مجله مکانیک سازه ها و شاره ها
سال هشتم شماره 3 (پاییز 1397)

In this research, opening welding on an aluminum shell and investigating the effect of welding sequence on residual stresses and distortion after welding by finite element simulation have been investigated. Then, the results are compared in ABAQUS and SYSWELD.Using experimental data, simulation and experimental results are compared. The temperature distribution is not uniform in different area of the welding zone, the most important factor in this incident is the non-uniform welding geometry. Thermal retransmission and the difference between thermal pick in different situations increases with increase of welding steps, which will affect the development of residual stresses as well as distortion after welding. The peak of the residual stresses is reduced and more uniform distribution occurs as the number of welding sequences increases.. The results show that the higher the distortion in the weld region (the elongation), the greater the amount of elongation. Also, the amount of elongation will be greater, with the higher the distortion in the weld area.

Nanoemulsions and their preparing technologies have become one of the most important fields in various industries such as chemical engineering, pharmaceutics and food. Ultrasonic irradiation is a method for preparing nanoemulsions, which is used in different scales. Microcontainers, by use of piezoelectric ceramic (abbr. piezo), are utilized to prepare nanoemulsions in some special researches. Irradiation of ultrasonic waves by these piezos in microcontainers is the most important part of nanoemulsion preparation process. Piezoes arrangement and their excite frequencies have a great effect on interacting waves and therefore, ultrasonic bath performance. In this paper, four configurations of cubic ultrasonic microcontainer have been analyzed by simulations in COMSOL Multiphysics software. Irradiation of ultrasonic waves performed at three frequencies 20, 200 and 300 kHz. In order to determine the best arrangement, the effect of adding piezoes in different frequencies and arrangements has been analyzed. It has been shown that adding two faced piezos, leads to increasing acoustic energy density logarithmically and this increment is more evident in lower frequencies.

One of the abilities of Ultrasonic method which has been less investigated, in comparison with other residual stress measurement methods, is the residual stress measurement capability in specimen depths. this capability is due to ultrasonic waves penetration in different depths of specimen, according to their transmittance frequency. In this research, the capability of Ultrasonic method in measurement of longitudinal welding residual stress in specimen depth has been studied. For this goal, four series of Ultrasonic sensors, including 1, 2, 4 and 5 MHz were used in order to reach four depths of pieces of aluminum alloy series 5000 joined by TIG welding. Welding residual stresses were simulated in Abaqus software. Then, simulation model was validated by comparing with the results of X-ray diffraction experimental method. The validated FEM model with x-ray diffraction method was used for validation of residual stress obtained from Ultrasonic method in four depths. Finally, good agreement was observed. Ultrasonic method could measure longitudinal residual stresses with the maximum error of 12% of yield stress of aluminum plate. The accuracy of this method in measurement of the maximum longitudinal residual stress was greater than 92%.

In this paper, a new method is presented for gear fault detection. The vibrational signals of gearbox set are collected in three conditions: normal, chipped and worn teeth. These signals are adaptively decomposed into a number of intrinsic mode functions (IMFs) by the empirical mode decomposition (EMD). Since, all of the IMFs drived from the EMD are not appropriate for fault detection, the cross-corrolation concept is used to select all most apptoptiate IMFs. Then, feature matrix corresponding to each condition, is extracted using statistical functions. “One-against-one” support vector machine (SVM-OAO) is utilized to classify the faults. Since, all of the extracted features are not suitable for fault detection and SVM has parameters to be set, the particle swarm optimization (PSO) is used to select the best feature and detect optimal parameters of SVM. Objective function in this paper is accuracy of the SVM classifier in predicting of gearbox condition. Obtained results show that the selected features in this method and optimized SVM have the excellent ability to classify the faults.

Friction Stir welding (FSW) is a solid state technique that was invented to eliminate the limitations of welding of aluminum alloys. In the present study numerical simulation of friction stir welding and friction stir spot welding (FSSW) of AA6061-T6 aluminum alloy by pinless tool which has an embedded part with same material of the workpiece was performed in four different diameters. The temperature peak generated in the process was recorded for all simulation states and compared with previous experimental data for validation purposes. It has been found that in the FSSW process, the heat generation and temperature increase is higher than the FSW process, which is due to the Lack of transitional speed in this case and the increase in heat in a smaller volume section. Investigation of the vertical reaction force of tool was performed in FSSW, it was observed that if an embedded part in tool is used, the peak force is reduced and the amount of this decrease will increase with increasing the diameter of the embedded aluminum section. In the case of using d10 tool, the peak force compared to the d0 tool was about 10% lower.

