Modares Mechanical Engineering
Year:2016 | Volume:16 | Issue:5|Papers Count:48

Residual stress measurement of in-service parts of a system is practically impossible by means of destructive methods. Therefore, the use of ultrasonic method as a non-destructive method has an important role. One of the problems in non-destructive measurement of residual stresses by means of ultrasonic waves is determination of acoustoelastic constants. In fact, for conversion of ultrasonic method data to stress state, it is necessary that these coefficients be determined very precisely. But for reasons like HAZ inclination and small width of this zone, determination of coefficient of this zone does not perform accurately. In this study, the practical simulation is performed for determination of acoustoelastic coefficient of HAZ. For this simulation, the heat affected zone is divided to four separate zones and then the microstructure of those four zones has been simulated on standard tensile test specimen by different heat treatment cycles. This coefficient has been used in evaluation of welding residual stresses of austenitic stainless steel by LCR Ultrasonic waves and the results compared with the hole-drilling strain-gage method. By comparison of stress values achieved by HAZ simulation method, the conventional method and hole-drilling strain-gage method, it is seen that the HAZ simulation method causes an improvement in welding residual stress measurement accuracy.

In this study, feedback-feed forward control system design and optimizing the performance of crude oil furnace process was investigated in order to recover from possible abnormal conditions. First, by developing an accurate nonlinear analytical model, the effects of changes in input parameters and operating conditions on the system’s outputs were determined. Then, in order to eliminate the effects of disturbances on furnace, a feedback- feed forward control system for combustion management was suggested, where its performances were optimized using genetic algorithm (GA). In addition, to enhance the thermal stability and maintain product quality, output difference temperature control system was considered for load distribution between furnace’s streams. Also, in order to recover the furnace from abnormal conditions due to burners’ failures, a supervisory system was designed to change the firing rate set points. With respect to different failure scenarios, the optimal burners’ firing rate was captured by applying genetic algorithms to the system model. A multilayer perceptron neural network was employed as the core of the controller to interpolate between different conditions. The obtained results indicate the superior performances of the designed control systems.

In this paper, free axial vibration of nanorods is investigated by focusing on the inertia of the lateral motions effects. To this end, Rayleigh and nonlocal theories considering the inertia of the lateral motions and the small scale effects, respectively, are used. Then, by implementing the Hamilton’s principle nonlocal governing equation of motion and boundary conditions are derived. Since using nonlocal elasticity causes the 2-order local governing equation to be changed to the 4th-order nonlocal governing equation while number of boundary conditions remains constant (one boundary condition at each end of nanorod), the governing equation is solved using Rayleigh-Ritz method. In Rayleigh-Ritz method a suitable shape function for the problem should be selected. The shape function must at least satisfy the geometrical boundary conditions. In the present study, orthogonal polynomials are selected as shape functions then they are normalized by using the Gram-Schmidt process for more rapid convergence.After that, the first five axial natural frequencies of nanorod with clamped-clamped and clamped-free end conditions are obtained. In the next step, effects of various parameters like length of nanorod, diameter of nanorod and nonlocal parameter value on natural frequencies are investigated. Results of the present study can be useful in more accurate design of nano-electro-mechanical systems in which nanotubes are used.

Topology optimization of structure seeks to achieve the best material distribution in the Pre-determined design domain. In this paper, the effect of design parameters including length scale parameter and evolutionary volume ratio in improved bi-directional evolutionary structural optimization method with soft kill approach is discussed. The main aim of this method is searching for the stiffest structure with a given volume of material using finite element method. At each iteration of finite element analysis, sensitivity number is calculated for each individual element in design domain and then converted to the nodal sensitivity number. With Filter Scheme and using length scale, an improved sensitivity number is defined. This number is used as a criterion for rating each element in design domain and determining the addition and elimination (remove) of elements. To increase the convergence of the optimization process, the accuracy of the new elemental sensitivity numbers is improved by considering the sensitivity history. This method is convergent and mesh-independent and there are no checkerboard patterns and local solutions in optimal topologies. Using three design samples, a cantilever and classical beam and Michell type structure, affecting factors will be discussed on the final design of the structure. Change of length scale parameter produces various schemes in final structures in which, with increasing this parameter, more iteration is needed for convergent solution. Reducing evolutionary volume ratio forms different and even asymmetric topologies. Better optimized topologies are obtained with higher evolutionary volume ratios.

Today, composite material and sandwich plate structures are used more and more due to the unique properties such as a high ratio of strength to weight, corrosion resistance and energy or sound absorption ability. Corrugating sandwich structures is an effective method to reinforce mechanical properties of the composite materials. In this paper, dynamic analysis of these corrugated structures was carried out for a desired performance in the vibratory condition. One of the most important types of damage in the composite material layers is an inter-layer crack and also the separation between two layers. Vibration analysis of the trapezoidal corrugated sandwich plate was accomplished with ANSYS software using the finite element method. Simulated sandwich plate is a new model of corrugated sandwich plate which has a soft corrugated foam core and a cover of composite layers made from epoxy/glass. In order to validate the vibration behavior of the simulated sandwich plate, the results of experimental modal analysis were compared to the finite element method. The geometry and location effects of inter-layer crack on natural frequencies of the plate were investigated. It was found that with increasing crack dimensions the natural frequencies of the plate decreases and also depth of crack causes a decrease in the natural frequencies, which are promising results compared to the other references. The changes in vibration characteristics of the sandwich plate can produce comprehensive data to be used in training and design of the artificial neural network for a promising approach in fault detection and prediction field.

