Modares Mechanical Engineering
Year:2017 | Volume:16 | Issue:10 |Papers Count:53

Characterization of mechanical properties of soft tissues using hyper-viscoelastic models has been of special attention in medical fields such as medical diagnosis. In most of these studies, only one single tissue has been analyzed and therefore, in cases that the lower tissue does not function well, generalization of obtained results for a tissue will not be suitable for other tissues. In the current study, mechanical properties of chicken chest and sheep liver, two different study cases, have been determined simultaneously using an indentation test. To determine the properties of the obtained model, inverse finite element method (IFEM) has been employed. Moreover, an optimization algorithm has been used for minimizing the differences of force-time curves that are obtained from indentation test and finite element analysis. By separating the force-time curve to two hyperelastic and viscoelastic parts, the parameters of each part have been determined individually using a separate inverse finite element method. This procedure results in reducing the computation time. Finally, the parameters of viscoelastic and hyperelastic models are determined by nonlinear root mean square error of 0.0695 and 0.0315, respectively. Comparison of the curves obtained from finite element analyses and those obtained from experiments shows the validity and capability of the employed method.

In this paper, the penetration process of anti-structure tandem projectiles is investigated by numerical and experimental methods. The used projectiles in this research have been composed of the forward shaped charge with conical copper liner and the following kinetic energy projectile with flat nose. For determination of cavity and tunnel geometry, at first follow projectile penetration test is done. In this process three shaped charge projectiles are tested. According to the same conditions for projectiles and concrete target, the obtained data of performed test are in good agreement with each others. Then numerical simulation of forward and follow projectiles penetration is analyzed by finite difference hydro code: AUTODYN. The numerical results obtained from the forward projectile penetration have been compared with experimental results. The comparisons between experimental and numerical results for forward projectiles show good agreement with each others. At the end of this research, the residual velocities of the follow projectiles are investigated by numerical method. The results also indicate that the residual velocity of follow projectile increases due to the damage in the concrete target, which is in agreement with which predictions.

In this study, the hybrid Lattice Boltzmann - Finite difference - Immersed Boundary method has been used for investigation of problems with heat transfer. For this purpose, mass and momentum conservation equations are solved by the Immersed Boundary- Lattice Boltzmann method and finite difference method has been used for solving energy conservation equation. The effect of Immersed Boundary has been shown as force and external energy source term in equations and therefore flow and heat transfer around circular cylinder and also the effect of how to move cylinder in heating of fluid inside the cavity has been studied. for this purpose four kinds of movements: circular reciprocating, normal circular, diagonal amplitude and horizontal amplitude have been considered for the cylinder and in all cases, the changes of force coefficients and Nusselt number have been discussed. It has been shown that the circular reciprocating movement has more effect on heating of fluid inside the cavity, which indeed reduces the time of fluid heating about 20 percent in comparison with normal circular and diagonal amplitude movement and approximately 37 percent in comparison with horizontal amplitude movement. In all of the studied problems, the efficiency of hybrid method has been proved.

This paper presents the control of a quadrotor using nonlinear approaches based on the experimentally measured sensors data. The main goal is the control and closed loop simulation of a quadrotor using feedback linearization and sliding mode algorithms. First, a nonlinear model of quadrotor is derived using Newton-Euler equations. To have a more realistic simulation the sensors noise performance was measured using a setup. Sensors data was measured under running motors. Since the experimental data for sensor had error and noise, Kalman filter was used to reduce noise effect. Results demonstrate good performance for Kalman filter and controllers. Results showed that feedback linearization and sliding mode controllers performance were good but angles changes were smoother on feedback linearization controller. With increasing uncertainty, feedback linearization performance was far from desired mode.The time to reach the preferred objective while increasing uncertainty had no significant impact on the performance of sliding mode controller. Thus feedback linearization controller added to PID is appropriate to maintain the quadrotor attitude while sliding mode controller has better performance to angle change and transient situations.

In the current study, with the aim of power and hydrogen production, combination of Matiant cycle with an ORC unit and PEM electrolysis has been analyzed from the viewpoints of energy and exergy. Waste heat of the Matiant cycle is used to run the ORC. Effect of some designing variables, i.e. evaporator temperature, minimum temperature difference in heat exchanger, degree of superheating in ORC turbine inlet and isentropic efficiency of ORC turbine on the rate of produced hydrogen, ORC produced power and exergy efficiency of the combined system has been investigated. It is observed that, increasing the minimum temperature difference leads to decrease in the rate of produced hydrogen, ORC produced power and consequently exergy efficiency of the combined system. Also, change in the evaporator temperature optimizes the rate of produced hydrogen, ORC produced power and therefore the exergy efficiency of the combined system. Also, results showed that increasing the degree of superheating in the ORC turbine inlet decreases the rate of produced hydrogen, ORC produced power and the exergy efficiency of the combined system. As expected, increasing the isentropic efficiency of ORC turbine leads to an increase in rate of produced hydrogen, ORC produced power and therefore the exergy efficiency of the combined system.

Composites are widely used due to their good properties such as high strength to weigh ratio, stiffness, resistance to buckling and fatigue, etc., in different industries. Parabeam three-dimensional composites have found a remarkable situation due to their high bending strength and extremely low weight compared to other sandwich composites. Drilling is necessary to connect them to other structures. In this research, the effects of rotational speed, feed rate and tool diameter have been studied regarding the amount of damage in drilling of 3D composites. A full-factorial design of experiments was used to assess the significance of drilling parameters, and digital photography technique with auto focus was used to evaluate the damages from drilling. The drilling operation was assessed based on two introduced factors including the matrix fracture factor (MFF) and uncut fiber factor (UCFF). The analysis of experimental results showed that among the main parameters, feed rate and rotational speed have the highest and lowest impact on MFF by 23.83% and 0.34%, respectively. But the experimental results for UCFF showed tool diameter with 17.17% is the most effective parameter. Both factors have similar behavior against the rotational speed which has the least impact on the output parameter. Rotational speed of 1750 rpm, feed rate of 0.1 mm/rev, and tool diameter of 10 mm were found to be optimal levels to obtain the minimum MFF and UCFF.

