Sharif Journal of Mechanical Engineering
https://sjme.journals.sharif.edu/
Sharif Journal of Mechanical Engineeringendaily1Thu, 21 Dec 2023 00:00:00 +0330Thu, 21 Dec 2023 00:00:00 +0330-
https://sjme.journals.sharif.edu/article_23465.html
-Investigation Of The Effect Of Shape Memory Alloy On Buckling And Post-Buckling Of Composite Panels In Supersonic Flow With Thermal Heating
https://sjme.journals.sharif.edu/article_23022.html
In the present work, the effect of smart shape-memory alloys on thermal buckling and post-buckling of monoclinic and unidirectional composite panels has been investigated. The aerodynamic pressure applied to the system was modeled using the piston theory method. The effect of thermal heating for ultrasonic flows was also estimated from the reference temperature method. The panel is modeled nonlinearly with large deformations based on Van Karmen's theory. The obtained results show that the shape-memory alloy was able to increase the critical temperature of thermal buckling. The effect of the arrangement of composite layers on increasing the thermal buckling temperature was also studied. The results show that the amount of thermal deflection is greatly reduced due to the use of this alloy. Also, in the higher temperature differences, the rate of reduction of the panel increases.
In this work, the effects of thermal stress on buckling and thermal buckling in a rectangular composite panel with hinge-hinge boundary conditions were investigated. Also, the effect of shape retention alloy in controlling these two phenomena has been studied. The shape memory alloy wire was placed in martensitic mode to apply a compressive force to the panel to control the heating and aerodynamic forces after changing the phase to austenite. The governing equations of the system were extracted through the layer theory method to show the effects of in-plane displacements better.
Investigations on the effect of different layers (symmetry effects and arrangement angle of composite sheets) were performed to investigate thermal buckling. According to the obtained results, the layer arrangement of plates (0.90 / 0.90), (-45.45), (30/60), and (0.90 / 90.0), respectively, had the greatest effect on raising the critical temperature of thermal buckling in dimensional ratios equal to or greater than one. This shows that the symmetry of the arrangements has a greater effect than the angle of the arrangements. Examining the buckling diagrams for the effect of a shape memory alloy, it can be concluded that by placing this alloy in the composite panel, in addition to raising the buckling temperature, this alloy has a greater effect on displacement control by increasing the temperature after the critical buckling temperature.Design And Comparison Of Combined, Parabolic, And Flat Plate Reflectors On The Performance Of A Solar Module
https://sjme.journals.sharif.edu/article_22979.html
Solar energy is the most abundant source of energy among renewable energies, which can be directly converted into electricity by solar modules. To tackle the low energy output of solar modules in places where there are not enough spaces to install many solar modules, the use of reflectors is recommended. The use of reflectors increases the solar radiation on the surface of the module, hence will boost its power output. In this study, two-dimensional simulations were performed using ANSYS Fluent 2021 R2 package software in which the effects of a flat plate, parabolic, and hybrid reflectors on the temperature and efficiency of the module were investigated. The numerical simulation of the current study was validated against an experimental case study. Although there were so many simplifications and assumptions for the validation, the maximum deviation between the present numerical result and the experimental was less than 3.86%, which certifies the results of this paper. Based on the output, the surface temperature of the solar module with ˚85 flat plate reflector and ˚85 parabolic reflector reached 360.82 (K) and 371.11 (K), respectively, while the temperature with ˚50 reflector for both parabolic and flat plate modes reached 345.94 (K) and 346 (K), which are approximately equal. It was also observed that with increasing the angle of flat and parabolic reflectors, the module temperature increased, and parabolic reflectors had higher temperatures at higher angles. The module temperature using a type 6 reflector increased by 7.14% and 0.92% compared to the ˚80 flat plate reflector and ˚80 parabolic reflector, respectively. In terms of efficiency, since reflectors will intensify the solar radiation on a solar module surface, it will enhance the operating temperature of the module so that in all cases with reflectors, the efficiency will drop from an initial maximum value to a certain minimum value. This drop is more significant in the parabolic reflectors compared to the flat plate reflectors.The Smart Design Of Heat Exchangers With Expanded Surfaces By Genetic Algorithm And Image Processing
https://sjme.journals.sharif.edu/article_22978.html
