Corrected Formula of Bed Resistance Coefficient for Plane Numerical Simulation of Tidal Current

By means of a logarithm law for the velocity profile, a corrected formula of bed resistance coefficient, which involves many factors such as gradient of still water depth, variation of surface elevation, flow direction, and so on, is derived from the 3D governing equations of tidal current by averaging over the whole water depth. Theoretical analysis and application have shown that the 2D plane tidal current numerical model would be more reasonable and could be applied to steep bottom topography when the corrected bed resistance coefficient is used, therefore the results of reproduction simulation and engineering calculation would be more scientific and reasonable.

Study on resistance coefficient in compound channels

This paper presents a further study of the Manning and Darcy-Weisbach resistance coefficients, as they play a significant role in assessing the cross-sectional mean velocity, conveyance capacity and determining the lateral distribution of depth mean velocity and local boundary shear stress in compound channels. The relationships between the local, zonal and overall resistance coefficients, and a wide range of geometries and different roughness between the main channel and the flood plain are established by analyzing a vast amount of experimental data from a British Science and Engineering Research Council Flood Channel Facility （SERC-FCF）. And the experimental results also show that the overall Darcy-Weisbach resistance coefficient for a compound channel is the function of Reynolds number, but the function relationship is different from that for a single channel. By comparing and analyzing the conventional methods with the experimental data to predict composite roughness in compound channels, it is found that these methods are not suitable for compound channels. Moreover, the reason why the conventional methods cannot assess correctly the conveyance capacity of compound channels is also analyzed in this paper.

Uphillshift decision strategy of an AMT off-road vehicle based on generalized road resistance coefficient

In order to improve the shift decision strategy for an off-road vehicle with automated manual transmission（AMT）,the generalized road resistance coefficient is defined based on the longitudinal dynamics analysis.Vehicle mass and generalized road resistance coefficient are estimated using the recursive least square（RLS）method with multiple forgetting factors.The improved shift schedule is designed based on the generalized road resistance coefficient under uphill road condition.The simulation and real vehicle test verify the effectiveness of improved shift strategy and the improvement of vehicle dynamic performance.

Bogie's Rotational Resistance Coefficient Analysis Based on Novel Parallel Mechanism

In this paper,a novel parallel mechanism which can be used to evaluate body-to-bogie yawtorque is proposed.It can satisfy experimental testing for rotation resistance coefficient(RRC) with various types of bogies,different rotational speeds,and different states of air spring.Aiming at the problem that computing speed of Newton iterative method for solving rotational angle is incompetence to meet the real-time requirements,and also that other methods adopting physical device such as laser displacement sensor to solve rotational angle possess larger measurement error,the analytical techniques method used for solving rotational angle is presented.Finally,by using the upper-single-6-DOF motion platform as an authentic urging mean to simulate a real vehicle,the test was carried out under the speeds of 0.2 and 1.0(°)/s,with the air spring at the inflated and deflated states,respectively.The results showthat the RRC of the bogie under various conditions is less than 0.06,which meets the standard requirement EN-14363.It was also found that the speed of vehicles moving along curves and the state of air spring were key factors influencing the RRC.The feasibilities of this model and test method are verified in this study.

Fabrication and characterization of NiCr-based films with high resistivity and low temperature coefficient of resistance

As a metal alloy,NiCr films have a relatively high resistivity and low temperature coefficient of resistance (TCR) and are widely used in electronic components and sensors.However,the resistivity of pure NiCr is insufficient for high-resistance and highly stable film resistors.In this study,a quaternary NiCrAlSi target (47:33:10:10,wt.%) was successfully used to prepare resistor films with resistivities ranging from 1000 to 10 000μΩcm and TCR within±100 ppm/K.An oxygen flow was introduced during the sputtering process.The films exhibit hightemperature stability at 450℃.The films were analyzed using Auger electron spectroscopy,x-ray diffraction,time-of-flight secondary-ion mass spectrometry,and x-ray photoelectron spectroscopy.The results show that the difference in the oxide proportion of the films caused the differences in resistivity.The near-zero TCR values were considered to be due to the competition between silicon and other metals.This study provides new insights into the electrical properties of NiCr-based films containing Si,which will drive the manufacturing of resistors with high resistivity and zero TCR.

Numerical simulation of flow through circular array of cylinders using porous media approach with non-constant local inertial resistance coefficient

Aquatic vegetation zone is now receiving an increasing attention as an effective way to protect the shorelines and riverbeds. To simulate the flow through the vegetation zone, the vegetation elements are often simplified as equidistant rigid cylinders, and in the whole zone, the porous media approach can be applied. In this study, a non-constant inertial resistance coefficient is introduced to model the unevenly distribution of the drag forces on the cylinders, and an improved porous media approach is applied to one circular array of cylinders positioned in a 2-D flume. The calculated velocity profile is consistent with the experimental data.

