نشریه مهندسی مکانیک مدرس
سال هجدهم شماره 3 (خرداد 1397)

In this paper, a new controller is presented based on robust feedback linearization controller in combination with integral-exponential error dynamics and potential functions for tracking control of an underwater robot in an obstacle-rich environment. Underwater robots are considered as nonlinear, underactuated systems with indefinite, uncertain dynamics. In this research, by assuming a boundary for external disturbances and uncertainties a proposed robust control method has been put to use. Along with the robust feedback linearization algorithm which has been developed based on the dynamics of the nonlinear error defined for the underwater robot, and in order to avoid the obstacles, the control laws are combined with the virtual potential functions. The considered virtual potential functions make a repulsive force between the robot and the obstacles which intersect the desired path and then they bring about a safe move of the robot in obstacle-rich environments. Finally, the performance of the proposed new control algorithm is compared with the results of the implementation of classical sliding mode control laws. The results show the effectiveness of potentially directed proposed controller through obstacle-rich paths which operate far better facing obstacles.

In this paper, thermal-viscous fingering instability of miscible flow displacements in anisotropic porous media is studied .for the first time An exponential dependence of viscosity on temperature and concentration is represented by two parameters β_T and β_C, respectively. The effect of anisotropic properties of permeability tensor, Lewis number and thermal lag coefficient are investigated. Creation and propagation of these fingers are playing an important role in displacement of fluids and especially on oil transformation from discovered oil reservoirs in enhanced oil recovery process. In nonlinear simulation, a spectral method based on the Hartley transforms are used to model the thermal-viscous fingering instability in anisotropic porous media. The results include concentration and temperature contours, sweep efficiency, and mixing length. The results indicated that by increasing the anisotropic permeability ratio, the fingers arrive later to the end of the front, instability decrease and more stable flow is obtained. Also, by increasing the Lewis number, thermal front appears without any fingers. Decreasing the thermal lag coefficient causes to the thermal front stays behind the flow front and increasing the stability of the flow field.

The Moving Least Square (MLS) interpolation method is proposed for approximation of adaptive fuzzy controller parameters for two degrees of freedom suspension system and each one has two inputs, one output with twenty-five linguistic fuzzy IF-THEN rules. Fuzzy systems are designed by using five Gaussian membership functions for each input, product inference engine, singleton fuzzifier and center average defuzzifier. The constructed fuzzy systems is composed with adaptation rules. For this purpose, Lyapunove approach is implemented for stability of the adaptation rules. The Gravity Search Algorithm (GSA) is implemented for achieve the optimum controller parameters. The relative displacement between sprung mass and tire and the body acceleration are two objective functions used in the optimization algorithm. Since, choose the suitable controller coefficients are important and when the parameter of the system change, Optimum coefficients of the controller will also change. In order to solve this obstacle, the MLS predictive model is purposed that is interpolation method based on a radius of the neighborhood, a basis function and a weight function for points of interest. Finally online model is implemented on the two degrees of freedom suspension system and results compared with the offline optimal systems.

Dispersion of oil pollutants is one of the important topics of great concern which should be modeled for a wide range of hydrodynamic systems such as seas and oceans. In this paper, the effects of using booms on the oil plume are simulated using the Smoothed Particle Hydrodynamics (SPH) Method. The open-source SPHysics2D code is developed into two phase by adding the effects of surface tension and an added pressure term to the momentum equation. Several problems of plume dynamics are shown, and the performance of the developed code is evaluated. Firstly, the rising pattern of an oil plume with the density ratio of 0.8 is simulated where the results are compared with the analytical solution. Then, the rising pattern of a plume with density ratio of 0.1 is simulated and the time evolutions of the rising velocity and center of mass are shown. The simulation of the cnoidal wave on beaches is conducted and compared with an available experimental result. Finally, the effects of a boom with different angles on the oil plume dispersion are investigated. It will be shown that the SPH method could be an optimized method for the numerical simulation of the complex problems such as water wave dynamics and two-phase flows.

Creation of a compressive residual stress in specimen that are exposed to fatigue induced failure, is considered to be a beneficial solution in order to neutralize all or some parts of the external force. Using components with this residual field stresses in high temperature applications can lead to reduction and termination of residual stress field and the effectiveness of this residual stress fields in high temperature is always questioned. So this paper aimed to simulate and study residual stress field made by multiple laser shot peening which is a novel method to create in depth residual stress. Thermal relaxation of this residual stress field due to working conditions was also investigated by FEM simulation in ABAQUS. Ti-6Al-4V was the employed material and since high strain rates were involved in dynamic loading process of simulation, Johnson-Cook material model was used to count for nonlinear material behavior. Results showed that created residual stress field from this method is much deeper than similar conventional shot peening process and by using multiple laser shot peening on the same spot, it is possible to achieve 640 MPa in one loading cycle, 834 MPa in two cycle loading and 889 MPa in three cycle loading. By applying 600 ℃ on specimen, it was observed that for each of single shot, double shot and triple shot specimens, a surface residual stress relaxation of 28.13%, 41.37% and 43.87% occurred, respectively.

In this paper, the single point incremental forming (SPIF) of friction stir welded (FSWed) 5083 aluminum alloy sheets are investigated experimentally and numerically. The aluminum sheets with 2mm thickness are friction stir welded with the same FSW parameters. In order to obtain the effect of FSW on the formability of SPIF, the base sheets and FSWed sheets are formed to conical shapes with different forming angles and then the limiting wall angles are determined for each condition. The experimental results indicate that the limiting forming angle of FSWed sheet is not so much different than the base sheet and FSW does not have a negative effect on the sheet metal formability in SPIF. To study the effect of SPIF and FSW in mechanical and microstructural properties of the formed parts, the effects of these process on the grain size and micro-hardness is investigated. Furthermore, the incremental forming is numerically simulated using the ABAQUS software and the sheet thickness distribution, obtained from the simulation, is compared with the experimental results. After verification of the numerical simulation model, the effect of FSW on the thickness distribution and strain distribution in SPIF is studied. The results indicate that in weld region and base metal region, the distributions of thickness and major strain are uniform while the distribution of minor strain is non-uniform.

