جستجوی مقالات مرتبط با کلیدواژه « خواص وابسته به دما » در نشریات گروه « مکانیک »

In this article, thermo-elastic analysis of a thick hollow cylinder under internal pressure is investigated. The material properties are considered to be temperature-dependent and functionally graded in radial direction. This temperature dependency caused the heat conduction equations to be nonlinear. The perturbation theory is performed for solving nonlinear heat conduction equations of the cylinder. Arbitrary combined thermal boundary conditions containing temperature and temperature gradient are considered. As the temperature field is extracted, it can be used to solve decoupling thermal stress governing equations. These thermo-elastic equations and related boundary conditions are discretized in strong form using differential quadrature method. Numerical results extracted from the suggested semi-analytical approach in a linear regime are then compared to the existing results. It is depicted that the presented method benefits from the low computational and high convergence behavior. The stress distribution of the cylinder is computed by considering the approximation of the temperature in zeroth-order, one-order as well as second-order. In order to achieve proper accuracy, more terms of the perturbation approximation series should be considered for the higher temperature difference between the inner and outer surfaces of the cylinder.

The use of thermoelectric generators has a special place in recovering the waste heat of combustion gases. In the proposed model, a thermodynamic analysis with the effect of the thermoelectric generator module area on the performance characteristics of the device was studied. To develop the model, the properties of the thermoelectric generator were assumed to be temperature dependent. The convective heat transfer of water in the cold channel was also considered as variable. The effects of water flow regime and the module area were investigated both in the longitudinal direction and for five different values of the module rows on the functional characteristics of the device. The results showed that increasing the number of module rows and module area decreased the power and efficiency of energy and exergy and increased the rate of exergy destruction. The module area is also optimized in two different cases. One was done to achieve the maximum net power and the second to achieve the maximum ratio of maximum net power to the area module. The optimal area in the first and second cases were 0.4641m2 and 0.2207m2 , respectively.

In this work, thermo – elastic analysis for functionally graded thick – walled cylinder with temperature - dependent material properties at steady condition is investigated. The length of cylinder is infinite and loading is consist of internal hydrostatic pressure and temperature gradient. All of physical and mechanical properties expect the Poisson's ratio are considered as multiplied an exponential function of temperature and power function of radius. With these assumptions, the nonlinear differential equations for temperature distribution at cylindrical coordinate is obtained. Temperature distribution is achieved by solving this equation using classical perturbation method. With considering strain – displacement, stress – strain and equilibrium relations and temperature distribution that producted pervious the constitutive differential equations for cylinder is obtained. By employing mechanical boundary condition the radial displacement is yield. With having radial displacement, stresses distribution along the thickness are achieved. The results of this work show that by increasing the order of temperature perturbation series the convergence at curves is occurred and also dimensionless radial stress decrease and other stresses with dimensionless radial displacement increase.

In this study three dimensional fluid flow and heat transfer of Al2O3-water nanofluid in a triangular microchannel heat sink, consisting from seven isosceles triangular microchannels, have been investigated numerically by considering conduction in solid parts. The governing equations have been solved using finite volume method based on finite element and utilizing coupled algorithm. The objective has been investigating the effects of four inlet/outlet flow arrangements on flow field and heat transfer of Al2O3-water nanofluid. These arrangements consist of: inlet from the center of the north wall and outlet from the center of the south wall (I-type), inlet from the right side of the north wall and outlet from the left side of the south wall (N-type), inlet and outlet from the top and bottom parts of the west wall (D-type) and inlet from the upper part of the east wall and outlet from the bottom of the west wall (S-type). Also the effects of the Brownian motion of nanoparticles and temperature-dependent properties of the nanofluid have been considered. The results showed that increasing the nanoparticles volume fraction from 0 to 4% increases the average Nusselt number between 4.72% and 5.47, decreases thermal resistance between 1.81% and 2.34% and decreases the ratio of maximum temperature difference of heat sink substrate to heat flux between 1.28% and 1.56%. Also the results indicated that the I-type arrangement has a better heat transfer performance, lesser thermal resistance and provides more uniform temperature distribution. In this case, the I-type arrangement has higher Nusselt number between 1.69% and 18.33%, lower thermal resistance between 3.55% and 29.29%, and a smaller ratio of maximum temperature difference of heat sink substrate to heat flux between 5.23% and 36.25%, when compared with those of other arrangements. The heat sink performance characteristics have improved between 0.1% and 0.75% by considering the Brownian motion and between 1.9% and 3.9%, by considering temperature dependent properties.

In this research a low velocity impact analysis of a sandwich plate with multilayered composite face-sheets and flexible core under thermal conditions is investigated. In this regard, thermal effects and temperature dependent properties of the core are considered. In this study, equations of motion are derived based on a hybrid LW/ESL finite element formulation considering the thermal effects by which the number of unknowns is independent on the number of layers. This new formulation is in the framework of Carrera’s Unified Formulation (CUF). The CUF unify many theories in a unified form such that can be differed by the order of expansion and definition of the variables in the thickness direction. In order to satisfy the interlaminar continuity of transverse stresses between the layers the Reissner Mixed Variational Theorem (RMVT) is employed. In this paper for considering the thermal effects, the nonlinear strains are used. In this research in order to modeling the low velocity impact a new modified spring-mass model is proposed using the two degree spring–mass model and also Choi linearaized law. Results of this formulation are compared with experimental results which show the high accuracy of the proposed formulation. Results show that with increasing the temperature, the impact force decreases and also impact time duration increases significantly. In this study, some new results are presented for different thermal conditions, aspect ratios, face thickness ratios and also different initial energy of impactor.

