Search

This work presents a physics-based predictive model for temperature rise in cylindrical solids heated by constant-strength, periodic-motion heat source. The heat source motion path, heat transfer boundary conditions and solid dimension are considered in the theoretical model. Analytical solutions to both the infinite or finite length cylinders are constructed with respect to convection and corresponding boundary conditions. Dimensionless controlling parameters are discussed to reveal temperature field evolution. The predicted results in the temperature rise agreed well with the measured data for a Z-direction feeding drive screw shaft system. The proposed model provides an efficient and accurate design tool for engineering calculation and process-parameter planning through inverse analysis.

The design of machine elements made by viscoelastic matrix can be improved by numerical analysis. The solution of the viscoelastic contact problem with prescribed geometry is difficult to obtain because (1) both contact area and pressure distribution are a priori unknown, and (2) the contact parameters keep changing with time, together with the compliance of the viscoelastic material. These difficulties are overcome in this paper by conducting numerical analysis based on both spatial and temporal model discretization. The viscoelastic contact process simulation is achieved by computing a series of subsequent contact states, the current state depending on the entire contact history. In this manner, the memory effect of the viscoelastic material is accounted for. The numerical predictions agree well with the classic solution of the spherical contact undergoing step loading. The history of pressure distribution and modification of contact area in the finite length line contact between a rigid profiled roller and a polymethyl methacrylate viscoelastic half-space are obtained. The case when the normal force is applied eccentrically in the longitudinal direction, leading to a tilting moment, is also considered.

The Particle Image Velocimetry is utilized to investigate flow behind a cylinder of finite length with subcritical value of Aspect Ratio (AR). The cylinder is submitted to uniform freestream with very low intensity of turbulence and thin laminar boundary layer. The flow field cannot be expected as 2D even for time-averaged quantities. The Strouhal number is evaluated in various planes of measurement. The wake is fully turbulent and is composed of many streamwise and spanwise-oriented structures. Such complex flow is very convenient to be subjected to dynamical decomposition analysis.

Based on the Lienard – Wiechert potentials for a uniformly and rectilinearly moving electron, a relativistic electric field is studied near a densely filled with potassium atoms single-walled carbon nanotube (K@CNT) with a stationary electric current inside it. The relativistic electric field in the laboratory coordinate system arises (due to the Lorentz transformations) only for a nanotube of a finite length. This field is a result of summation of the Coulomb fields of stationary positively charged ionic cores of potassium and an equal number of ballistically moving valence electrons of potassium that create a current. It is shown that the magnitude of the negative relativistic electric potential of K@CNT in the direction perpendicular to the nanotube does not depend on the direction of the current density. The relationship is obtained between the K@CNT radius and the number of open channels of ballistic electron transfer over potassium atoms. The Landauer formula is used, which relates the number of open quasi-one-dimensional channels and the direct current electrical conduction. For the first time, analytical formulas are obtained for the dependence of the relativistic potential near K@CNT on the electric voltage between the ends of the nanotube and on its radius in the limit of zero absolute temperature. The case is considered when the distance from the point of registration of the relativistic potential above the center of the nanotube is much less than its length. For nanotube with diameter of 2 nm and length of 100 mm, under an external electric field strength of 5 mV/mm, the magnitude of the potential of the relativistic electric field is of about 2 mV. Modern measurement techniques make it possible to register the predicted relativistic potential.

This article presents a technique for analytic-numerical evaluation of thermal stresses in a finite-length hollow cylinder subject to a steady-state temperature field. Based on the method of direct...

In this paper, based on the deformed cylinder method, the expression of the far-field acoustic scattering form function of a finite-length elastic elliptical cylinder is obtained. The target strength of elastic aluminum and polymethylmethacrylate (PMMA) elliptical cylinders, with different lengths varying with dimensionless frequency ka, is studied for different incident angles. In addition, the change of the target strength of a PMMA elliptical cylinder with incident angle is explored theoretically and experimentally when the frequency range is 20–40 kHz. Simulation results show that there is almost no change in the peak of the curve of the backscattering target strength versus frequency for a finite-length elastic elliptical cylinder with different lengths. As the length decreases, the target strength gradually decreases. When the theoretical simulation results are compared with the experimental results, it is found that the theoretical predictions are in good agreement with the experimental results. Furthermore, the study will provide theoretical and experimental basis for the prediction and recognition of underwater targets.

