Effect of Viscosity on Free-Surface Waves in Oseen Flows

Based on the complex dispersion relation for the two-dimensional free-surface waves generated by a moving body in the steady Oseen flows, the effect of viscosity on wavelength and wave amplitude was investigated by means of an asymptotic method and a numerical analysis. A comparison between the asymptotic and numerical analysis for the viscous decay factor demonstrates the validity of the perturbation expansions for the wave profile. The numerical result shows that the wavelength of viscous wave is slightly elongated in comparison with that of inviscid wave.

Flow Regimes in Bubble Columns with and without Internals: A Review

Hydrodynamics characterization in terms offlow regime behavior is a crucial task to enhance the design of bubble column reactors and scaling up related methodologies.This review presents recent studies on the typicalflow regimes established in bubble columns.Some effort is also provided to introduce relevant definitions pertaining to thisfield,namely,that of“void fraction”and related(local,chordal,cross-sectional and volumetric)variants.Experimental studies involving different parameters that affect design and operating conditions are also discussed in detail.In the second part of the review,the attention is shifted to cases with internals of various types(perfo-rated plates,baffles,vibrating helical springs,mixers,and heat exchanger tubes)immersed in the bubble columns.It is shown that the presence of these elements has a limited influence on the global column hydrodynamics.However,they can make the homogeneousflow regime more stable in terms of transition gas velocity and transi-tion holdup value.The last section is used to highlight gaps which have not beenfilled yet and future directions of investigation.

Reversible solid-liquid conversion enabled by self-capture effect for stable non-flow zinc-bromine batteries

Non-flow aqueous zinc-bromine batteries without auxiliary components(e.g.,pumps,pipes,storage tanks)and ion-selective membranes represent a cost-effective and promising technology for large-scale energy storage.Unfortunately,they generally suffer from serious diffusion and shuttle of polybromide(Br^(-),Br^(3-))due to the weak physical adsorption between soluble polybromide and host carbon materials,which results in low energy efficiency and poor cycling stability.Here,we develop a novel self-capture organic bromine material(1,10-bis[3-(trimethylammonio)propyl]-4,4'-bipyridinium bromine,NVBr4)to successfully realize reversible solid complexation of bromide components for stable non-flow zinc-bromine battery applications.The quaternary ammonium groups(NV^(4+)ions)can effectively capture the soluble polybromide species based on strong chemical interaction and realize reversible solid complexation confined within the porous electrodes,which transforms the conventional“liquid-liquid”conversion of soluble bromide components into“liquid-solid”model and effectively suppresses the shuttle effect.Thereby,the developed non-flow zinc-bromide battery provides an outstanding voltage platform at 1.7 V with a notable specific capacity of 325 mAh g^(-1)NVBr4(1 A g^(-1)),excellent rate capability(200 mAh g^(-1)NVBr4 at 20 A g^(-1)),outstanding energy density of 469.6 Wh kg^(-1)and super-stable cycle life(20,000 cycles with 100%Coulombic efficiency),which outperforms most of reported zinc-halogen batteries.Further mechanism analysis and DFT calculations demonstrate that the chemical interaction of quaternary ammonium groups and bromide species is the main reason for suppressing the shuttle effect.The developed strategy can be extended to other halogen batteries to obtain stable charge storage.

基于VRB/OW-GFRP混合结构的CTB电池包上盖总成轻量化设计研究

电池车身一体化(CTB)是提升电动汽车续航里程的关键技术。利用胶接工艺将变厚度(VRB)结构与正交编织玻璃纤维增强复合材料(OW-GFRP)粘接形成的VRB/OW-GFRP混合结构,是降低CTB电池包质量的创新结构,有助于进一步提升电动汽车的续航里程。以某款电动汽车为研究对象,设计了一种CTB电池车身一体化结构,实现了电池包上盖与车身地板的集成融合。分别采用VRB结构、UT/OW-GFRP及VRB/OW-GFRP混合结构替代等厚度(UT)CTB电池包上盖总成,并基于多阶段优化方法开展了3种类型CTB电池包上盖总成的轻量化设计。结果表明,在满足CTB电池包刚度性能前提下,VRB结构相比UT结构实现减质量6.4%;基于VRB/OW-GFRP混合结构的CTB电池包上盖总成轻量化效果约为金属结构的3倍,VRB/OW-GFRP相比UT/OW-GFRP混合电池包上盖总成进一步减质量4.2%。由此可见,VRB/OW-GFRP混合结构是未来汽车轻量化技术发展的重要趋势,在CTB电池包上盖总成中具有巨大的应用前景。

