Modares Mechanical Engineering
Year:2018 | Volume:18 | Issue:2 |Papers Count:48

Plume reversion due to missile ascending and related flow expansion and its interaction with missile body especially with missile base has been an important concern of investigators and missile designers. The aim of the current is investigation of effects of different parameters on the interaction of plume and missile body. To do this, heat flux on the missile body at different conditions including different flight conditions, turbulence modeling, base length and nozzle modeling has been studied. In the following, plume induced flow separation is studied. To model flow field, Gambit 2.4.6 and Ansys Fluent 17 are used for grid generation and flow simulation respectively. The results show that with increasing in flight height, plume at the base of missile gradually expands and finally covers the base completely. As well as, it can be seen that plume expands more rapidly in the base region and reduces heat flux when the nozzle is not considered. The reduction of heat flux is different in various parts of the base, ranging from zero to a maximum of 83% in areas far away from or near the nozzle. In the end, the effect of the base length was investigated. The results showed that as the base length is increased, the vortices are further expanded and this expansion leads to increased heat flux so that when the base length is doubled, the heat flux is increased by 20% at most.

Transient flows can also be analyzed in the frequency domain in addition to the time domain. The frequency domain needs no discretization in time and space and this is a one of the advantages of using this domain. Due to this reason, time of computations is reduced. For the frequency analysis of transient flows, the non-linear terms of the governing equations and boundary conditions must be linearized. It causes errors in the output of the frequency domain over the exact model of the characteristics method (MOC). Understanding the effect of each non-linear terms separately in the error caused by the frequency domain leads to a greater insight into this domain and provides the basis for future activities to improve this domain. In this study, the individual effects of each non-linear terms of the steady friction and valve in the generated error in the frequency domain output are shown by using a Reservoir-Pipe-Valve (RPV) system which has been excited oscillatory. This study has demonstrated that the effect of the friction term of steady flow on the generated error in the output of frequency domain is negligible, while the nonlinear term of the valve is the main cause of the error in the frequency domain.

Employing the powerful and adaptive method in time-frequency domain as well as proper and fault-related feature extraction is one of the most important subjects in the processing of nonlinear and non-stationary signals. The main objective of this paper is to improve Hilbert-Huang transform using the advantages of non-linear entropy-based features in the time and frequency domain to reduce noise effects. In addition, applying appropriate entropy-based features lead to restrict information redundancy and overcome the need for dimension reduction, in the fault detection of a rotating system. To modify the Hilbert-Huang method, the effect of added noise on various types of nonlinear entropy-based features is investigated for each intrinsic mode functions (IMFs) which extracted by ensemble empirical mode decomposition algorithm. Considering the approximate entropy (ApEn) sensitivity to noise, an evaluation index is presented for selecting the proper amplitude of the added noise based on the approximate entropy and mutual information coefficient of the different IMFs. Subsequently, taking into account of the high capability of permutation entropy (PeEn) and marginal Hilbert spectrum entropy (MHE) in the signal characteristic, a threshold is determined for fault detection based on their values associating to the main IMF which has the highest value of mutual information coefficient. As a result, the permutation entropy values and marginal Hilbert spectrum entropy of the main IMF can be used for detection of any deviation from normal operation ofthe rotor bearings system, regardless of the fault type. Consequently, to determine the type of defect, the higher-order spectra have been used.The bi-spectrum of envelope which is obtained from applying Hilbert transformto the main IMF is calculated. This bi-spectrum is employed to identify the coupling between the rotating frequency and fault-characteristic frequencies, for misalignment and unbalanced fault diagnosis of a rotating machinery vibration simulation system.

Electricity generation and consumption are the indicators of industrial development in each country. Most of the electricity generation in Iran is produced by the steam power plants. Optimum regulation of various parameters leads to the best operation of these power stations. Mass flow rates of the turbines extractions are one of the factors that effects on the fuel consumption and produced electricity of the power plant. The aim of this paper is the optimization of steam power plants by regulation of turbine's extractions mass flow rates in an optimum state. On the other hand, optimization of complex energy systems such as power plants by usual mathematical methods is very time-consuming. In this research, after the energy and exergy analysis of a 1000MW steam power plant, optimization of the plant will be done by one of the soft computing methods namely as the genetic algorithm. Using this method, the profit of the power plant at 60, 80, and 100% of the nominal power was increased 2242080, 2575360, and 1223840 $ per annum, respectively.

In this study, the performance of direct absorption solar collector is experimentally investigated using Fe3O4/Silica hybrid nanofluid based on deionized water. First, stability of prepared nanofluids is considered using spectral absorbency method. Then, spectrophotometry method is used for measuring optical properties of nanofluids. A prototype of this new type of collector was built with applicability for solar water heating systems. The procedure of EN 12975-2 standard was used for testing the thermal performance of the collector. Results show that collector efficiency is enhanced by nanofluid concentration, so that collector maximum efficiency is 73.9%, 79.8% and 83.7%using nanofluid with concentration of 500 ppm, 1000 ppm and 2000 ppm, respec/tively. This vaule is 63% using the base fluid as working fluid. Regarding very low volume fractions of nanofluids used in direct absorption solar collectors, the viscosity of the base fluid experience insignificant increase, therefore, pumping power will not increase significsantly. Such increase in efficiency show that direct absorption solar collector performance using hybrid nanofluid is much better than that of using the water at the same operating conditions. Application of stable hybrid nanofluid results in higher conversion efficiency of solar energy to useful energy.

Determination of the damage parameters for different materials can be beneficial to the analysis and assessment of rupture during forming of thin metallic plates. The amount of damage depends on the strain amplitude, the state of stress, and also the path and rate of the strain. The state of stress at the damage location is an important and effective parameter which is described by stress triaxilality, load angle and equivalent stress. In this paper, the mechanical behavior and ductile damage properties of Al 2024-O have been investigated. The aim was the determination of the mechanical behavior and development of an expression for correlation between the failure strain and the state of stress at the damage location. Hence, the experimental tests were carried out on both smooth and notched flat specimens. Various levels of stress triaxiality in notched specimens were created by variation of the notch radius. Based on the test results, a new expression has been developed for correlation between the failure strain and the triaxiality ratio for Al 2024-O in the plane strain regime. In order to evaluate the simulation procedure and applicability of the proposed expressions in more complex problems, the process was simulated using ductile damage criterion in the ABAQUS software, and the experimental and numerical results were compared. Very good agreements were observed between the simulation and experimental results.

