IRANIAN JOURNAL OF MECHANICAL ENGINEERING (ENGLISH)
Year:2018 | Volume:20 | Issue:3 |Papers Count:10

The significance of vibration omission in the engineering structures has led the striking vastness for the applied designing science. The role of vibration omission in materials with emphases on energy-saving and cost reduction is such a topic that has been analyzed and discussed as a challenge in the mechanical engineering. Here, a steel structure with a certain number of piezoelectric pieces with specific dimensions is considered. The aim is to omit vibrations or reduce the vibration range at the minimum time. In this paper, the placement of piezoelectric is carried out in order better to accelerate the suppression of vibration amplitude using the MOPSO, an optimization algorithm. Piezoelectric elements are installed as sensors and actuators on the top and bottom of structures. An early rise is applied to the structure and thus it begins vibration and the amplitude of these vibrations is suppressed by the piezo actuators. Piezoelectric sensors sense the structure’ s vibration motion and control operations are done based on it, and finally to suppress, a control signal is sent to the actuators. The result of this motion is the structural vibration suppression. In this thesis, the studied structure is Timoshenko beam. This beam is considered as a key and basic structure having the vast application in Robotics Science, Engineering, Aerospace Industry and etc. Timoshenko beam is accounted a more accurate model than Euler – Bernoulli beam because it considers the shear effect during deformation. Here, the beam describes its dynamism and constructs the related functions by a numerical method in which each node includes one beam element with 2 degree of freedom(Transitional displacement – Rotational displacement) that is placed under the influence of an external load such as transverse force and bending torque for analyzing the transverse vibration of beam. This external load is a temporal function in the forms of pulse, impulse, step, sine alternatives. Here, PID controller has been used in order to control the structure. In this controller there are three unknown coefficients in Kp, Ki and Kd matrices using multi-objective particle swarm optimization algorithm for or MOPSO, and the unknown coefficients are determined as result of searching this algorithm during the beam in order to determine an optimal point or points of beam to place sensor and piezoelectric actuator in the top and down for the structural suppression at the least possible time.

In this paper, a new pattern was offered for the fabrication of tissue engineering scaffolds by the 3D printing method. A photocurable resin, micro mirror and UV source were employed for the fabrication of scaffolds. Final patterns have a simple form and a gradient form that the mechanical behavior of each model was investigated under mechanical testing. For the investigation of precise mechanical behavior of porous samples, non-porous samples were investigated under mechanical testing and an empirical equation was used for the checking influence of base material properties on the behavior of porous samples. The results indicate that the gradient model, unlike the simple model has multiple elastic regions under the large displacement because of their special design. This behavior is very important for the scaffolds that were implanted in hard tissue and tolerate a high pressure using this type of layering beside the biological advantage of gradient model can improve the efficiency of scaffolds.

This article presents an efficient reliability-based optimization method for critical structural design, in which, the probability of failure (Pf) should remain in a small bound. Critical structures should be designed to be optimal and reliable. Despite significant progress in reliability and optimization techniques, their interaction, which is considered in reliability-based optimization (RBDO), is faced with several challenges, especially in reliability analysis of critical constraints (constraints with Pf less than 10-5). To address this issue, in this paper the cross-entropy method is intended for reliability analysis and is combined with Genetic Algorithm in a double-loop framework to implement RBDO. The cross-entropy method is based on Monte Carlo simulation, except that the variance of sampling is reduced, which leads to a faster and more accurate reliability analysis method. The proposed RBDO method is demonstrated on two structural design. The obtained results show a high capability in reliability-based optimization of critical structures. In addition, using the proposed method, in comparison with traditional safety factor method, provides a more substantial manner in reliability improvement.

HVAC systems are the biggest energy consumers in buildings. Hence, reducing energy consumption in this sector, while maintaining thermal comfort can be one of the vital policies in order to use saved energy in industrial section. In this paper, we proposed an HVAC system optimization algorithm to analyze and compares the effect of using different HVAC systems on energy consumption reduction. The purpose of this algorithm is to choose the best HVAC system for a building with respect to energy consumption in the pre-construction stage or to improve and optimize its performance in the constructed buildings. The performance of the proposed algorithm is based on choosing the right HVAC system with respect to the reduction of the energy consumption in the building and initial and current costs. A five story residential building in Tehran has been considered as a case study to analyze proposed algorithm performance. The comparison between the model and building’ s real energy consumption shows less than one percent error which is acceptable.

In this paper, the static problem of several cracks in a functionally graded piezoelectric– piezomagnetic (FGPP) rectangular plane subjected to concentrated anti-plane mechanical and in-plane electric and magnetic fields is described. The material properties are assumed to vary continuously according to exponential functions along the transverse of the FGPP rectangular plane. The dislocation method and integral transforms technique are applied to obtain a set of Cauchy singular integral equations. The field intensity factors for cracks, are obtained by using the corresponding solution to these equations. The numerical examples of mode-III problem are presented to illustrate the interesting mechanical and electromagnetic coupling phenomena induced by multi-crack interactions. Finally, the effects of material non-homogeneity constant, the cracks length and the cracks configuration upon the field intensity factors are investigated. The obtained conclusions seem useful for design of the magneto-electro-elastic structures and devices of high performance.

