JOURNAL OF MECHANICAL ENGINEERING
Year:2018 | Volume:48 | Issue:2 (83) |Papers Count:40

This paper presents experimental and numerical evaluations of convergent-divergent stators overlapping degree effects on an impulse supersonic turbine performance. The studied model is a small turbine with a large pressure ratio that is being used to produce high specific work output in the liquid propellant engine. Because of a low-mass flow rate, the turbine is used in partial admission condition. The turbine stator is a group of convergence-divergence nozzles that provide the supersonic flow. Five stators with different NAA are modeled and tested. In the turbine performance prediction code, an empirical efficiency relationship is used. This relationship is corrected in the turbine test rig that is designed by the author. The results of prediction code and numerical and experimental tests show that the NAA has a significant impact on the three-dimensional distribution of the flow in the stator downstream. The flow loss distribution and the turbine performance are changed as a result of the flow pattern changing.

Structural integrity assessments of pipelines play a key role in the design and safe operation of these structures. Pipelines are sometimes subjected to bending and tensile deformations, which places the girth welds in tension. Girth welds may contain weld imperfections and small flaws. Therefore, assessment of girth weld resistance against crack propagation and fracture is very important. In this study, the KIC toughness has been determined for girth weld metal of API X65 gas pipeline, following the ASTM E1820 standard. The fracture toughness tests employed side grooved and fatigue pre cracked compact tension specimens, which were made by plates extracted from the original pipe and welded to each other under the same welding condition as that employed for girth welding during construction of main natural gas transmission pipeline in Iran, to determine the crack growth resistance curves based upon the unloading compliance method using the single specimen technique. From these, KIC value of 166 MPam1/2 was obtained for girth weld metal.

In this paper, a new integrated power system based on biomass gasification and solid oxide fuel cell with low temperature gas cleaning system is proposed and the performance of the system is evaluated using thermodynamic calculations. The proposed system includes a gasification unit, a gas cleaning unit, a SOFC-GT hybrid system and an organic Rankine bottoming cycle. The generated raw syngas need to be purification before it can be used in SOFC system. For this reason, low temperature gas cleaning system is selected. A sensitivity study is carried out to investigate plant responses to different working parameters. The results obtained indicate that for the current system, the gross and net energy efficiency of the system are 54. 56% and 50. 55% respectively, while the gross and net exergy efficiency are 48. 57% and 45. 08% respectively. The proposed system has been modeled using Cycle-Tempo software.

The effect of installation sequence and center-to-center distance between pins on distribution of residual stresses and edge crack growth of single hole specimens under the fatigue loading are investigated. Hole edge cracks are observed in some industrial components similar to gas turbine casing. Residual stresses distribution induced in three-dimensional holes analyzed and redistribution of residual stress in adjacent holes are investigated. Finite element (FE) analysis on specimens similar to gas turbine casing of ductile cast iron were conducted and the behavior of material was assumed elastic– perfectly plastic. Mechanical fatigue crack growth is predicted by using Abaqus software and Zencrack fracture mechanics code. The results show that the mechanical fatigue life affected by variations in the installation sequence and distance between pins. When the second pin is installed, a residual stress relaxation process occurs near the first hole due to the secondary yielding produced by the expansion of the second hole, this redistribution of residual stress caused a decrease of fatigue life near first hole. Consecutively, the results from the numerical predictions were compared with the experimental data.

In this study, a fuzzy inference system based on look up table was used for modeling and predicting the diffusion coefficient of benzoic acid in the water based γ-Alumina and Silica nanofluids. Due to evaluate the designed fuzzy system, Nanofluids Diffusion coefficients of benzoic acid at constant temperature of 20 ◦ C were measured with using a simple and inexpensive technique. The results revealed that the designed fuzzy system could accurately mimic the diffusional mass transfer in nanofluids. The deviation between fuzzy model and experiments for γ-Alumina and Silica nanofluids were about 0. 939 and 0. 997, respectively. The measurements showed that nanoparticles at low concentration did not have a significant effect on benzoic acid diffusion in nanofluids relative to that in pure water. But diffusion in silica nanofluids strongly reduced at high concentration of nanoparticles, as in volume fraction of 0. 8% diffusion coefficient decreased up to 35% relative to that in base fluid. Such factors as the type of tests to determine the diffusion coefficient in nanofluids, nanoparticles concentration and type, could strongly influence of diffusional mass transfer in nanofluids.

