نشریه مهندسی مکانیک مدرس
سال هفدهم شماره 6 (شهریور 1396)

The existence of huge gas resource in Iran and the global demand for the replacement of fossil fuels with this cleaner energy resource has caused that the large-scale gas export becomes an interesting topic. One of the methods for large-scale gas exports is liquefaction which is done by refrigeration cycle. Considering the importance of the efficient use and the reduction in energy consumption, particularly in large energy consumers like liquefaction plants, it is imperative to optimize the refrigeration cycles used in these plants. While there have been many studies focusing on the power consumption minimization of refrigeration cycles, however, in most of these studies the performance limitations of the refrigeration cycle components have not been considered. Therefore, the results of such studies are not practical for in-use refrigeration cycles in gas refineries. The main goal of this paper is to propose a systematic method to minimize the power consumption of in-use refrigeration cycles in gas liquefaction processes by taking into account the performance limitations of refrigeration cycle components and the interactions between the refrigeration cycle and the core process. In this regard, a combination of thermodynamic viewpoints and pinch technology is used as well as considering the above mentioned limitations, to express the multi-stage refrigeration cycles’ power consumption minimization problem as a function of several independent variables. Up to 15% reduction in the specific power consumption is achieved when the proposed method are implemented on the optimization of a typical in-use three-stage refrigeration cycle, used in a propane liquefaction plant.

In recent years, increased pollution and traffic in urban has caused the development of underground transport. One conventional approach for urban tunnel ventilation is construction mid-tunnel shafts. These shafts are usually located in high-density urban areas and emissions from them can be harmful for the residents of adjacent buildings. The geometry of these shafts is determined so far based on taste and only for the purpose of compliance standards criteria for tunnel indoor air. In this paper, pollutant dispersion from different and conventional geometries of mid-tunnel shafts with the assumption of a taller downstream building was investigated for the first time. The results can help to reach a better design of these shafts and surrounding buildings to have healthier air for residents of buildings. For this purpose, simulations were done by OpenFOAM. Reynolds-Averaged Navier-Stokes equations method and standard k-ε model were used in simulations. The results showed for the same exhaust velocity, the effect of rectangular and square configuration on front wall depends on dimension of the side which is perpendicular to wind direction. For the exhaust velocity less than 6 m/s, the downstream building prevents pollutants to reach higher altitude and the amount of pollutants will be increased around 100 percent and for exhaust velocity of more than 6m/s, increasing velocity will cause to less changes in pollutant concentration at lower level. In addition, the results showed that exhaust velocity has more effect than geometry configuration on pollutant dispersion and this influence will be decreased by increasing the velocity.

In this paper heat transfer through argon gas between two stationary walls of a nano sized channel, is investigated by the use of molecular dynamic method. Comparison between two and three-dimensional solutions shows that for accurate modeling of wall force filed on heat transfer, the accuracy of two-dimensional molecular dynamic solution is inadequate. Two-dimensional solution predicts the value for density and temperature less than the value of three-dimensional solution near each wall. Considering the effect of domain size on accuracy of thermal solution shows that domain size should be extended at least for one mean free path in periodic direction to have domain independent results. Distribution of fluid properties in the width of the channel shows that independent of implemented temperature difference, presence of the wall force field changes the temperature and density profile in one nanometer from each wall drastically. In addition to variation in density due to the wall force filed, temperature difference between the walls cause additional variation in density profile near walls. Increasing the temperature difference between the walls to value more than 20 degree, make a notable density variation to more than 5 percent in comparison with gas density distribution in isothermal walls case. Variation in density near walls due to temperature differences leads to mismatch between the non-dimensional temperature profiles and calculated thermal conductivity coefficient of the gas for various temperature differences.

Implementing spatial structures is common in real-world structures such as bridges, space structures, and ships. This topic has attracted researchers to propose more efficient and pristine methods to obtain more robust and cheaper solutions for spatial structure optimization problems. This paper presents a hybrid approach for simultaneous optimization of sizing and topology of spatial truss structures using genetic programming and local search methods. It aims to find the optimal cross-sectional areas and connectivities between the joints of the truss to achieve minimum structural weight subjected to static constraints. These constraints include structural kinematic stability, maximum allowable stress in elements and maximum nodal displacements in joints. First, this approach utilizes the tree-form representation of trusses and evolves to the optimal structure in search space; afterward, Nelder-Mead algorithm enhances the obtained solution in the final step. The proposed method has the capability of identifying redundant truss members and joints in the design space. Our method applied to some numerical problems and compared with other existing popular and competent techniques in the literature. The findings provided lighter truss structures in comparison with other references.

In this paper, a 2D analytical model is introduced for predicting the ballistic behavior of the thin laminated composite plate based on tsai-hill and maximum strain criterions. At first, try to determine the moment deformation along with the expansion of transverse wave from impact point and the nonlinear strains and stresses in the composite plate. Then, the energy absorbed due to failure modes and deflection of composite plate such as elastic deformation energy, longitudinal and lateral fracture energy, kinetic energy of local movement, delamination and matrix cracking energy is calculated. For investigation of the various failed layers is used of tsai-hill and maximum strain criterions. In addition to the effects of strain rate on the mechanical properties of the composite layers is applied momentarily during Penetration process. Finally, the present analytical model based on tsai-hill and maximum strain criterions is compared with experimental results. The maximum strain criterion respect to tsai-hill criterion has shown a good agreement with experimental results in the calculation of ballistic limit velocity. According to the obtained results the share of fracture energy compared to the elastic deformation energy by increasing the thickness becomes more and more. And also, the kinetic energy of the local movement, delamination and matrix cracking energy have lower share in the process of energy absorption.