This paper utilizes a combined approach of the convection-diffusion theory and the moment analysis to conduct a comprehensive investigation of the solute dispersion under the influence of the interphase transport in finitely long inner coated microchannels. The present work has threefold novel contributions: (1) The 2D solute concentration contours in the stationary phase are calculated for the first time to facilitate the understanding the role of the interphase transport in the solute dispersion in the mobile phase. (2) The skewness of the elution curves is investigated to guide the control of solute band shape at the channel outlet. (3) The 2D diffusion-convection theory and zero-dimensional (0D) moment analysis complement each other to present a characterization of the solute dispersion behaviors more comprehensive than that by either of the two methods alone. Parametric studies are performed to clarify the effects of four major parameters related to the interphase transport (i.e., stationary phase Péclet number, interphase transport rate, partition coefficient, and stationary phase thickness) on the solute dispersion characteristics. The results from this study provide a straightforward understanding of the effects of interphase transport on the solute dispersion in finitely long microchannels and are of potential relevance to the design and operation of the microfluidics-based analytical devices.

The main purpose of the paper is to obtain solutions for new non-stationary inverse problems for elastic rods. The objective of this study is to develop and implement new methods, approaches and algorithms for solving non-stationary inverse problems of rod mechanics. The direct non-stationary problem for an elastic rod consists in determining elastic displacements, which satisfies a given equation of non-stationary oscillations in partial derivatives and some given initial and boundary conditions. The solution of inverse retrospective problems with a completely unknown space-time law of load distribution is based on the method of influence functions. With its application, the inverse retrospective problem is reduced to solving a system of integral equations of the Volterra type of the first kind in time with respect to the sought external axial load of the elastic rod. To solve it, the method of mechanical quadratures is used in combination with the Tikhonov regularisation method.

The accuracy and efficiency of the modelling techniques utilized to model the nonlinear behavior of structural components is a significant issue in earthquake engineering. In this study, the sufficiency of three different modelling techniques that can be employed to simulate the structural behavior of columns is investigated. A fiber-based finite length plastic hinge (FB-FLPH) model is calibrated in this study. In order to calibrate the FB-FLPH model, a novel database of the cyclic behavior of hollow steel columns under simultaneous axial and lateral loading cycles with varying amplitudes is used. By employing the FB-FLPH model calibrated in this study, the interaction of the axial force and the bending moment in columns is directly taken into account, and the deterioration in the cyclic behavior of these members is implicitly considered. The superiority of the calibrated FB-FLPH modelling approach is examined compared with the cases in which conventional fiber-based distributed plasticity and concentrated plasticity models are utilized. The efficiency of the enumerated modelling techniques is probed when they are implemented to model the columns of a typical special moment frame in order to prove the advantage of the FB-FLPH modelling approach.

The purpose of this article is to determine the effect of thermal loadings on the stress intensity factor of an edge crack of finite length in an orthotropic infinite strip of finite thickness under mechanical loading. Analytical expressions of the stress intensity factor at the crack tip in point and arbitrary constant loadings are found. Numerical values of the factor at any arbitrary location on the crack face due to mechanical loading and effects of thermal loadings are computed for various crack lengths in an orthotropic material composite, and the results are presented in the form of graphs. The effects of thermal conductivity parameters on the stress intensity factor for different particular cases are also shown graphically.

A two-dimensional elastic solution for the stress field of a dilatation line near an elliptical void in an infinite matrix is obtained. The dilatation line is used to represent a row of equally spaced solute atoms. This elastic solution is employed to study the shielding or anti-shielding effect of solute atoms near a finite length crack. The stress intensity factor of stress field induced by a dilatation line is analytically obtained. It is shown that whether solute atoms have a shielding or anti-shielding effect on the crack tips depends on the position of solute atoms. An equaling zero curve is defined, on which the solute dilatation line induces zero Mode I stress intensity factor at the crack-tip. It is found that the shape of equaling zero curve is independent of any model parameters. The shielding and anti-shielding effects of a lot of solute hydrogen (hydrogen atmospheres) are studied through an integral scheme. The hydrogen concentration field is assumed to equilibrate with external or internal stress fields. We consider two cases. One case is that an externally uniaxial load in the direction vertical to crack is applied. Another case is that there exists an edge dislocation near crack. Based on these studies, a new possible mechanism of hydrogen embrittlement is proposed, which can be referred to as hydrogen induced anti-shielding crack mechanism.

This study aims to investigate the conjugate heat transfer in a finite-length planar micro-combustor by using a two-dimensional analytical model. The primary objective is to thermally analyze the effects of ambient, solid wall, and gas mixture properties on wall and gas temperature profiles and heat recirculation via the micro-combustor wall. The micro-combustor is divided into three sections composed of pre-flame, reaction, and post-flame zones. The energy equation is solved in each zone for both wall and gas mixture regarding the matching boundary conditions. As a result, an appropriate correlation that is a combination of hyperbolic tangent and linear functions for estimating the wall temperature profile is developed. Moreover, since the absolute amounts of positive wall temperature gradient are larger than the negative ones, heat is conducted intensely toward the inlet side of wall which results in heat recirculation at pre-flame zone. These findings can be used to propose a simple approach for preliminary micro-combustor design.

