جستجوی مقالات مرتبط با کلیدواژه « Non » در نشریات گروه « مکانیک »

In this study, crankshaft failure of four-cylinder light-duty truck diesel engine was examined. The failure occurred by fatigue crack growth which was initiated from a surface defect after about 95000 km on the second crankpin from the crankpin-web fillet where the stress concentration was at the highest level. To evaluate the mechanical properties, some hardness and tensile tests were conducted and spectrometry analysis was used for studying the chemical composition of the crankshaft material. Additionally, for considering and evaluating the microstructure, microcracks, fracture surface, and the cause of failure, optical microscopy (OM) and scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS) were used. The morphology of the fracture surface showed a smooth and flat crack initiation with the beach marks and ratchet marks and second crack propagation zone with beach marks and fast final fracture zone near the end. The results of EDS observations indicated that inclusions of non-metallic aren’t distributed throughout on the steel and in some places leads to the formation of the microcrack clusters.

The instability of non-Newtonian power law fluid in double diffusive convection in a porous medium with vertical throughflow is investigated. The lower and upper boundaries are taken to be permeable, isothermal and isosolutal. For vertical throughflow the linear stability of flow is determined by the power law index (n), non-Newtonian Rayleigh number (Ra), Buoyancy ratio (N), Péclet number (Pe) and Lewis number (Le). The eigenvalue problem is solved by two-term Galerkin approximation to obtain the critical value of Rayleigh number and neutral stability curves. It is observed that the neutral stability curves, as well as the critical wave number and Rayleigh number, are affected by the parameters such as Péclet number, buoyancy ratio and Lewis number. The neutral stability curves indicate that power law index n has destabilizing nature when it takes values for dilatant fluid at low Péclet numbers while for the pseudoplastic fluids it shows stabilizing effect. In the absence of buoyancy ratio and vertical throughflow, the present numerical results coincide with the solution of standard Horton-Rogers-Lapwood Problem. The numerical analysis of linear stability for the limiting case of absolute pseudoplasticity is also done by using Galerkin method.

In this paper, semi-analytical method for asymmetrical eccentrically stiffened FGM cylindrical shells under external pressure and surrounded by a linear and non-linear elastic foundation is presented. The proposed linear model is based on two parameter elastic foundation Winkler and Pasternak. According to the von Karman nonlinear equations and the classical plate theory of shells, strain-displacement relations are obtained. The smeared stiffeners technique and Galerkin method, used for solving nonlinear problem. To finding the nonlinear dynamic response of fourth order Runge-Kutta method is used. The effect of parameters asymmetrical eccentrically stiffened on the nonlinear dynamic buckling response of FGM cylindrical shells have been investigated.

In this work, analytical solutions are provided to the nonlinear equations arising in thermal and flow-induced vibration in fluid-conveying structures using Galerkin-differential transformation method with cosine aftertreatment technique. From the analysis, it was established that increase of the length and aspect ratio of the fluid-conveying structures result in decrease the nonlinear vibration frequencies of the structure while increase in the fluid-flow velocity causes increase in nonlinear vibration frequencies of the structures. Also, increase in the slip parameter leads to decrease in the frequency of vibration of the structure and the critical velocity of the conveyed fluid while increase in the slip parameter leads to decrease in the dimensionless frequency ratio of vibration of the structure. As the Knudsen number increases, the bending stiffness of the nanotube decreases and in consequent, the critical continuum flow velocity decreases as the curves shift to the lowest frequency zone. Good agreement are established when the results of the differential transformation method are compared with the results of the numerical method and exact analytical method for the non-linear and linear models, respectively.

In this study, the steady incompressible flow of a non-Newtonian sodium alginate (SA) fluid conveying copper nanoparticles (Cu) which flow within two vertical parallel plates is investigated by using the homotopy perturbation analytical scheme to solve the coupled nonlinear ordinary equations arising from the mechanics of the fluid. The developed analytical solutions are used to investigate the effect of the fluid flow and heat transfer parameters such as the nanoparticle concentration, the non-Newtonian parameter and the viscosity variation parameter. The obtained analytical results as compared to existing works in literature are in satisfactory agreements. Moreover, the results obtained from the present study can be used for further analysis of the behavior of the sodium alginate in applications such as food processing and chemical and pharmaceutical industries.

