Journal of Applied and Computational Mechanics
Volume:5 Issue: 2, Spring 2019

The study of bubble dynamics, especially the interaction of bubbles, has drawn considerable attention due to its various applications in engineering and science. Meanwhile, the study of the oscillation effect of a bubble on the emitted pressure wave of another bubble in an acoustic field which has less been investigated. This issue is investigated in the present study using the coupling of Keller-Miksis and Gilmore models. The ordinary differential equations are solved using MATLAB software and Runge-Kutta forth order method with the adaptive step size control. The results show the dependence of bubbles behavior and the strength of their pressure waves on two parameters of the initial radius and the bubbles center-to-center distance. As the initial radius of the adjacent bubble grows, its effect on the other bubble increases and causes a reduction in the other bubble maximum radius, wall velocity, internal pressure, and emitted pressure wave intensity. However, increasing the initial distance of the bubbles reduces the effect of the bubbles on each other and causes their behaviors become closer to the single-bubble oscillation mode.

In this study, the localfractional variational iterationmethod (LFVIM) and the localfractional series expansion method (LFSEM) are utilized to obtain approximate solutions for Korteweg-de Vries equation (KdVE) within local fractionalderivative operators (LFDOs). The efficiency of the considered methods is illustrated by some examples. The results reveal that the suggested algorithms are very effective and simple and can be applied for linear and nonlinear problems in mathematical physics.

In order to achieve integrated condition in the girth welding of high pressure natural gas transmission pipelines, the weld zones and its surrounding area should have good mechanical properties. Residual stresses are an important defect especially in the girth welding of the pipeline. In this study, two API X70 steel pipes (with spiral seam weld) of 56 inches outside diameter and 0.780 inch wall thickness were girth welded first. The hole drilling tests were conducted for residual stress measurement on the surfaces of the pipes. The hoop tensile residual stress on the external surface of the pipe with the maximum value equal to 318-MPa was measured on the weld centerline. Hoop residual stress distributions in the internal and external surfaces of the pipe were approximately similar. The maximum axial residual stress was observed in the heat affected zone (a distance of approximately 30 mm from the weld centerline). The maximum axial residual stress on the external surface of the pipe was tensile, equal to 137 MPa, and on the internal surface of the pipe was compressive, equal to 135-MPa. Axial residual stress magnitudes in the weld centerline on the internal and external surfaces of the pipe were close together. Away from the weld centerline, axial residual stresses on the internal and external surfaces showed the opposite behavior. Therefore, in the girth welding of natural gas transmission pipelines, the peripheral direction on the internal surface of the pipe is the critical zone and have the highest tensile residual stresses.

In the present study, the conjugate turbulent free convection with the thermal surface radiation in a rectangular enclosure bounded by walls with different thermophysical characteristics in the presence of a local heater is numerically studied. The effects of surface emissivity and wall materials on the air flow and the heat transfer characteristics are the main focus of the present investigation. The conjugate convective heat transfer for the fluid (air), described in terms of linear momentum, continuity, and energy equations combined with k-ε turbulence model, is predicted by using the finite difference method. The results for the isotherms, streamlines, and average Nusselt numbers along the heat source are presented. The numerical experiments show that an increase in thermal conductivity of solid walls illustrates the enhancement of heat transfer. Eventually, the main result obtained in this work provides a good technical support for the development and research of energy-efficient building materials.

An interaction integral method for evaluating mixed-mode stress intensity factors (SIFs) for two dimensional crack problems using NURBS-based isogeometric analysis method is investigated. The interaction integral method is based on the path independent J-integral. By introducing a known auxiliary field solution, the mixed-mode SIFs are calculated simultaneously. Among features of B-spline basis functions, the possibility of enhancing a B-spline basis with discontinuities by means of knot insertion makes isogeometric analysis method a suitable candidate for modelling discrete cracks. Moreover, the repetition of two different control points between two patches can create a discontinuity and also demonstrates a singularity in the stiffness matrix. In the case of a pre-defined interface, non-uniform rational B-splines are used to obtain an efficient discretization. Various numerical simulations for edge and center cracks demonstrate the suitability of the isogeometric analysis approach to fracture mechanics.

