Concrete materials are exposed to special weather conditions, corrosion and significant damage. For this purpose, the effect of 28-day compressive strength changes on the samples studied in this study was investigated by considering the simultaneous effect of chloride ion penetration and carbonation phenomenon. For this reason, in the first case, the samples are exposed to carbon dioxide once and then to chloride ions. In the latter case, only samples under the influence of chloride infiltration are examined. To make the samples, which include 9 mixing designs, three water-to-cement ratios of 0.35, 0.4 and 0.5 and three percent of 0%, 7% and 10% silica fume have been used. Finally, an optimal model is introduced to predict the compressive strength of concrete containing micro silica exposed to carbonation using artificial neural network. Also, a relation for estimating compressive strength based on the ratio of water to cement and the amount of silica is presented. تفاصيل المقالة

phase change materials have a high capacity in thermal energy storage, these materials can be used to prevent the heat transfer into the building besides optimize and improve the performance of the refrigeration and air conditioning system. Adding phase change materials (PCM) to the building can improve the inside comfort temperature and save consumption energy of the building. In this article the parameters that affect the performance of PCM in the building walls, such as phase change temperature, latent heat, thickness, thermal conductivity, etc., have been investigated using ANSYS software. the numerical simulation of thermal energy storage in the solar walls of the building have investigated using phase change materials in different thicknesses with different heat flux rates. This wall is designed to capture the sun energy during the day, reducing energy consumption and optimizing it during peak times. تفاصيل المقالة

The permeability matrix of rock is a physical/mechanical characteristic that closely relates to the microstructure of this heterogeneous geomaterial, and the orientation of micro-cracks led to some naturally existing micro-cracks. Upon the effects of loading/unloading and high-temperature development, micro-cracks appear in critical zones of rock media that can effectively change the conductivity against gas or other fluids. Finally, macro cracks are generated and increase the porosity of the rock matrix on the distribution and geometrical arrangement. Consequently, the permeability becomes higher and depends on the stress/strain level of the rock body during loading/unloading and the passing fluidity interaction process. The influence of stress level and high temperature on rock's gas and water permeability has been studied in the literature. Fractured rock formations show vastly different properties, such as adsorption, etc., concerning permeability and storage capacity, thus giving rise to mass exchange processes between fractures and the surrounding matrix. This interaction between fracture and matrix impacts the flow and transport processes in the fractured subsurface, which can be observed on each scale considered for investigation purposes. The influence of fracture-matrix interaction has to be scrutinized upon the planned tests conforming to the natural condition when dealing with safety investigations or remediation possibilities. This paper shows some of the effects of fracture-matrix interaction and its geometry on groundwater flow in a saturated fractured rock/concrete media and the parameters describing those processes concerning different scales. A damage model concept contains fracture network generation, mesh generation, and appropriate discretization techniques based on presumed sampling between planes and polygons. The influence of a polygon matrix of finite porosity on the effective hydraulic conductivity tensor of a fractured system is illustrated by an example. In this research, we focus on determining the gas and water permeability of rock commonly used in transportation works, including loose/low strength and high strength/dense rock/concrete in interaction with pre-peak stress and damage level in post-peak behavior of rocks. تفاصيل المقالة

In polymer-based nanocomposites, carbon nanofibers have been used to improve mechanical properties in various applications. In this research, the tensile properties of carbon nanofibers have been used to create carbon-epoxy nanocomposite and improve the mechanical properties of epoxy nanocomposite, and the effect of the weight percentage of carbon nanofibers on the mechanical properties of epoxy nanocomposite has been investigated. Epoxy with weight percentages of 1.0, 5.0 and 1.5 carbon nanofibers were produced and their mechanical properties were investigated. The results showed that the use of even a small percentage of carbon nanofibers can lead to the improvement of mechanical properties. تفاصيل المقالة

Analysing the buckling behaviour of the two kinds of sandwich beams, the first one with functionally graded material faces and homogeneous core and the second one with functionally graded material core and homogeneous faces are presented in this paper based on a high order sandwich beam theory. Properties of the constituent materials are assumed temperature dependent and functionally graded materials are modelled by a power law rule. Even and uneven porosity distributions are considered to improve the accuracy of the model. Minimum potential energy principle is used to obtain the govern equations and Galerkin method is applied used to solve the equations in a clamped free boundary conditions. Lateral displacement, and thermal stresses of the core and Lagrange strains are considered. To verify the procedure, the results of the present study are compared with the literature. Thickness, length, porosity, wave number and temperature effect on the critical load are investigated too. تفاصيل المقالة

The phenomenon of failure in objects is one of the major issues that human beings have been facing for a long time, and because of advances in technology in the present age, this issue is more important than in the past.All engineering materials, on the other hand, have tiny cracks from which failure begins.Therefore, estimating the residual life of thin plates made from these materials and used in space and offshore structures requires knowledge of the stress distribution due to cracking in these components. Because of the singularity of the crack tip due to large stresses, the presence of a relatively small crack can lead to a hazardous situation. Therefore, this area should be given more attention.In this research, using the Inglis formula and considering the correction coefficient of the compensatory free surface, the value of the stress coefficient for edge crack is obtained. Then, by replacing the new stress coefficient in Westergaard formula, we calculate the stress field of Mode I (Opening mode) and Mode II (sliding mode) in the perforated plane containing the edge crack. Finally, we examine the effects of various parameters such as loading angle, crack length and hole radius on the values obtained for stress in both modes by plotting. تفاصيل المقالة

