JOURNAL OF SOLID AND FLUID MECHANICS
Year:2020 | Volume:9 | Issue:4|Papers Count:18

Laser shear interferometry or shearography is one of the novel NDE methods that is used to inspect and estimate the size of subsurface defects. In this research, a new method for estimating the size of plane defects was presented. In order to verify and compare the proposed method with conventional methods and studying the effect of defect depth and shear size on the accuracy of the measurements, different plane defects were tested. The size of the defects was measured in different conditions and the estimation error was reached in each case. Also, Finite element simulation was used to study the effect of loading time estimation error. The results showed that the proposed method was able to predict the defect more accurately than the conventional method. Also, the effect of shear size and defect size on the estimation error is less in the presented method and the lowest estimation error is obtained when the shear size is equal to the size of the defect. The results of the finite element simulation showed that in the proposed method, unlike the conventional method, increasing loading time does not affect the accuracy of estimation and its measurement parameters do not depend on the loading time.

ccording to high degrees of freedom of multiple-arm space manipulators, it is cumbersome to exploit equations of motion of such systems. In this paper, an algorithm is provided by using Lagrange equations in terms of quasi-coordinates to construct equations of motion of a space robot with multiple arms which each arm has an arbitrary number of links. Lack of constructing kinematic energy. To exploit equations of motion, first equations of motion have been expressed by Lagrange formulation in terms of quasi-coordinates. The innovation in this paper is lied within a novel form which results in the elimination of computing kinematic energy term and partial derivatives, therefore the common complexities of Lagrange method gets vanished Then the calculation of partial derivative terms has been done by using recursive kinematic equations. At the end a dual arm robot, which each arm has two links with spherical joints, has been modeled by the recursive algorithm presented in this paper and simulated by MATLAB. Then, the results of simulation have been compared by line graphs conducted by ADAMS. Authenticity of the aforementioned algorithm has been proved by correspondence of attained figures.

In this study, mass detection by frequency reponse analysis of piezoelectric actuators has been investigated. Bimorph piezoelectric actuators have been applied to increase the actuation force and decrease the nonlinear effects and vibrational coupling. In this regard, the theory of mass detection was investigates by analyzing the frequency response of piezoelectric actuators. For this purpose, first, the dynamic equation of bimorph piezoelectric actuators was calculated. Then, the natural frequency response of actuator without any added mass was analyzed. In addition, the effect of added mass on the frequency response and its behavior analysis were investigated to find the amount of mass. Finally, experiments were carried out to confirm the validity of the simulation results. The results reveals that if the measured masses, in the milligram order, are in the range of 0. 01 to 0. 2 times of the actuator mass, the measument’ s error is less than 13%, therefore, this setup has appropriate accuracy.

In this paper, a new hybrid intelligent method is suggested for the bearing fault detection at time – varying speed conditions. The vibration signals have been collected for two states as healthy bearing and defected inner race under variable speeds. In this study, the ensemble empirical mode decomposition (EEMD) technique and Johanson trace method are utilized for extracting the co-integration relationships from the vibration data. Then, the feature matrix corresponding to the co-integration relationships is calculated using the wavelet packet decomposition (WPD) method, and the time-domain statistical features. In the next stage, the compensation distance evaluation technique (CDET) has been used to determine the preselected feature subsets. The preselected features are utilized as input data of the support vector machine (SVM) to predict the bearing state. Finally, The optimal SVM parameters and the optimal feature subsets are determined using the binary particle swarm optimization (BPSO) algorithm. The obtained results demonstrate that the optimal features are well able to differentiate between different bearing states at time-varying speeds. Comparing the results of this article with other fault detection methods indicates the ability of the proposed method.

