In this article, surface and nonlocal effects are explored in the analysis of buckling and vibration in rectangular single-layered graphene sheets embedded in elastic media and subjected to coupled in-plane loadings and thermal conditions. The small-scale and surface effects are taken into account using the Eringen's nonlocal elasticity and Gurtin-Murdoch's theory, respectively. Using the principle of virtual work, the governing equations considering small-scale are derived for the nanoplate bulk and surface. The differential quadrature method (DQM) is utilized for the solution of the relevant problems and the results are validated against Navier's solutions. The impacts of the nonlocal parameter, Winkler and shear elastic moduli, temperature rise, boundary conditions, and the in-plane biaxial, uniaxial, and shear loadings on the surface effects of buckling and vibration are investigated. Numerical results show that increasing nonlocal parameter leads to enhanced surface effects on both buckling and vibration. This is in contrast to those reported elsewhere. Moreover, increasing in-plane loads are observed to enhance surface effects on vibration. On the other hand, the nonlocal parameter is observed to have more pronounced effects on shear buckling and vibration of plates subjected to coupled in-plane shear loads than those subjected to biaxial and uniaxial loads. This is while surface effects have greater impacts on biaxial buckling and vibration of nanoplates than on shear buckling and vibration.

Following the success of static analysis of free-free 2-D plane trusses by using a self-regularization approach uniquely, we further extend the technique to deal with 3-D problems of space trusses. The inherent singular stiffness of a free-free structure is expanded to a bordered matrix by adding r singular vectors corresponding to zero singular values, where r is the nullity of the singular stiffness matrix. Besides, r constraints are accompanied to result in a nonsingular matrix. Only the pure particular solution with nontrivial strain is then obtained but without the homogeneous solution of no deformation. To link with the Fredholm alternative theorem, the slack variables with zero values indicate the infinite solutions while those with nonzero values imply the case of no solutions. A simple space truss is used to demonstrate the validity of the proposed model. An alternative way of reasonable support system to result in a nonsingular stiffness matrix is also addressed. In addition, the finite-element commercial code ABAQUS is also implemented to check the results.

Influence of variable viscosity the peristaltic flow of pseudoplastic fluid in a tapered channel is discussed. The effects of magnetohydrodynamics (MHD) are also studied. Asymmetric channel is considered. The relevant problem is first formulated and then non-dimensionalized. The nonlinear different system subject to lubrication approach is solved. Expressions for pressure gradient, pressure rise and velocity are constructed. Graphs reflecting the variations of sundry parameters on pressure rise and velocity are examined. Trapping and pumping phenomena are also studied.

Biomimetic motions are helpful to underwater vehicles and new conception airplanes design. The lattice Boltzmann method with an immersed boundary method technique is used to reveal the propulsion and lift enhancement mechanism of biomimetic motions. The flow past a sphere and an ellipsoidal flapping wing were validated respectively by comparing with other numerical methods. Then a single flapping wing and three flapping wings in a tandem arrangement are accomplished respectively. It founds that the mean thrust coefficient of three plate wings is bigger than the one of the single plate wing. Three ellipsoidal wings and single ellipsoidal wing are compared. It shows that the single ellipsoidal wing has larger thrust coefficients than the three ellipsoidal wings. Ellipsoidal flapping wing and plate wing were further compared to investigate the influence of wing shape. It indicates the mean thrust coefficient of the ellipsoidal wing is bigger than the plate wing.

Nano-nozzles are an essential part of the nano electromechanical systems (NEMS). Cross-sectional geometry of nano-nozzles has a significant role on the fluid flow inside them. So, main purpose of the present study is related to the effects of different symmetrical cross-sections on the fluid flow behavior inside of nano-nozzles. To this accomplishment, five different cross-sectional geometries (equilateral triangle, square, regular hexagon, elliptical and circular) are investigated by using molecular dynamics (MD) simulation. In addition, TIP4P is used for atomistic water model. In order to evaluate the fluid flow behavior, non-dimensional physical parameters such as Fanning friction factor, velocity profile and density number are analyzed. Obtained results are shown that the flow behavior characteristics appreciably depend on the geometry of nano-nozzle's cross-section. Velocity profile and density number for five different cross sections of nano-nozzle at three various measurement gauges are presented and discussed.

The icing wind tunnel can simulate the air flow at a high altitude; such an air flow contains supercooled droplets moving at certain velocities. An integrated experiment method was proposed, and it included the icing test and shear stress measurements in the simulated environment of the icing wind tunnel. The error caused by the change in experimental environments was completely eliminated with this novel method. Thus, there was no discrepancy between the real-time and experimental values of shear stress between the ice and substrate. The experiments of icing and shear stress measurements are carried out by varying the following parameters: icing temperature, mean volume diameter (MVD) of droplets, and surface roughness of the substrate. The results indicate that the shear stress between the ice and the substrate increases with the decrease in temperature provided the temperature is relatively high. When the MVD value is 22 μm, the liquid water content is about 1 g/m3 and surface roughness is 2 μm. Under these conditions, the shear stress reaches its maximum value at a temperature of –15°C. The shear stress is also affected by the MVD values of droplets, and the surface roughness of substrate.

