Abstract: The heat transfer of Homann flow in the stagnation region of the Al2O3-Cu/water hybrid nanofluid is investigated by adopting the Tiwari-Das model over a cylindrical disk. The effects of the nanoparticle shape, the viscous dissipation, and the nonlinear radiation are considered. The governing equations are obtained by using similarity transformations, and the numerical outcomes for the flow and the temperature field are noted by bvp4c on MATLAB. The numerical solutions of the flow field are compared with the asymptotic behaviors of large shear-to-strain-rate ratio. The effects of variations of parameters involved are inspected for both nanofluid and hybrid nanofluid flows, temperature profiles, local Nusselt numbers, and skin frictions. It is concluded that the velocity and temperature fields in the hybrid nanophase function more rapidly than those in the nanofluid phase. PubDate: 2020-07-07

Abstract: Thermal conduction which happens in all phases (liquid, solid, and gas) is the transportation of internal energy through minuscule collisions of particles and movement of electrons within a working body. The colliding particles comprise electrons, molecules, and atoms, and transfer disorganized microscopic potential and kinetic energy, mutually known as the internal energy. In engineering sciences, heat transfer comprises the processes of convection, thermal radiation, and sometimes mass transportation. Typically, more than one of these procedures may happen in a given circumstance. We use the Cattaneo-Christov (CC) heat flux model instead of the Fourier law of heat conduction to discuss the behavior of heat transportation. A mathematical model is presented for the Cattaneo-Christov double diffusion (CCDD) in the flow of a non-Newtonian nanofluid (the Jeffrey fluid) towards a stretched surface. The magnetohydrodynamic (MHD) fluid is considered. The behaviors of heat and mass transportation rates are discussed with the CCDD. These models are based on Fourier’s and Fick’s laws. The convective transportation in nanofluids is discussed, subject to thermophoresis and Brownian diffusions. The nonlinear governing flow expression is first altered into ordinary differential equations via appropriate transformations, and then numerical solutions are obtained through the built-in-shooting method. The impact of sundry flow parameters is discussed on the velocity, the skin friction coefficient, the temperature, and the concentration graphically. It is reported that the velocity of material particles decreases with higher values of the Deborah number and the ratio of the relaxation to retardation time parameter. The temperature distribution enhances when the Brownian motion and thermophoresis parameters increase. The concentration shows contrast impact versus the Lewis number and the Brownian motion parameter. It is also noticed that the skin friction coefficient decreases when the ratio of the relaxation to retardation time parameter increases. PubDate: 2020-07-07

Abstract: A mathematical study is developed for the electro-osmotic flow of a non-Newtonian fluid in a wavy microchannel in which a Bingham viscoplastic fluid model is considered. For electric potential distributions, a Poisson-Boltzmann equation is employed in the presence of an electrical double layer (EDL). The analytical solutions of dimensionless boundary value problems are obtained with the Debye-Huckel theory, the lubrication theory, and the long wavelength approximations. The effects of the Debyelength parameter, the plug flow width, the Helmholtz-Smoluchowski velocity, and the Joule heating on the normalized temperature, the velocity, the pressure gradient, the volumetric flow rate, and the Nusselt number for heat transfer are evaluated in detail using graphs. The analysis provides important findings regarding heat transfer in electroosmotic flows through a wavy microchannel. PubDate: 2020-07-02

Abstract: A procedure of the method of reverberation ray matrix (MRRM) is developed to perform the buckling analysis of thin multi-span rectangular plates having internal line supports or stiffeners. A computation algorithm for the reverberation ray matrix in the MRRM is derived to determine the buckling loading. Specifically, the analytical solutions are presented for the buckling of the structure having two opposite simply-supported or clamped-supported edges with spans, while the constraint condition of two remaining edges may be in any combination of free, simply-supported, and clamped boundary conditions. Furthermore, based on the analysis of matrices relating to the unknown coefficients in the solution form for the deflection in terms of buckling modal functions, some recursive equations (REs) for the MRRM are introduced to generate a reduced reverberation ray matrix with unchanged dimension when the number of spans increases, which promotes the computation efficiency. Several numerical examples are given, and the present results are compared with the known solutions to illustrate the validity and accurateness of the MRRM for the buckling analysis. PubDate: 2020-07-01