Forster Resonance Energy Transfer (FRET) is a mechanism widely used to describe the luminescent behavior of a great variety of systems. However, there is a strong need for a complete model of Forster theory to understand donor-acceptor interactions in different confinement geometries and their effects on the luminescent dynamics. Here, a methodology based on Forster theory that allows finding the probability distribution of donors and acceptors in systems of any geometry is presented. We have considered the particular cases of lines with finite length, finite cylinders, and bi-dimensional arrangements of lines and cylinders. Furthermore, using our results, we calculate the quantum yield as a function of the geometric parameters of the structures. Our numerical results show that this methodology is useful to calculate and predict the donor luminescent dynamics in structures of finite length. We find that our model explains the decrease of the transferred energy from donors to acceptors with the separation between lines or cylinders, this behavior is physically consistent. The model presented here extends the use of FRET to the study of structures with bi-dimensional arrays of lines or cylinders (as could be the case of porous media), and finite cylinder structures (as could be the case of nanotubes). In our knowledge, this work is the first theoretical approach to describe the donor-acceptor luminescent dynamics in this kind of systems.

The scattering theory for two crossing metallic single-walled carbon nanotubes of finite length exposed to an electromagnetic field has been developed based on a synthesis of the quantum transport formalism and classical electrodynamics. The model of the point contact has been developed to be incorporated into the Hall\'en and Pocklington equations for crossing carbon nanotubes. The influence of the contact conductance and position as well as the angle between the tube axes on the tube polarizability has been analyzed in the range of 1 GHz to 10 THz. The physical mechanisms responsible for the electromagnetic interaction between crossing tubes with zero and nonzero intertube contact conductance are shown and discussed. The influence of the coupling between the tubes on the localized plasmon resonance in them has been demonstrated.

This paper presents solutions for guided wave motion (Lamb and shear horizontal) due to tensile and shear cracks in an isotropic plate using elastodynamic reciprocity. Finite-length through-thickness cracks are considered via Huygens’ principle by representing them as a superposition of point cracks. Far-field solutions are then derived in order to simplify the results and facilitate a direct comparison of guided mode excitability due to various cracking modes. Relatively short- and long-length line cracking are compared to point cracking for the fundamental modes S0, A0, and SH0. It is shown that the A0 modal response is the most sensitive to crack length, with S0 and SH0 being relatively insensitive. Additionally, the radiation patterns of S0, A0, and SH0 are relatively insensitive to crack length. The results have applications in acoustic emission monitoring of plate-like structures, where modal responses may be used to characterize crack growth.

To improve the efficiency in nonlinear dynamic calculation of finite-length tilting-pad journal bearings (TPJBs) under dynamic loads, an analytical method for hydrodynamic bearing forces, which considers the turbulence effect, is proposed using the method of separation of variables under the dynamic Gümbel boundary condition. No thermal effects are considered because this method is designed for the low viscosity case. The infinitely long bearing pressure is introduced as the circumferential pressure, and a general solution of the nonhomogeneous Reynolds equation is derived as the axial pressure. The turbulence model of Ng and Pan is characterized by a linear function of film thicknesses. A complete analytical expression of hydrodynamic bearing forces is derived. The analytical simulation shows slight differences and extremely low time expense in lubricating and dynamic performance compared to published data and finite difference method (FDM) simulation. The analytical method could be used to fast evaluate the nonlinear dynamic performance of a TPJB-rotor system in the low viscosity environment, supporting the nonlinear dynamic design of the system.

Kinetic simulations are used to compute current characteristics of finite-length cylindrical probes, with particular attention to end effects. Currents collected per unit lengths, as a function of distance to the ends, are calculated and fitted to empirical analytic functions. These fits, in turn, can be interpolated and used to predict probe characteristics; that is, collected current as a function of applied voltage, for a broad range of physical parameters of relevance to laboratory and space plasma.

The article addresses the extended Graetz–Nusselt problem in finite-length microchannels for prescribed wall heat flux boundary conditions, including the effects of rarefaction, streamwise conduction, and viscous dissipation. The analytical solution proposed, valid for low-intermediate Peclet values, takes into account the presence of the thermal development region. The influence of all transport parameters (Peclet Pe, Knudsen Kn, and Brinkman Br) and geometrical parameters (entry length and microchannel aspect ratio) is investigated. Performances of different wall heat flux functions have been analyzed in terms of the averaged Nusselt number. In the absence of viscous dissipation Br=0, the best heating protocol is a decreasing wall heat flux function. In the presence of dissipation Br>0, the best heating protocol is a uniform wall heat flux.