In the present study, unsteady MHD boundary layer flow of a rotating Walters’-B fluid (viscoelastic fluid) over an infinite vertical porous plate embedded in a uniform porous medium with fluctuating wall temperature and concentration taking Hall and ion-slip effects into consideration is discussed. The MHD flow in the rotating fluid system is induced due to the non-torsional oscillations of the plate in its own plane and the buoyancy forces arises from temperature and concentration differences in field of gravity. The partial differential equations governing the fluid motion are solved analytically by using regular perturbation and variable separable methods by assuming very small viscoelastic parameter. Solution for velocity field in the case when natural frequency due to rotation and Hall current is equals to the frequency of oscillations i.e. in the case of resonance is also obtained. In order to note the influences of various system parameters and to discuss the important flow characteristics, the numerical results for fluid velocity in the non-resonance case, temperature and species concentration are computed and depicted graphically versus boundary layer parameter whereas skin friction, Nusselt number and Sherwood number at the plate are computed and presented in tabular form. An interesting observation recorded that there arises flow reversal in the primary flow direction due to high rotation. When natural frequency is greater than the frequency of oscillations the fluid velocity in the primary flow direction is maximum at the plate whereas incase when natural frequency is smaller than the frequency of oscillations, it is maximum in the neighborhood of the plate.

A two-phase flow parametric study on an air induction nozzle with water and air as the working fluids is presented. Liquid was supplied at the pre-orifice with various inlet pressures ranging from 3 to 6 bar. The interaction between air and water at the molecular level at the orifice exit leads to formation of a strong shear layer that is intensified with the increase in inlet pressure. Thus, it is vital to regulate the ratio of the intake air to the supplied liquid so that the generated micro bubbles fit the design criteria. CFD analysis was conducted using the commercial software STAR CCM+ from Siemens and validated against experimental data to investigate the design parameters and their effect on the ALR. A volume of fluid (VOF) method of the RANS models was used to undertake the air-water interaction. Parameters such as the throat, air orifice, and air inlet diameter, along with the diffuser angle, were investigated. It was found that certain parameters such as the throat diameter have a more significant effect on the air/liquid entrainment ratio than other parameters.

The increasing demands on renewable energy nowadays caused the development of marine current turbine industry. In order to improve the current design of marine current turbines, studies were conducted to analyse their hydrodynamic performances during operation. Since most of the time marine current turbines operate in arrays, it is important to understand the interactions between the turbines in order to design the optimum turbine farm. OpenFOAM® was used to simulate the turbine interactions of conventional and biomimetic marine current turbines in tandem configuration. The conventional marine current turbines were referred to Pinon et al. (2012) and Mycek et al. (2013) while the biomimetic marine current turbine was adopted from Chu (2016). The numerical simulations were conducted with turbines in different inter-device distances, A/D. The percentage differences of ‘‘efficiency’’, η between the IFREMER-LOMC and the biomimetic turbine case of inter-device distances, A/D = 4, 6, 8 and 10 are 14.3%, 6.4%, 3% and 1.92% respectively. The results show that the power produced by the biomimetic turbines in tandem is comparable with the IFREMER-LOMC turbines when A/D > 4. The biomimetic marine current turbines can be a fair choice due to their potential to have alternative fabrication method of their sheet-like turbine blades.

The dynamic ground effect enhances the swimming of fish. The dynamic ground effect affects the kinematic conditions of fish, causing them to swim more efficiently. However, predicting the degree to which the dynamic ground effect can improve the swimming performance of fish is difficult. The dynamic ground effect can potentially save energy for biomimetic underwater vehicles. Therefore, a theoretical model was developed to investigate the effect of a planar boundary on the swimming performance of a two-dimensional undulating plate. General expressions for the thrust, power input, efficiency, and energy loss of the plate were obtained. As examples, cases in which an undulating plate with linearly varying amplitude swam far from and close to a wall under a range of different kinematic conditions were studied. The dynamic ground effect improved the swimming performance of the plate by reducing the power input while maintaining an almost constant thrust; the degree of improvement depended on the kinematic conditions of the plate. Furthermore, the swimming performance of the plate was improved over a range of distances from the wall; this range of distances also depended on the kinematic conditions of the plate.

In this article, a series of simulations of a rotating disk system with air cooling is introduced. These simulations are performed with the realizable k-ε eddy-viscosity model. Computational results illustrate the effect of the cooling air and disk rotation on the temperature of the disk surface. The maximum rotating disk speed reaches about 78300 rpm and the range of Reynolds numbers based on rotation speed is from about 0.7 × 106 to 3 × 106. The present work shows that the flow structure in the gap, which is on the opposite side of the cooling air, is rather similar to different cooling air flows. The temperature goes up as the rotating speed increases. The temperature in this gap will first decrease when the cooling air increases under lower mass flow rate. But when the cooling air continues to increase, the temperature will rise up indicating the existence of an optimum value of the cooling flow rate.