Abstract: In this study, the effects of elastic foundations (EFs) and carbon nanotube (CNT) reinforcement on the hydrostatic buckling pressure (HBP) of truncated conical shells (TCSs) are investigated. The first order shear deformation theory (FOSDT) is generalized to the buckling problem of TCSs reinforced with CNTs resting on the EFs for the first time. The material properties of composite TCSs reinforced with CNTs are graded linearly according to the thickness coordinate. The Winkler elastic foundation (W-EF) and Pasternak elastic foundation (P-EF) are considered as the EF. The basic relations and equations of TCSs reinforced with CNTs on the EFs are obtained in the framework of the FOSDT and solved using the Galerkin method. One of the innovations in this study is to obtain a closed-form solution for the HBP of TCSs reinforced with CNTs on the EFs. Finally, the effects of the EFs and various types CNT reinforcements on the HBP are investigated simultaneously. The obtained results are compared with the results in the literature, and the accuracy of results is confirmed. PubDate: 2020-07-01

Abstract: The laminar-turbulent transition in boundary-layer flows is often affected by wall imperfections, because the latter may interact with either the freestream perturbations or the oncoming boundary-layer instability modes, leading to a modification of the accumulation of the normal modes. The present paper particularly focuses on the latter mechanism in a transonic boundary layer, namely, the effect of a two-dimensional (2D) roughness element on the oncoming Tollmien-Schlichting (T-S) modes when they propagate through the region of the rapid mean-flow distortion induced by the roughness. The wave scattering is analyzed by adapting the local scattering theory developed for subsonic boundary layers (WU, X. S. and DONG, M. A local scattering theory for the effects of isolated roughness on boundary-layer instability and transition: transmission coefficient as an eigenvalue. Journal of Fluid Mechanics, 794, 68–108 (2006)) to the transonic regime, and a transmission coefficient is introduced to characterize the effect of the roughness. In the sub-transonic regime, in which the Mach number is close to, but less than, 1, the scattering system reduces to an eigenvalue problem with the transmission coefficient being the eigenvalue; while in the super-transonic regime, in which the Mach number is slightly greater than 1, the scattering system becomes a high-dimensional group of linear equations with the transmission coefficient being solved afterward. In the large-Reynolds-number asymptotic theory, the Kármán-Guderley parameter is introduced to quantify the effect of the Mach number. A systematical parametric study is carried out, and the dependence of the transmission coefficient on the roughness shape, the frequency of the oncoming mode, and the Kármán-Guderley parameter is provided. PubDate: 2020-07-01

Abstract: In this paper, the stresses and buckling behaviors of a thick-walled micro sandwich panel with a flexible foam core and carbon nanotube reinforced composite (CNTRC) face sheets are considered based on the high-order shear deformation theory (HSDT) and the modified couple stress theory (MCST). The governing equations of equilibrium are obtained based on the total potential energy principle. The effects of various parameters such as the aspect ratio, elastic foundation, temperature changes, and volume fraction of the canbon nanotubes (CNTs) on the critical buckling loads, normal stress, shear stress, and deflection of the thick-walled micro cylindrical sandwich panel considering different distributions of CNTs are examined. The results are compared and validated with other studies, and showing an excellent compatibility. CNTs have become very useful and common candidates in sandwich structures, and they have been extensively used in many applications including nanotechnology, aerospace, and micro-structures. This paper also extends further applications of reinforced sandwich panels by providing the modified equations and formulae. PubDate: 2020-07-01

