Search

Large-eddy simulations are performed to study the wake of a wall-mounted finite-length rectangular prism at a Reynolds number Re ​= ​1.2 ​× ​104 for the prism aspect ratio AR (= h/a) ​= ​7 and the boundary-layer thickness ratio δ/h ​= ​0.08, where h is the prism span and a is the frontal width of the prism cross-section. Besides, parallel experiments are conducted to provide validation for the numerical simulations. This work aims to explore the dependence of the wake dynamics on the prism cross-sectional aspect ratio CR (= b/a) that is varied from 1 to 4, where b is the side width of the prism cross-section. It has been found that the flow separating from the leading edges of the side and top faces does not reattach for CR ​= ​1–2 but does once CR ​> ​2. This difference produces a profound effect on Strouhal number, drag coefficient, and flow structure. Two types of spiral streamwise tip vortices are captured over the top face, i.e. the primary and secondary vortices. The primary vortices give rise to the dipole structure in the wake for CR ​≤ ​2 but the spiral vortices on the side faces for CR ​> ​2. The formation and evolution mechanisms of these vortical structures including their interconnections and dependence on CR are discussed in detail. The conceptual models for the near-wake flow structures are also proposed with and without flow reattachment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Corrosion resistance increases with increasing tempering temperature. • SSP transforms the coarse grained structure into a nanostructured one. • SSP decreases corrosion resistance despite inducing the formation of nanograins. • Dislocations strongly influence corrosion resistance. • Pitting corrosion has been observed at the Mn inclusion in the SSP series. In this study, the effect of tempering temperature on the corrosion behavior of a low carbon steel (F1272) was analyzed by means of electrochemical tests: linear polarization resistance, potentyodinamic polarization and electrochemical impedance spectroscopy (EIS) in freely aerated 3.5% NaCl solution, at room temperature. The results show that corrosion resistance of the steel increases with elevating tempering temperature from 200 to 500 °C and finally, to 680 °C. Additionally, a severe shot peening (SSP) treatment was applied in the sample with the best corrosion behavior (TT680), in order to modify the grain structure. Results evidence that corrosion resistance of the TT680 sample decreases after the applied SSP treatment (10A and 5000% coverage). Corrosion behavior is discussed through the different microstructural singularities induced both the heat treatments and the SSP. [ABSTRACT FROM AUTHOR]

• Uni-directional wave propagation is investigated in time-modulated lumped-mass-inerter lattices. • General model is provided for the time-modulated mass, stiffness and inerter properties of 1D lattices. • The procedure based on Bloch-Fourier expansions is suggested to determine the asymmetric band-gaps. • Elastically connected beam array system with time-varying axial load is investigated. • The introduction of time-modulated inerters results in shifting of the frequencies of asymmetric band-gaps to lower values. Non-reciprocal wave propagation in acoustic and elastic media has received much attention of researchers in recent years. This phenomenon can be achieved by breaking the reciprocity through space- and/or time-dependent constitutive material properties, which is an important step in overcoming the limitations of conventional acoustic- and phononic-like mechanical lattices. A special class of mechanical metamaterials with non-reciprocal wave transmission are latices with time-modulated mass and stiffness properties. Here, we investigate the non-reciprocity in elastic locally resonant and phononic-like one-dimensional lattices with inerter elements where mass and stiffness properties are simultaneously modulated through inerters and springs as harmonic functions of time. By considering the Bloch theorem and Fourier expansions, the frequency-band structures are determined for each configuration while asymmetric band gaps are found by using the weighting and threshold method. The reduction in frequency due to introduced inerters was observed in both phononic and locally resonant metamaterials. Dynamic analysis of finite-length lattices by the finite difference method revealed a uni-directional wave propagation. Special attention is given to phononic-like lattice based on a discrete-continuous system of multiple coupled beams. Moreover, the existence of edge modes in the discrete phononic lattice is confirmed through the bulk-edge correspondence and their time evolution quantified by the topologically invariant Chern number. The proposed methodology used to investigate non-reciprocal wave transmission in one-dimensional inerter-based lattices can be extended to study more complex two-dimensional lattices. [ABSTRACT FROM AUTHOR]

• The wave diffraction problem by arrays of cylinders in front of a vertical wall, with infinite or finite length is examined. • The employed solution method relied on the multiple scattering approach and the direct matrix inversion method. • Two different cylinder arrangements have been investigated (i.e. a bottom-fixed and a floating cylinder array). • Additional resonances arising around the trapped and the near trapped modes for the array in front of a breakwater. The present paper deals with the investigation of the interaction phenomena of regular waves with arrays of circular cylinders either bottom-mounted or floating in front of a vertical breakwater of infinite and finite length. The acting loads on the array have been modeled using an analytical solution to the diffraction problem. The method of images is applied to define the fluid flow around the bodies of the array in front of a breakwater of infinite length, whereas the finite-length breakwater is represented by an elliptical cylinder with zero semi–minor axis. The multiple scattering approach and the direct matrix inversion method are compared to describe the hydrodynamic interaction phenomena among the members of the array. Focus is placed on the so called "near trapped" mode phenomena, created by an array of finite length, associated to the presence of the breakwater supplemented by representative numerical results concerning the exciting loads on the cylindrical bodies. [ABSTRACT FROM AUTHOR]

While extensive research has been conducted on elastic wave propagation in infinite phononic crystal (PC) rods, practical applications often involve PC rods of finite length. Therefore, it is essential to consider not only their functional properties, such as wave filtering, but also their mechanical behavior, including free vibration. Motivated by this concern, this study aims to establish a homogenized model for a finite-length PC rod based on the strain gradient theory (SGT) and provide simple closed-form expressions for its natural frequencies. To achieve this objective, an innovative method is developed to determine the material length scale parameters within the SGT. The investigation begins by analyzing the propagation of longitudinal waves in an infinite PC rod. By using the dispersion obtained from Bloch's theorem as a benchmark, it is demonstrated that the material length scale parameters associated with strain energy and micro-inertial effects in the SGT can be effectively determined by fitting the dispersion obtained from the SGT to the benchmark dispersion obtained from Bloch's theorem. With the determined parameters, the study proceeds to investigate the free vibration of a finite PC rod. The natural frequencies obtained from both the classical continuum theory (CCT) and the SGT are compared with those calculated by finite element (FE) simulations, which are based on an actual periodic structure and serve as a reliable benchmark. This comparison clearly highlights the superiority of the developed mesoscopic model based on the SGT in accurately predicting the natural frequencies, particularly for higher-order modes, compared to the CCT. • Free vibration of a finite phononic crystal rod is analyzed. • A homogenized model is developed based on the strain gradient theory. • Material length scale parameters within the strain gradient theory are determined. • Simple closed-form solutions for natural frequencies are presented. • Finite element simulation demonstrates the effectiveness of the developed model. [ABSTRACT FROM AUTHOR]