The problem on the extraction of a gas from a porous stratum of finite length saturated with this gas, water, and a gas hydrate under a depression action was solved in the radial-symmetric approximation with regard for the possibility of formation and decomposition of a hydrate in the stratum, the mobility of the liquid, and the Joule–Thomson effect. It was established that, on the opening of the stratum, a hydrate may or may not be formed in the bottomhole zone of the well depending on the initial gas saturation of the stratum and that, in the case where the gas saturation of the stratum is low, in it there take place aperiodic damped oscillations of the gas flow rate.

We investigated the effect of superhydrophobic walls on electrokinetics phenomena in a finite-length microchannel with superhydrophobic walls (in both transient and steady-state). We implemented the effect of superhydrophobicity using Navier’s slip-length. To include the importance of the electric double-layer, we scaled the slip-length with respect to Debye-length ( κ - 1 ). By increasing the slip-length from 0 to 144 nm (1.5 κ - 1 ), streaming-current, streaming-potential, flow-rate and electrokinetic energy conversion increased by 2.55, 2.44, 1.8, and 3.4 folds, accordingly. The electrokinetic energy conversion of each microchannel was in the order of picowatt. To produce more energy, an array of microchannels should be used.

The double cantilever beam specimen is assumed as two finite length beams, connected together, except at the initial delamination length. The energy release rate ( GI) is evaluated analytically by considering a Timoshenko beam on Winkler and Pasternak elastic foundations. The current data reduction methods have a blind spot in calculating GI when crack approaches the end of the ligament, which is considered in this study and, therefore, the simplifying assumption of infinite ligament length is not assumed here. GI will be strongly dependent on the ligament length if it is less than twice the thickness. Furthermore, the R-curves of different layups including their first points (fracture toughness) are drawn using Ρ–δ curves reported in the literature and they are compared to the experimental results. These comparisons show that Timoshenko beam on Winkler foundation gives the best results in comparison with experimental results for unidirectional and angle-ply laminates.

In this study, vortex-induced vibrations of an elastic cylinder near a finite-length plate were experimentally investigated. A rubber cylinder of diameter D was spanned in a test section of a wind tunnel near a rigid plate of length ≈ 6 D . The oscillation amplitude peak for an isolated cylinder was 0 . 3 D , and the Reynolds number of the peak-amplitude regime based on cylinder diameter was in the range of 180–260. For a cylinder located sufficiently upstream relative to the plate trailing edge, it was found that oscillation amplitude ratio A / D decreased if the gap ratio G / D between the cylinder surface and the plate decreased. However, for the cylinder location at the same level or downstream from the plate trailing edge, there were regions of essentially larger oscillation amplitude compared to an isolated cylinder case. Maximum amplitude growth by 39% was observed.

Particle image velocimetry (PIV) measurements are carried out in an experimental investigation of laminar opposing mixed convection in a vertical flow cell of finite length with a square cross-section. The bulk downward flow is driven by gravity while a portion of a lateral side is heated with laser irradiation. The working fluid is a copper nitrate aqueous solution, and the experiments are performed for three values of the Reynolds number of Re = 20, 40 and 60 and three values of the nondimensional absorption coefficient of a∗ = 0.5, 4.2 and 6.7. These parameters correspond to modified Richardson number range from 67 to 8084. A parametric study has been carried out to assess the effect of light penetration depth (i.e. absorption coefficient or solution concentration) on the final flow configuration; shear stress distributions have been calculated from the velocity field. Numerical simulations are also carried out to determine the thermal distributions, local and overall nondimensional heat transfer rates (Nusselt numbers) along the irradiated cell wall, and the complex flow features are presented in the form of contours of velocity, vorticity and temperature. The results reported herein demonstrate the modulation effect of Re and a ∗ on the flow and temperature distributions, and explore the convenience of laser irradiation heating for the purpose of selectively localizing energy deposition during thermal therapies by modeling biological tissues as light-absorbing media.

The material composition evaluation in functionally graded materials is the main concern of a designer to enhance the appropriate functionality of these materials to adopt them in their applications. In this study, new 2D-FGM material model based on the Mori-Tanaka scheme and third order transition function was developed for a thick hollow cylinder with finite length. The cylinder is subjected to the internal or external non-uniform pressure and also the finite element method was performed to analyse axisymmetric elastic stress. It has been demonstrated that the values of the stresses evaluated from external pressure loading were higher than the internal pressure loading ones. Subsequently, the values of Normalized Effective Stress (NES) vs. metallic volume fraction along the horizontal centre line have not been changed significantly by the variation of nz. In addition, the values of the NES which evaluated on the centre point of cylinder wall have been increased by increasing of the nr. Finally, it has been shown in details that the lowest value of the maximum NES was related to the nr = 20 and nz = 0.1 for both internal and external pressure loading. It means that the ceramic 2 (Si3N4) rich cylinder wall has the lowest value of maximum NES.