Hydrokinetic turbine performance depends on different parameters such as blade geometrical parameters (i.e. chord length, blade pitch angle, hydrofoil shape, blade yaw angle and etc.) Kinematic parameters (i.e. water speed, rotational speed and etc.) and another important parameters include tip speed ratio (TSR) and The location of turbine in the Channel or river bed. In this project Computational fluid dynamics (CFD) and commercial software ANSYS Fluent 16 are used to simulate hydrokinetic turbine. In numerical simulation used multiple reference frame (MRF) model and the shear-stress transport k-ω SST turbulence model. the grid independency is studied To ensure of numerical results. Also the results are validated with experimental data. At first, for investigate the effect of blade pitch angle and chord length on power coefficient, three different chord length were considered and blade pitch angle over a range of blade pitch angles (0° to 16°) with TSR (2.17 to 6.22) are studied and The results show that maximum power coefficient was found at 10 ° blade pitch angle with 1.676 cm chord length. Based on the results, stall delay depends on blade pitch angle and chord length.

Flight schedule design and fleet assignment are the main sub problems of the airline schedule planning which have the most effect on the costs and profit of the airline. In this paper, integrated flight schedule design and fleet assignment problem is described and genetic algorithm has been developed to solve this problem. It has numbers of constraints and multi-layer permutation chromosomes with variable length. So, creating the initial population randomly and use of customary operators of evolutionary algorithms will not be efficient since the probability of feasibility is very low. For this purpose, a new function based on loop concept to create an initial population and new crossover and mutation operators have been developed. A genetic algorithm has been used within the main loop to optimize the redirection of the passengers. Four models with different numbers of airports and fleets are created as an input for the problem which have been solved by two and three islands genetic algorithms. Results show that in each iteration of the main loop, feasible answers are obtained and finally there was a proper improvement in the costs. In larger models, there is a better Improvement in the costs and more difference between two and three islands algorithms. Three islands mode results in a better solution within a longer time. The developed algorithm can successfully find feasible optimal solution and it can be used for high-dimensional problems in which there is no possibility to find the optimal solution by using conventional methods such as MILP.

Degradation of Fuel Cell (FC) components under dynamic loads is one of the biggest bottlenecks in FC commercialization. A novel experimental based model is presented to predict the Catalyst Layer (CL) performance loss under a given cyclic load. It consists of two sub-models: Model 1 computes CL Electro-Chemical Surface Area (ECSA) under an N-cyclic load with aid of an analogy with fatigue phenomena of carbon steel by using some correction factors. Ostwald ripening of agglomerate particles in the CL is also modeled. Model 1 validation shows good agreements between its outputs and a large number of experiments with maximum 7% error. Model 2 is an already-completed task in an earlier study which uses the agglomerate model to calculate the CL performance for a given ECSA. Combination of Models 1 & 2 predicts the CL performance under a dynamic load. A set of parametric studies was performed to investigate the effects of operating parameters on the Voltage Degradation Rate (VDR). The results show that temperature is the most influential parameter; that an increase from 60oC to 80oC leads to 20.26% VDR increase, and pressure is the least effective one; that an increase from 2atm to 4atm leads to 1.41% VDR rise.

In the present study, modeling of two-phase flow through porous medium is performed by Lattice Boltzmann method; moreover, the porous medium with different porosity ratio are examined. The Shan–Chen-type (SC) multiphase lattice Boltzmann model at D2Q9 network is used to simulate the two phase flow. To validate the used Fortran code in the simulations, first, two-phase flow in channel with hydrophobic and hydrophilic surface, and then a droplet on the surface with different hydrophilic and hydrophobic are simulated. Achieving optimized array of porous medium which reduces the leakage flow rate and fluid penetration was the primary aim of our study. To achieve the mentioned purpose, first, the flow penetration through different porous medium arrays is compared; then, effect of hydrophobicity on penetration is studied. Finally, the leakage flow rate of various arrays is investigated. The results indicate that utilizing a combined porous medium can drastically reduce the penetration and leakage. This optimized configuration has lower porosity in underneath part. Also, result show when the surface is hydrophobic, the penetration of fluid through the porous medium is slower, compared with the hydrophilic surface.

Jet engines working near the ground, with low speed and high thrust can experience flow separation between ground and inlet which would lead to vortices, called Ground Vortex that have harmful effects on engine performance and can disrupt integrity of inlet flow. Deep understanding of the physics of this phenomenon could omit the injuries of foreign objects damages, engine surge, compressor stall, and fan vibration. In this study, the ground vortex formation near the inlet air duct of an aircraft engine is investigated using computational fluid dynamics. Simulations are performed for a 1:30 scale. The fluid flow is assumed to be compressible, three-dimensional and steady.The k-ω SST model is employed for incorporating turbulent characteristics. After mesh study, the boundary of Vortex or No-Vortex for results of this study compared with a theoretical and an empirical correlation by Murphy which showed good agreement. Moreover, despite free stream existence, decreasing non-dimensional velocity ratio causes the movement of vortex core and by approaching to the critical non-dimensional velocity ratio; the ground vortex would gradually disappear. For U^*= 33,44,66,132 ground vortex is formed, but for U^*=26.4 ground vortex disappears. The computational method has subsequently been applied to configurations that are difficult to test experimentally including headwind flows. According to this study, the formation of the vortical flow field permanently affects the total pressure distortion on the engine fan face. In this paper, DC60 is calculated under headwind condition. These coefficients are 0.39, 0.391, 0.447 and 0.3957 at U^*=33,44,66,132 respectively.

In this paper, transient liquid phase (TLP) bonding process between Inconel 718 alloy and Inconel 600 alloy using a BNi-2 interlayer with 50 μm thickness was investigated. Transient liquid phase bonding process was performed at 1050 °C for 5, 25 and 45 min. Microstructure evaluation was carried out through optical microscopy, field emission scanning electron microscopy (FE-SEM). Also, bonding shear strength was measured. The results showed that the joint microstructure was formed of three zones including isothermal solidification zone (ISZ), thermal solidification zone (ASZ) and diffusion affected zone (DAZ). At the time of 5 min, boride intermetallic compounds in thermal solidification zone were formed. Isothermal solidification was completed and thermal solidification zone was vanished by increasing the bonding time from 5 to 45 min. Diffusion affected zone of the Inconel 718 alloy was persistent and expanded by increasing the time and diffusion of B element to parent metals, but this region in Inconel 600 alloy was vanished and the homogenization process was occurred by increasing the bonding time. Also, because of remove of boride intermetallic compounds, changes of hardness in joint region were more smoothly and the hardness value of joint region was about 280 HV. The results of shear strength showed that the bonding strength was increased from 250 MPa to 410 MPa with increasing the bonding time from 5 to 45 min, respectively.