The analysis of heat transfer in the channel in many types of heat exchangers, such as electric cooling equipment, solar collectors, heat exchanger systems, high-performance boilers, gas turbine blade coolers, etc., is the basis of the design, construction, and optimization. Controlling heat transfer to increase the rate of heat transfer in such systems by improving the cooling method is an effective energy engineering from the point of saving energy. Increasing the heat transfer performance in the scales of macro and microchannels is crucial. The use of expanded surfaces in the channel is a practical method to increase the heat transfer coefficient. In the upcoming article, the smart design of a two-dimensional nanofluid heat exchanger has been studied numerically in order to achieve optimal performance conditions in terms of heat transfer rate, the amount of deposition of nanoparticles in the structure of the exchanger, as well as the fluid pressure drop while passing through it. It can be seen that the geometric structure optimized by the combination of genetic algorithm and computational fluid dynamics of this channel causes an increase of 1.14% in the enthalpy of the passing nanofluid, a decrease of 11.21% in the pressure drop of the passing nanofluid, and a reduction of 8.44% percentage in the deposition of nanoparticles inside the channel and a total increase of 24.82% in the fitting function defined in terms of these three variables, compared to the channel designed in previous studies. Therefore, this optimal channel has a higher heat transfer rate with a pressure drop and a lower amount of nanoparticle deposition compared to the previous channel, which proves the ability of the genetic algorithm with computational fluid dynamics in the optimal design of all types of heat exchangers.Experimental Study Of Multi-Point Incremental Forming For Conical Parts
https://sjme.journals.sharif.edu/article_22980.html
The development of rapid prototyping methods has been very drastic in recent years. One of these methods, with a nature similar to sheet-forming processes, is the incremental forming method. In the last two decades, this technique has attracted much attention in industrial applications. The incremental forming process has been able to play a major role in advancing industrial projects in the production of low-volume prototypes. This process is a suitable alternative to conventional forming processes in the single production of conical geometries because of the low cost of machinery, equipment, and tools. In this paper, the two-point incremental forming of conical parts by three multi-point matrix designs, including single, double, and three-step cylinders, were investigated. For this purpose, the feed rate (400-1000 mm/min) and the penetration step of the tool (0.5-1.1 mm) were investigated in three levels to form the aluminum sheets with a thickness of 0.5 mm. In the following, the effect of the input parameters on the limiting height of the formed specimens, thickness distribution, surface roughness, and geometric accuracy of longitudinal cut specimens was assessed. According to the results, using the multi-point matrixes, despite increasing the final geometric accuracy, friction was reduced compared to the conical matrix. Using a two-step matrix, deeper pieces were formed by increasing the formability of the sheet, in which the average height was improved by an average of 12%. However, no significant change was observed in the roughness of the samples formed by all three types of matrixes. Therefore, the design of the proposed matrix had almost no tangible effect on the final surface roughness output. From the view of geometric accuracy, the matrix design with three steps created the highest geometric accuracy, as well as the least deviation relative to the planned path.Rotor Design And Performance Study Of An Airborne Wind Energy System With Flight Dynamics Simulator
https://sjme.journals.sharif.edu/article_23023.html
Airborne wind energy system (AWES) is a novel approach in wind energy harvesting. It has several advantages against conventional horizontal axis wind turbine (HAWT), like using less material and thus lower manufacturing cost, higher efficiency, stable electricity output and higher capacity for energy harvesting. It is obviously embedding a complex control system which makes the appropriate flight trajectory for the vehicle. These systems need to be carefully designed so using virtual flight simulators in design process is crucial. The main components of a typical AWES are: tether, flyer, and rotors. The flyer is designed to have a tether-constrained flight across the wind in a circular path. Consequently, the mounted rotors on the flyer’s wings will capture energy and this mechanical/electrical energy would be sent back to the ground via the same tether. It is notable that the flight path and the special design of the flyer, would make it capable to have a sustained motion in the circular loop with no energy consumption. A tethered drone equipped with several rotors is an example of such devices, already has been built and tested. In previous literature, the flight simulators usually contain some simple aerodynamic models for predicting the forces and moments generated by the rotors. It is derived by constant aerodynamic coefficients. In the current study, it has been developed a flight simulator for a typical AWES having onboard rotors. To make this flight simulator more accurate and to improve its fidelity in different environmental conditions, proper estimation of the external forces, particularly the aerodynamic forces and moments, seems to be necessary. Therefore, toward developing a high-fidelity simulator, Lagrangian dynamics and a new algorithm for estimation of the rotor aerodynamics, has been utilized. This new method is shown to have more accurate approximations of the system performance and also better description of the vehicle trajectory. By this framework, one could design optimized blades of the rotors and also the rotors arrangement. Implementing the new simulator, a single drone, as the flyer in AWES, having 3m wing span, would experience 40 percent improvement in the average power extracted which is near 2 KW.Boundary Feedback Trajectory Tracking Control Of Rigid Bodies With Interior Shallow-Water Sloshing
