نشریه مهندسی مکانیک مدرس
سال هفدهم شماره 3 (خرداد 1396)

When a Horizontal axis wind turbine works under yaw condition, each blade element can be considered as an oscillating pitch airfoil while the free stream velocity oscillates horizontally. The unsteady free stream velocity, which is usually ignored, oscillates with the same frequency as the airfoil oscillations and has a great impact on the periodic forces produced by the airfoil oscillation. In order to study the effects of unsteady free stream
velocity on the aerodynamic loads, a 2D NACA0012 oscillating airfoil at Reynolds number of 135000 has been simulated. In this simulation, reduced frequency, reduced amplitude and the phase difference between the free stream velocity oscillation and the airfoil angle of attack oscillation are 0.1≤k≤0.25 ¡ 0.2≤λ≤0.8 æ ϕ=0 ,π, respectively. Results show that free stream oscillations affect the aerodynamic loads, vortex strengths
and dynamic stall characteristics. The lift force can be increased by more than 7 times than that of static case and 3 times compared to the load from steady free stream velocity. Depending on 𝜙 value, the dynamic stall angle of attack can be advanced 1 degree or delayed by more than 7 degrees by increase of reduced amplitude. Also, increase of k always causes delay in leading edge vortex formation and consequently delay in dynamic stall occurrence.

In the present paper, the effect of fins presence on natural convection between coaxial annuli was investigated, numerically. The external duct was circular and the internal ducts included three circular, square, and triangular cross sections for discussed annuli. As a geometrical constrain, both cross section area and diameter of external duct of annuli were considered equivalent together for all investigated cases. The area of fins installed on the internal ducts was constant, and their effects on thermal behavior of annuli were compared with considering the constant wall temperature boundary condition for surfaces in the range of 105≤Ra≤108. The results showed that with increase of Rayleigh number and consequently velocity, the heat transfer coefficient was increased for both surfaces. However, presence of fins reduced the values of heat transfer coefficient of internal ducts about 50%, while they increased those values for external ducts. Also, in the case of circular annulus, with increase of Rayleigh number, the Nusselt number wincreased about 71% and 64% for non-finned and finned ones, respectively. As a result, fins increased the overall heat transfer rate of both surfaces of annuli about 13% in comparison of non-finned surfaces.

The supercooled steam in low pressure turbines creates the nucleation phenomenon. In most modeling approaches, to reduce the computation time a monodispersed model is used. However, experimental evidence even on one dimensional condensing flow demonstrates the existence of droplets with several sizes. In this paper to develop the modeling of the droplets more realistic, a polydispersed model is used along with the one dimensional HHL Riemann solver. In this study, a simple method is proposed for polydispersed model in Eulerian-Eulerian method. In this scheme, first, a number of elements are considered in the nucleation region and the droplets formed in each of the elements are put into a group. Then the new droplets formed in consecutive elements are distributed based on the ratio between the number of droplets in each group available for merging constrained by having the same number of groups. These groups grow individually until the end of the nozzle and each group has their own wetness, temperature, number of droplets and radius. Based on the results of the proposed polydispersed, the nucleation rate and the number of droplets are found to be more than the results of the monodispersed model, but the average droplet radius is less, with 10% differences is closer to the empirical radius of the Moore nozzle. The pressure distributions for both models have good agreement with experimental data, but in overall, the results of the proposed polydispersed method is significantly closer to experimental results especially with regards to the droplet radius.

Prediction of spray droplet diameter distribution depends on the various parameters such as physical properties, fluid velocity, and discharge environment and injector geometry. The stage of forming droplets has a great variety in size and therefore will be predictable with a statistical approach. The maximum entropy principle is one of the most popular and best ways to predict the spray droplet size distribution along with the conservation equations. Due to some drawbacks in this model, the predicted results do not match well with the experimental data. It is suggested to improve the available energy source in the MEP model equation by numerical solution of flow inside the injector based on the CFD technique. This will enhance the calculation accuracy of the turbulent kinetic energy of the output spray. In fact, by using this sub-model in the maximum entropy model, the prediction accuracy of the spray characteristics is improved. Also, the requirement of the maximum entropy model to the experimental data as inputs has been reduced. By the present coupled model, the effect of spray upstream on the droplet size distribution can be considered with a good accuracy. The results show a close agreement with the available experimental data.

At the core of the conventional hydro cyclone, the secondary flow is created in opposite direction of the primary flow which is adjacent the wall and causes a sink pressure on the central axis of the hydro cyclone. This low pressure zone may drag fine particles to the core and escape them from the upper section of hydro cyclone. In this research by adding a sound source at the core of the hydro cyclone, the separation performance of an acoustic hydro cyclone is studied. Then the effects of the hydro cyclone’s body tilt angle with the horizon reviewed in next step. To this end, the flow simulation carried out by the appropriate turbulent and two-phase fluid flow model selection and consequently the results validated with experimental data. The result shows the optimum strength and frequency of acoustic stimulation and the performance of conventional hydro cyclone in different tilt angles, particles diameter and inlet velocities. In addition in this study, the optimum injection velocity for any diameters which use of sound source impacts greatly on increasing the separation efficiency, is introduced. Finally, by applying a genetic algorithm with two objectives function, among all the states, the model that have the highest efficiency and lowest pressure drop is selected.

Bone fracture occurs as a result of accident, old age and disease. Generally bone fracture treatment consists of stabilizing the fractured bone in the right position. In complex fractures, stabilizing internal and external tools and equipment is used to stabilize the fractured bone in position. Bone drilling is required in order to connect fixating devices. The forces required for chip formation, increase the temperature during bone drilling. The phenomenon of thermal necrosis of the bone occurs if the temperature exceeds 47 degrees Celsius. Thermal necrosis inhibit bone fixation and causes the wrong bone healing. The current study has been trying to examine the effect of the cooling gas on the reduction of temperature rise on drilling site as well as statistical analysis of the process. Tests have been carried out using direct injection of nitrogen gas using internal coolant drill bits. Using cooling gas reduced the increase in drilling temperature to 15 degrees Celsius and prevented the thermal necrosis. The maximum increase in temperature in conventional drilling was 56 degrees Celsius, while using cooling gas the increase in temperature of 43 degrees Celsius was achieved. This reduces the risk of thermal necrosis. Statistical analysis also indicates that in the drilling with direct cooling with nitrogen gas the temperature changes are almost independent of the rotational speed.

