检索结果-南通市图书馆

Effects of Navier slip on unsteady flow of a reactive variable viscosity non-Newtonian fluid through a porous saturated medium with asymmetric convective boundary conditions

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2015年第6期27卷 934-944页

作者： RUNDORA Lazarus MAKINDE Oluwole daniel Department of Mathematics and Applied Mathematics University of LimpopoTurfloop Campus faculty of Military Science Stellenbosch University

A study on the effects of Navier slip, in conjunction with other flow parameters, on unsteady flow of reactive variable viscosity third-grade fluid through a porous saturated medium with asymmetric convective boundary conditions is presented. The channel walls are assumed to be subjected to asymmetric convective heat exchange with the ambient, and exothermic chemical reactions take place within the flow system. The heat exchange with the ambient obeys Newton＇s law of cooling. The coupled equations, arising from the law of conservation of momentum and the first law of thermodynamics, then the derived system are non- dimensionalised and solved using a semi-implicit finite difference scheme. The lower wall slip parameter is observed to increase the fluid velocity profiles, whereas the upper wall slip parameter retards them because of backflow at the upper channel wall. Heat pro- duction in the fluid is seen to increase with the slip parameters. The wall shear stress increases with the slip parameters while the wall heat transfer rate is largely unaltered by the lower wall slip parameter but marginally increased by the upper wall slip parameter.

关键词： Navier slip saturated porous medium third-grade fluid temperature dependent viscosity convective boundary condi-tions

Numerical study on the use of soft material walls to enhance seismic performance of an existing tunnel

在线全文

学校读者我要写书评

暂无评论

Underground Space 2024年第2期15卷 90-112页

作者： Qiangqiang Sun Menghao Hou daniel Dias Institute of Geotechnical Engineering College of Civil Engineering and ArchitectureHebei UniversityBaoding 071002China Laboratory 3SR CNRS UMR 5521Grenoble Alpes UniversityGrenoble 38000France

Seismic risk is one of the biggest challenges for tunnel safety,and several mitigation techniques have been proposed to enhance the seismic performance of existing *** paper aims to investigate the effectiveness of an innovative approach for reducing the seismic risk of existing tunnels by using soft material walls(SMW)symmetrically installed in the surrounding *** investigation is performed with a two-dimensional numerical model and the effectiveness of SMW in mitigating the seismic-induced lining forces is quantitatively evaluated by reduction *** influences of nonlinear properties of soil,SMW and tunnel lining on the isolation effectiveness are also *** parametric studies show that the computed reduction ratio is strongly affected by the modulus ratio between the SMW and the soil,the wall geometric parameter,and the flexibility *** is more effective for the thick and soft isolation walls that are inserted near a stiff tunnel in the soft *** tunnel seismic response can be reduced by up to 50%for the scenarios ***,the parametric study identifies an optimum normalized depth of SMW and recommends a relation between the maximum isolation effect and the flexibility ***,simple charts are suggested in this work for estimating the isolation effect in specific conditions of the soil and the *** these lines,the results of this work may be used in the seismic retrofitting of an existing tunnel,aiding the preliminary design of the isolation walls.

关键词： Tunnels Earthquakes Seismic analysis Isolation walls Soft material

Achieving work hardening by forming boundaries on the nanoscale in a Ti-based metallic glass matrix composite

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Materials Science & Technology 2020年第15期47卷 192-203页

作者： Jing fan Wei Rao Junwei Qiao PKLiaw daniel Sopu daniel Kiener Jürgen Eckert Guozheng Kang Yucheng Wu College of Materials Science and Engineering Taiyuan University of TechnologyTaiyuan030024China Key Laboratory of Interface Science and Engineering in Advanced Materials Ministry of EducationTaiyuan University of TechnologyTaiyuan030024China Key Laboratory of Advanced Technologies of Materials School of Mechanics and EngineeringSouthwest Jiaotong UniversityMinistry of Education of ChinaChengdu610031China Department of Materials Science and Engineering The University of TennesseeKnoxvilleTN37996-2200USA Technische Universitat Darmstadt Institut fiir MaterialwissenschaftFachgebiet MaterialmodellierungOtto-Bemdt-Strasse 3D-64287DarmstadtGermany Erich Schmid Institute of Materials Science Austrian Academy of SciencesJahnstra'e 12A-8700LeobenAustria Department of Materials Science Montanuniversitat LeobenJahnstra'e 12A-8700LeobenAustria

Achieving work hardening in metallic glass matrix composites(MGMCs) is the key to the extensive use of these attractive materials in structural and functional *** this study,we investigated the formation of nanoscale boundaries resulted from the interaction between matrix and dendrites,which favors the work-hardening deformation in an in-situ Ti41Zr32Ni6 Ta7 Be14 MGMC with β-Ti dendrites in a glassy matrix at room *** microstructures of samples after tension were observed by highresolution transmission electron microscopy(HRTEM) and X-ray diffraction(XRD).The work-hardening mechanism of the present composites involves:(1) appearance of dense dislocation walls(DDWs),(2)proliferation of shear bands,(3) fo rmation of boundaries on the nanoscale,and(4) interactions between hard and soft phases.A theoretical model combined with experimental data reveals the deformation mechanisms in the present work,proving that the in-situ dendrites with outstanding hardening ability in the glass matrix can provide the homogeneous deformation under tensile loading at room temperature.