In this study, effects of the aerocyclone outlet diameter on its performance are studied. The Reynolds Stress Model (RSM) model has been used in order to predict the turbulent flow patterns inside the aerocyclone and its droplet removal efficiency. The Eulerian-Lagrangian method was used for gas droplet flow simulations. Due to the precessing vortex core (PVC), unsteady simulation of the flow is performed for duration of 0. 73 s. The results show that for smaller diameter of the outlet pipe, the gas flow pressure loss and tangential velocity are increased. Also, by decreasing the outlet diameters of aerocyclone (e. g. at the velocity of 10m/s) the Euler number increases. Increasing in the velocity can change the Euler number significantly. The wall reflection term effects (in RSM model) on the flow field and droplet trajectories are studied. By implementation of wall reflection effects, the numerical results approach to the experimental data. The simulation results show that the cyclones with the smaller outlet diameter has the higher efficiencies at different velocities than others.

Regarding to the vast application of composite materials in the modern and advanced industries, accurately predicting the fracture and damage behavior of these materials is very important. Carrying out less and simple experiments leads to reducing the cost and time, therefore, designing and analyzing of the above mentioned materials need to find and applying the fracture and damage criteria. In the Iran country, these materials are more used for manufacturing the aircraft and for this reason, in this research airfoil piece is selected and simulated. For this aim, The Puck, Tsai-Wu, and Sun damage and fracture criteria are implemented into the ABAQUS commercial software, employing an implicit subroutine. After the simulation of the airfoil, the damaged zones and critical points of the airfoil are predicted by the three mentioned criteria, results of the numerical simulations are compared with the experimental results and validated. Comparison of the numerical and experimental results reveals that the predicted results of the Puck's damage criterion is closer to the practical results and is more reliable for predicting the damage in the airfoil loading test.

This paper presents a control algorithm based on pure fuzzy method for attitude control of the quadrotor. Error and error rate are the input parameters of the fuzzy system and control inputs will be generated based on predetermined fuzzy rules. Based on the nonlinear dynamics of quadrotor, fuzzy controller provides a satisfactory response for stabilization and attitude control of the robots. To study the performance of fuzzy control algorithm, a set of sensors and the quadrotor is used in the experimental model. The system consists of accelerometer and gyroscope sensors and a microcontroller which is used to design fuzzy attitude controller for the quadrotor. Three-axis gyroscope and accelerometer sensors are used to estimate the angular position of the quadrotor. Considering that the experimental data has lots of errors and noises, Kalman filter is used to reduce the noises. The experimental results indicates the successful design of fuzzy controller for the quadrotor.

In this paper, the effect of adding hydrogen to the performance of D87 gas engine has been discussed. The base system is an engine with power of 1000 kW and rotational speed of 1500 rpm which by changing the fuel system and compression ratio from 15 to 11. 5 it is modified to a gas engine. Among many additives, hydrogen with its unique criteria seems to be the most promising additive which can significantly reduce fuel consumption and harmful emissions in internal combustion engines. It seems, the hydrogen is the best additive among various cases, which can greatly reduce fuel consumption and harmful emissions in internal combustion engines. Here the effect of adding different mass ratios of hydrogen fuel to natural gas fuel flint to see a change in behavior of flint fuel is examined. In this paper, the hydrogen mass ratios of 0, 0. 002, up 0. 014 are considered which is equivalent to adding 50% of chamber imported energy and according to these points the optimal point has been determined based on performance and pollution viewpoints. By considering these viewpoints, the optimal point of 0. 006 for mass ratio of hydrogen which is equivalent to adding approximately 18% energy to the combustion chamber is achieved. Then the appropriate ignition timing for 0. 006 of mass ratio with advance and retard of the ignition timing is estimated. The results show that 3 degree for advance of ignition timing is suitable for this mass ratio.

One of the most appropriate methods for providing compressive residual stresses in the surface layer of parts is low plasticity burnishing that can increase fatigue life of metals. Low plasticity burnishing reduces or completely eliminates surface tensile stresses, without optimizing the environment, materials or design components. During this process, a free-rolling ball with proper vertical load is moved on the work-piece in order to create plastic deformation and compressive residual stress. In this study, finite element modeling of the process on Aluminum Alloy 7075-T6 shaft is presented in two conditions, single and double ball. Effect of the process on residual stresses and fatigue life of work-piece by strain-based approach is investigated. Results show that, using double ball instead of single ball in this process can increase axial and radial compressive residual stresses up to 1. 5. Also, residual stress depth in double ball condition is higher than single ball condition. The fatigue strength in the work-piece with double ball LPB against without LPB and single ball is increased 3 and 2 times, respectively.