In this paper, dynamic modeling and control of a three-degrees-of-freedom parallel robot with pure translational motion is performed. Constraint equations are derived based on the kinematic model of the robot and Lagrange method is applied to derive the dynamic equations. In order to control the robot position on planned reference trajectories, in presence of uncertainties of the dynamic model a sliding mode controller is designed which is robust against the uncertainties and induced noises. Performance of the designed controller is simulated and evaluated in different conditions including the presence of noise and parameters variation. In this regard, a comparison has been made between the response of the proposed sliding mode controller and response of a feedback linearization controller, indicating their capabilities in noise rejection and compensation of parameters variation. Also, the effect of defining different sliding surfaces on the performance of the sliding mode controller, and using the integral of error instead of the error itself, have been studied and examined. Results show that the proposed sliding mode controller has a desirable performance in tracking the reference trajectories in presence of the model uncertainties and noise for this kind of parallel mechanism.

In this paper a nonlinear controller is designed for micro-beam’s deflections under mechanical shock effects. The micro-beam is supposed to undergo mechanical shocks. Mechanical shocks are one of the failure sources and the controller is to considerably suppress shock’s unfavorable effects. Half-Sine, rectangular and triangular pulses are chosen as reference shock signals to represent true complicated shock signals in nature which consist of different harmonics. Two layers of electrodes are placed in both sides of the micro-beam and are used to actuate the micro-beam by different voltage levels. Upper layer is specifically meant for control purpose. Nonlinear equations governing micro-beam’s deflection dynamics are derived, discretized by Galerkin method to a set of nonlinear duffing type ODEs and used to investigate micro-beams response to each shock input signal. Controller design is based on a simple nonlinear model formed by micro-beam’s first mode shape. Proper second order behavior is generatedby feedback linearization method as controller logic. Finally, controller performance and shock rejecting capability are evaluated by numerical simulations. Controller is shown to be very effective in diminishing shock unfavorable effects and postponing pull-in instability by numerical simulations.

Chattering is a kind of self-excited vibration encountered in different machining processes such as milling and turning. This type of self-excited vibration rapidly develops after commencement and destabilizes the whole process. This phenomenon leads to, among other issues, increased noise, wavy surface finishes, discontinuous chips, and failure in the tool or machine parts. The depth of cut is the main parameter in the occurrence of chattering in machining processes. Avoiding the critical depth of cut ensures the stability of the process. Process modeling is a way to obtain the critical depth of cut. The vibration-assisted turning process has many advantages and is of a different nature than the conventional machining. In this paper, the vibration-assisted turning process is modeled and numerically solved and the critical depth of cut is obtained. Validation of the results is performed using experimental data and comparison with conventional machining. In the vibration-assisted turning process, higher stability is obtained with lower ratios of cutting duration to the total vibration period.This ratio is directly proportional to vibration frequency and amplitude and is inversely proportional to the cutting speed.

in this paper, use of the spherical ground storage tank as a heat sink for cooling of the residential and office buildings in the climatic condition of Tabriz city is studied. For computing the heat transferred between the underground storage tank and the soil around it a new analytical solution is presented.Inside the storage tank, the analogy between thermal and electrical conduction is used for deriving heat balance equations. In ground around the storage tank, the transient conduction heat transfer equation in spherical coordinates is considered. The Sample building envelope is simulated in Energy Plus and the storage tank and fan coil are simulated in Matlab software. Finally the building and the underground storage tank is linked together and the performance of the direct cooling system is investigated. Results show that the dimension of the storage tank has significant effect on the comfort condition of the building. The optimum diameter is 3.5m and 3.0m for residential and office building. By decreasing the storage tank optimum diameter the discomfort hours increase significantly. Using storage tank with larger diameters than optimum diameter the discomfort hours increase very slightly. Also, results show that the optimum diameter for office building is lower than the residential building.

In this article, an immiscible two-phase flow in two dimensional ordinary and modified T-junction microchannels is numerically studied. To this approach, the Lattice Boltzmann method with Pseudo-Potential model is used. The accuracy of the present model is examined by the Laplace test, drop contact angle, and drop formation in an ordinary T-junction microchannel. The comparison shows that the present results have good agreement with previous numerical and experimental data. The effects of various parameters including Capillary number, flow rate ratio, width ratio, and drop contact angle on the width of the drop and on the distance between drops for ordinary and modified T-junction microchannels are investigated in detail. The results reveal that by simple modifications to the ordinary T-junction, smaller drops and lower distances between them are generated in the comparison of ordinary T-junction geometry under the same conditions. On the other hand, this study demonstrates that the multiphase flows in micro-devices are very sensitive to even small changes in the channel geometry. It also indicates that Lattice Boltzmann method with Pseudo-Potential model is an effective numerical technique to simulate the generation of drops in microchannels.

In this study, the double stage mixed refrigerant LNG system is investigated, which is known for having the highest efficiency among the liquefaction cycles. The main purpose is to evaluate the performance of double stage mixed refrigerant LNG system due to variations on the environmental and operating conditions of feed. Temperature, pressure and feed gas compositions are considered as variable environmental conditions during liquefaction processes. A basic system has been chosed to view the response of the DMR liquefaction system to these changes. Results show that with decreasing temperature and increasing pressure of feed natural gas, specific shaft work decreases. Moreover, since in this case, minimum approach temperature in heat exchangers are reduced only slightly from allowed value (3oC). Therefore this adventage can be used with accepting a slightly lower safety factor than the optimal case. Increasing temperature and decreasing pressure of feed natural gas cause increasing the specific shaft work as well as temperature cross occurance in heat exchangers and therefore these areas should be prevented using control strategies. Also, any changes in mole fraction of natural gas components make temperature cross in heat exchangers. Finally, due to the change of the natural gas components mole percentage, during the life of the well, the refrigerant composition in the cycle should be optimized regarding the new conditions.