Study of deep transportation and plugging performance of deformable gel particles in porous media

Deformable gel particles(DGPs) possess the capability of deep profile control and flooding. However, the deep migration behavior and plugging mechanism along their path remain unclear. Breakage, an inevitable phenomenon during particle migration, significantly impacts the deep plugging effect. Due to the complexity of the process, few studies have been conducted on this subject. In this paper, we conducted DGP flow experiments using a physical model of a multi-point sandpack under various injection rates and particle sizes. Particle size and concentration tests were performed at each measurement point to investigate the transportation behavior of particles in the deep part of the reservoir. The residual resistance coefficient and concentration changes along the porous media were combined to analyze the plugging performance of DGPs. Furthermore, the particle breakage along their path was revealed by analyzing the changes in particle size along the way. A mathematical model of breakage and concentration changes along the path was established. The results showed that the passage after breakage is a significant migration behavior of particles in porous media. The particles were reduced to less than half of their initial size at the front of the porous media. Breakage is an essential reason for the continuous decreases in particle concentration, size, and residual resistance coefficient. However, the particles can remain in porous media after breakage and play a significant role in deep plugging. Higher injection rates or larger particle sizes resulted in faster breakage along the injection direction, higher degrees of breakage, and faster decreases in residual resistance coefficient along the path. These conditions also led to a weaker deep plugging ability. Smaller particles were more evenly retained along the path, but more particles flowed out of the porous media, resulting in a poor deep plugging effect. The particle size is a function of particle size before injection, transport distance, and different injection parameters(injection rate or the diameter ratio of DGP to throat). Likewise, the particle concentration is a function of initial concentration, transport distance, and different injection parameters. These models can be utilized to optimize particle injection parameters, thereby achieving the goal of fine-tuning oil displacement.

Investigation on the Novel High-performance Copper/Graphene Composite Conductor for High Power Density Motor

High-performance Cu/Graphene composite wire synergistically strengthened by nano Cr_(3)C_(2) phase was directly synthesized via hot press sintering followed by severe cold plastic deformation, using liquid paraffin and CuCr alloy powder as the raw materials. Since graphene is in situ formed under the catalysis of copper powder during the sintering process, the problem that graphene is easy to agglomerate and difficult to disperse uniformly in the copper matrix has been solved. The nano Cr_(3)C_(2)-particles nailed at the interface favor to improve the interface bonding. The Cu/Graphene composite possesses high electrical conductivity, hardness, and plasticity. The composite wire exhibits high electrical conductivity of 96.93% IACS, great tensile strength of 488MPa, and excellent resistance to softening. Even after annealing at 400℃ for 1 h, the tensile strength can still reach 268 MPa with a conductivity of about 99.14% IACS.The wire's temperature coefficient of resistance(TCR) is largely reduced to 0.0035/℃ due to the complex structure,which leads the wire to present low resistivity at higher temperatures. Such Cu/Graphene composite wire with excellent comprehensive performance has a good application prospect in high-power density motors.

Negative Temperature Coefficient of Resistivity in Bulk Nanostructured Ag

The change of the temperature coefficient of resistivity (a) with the particle size, dp, and the grain size, dc, in the nanostructured Ag bulk samples was investigated. dp and dc were controlled by heating the nano-Ag powders over the temperature range from 393 to 453 K. The electrical resistance measurements of the nanostructured Ag bulk samples obtained by compacting the Ag powders after heat treatments showed a change in the sign of a with dP and dc. When dp and dc are smaller or equal to 18 and 11 nm below room temperature or 20 and 12 nm above room temperature, respectively, the sign of the temperature coefficient of resistivity changes from positive to negative. The negative a arises mainly from the high resistivity induced by the particle interfaces with very lowly ordered or even disordered structure, a large volume fraction of interfaces and impurities existing in the interfaces, and the quantum size effect appearing in the nano-Ag grains.

The Study on Pipe Sudden Enlargem entLocal Resistant Coefficient

During the design of pipeline,the determination of local resistant coefficient is often come arcoss.The sudden enlargement local resistant coefficient ξ 1=1-A 1A 2 2 is determined through theory.In the paper,the sudden enlargement local resistant coefficient under the conditions of three kinds of A 1A 2 was studied in experiment.In the end ,the result shows that ξ 1 is related not only to two flow cross sections,but also to the velocity.Through experimental research,the relationship between ξ 1,A 1A 2 and V 1 was determined.In a word,the hydraulic calculation of pipeline can be done by taking correspondent ξ 1 ,according to the design velocity V 1 and A 1A 2.