In this paper, an experimental study has been conducted on the rheological behavior of Water (80%) and Ethylene-glycol (20%) in presence of Al2O3-MWCNTs hybrid nanomaterials. For this purpose, nanofluid samples were prepared by suspending the nanomaterials in a mixture of water and EG with solid volume fractions of 0.0625%, 0.125%, 0.25% and 0.5% Viscosity measurements were performed at various shear rates and in the temperatures range of 25 to 50⁰C. Experimental data showed that all hybrid nanofluid samples had Newtonian behavior. also Results showed that nanofluid viscosity decreased with increasing temperature and augmented with increasing the volume fraction. Eventually, a new accurate correlation was developed to assist the calculation of the viscosity of the Al2O3-MWCNTs/water-EG at different temperatures and volume fractions.

The development of mathematical models for describing the dynamic behaviours of fluid conveying pipes, micro-pipes and nanotubes under the influence of some thermo-mechanical parameters results into nonlinear equations that are very difficult to solve analytically. In cases where the exact analytical solutions are presented either in implicit or explicit forms, high skills and rigorous mathematical analyses were employed. It is noted that such solutions do not provide general exact solutions. Inevitably, comparatively simple, flexible yet accurate and practicable solutions are required for the analyses of these structures. Therefore, in this study, approximate analytical solutions are provided to the nonlinear equations arising in flow-induced vibration of pipes, micro-pipes and nanotubes using Galerkin-Newton-Harmonic Method (GNHM). The developed approximate analytical solutions are shown to be valid for both small and large amplitude oscillations. The accuracies and explicitness of these solutions were examined in limiting cases to establish the suitability of the method.

In this paper, an analytical solution for computing the linear plastic stresses, critical temperature and pressure in an FGM hollow cylinder under the internal pressure and temperature is developed. It has been assumed that the modulus of elasticity and thermal coefficient of expansion were varying through thickness of the FGM material according to a power law relationship. The Poisson''s ratio was considered constant throughout the thickness. The general forms of thermal and mechanical boundary conditions were considered on the inner surface. In the analysis section, the effect of nonhomogeneity in FGM cylinder was implemented by choosing a dimensionless parameter, named m, which could be assigned an arbitrary value affecting the stresses in the cylinder. Distribution of stresses in radial and circumferential direction for FGM cylinders under the influence of internal pressure and temperature gradient were obtained. Graphs of critical temperature and pressure versus radius of the cylinder were plotted. Cases of pressure and temperature loadings were considered separately. The direct method has been considered to solve the heat conduction and Navier equations. The outer pressure for all over the cylinder goes to the plastic region when ===0 and by increasing the modules of elasticity the pressure will increase. By substituting M=0 in radial linear plastic stress formula, the perfect plastic equation will yield. By putting , 0 pp rr rr r єє in radial linear plastic stress formula, it turns to the radial elastic stress.

In this research, the coupling between non-gray radiation and separation convection flow in a duct is investigated numerically. Distributions of absorption coefficients across the spectrum are obtained from the HITRAN2008 database. The full-spectrum k-distribution method is used to deal with the non-gray part of the problem, while the gray radiation calculations are performed using the Planck mean absorption coefficient. To find the divergence of radiative heat flux distribution, the radiative transfer equation (RTE) is solved by the discrete ordinates method (DOM). The effects of radiation-conduction parameter, scattering coefficient and wall emissivity on thermal behaviors are investigated for both gray and non-gray mediums. In addition, the results of gray medium are compared with non-gray results as a real case. The results show that in many cases, use of gray simulations is not acceptable and leads to significant errors, especially in non-scattering medium with high values of radiation-conduction parameter and wall emissivity.

