Abstract in English:Abstract The global optimization of integer and mixed integer non-linear problems has a lot of applications in engineering. In this paper a heuristic algorithm is developed using line-up competition and generalized pattern search to solve integer and mixed integer non-linear optimization problems subjected to various linear or nonlinear constraints. Due to its ability to find more than one local or global optimal points, the proposed algorithm is more beneficial for multi-modal problems. The performance of this algorithm is demonstrated through several non-convex integer and mixed integer optimization problems exhibiting good agreement with those reported in the literature. In addition, the convergence time is compared with LCAs' one demonstrating the efficiency and speed of the algorithm. Meanwhile, the constraints are satisfied after passing only a few iterations.
Abstract in English:Abstract In this paper the nonlinear forced vibration of an orthotropic circular plate resting on Winkler, Pasternak and nonlinear Winkler foundation is investigated. Plates with edges elastically restrained against rotation and inplane displacement are analyzed and the Von-Karman geometric nonlinear equations are employed. In this study it is assumed that the plate can be subjected to any periodic distributed lateral loading with respect to time. The Galerkin method is used to obtain Duffing's equation for the central deflection. The Homotopy Perturbation Method was used to study the effects of various parameters including orthotropic parameter, elastic foundation parameters and initial deflection on frequency ratio. Highly accurate results were obtained by the application of the aforementioned method.
Abstract in English:Abstract An experimental investigation was performed on stainless steel hemispherical shells under axial compression. Eight kinds of shells with radius-to-thickness ratios that range from 57.1 to 125 were designed and manufactured for this study. The shells were compressed to more than 50% of their radii by a solid flat plate. To avoid contact between the base plate and the deformed central part of the shells, most of the shells were placed on a plate with a hole in the center. Nonetheless, one type of shell was placed on a solid base plate without a hole to analyze the effect of the base plate. As per an observation of collapse modes and load-deformation shell relations, the deformation process of a hemispherical shell that is compressed by a flat plate can be divided into four stages: local flattening (Stage I), axi-symmetric inward dimpling (Stage II), non-symmetric multiple lobes (Stage III), and peripheral deformation and buckling stage (Stage IV). The present study mainly studies Stage IV, which can be categorized into peripheral compression (Stage A), peripheral buckling (Stage B), buckling expanding (Stage C), and overall collapse (Stage D).
Abstract in English:Abstract Profiled Steel Sheet Dry Board (PSSDB) system is a lightweight composite structure comprises Profiled Steel Sheeting and Dry Board connected by self-drilling and self-tapping screws. This study introduced geopolymer concrete, an eco-friendly material without cement content as an infill material in the PSSDB floor system to highlight its effect onto the PSSDB (with full and half-size dry boards) floor system's stiffness and strength. Experimental tests on various full scale PSSDB floor specimens were conducted under uniformly distributed transverse loads. Results illustrate that the rigidity of the panel with geopolymer concrete infill with half-size dry board (HBGPC) increases by 43% relative to that of the panel with normal concrete infill with full-size dry board (FBNC). The developed finite-element modeling (FEM) successfully predicts the behavior of FBGPC model with 94.8% accuracy. Geopolymer concrete infill and dry board size influence the strength panel, infill contact stiffness, and mid-span deflection of the profiled steel sheeting/dry board (PSSDB) flooring system.
Abstract in English:Abstract This paper is devoted to the vibration of rotating flexible spacecraft. The maneuver of the spacecraft is modeled by a constant torque input acting on the hub. For the first time in this paper the equations of motion of flexible spacecraft are derived based on higher order sandwich panel theory (HSAPT). Hamilton's principle is used for driving the governing partial differential equations of motion. The generalized differential quadrature method (GDQ) is utilized to solve the partial differential equations of motion. The effect of different parameters on vibration of rotating flexible spacecraft appendage is investigated. It is also investigated the effect of these parameters on natural frequencies. The result of HSAPT and Euler Bernoulli theory is compared with each other. To show the accuracy the natural frequencies of recent paper are compared with the literature.
Abstract in English:Abstract In the present study, an analytical closed form solution for free vibration response of hybrid composite plate reinforced with shape memory alloy (SMA) fibers is derived. Recovery stresses generated during martensitic phase transformation are obtained based on one- dimensional Brinson's model. The mechanical properties of plate are assumed to be temperature dependent. Based on the first-order shear deformation theory (FSDT) the governing equations are obtained via Hamilton's principle. Ritz method is used to obtain the fundamental natural frequency of the plate for different temperatures. A detailed parametric analysis shows the strong influence of the volume fraction, pre-strain, orientation and location of SMA fibers as well as the aspect ratio of the plate on the fundamental natural frequency and the onset of the thermal buckling.
Abstract in English:Abstract In this paper, an adhesively-bonded stepped-lap joint suffering from a void within its adhesive layer is investigated. The void separates the layer into two sections. The joint is under tensile load and materials are isotropic and assumed to behave as linear elastic. Classical elasticity theory is used to determine shear stress distribution in the separated sections of adhesive layer along the overlap length. A set of differential equations was derived and solved by using appropriate boundary conditions. Finite element solution was used as the second method to verify the obtained results by analytical method. A two-dimensional model was created in ANSYS and meshed by PLANE elements. A good agreement was observed between two methods of solutions. Results revealed that the stepped-lap joint performed better in stress distribution with a void rather than single-lap and double-lap joints.
Abstract in English:Abstract High performance composites are exposed to severe loading and environmental conditions. In this work, mechanical properties of Fiberglass Reinforced Polyester (FRP) manufactured by resin transfer molding were evaluated. The effect of the strain rate on mechanical properties under three quasi-static testing conditions, four fiber contents and several orientations was studied using instrumented tensile tests. A model was fitted to predict Tensile strength, Young's modulus and shear modulus and the failed samples were analyzed to understand the failure mechanisms. The results showed that the fitted model is reliable enough to conclude about the effect of the fiber volume fraction and the strain rate on the mechanical properties. Young's modulus and tensile strength increased when the strain rate is higher. Tensile strength also increased with fiber content (Vf) up to Vf = 41% .The predominant failure mechanism is fiber rupture for the main directions and for the off-axis directions, the failure mechanisms are fiber pullout and delamination.
Abstract in English:Abstract In this paper, the Euler-Bernoulli beam model is used to predict the structural instability of rotating cantilever tubes conveying fluid and subjected to uniform distributed tangential compressive load. The governing equation of motion and boundary conditions of the system are derived using the Hamilton's principle. Then, Galerkin method is applied in order to transform the resulting equation into a general eigenvalue problem. The present analysis is validated by comparing the results with those available in literature. Furthermore, the model is utilized to elucidate the stability characteristics of the system for different conditions.
Abstract in English:Abstract In this paper, the smoothed finite element method, incorporated with the level set method, is employed to carry out the topology optimization of continuum structures. The structural compliance is minimized subject to a constraint on the weight of material used. The cell-based smoothed finite element method is employed to improve the accuracy and stability of the standard finite element method. Several numerical examples are presented to prove the validity and utility of the proposed method. The obtained results are compared with those obtained by several standard finite element-based examples in order to access the applicability and effectiveness of the proposed method. The common numerical instabilities of the structural topology optimization problems such as checkerboard pattern and mesh dependency are studied in the examples.