https://sjme.journals.sharif.edu/article_23094.html
The problem of tracking control is addressed for rigid bodies with interior shallow-water sloshing. The liquid motion is modeled by the Saint-Venant equations, coupled with the ODE of the rigid body, leading to a global system with an ODE-hyperbolic PDE cascade structure. The paper aims to design an innovative boundary feedback framework for a pre-specified position to deal with rigid body tracking errors. Using only one control force applied to the rigid body, the formulated strategy efficiently stabilizes both the finite- and infinite-dimensional states. The main complexity lies in the fact that no sensor can be implemented in the liquid domain. Indeed, the proposed stabilizing feedback law simply requires measurements of (i) the rigid body position error and velocity and (ii) the liquid pressure at the cavity walls (liquid boundary). The asymptotic stability of the closed-loop system is analyzed using the Lyapunov direct method and LaSalle’s invariance principle without any discretization, reduction, and linearization. Additional controller features are highlighted by simulation results, including its benefits in contrast to the corresponding PD controller and its robustness to time delay and system uncertainty.Numerical Simulation Of Energy Harvesting From A Flexible Plate Behind A Cylinder Using Flow-Induced Vibrations
https://sjme.journals.sharif.edu/article_23129.html
Energy harvesting is the process of converting different kinds of energy, such as solar, thermal, kinetic energy of fluid, etc., to a usable form of energy. Different kinds of transduction mechanisms are used for energy harvesting. The piezoelectric mechanism has received considerable interest because of its advantages, such as ease of application and working over a wide range of frequencies. Simulation and investigation of energy harvesting from a piezoelectric plate, which is mounted on an elastic beam and located behind a cylinder through flow-induced vibrations, is the subject of the present research. First, the results of the lift and drag coefficients in the fluid flow around a stationary cylinder at Reynolds 200 are compared and validated with the previous studies. After that, by placing an elastic beam and a piezoelectric behind the cylinder, flow around the cylinder, and the fluid-solids interactions are investigated. Due to the vortex shedding phenomenon, which happens in the fluid flow past the cylinder, the elastic piezoelectric beam deforms periodically, and thus, the mechanical energy of the flow is converted into electrical energy. In this problem, the beam effect on both the drag/lift reduction and the amount of voltage extracted from the piezoelectric layer were investigated, and the optimal mode obtained was selected based on the extraction of more energy. In this regard, the process of finding the most optimal energy harvesting mode for the location of the elastic beam, the length of the beam, and the fixed point of the elastic beam in different geometries are carried out. The results of the optimal investigations are as the length of the elastic beam of 2D, the distance of the beam from the back of the cylinder 2.5D, and the state in which the beam is fixed from the right side, where D is the diameter of the cylinder.Processing Of Thin Magnesium Tubes By Tubular Channel Angular Pressing (TCAP) Process With Trapezoidal Geometry
https://sjme.journals.sharif.edu/article_23123.html
Due to the compatibility of Magnesium with the body, it is a suitable material for making biodegradable stents, although its mechanical properties are not desirable for stent application. Accordingly, lately, microstructure and mechanical properties of magnesium have been improved using various methods, including Severe Plastic Deformation (SPD). Many SPD methods have been introduced for the fabrication of ultrafine grain tubes until now, and the process of Tubular Channel Angular Pressing (TCAP) is the most effective one. In this research, by optimally designing the geometrical parameters of the trapezoidal channel, the process force in TCAP has been reduced, and for the first time, magnesium tubes with a thickness of 1 mm have been processed using this process. At the beginning of the research, using the finite element model, the process was simulated in Abaqus software, and the effect of the geometric parameters on the process force was investigated. To investigate the performance of the process with optimal geometric parameters, magnesium tubes with an outer diameter of 5 mm and a thickness of 1 mm were processed at a temperature of 200°C in three passes. The results of metallographic, microhardness, and tensile tests show that the TCAP process with trapezoidal geometry and optimal geometrical parameters is a suitable process for modifying the microstructure and improving the mechanical properties of magnesium tubes with a thickness of one millimeter. The values of yield strength and ultimate strength in the second pass are 1.6 and 1.26 times the initial sample, respectively, and have reached 60 and 92 MPa. The average grain size and hardness have reached from 200 µm and 30 HV in the initial sample to 3 µm and 40 HV after the third pass, respectively. The ductility and strength of processed samples have improved compared to the initial sample.Boundary Feedback Trajectory Tracking Control Of Rigid Bodies With Interior Shallow-Water Sloshing