Vacuum tube solar water heaters are one of the most common types of solar water heaters, and they have been used widely in recent years. Evacuated tube solar collectors compared to flat plate collectors have higher absorption coefficient and lower heat loss. Many factors are effective on thermal efficiency of evacuated solar water heaters and many studies have been done to increase their efficiency. In this study, thermal performance of a modified model has been investigated experimentally. Two laboratory samples, one of them with the modified structure and the other like commercial samples have been made and their performance has been studied under equal solar radiation and ambient temperature. The results have shown that this structure modification has a positive effect on collector performance. This change has made the temperature distribution in the pipe and tank more uniform, and has increased the efficiency to 11 percent. Absorbing thermal energy in the modified model was more than typical model about 25 percent in duration one hour. Also, effects of solar radiation on the average temperature of water in the storage tank have been investigated in both cases. In this study, an experimental method is used to calculate the radiation received to vacuum tubes.

Blast walls are implemented in order to attenuate the explosion blast wave and protect the important objects. These obstacles decrease the blast wave intensity by reflecting a portion of the wave to the explosion source and producing turbulence in the blast wave flow. The geometrical shape of the blast wall, as an influential factor, decrease the intensity and increase the protective effect of these obstacles. In this thesis, the angle of curvature of the canopy blast walls was studied to find the optimum angle with the most attenuation effect. To simulate the interaction of the blast wave with the blast wall, computational fluid dynamic with finite volume method and OpenFOAM software (an open source software) was used. The results of the simulation with LES turbulence model, was presented the more exact description for the attenuation of the blast wave interacted with the canopy blast wall. The comparison of the overpressure peak and the created vortexes behind the canopy and oblique wall, shows that the canopy wall was increased the attenuation of the blast wave up to 14%. On the other hand, by increasing the angle of curvature of the canopy wall from 0° to 67.5°, the attenuation of the interacted blast wave with the obstacle was increased step by step up to 4%.

Hydro-mechanical deep drawing is an advanced process in metal forming in which high pressure fluid is used to form complicated parts. Conical parts are kind of complex parts in which there is a high possibility of thinning and rupture during the forming process due to low contact area between the punch head with the blank. In this paper, the Hydro-mechanical deep drawing of Al3003-IF Steel two-layer conical parts is studied using the experimental and numerical approaches. The effects of process parameters such as friction coefficient, arrangement of layers and thickness ratio of two-layer sheet on working zone are investigated. Allowable working zone in this process indicates the applicable range of chamber pressure and drawing ratio to achieve a part without rupture. The results show that with decreasing the friction between blank and blank holder, increasing the friction between blank and punch, increasing the thickness of high formable layer and setting IF steel layer as outer layer increase the limit drawing ratio and make the allowable working zone more extensive. Finally comparison of the results obtained from experimental investigation and numerical simulation shows a good agreement between the results.

Precise Prismatic actuators are one of the most important actuators used in robotic industry and the main base of parallel robots as 6PUS Stewart-Gough robot. Because of bearing large axial forces by this actuators, elastic deformations are inevitable in the main parts of them. This results in elongation and compression of the piston and ball screw, which deteriorates the dynamic linear positioning accuracy of these actuators. The existence of accurate dynamic equations can seriously help to control these errors. Most of the dynamic models which have been used for these actuators based on lumped parameter approach have one DOF for rigid and two or three DOF for flexible state and the stiffness of parts are considered as constant. In this study, the direct dynamic equations of a rotating prismatic actuator which has three DOF in axial direction and ball screw drive system, are proposed using the Lagrange method. In addition to the flexibility of the moving piston, the ball screw is considered with variable stiffness. The important point of this study is the variability of ball screw stiffness. As the nut moves along the shaft, the active length and stiffness of the shaft change; which is very similar to the reality. In addition to the analytical method, the actuator is modeled in the finite element software, ABAQUS and the results of the analytical method and the finite element method are compared.

The purpose of this paper is to deal with fracture behavior of carbon nanotubes with presenting a revised structural molecular mechanics model in the finite element method. Structural molecular mechanics modified model, uses a three-dimensional beam element with general section to make nanotube structural model in which bending stiffness and inversion are defined independently. In analysis which are done, a bridged carbon nanotube with constant strain rate is examined under tensile stress until the failure of nanotube. Carbon-carbon bonds behavior has been assumed nonlinearly and will be ruptured when the strain reaches 19%. It is predicted that fracture behavior in carbon nanotubes depends on the environment temperature due to mechanical behavior of carbon nanotube's bonds. Based on the present research, we found that by increasing the temperature, Poisson's ratio increases and Young's modulus decreases. Further, it can be said while the temperature increases, both the fracture ultimate strain and stress decrease. Finally, a nonlinear relationship is presented in which the constants depend on chirality of the carbon nanotubes.

Spray plays an important role in many engineering and industrial processes. Therefore, it is important to investigate the heat transfer rate of particles in an environment with a wide spectrum of vortical structures resembling turbulent eddies. The interaction between these vortical structures and spherical particles significantly influences the heat transfer rate of particles and their life time. In the present study, transient heat transfer of a spherical particle interacting with random vortexes in an incompressible and viscous flow has been studied using numerical solution of the Navier-Stokes and energy equations at Re=100 by the developed computational algorithm. In order to ensure the accuracy of the calculation, the results are compared with numerical data available in literature, where good agreements were observed. The influential vortex domain around the particle was first identified with simulating two similar vortexes based on their impact on the Nusselt number. Then, using this domain of influence, effects of the number of random vortexes with different structures and positions on the heat transfer rate of the particle were considered. It was found that only 4 or 5 vortexes can well predict the influences of a vortical domain with larger number of vortexes on the heat transfer rate of a particle. The results also indicate that for 4 or more vortexes the Nu varies in a limited range of that for the case with no vortex flow. Furthermore, increasing vortexes sizes, leads to the higher heat transfer rates.