Abstract: In this work, the nonlinear behaviors of soft cantilevered pipes containing internal fluid flow are studied based on a geometrically exact model, with particular focus on the mechanism of large-amplitude oscillations of the pipe under gravity. Four key parameters, including the flow velocity, the mass ratio, the gravity parameter, and the inclination angle between the pipe length and the gravity direction, are considered to affect the static and dynamic behaviors of the soft pipe. The stability analyses show that, provided that the inclination angle is not equal to π, the soft pipe is stable at a low flow velocity and becomes unstable via flutter once the flow velocity is beyond a critical value. As the inclination angle is equal to π, the pipe experiences, in turn, buckling instability, regaining stability, and flutter instability with the increase in the flow velocity. Interestingly, the stability of the pipe can be either enhanced or weakened by varying the gravity parameter, mainly dependent on the value of the inclination angle. In the nonlinear dynamic analysis, it is demonstrated that the post-flutter amplitude of the soft pipe can be extremely large in the form of limit-cycle oscillations. Besides, the oscillating shapes for various inclination angles are provided to display interesting dynamical behaviors of the inclined soft pipe conveying fluid. PubDate: 2020-06-30

Abstract: This paper deals with the nonlinear large deflection analysis of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) plates and panels using a finite element method. Based on the first-order shear deformation theory (FSDT), the proposed model takes into account the transverse shear deformations and incorporates the geometrical nonlinearity type. A C0 isoparametric finite shell element is developed for the present nonlinear model with the description of large displacements and finite rotations. By adopting the extended rule of mixture, the effective material properties of FG-CNTRCs are approximated with the introduction of some efficiency parameters. Four carbon nanotube (CNT) distributions, labeled uniformly distributed (UD)-CNT, FG-V-CNT, FG-O-CNT, and FG-X-CNT, are considered. The solution procedure is carried out via the Newton-Raphson incremental technique. Various numerical applications in both isotropic and CNTRC composite cases are performed to trace the potential of the present model. The effects of the CNT distributions, their volume fractions, and the geometrical characteristics on the nonlinear deflection responses of FG-CNTRC structures are highlighted via a detailed parametric study. PubDate: 2020-06-15

Abstract: This research paper analyzes the transport of thermal and solutal energy in the Maxwell nanofluid flow induced above the disk which is rotating with a constant angular velocity. The significant features of thermal and solutal relaxation times of fluids are studied with a Cattaneo-Christov double diffusion theory rather than the classical Fourier’s and Fick’s laws. A novel idea of a Buongiorno nanofluid model together with the Cattaneo-Christov theory is introduced for the first time for the Maxwell fluid flow over a rotating disk. Additionally, the thermal and solutal distributions are controlled with the impacts of heat source and chemical reaction. The classical von Kármán similarities are used to acquire the non-linear system of ordinary differential equations (ODEs). The analytical series solution to the governing ODEs is obtained with the well-known homotopy analysis method (HAM). The validation of results is provided with the published results by the comparison tables. The graphically presented outcomes for the physical problem reveal that the higher values of the stretching strength parameter enhance the radial velocity and decline the circumferential velocity. The increasing trend is noted for the axial velocity profile in the downward direction with the higher values of the stretching strength parameter. The higher values of the relaxation time parameters in the Cattaneo-Christov theory decrease the thermal and solutal energy transport in the flow of Maxwell nanoliquids. The higher rate of the heat transport is observed in the case of a larger thermophoretic force. PubDate: 2020-06-07

Abstract: This paper presents an investigation into the effect of surface asperities on the over-rolling of bearing surfaces in transient elastohydrodynamic lubrication (EHL) line contact. The governing equations are discretized by the finite difference method. The resulting nonlinear system of algebraic equations is solved by the Jacobian-free Newton-generalized minimal residual (GMRES) from the Krylov subspace method (KSM). Acceleration of the GMRES iteration is accomplished by a wavelet-based preconditioner. Profiles of the lubricant pressure and film thickness are obtained at each time step when the indented surface moves through the contact region. The prediction of pressure as a function of time provides an insight into the understanding of fatigue life of bearings. The analysis confirms the need for the time-dependent approach of EHL problems with surface asperities. This method requires less storage and yields an accurate solution with much coarser grids. It is stable, efficient, allows a larger time step, and covers a wide range of parameters of interest. PubDate: 2020-06-01