Plate girders are flexural members and they usually use instead of hot rolled sections in the matter of their high flexural capacity. Plate girders are made by suitable combination of steel plates the reason why monitoring of shear stresses in plate girders with thin-walled webs are important is the probability of shear buckling and failure of web due to the initial steps of loading. Experiences illustrate that if intermediate and bearing stiffeners used in plate girders, not only the shear buckling do not cause failure but also it stay stable for bearing loads. The main objective of this research was study on their behavior of plate girders with corrugated web in comparison with plate girders with bearing stiffeners due to controlling of shear buckling (local corrugated web created by applying incremental static loading). In this research several items got studied like how to create local corrugated web and their properties and performances in shear buckling large deformations and some analytical methods like numerical buckling analysis. Results provides information about the higher shear capacity in plate girders in local corrugated web in comparison with simple plate girders without any stiffeners.

Sandwich panels, due to high strength to weight ratio and energy absorption properties, are widely used in various industries including aerospace industries, marine and automotive industries. This study explored the strength and performance of panels composed of low-density polyurethane foam core sandwiched between two aluminum skins. In this article several aluminum sandwich panels with polyurethane foam core having different thickness were designed and tested using a shock tube facility. Some blast test were performed in order to determine the effects of foam thickness on displacement of back face-sheet and energy absorption of sandwich structures. Also using the compression test results performed on the foam, numerical simulation using Autodyn software were performed. There was a good agreement between experimental investigation and numerical results. Using experimental investigation and parametric studies, it is shown that the amount of displacement of back face-sheet of sandwich structures is decreased and energy absorption is increased as foam and back face-sheet thickness is increased.

In this paper, a fuzzy sliding mode controller is presented for controlling a class of underactuated systems. In order to present the proposed method, at first, the sliding mode method for a single input-single output system is expressed. In the following, based on this design method, a sliding mode controller for a class of single input-multi output systems is presented. The mathematical proof shows that the closed loop system, in the presence of structured and un-structured uncertainties, has global asymptotic stability. In the proposed control due to the use of the sign function in the control input, the incidence of chattering is inevitable. For this reason, a fuzzy system is designed and added to the sliding mode controller. The proposed fuzzy sliding mode control eliminates existing problems and its design is done in such a way as to ensure the global asymptotic stability of the closed loop system. Finally, to demonstrate the proposed control performance, three-stage simulations are implemented on the inverse pendulum system. Simulation results show the performance of the proposed control.

In this paper, free lateral vibration of exponentially functionally graded beams is studied. For these inhomogeneous axial beams, characteristic equations in closed form are derived under various boundary conditions. The frequency and characteristic equations convert to analytical classical Euler-Bernoulli beams equations with ignoring gradient index. In addition, variation of mode shapes of the structure in terms of gradient parameter is demonstrated and compared with isotropic materials. In order to comparison and validation, the obtained results were compared with other available references. The results show that the natural frequency of the beams and mode shapes of the systems are strongly dependent to end conditions and gradient index. Furthermore, for functionally graded beams, there exists a critical frequency which leads to jump phenomenon in frequency spectrum so that harmonic vibration occurs in frequencies higher than the critical value and in frequencies lower than the critical value or pseudo-frequency, non-propagating fields occur. This feature does not exist in homogeneous beams. The presented results can be used for beams with exponentially decaying width and constant thickness. Moreover, the minimum frequency of the considered systems is helpful for engineers to design optimum non-uniform and nonhomogeneous structures.

In this research, the behavior of functionally graded micro-beams under electrostatic excitation is investigated. The system model is developed based on Euler-Bernoulli beam theory. In the developed model, the effects of electrostatic excitation and mid-layer stretching are considered. In order to solve the nonlinear governing equation, Generalized Differential Quadrature method and the Newton-Raphson method are used. To develop the pull-in voltage through the numerical results, a novel algorithm is developed. For numerical integration, Generalized Integral Quadrature is also used. Finally, the major problem of this method that prevent it from being used more frequently is discussed and a solution of that problem is suggested. In numerical results of this research, the pull-in voltage variation with respect to the functionally graded micro-beam stiffness distribution and initial gap of micro-beam is studied. Results show that increasing the micro-beam equivalent stiffness or beams initial gap, will increase the pull-in voltage. The boundary conditions effect on the micro-beam pull-in voltage is also studid in the numerical results.