THE EFFECT OF COLD DEFORMATION AND HEAT TREATMENT ON COEFFCIENT OF STRAIN RESISTANCE

The coefficient of strain resistance for metals,solid solutions and ordering alloys in annealing state decreases,while K increases in cold working state.The value K of pure metals and solid solutions invaraibly decreases with temperature increass.The main factors influencing the coefHcient of strain resistance are crystal defect,dispersion and degree of atomic arrangement.

Positive temperature coefficient of resistivity effects of semiconducting (Bi(1/2)Na(1/2)) TiO_3-CaTiO_3-BaTiO_3 ceramics sintered in air atmosphere

Y^3＋-doped （Bi 1/2 Na 1/2） TiO 3-CaTiO 3-BaTiO 3 （BNCBT） positive temperature coefficient of resistivity （PTCR） ceramics sintered in air atmosphere were investigated in this study. （Bi 1/2 Na 1/2） TiO 3 （BNT） component can remarkably increase the onset temperature T c of PTCR ceramics with the expense of the resistivity R 25 increase. CaTiO 3 （9–27 mol%） component can decrease the resistivity, and adjust the effects of BNT phase on the T c point. For the sample containing 3 mol% CaTiO 3 , T c raises from 122 ℃ to 153 ℃ when only 0.6 mol% BNT added, while for the ones with higher CaTiO 3 content （9–27 mol%）, T c is only increased by a rate of 8–9℃/1.0 mol% BNT. The effects of BNT and CaTiO 3 components on R25/Rmin （negative temperature coefficient effect） are also discussed.

Analysis of Water Transport inside a Plant Xylem Vessel with Pitted Thickening

In this article,computational fluid dynamics(CFD)are used to explore the dynamics of water transport inside the pitted thickening of a plant xylem vessel.A pitted thickening model combined with the Bernoulli equation is used to analyze the influence of various factors(namely,the inner diameter,thickening width,thickening height,thickening spacing,number of laps and adjacent pit axial rotation).The pressure drop and the flow resistance coefficient are the variable parameters for our analysis.The results show that these two parameters are proportional to the thickening height and thickening width,and inversely proportional to the inner diameter,thickening spacing and number of laps.Three different wall thickening structures of the vessel are compared and the pitted thickening vessel is shown to provide the largest structural flow resistance,the annular thickening vessel has the second largest resistance and the helical thickening vessel corresponds to the smallest resistance of the three structures.

Feasibility Study on Chemical Flooding in Super High Porosity and Permeability Heavy Oil Reservoir

In this paper, the feasibility study of chemical flooding is carried out for ultra-high porosity and high permeability heavy oil field with permeability higher than 10 μm2 and porosity greater than 35%. The viscosity-concentration relationship of four kinds of oil flooding systems such as hydrolyzed polyacrylamide, structural polymer A, structural polymer B and gel was studied. The results showed that the viscosity of ordinary polymer and structural polymer B was lower compared with other two types of oil displacement agents, and the viscosity of structural polymer A was higher. The higher the concentration, the higher the viscosity retention rate. The gel system has the highest viscosity and best anti-shear ability. The resistance coefficient and residual resistance coefficient of structural polymer A and gel system were further studied. The results show that permeability, velocity and polymer concentration all affect the resistance coefficient and residual resistance coefficient. From the point of view of resistance establishment ability, it is considered that structural polymer A is not suitable for permeability formation above 10 μm2. Gel system has stronger ability to establish resistance coefficient than structural polymer A flooding system, and it is more feasible for formation system with permeability above 10 μm2.

Study of Bed Friction Factor for the Wu River Estuary

In this research the bed friction effect is estimated of a river estuary by use of hydrodynamic analysis. The on-site sampled data of the Wu River estuary is applied to the analysis. There are many dynamic factors that affect the flow characteristics in the estuary. The effect of tide on the generation of tidal current, bottom friction and geometry effect is the focus of this paper. The Wu River estuary is about 15 hn in length, with a small bottom slope and no physical obstruction; thus the incident wave at the estuary is considered a progressive wave with damping effect. The amplitude reduction and phase shift of the incident wave are analyzed. By the analysis of celerity reduction factor of the estuary, the estimated value of mean resistance coefficient M（μ ,κ）, damping modulus μ, and wave number κ for the sections at observation stations can be determined. Furthermore, data gathered from on-site observations are applied for validation. Finally, Manning＇ s coefficient for each section of the observation stations can be determined. It is found that the value of Manning＇ s coefficient is small downstream and increases towards upstream, and that the bed friction effect of an estuary varies largely. The estimated results of the paper are compared with the empirical formulas and the modified solution for practical application is discussed.