Laser Cladding is one of the processes that is considered in manufacturing of different objects such as airplane blades and shafts. Many studies have been presented to optimize this process, but there is a research gap in the field of temperature simulation effect. The reason for the importance of temperature simulation is the direct correlation of the temperature gradient with the properties of manufactured object. The purpose of this study is to simulate temperature field of laser cladding process with COMSOL6.0 software. After verification of presented temperature with previous study with 0.2 % error, parameter studies including temperature dependent parameters and heat loss are presented verses temperature, time and laser power were presented with mathematical models. تفاصيل المقالة

In polymer-based nanocomposites, carbon nanofibers have been used to improve mechanical properties in various applications. In this research, the tensile properties of carbon nanofibers have been used to create carbon-epoxy nanocomposite and improve the mechanical properties of epoxy nanocomposite, and the effect of the weight percentage of carbon nanofibers on the mechanical properties of epoxy nanocomposite has been investigated. Epoxy with weight percentages of 1.0, 0.5 and 1.5 carbon nanofibers was produced and their mechanical properties were investigated. The results showed that the use of even a small percentage of carbon nanofibers can lead to the improvement of mechanical properties. Considering the fact that the non-uniform distribution of these nano-fibers in the epoxy matrix on the one hand and also the lack of acceptable adhesion between these two phases are critical issues that lead to the formation of lumps in the matrix and finally the loss of mechanical properties in will find. تفاصيل المقالة

The geometrical characteristic of products is one of the crucial quality indicators in the cold roll forming process. In this process, an appropriate flower pattern for rolls is vital to achieve the desired geometry and quality for high-strength steel pipes. In this paper, four different flower patterns, including circular, edge bending, double radius, and reverse bending are designed for the roll forming process of the high-strength steel pipe. Then, the effect of the flower pattern on the curvature distribution of the deformed strip is investigated using finite element analysis. The accuracy of the finite element model is evaluated by performing experimental tests. The results show that forming the strip with the reverse bending flower pattern leads to a more uniform curvature distribution in its cross-section, especially in the edge portion. Thus, this flower pattern design method is recommended for the roll forming process of the high-strength steel pipes. تفاصيل المقالة

The behavior of the earth-dam body as a soil structure made of cohesive soil in the core and non-cohesive soil as the core supports, including water interaction upstream through earthquake upon multi-line constitutive equations, is the aim of this paper. A multi-plane mechanism-based approach is successfully employed for assigning post-liquefaction displacement of earth-dam structures. This approach is derived from total stress procedures with two major advantages:1) the triggering and post-liquefaction responses have been multi-lined into one analysis.2) the modeling of post-liquefaction element behavior is greatly improved.To sum up, a multi-plane-based framework is employed. The strength effects on integrated sampling planes and the resultant of this simulated multi-lined behavior are implemented for each finite element gauss point. This multi-plane-based model can also predict the effects of induced and inherent anisotropy plus the rotation of principal stress/strain axes through the plastic behavior of both cohesive and non-cohesive soils.The approach is presented through the simulation of the case history as the response of the lower San Fernando dam to the 1971 San Fernando earthquake. The magnitude and pattern of the predicted displacements are shown to be in good agreement with the measured values تفاصيل المقالة

This paper presents a novel model for prediction of energy consumption and heat transfer in houses on the basis of neural network by the use of experimental dataset of some cities of Iran for the learning process. To this end, a deep learning neural network (DNN) is designed by means of real set of data as input. In order to evaluate the proposed network, the predicted results are compared with the results obtained from the practical schemes. The comparison approved the effectiveness and feasibility of the suggested network in prediction of energy consumption and heat transfer with a low error for regression. تفاصيل المقالة

Two dimensional analysis of fluid flow and heat transfer through the trapezoidal microchannel has been done. The energy and Nervier stokes equations have been solved considering the wall slip velocity and temperature jump using the Lattice Boltzmann method (LBM). The relation between relaxation times and Knudsen number has been derive in LBM. The effects of Reynolds number, Nusslelt number, temperature jump and velocity slip on different Knudsen number (0.001<Kn<0.1) and different aspect ratios (0.2<AR<1.2) were investigated. The good agreement between results and earlier studies were found. Results show the important effect of AR and Knudsen number on Nusselt number in trapezoidal microchannel. At low Reynolds number the significant influence on Nusselt number has been seen. تفاصيل المقالة

The purpose of this paper is to evaluate the free vibration of sandwich panels with corrugated core using the element-free Galerkin method and based on the first-order shear deformation theory (FSDT).The sandwich panels' free vibrations with corrugated core consist of two sheets above and below the panels, and a corrugated core in middle of these panels. The core equals to orthotropic sheet and the two panels equal to isotropic sheet. Dynamic equations of the members are obtained through FSDT. The present research applies Galerkin numerical element less method to solve equations of the problems. This method uses the functions of minimum moving squares. The model is simulated in cosmos software; the results are compared with the results of present papers, and show the accuracy of the method applied in the present paper. تفاصيل المقالة