Todays, parallel robots with six degrees of freedom are widely used in motion simulation industry. Spreading application of motion simulation for different means of transportation has led to advance training in a safe way with less time and equipment cost. Mostly, the 6-UPS structure Stewart parallel manipulator is used as motion simulators due to their large workspace, rigidity and load capacity. Since the massive moving actuated prismatic joint is located between fixed and moving platforms, the dynamic performance of the mechanism is not efficient. The robot with PUS structure can be a good alternative for UPS type as its actuators are fixed to the ground. This results in lowering of the overall robot cost in addition to stiffness increase. In this paper the inverse kinematic and dynamic of a general 6-PUS robot is presented using Newton-Euler method. The theoretical dynamic model results are verified using motion analysis software. A simplified dynamic model is prepared eliminating links’ inertial terms from dynamic equation. The accuracy of the model is evaluated for different link to payload mass properties ratio. The simplified dynamic model used to improve the computational efficiency of the inverse dynamics.

High potential regions for using clean and wide solar energy are suitable choices to apply solar distillation systems. Iran has large area with exposed solar radiation and also vast salty water sources at south and north, hence has an appropriate situation to use solar stills and solar distillation equipment. Researchers have focused on development and improvement of working solar distillation champers in recent years to get benefit from this modern technology in water crisis conditions. In this research, effect of storage of further heat and also using PCM were surveyed when flow turbulators were applied in the spiral heat exchanger and the salty water flow rates were changing simultaneously and it is the novelty of this research.. These experiments were carried out in mild and wet region in north of Iran, Babol city. These tests also were done during a year. The experiment results determined that during cold months (December to April) using PCM has no effect on efficiency of system. But in warm months (May to November) the effect of PCM is more than effect of stored heated water. The results show that using heat storage and also applying PCM increase the distilled water gain of system up to 7% and 14% respectively. Furthermore using turbulators can improve system’s water gain by increasing the heat transfer up to 14%. Maximum distilled water gain was equaled to 2250 milliliter/day.

This paper presents a numerical model for predicting pressure, impregnation and pulling force in pultrusion die which circular cross section witch two reinforcement fibrous tows pass through it. Pulling force and degree of impregnation are the most important parameters associated with pultrusion process that determine production cost and quality of pultruded profile respectively. Main idea in this approach is obtaining characteristic equations in purely polymer region and purely fibrous region and establishing relations between them by using conservation law. The superiority of this approach compared to other methods is ability to considering both straight and conical part of the die, calculating pulling force, ability of investigating influence of a variety of parameters such as those associated with die geometry, material rheology and process parameters. In this paper the influence of fibers position and fibers radius on pulling force, impregnation and pressure inside die is investigated. Due to the ability of simultaneous calculation of force and impregnation, this model can be used to establish an optimum condition between cost and quality of produced profiles.

In this paper, the heat transfer of viscoelastic fluid flow have numerically simulated inside a symmetric planar channel with 1:3 abrupt expansion. For modeling the rheological and nonlinear behavior of inertial flow related to the viscoelastic fluid, exponential form of the Phan Thien-Tanner (EPTT) model has been used. The thermal boundary condition of constant temperature has been considered at the inlet and on the walls of channel. Also, velocity is uniform and constant at the inlet of channel and its value is determined by the Reynolds number of flow. Due to the significant effect of temperature on the viscoelastic fluid properties, viscosity, relaxation time, specific heat capacity and thermal conductivity have been taken as a function of temperature and dissipation term has been employed in the energy equation. For coupling the governing equations, the PISO algorithm is utilized and finite volume method (FVM) is employed for discretizing these equations. In this study, the effect of inertial force is investigated on the velocity distribution, temperature distribution and variation of local and average Nusselt numbers in the expanded part of channel. Despite the symmetry in the planar channel, increasing the Reynolds number forms the symmetric and asymmetric flows inside the expanded part of channel. For asymmetric flows, increase of Reynolds number from 40 to 100 (growth of 2.5 times the Reynolds number) resulted in a 1.7-fold increase for the maximum values of local Nusselt numbers in the vicinity of the upper and lower walls of the channel expanded part.

The centrifugal pumps are widely used in the oil industry and play a vital role. Thus, performance optimization is very important in the centrifugal pumps. In this paper, 3-D flow of centrifugal ESP pump has been numerically simulated. This study aimed to investigate the geometrical variation effect on the performance and flow pattern inside one stage of the pump. For this purpose, the effect of distance and angle between hub and shroud at passage outlet of impeller on pump performance has been assessed. The presented model is centrifugal pump with 3500 rpm with six blades for impeller and eight blades for diffuser. The ANSYS-CFX software has been used in this investigation. In order to modeling the impeller and diffuser, movement the multi reference frame and for interconnection of them the frozen rotor is used. Furthermore, the K-ω sst turbulence model is applied. The results of simulation are well-adapted with experimental results. The result of this study disclosed that by increasing 8.25 degree of the angle between hub and shroud, the amount of head and efficiency rise up in the pump. It also shows that the optimum distance between hub and shroud by considering a goal of simultaneous maximizing of head and efficiency is 1 mm. Variation of two parameters of one stage of pump, simultaneously, cause to increase head by 7.6% and efficiency by 1.65%. These variations have been occurred due to the separation region of flow decrease on the surface of the diffuser blades.

In this paper the problem of optimal multiple-burn injection of a satellite into geostationary orbit using an upper stage with a limited thrust and restart capability, and comparison with sub-optimal case is considered. The goal is finding thrust vector angle, times of the engine firings and optimal duration of active phases of the upper stage so as to minimize fuel consumption and to meet desired boundary conditions. The contribution of this research is developing an accurate and rapid convergence algorithm for solving multiple-burn trajectory for satellite injection into geostationary orbit. To solve the multipoint boundary value problem, an improved indirect shooting method with high performance and modified Newton’s method is presented and used for optimal solution. Moreover, the novel method presented for multi burn problem, not only has very good accuracy, but also, it converges very fast to the desired end conditions. Various flight sequences with multiple burns are considered and the optimal trajectory with minimum fuel consumption criteria, for each flight sequence is derived. The verification and validation of the proposed algorithm is made via comparison with references. Finally, the results of optimal solutions are compared with the results of sub-optimal solution which its thrust direction is aligned to the velocity vector direction.

