Turbulent boundary layer of water waves near a smooth bottom

Abstract

A one‐layer model describing wave‐induced turbulent flows near a smooth bottom is presented. A time‐invariant effective viscosity model, which is more realistic under natural conditions, is specified near a smooth bottom. The first and second order solutions are presented. These include the velocity profile, shear stress, friction Investigated. These include the velocity profile, shear stress, friction factor and mass transport. The present study simplifies much of the mathematical complexity in many of the existing models. Furthermore, the results compare favorably with available observations, indicating that the approach adopted in the present model is physically sound.     

Steady‐state responses of a compliant friction slider under harmonic excitations

Abstract

Steady‐state solutions are presented for a harmonically exciting single‐degreeof‐ freedom friction oscillator with an elastic compliant support. The validity and accuracy are confirmed by comparing them with the exact time‐marching solutions.     

The preparation and characteristic of maleic anhydride grafted polyethylene (PE-g-MA) filled CNT/PMMA composite film

ABSTRACT

In order to improve the tribological properties of PMMA, the PMMA composites incorporated with CNT powders were prepared. The effect of CNT content on tribological properties of the composites was investigated. When CNT content is 0.5 wt%, the friction coefficients of the 0.5%CNT/PMMA composite are the smallest, which are about 0.15 and are 67% less than those of the pure PMMA composite, and its wear resistance remains the same as the pure PMMA composite. Incorporating 0.5 wt% CNT into the PMMA composite may develop a continuous transferred film on the worn surface. As a result, the friction coefficients of the composite are reduced and its wear mechanism is mainly fatigue spalling. The addition of PE-g-MA improved the friction and wear properties of CNT/PMMA composite.     

Dynamic characteristics of wide tapered‐land slider bearings

Abstract

Taking into account squeezing‐action effects, the present study is concerned with the dynamic characteristics of a tapered‐land slider bearing with infinite width. According to the results obtained, the bearing characteristics are significantly affected by the shoulder parameter δ and the geometric parameter α of tapered‐land bearings. For a fixed α, there exist some δ such that the bearing possesses a maximum load, a minimum friction parameter and a maximum stiffness. Compared to the plane‐bearing case, the tapered‐land bearing produces higher damping coefficients, and provides higher load capacity and dynamic stiffness at large α. These results provide useful information for engineers in selecting and designing bearing systems.     

The analysis of elastic liner in a cylindrical tunnel subjected to sh‐waves

Abstract

In this paper, we investigate the dynamic stresses of an elastic liner around a cylindrical tunnel subjected to an incident plane SH‐wave in an infinitely extended elastic medium. The investigation is based on the anti‐plane strain approximation of the dynamic theory of elasticity. The solutions are obtained by applying the method of wave functions expansion. Numerical results of dynamic stress concentrations at the outer and inner boundaries of the liner for various parameters are discussed in detail.     

A constitutive model for the uplift behavior of anchors in cohesionless soils

Abstract

A series of triaxial tests has been performed to establish the stress‐strain curves for I‐Lan sand and Taipei silty sand. A constitutive model for the continuous strain hardening‐softening and volumetric dilatancy of these two soils is proposed, based on the results of triaxial tests. Using this model, a numerical program is then established, with FLAC software, to analyze the uplift behavior of model anchors in sand and field anchors in silty soil.

It was found from triaxial tests, that the peak friction angle increases with relative density of soil and decreases with confining pressure. A non‐associated flow rule between plastic strain increment and stress tensor was found. As accumulative plastic strain, relative density and confining pressure were changed, the mobilized friction angle and mobilized dilatancy angle also changed. All parameters needed for the proposed model can be expressed as functions of relative density and confining pressure. This model can calculate the stress‐ strain curves of cohesionless soils determined from triaxial tests accurately.

The load‐displacement behaviors determined from anchor tests are compared with those calculated from this numerical program, the numerical results are in good agreement with the test results not only for model anchors in sand but also for different types of field anchors in silty soil.     

The effect of grease on the activated sludge process in wastewater treatment

Abstract

The purpose of this paper is to introduce the major potentials and perspectives of applications of finite element analysis in solving the problems of shallow water wave equations. One‐dimensional and two‐dimensional shallow water wave equations will both be incorporated into the modeling procedures. For one‐dimensional flows, the models will cover the typical single channels, confluence channels system, division channels system, and natural river systems. As far as two‐dimensional flows are concerned, the overland flows are investigated. The simulation results are compared with the data obtained by physical modeling and field observation and with the results of other existing literature. The models were found to be very feasible in modeling the complex flow fields of shallow water wave equation problems.     