Helically symmetric equilibria for some ideal and resistive MHD plasmas with incompressible flows

In this paper, the problem of finding exact solutions to the magnetohydrodynamic(MHD) equations in the presence of incompressible mass flows with helical symmetry is considered. For ideal flows, a similarity reduction method is used to obtain exact solutions for several MHD flows with nonlinear variable Mach number. For resistive flows parallel to a magnetic field, the governing equilibrium equation is derived. The MHD equilibrium state of a helically symmetric incompressible flow is governed by a second-order elliptic partial differential equation(PDE) for the helical magnetic flux function. Exact solutions for the latter equation are obtained. Also, the equilibrium equations of a gravitating plasma with incompressible flow are derived.

A dual-RPA based lateral flow strip for sensitive,on-site detection of CP4-EPSPS and Cry1Ab/Ac genes in genetically modified crops

Traditional transgenic detection methods require high test conditions and struggle to be both sensitive and efficient.In this study,a one-tube dual recombinase polymerase amplification(RPA)reaction system for CP4-EPSPS and Cry1Ab/Ac was proposed and combined with a lateral flow immunochromatographic assay,named“Dual-RPA-LFD”,to visualize the dual detection of genetically modified(GM)crops.In which,the herbicide tolerance gene CP4-EPSPS and the insect resistance gene Cry1Ab/Ac were selected as targets taking into account the current status of the most widespread application of insect resistance and herbicide tolerance traits and their stacked traits.Gradient diluted plasmids,transgenic standards,and actual samples were used as templates to conduct sensitivity,specificity,and practicality assays,respectively.The constructed method achieved the visual detection of plasmid at levels as low as 100 copies,demonstrating its high sensitivity.In addition,good applicability to transgenic samples was observed,with no cross-interference between two test lines and no influence from other genes.In conclusion,this strategy achieved the expected purpose of simultaneous detection of the two popular targets in GM crops within 20 min at 37°C in a rapid,equipmentfree field manner,providing a new alternative for rapid screening for transgenic assays in the field.

Failure Prediction for Scientific Workflows Using Nature-Inspired Machine Learning Approach

Scientific workflows have gained the emerging attention in sophisti-cated large-scale scientific problem-solving environments.The pay-per-use model of cloud,its scalability and dynamic deployment enables it suited for executing scientific workflow applications.Since the cloud is not a utopian environment,failures are inevitable that may result in experiencingfluctuations in the delivered performance.Though a single task failure occurs in workflow based applications,due to its task dependency nature,the reliability of the overall system will be affected drastically.Hence rather than reactive fault-tolerant approaches,proactive measures are vital in scientific workflows.This work puts forth an attempt to con-centrate on the exploration issue of structuring a nature inspired metaheuristics-Intelligent Water Drops Algorithm(IWDA)combined with an efficient machine learning approach-Support Vector Regression(SVR)for task failure prognostica-tion which facilitates proactive fault-tolerance in the scheduling of scientific workflow applications.The failure prediction models in this study have been implemented through SVR-based machine learning approaches and the precision accuracy of prediction is optimized by IWDA and several performance metrics were evaluated on various benchmark workflows.The experimental results prove that the proposed proactive fault-tolerant approach performs better compared with the other existing techniques.

