نشریه مهندسی مکانیک مدرس
سال چهاردهم شماره 10 (دی 1393)

In this research, low velocity impact tests have been carried out on laminated composite plates to investigate the impactor shape and temperature effect on the dynamic behavior and material damage. The woven E glass/ epoxy laminates were manufactured. The studies have been done on plate with dimensions of 120 mm× 120 mm× 3 mm, impactor with 1.4 m/s incident velocity and 7 kg mass. Specimens have been impacted by using steel flat, hemispherical, ogival and conical impactors, all 12.7 mm in diameter. The specimens impacted by the conical impactor absorbed most energy because of local penetration. The flat impactor caused the highest peak force and lowest contact duration as expected. The force history of the impactor, projectile displacement and absorbed energy of different impactor shapes has been measured and compared with each other. The temperatures were in the range of room temperature to 150 °C. The parameters including maximum contact force, projectile displacement and the absorbed energy of different temperature have been investigated. Maximum contact force decreased with increasing of temperature, and deflection of impactor increased with increasing of temperature.

In this study, the reinforcing effect of organically modified layered clay in two epoxy matrices, TETA-cured and F205-cured, was studied. The epoxy resin system is made of a diglycidyl ether of bisphenol A, Epon 828, as the epoxy prepolymer and the two hardeners were Epikure 3234, namely TETA, and Epikure F205. The organically modified clay, Closite 30B, is dispersed into the epoxy system in a 0%, 1.5%, 3% and 5% ratio in weight with respect to the matrix. The state of dispersion was characterized by X-ray diffraction method. In both systems of epoxy resin, the results of XRD show that the clay has been further intercalated by the epoxy matrix. The tensile and flexural properties of the epoxy/clay nanocomposites were investigated according to the standard tests. The results of mechanical tests indicate that the mechanical behavior of two epoxy resin systems reinforced with clay nanoparticles, are different from each other, so that adding clay into the epoxy matrices makes the TETA-cured nanocomposites more brittle and the others cured with F205 more soften. By comparing the results of two epoxy resin systems reinforced with clay nanoparticles, it is concluded that positive effect of presence of the clay nanoparticles is evident on the mechanical properties of the F205-cured epoxy resin.

Due to high strength and stiffness in comparison with their weights, laminated composite materials are widely used in many structures such as aerospace and naval structures. Therefore, the understanding of their failure mechanisms to predict their mechanical response is of high importance. One of the major aforementioned mechanisms is the delamination which commonly occurs in skin/stiffener joints. In the present paper, a comparative study on the delamination in composite skin/stringer structures under 3 point and 4 point bending loads is performed by the finite element method (FEM) employing the cohesive elements. The detailed effects of stacking sequence on the damage of structure are investigated. A user defined interface element has been implemented in the Ansys software in continuum damage mechanics framework based on the bilinear cohesive zone model. The advantage of this method is the modeling of delamination growth without any requirements to the presence of initial crack and remeshing. Comparison of the obtained results from FEM with that of experiment justifies the capability of the employed model to predict the delamination initiation and propagation. The results indicate that in the 3 point bending load, the damage initiates from the adhesive between skin and stringer, while in 4 point bending load it initiates from the interface elements between skin layers near the adhesive bond. Finally, in order to increase the strength of skin/stringer structures, the results strongly recommends preventing the use of 45 and 90 degrees plies near each other around the adhesive bond.

In the present study the problem of a two-layered model for an unsteady and pulsatile flow of blood through a stenosed artery is numerically simulated. The model consists of a core layer of suspension of erythrocytes and a peripheral plasma layer. The core is assumed to be represented using a micropolar fluid and the plasma layer using a Newtonian fluid. The artery is considered to be elastic and the geometry of the stenosis is taken as time-dependent, however a comparison has been made with the rigid ones. The shape of the stenosis in the arterial lumen is chosen to be axially non-symmetric but radially symmetric in order to improve resemblance to the in-vivo situations. By applying a suitable coordinate transformation, the stenosed artery turns into a rectangular and rigid artery. The Navier-Stokes equations of motion of the blood flow, subjected to a pulsatile pressure gradient are solved numerically using the finite difference scheme. Dynamical characteristics of the blood flow such as the velocity profile, the volumetric flow rate and the resistance to flow are obtained and the effects of the wall motion and the severity of the stenosis on these flow characteristics are discussed. The results are found to be in good agreement with the available analytical results.