In most of the bridge health monitoring techniques based on vibration, a large number of sensors are installed on the structure which may be costly and time-consuming. Recently, some methods have been proposed in which the response of a passing vehicle is utilized in order to achieve the modal properties of the bridge. In this paper, transmissibility measurement of the vehicle response is dedicated to detect the bridge damage indirectly. Since the data is transmitted by accelerometers embedded on the axles of the vehicle, the vehicle is passing over the bridge without stopping and accelerometer is recording without interruption. As another advantage of the method is that the white noise assumption in not necessary for the excitation signal unlike the other related methods. Here, the bridge is modeled by finite element and vehicle is assumed to be two 2DOF systems of mass-spring-damper. By solving the vehicle-bridge interaction equations, the vehicle response is obtained in order to estimate the intact mode shape. Afterwards, a damage is considered in the bridge and the change in mode shape curvature are used for damage localization. Numerical investigations reveal that the proposed method can localize the damage by acceptable accuracy in the presence of noise.

Penetration of projectile in the combined targets is one of the most important issues in mechanics. In this article, penetration of projectile evaluation in three parts. The first part is related to models of penetration into metals, the second part is related to models of penetration by the dimensionless and the third part is related to penetration into ceramics. In the first section, in addition to reviewing analytical models of penetration, their categorization and summary are also have been stated. The models include the Poncelet Equation, the Hydrodynamic Theory, Modified Hydrodynamic Theory, Recht-Ipson, Tate-Alekseevskii, Cavity Expansion, Ravid-Bodner, Walker-Anderson, and simulation models. Model assumptions are fully determined and some data has been obtained from model predictions in comparison to empirical data. These assumptions contained rigid body penetration, abrasive penetration, sustained and transitional penetration, and full penetration. The second and third parts are investigated dimensionless models of penetration and penetration into ceramic-metal combined targets, respectively. In this article, basic models of projectile penetration in metal and ceramic targets were categorized. Also, precision analysis of these models was done.

The welded zone of API X70 steel pipe, due to the inherent defects of welding, is a potential area for initiation and propagation of cracks which can eventually lead to damage of the structure. In this research, mechanical behavior of spiral seam weld was evaluated in API X70 pipe steel in three zones (base metal, HAZ and weld metal) using uniaxial tensile and three point bend (3PB) experiments. Three tensile specimens were used in each zone for measurement of mechanical properties. For studying the mechanical behaviour of the pipe, one specimen with 3PB geometry was tested for each zone. Specific values including yield, peak and final load for 3PB specimen were determined from load-displacement plots. The associated energy for each load plus initiation and propagation energies were calculated and the results were analyzed in relation to microstructure in each zone. With an analytical equation based on slip-line field analysis, yield strength was determined with 3PB specimen in each zone and compared with the result of uniaxial tensile experiment. From uniaxial tensile experiment, yield strength levels of 560, 514 and 507 MPa were found for base metal, HAZ and weld metal respectively and from 3PB experiment 604, 582, 575 MPa respectively.

The pipes conveying fluid are capable of displaying complex dynamical behaviors. In this paper, the dynamic behavior of a simply supported fluid-conveying pipe made of functionally graded material in thickness direction, is analysed. The Young Modulus are assumed to be graded along the thickness direction according to a simple power law and equations of motion of the Euler– Bernoulli beam are derived. The partial differential equation is discretized to ordinary differential equations by the Galerkin method. The natural frequencies are obtained for different dimensionless parameters and compared with a homogenious pipe conveying fluid, and the effect of gradually changed material has been studied. Dimensionless critical flow velocities which couse instability are obtained for particular mass parameter and different distribution of Young Modulus. The results show that by increasing Young Modulus from inner to outer surface of pipe, the natural frequencies of system increase and instability is occurred in higher critical velocities.

This paper is devoted to numerical simulation of steady and unsteady natural heat transfer convection of nanofluids in an eccentric porous annulus. Governing equations including mass, momentum, and energy conservation are discretized by means of finite difference methods and they are solved by Alternating Direction Implicit (ADI) method and Successive over Relaxation (SOR) method. In the present study, the effect of Rayleigh number, nanoparticle volume fraction (in the range of 0 to 4 percent), Darcy number, porosity coefficient, and eccentricity ratio on average Nusselt number, local Nusselt number, streamlines, and isothermal lines are investigated. The results show that by increasing Rayleigh number, the porosity coefficient, and the nanoparticle volume fraction, the heat transfer rate increases. Reducing the Darcy number reduces the permeability of the porous medium and therefore reduces the heat transfer. In unsteady conditions, by increasing the amplitude of the inner wall temperature fluctuation, (due to the increase of the temperature gradient between the two walls), the average Nusselt number increases, and the frequency of the variation of the average Nusselt number is consistent with the inner wall temperature variation frequency.