This computational fluid dynamic analysis attempts to simulate the incompressible steady fluid flow and heat transfer in a solar air channel with wall-mounted baffles. Two ꞌSꞌ-shaped baffles, having different orientations, i.e., ꞌSꞌ-upstream and ꞌSꞌ-downstream, were inserted into the channel and fixed to the top and bottom walls of the channel in a periodically staggered manner to develop vortices to improve the mixing and consequently the heat transfer. The analyses are conducted with the Commercial CFD software FLUENT using the finite volume method for Reynolds number varying from 12,000 to 32,000. The numerical results are presented in terms of streamlines, velocity-magnitude, x-velocity, y-velocity, dynamic pressure coefficient, turbulent kinetic energy, turbulent viscosity, turbulent intensity, temperature field, coefficient and factor of normalized skin friction, local and average numbers of normalized Nusselt, and thermal performance factor. The insertion of the S-shaped baffles in the channel not only causes a much high friction loss, f/f0 = 3.319 - 32.336, but also provides a considerable augmentation in the thermal transfer rate in the channel, Nu/Nu0 = 1.939 - 4.582, depending on the S-baffle orientations and the Reynolds number. The S-upstream baffle provides higher friction loss and heat transfer rate than the S-Downstream around 56.443 %, 55.700 %, 54.972 %, 54.289 % and 53.660 %; and 25.011 %, 23.455 %, 21.977 %, 20.626 %, and 19.414 % for Re = 12,000, 17,000, 22,000, 27,000, and 32,000, respectively. In addition, the result analysis shows that the optimum thermal performance factor is around 1.513 at the highest Reynolds number and S-downstream.

The creation of modified layer on metal surfaces using new methods is one of the procedures in surface engineering which can improve the surface mechanical properties. The electrical discharge process is a new method that can form a modified layer on the metal surfaces. This study aims to improve of pure aluminum surface properties through Electrical Discharge process with Monel 400 electrode. In order to design the experiments, the pulse on time and the pulse current were considered as input parameters. The SEM images indicated that the increase in the pulse on time and the pulse current can increase the thickness of the modified layer. Based on the obtained results, the thickness of improved layer varied between 35 to 75 microns. The results of the EDX analysis showed the diffusion of the copper and nickel to the aluminum surface. Moreover, the results of microhardness testing of the surface layer showed that after Electrical discharge process, the surface hardness has increased and the surface hardness as 35 Vickers has reached more than 400 Vickers.

The present study introduces two quantitative parameters to compare the accuracy of ultrasonic C-scan testing and X-ray radiography methods in the damaged area detection under low-velocity impact in polymer-based composites. For this purpose, the hand lay-up technique of composite processing was employed to prepare the composite specimen. A composite specimen consisting of the glass fiber reinforced with the unsaturated polyester resin was considered for this investigation. The impact tests at different energy levels were carried out to create three damaged areas in this composite specimen. Because the glass/polyester specimen had a transparent surface, a digital scanner was used to obtain an ideal image of specimen representing the region and edge of the impacted areas. Two image quality factors were introduced as quantitative parameters to compare the ultrasonic C-scan and X-ray radiography results with those of an ideal image. The results of this study showed that the ultrasonic C-scan is a more accurate method for inspection of the GFRP specimen.

A model of fractional-order of thermoelasticity is applied to study a 2D problem of mode-I crack in a fibre-reinforced thermal environment. The crack is under prescribed distributions of heat and pressure. The normal mode analysis is applied to deduce exact formulae for displacements, stresses, and temperature. Variations of field quantities with the axial direction are illustrated graphically. The results regarding the presence and absence of fiber reinforcement and fractional parameters are compared. Some particular cases are also investigated via the generalized thermoelastic theory. The presented results can be applied to design different fibre-reinforced isotropic thermoelastic elements subjected to the thermal load in order to meet special technical requirements.

Optimization concept in the context of shear deformation theories was born for the development of accurate models to study the bending problem of structures. The present study seeks to extend such an approach to the dynamic analysis of plates. A compact and unified formulation with non-polynomial shear strain shape functions (SSSFs) is employed to develop a static and free vibration analysis of simply supported functionally graded plates. In this context, three new non-polynomial displacement fields are proposed using trigonometric and hyperbolic SSSFs. Then, the non-polynomial SSSFs are optimized by varying the arguments of the trigonometric and hyperbolic functions. Additionally, the Mori-Tanaka approach is used to estimate the effective properties of the functionally graded plates. The Principle of Virtual Displacement (PVD) and the Hamilton’s Principle along with the Navier closed-form solution technique are used to obtain exact results. The obtained numerical results are in a good agreement with 3D and 2D higher order shear deformation theory solutions available in the literature.

In this study, the second type of Green and Naghdi's thermoelasticity theory is applied to present the vibration of a nanobeam subjected to rectified sine wave heating based upon the nonlocal thermoelasticity theory. Both Young's modulus and thermal conductivity are considered to be linear functions of the temperature. The Laplace transform domain is adopted to solve the governing partial differential equations using the state space approach. Numerical computations are carried out using the inverse of Laplace transforms. The effects of nonlocal parameter and angular frequency on the thermal vibration quantities are discussed. The results of all quantities are illustrated graphically and investigated.