This article investigates the effect of the addition of graphite nanoparticles with average grain sizes of 400nm and purity of 99.9% in cutting fluid on machining process of 16MnCr5 steel. Machining was performed at three cutting depths of 1, 2 and 3mm and three feed rates of 0.15, 0.25 and 0.35mm/rev using ordinary cutting fluid and cutting fluid containing graphite nanoparticles. Microstructural studies of the machined surfaces, hardness tests from surface toward the center and surface roughness and tool wear evaluations all were implemented in order to evaluate different machinability aspects. Results indicated that, regardless of the depth of cut and the feed rate, using the graphite nanoparticles within the cutting fluid decreased the amount of the tool wear and improved the surface quality of the material due to its effect on decreasing the friction between tool and material, decreasing the generated heat and decreasing the cutting force. The highest and the lowest amounts of cutting tool weight losses were 0.022 and 0.002gr, respectively when using the graphite nanoparticles. In addition, the surface roughness of test pieces decreased from Ra=4.79μm when using ordinary cutting fluid to Ra=3.29μm when using graphite nanoparticles in cutting fluid both in the case of the highest depth of cut and the highest feed rate. Furthermore, microstructural characterizations illustrated that using the graphite nanoparticles resulted in lower microstructural textures, lower work hardening and lower thickness of stress affected layer at the surface of the material.

One of the most important difficulties of the vorticity confinement method is the need for manual adjustment of confinement parameter. In other word, user must adjust the parameter for each new problem. The small values deactivate this method and high values lead to non-physical results. Many attempts have been made by researchers to overcome this problem, but the dependence on manual adjustment has not been resolved. One way to conquer this problem is to reduce the effect of the confinement parameter on the final solution. At the present study, reducing the sensitivity of the vorticity confinement method to confinement parameter variations has been proposed by combining this method with FCT scheme for various limiters. In order to validate the proposed method, the problem of single vortex has been investigated. At first stage, the effect of changes in the confinement parameter on the final results has been compared for central difference scheme against the FCT scheme) using different limiters(. Then, the best way to combine the FCT scheme and the vorticity confinement method is discussed. It has been shown that, the best results were obtained using the minmod limiter at the middle step.

Biologic tissues modeling play an important role in understanding the tissue behavior and development of synthetic materials for medical applications. It is also a vital action to develop the predictive models for a wide range of uses including medical and tissue engineering. Various strain energy functions have been introduced to model arteries to date. The newest introduced strain energy function is the Nolan strain energy function. Two-layer arterial modeling using this strain energy function has not been performed so far. In this paper, modeling the arteries was carried out in the form of double layers including media and adventitia and hyperelastic material assumption. At first, governing equations were driven based on continuum mechanics. Boundary conditions including inner pressure of artery, axial load and torque as well as static equilibrium were applied. Moreover, Cauchy stress components were gotten by using the continuum mechanics relations. Then, the equilibrium equations in cylindrical coordinate were obtained by using the Cauchy stress. Stress distribution through the artery wall was specified by solving the resulting nonlinear partial differential equations based on generalized differential quadrature method. In the beginning, the artery modeling was conducted in the form of monolayer including the media layer and the results were compared with experimental ones, comparison between stresses in the artery wall and experimental data showed that the volcanic energy function of Nolan is suitable for modeling. After that, the stress distribution was obtained by artery modeling in the form of double layers including the media and adventitia layers.

With the advent of shape memory alloys (SMAs), several commercial and industrial applications were proposed due to their superior mechanical and biological properties. Among these materials, Nickel-Titanium (NiTi) alloys are widely applied and well-researched since they are characterized not only by good thermal and mechanical properties but also by excellent biocompatibility compared to other SMAs. In most of the applications, the structural components and devices made of NiTi SMAs work under cyclic thermomechanical loading and one of the major limitations facing the industrial use of this alloy is the degradation of the material when subjected to cyclic loadings (i.e., training). In this study, pseudoelastic training procedure in NiTi shape memory alloy and the resultant two-way shape memory effect are studied using in-situ electric resistivity measurement. At first, variations in the residual strain and in the electric resistivity during pseudoelastic training method are revealed. Then, by measuring the electric resistivity after training procedure (upon specified thermal cycling at stress-free condition) as well as the induced two-way shape memory strain, the effects of residual martensite and dislocation (plastic deformation) on the residual strain are investigated. The obtained results show that about 33% of the residual strain accumulated in 100 pseudoelastic cycles can be ascribed to the residual martensite and about 67% of the residual stain is attributed to the dislocations (plasticity).

Since transformers are one of the most important and most used equipment in power network, investigating the factors which affect the loss of these equipments is of particular importance. Nowadays Amorphous metal core transformers have a significant place in today power market, since they exhibit 60-70% lower no-load losses compared to the Silicon crystalline steel core transformers. In order to enhance the design and cost and also to shorten the time to produce Amorphous metal core transformers, numerical analysis of the no-load as well as load conditions are of paramount importance and hence should be considered. On the other hand, temperature is one of the important and effective factors in transformer life, because increasing the transformer temperature leads to reduction of its rated life. In this paper, a 100 KVA unit transformer has been simulated by coupling ANSYS Maxwell and ANSYS FLUENT softwares and no-load and load losses are investigated. The results show that amorphous core transformer compared to Silicon Crystalline Steel core transformer reduce no-load losses about 65 percent. Furthermore, thermal analysis shows amorphous core transformer has lower temperature compared to the Silicon core transformer in no-load conditions.

In this study, application of a dynamic vibration absorber system consists of two symmetric cantilever beams with tip mass and piezoelectric layer, in order to suppress undesired vibrations and harvest electrical energy, is studied. The main vibratory system is a simply supported beam, which is excited by a DC motor with rotating unbalance mass. To derive the governing electromechanical equations, the Euler-Bernoulli beam theory and the energy method are used. Then the governing electromechanical equations are experimentally validated and accommodation between theoretical and experimental results is shown using several frequency response plots. Using the non-dimensional governing equations, effect of changing the system parameters such as the tip mass, load resistance and length of the cantilever beam is studied. Then, considering ability of system to effectively suppress undesired vibrations and increase the harvested electrical energy, the proper range for selecting the non-dimensional tip mass and non-dimensional load resistance is presented. Finally, using the so-called perfection rate parameter, the best parameters, to have a good vibration suppressor and energy harvester, are obtained. Results shown that both of energy and vibration considerations can be satisfied using the system.