Sand bed configurations under 2‐D standing waves

Abstract

Laboratory experiments conducted in a wave basin with movable sand bed have shown that, under the action of 2‐D standing water waves, longitudinal sand bars with small ripples riding on their tops are formed beneath the nodes of standing waves. Wavelengths of the sand bars are approximately equal to one‐half of those of standing water waves. The formation of sand bars under standing waves over an initially horizontal sand bed is explained by the suction and impinging effects of the wave action. A mathematical model for describing the induced density of sediment‐water mixture due to wave action is proposed. By employing the induced‐density model and mass conservation of sediment‐water mixture, a numerical simulation model is constructed. Bed configurations resulting from the actions of 2‐D standing waves are studied by using the simulation model. The simulation results of sand bed configuration under the action of 2‐D standing waves are in good agreement with those obtained from laboratory experiments.     

Shear‐friction strength in orthogonally reinforced concrete with tension acting across the shear plane

Abstract

An experimental and analytical study of the shear‐friction strength in orthogonally reinforced concrete with tension acting across the shear plane is presented in this paper. The parameters included in this study are the strength of the concrete, the magnitude of the tensile stress acting across the shear plane, the spacing of the orthogonal array of reinforcement and the angle of the shear plane to the orthogonal array of reinforcement. Based on test results in this study and results obtained by Hofbeck [3], Lin [4], Mattock [6–9] and Wu [11], the design equations in ACI Code [2], PCI Design Handbook [10] and Ref. [7] are modified to predict the shear‐friction strength of concrete reinforced with an orthogonal array of reinforcement.     

Limit cycle analysis for electro‐hydraulic systems with friction

Abstract

In this paper, a graphical prediction method is developed to effectively predict the existence of the limit cycles induced by nonlinear friction force in an electro‐hydraulic control system. The friction‐induced nonlinearity is linearized by its corresponding describing function. Then the stability equation method, accompanied by the parameter plane method, provides a useful tool for the establishment of necessary conditions to sustain a limit cycle in the controller coefficient plane. Henceforth, the limit cycles are predicted in a graphical way, and simulations are carried out to verify the accuracy of the prediction method.     

Thermodynamic analysis of free convection film condensation on an elliptical cylinder

Abstract

This paper aims to perform thermodynamic analysis of saturated vapor flowing slowly onto and condensing on an elliptical cylinder. This is the first approach to investigate how the geometric parameter‐ellipticity and surface tension affect local entropy‐generation rate during film‐wise condensation heat transfer process. The results observe that entropy generation decreases with decreasing ellipticity. It indicates that the entropy generation number is nearly unaffected by surface tension forces at small ellipticity like e ≤ 0.7, but somewhat influenced at large ellipticity for the whole perimeter. From the second law point of view, local entropy generation increases with ellipticity as local heat transfer coefficient does. Furthermore, the entropy‐generation rate due to gravity‐driven film flow friction is proportional to Brinkman group parameter. The irreversibility ratio indicates that film flow friction irreversibility starts to dominate over heat transfer irreversibility in the lower half of streamwise length for higher values of Brinkman group parameter (Br/T = 1).     

Analysis for vertical velocity of seismic waves

Abstract

Presented here are the results of seismic wave velocities analyzed using the acceleration time‐histories recorded at the downhole strong motion array of the Lotung large scale seismic test site during the May 20, 1986 Hualien earthquake. The spectral ratios between the surface and downhole accelerograms were used to identify the frequencies of maximum amplification of soil layers, and an elastic 1‐D wave propagation model was proposed to estimate the wave velocities of the ground during the earthquake. The results obtained indicate that significant reduction of shear wave velocity as well as soil modulus was induced by earthquake excitation as compared to the values obtained from low strain level soil testings.     

A multiscale DEM-FEM approach to investigate the tire–pavement friction

Abstract

Fundamental understandings of the pavement-tire friction are vital to improve the design of asphalt pavements. Most of the current research on pavement-tire friction is based on Finite Element Method (FEM), which is relatively complex and difficult to simulate the discontinuity during friction. To overcome the limitations, in this paper, the pavement–tire friction process is investigated using a coupled Multi-scale Discrete Element Method (DEM) – FEM approach. The benefit of such a multiscale method is that DEM has the advantage of simulating the discontinuity behaviour during friction, and FEM is good at simulating the continuum material with low computation consumption. The multi-scale approach provides an innovative and promising approach to simulate the tire-pavement friction behaviour.     

Velocity depending effect in FPS isolators

Abstract

In order to understand the velocity depending effect in an FPS isolator and to verify its ability to achieve the desired dynamic friction coefficient, individual FPS isolators, both 1/4 and full size model, were tested. In addition, a two‐story frame model was tested on a shaking table [10] to investigate the feasibility of FPS connections. The characteristics of the friction coefficient of FPS bearing were studied and it was confirmed that FPS connections are able to achieve seismic isolation by dissipating the earthquake input energy during sliding. An analytical model of the test structure containing the mathematical expressions of the velocity depending effects is employed in the analysis, and the theoretical results agree strongly with the experimental results.     