In this Paper transient thermo-elastic analysis of a thick hollow finite length cylinder made of two dimensional functionally graded materials (2D- FGMs) has been investigated. The transient heat conduction and the thermo-elastic equations have been solved for the cylinder subjected to thermal loading utilizing finite element method. The higher order Lagrange shape function elements have been used to improve the accuracy of the temperature and thermal stress distribution in the axisymmetric thermo-elastic analysis. In addition, a new effective material model according to the Mori-Tanaka scheme for 2D- FGM has been developed and implemented. The nonlinear temperature-dependency of material properties as well as their variation along two directions led into highly nonlinear equations. In consequence, the temperatures and stresses have been evaluated in the different time frames and the effects of the material distributions in two radial and axial directions have been investigated. The results mainly indicate that the variation of the material distribution along the axial direction significantly influence the temperature and stress distributions. Also the material distribution along the z-direction increases the design variables, so it will be helpful to achieve more desirable results.

An analytical investigation is presented to study the unsteady peristaltic transport of nanofluids. Three different geometries of nanoparticle viz bricks, cylinder and platelets are considered in our analysis. The flow geometry is taken as nonuniform channel of finite length to explore our model for wide range of biomedical applications. Exact solutions are obtained for the non-dimensional governing equations subject to physically realistic boundary conditions. The effects of nanoparticle shapes on effective thermal conductivity, axial velocity, transverse velocity, temperature, and pressure difference distributions along the length of non-uniform channel with variation of different flow parameters are discussed with the help of graphical illustrations. It is observed that platelet shaped nanoparticles carry maximum velocity whereas brick shaped nanoparticles are the best to enhance the thermal conductivity. An inherent property of peristaltic transport i.e. trapping is also discussed. This model is applicable in drugs delivery system where different geometries of drugs are delivered and it is also applicable to design a microperistaltic pump for transportation of nanofluids. Keywords: Unsteady flow, Peristalsis, Nanofluids, Nanoparticle shapes, Non-uniform channel

The state switching in an extended quasi-one-dimensional material is modeled by the stochastic formation of local new-state nuclei and their subsequent growth along the system axis. An analytical approach is developed to describe the influence of defects, dividing a sample into an ensemble of finite-length segments, on its state switching kinetics. As applied to magnetic systems, the method makes it possible to calculate magnetization curves for different defect concentrations and parameters of material.

A simple analytical method for study the magnetic properties of the finite-length biatomic chains in the framework of Heisenberg model with uniaxial magnetic anisotropy is proposed. The method allows to estimate the reversal time of the magnetization of ferromagnetic and antiferromagnetic biatomic chains. Three cases are considered: the spontaneous remagnetization, the remagnetization under the interaction with a scanning tunneling microscope, and the remagnetization in the external magnetic field. The applicability limits of the method are discussed. Within its limits of applicability the method gives results which are in perfect agreement with the results of the kinetic Monte Carlo simulations. As the examples, two physical systems are considered: biatomic Fe chains on Cu2N/Cu(001) surface and biatomic Co chains on Pt(997) surface. The presented method is incomparably less time-consuming than the standard kMC simulations, especially in the cases of low temperatures or long chains., 16 pages, 17 figures

A model is presented to determine the change in mutual impedance between a driver and pickup coil due to eddy-current interaction with a crack in a conductive two-layer plate system where the plates are separated by a non-conducting layer of constant thickness. Here, the impedance change of interest arises from a through-thickness crack of finite length located in the hidden lower plate. The model assumes that both conducting plates are electromagnetically thin and is therefore valid for large electromagnetic skin-depth. The model predictions are compared with experimental measurements using a pair of cylindrical air-cored coils arranged to simulate an eddy-current sliding probe. Agreement between the calculated and measured impedance change is obtained over the frequency range 10 Hz–3 kHz for which the plates can be treated as electromagnetically thin, and reasonable qualitative agreement was obtained at higher frequencies. A method for computing the induced current streamlines in the presence of the crack is also described and visualisation of the computed streamlines is used to assist in the interpretation of the impedance change for different probe orientations. These results provide a valuable initial insight into the interaction between a buried crack in a multilayer structure and the electromagnetic fields induced and detected by eddy-current sliding probes.