Herein, two commercial grades of nanosilica particles with various surface acidities were incorporated into a glycidyl-based polyester acrylate resin. The effect of the surface acidity of the SiO 2 nanoparticles on the photopolymerization-induced microgelation process was studied using electrochemical impedance spectroscopy technique. The diffusion-limited behavior was observed in both nano-UV-coatings loaded by two nano SiO 2 particles with different surface acidity. The structural heterogeneity caused by the microgelation phenomenon was decreased as the highly-acidic nanoparticles were included in the photopolymeric matrix. The highest value of the pore resistance and the finite length Warburg resistance were obtained for the UV-coatings incorporated by the highly-acidic SiO 2 nanoparticles. The apparent diffusion coefficient of Cl − through the microgel domains at the beginning of the immersion test was calculated to be 70 μm 2 /s for both coatings loaded by the slightly-acidic particles and highly-acidic particles. [ABSTRACT FROM AUTHOR]

By physical modelling we investigated the buckling and post-buckling behaviour of an elastic layer hosted in a viscous medium, as analogue of the elastic response of crustal rocks. The experiments were performed by embedding thin elastic layers of finite length in a linear viscous medium, and in two successive stages: a first stage of layer-parallel shortening in pure shear, followed by a second stage of post-buckling unfolding with zero velocity at the bounding walls. The experimental results show that the fold wavelength varies inversely with applied piston velocity, following an exponential function for which the higher the piston velocity the higher the number of waves. With cessation of layer-parallel shortening, the buckled layers underwent post-buckling relaxation in response to the elastic strain accumulated during the buckling stage. Such relaxation reduces the number of waves by successive elimination of the lower amplitude folds. The relaxation process gives rise to larger folds of higher amplitude in the centre of the elastic layer, concomitantly with the production of a train of gentle folds in the outer domains by outward motion of the ends of the elastic layer. This means that relaxation is more efficient away from the central domain. Comparison of our experimental results with available analytical solutions reveals significant discrepancies. Finally, we suggest that a similar process of relaxation of the elastic strain, although of lower amplitude, may explain the late stage open folding and the formation of overlying extensional basins observed in past orogens like the Caledonides in western Norway. [ABSTRACT FROM AUTHOR]

A dynamic implementation of the coupled criterion under quasi-static loading, based only on the mean velocity during crack initiation, is proposed. It relies on a simultaneous node release method. It consists of computing the dynamic incremental energy release rate by simultaneously opening a crack of a finite length during a given time increment rather than progressively opening smaller crack increments following a velocity profile as in the progressive node release method. Both methods result in significantly different kinetic energy variations as a function of the crack length, and thus different incremental energy release rates for large enough crack velocities, for which the kinetic energy magnitude is similar to the elastic strain energy magnitude. Both simultaneous node release method and progressive node release method can however be equivalently used for small enough crack velocities since similar incremental energy release rates are obtained with both methods. Inverse identification of fracture properties based on dynamic crack initiation at a hole in Brazilian disk specimens yields critical energy release rates in the same order of magnitude as the one obtained based on dynamic crack propagation modeling. • Dynamic implementation of the CC considering only initiation crack mean velocity. • Critical loading, initiation and stop length prediction considering inertial effects. • Inverse identification of tensile strength and critical energy release rate. [ABSTRACT FROM AUTHOR]

The effect of a finite length of hot-wire probe sensor length on the measured streamwise velocity fluctuations is well understood in canonical wall-bounded flow, where the small-scale energy has been found to be universal and invariant with Reynolds number. A straightforward application of that assumption to non-canonical flows such as strong adverse pressure gradient (APG) flows has, however, been hampered since the effect of Re and APG could not conclusively be studied separately due to the lack of data with a clear scale separation. The present experimental investigation at R e τ ≈ 4000 in weak, moderate and strong APGs with different wire length shows that spatial averaging effects are not only limited to the inner layer. A note of caution is hence warranted for measurements that seemingly try to take the bias effect of spatial attenuation into account by performing measurements with albeit long but fixed viscous-scaled wire length. • Measurements of TBL with varying hot-wire length at high Re covering wide range of APG conditions. • Small-scale energy attenuation in hot-wire measurements not limited to inner layer in strong APG TBLs. • Hot-wire spatial averaging effects remain present for strong APG conditions even at high Re. • Contrary to other studies, small-scale energy remains important albeit small in outer layer. [ABSTRACT FROM AUTHOR]

Time-vertex graph signal (TVGS) models describe time-varying data with irregular structures. The bandlimitedness in the joint time-vertex Fourier spectral domain reflects smoothness in both temporal and graph topology. In this paper, we study the critical sampling of three types of TVGS including continuous-time signals, infinite-length sequences, and finite-length sequences in the time domain for each vertex on the graph. For a jointly bandlimited TVGS, we prove a lower bound on sampling density or sampling ratio, which depends on the measure of the spectral support in the joint time-vertex Fourier spectral domain. We also provide a lower bound on the sampling density or sampling ratio of each vertex on sampling sets for perfect recovery. To demonstrate that critical sampling is achievable, we propose the sampling and reconstruction procedures for the different types of TVGS. Finally, we show how the proposed sampling schemes can be applied to numerical as well as real datasets. • We prove the necessary conditions for the stable reconstruction of JBL TVGS. • We prove lower bounds on sampling densities (or ratios) of the signals on subsets of vertices to be sampled. • We construct a multi-band sampling scheme to prove that critical sampling is achievable for any JBL TVGS. [ABSTRACT FROM AUTHOR]