In In this paper nanofluids condensation heat transfer on an inclined flat plate is investigated. To do this, thermal resistances of single droplets are calculated and the total heat flux is evaluated using population balanced theory. The nanofluids include alumina, titanium dioxide and silver as nanoparticles and water as a base fluid. Effects of different surface inclinations, nanofluids types, and nanoparticles concentrations are investigated on the heat transfer. Nanofluids properties consisting of thermal conductivity, density, dynamic viscosity, and latent heat are extracted from literature and introduced into the equations. The results are compared with some experimental data in the same conditions. The Nusselt theory is used to compare the heat transfer rate of filmwise condensation with dropwise condensation. Inspecting the results shows that the heat transfer coefficient of a vertical plate is maximum, and decreases with decreasing in inclination due to lower washing rate of small droplets by sliding droplets. The results also show that the heat transfer coefficients of various nanofluids are different but they are constant all over the surface. As well as, addition of nanoparticles to the base fluid increases heat transfer rate. It can be seen that water-silver nanofluid has the maximum heat transfer rate among three beforehand mentioned nanofluids in the same conditions and the heat transfer rate increases with increase in volume fraction of nanoparticle for a specific nanofluid.

Mathematical modeling of tumor growth as modeling of other biological tissues is important since these models enable us to predict and evaluate the parameters that could not be measured easily. The accuracy of a derived model depends upon considering more involved factors and mechanisms and will lead us toward a realistic modelling. In this study, a finite element model of avascular tumor growth is represented. This model concentrates on the constitutive behavior of tissues and the resulting stresses. The tumor and its host are assumed to behave as a hyperelastic material. The tumor model is supplied with a growth term which is a function of nutrient concentration, solid content of the tumor and rate of cell proliferation and death. The evolved stresses during growth and interactions between tumor and the surrounding host could be evaluated using the presented model. The results show that the exerted stresses on tumor increase as time passes which lead to reduction of tumor growth rate until it gradually reaches an asymptotic radius. The effects of variation of the bulk modulus which is a determinant of compressibility are investigated. Since biological tissues consist mainly of water so we should impose the condition of incompressibility. It is found that the increase of bulk modulus which leads to more incompressibility causes stress elevation.

The flow induced vibration in transonic turbomachines is an important and challenging issue in this field. Blades aeroelastic behavior, in addition to the aeroelastic instability, can leads to blades failure, flow instability and reduce efficiency of the system. Aerodynamic behavior of the system should be investigated prior to aeroelastic study. The purpose of this article is an investigation of aeroelastic instability and behavior of a selected turbomachine. For this purpose, transonic flow in Nasa 37 rotor is simulated and verified using CFX software. Then, rotor blade aeroelastic stability is investigated in three operating points; design, near stall and stall using blade forced vibration in the specified inter blade phase angle (IBPA). In order to reduce grid points and consequently, computational time, phase-lagged boundary condition and fourier transformation method is used. Also, in this research, the algorithm of simultaneous structure-fluid grid generation and the solution algorithm of force vibration structure-fluid interaction of turbomachines is codified and introduced in detail. Employment of fourier transformation method in CFX software for aeroelastic simulation is another innovation of this article. The value of the critical inter blade phase angle which is independent from rotor operational conditions, is obtained in the present research. Aeroelastic simulations show aeroelastic instability of Nasa 37 rotor in the stall condition. In this condition, flow entropy is increased rapidly relative to the design and near stall condition. The blade pressure side has more important role in stall aeroelastic instability and needs further attention in re-design phase.

Despite significant improved survival rate in patient with heart failure by Ventricular Assist Devices (VADs), complications related to blood hemolysis and pump thrombosis have challenged the improvement of these devices. Hence, the first step of VADs improvement is studding the flow field and the effect of different parameters on blood hemolysis. Consequently, at the first step of the current study, the CFD analysis of hemolysis in laminar flow inside a pipe and turbulent flow inside a chamber with rotating disc were compared with Analytical solution and experimental results, respectively, and good agreements were achieved. Then, numerical simulation was used to calculate the hemodynamics in one axial and one centrifugal pump as a Left Ventricular Assist Device (LVAD), and a comparative analysis of operating conditions, efficiency and hemolysis index was performed among them. The results showed that the axial VAD had a higher hemolysis index, due to its longer residence time and higher shear stress. The higher shear stress in simulated axial VAD compared to centrifugal VAD arises from its higher operating speed and lower gap size. Furthermore, at the required conditions for blood flow in the human body, the centrifugal VAD has higher efficiency than axial VAD.

Viscoelasticity is a property of materials that exhibit both viscous and elastic characteristics. In linear viscoelasticity, the stress is linearly related to the history function of strain. This paper discusses vibration analysis of functionally graded viscoelastic rectangular plate. The viscoelastic behavior of the plate is modeled using the Zener three-parameter model. Also, the material properties of the plate are graded through the thickness according to the volume fraction model. The maximum stress and strain are calculated based on the linear first-order shear deformation theory and the simply support boundary conditions is assumed at all four edges of the plate. A code is prepared using the Mathematica software to obtain the frequency values and effect of inherent and geometric characteristics of the sheet on natural frequency of the plate. These effects are studied using the tables and graphs represented in the results and discussion section of the paper. The results obtained in this paper are simplified to a functionally elastic plate to compare with those given in the literature search. The comparison of results shows good agreement against data given in literature for both cases.

Dielectrophoresis is a phenomenon with wide application in the cell sorting system, in which, the dielectrophoresis force acts on a dielectric particle located in the non-uniform electric filed is used. In this study, governing equations on this phenomenon is presented and a new method for measuring dielectrophoresis force is developed. This method is based on measuring drag force on particle and solving the equilibrium equations. For this purpose drag force is measured in two directions, parallel and perpendicular to electrodes. To evaluate the method, an actuator has been developed which has paralleled electrodes with 50 μm widths and 50 μm intervals and a PDMS channel with height of 80 μm is mounted on them. In experimental result, the exerted dielectrophoretic force on U-87 tumor cell and white blood cell were measured. Since electrical properties of white blood cells are known, the accuracy of presented method was evaluated by using numerical simulation of their dielectrophoretic force and comparing with experimental results. Experimental results prove that the error of force measurement in traditional models, may be even more than 3 time of the actual dielectrophoresis force, while in presented method the source of this error is eliminated

