The flow patterns, vortex-shedding frequency and aerodynamic performance of the square-cylinder flow were modulated using an upstream control rod. Additionally, the flow behaviors were examined using various Reynolds numbers, rotation angles, and spacing ratios. The flow patterns were visualized using the smoke-wire scheme. The global velocity fields and streamline patterns were analyzed using the particle image velocimetry (PIV). Additionally, the flow modes were characterized based on the kinematics theory. Moreover, the vortex-shedding frequencies behind upstream control rod and the square cylinder were detected using two hot-wire anemometers. The surface pressure on square cylinder was determined using a linear pressure scanner. Then, the aerodynamic parameters were calculated using the surface-pressure profiles. Three characteristic flow modes — single, attached, and bi-vortex-street — were categorized by varying the Reynolds number and spacing ratio. In the attached mode, the position of upstream control rod determined the flow characteristics. Furthermore, in the attached mode, the mean drag force of the square cylinder is about 57% lower than of single-square cylinder.

A hybrid differential transformation / finite difference scheme is used to analyze the complex nonlinear behavior of an electrostatically-actuated micro cantilever beam which high aspect ratios (length/width). The validity of the proposed method is confirmed by comparing the numerical results obtained for the tip displacement and pull-in voltage of the cantilever beam with the analytical and experimental results presented in the literature. The hybrid scheme is then applied to analyze both the steady-state and the dynamic deflection behavior of the cantilever beam as a function of the applied voltage. Overall, the results confirm that the hybrid method provides an accurate and computationally-efficient means of analyzing the complex nonlinear behavior of both the current micro cantilever beam system and other micro-scale electrostatically-actuated structures.

This paper deals with the static response of simply supported functionally graded material (FGM) viscoelastic sandwich plates subjected to transverse uniform loads. The FG sandwich plates are considered to be resting on Pasternak's elastic foundations. The sandwich plate is assumed to consist of a fully elastic core sandwiched by elastic-viscoelastic FGM layers. Material properties are graded according to a power-law variation from the interfaces to the faces of the plate. The equilibrium equations of the FG sandwich plate are given based on a trigonometric shear deformation plate theory. Using Illyushin's method, the governing equations of the viscoelastic sandwich plate can be solved. Parametric study on the bending analysis of FG sandwich plates is being investigated. These parameters include (i) power-law index, (ii) plate aspect ratio, (iii) side-to-thickness ratio, (iv) loading type, (v) foundation stiffnesses, and (vi) time parameter.

An annular elastic layer bonded between rigid plates and subjected to a compressive force normal to the layer is analyzed through a theoretical approach. On the basis of two kinematic assumptions, the governing equation for the mean pressure is established from the equilibrium equation, which is then solved by satisfying the stress boundary conditions. Through the obtained pressure expression, the compression stiffness of the bonded annular layer is derived in closed form and is very close to the finite element solution. The derived formula has no limitation on the Poisson's ratio and is more concise than the previous research. Through the asymptotic approach, the compression stiffness for the incompressible elastic layers is derived and is more accurate than the previous research obtained by directly neglecting the bulk compressibility. The stiffness reduction caused by the central hole is more prominent when the Poisson's ratio is close to 0.5.

Chang explicit method (2007) has been shown to be unconditionally stable for a linear elastic system and any instantaneous stiffness softening system while it is only conditionally stable for any instantaneous stiffness hardening system. Its coefficients of the difference equation for displacement increment are functions of initial tangent stiffness. Since Chang explicit method is unconditionally stable for a linear elastic system and any instantaneous stiffness softening system, its stability range can be enlarged if the initial tangent stiffness is enlarged by an amplification factor and then this amplified initial tangent stiffness is used to determine the coefficients. The detailed implementation of this scheme for Chang explicit method is presented and the feasibility of this scheme is verified.

An analytical study on entropy generation considering viscous dissipation effect in the circular microchannel is reported. The fluid flow is steady, laminar, hydrodynamically fully developed and thermally developing. In the first law analysis, appropriate dimensionless variables are applied to solve the energy equation in the thermal entrance region of microchannel. Subsequently the obtained temperature field is used to derive an expression for entropy generation rate. The effect of Knudsen number and Brinkman number on the entropy generation rate and Bejan number in different axial location is presented.