In this paper, an optimization-based nonlinear control strategy is applied to air path control of a turbocharged diesel engine. For this aim, the air-fuel ratio (AFR) and the pressure of exhaust manifold are controlled by calculating the air mass flow rates of turbocharger and exhaust gas recirculation. Controlling AFR which affects engine power, fuel consumption and exhaust emissions, is carried out by calculating the air mass flow rate with the assumption of known fuel path. For air path modelling, the mean value model which is a suitable method with low computational time is used to achieve the air path equations. Air mass flow is calculated by the developed control laws and applied by the turbocharger and exhaust gas recirculation. In the proposed control method, the nonlinear system response is firstly predicted by Taylor series expansion and then the optimal control law is developed by minimizing the difference between the desired response and the actual response. To compare the performance of the proposed optimal controller, a sliding mode controller has been also designed. The simulation results show that the rate of air mass and the pressure of exhaust manifold are close to their desired values and consequently the AFR is well controlled. Therefore, the designed controller with optimal inputs can successfully cope with the nonlinearities existing in engine dynamics model.

This paper investigates the Tri-Tilt Rotor VTOL UAV. The aim of this study is to represent a comprehensive dynamic model, eleven degree of freedom at six flight phases (hover, descend, climb, forward, transient and cruise) and control the vehicle to reach best flight condition. For this purpose, the vehicle equations of motion are derived in tensor form and have been expanded in the coordinate systems, based on multi-body (vehicle and three electric motors) modeling approach in order to consideration of motors gyroscope effects on flight dynamic. Depending on vehicle flight phase, propulsion and aerodynamic forces and moments are determined separately. Blade Element Momentum Theory (BEMT) is used to obtain motors propulsion forces and moments at hover, descend, climb and forward phases. After that, with utilizing of controller for each channel flight, the trim condition is calculated and then for the sake of linearization using analytical method, dynamic and control matrixes are derived. This calculated model is qualified as linear model in order to design the model predictive and adaptive controller. For climb phase, as the nonlinear model receding from linear model, the linear model predictive controller performance was diminishing whereas the function of model reference adaptive control in spite of the uncertainties was better.

This study is a try to design a spike nozzle and simulate its flow-field in different conditions. Hence, spike nozzle design methods were studied and accordingly the design code was developed. Then the behavior of flow in this type of nozzle was simulated numerically by means of computational fluid dynamics. In order to conduct the simulations, four turbulence models suitable for solving the flow-field of spike nozzle were used, not only to model the performance of the nozzle in design and off-design conditions, but also to identify the best model for the accuracy of the solutions. To ensure the accuracy of the simulations, numerical results and experimental data were compared. It was found that applied models in case of using high quality grids with proper dimension near the nozzle walls, can predict the nozzle flow pattern with acceptable approximation. Also the comparisons revealed that the amount of pressure on the spike wall calculated by Realizable k-ε model, is generally identical with experimental results and in the worst condition the difference between them is 15%, so this model has the best agreement with experimental results. Besides, comparison of taken photos during experiments and extracted contours from numerical analysis, shows the high ability of applied numerical method to predict spike nozzle flow-field. Therefor it can be claimed that by using the proposed method in this research, there is no need to perform cold-flow tests during the design and construction of spike nozzles.

One of the focused problem in airway flow simulation is pulmonary airways modeling. There are two kind of Lung models, one is created anatomically based on bronchial data and second is realistic model which is created based on CT scan images. Unfortunately cause of modeling process or simplification cause of restriction of CPU and time, the result model is different from a really pulmonary airways. Anatomically model are many simplification and realistic model from CT scan have major limitation in CT image resolution and smoothing stage of make out the 3D model. Anyway the lung has many rough and the first thing that is vital on this way is cartilage rings as macro scale roughness. So the presented work, compared the airflow in both simple and modified Horsfield model by cartilage rings in term of time averaged wall shear stress which are important in engineering of Cell-Fluid Interactions (CFI). This is shown that cartilage rings affected the trachea and second generation of brunches so this is not reasonable to neglect the cartilage rings.

This paper presents a new method based on machine vision for mobile robots to detect and avoid obstacles in unknown environments. One of the challenges of mobile robots trajectory control in unknown environments is that their obstacle avoidance system to be designed robust to material and shape of the obstacle. In this research a mobile robot equipped with a camera is designed and fabricated. Also an algorithm is proposed and implemented on the robot in order to detect obstacles by image processing and to control the robot trajectory. Three color laser pointers are mounted on the robot with certain angles that emit beams to the ground at ahead of the robot. The received images from camera contain these colored points that their coordinates are determined by image processing. Then position of any possible obstacle is detected using the proposed algorithm and the robot is commanded to avoid obstacles by changing its path. These obstacles can be static or dynamic. Our experimental results show that the proposed method, with a high reliability, has the ability to detect and avoid obstacles with any shape and material whereas other similar methods had restrictions in this regard.

In recent years, to reduce positioning cost for civil and robotic applications, low-cost inertial sensors especially Micro Electro Mechanical System (MEMS) types have been produced. Positioning Error of an inertial navigation system comprising low-cost inertial sensors increases due to significant uncertainty of noises, bias and drift of MEMS sensors in short times. Therefore, combination with an auxiliary system such as the Global Positioning System (GPS) is proposed in order to reduce the errors trough integration estimator algorithms. This paper aims developing a new estimation algorithm for integrated attitude and heading reference system (AHRS) with GPS. Kalman Filter is commonly used for linear systems and its extended version has been used for nonlinear system. Generally, the Kalman type estimators fall in trouble when the system exhibits nonlinear behavior and to overcome these issues, the predictive estimator is considered in the paper. Design process of Model Predictive Observer (MPO) is proposed based on the duality between the problems of control and estimation in linear systems. To assess the performance of the proposed method compared with the extended Kalnman filter, practical tests of AHRS/GPS have been done on car and flight vehicles. The test results of the designed MPO during all tests show the significant superiority in comparison to the extended Kalman filter.