In the current paper the impact of the presence of a damped nonlinear Dynamic Vibration Absorber on dynamic behavior of an Euler-Bernoulli clamped-free beam is investigated under resonant and non-resonant excitations. Accordingly, the governing equations of motion are derived and converted to the form of non-dimensional equations. Then, these equations are solved using the Multiple Scales Method after applying the Galerkin Method. It is assumed that the Dynamic Vibration Absorber damping is linear, and its stiffness is composed of two parts, a linear and a third order nonlinear one. Resonant and non-resonant cases have been taken into account for sinusoidal excitation. The influence of the Dynamic Vibration Absorber parameters on the system vibrational behavior is provided. Obtained results illustrate the possibility that under specific circumstances the nonlinear dynamic vibration absorber could have a better performance in suppressing the oscillation amplitude than a similar linear one in jumping phenomenon region. In addition, the results show that in non-resonant frequency regions, there is no major difference in system vibrational behavior in presence of linear damped, undamped and nonlinear vibration absorbers. Furthermore, in comparison with similar linear case, the nonlinearity of the absorber stiffness relocates the resonant frequencies, and makes changes in the non-resonant frequency region.

In this study, thermally induced vibrations of a Functionally Graded Material (FGM) Spherical Cap discussed. Distribution of shell properties in the direction of thickness is calculated from volume fraction relationship. Dependency to temperature is expressed based on the Touloukian formula. Thermal loading on the shell is axisymmetric and the response of the shell have been considered axially symmetric. Ceramic rich surface of the shell is subjected to temperature rise, whereas the metal rich surface of the shell is kept at reference temperature or thermally insulated. Temporal evolution of temperature profile across the shell thickness is obtained through solution of one-dimensional heat conduction equation. This equation is originally nonlinear since temperature dependency of thermal conductivity is taken into account. The first-order shear theory and Von-Karman compatibility relations has been used for deriving the equation. Dynamics equations are derived using Hamilton's principle and with the application of Ritz method has become a set of nonlinear time-dependent algebraic equations. Solving this set of equations is done with Newmark integral method help with numerical method Newton-Raphson. Solution of the transient one dimensional heat conduction equation with the arbitrary type of time-dependent boundary conditions is carried out employing the central finite difference method combined with the Crank– Nicolson time marching scheme. After validating the developed computer code, some parametric studies are accomplished to show the influences of various involved parameters. It is shown that temperature dependency, geometrical non-linearity, shell thickness, power law index, and the type of thermal loading, all affect the temporal evolution of plate characteristics.

Waves propagation is one of the issues which is considered in defense industry, construction and passive defense. Among the various sources of waves, the explosion is an important factor. After explosion, considerable energy is released in a short time. This energy is emitted into the environment as seismic waves and vibrates the particles in the environment and after that, energy absorption in the environment eventually lead to the weakening of wave propagation and finally wave attenuation. In this paper, at first, the analytical solution of two-dimensional wave equation with a source of shock and boundary value using the Green's function method is discussed and then the analysis of explosion process is done by using the Finite Difference Time-Domain Method. The analysis conducted in this paper examine the effect of distance and weight of the explosive.

This paper presents a method for maintaining the battery safe operating voltage region in a electric vehicle. Using the instantaneous value for the battery voltage in the proposed method, the traction motor maximum torque is limited through an interaction between the BMS and vehicle control unit. Unlike the methods based on battery State of Power (SoP) estimation in which the battery safe operation cannot be guaranteed because of the model-based nature, performance of the proposed method does not rely on the precision of battery modelling and can be used in different life conditions for the battery. In addition, due to low computational costs, the proposed algorithm can be easily implemented on the BMS. Performance of the designed algorithm has been evaluated in a Hardware-in-the-Loop (HiL) test bench for a series hybrid electric bus and compared with the results of SoP estimation based methods. Results indicate the improvement towards maintaining the safe operating voltage region in various life conditions for the battery.

In the present research, stress analysis of a functionally graded material cylindrical pressure vessel subjected to the simultaneous action of thermal loading, rotation and internal pressure is performed. Also it is assumed that vessel in located in an elastic medium which is designated according to the Winkler model. Except for Poisson’ s ratio, all of the thermomechanical properties of the vessel are assumed to follow a power law model and vary across the radius of the vessel. Heat conduction equation and Navier equation which govern the temperature and radial displacement distribution across the radius of vessel are established and solved analytically. Closed form expressions are obtained for temperature distribution, radial displacement profile, strains and stresses components in the vessel. Parametric studies are provided to explore the effects of rotation and foundation stiffness on the structural responses of the vessel. It is shown that, foundation stiffness, power law index of the properties and angular speed all affect the stresses and displacement components of the vessel, significantly.