Free surface vortex formation phenomenon at intakes is one of the most important problems in the water withdrawal process. In the present study, the free surface vortex formation was experimentally investigated. Experiments were performed on a single intake with three common intake withdrawal directions (vertical, horizontal and with angle of 45°). One of the main objectives of present study was determination of the strength of vortices. The tangential velocity component of vortices was measured by an Acoustic Doppler Velocimeter (ADV). The results indicated that, by varying the withdrawal angle from vertical to horizontal, the strength of vortices decreased by about 31%. Based on analyzing of experimental data, an empirical relationship between the circulation number and Froude number for various submergence depths was developed for each withdrawal direction. The critical submergence for an air entraining vortex at intakes was also investigated. The results indicated that the critical submergence was considerably affected by the changing of withdrawal direction. It could be concluded that the minimum of critical submergence was occurred at horizontal direction. Based on analysis of the experimental data for each withdrawal direction, an empirical equation was also obtained, which is used to calculate the critical submergence. The results also were compared and analyzed by other researcher’s investigations and showed satisfactory agreement.

Hydraulic engine mounts are applied to the automotive applications to isolate the frame from the high frequency noise and vibration produced by the engine. It also designs to reduce the engine shake motions from the road distribution usually occurred at low frequencies. This implies that the stiffness and damping properties of the engine mount should be amplitude- and frequency- dependent. In the semi-active engine mounts this task will be done by changing the mount parameters such as stiffness and damping. Magneto-rheological fluids are used in the mounts to change their damping by applying the magnetic field. When the current is applied to the electromagnet and the magnetic field is present, the behavior of the magneto-rheological mount is changed by the magneto-rheological effects. In this paper, a prototype magneto-rheological mount was built and experimentally evaluated. Also, the mathematical model of the mount was developed to represent the dynamic behavior of the engine mount system. The model was numerically solved based on the prototype parameters and simulated in MATLAB. The experimental results were used to verify the model in predicting the mount characteristics.

Elliptical subsurface cracks are one of the probable types of cracks that occur in engineering structures. Due to the non-symmetrical geometry with respect to the crack surface, coupling of the fracture modes occurs in an elliptical subsurface crack and so, the crack under normal loading will experience all fracture modes. Mode III caused by the coupling effect under normal loading is negligible whereas mode II is significant. In this paper, mixed mode two dimensional weight functions of the elliptical subsurface cracks parallel to the surface are derived for aspect ratios of αlpha=0.2, 0.4, 0.6, 0.8, 1.0 and ratios of crack depth to crack length of Betta=0.05, 0.06, 0.08, 0.1, 0.14, 0.2, 0.3, 0.5, 1.0. Mixed mode stress intensity factors under uniform normal loading are used as reference stress intensity factors. By curve fitting on the calculated weight functions coefficients, the derived weight functions are able to be used for any αlpha and Betta. To verify the weight functions, the stress intensity factors of all points of the crack front are calculated under linear, elliptic paraboloid and trigonometric paraboloid stress distributions and compared to the finite element results. Comparison of the results shows high accuracy with mean relative error less than 7%. Using derived weight functions, mixed mode stress intensity factors of the subsurface elliptical crack can be determined for any αlpha and Betta and under any normal stress distributions.

In this paper, 5 samples of one kind of swirl injector with tangential inlets, which has been designed and manufactured by using CNC, have been tested. Above injector has a spray cone in the shape of very thin layer because it is formed an air core in injector center. In fact, this is a one-fluid injector but its operation is two-phase. In order to detect acceptable injector among them, characterization tests have been done in the propulsion laboratory of Tarbiat Modarres University for all sample injectors. The methods of experimental characterization have been described in detail in current paper and also important parameters introduced. In these tests, injection uniformity, symmetry, mass flow rate versus pressure difference and some other parameter such as spray cone angle are investigated. Experimental results have been compared with design points. Finally, one injector has been selected as a suitable and nearer to theoretical design injector among them. The selected injector can be used for validation of numerical analysis results and also doing some complemental microscopic experiments. The results show good agreement between theoretical predictions and experimental results.