In this paper, numeral and experimental analysis of composite metal vessel is investigated under variable pressure loading. For this purpose, a sample of multi section cylindrical vessel is considered. The pizo electric 1000 bars sensors are used to measure pressure. The sensors are installed in the holes on the metal cylindrical vessel. The amplification parts are used to adjust sensors. The test is done under dynamic loading. The results are recorded by data logers in pressure-time chart. The aim of this study is to optimize the weight and strength of the vessel with using trial and error by numeral analysis inverse explosive loading. For this, a sample of multi section cylindrical vessel is analyzed with abaqus finite element software. The load in the vessel is derived by charts from experimental tests. The load obtained from experimental tests as a dynamic load is analyzed and compared with metal vessel and metal composite vessel. The results obtained from abaqus finite element software discuss a different case. Finally, geometric and material properties of liner and composite are suggested for optimization of the weight and strength of the vessel.

Investigation of frequency variations of acoustic impedance can play an important role in identification and optimization of a musical instrument. For a simple tube, the input acoustic impedance can be calculated by analytical methods; for complex geometry objects like wind instrument, however, it cannot be simply computed. Therefore, the impedance is measured for wind instruments. This paper is a report of the first experiment for measuring the input acoustic impedance of Ney (an Iranian woodwind instrument). For this purpose, a pulse reflect meter device was made. To ensure correct operation of the reflect meter, in the first step, the input acoustic impedance of a three sections step tube was measured and the results were compared with calculated results using a well-known formula. The acoustic impedances of a Do-ney for various fingering in six case (from all holes closed to all holes opened) were measured. The results show that, contrary to what was seen for flute, the frequencies of minima of the impedance curves have some discrepancies with the frequencies of corresponding playable notes. This may be related to the role of the mouth of the instrument player in producing tones of ney.

The correct placement of supply air inlets and pollution extraction outlets plays an important role in increasing indoor air quality and reducing the amount of pollution in enclosed car parks. In this paper the effect of exhaust locations, exhaust height and parking dimensions on indoor air quality of car park is investigated with numerical simulation. For this purpose conservation equations are solved with open Foam. For validation, air flow and pollution are simulated in a simple car park and compared with experimental results. In the next section, the effect of exhaust vent locations on increasing indoor air quality is investigated and compared with other solutions. The result of numerical simulation indicates that, if inlets and exhausts are located in end sides of car park and if exhaust vent locations are in the optimized height, the indoor air quality in the car park is increased. In this paper, the graph of CO concentration in different heights is explained and by using it, the optimum range for exhaust vent locations is proposed. Moreover, the standard criteria for using jet fans is expressed and the results showed that, for ventilation of car parks with length more than criterion, jet fans should be used.

Carbon nanotubes have excellent mechanical, electrical, thermal and magnetic properties, among the extraordinary properties of these materials that can be traced to the absorption of electromagnetic waves. By placing these materials in the direction of electromagnetic waves, significant volumes of these waves have been absorbed and the radar cross section from a finder view has also been reduced. In this study composite samples containing SWCNTs in the context of an epoxy resin based on standard dimensions for X-band with a multi-stage built method were produced and then the samples were analyzed by Vector Network Analyzer. Composite samples have been made in three weight percentages, 1, 3 and 10. The result of this experiment shows the high amount of wave absorption for samples reinforced by carbon nanotubes. This amount of absorption greatly increases due to increase of nanotubes weight percent, so that the average amount of absorption in the whole X-band for the mentioned percentages is 3.33712, 4.5889 and 12.6542 dB respectively. Also, the amplified samples with 1, 3 and 10 weight percentages show increase in wave absorption about 22, 67 and 362 percent in comparison with pure resin. Finally, samples were evaluated with Micro Raman Spectroscopy and SEM images.

Consideration of dynamic and static behavior of structures in nano and micro scale for analysis and prediction of their performance and accuracy has become more important. In this study, the effect of size and intermolecular van der Waals force on dynamic behavior of torsional nanomirror considering bending-torsion two degree of freedom model using the higher order modified couple stress theory has been investigated. First, by considering the higher order modified couple stress theory and intermolecular van der Waals force, equation of motion of system is developed, afterwards using Runge-Kutta method, this equations is solved and dynamic performance of nanomirror and its phase portraits have been obtained. Also, translational and torsional natural frequencies of system considering applied voltage are investigated. So pull-in instability parameters of system are considered and their dependency upon van der Waals force and size effects are determined. Results demonstrate that equilibrium points of system include center points and focus points and phase portraits related to these points exhibit periodic orbits and heteroclinic orbits. Moreover, size effect and modified couple stress model on amplitude and frequency of vibration of system have been investigated. Proposed model in this study is able to predict experimental results with higher precision than previous classic models and reduce the difference between past theories and empirical results.

The purpose of this article is implementation of upper stage design according to multistep sequential optimization design process for specific maneuvers with less mass in reality. In this method there are two optimization and design loops which are connected to each other in mass analysis. So all the output parameters in inner loop are used as input parameters of outer loop. In the inner loop, optimization control algorithm is used to optimize the target function, as for two control factors including thrust vector angle and thrust magnitude for putting upper stage into final orbit. In outer loop, subdivision is designed separately according to design matrix using input parameters from the inner loop. Design convergence is checked in mass analysis. Innovation of this article is the implementation of a fully systematic upper stages design. Also, a system-based method is provided by cooperation of human and machine (multistep collaborative design) which, in addition to system design, discussed subsystem design such as orbital optimization and subdivision algorithms. Results of this design are verified according to the result of statistical analysis.