Influence of sintering schedule on the electrical properties of Mn(NO_3)_2-doped Ba_(0.92)Ca_(0.08)TiO_3 PTCR ceramics

The relationship of electrical properties of Mn-doped Ba_(0.92)Ca_(0.08)TiO_3PTCR (positive temperature coefficient resistance) ceramics with two sintering schedules wasdiscussed. Using TEM (transmission electron microscope) combined with EDS (energy dispersive X-rayspectrometer), the Mn ions distributed at grain boundaries were analyzed. The results show that thePTCR effect of Mn-doped PTCR ceramics is more dependent on the sintering schedule than those of Mnfree. The phenomenon may be caused by the valence states variance of Mn ions segregated at the grainboundaries.

Mn_(3)Ag_((1-x))Cu_((x))N antiperovskite thin films with ultra-low temperature coefficient of resistance

We demonstrate the first successful attempt to partially substitute Cu into the Mn_(3)AgN-antiperovskite system to form Mn_(3)Ag_((1-x))Cu_((x))N thin films with an ultra-low temperature coefficient of resistance(TCR)for fabrication of ultra-precise passive components.Films were grown by reactive magnetron sputtering on alumina and glass substrates and were found to be amorphous in nature with highly negative TCR of-233 to-351 ppm/℃in their as-grown state.Increasing Cu alloying from x=0 to 1,resulted in increased sheet resistance,a negative shift of TCR and a change of grain morphology from spherical to elongated.Post-deposition heat treatment at 300-375℃,resulted in a positive shift of TCR and an ultra-low TCR of-4.66 ppm/℃for films with x=0.6.The heat treatment induces grain growth,surface roughness and the formation of a manganese oxide upper surface layer up until temperatures of 350℃,after which surface oxidation begins to dominate.The growth rate of the surface layer is controlled by the Cu concentration and heat treatment temperature,which both play a central role in the development of these novel ultralow TCR Mn_(3)Ag_((1-x))Cu_((x))N thin film structures.

Influence of Non-smooth Surface on Tribological Properties of Glass Fiber-epoxy Resin Composite Sliding against Stainless Steel under Natural Seawater Lubrication

With the development of bionics, the bionic non-smooth surfaces are introduced to the field of tribology. Although non-smooth surface has been studied widely, the studies of non-smooth surface under the natural seawater lubrication are still very fewer, especially experimental research. The influences of smooth and non-smooth surface on the frictional properties of the glass fiber-epoxy resin composite（GF/EPR） coupled with stainless steel 316 L are investigated under natural seawater lubrication in this paper. The tested non-smooth surfaces include the surfaces with semi-spherical pits, the conical pits, the cone-cylinder combined pits, the cylindrical pits and through holes. The friction and wear tests are performed using a ring-on-disc test rig under 60 N load and 1000 r/min rotational speed. The tests results show that GF/EPR with bionic non-smooth surface has quite lower friction coefficient and better wear resistance than GF/EPR with smooth surface without pits. The average friction coefficient of GF/EPR with semi-spherical pits is 0.088, which shows the largest reduction is approximately 63.18% of GF/EPR with smooth surface. In addition, the wear debris on the worn surfaces of GF/EPR are observed by a confocal scanning laser microscope. It is shown that the primary wear mechanism is the abrasive wear. The research results provide some design parameters for non-smooth surface, and the experiment results can serve as a beneficial supplement to non-smooth surface study.

Temperature coefficients of grain boundary resistance variations in a ZnO/p-Si heterojunction

Heteroepitaxial undoped ZnO films were grown on Si （100） substrates by radio-frequency reactive sputtering, and then some of the samples were annealed at N2-800℃ （Sample 1, S1） and 02-800℃ （Sample 2, S2） for 1 h, respectively. The electrical transport characteristics of a ZnO/p-Si heterojunction were investigated. We found two interesting phenomena. First, the temperature coefficients of grain boundary resistances of S 1 were positive （positive temperature coefficients, PTC） while that of both the as-grown sample and S2 were negative （negative temperature coefficients, NTC）. Second, the I-V properties of S2 were similar to those common p-n junctions while that of both the as-grown sample and S 1 had double Schottky barrier behaviors, which were in contradiction with the ideal p-n heterojunction model. Combined with the deep level transient spectra results, this revealed that the concentrations of intrinsic defects in ZnO grains and the densities of interfacial states in ZnO/p-Si heterojunction varied with the different annealing ambiences, which caused the grain boundary barriers in ZnO/p-Si heterojunction to vary. This resulted in adjustment electrical properties ofZnO/p-Si heterojunction that may be suitable in various applications.

Resistivity-temperature Characteristics of Conductive Asphalt Concrete

The changes of resistivity of conductive asphalt concrete at different temperatures were studied,and positive temperature coefficient（PTC）modelwas established to estimate the influence of temperature on the resistivity quantitatively,which eliminated the interference with conductivity evaluation brought by temperature variation.Finally,the analysis of temperature cycling test results proves that the changes of percolation network structure caused by temperature variation prompt the emergence of PTC of conductive asphalt concrete.