Systems of recognition and location identification of underwater moving bodies which using acoustic waves are called sonar. Electroacoustic transducers have an important role in underwater communication systems such as Sonar. A set of electroacoustic transducers which is called sonar array, can be used for sending and receiving underwater sound. The most widely used transducer in these arrays are Tonpilz transducer. In this paper, a full simulation of Tonpilz transducer is given and the most important factors for evaluating transducer performance are checked experimentally and numerically. Also for validation of finite element model, the sample of transducer was designed and made. This transducer was tested in two methods, electrically and acoustically. Electrical behavior was tested by Impedance gain analyzer devise. Acoustic test was carried in the acoustic pool. Then the result of FEM compared with experimental results. With comparing FEM results and tested model, it is observed that the finite element model can predict electrical and acoustical behavior of Tonpilz transducer so well. Finally it is tried to improve frequency response of transducer with making changes in the structure. While the addition of damping factors can increase frequency bandwidth.

One of the most important issues in industry, particular casting industry is to determine the internal structure of objects such as identifying the interfacial boundary configurations between material, identification of impurities or mechanical properties of the material. The objective of the present inverse problem is to identified simultaneously two regular interfacial boundary configurations and mechanical properties of the components of a multiple (three) connected domains using a discrete number of displacement measurements obtained from an uniaxial tension test. A unique combination of a global optimization method i.e. the Imperialist Competitive Algorithm (ICA) and local optimization methods i.e. Simplex Method (SM) along with the inverse application of the Boundary Elements Method (BEM) are employed in an inverse software package. A fitness function, which is the summation of squared differences between the measured displacements and computed at identical locations on the exterior boundary, is minimized. The obtained results (run-time and error-rate), clearly demonstrate the efficiency of this present algorithm (the Imperialist Competitive Algorithm and Simplex Method) to optimize the objective function and the estimation simultaneously two regular interfacial boundary configurations and mechanical properties.

In this paper, in order to avoid the problems induced by cutting liquids like higher cost, environmental pollution and dangerous for operator health in milling process and also using the benefits of them such as increasing tool life and machined surface quality, machining by minimum quantity of lubrication (MQL) or near dry lubrication was introduced and that’s effects on main outputs (consumed power and surface roughness) was compared with other lubrication methods such as lubrication by cutting fluids and by air. In order to perform a series of experiments and investigate the effects of different process parameters such as tools rotational speed, feed rate, gas pressure and liquid flow rate on main outputs, the Taguchi method of design of experiments was employed and then the analysis of variance (ANOVA) was used to find the most important factors effecting main outputs. The results obtained by experiments showed that employing near dry lubrication leads to lower electrical power and comparable surface roughness as compared with other lubrication methods. The analysis of variance showed that feed rate is the most important factor affecting consumed power and liquid flow rate is the most important factor influencing surface roughness.

In this paper, a control system is designed to reduce roll angle which consequently leads into increasing vehicle roll threshold during high lateral accelerations. Accordingly, the two same rotation-electric actuators are mounted on front and rear suspension system anti-roll bars. This control system turns by applying an opposite couple that is acted upon the chassis, as time varying, reduce the lateral acceleration as it possible and improves lateral stability and roll threshold during extreme maneuvers. In order to find out the effects of the performance of this active system on vehicle stability, firstly based on a nonlinear eight degrees of freedom model of the lateral dynamics of the vehicle and by taking Steering angle as an input, the kinematic parameters and finally roll threshold that is defined lateral load transfer, is estimated. Then, the optimized second order control theory with three degrees of freedom of the vehicle model is used to design the controller. Finally, with the aid of comprehensive model of the vehicle, the lateral dynamics of the vehicle as well as the effects of the controller during path of standard Fish hook maneuver are investigated.