Abstract: The problem of the creeping flow through a spherical droplet with a non-homogenous porous layer in a spherical container has been studied analytically. Darcy’s model for the flow inside the porous annular region and the Stokes equation for the flow inside the spherical cavity and container are used to analyze the flow. The drag force is exerted on the porous spherical particles enclosing a cavity, and the hydrodynamic permeability of the spherical droplet with a non-homogeneous porous layer is calculated. Emphasis is placed on the spatially varying permeability of a porous medium, which is not covered in all the previous works related to spherical containers. The variation of hydrodynamic permeability and the wall effect with respect to various flow parameters are presented and discussed graphically. The streamlines are presented to discuss the kinematics of the flow. Some previous results for hydrodynamic permeability and drag forces have been verified as special limiting cases. PubDate: 2020-06-01

Abstract: The interaction between a screw dislocation and an elliptical hole with two asymmetrical cracks in a one-dimensional (1D) hexagonal quasicrystal with piezoelectric effect is considered. A general formula of the generalized stress field, the field intensity factor, and the image force is derived, and the special cases are discussed. Several numerical examples are given to show the effects of the material properties and the dislocation position on the field intensity factors and the image forces. PubDate: 2020-06-01

Abstract: In this paper, an analytical method is used to investigate the Rayleigh wave generation in a stratified structure and the wave generation in a dry sandy layer constrained between the couple stress and inhomogeneous orthotropic half-spaces. This study is devoted to analyzing the impact of various effective parameters associated with the media on the phase velocities of the wave. The displacement components for each medium are derived by implementing the separable variable method. The frequency equation is secured by using the displacement components in the boundary conditions, imposed at the interfaces between the layer and half-spaces. Moreover, the secured equation is the relation between the phase velocity and the wave number. Numerical computations are performed, and graphical representations are demonstrated between the phase velocity and the wave number for both phase velocities with different values of the parameters. The comparison between the phase velocities is observed for the same value of each parameter. PubDate: 2020-05-26

Abstract: A nanofluid is composed of a base fluid component and nanoparticles, in which the nanoparticles are dispersed in the base fluid. The addition of nanoparticles into a base fluid can remarkably improve the thermal conductivity of the nanofluid, and such an increment of thermal conductivity can play an important role in improving the heat transfer rate of the base fluid. Further, the dynamics of non-Newtonian fluids along with nanoparticles is quite interesting with numerous industrial applications. The present predominately predictive modeling studies the flow of the viscoelastic Oldroyd-B fluid over a rotating disk in the presence of nanoparticles. A progressive amendment in the heat and concentration equations is made by exploiting the Cattaneo-Christov heat and mass flux expressions. The characteristic of the Lorentz force due to the magnetic field applied normal to the disk is studied. The Buongiorno model together with the Cattaneo-Christov theory is implemented in the Oldroyd-B nanofluid flow to investigate the heat and mass transport mechanism. This theory predicts the characteristics of the fluid thermal and solutal relaxation time on the boundary layer flow. The von Kármán similarity functions are utilized to convert the partial differential equations (PDEs) into ordinary differential equations (ODEs). A homotopic approach for obtaining the analytical solutions to the governing nonlinear problem is carried out. The graphical results are obtained for the velocity field, temperature, and concentration distributions. Comparisons are made for a limiting case between the numerical and analytical solutions, and the results are found in good agreement. The results reveal that the thermal and solutal relaxation time parameters diminish the temperature and concentration distributions, respectively. The axial flow decreases in the downward direction for higher values of the retardation time parameter. The impact of the thermophoresis parameter boosts the temperature distribution. PubDate: 2020-05-23