In this work, density functional theory is used to study the effect of finite length on electronic property of different types of Single Walled Carbon Nanotubes (CNT). The change in band gap due to short length effect in case of metallic (5,2) CNT and semiconducting (4,5) CNT is discussed here. Ordinarily electrons are restricted along the circumference of carbon nanotubes. But in this investigation a supplementary restraint of electrons has been applied along the axis of tube by making the tube lengths short. Due to this short length effect, band gap value of both types of CNT reduces as length of the tube increases. But this change is not tedious. Rather it exhibits observable oscillations in short length. These oscillations have been interpreted with reference to the bonding characteristics of frontier orbitals. This investigation providing novel acumen into the large band gap opening of chiral CNTs could be valuable in advancing future applications of CNTs in optical, electronic devices.

Numerical simulations are prevalently used to evaluate the seismic behaviour of structures. The accuracy of the simulation results depends directly on the accuracy of the modelling techniques employed to simulate the behaviour of individual structural members. An empirical modelling technique is employed in this paper to simulate the behaviour of column members under cyclic and seismic loading. Despite the common modelling techniques, this technique is capable of simulating two important aspects of the cyclic and seismic behaviour of columns simultaneously. The proposed fiber-based modelling technique captures explicitly the interaction between the bending moment and the axial force in columns, and the cyclic deterioration of the hysteretic behaviour of these members is implicitly taken into account. The fiber-based model is calibrated based on the cyclic behaviour of square hollow steel sections. The behaviour of several column archetypes is investigated under a dual cyclic loading protocol to develop a benchmark database before the calibration procedure. The dual loading protocol used in this study consists of both axial and lateral loading cycles with varying amplitudes. After the calibration procedure, a regression analysis is conducted to derive an equation for predicting a varying calibrated modelling parameter. Finally, several nonlinear time-history analyses are conducted on a 6-story steel special moment frame in order to investigate how the results of numerical simulations can be affected by employing the intended modelling technique for columns instead of other common modelling techniques.

The aim of this manuscript focus on the effect of the number of grating period on the performance of the photonic jet produce from a rectangular grooves based finite length finite diffraction grating. The computational analysis is carried out using three dimensional finite difference time domain method. From simulation result it is evident that, propagation length and Full width half maxima of the PNJ produce from the central period of the FRGG decreases with increase in number of grating period of the proposed rectangular grooves based finite length grating. Whereas in case of maximum possible length (MPL) which appears due to the increase in grating period, a reverse situation was observed. Therefore, PNJs generated from proposed FRGG having below defection limit can be used for high resolution microscopy.

Balloon dilation catheters are often used to quantify the physiological state of peristaltic activity in tubular organs and comment on their ability to propel fluid which is important for healthy human function. To fully understand this system's behavior, we analyzed the effect of a solitary peristaltic wave on a fluid-filled elastic tube with closed ends. A reduced order model that predicts the resulting tube wall deformations, flow velocities and pressure variations is presented. This simplified model is compared with detailed fluid-structure 3D immersed boundary simulations of peristaltic pumping in tube walls made of hyperelastic material. The major dynamics observed in the 3D simulations were also displayed by our 1D model under laminar flow conditions. Using the 1D model, several pumping regimes were investigated and presented in the form of a regime map that summarizes the system's response for a range of physiological conditions. Finally, the amount of work done during a peristaltic event in this configuration was defined and quantified. The variation of elastic energy and work done during pumping was found to have a unique signature for each regime. An extension of the 1D model is applied to enhance patient data collected by the device and find the work done for a typical esophageal peristaltic wave. This detailed characterization of the system's behavior aids in better interpreting the clinical data obtained from dilation catheters. Additionally, the pumping capacity of the esophagus can be quantified for comparative studies between disease groups., Paper was updated based on comments. Some content was moved to supplementary materials section to reduce the length of the paper

The performance of Stirling engines is directly related to the amount of energy that, in the form of heat, participates in the thermodynamic cycle. A peculiar characteristic of this type of engine is the closed circuit of the working fluid, implying a periodic admission and extraction, ideally involving the whole working fluid, of the heat exchanged during the cycle without any exchange of material with the external environment. Several correlations have been proposed in the literature to predict the heat exchange in the hot side heat exchangers, but most of them are based on nondimensional numbers, usually expressed in terms of an oscillatory Reynolds number and a non-dimensional length, that even if they take into account the amplitude and frequency of the oscillating flow inside the tube with respect to its diameter, do not include any dependency upon the length of the tube. Nevertheless, the length of the tube can have a great impact on the performance of a Stirling engine. The heater forms a significant part of the dead volume of the engine, making the optimization of the volume to surface ratio necessary. The friction losses increase by increasing the length of the tubes, determining a negative impact while the exchange surface increases. Even the Nusselt number in the inner side of the tubes changes along the length, achieving the largest values alternatively in the first portions of the tube lengths because of entrance effects (Graetz problem). The picture is made even more complex because of the special velocity profiles that develop in oscillating flows in tubes. One of the effects less investigated in previous studies, which we could call a “breathing effect”, regards the amount of working fluid that, in a real engine, can effectively travel from the hot side to the cold side, thus reaching the conditions of nominal heat exchange with the thermal source and sink of the cycle. An idealized configuration has been devised to investigate, using CFD simulations, these effects. Results reporting how the friction coefficient and the Nusselt number depend on the finite length of the tube will be illustrated.