Rapid prototyping (Additive manufacturing or 3D printing) is defined as the process that can build 3D physical part from the designed model in CAD software by joining materials directly. In the RP process, the orientation pattern of the part is one of the most important factors that significantly affect the product properties such as the build time, the surface roughness, the mechanical strength, and the amount of support material. The build time and the surface roughness are the more imperative criteria than others that can be considered to find the optimum orientation of parts. In this paper, two algorithms based on analytical and empirical optimization methods are presented to determine optimum part build orientation in order to minimize build time and surface roughness. To implement this method, the user's part is received in standard triangle language (STL) format. Then, using the geometric characteristics and type of part orientation, the build time and the average of surface roughness is calculated. In order to determine the optimum part build orientation, two analytical (NSGA-II method) and experimental (new and developed Taguchi method) optimization methods have been used. After introducing the steps of these two methods, in order to determine optimum part build orientation, the steps of these two proposed algorithms are implemented on a part as a case study and obtained results are compared and discussed.

In this research, influence of foam filling technique in sandwich beams with expanded metal sheet as core by using lightweight rigid polyurethane foam is investigation. Relationships between the force and displacement at the midspan of the sandwich beams are obtained from the experiments. Three types of Steel lattice cores both bare and foam-filled were subjected to quasi-static. The performance of sandwich structures with expanded metal sheets as core were studied under transverse bending. In the following, by studying the orientation of the core layers to evaluation the impact parameters, including Specific Energy Absorption (SEA) as discussed testing purposes. the energy absorbing system can be used in the aerospace industry, shipbuilding, automotive, railway industry and elevators to absorb impact energy. experimental results showed that foam filling technique can significantly increase specific absorbed energy. Results of three point bending crushing tests showed that the SEA of foam-filled sandwich beam increased by 74 %, comparing to the hollow beam. Also, appropriate orientation of core in the sandwich beam caused to increase the specific energy absorption by 66.5%. Finally, appropriate geometric parameters and the best examples of criteria considered with respect to the objectives, are introduced.

This paper focuses on the dynamic modeling of quadrotor with respect to changes in operating conditions. The main objective of this investigation is to provide complete governing quadrotor dynamic equations using the Euler-Lagrange method considering all aerodynamic forces which affect it's motion. In previous papers, dynamical equations are never considered comprehensively. The study of quadrotor's dynamics permits to understand it's physics and behavior and provides a precise model of the system. Once such a model is obtained, the control of quadrotor turns much simpler than current inaccurate models. In order to take into account, the set of forces and torques involved in quadrotor dynamics, the previous studies are used and after describing each of the forces and their precise terms, the complete dynamic quadrature model is presented. At the end, the system's performance is simulated in two different operating conditions, one regardless of the external object coupled with quadrotor, and the other in the coupled condition with a camera, and by this means, the achieved dynamic model is validated. In the first operating conditions in two different tests, the dynamic equations of the present work will be compared against the previous ones. In the second operating conditions, the quadrotor performance under influence of a connected camera whose motion changes continuously the system dynamic equations is studied.

The collision of droplets on solid surfaces is widely used in oil and gas industry, surface painting, hot surface cooling and spraying of agricultural products. In the present study, the spreading factor of Boger non-Newtonian fluid is experimentally investigated on the dry solid surface such as an acrylic (Plexiglas) and stainless steel sheet and is compared with Newtonian droplets (water and glycerin). The plates of Plexiglas and stainless steel both have a hydrophilic surface. In this research, the Newtonian and non-Newtonian fluids droplets collapse at two heights of 27 and 47 cm from the dry solid surface and are examined in the range of Weber numbers 245≤We≤"538" . The purpose of this study is to investigate the effects of contact velocity on the spreading factor of non-Newtonian and Newtonian droplets during the collision. The results of this study show that with the growth of Weber number (increasing contact velocity), the maximum value and velocity of spreading and receding are increased for the Newtonian or non-Newtonian droplets. Also, with increasing the viscosity of droplets, the value and velocity of spreading and receding are decreased for the Newtonian and non-Newtonian droplets. By increasing the velocity of collision on the Plexiglasas surface (raising the Weber number) up to 32%, the maximum value of droplets spreading is increased 22, 31 and 20 percentage respectively for the fluids of Boger, water and glycerin.

The numerical simulation of near-stall condition in a passage of an isolated subsonic rotor is studied in detail. The requirements of numerical simulation in order to resolve turbulent spectra around the blade are studied. According to the fact that most of unsteady aerodynamic phenomena incept from blades leading edge, and the role of this part in types and intensity of instabilities, the goal of this paper is to investigate the effects of changes in radius of leading edge of airfoil on flow phenomena in different scales of wave numbers. The governing equations of flow-field are solved using different numerical approaches. Resolution characteristics of different modeling and simulation techniques are investigated. The primary geometry of blade uses a standard NACA-65 series airfoil, which has been tolerated by 50% variation in circular leading edge radius. Mesh requirements of flow simulation for intended purposes are studied in detail and some recommendations are proposed to be implemented in numerical aeroelastic simulations. Accuracy and fidelity of LES results are studied with extraction of power spectra around the blade and the portion of resolved energy is also estimated. Results suggest that the order of accuracy and grid density highly affect the small-scale flow phenomena. The variations in leading edge radius also have great effect on energy distribution among resolved scales.