In the present paper, a gas turbine (GT) unit with nominal capacity of 26.8 MWe, which is used for continuous production of electricity in Ilam Gas Refinery Company, has been investigated for combined production of cooling, heating, power and process (CCHPP). Critical parameters are measured and the potentials of transforming the GT unit to CCHPP are investigated from technical, economic, and environmental points of view. A heat recovery steam generator (HRSG) converts the exhaust energy to steam that can be used for three purposes of cooling, heating and process. The cycle is first evaluated thermodynamically, and to be assured regarding HRSG, its operation is studied by using the pinch technology. Economical evaluation is carried out by calculating initial investment, payback period, net present value (NPV) and internal rate of return. In addition, the impact of using CCHPP on reduction of environment pollutant gases such as CO, CO2, and NOx is studied. The results reveal that, the fuel energy saving ratio of 36% is achieved for the minimum pinch point temperature of 19 C in the HRSG unit. The payback period is only 5.2 years, and the NPV during the project lifetime is 1.87 M$.Moreover the CO2, CO, and NOx reduction is about 32000, 22 and 27 tons/year respectively.

The present paper introduces a new electro-hydro mechanical fuel metering and control system for a turbojet engine. The developed metering system uses a new direct drive rotary proportional metering valve, which is coupled to a servomotor. The aim of this new design is to modify and optimize the mission of a constant speed turbojet engine. The main innovations in the present design include: the rotary actuating mechanism, rotary metering valve configuration, direct drive rotary metering valve configuration and the special metering flow geometry. Due to rotary direct drive metering section design, the parts count, manufacturing cost and system weight are decreased with respect to usual methods. Another benefit of the innovated valve is improvement of the control resolution. The fuel metering area in the present developed system consists of a triangular shape on sleeve and a rectangular shape on plunger. Mathematical modeling and system simulations are applied to acquire design parameters for different working conditions. After manufacturing a prototype, rig testing is done. The results of simulations and experimental measurements are compared in the last section of the paper.

In this paper, an analytical model has been developed for modeling high velocity impact on ceramic/nanocomposite targets. In this model, penetration resistance of ceramic is determined based on cavity expansion analysis and variables during perforation of projectile onto ceramic are considered.Also, the force of ceramic-composite interface is modified. Ballistic performance of the ceramic/composite target is investigated with addition and dispersion of nano particles of zirconia (ZrO2) in the matrix of back up composite. Ballistic impact tests were performed to validate the analytical predictions. These tests were performed by firing 10 mm steel flat ended projectile onto ceramic/composite target. Front layer is alumina ceramic and composite laminates of back up made of E-glass/epoxy with and without nano-zirconia particle of 5 wt%. The effect of nano-zirconia dispersion in the matrix for different failure modes is discussed. Experimental results revealed an improvement in the ballistic performance of samples with nano-zirconia particle. The analytical predictions of ballistic limit velocity and residual velocity of projectile are found to be in good agreement with the experimental results.

The thermoelasticity problem in a thick-walled isotropic and homogeneous cylinder is solved analytically using finite Hankel transform and Laplace transform. Time-dependent thermal and mechanical boundary conditions are prescribed on the inner and the outer surfaces of the hollow cylinder. For the thermal boundary conditions, the temperature itself is prescribed on the boundaries.For the mechanical boundary conditions, the tractions are prescribed on both the inner and the outer surfaces of the hollow cylinder. Obtaining the distribution of the temperature throughout the cylinder, the dynamical structural problem is solved and closed-form relations are derived for radial displacement, radial stress and hoop stress. As a case study, exponentially decaying temperature with respect to time is prescribed on the inner surface and the temperature of the outer surface is considered to be zero, where the mechanical tractions on the inner and the outer surfaces of the hollow cylinder are assumed to be zero. On solving the dynamical thermoelasticity problem, a thermal shock was observed after plotting the results. Using the obtained plots, instants of dilatation wave being reached to specific radial positions are computed and compared with those from the classical formula.

Accurate measurement of unsteady pressure fluctuations along a surface requires experimental set up with high spacing resolution and high frequency domain. Therefore, in recent decades extensive studies have been conducted on remote microphone approach. In this method, instead of using flash mounted sensors, they were installed remotely and connected to the model surface through one or several continuously connected tubes. Surface pressure fluctuations travel within the tubing in the form of sound waves and they are measured when passing over the remote pressure sensor, mounted perpendicular to the tubing. In the present study, an analytical solution of sound waves propagation inside the rigid tubes is used for modelling of the remote microphone system and to investigate the effects of its parameters on dynamic response. In order to verify the accuracy of proposed modeling, the dynamic response of a typical remote microphone has been obtained through experimental calibration.Comparing the analytical and experimental results indicates high accuracy of the analytical modeling.Results show that changes in tubing diameter lead to occurrence of resonance and creating harmonics in two frequency regions. The amplitude of low-frequency harmonics depends on the length of the damping duct and decreases with increasing of its length. Instead, the amplitude and frequency of highfrequency harmonics depend on the length of the first tube and they decrease with the increase of first tube length. Also, increase of the first and second tube lengths leads to an increase in phase of dynamic response of the remote microphone system.

This paper presents a new Neuro-fuzzy control system to control rigid-flexible manipulators. Enhancing the performance of fuzzy controller and intelligence in fuzzy and non-fuzzy units is the goal of this research. Proposed control system includes a fuzzy controller in the feedback and a neural network is the feed-forward. The network has the responsibility of estimating the inverse dynamic of device and then, the production of control command. Updating weighting coefficients of network is done online using the fuzzy controller output. On the other hand, two dynamic recurrent neural networks are used for making fuzzy unit intelligent. Networks are responsible for regulating the main factors of membership functions in the fuzzy controller. The input of these networks is error and error change rate and their weights are done by using an error back-propagation algorithm. To verify the effectiveness of the proposed method, simulation is conducted for skilled manipulators with three interfaces where the end interface is flexible. System responses to step input and sinusoidal input are separately obtained for fuzzy controllers and proposed controller and compared. Comparison and studies indicate the effectiveness of the provided method.