In this research the influence of the striker shape on orthotropic composite plates for states, no damage (delamination) and damaged (delamination) are studied. In the analytical method, the spring mass system is used and new analytical model for flat and conical strikers are investigated. In the numerical method, the impact of different strikers on the composite laminate is simulated by using of finite element package (Ansys\Ls Dyna). These studies have been done on plates made of carbon and epoxy and the sheet thickness has been investigated in the size of 2, 4 and 6 mm. The striker mass is 3 g and its velocity for each thickness is different. To investigate the effects of the striker shape, three nose shapes spherical, conical and cylindrical with flat nose are modeled. The impacting time, the displacement time history and the maximum central deflection, and the contact force for all strikers are obtained and compared with each other. The results of analytical model are good agreement with numerical simulation. According to the results, when the delamination occurs, the maximum central deflection is more than once that damage dose not occurs. According to the results, the maximum central deflection of the flat striker on for both cases, with and without delamination, is less than the other strikers, conversely, the maximum contact force is more than the other strikers.

In this paper, performance analysis and optimization of a trigeneration system based on different thermodynamic criteria such as energy and exergy efficiency, power and dimensionless power have been investigated. The trigeneration system consists of three subsystems which including the solar subsystem, Kalina subsystem and lithium bromide-water absorption chiller subsystem. The proposed system uses solar energy generates power, cooling and domestic water heating. Power is introduced as a tool for understanding thermodynamic concepts of limited time. Dimensionless power is defined as the ratio of power to the product of total thermal conductivity and minimum temperature of the system. Dimensionless power can be used as a tool to understand the concepts of finite time thermodynamics. The exergy analysis has shown that the most exergy destruction is related to boiler. As a result, energy and exergy efficiencies, capital cost rates and dimensionless power are 17.37%, 18.82% and 9.63 dollars per hour, 0.01781 respectively. Sensitivity analysis has shown that increasing parameters such as ambient temperature, solar radiation, the dimensionless mass flow rate of the Kalina cycle, collector inlet temperature and pressure ratio of the Kalina cycle increase energy and exergy efficiencies. Also increasing pressure ratio the of Kalina Cycle, reducing the dimensionless mass flow rate of the Kalina cycle, the ambient temperature and collector inlet temperature has led to increased dimensional power. In addition, the optimization criteria such as energy efficiency, exergy efficiency, power and dimensional power have been compared. The results showed that power and dimensional power are the best thermodynamic optimization criteria.

Exact and numerical solution of eccentrically stiffened panels in the industry is a major step forward in the design of these structures. This paper presents an analytical approach to investigate the nonlinear stability analysis of eccentrically stiffened thin FG cylindrical panels on elastic foundations subjected to hygro-thermo-mechanical loads. The stiffeners are assumed to be spiral-type. The panel has the initial geometrical imperfection. The material properties are assumed to be temperature-dependent and graded in the thickness direction according to a simple power law distribution. The elastic foundation is considered based on Winkler and Pasternak proposed model. Governing equations are derived basing on the Lekhnitsky smeared stiffeners technique and classical shell theory incorporating Von Karman-Donnell geometrical type nonlinearity. Explicit relations of load–deflection curves for FG cylindrical panels are determined by applying stress function and Galerkin method. The effects of angel of stiffener, different dimensional parameters, volume fraction index, initial geometrical imperfection, the stiffness of elastic foundation and moisture concentration on the post buckling of FG panel are investigated. Also effects of temperature gradient through the thickness and effects of different boundary conditions are investigated for thermo-mechanical loading. The obtained results are validated by comparing with those in the literature.

The purpose of this article is to system design methodology of Propellant Management Device (PMD) for hydrazine fuel tank which used in low (zero) gravity conditions. To this end, the suggestion system design flowchart has three main steps that concluded: step one, Tank design and modeling; step two, PMD design and modeling and step three, stored fuel treatment simulation and analysis. In the design flowchart has performed the result of each step based on mission inputs. Therefore, rejected results in each step led to vary the related parameters. Thus Solid Works software is used to primary PMD and tank modeling. Then, numerical simulation is performed to consider PMD's performance and to illustrate the capillary phenomenon for continues fuel transferring in zero-gravity conditions. Also, numerical methods are used to analysis of the tank and the fuel behavior inside the tank with PMD to optimize system design parameters. Hence, Ansys software used to finalize modelling, analysis, meshing and consideration of fuel behavior in PMD by utilizing the Volume Of Fluid (VOF) method. The optimal system parameters related to specifications of PMD with maHimum performance of mass and volume flow rates in zero gravity. In conclusion, by comparing the results (PMD performance) with experimental and existing results will be verified.

Polyvinylidene fluoride polymer poses unique properties such as piezoelectric and high mechanical, thermal, and chemical resistance due to the consisting of the most electronegative element, fluorine, in its combination. In this paper, molecular dynamics simulation of amorphous polyvinylidene fluoride polymer containing polarized monomers is utilized to study its mechanical properties. Firstly, by using tensile test, elastic modulus and ultimate stress are determined and their changes due to temperature and strain rate change are studied. Then, by using dynamic mechanical analysis, tensile and shear dynamic complex modulus are calculated and their changes are studied while strain rate changes. This is for the first time that dynamic mechanical analysis is simulated by molecular dynamics. In addition to determining the viscoelastic properties of the material, straight forward elimination of temperature disturbances due to the sinusoidal pattern of stress and strain functions in terms of time is one of the advantages of the dynamic mechanical analysis. Consistency between simulated and actual trends shows the efficiency of the proposed model.