In this research the effect of roughness on airfoil sections with one dimensions hot-wire anemometer has been studied. The factors of oscillating and the average time of flow velocity was measured for two positions. Soft and rough surfaces in 5 and 10 m/s speed, also changes in the drag coefficient was obtained and examined in two modes. For measuring the parameters the sequence method (experimental) for calculating the speed component measurements have been performed without dimension at x/c=0. 01, 0. 5, 1, 2 and 3 (c means chord length and x means distance from the back of airfoil) was used. According to the graphs and results of experiments it is observed that with increasing distance from the longitudinal direction the width of the trail increased more surface will affect. Also moving away from blade in the longitudinal direction makes minimum speed peaks spread eventually it will go away but in case of a rough surface width of the trail increase and to achieve free-stream velocity we need more distance from blade.

In this research, procedure of aerodynamics design for hypersonic wind tunnel test section is investigated by using computational fluid dynamics. The type of test section is chosen closed-type free jet. First, conceptual design is done by using the available statistical data in the hypersonic wind tunnel test section in the world. Then, quality of design is investigated by numerical simulation by solving Navier-Stokes equations in compressible, viscous (k-w SST model) and axisymmetric form. With changing the parameters of the test section, the test section dimensions have been optimized. The important parameters in test section are length of the test section, the test section diameter, the diameter of the inlet diffuser, the diffuser and the nozzle indentation inside the test section. Design criteria are chosen the formation of uniform flow, better swallow the slip line and the flow deflection in the test section. Finally, dimensions, specifications and aerodynamics functional requirements of the hypersonic wind tunnel test section have been determined at Mach 5 to 7. The effect of cone and curved nozzles is also investigated for flow quality in test section of wind tunnel.

This paper investigates maximum coefficient of performance and partial load corresponding to it’ s and also optimizing energy for each part load and each size of chiller with any cooling capacity. The condensation temperature and outside temperature are considered as input data. The purpose of this paper is to achieve maximum coefficient of performance with changing the number of condenser fans that depends on the condensation temperature and outside temperature and finding a relationship between cooling capacity chiller, outside temperature and the chiller partial load in different sizes. The range of the maximum coefficient of performance is 0. 7 to 0. 8. In other partial load range, maximum coefficient of performance will be less though energy consumption is also higher. Also with increasing ambient temperaturefrom 30° C to 50° C, COP coefficient is reduced about 2 units.

In this study the steady dimensionless temperature and convective heat transfer in the vicinity of stagnation point flow of a nanofluid along with uniform transpiration 0 U on a Stationary cylinder have been investigated. The impinging free-stream is steady and with a constant strain rate k. Similarity solution of the momentum and energy equations is derived by use of transformations introduced in this research. Self-similar solution is obtained when the wall temperature of the cylinder or its wall heat flux is constant. All the solutions are presented for Reynolds numbers f Re  ka 2 / 2 ranging from 0. 1 to 1000 for different values of dimensionless transpiration, S U k a o  /, and selected values of particle fractions where a is cylinder radius and f  is kinematic viscosity of the base fluid. Results show that for all Reynolds numbers, as the particle fraction decreases or suction rate increases, the depth of diffusion of the fluid velocity field in radial direction, the depth of the diffusion of the fluid velocity field in-direction and shearstresses increases as well as by increasing the particle fraction or suction rate, heat transfer coefficient and Nusselt number increases.

A thermodynamic analysis of a flash/ORC geothermal plant using zeotropic mixtures as working fluid is carried out to investigate and improve the performance of the system from the viewpoint of first and second laws of thermodynamic. The mixtures of three hydrocarbons (Hexane, Cyclohexane and Isohexane) with two refrigerants (R245fa and R236ea) are investigated as the working fluid of organic Rankine cycle (ORC). Variation of first and second laws efficiencies, net output power and exergy destruction as a function of the mass fraction of refrigerants from 0 to 1 is reported. The results showed that the first and second laws efficiencies maximized at a specific value of refrigerant mass fraction. Also, the net power output of ORC shows an optimum amount by changing the refrigerant’ s mass fraction. Furthermore, exergy destruction in evaporator which is the main source of exergy destruction in ORC has its lowest value in the average amounts of refrigerant mass fraction. According to the results, Cyclohexane/R236ea mixture with a ratio of 0. 6/0. 4 represents the best performance from the viewpoint of energy and exergy which leads the system net output power production of 7. 31 MW.