Analytical study of wave‐induced nearshore currents

Abstract

Nearshore circulation, produced by a wave‐induced radiation stress gradient, forms different circulation patterns under different wave characteristics and topographical conditions. A more general equation was deduced on the orthogonal curvilinear coordinate system to unify the diversities among related theories and to investigate the nearshore circulation on an arc‐shaped coast. The results show that circulation patterns depend on the flow torque factor which is in turn determined by both the wave characteristics and the topographical conditions. Due to the differences of this torque factor, the straight coast and the arc‐shaped coast will produce different circulation patterns.     

Unsteady forced and free convection flow with mass‐transfer and chemical reaction past an infinite vertical porous plate with oscillating plate temperature

Abstract

An approximate analysis of a two‐dimensional unsteady flow of chemically reacting gases is presented under the following conditions: (1) Constant suction at the plate, (2) the plate temperature is oscillating about a non‐zero constant mean, (3) the uniform free‐stream velocity, (4) presence of foreign mass with negligible Soret‐Dufour effects, (5) first‐order chemical reaction, and (6) small amplitude. Solutions to the mean velocity, the mean temperature, the transient velocity, the transient temperature, the amplitude and phase of the skin‐friction and the rate of heat transfer are derived. It is observed that due to the presence of a chemical reaction, the mean skin‐friction decreases but the mean rate of heat transfer increases.     

Boundary integral equation analysis for radiation and scattering of elastic waves in three dimensions

Abstract

In this paper, the boundary integral equation (BIE) method is employed to investigate the radiation and scattering of time‐harmonic elastic waves by obstacles of arbitrary shape embedded in an infinite medium. Based on the vector BIE, entirely free of Cauchy principal value integrals, an efficient numerical scheme using quadratic isoparametric boundary elements is proposed. Furthermore, the difficulty of non‐uniquess of a solution inherent with BIE formulations for exterior elastodynamic problems is studied numerically and analytically. The counterparts of the combined Helmholtz integral formulation method for elastodynamics together with the least‐square or Lagrange‐multiplier technique are derived and applied to overcome this difficulty successfully. In addition, the elastic‐wave fields radiated or scattered by either a spherical cavity or a rigid sphere in an infinite medium are calculated and the results are compared with the analytical solutions to demonstrate the accuracy and versatility of the proposed numerical scheme.     

The effect of titanium addition on the microstructure,mechanical and tribological properties of Ni3Si alloys prepared by powder metallurgy method

Ni₃Si alloy with different content of titanium was fabricated by powder metallurgy method. The microstructures, hardness and tribological properties of the alloys were investigation. The results showed that pure Ni₃Si alloy was composed of β₁‐Ni₃Si phase and γ‐Ni₃₁Si₁₂ phase, and Ni₃Ti phase formed with titanium addition. The hardness of the alloy decreased with the increasing titanium content. The friction coefficient of pure Ni₃Si alloy increased with the increasing load, while the friction coefficient of the alloy with titanium addition decreased. The wear rates of the alloys were all increased with increasing load, and the alloy with 5 % titanium addition had the best wear resistance properties. The wear mechanisms of the alloys were abrasive wear at low load, and the wear mechanisms changed to oxidative wear at high load.     

A high performance step up/down three phase AC to DC converter

Abstract

In this paper, a new three phase AC to DC converter is proposed to achieve a sinusoidal current waveform and the unity power factor at the input, and clean DC at the output. Control of the converter is so simple that only one PWM control circuit with fixed switching frequency is required. In addition, the new converter has both step‐up and step‐down capabilities. Also, no current sensor is required for the current control. The small signal model and some design considerations are also presented. Finally, some experimental results are provided for the purposes of demonstration.     

Damping properties of open cell microcellular pure Al foams

Abstract

Damping behaviours of the open cell microcellular pure Al foams fabricated by sintering and dissolution process with the relative density of 0·31–0·42 and the pore size of 112–325 μm were investigated. The damping characterisation was conducted on a multifunction internal friction apparatus. The internal friction (IF) was measured at frequencies of 1·0, 3·0 and 6·0 Hz over the temperature range of 298–725 K. The measured IF shows that the open cell pure Al foam has a damping capacity that is enhanced in comparison with pure Al. At a lower temperature (～400 K), the IF of the open cell pure Al foams increases with decreasing relative density, with decreasing pore size and with increasing frequency. The IF peak was found at the temperature range of 433–593 K in the IF curves. It is clear that the IF peak is relaxational type and the activation energy associated with the IF peak is about 1·60 ± 0·02 eV. Defect effects can be used to interpret the damping mechanisms.