In this study MHD flow around and through porous cylinder is numerically investigated. The governing equations are developed in polar coordinate arrangement in both porous and non-porous media on the basis of single-domain technique. The equations are solved numerically based on finite volume method over staggered grid structure. Nusselt number and drag coefficient are selected as two key parameters describing performance of this system. By applying response surface methodology the sensitivity of these parameters to main factors of the problem, including Stuart number, Darcy number and Reynolds number are quantified. RSM is also utilized to perform an optimization process to find the best condition in which the lowest drag force and highest heat transfer rate occur simultaneously. The CFD analysis is carried out for variant Reynolds numbers (10 ≤ Re ≤ 40), Darcy numbers (10-6 ≤ Da ≤ 10-2) and Stuart numbers (2 ≤ N ≤ 10). Streamlines and isotherms are presented to indicate the impacts of such parameters on heat and fluid flow. It can be seen that, Drag coefficient and Nusselt number increase by augmenting magnetic field strength. Beside, Darcy number and Reynolds numbers have a direct and inverse effect on Nuave and Cd, respectively. Results of optimization process show that Nuave and Cd are more sensitive to Reynolds and Stuart numbers, respectively, while they less sensitive to Darcy number. Moreover, it is revealed that the optimum condition occurs at Da = 10-2, Re = 38.1 and N = 4.49.

In this study, the dynamic stability of double-walled carbon nanotubes (DWCNTs) conveying pulsating viscous fluid located on visco-Pasternak medium is investigated. The effects of small scale are considered using Eringen's non-local theory. The surrounding medium of DWCNT is anticipated as a visco-Pasternak foundation including the normal, shear, and damping forces. The van der Waals (vdWs) force is considered among the inner and outer layers of DWCNT. Three types of temperature changes, i.e. uniform, linear and sinusoidal temperature rise, through the thickness are studied. The equations of motion are obtained using higher order sinusoidal shear deformation shell theory (SSDT), in which the surface effects are included. Dynamical equations of DWCNT are extracted using the energy method and Hamilton's principle. Due to orthogonal conditions, the governing equations are solved based on Bolotin method. The effects of different parameters such as surface stress, non-local parameter, fluid velocity, Knudsen's number, fluid density, dimensions ratio and various temperature loadings on the dynamic stability regions of DWCNTs are discussed.

In this paper, the dynamical behavior and stability of hanging micropipes conveying fluid with pinned-free boundary conditions are investigated. For a pinned-free rigid micropipe, the dynamical system is found to be stable for various flow velocities. Particular emphasis is placed on the effects of flow velocity, mass ratio and gravity on the dynamics and flutter instability of flexible micropipe system with pinned-free boundary conditions. The governing equations for flexible micropipes are discretized using the differential quadrature method (DQM), yielding a generalized eigenvalue problem which is then solved for various flow velocities, mass ratios and gravity parameters. It is shown that, with increasing flow velocity, the flexible micropipe with pinned-free boundary conditions is stable until it becomes unstable via a Hopf bifurcation leading to flutter. The system may lose stability first in the second or third mode, mainly depending on the selected value of mass ratio. The existence of mode exchange between the second and third modes is possible. The gravity parameter of positive values causes additional restoring force and hence enhances the stability of the micropipe system; however, it can generate the complexity of stability diagrams.

Based on the basic equations of electromagnetic elastic motion and the expression of electromagnetic force, the electromagnetic vibration equation of the rectangular thin plate in transverse magnetic field is obtained. For a rectangular plate with one side fixed and three other sides simply supported, its time variable and space variable are separated by the method of Galerkin, and the two-degree-of-freedom nonlinear Duffing vibration differential equations are proposed. The method of multiple scales is adopted to solve the model equations and obtain four first-order ordinary differential equations governing modulation of the amplitudes and phase angles involved via 1:1 or 1:3 internal resonances with different size ratios. With a numerical example, the time history response diagrams, phase portraits and 3-dimension responses of two order modal amplitudes are respectively captured. And the effects of initial values, thickness and magnetic field intensities on internal resonance characteristics are discussed respectively. The results also present obvious characteristics of typical nonlinear internal resonance in this paper.

Magnetohydrodynamic entropy generation of two immiscible fluids inside an inclined channel in the presence of different types of nanoparticles is examined. Channel consists of two regions, one Newtonian clear fluid and another Newtonian nanofluid with water as the base fluid and different nanoparticles including copper (Cu), copper oxide (CuO), aluminum oxide (Al2O3) and titanium dioxide (TiO2). Governing equations are solved with homotopy analysis method to highlight the effect of magnetic parameter, Grashof number, inclination angle and solid volume fraction on the total entropy generation for all types of nanoparticles. Results demonstrate that increasing of Grashof number, inclination angle and solid volume fraction amplifies the total entropy generation, while the enlargement of magnetic parameter reduces it especially for solid volume fractions greater than 15%. Among the several case studies performed, it is seen that water-TiO2 nanofluid is the best nanofluid from the viewpoint of entropy generation minimization. It is also found that the maximum total entropy generation is 1.268 and takes place for water-Cu nanofluid. Moreover, it is observed that the entropy generation component due to heat conduction of water-Cu nanofluid occupies 33.62% of the maximum total entropy generation and consequently that is the main cause of irreversibility in this study.