In this paper, the effect of thermal radiation, variable viscosity and variable thermal conductivity on the flow and heat transfer of a thin liquid film over an unsteady stretching sheet is analyzed. The continuity, momentum and energy equations, which are coupled nonlinear partial differential equations, are reduced to a set of two non-linear ordinary differential equations, before being solved numerically. Results for the skin-friction coefficient, local Nusselt number, velocity profiles as well as temperature profiles are presented for different values of the governing parameters. It is found that increasing the viscosity parameter leads to a rise in the velocity near the surface of the sheet and a fall in the temperature. Furthermore, it is shown that the temperature increases due to an increase in the values of the thermal conductivity parameter and the thermal radiation parameter, while it decreases with an increase of the Prandtl number.

Mathematical formulation for Magnetohydrodynamic (MHD) stability of a streaming cylindrical model penetrated by varying transverse magnetic field is presented. Eigen value relation is derived and discussed analytically. In the current paper, Artificial Neural Network (ANN) model, one of the artificial intelligence techniques, is developed to simulate the stability of streaming jet penetrated by magnetic field. The ANN results presented in the current study showed that ANN technique, with less effort and time, is very efficiently capable of simulating and predicting the effect of magnetic field variation and axial exterior field on the stability of the streaming jet. The influence of magnetic field has a stabilizing effect for all short and long wavelengths. However the streaming is strongly destabilizing.

To realize the relationship between flow structures of wingtip vortices and post stall characteristics of low aspect-ratio wings, this paper experimentally studies the aerodynamic characteristics and the corresponding flow structures of the rectangular thin-plate wings at Reynolds numbers between 104 and 105. The aerodynamic properties to be studied include lift, drag, slopes at linear and nonlinear range of the lift curves and lift-to-drag ratios of the tested wings with the aspect ratio varying from 1.0 to 3.0. The flow structures regarding the leading-edge separation vortices and wingtip vortices at upper surface and near-wake regions of the wings are also investigated by smoke-wire visualization. Results indicate that the high stall angle of attack and vortex lift are clearly manifested to induce the nonlinear increase in the lift curves as the aspect ratio reaches less than 1.6. This phenomenon is specifically observed to augment the aerodynamic properties with the decrease of the aspect ratio. Additionally, the corresponding flow visualization also indicates that the wingtip vortices and the areas of highly affected regions are duly increased with the increase of the angle of attack up to 40°, which makes certain that the extra increase of the nonlinear lift results from these vortices. This result can be practically applied to the planform design for unmanned aerial vehicles.

The phenomenon of Karman-type vortex shedding from finite square cylinders of the aspect ratios 2, 4 and 6 at Reynolds number of 1.9 × 105 were examined with the employment of a three-component force balance to measure the aerodynamic forces. The signals of the lateral force measured were first analyzed by the HHT (Hilbert-Huang Transformation) together with a conditional sampling technique for identifying the time periods during which the vortex shedding frequency component was prominent. Meanwhile, the force measured in the vertical direction was analyzed by the same procedure to identify the events of pronounced unsteady downwash motion induced by the flow over the finite end of the model. Therefore, the unsteady flow motions around a finite cylinder model could be categorized into four patterns. Namely, the patterns 11 and 10 denote the situations of pronounced Karman-type vortex shedding with and without strong downwash motion, respectively; and the patterns 01 and 00 denote the situations of no pronounced vortex shedding with and without strong downwash motion, respectively. The results obtained show that the pattern 00 occupied more than 60% of the time sampled, apparently dominant over the other three patterns, whereas the second popular pattern 10 (Karman type vortex shedding) occupied no more than 30% of the time sampled. Further experiments were made for the square cylinder of the aspect ratio 6, with a hot-wire situated near either side of the cylinder. By analyzing the unsteady lateral forces experienced by the cylinder and the hot-wire velocity data with the data reduction scheme employed, it is unveiled that the Karman-type vortex shedding induced an anti-symmetric, unsteady flow motion around the cylinder, although this component was not the dominant one. On the other hand, it is found that a large portion of the fluctuating energy was resided in the low-frequency component featuring a symmetric unsteady flow motion around the cylinder. This finding further supports the earlier observation that the flow pattern 00 is most commonly seen in the unsteady flow motions around a finite square cylinder.

This paper is concerned with the effects of column size, carbon fiber-reinforced plastics (CFRP) volumetric ratio, column side to corner radius ratio and column side aspect ratio on the confinement efficiency of rectangular concrete columns confined with CFRP. The confined concrete nonlinear constitutive relationships are adopted which account for concrete under unequal lateral confining stresses under multiaxial stress conditions. A stiffness reduction procedure upon concrete cracking or crushing is also proposed. The finite element model is initially confirmed by comparing its numerical solutions with the experimental results for various parameters. The effects of above parameters on the peak strength and ultimate strain of the confined concrete are then parametrically studied. The test results and results of the parametric study indicate that the column axial compressive strength and ultimate strain increase with CFRP volumetric ratio, but decrease as the column side to corner radius ratio or the column side aspect ratio increases. For columns of a particular corner radius and CFRP volumetric ratio, the column axial compressive strength and ultimate strain decrease as column size and column side to corner radius ratio increases.