In present paper the Inamuro Model based on free energy approach of the Lattice Boltzmann Method (LBM) was used to simulate the motion of bubble and coalescence of two bubbles under buoyancy force. By combining the Tanaka and Inamuro models, three-dimensional model of Inamuro was used in two-dimension for decreasing the computational cost. Firstly it was ensured that the surface tension effect and Laplace low for two density ratio 50 and 1000 were properly implemented. Secondly in next step, effect of governing dimensionless numbers problem such as Etvos number and Morton number on Reynolds number and terminal shape of bubble were investigated. Different flow patterns in various dimensionless numbers were obtained and by changing the dimensionless number, terminal change of bubble’s shape was seen. Finally, motion of two bubbles and terminal shape of coalescence of two bubbles were studied in different dimensionless number, which shape of first bubble was same to single bubble, but it was seen that second bubble experienced various shapes due to its location in wake of first bubble and less difference pressure on two sides of this bubble.

The nitrogen oxide emission is known as a potentially hazardous pollutant in reacting flows. To improve this process, it is of fundamental importance to take into consideration environment protection through reduction of fuel consumption in addition to increasing combustion efficiency. The control of NO emission from the combustion process is an important design criterion in modern gas turbine technology. In the present work a two-dimensional combustion simulation is developed for a model gas turbine combustion chamber. The k−ε turbulence model and the eddy dissipation concept model are applied for flow predictions and reaction rate simulation respectively. The flow field pressure linked equations are solved using the SIMPLE algorithm. In the present work, the thermal and prompt NO formations are estimated and calculated for three different methane, propane and pentane fuels. Also the effects of equivalence ratio and primary aeration on nitrogen oxide emission are considered. Results of numerical simulation show that the nitrogen oxide emission significantly affected by the equivalence ratio for all three type of fuels. Also by applying primary aeration the averaged nitrogen oxide production can be significantly reduced.

In this paper, differential quadrature element method (DQEM) is used to analyze the free transverse vibration of multi-stepped rotors resting on multiple bearings. Timoshenko beam theory is used to show the gyroscopic effects; Also each bearing is replaced with four springs; two translational and two rotational acting on two perpendicular directions. Governing equations, compatibility conditions at the each step and each bearing and external boundary conditions are derived and formulated by the differential quadrature rules. First, convergence and versatility of the proposed method are tested by the presented exact solutions. Then, the Campbell diagram is derived for a desired case study and variation of natural frequencies is investigated versus angular velocity of spin. The most advantage of the proposed method is being less time-consuming in comparison with the other methods, especially for cases with high number of steps and bearings. Accuracy of the proposed method is confirmed by the presented exact solutions and effect of angular velocity of spin on natural frequencies (Campbell diagram) is investigated. Comparison of the proposed method with the exact solutions revealed the convergence and accuracy of the proposed method.

Metal foams as a new class of materials with interesting properties such as high stiffness and strength to density ratios, capacity to absorb impact energy, and reproducibility, are rapidly growing their share in engineering applications such as aerospace, automotive industry, lightweight structures, and energy absorbers. Different numerical approaches have been already developed for the simulation of this class of materials from which the two-scale microplane model has been focused in this research. First a simple algorithm has been proposed for the numerical implementation of microplane model to simulate the mechanical behavior of closed-cell metal foams. The structure of foam is assumed to be an assembly of firmly bonded spherical shells. Next, in order to calibrate the microplane model, the mesostructure of foam has been simulated using non-linear finite element model. The FE model has been subjected to both uniaxial and hydrostatical loads and required steps for the extraction of model parameters from the results have been outlined. Finally, the results of microplane model and mesomodel have been compared for a more general biaxial loading condition. Despite tremendous reduction of computational cost, good agreement has been achieved.