The article deals with the problem of determining the stressstrain state of a thick-walled cylindrical shell hinged on the rim near the ends, which is exposed to temperature effects. The shell consists of three layers: two layers of heat-resistant concrete and a steel outer layer. The calculation takes into account the continuous inhomogeneity of materials caused by a stationary temperature field, as well as the nonlinear nature of concrete deformation. The nonlinear problem with variable parameters of elasticity E and ν was solved by the method of successive approximations.

Squeeze film of finite length rectangular plate is widely used in MEMS devices, immersion lithography machines and other engineering fields. The damping force of squeeze film of finite length rectangular plates can be obtained by multiplying the solution of infinite length rectangular plates with a correction factor depending on the aspect ratio. Whether the correction factor is the same for the inertia force is attractive to be studied. The distributions of velocity and pressure are obtained by solving the 3D Navier–Stokes(NS) equations with free and half sealed outlets, which shows the leakage of flow in the length direction causes the drop of maximum pressure comparing with the infinite case, which is about 56.6% for square plates. The squeeze film force ratios for 3D to 2D models with different aspect ratios have been obtained under the conditions of different film thickness, viscosity and rectangular width. It is concluded that the correction factor of damping force can be used to modify the inertia force. The damping and inertia coefficients can be easily extracted from the modified analytical solution of parallel rectangular squeeze film with finite length, which can be applied to the modelling of system dynamics.

The stability behavior of a simply-supported tube subjected to narrow annular flow in a finite-length gap support at the mid-length of the tube is experimentally investigated. For the experiments, a simply-supported tube and several finite-length gap supports were made considering different gap sizes. Several diffuser angles at the downstream of the support were also tested, since it is believed that the pressure recovery at the exit of the support is much more important than pressure loss at the entrance of the support. In this study, we observed that the tube lost its stability by flutter, and that the critical flow velocity at which the tube lost stability was dependent on the annular gap size and the diffuser angle. Interestingly, the tube with the diffuser angle of 10° lost stability at a lower flow velocity than with the diffuser angle of 20°, for relatively narrow gaps that are in the range of 0.018 to 0.042 gap-to-tube diameter. Differently, for the largest gap of 0.138 gap-to-tube diameter, the diffuser angle of 20° resulted in a lower instability flow velocity. We concluded that there may be different instability mechanisms depending on diffuser angle and related to the narrowness of the gap.

The configuration of film-substrate structure is widely involved in many aspects of technologies. To ensure high reliability and sound performance, it is of importance to understand the stress distribution and the adhesion at the interface. In the present work, within mind the film of finite width, a mechanical model has been proposed to analyze the traction at the interface between the film and an elastic substrate that may be subjected to either uniaxial stretching or bending. For incompressible substrates, the problem may be reduced to the solution of singular integral equations of Cauchy type and the tractions at the film’s edges have been revealed to exhibit the square-root singularity. Mode mixity has been calculated. By comparing the strain in the film when the system is subjected to uniaxial stretching with that from experiments on the adhesion between graphene and substrates, an agreement has been found and the implications of the present model in the measurement of adhesion energy have been discussed.

This study deals with the static bending of a finite length double-layered structure under radially symmetric mechanic and thermal loadings. The double-layered hollow structure is constructed of inner thermal barrier cylinder and outer FGPM(functionally graded piezoelectric material)cylindrical shell. The inner hollow cylinder is subjected to symmetric mechanic and thermal loadings, the outer shell is under an extra electric field. The material parameters of the double-layered structure are assumed to be inhomogeneous, or, rather, follows a power-law distribution. The inner thermal barrier cylinder is solved by the finite difference method, and the outer cylindrical shell is solved by using the analytical method. In the examples, numerical results separately show the effect of material properties, geometric shapes, mechanical and temperature loads on the double-layered structure. The distributions of material properties and the thickness ratio have a great influence on displacement and stress of the double-layered structure. Results in this study may be useful for the optimal design of FGPM cylindrical shell with thermal barrier layer.