In this paper, a commercial metal-oxide gas sensor was first placed under temperature modulation regime and simultaneously their transient response to various concentrations of ethanol vapors was recorded. By applying the temperature modulation, the sensor surface temperature was also recorded by a S-type thermocouple. Then, the performance of these sensors was expressed based on the both air oxygen absorption model and ethanol absorption on the surface of the sensitive layer using the Freundlich isotherm equation. Further, this model is simulated using the MATLAB software in the simulink environment. Using this model, one can see the sensor's dynamic response to ethanol. In this model, the concentration of a gas is considered as a voltage. This parameter, along with the temperature profile of the sensor surface under temperature modulation and sensor conductance under the influence of air oxygen, are considered as inputs of the model and transient response of the sensor as output of the model. The parameters of this model are calculated based on the approximate criterion of simulated responses and the responses recorded for each concentration of ethanol gas. The simulation results based on the average simulated parameters also showed that the simulated responses were close to the actual recorded responses.

Ti-6Al-4V alloy due to excellent mechanical properties mainly is used in the aerospace, automobile and biomedical industries. Electrical discharge machining (EDM) are used extensively for machining of this alloy. Due to the thermoelectric nature of this process, unwanted changes happen on machined surface such as development of residual stresses and the change in the corrosion resistance. The aim of this study is the experimental investigation of the effect of input parameters (discharge current and pulse on time) on the amount and distribution of residual stresses and corrosion resistance changes of the machined surface in EDM process of Ti-6Al-4V alloy. For this purpose, samples of Ti-6Al-4V alloy were machined by EDM process and residual stresses induced successive sparks in different setting (different discharge currents and pulses on time) were measured by nanoindentation method and SEM images of machined surface used to better assess of samples surface integrity. TOFL measurement method used to determine the corrosion resistance of the samples. Results indicate that at this process tensile stresses is formed on surface and mentioned stresses increase with depth initially and after reaching a maximum dropping out and eventually leads to pressure stress. By increasing pulse on time and discharge current, maximum tension residual stress only slightly increases and is near ultimate tensile strength of work piece material. Comparison of corrosion results indicated that the corrosion resistance of EDMed samples, was less than the not machined specimens.

Laser surface hardening is one of the modern technology used to improve the surface of materials in order to modification of tribological properties. This paper investigate the ability of laser surface hardening of AISI 410 martensitic stainless steel using a continuous high power diode laser with a maximum power of 1600w. Laser power, scanning speed and focal plane position are variable parameters in this research. The effect of the process parameters on the hardness, depth and width of the hardened layer has been investigated. The results show that with increasing laser power and reducing the scanning speed, higher hardness and hardening depth are obtained. Results also reveal that width of hardened layer increases by increasing in focal plane position and reduction the laser power. Modeling of controllable variables (laser power, scanning speed and focal plane position) by Response Surface Methodology method to study the effect of process input parameters on how to change responses, and analysis of ANOVA tables, providing regression equation for output parameters, analysis The Surface Plots, Interaction Plots of the input parameters, were investigated. The results show that in RSM modeling method, the effect of laser power parameter on the results of maximum hardness, depth and width of hardness is more than the parameters of the focal plane position and scanning speed. Due to percentage of coverage of the parameters by the regression equations the RSM method is a suitable model for investigating the effects of the surface hardening process by diode laser.

In direct injection diesel engines, diesel nozzle geometry is a major issue in order to fulfill control of emission due to the influence on internal flow, cavitation phenomenon, spray characteristics and therefore atomization behavior, which are very important for engines performance and
pollutant formation. The aim of this article is to study the effect of cavitation on Diesel spray behavior such as spray penetration lengths and sauter mean diameter. In this study To create a cavitation phenomenon and to investigate its effect on the fuel spray characteristics two similar injector different in the inlet cross section nozzle have been considered and their internal liquid flow and the behavior of their resulted sprays have been investigated( this has been done by moving nozzle on the injector body). AVL-Fire CFD code has been used for meshing and simulating and solving the conservation equations. The results show that by placing the nozzle hole in lower part of the injector sac, the volume fraction of the vapor phase increases. So the growth of the cavitation phenomenon increases. Also the results of the spray show that the spray penetration length for lower nozzle hole increases. An interesting point is that there is no significant change in the size of the spray droplet for two injectors. Most importantly, the spray penetration length can be controlled by place of nozzle hole.

In this research, the Asphaltene particles deposition is modeled using species transport equations. It is assumed that the deposition phenomenon consists of two steps: transport of Asphaltene particles toward the wall and attachment of them to the wall. Due to the small size of Asphaltene particles, their motion is simulated using species transport equation. Transport of Asphaltene particles is modeled by turbulent and Brownian diffusion and attachment mechanism is modeled employing first order chemical reaction. Effects of surface temperature and velocity is considered in the model. Finally the effects of velocity, surface temperature and Asphaltene concentration is investigated and compared with experimental data. The simulation results are agreed well with experimental data and the maximum error of is about 20 percentage. Also in addition of deposition rate, transport and attachment rate are investigated. The results indicate that Asphaltene attachment is more important than transport of Asphaltene, so accurate modelling of attachment has significant effect on prediction of Asphaltene deposition rate.

One of the serious problems in the oil and petrochemical industry is the deposition of crude oil in the preheaters of the distillation unit. Deposition increases the thermal resistance and increases the pressure drop in preheaters, which leads to increase of energy consumption and decrease of overall system efficiency. The main source of deposit in preheaters is a substance called asphaltene, which does not have a definite molecular composition. Generally, deposition involves two stages; one is the transport of insoluble particles to the surface and the other is to stick particles to the surface. So far, a major problem in the simulations is the lack of attention to phenomena that can play an important role near the surface and failure in modeling of particle stacking correctly. In this study, focusing on the boundary layer flow, phenomena that affect the particle deposition process near the surface were investigated. In this regard, the path of motion of particles is followed by Euler-Lagrangian approach, and the bonding stage is modeled using the concept of deposition critical velocity. Numerical solver is validated using available experimental data for aerosol and also with the scanning electron microscopy data. Obtained results show that the dominant force that affects the particle motion in the boundary layer is Brownian force. The deposition velocity is calculated for different diameters and it is shown that with the decrease in the diameter of the particles, the deposition velocity increases.