Investigation of forced convection heat transfer of nanofluid with different distribution functions inside a duct is the subject of this article. The dispersive elements or nanoparticles can be distributed with different distributions such as parabolic, exponential and uniform functions. Injections of nanoparticles with various distribution functions into the fluid regime are compared to achieve maximum heat transfer. Due to the many applications of the parallel plates channel and also the pipe, as the flow duct, the numerical results for these two geometries are presented and compared. For a complete and useful comparison, the number of the dispersive elements is the same for each arrangement. For each of the distribution functions, the energy equation is dimensionlessed and solved numerically. The validation of results is verified by the analytical solution for a simple status of the problem. The presence of the nanoparticels with parabolic distribution and increase the particle size index decrease the Nusselt number and heat transfer characteristics with univocal form. For the exponential arrangement, increase the particle size index lead to an ascending-descending behavior for Nusselt number. Therefore in this distribution, the optimum size for dispersive elements is obtained.

In this study, effect of chromium addition on the fracture toughness of Hadfield steel was investigated by using charpy impact test. For this purpose, 3 casting blocks were prepared from Hadfield steel (without Cr addition, and containing 1. 5% Cr and 3% Cr) by using coreless induction furnace. After casting, all blocks austenitized in 1100° C for 2 hours and immediately quenched in the pure water. In the next step, uniaxial tensile test, hardness test and charpy impact test were applied on specimens. Evaluation of the microstructures was conducted by optical microscope and the fractured surfaces were observed by scanning electron microscope. The results of charpy impact test and fracture toughness empirical relationships were used for determination of fracture toughness values of specimens. As a result, it was found that sample without Cr had lowest hardness – highest fracture toughness value – highest critical crack length and the sample containing 3% Cr had the highest hardness – lowest fracture toughness value – lowest critical crack length. Also, scanning electron microscope images indicated increasing crack growth in the charpy impact test specimens by addition of Cr to chemical composition of Hadfield manganese steel.

In the present work, the effect of number of blades of a turbocharger is investigated numerically. First, the geometry of impeller and volute of Garrett T25 turbo compressor is acquired using 3D scanning. Then the acquired geometry is modeled in Ansys software. The flow is acquired for a compressor with default number of blades (6 blades) first, and the number of blades is changed to 5 blades. This study is also done for 4 and 7 blades. The effective area is increased when the number of blades is decreased, so the compressor is chocked later. As a result, mass flow can increase in a compressor with fewer blades. On the other hand, slip factor and transferred power to fluid are augmented when the number of blades is increased, while the power and pressure ration is decreased when the number of blades is more than 6 blades. The acquired results show that the optimum performance of the compressor is obtained in a compressor with default number of blades in a wide range of mass flow rate.

In this paper, the simultaneous effect of micro and nano-sized polymers on the hydrodynamic properties of turbulent flow (including pressure lose and friction coefficient) in a horizontal pipe at different Reynolds numbers studied experimentally. In this article, partially hydrolyzed polyacrylamide polymer is used as superfloc A110. In order to perform the comprehensive analysis, experiments were investigated with different concentrations of micro and nano-sized polymers and impact of various conditions on the pressure lose and friction coefficient. The results show that the addition of micro-sized polymers particles up optimum concentration (0625/0% by volume) reduced the friction coefficient. Also adding the nano-sized polymer particles to the solution containing the micro-sized polymer particles at the same time, the friction coefficient is reduced by about 58%. With increasing the temperature of solution up to 30 ° C drag reduction improved.

Nowadays manipulation by using atomic force microscopeis one of the modern methods of construction micro/nano-scale equipment has been of interest to researchers. Because of this method requires detailed and complex processes and involves high costs, before any experimental work should be paid to accurate modeling of this process. The accurate modeling of 3D manipulation process is made of four major parts including the kinematic, dynamic, friction and contact. 3D modeling of static and dynamic manipulation previously has been studied by various researchers, but less attention has been to the frictional and contact modeling. In this paper for the first time, four contact spherical models, including Hertz, JKR, DMT and BCP models for 3D nanomnipulation have been developed and used. The purpose of the application of these models is investigating their effects on critical force and time in 3D manipulation, in order to accurate modeling of motion of nanoparticles on the substrate. The results indicate that, Hertz contact model, because regardless of the adhesion forces, shows the least amount of critical force and time, also the results show that the rolling particles around the x axis is the most likely mode of motion and sliding particle along the x axis is the less likely mode of motion.