Nowadays, due to energy crisis and the increase in the energy demand, the use of alternative fuels is essential. Landfill gas (LFG) is a natural product of the decomposition of organic material in landfills which is composed of methane and carbon dioxide. Impinging flames are unique configuration which leads to an increase in the amount of mixing and improving combustion efficiency. In this study, temperature field and flame structure of laminar premixed flame of landfill-air in cross burners have been examined. The flame temperature field of combustion products was obtained by the Mach-Zehnder interferometry method. To validate the results, the obtained temperatures of Mach-Zehnder method were compared to measured data by thermocouples and good agreement was observed. The effects of angle and distance between two burners have been studied to investigate the effect of burner’s configuration on the flame structure. These two parameters in laminar flow regime have been studied, while the angle between two burners varied from 60 to 100 degree and dimensionless distance (S⁄D_h ) varied from 3.44 to 9.63. The obtained results showed the burner’s angle does not have much impact on the maximum flame temperature but the flame structure is very affected by this parameter. On the other hand, the distance between burners has strong effect on the maximum flame temperature, flame structure, and the region of maximum flame temperature.

Machining of hard steels has it’s own problems. According to the recent advances in implementing of new cutting tools, the machining of hard steels with operations such as turning and milling is possible and it can replaced with some of grinding operations. Turning of workpieces with 45 HRC or upper hardness, is said hard turning. The aim of this article is the investigation of the effect of workpiece hardness and cutting speed and feed rate parameters on surface roughness in hard turning of cold work tool steel X210Cr12 or SPK in dry condition. For achieving this goal, the workpieces of X210Cr12 steel where hardened with different heat treatments cycles such that their hardnesses lie in the hard turning range. Then the workpieces were machined with different cutting parameters using CBN tool and the resulted surface roughness were compared. Experimental tests designed with full factorial method and totally 36 tests have been done. According to obtained results of experimental tests and analysis of variance, the effect of feed rate and workpiece hardness on surface roughness was 90.4% and 8.3%, respectively. The effect of cutting speed on surface roughness is negligible. Increasing the feed rate results in the upper surface roughness. Increasing the workpieces hardness to 50 HRC, decreases surface roughness and increasing workpieces hardness from 50 to 65 HRC, increased surface roughness.

Detecting and Preventing wheels slipping is at the core of all researches related to railway vehicle dynamics. In this paper, three fast non-elliptic contact models are evaluated and compared to each other in terms of contact patch, pressure and traction distributions as well as the creep forces. Among them Johnson and Kalker method was really useful to the similar problems while the common assumption is elastic half-space that many errors could be made especially in gauge-corner contact. Based on the conclusions drawn from this evaluation, two new methods is proposed which results in more accurate contact patch and pressure distribution estimation while maintaining the same computational efficiency. The Beam and Bristle model are proposed for tire engineering in automotive industries but they can predict slip in wheel-rail contact too. New methods are typically used for tire engineering. Tire engineering usually is dealing with higher values of slippage than there is rail engineering. So that they can be applied into the saturation zone. At last a FEM analysis will be done for evaluating the methods proposed. Also in the special case there is similar experimental projects done by other scientists. It should be noted that good agreement between FEM analysis results, tire engineering models, experimental results has been found for several contact applications including S1002 wheel profile over UIC60 rail profile for four different initial braking speed 30, 60, 100, 140 km/h have been compared with experimental results.

Any industry needs an efficient predictive plan in order to optimize the management of resources and improve the economy of the plant by reducing unnecessary costs and increasing the level of safety. Rotating machinery is the most common machinery in industry and the root of the faults in rotatingmachinery is often faulty rolling element bearings. Because of a transitory characteristic vibration of bearing faults, combining Continuous wavelet transforms with envelope analysis is applied for signal proseccing. This paper studies the application of independent component analysis and support vector machines to for automated diagnosis of localized faults in rolling element bearings. The independent component analysis is used for feature extraction and data reduction from original features. The principal components analysis is also applied in feature extraction process for comparison with independent component analysis does. In this paper, support vector machines-based multi-class classification is applied to do faults classification process and utilized a cross-validation technique in order to choose the optimal values of kernel parameters.

This study, deals with the investigation of the accuracy and performance of a novel method for simulation of oscillating wave surge converter (OWSC). The OWSC is an instrument with one degree freedom mounted in near shore areas which oscillates back and forth. This device is used to harvest sea wave energy. The developed model is based on the well-known volume of fluid (VOF) method. Due to the nature of the OWSC motion, the VOF method in conjunction with unstructured dynamical grid mesh has been used in the literature. But in this study, a structured grid mesh is employed which facilitates the numerical preparation and the speed of simulation process. The results are compared with the experimental data and the results of numerical method in the literature by dynamical grid mesh. This comparison shows the high accuracy of the developed model in this study. The model validation is performed in an extreme condition with steep waves which need an accurate numerical scheme. The external forces including power take off (PTO) forces are also simulated. The capture factor, energy absorption condition and the effect of PTO on angle, angular velocity and slamming of the OWSC are also investigated. Finally, the effect of wave height and the PTO stiffness on the capture factor and absorbed energy by the OWSC for waves with a specific period are investigated.

In this paper, using a solution of the Boltzmann equation along the walls, a new model of slip velocity boundary condition is presented. In the continuation of researches on the effect of gas compressibility on the flow through micro/nano channels, the present slip model shows analytically how the slip velocity boundary condition affected by compressibility of gas. In comparison with shen’s slip velocity model, this model includes an additional term due to compressibility factor gradient along the flow direction. We used the virial equation of state to calculate the compressibility factor gradient along the flow direction. In order to verify the present slip velocity boundary condition and investigate the advantages of it, poiseuille flow through a micro/nano channel in the slip regime and transition regime is studied. The non-dimensional velocity in three inverse Knudsen number calculated. Also, non-dimensional flow rate calculated from Knudsen number 0.005 until 5. The new model accurately predicts minimum flow rate around D=1. In addition, in whole range of Knudsen in comparison with other slip boundary conditions such as first order model, second order model and shen’s model, the present model shows better agreement with that calculated by the linearized Boltzmann equation which is specifically the result of taking the effects of compressibility into account.