The purpose of this research is to develop an advanced driver assistance system (ADAS) for the integrated longitudinal and lateral guidance of vehicles in high speed lane change maneuver. At the first step, the ADAS by considering the target vehicle position, the speed limit of the road and the available range of longitudinal acceleration produced several trajectories with different acceleration. Then, by considering vehicle and tire dynamics, the optimal trajectory is selected. Therefore, the chosen trajectory is collision free and feasible. Because the trajectory planning is carried out algebraically, its computational cost is low. This feature is very valuable in the experimental implementation. In the next step, using a combined longitudinal-lateral controller, the control inputs are calculated and transmitted to the brake/gas and steering actuators. The integrated controller design is based on sliding mode technique. Trajectory planning and controller design is based on a nonlinear tire model. Simulation results are presented and the results show the effectiveness of the integrated longitudinal and lateral guidance system.

Free convection heat transfer of a non-Newtonian thickening power law (n>1) fluid in a closed asymmetrical enclosure with fixed aspect ratio was investigated in this study. Many of the previous studies, addressed the case with symmetrical heat transfer enclosure and for a given inclination. The governing equations were established by the finite volume method and solved by the SIMPLEC algorithm. In order to evaluate the code, its results were compared to those of other papers in the field of Newtonian and non-Newtonian fluids. The impact of the enclosure inclination (y) and the Rayleigh number (Ra) on the heat transfer and the flow field were investigated. It was found that for Rayleigh numbers smaller than Ra<105, inclination has little impact on heat transfer, while at Rayleigh numbers larger than Ra>105, the lowest heat transfer was observed at an angle of=45o. Moreover, the results pertaining to Newtonian (n=1) and non-Newtonian thickening fluids were compared. The results show that heat transfer by thickening non-Newtonian fluids, in addition to other parameters, depends on the parameter 𝑛 and in the case of the angle of inclination y=45o, the heat transfer of Newtonian and non-Newtonian thickening fluids is equal. Considering the non-Newtonian behavior of the fluid and nondimensionalization of the problem, a new dimensionless number known as the extended Prandtl number (Pr∗) appeared in the equations that depends on fluids characteristics, flow geometry, and the power law exponent (n). Its optimal value was observed at (Pr∗=0.07) where heat transfer from the enclosure was at maximum.

In axial flow compressor there is a gap between stationary and rotating members since the stator vane is fixed at the casing and the shaft is rotating at the root. Also, the pressure increases when the air flows through the stator vanes. Therefore, due to pressure increase and existence gap under vanes, the leakage is inevitable in the stator tip. This leakage can change the flow pattern near the stator tip, which causes more separation. Therefore the loss has been increased so it adversely effects on performance. In this paper, the effect of stator tip sealing with honeycomb on compressor performance is investigated. For this purpose, the 9th stage of a ten-stage compressor is examined in two cases of solid wall and sealing with honeycomb. The numerical results have good agreements with experimental results. The results show that by reduction of leakage at stator tip, the size and depth of tip corner separation decreased significantly leading to loss reduction. Also the effect of the leakage on flow angles shows that to have more accurate analysis of compressor performance, it is necessary to be considered the stator tip leakage. On the other hand, according to same effect of honeycomb on reducing stator tip leakage than solid wall, here the honeycomb roles as an abradable material to prevent direct contact between rotor and stator. Also in analysis of stage the honeycomb can be replaced with solid wall model.

In this study, the flow characteristics around two tandem square and equilateral triangle cylinders have been experimentally investigated. Experiments were conducted in an open-circuit subsonic wind tunnel with maximum free-stream turbulence level of 0.3%. Investigations for tandem arrangement were performed by moving the downstream square cylinder along the flow direction at various distances from the upstream triangular cylinder. Measurements were performed using 32-channel pressure transducer, three-component balances and hotwire anemometer. Square cylinder was placed at various distances from the upstream triangular cylinder and the flow Reynolds numbers were chosen to be 26000, 37000, 46000, and 51000. In this study, the mean and fluctuating lift and drag forces were measured for square cylinder at different spacings. Also, the distribution of mean and fluctuating surface pressure on the two-cylinders were measured. The vortex shedding frequency was measured by using both hotwire and surface pressure fluctuations on both cylinders and the results obtained by these two different measurement methods were compared. One of the most important outcome of the present study is the observation of two different flow patterns. It is noticed that the vortex shedding from the upstream cylinder was eliminated for cylinder distances lower than the critical spacing while for distances more than the critical spacing, the vortex shedding occurs from both triangular and square cylinders. The critical distance for this arrangement was obtained to be around three times of the length of the side length of the cylinders.

In this research, pitching and plunging motion of bio inspired and NACA airfoil are simulated numerically and the effects of reduced frequency, pitching and plunging amplitude on aerodynamic coefficients, power-extraction and propulsion efficiency are investigated and compared with each other. The simulation is done at Reynolds number of 1100 which is correspond to insect flight regime, using dynamic mesh capability of Open Foam and fluid flow is assumed unsteady, viscous and laminar. Reduced frequency, plunging and pitching amplitudes vary between 0.05-0.5, 0.25-1.75, 15-75 respectively and phase difference between pitching and plunging motion is kept constant at 90 degrees. Comparison of result with published data confirms the validation of research. Combination of different motion parameter such as reduced frequency, pitching and plunging amplitudes determine that bio inspired airfoil acting in power-extraction (fluid works on the airfoil), propulsion (airfoil works on the fluid) or feather (no producing power or propulsion) regime, and qualitatively is the same as NACA airfoil. The obtained results shows that with variation of reduced frequency, pitching and plunging amplitudes, whatever close to the feathering regime, bio inspired airfoil shows higher efficiency than NACA airfoil and vice versa.

In this paper, the interior air of the room heated by the solar wall (Trombe) with respect to Heat conduction in the wall is numerically simulated. Momentum and energy equations have been Algebraic with finite volume method and at the same time are solved with SIMPLE algorithm. First, a reference model is introduced and the results are presented and then with this reference model, the effective parameters on the performance of the wall were investigated and ultimately the most optimal geometry for the solar wall with the best performance was voted. As well, rectangular fins has been put on the surface of the absorbent wall, in order to increase its efficiency. The results show that solar wall with rectangular fins in all air gaps has better performance than plain wall and for example, with rectangular fins in the air gap equal to 1 m, room temperature is approximately 1.24% more than the simple Trombe wall. Then, using Artificial Neural Networks and ANFIS the values increase of room temperature by increasing the number of fins has been projected on the wall. The neural network was trained in such a way that the average temperature of the room depends on the number of fins on the surface of the absorbent the solar wall. The results obtained and compare mean squared error and root-mean-square error showed that ANFIS With the mean squared error equal to 0.742599 has good performance and acceptable accuracy compared with Neural Network With the mean squared error equal 1.1 to predict temperature.