Noncircular lobed journal bearing performance, in comparison with circular types, depends on various design parameters such as tilt and mount angles. Mounting orientation of this kind of bearings with respect to machine frame (mount angle) and also the way of setting their lobes with respect to each other (tilt angle), can change the bearings configuration and, as a result, their performance. In present study the thermo-hydrodynamic performance of noncircular two, three and four lobed journal bearings for different values of tilt and mount angles, using generalized differential quadrature (GDQ) method, are investigated. The results show that the thermal effects on these bearings performance are considerable and that the thermal consideration makes the results closer to real performance situations. The results of bearings performances due to rise in temperature in rotor, lubricant fluid and bearing shell, when compared to their isothermal conditions, show that viscosity of lubricant as well as load carrying capacity of bearings are decreased, depending on tilt and mount angles, especially in case of two lobed bearings. The results also show that the effects of tilt and mount angles on bearing performance are periodic and so it is possible to select these angles suitably for bearings to be optimum.

Nowadays thin-walled tube rotary draw bending in small bending ratio is a production process widely used in advanced industries such as aerospace and automotive. Cross section ovality, wall thickness changing during tube bending are the main inevitable defects in this process. The purpose of this research is to obtain the smallest bending ratio and maximum pressure applicable in hydro-rotary draw bending of thin-walled aluminum alloy 8112 tube using failure criterion. For this purpose, the equivalent plastic strain at the critical extrados region is used for necking prediction. Concluded results showed that this failure criterion by a maximum difference of 12.5% from experimental tests, is a useful method for predicting the necking onset in the bending process. Moreover, the effects of bending ratio and internal pressure on the defects such as cross section ovality and changes in thickness are investigated with simulation in the ABAQUS software and experimental methods. The maximum ovality is not located at the mid-cross section of bent tube unexpectedly and regardless of the internal pressure and bending ratio, occurs at the cross-section with an angle of approximately q=33o. The minimum achievable amounts of ovality at R/D1.6, R/D1.8 and R/D2 were 11.42%, 7.72% and 4.35% respectively. Furthermore, bending ratio and internal pressure had noticeable effects on the cross section of the bent tubes, so that as the bending ratio or pressure increased, cross-section ovality and the thickening of the tube wall at the intrados decreased, but contrary to bending ratio, as the internal pressure increased, extrados thinning increased.

The most successful ‘‘top–down’’ approach to produce bulk ultra-fine grained or nanostructured materials involves the use of severe plastic deformation (SPD) processing. The amount of higher effective plastic strain per pass plays a key role on the final microstructure of SPD processed samples. In the present study the numerical experiments of the combination of the equal channel angular pressing (ECAP) and simple shear extrusion (SSE) as a new process entitled “planar twist channel angular extrusion (PTCAE)” was performed based on the Response Surface Methodology (RSM), as a statistical design of experiment approach, in order to investigate the effect of parameters on the response variations, achieving the mathematical equations, predicting the results to impose higher effective plastic strain values. A and F angles, radius and friction coefficient was imposed as the input parameters while average, minimum and maximum effective strain and maximum load was imposed as the output parameters. Governing regression equations obtained after analysis of the simulation data by Minitab software. Optimum process parameters are: a=400, F =450, r=2 mm and m=0.1. Verification of the optimum results using simulation experiment was done. Good agreement between simulation, experimental and optimization was occurred.

The unidirectional composite DCB specimen is considered as two finite length Timoshenko beams, attached together along a common edge except at the initial delamination length. Because of symmetry, only one half of the specimen is considered, which is partly free and partly resting on an elastic foundation. The problem is analytically solved by considering Timoshenko beam resting on Winkler and Pasternak elastic foundations and fracture toughness is generally derived. In the prior researches on this specimen using Timoshenko beam theory, the effect of the ligament length on the energy release rate was ignored. This research presents the solution for finite ligament length. Besides, the effect of ligament length on energy release rate and its minimum value that makes the energy release rate independent of the ligament length, is presented. For the special case when the ligament is large compared with the beam thickness, a closed form solution is derived for Timoshenko beam resting on Winkler elastic foundation. The analytical results are compared to prior researches on this subject and good agreement is observed. The fracture toughness and compliance obtained by Timoshenko beam resting on Winkler elastic foundation predicts more accurate results with respect to experimental results.

Cavity length estimation is important as supercavity condition is generated. The natural cavity length is function of cavity number and is calculated by relations deduced from experimental results which are different from each other and are not driven from analytical approaches. Literature survey shows that correlations based on cavity length in relation with Reynolds and cavity numbers have not been attempted. The purpose of the present work is to estimate analytical based relations for cavity length with respect to mass transfer, continuity and momentum conservation equations. This attempt, which was conducted by order of magnitude method resulted in three relations. The first analytical based relation calculates cavity length versus cavity number. The obtained relation shows that cavity length is proportional to the inverse square root of cavity number. The second analytical relation calculates cavity length with respect to Reynolds number. It shows cavity length has a proportional relation to Reynolds square root. The third analytical relation considers cavity number with respect to Reynolds number. The third relation shows that cavity number has inverse relation to Reynolds number. Unknown coefficients values of the relations are obtained through comparison with the already existed experimental results. These analytical relations which are an appropriate alternative to experimental based relations estimate cavity length with respect to cavity and Reynolds number.