In this paper, a novel dynamical model is proposed for the multi-input multi-output electrically driven robot manipulators, by an observer-based robust adaptive fuzzy controller. The proposed control scheme utilizes current control effort, which is more efficient than the torque control approach. The proposed method is very simple, accurate and robust. Based on the adaptive fuzzy system an observer-based estimator is presented that uses feedback error function as the input of fuzzy system to approximate and adaptively compensate the unknown uncertainties and external disturbance of the system under control. Although the proposed controller scheme requires the uncertainties to be bounded, it does not require this bound to be known. An H_∞ robust controller is employed to an attenuate the residual error to the desired level and recompenses the both fuzzy approximation errors and observer errors. The proposed method guarantees the stability of the closed-loop system based on the Strictly Positive Real (SPR) condition and Lyapunov theory. The proposed control scheme is not limited only for controlling of robotics vehicles, it can be applied for a class of nonlinear MIMO systems. Finally, in simulation study, to demonstrate the usefulness and effectiveness of the proposed technique, a two-link robot manipulator system is employed.

In this paper, dynamic modeling and position control of a nonlinear servo – hydraulic actuator system under variable loads is proposed. In dynamic model of the under studied system, governing equation of valve, leakage and friction is considered. To achieve to the desired performance of the system under variable loads with extend variation amplitude, a one control method is applied which is robust in the presence of the variation. Also, as a nonlinear servo hydraulic actuator system has a nonlinear dynamics and the extracted dynamic model is not accurate to proposed behavior of the system, one controller can be required which is robust against the nonlinearity and uncertainty effects. The controller should be having an appropriate response, more accuracy and stability. Regarding to position control of the nonlinear servo hydraulic actuator system in presence of variable loads, nonlinear controllers are designed using feedback linearization and sliding mode techniques. In addition, in order to show the robustness of proposed controllers, a time varying disturbance and noise are applied in the simulation and results of the simulation are compared with classical PID controller. Controller parameters is optimized using harmony search algorithm and simulation results show the outperforming of sliding mode control in spite of variable loads against feedback linearization technique and PID controllers.

In this paper, the forward kinematics of a parallel manipulator with three revolute-prismatic-spherical (3RPS), is analyzed using a combination of a numerical method with semi-analytical Homotopy Continuation Method (HCM) that due to its fast convergence, permits to solve forward kinematics of robots in real-time applications. The revolute joints of the proposed robot are actuated and direct kinematics equations of the manipulator leads to a system of three nonlinear equations with three unknowns that need to be solved. In this paper a fast and efficient Method, called the Ostrowski-HCM has been used to solve the direct kinematics equations of this parallel manipulator. This method has some advantages over conventional numerical iteration methods. Firstly, it is the independency in choosing the initial values and secondly, it can find all solutions of equations without divergence just by changing auxiliary Homotopy functions. Numerical example and simulation that has been done to solve the direct kinematic equations of the 3-RPS parallel manipulator leads to 7 real solutions. Results indicate that this method is more effective than other conventional Homotopy Continuation Methods such as Newton-HCM and reduces computation time by 77-97 % with more accuracy in solution in comparison with the Newton-HCM. Thus, it is appropriate for real-time applications.

In this paper the capability of laser surface hardening of martensitic stainless steel AISI 410 is conducted by using a Nd:YAG pulsed laser with a maximum power of 700 W. Focal point position (22mm to 34mm) and laser pulse energy (14.7J to 16.8J) were considered as process variable parameters. microhardness was measured in depth and surface of hardened layer. Metallography of samples was conducted in order to study the microstructure of hardened zone. Also geometrical dimensions of hardened zone (width and depth), microhandness distributions in depth and width of hardened layer, microstructure of hardened layer were investigated. Results show that by increasing laser pulse energy and decreasing the laser focal point position, the hardness and depth of hardened layer increases. Observations indicated that solid state transformation and carbide solution in steel during laser surface hardening process, improved the surface hardness. Lower delta ferrite in martensitic structure in laser hardened layer lead to higher microhardness. Maximum hardened layer of 350 µm in depth and 2208 µm in width and maximum surface hardness of 747 HV0.3 is obtained in maximum pulse energy of 16.8J.

In this paper, numerical and analytical solution of composite metal cylindrical vessel are investigated under dynamic load using first-order shear deformation theory and differential quadrature method. For this purpose, the shell equilibrium equations are derived based on the first order shear deformation theory. The load applied to the shell is achieved from the experimental test of a double-base propellant and then, is applied to the model in numerical and theoretical analysis. The aim of this paper is study and investigate the behavior of the composite metal cylindrical vessel under dynamic load with first-order shear deformation theory and comparing its results with the numerical solution. Therefore, after extracting the shell equilibrium equations are used from differential quadrature method for solve the equations. Then, the governing equations are extracted in a composite metal cylindrical vessel to form the matrix equations to solve with differential quadrature method. To apply boundary conditions from free and support clamping conditions are used and the results of these two modes are compared together. The MATLAB programming code is used to solve differential quadrature equations. To validate theoretical results, modeling and numerical analysis done by Abaqus finite element software and then, results are compared with the analytical solution using the differential quadrature method.

