Although the direct heat gain method is simple and inexpensive, it suffers from large temperature swings, besides strong directional daylight. In addition, the direct heat gain method can be affected very quickly by outside emperature fluctuations, which results in an indoor bed comfort level. For thermal storage buildings, walls and floors are used as heat storage elements, and stored energy in the walls and floors during the day period can be used for heating during the night. Time lag and decrement factors are very important characteristics for determining the heat storage capabilities of materials. Evaluation of the time lag and decrement factor provides a measure of the developed indoor thermal comfort conditions and, from an energy point of view, the possibility of reducing energy load demands. In the present study, time lags and decrement factors for different building materials utilized in Iran have been investigated analytically. Unlike previous studies, which mainly focused on numerical methods, in this research, the transient heat conduction equation is solved analytically using a Green function under time-dependent convection boundary conditions. According to the climate of Tehran, periodic boundary conditions are applied to the outer surface of the wall for modeling outdoor temperature variations over 24 hours. The effects of different parameters, such as wall thickness and both inner and outer heat transfer coefficients, as well as the effect of thermal insulation layers in sandwich walls, on the time lag and decrement factor, are investigated. The results indicate that the thickness and type of material have a significant effect on the time lag and decrement factor. The results of the present study are applicable for designing more effective passive solar buildings, optimizing the design of walls and other related areas, resulting in a reduction of energy consumption and environmental pollution through diminishing pollutants such as

In this paper، an exact closed-form solution is presented for out-of-plane free vibration of thick homogeneous and isotropic multilayered rectangular plates with simply supported boundary conditions based on the linear three-dimensional elasticity theory. The solution procedure is on the basis of using of some proposed displacement fields. Proposed displacement fields satisfied simply supported boundary conditions on the edges of the plate. On the continuation of the solution، by replacing the proposed displacement fields into the three-dimensional elasticity equations of motion and simplifying the results some independent ordinary differential equations are obtained. The natural frequencies are extracted by satisfying the boundary conditions on the surfaces of the plate and surfaces between the layers. In order to establish the accuracy and stability of the proposed solution، several numerical results for one layered and two layered square and rectangular plates are presented and compared with corresponding results in the literatures and obtained results of 3-D finite element method.

In this paper, a three-dimensional solution with mixed layerwise formulation is presented for multi-layer composite plates with arbitrary geometry and boundary conditions.  In this study, the displacement field the out-of plane stresses are considered as a sum of a series of functions with unknown coefficients. The boundary conditions and the continuity of the displacement field and the traction stresses between the layers are exactly satisfied. Equilibrium and compatibility equations are also applied using the Reissner's variational principle. The results show that the mixed formulation has faster convergence than displacement based formulation, and provides more accurate values of interlaminar stresses.

This work considers an effective analytical method based on Displacement Potential Function (DPF) for solving 3-D thick and multi-layered transversely isotropic linearly elastic cylindrical shells (non-homogeneous in radial direction) with simply-supported end boundary conditions. Axisymmetric radial loads are applied on the inner and outer faces of the cylindrical shell. Three-dimensional elasticity equations are simplified using displacement potential function result in one single linear partial differential equation of fourth order as governing differential equation in term of displacement potential function. The governing equation is solved via the separation of variable method with exact satisfaction of two end boundary conditions including stress and displacement boundary conditions, stresses on the inner and outer surfaces of the shell, and the continuity conditions of the displacement and tractions on the interfacial surfaces of the multi-layered cylindrical shell. After determining displacement potential function, all other functions such as stresses and displacements can be obtained at each point of the examined shell. Comparison of the results with existing analytical results show excellent agreement at different thickness ratios and aspect ratios of the shells. Some practical problems are solved for one-layered and three-layered cylindrical shells. For this purpose, three types of materials are defined for a one-layered cylindrical shell such as composite material (Graphite epoxy), metallic substance (e.g. Zinc), and isotropic material (Aluminum). Also two combinations of materials are considered for three-layered cylindrical shell so that the inner and outer layers of the shell are made of transversely isotropic material (Graphite epoxy), while the middle layer of the isotropic material is made of aluminum and foam. The values of the non-dimensional functions containing stress and displacement components are calculated for these problems to demonstrate the effect of thickness ratio and anisotropy of the shell on the distribution of the stresses and displacements.