In this paper, a practical method of combined finite element simulation and adaptive simulated annealing optimization was developed to design and analyze sheet hydroforming process. Process simulation using finite element code with parametric definition of process parameters creates flexibility on the proposed method in which geometrical dimensions and properties of the workpiece and the die comprise a part of input data of optimization program. This makes it possible to investigate any cupshaped products through the proposed method. Redefining of simulated annealing parameters with respect to hydroforming process enabled data convergence to be achieved in a shorter time and with higher precision. An intermediate MATLAB code was developed and used to manage data transfer automatically between optimization and simulation codes, in which there would be no need for any interaction of user/designer during the optimization process execution. The research aim of presenting the combinatorial procedure of flexible process simulation together with adaptive simulated annealing technique is to achieve optimal forming pressure loading path, to determine desired punch velocity, to produce desired work piece with minimum thinning and to avoid wrinkling and rupturing defects. In this research, two different loading paths proportionate to the ram’s stroke of press unit (constant/variable velocity) are proposed to synchronize optimal pressure path and desired punch velocity in forming cup shaped products. Using the optimization approaches of constant and variable velocity, thinning values of 12.9778 and 12.3295 for a steel part with conical shape were obtained respectively by implementing simulation iteration of 202 and 148, which demonstrates improved product quality and decrease of simulation iteration in variable velocity. Appropriate conformity between numerical data and experimental results verified reliability and accuracy of the proposed optimization procedure.

Numerical simulation of boiling has always been a challenging problem in terms of the variety and effectiveness of two-phase models. Moreover, choosing an appropriate heat and mass transfer model increases the complexity of the solution. Problem of film boiling of saturated liquid is numerically simulated in this investigation by use of VOF (volume of fluid) model together with the georeconstruction of interface. Three phase change models of sharp interface model, Lee model and Tanasawa model are used at the same time on a single problem in order to calculate the rate of phase change and source terms. One-dimensional Stephan benchmark is solved for verification the numerical solver. The periodic Nusselt, flow pattern, bubble form and its detachment time have been studied in mentioned various phase change models. Also, empirical coefficients used in both models of Lee and Tanasawa are presented. The results of Nusselt number obtained from simulation is compared with two empirical Nusselt correlations of Berenson and Klimenko. The results show good agreement with the Klimenko’s Nusselt. The results reveal although the Lee model is dependent on empirical coefficient, it is more accurate than the two other models for prediction of film boiling on flat plate.

These days overhead crane is widely used in different industries such as automobile, harbor, navigation and also transportation of tools in storerooms. Most models which are done through industrial dynamic systems include some vitiated parameters with noise and disturbance and overhead crane model is no exception. Disturbance in system can be due to its model or measuring tool. Kalman filter is a practical method in order to recognize the model and also filtration of disordered data. Given that overhead crane is a nonlinear model, asymmetric sigma-point Kalman filter improved by genetic algorithm (GA-ASKF) is intended to estimate system parameters. One of the common ways to controlling overhead crane parameters is using controlling force, Bang-Bang. By the way, function of Bang-Bang controller depends on controlling force switched times. In this paper, besides using this controller, its switched times are found by using genetic algorithm for noisy system. The design aim is to achieve the target point in minimum time with minimum error. Also, by considering Bang-Bang controller entrance part, the article compares the situation of the system in different mass relativeness. Simulation results shows improved performance of the GA-ASKF algorithm to determine the switching time of controller and also achieve the target point in minimum time.

In this paper the flutter phenomenon in turbomachinary is introduced. The importance and characteristics of the flutter as a dynamic aeroelastic instability is presented. Conventional methods for the blade flutter test and different approaches in flutter analysis of blade are described. Among the existing analysis methods, one approach which only examines the stabilizing effect of fluid is used in order to analyze the flutter in this paper. Firstly, its equations are described and a criterion for the determination of the stability based on the analysis results is presented. According to the criterion the local and global stability can be concluded. Numerical analysis has been performed by ANSYS CFX. Mesh independence and two different turbulence models have been examined and results have been validated by test results. Numerical analysis has been carried out for two steady and unsteady states. In unsteady state the response of fluid to blade vibration in three modes has been calculated. In order to assess the total response two methods have been used and the results have been compared. Eventually local instability is calculated and the results presented in the figures, which illustrates the contribution of adjacent blades in instability of specific blade. The evaluation of global instability for three modes has been presented and the obtained results are in excellent agreement with the experiment.

This paper presents a new analytical model to study the thermal behavior of borehole heat exchangers (BHE) in short time periods. Transient heat transfer is considered inside the borehole and at the ground around the borehole, transient heat conduction is considered inside the borehole and ground around the borehole. For this purpose, the analytical solution has been developed in two stages. First, new analytical equation is provided for the short-time thermal response of the BHE (dimensionless G-function). In the second phase, the outlet temperature calculation using the G-function is described. Inside the borehole, the analogy between thermal and electrical conduction is used for deriving heat balance equations. For this purpose, new equivalent thermal network for modeling of the heat transfer inside the borehole is developed. In ground around the borehole, the conduction equation in the radial direction is considered. The governing equations are solved by Laplace transform. Finally, the mean fluid temperature and short thermal response of the BHE is computed. Then in the second phase, the outlet temperature in the on and off times of the system is calculated using the G-function. The solution of the proposed analytical model is compared with experimental measurements. Results show that the outlet temperature of the analytical model matches very well with the reference experimental measurements.