Double-Doped Carbon-Based Electrodes with Nitrogen and Oxygen to Boost the Areal Capacity of Zinc-Bromine Flow Batteries

Ensuring a stable power output from renewable energy sources,such as wind and solar energy,depends on the development of large-scale and long-duration energy storage devices.Zinc–bromine fl ow batteries(ZBFBs)have emerged as cost-eff ective and high-energy-density solutions,replacing expensive all-vanadium fl ow batteries.However,uneven Zn deposition during charging results in the formation of problematic Zn dendrites,leading to mass transport polarization and self-discharge.Stable Zn plating and stripping are essential for the successful operation of high-areal-capacity ZBFBs.In this study,we successfully synthesized nitrogen and oxygen co-doped functional carbon felt(NOCF4)electrode through the oxidative polymerization of dopamine,followed by calcination under ambient conditions.The NOCF4 electrode eff ectively facilitates effi cient“shuttle deposition”of Zn during charging,signifi cantly enhancing the areal capacity of the electrode.Remarkably,ZBFBs utilizing NOCF4 as the anode material exhibited stable cycling performance for 40 cycles(approximately 240 h)at an areal capacity of 60 mA h/cm^(2).Even at a high areal capacity of 130 mA h/cm^(2),an impressive energy effi ciency of 76.98%was achieved.These fi ndings provide a promising pathway for the development of high-areal-capacity ZBFBs for advanced energy storage systems.

Analysis of Snow Distribution and Displacement in the Bogie Region of a High-Speed Train

Snow interacting with a high-speed train can cause the formation of ice in the train bogie region and affect its safety.In this study,a wind-snow multiphase numerical approach is introduced for high-speed train bogies on the basis of the Euler-Lagrange discrete phase model.A particle-wall impact criterion is implemented to account for the presence of snow particles on the surface.Subsequently,numerical simulations are conducted,considering various snow particle diameter distributions and densities.The research results indicate that when the particle diameter is relatively small,the distribution of snow particles in the bogie cavity is relatively uniform.However,as the particle diameter increases,the snow particles in the bogie cavity are mainly located in the rear wheel pairs of the bogie.When the more realistic Rosin-Rammler diameter distribution is applied to snow particles,the positions of snow particles with different diameters vary in the bogie cavity.More precisely,smaller diameter particles are primarily located in the front and upper parts of the bogie cavity,while larger diameter snow particles accumulate at the rear and in the lower parts of the bogie cavity.

Pairing nitroxyl radical and phenazine with electron-withdrawing/-donating substituents in “water-in-ionic liquid” for high-voltage aqueous redox flow batteries

Aqueous redox-active organic materials-base electrolytes are sustainable alternatives to vanadium-based electrolyte for redoxflow batteries(RFBs)due to the advantages of high ionic conductivity,environmentally benign,safety and low cost.However,the underexplored redox properties of organic materials and the narrow thermodynamic electrolysis window of water(1.23 V)hinder their wide applications.Therefore,seeking suitable organic redox couples and aqueous electrolytes with a high output voltage is highly suggested for advancing the aqueous organic RFBs.In this work,the functionalized phenazine and nitroxyl radical with electron-donating and electron-withdrawing group exhibit redox potential of-0.88 V and 0.78 V vs.Ag,respectively,in“water-in-ionic liquid”supporting electrolytes.Raman spectra reveal that the activity of water is largely suppressed in“water-in-ionic liquid”due to the enhanced hydrogen bond interactions between ionic liquid and water,enabling an electrochemical stability window above 3 V.“Water-in-ionic liquid”supporting electrolytes help to shift redox potential of nitroxyl radical and enable the redox activity of functionalized phenazine.The assembled aqueous RFB allows a theoretical cell voltage of 1.66 V and shows a practical discharge voltage of 1.5 V in the“water-in-ionic liquid”electrolytes.Meanwhile,capacity retention of 99.91%per cycle is achieved over 500 charge/discharge cycles.A power density of 112 mW cm^(-2) is obtained at a current density of 30 mA cm^(-2).This work highlights the importance of rationally combining supporting electrolytes and organic molecules to achieve high-voltage aqueous RFBs.