This paper proposes model-based and model-free policy gradient methods (PGMs) for designing dynamic output feedback controllers for discrete-time partially observable deterministic systems without noise. To fulfill this objective, we first show that any dynamic output feedback controller design is equivalent to a state-feedback controller design for a newly introduced system whose internal state is a finite-length input–output history (IOH). Next, based on this equivalence, we propose a model-based PGM and show its global linear convergence by proving that the Polyak–Łojasiewicz inequality holds for a reachability-based lossless projection of the IOH dynamics. Moreover, we propose a model-free implementation of the PGM with a sample complexity analysis. Finally, the effectiveness of the model-based and model-free PGMs is investigated through numerical simulations. [ABSTRACT FROM AUTHOR]

This paper proposes a generalized hardware architecture for performing the half-sample and whole-sample symmetric/anti-symmetric extension of a finite-length signal to handle the effect of border discontinuities. The symmetric extension is performed by duplicating the required number of data samples at the boundary followed by reflection about the symmetry axis. The proposed architecture comprises of a shift register that directly streams the data samples, and last-in-first-out (LIFO) buffers to duplicate the data samples at the boundaries. The symmetrically extended signal is obtained by selectively passing the outputs of shift register and LIFO buffers at required instants. Further, a two's complement circuit is used to invert the data samples at the boundary to perform anti-symmetric extension. The proposed architecture is implemented on field-programmable gate-array (FPGA) to perform the half-sample symmetric extension to favor the low pass Daubechies-8 finite-impulse response (FIR) filter and whole-sample extension for bi-orthogonal 9 × 7 FIR filter with 9 low-pass and 7 high-pass coefficients. The implementation results show that the proposed architecture achieves a maximum operating clock frequency of 275 MHz and 300 MHz for half-sample and whole-sample extension, respectively. The resource utilization of proposed router architecture is approximately reduced by a factor of L (filter length) compared to the conventional router architectures that performs the signal extension by dynamically routing the data samples to the computational part of the FIR filter. The proposed architecture is compatible to various filter architectures without any speed penalty on the performance of FIR filters. [ABSTRACT FROM AUTHOR]

In this paper we study the motion of a finite composite cylindrical annulus made of generalized neo-Hookean solids that is subject to periodic shear loading on the inner boundary. Such a problem has relevance to several problems of technological significance, for example blood vessels can be idealized as finite anisotropic composite cylinders. Here, we consider the annulus to be comprised of an isotropic material, namely a generalized neo-Hookean solid and study the effects of annular thickness on the stress distribution within the annulus. We solve the governing partial differential equations and examine the stress response for the strain hardening and strain softening cases of the generalized neo-Hookean model. We also solve the problem of the annular region being infinite in length, that reduces the problem to a partial differential equation in only time and one spatial dimension. When the thickness of the annulus is sufficiently large, the solutions to the problems exhibit very interesting boundary layer structure in that the norm of the strain has a large gradient in a narrow region adjacent to one of the boundaries, with the strain being relatively uniform outside the narrow region. We also find that beyond a distance of two times the annular wall thickness from the ends of the cylinder the solutions for the infinite length cylinder match solutions for the finite length cylinder implying that end effects are not felt in most of the length of a sufficiently long annulus. • Boundary layers formed strain softening generalized Neo-Hookean materials. • Comparison of infinite and finite length solutions to axial shear. • Boundary layers formed in composite generalized Neo-Hookean materials. [ABSTRACT FROM AUTHOR]

Abstract Injection of fluids in deep subsurface geological formations has created a series of challenges in recent decades. Possibility of upward fluid leakage along nearby wells and faults is one of the main issues related to these operations. It is important to ensure that such conduits, if present, can be detected, characterized and treated. Looking for pressure abnormalities in intervals above the injection zones, is one the methods used to monitor for these conduits. We propose an analytical solution to detect and characterize the vertical leakage from a fault of finite length using pressure data collected from monitoring zones. The proposed closed form analytical model would allow to not only distinguish the pressure signal of leakage from a fault of finite length from other possible leakage conduits but also to estimate the leakage rate, length of leaky section of the fault and relative position of the fault with respect to the location of monitoring well. Highlights • For first time based on Theis solution a mathematical solution for fault leakage is derived. • Derived analytical solution were used to study fluid movement out of a linear-finite fault [ABSTRACT FROM AUTHOR]

Highlights • Effects of magnetic field and porous medium on forced convection are studied. • Effects of a magnetic field (MF) induced by a solenoid on the heat transfer are studied. • The MF distribution of a finite length solenoid on the porous medium was modeled. • Effects of different media on the distribution of the MF were considered. Abstract In this article, effects of magnetic fields induced by a finite length solenoid on the forced-convection heat transfer in a pipe partially filled with porous medium have been investigated. In this regard, two-dimensional steady-state fluid flow in the pipe was considered and the Darcy–Brinkman equation of motion was applied to model the fluid flow in the porous medium, as well as the thermal equilibrium was assumed between the solid phase and the magnetic nanofluid. Effects of electric current passing through the solenoid and the solenoid dimensions (i.e.; diameter and length) on the forced-convection heat transfer were studied carefully. The combined effects of the magnetic field and the porous medium lead to a higher mixing intensity and disruption of the thermal boundary layer which in turn result in the enhancement of the local Nusselt number value at the expense of low-pressure drop increase due to partially filling the pipe. In the simulation study, variations of the magnetic field in different media were taken into account and the assumption of the linear function of magnetization with respect to the applied magnetic field intensity was relaxed. The obtained simulation results indicate that under the influence of the magnetic field induced by a solenoid with a current intensity of 10 A, the average Nusselt number value increases up to 30%. [ABSTRACT FROM AUTHOR]

Abstract This paper is devoted to the construction of multiresolution frameworks related to general but linear subdivision schemes applied on sequences of finite length. Thanks to the flexible properties of subdivision schemes, a subdivision-based multiresolution is a promising powerful tool for compression, control and analysis of data. However, its construction is not straightforward either for non-interpolatory subdivisions, or for sequences of finite length. In this paper, given a subdivision for finite length sequences, we provide a first approach to construct compatible multiresolutions thanks to an extension of some classical wavelet results. As it will become clear that this type of approach can become computationally costly in practice, a new edge-adapted method that combines local consistent decimation is then developed to circumvent this limitation. An illustration in the case of the 4-point shifted Lagrange subdivision scheme, for which there is no available multiresolution up to now, is then provided. Finally, some properties of the new multiresolutions are analyzed and their performances are evaluated in the framework of image approximation. [ABSTRACT FROM AUTHOR]