Structures might be subjected to impulse loads such as impact loads in their usefull lifetime. Production of new materials that are shown less vulnerable to sudden shocks and vibrations, is an issue that should be considered. Concrete is a brittle material and when is exposed to dynamic loads, in addition to its injury, it may cause damage to the environment due to disintegration. In this study, waste rubber particles were replaced with fine aggregate in concrete mixture in 3 sizes, 0-1, 1-3 and 3-5 mm and in volume ratio of 0%, 10%, 20%, 30%, 40% and 50%. First, with compressive strength test, optimum sizes of rubber particles were obtained, then silica fume and polypropylene fiber were added to concrete mixture that contained optimum size of rubber particles. In addition, compressive strength, dry unit weight, velocity of ultrasonic wave, impact with drop hammer and gas gun device test were done. The results show that, adding rubber particles to concrete mixture decreases compressive strength but increases ductility. Also, silica fume because of pozzolanic properties increased adhesive in concrete matrix, so the increased strength of concrete and polypropylene fiber increased the ductility of concrete.

In this paper, constraint equations are derived based on the kinematic model of the robot and Lagrange method is applied to derive the dynamic equations. In order to control the robot position on planned reference trajectories, in presence of uncertainties of the dynamic model, an adaptive robust controller with uncertainty estimator is designed which is robust against the uncertainties and induced noises. The proposed controller consists of an approximately known inverse dynamics model output as model-based part of the controller, an estimated uncertainty term to compensate for the un-modeled dynamics, external disturbances, and time-varying parameters, and also a decentralized PID controller as a feedback part to enhance closed-loop stability and account for the estimation error of uncertainties.Performance of the designed controller is simulated and evaluated in different conditions including the presence of noise and parameters variation. In this regard, a comparison has been made between the response of the proposed adaptive robust controller and response of a feedback linearization controller, indicating their capabilities in noise rejection and to compensate parameter variations. Also, the results show that the proposed sliding mode controller has a desirable performance in tracking the reference trajectories in presence of the model uncertainties and noises for this kind of parallel mechanism.

Bulging with elastomer tool has been used in the production of integrated hollow parts as one of the flexible forming methods. Nowadays, most industries such as Aerospace and military are using flexible die forming methods due to their flexibility, high quality and lower cost. In this research, finite element simulation has been implemented by ABAQUS software to investigate the behavior of stainless steel 304 tube bulging process using elastomer tool. By comparing the geometry of deformed tubes in experimental tests and simulation results, the FEM model was verified. The aim of this study is to determine the process factors and their effects on the average thickness and depth of bulged tube. In this regard, design of experiment (DOE) was performed using a full factorial method and the results were interpreted using analysis of variance (ANOVA). Also, a regression model was presented to predict these responses. Results showed that among the studied factors, friction (between tube and rubber), rubber height, punch displacement and tube axial feeding have significant effects on the process.Finally, the optimal values for significant factors were presented.

In this paper, the effect of heat treatment on the impact behavior of A356 aluminum alloy foams reinforced by SiC particles was studied and new results were generated. The foam was manufactured by direct foaming of melts with blowing agent CaCO3. A number of foam specimens were processed by T6 aging treatment. The drop-weight impact test with a hemispherical striker tip and velocity of 6.70 m/s was carried out on five untreated foam specimens and five heat-treated foam specimens, and the load versus time history data was obtained. The obtained impact response of A356/SiCp composite foam includes three stages: an elastic region, a plateau of load region and complete failure region. In plateau region, the plastic deformations can be tolerated by the foam at nearly constant load. The small amounts of standard deviation and coefficient of variation (for different parameters) obtained from statistical analysis of experimental data indicates the reliance on the results for quantitative analysis of them. The measurements showed that heat treating of Al foam results in an increase of the plateau load level and energy absorption capacity of the foam with 48.1% and 40.3% increase respectively. The length of plateau region is also decreased due to heat treatment. Regarding the significant improvement of mechanical properties of the foam and increase of its impact strength, the heat treatment after foam casting can be considered as a suitable approach for various industrial applications of aluminum foam.

In the current study, seismic cracking identification of concrete dams is conducted based on extended finite element method (XFEM) and Wavelet (WT) transform. First, the dam is numerically modeled and analyzed using the finite element method (FEM). Then cracking capability to the dam structure is added by applying the XFEM without introducing the initial crack, and the dam is analyzed under the seismic excitation. In fact, the whole dam structure is potentially under damage risk, and any zone reaching the fracture limit, begins to crack, which grows in the structure. This crack is usually unpredictable and is not easy to detect, therefore the structural modal parameters and their variation should be investigated based on structure response by using time-frequency transform. Results show that, investigating timefrequency window of the structure response and model parameters obtained from the numerical model, the history of physical changes occurred in the structure, cracking initiation time, and damage localization is done from comparing the intact and damaged vibration modes. Moreover, investigating the first natural modal indices of the intact and damaged structure, damage initiation and its location on Koyna dam height is easily detected, while for the second natural frequency it is not true.

One of the important purposes of aero-engine high speed compressor design is to decrease compressor weight. In order to achieve this purpose, it is required to increase the capability of producing pressure in each individual stage of the compressor. The most common way is use of high pressure aspect ratio blades. These long and thin blades are exposed to serious vibrations in the high speed flow because of the aeroelastic instability. Mechanical designers link adjacent blades by using mid-span shroud (damper) to decrease the blades destructive vibrations. These dampers cause flow blockage and turbomachine performance loss. In this study, the effect of mid-span damper on turbomachine aerodynamic operation has been investigated. In the previous studies there was less focus on the effect of damper on blade shocks, trailing edge vortices and near stall condition. Both with and without midspan damper have been investigated and compared. On the other hand, the damper effect on the formation and behavior of shock induced separation has been investigated in each of the two cases. As a result isentropic efficiency is decreased. These dampers also cause 33% pressure on blades. To avoid this pressure loss, the blade length is increased by 2.7%. Turbulence due to presence of damper leads to the distortion of vortices pattern in training edge.