In this study, effects of zeta potential distribution and geometrical specifications are numerically investigated on mixing efficiency in electroosmotic flows. Considered geometries include straight, converging, diverging, and converging-diverging microchannels. Electroosmotic flow simulations are conducted based on the N-S and Nernst-Planck equations for momentum and ionic charges distributions, respectively, by lattice Boltzmann method. Numerical simulations are validated against available analytic electroosmotic flow solutions in homogeneous straight channels, and then flow patterns and mixing performances in the presence of non-uniform zeta potential distributions are investigated in search for enhanced mixing performances. Numerical results indicate that converging channel leads to a sizable increase in mixing efficiencies, while the flow rate decreases at the same time. In contrast, diverging channels increase the flow rate, while decrease the mixing efficiency. Therefore, it is expected to achieve a balance between the mixing efficiency and mass flow rate using converging-diverging geometries. Numerical results indicate that mixing efficiency of about 90% can be reached with a converging-diverging microchannel with a reasonable decrease in mass flow rate as compared to its geometrical diverging-converging counterpart channel.

In this paper, we show how Ferrite- martensite steel are produced by annealing operation, meanwhile tensile behavior of resistance spot weld and the effects of the resistance spot welding parameter and tensile failure modes in this type of steel will be examined. Design experiments was done by Taguchi statistical method and because of the number of studied parameters and factors, we choose L8 array. Parameters which could be controlled in resistance spot welding include welding time, the electrical current through the electrodes and the pressure that here considered as factors affecting the operation and tensile strength welded factor is examined as a test answer. In order to predict the optimal parameters of the resistance spot welding, signal to noise ratio is used in Taguchi statistical method. Generally, spot weld failure occurs in two modes: interfacial and pullout. The results show that by increasing the diameter of the weld nugget, pullout failure and the pullout with tear sheets becomes more likely to happen. Results of Taguchi statistical method also shows that the impact of the electrical current parameter of the spot welding machine compared to other properties was higher and it is less effective with increasing current. As well as SEM images of weld fracture surfaces have been taken and the results indicate ductile fracture in pullout mode and cleavage in interfacial mode of fracture.

In this paper, according to flight devices categories, advantages and features of quadrotors and its performances are investigated. Then, the main challenges in quadrotors control and stability in the presence of obstacles have been considered in such a way that the system crosses the maximum number of obstacles in the best distance and time. For this purpose, the equations of motion of the system are derived and a controller for command tracking is designed without obstacles based on sliding mode method. The simulation results of the controller performances are given in the paper. In continuous, trajectory planning for crossing the system from the obstacles in alternative positions is presented and the quadrotor with the designed control system are simulated using the designed trajectory. The preference of the proposed trajectory planning is that the system can cross the number of obstacles in alternative positions in minimum time and using fewer sensors. Because of free shape of designing method and alternative initial velocity, the proposed method are applicable for piecewise trajectories. As a result of considering the drag force, the proposed approach is more successful in the various problems.

Micro-milling is prominent among other micro-manufacturing processes due to their abilities in manufacturing of 3D features, high material removal rates and high precision. One of the most important challenges of this process is tool deflections which contribute even up to 90% of dimensional errors of the finished product. This paper addresses a novel method to estimate micro-milling tool deflections applicable in micro-milling machines equipped with linear motors. In this method, position feedbacks and inputs to the amplifiers are used to real-time estimation of cutting forces by applying Kalman filter. Outputs of the estimator include a resultant of all disturbing forces in servo control loop of the motors. Therefore, cutting forces need to be compensated for other disturbing forces that are mostly friction and force ripples in linear motors. To compensate them, neural networks were used. A neural network with a hidden layer and 16 nodes inside, and with two time-delayed lined (TDL) could well model friction and force ripples. Results showed that the proposed tool deflection method is able to estimate 22% of micro-milling tool deflections.

Tube hydroforming is a process which is considered to produce integrated and seamless parts in recent years. The numerical prediction of tearing to design the right equipment in this process is important. In this study, the formability of 304 stainless steel tube by free bulge test was experimentally and numerically evaluated to determine the forming limit diagram. The Gurson- Tvergaard- Needleman (GTN) is a micromechanical model to predict ductile fracture of metals. In order to determine the defining parameters of the GTN damage model, the experimental tensile test of the standard sample and the finite element simulation using ABAQUS software was performed. Using this criterion in the ABAQUS software and comparing the force-displacement diagram obtained from the experimental tensile test and the finite element simulation, the parameters of the GTN model was obtained by the inverse method. Then, the geometrical parameters of the die in the free bulge hydroforming process were investigated by the GTN ductile fracture criterion and the forming limit diagram of the 304 stainless steel tube was numerically obtained. The experimental tests were also carried out to verify the results of the finite element simulation. It’s shown an acceptable agreement

In this study, a modified method has been introduced for forward dynamic analysis of fast parallel robots. For this purpose, inspired by the Lagrange-Virtual Spring (LVS) method, the Decoupled Natural Orthogonal Complement (DeNOC) method is modified which is a Newtonian based method. So far, virtual springs have been already used in energy based methods. However using the virtual springs in DeNOC method is a novel approach which is proposed in current study. In order to clarify the advantages of Modified Decoupled Natural Orthogonal Complement (MDeNOC) method, a planar 3RRR mechanism is chosen as case study. According to the results, the process of deriving the equations of motion is much less costly while the accuracy of MDeNOC is similar to the LVS and unlike the energy methods, the modified method is also able to calculate the constraint reactions, as well. On the other hand, the calculation time of MDeNOC is much more than the DeNOC and hence, is not suitable for real time calculations. Also, in closed loop systems, constraints must be defined in such a way that express the virtual springs’ longitudinal changes; otherwise, MDeNOC will not give proper results.

In the process of steel continuous casting, tundish as an intermediate compartment between the cauldron and mold has an important role in inclusion removal and the turbulence reduction process before entering the mold. Basically, the cleanliness of molten steel entering the mold is effected by the type of tundish flow pattern and the it’s behaviore in the flotation and removal of non-metallic impurities.Therefore, suitable flow pattern and increase of inclusion residence time in tundish improve the process of inclusion removal and lead to get clean steel. In this research, by manufacturing of the glass tundish in 1:4 scale to do flow physical modeling, the effect of melt height on the flow behavior in single tundish was studied, by implementing of dam in tundish then, its performance in inclusion removal is compared. Independent variables in this study are as the diameter of the inclusions and different water levels in the tundish and the dependent variables are as the separation rate of inclusions from the melt and inclusions residence time in the tundish. By increasing the water height in tundish, the inclusion removal and residence time get reduce. In addition, by using the dam near inlet nozzle the flow pattern gets improved and the inclusion removal will be as slag.

