In this research, the influence of hygro-thermo-magnetic fields on the dynamics of axially moving functionally graded beams is investigated by considering various porosity models. Also, parametric studies are performed to clarify the effects of rotary inertia factor, visco-Hetenyi substrate, material power index, follower force, and boundary conditions on vibration frequencies and instability threshold. The mechanical properties are graded transversely according to a power law. Different uniform and non-uniform porosity models are considered. The beam vibrates in variable moisture and humidity conditions and is under an external longitudinal magnetic field. The dynamical equation is derived based on generalized Hamilton’s principle and Rayleigh beam theory assumptions. With the aid of the Galerkin method, the eigenvalue problem is solved and frequency characteristics and instability boundaries are determined numerically. The axial velocity related to static instability is determined analytically. The results show that by increasing the porosity of the system with the first type of non-uniform porosity, the stability improves. Similar to hygro-thermal environments, the critical axial velocity decreases by increasing the power index. It is proved that the stability decreases/increases by increasing the rotary inertia factor/magnetic field. The results can be useful for the design of axially moving inhomogeneous systems in complex environments.

The application of Shape Memory Alloy (SMA) materials, which are one of the subcategories of smart materials, as an actuator has significantly increased in recent years. However, the application of SMA actuators is restricted due to their slow response and complexity resulting from the nonlinear characteristics of these materials, such as asymmetric hysteresis and saturation. Several methods have been introduced to model these actuators. One of the most powerful and well-known structures for modeling systems with hysteresis behavior is the Generalized Prandtl-Ishlinskii (GPI) model, which is widely used to control these actuators due to its analytical inverse. The current research investigates the reduction of the response time of a micro-positioning platform with two mutual actuators. Based on the obtained experimental results, an experimental-based model using the GPI model was identified. By extracting the inverse of this identified model and implementing it into the input of the system, the issue of removing nonlinear characteristics and linearizing the system was considered for controller design. The results showed that the GPI model properly described the nonlinear behavior of the system despite the complexity caused by the interaction of two mutual actuators. However, identifying a comprehensive model to accurately describe the SMA actuator requires great effort.

One of the applications of optimization methods is solving the inverse problems of identifying internal boundaries, estimating the mechanical properties of materials and etc. In most of the articles, due to the simplicity of the relationships, the cases where the material is a homogeneous body have been considered, But in industry, when two molten material are combined together, there is a possibility that the resulting material is non-homogeneous material.In this article, identifying the geometry of the irregular internal boundaries between three materials and estimating the mechanical properties is presented. The intermediate material has a variable modulus of elasticity. This problem has been studied by combining three methods of colonial competition algorithm, simplex and conjugated gradian method along with the numerical method of Boundary Elements Method. The effect of the type and hardness of the constituent materials of the non-homogeneous body and the effect of the geometry and position of the internal boudaries on the convergence have been investigated. The obtained results indicate the power and ability of the presented method to estimate unknown parameters.

Nowadays, composite panels are widely used in various industries, and the study of the behavior of these panels under acoustic vibrations is one of the important cases in engineering analysis. Also, the effects of incidence and azimuthal angles and Mach number are investigated and the calculated critical frequency and sound transmission loss are validated with other works. The results show that the critical and coincidence frequencies and sound transmission loss are influenced by factors such as the orthotropic behavior of the panel and its thickness, incidence and azimuthal angles, sound wave Mach number, and transverse shear flexibility. Based on the resulting graphs, increasing the incidence and azimuthal angles causes the enhancement of the critical frequency and sound transmission loss, while the orthotropic parameter has the opposite effect. On the other hand, increasing the Mach number and decreasing the thickness of the panel reduces the sound transmission loss and increases the critical frequency of the panel. Also, with the increase of the transverse shear flexibility of the panel, the critical frequency is increased. The trends of coincidence frequency changes are also similar to the mentioned trends of critical frequency with respect to the effective parameters except for the incidence angle. According to the presented results, the coincidence frequency of the panel, unlike the critical frequency, decreases with the increase of the incidence angle.

The use of cold rolling, is one of the methods of producing multilayer clad sheets. The advantages of this method over other methods of producing multilayer clad sheets have led to its widespread use in recent years. Existence of several parameters affecting the mechanical properties and bond strength of multilayer sheets produced by cold roll bonding, has made research in this field important. In this paper, using experimental method, the effect of several effective parameters such as temperature and time of thermal operation and type of sheet surface preparation on the mechanical properties of AA5456 / AA1020 / St321 three-layer sheet produced by cold rolling has been investigated. In this regard, two sanding methods including flap disc and Cylindrical Sandpaper have been used to prepare the surface of the sheets and heat treatment has been performed at three temperature levels of 310, 355 and 400 ° C for three periods of 30, 60 and 90 minutes. The results of these tests showed that the highest increase in tensile strength was obtained in the sample of heat treatment at a temperature of 400 ° C for 60 minutes and surface preparation by Cylindrical Sandpaper.