In this paper, with a comprehensive approach the energy, exergy, economic and environmental (4E) analyses of an organic Rankine cycle (ORC) to produce combined heat and power (CHP) based on solar energy have been performed. In order to perform a plenary survey, after thermodynamic modeling of the ORC, the study of the flat plate solar collectors (FPC), parabolic through solar collectors (PTC) and gas-fired boiler as the energy supplier equipment in the independent or combination models, as well as in the open or circulated state of the heat source flow have been done. In the open heat source flow state, the outlet flow of heat source at temperature of 80 °C is used to provide required heat in different sectors; however, in the circulated flow state, the amount of required primary energy is less than the open heat source flow state. Also, the use of photovoltaic panels to provide the pumping power of cycle is studied. The calculations show that the cost of produced power from lowest to highest is related to the use of gas-fired boiler, parabolic trough solar collector, photovoltaic panels and flat plate solar collectors respectively. Also, because of the efficient use of energy resources in the combined heat and power generation (open heat source flow) compared to power generation (circulated heat source flow), the energy and exergy efficiencies are increased %8.61 and %8.11 respectively; although the open heat source flow system compared to circulated flow system require higher investment cost.

In this paper a method for online solution of the Hamilton-Jacobi–Bellman (HJB) equation is proposed.The method is utilized to design an optimal controller for continuous-time nonlinear systems. The main concept in this approach is using experiences to reinforce the controller, which is called Reinforcement Learning (RL). The online solution is based on the actor-critic (AC) structure where two Neural Networks (NNs) approximately solve the HJB equation. Optimal control and optimal value function are approximated by the actor and the critic, respectively. Then, employing gradient descent algorithm, accuracy of the approximation is improved. Since some items like friction and damping are difficult to model and calculate, a neural-robust identifier is used in conjunction with the AC to approximate drift dynamics. Finally, the Actor-Critic-Identifier (ACI) structure is proposed to solve the HJB equation online with no prior knowledge of drift dynamics. The closed-loop stability of the overall system is assured by the Lyapunov theory employing the direct method. Then the effectiveness of the proposed method is illustrated by experiment for DC motor and simulation for a nonlinear system. Results indicate satisfactory performance of the proposed method to solve the Hamilton-Jacobi-Bellman equation.

The main task in finite volume methods (FVM) is to estimate proper values on the cell faces based on the calculated values on the nodes or cell centers. In this way, upwinding schemes are the most successful schemes for estimation of values on the control volume faces. These schemes have been developed in FVM for various techniques with proper accuracy on different kinds of structured and unstructured grids. In this research, the physical influence scheme (PIS) is developed to the cellcentered FVM in an implicit coupled solver and the results are compared with other two main branches of upwinding methods: exponential differencing scheme (EDS) and skew upwind differencing scheme (SUDS). Accuracy of these schemes is evaluated in lid-driven cavity flow at Re=400-10000 and backward-facing step flow at Re=800. Simulations show considerable difference between of the results EDS scheme with benchmarks, especially for lid-driven cavity flow at high Reynolds numbers which occurs due to false diffusion. Comparing SUDS and PIS schemes shows relatively close results in backward-facing step flow and different results in lid-driven cavity flow. The poor results of SUDS in cavity flow can be related to its non-pressure sensitivity between cell face and upwind points which is critical for such vortex dominant flows. Instead, the PIS scheme by applying a momentum equation between the cell face and upwind points, is able to capture flow vortices properly and matching well with benchmarks.

In the present study, the direct utilization of borehole as a heat sink for both residential and office building is investigated in Tabriz city. The effect of external wall insulation and window glazing is studied in the form of four cases and the performance of the ground sink direct cooling system is investigated for these cases. The borehole design depth is calculated by analytical method. Both sample residential and office buildings are investigated. The borehole design depth depends on the quality of the building design and its heat emission. The results show that using double glazed windows, compared to single glazed windows reduces the borehole design depth by about 10 percent. Also, the utilization of insulation in external walls and roof decreases the borehole design depth more than half compared to buildings without insulation. Finally, the potential of the ground sink direct cooling in sample residential and office buildings is investigated for four cases. The results show that by using ground sink direct cooling system, thermal comfort is satisfied in almost all of the cooling hours in both sample residential and office buildings.

Nowadays, atomic force microscopy has widely attracted researchers’ attention in manufacturing of micro/nano equipment. For this purpose, the displacement and manipulation equations for micro/nanoparticle are essential. Although surface forces such as friction and adhesion are ignorable in macro scale, increased surface to volume ratio in micro/nano scale makes them very important. Various friction models have been used for two-dimensional manipulation in previous works. In this paper, HK friction model has been used to model and simulate three dimensional manipulation dynamically in order to have closer results to real manipulation. For this purpose, the important friction models have been studied and developed for use in micro/nano scale. Then, three-dimensional manipulation equations have been obtained and stiffness coefficient matrix for beam is extracted and all of the equations are combined to calculate the critical force and time of manipulation. Finally, simulation of obtained equations was used to calculate the critical force and time values of the three-dimensional manipulation for gold particle using HK friction model. The results indicate that rolling starts aroundx axis beforey -axis, and sliding starts along y -axis before x -axis.

In this paper, the effect of extrusion die profile on the dimensional tolerance of a cross section of a part in a forward extrusion process was studied. In these experimental and numerical investigations, some parameters such as extrusion speed, metal flow, extrusion temperature and extrusion force were considered as process variables. The specimen was aluminium alloy 2014 with a variable wall thickness. The variable wall thickness causes the metal flow rate to be changed along the die orifice. As a result, the die which is used to produce this part must be suitable to control the flow rate of metal. In this study, two different dies were used to produce this part. In the first die, to control the metal flow, variable bearing length method is used. In the second die, in addition to the bearing length method, a feeder is used in the narrow channels. From the experimental and numerical results, it was found that the first die is not good enough for manufacturing of this part. Because, the first die was not able to control uniform metal flow rate through the die orifice during the extrusion process. This drawback causes the die cavity to remain empty at the sharp corners which results in a low quality and low dimensional accuracy in the product, especially in narrow channels. The numerical analysis results have shown that, the second die performance was much better than the first one. It was able to control uniform metal flow rate which causes high quality products.