Abstract: A nonlinear vibration isolation system is promising to provide a high-efficient broadband isolation performance. In this paper, a generalized vibration isolation system is established with nonlinear stiffness, nonlinear viscous damping, and Bouc-Wen (BW) hysteretic damping. An approximate analytical analysis is performed based on a harmonic balance method (HBM) and an alternating frequency/time (AFT) domain technique. To evaluate the damping effect, a generalized equivalent damping ratio is defined with the stiffness-varying characteristics. A comprehensive comparison of different kinds of damping is made through numerical simulations. It is found that the damping ratio of the linear damping is related to the stiffness-varying characteristics while the damping ratios of two kinds of nonlinear damping are related to the responding amplitudes. The linear damping, hysteretic damping, and nonlinear viscous damping are suitable for the small-amplitude, medium-amplitude, and large-amplitude conditions, respectively. The hysteretic damping has an extra advantage of broadband isolation. PubDate: 2020-05-16

Abstract: An Uzawa-type algorithm is designed for the coupled Stokes equations discretized by the mixed finite element method. The velocity solved by the presented algorithm is weakly divergence-free, which is different from the one solved by the common Uzawa method. Besides, an optimal relaxation parameter of the presented algorithm is provided. PubDate: 2020-05-15

Abstract: The electric band energy variation in a bent piezoelectric semiconductor (PSC) nanowire of circular cross-section induced by the mechanical force is analyzed based on a six-band k · p method. The electric-mechanical fields are first obtained analytically in a cantilever bent PSC nanowire by solving the fully-coupled electro-mechanical equations. Then, the band energy is acquired numerically via the six-band Hamiltonian. By considering further the nonlinear coupling between the piezoelectric and semiconducting quantities, the contribution of the redistribution carriers to the electric field is analyzed from the Gauss’s law. Numerical examples are carried out for an n-type ZnO nanowire in different locations induced by an applied concentrated end force. These include the electric potential, heavy hole (HH), light hole (LH), spin-orbit split-off (SO), and conduction band (CB) edges along the axial and thickness directions. Our results show that the applied force has a significant effect on the band energies. For instance, on the bottom surface along the axial direction, the bandgaps near the fixed end are greater than those near the loading end, and this trend is reversed on the top surface. Moreover, at a fixed axial location, the energy level of the lower side can be enhanced by applying a bending force at the end. The present results could be of significant guidance to the electronic devices and piezotronics. PubDate: 2020-05-15

Abstract: Finite-sized inertial spherical particles are fully-resolved with the immersed boundary projection method (IBPM) in the turbulent open-channel flow by direct numerical simulation (DNS). The accuracy of the particle surface force models is investigated in comparison with the total force obtained via the fully-resolved method. The results show that the steady-state resistance only performs well in the streamwise direction, while the fluid acceleration force, the added-mass force, and the shear-induced Saffman lift can effectively compensate for the large-amplitude and high-frequency characteristics of the particle surface forces, especially for the wall-normal and spanwise components. The modified steady-state resistance with the correction effects of the acceleration and the fluid shear can better represent the overall forces imposed on the particles, and it is a preferable choice of the surface force model in the Lagrangian point-particle method. PubDate: 2020-05-04

Abstract: Studying and analyzing the dynamic behavior of offshore wind turbines are of great importance to ensure the safety and improve the efficiency of such expensive equipments. In this work, a tapered beam model is proposed to investigate the dynamic response of an offshore wind turbine tower on the monopile foundation assembled with rotating blades in the complex ocean environment. Several environment factors like wind, wave, current, and soil resistance are taken into account. The proposed model is analytically solved with the Galerkin method. Based on the numerical results, the effects of various structure parameters including the taper angle, the height and thickness of the tower, the depth, and the diameter and the cement filler of the monopile on the fundamental natural frequency of the wind turbine tower system are investigated in detail. It is found that the fundamental natural frequency decreases with the increase in the taper angle and the height and thickness of the tower, and increases with the increase in the diameter of the monopile. Moreover, filling cement into the monopile can effectively improve the fundamental natural frequency of the wind turbine tower system, but there is a critical value of the amount of cement maximizing the property of the monopile. This research may be helpful in the design and safety evaluation of offshore wind turbines. PubDate: 2020-05-04