In this paper, the goal is to provide analytical solutions for the thin film flow of a non-Newtonian fluid in different geometries and boundary conditions. An analytical solution for the non-Newtonian fluids is one of the most important and challenging issues that helps in understanding the physics of these fluids. For this purpose, the theory of micropolar fluids has been used. Thin film in three specific geometries, including flow downward on an inclined surface, flow on a moving ribbon, and flow downward on a vertical cylinder is considered. In order to solve the governing equations and obtaining the velocity and rotational fields, in the first two geometries, an analytical methods and in the third geometry a combined analytic and numerical methods are used with respect to the complexity of the equations. The rotational and velocity fields are plotted for all three cases and the results are discussed for different values of the parameters of a micropolar fluid. Also, the effect of the concentration of microelements in the fluid has been studied. It was observed that with the increase of the micropolar fluid parameter, the magnitude of velocity and rotation decreases.

In this paper, a new hybrid adaptive intelligent controller is introduced to track a dynamic trajectory in finite dimensional closed quantum systems. The problem of inherent singularities in control signals of trajectory tracking in quantum systems leads to a sharp increase in control signal amplitude. As a result, the amplitude of the large signal increases the control cost and control system instability. Consequently, the large control signal amplitude increases the control cost and leads to instability in control system. Firstly, according to the Lyapunov stability theory, an adaptive controller is designed to track the dynamic path. Then, to overcome the singularity drawback, a quantum intelligent controller is designed based on a quantum adaptive wavelet neural network with batch back propagation learning and combined with adaptive controller by a singularity observer. The proposed hybrid adaptive intelligent controller by combining the adaptive and intelligent control signals adjusts the quantum state so that the desired dynamic trajectory is traced effectively and simultaneously eliminates the effects of singularities and reduces the control amplitude. The performance of the hybrid adaptive intelligent controller is checked for step response tracking in a population transfer of a four-level closed quantum system. The simulation results show that the introduced controller reduces the tracking error and significantly decreases the number of singular points. Also, the control cost is reduced by effective adjustment of the control signal’s amplitude.

Iran is located in the warm and dry region of the Middle East, where summer temperature ranges from 35 to 50oC in the majority of the regions. Some critical factors including hot weather, population growth, and reduction in water resources as a highly impressive factor in the recent decades, all have underlined more efficient use of power plant in Iran, such that the existing power plants must function properly in simultaneous generation. Thus, the current research presents a techno-economic analysis of the function of a combined cycle unit under the condition of conversion into a water and power co-generation system. In the system, both membrane and thermal water sweetener mechanisms are used in parallel. The performance of the system in different conditions of water and power demand has been investigated. The results show that when the Thermal and Revers Osmosi are in the system alone, they can produce about 7, 000 and 1, 400, 000 cubic meters of fresh water per day. Following the modelling of the system, the economic analysis was also performed, and Changes in the price of water sales are shown in each of the water desalination units with increased capacity. Finally, considering the average water sale price as a objective function and combined cycle efficiency as another function, two-objective optimization was performed, and the results are presented in the form of Pareto Graph, which the highest efficiency and lowest sale price are 0.454 and 1.511, respectively.

In this study, the strain ratcheting behavior of piping branch under the influence dynamic bending moments are evaluated. The Chaboche nonlinear kinematic hardening model and combined Armstrong-Fredrick model with isotropic rule are used to predict the plastic behavior of the piping branches. The results of FE method by using the hardening models have been compared with the results of the experimental method and Armstrong-Fredrick kinematic hardening results. The constant parameters of the hardening model and stress-strain data have been obtained from several stabilized cycles of specimens that are subjected to simulated seismic bending cycles. Both the FE and experimental results showed that the maximum strain ratcheting occurred on the flanks in the piping branch hoop stress direction just above the junction. The ratcheting strain rate increases with increase of the dynamic moment levels. The FE results show that initial rate of ratcheting is large and then it decreases with the increasing of loading cycles. In BMS1 sample, the FE hoop strain ratcheting data by using chaboche nonlinear kinematic hardening model comparing with the other hardening models to be near that found experimentally values. In BMS2 and BMS3 components, the FE hoop strain ratcheting data by using chaboche nonlinear kinematic hardening model and combined hardening model comparing with the A-F hardening model to be near that found experimentally values. The hoop strain ratcheting rate by Armstrong-Fredrick model gives overestimated values comparing with the experimental data.

Due to the depletion of shallow water resources, the development of exploration and production has shifted towards the deep and ultra-deep water region. The types of floating platforms are all need to be moored when they are working as production platforms. Applying buoys to the catenary mooring system in deep water may reduce part of the weight and radius of a mooring. In this article, Dynamic responses of the Amirkabir semi-submersible platform was obtained under the combination of wind and wave loads in frequency domain and time domain simulation calculated. The JONSWAP wave spectrum and API wind spectrum are considered as environmental conditions, and also the effects of buoy size on the semisubmersible motion response are investigated. Dynamic responses of the semi-submersible platform determine by using the Morison equation and diffracting theory in AQWA ANSYS software and each dynamic mooring line is modeled as a chain of Morison-type elements subjected to various external forces. The obtained result from AQWA ANSYS in time and frequency domain shows that increasing buoy size, could increase motions of the semisubmersible platform but instead could decreasing the mooring line tension.

The Griffith crack, a central crack in an infinite plane under uniform loading, is converted to a subsurface one by moving close to a loaded edge of the plane. Subsurface cracks initiate under rolling contact fatigue conditions. In this paper, first, finite element model of the Griffith crack has been developed and validated by calculating stress intensity factors (SIFs) under uniform tension and shear loadings. Then, by moving the crack close to a parallel edge of the plane, mixed mode SIFs of the subsurface crack have been determined for a wide range of the cracks depths. Non-symmetrical geometry with respect to the crack edge causes coupling between fracture modes and so, considerable shear and tension fracture modes under tension and shear loadings, respectively. The ratio of SIF for the coupling mode to the direct mode is creased up to 69% for the length to depth ratio of 20. Also, by fitting third-degree polynomials to the mixed mode SIFs, four geometry correction factors have been obtained for SIFs of subsurface cracks under uniform loadings. These approximate equations can be used easily and efficiently by engineers. Also, the relations can be utilized as a primary estimation for non-uniform loadings, especially when the crack length as well as the load variation along it is small.