Kinematic performance indices are used to have an evaluation of the potential efficiency of the robots. Some of these items are designing the optimal structure, trajectory planning, programming, and evaluation of behavior of the robot in positioning and orienting with desired rates or resolution. These indices will be used when the robot has even translational or rotational degrees of freedom (DoF). Due to dimensional incompatibility of the Jacobian entries in the complex DoF’s robots with both types of DoF’s, performance indices such as Jacobian condition index and associate singular values, are not applicable. In this paper, inhomogeneity of Jacobin matrix has been resolved by introducing a new Jacobian matrix which is called Cartesian Jacobian Matrix (CJM). Cartesian Jacobian Matrix maps Cartesian velocity vector of End-Effector (EE) to the joint space velocity vector. As a case study, the suggested method has been used for a Tricept parallel kinematic manipulator. Moreover, considering Local Conditioning Index (LCI) and associated singular values through the workspace have been led to structure optimization of the robot in order to have maximum positioning and orienting rates of EE through the maximum cuboid workspace. The optimization has been performed by Genetic algorithm via GA toolbox of MATLAB 2012 software.

Although chemotherapy is one of the effective methods in cancer treatment its effects may be moderated due to drug resistance. The main objective of this paper is to propose optimal finite cancer treatment duration. In this paper, a mathematical model of tumor growth by adding radiotherapy, chemotherapy and metastasis of cancer cells terms is extended. Stability analysis shows that the tumor free equilibrium point is unstable. Hence, changing the dynamics of the system around this equilibrium point for achieving finite duration treatment method is essential. Therefore, the effects of chemotherapy drug are considered not only on cells populations but also on the dynamics of the system. For this purposes, State Dependent Riccati Equation (SDRE) based optimal control is used. So chemotherapy agent is used as the control input to the extended cancer nonlinear model. Then, in order to show the flexibility in design, two different types of input weighting matrices are selected. Moreover, the robustness of this control method is investigated by simulation. Results show that changing the dynamics of the system is necessary for finite duration cancer treatment method.

Bipolar plates are the most important of fuel cells components. These plates are made with different methods such as machining, molding and forming and they are made of variety materials such as graphite, composite and metal plates. In this research, forming of metallic bipolar plates with pin-type pattern from stainless steel 304 with 0.11mm thickness is investigated numerically and experimentally using hydroforming process in convex die. In this regard, several parameters such as applied pressure, pin geometry, and depth to width ratio of the profiles has been changed and the experimental and simulation results of formed profiles, filling percent, thickness distribution and thinning percent of the formed parts have been compared. The results have been shown that no safe sample has been reached in depth to width ratio 1, while safe samples have been formed in depth to width ratio 0.67 in circle (a/b=1) and ellipse (a/b=0.7) samples and all samples in depth to width ratio 0.33 at 300 MPa pressure level in viewpoint of filling and thinning percentage. In general, increasing the small diameter to big diameter ratio (a/b) and decreasing the depth to width ratio (h/w) makes the thinning percent and filling percent more desirable.

In this study, longitudinal dynamic derivatives of an airfoil of the type NACA 6-series, oscillating in pitching and plunging motions were calculated using variation of pitching moment coefficients with angle of attack in various conditions, based on wind tunnel data. Various parameters of the tests were mean angle of attack, reduced frequency and amplitude of oscillation. To calculate the longitudinal dynamic derivatives in harmonic oscillations, the Taylor's series and integral of Fourier were used. Both the methods had the same results and could be extended to each flight vehicles. The effect of parameters on variation of longitudinal oscillatory derivatives was investigated, in three different regions of oscillation: before, over and post stall conditions. The results showed that variation of the longitudinal oscillatory coefficients with angle of attack is different in the pre-stall and over stall conditions with respect to post-stall region. The effect of reduced frequency on stability of the motion is different for two types of oscillations. Increasing the reduced frequency resulted in reducing the stability of plunging motion, but has a little effect on the stability of pitching motion.

Gears are one of the most important elements of any power transmission system. Among all types of gears, helical gears are more common due to their high capacity in power transmission as well as lower level of noise. The aim of this study is to present a model for analyzing the contact of teeth of helical gears considering thermal effects and surface roughness. In the present model, each helical gear is divided to several narrow spur gears in which each of the spur gears have a small rotation angle relative to the previous one. Also each contact point of gears is replaced with contact of two equivalent cylinders. Considering the fact that the governing regime for gears lubrication is the mixed-elastohydrodynamic regime, the total load is carried by lubricant and asperitie's contact. Meshing and lubrication analysis of a pair of helical gears is conducted based on the load-sharing concept and parameters such as film thickness, friction coefficient and temperature rise are predicted. The predictions based on the load-sharing concept are compared to other published results Acceptable accuracy, short execution time along with considering thermal and roughness effects are some of the major characteristics of this study.