In this study friction stir welding was used to perform butt joint of Al5083 and simultaneous production of Al-ZrO2 nanocomposite in weldment. Welding parameters such as rotational speed, travel speed and tilt angle were varied to obtain optimum weldment with no defect and high tensile strength, and then by adding zirconia nanoparticle to welding zone of optimum sample, the effects of pass number on microstructure, mechanical properties and wear characteristics of welded specimens were investigated. In order to investigate microstructure, optical and scanning electron microscope and atomic force microscope was used. Results showed that by increasing pass number, the distribution of nanoparticles in the matrix become more homogenous and grain size in the stir zone has considerably decreased. The reason of this phenomena could be attributed to the presence of reinforcement nanoparticles which it causes pinning the grain boundary, enhancing nucleation of new recrystallized grains and the effect on breaking of initial grains. The maximum microhardness and tensile strength of weldment were obtained for composite weldment after four pass of 111 Hv and 328.3 MPa, which these values were 24 and 26% higher than weldment without reinforcement. Wear resistance of the weldment was determined by pin on disk test and revealed that by increasing pass number of FSW, the wear resistance increased.

in this paper, conjugate heat transfer in wavy microchannels filled with nanofluid is studied numerically. Homogeneous single-phase models underestimate the experimental results. Then, nanofluid simulated by two-phase model using an Eulerian-Lagrangian approach. Nanofluids are water-Cu or water-Al2O3 suspensions with a particle diameter of 100-150nm and a volume fraction of up to 2%. The three-dimensional governing equations including continuity, Navier-Stokes and energy equations are solved by the well-known SIMPLE method. The governing equations for particles are solved by a 4th order Runge-Kutta algorithm. due to the 3-D governing equation four equations includinf velocity components and energy should be solved for all particles. the computer program has been written in parallel processing method (MPI). Then a super computer with several CPU,s should be used. In one phase model there some supposes, one of them is that the velocty and temperature of a particle is equal to the velocity and temperature of its surrounding fluid. But the main suppose is that the particle distribution is homogeneous. Results show that the main reason of difference between the results of Homogeneous single-phase models and two-phase model is non-homogeneous particle distribution in the domain.

Damage occurrence in structural and mechanical systems during utilization is an inevitable phenomenon. Death and financial losses could be prevented by health monitoring systems and damage detection processes in structures. In the mentioned framework, damage detection based on dynamics properties, is one of the most important and efficient methods, without concentration on special zones in structure. In this study frequency response functions were analyzed by principle component analysis, then, in order to complete process, dimension reduction and damage indices extraction were conducted. At the end, plate damage detection was introduced as an optimization problem considering extracted damage indices, and solution of the problem were given by PSO and Genetic algorithms. Output results consist of estimation about location and intensity of applied damage. Several scenarios including single, simultaneously dual and triple stiffness losses were figured out to investigate and evaluate the efficiency of the mentioned algorithms. Finally, outcome result around performance and utility of method had been discussed. It's obviously demonstrated that Particle Swarm Optimization algorithm has more accurate result, especially in estimation of damage location than Genetic algorithm optimization solution, during health monitoring processes. The mentioned conclusion has been gotten more explicit with getting scenario complicated.

Reliability-based design optimization (RBDO) has been used for optimizing engineering systems in presence of uncertainties in design variables, system parameters or both of them. RBDO involves reliability analysis, which requires a large amount of computational effort, especially in real-world application. To moderate this issue, a novel and efficient Surrogate-Assisted RBDO approach is proposed in this article. The computational intelligence and decomposition based RBDO procedures are combined to develop a fast RBDO method. This novel method is based on the artificial neural networks as a surrogate model and Sequential Optimization and Reliability Assessment (SORA) method as RBDO method. In SORA, the problem is decoupled into sequential deterministic optimization and reliability assessment. In order to improve the computational efficiency and extend the application of the original SORA method, an Augmented SORA (ASORA) method is proposed in this article. In developed method, A criterion is used for identification of inactive probabilistic constraints and refrain the satisfied constraints from reliability assessment to decrease computational costs associated with probabilistic constraints. Further, the variations of shifted vectors obtained for satisfied constraints are controlled to be exactly equal to zero for the next RBDO iteration. Several mathematical examples with different levels of complexity and a practical engineering example are solved and results are discussed to demonstrate efficiency and accuracy of the proposed methods.

The effect of counterflow jet through an extended nozzle on reducing aerodynamic drag is analyzed by using a combined method. Flow field is simulated around a hemispherical body in a free stream with Mach 4. The results are reached by providing a 3D solver and applying the complete form of Navier-Stoke and energy equations along with modified shear stress transport model. Appropriate numerical validation has been made by comparing the surface pressure distribution in the zero pressure ratio of jet to free-stream and drag on the nose at a pressure ratio of 0 to 3. Four nozzles were used to analyze the effect of extending. The results show that the nozzle extensions have a significant effect on the wave drag after changing the shape of the bow shock. In a given pressure ratio, the effect of injected jet from the extended nozzle over the reduction of the nose is higher than that of direct jet injection from the nose. The effect is visible in all pressure ratios. Furthermore, a limited increase in the pressure ratio over a fixed length of the extended nozzle has led to a further reduction of total drag. However, in the higher pressure ratios, the linear increase of the retro jet has led to an increase in the total drag on the nose. The results also show that increasing the nozzle length in a constant pressure ratio leads to an increase in the depth of jet penetration and a larger reduction of total drag.

In this paper, Saffman-Taylor instability of an immiscible displacement in a Hell-Shaw cell is studied numerically for the first time. The VOF method is used for two phases flow simulation. Viscoelastic fluid with less viscosity is considered as the displacing fluid and Newtonian fluid with high viscosity is used as the displaced fluid. The upper convected Maxwell constitutive equation is applied to simulate the viscoelastic fluid. In this research, the effects of dimensionless parameters consisting of the mobility ratio, elasticity number and capillary number are studied and the sweep efficiency diagram is depicted. The results show that, increasing the elasticity number and capillary number, and decreasing the mobility ratio can stabilize the flow. It is also found that, changing these parameters has a significant effect on the phase contours and mechanisms of viscous fingering patterns. The results of this numerical study could be helpful for enhanced oil recovery process, especially in polymer flooding technique. As a main consequence, it is concluded that, the elastic properties of displacing viscoelastic fluid in the presence of capillary forces has a stabilizing effect on the flow instability.