Highlights • Cohesive zone model and coupled criterion both predict sudden crack initiation. • A crack initiates over a finite length in very short time and loading increments. • Initiation force and crack arrest length depend on the cohesive zone model profile. • The coupled criterion seems more efficient computationally than cohesive zone models. Abstract Numerical predictions of initiation loading and crack length in a rhombus hole specimen made of a brittle material under quasi-static compression using either cohesive zone model or coupled criterion based on finite fracture mechanics are compared. Both methods lead to the conclusion that crack initiation results in a crack jump over a finite length at a given loading level, which depends on the material parameters and on the specimen geometry. The initiation load level and crack extent depend on the cohesive zone traction-opening displacement profile which represents the underlying failure mechanism. The ranges of initiation force and crack lengths obtained with various traction-opening profiles respectively comprise the initiation force and lower bound for crack arrest derived from the coupled criterion. For the configuration under investigation, similar initiation forces and crack arrest lengths as those predicted using the coupled criterion are obtained using a bilinear cohesive zone model. [ABSTRACT FROM AUTHOR]

Abstract In this research, Ti-Cr-N coatings on tool steel were prepared using DC magnetron sputtering at 25 °C (RT), 130 °C and 190 °C. Coating corrosion behavior was observed in a 3.5% NaCl solution at 25 °C using Potentiodynamic Polarization and Electrochemical Impedance Spectroscopy (EIS). EIS circuit models for corrosion kinetics were proposed and the surface area and porosity of the coatings were recorded. Corrosion resistance was found to be higher for the coatings grown at 190 °C. This could be attributed to high density as well as low porosity. The EIS circuit model suggests the penetration of corrosive electrolytes into pores reaching the steel substrate for the coatings grown at RT. Finite length diffusion inside pores was also observed. The slow infiltration of corrosive electrolytes into the steel substrate could be seen in coatings grown at 130 °C with diffusion inside the pore similar to that in the coatings grown at RT. However, the EIS circuit model did not exhibit a finite length diffusion of the coatings grown at 190 °C. Owing to high coating density and smaller pore size, corrosive electrolytes could hardly penetrate through and reach the steel substrate. Highlights • The corrosion study of PVD coating has not been so much investigated especially by EIS. • Effect of different microstructures on corrosion behavior has been investigated. • EIS analysis confirms that coating microstructure strongly affects corrosion behavior. [ABSTRACT FROM AUTHOR]

Inhibition of subsurface crack growth under contact loading is key to enhancing the service performance of brittle materials. However, the understanding of crack extension mechanism under complex conditions is still limited. In this paper, scratch experiments and stress field analysis were used to investigate the damage evolution of glass materials induced by the curvature effect of abrasive trajectories. A cycloid or trochoid analytical model was developed to identify curvature-sensitive paths. On this basis, Curvature scratching experiments were conducted on the self-developed scratching experimental platform. The results revealed that surface cracks appeared outside the scratch grooves at the maximum curvature. Scratches with higher curvature peaks demonstrated less depth of crack initiation, and deeper cracks were induced inside the scratch. A novel finite-length, curved stress field model is proposed to evaluate the damage evolution from the inner and outer sides of the scratch. Based on the theory of maximum principal stress and tensile stress, the mechanism of crack extension under the curvature effect is revealed. This study improved the understanding of abrasive scratching and cracks extension under broad physical conditions. [Display omitted] • The curvature causes a different crack distribution on both sides of the scratch. • Surface cracks always appeared outside the scratch at the maximum curvature. • Subsurface cracks inside the scratch are more severe than those on the outside. • A novel finite-length, curved stress field model is proposed. • Stress deflection induces a special crack extension mechanism. [ABSTRACT FROM AUTHOR]

The acoustic radiation efficiency of a cylindrical shell is an important parameter in estimating the sound radiation emitted by a structure. However, many of the relevant previous studies have approached acoustic radiation problem by employing numerical methods, requiring large computational resources. In this study, an analytical method is developed to calculate the acoustic radiation efficiency of a finite-length, submerged, periodically stiffened cylindrical shell excited by a radial line force. Using the Flügge shell equations and Helmholtz equation, the motions of the shell wall and the acoustic pressure field in the outer fluid can be expressed analytically. Furthermore, to investigate the effects of finite length on the acoustic radiation efficiency, a stiffened cylindrical shell of infinite length is assumed to have a finite-length vibration distribution and to be constrained by simply supported boundary conditions. Numerical simulations are performed to investigate the acoustic radiation efficiency's dependency on the finite-length vibration and the presence of stiffeners. [ABSTRACT FROM AUTHOR]

• Bandgap formation in a fluid conveying pipe using local resonators. • Pipe modelled as a Euler-Bernoulli beam. • Bandgaps predicted using unit cell method based on infinitely long beam. • Bandgaps also predicted using unit modal analysis approach based in finite length beam. • Effect of flow velocity, ratio of resonator's mass to that of pipe in addition to other parameters on bandgap formation. The objective of this paper is to investigate the effects of fluid flow velocity on the edge frequencies of the bandgap in an acoustic metamaterial pipe in a non-dimensional framework. Two methodologies are presented to predict the formation of the bandgap. In the first methodology, the pipe is considered to be infinitely long and the dispersion of an elastic wave in a single representative periodic unit cell of the structure is used to estimate the bandgap edge frequencies. In the second method, the pipe is modeled as a finite structure with defined boundary conditions and a modal analysis-based method is used to estimate the edge frequencies. A parametric study is performed wherein parameters identified from the non-dimensional analysis are varied, namely, the dimensionless flow velocity, the ratio of the resonator's mass to that of the pipe and the fluid and the ratio of the fluid's mass to that of the pipe and the fluid. It is shown that a close agreement in the bandgap edge frequencies is achieved using both methodologies. Furthermore, it is observed that an increase in the fluid velocity induces a decrease in the bandgap width, an increase of the mass ratio of the fluid to that of the pipe and the fluid results in a small decrease in the bandgap width and finally an increase in the mass of the resonators relative to that of the pipe leads to an increase in the bandgap width. [ABSTRACT FROM AUTHOR]