This paper presents an study and analysis of acoustic wave scattered and radiated from a truncated conical shell excited by an time-harmonic constant amplitude acoustic wave arriving from infinity by specified angle of incidence. The shell immersed in unbounded air and inner face has in-vacuo condition. Donnel-mushtari theory of shell displacement field proposed to investigate the kinetic and potential energy of shell and Hamilton principal is employed to extract the shell dynamic equation. Incident sound wave is considered as plane wave which is an incoming wave solution of reduced homogenous wave equation. The Helmholtz integral equation is use to model the scattered and radiated sound by shell. Boundary element method (BEM) is employed to relate the surface nodal pressure to nodal displacement. Then by combination of BEM and Rayleigh-Ritz method, the coupled structural-acoustic problem is solved and the sound pressure in any point of medium and shell surface is obtained. The final result has been compared with Finite Element – Boundary Element (FE-BE) method and result shows that the analytical result is in good agreement with the numerical FE-BE method. Also the bahaivor of medium fluid is studied by considering air and water as two case of fluid medium

In this paper, an optimal Fractional-order Proportional-Integral-Derivative (FOPID) controller is proposed to control an offshore 5MW wind turbine’s pitch angle in above rated speed. The proposed pitch controller regulates the generator angular speed and consequently the generator power to its nominal value without any knowledge of the model. In order to find the parameters of the controller, a hybrid cost function is proposed, which consists of sum of absolute error signal and absolute rate of control signal in three different wind speeds. The wind speeds are chosen in the beginning, middle and at the end of the interval, thus, the optimized controller is able to show an acceptable performance in whole range of wind speeds, without any demand to nonlinear and complex controllers. To this end, the proposed cost function is minimized using three optimization algorithms: Differential Evolution (DE), Firefly algorithm and Particle Swarm Optimization (PSO). In order to evaluate the robustness of proposed FOPID, numerous wind profiles with different speeds and fluctuations are applied and the results are compared with the optimal integer order PID controller. The comparison demonstrates that the proposed FOPID has more effective performance and robustness than optimal integer order PID.

Concerning the adverse environmental impacts of fossil fuel consumption, many investigations have been performed on choosing more environmentally friendly fuel alternatives and sustainable resources. In this regard, hydrogen is considered to be one of the promising alternative fuels as its combustion features are the most similar to fossil fuels and it also falls into the category of renewable and clean fuels. This article studies the simulation of hydrogen-diesel combustion in heavy duty engine at full load and speed of 1600 rpm. All engine features including speed, spray angle, spray duration and input power are held fixed in the simulation. Variable parameter is the ratio of mass or hydrogen energy to diesel. Depending on input power of diesel, hydrogen is changed from 0% (pure diesel) to 70% (i.e. 70% is supplied from the input power of hydrogen and the remaining 30% from diesel fuel). The results of simulation show that hydrogen substitution with diesel at the best state leads to reduction of pollutants such as nitric oxides, carbon dioxide, unburned hydrocarbon, soot and carbon monoxide to 8%, 14%, 54%, 14% and 70%, respectively. This substitution however causes the reduction of indicated efficiency to 2.8%. Hydrogen substitution with diesel can also postpone the combustion, and resulting to increase PRR and HRR; however, this pressure enhancement does not lead to knocking.

Magnetic levitation systems are widely used in various industries. These kind of systems are usually open-loop unstable and are described by highly nonlinear differential equations which present additional difficulties in controlling these systems in the presence of disturbance and sensor noise. We consider the stabilization and the tracking problems of a magnetic levitation system. In this paper an adaptive fractional order Backstepping sliding mode control schemes is proposed. Backstepping algorithm is based on the Lyapunov theory. The proposed controller in this paper is designed by a combination of a Backstepping algorithm, sliding mode control and fractional calculus to make more degree of freedom and robustness. The stability of the closed loop system is investigated by using the Lyapunov stability theorem and the new extension of Lyapunov stability theorem for fractional order systems. Simulations are performed to confirm the theoretical results of the proposed controller for the magnetic levitation system. The proposed controller is able to reject the sensor noise and disturbance with a chattering free control law. Finally the simulation results of the proposed controller are compared with the adaptive fast terminal sliding mode control.

Centrifugal pumps as a heart of the system which are used to move fluids are used widely in most of the industries and have considerable contribution in the amount of energy consumption, so improving of their performance has been attended for researchers .In this paper the aim of studying is the effect of double splitter blades on pump’s performance numerically and experimentally. Three type impellers have been made as experimental investigation. Pump with this impellers is tested and extracted the performance curve. Also, for investigation of the flow pump has been simulated numerically by ANSYS-CFX commercial code. Numerical method of finite volume with k-ω SST turbulence model for numerical analysis. Numerical and experimental results show reasonable agreement that increasing of head and variation of NPSHR due to adding of double splitter blades. The maximum head increased was obtained related to third type of Impeller about 6.33 percent. Furthermore, third type is selected as best impeller. Also, it is observed that around point of designing of pump the effect of double splitter blades on pump’s performance is more significant and deviation from this point will decrease the effect of it.

In this paper, the elastoplastic buckling of rectangular plates over the Pasternak foundation has been analyzed with the fixed and simply supported boundary conditions. Associated with the uniform loading conditions on the plate by the in- plane compression and tension, the influence of the elastic foundation is investigated in terms of two stiffness parameters; including the Winkler spring and the Pasternak shear coefficients. In order to extract governing equations, two theories are used from the plasticity: deformation theory (DT) with the Hencky constitutive relations and the incremental theory (IT) based on the Prandtl-Reuss constitutive relations. By implementing the generalized differential quadrature method to discrete the differential equations, influences of loading ratio, length to width ratio, plate thickness, and the elastic foundation characters are studied. By comparing the obtained results with the data reported in references, the accuracy of the model is verified. Consideration of results shows that applying the elastic foundation causes to increase critical buckling load. In addition, enhancing the elastic foundation parameters leads to amplifying the difference between buckling loads obtained from two theories, especially in the larger thicknesses. Moreover, according to increasing the plate thickness in the tensile state of the loading, application of the elastic foundation causes to reach plate stress to a value more than the ultimate stress of the specimen.