Sheet Metals are widely used in different industries such as ship building. One important subject in these industries is to create the desired sheets through line heating process. In this paper, first, the simulation of heat transfer between a gas torch and a plate during the line heating process is investigated. Impingement jet model is used to simulate the effect of a heat source (flame) and air cooling on the plate by using the commercial engineering software, FLUENT. Then, the computed temperature distribution by FLUENT is fed into the ANSYS FEM package for thermo Elasto-Plastic deformation analysis and the results are validated. Process execution needs heat paths and heat conditions. For this purpose heat paths of the cylindrical shape were obtained based on the Strain-Based Method. For thermal conditions a neural network was trained. In this regard, close to 63 different situations in different powers and torch speeds were run. Finally, to verify the thermal characteristics obtained for the cylindrical shape, paths and thermal conditions obtained were passed on a flat sheet metal by simulation and the result was compared with the desired shapes. It was shown that the Strain-Based Method is very practical in determining the thermal paths.

Accumulative roll bonding is new method of severe plastic deformation that in the last decade, utilized to produce many materials. In present study, investigated mechanical properties and fracture mode of microstructure and multi-layered Al-Al fabricated during accumulative roll bonding process.Accumulative roll bonding process applied without using lubricant, in the ambient temperature repeated in seven cycle continuously and without heat treatment between cycles of process that the value of reduction thickness is 50% in each cycle. The evaluation of mechanical properties and fracture mode performed by uniaxial tensile test, micro hardness and scanning electron microscope (SEM) and reveled that by increasing number of ARB cycles, micro hardness and tensile strength increased that increasing rate at initial cycles more than last cycles. Also elongation after first cycle decreased and then increased.The variation for mechanical properties during ARB due to governing cold work and high strain hardening at initial cycles and improve microstructural and grain refinement at last cycles. Maximum value of tensile strength and micro hardness achieved in last cycle (seventh cycle) that compared with primary annealed sheet 241.4 and 106% increased, respectively. Also results of SEM demonstrated that by rising the number of ARB cycles, viewed dimples with shallower and smaller than the initial sample and changed fracture mechanism from ductile to shear ductile.

Precise modeling has great importance in systems which are designed to work in transonic regions. The scope of current investigation includes numerical simulation of static aeroelastic phenomena of deformable structures in transonic regimes. Transonic flow brings lots of instabilities for aerodynamic systems. These instabilities bring nonlinearity in flow and structure solvers. Due to improvements in numerical methods and also enhancement in computing technologies, computational costs are reduced and high-fidelity simulations are more applicable. Simulations in this paper are done in transonic flow (M=0.96) on the benchmark wing AGARD 445.6. The procedure includes modal analysis, steady flow simulation and investigation of structure’s elastic behavior. At the first phase, the geometry model is validated by modal analysis with regard to comparison of first four natural frequencies and corresponding mode shapes. Then, a loose or staggered coupling is used to analyze aeroelastic behavior of the wing. In each simulation step, imposed pressure on the surfaces of the wing caused by transonic flow regime deforms the structure. In the results section, a comparison between imposed pressure coefficients in each step with the existing literature and experimental results is reported. Also, pressure coefficients in each step is calculated and reported. In this investigation by using multiple steps in oneway fluid-structure analysis, deformations are reduced in each step and, as a result, the structure reached its static stability point.

Metal forming is a conventional manufacturing process whereby a material with simple form is subjected to plastic deformation and results in industrial end products. Reduction of forming forces and improving product quality has been a promising subject for investigators and artisans. For this purpose, primary methods such as increasing material temperature and modern methods such as use of high power low amplitude ultrasonic vibrations were introduced. In ultrasonic assisted forming, high power ultrasonic transducer produces low amplitude high frequency mechanical vibrations which were transmitted to material subjected to deformation and contacting surfaces of tool/workpiece. Results show reduction of forming forces and tool wear as well as improved surface integrity and dimensional stability that lead to increasing production rate and process efficiency. Considering the importance and capability of ultrasonic assisted metal forming, this paper is concerned with application of ultrasonic vibration on metal forming processes. To this purpose, fundamental principles and mechanisms of application of high power ultrasonic were introduces and discussed. Also, industrial future of this technology as well as its advantages, range of application and its restrictions were mentioned.

In this study, A356 aluminum alloy matrix composites reinforced with different weight percentages of SiC nano- and microparticles respectively with 50 nm and 5 mm average particle sizes were fabricated by stir casting method. Due to the effect of T6 heat treatment on the strength and hardness of A356 alloy, the obtained composites were subjected to the T6 heat treatment. The mechanical properties such as hardness and compressive properties of the composites were investigated. Microstructures of the samples were also investigated by an optical microscope (OM), scanning electron microscope (SEM) and field emission scanning electron microscope (FESEM). Microstructural investigation indicated that T6 heat treatment led to the change of eutectic silicon morphology and formation of the Mg2Si precipitates during age hardening stage, leading to increased hardness and compressive strength. The results showed that an increase in wt.% of nanoparticles leading to increased hardness and compressive strength. The results of microstructural investigation showed the relatively uniform distribution of reinforcement particles. Also, the strength and hardness of the composites reinforced with nanoparticles were greater than those of the composite reinforced with microparticles, even with higher weight percent of reinforcement particles. Hardness and compressive strength at 35% strain for the composite reinforced with 1.5 wt.% nanoparticles were respectively obtained 62 HBN and 252MPa, which are improved compared to the base alloy.