In this paper, the Semi-Empirical and numerical methods that can be used to investigate the effects of dynamic stall are compared with each other, and the capabilities of the methods are studied. The experimental measurements have been used in order to compare the methods. The Semi-Empirical Leishman-Beddoes (L-B), Snel and ONERA methods have been used, and the finite volume method was being used for numerical simulations. The lift coefficient was being calculated by all the methods at various conditions, and the drag coefficient had been computed by the numerical and Leishman-Beddoes methods. The parameters that have been used in order to compare the methods, are the maximum lift coefficient value, the angle of attack of the largest lift coefficient, the error at upstroke phase and the error at down stroke phase. The results show among the semi-empirical models; the L-B method has the highest precision to predict the lift coefficient, and although the numerical method can investigate the flow with more details, but the error percentage at the down stroke phase is higher than expectations. The results from the drag coefficient modeling show that the numerical method can predict this coefficient better than the L-B method. The results also can help other researchers to select the best dynamic stall model in order to investigate the wind-turbine aerodynamics.

Rotary Regenerative Air Preheater (RRAPH) is one of the main equipments for energy recovery in the steam power plants. In this study, air preheater of the Bisotoun Power Plant of Kerrmanshah has been investigated with the aim of optimizing its thermal performance. So, with Computational Fluid Dynamics (CFD), three-dimensional simulation of the rotary air preheater has performed to solve the continuity, momentum and energy equations in porous medium by using moving refrence frame (MRF) method. The results showed acceptable accuracy in comparison with the experimental results which is achieved from the power plant data. In this research, the effect of rotational speed on the efficiency of air preheater in different loads and mass flow rates for both without and with leakage conditions has investigated. The results showed that the impact of the rotational speed on the performance of RRAPH is noticeable in the range of 0.5 to 4 rpm, and after this increase in speed does not have a significant effect on efficiency. The present study also showed that leakage has a significant effect on reduction of the efficiency of the RRAPH in all loads and rotational speeds. In the following, the effect of matrix material change on the efficiency of RRAPH has investigated. According to the results, for both without and with leakage, the best thermal performance is related to the stainless steel, which has the least thermal diffusivity, also the least thermal performance is related to the copper, which has the highest thermal diffusivity.

Several factors such as shape of the jet hole, blowing ratio, density ratio, mainstream turbulence intensity, and …, affect the film cooling effectiveness. Among the above mentioned factors, the film cooling effectiveness is strongly influenced by the shape of the jet hole. This geometry should be designed in such a way to minimize the jet's vertical momentum and produce more surface coverage. In this research, cooling performance of a novel integrated compound (earring) jets design is investigated experimentally, using an infrared thermography method. Steady state heat transfer experiments at the jet Reynolds number of 10,000 (based on the jet diameter) are performed over the test plate. The jets injection angle into the mainflow are considered to be 30 degrees relative to the surface. The measurements are carried out at the mainstream speed of 27 m/s and at four different blowing ratios of 0.4, 0.5, 0.7, and 0.8. The obtained results show that at constant jets cross section, the earing jets geometry leads to higher film cooling effectiveness, compared to the cylindrical hole geometry. Optimum blowing ratio is 0.8 and the lowest effectiveness is obtained on the surface at the blowing ratio of 0.4. The flow structures which are introduced by this novel geometry, reduces the flow mixing between the mainstream and the cooling jets. Therefore, enhances the film cooling effectiveness and the coolant fluid more uniformly distributes over the surface laterally.

The design process of an Autonomous Underwater Vehicle (AUV) requires mathematical model of subsystems or disciplines such as guidance and control, payload, hydrodynamic, propulsion, structure, trajectory and performance and their interactions. In early phases of design, an AUV are often encountered with a high degree of uncertainty in the design variables and parameters of system. These uncertainties present challenges to the design process and have a direct effect on the AUV performance. Multidisciplinary Design Optimization (MDO) is an approach to find both optimum and feasible design and robust design is an approach to make the system performance insensitive to variations of design variables and parameters. It is significant to integrate robust design and MDO for designing complex engineering systems in optimal, feasible and robust senses. In this paper, an improved robust MDO methodology is developed for conceptual design of an AUV under uncertainty with considering tactic and system design simultaneously. In this methodology, Uncertain MultiDisciplinary Feasible (UMDF) framework is introduced as uncertain MDO framework. Two evolutionary algorithms are also used as Pareto-based Multi-Objective optimizers and results of two algorithms are compared. The results of this research illustrate that the new proposed robust multidisciplinary design optimization framework can carefully set a robust design for an AUV with coupled uncertain disciplines.

Various solutions have been suggested to overcome the issue when cooling peak hours and electric energy consumption coincide. One of the solutions is to store the cooling load at off-peak hours. One of the most conventional types of storage systems is the ice-on-coil storage system. The low heat transfer rate in this system is one of the challenges. Since the conduction heat transfer coefficient of ice is low, by starting the ice formation, the heat transfer between the refrigerant inside the coil and the reservoir’s water will reduce. One idea to increase the heat transfer rate is to postpone the starting time of the freezing process to keep active the natural convection mechanism. In the present study, mechanical vibration has been used to linger freezing initiation in ice-on-coil energy storage system. The effect of longitudinal and lateral positioning of the probe, on the amount of temperature and initiation time of freezing as well as the amount and structure of formed ice has been investigated. The results revealed that placing the vibrator at the middle of coil over its two ends leads to further increase in the amount of formed ice. It is found that applying mechanical vibration can postpone the initiation time of the freezing process and decrease the subcooling temperature. Moreover, it is shown that the amount of ice formation is a function of subcooling temperature and initiation time of freezing. Finally, the energy consumption of the vibrator and the energy consumption reduction in peak-hour are calculated.