Airship is kind of aerial vehicles that has been a significant development of scientific research in recent years. Furthermore, stratospheric airship is in group of lighter-than-air aerial vehicles. This device is designed in order to the ability of unmanned autonomous operation with remote control at a height of 22 kilometers from Earth. With the development of control systems, there are still major challenges in this area. In this paper, in order to stabilizing and trajectory tracking of stratospheric airship, nonlinear H_∞ method has been developed. At first, the dynamic model of an airship is introduced and descriptive equations are presented in an appropriate state-space in order to design a controller based on nonlinear H_∞ method. Then the nonlinear H_∞ controller is designed. In the controller the integral of the position error is considered, allowing the achievement of a null steady-state error when sustained disturbances are acting on the system. The external disturbances are considered as aerodynamic forces and torque. This strategy is designed robustness, against of external disturbance. The results are shown that decrease in steady error and stabilizing system against external disturbance and uncertainties. Also for robustifying of designed control, comparison is done with adaptive control. Simulation results in the presence of aerodynamic disturbances, parametric and structural uncertainties are presented to corroborate the effectiveness and the robustness of the proposed strategy.

In this paper, the behavior of free vibrations and buckling of the thick cylindrical sandwich panel with a flexible core and simply supported boundary conditions using a new improved ýhigh-order sandwich panel theory were investigated. An axial compressive load is applied on the edges of the top and bottom face sheets simultaneously. The formulation used the third-order polynomial description for the displacement fields of thick composite face sheets and for the displacement fields in the core layer based on the displacement field of Frostig's second model. In this model, there are twenty seven degree of freedom. The transverse normal stress in the face sheets and the in-plane stresses in the core were considered .For calculated exact solution, according to thick face sheets, all of the stress components were engaged. The equations of motion and boundary conditions were derived via the Hamilton principle. Moreover, the effect of some important parameters such as those of thickness ratio of the core to panel, the length to radius ratio of the core, cumferential wave number and composite lay-up sequences on free vibration response and buckling of the panel were investigated. In order to validate the results, the obtained results were compared with those obtained using finite element ABAQUS software. The advantage of this paper is simplicity, considering face sheets as thick, exact solution and the considering of important terms such as (1_c/R_c ) in equations.

In today’s world, using of biogas is increasing due to its methane content, renewability, and low price. Solid oxide fuel cell is one of the best energy conversion technologies, in order to use biogas and it has a high potential to integrate with the gas turbine. In this paper, solid oxide fuel cell-gas turbine hybrid system, which is fed by biogas is modeled with respect to energy and economic aspects. Maximization of electrical energy efficiency and minimization of total investment cost are objective functions, which are considered to find the optimal design variables of the hybrid system. First, each component of the hybrid system is modeled and validated individually. Then, in order to optimize the hybrid system, multi objective optimization via NSGAII is implemented and optimal values of design parameters of the hybrid system were calculated. Optimal point is obtained using Euclidian non-dimensionalization and LINMAP decision making method in Pareto front. So, optimal design values are 66 percent and 175227.4 $, which are electrical energy efficiency and total investment cost, respectively. In optimal point Levelized unit cost is 6.3 cent per kWh. Finally, in order to determine the effect of design parameters on the objective functions, sensitivity of each design parameters were analyzed using Sobol's sensitivity analysis method. Results show that compressor pressure ratio has the maximum effect on electrical energy efficiency. Furthermore, turbine isentropic efficiency and fuel cell current have the maximum effect on the total investment cost.

The composite conical lattice structure in this paper made of helical ribs and thin outer skin. In this research, free vibrations of these structures with and without outer skin were investigated. A smeared method is employed to obtain the coefficients of stiffness of conical shell. Theoretical formulations are based on sander thin theory of shell. For verification of the analytically obtained results, using ANSYS software the 3D finite element model of composite lattice conical shell is built and analyzed. To verify the accuracy of this method, comparison of the results are made with numerical results from ANSYS Software and show a good agreement between them. Also, some special cases as influences of the semi vertex angle and thickness of the outer skin on the natural frequencies of the conical shell are studied. It is concluded that, the increasing of the semi vertex angle leads to increasing the natural frequencies of conical shell. Moreover for outer shell thicknesses greater than a specific value, the increment of the thickness of the outer skin leads to decreasing the natural frequencies. Because of few researchers investigated merely vibrational behavior of the composite lattice cylindrical shell, the obtained results of this paper have novelty and can be used for further and future researches.

One of the new lubrication methods in machining processes is Minimum Quantity Lubrication (MQL). In this method, a very small amount of fluid by compressed air creates a spray and is used as lubricant. One of the advantages of this method compared to conventional (wet) lubrication is the reduction of environmental pollution and undesired effects on operator health. In the present study, the effect of minimum quantity lubrication on surface roughness in hard turning of 100Cr6 bearing steel has been investigated and compared with dry and wet machining methods. To perform MQL, some equipment have been added to the lathe machine. The tool used for material removal of 100cr6 steel is Nano-CBN that is a new generation of CBN tools with Nano technology. All experimental tests performed in dry, wet and MQL conditions. For investigation of surface roughness, each of cutting parameters include cutting speed, feed rate and cutting depth were selected in three different levels and all possible combinations of these parameters has been tested. According to experimental results and analysis of variance, feed rate 68%, lubrication method 14%, cutting speed 4% and cutting depth less than 1% affected on the surface roughness. The obtained results showed that the surface roughness in MQL method has been averagely decreased 42% and 30% in comparison with dry and wet machining, respectively.

In this study, dynamic and heat transfer equations of two-dimensional laminar plane and axisymmetric stagnation flow are solved by Optimal Homotopy Analysis Method, Boundary Knot-Homotopy analysis method and compared by numerical solution. The optimal convergence-control parameter value is calculated using Chebyshev points. These points are corresponding to the range of solutions to get the best answer for both flows. Boundary Knot Method gives the best initial guess that applies in terms of primary answer of homotopy analysis method. Results are reported by the 50th order approximation. Also, it is considered that the total numbers of knots on the domain and the boundary is 40. It is shown that results have a good agreement with the numerical solution. The stream function, the velocity function, the shear stress function and the temperature distribution for small Prandtl values is shown for plane and axisymmetric stagnation flows using BK-HAM compared with the numerical solution. It can be found that, with increasing vertical distance, because of decreasing the effects of wall, the fluid shear stress will be reduced. Also the temperature distribution in the boundary layer changes linearly with distance from the wall. Also, increasing the Prandtl number and decreasing the thermal boundary layer thickness is leading to increase temperature distribution.