Free vibration of sandwich plates with temperature dependent functionally graded (FG) face sheets in various thermal environments is investigated. The material properties of FG face sheets are assumed to be temperature-dependent and vary continuously through the thickness according to a power-law distribution in terms of the volume fractions of the constituents. Also, the material properties of the core are assumed to be temperature dependent. The governing equations of motion in polar system and in free natural vibration are derived using Hamilton’s principle and Galerkin method is used to solve the equations and obtain the natural frequency. In-plane stresses of the core that usually are ignored in the vibration characteristics of the sandwich structures are considered in this formulation. The results obtained by Galerkin method for symmetric circular sandwich plate with fixed support is compared with finite element method that obtained by ABAQUS and good agreement is found. The results show that varying the power-law index and temperature have important effects on natural frequency.

This research work is directed toward determining the thermal stresses in a Ni-Resist cast iron commercial exhaust manifold of a turbo-charged gasoline engine. At first, based on a fluid-structure interaction (FSI) method, the steady state temperature distributions in the exhaust gas as well as in the exhaust manifold set are determined, using a CFD model. The thermal B.C.’s previously estimated by conducting a motor temperature detection test. Next, to conduct a thermal stress analysis, a full FEM model for the manifold set has been generated in the Abaqus software, and the mechanical B.C.’s are imposed in that. Also, the temperature distribution resulted from the thermal analysis imputed to the nonlinear FEM model as a predefined temperature field. Also, the range of temperature variations in the manifold is defined for the software material property module, so that Abaqus computes the material properties and stresses in each point according to the local temperature. Finally, executing the FEM model, the thermal stress distributions are computed. The numerical results show that the thermal stresses have the most critical values at the confluence region of the manifold, and maximum shear stresses occur around the bolted joints.

In this paper, Asymmetric buckling analysis of functionally graded (FG) Circular plates with temperature dependent property that subjected to the uniform radial compression and thermal loading is investigated. This plate is on an elastic medium that simulated by Winkler and Pasternak foundation. Mechanical properties of the plate are assumed to vary nonlinearly by temperature change. The equilibrium equations are obtained using the classical plate theory (CPT), Von Karman geometric nonlinearity and virtual displacement method. Existence of bifurcation buckling is examined and stability equations are obtained by means of the adjacent equilibrium criterion. The effects of elastic foundation coefficient, thickness to radius, power law index, and temperature-dependency of the material properties on critical buckling load of FG plates are presented. The results of the present work have been compared with the results of other investigator and the results of the comparison are very good. It is found that by increasing temperature, critical buckling load decreases. It is also concluded that the critical buckling load of (FG) Circular plates increases with an increase in the Winkler and Pasternak constants of elastic foundation.

In this study a frequency analysis of a sandwich plate with multilayered composite face-sheets and flexible core under thermal conditions is investigated for different boundary conditions. In this regard, thermal effects and temperature dependent properties of the core are considered. In this study, for driving the equations of motion, a hybrid LW/ESL finite element formulation, considering the thermal effects is proposed by which the number of unknowns is independent on the number of layers. This new formulation is in the framework of Carrera’s Unified Formulation (CUF). The CUF unify many theories in a unified form which can be differed by the order of expansion and definition of the variables in the thickness direction. In order to satisfy the interlaminar continuity of transverse stresses between the layers the Reissner Mixed Variational Theorem (RMVT) is employed. In this research for considering the thermal effects, the nonlinear strains are used. Results of this formulation are compared with available results which show the high accuracy with low computational cost of the proposed formulation. Results show that with increasing the temperature, the frequency of structure decreases significantly, due to the degradation of the properties of the core. In this study, some new results are presented for different thermal conditions and also different boundary conditions.

The analysis of sandwich beams with FG face sheets loaded by central indentor in various temperature conditions is carried out in this paper. Property distribution in the FG face sheets is according to power law function of FGMs and all properties of them are temperature dependent. In this model, First order shear deformation theory is used for the FG face sheets while three-dimensional elasticity is used for the flexible core. Two spreading length scales are introduced and calculated for defined sandwich beam, that characterized the behavior of sandwich beam under local loads. These spreading length scales, which are two functions of the beam material and geometrical properties, characterize the length over which a load on the upper surface of a beam is spread out by the face sheets and the core. The theoretical predictions in the present work are compared with FEM results by ANSYS and the results published in the literature for special cases, and reasonable agreement is found between them.

In this research، validity of temperature-independent thermophysical properties assumption of water-Al203 nanofluid in natural convection problems within the enclosures is investigated. The numerical results are obtained utilizing an in-house finite volume code based on the SIMPLE algorithm. In order to do the validation the numerical results and those of existing correlations are compared. In order to evaluate the thermal performance of the enclosure، the average Nusselt number on the hot side wall in both temperature-independent and dependent cases is compared Results show that، in the all considered solid volume fractions، the difference in the Nusselt number in the case of temperature-independent properties is less than 10 percent in comparison with the case in which the properties are temperature-dependent when temperature difference is less than 5 ○C. As the temperature increases، the difference between Nusselt number in both cases increases and the effect of increase in solid volume fraction is to increase this difference. Results also show that the difference between these two cases is dependent solely on temperature differences between the hot and cold walls regardless of the temperature they have.