In high speed roller bearings, the drag force due to the oil-air mixture present in the bearing cavity – that is acting against the roller movement – is usually computed with a two-dimensional model of flow around a cylinder of infinite length. However rollers are of finite length, and the flow is perturbed by the two free ends, the surrounding rings, the cage and other rolling elements. In this article, the Computational Fluid Dynamics (CFD) method is employed to analyze first the flow around one finite-length circular cylinder with two free ends in an open space. Then the model is changed to one finite cylinder and then several in-line circular cylinders sandwiched by two flat walls, which represents a simplified approach. The results indicate that both the flow pattern around the cylinder and its drag coefficient are modified in comparison with the two-dimensional model. Finally a relationship between the drag coefficient and the Reynolds number suitable for circular cylinder in roller bearings is proposed. [ABSTRACT FROM AUTHOR]

Electrochemical Impedance Spectroscopy (EIS) is a frequently used method to characterize electrodes for Solid Oxide Fuel Cells (SOFC) or Electrolyzer Cells (SOEC). The porous microstructures, use of composite structures and sometimes extra functional layers in an electrode, result often in impedance spectra that are difficult to analyze. Transformation of the impedance into a distribution function of relaxation times (DFRT) is about to become a new standard in EIS analysis. This inversion to the τ-domain requires solving a Fredholm integral of the second kind, which is known as an ‘ill-posed inverse problem’. Hence the resulting DFRT's should not be trusted directly. In cases were impedance data can be modelled satisfactory with an Equivalent Circuit (EqC), built of known dispersion relations (e.g. (RQ), Gerischer, Finite Length Warburg) an analytic distribution function, G (τ), can be constructed. This can be compared with the inversion results obtained from Fourier Transform (FT), Tikhonov Regularization (TR) and multi-(RQ) CNLS fits ( m (RQ)fit), thus allowing evaluation and validation of these methods This is illustrated in this contribution with four examples of SOFC cathodes with quite different properties. The results apply equally well to SOFC anodes (or SOEC cathodes). [ABSTRACT FROM AUTHOR]

• A novel modeling methodology of monorail train and large-scale bridge interaction is developed and validated with a field test. • Convergence, accuracy, and computational efficiency of the proposed methodology are all discussed. • Comparison with traditional model illustrates the advantages and significance of the proposed methodology. • Effects of the varying bridge profiles on the vehicle-bridge interaction are elaborately evaluated. High–efficiency solutions for extremely long bridge structures are a challenge in vehicle-bridge interaction modelling. In the present work, a novel modelling methodology for a monorail train and large-scale bridge interaction system is developed based on moving element technology. First, the governing equations for the monorail train subsystem are derived by adopting the Newton-Euler method, and an extremely long bridge is modelled based on an improved component mode synthesis method in which a bridge unit with finite length is updated and moved as the train moves forward. The train and bridge subsystems are coupled together by a nonlinear wheel–track interaction model. Subsequently, the convergence of the proposed method is discussed in detail, and reasonable values of several crucial model parameters are determined. On this basis, the simulation results obtained by the proposed methodology are compared with those of the finite element method (FEM) and field test data, validating the reliability of the proposed methodology and revealing its remarkable advantages. Finally, by applying the proposed methodology, the dynamic performance of the monorail train-bridge system is evaluated under different operating conditions. Results indicate that the proposed methodology can achieve good calculation accuracy for the vehicle-bridge dynamic responses; additionally, its computational efficiency is much higher than that of the FEM. The variation of the bridge section profile has a notable effect on the dynamic performance of the monorail vehicle-bridge system, which becomes more significant with increasing train speed. [ABSTRACT FROM AUTHOR]

• Analytical method is developed for forced vibration of plates with part through surface cracks. • Wave propagation framework is developed for cracked plate for the first time. • Classical and refined line–spring models of all-over and finite-length cracks are considered. • Dual equations is formed based on the kinematic and dynamic variables of plate. • Parametric studies on the effects of position and depth of crack are presented. An analytical wave propagation framework is developed in this study for steady state forced vibration of plates with part through surface cracks for the first time. Rectangular thin plates with partial-width and full-width cracks are considered. The analytical waves are obtained by solving the dual equations of the plate established considering the line–spring model (LSM) of crack. The dual equations formed here are characterized by simultaneously solving kinematic variables and their dual dynamic variables. Both conventional and refined LSMs are considered. Two ways are proposed to generate the system equation in wave space based on the relationships of wave propagation, wave reflection and wave scattering. Compared with the traditional methods, most of them can only give exact analytical solutions under the condition of opposite-side simply supported boundaries, the developed analysis framework can treat arbitrary combinations of simple boundary condition of the cracked plate. Comparisons of results of the proposed method with those from the literature and finite element method (FEM) validate the effectiveness of the proposed method. A series of parametric studies for investigating the effects of length, position and depth of crack on the forced response of cracked plate are also presented. The proposed framework are effective for predicting the forced responses and natural frequencies of thin plates with part-through surface cracks. [ABSTRACT FROM AUTHOR]

There is a strong incentive to enhance in-situ ground characterisation tools to provide additional data that supports early infrastructure design in engineering projects, prior to completion of laboratory element testing on borehole samples. Advances in robotic technology allow additional soil deformation modes to be probed by integrating a cylindrical section of cone capable of horizontal translation into an expanded standard cone penetrometer, referred to here as ROBOCONE p-y module, which can mimic the load and displacement behaviour of laterally loaded pile element. This paper presents a series of three-dimensional elasto-plastic finite element simulations and semi-analytical upper bound analyses of this p-y module in homogeneous, undrained clay. The aim is to support the optimal choice of p-y module geometry and to lay the foundation of an interpretation method. In particular, the paper investigates the lateral bearing factor (N RC) and elastic stiffness factor (K RC) required for the measured load–displacement curves to be converted into practical design soil parameters such as undrained shear strength and elastic shear modulus. The numerical results reveal that N RC varies inversely with the height-diameter ratio (H R / D R) of the p-y module and interface roughness, and these factors are compared to semi-analytical upper-bound solutions. Correction factors that allow for the finite length of the p-y module are derived, and these have minimal variation with interface roughness. The height-diameter ratio H R / D R has a similar influence on K RC. Simple mechanism-based expressions for the lateral bearing and stiffness factors are devised to generalize the numerical results and provide definitive solutions to determine soil undrained strength and elastic stiffness from ROBOCONE p-y module measurements. [ABSTRACT FROM AUTHOR]