Deep drawing is a process that is usually performed in cold conditions, but there are also cases of using this process in hot conditions to reduce the forming force. The use of a blank holder in the forming process leads to an increase in the forming force and changes the thickness of the sheet, especially in the hot state, due to the increase in friction. On the other hand, omition of blank holder will cause wrinkling of the sheet due to development of periferal stresses, and this problem is aggravated by increasing the depth of drawing. In this research, the finite element analysis for forming a hemispherical head from a high strength steel sheet in the hot deep drawing process without using a blank holder is studied. Simulations are done for two types of tractrix and pseudo tractrix dies and for sheets with different thicknesses and diameters, and the results are compared with each other. The results of the analyzes show that with the increase in the thickness and diameter of the sheet, the force required by the mandrel for forming increases. In general, less forming force is required in the tractrix die and at the same time it brings less thickness changes. Furthermore, the formation of hemispherical objects lacking cylindrical tiles in thicknesses higher than one centimeter will be healthy and free of wrinkles.

In this paper, using homotopy analysis method, an analytical solution for the nonlinear free vibrations of the functionally graded porous micropipes conveying fluid flow is presented. The equations of motion are obtained based on Euler-Bernoulli beam theory and modified couple stress theory with consideration of geometric nonlinearity. It is assumed that the micropipe is porous and the porosity distribution is in three forms; uniform, non-uniform symmetric, and non-uniform asymmetric distributions. The Hamilton principle is used to obtain the governing equations of motion. Also, the Galerkin method is used to convert partial differential equations to ordinary differential equations. Finally, by considering immoveable simply-supported boundary conditions and using the homotopy analysis method, the analytical solution for the governing equations is performed. The results obtained from this method has been verified by the Runge-Kutta numerical method which shows that the homotopy analysis method has good accuracy by considering two terms of the Taylor series. The results showed that between the proposed porosity distribution schemes in the micropipe, the non-uniform asymmetric distribution pattern is the most suitable, because the microtube becomes unstable at a higher fluid velocity.

In this paper, an algorithm for the conceptual design of the aerostat is developed. This tactical aerostat is an intermediate step for stratospheric high altitude platforms. In the presented algorithm, the design and operational parameters of the aerostat such as geometry and dimension of the aerostat hull, shape and configuration of the tails, the mass budget of the balloon components, ballonet percentage, fabrics materials, stress of hull fabric, tether tension at the winch, static margin, angle of attack, blow by, tether length, tether profile, the confluence point position, etc. are determined via 4 distinguished loops. In addition, an aerostat is designed for the special given requirements using this algorithm, and the results are prepared in the paper. Furthermore, to optimize the tail sizing, the Taguchi orthogonal array L16 (45) is used. 16 different tails are designed and the static stability of the aerostat is analyzed using these tails and the final optimum geometry of the tail is introduced. Finally, the influence of the wind velocity, payload mass, payload position, and the operational height above mean sea level on the operational parameters of the aerostat are explored.

The polymer membrane fuel cell, which works with hydrogen and air and has high efficiency and power density, low-temperature operation, and the ability to start quickly and without pollution, can be a good alternative to fossil fuels. The performance of a proton exchange membrane fuel cell is highly dependent on the geometry, flow channel configuration, and size. In the current research, which is a numerical study, the performance of the polymer membrane fuel cell has been investigated by relying on the design of gas injection channels with different geometries in an unsteady state. The computational fluid dynamics method has been used to solve the governing equations. In this method, the finite volume method is used to discretize and solve the equations. Different geometries have been used for this research, including pseudo-spiral (model A), parallel (model B), and pin (model C), whose dimensions are the same as the spiral base model. Using dynamic simulation, it was observed that after about 70 seconds, the flow reached a stable state, and water production gradually increased. The results show that model C performs better than other models, and model B shows the worst performance.

In this paper, a bidirectional single unit air compressor equipped with two reciprocating pistons and operating with a new mechanism of semi gear and rack type in power transmission has been made, developed and analyzed. In this structure, there are two reciprocating pistons in two opposite positions to produce compressed air, therefore, there are two compressed air strock in each rotation of the output shaft. In the power transmission mechanism, a rack gear and a semi gear have been used, so that The rotation of the compressor shaft causes the rotation of the semi gear and finally, the reciprocating movement of the rack and the pistons. The results show that in the experimental situation, the amount of energy consumed to reach the tank pressure of 4 bar is equal to 142.6 kJ, while the minimum theoretical work of the compressor in the isotherm state to reach the same pressure is equal to 72.5 kJ and this represents 51% efficiency of this structure in the form of working in compressor mode. Also, the results show that using heat from waste sources to increase the tank pressure from 4 bar to 5 bar will lead to an increase in efficiency of about 60 percent.