In this paper, an investigation was done on modulated IR thermography for detection and evaluation of artificial subsurface defects in composite materials. In this method, In order to stimulate the test specimen, the heat flux is applied periodically over the surface of the specimen and the thermal response is decomposed by the Fourier transform method in order to extract its amplitude and phase images. The non-uniform backgrounds in the obtained images often reduce detection ability, In order to improve the evaluation of this method; an edge detection filter and a morphological attribute profile were applied to the images. Experimental investigations were applied for different frequencies on specimens made with common controlled defects in composite materials. Interpretation of the results were utilized in the calculation of defects’ size and location, it was observed that in specimen with 2 mm thickness delamination defect with a minimum size of 20-10 mm, dry fiber and inclusion defects with a minimum size of 50-40 mm is detected and is measured. The same geometry and the artificial defects used in experiments were considered in the finite element analysis. The results of finite element analysis were found to have an agreement with the experimental results and can be used to find the optimum parameters in investigation of modulated IR thermography for detection of defects on composites.

The torsional vibrational characteristics of nano-scale sphere using an exact size-dependent elasticity solution based on Gurtin-Murdoch’s surface elasticity model are studied. In the absence of body forces, the displacement field is governed by the classical Navier’s equation. Helmholtz decomposition is used to separate the dynamic equations of motion into the decoupled vector wave equations. The motion under consideration is assumed to be torsional and vector wave equation exactly is solved and displacement field and stress tensor are obtained. Size-dependent elasticity solution based on Gurtin-Murdoch surface energy model is employed to incorporate the surface stress terms into the pertinent boundary conditions, leading to frequency equations involving spherical Bessel functions. Isotropic aluminum with two different set of surface properties corresponding to the crystallography directions are considered and extensive numerical calculations have been carried out to illustrate the size effect of the nano-sphere on the first and second dimensionless vibrational natural frequencies. The numerical results describe the imperative influence of surface energy and radii ratio on vibrational characteristic frequency of nano-sphere. In particular, the surface energy is much important when inner radius is smaller than 50 nm.

Microburst wind shear is very dangerous and threatening for aircraft in low altitude flight, which makes aircraft uncontrollable and also difficult in forecasting and detection. This is consequential research in order to make the aircraft controllable when encountering the phenomenon. Most studies have simulated aircraft encountering the microburst by applying single-point model. This model, consider location of microburst on the aircraft center of gravity, where microburst must be applied all through fuselage, wing and tail combination. For more realistic simulation, microburst should be applied to more points of aircraft body in addition to C.G., which is known as developed multi-points model. Applying the influence of wind gradients to aircraft body is the advantage of this model. In this paper, results of both single and multi-points was conducted and compared. In comparison of single-point model with existing methods in references, has provided a proper consistency with the tolerance of 10%. Considerable results have shown in comparison of single-point and multi-points model in accordance to flight trajectory response, heading angle and pitching moment to wind shear model and the ability of the multi-points model for modeling of aircraft realistic flight encountering microburst has been proved.

In this paper, numerical analysis and experimental study on Friction Stir Welding (FSW) is considered. Generalized Differential Quadrature (GDQ) method was used to solve the equations of the material flow during the process. This method which is known as the highest-order finite difference scheme is one of the meshless method and has a very high convergence speed respect to ordinary finite difference and finite element methods. After validating the application of this procedure with the results of experiments on aluminium alloy, friction stir welding of mild steel considered and the results compared with the published results of other researchers. Numerical analyses show that at high rotational speed of the welding tool the analysis of the process should be done in 3-dimentional framework. The results of FSW on aluminum features along with the welding results on steel ones considered in order to better understanding of the process nature of dissimilar alloys. Results of this study show that the macroscopic behavior of both materials during friction stir welding is the same. Furthermore, viscosity spectrum shows high fluidity of steel in the range of solidity to melting temperatures, so the ratio of rotational to welding speeds (w/v)in friction stir welding of steel work pieces could be higher which it should be mentioned whenever joining of aluminium to mild steel work pieces is planned.

In this paper, the nonlinear vibration of a Euler–Bernoulli nanobeam resting on a non-linear viscoelastic foundation is investigated. It is assumed that the nanobeam is subjected to a harmonic excitation that can be representative of an electrostatic field. The non-linear viscoelastic foundation is considered for both hardening and softening cases. By neglecting of the in-plane inertia, Eringen's nonlocal elasticity theory is used to model and derive the equation of motion of the nanobeam. Using the Galerkin method and the first mode shape, the obtained partial differential equation is reduced to the ordinary differential equation. Calculating the system's equilibrium points lead to heteroclinic bifurcation and the heteroclinic orbits are obtained. Then, using the Melnikov integral method, the chaotic motion of the system is studied analytically, and the safe region of the system is determined respect to the parametric space of the problem. When the viscoelastic foundation has a hardening characteristic, the chaotic behavior in the system does not occur. It has been observed that the use of nonlocal elasticity theory is necessary to investigate the chaotic behavior of nanobeam, and using the classical theory of elasticity may place the system in the chaotic region.

Today, heart disease is the first cause of death in the world. The heart pump is a mechanical device used to help heart patients. The blood of people who use the heart pump, due to being in contact with the mechanical device, suffers from damage such as thrombosis and hemolysis. When the heart pump starts from a resting state, its angular velocity increases in a short period of time, and then operates at a constant rate. Transient blood flow analysis is very valuable when the pump speed is changing. In this paper, the fluid flow inside the heart pump and the amount of damage to the red blood cells were numerically analyzed. In this analysis, the effect of shear stress caused by the blades of the pump into the red blood cells was also investigated. In this study, blood was assumed as a Newtonian, viscous, and incompressible fluid, and a sliding mesh method was used to identify changes in the velocity of the blades of the pump to the problem. Total pressure and flow rate at the inlet and outlet of the pump as well as relative velocity through the blade passages have been discussed. Finally, the hemolysis created during the simulation period was calculated. In the study, hemolysis analysis showed that the heart pump during starting period causes serious damage to the red blood cells and the possibility of rupturing the red blood cells in this short period of time is high.

