural network (PINN). The results demonstrate that in full contact case, the diffusion equation coefficient aligns almost perfectly with Persson's theoretical prediction. In cases of partial contact, assuming the diffusion coefficient follows a power-law function of the length scale, the stress distribution predicted by PINN exhibits an error of less than 0.5%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}\end{document} compared to GFMD. Furthermore, we verified that PINN can predict contact stress distribution and relative contact area at larger scales based on small-scale data, with predictions closely matching GFMD results
Atomistic mechanisms of dynamics in a two-dimensional dodecagonal quasicrystal
No full textQuasicrystals have been observed in a variety of materials ranging from metal alloys to block copolymers. However, their structural and dynamical properties cannot be readily described in terms of conventional solid-state models of liquids and solids. We may expect the dynamics of this specific class of quasicrystalline materials to be more like glass-forming liquids in the sense of exhibiting large fluctuations in the local mobility ("dynamic heterogeneity") and non-Arrhenius temperature dependence of relaxation and diffusion. In this work, we investigate a model dodecagonal quasicrystal material in two dimensions (2D) using molecular dynamics simulations, with a focus on heterogeneous dynamics and non-Arrhenius relaxation and diffusion. As observed in glass-forming liquids and heated crystals, we observe a two-stage relaxation dynamics in the self-intermediate scattering function F-s(k, t) of our quasicrystal material. It involves a fast beta-relaxation and alpha-relaxation process having a highly temperature dependent relaxation time whose activation energy varies in concert with the extent of string-like collective motion, a phenomenon recognized to occur in glass-forming liquids at low temperatures and crystalline materials at elevated temperatures. After examining the dynamics of our dodecagonal quasicrystalline material in great detail, we conclude that the dynamics of these materials more closely resembles observations on metallic glass-forming liquids than crystalline materials
An Investigation of the Flashing Process of Liquid Xenon in a Refueling Pipe
No full textTo investigate the phenomenon of liquid xenon flashing in a filling pipeline, the two-phase flow in a pipe is calculated and analyzed by using a one-dimensional homogeneous equilibrium model (HEM) and a two-dimensional mixture model. The distribution of xenon two-phase flow parameters along the pipeline is observed by the numerical solution of a one-dimensional HEM and simulation by Fluent. The comparison and analysis of the results of different models show that the one-dimensional HEM can quickly attach the critical mass flux faster than Fluent's simulation under the given filling conditions, which verifies the rationality and rapidity of the numerical solution in calculating the flash process. The influence of the diameter and length of the pipeline on the flashing process of liquid xenon is analyzed by a one-dimensional theoretical model. The results show that the geometric parameters of the pipeline have a great impact on the mass flow rate and the position of the initial phase transition point, but have little effect on the void fraction at the outlet. An increase in pipe diameter and pipeline length delays the onset of phase transition. Compared with liquid oxygen and liquid nitrogen, liquid xenon is more likely to undergo a phase transition. The phase change kinetics of oxygen and nitrogen are roughly 70% as fast as those of xenon
基于MEMS和光学同步测量的壳状IMU及其使用方法
No full text本发明提供了基于MEMS和光学同步测量的壳状IMU及其使用方法， 所述壳状IMU包括MEMS芯片、电池包和外部壳体， 所述MEMS芯片和所述电池包相连接固定在所述外部壳体内；所述外部壳体的外表面染有黑白颜色相间的布尔图像， 使得所述壳状IMU适用于MEMS和光学同步测量， 通过得到的光学测量数据和电子测量数据相互校准以标定。本发明还提供了基于MEMS和光学同步测量的壳状IMU的使用方法， 可分别通过MEMS芯片和染色外壳获得电子测量和光学测量两套数据， 保持两种测量方式同步进行， 能够相互校准， 避免IMU数据偏离， 可用于动态性大的测试场景
一种增黏箱
No full text本实用新型提供了一种增黏箱。一种增黏箱包括：外壳， 外壳具有圆柱面和平面， 圆柱面朝向车轮的踏面设置， 且圆柱面的圆心与车轮同心， 平面朝向钢轨的轨顶设置， 且平面与钢轨平行设置， 圆柱面上设有一个激光出口， 以及设有位于激光出口两侧的一号气流出口和二号气流出口；一号出口通过一号管路与一号气流出口相连的喷嘴的入口密封连接， 二号出口通过二号管路与二号气流出口相连的喷嘴的入口密封连接。本实用新型提供的一种增黏箱解决了现有的解决方案存在长期撒砂造成砂子堆积、道床板结， 需要定期清理， 运维成本高， 作业效率低， 以及砂子的成本大幅提高的缺陷
低重力池沸腾双气泡相互作用数值模拟
No full text核态池沸腾现象中气泡动力学行为与其传热性能间具有密切关联，一直是多相流和传热传质领域的研究热点。基于OpenFOAM开源代码开发了微重力沸腾过程流固耦合传热求解器μg BCHT，以实现流固共轭传热求解、气液宏观区与微观区相变传热与流动耦合求解、气泡核化点随机与定位活化等功能。针对一维Stefan问题和一维Sucking问题进行的仿真结果与解析解相符合，验证了求解器预测能力。利用该求解器对0.1g低重力条件下FC-72双气泡核态池沸腾过程进行了三维数值模拟研究，揭示了低重力条件下气泡生长过程特点及其间相互作用机制，提供了理解低热流密度核态池沸腾传热机理的细观尺度物理图景