A proportional-derivative sliding-mode control (PD-SMC) scheme is addressed for tracking problem of a two-degree of freedom robot manipulator. The sliding-mode control (SMC) may be a robust method in presence of parameters change and system uncertainties. In a typical control problem, the proportionalderivative (PD) control law provides a fast response while the stability of the closed loop system is increased. Hence a two degree of freedom robot manuplator is considered. Then the asymptotic stability of closed loop system with the PD-SMC policy would be shown by using of the well-known Lyapunov stability theory. As a result of this paper, the asymptotic stability criteria would be checked in term of some simple matrix inequalities. Having satisfaction of such matrix inequalities in the tracking problem of the robot manipulator, the tracking error and its derivative would be converged to zero. In order to compare the results with the other control approaches, the controller parameters are firstlty tuned in an optimization way via the genetic algorithm (GA) method. Then some numerical examples are provided to show the effectiveness and robustness of the PD-SMC in comparing with the existing methods.

In this study, laser forming of steel was investigated in order to create V-Shape bend. The result shows, Increases in laser power within the temperature gradient range, lead to higher bending angle. Scan velocity, beam diameter, and thickness of the sheet metal were known as effective factors on bending angle. Increases in value of mentioned parameters caused lower bending angle. Also, the beam diameter is the most effective parameter in determination of the bending angle to form A-131 steel into V shape product. In addition to main factors, the interaction effect of power-thickness, scan velocity-thickness, beam diameter-thickness, and scan velocity-beam diameter were considered as effective parameters in forming of A-131 by using laser beam. Also, maximum difference between result of FE model and regression equation was 6. 5 %. This indicates the appropriate accuracy of the proposed model. Also in this study, a new method was developed based on the entropy generation for prediction of the increasing and decreasing trend of bending angle. According to the result, entropy generation method is capable to predict the effect of laser power, beam diameter, and scan velocity.

In this paper, free vibration of the joined sandwich conical-conical shell is investigated by using differential quadrature method (DQM). It is assumed that the conical shell is truncated. The core of sandwich conical-conical shell is made from the four different types of materials such as Polyether ether ketone (PEEK), Polycarbonate (PC), Solid polypropylene (SPP) and high density polyimide foam (HDPF), and Aluminum is supposed for material of inner and outer skin layers. The first-order shear deformation shell theory (FSDT) is adopted to formulate the theoretical model and governing equations of motion are derivated by Hamilton’ s principle. The governing equations of motion, the boundary conditions of the two ends of the shell and the continuity conditions at the interface section of shell segments, are discretized by means of the DQM. Then, eigenvalue problem, and, consequently natural frequencies are achieved. The effects of thickness, length of the shell, cone angle, material of the core and boundary conditions on natural frequencies are investigated. To verify the accuracy of this method, comparisons of the present results with results available in the open literature and Abaqus software are performed.

One of the simplest and most commonly used control methods for using in automatic voltage regulators (AVR) is the PID controller. On the other hand, Fractional calculus has recently been proposed as a powerful tool in the modeling and control of dynamic systems in control engineering, whose abilities and applications of this theory are being studied in academic research. In the control of dynamic systems, fractional-order controllers can improve the performance and control capabilities of the system. In this paper, a multiobjective approach to designing an optimal fractional PID controller for regulating the output voltage of the synchronous generator is investigated using cuckoo optimization algorithm. The proposed cost function includes rise time, settling time, steady state error and overshoot. The comparative results obtained show that the fractional PID controller has a higher robustness to parametric uncertainties and disturbance than the classic PID controller.