Incremental sheet forming has already provided distinct advantages such as inexpensive tools and the simplicity of the process over conventional sheet forming processes. However, the method still has some limitations. Among these limitations, severe thinning has significant effects on the performance of the final product. Also, some parts with high wall angles cannot be formed by single stage incremental forming. To overcome these restrictions, multistage incremental forming can be implemented to achieve the desired wall angle, better thickness distribution, and lower thinning. In this study, a two-stage incremental forming of an aluminum truncated pyramid with a wall angle of 70o was studied experimentally and numerically in order to improve the achievable minimum thickness. By introducing two-stage forming strategies and achieving their defining parameters using finite element simulation, the sheet thinning was compared to the one in the single-stage forming. Experiments were used to validate the finite element analysis. The results revealed that using the two-stage forming strategy, the minimum thickness can be improved twice than the one in the single-stage forming. A good agreement was observed between the thickness distribution obtained by experiments and predicted by the finite element modeling. Finally, the effect of forming strategies on the strain paths was investigated through the finite element simulation and the experimental fracture forming limit diagram.

Since the majority of fluids in engineering and biologic applications are non-Newtonian, the study on mixing of non-Newtonian fluids is very important. Secondary flows are used in curved micromixers to improve the mixing of fluids. In this study, a numerical study was performed on the mixing of non-Newtonian fluids in curved micromixers using Open source CFD code of Open FOAM. The flow was assumed three-dimensional, steady and incompressible and Reynolds numbers were between 0.1-300. Also, water and CMC solution were used for simulation of Newtonian and non-Newtonian fluid flows, respectively. The effect of Reynolds number, power-law viscosity parameters and micromixer geometry on mixing index and non-dimensional pressure drop was studied and results were compared with those of the straight channel micromixer. The results showed that the mixing index decreased by decreasing the power law index. The mixing index was high for shear thinning flows in micromixers with sharp turns. Also, by increasing the Reynolds number, and therefore velocity, centrifugal force effects increased and mixing improved. Simultaneous investigation of mixing index and pressure drop showed that, for low Reynolds numbers and small power law indexes micromixer-b had better performance.

This paper focuses on the problem of finding object orientation around Yaw & Pitch & Roll angels. The object orientation is computed in a real time manner using a mono-camera and three points on a solid object in a machine vision software. Three points should be selected from environment at the beginning. In order to reduce wreckful effects of environmental lights on detecting colorful objects and also to reduce the number of used software filters, IR LEDs with 850nm invisible wavelength are used. Artificial Neural Network (ANN) is used for solving this problem since orientation's equations are nonlinear and real-time solving for them is impossible. For solving the problem a feed forward artificial neural network with one hidden layer and 21 nodes in that is used, which has 3 nodes for output layer and 6 nodes for input layer. For having high accuracy in ANN, output data is also obtained from a MPU-9150 installed on a 2-DOF orientional parallel robot and compared to ANN outputs. 7243 data from Roll and Yaw angles and 751 data from Pitch angle is obtained from MPU-9150 sensor and the later 2-DOF orientional parallel robot and 467 data remains unused for learning ANN. After learning the neural network, results compared to unused data for ANN learning and desire results obtained with 0.038 maximum error.

Grasping in unstructured environments is one of the most challenging issues currently facing robotics. The inherent uncertainty about the properties of the target object and its surroundings compels the use of robot hands, which typically involve complex hands, require elaborate sensor suites, and are difficult to control. For this purpose, in this paper combining the kinematic structure of a three and two links finger for design and fabrication of robotic gripper will be evaluated. First, the challenges associated with grasping by careful mechanical design of gripper are analyzed. Then, the design and fabrication of a sample gripper by combining a three-links finger similar to the human index finger and a two-links finger similar to the thumb are described. In the following, the performance of this hand for grasping various objects will be examined. The results show that with two fingers and simple design, without the need for the complex control, c various objects can be grasped successfully. Also, the results demonstrate that compared with the previous researches and by proximity to the kinematic structure of the human hand fingers, by combining two with three link fingers this gripper will have a better performance than the previous symmetric gripper for successfully grasping large objects.

In this article, the Charged System Search (CSS) algorithm is utilized for structural shape optimization that aims to minimize weight of a plane structure under stress constraints. Also, the Isogeometric Analysis (IA) is employed in order to analyze the structure. In the IA method, Non Uniform Rational BSpline (NURBS) basis functions are used for approximation and interpolation of the displacement field as well as modeling geometry of the structure. Coordinates of the NURBS control points, that construct the geometry, can be considered as the design variables of the shape optimization problem. In earlier studies in structural shape optimization using the Finite Element (FE) method, boundaries of the structure were made by NURBS and the finite element discretization changed when the boundaries were modified in every iteration of the optimization process. As it mentioned, when the IA method is used the geometry is constructed by NURBS, therefore, contrary to using the FE method, the need for remeshing of the domain is eliminated and the computational cost will be remarkably decreased. In this paper, the IA method is briefly reviewed for analysis of the plane-stress elasticity problems. Also, the CSS formulation is derived based on physics laws for shape optimization problems. A few examples are presented to demonstrate the performance of the method and the results are compared when the Sequential Quadratic Programming (SQP) is used as a mathematical based method for structural shape optimization.