This paper discusses an experimental investigation of the behavior of sharp-notched circular tubes subjected to cyclic bending. The sharp-notched circular tubes of 304 stainless steel with three different diameter-to-thickness ratios (Do / t) were tested under symmetric curvature-controlled cyclic bending. It has been shown that the moment-curvature curves exhibited the loops with cyclic hardening and gradually becoming steady after a few cycles for all tested tubes. The ovalization-curvature curves revealed unsymmetric, ratcheting and increasing behavior with the number of cycles. In addition, five almost parallel lines corresponding to five different notch depths for each Do / t ratio were found from the experimental relationship between the cyclic controlled curvature and the number of cycles necessary to produce buckling on a log-log scale. Finally, an empirical relationship was proposed so it could be used for simulating the aforementioned relationship. By comparing with the experimental finding, the derived empirical relationship was in good agreement with the experimental data.

The present study utilized audio recordings of snoring during natural sleep to analyze characteristics related to the snoring duration at the soft palate, epiglottis, and tongue base. 10 subjects were recruited for the study, with an average age of 23.7 years. These audio files were then used to analyze the characteristics of snoring duration at the soft palate, epiglottis, and tongue base responsible for sound generation. Findings indicated that snoring duration was 3.7 seconds at the soft palate, 2.2 seconds at the epiglottis and 1.29 seconds at the tongue. Since the soft palate is the softest structure of the three, snoring sound by vibration was most easily induced at this structure, leading to the longest snoring duration. This was followed by the epiglottis and the tongue base respectively. Of the 10 subjects, 6 had BMI in the overweight range, and snoring durations for these individuals were seen to be lengthened by 0.13 seconds, with the tongue base snoring duration lengthened by 0.11 seconds but unchanged for the epiglottis. Prior studies from this laboratory have established a non-invasive system for measuring snoring. This can be used to analyze the sound frequency, amplitude and duration of snoring. Snoring duration was found to be the longest at the soft palate, followed by the epiglottis and tongue base in the present investigation. Clinically, this finding has implications in snoring assessments prior to uvula-palato-pharyngoplasty procedures. Snoring duration may also be used as a parameter in post-operative monitoring.

Skin has a complex structure and its deformation mechanics is still not well defined. In the study of skin biomechanics, the stretch ratio, λ, is an important property, which is determined using strain data. This paper attempts to develop a novel tool by integrating experimental-numerical approach to measure full-field strain distribution of human skin in vivo. Skin deformation in vivo was measured using motion capture system, (which is not a full-field measuring tool) and then by constructing finite elements, its full-field strain contour is produced. The experimental procedure starts by attaching a set of reflective markers onto the skin at the forearm of healthy volunteers. Skin deformation is induced by pulling a nylon filament attached with a loading tab. Three infrared cameras are used to capture the movement of markers during load application. QTM (Qualisys, Sweden) software is used to track markers trajectories and generate data consisting of 3-dimensional markers coordinate. The initial capture is set as the reference marker positions (undeformed skin) and the subsequent images represent the deformed skin relative to the initial. Representing markers as nodes, finite elements are constructed by adjoining three adjacent markers using Delaunay mesh. Strains were deduced from the strain displacement matrix and measured for three subjects at three loading directions. The results are in fair agreement with those obtained by others. The method and output provide a useful addition to understanding skin deformation.

In this paper, the thermomechanical behavior of shape memory alloys (SMAs) subjected to uniaxial cyclic loading is investigated. To obtain experimental data, the strain-controlled cyclic loading-unloading tests are conducted at various strain-rates and temperatures. Dislocations slip and deformation twins are considered to be the main reason that causes the unique cyclic mechanical behavior of SMAs. A new variable of shape memory residual factor was introduced, which will tend to zero with the increasing of the number of cycles. Exponential form equations are established to describe the evolution of shape memory residual factor, elastic modulus and critical stress, in which the influence of strain-rate, number of cycles and temperature are taken into account. The relationship between critical stresses and temperature is modified by considering the cycling effect. A macromechanical constitutive model was constructed to predict the cyclic mechanical behavior at constant temperature. Based on the material parameters obtained from test results, the hysteretic behavior of SMAs subjected to isothermal uniaxial cyclic loading is simulated. It is shown that the numerical results of the modified model match well with the test results.