This paper is concerned with design, develop and implementation of a quaternion based attitude control system for a rigid suborbital module which using cold gas thrusters over a short-duration mission. The quaternion controller produces a demand torque, and a pulse-width pulse-frequency (PWPF) modulator determines the necessary thruster fire signals. The effect of disturbances on module attitude has been investigated and the most significant found to be due to misalignment of thrusters effects. The system concept has been evaluated through modeling in Simulink and a rapid prototype hardware-in-the-loop platform and has been found to meet the requirements laid out for a typical module mission.The satisfactory performance of the controllers was illustrated through both numerical and hardware-in-the-loop simulations, where a system of twelve thrusters and load sensors were implemented in the hardware and disturbance effects such as thrust misalignment and sensor noise were studied. The results show the effectiveness of the proposed control method for agile attitude maneuvers of suborbital modules. The results of the HIL simulation were also used for tuning the parameters of the module’s numerical simulation that is to be used for error budgeting analyses.

Aluminum alloys are using widely duo to high strength-to-density ratio in the industries of automotive, shipbuilding and aerospace as a substitution of steel sheets.. To increases the formability of aluminum alloys in deep drawing process and due to formability problems of these alloys in room temperature using of warm deep drawing process is necessary. According to recent researches, warm deep drawing in gradient condition has better results as isothermal case. In this paper the process parameters in production of cylindrical parts from aluminum alloys 5083 sheet with 2mm thickness is investigated. For this purpose, gradient warm deep drawing in temperatures of ambient (25˚C), 80˚C, 150˚C, 180˚C, 250˚C, 350˚C, 450˚C and 550˚C have been used. The blank in flange region is heated by die heating and the blank center to increases the strength of the region which contact with punch corner radius is cooled by water circulating punch. The results show that increasing the temperature of the blank in flange region and also cooling of blank center lead to improve the limit drawing ratio. In forming temperature of 550˚C and ram speed of 378 mm/min and lubrication by graphite powder can reach to the limit drawing ratio equal to 2.83.

In this study, static and free vibration behaviors of two type of sandwich plates based on the three dimensional theory of elasticity are investigated. The core layer of one type is functionally graded (FG) with the homogeneous face sheets where as in second type the core layer is isotropic with the face sheets FG material. Plate is under uniform pressure at the top surface and free from traction in the bottom surface. The effective material properties of FG layers are estimated to vary continuously through the thickness direction according to a power-law distribution in terms of the volume fractions of the constituents. State space differential equations are obtained from equilibrium equations and constitutive relations. The obtained governing differential equations are solved by using Fourier series expansion along the in plane directions and state space technique across the thickness direction. Accuracy and exactness of the present approach is validated by comparing the numerical results with the published results. Furthermore it is possible to validate the exactness of the conventional two dimensional theories. Finally the influences of volume fraction, width-to-thickness ratios and aspect ratio on the vibration and static behaviors of plate are investigated.

In this paper, squeeze film damping in a micro-beam resonator based on micro-polar fluid theory has been investigated. The proposed model for this study consists of a clamped-clamped micro-beam suspended between two fixed stratums. The gap between the micro-beam and stratums is filled with air. Equation of motion governing the transverse deflection of the micro-beam based on strain gradient theory and also non-linear Reynolds equation of the fluid field based on micro-polar theory have been non-dimensionalized, linearized and solved simultaneously to calculate the quality factor of the squeeze film damping. The effect of non-dimensional length scale parameter of the air and micro-beam for different values of micro-polar coupling parameter has been investigated. It has been shown that applying micro-polar theory underestimates and also applying strain gradient theory overestimates the values of quality factor that are obtained in the case of classic theory. The quality factor of the squeeze film damping for different values of non-dimensional length of the beam, squeeze number and non-dimensional pressure have been calculated and compared to the obtained values of quality factor based on classic theory.