Electrohydraulic forming is a pulsed metal forming process that uses the discharge of electrical energy across a pair of electrodes submerged in fluid to form sheet metal. An experimental procedure was developed to quantify the formability in electrohydraulic forming (EHF) that is consistent with the quasi-static formability assessment convention. Furthermore, we investigate the procedure to comparison of theoretical forming limit diagram and experimental results. The experimental EHF forming limit diagram (FLD) was determined for aluminum alloy sheet and circle grids used to determine the minor and major strain in the path of necking on the specimens. Not only good agreement was found between the experimental curve that derived by quasi-static tests and theoretical forming limit curve, but also EHF on aluminum alloy shows formability improvement on major strains including 26% in comparison to low strain rate process.

During chemotherapy children with cancer have a great need for special care and attention. The more familiar they are with the disease and its treatment process affects their collaboration with doctors and psychologists which can improve their condition. Using modern and intelligent technologies like social humanoid robots as a tool for motivation and encouragement could be remedial in this regard. In this study, a humanoid robot with various communication abilities is used to interact with 6 children with cancer, and its impact on the reduction of "distress" due to the disease and the treatment process is explored. Distress in cancer patients results in psychological disorders such as anxiety, depression, reluctance and so on. The variables in the treatment process of children with cancer includes depression, anxiety, loss of appetite, and anger. In this research, the social impacts of a humanoid robot programed to perform specially designed scenarios in 8 therapeutic sessions in the presence of psychologists and specialists have been studied and analyzed. Preliminary results confirm the positive effect of utilizing social robots as co-therapists during the treatment process of children with cancer.

The composition of several different materials is often used in structural components in order to optimize the responses of structures subjected to severe thermal and mechanical loads. Functionally graded materials (FGMs) are suitable to achieve this purpose in the case of pressure vessels. On the other hand these structures usually sustain cyclic loadings resulting in ratcheting and shakedown behavior. In this study the nonlinear kinematic hardening theories are used to evaluate the cyclic loading behavior of a thick walled FGM Cylinder under internal pressure. The power law volume fraction distribution of materials, geometry and mechanical load are assumed to be axisymmetric. The finite element method combined with a multi-layered approach is used to model the structure by ABAQUS software. The response of structure under cyclic loadings is considered. Fredrick & Armstrong nonlinear kinematic hardening theories based on different type of back stress numbers are used to predict the ratcheting and shakedown behavior of the structure. The effects of variation of materials distribution on cyclic behavior are also studied. The achieved results show that using functionally graded material leads to a more flexible design so that cyclic rupture can be improved by selecting a suitable material distribution profiles.

In the current study, the non-Newtonian flow over a cylinder is simulated using the lattice Boltzmann method. Two-dimensional unsteady flow at Re=100 and Pr=20 for different non-Newtonian power-law indices (0. 4≤ n≤ 1. 8) and rotational ratios (0≤ β ≤ 3) is investigated. The effects of dimensionless rotational ratio and the power– law index on the vorticity contour, isotherm contour, local Nusselt number, average Nusselt number, periodic average Nusselt number and periodic-surface average Nusselt number are studied in detail. The results show that the fluid behavior changes from Newtonian to shear-thickening, the isotherms contour become elongated and wide, while the change in the liquid behavior from Newtonian to shear-thinning shows the reverse influence on the isotherm patterns. As dimensionless rotational ratio increases, the fluid and the thermal fields become steady. This behavior occurs in both Newtonian and non-Newtonian fluids. It is found that the increment of the shear-thinning and shear thickening of the fluid leads to the increase and decrease of heat transfer rate of circular cylinder surface, respectively. Results also show that the heat transfer rate of circular cylinder surface decreases with increasing of dimensionless rotational ratio.

Nanoclay is added to rubber formulation to enhance mechanical properties of rubber. In this study, the non-destructive inspection method of ultrasonic waves was used to investigate the nanoclay reinforced rubber formulation. In this method, the time between the transmission and the reflection of ultrasonic waves is measured. Longitudinal propagation velocity is obtained by the thickness of sample divided on time. In this study, an image processing method was used to measure the sample thickness due to the flexibility of rubber materials. By changing raw material composition of the rubber, the physical and mechanical properties of nanoclay reinforced rubber are altering and as a result, the velocity of ultrasonic propagation is changing. To investigate the nanoclay reinforced rubber formulation at first samples with different formulations were prepared and for each of the samples, the propagation velocity of the longitudinal sound waves was measured. Another sample with a new formulation was developed and longitudinal wave velocity was measured for validation of proposed method. The results show that the proposed method can accurately predict longitudinal wave propagation velocity in reinforced rubber formulation. Thus, this method can be used for validation of compound formulation in rubber production lines.