In this paper, an implicit finite element-discontinuous Galerkin method for compressible viscous and inviscid flow is developed using Newton-Krylov algorithm with the objective of increasing the accuracy and convergence rate. For inviscid flows, an artificial viscosity is implemented in sharp gradient flow regions especially at high-order cases, increasing the accuracy of the solution. Moreover, for viscous flows, the accuracy is improved by using compact discontinuous Galerkin discretization method for elliptical terms. To reduce the computing CPU time and increase the convergence rate, an iterative Krylov type preconditioned linear solver is applied. For preconditioning, restarting, Block-Jacobi and block incomplete-LU factorization are employed for solving the linear system of the Jacobian matrix. The Jacobian matrix is constructed via finite difference perturbation technique. In this context, the performance of preconditioning matrix for three types of flow regimes of inviscid subsonic, inviscid transonic and viscous laminar subsonic are studied. In addition to complete the discussions, multigrid smoother with special conditions is applied for all preconditioning matrices. To improve the solver performance for higher order discretization, a lower order solution may be used as higher orders initial condition. Therefore, a middle phase is needed to transfer calculations from low to high order discretized domain and then the final Newton phase is continued. In addition, local time stepping is implemented to improve the rate of convergence. Consequently, the presented numerical method can be used as an efficient algorithm for high-order Discontinuous Galerkin flow simulation, especially for transonic inviscid and laminar viscous flows.

Due to easy manufacturing technology and implementation of passive micromixers in a complex microfluidic system, in this study, a type of passive micromixer has been investigated. Passive micromixers increase the mixing rate by increasing the contact surface of two fluids and reducing the distance of molecular diffusion. In the present study, numerical analysis of an L-micromixer has been performed to investigate the mixing behavior and characteristics of fluid flow with changes in key geometrical parameters at four Reynolds numbers. Three non-dimensional geometrical parameters, i.e., normalized length (ZR), length ratio (LR), and aspect ratio (AR) have been defined. Simulations have been performed at the Schmidt number of 900.18. The Reynolds number has been also selected in the range of 50 to 200. A mixing index has been used to quantify mixing behavior in the microchannel. The accuracy of simulation done has been proved by comparing current results with the results of other valid studies. The results reveal that mixing index and pressure drop in a serpentine channel are sensitive to the changes of geometric parameters of the microchannel, and showing different behavior at various Reynolds numbers. Furthermore, due to the sharp 90° turns in the microchannel, the inertial force is large enough to cause vortices, which leads to chaotic advection.

In-stent restenosis is one of the important inefficient reasons about Drug Eluting Stents (DESs). Awareness of how polymer coated drug distributes by these devices provides valuable informations about its efficacy. Porous media theory has been employed in the modeling of drug polymer and the injured arterial wall composed of media and adventitia. The stabished coupled PDEs describing local pharmacokinets of heparin has been solved numerically by finite volume method. Two approaches, single phase and two phases models, has been chosen for coating and the effect of local mass non-equilibrium dynamics in the coating on drug distribution has been evaluated by allocating three magnitude for solid-liquid transfer time characteristic. Moreover, the effect of lost drug by vasavasorum and microcapilaries has been considered as well as cell metabolism. The results show a significant change in drug concentration distribution in the presence of phase change happening. Reducing in solid-liquid transfer time characteristic is associated with drastic reducing in both drug egression from polymer and wash out from adventitia and has a pleasant effect. Also, consumtion of drug declines concentration level in the wall dramatically, specially in adventitia.

A nonlinear model for Autonomous Underwater Vehicles is proposed. In order to describe a more precise dynamic behavior, the nonlinear model for both Lateral and Longitudinal subsystems is derived based on all applied forces and moments. The proposed model can be explained as an extended linear model for AUV in depth and azimuth motions where some nonlinearities are taken into account. Due to some practical issues as well as the form of proposed model, the identification problem based on Least Square method is formulated to achieve the system parameters. By considering unstable dynamic of system, the open loop system cannot be excited. In this case, the PID regulators with simple tuning parameters are proposed in both Lateral and Longitudinal subsystems and the identification problem by utilizing sinusoidal inputs is followed within a feedback loop. Based on measurable variables i.e. linear moments, angular velocities and Euler angles, and utilizing some dynamic filters, the Least Square method is then applied to estimate the model parameters. The effectiveness of proposed nonlinear model as well as the parameter identification approach are finally demonstrated through some numerical simulations.

The steady flow test rig is a device for in-cylinder swirl and tumble flows velocity measurement and the analysis of the flow performance of cylinder head (intake and exhaust ports), manifold and carburetor in internal combustion engines. The test rigs can also to maintain quality control on parts for various gas turbine components. In this study we have investigated the effect of pressure on in-cylinder swirl flow velocity in the steady flow test rig which is equipped swirl meter with experimental and numerical simulation methods. The repeatability of experiments and the uncertainty analysis are performed to ensure the quality of the measurements. Three dimensional numerical simulations are applied by using the finite volume method by the ANSYS Fluent software. The flow around the swirl meter is simulated by moving reference frame method. The simulation results show good agreement with experimental results and also due to limitations of operating conditions of the rig this simulation approach can compensate the limitations of operating conditions of test rig. In this work it is showed that correlation between given rotational speed to the swirl meter and torque applied on it, is a linear function of rotational speed. The study also showed that by increasing the pressure, in-cylinder swirl flow velocity increase and created correlation between swirl flow velocity and pressure difference can be approximated by an exponential function.

In the case of presence of deep micro-cracks within the composite structures, they must be replaced. The self-healing phenomenon which is inspired from the biological systems such as vascular networks in plants or capillary networks in animals, is an appropriate strategy to control the defects and micro-cracks. In the present research, by taking accounts the advantages of self-healing concept, an attempt has been made to control the micro-cracks and damages which were created in composite structures. To do so, series of micro glass tubes were employed to provide a self-healing system. These micro-tubes were filled with epoxy resin/anhydride hardener as a healing agent. When the structure is subjected to loading conditions, some damages or micro-cracks are created. In this situation, the micro glass tubes will rupture and the healing agent flows in the damage area, leading to the elimination of the defects over a time span. The aim of this study is to find out the appropriate self-healing material volume fraction and healing time to obtain an efficient healing. For this purpose, glass micro-tubes containing various healing agent loadings of 0.75, 1.65 and 2.5 vol.% were incorporated in epoxy-carbon fibers composites and the tensile behavior of the specimens were assessed during different time span from defect creation. The highest tensile strength recovery of 89% was observed for the specimen with 1.65 vol.% healing agent. Also the results show presence of micro tube decrease the fracture strain and over the time span fracture strain recovered.