In this paper, the constrained groove pressing (CGP) process of Al 5052 sheets are experimentally and numerically studied. The CGP process produces the micro-grained-size sheets to enriched strength nano-grained-size ones. The goal of this investigation is the development of an algorithm for the mechanical behavior (Strength and Hardness) prediction of the sheets fabricated by the process. The algorithm enables one to evaluate the die geometry and pressing pass definition effects on mechanical behavior of the fabricated sheet. The proposed algorithm is based on the available relation in literature between the macroscopic behavior and the grain size in metal sheets and between the hardness and the strength properties of metal sheets. The Al 5052 samples are fabricated by two passes of the CGP process. The yield strength and the Vickers hardness of the annealed, the one and two pass CGPed samples are experimentally obtained. The predicted results by the developed algorithm are in good agreement with the experimental data. The comparison of the predicted results by the algorithm with available experimental data for the mechanical behavior of the CGPed pure aluminum sheets with different dies reveals the good accuracy of the proposed algorithm. The algorithm enables one to economically save from the time-consuming experimental evaluation of groove geometry effects on the fabricated sheets and optimum die selection. The effects of the die groove angle on the yield strength and the hardness of the CGPed Al 5052 sheets are estimated using the developed algorithm.

In this paper, the strain energy release rate of first mode of failure in the adhesive bonding of two composite plates composed of unidirectional glass fiber is calculated using double cantilever beam specimen. Araldite 2011 adhesive connection which is widely used in the aerospace industry has been employed. Strain energy release rate is calculated by the modified beam method, compliance calibration method and modified compliance calibration method from experimental results. For modeling crack growth in adhesive bonding of two composite plates, the Extended Finite Element Method has been employed. Average value of critical strain energy release rate calculated by the modified compliance calibration method is considered as software input. After comparing force - displacement curve obtained from experimental data and numerical solution that represents good precision of the Extended Finite Element Method in calculating the maximum force and corresponding displacement and also linear part of force-displacement curve, strain energy release rate - force curve, stress intensity factor- force curve, strain energy release rate- displacement of the load effective point and failure stress - stress intensity factor curve are evaluated.

In this paper, the static stiffness and strength as well as fatigue life of adhesively bonded single lap joint (SLJ) are numerically studied using the cohesive zone model (CZM). In order to simulate the SLJ using mixed-mode bi-linear CZM, the failure behavior of adhesive in modes II and III is considered the same. Fatigue damage propagation is simulated through scripting USDFLD Subroutine in ABAQUS/Standard. Static stiffness and strength and fatigue life obtained in this study are consistent with experimental results available in literature. Then, the effect of geometric parameters including overlap length, substrate thickness, and tapered substrates are investigated. The obtained results reveal that the increase of the overlap length would lead to increase in the static strength and fatigue life prediction. While increasing substrate thickness results improved fatigue life, there are no a known relations between the static strength and substrate thickness due to the changes of the loading modes. Tapered substrates also have positive effect on the strength and fatigue life because of more compatible rotations. Therefore, to improve the strength and fatigue life of a SLJ, authors suggest greater overlap length and thickness along with tapered substrates.

Knowledge of broadband transducers is a new technology in the field of sonar science. Considering that Iran has sea water resources, its importance becomes more and more. In this article, after studying the performance of the kinds of transducers in the field of sonar transducers, a proper broadband transducer with the specific impedance and acoustical characteristics that can send and receive signals, is designed, simulated, fabricated and tested. At first, overall dimension of a broadband transducer with lumped parameter model and electrical equivalent circuit model was approximated and then, with increasing the degrees of freedom of analytical models, all characteristics of the optimum transducer parts were obtained in order to have a large bandwidth. By using finite element software (COMSOL Multiphysics), the designed model was simulated and the obtained results have been compared with analytical design solution. Finally, the transducer was fabricated and tested in order to validate the modeled and simulated data by comparing them with practical ones. The obtained experimental results showed that the simulation with COMSOL Multiphysics can predict the resonance frequency and maximum transmitting voltage response (TVR) of the broad bandwidth transducer with reasonable precision. The prediction error of resonance frequency and maximum TVR by COMSOL is 3.8% and 5.7%, respectively. The use of lumped parameter and electrical equivalent circuit models gives an initial approximation for transducer dimensions, but in determination of the resonance frequency and the frequency of maximum TVR has a higher error in comparison with the finite element method.

The main scope of this paper is the analysis of the specifications of deflagration-induced and detonation-induced deformation and fracture behaviors of cylindrical tubes. The main characteristics of deformation and fracture behaviors were studied through experimentations on steel pipes and failure analysis of a compressed natural gas (CNG) cylinder. The paper also reports the results of transient dynamic elasto-plastic finite element (FE) analyses of the combustion-induced deformation and fracture behaviors of the pipe and the CNG cylinder. The FE models were composed of 3D brick elements equipped with interface cohesive elements for crack growth analysis. Very good agreement was found between the simulation results and the observed deformation and fracture patterns. It was shown that, because of different loading conditions, specific deformation and fracture features can develop during the explosion process.

The aerodynamic coefficients characteristics over a lambda-shaped flying wing aircraft with 55o-30o leading edge sweep angles have been investigated in a closed circuit low speed wind tunnel. The experiments were conducted at tunnel velocity of 90 m/s, the angles of attack of -6 to 17 and the sideslip angles of -8 to 8 degrees. All forces and moments were measured using an external six-component force balance located below the wind tunnel. The wall corrections were also performed for all test conditions. To improve the aircraft longitudinal stability characteristics, a new model with an increased leading edge sweep angle of 2 degrees was also tested and compared with the original model. A “pitchup” phenomenon determined to occur at a rather low angle of attack of a=7.7 degrees, although it occurred at the higher angle of attack of a=8.7 degrees for the increased sweep angle model which means an increase in useable lift of the aircraft. Moreover, off-surface pressure measurement over the wing surface was conducted to examine the onset and development of the flow separation over the wing surface. The results showed that the flow separation started at the trailing edge crank location and extended to the other parts of the wing, especially the outer wing.