Bone drilling process is indispensable in orthopedic surgeries and treating bone breakages. It is also very important in dentistry and bone sampling operations. Therefore, bone drilling is one of the most important, common and sensitive processes in biomedical engineering field. Orthopedic surgeries can be improved using robotic bone drilling systems and also mechatronic bone drilling process can be promoted using automatic drilling machines and surgery-assisting robots. Furthermore, imposing higher forces to bone might lead breaking or cracking and consequently serious damage in bone. In this paper a mathematical second order linear regression model is introduced to predict process force behavior during bone drilling process as a function of tool drilling speed, feed rate, tool diameter and effective interactions. Design of experiments using response surface methodology is followed. Then second linear governing equation is assigned to the model and its accuracy is evaluated. Later, Sobol Statistical sensitivity analysis is used to ascertain the effect of process input parameters on process force. Results show that among all effective input parameters tool rotational speed, feed rate and tool diameter have the highest influence on process force respectively. The behavior of each output parameters with variation in each input parameter is further investigated.

Stability control system is a part of active safety systems in vehicles which is designed to control the vehicles’ dynamic motion in emergency maneuvers. In the present study, design and simulation of sliding mode controller has initially been conducted for a suspension system with 4 degrees of freedom (4 DOFs). In order to improve the efficiency of controlling system, a new suspension system with 6 DOFs and using hybrid semi-active damper is developed. By employing this novel approach, the passive model with 4 degrees of freedom is modified to hybrid semi-active model with 6 DOFs. Thereupon, to examine the effects of enhancing of DOF on the stability, a new hybrid semi-active suspension system with 8 DOFs by combining passive 4 DOFs and hybrid semi-active 6 DOFs suspension system is designed and simulated. Numerical results from a typical vehicle that is simulated in CarSim are the input for MATLAB simulation. Investigations show that increasing DOFs accompany with applying hybrid semi-active damper lead to better stability and good handling characteristics of vehicle.

In present study, natural convection heat transfer of a nanofluid in a trapezoidal enclosure saturated by a porous medium is investigated. A local thermal non-equilibrium model including three thermal equations for the phases of fluid, nanoparticles and solid porous matrix is utilized. Moreover, in order to determine comprehensive behavior of dispersed nanoparticles inside the fluid phase, a non-homogeneous model (Buongiorno, s model) is employed. Governing equations in present study are transformed into a non-dimensional form and finally are solved by using the finite element method. The obtained results indicate that the increase of Rayleigh number has a significant increase in the average Nusselt number for the fluid phase and a less significant increase in the average Nusselt number for the nanoparticles. In addition, raising of the buoyancy ratio parameter tends to reduce the average Nusselt number for fluid phase and nanoparticles. In other hand, the variation of Rayleigh number and buoyancy ratio parameter shows a less impact on the average Nusselt number for the phase of porous sold matrix.

The inverted pendulum system is recognized as one of the most challenging dynamic systems. The complication becomes even more involved when switching from the downside to upside configurations by reciprocating motions of the base cart is intended. Considering the large range of motion, the swinging-up control of the pendulum is not achievable through linearization and conventional nonlinear control methods do not apply due to the under-actuated character of the system. In the present research, an energy-based method with sliding control aspects is designed that assures a smoothly transition from the lower stable to upper unstable equilibrium state. This approach permits to design a proper Lyapunov candidate established on physical intuition. The controller permits to reach and stabilize to the new state while tracking a defined path with minimal effort simultaneously. The dynamics of the actuator has been included in the controller to reach a realistic model. The proposed method is implemented on an experimental apparatus that perfectly supports the simulation results.

Due to the increasing applications, micro droplet generators have become an important research area. Researchers presented different methods to produce controlled microdroplets. In this article, spark bubble-induced droplet generation has been studied through an axisymmetric chamber. The process includes the growth and collapse of the bubble and the formation resultant droplet until the pinch-off time. Pressure contours and velocity vectors in the fluid surrounding the bubble are obtained by using a combination of boundary element and finite difference method, and the effect strength parameter, chamber depth and inclination angle of feeder canal on the behavior of bubble and droplet is assessed. The results showed that by increasing the strength parameter, the length of droplet and its volume increase and droplet pinch-off happens earlier. By increasing inclination angle of feeder canal the droplet length and its volume will increase. The maximum pinch-off time belongs to-15 degree. By increasing the chamber depth, the droplet length will increase. In addition, for-15 degree the pinch-off time increases and the droplet volume decreases, while for 0 and 15 degrees the pinch-off time will decrease and the droplet volume will increase. Besides, by increasing bubble-free surface distance the droplet size decreases.