Nowadays, the use of polymer composite materials in various industries has been increased due to their good mechanical properties, lightness, sound and thermal insulation and corrosion resistance. Over the past two decades, carbon fiber reinforced polymer (CFRP) materials have been widely used in aerospace and automotive industries. These materials may be subjected to impact during manufacturing or service period and a lsmal impact region may be produced in them. This small defect can reduce the mechanical properties of the structure and lead to its failure. Therefore, it is necessary to use a method for defect detection in these materials. In this study, a polymer composite sample made of carbon fiber in polyester resin was made and subjected to impact test. To consider the repeatability of the defect detection process, the sample was subjected to four various impact tests and the defect areas were evaluated using penetrant-enhanced X-ray radiography and ultrasound immersion pulse-echo C-scan. The image obtained from the penetrant-enhanced X-ray method was scanned using a digital scanner, and the image of the ultrasound C-scan test was calibrated, taking into account the step of scanning.The areas of the defect region were obtained using Imagej software. The results show that these methods are able to detect and measure the impact area in the composite sample and Ultrasonic C-scan method detect impact area more accurately.

In the present study, a novel integrated system containing biomass gasifier, sodium high-temperature heat pipes, and solid oxide fuel cells is introduced. The integrated system is taken into consideration due to its high efficiency and power in order to simultaneous producing electrical power and heat. The modeling of system is performed using equilibrium constants, mass and energy conservation law and the analysis of codes is done in EES software. The effect of gasifier STBR, current density, fuel utilization factor, and outlet fuel cell’s temperature as variable parameters is investigated on the power and total energy efficiency of integrated system using response surface method; after validation of modeling in comparison to the experimental results. The analysis of variance results indicate that fuel utilization factor (with 53% contribution) and current density (with 33% contribution) are the most effective parameter on the power and total efficiency, respectively. The power of integrated system is increased by increasing of temperature while power has an increasing behavior follows by decreasing behavior by increasing fuel utilization factor. The total efficiency is increased by increasing temperature and STBR while it is decreased by increasing current density and fuel utilization factor. The results revealed that the power and total efficiency is obtained at optimum states as high as 300 kW and 90%, respectively.

In this paper, a coupled plasticity-phase field model for ductile fracture is proposed. The Drucker-Prager plasticity model, which have been applied to metals, concrete, polymers, foams, and other pressure-dependent materials, is coupled with the phase field method. The governing equations are determined by a minimization principle that results in balance laws for the coupled displacement-fracture phase field problem. Furthermore, the finite element implementation, discretization and integration algorithms for the proposed model are presented for three-dimensional, plane strain and plane stress states. In addition, to control the influence of the plastic work and its effect on the crack propagation process, a threshold variable is introduced. Using a numerical example, it is demonstrated that a specific length scale and a certain minimum element size is necessary such that the regularized crack surface converges to the sharp crack. The accuracy of the proposed model and integration algorithm is verified by comparing the obtained results with existing experimental data. In addition, the Arcan sample, by means of a special test setup, allows to load a sample at different direction, and thus performing mixed mode fracture investigation using the model.

In this study, quasi-static compaction is employed to produce Mg-SiC nanocomposite samples. Different volume fractions of SiC nano reinforcement and micron-size magnesium (Mg) powder as the matrix are used to fabricate nanocomposite specimens. The powder mixture for each percent of SiC are mechanically milled. The mixed powder is then placed into a mold and is consolidated at different temperatures using Instron machine. MoS2 is utilized as a lubricant to decrease the friction between the fabricated specimen and the mold. It is found that with the increase of temperature the sintering requirements is met and higher quality samples are fabricated. The density, hardness, compressive strength in high and low strain rate of the compacted specimens are compared for different volume faction of SiC at 25, 250 and 450 oC. It was found that by increasing the content of nano reinforcement, the relative density of the compacted samples decreases, whereas, the micro-hardness and the strength of the samples enhance. Furthermore, higher densification temperatures lead to density increase and hardness reduction. Additionally, it is shown that the compressive strength at high strain rate compared to low strain rate is significantly improved by increasing the SiC nano reinforcement so that dynamic strength for the same level of SiC was 55% higher than the quasi-static strength.

Due to various benefits of composite materials such as light weight, high strength and their excellent formability, the externally bonded composite patches have been proved to be a preferable method of repairing flaws and cracks in various engineering structures. In this paper, the behavior of various patches such as composite and metallic patches has been studied by calculating the stress intensity factor and the T-stress via 3D finite element method. The study of the out-of-plane bending role in repair of plates with single-sided patch is another aims of this research. The results showed that the higher stiffness of the composite patch leads to further reduction in stress intensity factor. It is found that in the studied specimens, the boron/epoxy patch has the better behavior compared with glass/epoxy one. Furthermore, using single-sided and double-sided patches leads to change in the T-stress value. The largest change achieved by the crack angle equals to 0 and the smallest on achieved by the crack angle equals to 45 degrees. Increasing the adhesive thickness leads to increasing the stress-intensity factor in repaired plate. Finally, it is found that the out-of-plane bending has the significant effect on behavior of repair with single-sided composite patch.

The fixtures play a significant role in harnessing the metal sheets in the assembly stage. The high flexibility of the metal sheets and the initial deviation in the pressed sheets cause deviation in the final product. Using the optimal layout of the clamping points in the fixture can reduce the deviation effectively and raising the final product quality. On the other hand, the cost of construction is intensively influence by the number of clamps, rising the number of clamps causes the cost of construction to increase and reducing it cause the deviation in the final product to increase. Therefore, the number of clamps should be considered in the optimal design of the fixture. It is challenging to achieve optimal design for fixture due to the difficulty in predicting sheet behavior and computational constraints. In this paper the relationship between the initial deviation of sheet and the deviation of final product is investigated and a method is proposed by using ant colony algorithm and finite element method for optimizing the position of the clamping points to reducing the deviation of the product after assembly with considering the minimizing the number of clamping points. Finally the proposed method is applied to a simple square sheet with initial deviation and based on the cost function, the number of clamping points and their position are optimized. The results show that reducing the amount of sheet deviation in the fixture causes reduce the deviation of final product.