This paper analytically investigates the reaction phenomenon in micro-combustors using a two-dimensional model. The length of micro-combustor is considered at finite length that makes a better physical model than other works. The micro-combustor medium is divided into three integral zones composed of preheat, reaction and post flame where the governing equations are solved using the matching conditions of neighboring zones. The reaction zone thickness is considered as a variable and predicted by an iterative solution. In order to validate the model, normalized magnitude of maximum temperature is compared with published computational data for different values of Peclet number that shows an acceptable agreement that confirms the accuracy of the predicted data. Since a higher wall temperature causes the reaction to be faster, increasing the normalized wall temperature will result to reduce reaction zone thickness.

A global analysis of steady states of low Mach number inviscid premixed reacting swirling flows in a straight circular finite-length open pipe is developed. We focus on modelling the basic interaction between the swirl and heat release of the reaction. For analytic simplicity, a one-step first-order Arrhenious reaction kinetics is considered in the limit of high activation energy and infinite Peclet number. Assuming a complete reaction with chemical equilibrium upstream and downstream of the reaction zone, a nonlinear partial differential equation is derived for the solution of the flow stream function downstream of the reaction zone in terms of the specific total enthalpy, specific entropy and circulation functions prescribed at the inlet. Several types of solutions of the nonlinear ordinary differential equation for the columnar flow case describe the outlet states of the flow in a long pipe. These solutions are used to form the bifurcation diagram of steady reacting flows with swirl as the inlet swirl level is increased at a fixed heat release from the reaction. The approach is applied to two profiles of inlet flows, the solid-body rotation and the Lamb–Oseen vortex, both with constant profiles of the axial velocity, temperature and mixture reactant mass fraction. The computed results provide theoretical predictions of the critical inlet swirl levels for the appearance of vortex breakdown states and for the size of the breakdown zone as a function of the inlet flow swirl level, Mach number and heat release of the reaction. For the inlet solid-body rotation, flow is decelerated to breakdown as the inlet swirl is increased above the critical swirl level, and there is a delay in the appearance of breakdown with the increase of the heat release of the reaction. For the inlet Lamb–Oseen vortex at low values of heat release, the critical swirl for breakdown is decreased with the increase of heat release while, at high values of heat release, the appearance of breakdown is delayed to higher incoming flow swirl levels with the increase of heat release. The analysis sheds light on the global dynamics of low Mach number reacting flows with swirl and vortex breakdown and on the interaction between vortex breakdown and heat release that affects the shape of the reaction zone in the domain.

A considerable portion of the power loss in a valve train mechanism is due to the losses in the cam follower mechanism. The surface of cam and follower experience counterformal contact with a varying nature that makes it a difficult component in an engine to model. Transient contact geometry and entraining may cause the inlet boundary reversal and short lived cessation of entraining motion which can lead to mixed regime of lubrication. Thermal effects and side leakage intensify the adverse governing tribological condition. This paper presents a thermo-elastohydrodynamic model with considering roughness of surfaces for a finite length cam-follower mechanism. Temperature variation, friction coefficient, and film thickness are the outputs of this model which can be used to evaluate the performance of this mechanical element. The results are validated by comparison to other published data. The results show that thermal effects, side leakage and roughness of contacting surfaces play an important role in the tribological performance of the mechanism. A friction analysis considering a comprehensive asperity interaction model is conducted to investigate the proposed lubrication model capability.

This article deals with free vibration analysis of thick nanocomposite laminated curved panels with finite length resting on two-parameter elastic foundations, based on the three-dimensional elasticity theory. The main objective of this research paper is to present a 3D elasticity solution for free vibration analysis of thick laminated curved panels with continuously graded carbon nanotube-reinforced (CGCNTR) sheets. The structure is supported by an elastic foundation with Winkler's (normal) and Pasternak's (shear) coefficients. The volume fractions of oriented, straight single-walled carbon nanotubes (SWCNTs) are assumed to be a three-parameter power-law distribution which is graded in the radial direction of the panels. An equivalent continuum model based on the Eshelby-Mori-Tanaka approach is employed to estimate the effective constitutive law of the elastic isotropic medium (matrix) with oriented, straight carbon nanotubes (CNTs). Because of using two-dimensional generalized differential quadrature method, the present approach makes possible vibration analysis of cylindrical panels with two opposite axial edges simply supported and arbitrary boundary conditions including Free, Simply supported and Clamped at the curved edges. The convergence of the method is demonstrated and comparisons are made between the present results and results reported by well-known references and have confirmed accuracy and efficiency of the present approach. This study serves as a benchmark for assessing the validity of numerical methods or two-dimensional theories used to analysis of laminated curved panels. POLYM. COMPOS., 2016. © 2016 Society of Plastics Engineers