Super alloys due to special features such as high resistance to corrosion and heat, have the ability to maintain mechanical and chemical properties at extremely high temperatures which are used in various industries, especially in the aerospace industry. On the other hand, very low heat transfer coefficient and high toughness with work hardening in these alloys caused the machining of them to be seriously challenged. In the present study, the effect of cutting parameters on surface roughness of A286 superalloy has been studied in different lubrication conditions. Response surface method experimental design was used to plan experiments. In order to investigate the effects of machining parameters and conditions of lubrication on the surface roughness, Two factors - cutting speed and feed rate- on three levels and minimum quantity lubrication conditions and wet method are considered as the main parameters. In order to investigate the Tool wear and workpiece surface quality, the images of Scanning Electron Microscope and optical microscope are used. The results show that using the minimum quantity method of lubricant caused cooling-lubrication fluid particles penetrating power to the cutting zone to increase and improves the process by reducing the surface roughness. It was observed that with increasing feed rate in fixed cutting speed, numerical values of surface roughness in Ra criterion are taken apart for different lubrication circumstances and its value for the minimum quantity method of lubricant is less, which shows the superiority of this method over the wet method.

In this paper, a single bubble free ascending in a vertical channel was studied experimentally. Five different Newtonian fluids were used where the surface tension force is dominant. The bubble trajectory was considered in water, glycerin 30 and 50 Vol% that is zigzag, however, linear behavior is observed while the weight concentration of the glycerin reaches to 80 and 100 percent. The bubble rise velocity and aspect ratio coefficient are calculated by image analysis via MATLAB software. The results are in a very good agreement with the literature for the bubble velocity. The effect of magnetic field (perpendicular to the bubble flow) on the hydrodynamic characteristics of the bubble for each of the working fluids has been scrutinized. Although the presence of the magnetic field does not affect the bubble trajectory type or change the flow pattern from zigzag to linear, it reduces the flow domain where this descending trend decreases with the increase in viscosity. It should also be noted that the magnetic field causes the bubble rise velocity to increase while this enhancement increases with higher viscosity. The magnetic field effect on the bubble aspect ratio was also considered and it was found that as viscosity increases the aspect ratio change decreases.

Hot gas forming process forms materials with low formability or high strength at room temperature such as aluminum, magnesium and titanium. With increasing temperature, the formability of these metals increases and the strength decreases. In this process, for producing products with desirable properties, determination of optimal parameters is essential. In this study, hot gas forming process was investigated numerically by using Abaqus software, and the effects of input parameters on the outputs were studied by analyzing simulation results. In order to validate simulation results, the experimental test was carried out by using hot gas forming setup. For modeling hot gas forming process, artificial neural network and regression models was created by using data obtained from the numerical simulation and then the accuracy of these models was examined. In these models, pressure, axial feeding and time were assumed as input parameters and the radius, minimum and maximum thickness were considered as output. In the next stage, best model was used as input function in multi-objective genetic optimization algorithm to obtain Pareto front and optimum process parameters. Optimum parameters were obtained as follows: pressure 15.82bar, axial feeding 2.76mm and time 69.02s. In addition, values of radius corner, minimum and maximum thickness achieved from using optimum parameters are 4.43mm, 0.808mm and 1.93mm respectively.

In the current study a combined heat and power (CHP) system based on diesel engines is studied. After modeling the different components of a CHP system, the system is investigated parametrically according to first and second laws of thermodynamics. In this investigation instead of modeling the air standard cycle, the fuel air standard cycle and fuel combustion are simulated, which leads to more accurate results. However, a standard cycle has many differences with an actual cycle, and therefore the results of its analysis will be, to some extent, different from the results of analyzing the corresponding actual cycle. Therefore, the exhaust gas from combustion chamber of a diesel engine is also used to simulate the CHP system, and the heat exchanger of the CHP is investigated from exergetic and economic viewpoints. It was seen that, applying the pre-described system, it is possible to warm up 0.17kg/s water from 25°C to 68.64oC. This enhances the overall efficiency of the system about 20%, raising it up to 80%. Exergy destruction in heat exchanger is slightly high which is due to heat transfer process and high temperature difference in the heat exchanger.

Electrochemical supercapacitors store energy in the electric field formed at the interface of electrode/electrolyte in the electrochemical double layer. Compared to conventional capacitors, using high surface area electrodes results in the extremely large capacitance in supercapacitors. A mathematical model has been developed to investigate the effect of electrode thickness and porosity on the performance of double-layer supercapacitor. The model is based on the conservation of species and charge governing equations. This model drops the common simplifying assumptions of concentrations uniformity and capacitance independence of voltage in supercapacitors models. The model can predict the experimental data of cell voltage with high accuracy and is used to examine the effect of utilizing different electrode thicknesses and porosities on the performance. In the design and operation condition of supercapacitor considered here, specific capacitance increases as electrode thickness increases for electrode thicknesses from 70 to 90 micrometer and decreases as electrode thickness exceeds 90 micrometer. Employing more porous electrodes enhances specific capacitance. The amount of increment is such that if the electrode porosity is doubled, specific capacitance increases byapproximately 5%.

Heavy oil and tar sands resources comprise about 70 percent of the world's oil reserves and this reservoirs can offset the declining production from conventional reservoirs. Thermal enhanced oil recovery (EOR) methods are employed to exploit the huge reserves of heavy oil due to their high viscosity values. Thermal processes aim to increase its mobility in order to improve its production.Among these methods, the steam-assisted gravity drainage (SAGD) is one of the most efficient techniques. In this method, two horizontal wells are drilled and hot steam is injected from a well to move oil toward the other well. Optimization of operating parameters during this process is very important. The injection rate or pressure control of wells are the most common EOR methods. In this paper for the first time, in addition to the injection rate of the injector and production wells, the steam injection temperature is also optimized. It was shown that there is an optimum amount for the temperature of injected steam. In addition entropy generation analysis was performed for different cases. To simulate the process, a commercial software was used and optimization of operating parameters is performed using the pattern search algorithm. Entropy generation calculated based on the results of numerical simulations using a computational code has been written for this case. The results show that the maximum oil production corresponds with the minimum entropy generation number and thus the entropy number can be used as an appropriate objective function in order to enhance oil recovery.