Fluid flow around bluff bodies occurs in numerous fields of science and engineering, such as flows pass vehicles, cables, towers and bridges. These flows have been studied experimentally and numerically for the last several decades. The investigation of flow around high-speed trains is an important application of bluff bodies. Fluid flow, aerodynamic forces and moments, separation and wake region have been studied for the last several decades. This paper brings together a comprehensive review of the research on air flow around high-speed trains and their impacts.

An analysis has been conceded to study the effects of Soret and thermal radiation effects on the magnetohydrodynamic convective flow of a viscous, incompressible, electrically conducting fluid with heat and mass transfer over a plate with time-dependent suction velocity in a slip flow regime in the presence of first-order chemical reaction. The slip conditions at the boundaries for the governing flow are taken for the velocity and temperature distributions and a uniform magnetic field of strength is applied normal to the flow direction. The free stream velocity is assumed to be subject to follow an exponentially small perturbation law. Analytical solutions are obtained for velocity, temperature and concentration fields for the governing partial differential equations depending on slip flow boundary circumstances by using the traditional perturbation method.

We present some variants of Burgers-type equations for incompressible and isothermal planar flow of viscous non-Newtonian fluids based on the Cross, the Carreau and the power-law rheology models, and on a symmetry assumption on the flow. We numerically solve the associated traveling wave equations by using industrial data and in order to validate the models we prove existence and uniqueness of solutions to the equations. We also provide numerical estimates of the shock thickness as well as the maximum stress associated with the traveling waves.

This paper examines the solution of a damped beam equation whose damping characteristics are well-defined by the fractional derivative (FD). Homotopy Analysis Method (HAM) is applied for calculating the dynamic response (DR). Unit step and unit impulse functions are deliberated for this analysis. Acquired results are illustrated to show the movement of the beam under various sets of parameters with different orders of the FDs. Here FD is defined in the Caputo sense. Obtained results have been compared with the solutions achieved by Adomian decomposition method (ADM) to show the efficiency and effectiveness of the presented method.

This article investigates the static behavior of functionally graded plate under mechanical loads by using a new quasi 3D model. The theory is designated as fifth-order shear and normal deformation theory (FOSNDT). Properties of functionally graded material are graded across the transverse direction by using the rule of mixture i.e. power-law. The effect of thickness stretching is considered to develop the present theory. In this theory, axial and transverse displacement components respectively involve fifth-order and fourth-order shape functions to evaluate shear and normal strains. The theory involves nine unknowns. Zero transverse shear stress conditions are satisfied by employing constitutive relations. Analytical solutions are obtained by implementing the double Fourier series technique. The results predicted by the FOSNDT are compared with existing results. It is pointed out that the present theory is helpful for accurate structural analysis of isotropic and functionally graded plates compared to other plate models.

A series of tests have been conducted to investigate fatigue damage characterization in corroded welded steel plates using structural health monitoring (SHM) techniques. Acoustic Emission (AE) is a non-destructive testing (NDT) technique with potential applications for locating and monitoring fatigue cracks in service. In the present work, AE is implemented to characterize damage during crack evolution. It is considered to be based on the relationship between RA value (the rise time divided by the amplitude) and the average frequency of the recorded data. Results are confirmed by visual observation of the crack geometry at the end of the test and by Digital image correlation (DIC) measurements. It is seen that the obtained results allow a better understanding of such damage mechanisms, and enabling an early warning against final failure. Thus, ensuring the safety and integrity of the structures is feasible.

The present investigation draws scholars' attention to the effect of exponential variable viscosity modeled by Vogel and variable permeability on stagnation point flow of Carreau Nanofluid over an electromagnetic plate through a porous medium. Brownian motion and thermophoretic diffusion mechanism are taken into consideration. An efficient fourth-order RK method along with shooting technique are implemented to obtain the required solution of the non-dimensional modeled equations. The contribution of the present study is that augmented electromagnetic field strength due to the suitable arrangement of the plate and that of porosity parameter yield an accelerated motion while that of viscosity parameter produces retarded motion of shear-thickening fluid, contrary to shear-thinning fluid. At the same time, it discusses the inclusion of porous matrix which controls the thermal as well as concentration boundary layers, while enhanced Brownian motion exhibits diametrically opposite trend for them in response to shear-thickening fluid.