Heat transfer and cost are two important parameters of designing a heat exchanger. Mostly, in engineering affairs the goals of interest for optimization are in conflict with each other. In the other hand, by making progress in one parameter, an undesirable factor appears. There is the same problem in heat exchangers. By increasing the heat transfer, heat area, cost and pressure drop increase. Thus, instead of one solution, there are several solutions. In this study firstly, the heat model of exchanger is estimated through e-NTU heat transfer method then for computing the heat transfer and pressure drop, Bell Delaware method is used. Lots of usual optimization methods for extracting the solutions are not efficient. At current research an efficient method is presented based on group particle algorithm and genetic, according to multi goaled function for optimizing of these exchangers. In addition, in optimization by two algorithms, two tube arrangement modes were considered, both square and triangular arrangement, which, At the end of this research, the results obtained from two algorithms for different modes and other research results have been compared.

In this study, dynamic behavior of thick rectangular plates under a moving mass with constant velocity traversing the plate on a rectilinear path is investigated. A semi-analytical method with the aim of BCOPs (Boundary Characteristic Orthogonal Polynomials) is utilized to tackle with the solution of motion equations for different boundary conditions of the plate while accounting for shear deformations. The effects of thickness and boundary conditions of plate and weight and velocity of the moving mass on the dynamic response of plate are scrutinized. The obtained results revealed the accuracy of the proposed method in comparison with the other researchers’ results. The results also demonstrated the importance of the moving load inertia as well as the shear deformations of the host structures on its dynamic behavior. The importance of this study lies on the vibration of bridge-type structures with plate decks, where, the shear deformation of the base structure could be no more ignored, especially for heavy vehicles moving with high speeds.

It is impossible to measure the random excitation loads of structures during transportation under road excitations or satellite carriers thrown under environmental excitations in order to identify modal parameters; thus in this research, our challenge and purpose is to determine the modal properties of structures without having the input excitation load and, but only by having the response. In the studies have been performed so far in the field of modal analysis, less attention has been paid to comparing time and frequency methods, especially in the determination of damping. In addition, no sensitivity analysis between different excitations of white noise, sinusoidal sweep and the effect of these excitations on time and frequency domain methods of modal functional analysis have been performed so far. At first, these methods are implemented and validated on a 5-DOF discrete model (mass, spring, and damper), and finally they are industrially implemented on an actual structure. This paper shows that the decomposition methods are capable to extract the modal parameters of the primary modes of an actual sample. At the end, a comparison is made between the results and the effectiveness of each method is evaluated.

Armored vehicles almost experience explosive loading in battle field. In this article, the structural integrity of armored vehicle under explosive loading will be studied experimentally and numerically. A finite element method has been developed to find the effect of explosion by 10 kg TNT at 97 cm distance from bottom of armored vehicle on the structure of vehicle. After determination of stress and strain distribution induced in the structure, part of the vehicle, which has maximum stress, is selected for detail analysis. The selected part consists of welding joints. The selected structure is modeled in the finite element software and an equivalent explosive loading was applied to the structure. The equivalent explosive loading on selected welded structure is so that same loading condition was applied to the structure as the real condition. The equivalent explosive welding is carried out by 500 gr TNT at 12.5cm distance. Experimental tests had been implemented on the selected structure by the equivalent explosive loading. A particular fixture was designed and manufactured for experimental tests. The finite element results show that the stress magnitude in the welded structure exceeds from the yield strength of the used material, the structure experiences plastic deformation. But fracture did not happen in the structure. Similar conditions have been observed in the experimental results. The explosion steps which was recorded by a high-speed camera shows that the blast wave is similar to the results of smoothed particle hydrodynamics (SPH).