关键词： Metallic glass matrix composites Plastic deformation Work hardening Dense dislocation walls Nanoscale boundaries

Validation of a discrete element model using magnetic resonance measurements

在线全文

学校读者我要写书评

暂无评论

Particuology 2009年第4期7卷 297-306页

作者： Christoph R.Müller Stuart A.Scott daniel J.Holland Belinda C.Clarke Andrew J.Sederman John S.Dennis Lynn f.Gladden Department of Chemical Engineering and Biotechnology University of CambridgePembroke StreetCambridge CB2 3RAUnited Kingdom

The discrete element model （DEM） is a very promising modelling strategy for two-phase granular systems. However, owing to a lack of experimental measurements, validation of numerical simulations of two-phase granular systems is still an important issue. In this study, a small two-dimensional gas- fluidized bed was simulated using a discrete element model. The dimensions of the simulated bed were 44mm × 10mm × 120 mm and the fluidized particles had a diameter dp = 1.2 mm and density ρp = 1000 kg/m^3. The comparison between DEM simulations and experiments are performed on the basis of time-averaged voidage maps. The drag-law of Beetstra et al. [Beetstra, R., van der Hoef, M.A., ＆ Kuipers,J. A. M. （2007b）. Drag force of intermediate Reynolds number flow past mono- and bidispersed arrays of spheres. AIChE Journal, 53,489-501 ] seems to give the best results. The simulations are fairly insensitive to the coefficient of restitution and the coefficient of friction as long as some route of energy dissipation during particle-particle and particle-wall contact is provided. Changing the boundary condition of the gas phase at the side-walls from zero-slip to full-slip does not affect the simulation results. Care is to be taken that the cell sizes are chosen so that a reasonable number of particles can be found in a fluid cell.

关键词： Discrete element modelling Magnetic resonance imaging Voidage Gas-fluidized beds

Drag reducing nose fairings for existing freight train locomotives

在线全文

学校读者我要写书评

暂无评论

Advances in Aerodynamics 2022年第1期4卷 780-797页

作者： Chad L.Stucki daniel Maynes Corvid Technologies MooresvilleNC28115USA Department of Mechanical Engineering Brigham Young UniversityProvoUT84602USA

At cruising speed,one of the most significant contributing factors to train fuel consumption is aerodynamic drag,and the leading locomotive experiences much more drag than any other car in the *** work reports on the drag reduction that can be realized by the use of add-on nose fairings that are deployed on leading locomotives in a train *** types of fairing shapes were considered and all fairing walls are *** is anticipated that the fairing shapes would result from the deployment of easily stowed panels in an origami inspired *** of the fairing shapes has the appearance of a wedge and the other fairing is also wedge shaped,but with flow directing side wall *** each general fairing shape,the important dimensions were parametrically varied in a systematic manner to identify the dimensions that yield maximum drag *** the first shape,45 different scenarios were considered;for the second shape,15 were considered.A steady commercial computational fluid dynamic solver was employed to solve the flow field and locomotive drag for each of the *** best performing wedge-shaped fairing reduced the leading locomotive drag by nominally 14%and the best performing fairing shape with the side walls reduced the drag by 17%.

关键词： Drag reduction front-fairing Origami Locomotive

Assessment of thermal behaviour of thermo-active diaphragm walls based on monitoring data

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Rock Mechanics and Geotechnical Engineering 2018年第6期10卷 1145-1153页

作者： Donatella Sterpi Adriana Angelotti Omid Habibzadeh-Bigdarvish daniel Jalili Department of Civil and Environmental Engineering Politecnico di MilanoMilanoItaly Energy Department Politecnico di MilanoMilanoItaly

Thermo-active diaphragm walls have proved their effectiveness in the thermal conditioning of buildings and infrastructures. However, some aspects still need to be investigated in order to tailor methods and tools for an accurate prediction of their energy and structural performance. In this perspective, some issues are addressed that concern the definition of models for the numerical analysis, in particular issues about the modelling of geometry and thermal boundary conditions. Taking advantage of a monitoring programme on a real full-scale structure, this research focuses on the assessment of heat transfer process and thermal response of diaphragm wall and soil mass on the basis of field data. Understanding of the heat transfer process contributes to the definition of the time-dependent thermal boundary conditions at the excavation side. from the analysis of thermal gradients in the wall, the condition at the excavation side is recognised as a major factor that influences the heat transfer process, governing the direction of the heat flux in different seasons of operation of the geothermal system.