Size-dependent longitudinal and torsional vibrations of nano-beams are examined by two-phase mixture integral elasticity. A new and efficient elastodynamic model is conceived by convexly combining the local phase with strain- and stress-driven purely nonlocal phases. The proposed stress-driven nonlocal integral mixture leads to well-posed structural problems for any value of the scale parameter. Effectiveness of stress-driven mixture is illustrated by analyzing axial and torsional free vibrations of cantilever and doubly clamped nano-beams. The local/nonlocal integral mixture is conveniently replaced with an equivalent differential law equipped with higher-order constitutive boundary conditions. Exact solutions of fundamental natural frequencies associated with strain- and stress-driven mixtures are evaluated and compared with counterpart results obtained by strain gradient elasticity theory. The provided new numerical benchmarks can be effectively employed for modelling and design of Nano-Electro-Mechanical-Systems (NEMS).

Topology optimization has been an interesting area of research in recent years.  The main focus of this paper is to use an evolutionary swarm intelligence algorithm to perform Isogeometric Topology optimization of continuum structures.  A two-dimensional plate is analyzed statically and the nodal displacements are calculated.  The nodal displacements using Isogeometric analysis are found to be in good agreement with the nodal displacements acquired by standard finite element analysis.  The sizing optimization of the beam is then performed.  In order to determine the stress at each point in the beam a formulation is presented.  The optimal cross-section dimensions by performing Isogeometric analysis are acquired and verified with the cross-section dimensions achieved by hiring bending stress and shear stress criteria, as well.  The topology optimization of a two-dimensional simply supported plate continuum and a problem on three-dimensional continuum are optimized and presented.  The results show that the minimum weight which is found by applying Isogeometric topology optimization gives better results compared to the traditional finite element analysis.

The intent of this analysis is to explore the influence of thermal radiation paired with variable thermal conductivity on MHD micropolar fluid flow over an upper surface. The novelty of the present model is to consider the fluid flow along an upper horizontal surface of a paraboloid of revolution (uhspr) with the porous medium.  This physical phenomenon is described by a set of coupled non-linear ODEs by using suitable scaling analysis. The ODEs along with the boundary conditions are solved numerically. Influence of various flow parameters on momentum, thermal and concentration boundary layers is discussed graphically. It is noticed that the variable thickness of the surface has a leading consequence on the boundary layer progression along the surface. Moreover, the results of this study are not only useful for industrial applications but also present a basic understanding of the physical model.

In this paper, the boundary layer flow of an Eyring-Powell non-Newtonian fluid over a linearly stretching sheet is solved using the combination of the quasilinearization method and the Fractional order of Rational Chebyshev function (FRC) collocation method on a semi-infinite domain. The quasilinearization method converts the equation into a sequence of linear equations then, using the FRC collocation method, these linear equations are solved. The governing nonlinear partial differential equations are reduced to the nonlinear ordinary differential equation by similarity transformations. The physical significance of the various parameters of the velocity profile is investigated through graphical figures. An accurate approximation solution is obtained and the convergence of numerical results is shown.

This article is proposed to address the melting heat transfer of a Jeffrey fluid in Blasius and Sakiadis flow caused due to a moving surface. Thermal radiation and a constant free stream are considered in this mathematical model. The non-linear coupled dimensionless equations from the governing equations are attained by employing appropriate similarity transformations. The resulting dimensionless equations are solved by implementing RKF method. The impact of sundry emerging parameters on different flow fields are interpreted with the help of figures and tables. For augmented values of Deborah number, the velocity profile diminishes in the case of Blasius flow and the reverse behavior in the Sakiadis flow is observed. Moreover, the velocity of non-Newtonian liquid in case of Blasius flow is superior to that of the Sakiadis flow. The present work is demonstrated by matching with the computational results in the literature and found to be outstanding agreement.

Nonlinear behavior of a functionally graded cantilever beam is analyzed under non-uniform hygro-thermal effect. To solve this problem, finite element method is applied within plane solid continua. Total Lagrangian approach is utilized in the nonlinear kinematic relations. Newton-Raphson method with incremental displacement is used in nonlinear solution. Comparison study is performed. Effects of material distribution, temperature and moisture changes on nonlinear deflections of the functionally graded beam are presented and discussed.

The accelerating fields (e. g. centrifugal acceleration and constant acceleration) can change the physical performance of nano-sensors significantly. Herein, a new size-dependent model is developed to investigate the scale-dependent dynamic behavior of nanowire-fabricated sensor operated in an accelerating field. The scale-dependent equation of motion is developed by employing a consolidation of the strain gradient elasticity (SGE) and the Gurtin–Murdoch theory (GMT). A semi-analytical solution is extracted for calculating the stability parameters. Effects of different phenomena including centrifugal force, microstructure dependency, surface layer, length-scale-parameter, dispersion forces, squeezed film damping on the dynamic stability parameters are demonstrated.