In this paper, the effects of supersonic flutter and moving load are studied simultaneously on a honeycomb sandwich beam with a cermet covered layer. The core layer ratio is considered as a regular nomex honeycomb which has the high stiffness to weight ratio. Also cermet layer which has a high thermal strength is considered as aluminum oxide in mild steel matrix, for optimized fractional ceramic concentration. The structural formulation is based on the classical Euler-Bernoulli beam theory and the quasi-steady first order supersonic piston theory is employed to describe the aerodynamic loading. Hamilton’ s principle in conjunction with the generalized Fourier expansions and Galerkin method are used to develop the dynamical model of the structural systems in the statespace domain. The critical dynamic pressures are obtained by p method for a honeycomb sandwich beam. Simulation results shows that using cermet layer as a constrained layer has an important role in postponding the flutter to higher dynamic pressures compared to the same sandwich layer with aluminum constrained layer. The thickness effect of cermet layer on flutter phenomena is also considered. Finally, in order to obtain efficeient operational results, the aeroelastic responses of honeycomb sandwich beam in supersonic regime under moving loads with different velocities are calculated.

In this article, a new method has been proposed to enhance two-dimensional differential transform method (2D-DTM) for solving initial boundary value problems (IBVPs) including partial differential equations (PDEs) with homogeneous Dirichlet boundary conditions. The method is inspired by the Ritz method which is utilized in variational calculus. To this end, multiplying the basic relation of DTM by specific functions which satisfy the boundary conditions, would resolve the weakness of the classical version of 2D-DTM in precisely satisfying the boundary conditions. Obviously, implementing this will change the governing relations of the classical DTM, such as recursive formula related to differential equation of the problem. It should be mentioned that, these changes are comprehensively described in the article. Moreover, to show the robustness of the proposed method, two heat transfer problems in the bars are thoroughly solved by classical and enhanced DTM and the results are compared with the exact solutions. The thermal diffusivity of the bar is considered constant and spatially varied in mentioned problems. The numerical results show the accuracy of the proposed method, especially in satisfying the homogeneous Dirichlet boundary conditions of the problem.

In this paper, Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) method was used to numerically simulate the three dimensional dam-break with obstacle in front of the flow. Euler equations as governing equations of inviscid fluid flow were used. Large and unphysical oscillations in pressure and velocity field are one of the most important problems in this method. In present study these oscillations were controlled by using density filter and conservative Riemann solvers, and results of these two methods were compared with experimental data. Furthermore due to common using of artificial viscosity in WCSPH method, the simulation was implemented using artificial viscosity in momentum equations without density filtering and compared with last two methods. This comparison showed that the conservative Riemann solvers could well control the oscillations in pressure and velocity field and gives correct pressure results in WCSPH method. Finally two boundary conditions called dynamic and Repulsive forces were investigated in this paper.

In Iran, Sabalan geothermal power plant has been utilized with two wells having different and mass flow rates and thermal properties. In this study, in order to achieve the maximum power, four new configures; a single flash-binary, a double flash (I)– binary, a double flash (II)– binary and a triple flash-binary cycles were examined. These four configurations were initially investigated considering the effective parameters of energy and exergy analysis, and then optimization was performed using three working fluids. The results show that in the optimum state, the double flash (II)– binary using isobutane shows better results compared to the other three configurations. Furthermore, for the optimum case, the net power of 23084 kW, the thermal efficiency of 19. 74%, the exergy efficiency of 75. 7%, and the exergy destruction rate of 6250 kW were obtained which show an improvement in terms of energy and exergy for the Sabalan geothermal power plant compared to the previous studies.

Nowadays, premixed flames are broadly utilized in various residential/industrial applications. Therefore, simultaneously increasing the quality of combustion and reducing the pollution of these flames is of great importance. In this study, collisions of two flame jets of H2/CH4 have been simulated; and flame structure, temperature, and NOx emission are reported at different conditions. The main purpose of this work was to study the effect of angle between the burners and the effect of air and fuel preheating on the key design factors of impinging jets. It was observed that by increasing the angle between two burners, mixing and recirculating flow is enlarged, and the maximum flame temperature and NOx production is increased accordingly. By increasing the angle from 0 to 180 degrees, the maximum flame temperature of methane and hydrogen increases by 11. 5 and 12. 4%, respectively. Preheating showed that with 400 K increase in the fuel and inlet air temperature, the maximum flame temperature for methane and hydrogen increases 6% and 4%, respectively, which eventually results in a higher NOx.