In this study, an application of support vector machine (SVM) for early fault detection in a Benson type once-through boiler is presented. Thermal conditions disruption inside the boiler during load changes is the main reason for level changes of the start-up vessel. Because of complexity of the system’s dynamics, first the effective variables on increasing the level of start-up vessel were identified based on experimental data from a power plant unit. Then, the dimension of input variables was reduced by selecting appropriate features. Experimental results show that the hotwell surfaces’ temperature could be considered as the most appropriate indicator for steam quality deterioration. By comparing the extracted features from healthy and unhealthy conditions, appropriate fault model was developed using SVM with radial basis function (RBF) as the kernel. The performance of fault detection system was evaluated with respect to the similar faults at two different time periods that happen in a steam power plant. The obtained results show the accuracy and feasibility of the proposed approach in early detection of faults during the unit’s load variations. Advantage of the proposed technique is the prevention of false alarm in power plants’ boilers as load changes.

In transmission lines the environmental disturbances causes vibration of the lines (cables) as well as the structure which have destructive effect on the line and its components. To overcome this harmful effect, it seems necessary to reduce the transmission line vibration level. One of the most frequent methods for reducing the transverse vibration of cables is using dynamical dampers such as Stockbridge damper.Complication of calculating the bending stiffness as well as the energy absorption mechanism of these dampers makes it more difficult to be modeled. In this study the dynamical characteristics of Stockbridge damper considering the damping effect are studied. For system identification of Stockbridge damper, it is modeled as a 4DOF system and its various unknown parameters are obtained using model updating method and experimental modal analysis (EMA) which is optimized by Artificial Intelligence (AI) method. Then the effects of varying these parameters on its energy absorption are discussed. Finally, to validate the analytical results, some experimental tests were carried out on the energy absorption of Stockbridge damper. The analytical results are in good agreement with the experiments.

In recent decades, experimental studies of the vortex-induced vibration (VIV) became one of the interesting fields of science. However, a variety of assumptions and methods of experiments have led to different results in various researches. Several parameters such as mass ratio, aspect ratio, degrees of freedom, and boundary conditions affect the VIV response of a simple circular cylinder. The current paper reports and discusses the results of in-water VIV experiments on an elastically mounted rigid cylinder with various types of end conditions. This paper focusses on the effects of the end condition by attaching an endplate to a circular cylinder and the results are compared with those from a cylinder with no endplate. The Reynolds number ranges from 5.8×103 to 6.6×104. Experimental setup has also been compared and verified with some classical results of VIV. Results of current study were favorably compatible with previous researchers’ results. The experimental results show that, the end condition noticeably changes the VIV amplitude, especially in the lock-in area. Moreover, non-dimensional amplitudes shift to the higher reduced velocities when the endplate is removed. In the frequency responses, the cylinder with no endplate has lower quantities rather than the cylinder with an attached endplate. Evaluation of lift force coefficients also shows a similar pattern of effects on the nondimensional amplitude. Consequently, the excitation of the structure in the lock-in region increases when the endplate from the cylinder’s end is removed.

The design of combustor has long been the most challenging portion in the design process of a gas turbine. This paper focused on the conceptual design methodology for aircraft combustors. The necessity of this work arose from an urgent need for a comprehensive model that can quickly provide data in the initial phases (conceptual design and preliminary design) of the design process. The proposed methodology integrated the performance and the design of combustors. To accomplish this, a computer code has been developed based on the design procedures. The design model could provide the combustor geometry and the combustor performance. Based on the available inputs data in the initial phases of the design process, a chemical reactor network (CRN) approach is selected to model the combustion with a detailed chemistry. In this way, three different chemical mechanisms are studied for Jet-A aviation fuel. Furthermore, the droplet evaporation for liquid fuel and the non-uniformity in the fuel-air mixture are modelled. The results of a developed design tool are compared with data of an annular engine’s combustor. The results have good agreement with the actual geometry and outputs of engine test rig emissions.

In this research, the influence of multi-walled carbon nanotubes (MWCNTs) on the fracture resistance of epoxy-based nanocomposites under out-of-plane shear (mode III) was investigated experimentally and compared with their effect in the case of tensile (mode I) loading. Due to its wide industrial applications and low viscosity, epoxy LY 5052 was used to manufacture the nanocomposite specimens.The MWCNT contents considered for nanocomposite samples were 0.1, 0.5 and 1.0 wt.%. Ultrasonic homogenization technique was employed for dispersing nano-fillers in the matrix resin. In order to measure the fracture resistance of pure epoxy and nanocomposite specimens under mode I and mode III loading conditions, a loading fixture recently developed for mixed mode I/III fracture tests was utilized.The obtained results showed that in both loading conditions, increasing MWCNTs content up to 1.0 wt.% enhanced the fracture resistance. However, the maximum values of mode I and mode III fracture toughness were attained in the nanocomposites containing 0.5 wt.% and 1 wt.% MWCNT, respectively.Finally, the observed trends in the experimental results have been discussed using the effective micro mechanisms of CNTs inside the polymer matrix.

Various configurations for Stirling engines have been presented. In Beta and Gamma type configurations, a displacer moves the working fluid between hot and cold sources. In the Alpha type there is no such part and it has a much simpler structure than the Beta and Gamma type. Therefore in this study, a novel configuration is introduced for Stirling engine where the displacer is replaced by two pistons and cylinders. With this replacement, the new configuration can be called 3-Cylinders Gamma configuration for Stirling engine. Similar to Alpha type engine, this configuration has a simpler structure and manufacturing process. For evaluation of new configuration, a simulated model of fabricated Gamma Stirling engine is prepared based on new configuration and geometry of ST-500 engine. The modeling is developed in GT-Suit software which is an industry-leading simulation tool.Maximum error between the experimental results and simulation of the new engine is about 20 percent for heat consumption and 14.7 percent for power generated. Thermodynamic analysis of performance parameters is done after the validation. The thermodynamic analysis results indicate that the increment of engine speed does not have appropriate effect on the performance and this led to engine efficiency reduction. On the other hand, increasing the pressure and hot source temperature led to improvement in engine performance and higher thermal efficiency.