Advanced ceramics are a group of materials that have been used in many industries due to their properties such as high temperature stability, high strength, high abrasion resistance and high corrosion resistance. Grinding process is one of the most important and most commonly used techniques for machining and polishing of ceramics. However, poor grindability, high surface defects in the work piece due to the brittleness of ceramics and the high grinding forces, high wear rate of diamond wheel (tool), high costs due to the use of cutting fluid, low cutting productivity (low production rate), are of the problems of ceramics grinding. The minimum quantity lubrication (MQL) new technique is one of the methods recently introduced in machining processes aimed at improving lubrication performance of cutting fluids, reducing fluid consumption and promoting the use of low-hazard and environmentally friendly fluids. In this study, the minimum quantity lubrication technique was used in the grinding process of zirconia ceramic in order to investigate its effects on the grindability of ceramics. Also, since the type of lubricant and grinding wheel can affect the performance of minimum quantity lubrication in this process, the type of lubricant and diamond wheel were used as variables in the experiments. The grinding forces, surface roughness and surface texture of the grinded samples have been evaluated. The results show that under the minimum quantity lubrication conditions, applying the appropriate type of lubricant and grinding wheel can significantly affect the grindability of zirconia ceramic.

Use of oil journal bearings in recent decades has grown considerably because of their desirable performance in light and heavy loading condition and also for reducing noise pollution, as a suitable supports in different industrial equipment such as turbo machines, combustion engines and nuclear reactors. Due to the influence of the geometry of these bearings on their performance, a variety of models such as elliptical, lobed, waved, pivoted pad and axial grooves have been introduced to market for purposeful improvement in their steady-state and dynamic operating conditions. In recent decade, with the development of advanced non-traditional machining equipment, the ability to create textures on the bearings shell has been provided by manufacturers. Cubic, cylindrical, spherical and cone shaped textures can have a different effect on the performance of journal bearings. In this study, the performance of two lobe bearings with cylindrical textures is evaluated. For this purpose, the governing Reynolds equation of Newtonian lubrication has been investigated, regarding to the changes in the lubricant film thickness according to the geometry and position of textures, by the FEM using the Reynolds boundary condition for determining the cavitation zone. Then, the bearing performance is evaluated based on the pressure distribution of the lubricant film and the location of the textures. The results show that the location of the textures, to achieve a more favorable performance, is different for various values of noncircularity index. Also, with increasing the bearing noncircularity, the effect of textures formation on the bearing performance will be more noticeable.

In recent years, Aerodynamic analysis of automobiles became one of the most important parameters which affect the power of the companies to be present in world markets. Therefore, they can be considered as one of the most important factors in aerodynamic design of vehicles. The formation of the vortex and consequently the pressure drop in the rear of the vehicle can increase the aerodynamic forces. This paper investigates the methods for reduction of the vortices volume in the rear part of a sedan type vehicle by changing in geometry of the vehicles. For this purpose, firstly in order to choosing the appropriate turbulence model and 3D simulation of incompressible flow around the Ahmed model (which its experimental results are available) was simulated using computational fluid dynamics. Then, the values of aerodynamic coefficients of a car model were studied by adding spoiler and creating curvature at its lateral surfaces. The results of this study indicated that the vortex volume formed at the rear of the vehicle can be simulated more precisely by using the Boundary-layer mesh around the model and analyzing the flow using the DES-SSTK-ω turbulence model Relative to the model K-ω-SST. Additionally, simultaneously use of the spoiler and the curvature of the lateral surfaces reduce fuel consumption and increase the stability of the vehicle due to a 26.3 % reduction in rear drag coefficient and a 5.2 % reduction in the lift coefficient, with respect to the simple car model.

In this article, the Flutter speed of a composite wing carrying two power engines is analyzed. The wing is modeled as a beam with two degrees of freedom, which is a cantilever, with two thrust as a follower force and mass of the engines. Wagner theory has been used for aerodynamic model and using the assumed mode, the wing dynamic equations of the motion has been achieved by Lagrange equations. Linear flutter speed according to the eigenvalues of the motion equations was calculated. In order to valid the results of present work, at first composite wing assumed without engines and then wing modeled with two engines that results are compared with published results and good agreement has been observed. Composite wing has been analyzed as one layer and also laminate layers, and effect of variables such as follower force, engines mass, position of engines and number of layers has been investigated and the results show that with increase in mass and force of engines and also with increases distance between engine and wing root, flutter speed decreases and with decrease distance between engines and leading edge, flutter speed increases.

Applying an Electric potential between two electrodes with different thicknesses will cause corona discharge if the electric field around the corona electrode is strong enough to ionize the surrounding gas and weak enough to avoid arcing. Corona discharge used to be known as an unpleasant phenomenon but it has lots of applications today including the ionic thrusters. In this research, the specifications of the flow resulted from corona discharge such as velocity, thrust, and temperature, electric current, flow streamlines and thrust effectiveness have been numerically studied. To do so, the electrostatic and Navier-Stokes equations have been coupled and solved by finite element method (FEM) using the COMSOL Multiphysics software version 5.2. Data validation shows that the maximum errors between the numerical and experimental results in computing thrust, current and thrust effectiveness are respectively below 2%, 14% and 6%. Also the results show that with rising the applied Voltage, the resulted thrust and electric current will increase and the thrust effectiveness decreases. Furthermore, by considering the effect of Ohmic heating in the energy equation, it has been found that the maximum temperature raise happens around anode.