关键词： Heat transfer Monitoring data Near-surface geothermal energy Energy geostructure

Green walls as Mitigation of Urban Air Pollution:A Review of Their Effectiveness

在线全文

学校读者我要写书评

暂无评论

Research in Ecology 2023年第2期5卷 1-13页

作者： Kuok Ho daniel Tang Department of Environmental Science The University of ArizonaTucsonAZ 85721USA

Mitigation of urban air pollution has been constrained by the availability of urban spaces for *** walls offer the prospect of greening spaces and surfaces without requiring large *** walls can largely be divided into green facades where the aboveground parts of plants rooted in soil and pots grow directly on,and living walls holding bags,planter tiles,trays and vessels containing substrates in which plants are *** facades and living walls can be continuous or modular with repeating units that can be assembled for *** review aims to present the effectiveness of green walls in removing different types of air pollutants in indoor and outdoor *** examined more than 45 peer-reviewed recently published scholarly articles to achieve the *** highlights that most of the studies on green walls focus on particulate matter removal and green walls could effectively remove particulate matter though the effectiveness varies with plant types,air humidity,rainfall and its intensity,leaf area index and contact angle,green wall surface coverage ratio,as well as the height of green *** the height of green walls and optimizing their distance from roadsides could promote the deposition of particulate *** off could regenerate plant surfaces for capturing *** walls are also effective in removing NO2,O3,SO2 and *** active living walls,when properly designed,could have air purifying performance comparable to a HVAC *** performance of green walls could be optimized through polycultures,selection of plants,surface coverage and height,and air inflow.

关键词： Air pollution Green facade Leaf surface Living walls Particulate matter Outdoor

Microfluidic QCM enables ultrahigh Q-factor:a new paradigm for in-liquid gravimetric sensing

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Microsystems & Nanoengineering 2024年第4期10卷 377-389页

作者： Yicheng Zhao Zehra Parlak Wenjun Yu daniel french Wilkins Aquino Stefan Zauscher Thomas Lord Department of Mechanical Engineering and Materials Science Duke UniversityDurhamNCUSA Qatch Technologies LLC.DurhamNCUSA Department of Civil and Environmental Engineering Duke UniversityDurhamNCUSA

Acoustic gravimetric biosensors attract attention due to their simplicity,robustness,and low ***,a prevailing challenge in these sensors is dissipation which manifests in a low quality factor(Q-factor),which limits their sensitivity and *** mitigate dissipation of acoustic sensors in liquid environments we introduce an innovative approach in which we combine microfluidic channels with gravimetric *** implement this novel paradigm we chose the quartz crystal microbalance(QCM)as our model system,owing to its wide applicability in biosensing and the relevance of its operating principles to other types of acoustic *** postulate that the crucial determinant for enhancing performance lies in the ratio between the width of the microfluidic channels and the wavelength of the pressure wave generated by the oscillating channel side walls driven by the *** hypothesis is supported by finite element analysis(fEA)and dimensional studies,which revealed two key factors that affect device performance:(1)the ratio of the channel width to the pressure wavelength(W=λp)and(2)the ratio of the channel height to the shear evanescent wavelength(H=λs).To validate our hypothesis,we fabricated a microfluidic QCM(μ-QCM)and demonstrated a remarkable 10-fold improvement in its dissipation when compared to conventional *** novel microfluidic approach offers several additional advantages,such as direct data interpretation,reduced volume requirement for sample liquids,and simplified temperature control,augmenting the sensor’s overall *** fostering increased sensitivity,accuracy,and ease of operation,our novel paradigm unlocks new possibilities for advancing gravimetric technologies,potentially for biosensing applications.

关键词： QCM enable hypothesis

The Ophir Chasma Dyke Swarm: Description and Implications for the Genesis of the Valles Marineris Northern Troughs

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Acta Geologica Sinica(English Edition) 2016年第S1期90卷 180-182页

作者： daniel MèGE Joanna GURGUREWICZ Space Research Centre Polish Academy of Sciences Planetology and Geodynamics Laboratory UMR CNRS 6112 University of Nantes Institute of Geological Sciences Polish Academy of Sciences

An extensive survey of dykes in the Valles Marineris troughs(chasmata)on Mars has been *** dykes are observed along the chasma walls(Mège and Gurgurewicz,2016),in the spur-and-gully morphology that

关键词： The Ophir Chasma Dyke Swarm Description and Implications for the Genesis of the Valles Marineris Northern Troughs