Numerical Simulation and Optimization of the Gas-Solid Coupled Flow Field and Discharging Performance of Straw Crushers

The quality of crushing,power consumption,and discharging performance of a straw crusher are greatly influenced by the characteristics of its internalflowfield.To enhance the straw crusher’sflowfield properties and improve the efficiency with which crushed material is discharged,first,the main structural parameters influencing the airflow in the crusher are discussed.Then,the coupled gas-solidflowfield in the straw crusher is numerically calculated through solution of the Navier-Stokes equations and application of the discrete element method(DEM).Finally,the discharge performance index of the crusher is examined through detailed analysis of the crushed material dynamics.Additionally,a multi-island genetic algorithm is used to optimize the structure and operational factors that have significant effects on the discharge performance.With optimization,the accumulation rate of crushed materials in the bottom region of the straw crusher decreases by 20.08%,and the massflow rate at the discharge outlet increases by 11.63%.

Impact of the Inlet Flow Angle and Outlet Placement on the Indoor Air Quality

This study aims to optimize the influence of the inlet inclination angle on the Indoor Air Quality(IAQ),heat,and temperature distribution in mixed convection within a two-dimensional square cavityfilled with an air-CO_(2)mixture.The air-CO_(2)mixture enters the cavity through two inlet openings positioned at the top wall,which is set at the ambient temperature(TC).Three values of the Reynolds numbers,ranging from 1000 to 2000,are considered,while the Prandtl number is kept constant(Pr=0.71).The temperature distribution and streamlines are shown for Rayleigh number(Ra)equal to 104,three inlet inclination anglesϕ(0,π/6 andπ/4)and three CO_(2)concentrations values(1500,2500,3500 ppm)applied at both hot vertical walls(maintained at a constant temperature TH).Afinite volume method is used under the assumption of two-dimensional laminarflow to solve the NavierStokes and energy equations.The results indicate that inlet inclination angle has an impact on the indoor air quality(IAQ),which,in turn,affects the heat transfer distribution and thermal comfort within the cavity.

Simulation of Two-Phase Flowback Phenomena in Shale Gas Wells

The gas-water two-phaseflow occurring as a result of fracturingfluidflowback phenomena is known to impact significantly the productivity of shale gas well.In this work,this two-phaseflow has been simulated in the framework of a hybrid approach partially relying on the embedded discrete fracture model(EDFM).This model assumes the region outside the stimulated reservoir volume(SRV)as a single-medium while the SRV region itself is described using a double-medium strategy which can account for thefluid exchange between the matrix and the micro-fractures.The shale gas adsorption,desorption,diffusion,gas slippage effect,fracture stress sensitivity,and capillary imbibition have been considered.The shale gas production,pore pressure distribution and water saturation distribution in the reservoir have been simulated.The influences of hydraulic fracture geometry and nonorthogonal hydraulic fractures on gas production have been determined and discussed accordingly.The simulation results show that the daily gas production has an upward and downward trend due to the presence of a large amount of fracturingfluid in the reservoir around the hydraulic fracture.The smaller the angle between the hydraulic fracture and the wellbore,the faster the daily production of shale gas wells decreases,and the lower the cumulative production.Nonplanar fractures can increase the control volume of hydraulic fractures and improve the production of shale gas wells.

Dissipative free-surface solver for potential flow around hydrofoil distributed with doublets

A doublet integral equation is formulated for the two-dimensional dissipative potential flow around a hydrofoil submerged below a free-water surface. The free-water surface is assumed to involve energy dissipation, and thus it is the source of damping. A doublet panel method is developed from incorporation of the dissipative Green function approach and the doublet distributions on the hydrofoil surface. Numerical computations are implemented, and the derived numerical results are in good agreement with analytic solutions and experimental measurements.