We introduce Koszul modules associated with (graded) Kac-Moody Lie algebras. We provide a precise criterion for when these modules are of finite length. As an exemplary application we deduce a bound on the dimension of the second graded component for a certain class of graded Kac-Moody Lie algebras. We also provide an exact description of all nilpotent Kac-Moody Koszul modules. [ABSTRACT FROM AUTHOR]

• Deal with the nonlinear term using product to sum formula for the first time. • Simulate the variation of elastic layer depth by sine wave. • Discretize the stresses in the J-integral loop to compute SIF. • Study the effect of vehicle-road coupled vibration on crack propagation. To reflect the characteristics of soil more accurately, an improved two-parameter foundation-plate model is built. A vehicle-road coupled model is modeled as a 2-DOF vehicle moving along a plate with finite length and width on a cubic nonlinear foundation. The variation of depth of elastic layer is modeled using sine wave. The Galerkin truncation method is used to discretize the partial differential equations into ordinary differential control equations. Using product to sum formula and introducing the Dirac delta function, the double integral term resulted from nonlinearity is removed. The effects of parameters from vehicle and foundation-plate on vehicle-road coupled model responses are studied. In addition, in order to analyze the influence of vehicle-road coupled vibration on crack propagation, initial cracks with certain length and width are set on the pavement. Using the J-integral Criterion of crack propagation, the stress intensity factors (SIF) of mode I and mode II cracks for mixed cracks are obtained through the stress on the discrete integral loop, and then the propagation path of surface crack of road is obtained. The propagation of the vehicle-road coupled model considering pavement crack, the vehicle-road coupled model without considering pavement crack and the traditional foundation-plate model are computed and compared. It can be found that the influence of vehicle-road coupled vibration for pavement crack can not be ignored. In short, the results presented in this paper realize the fast and accurate calculation of foundation-plate model described by ultra-high dimensional nonlinear ordinary differential equations, and then can realistically simulate the crack propagation path, which is helpful to better understand the cracking behavior of asphalt pavement. [ABSTRACT FROM AUTHOR]

In this study the role of vergence in relation to age-dependent scaling of eye and photoreceptor parameters is studied. The underlying hypothesis is that the size and packing of outer segments is matched to the pupil size outdoors in photopic conditions. Vergence is analysed in relation to the angular spectrum of waves being incident using age-dependent data from the literature for the actual geometry and density of photoreceptor cones and rods. This approach is used to derive simple relations for the angular confinement of light along outer segments. Only with a small photopic pupil can leakage and crosstalk for both central and peripheral photoreceptors be entirely ruled out due to the finite length of the outer segments. A limiting 3 mm pupil size is found for children in the school age. Larger pupils will increase the likelihood of leakage and crosstalk that may therefore impact on emmetropization. This study has introduced a new paradigm in myopia research by considering vergence across the 3-D retina as being matched to the angular spectrum of waves being incident from the eye pupil. Emmetropization suggests a delicate balance between photoreceptor outer segment length and density in relation to pupil size. Only when balanced will leakage and crosstalk between adjacent outer segments be effectively suppressed thereby ensuring the highest possible light capture efficiency by visual pigments in the outer segments whether an image is formed on the retina or not. [ABSTRACT FROM AUTHOR]

A derivation of the fundamental impedance of a Lithium-Ion battery electrode is given, exemplarily conducted for a solid thin-film electrode. The focus of this derivation is not on developing a model which is able to reproduce the exact behaviour of a given electrode, but rather on deriving its fundamental characteristics from few and intuitive assumptions in a simple and transparent way. It is thus shown, that the fundamental impedance of a solid thin-film electrode consists of an RC-element for charge-transfer, a Finite-Length Warburg element for diffusion in the electrolyte and a Finite-Space Warburg element for diffusion in the solid-state. The use of a Finite-Length Warburg element with a serially connected capacitor for modelling diffusion in the solid-state is thus indicated to be physically questionable. In addition, the theoretically expected behaviour of charge-transfer and solid-state diffusion on the degree of lithiation (State-of-Charge) is derived and discussed. [ABSTRACT FROM AUTHOR]

This paper presents Method of Continuous Source Functions (MCSF) for homogenization of material properties both elasticity and heat conduction in composite material reinforced by finite length regularly distributed, parallel, overlapping fibres. Stiffness/conductivity is incrementally reduced starting with rigid/super-conductive material properties of fibres and the fibre-matrix interface boundary conditions are satisfied by iterative procedure. Computational examples have to show: (1) the possibilities and difficulties connected with present numerical models and suggested ways for further developments, (2) similarities and differences in composite behaviour in heat flow and elasticity and (3) the way of choosing control volume for homogenization of composite materials reinforced by finite length fibres with large aspect ratio. Parallel MATLAB computational models increase computational efficiency. The results indicate that the proposed method is efficient and accurate in analysing the micromechanical elasticity and thermal behaviour of short fibre-composites. [ABSTRACT FROM AUTHOR]

• Electrochemical impedance of heterogeneous ion-exchange membrane is studied. • Impedance spectrum of a heterogeneous membrane consists of two loci. • The relatively low-frequency locus is a finite-length diffusion Warburg impedance. • The higher frequency locus, caused by surface heterogeneity, has a nose-like shape. • Curvature of current streamlines in solution leads to an increase in the system resistance. Understanding of the effect of membrane/electrode surface heterogeneity on the electrochemical behavior of membrane/electrode systems in conditions of current-induced concentration polarization is an important issue. In this paper, low-frequency electrochemical impedance spectra (EIS) of electrically heterogeneous ion-exchange membranes (IEMs) are studied experimentally and theoretically. A 2D model for calculating these spectra is proposed. Non-stationary ion transport through a heterogeneous membrane and two adjacent diffusion layers is studied. The corresponding mathematical problem is solved numerically and analytically under conditions of zero DC bias of the applied AC signal. It is shown that at sufficiently low frequencies, the impedance spectrum of a heterogeneous IEM is described by the finite-length-Warburg-type impedance. However, in the range of relatively high frequencies, a nose-shaped element appears on the complex plane plot. This element reflects an increase in the system resistance due to a higher concentration polarization of the boundary solution caused by nonconductive surface areas. An exact analytical solution describing the impedance is found in the case where the diffusivities of anion and cation are the same. The form of this solution is convenient for the experimental data analysis. A good quantitative agreement between the calculated and experimental impedance spectra for several commercial and specially prepared heterogeneous membranes is established. [ABSTRACT FROM AUTHOR]