In the present paper a numerical simulation based on the LBM is performed to analyze a viscous micropump with a single elliptic rotor. The effects of three important geometric parameters including aspect ratio of rotor, micropump height and rotor eccentricity are investigated on the average flow rate and entropy generation. The obtained results from the simulations are analyzed by response surface method (RSM). The results indicate that the average flow rate increases by increasing the aspect ratio and rotor eccentricity and decreases by increasing the micropump height. Moreover, the sensitivity of the average flow rate to changes of aspect ratio and eccentricity is more than the change of microchannel height. The results also show that by increasing all three geometric parameters, the average entropy generation increases and is sensitive to changes of three geometric parameters. Finally, the optimal geometric parameters are determined by RSM that for maximizing the flow rate, the optimum values of 1, 1.5 and 0.9 are for aspect ratio, height and eccentricity respectively and for minimizing the entropy generation, the optimum values of 0.2, 1.5 and 0.1 are achieved.

In this study, the effects of attack angle in opposing jet injection through supersonic blunt bodies on drag reduction and distribution of surface temperature is studied through developing a three dimensional multi-block code. Inviscid terms are calculated by AUSM scheme. The viscous terms is obtained by central difference method and using 4-stage Rung-Kutta algorithm, integral time is computed. Shear stress transport model is used to simulate the effects of turbulence. The effects of pressure ratio and properties of flow field have been verified and validated with experimental and numerical results of other researchers which is indicator of method accuracy. The results show that the sonic jet injection is able to significantly reduce drag nose by changing the shape of the bow shock and it also prevents a sharp increase in the surface temperature by covering the body. Increasing the total pressure ratio, improved performance of jet in both drag reduction and distribution of surface temperature. However due to the sharp increase in retro propulsion of jet there is a limitation in increasing the ratio of total pressure. In addition, the increase of pressure ratio will reduce the friction coefficient. Angle of attack of the free stream reduces the efficiency of the jet injection. Although in this situation the result can be improved to somehow by paralleling the jet and free stream.

The medium caliber armor piercing projectiles, commonly being used against armored and aerial targets, have high kinetic energy and in practice, it is impossible to prevent these projectiles from penetration through different types of targets. So this is essential to demonstrate a solution to repel these projectiles by studying on behavior of the targets. In this study, numerical simulation of oblique penetration of medium caliber armor piercing projectile through the flat targets of GLARE3 2/1 and GLARE5 2/1 has been investigated by ABAQUS finite element software, and using explicit-dynamic solver. 625m/s and 1250m/s strike velocities and 0, 30, 45, and 60 degree strike angles have been studied. Damaged area have been investigated. To verify the solving method, an experimental equation, which has determined the penetration energy of a thin GLARE target, has been used. Results have shown that some special phenomena (e.g. asymmetric petalling, and small-cracks formation) appear when penetration occurs obliquely. This is also has been shown that lower strike velocity, and higher strike angle will result in higher target damage. Furthermore, delamination of target has been investigated.

In this article, a novel method, namely full modified nonlocal (FMNL) theory, for analysis of nano structures under different case loading. Also bending analysis of rectangular nano plates and nano beams are investigated in order to demonstrate the effectiveness of the presented theory. For this purpose, a complete representation of governing equation and boundary conditions are derived based on the infinite series of modified nonlocal constitutive equations by applying the variational principle. It is shown that by rearranging and then computing the sum of the infinite series which appears in the maximum bending deflection, the truncation errors will be eliminated. In addition, the results of the presented method are compared with MD simulations to confirm the validity of FMNL theory. One of the advantages of the FMNL theory is that the defect of nonlocal (NL) theory in vanishing of small scale effect for some problems can be resolved. Furthermore, the FMNL theory will be a criterion for accuracy of the primary modified nonlocal (PMNL) theory that considers only two terms of the series of the modified nonlocal constitutive equation in predicting maximum bending deflections.

The main aim of this paper is the numerical investigation of air-fuel mixture formation and spray and combustion characteristics of EF7 engine equipped with spray-guided direct injection system. For this purpose, first, a six-hole injector is simulated in three different injection pressures and to validate the fuel injection characteristics, the results are validated against the Istituto Motori-CNR experimental data. Then, the injector position is selected near the spark plug and by changing of injector angle relative to the axis of combustion chamber, the appropriate angle for optimization mixture formation is obtained. Then, the effect of injection pressure, start of first and second injection as well as the effect of two-stage fuel injection with different proportions of fuel mass at primary and secondary injection are studied on the mixture formation, wall film and engine emissions. The results showed that the injector angle is extremely effective on the mixture formation, pressure and the amount of unburned hydrocarbons due to its direct impact on wall film mass. Also, in the two-stage injection, relatively homogeneous lean mixture compared to the stratified mixture results better combustion at part load condition.

In this paper, an exact analysis of thermal post-buckling behavior of eccentrically stiffened functionally graded (FG) thin circular cylindrical shells subjected to thermal radial loading and surrounded by elastic foundation, is presented. Stringer and ring stiffeners are assumed to be placed on the inner surface of the FG cylinder shell and the material properties of the shell and stiffeners are assumed to be temperature dependent and continuously graded in the thickness direction. The elastic medium around the circular cylindrical shell is modeled by a two parameter elastic foundation based on the Winkler and Pasternak model. Fundamental relations and equilibrium equations are derived based on the smeared stiffeners technique and the classical theory of shells according to the von- Karman nonlinear equations. By using the Galerkin method, the thermal post-buckling response of eccentrically stiffened FG thin circular cylindrical shells are obtained. In order to validate the method, the obtained results are compared with available solutions and in continue, the effects of different parameters such as volume fraction exponent, number of stiffeners and elastic foundation parameters, on the thermal post-buckling response of eccentrically stiffened FG thin circular cylindrical shells are considered. Numerical results show that stiffeners and elastic foundation enhance the stability of the FG shells. Moreover, increasing the shell thickness, reducing the volume fraction index, increasing the number of Stringer and ring stiffeners and applying stiffer elastic foundation lead to increase the thermal post-buckling response of stiffened FG circular cylindrical shells.