Lid-driven cavity flow is characterized by large-scale energetic eddies which are potential for energy harvesting purposes. The present article deals with numerical study of vortex-induced autorotation of an elliptic blade hinged at the center of a lid-driven cavity.Immersed boundary method is utilized to solve the governing equations for this moving boundary problem. Four different blade dimensions are considered at a fairly high-Reynolds number to evaluate the impact of various vortex types and flow unsteadiness on the blade dynamics. Small-amplitude fluttering, clockwise autorotation and counter-clockwise autorotation are three dominant modes observed at various configurations and different temporal stages. The average-length blade is equally characterized by vortices at both directions, and consequently experiences a fluttering mode. In contrast, short (long) bladeis mainly affected by one dominant vortex type, leading to steady autorotation in counter-clockwise (clockwise) direction. At stable autorotation of blade in both directions, regular cyclic temporal oscillations are observed in the rotational speed, which are due to cyclic evolution of the near-blade vortices and their alternating moment applied to the blade. تفاصيل المقالة

This article presents an optimal shape design methodology for heat conduction and convection problems. In this study, the shape of the conductive and convective medium is parameterized by means of non-uniform rational B-spline (NURBS) surfaces, and their control points represent the design variables. The conductive and convective domain is discretized by choosing the parameters of NURBS surfaces as generalized curvilinear coordinates, and the heat conduction and convection equation is solved using the finite difference method. The simplified conjugate-gradient method (SCGM) is used as the optimization method to obtain the optimal shape and adjust the design variables intelligently. By optimizing the profile of a straight fin with the objective of enhancing heat transfer rate and reducing the fin mass the methodology is demonstrated for conduction problems and by optimizing the shape profile of a natural convective cavity with the objective of reducing the maximum wall temperature the methodology is shown for convection problems. تفاصيل المقالة

The chaotic dynamics of Roto-Translatory motion for a triaxial Gyrostat satellite is considered in this study based on the Hamiltonian approach. Higher complexity in the coupled spin-orbit equations motivates the reduction of the Hamiltonian in the study of this nonlinear system. This reduction is done by the use of the Deprit canonical transformation developed here by the new Serret-Andoyer variables used as rotational and translational variables. The results obtained from the Hamiltonian reduction can be written as a perturbed equation near Integrable-Hamiltonian form, where the perturbed part of the equations consists the orbital and gravity gradient effects. Increasing the perturbation parameter causes the trajectories of the system to pass throughout heteroclinic bifurcation zone introducing chaos in the system. Also heteroclinic bifurcation and transversally stable and unstable manifolds are mathematically proven using Melnikov method. Through the Melnikov integral, the bounded variations in the design parameters are determined so as to prevent the system from a chaotic behavior. The simulation results based on the numerical methods such as the time series responses, trajectories of phase portrait, Poincare section, and Lyapunov exponent criterion quantitatively verify chaos in the system in the presence of perturbation influences.. تفاصيل المقالة

One of the best methods to achieving renewable and clean energy is piezoelectric energy harvesters (PEHs), which convert mechanical and vibration energy into electrical energy. These generators appeared after the special and unique capabilities of piezoelectric and vibration to electrical energy can be directly converted. The use of these generators is seen in many fields including the use of roads and bridges to convert vibrations caused by the vehicles in to electrical energy and other thing. In this study a piezoelectric energy harvester with the feature of parallel piezoelectric connections was computer simulated using a finite element method. In a computer simulation unlike laboratory method that can only analyze one form of a system, different states and situations of factors can be simulated. In this study, to achieve an optimal state of power and output voltage of an existing PEH, the effects and behaviors of different parameters such as forces, frequencies, temperatures, housing dimensions, piezoelectric materials and the presence of isolators have been investigated. In addition, to obtain the significance of these factors, using the analysis of variance method, the importance and effectiveness of each of these parameters has been investigated. The results revealed that increasing the amount of force and frequency and decreasing the temperature increases the output voltage of this kind of PEH. Changing the dimensions of the housing if its area is constant, does not change the output result and the use of isolators reduces the output voltage. The effect of these parameters is compared to previous studies and the results are presented. تفاصيل المقالة

The present study examines the possibility of completing gappy flow fields with the method of gappy proper orthogonal decomposition (GPOD). The procedure is performed on a numerically simulated cavity flow. The DNS data is artificially made incomplete by randomly omitting localized data. Two levels of gappiness are examined to evaluate the GPOD procedure. The results indicate that the relative error between the GPOD estimation and the real field directly depends on the level of gappiness. As the gappiness increases, the prediction accuracy decreases. It is shown that the relative error does not monotonically decrease because of inherent noise in higher-level modes of energy. The optimal count of modes in GPOD procedure is obtained and discussed. The contribution of GPOD procedure on spatial experimental data is also addressed. تفاصيل المقالة