• Mechanical model for the peeling behavior of a film with finite length perfectly bonded to an elastic substrate has been proposed. • The effects of root rotation, ratio between Young's moduli of the film and the substrate, and film's aspect ratio on peeling behavior have been demonstrated. • Empirical expression for estimating peeling force in relation to those parameters has been established. A mechanical model for the peeling behavior of a film with finite length perfectly bonded to an elastic substrate has been proposed. The film has been considered as an elastic beam from which the root rotation at the boundary between the debonded and bonded portions can be obtained. Numerical results have demonstrated significant effects of the parameters including root rotation, ratio between Young's moduli of the film and the substrate, and film's aspect ratio on the stress intensity factors that were used to measure the interfacial tractions. Based on the numerical results, empirical expressions for the stress intensity factors have been presented. And hence expression for estimating peeling force in relation to those parameters has been established. The results in the present paper may be helpful for characterizing the peeling behavior of film-substrate systems. [ABSTRACT FROM AUTHOR]

In industrial plants, pneumatic systems are often used to convey particles. In bench-scale experimental setups, clusters of particles sometimes flow backward or upstream in the conveying channel. In this paper, the effect of electrostatic charge and forces on particle backflow was investigated. Different conveying conditions with varying particle charges were simulated using computational fluid dynamics (CFD), and the resulting flow patterns were compared with CFD simulations of uncharged particles. In a channel flow, it was found that electrostatic forces drive particles into low-velocity regions but do not reverse their flow. In flow through a finite-length duct, electrostatic forces cause particles to settle close to the duct's inlet. Finally, when particles were injected into the duct in a pulse, backflow was observed at particle charge values of 5.04 femto Coulombs (fC) and higher. Thus, it was concluded that electrostatic forces can cause particle backflow in pneumatic conveying systems if fed discontinuously. [Display omitted] • Powder conveying was simulated using computational fluid dynamics (CFD). • In a periodic channel flow, electrostatic forces drive particles into low-velocity regions. • In a finite-length duct, electrostatic forces cause particles to settle close to the duct's inlet. • Particle backflow occurred when particles of a charge of at least 5.04 fC were injected in pulses. [ABSTRACT FROM AUTHOR]

In the development of smart home products, energy monitoring, and control systems, there is a significant need for precise and reliable electric current measurement. Most domestic appliances, whether residential or commercial, are powered by power cords with two wires. A reliable and accurate current probe would be required to detect current in two-wire power cables. Existing current sensors for two-wire power cables are complex, bulky (they use a magnetic core), and need full access to the power cord. In this paper a coreless, contactless current probe that requires only limited access of the space around the two-wire power cable is proposed. The sensor unit presented here measures the current accurately even for certain types of misalignments of the power cord. This makes the current measurement less sensitive to minor mechanical displacements, radius of the conductors, and the overall insulation thickness of power cord. In the proposed current probe, one-of-a-kind and highly reliable arrangement of magnetic field sensors, are used to measure the magnetic flux density caused by the current passing in the power cord. The current is computed using a derived mathematical formula which is expressed in terms of the voltage outputs of the magnetic sensors. To provide a clear understanding of the measurement process, an analysis using the Finite Element Method (FEM) is performed. The functionality of the proposed current probe is theoretically tested. Considering different sources of errors, an accuracy of less than 1.5% is obtained. [Display omitted] • The proposed current probe does not require 360° space around the power cord, this method requires only partial space by the side of the power cord. • The proposed probe enables distance-independent current measurement, varying based on power cord insulation thickness and diameter. • The probe offers efficient, simple, cost-effective current measurement in power cords with three magnetic sensors. • To keep up with the errors, mathematical analysis was done with finite length of the power cord. • In addition, FEM analysis validated in presence of ferromagnetic materials and with interference due to external magnetic field. [ABSTRACT FROM AUTHOR]

The nonconvex and nonsmooth finite-sum optimization problem with linear constraint has attracted much attention in the fields of artificial intelligence, computer, and mathematics, due to its wide applications in machine learning and the lack of efficient algorithms with convincing convergence theories. A popular approach to solve it is the stochastic Alternating Direction Method of Multipliers (ADMM), but most stochastic ADMM-type methods focus on convex models. In addition, the variance reduction (VR) and acceleration techniques are useful tools in the development of stochastic methods due to their simplicity and practicability in providing acceleration characteristics of various machine learning models. However, it remains unclear whether accelerated SVRG-ADMM algorithm (ASVRG-ADMM), which extends SVRG-ADMM by incorporating momentum techniques, exhibits a comparable acceleration characteristic or convergence rate in the nonconvex setting. To fill this gap, we consider a general nonconvex nonsmooth optimization problem and study the convergence of ASVRG-ADMM. By utilizing a well-defined potential energy function, we establish its sublinear convergence rate O (1 / T) , where T denotes the iteration number. Furthermore, under the additional Kurdyka–Lojasiewicz (KL) property which is less stringent than the frequently used conditions for showcasing linear convergence rates, such as strong convexity, we show that the ASVRG-ADMM sequence almost surely has a finite length and converges to a stationary solution with a linear convergence rate. Several experiments on solving the graph-guided fused lasso problem and regularized logistic regression problem validate that the proposed ASVRG-ADMM performs better than the state-of-the-art methods. [ABSTRACT FROM AUTHOR]

