oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Tidally induced cross – shore sand – mud transport and long-term bed-profile evolution  [PDF]
Mohammad Fadhli AHMAD a, Ping DONG b
Journal of Sustainability Science and Management , 2009,
Abstract: A one-dimensional numerical model based on the shallow-water equations, suspended-sediment transport formulae and bed-material conservation equation was developed in order to study the morphological behaviour of idealised hump bed under cross-shore tidal current. A series of tests were carried out for some benchmark problems, such as wave propagation and hump morphodynamics, to validate the numerical scheme. The system of hydrodynamic equations was solved using the finite-volume numerical scheme associated with approximate Roe’s Riemann solver, a data-reconstruction and slope limiter. Hump beds consisting of sand/mud mixtures were examined. It was found that the predicted morphological behaviours of the hump beds under the cross-shore tidal current for a five year period show quite similar trends and the height of hump-profiles is reduced at the top and increased at both sides. Moreover, sand content of 40 percent produces the highest peak of hump-bed profile. This study shows that the amount of decreasing and increasing of bed-profile depends on the critical shear-stress and quantity of sand and mud in the sediments fraction.
Persistent currents due to point obstacles  [PDF]
Taksu Cheon,Pavel Exner
Physics , 2002, DOI: 10.1016/S0375-9601(02)01719-X
Abstract: We discuss properties of the two-dimensional Landau Hamiltonian perturbed by a family of identical $\delta$ potentials arranged equidistantly along a closed loop. It is demonstrated that for the loop size exceeding the effective size of the point obstacles and the cyclotronic radius such a system exhibits persistent currents at the bottom of the spectrum. We also show that the effect is sensitive to a small disorder.
COMPARATIVE STUDY OF ALUMINUM ALLOYS SACRIFICIAL ANODE FOR OIL- CARRYING PIPELINES IN SEA BED MUD
海底输油管线牺牲阳极用Al合金的选材研究

LI Yi,LI Yongguang,LI Jiansan,
李异
,李永广,李建三

腐蚀科学与防护技术 , 2001,
Abstract: Several Al anodes were evaluated by a serious tests:i.e.current static tests in sea bed mud under normal and moderate temperature for long-term and short-term, anode close circuit discharge tests, microanalysis of anode surface dissolution morphology and measurement of anodic polarization curve.A high quality Al anode (WPT 2) was finally recommended to fit the reqnirements for the protection of oil-carrying pipelines in sea bed mud.
Thermal convection of dusty compressible Rivlin-Ericksen viscoelastic fluid with hall currents  [PDF]
Gupta Urvashi,Aggarwal Parul,Wanchoo Kumar Ravinder
Thermal Science , 2012, DOI: 10.2298/tsci110128113g
Abstract: An investigation is made on the effect of Hall currents and suspended particles on the hydromagnetic stability of a compressible, electrically conducting Rivlin-Ericksen elastico-viscous fluid. The perturbation equations are analyzed in terms of normal modes after linearizing the relevant set of hydromagnetic equations. A dispersion relation governing the effects of viscoelasticity, magnetic field, Hall currents, compressibility and suspended particles is derived. For the stationary convection Rivlin-Ericksen fluid behaves like an ordinary Newtonian fluid due to the vanishing of the viscoelastic parameter. Compressibility and magnetic field are found to have a stabilizing effect on the system whereas Hall currents and suspended particles hasten the onset of thermal instability. These analytic results are confirmed numerically and the effects of various parameters on the stability parameter are depicted graphically. The critical Rayleigh numbers and the wavenumbers of the associated disturbances for the onset of instability as stationary convection are obtained and the behavior of various parameters on critical thermal Rayleigh numbers has been depicted graphically. It has been observed that oscillatory modes are introduced due to the presence of viscoelasticity, suspended particles and Hall currents which were not existing in the absence of these parameters.
Stress Distributions Due to a Concentrated Force on Viscoelastic Half-Space  [PDF]
Yun Peng,Debao Zhou
Journal of Computations & Modelling , 2012,
Abstract: A model of a viscoelastic infinite half-space with a concentrated tangential force applied on the boundary, namely, the viscoelastic Cerruti’s problem, is presented in this paper, with the derivation of the stress distributions by applying the elastic-viscoelastic correspondence principle to the displacements from the classic Cerruti’s problem. In the background viscoelastic materials, based on elastic-viscoelastic correspondence principle, the displacements of the classic Cerruti’s problem should have the similar expressions to elastic solutions but vary with time. Two auxiliary functions were used to replace the time components in displacements, which reduces the complexity. By satisfying the boundary conditions and balance conditions, the two auxiliary functions can be determined after solving two Volterra integral equations. With displacements known, the strains and stresses can be obtained. The results were also show that the two solutions match.
基床翻浆冒泥土的物理力学性质
Physical and Mechanical Properties of Mud Pumping Soils in Railway Subgrade Bed
 [PDF]