In the pultrusion process, continuous fibers reinforcement in roving forms are drawn through a pultrusion die. Therefore, the fibers reinforcement in the final product are generally oriented in the longitudinal axis. In this research, for manufacturing of composite rods, on the basis of previous studies and researches, the E-glass fiber-polyethylene prepregs were produced firstly. Then due to the Design of Experiments (DOE), the pultruded rods with unidirectional and helically-wound layers were produced by using the prepregs. In this study, mechanism of the pull-winding process is created as a secondary process during the main process to improve the mechanical and physical properties in the other directions. One of the most important issues in the thermoplastics pultrusions is the fibers impregnation quality with the polymer base. The fiber volume fractions of the productions are found by the burn tests. The density of the specimens is found by the liquid displacement method. The microscopic images were taken from cross-section of the pultruded rods to investigate the fiber impregnation and the void distribution. Due to the surveys conducted, the fiber volume fractions in the pultruded rods was increased, using the pull-winding technique, and also the void content of these rods was decreased.

In the present study, adsorbent bed of an adsorption chiller with finned flat-tube heat exchanger has been simulated three dimensionally based on the heat and mass transfer model with finite volume method. To examine the inter-particle mass transfer resistance effects on the system performance parameters, two different configurations of adsorbent bed including rectangular and trapezoidal fins with identical length and adsorbent mass have been considered and the effects of bed length on the system performance for different fin height and fin pitch have been studied. Moreover, effects of bed length for different particle diameters and also heating source temperatures have been investigated. Results indicated that increasing of bed length (or in the other words increasing of inter-particle resistance) increases and decreases cycle time and specific cooling power, respectively, yet the coefficient of performance is not influenced. Also, increasing bed length reduces the difference between specific cooling power of rectangular and trapezoidal beds if there is any. Moreover it is clear that optimum particles size increase with bed length increase. Finally, it is shown that effect of higher heating fluid temperature on specific cooling power improvement for beds with smaller length is more significant than those with longer length.

This work presents the numerical results on reduction of sulfur emission from combustion of heavy oil in a combustion chamber. One of the most practical methods for sulfur emission reduction is flue gas desulfurization (FGD). In this study various FGD absorbers have been studied by means of numerical simulations. The flow is assumed turbulent two-phase flow while gas is the continuous and droplets form the dispersed phase. Heavy oil with considerable sulfur contents has been used as the fuel. The results show that, the Na-based absorbers are more efficient than the calcium-based absorbers. In addition, it is found that the efficiency of Sodium bicarbonate (NaHCO_3) is about 96% while the efficiency of calcium oxide (CaO) is about 74%. The efficiency of the Na-based absorbers is higher than the Ca-based absorbers due to the low density of Na-based absorbers. The low density of Na-based absorbers leads to a better dispersion of the absorber particles. The second reason for higher efficiency Na-based absorber is lower activation energy compared with Ca-based absorber. In addition, the mixing of Na-based absorbers dominates the mixing of the Ca-based absorbers. Thus, the reaction efficiency and kinetics of Na-based absorbers dominate in the same conditions with Ca-based absorbers.

To investigate the effects of drugs on viruses, interactions between proteins and inserting desirable genetic changes on DNA, precise study of biological cells is a necessary demand for nowadays. In this way, exploring mechanical properties of these particles and their mechanical behavior in different situations is needed; manipulation of bioparticles in nano scale is an important process for investigating nanoparticles behavior; because the amount of exerted force, deformation and investigating the damage possibility can provide useful information. In this paper, a molecular dynamics modeling of bioparticles nanomanipulation based on AFM has been done. Bioparticles include virus, protein and ssDNA. The main goal of this study is investigating the substrate effect on exerted force on the bioparticles and exploring damage possibility. Three types of substrates have been used, including silicon, graphene sheet and golden substrate. Widespread usage and low level interactions with other materials are the reasons of choosing these substrates. Results show that on gold substrate, the maximum manipulation force occurs and damage possibility is high. Also on graphene substrate manipulation force and deformation of particle are more than the silicon substrate.

In recent years, various studies about non-Fourier heat transfer in various media including porous media have been performed that have provided ýcontradictory results. In this article, the non-Fourier heat transfer in the porous media, especially the sand has been examined. In this regard, the ýnumerical solution of a non-Fourier thermal conductivity with a pulsed heat flow boundary condition has been studied and this condition for the non-ýFourier models has been discretized and applied in the non-Fourier manner. In this way, first, the governing equation for the DPL model has been ýsolved with an explicit finite difference numerical method and its results have been studied and compared with the experimental data [1]. However, in ýthe process of numerical solution of the DPL model, the grid study has been performed before anything. Also, the Single-Phased Lagging (SPL) ýmodel has been solved with an explicit numerical method and its results have been compared with the results of the DPL model and the experimental ýdata. In this article, like the reference [1], it has been shown that the DPL model can model the non-Fourier heat transfer so much better that the ýCattaneo’s model. ý

Cold roll bonding process, as a solid phase method of bonding same or different metals by rolling. In this study, for the first time, formability of two-layer aluminum strips fabricated by the CRB process are investigated by Nakazima tests and experimental. To produce two-layer aluminum strips using a rolling machine and apply thickness reduction was %50 at room temperature. Mechanical properties, tensile fracture surfaces were studied and compared. It was observed that strength and microhardness 149.5 and 80% increased respectively, but elongation and ductility decreased compared to the initial strip due to strain hardening and cold work. Also results of SEM demonstrated that after CRB process, ductile fracture accompanied by dimples samples and shear zones were observed.

In the present work, the effect of using four types of nanofluid including alumina/water, titania/water, silver/water, and copper/water, in volume concentrations of 1% to 4% within a shell and tube heat exchanger in three thermal loads has been investigated. This study is done based on investigating of 102 design cases concerning industrial experiences and Tubular Exchangers Manufacturer’s Association Standard (TEMA) requirements. The thermo physical properties of nanofluid have been taken as temperature dependent and calculated by use of proper valid experimental formulas. Most of the results show that using nanofluid will always cause enhancement in performance of heat exchanger and utilizing it in shell side is preferable, regardless of size of heat exchanger.