Mine ventilation is one of the important functions in mining. The purpose of mine ventilation is to provide enough oxygen to breath, create comfortable working conditions and dilute and remove the gases and dust from mine. Methane gas is released from minerals while extracting in coal mines. To prevent the accumulation of this gas and intense explosions, the use of auxiliary ventilation besides the main ventilation is essential. In auxiliary ventilation in room and pillar coal mining, generally two methods of stopping and brattice are used. In this study, the equations of conservation of mass, momentum, species and energy are discrete by using computational fluid dynamics and the results have been validated with experimental work and then several scenarios have been predicted to improve mine ventilation. Results show that concentration of methane decreases 47 % using stoppings, but the concentration is still higher than the standard level. By using brattice, the level of methane concentration decreased to 74.2%, but methane concentration in side walls of coal face is 3.4%, which is still higher than the level of standard. Optimized case was simulated by using stoppings and brattice simultaneously and quality of air improved 88.8% and concentration of methane was fully respected and mine safety and explosive gas concentration are satisfactory.

Polymeric foams have a cellular structure composed of a polymeric matrix with gaseous cells which are achieved by expansion of a blowing agent in polymer melt matrix during a foaming process. In the present study, the bubble expansion step in Polystyrene/CO2 batch foaming process was simulated and compared to the reported experimental results. A single spherical bubble surrounded by an incompressible viscoelastic fluid (upper-convected Maxwell model) was considered. To calculate concentration profile in the shell, mass diffusion equations were solved using finite element method, potential function definition and integral methods. The predicted results show that when the gas concentration profile obtained by finite element method and the concentration gradient near the bubble shell interface were used to calculate the pressure inside the bubble, the predicted results were in good agreement with the experimental ones as there was less than 1% error at each foaming time. The effects of the thermo-physical and rheological properties on the bubble growth dynamics were also studied and it was found that increasing the diffusivity coefficient by a factor of 10 would increase the bubble size up to 1.5 times, whereas increasing the viscosity by 3-fold would only change the bubble size about 2%, which shows that the bubble growth step in foaming process was a mass transfer controlled process.

Today, with the development of technology, industries such as automotive and construction require products with variable cross section. Multiplicity of steps, dimensional limitation and high production costs of the components are the reason flexible roll forming process is used to produce these products. One of the main defects in this process is the fracture phenomenon. The fracture is observed on the bending edges at transition zone where sheet thickness is large compared to the bending radius. In this research the fracture phenomenon is investigated on flexible roll forming process of channel section using ductile fracture criteria. For this purpose finite element simulation of the process using Abaqus software is done. The fracture defect in this process is investigated using six ductile fracture criteria by developing a subroutine. Experimental tests are performed on 27 specimens precut sheets of AL6061-T6, using flexible roll forming machine built in Shahid Rajaee University. Numerical results were validated by comparing simulation results with experimental results, In addition, by comparing the results of ductile fracture criteria with experimental results, the Argon ductile fracture criteria, was chosen as the most appropriate criterion to predict fracture. Also the effects of parameters as sheet thickness, bending radius and bending angle on fracture with argon selected criterion are studied.

Stenting is considered to be the favoured tool for therapy of coronary stenosis disease. However, despite the many advantages of this treatment strategy, its outcome may be undermined by the restenosis occurrence in the stent deployment site. Observations have shown that stent deployment in the artery alters the hemodynamic parameters such as wall shear stress and vortice size and prepares the conditions for in-stent restenosis development. Considering this fact, in this paper, the effect of some geometrical parameters such as the shape and the size of the stent strut on the wall shear stress distribution and vortice size is investigated. Furthermore, employment of a stent with partial flexible strut is suggested to decrease the restenosis risk, and the effect of the flexible part stiffness is explored. For this purpose, the interaction between the blood flow and the flexible part is simulated by arbitrary Lagrangian-Eulerian approach in the framework of the finite element method. The results indicate that in stents with circular strut, the partial flexibility of the cross-section can be effective in reducing the restenosis risk by lowering the maximum value of the wall shear stress and considerably decreasing the vortice size. On the other hand, in stents with rectangular struts, not only does it not decrease the shear stress maximum value, but also, the vortices size is significantly increased and may lead to increased restenosis risk.

In many cases, journal vibrations in the radial direction have been observed in the various rotating machinery using journal bearing. In this investigation the effects of forced oscillation of a journal on the hydrodynamic pressure profile of a two dimensional plain journal bearing are evaluated. Gambit and ANSYS- Fluent software are used to produce mesh and simulate the flow field respectively. Fluid is Newtonian and viscosity is constant. Also, flow is laminar, isothermal, and heat transfer is neglected. It is assumed that there is no phase change and cavitation does not exist. A user defined function is written in C language and compiled by Fluent to apply the oscillation motion to the journal. Results are obtained for three non-dimensional vibration frequencies of journal (0.001, 0.1 and 1), and two eccentricity ratios (0.54 and 0.8). Results show that the hydrodynamic pressure profile is significantly dependent on the oscillation frequency of journal. It can be observed that the pressure distribution variations are independent of frequency when oscillation frequency is low. However, the pressure distribution is considerably affected by increasing oscillation frequency which leads to appearance of different hydrodynamic pressure distribution. These influences become more and more intense by rising non-dimensional vibration frequency ratios, especially when it is 1.

