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In this paper, an approximate solution using layer-wise theory for the vibration analysis of rotating laminated cylindrical shells with ring and stringer stiffeners under axial load and pressure is presented. The cylindrical shells are stiffened with uniform interval and it is assumed that the stiffeners have the same material and geometric properties and cylindrical shell reinforced by outer stiffeners while stiffeners are treated as discrete elements. The equations of motion are derived by the Hamilton’s principle. In deriving the governing equations three-dimensional elasticity theory are used and the study includes the effects of the Coriolis and centrifugal accelerations and the initial hoop tension. The layer-wise theory is used to discretize the equations of motion and the related boundary conditions through the thickness of the shells. The edges of the shell are restrained by simply supported boundary conditions. The presented results are compared with those available in the literature and also with the FE results and excellent agreement is observed. Finally, the results obtained include the relationship between frequency characteristics of stiffened cylindrical shell and different geometry of stiffeners, stiffener type, rotating velocities, amplitude of pressure and amplitude of axial load.

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In this paper, an algorithm is presented based on using bspline function for optimizing tank cross section. This process minimizes fluid c.g. height and overturning moment and improve rollover threshold of tank vehicles. This algorithm receives tank capacity specifications as inputs and offers fourth order bspline function with 10 control points that has more roll stability, and then optimizes it for different filling conditions. This algorithm is based on the third order bspline function with 8 control points, initially. Therefore, with averaging and optimizing, range of control points is modified and the numbers of control points and degree of bspline function are increased. The results show that, the mutation rate is better to be between 4 and 6%, and the number of individuals in each generation should be at least 40. The algorithm presented in this paper, is a fast and accurate method for optimization of tank cross section in different filling conditions. The Algorithm based on GA maintains simplicity applicable for industries and specially has a rollover threshold of 10% higher than conventional tanks.

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In this paper, viscoelastic insulators are employed into an automotive brake system to improve the vibration stability. Thus, the system stability has been considered with hypothesis of couple modes. Therefore, the originality of the paper includes the complex eigenvalue analysis of viscoelastic model in brake squeal phenomenon. Accordingly, the brake system is simulated in a FEM code and then, the viscoelastic materials are applied using Negami-Havriliak model. Comparing the eigenvalue results in both cases, in which the viscoelastic material is treated as an absorber at the first case and without treatment for another case, indicates an improvement in instability mode at 12 kHz. In addition, applying these absorbers has no significant effects in low frequency. Furthermore, comparison of the results presented here with experimental ones done by other author, indicates the reliability of the presented model. Finally, with applying the strain energy analysis, the location of absorber treatment as well as its optimum thickness is concluded.

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In the present paper, power transmission interaction of multilayered sound isolation panels consists of porous, solid materials and air gaps using Transfer Matrix Method (TMM) has been considered. Considering the theories related to acoustical behavior of multilayered panel lined with poroelastic materials, detail explanation of Transmission Loss (TL) of a panel via TMM has been presented. Calculation of TL for a specified panel via TMM has been compared to existed experimental data in the literature and excellent agreement is observed. Next, based on this verified model, a multi-objective optimization of multilayered panel has been conducted using NSGA-II to maximize TL of panel while the panel weight is kept to a minimum. Results of two-objective optimization reveals, if the designer target is to achieve a specific average TL in the frequency band of 10 to 500 Hz, for a panel with constant width, selecting a panel with lower layers (three layers) can bring lower weight. But, if a higher average TL in the same frequency band is desired, a panel with more layers (six layers) has much better conditions in terms of weight.

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The different factors such as material, height, thickness, installation status, and geometry of the wall's head can influence on the efficiency of the sound walls to decrease the noise pollution of theairports. This paper is presented to improve the effective geometry of the wall's head as well as finding the best wall's head to maximize the noise reduction in an airport. To investigate the performance of the sound wall, the boundary element method is used. Then, in order to modeling the sound walls with different dimensions and sizes, PATRAN software is utilized. In the next step, the models are meshed and finite element method is used to analyze the vibrations of the models. Consequently, the natural frequencies and the mode shapes of sound's walls are predicted and finally the insertion loss via modeling of sources of noise and sound receivers are calculated. The design method of Taguchi experiments is applied to decrease the total numbers of the different models of Y shape geometries. Lastly,the governing equations with approximately fitted over the test cases are determined by neural network. Finally, the genetic algorithm is used to obtain the ideal head's wall.

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The objective of this investigation is to present a semi-analytical method for studying the buckling of the moderately thick composite conical shells under axial compressive load. In order to derive the equilibrium equations of the conical shell, first order shear deformation shell theory is used. The equilibrium equations are derived by applying the principle of minimum potential energy to the energy function that they are in the type of partial differential equations. In the following, the partial differential equations are transformed to algebraic type by using Galerkin and differential quadrature methods and then the standard eigenvalue equation is formed and critical buckling load is calculated. Also, to validate the results obtained in this study, comparisons are made with outcomes of previous literatures and the results of Abaqus finite element software. Analyzing the results, shows the convergence speed and good accuracy of differential quadrature method and desired precision of Galerkin method in calculating the critical buckling load. Finally, the effect of cone angle, fiber orientation, boundary conditions, ratios of thickness to radius and length to radius of the critical buckling load are studied.