In this study, the two-stage fuel injection strategy as an effective method for the simultaneous reduction of soot and nitrogen oxides emissions and also increase engine efficiency is investigated. AVL FIRE software for numerical simulation of combustion is used. The direct injection diesel engine OM355 of the research center of Idem Tabriz is selected as the studied engine. The results of the simulation show that for the two-stage fuel injection, the average temperature and pressure in the combustion chamber are the most when 70% and 30% of the fuel is injected in the first and second stages, respectively. The best performance in terms of reducing the emissions of carbon and nitrogen oxides emissions have been achieved by using a design which 90% and 70% of the fuel is sprayed in the first stage, respectively. Considering the interval of 20 degrees of the crankshaft for the start of the second injection can optimize the combustion process and reduce emissions of the engine.

Using the nanofluid instead of pure water is one of the ways for increasing the heat transfer and rate of cooling. This article studies the laminar flow of nanofluid over a superheated surface. The nanofluid evaporates after contact with the surface and as a result the volume fraction increases. The governing equation including continuity, momentum, and energy are transformed to ODE by similarity solution and solved using 4th order Rung-Kutta method with a shooting procedure. The results show that water-Cu with the volume fraction of 0. 2, increases the heat transfer and rate of cooling about 42% and the drag force about 15%. Moreover, the results are demonstrated for moving surface to increase the rate of cooling of the quenching process and control the hardness of steels.

In this paper time-dependent creep evolution analysis of thick-walled rotating FGM cylinders made of Al-SiC composite has been carried out, using method of successive elastic solution. The material creep constitutive model has been described by Norton’ s law, considering the experimental results of Pandey on Al-SiC composite. All mechanical and thermal properties except Poisson’ s ratio are radial dependent, based on the volume content of SiC reinforcement. Loading is composed of an inertia body force due to rotation and a distributed temperature field because of steady state heat conduction from the inner to the outer surface of the cylinder. It has been found that the volume-content distribution of SiC reinforcement has a significant effect on initial elastic stress distribution. It has been concluded that radial stresses are increasing with time during creep evolution, while circumferential and effective stresses become more uniform, due to stress redistribution and finally the solution converges to stationary stresses, displacement and strains almost after fifty years.

Y2O3 nano powder was synthesized using yttrium nitrate (source of Y3+), NaOH (control of pH) and citric acid (CA, complexing agant) by hydrothermal method. Many methods using citric acid asisted sol-gel method and combustion method for the synthesis of yttria nanoparticles is performed. In this study, by using citric acid as complexing agent, yttria nanoparticles have been synthesized by hydrothermal method. Also, the effect of pH and citric acid to Y3+ mole ratios on the phase and morphologies of the product was evaluated. The prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and inductively coupled plasma (ICP). Pure cubic yttria nanoparticles with average size of ~ 44 nm was prepared with CA: Y3+ = 1. 6: 0. 01, pH=10 and calcinations temperature of 900° C for 90 min. Furthermore, the luminescence properties of as-synthesized nanoparticles were also investigated.

A new combined system based on a biomass gasifier, SOFC and single effect Li-Br refrigeration cycle for generation of power, heating and cooling is proposed and assessed thermodynamically. With the aid of the Engineering Equation Solver software (EES) Exergy analysis is conducted to determine the irreversibilities in system components. In addition, an environmental impact assessment is performed for each of the three cases in combined system based on each cycle of the proposed system. Also an economic analysis to find unit product cost is carried out. To understand the system performance more comprehensively, a parametric study is performed to investigate the effect of several important design parameters on the net power output as well as exergy efficiency of the system. The results demonstrate that an increase of 75oC in stack temperature difference results in 8. 99% and 17. 47% increases for the exergy and energy efficiencies, respectively. Also net power output is maximized at certain values of current density and fuel utilization factor. In addition, compared to the SOFC system (power generation system alone), the exergy efficiency of the combined system is 12. 04% higher and the CO2 emission of the combined system is 62. 34% lower. Results demonstrate that power unit product cost becomes 15. 76 $/GJ.