直播信息特性和产品感知对冲动购买的影响研究——基于Howard-Sheth模型

基于Howard-Sheth模型,本文从外部信息和感知刺激角度实证探索社交电商直播信息特征和产品感知价值对冲动购买意愿的影响机制,采取便利性抽样收集245份有效问卷,运用AMOS-结构方程模型对效应路径进行实证检验。结果表明:社交电商直播信息交互性、产品感知享乐价值和感知实用价值对心流体验有显著的促进作用,心流体验进一步影响消费者冲动购买意愿;信息时效性对心流体验的影响不显著。基于此,文章通过将Howard-Sheth模型拓展到社交电商直播场景中,并为社交电商提出几点营销思考进而为电子商务行业理解社交电商消费者行为提供了新视角。

基于Web搜索搭建OWS索引服务中心

OWS(OGC Web Service)为空间数据共享提供了可行的方法,但如何在浩瀚的互联网上快速、准确地查询到符合用户需要的OWS是一件比较困难的事情。在对Web搜索方法进行深入理解的基础上,提出一种基于全文检索搜索引擎搭建OWS索引服务的思路,并采用Google实现了OWS索引服务中心的原型系统,该系统可以为互联网用户提供OWS搜索服务。

OWS性能监测评价方法研究及其原型系统实现——以OGC WMS为例

针对互联网上所共享发布的开放地理空间联盟网络服务(OWS)经常会出现不能访问或运行速度缓慢而导致难以利用的问题,为测试和评价这些地理信息服务的可用性和性能,通过研究OWS服务的固有特点,提出了实时监测OWS状态的动态规划模型和基于评价因子、评价权重等参数的评价模型,用以实现对OWS的监测与评价;基于上述模型与因子,设计开发了面向OWS的实时监测和性能评价原型系统,并以OGC网络地图服务(WMS)为例对模型与原型系统进行了实验验证。结果表明:该系统能够对相应的OWS进行实时监测与评价,所提的监测与评价方法与模型可为用户在众多的服务资源中获取其所感兴趣的数据提供参考信息,为地理信息服务使用者查找更优的服务资源提供帮助。

基于OWS标准空间数据服务的数据源模式提取接口设计与实现

要在Web环境下实现不同分布式节点间的空间数据集成应用是一个难度相当大的问题。网格技术的出现为实现基于空间数据服务的分布式空间数据集成提供了有效的技术手段。本文基于OGC标准的空间数据网格服务的实现方法,主要研究了空间数据网格服务的数据源模式构建方法。最后以实例验证了该方法的技术可行性。

AJAX和OWS在GIS中的应用研究

随着网络技术的不断成熟,许多新技术成功地运用到GIS系统的客户端数据展现当中,而最引人注目的技术就是A-JAX;另一方面,开放地理信息系统联盟(OGC)开发了一系列基于Web服务技术的地理空间数据互操作协议OGC Web Services(OWS),其中的Web Map Services(WMS)已经广泛地应用于GIS领域。本文首先对于AJAX技术和OWS规范进行基础性的阐述,之后将详细介绍一个结合AJAX技术和OWS规范构造的GIS系统—ACT-GIS。

Numerical and Experimental Investigation of Interactions Between Free-Surface Waves and A Floating Breakwater with Cylindrical-Dual/Rectangular-Single Pontoon

This paper investigates the hydrodynamic performance of a cylindrical-dual or rectangular-single pontoon floating breakwater using the numerical method and experimental study. The numerical simulation work is based on the multi-physics computational fluid dynamics(CFD) code and an innovative full-structured dynamic grid method applied to update the three-degree-of-freedom(3-DOF) rigid structure motions. As a time-marching scheme, the trapezoid analogue integral method is used to update the time integration combined with remeshing at each time step.The application of full-structured mesh elements can prevent grids distortion or deformation caused by large-scale movement and improve the stability of calculation. In movable regions, each moving zone is specified with particular motion modes(sway, heave and roll). A series of experimental studies are carried out to validate the performance of the floating body and verify the accuracy of the proposed numerical model. The results are systematically assessed in terms of wave coefficients, mooring line forces, velocity streamlines and the 3-DOF motions of the floating breakwater. When compared with the wave coefficient solutions, excellent agreements are achieved between the computed and experimental data, except in the vicinity of resonant frequency. The velocity streamlines and wave profile movement in the fluid field can also be reproduced using this numerical model.