In this research, interaction and oblique coalescence of bubbles under buoyancy force was simulated, numerically. The governing equations are continuity and momentum equations which have been discretized using the finite volume method and the SIMPLE algorithm. For simulating the interface of two phases, the level set method has been incorporated. Level Set method suffers from poor mass conservation of dispersed phase especially in the case of severe deformation of interface. In order to control of mass conservation of the level set method, re-initialization equations and a geometric mass control loop are used which this loop is implemented in the level set method for the first time in this research. Using proposed geometric mass control loop, mass dissipation drawback of the level set method is handled in simulation of bubbles’ coalescence. The results outlined in the present study well agree with the existing experimental results. Also results of investigation of mass dissipation of the proposed scheme to simulation of oblique coalescence problem show that the maximum amount of this mass dissipation was less than 4%. Therefore, the level set method with proposed geometric mass control loop could be used properly for simulation of oblique interactions and coalescence of bubbles in multiphase flows.

In this paper, an optimal robust hybrid active force controller based on Harmony Search Algorithm is designed for a lower limb exoskeleton robot. Dynamic equations are derived using Lagrange method by considering three actuators on the hip, knee and ankle joints to track a specific trajectory. One of the major problems of exoskeleton robots is non-synchronization of movements and transfer of power between the robot and human body which affects the robot in form of disturbance. In order to mitigate the effect of disturbances and increase precision, combination of active force control (Corrective loop of control input) with position control is used as an effective and robust method. In the active force control, to elicit robust input control against disturbances, the moment of inertia of the links is estimated at each instant by minimizing the Criteria of ITAE and the control input rate, using the Harmony Search algorithm and the control input is modified. Also, two controllers are designed for the position control loop using sliding mode and feedback linearization methods. In order to validate the performance of the designed controllers, the robot is modeled in ADAMS and control inputs are applied to the Adams model. For appropriate comparison, all control parameters are optimized using the harmony search algorithm and then performance of position controllers are compared in hybrid and conventional (without the force control loop). Results indicate the outperforming of the hybrid sliding mode controller rather than to the other designed controllers.

In surface acoustic wave sensors, target cells are trapped by sacrificial layer, containing antigens and antibodies. In this new idea, sacrificial layer is replaced by diectrophoresis electrodes. Fast response and not being disposable and usability for various types of cells are its advantages. In order to design and fabricate the sensor, the optimized values of effective parameters have been investigated. The behavior Love wave - which is used in this sensor - is simulated with lithium Niobate as substrate and ZnO layer as guiding layer. Two types of focus and unfocused interdigital transducer electrodes for sensor are investigated. The results of the sensitivity analysis and its relationship with the sensor displacement are presented. In graphs, results indicate that the focused circular structure is more sensitive, when the number of target cells in the fluid channel is more. The sensor was tested in 142 MHz for healthy and cancerous brain and intestinal cells. The suggested sensor has good results for measurement of cells aggregation. Wave power loss in transmission from sender to receiver ports and frequency shift are two special properties for detecting healthy and cancerous cells. Results show 80 and 90 KHz decrease in frequency and 4.99 and 6.69 dB loss decrease in cancerous cells comparing to healthy cells in brain and intestinal cells respectively. In this sensor, trapping, detecting and measurement of aggregation, happens in 5-10 second, which is an outstanding result compare to 10-15 minutes in conventional methods.

In conventional internal combustion engines, about 40% of fuel energy is turned into useful power and the rest is driven by cooling and exhaust system out of the engine. Therefore, there is a ground to recover energy from this wasted energy by fixing an additional cycle inline with the exhaust gas outlet. In this research, a stirling cycle was used for this purpose. Initially, the internal combustion engine was simulated. The engine studied was an EF7-NA spark ignition internal combustion engine and the simulation results were validated by using experimental results. The results showed that the exhaust gas outlet temperature varies from 393 to 848oC, according to engine operating conditions. Therefore, by installing a Stirling engine heater inline with the exhaust gases from the EF7 engine, the wasted energy can be turned into useful work. To validate the results of one-dimensional Stirling engine simulation, the experimental results of the Stirling Solo V161 engine were used. After validating the Stirling engine model, the combined cycle was simulated, combining a Stirling engine at working pressure of 50, 60 and 70 bar and EF7 engine at engine speed of 2000 to 4500 rpm. The results showed that at an optimal pressure of 50 bar for the Stirling engine, the EF7 power gain was 12.2% and an average efficiency increase of 5.2%, regardless of the weight of the added stirling engine in the car which considering that, a low impact on the power of the combined cycle is expected.

Commercial pure (CP) titanium has many biomedical applications, especially in implants due to its excellent biocompatibility. The major weakness of CP titanium is its low strength compared to the other titanium alloys. One of the methods which can be utilized for enhancement of CP titanium strength is severe plastic deformation methods. Therefore, the aim of this research is to improve the strength of CP titanium by grain refinement through multi directional forging (MDF). For this purpose, after one hour annealing at 800oC, the CP titanium was forged by MDF process up to six passes at ambient temperature. Microstructural analysis was performed by optical microscope and scanning electron microscope equipped with EBSD. Mechanical properties were also studied by Vickers micro hardness and tensile tests. The finite element simulation was also applied to predict the strain distribution during MDF process. The results of microstructural analysis showed that the average grain size decreased significantly after the MDF process and increasing pass numbers led to the refinement of grain size. After six passes of the MDF process, the average grain size decreased from 45 micrometers to 390 nm. Mechanical properties results showed that the strength and hardness of specimens were enhanced with MDF process and increasing the number of passes. The hardness and strength of six passes MDFed specimen was about 2 times greater than those of the annealed one. The strain distribution results obtained from the simulation showed good agreement with experimental results of microhardness distribution.

Ice slurry is called a mixture of fine ice particles with a fluid carrier such as water. The phase change ability is reason for use of this mixture as the refrigerant cooling. In this research, flow of ice slurry in horizontal tubes faring the phase change is numerically investigated using FLUENT software. The two-phase nature of ice slurry mixture is studied using the Euler-Euler two-phase model based on kinetic theory of granular flows. The effect of ice particles phase change on heat and mass transfer between phases are investigated, the obtained results show that the local heat transfer coefficient for the use of the icy slurry mixture is increased 12% compare to the pure water. It is also determined by examining heat and mass transfer rate along tube, that the heat transfer coefficient for the pipe lengths larger than 10-15 times pipe diameter, remains constant. The variation of mean mass transfer is maximum at distance of 10-15 times of pipe diameter. The maximum value is 2-5 times larger than mean mass transfer in the pipe outlet. At the 20% end of the pipe, the decreasing trend of mass transfer accelerates.