In this paper, the performance of two robust control algorithms, μ-synthesis and high order sliding mode are evaluated on a spacecraft attitude control subsystem simulator as the hardware in the loop. This tabular simulator is placed on a spherical air bearing to validate real-time environment. All actuators and sensors on the platform of spacecraft simulator prepare real conditions as attitude control test bed. Beginning, both designed controllers are simulated by Matlab software, next they are applied on the subsystem. At first, μ-synthesis robust controller is designed for simulator. In this method, weighting matrix are chosen such that the controller becomes robust in combined uncertain condition such as system uncertainties, environmental disturbances and sensor noises. Uncertainty, performance, actuator saturation, disturbance and noise weighting functions are designed based on the dynamics and environmental platform properties. At least high order sliding mode controller based on super twisting algorithm is designed to reduce chattering effects. Contrary to the other second order sliding mode algorithms, in the super twisting method sliding surface derivatives are not used. The Computer and experimental hard ware in the loop simulations are compared together.

Nowadays the use of nano-fluids as base fluid in the heat exchanger has expanded impressive. in this study, we tried to examine the use of Alumina Nano-particles and coil wires for enhancing heat transfer of water as base fluid. Therefore, Nano-fluid made with different concentrations and difference patches of coil wires tested at different R eynolds numbers. The coil wires inside the heat exchanger was used to increase turbulency. the results shows use of Nano-particles terminated to high thermal efficiency. Also, increasing concentration of Nano particles and increasing of Reynolds numbers play important role in increasing efficiency of heating systems. also, the results shows that for Nano fluid with concentration of 0. 35% and coil wire with pitch of 2 has best performance. For this condition the enhanced heat transfer 30-45% calculated. however, the increased friction factor for this situation is 1-6%. the results shows that enhanced heat transfer over come to increased pressure drop and control function is heat exchanger performance.

In this study, the proper orthogonal decomposition has been used to develop a reduced order model of the unsteady incompressible flows. After projection of governing equations along high level energy modes, a low-dimensional dynamical system is constructed. Usually, this model is developed using velocity field modes therefore pressure term representation in momentum equation will have an important role for stability and accuracy of outcome reduced order model. Two approaches are available for pressure term deputation, the first is based on elimination of pressure term due to homogenous condition on control volume boundaries and the second used appropriately method for pressure term representation in momentum equation. The method, which is used in this research, is based on using pressure snapshots and velocity field modal coefficients for calculation pressure field modes. The obtained results from proposed model have been compared with related DNS results. Because the instability behavior of reduced order model is not only related to pressure term modeling therefore response of low-dimensional dynamical system is not exactly verified with DNS data. But the outcome results from proposed model have higher accuracy than classic reduced order models.

Creation of the enhanced mechanical properties in Ni-alumina nanocomposite coatings needs to increase the amount of alumina nanoparticles participation in nickel matrix. In this study, the effect of nanoparticles’ zeta values, affected by adding six organic solvents (triethanolamine, glycerol, formaldehyde, ethanol, methanol and carbamide) to electrolyte, on their adsorption was investigated. The results showed that, 10 gL-1 of the organic solvent was essential to conduct nanoparticles’ zeta potential to the range 23-36 mV. Obtained coatings examined by field emission scanning electron microscopy (FESEM) coupled with energy dispersive X-ray spectroscopy (EDS). In this study, the maximum incorporated alumina in the coatings was acquired with adding of carbamide to electrolyte. In this case, the amount of nanoparticles was 5. 7 wt. %. Whereas, adding of triethanolamine to electrolyte leads to 3. 1wt % of alumina content. This result confirms the important effect of optimum zeta potential of 23 mV due to adding of carbamide. In this case, the adsorbed nanoparticles increased up to 46% compared to zeta potential of 36 mV due to adding of triethanolamine.

In the nanoscale, the continuity assumption may be violated, and hence, the classical theories, which have been introduced based on the continuity assumption, may lose their accuracy. Therefore, new size-dependent continuum theories are demanded for proper design and analysis of micro/nano-electro-mechanical systems. The aim of the present study is to develop a new non-linear theoretical model, based on the Modified couple stress theory, for analysis of static and dynamic pull-in instabilities of nanobeams, utilized in nano switches. In the present model, the size effect parameter, the fringing field effect, the electro static forces, the intermolecular forces (Casimir and Van der Walls) are taken into account. The non-linear Euler-Bernoulli governing equation of the beam motion and the corresponding boundary conditions are derived by using Hamilton’ s principle. The results show that the decrease in the size of the beam increases the beam stiffness. An increase in the fringing field effect, the size effect parameter or decrease in intermolecular forces as well as decrease in the substrate length would increase the ultimate pull-in voltage. Also, when a cantilever nanobeam is affected partially from the free-side end, the effect on the increase of the pull-in parameters of the intermolecular forces and the voltage is greater than that of the nanobeam is affected partially from its support side.