The temperature distribution in the laser-irradiated biological tissue is investigated considering heat convection. The first- and the second-degree burn times are predicted using estimation of thermal damage. A non-Fourier equation of bio-heat transfer based on dual phase lag model is employed. The transport behavior of laser light in the tissue is regarded as highly absorbed and effects of the phase lag times on thermal response and thermal damage are explored considering different heat convection coefficients. The Laplace transform with discretization technique and also using boundary conditions, a set of algebraic equations in Laplace domain is generated which are solved by numerical Laplace inverse transform. The results show that the highly absorbed laser light in the tissue plays an important role in the burned skin time. Also, convective heat transfer boundary condition on the surface provides different results, even by considering the natural convection on the surface, and the first- and the second-degree burns are postponed at least 0.02 second.

In this paper static analysis of orthotropic functionally graded material (FGM) cylinders with finite length was carried out by a mesh-free method. MLS shape functions are used for approximation of displacement field in the weak form of equilibrium equation and essential boundary conditions are imposed by transformation method. In this simulation, an ax symmetric model is used. Mechanical properties of cylinders were assumed to be variable in the radial direction as a function of volume fraction. In this analysis, effects of the cylinder thickness and length, volume fraction exponent, type of materials layout and essential boundary conditions on displacement fields and stress distribution for orthotropic cylinders are investigated. The results of the proposed method for isotropic FGM cylinders were compared with corresponding results obtained from FEM and previous published works and a very good agreement are seen between them. Also by comparing the stress distributions of orthotropic FGM cylinders and corresponding results of homogeneous multilayered orthotropic cylinders were confirmed.

This paper is intended to analyse the post buckling behavior of annular plate under the effects of symmetric uniform loading using Rayleigh-Ritz method. This is done first by formulating the problem in large defection using Von-Karman nonlinear theory. The geometry in natural coordinate system using the correct and useful mapping and the development of displacement fields in natural coordinate system using Hierarchic, Hermitian and Lagrange shape functions respectively in interpolation of out-of-plane and in-plane displacement field of plates are also considered. Finally, we deal with thepresentation of a proper Hookian displacement field for controlling post buckling behavior of circular plates. To solve the problems, this methid enjoys a number of advantages including continuity in stress and strain, few numbers of degree of freedom and application of bounder easy conditions.,

In this paper hyperbolic heat conduction equation in spherical media with its outer surface subjected to time dependent laser heat source and combined convective-radiative cooling is solved using Laplace transform method. In order to perform this method، the nonlinear boundary condition is linearized by Taylor’s series expansion. The Riemann-sum approximation method is used to obtain the inverse of Laplace transform. The temperature distribution is studied for different values of thermal relaxation time، pulse duration، convection-conduction and radiation-conduction parameters and the solutions of hyperbolic and Fourier equations are also compared. The results of the present method is verified by being compared with available analytical solution results under a simpler boundary condition.

In this article, analytical formulation of axisymmetric FGM thick-walled cylinders with power varying of mechanical and thermal properties under transient heating using first order shear deformation theory is presented. Equilibrium equations are derived from virtual work principles and energy method. Also, the transient heat transfer equation is solved by separation of variables, generalized Bessel function, and Eigenfunction method. General thermal boundary condition involving conduction and convection without heat source is considered. At the end the results of the analytical solution are compared with the finite element method, for this aim cylinder is modeled in Abaqus. The effects of time varying on stress and displacement distribution has been studied in this paper. according to results increasing time lead to increase the stress and displacement, by the way after a moment the stress and displacement are time-independent and they become constant. the boundary condition of two ends and thermal boundary condition play a significant role in results.

This study presents a new quadrilateral element for layered finite element analysis of laminated composite plates which is obtained through assemblage of membrane and plate bending elements. The membrane component is a new unsymmetric quadrilateral element with drilling degrees of freedom, in which two different types of displacement fields are used as the test and trial functions. The test function is a new kind of displacement field with drilling degrees of freedom obtained by using interpolation along the element edges. The trial function is a stress field computed through analytical solutions of Airy stress function. The bending component of lroposed element is a non-conforming plate element that its displacement is computed using third-order deformation modes and the rotational field of element is defined by using first-order Jacobean matrix. The results of numerical benchmark problems show that the the proposed element is capable for analysis of laminated composite plates with varius geometry and boundary. The maximum error of the proposed element among the considered numerical problems is only 1.5 percent.