Human walking is one of the most robust and adaptive locomotion mechanisms in nature, involves sophisticated interactions between neural and biomechanical levels. It has been suggested that the coordination of this process is done in a hierarchy of levels. The lower layer contains autonomous interactions between muscles and spinal cord and the higher layer (e.g. the brain cortex) interferes when needed. Inspiringly, in this study, we present a hierarchical control architecture in order to control under-actuated and high degree of freedom systems with limit cycle behavior and it is implemented for the walking control of a 3-link biped robot. In this architecture, the system is controlled by independent control units for each joint at the lower layer. In order to stabilize the system, these units are driven by a sensory feedback from the posture of the robot. A central stabilizing controller at the upper layer arises in case of failing the units to stabilize the system and take the responsibility of training the lower layer controllers. We show that using this architecture, a highly unstable system can be stabilized with identical simple controller units even though they do not have any feedback from all other units and the robot.

The purpose of this research was to investigate the hydraulic parameters affecting the performance of the distillation column and the hydrodynamic characteristics of the flow field on the industrial scale sieve tray using numerical simulation. Computational fluid dynamics method was used for analyzing and predicting flow behavior. The desired geometry including the space between two trays of the distillation column and the down comer region was considered. After plotting geometry, three dimensional grids were generated in Gambit software and the analysis of the flow field was traced in Fluent software. The Eulerian-Eulerian approach was applied to simulate two-phase flow and k-ε RNG model for turbulence modeling. Validation of the results was done successfully using Solari and Bell experiment data and the correlation presented by Colwell. The velocity distribution and volume fraction of liquid and gas in different zones were determined. The influence of inlet volumetric flow rate of liquid and gas, as well as the geometry of the weir, on parameters related to the tray performance such as clear liquid height and froth height were investigated. The results indicated that a better separation would occur in lower gas and liquid loads.

A natural circulation loop receives heat from a high-temperature source and rejects it to a low-temperature source without using a mechanical pump. Single phase natural circulation loop has been applied in many industrial systems for cooling. The heat transport capability of natural circulation loops (NCLs) is directly proportional to the flow rate that it can generate. To establish the heat transport capability of a natural circulation loop, it is essential to know the flow rate. Friction force and gravitational force are balanced with each other along the loop at steady state. In this paper, firstly the governing equations have been written for a natural circulation loop. Then the governing equations have been rewritten in the dimensionless form. Then, effects of heater length, cooler length, tube diameter, loop height, loops inclination angle, the distance of heater from the right side or left side, the distance of cooler from right or left sides and power of the heater on the loop mass flow rate and loop temperature distribution have been investigated. The results show that increasing of loop height, loop diameter and power of heater increase the mass flow rate. Also, increasing or decreasing of heater length, has no effect on the mass flow rate, whereas increasing of loop inclination angle decreases the mass flow rate. In this study, the friction coefficient is considered as continues for all regimes. In addition, the position of the heater and cooler has been unsymmetrically investigated.

One of the important ways for improving performance of diesel engines is selecting of a proper and efficient fuel injection pattern. In this study six different patterns of fuel injection have been considered and performance of a diesel engine by using these patterns of fuel injection have been investigate numerically by employing AVL Fire. An annulus nozzle have been consider for the fuel injection system. It is expected that considering an annulus nozzle lead to increase of spry cone angle and proper distribution of the fuel inside the combustion chamber. Results show that employing proper and efficient patterns of fuel injection lead to increase of engine power and decrease of exhaust pollutants gases. Results also show that by employing a quasi-triangle fuel injection pattern, the diesel engine has better performance in competition with the case of using a constant fuel injection. It is found that by employing a quasi-triangle pattern of fuel injection, SFC reduces to 0.2043 kg/kJ, while the engine power increased by 27.5% and the magnitude of NO increases slightly. In the case of employing a constant-decreasing fuel injection pattern, the magnitude of SFC reduces to 0.2029kg/kJ whereas the magnitude of NO increases in comparison with the case of using constant fuel injection pattern. Numerical results show that by employing a constant-increasing pattern of fuel injection, the engine power is approximately equal to the engine’s power in the case of using a constant fuel injection pattern. But in this case the magnitude of NO reduces considerably.

In this paper, the nonlinear electromechanical formulations of a piezoelectric energy harvester are proposed to investigate the effect of exponential tapering on generating more power with less mass from energy harvester. For this purpose, geometric, inertial, material and damping nonlinearities are included. The governing equations are derived using the Euler-Bernoulli and linear variation of electric voltage along the thickness assumptions. The coupled nonlinear equations are discretized by the mass normalized mode shapes of an exponentially tapered piezoelectric beam with tip mass, and resulting differential equations are solved employing the method of multiple scales. An experiment is set up, and the damping coefficient of the beam is calculated from the tip acceleration to base acceleration frequency response function in the case of low exciting acceleration and short circuit. Material nonlinear coefficients are identified using the experiment, when the exciting acceleration of the shaker is increased, and the proposed solution accuracy is verified. The effect of tapering exponentially on the behavior of the piezoelectric energy harvester is investigated by studying length, tapering parameter and exciting acceleration amplitude in some examples.

In this paper, the three dimensional ventilated cavitating flow in the steady condition around a projectile model is simulated using CFD method combined with a sst k-w turbulence model and volume-of-fluid technique, With the aid of CFD software ANSYS CFX. The numerical model is validated using comparisons between numerical predictions and existing experimental data and fairly good agreement is revealed. The numerical results show that with increasing the ventilation gas rate at constant Froude number, the cavity length gradually increases to a critical value and then remains fixed upon further increase in gas ventilation rate. Also, it has been observed that rear portion of larger cavity moves upwards due to gravitational effect. With increasing the ventilation gas rate, the gas leakage mechanism at rear portion of ventilated super cavity changes from the re-entrant jet closure mode to twin vortex closure mode. The variation of ventilation gas rate versus cavity length is a function of Froude number and the critical ventilation gas rate increases linearly with Froude number.