In this study elastic dampers are implemented to a plate edges to find the damper influence on reflected waves. Most of the published papers in the sound localization on plates were not considered the effect of reflected waves on the final localization. As an experimental example, the sound caused by ping pong ball impact on a Plexiglas plate is used. The effect of the elastic dampers on reflected waves are experimentally analyzed. For this purpose, a database is gathered using recorded signals by low sampling rate electret and pickup microphones. These sound’s signals were recorded for different dampers position on the plate edges. In the proposed method, first the data related to the propagated waves are detected and isolated from the whole signals which are sent by the microphone. Then the effect of elastic dampers on reflected waves are analyzed by a space feature extracted from the energy of recorded signals. Furthermore, in order to evaluate experiment results, statistical analysis are used. The results show reflected waves from edges are clearly influenced by all elastic dampers in different efficiency.

Titanium is one of the most important microalloy elements of high strength low-alloy steels used in gas transmission industry. In this paper, titanium nano -oxide and titanium nano- carbide were added to two separate samples in the binding point. Then the Shielded metal arc welding (SMAW) was performed on high-strength low alloy (HSLA) steel with high grade of X-65 according to the special welding method of the National Iranian Gas Company. The results show that the percentage of titanium in both nano-alloy samples has been increased compared to the microalloy. The percentage of titanium in the sample of titanium carbide nanoparticles has increased more than that of titanium oxide nanoparticles. The charpy test results show that in the sample containing titanium oxide nanoparticles compared to the sample containing titanium carbide nanoparticles, has been increased by 70%. Also, the final strength (sample containing titanium carbide nanoparticles compared to the sample containing titanium oxide nanoparticles) has been increased by 40%.

A lot of researchers have focused on vibration-based structural damage detection in last few decades. Most of proposed methods are based on modal parameters. Due to difficulties in performing modal tests, response- based methods have got much more attention. In this paper, a new technique for processing random vibrational response with the aim of structural damage localization is introduced. The technique is based on Multi-channel Empirical Mode Decomposition of random response of the structure. The main advantage of Multi-channel Empirical Mode Decomposition over traditional Empirical Mode Decomposition is its ability to extract consistent Intrinsic Mode Functions in the case of multi-channel measurements. Regarding the fact that a local stiffness reduction in a beam causes an abrupt change in the curvature of deformation, spatially distributed Intrinsic Mode Functions are employed for damage localization. The proposed method has been carried out on a finite element model of a damaged cantilever beam. To investigate the efficiency and robustness of the method, the effect of number of measurement points, damaged zone location as well as damage intensity have been studied in detail. The results in all cases are satisfactory.

This paper presents the study on natural frequency of reinforced multi-layered isotropic cylindrical shells with three rings under external pressures. The multi-layered cylindrical shell is formed by three layers of isotropic where the inner and outer layers are stainless steel and the middle layer is aluminum. The reinforced multi-layered shell equations with three rings and external pressures are established based on first order shear deformation theory (FSDT). The governing equations of motion were employed, using energy functional and by applying the Ritz method. The boundary conditions represented by end conditions of the multi-layered cylindrical shell are simply supported-simply supported (SS-SS), clamped-clamped (C-C) and free-free (F-F). This research was solved with computer programming using MAPLE package. The influence of external pressure, rings position and different boundary conditions on natural frequencies characteristics is studied. The results shows that reinforced rings and external pressures have effect on the natural frequency of multi-layered isotropic cylindrical shell and cause the natural frequency to increase. The results presented can be used as an important benchmark for researchers to validate their analytical methods.

Geometry of the specimen has been known to be one of the main challenges of determining the fracture strength of the materials. In this paper, a new specimen called "semi-disc bend specimen containing a 3D crack" has been proposed in order to study mixed mode I/III fracture behavior of the materials. This SCB specimen contains a tilted crack and is loaded by three-point bend fixture. Extensive three dimensional finite element analyses were carried out for different geometrical and loading parameters to obtain the stress intensity factors at the crack tip. The results showed that this specimen was capable of creating the mixed mode I/III loading such that the mode III component increases as the crack angle enhances. In the next step, in order to consider practicability of the proposed specimen, several specimens made of asphalt concrete were produced, and were then tested under different mixed mode I/III loading. The results showed that the suggested specimen can correctly simulate the mixed mode I/III loading. In addition, based on the experiments, fracture resistance of the asphalt concrete reduces as the mode III component increases. On the other hand, twisted fracture trajectory was observed from considering fracture surface of the specimens.