In this article, the free and forced convectional heat transfer in a rectangular porous fin with considering pressure loss across the fin length is investigated analytically. A well-known Differential transformation method is employed to obtain the solution of energy balance equation. Convergence of obtained solution is examined by previous works and they are found to be in a good agreement. In order to simulate heat transfer through porous media, Darcy model is applied. Also convective heat transfer coefficient is assumed to be constant. Dimensionless temperature distribution is defined as a function of convection and porosity parameters. Also the effects of pressure loss across the fin length on the temperature distribution, rate of heat transfer, fin efficiency and effectiveness of fin are studied. A comparative study is also made between the porous and solid fins for an equal mass of fins. It is highlighted that the porous fin transfer always more heat at specific condition compared to the solid fin. Results show that all of thermal parameters are influenced by pressure loss parameter. So in order to reach to high fin efficiency, pressure loss across the fin length should be controlled.

Nowadays wobble motors are widely utilized as actuators with high torque rotary motion producing capability without the need for external gearbox. This study contains theoretical, numerical and experimental analysis of a planar wobble motor with compliant mechanism driven by shape memory alloy (SMA) wires. The cyclic expansion and contraction of SMA wires is converted to the plane curvilinear motion with circular path and then to the continuous unlimited rotary motion by means of a compliant mechanism and a gear system consisting of an internal and an external gear. After gear system designing based on achievable motion range caused by SMA wires length change, the relations between output torque, geometrical properties of motor and stress in SMA wire were derived. Also compliant mechanism parameters consisting of length, height, thickness and number of flexures were analyzed with the aim of mechanism stiffness calculating. Then the frequency analysis with finite element method is performed to investigate structural robustness and operational stability of designed mechanism. The designed motor is fabricated as a prototype to investigate its operational feasibility and working performances. The experimental results demonstrate motor capability in producing unlimited continuous rotary motion and repeatability of maximum output torque. The Maximum output torque was measured as 29.9, 32.7 and 34. 3mN.m for 1.6, 1.8 and 2v applied voltages respectively. With consideration of motor characteristics, it is appropriate for high torque and low speed applications with limited work space.

In this paper, reliability of missile system in its total life cycle is evaluated in terms of its subsystems’ reliability, using Continuous Time Markov Chains (CTMC) and Monte Carlo simulation method, finally results of both methods are compared. Missile system’s life cycle includes storage, pre-launch and operation states. Missile system is composed of variety of components and materials, hence different environmental conditions and various stresses imposed on missile system in each state during its life cycle, stimulates diverse failure modes and mechanisms. Therefore, failure probability distribution function differs for each subsystem in each state. Flight control, mechanical parts and equipment, engine and warhead are four main subsystems of the missile system. They are linked in series therefore each one’s failure will result in system’s failure. Exponential, Weibull, Lognormal and Gompertz distributions are used for subsystems’ modeling in different life cycle states. Unlike many other researches in this field, failure rates are time variant. System is supposed to be unrepairable during life cycle. Finally, Continuous Time Markov Chain’s superiority in comparison with Monte Carlo method, both in accuracy and required amount of calculations is demonstrated and a few suggestions, based on obtained results, are presented for system reliability improvement.

In the present study, performance of nonlinear low Reynolds number k-ε model of turbulence has been investigated in order to predict turbulent flow field through three dimensional U bend channel of intercooling passage of gas turbine blade. Finite volume method is used to solve governing equations of mean fluid flow. In this study, linear low Reynold number model of turbulence and Zonal Eddy Viscosity model k-ε/1-eq. and cubic nonlinear low Reynolds number model has been used to model the turbulence field. Results of Computations show that the zonal model predicts the profiles of velocity and turbulent stress as same as linear model and overestimate the turbulent stresses in separated zones but results of nonlinear model shows improvement in prediction of velocity and turbulent stresses in separated zones. Also, linear, nonlinear and zonal models have similar prediction about separation point of flow but nonlinear model has been predicted the level of Reynolds stresses and its changes from inner side toward outer side and maximum level of Reynolds stresses more accurate in comparison with zonal and linear models specially on near-wall plane.

This paper presents a steady state simulation model to analyze a direct expansion ground source heat pump that uses carbon dioxide as refrigerant in a transcritical cycle. The analysis considers pressure drop characteristic in heat exchangers of the system. The present numerical model has been developed to examine the system in different operating conditions in two discrete cases. These cases include constant evaporator loop length and specified heating capacity. Then model evaluate the system based on COP and heating capacity in the first case and COP and evaporator loop length in the second case. To evaluate the performance of the system, a parametric study is performed to investigate the effect of different parameters such as difference between soil temperature and evaporator outlet temperature, compressor speed, water inlet temperature, water mass flow rate, area ratio heat exchanger and soil temperature. In both studies, It can be concluded that in a specific temperature difference of the difference between soil temperature and the outlet temperature of the evaporator, there is a maximum value for COP. Also, increasing the compressor speed and the temperature of inlet water to the gas cooler is accompanied with the diminution of COP. Increasing the mass flow rate of inlet water to the gas cooler leads to surge in COP. The results of this study include heat capacity, coefficient of performance and ground heat exchanger loop length can be used for design and optimization of a direct expansion geothermal heat pump.

This paper proposes a new inexpensive soft force sensor suitable for soft robotics applications that require high flexibility and wide range of sensing area. All Hall Effect sensors developed so far use a Hall Effect sensor to detect the magnetic field of a piece of solid magnet. The proposed force sensor in this paper uses a Hall Effect sensor to detect the magnetic flux density change induced by aligned magnetic powder blended with silicone rubber when a normal force is applied. The sensor is designed and tested with different magnetic powder density and sensor dimensions to achieve an optimum design in sensitivity as well as linearity. The experimental results show that different force measurement range with specific desired sensitivity can be achieved by adjusting certain physical properties of the sensor. This is a useful feature for lots of soft sensing elements in today's applications requiring more compliance and reliable sensors, especially in soft robotics applications.