The study of wave transmission over submerged obstacles and the flow pattern that forms around the obstacle has always been an important subject because of the direct affect on wave and the changes in wave energy that is crucial in the design of devices that absorb wave’s energy and coastal breakwaters. In this research, the flow pattern induced by solitary wave passing over a submerged vertical thin plate has been studied. A wave maker piston has been used to generate the solitary wave and particle image velocimetry (PIV) technique has been used for flow visualization a technique that is non- introsire optic method, which can measure the fluid velocity with any changes in flow pattern. The study of the flow pattern visualization, velocity values and vorticity shows, at first, the flow separation shear layer forms and the clockwise vortex generate at the rear edge of the obstacle before the wave arrives at the barrier. Then the vortex grows in size and causes the water to move upward like a vertical jet on upstream. Then the fluid enters to the downstream and generates the counterclockwise vortex in this region, which is less than the first clockwise vortex in power which makes an important difference with the thick geometry researches. In addition, the non-dimensional horizontal components of fluid velocity at the time of shear layer formation at the rear edge of the plate have been studied and compared with the case that the barrier is rectangular.

Electrospray is a branch of the scientific area of electro hydrodynamics which is based on electrical charging of liquids. The electrospray governing equations are a combination of hydrodynamic and electrostatic equations to which the addition of liquid breakup process escalates their complexity. This research work aims at developing a numerical solver to simulate the electrospray process in an emitter disc configuration using Heptane as a working liquid under various electrical potentials. The simulation results in comparison with CFD and experimental data show good agreement both quantitatively and qualitatively. The results clearly have captured the formation of liquid flow profiles at the emitter exit, demonstrating various electrospray modes. These modes initiate a micro dripping mode at the lowest voltage, i.e. 3.5kV, prompting consecutively to spindle and pulsating cone-jet modes and ending in a stable cone-jet mode at the highest charging voltage, i.e. 6.5kV. In addition, it is also observed that the liquid cone and the vortex shaped within it would shrink as an increase in the electric potential is imposed. Although the increase in electric potential results in rise of the maximum magnitudes of electric field and velocity, the electric charge accumulation at all electric potential values occurs on the outer surface of the liquid flow, implying its electrical conductivity.

In this paper, modeling of Min-Max controller and evolutionary multi-objective optimization for gain tuning controller of turbofan engine are presented. To achieve this purpose, first a turbofan engine is modeled in GSP software. Then engine parameters model, by using extracted GSP simulation data and based on NARX structure of neural network is developed. For model validation a test fuel signal is produced and model performance is assessed. Next, turbofan engines control requirements and constraints are described and a fuel controller based on Min-Max strategy is designed and diverse control loops in controller are described. Each of these loops has a proportional controller known as control gain of the min-max controller. For determining the gains of the controller, gain tuning process is formulated as a Genetic Algorithm Optimization problem in order for GA algorithm to find the best solution via its evolutionary generations. In this optimization problem, the settling time during acceleration and deceleration, engine fuel consumption and the amount of engine emissions are considered as objective functions to be minimized. The obtained results from simulation of optimized controller and engine show the final controller not only optimizes objective functions but also satisfies all control modes of engine during acceleration and deceleration modes.

Super hydrophobic surfaces receive many applications in various industries such as desalinization, heat exchanger, anti-fog and self-cleaning surface production. In this study a wet etching process was used to produce super hydrophobic copper surfaces. The specimens were etched by multiple ferric chloride and deionized water solutions to create micro-nano structures on their surfaces. The electronic scanning electron microscopy (SEM) images of the resulted surfaces show a formation of micro-nano structures with specific templates. Contact and sliding angle measurement of surfaces after etching process showed that contact angles of specimens increased to nearly 140o while sliding angle of all samples was 180o, which is the same as a rose petal property. In the next step, to promote hydrophobicity of surfaces, increased contact angle and decreased sliding angle specimens were immersed in an ethanol and stearic acid solution with a specific concentration. Moreover, effects of etching time and etchant concentration on the sliding and contact angles with/without stearic acid modification were investigated. Results show that contact angles increased and sliding angles decreased remarkably so that it reduced to lower than 10o in some cases and lotus effect was achieved.

In the present study, the effect of high temperature radiant heaters’ arrangement on providing appropriate and uniform thermal conditions under asymmetric flow field have been investigated in an industrial environment. For this reason, a sample industrial environment with one inlet and outlet opening has been considered with two different types of high temperature radiant heaters’ arrangement: single radiant heater and couple radiant heaters. For the mentioned conditions, continuity equation, momentum equations, energy equation and radiative transfer equations have been solved by Open Foam numerical solver. Also, energy consumption has been evaluated in the present study. The results show that in presence of asymmetric flow field, using couple high temperature radiant heaters in comparison with single radiant heater causes more uniform temperature distribution and decrease of about 10 degrees Celsius in maximum temperature of floor. Also, this can cause a nearly 35 percent decrease in floor temperature distribution deviation from the average appropriate temperature (27 degrees of Celsius). Moreover, the results indicate that utilizing couple high temperature radiant heaters leads to increase in energy consumption of about 10 percent in comparison with single radiant heater.