Persistent strength training can increase ventricular blood pressure and volume and the resultant loading in ventricles of the human heart. It is proved that pressure overload can increase ventricular thickness and volume. In this article, we modeled athlete’s heart syndrome macroscopically arising from pressure overload using continuum mechanics and finite elements methods. We tried to improve previous results by using a more precise geometry and loading and by modifying previous equations. Firstly, we saw that because the left ventricular pressure was more than the right ventricular pressure, increase in myocardium thickness started from the left ventricle and secondly, this increase in myocardium thickness started from lower regions that located far from the right ventricle. Then, it was shown that thicker regions with greater values of the growth multiplier had less stress than regions with less values of the growth multiplier. As time passed and more loading cycles were applied to the endocardium, myocardium thickness increased gradually until the growth multiplier reached its maximum threshold value. Finally, we demonstrated that when the ventricular pressure rises and hypertrophy occurs, residual stresses remain in the myocardium after unloading.

One of the important issues in shooting by air guns is to select the appropriate projectile for different distances of the target. In this paper, the performance of four samples of air gun projectiles (pellets) is studied. The motion of these projectiles is assumed in four degrees of freedom including three translational motions and one rotational motion. The considered projectiles have three calibers of 4.5, 5.5 and 6.35 mm, and four different types, namely flat nose, sharp nose, round nose and spherical. In order to numerical simulation of the problem, after these projectiles have been modeled geometrically, the 3-D compressible turbulent Navier-Stokes equations and dynamic equations of the projectiles motion are solved in a coupled form and in a moving computational grid. The numerical simulation is based on “Roe” scheme with second-order accuracy in space and time using a finite volume method. To validate the computer program operation, the results are compared to valid experimental data. Computed results describe the trajectory, velocity variations and altitude loss of the projectiles with time and location. Comparison of the projectiles performance including the trajectory, velocity variations and altitude loss indicate that the round nose projectile has the best performance in long distances compared to the other samples and the flat nose projectile has a great performance in short distances, while it has a weak behavior in long distances. Additionally, effect of nose shape on the performance of the sharp and round nose projectiles is investigated and the optimum nose shapes are obtained.

This paper discussed nonlinear adaptive control of a 6 DOF biped robot. The studied robot was divided to three part, fix leg, moving leg and a torso and all the joints were considered rotational. Generally, for calculations, robots are considered as a whole which makes the related calculations complex. For balance calculations, the zero moment point (ZMP) was either considered as a fix point on the ground or a moving point on the foot plate. In the presented robot in this study with priority of movements, first, the calculations were carried out on the moving foot, then the effect of the motion on the foot was inspected and a pendulum was used to balance the robot. To check the balance, ZMP in the simulation in MATLAB software was considered as a fix point While in Adams software simulation, ZMP was considered moving along the bottom of the sole. All the charts active with both software met each other. In the presented study the inverse kinematics was calculated by trigonometric method and inverse dynamics of each leg was investigated by Newton-Euler iterative method. All calculations were carried out in MATLAB software and were verified by ADAMS software. By writing the equilibrium equations, the angle of torso at each time was achieved. In the next step, because of uncertainties in manufacturing and some parameters like mass, length, etc. adaptive computed torque control was used on each leg to achieve the maximum torque that each joint needs for stable walking.

A Finite Volume-Lattice Boltzmann Method (FVLBM) for simulation of viscous laminar compressible flows in 2-D structured curvilinear coordinate system has been developed. In the present study, validation of the presented software and accuracy assessment of four new 2D lattices D2Q9L2, D2Q13L2, D2Q17L2 and D2Q21L2 based on increasing discrete velocities of lattice has been studied and the optimum lattice has been introduced. The presented LBM has developed using new method of circular function idea instead of expansion or correction of Maxwelian function for evaluation of equilibrium distribution functions. Moreover, in order to capture discontinuities in the flow field, 3rd order MUSCL scheme has been implemented for approximation of convective term. The laminar compressible viscous flow over the NACA0012 airfoil has been simulated in the curvilinear coordinate system for two angle of attacks, 0 and 10 Deg. The obtained results have been compared with validated N.S. solutions. Although the results have desirable accuracy in comparison of those of the N.S. solutions, limitation of the presented method and results assessment obtained by the different lattices have been investigated.

In this study, the performance of a cylinder absorbing wave energy from irregular incident waves, as one of the renewable energy systems, is investigated numerically using complete solution of the Navier-Stokes equations. For this purpose, the control volume approach in conjunction with the fictitious domain method, for modeling the solid object motions inside fluid, are used where a two-step projection method is used to solve the governing equations. The results show that despite the cylinder absorbs energy in two main directions, its energy absorption efficiency in irregular waves is about 8%. Due to the employed spring and damper in these devices, the system has only one natural frequency which is the reason for its low efficiency at irregular waves. Results also show that for steep waves at deep waters, the maximum efficiency occurs at larger spring coefficient and smaller damping coefficients, while at moderate water depths and wave steepness, the maximum efficiency occurs at smaller spring coefficients and larger damping coefficients. Therefore, to reach maximum energy absorption efficiency at irregular waves, not only these coefficient has to be adjusted carefully, but also it is recommended to use multi-resonance systems or several cylinders with different natural frequencies.

In the present study, the numerical solution of the Ansys Fluent software has been used to calculate the sound produced by the high-speed flow on a cylinder using the Lighthill acoustic analogy. The calculations were carried out on a cylinder (part of the landing gear) at a speed of 70 m/s (take-off and landing speeds of airliners). The problem is initially caried out as a regular unsteady numerical solution. During the solution, aerodynamic noise data sources are stored as inputs of acoustic analyzes in files. Then, by solving the acoustic equations, the volume of produced sound (in decibel) is calculated at points that are pre-defined as the microphone in the desired coordinates. The purpose of this study is to study the ability of Fluent solution to calculate the sound generated by the flow, in addition of using a method for estimating the amount of sound increase by increasing the length of the cylinder. In the other words, due to the timing of the numerical solution, one can calculate sound generated by small length cylinder, and then, using engineering approximation, it estimates the sound of the flow around the larger-length cylinder. After the necessary calculations, results are provided as sound pressure level curves using the acoustic analogy and fourier spectral analysis. The results show that large eddy simulation turbulence model is most appropriate model for acoustic simulations. Also, the approximate method for evaluating the effect of increasing the length of the cylinder is in good agreement with the experimental results.