In this study, the effects of aluminum particle additives in porous beds on the adsorption chillers performance have been investigated. For this purpose, an adsorbent bed with rectangular finned flat-tube heat exchanger by employing a three-dimensional control volume scheme is simulated. Furthermore, silica gel SWS-1L-water has been used as a working pair. The effects of aluminum particle additives on the system performance is investigated in the presence and absence of the fins. The results showed that the use of aluminum particles increases the thermal conductivity coefficient of the bed and, consequently, leads to reduction and increment of the cycle time and the specific cooling power, respectively, while it decreases the coefficient of performance. Moreover, the results indicated that employing the aluminum particles in the presence of fins has led to a greater increase in the specific cooling power which this effect is more pronounced in larger bed dimensions, while the coefficient of performance reduction is lower in the absence of fins.

Turbine blade cooling system is directly related to increasing the efficiency and power output and also growing the life time. By increasing the turbine inlet temperature, the efficiency and power output can be increased. Since the turbine blades are rotating at high rotational speeds, the blade cooling is also influenced by the rotation state. The Coriolis and centrifugal buoyancy forces are two important forces that will be created by the rotation. Therefore, in current study, the effects of Coriolis and centrifugal buoyancy forces on local and overall heat transfer coefficients in leading and trailing edges will be investigated. The experimental study will consider 5,000

The inducer is an axial Turbo-machinery installed at the inlet of Rotary Gas Separators of Electrical Submersible Pump to increase the head and overcome the pressure drop of the outlet pipes. In this study the inducer optimization in order to increase the head and the efficiency has been addressed using the computational fluid dynamics,. After the initial design, the inlet angle and outlet angle on the shroud, the position of the leading edge and trailing edge on the shroud as well as the blade thickness, selected as effective parameters. To reduce the computational cost a Surrogates model based on the Kriging model is used to predict the objective function. Flow analysis of the single and two phases are conducted by solving three-dimensional steady Navier–Stokes equations. Inhomogeneous two-phase flow is modeled in the ANSYS-CFX software using the Euler-Euler approach and considering interphase forces. From the genetic algorithm, the values of the parameters in the optimal points are calculated and the results are used for sensitivity analysis. Regarding the sensitivity analysis, the input angle and the blade thickness have the greatest impact on the head and also the outlet angle has the greatest impact on the inducer efficiency. Numerical simulation results show that the optimum geometry in single-phase and two-phase conditions provide more head.

General Purpose Graphics Processing Unite (GPGPU) allows the user to utilize GPU for general computing purposes. Using these processors can cause a significant speedup in numerical calculation for solving CFD problems. Several studies have been performed to investigate the advantages of using the GPGPU in numerical calculations including solving tridiagonal set of equations. In 2016, Checkerboard method introduced for solving tridiagonal set of equations in ADI solvers. In this method each set of equations is divided in to several smaller independent set of equations. Then each one of them will be solved by Thomas algorithm in checkerboard style. In addition to the participation of many threads, in this method it is possible to store the information of each set of equation in shared memory. In the present research, according to consideration around using shared memory, a strategy for using this memory in checkerboard Thomas method has been offered. Results shows that utilizing shared memory has been caused to computing speedup between 1.2x to 1.6x, compared with utilizing global memory. Also, it was found that bank conflict causes to decrease the speed from 10.9% to 18.8% in checkerboard Thomas method.

In this study, a characteristic-based finite-volume solution has been developed to obtain accurate results, improve the convergence rate, and provide the stability for the numerical solution of incompressible, steady, laminar, and two-dimensional flows with heat transfer. The artificial compressibility in order to couple the continuity and momentum equations and the fifth-order Runge-Kutta algorithm in order to marching the solution in time have been used. The convective terms have been calculated by a scheme based on the virtual characteristics and the viscous and thermal conduction terms have been calculated by a second-order scheme. In order to assess the capability of aforementioned developed finite-volume solution, the laminar, incompressible, steady, and two-dimensional cross flow of air on a NACA0012 airfoil without heat transfer and on a long horizontal circular cylinder with the forced convective heat transfer have been numerically simulated. The results obtained in these simulations have been compared with the data available in the literature. This comparison showed a good agreement between them.