This paper presents the optimal design of an electromagnetic vibration-based generator using the simulated annealing method (SA). To optimally extract the vibrational energy of a system vibrating at a specific frequency, the selected mass and spring stiffness of a resonant vibration is required. The relationship between induced energy and the generator's structure, its permanent magnet height and diameter, number of turns, and wire diameter in a single air coil are discussed. Also, a prototype of the vibrationbased electrical generator is built and tested via a shaker excited at resonance frequency and input amplitude of 0.06mm. Consequently, results reveal that the design parameters (permanent magnet height and diameter, number of turns, and wire diameter) play essential roles in maximizing electrical power.

Element Free Galerkin method was used to analyze bending of thin plates with variable thickness resting on one parameter elastic foundation. Thickness of plate is considered as linearly varying in one direction. Formulation could be applied to plates of any shape with general boundary conditions and loadings. Convergence of solution was examined for different number of nodes, thickness variation and foundation parameters. It was found that for deflection good results were achieved even with small number of nodes regardless of boundary condition, thickness variation and foundation parameters. Accuracy of method is checked against available results and good agreements were found. Applicability of method is demonstrated by solving numerical examples with different boundary conditions, thickness and foundation parameters, and loadings.

This article aims to study numerically three-dimensional (3D) reactive turbulent flow in a combustion chamber of a gas turbine by solving a steady Reynolds-Averaged Navier-Stokes (RANS) )and energy equations. The Reynolds stress model (RSM) is coupled with the probability density function (PDF), laminar flamelet and Chemistry models to describe the turbulent flow and turbulence–chemistry interaction. Numerical computations are conducted to exhibit thermal and concentration behaviour under a quite number of factors, which influence the combustion process. Their influence are examined and compared favourably with available experimental results. Concentration of some radicals as O and OH are obtained assuming the partial-equilibrium assumption and using a PDF in terms of temperature. The 3D simulations demonstrate that the use of RSM, PDF and flamelet model allow simulating velocity and thermochemical fields.

Using conventional virtual work method to derive geometric stiffness of a thin-walled beam element, researchers usually have to deal with nonlinear strains with high order terms and the induced moments caused by cross sectional stress results under rotations. To simplify the laborious procedure, this study decomposes an I-beam element into three narrow beam components in conjunction with geometrical hypothesis of rigid cross section. Then let us adopt Yang et al.'s simplified geometric stiffness matrix [kg]12×12 of a rigid beam element as the basis of geometric stiffness of a narrow beam element. Finally, we can use rigid beam assemblage and stiffness transformation procedure to derivate the geometric stiffness matrix [kg]14×14 of an I-beam element, in which two nodal warping deformations are included. From the derived [kg]14×14 matrix, it can take into account the nature of various rotational moments, such as semi-tangential (ST) property for St. Venant torque and quasi-tangential (QT) property for both bending moment and warping torque. The applicability of the proposed [kg]14×14 matrix to buckling problem and geometric nonlinear analysis of loaded I-shaped beam structures will be verified and compared with the results presented in existing literatures. Moreover, the post-buckling behavior of a centrally-load web-tapered I-beam with warping restraints will be investigated as well.

This study investigates evaporation heat transfer performance of refrigerant R-134a falling film on three horizontal copper tubes in a vertical column. Experiments were performed at saturation temperatures of 10 and 26.7°C. The liquid flows through a liquid feeder with a row of circular holes at a rate of 0.0075 ∼ 0.0363kg/ms, while heat fluxes varied from 4.5 to 48.5kW/m2. A smooth tube, a fin tube of 0.4mm fin height, 60FPI (Fins Per Inch), and a new boiling enhanced tube (mesh tube) were tested. The test results show that heat transfer coefficient of the smooth tube increases with increasing heat flux and fluid temperature, and increases slightly with increasing flow rate before dry-out occurs. At low flow rates (less than 0.015kg/ms) or when Ref (≤ 255), the fin tube is in thin film evaporation mode and results in a large heat transfer coefficient. At high flow rates (0.0225, 0.03, and 0.0375kg/ms) the falling film evaporation curves are similar to those in pool boiling. For all tubes, the fluid temperature and the flow rate have only minor influences on heat transfer coefficient before dry-out occurs. The 60 FPI tube and the mesh tube enhance the falling film evaporation heat transfer coefficient 6.3 ∼ 8.29 fold and 1.9 ∼ 5.0 fold, respectively, as compared with the smooth tube. A new correlation of falling film evaporation, accounting for contributions of nucleate boiling and spray convection, is proposed. It predicts h-values of the falling film evaporation data of the smooth surface within ±30%.