The available multifractal traffic finite-length time series to implement performance test of the management, control and admission algorithms, and level of service about M/M/1 models for WAN/LAN communication systems are very few and their recollection through current mechanisms is very slow due to the amount of data that must be obtained. Hence, it is necessary to develop a tool which synthesizes traces with multifractal features and allows the stochastic parameters configuration as its average, Hurst parameter and, multifractal spectrum width. This article describes the development of a proposed algorithm to generate multifractal traffic finite-length time series with a Hurst parameter and the multifractal spectrum width, sampling and adjustable, called MultiFractal Hurst Spectrum Width (MFHSW). The MFHSW algorithm is based on the MultiFractal Hurst model (MFH) and on the Multifractal Wavelet Model (MWM), to construct the time series through a binomial multiplicative cascade. The main contribution of the MFHSW algorithm is to allow adjusting both the Hurst parameter and the multifractal spectrum width, the aforementioned is achieved by appropriately modifying the beta distributions that conform the binomial cascade. Consequently, the impact developed by the algorithm to the trace generation with multifractal features will be the improvement in the simulation and data network modeling. The MFHW algorithm behaves as an expert system when inferring to distribution of the beta coefficients present in the scales that make part of the binomial cascade starting from the stochastic parameters configured by the user, and obtaining the corresponding time series through an inference engine. To validate the algorithm effectiveness, a trace with the Hurst parameter sampling and the multifractal spectrum width similar to the presented in a network traffic time series are synthetized. The MFHSW happens to be a promising tool for the modeling of time series applicable to diverse fields as the traffic engineering, finances, biomedical signals, among other real traces with multifractal features. [ABSTRACT FROM AUTHOR]

We have theoretically investigated the first correction to conductance of armchair single wall carbon nanotubes (SWCNTs) with finite length, embedded between two electrodes, due to the presence of electron–transversal phonon interaction. The perturbative scheme has been used with finite length real space nearest neighbors tight binding method. Both radial breathing and tangential modes are investigated separately. It is found that not only the conductance correction crucially depends on source-drain voltage but also it strongly depends on the length and diameter of SWCNT. So, this work opens up opportunities to control the electrical conductance of SWCNT and increases yield of micro or nanodevices based on carbon nanotube. [ABSTRACT FROM AUTHOR]

The development of embedded de-icing elements for polymer-based composite materials, coupled with mathematical models that describe their performance, is of interest to the aerospace, communications, and energy industries. Nickel–chromium–aluminum–yttrium (NiCrAlY) coatings were deposited on to fiber-reinforced polymer composite (FRPC) plates by using a flame spraying process. Electric current was supplied to the metal alloy coatings to generate energy by way of Joule heating (or resistive heating) and to enable the coatings to act as heating elements for the FRPC structures. De-icing tests were performed at ambient temperatures of −5 °C, −15 °C, and −25 °C, after liquid water was sprayed on the samples. Heat transfer models were developed to predict the heating and melting times of the ice during the de-icing process with the flame-sprayed coatings. The models were based on the separation of variables method for a finite length-scale melting problem and Stefan’s problem applied to a semi-infinite medium. It was found that a coating that was on the order of 100 μm thick was effective for melting accumulated ice on polymer composite structures that were exposed to cold environments. The results of the finite length-scale model and its agreement with experimental data suggest that a heat conduction model based on the separation of variables method may be applied to free boundary problems to predict phase change phenomena induced by thermal-sprayed coatings. [ABSTRACT FROM AUTHOR]

An exact elastodynamic model based on Navier equations of linear elasticity is formulated to describe the three-dimensional natural oscillations of an elliptic cylinder of finite length with shear diaphragm end conditions, and containing an inner (coaxial) elliptical cavity of arbitrary size, location, and orientation. The formulation is based on Helmholtz decomposition theorem, the method of separation of variables in elliptical coordinates, and the translational addition theorems for Mathieu functions. The first three natural frequencies are calculated for selected cylinder lengths, cross-sectional aspect ratios, and cavity location/orientation parameters. Also, some representative 3D deformation mode shapes are depicted in vivid graphical form. The precision of solutions is checked through proper convergence studies, and the validity of results is verified with the aid of a commercial finite element package as well as by comparison with the available literature data. The presented exact Mathieu series solution is believed to be the first attempt on the vibrational characteristics of finite-length eccentric elliptical cylinders. [ABSTRACT FROM AUTHOR]

This paper presents work to identify the sound source location within a finite length duct with beamforming methods. Two types of problems were studied in this paper. First, the deconvolution approach for the mapping of acoustic sources (DAMAS) method is applied to minimize the side-lobe effects, and improve the spatial resolution at low frequencies. Second, the beamforming results may deteriorate when the sound frequency is close to the cut-on frequencies. In order to improve the results, an algorithm was developed. To validate the methods, both simulations and experiments were implemented. In the experiments, a synchronized system with forty-eight wall-mounted microphones in a finite length duct was established. The dependence of the azimuthal sound source localization and the planar sound source localization on the measurement frequency was studied. The results indicate that the accuracy of the localization is highly dependent on the number of the spinning modes that are able to propagate in the duct. The localization may fail when the frequency is close to the cut-on frequencies. Significant improvements can be achieved when DAMAS and the improved algorithm are implemented. [ABSTRACT FROM AUTHOR]

In this paper, the initiation characteristics of the oblique detonation flow field induced by single- and double-wedge surfaces of finite length in a confined space are investigated. Numerical simulations with a detailed H 2 /air reaction and theoretical shock polar analyses are combined to study the influence mechanism of a complex wave system structure on the characteristics of the oblique detonation. The effects of expansion waves on the oblique detonation waves (ODWs) and their flow field characteristics for different equivalent ratios and geometric sizes are analyzed in single-wedge and double-wedge structures with the same inflow parameters. The results show that the length of the induced ODW is shorter in the double-wedge structure than in the single-wedge structure. For the single-wedge structure, the strength of the expansion wave increases, the wall temperature drops, and the characteristic length of the induction zone decreases with increasing deflection angle of the second wedge. If the strength of the expansion wave is sufficiently large, the ODW is initiated. For the double-wedge structure, the ODWs interact and form a complex wave system structure, consisting of a Mach stem, two reflected detonation waves and slip lines. The length and the temperature before and after the Mach stem decrease with an increase in the strength of the expansion waves. The effects of the expansion waves on the flow field of the ODW are relatively small at a large equivalent ratio and significantly larger at a small equivalent ratio. • The oblique detonation is investigated with detailed chemical reaction model. • The wave structures in the confined space are very complicated. • The expansion waves have significant effects on the flow field characteristics. • Theoretical detonation curves based on the thermal and chemical balance are used. [ABSTRACT FROM AUTHOR]