聂如松, 冷伍明, 粟雨, 郭一鹏
NIE Rusong
, LENG Wuming, SU Yu, GUO Yipeng

- , 2018, DOI: 10.3969/j.issn.0258-2724.2018.02.010
Abstract: 随着列车提速和轴重大幅增加,基床出现翻浆冒泥病害的几率加大.为了进一步研究翻浆冒泥发生机理和探究其发生条件,系统研究了60多组翻浆冒泥实例,分析了翻浆冒泥土的颗粒组成、可塑性指标、渗透性及矿物成分等物理力学性质.研究结果表明:翻浆冒泥土中,绝大部分黏粒含量大于20%、粉粒含量大于20%,黏粒含量大于30%和粉粒含量大于40%的土所占数量最多;翻浆冒泥土中粉粒的含量一般要高于黏粒含量;翻浆冒泥土(主要包括砂黏土、粉质黏土、黏土和部分低液限粉质黏土)液限大于23%,塑性指数大于6.5;翻浆冒泥土渗透系数小于1.0×10-5 m/s;翻浆冒泥土的渗透系数与细颗粒含量之间存在较好的负指数关系.
:Substantial increase in train speed and axle load may result in an increase in the probability of occurrence of the mud pumping problem in subgrade bed. In this study, to further study the mechanisms and occurrence conditions of the mud pumping problem, more than 60 mud pumping samples reported in published literature were studied systematically. Further, the physical and mechanical properties of mud pumping soils, such as particle composition, plasticity index, permeability, and mineral composition were analysed and summarized. The results indicate the followingFor the most mud pumping soils, clay and silt particle content is greater than 20%; soils with clay content greater than 30% and silt content greater than 40% account for the largest proportion of the samples. In mud pumping soils, the silt content is generally greater than the clay content. The liquid limit is more than 23%, and plasticity index greater than 6.5, i.e.,sandy clay, silty clay, clay and part of low liquid limit silty clay. Generally, the permeability coefficient of mud pumping soils is less than 1.0×10-5 m/s. The permeability coefficient and fine particle content show good negative exponential correlation
Application of Phytoplankton Community and Trophic Index in the Evaluation of dredging bed mud of Southern Area of the Tai Lake
应用浮游植物群落结构及富营养化指数评价南太湖底泥疏浚效果

yuanjulin,
原居林
,沈锦玉,尹文林,张爱菊,叶金云

水生态学杂志 , 2010,
Abstract: The ecological effect of dredging bed mud of southern area of the Tai Lake was assessed using phytoplankton community and trophic index.The result was indicated that the kind of phytoplankton was increased,while the density,biomass and the rate of Cyanobacteria were decreased obviously after dredge.The change of Shannon-Weaver index and TSIM index was indicated the dredging bed mud was helpful to trophic status of southern area of the Tai Lake.
Modeling of dynamic rotors with flexible bearings due to the use of viscoelastic materials
Bavastri, Carlos Alberto;Ferreira, Euda Mara da S.;Espíndola, José Jo?o de;Lopes, Eduardo Márcio de O.;
Journal of the Brazilian Society of Mechanical Sciences and Engineering , 2008, DOI: 10.1590/S1678-58782008000100004
Abstract: nowadays rotating machines produce or absorb large amounts of power in relatively small physical packages. the fact that those machines work with large density of energy and flows is associated to the high speeds of rotation of the axis, implying high inertia loads, shaft deformations, vibrations and dynamic instabilities. viscoelastic materials are broadly employed in vibration and noise control of dynamic rotors to increase the area of stability, due to their high capacity of vibratory energy dissipation. a widespread model, used to describe the real dynamic behavior of this class of materials, is the fractional derivative model. resorting to the finite element method it is possible to carry out the modeling of dynamic rotors with flexible bearings due to the use of viscoelastic materials. in general, the stiffness matrix is comprised of the stiffnesses of the shaft and bearings. as considered herein, this matrix is complex and frequency dependent because of the characteristics of the viscoelastic material contained in the bearings. despite of that, a clear and simple numerical methodology is offered to calculate the modal parameters of a simple rotor mounted on viscoelastic bearings. a procedure for generating the campbell diagram (natural frequency versus rotation frequency) is presented. it requires the embedded use of an auxiliary (internal) campbell diagram (natural frequency versus variable frequency), in which the stiffness matrix as a frequency function is dealt with. a simplified version of that procedure, applicable to unbalance excitations, is also presented. a numerical example, for two different bearing models, is produced and discussed.
Flux Quantization Due to Monopole and Dipole Currents  [PDF]
Wei Chen,Peter Horsch,Dirk Manske
Physics , 2013, DOI: 10.1103/PhysRevB.87.214502
Abstract: By discussing field-induced quantum interference effects due to monopole moments and those due to dipole moments on equal footing, their similarities and differences are clarified. First, we demonstrate the general principle for flux quantization. For particles carrying a monopole moment, the interference causes monopole current to oscillate periodically with flux defined as inner product of field and area, whereas for particles carrying a fixed dipole moment, the dipole current oscillates periodically with flux vector defined as cross product of field and trajectory. Our analysis unifies the oscillation of monopole or dipole currents in various devices, such as SQUID and spin-FET, into the same physical picture. Second, we show that interference effects can also happen in open trajectory devices that transport dipole currents, such as spin Josephson effect, based on the non-gauge field nature of the interference effects of dipole moments. In addition, we propose that the interference effect of electric dipoles, known as He-McKellar-Wilkens effect, can be realized by the bilayer exciton condensates observed in semiconductor heterostructure and bilayer graphene.
Critical conditions of bed sediment entrainment due to debris flow  [PDF]
M. Papa,S. Egashira,T. Itoh
Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD) , 2004,
Abstract: The present study describes entrainment characteristics of bed material into debris flow, based on flume tests, numerical and dimensional analyses. Flume tests are conducted to investigate influences of bed sediment size on erosion rate by supplying debris flows having unsaturated sediment concentration over erodible beds. Experimental results show that the erosion rate decreases monotonically with increase of sediment size, although erosion rate changes with sediment concentration of debris flow body. In order to evaluate critical condition of bed sediment entrainment, a length scale which measures an effective bed shear stress is introduced. The effective bed shear stress is defined as total shear stress minus yield stress on the bed surface. The results show that critical entrainment conditions can be evaluated well in terms of Shields curve using the effective bed shear stress instead of a usual bed shear stress.
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.