The high blood rate that often occurs in arteries may play a role in artery failure and tortuosity which leads to blackouts, transitory ischemic attacks and other diseases. However, vibration and instability analysis of carotid arteries are lacking. The objective of this study is to investigate the vibration and instability of the carotid arteries conveying blood under axial tension with surrounding tissue support. Arteries are modeled as elastic cylindrical vessels based on first order shear deformation theory (FSDT) within an elastic substrate. The elastic medium is simulated with visco-Pasternak foundation. The blood flow in carotid artery is modeled with non-Newtonian fluid based on Carreau, power law and Casson models. Applying energy method, Hamilton principle and differential quadrature method (DQM), the frequency, critical blood velocity and transverse displacement of the carotid arteries are obtained. It can be seen that increasing the tissue stiffness would delay critical blood velocity. The current model provides a powerful tool for further experimental investigation arteries tortuosity. In addition, the dimensionless transverse displacement predicted by Newtonian model is lower than that of non-Newtonian models.

In present study, thermo-elastic buckling analysis of multi-layer orthotropic annular/circular graphene sheets is investigated based on Eringen’s theory. The moderately thick and also thick nano-plates are considered. Using the non-local first and third order shear deformation theories, the governing equations are derived. The van der Waals interaction between the layers is simulated for multi-layer sheets. The stability governing equations are obtained according to the adjacent equilibrium estate method. The constitutive equations are solved by applying the differential quadrature method (DQM). Applying the differential quadrature method, the ordinary differential equations are transformed to algebraic equations. Then, the critical temperature is obtained. Since there is not any research in thermo-elastic buckling analysis of multi-layer graphene sheets, the results are validated with available single layer articles. The effects of non-local parameter, the values of van der Waals interaction between the layers, third to first order shear deformation theory analyses, non-local to local analyses, different values of Winkler and Pasternak elastic foundation and analysis of bi-layer and triple layer sheets are investigated. It is concluded that the critical temperature increases and tends to a constant value along the rise of van der Waals interaction between the layers.

In this paper, an analytical solution for computing the linear plastic stresses and critical pressure in a FGM hollow cylinder under the internal pressure due to non-Axisymmetric Loads is developed. It has been assumed that the modulus of elasticity was varying through thickness of the FGM material according to a power law relationship. The Poisson's ratio was considered constant throughout the thickness. The general form of mechanical boundary conditions is considered on the inside surfaces. In the analysis presented here the effect of non-homogeneity in FGM cylinder was implemented by choosing a dimensionless parameter, named m, which could be assigned an arbitrary value affecting the stresses in the cylinder. Distribution of stresses in radial, circumferential and shear directions for FGM cylinders under the influence of internal pressure were obtained. Graphs of variations of stress versus radius of the cylinder were plotted. The direct method is used to solve the Navier equations.

The flow of a thin film down an inclined surface over topography is considered for the case of liquids with Sisko’s model viscosity. For the first time lubrication theory is used to reduce the governing equations to a non-linear evolution equation for a current of a Sisko’s model non-Newtonian fluid on an inclined plane under the action of gravity and the viscous stresses. This model is solved numerically using an efficient Full Approximation Storage (FAS) multigrid algorithm. Free surface results are plotted and carefully examined near the topography for different values of power-law index np, viscosity parameter m, the aspect ratio A and for different inclination angle  of the plane with the horizontal. Number of complications and additional physical effects are discussed that enrich real situations. It is observed that the flows into narrow trenches develop a capillary ridge just in front of the upstream edge of a trench followed by a small trough. For relatively small width trenches, the free surface is almost everywhere flat as the dimensional width of the trench is much smaller than the capillary length scale. In this region, surface tension dominates the solution and acts so as to stretch a membrane across the trench leading to smaller height deviations. The ridge originates from the topographic forcing which works to force fluid upstream immediately prior to the trench before helping to accelerate it over. The upstream forcing slows down the fluid locally and increases the layer thickness.