https://sjme.journals.sharif.edu/article_23130.html
The problem of tracking control is addressed for rigid bodies with interior shallow-water sloshing. The liquid motion is modeled by the Saint-Venant equations, coupled with the ODE of the rigid body, leading to a global system with an ODE-hyperbolic PDE cascade structure. The paper aims to design an innovative boundary feedback framework for a pre-specified position to deal with rigid body tracking errors. Using only one control force applied to the rigid body, the formulated strategy efficiently stabilizes both the finite- and infinite-dimensional states. The main complexity lies in the fact that no sensor can be implemented in the liquid domain. Indeed, the proposed stabilizing feedback law simply requires measurements of (i) the rigid body position error and velocity and (ii) the liquid pressure at the cavity walls (liquid boundary). The asymptotic stability of the closed-loop system is analyzed using the Lyapunov direct method and LaSalle’s invariance principle without any discretization, reduction, and linearization. Additional controller features are highlighted by simulation results, including its benefits in contrast to the corresponding PD controller and its robustness to time delay and system uncertainty.Simulation And Theoretical Analysis Of The Nanofluid-Based Oil Transformers For Improving The Cooling Performance Of The Transformer
https://sjme.journals.sharif.edu/article_23122.html
Transformers are one of the most important and expensive equipments in industries whose optimal performance has been influenced by various parameters such as weather conditions (temperature, humidity, etc.) and consumption patterns of the region. Transformer oils are one of the most vital materials used in this equipment. The oil of the transformer coils has been controlled by two factors: First, it acts as an electrical insulator between the coils and the body. Second, the heat created in the parts and the core of the transformer is transferred to the outside. In the electrical industry, many problems may be caused by transformers. Most of these cases have been affected by the performance of oils. In case of improper operation of the oil, it will cause disruption in electricity distribution and even damage and destruction. The oil should perform both tasks of cooling the transformer and insulating the body with electricity at the ideal level. However, due to the low thermal conductivity of such mineral oils, transformers cannot provide optimal performance.
In this research by the simulation study, sufficient and acceptable information has been obtained to create the most optimal nano-oil in the operational range with comprehensive library reviews. On the other hand, according to the theoretical analysis, it has been presented that metal oxide nanoparticles, such as CuO, TiO2, Al2O3, SiO2, and MWCNT as hybrid NMs, have been used so far. The most important result of this study, in addition to the type of hybrid nanoparticles, is to find the best combination to increase thermal conductivity and the principles of electrical conductivity and standard indicators of transformer industries. To start the experimental design, the best and most optimal instruction is simulating the function of the transformer using different nano-oils by a computer. Then, in the next step, this simulation has been done by COMSOL software. So, first of all, precise prioritization for using different nanoparticles can be obtained.ABSTRACT OF PAPERS IN ENGLISH
https://sjme.journals.sharif.edu/article_23463.html
-List of Articles and Journal Info
https://sjme.journals.sharif.edu/article_23464.html
-Investigating of size-dependent buckling and instability caused by support forces and electrostatic field in porous annular microplates
https://sjme.journals.sharif.edu/article_23161.html
In this paper, the static behavior, instability and buckling in porous micro/nano plates under electrostatic field are investigated based on the modified couple stress theory and with regard to modeling, determining equations and solution methods. The plate is considered to be porous and the porosity distribution is considered to be non-uniform. The equations are obtained considering the distributed support load. By using the definition of dimensionless parameters such as load, voltage and length scale, the equations of motion become dimensionless. It can be seen that in the special case, by removing the dimensionless non-classical parameters, the equation of the classical plate under the electrostatic field is obtained. Galerkin mode summation and finite element methods are utilized to solve the static deformation equation and assess the pull-in instability voltages and buckling loads. Convergence analysis is done and the number of approximation functions and elements required for both methods are calculated and the compatibility of the results obtained from the two methods is examined. In the results section, the difference between classical and non-classical theories is examined and the effect of dimensionless parameters of length scale and porosity ratio on maximum displacement, pull-in instability voltages and buckling load is studied. The results show that the use of modified stress couple theory leads to a very large stiffness prediction compared to modified couple stress theory. This result highlights the necessity of using the modified couple stress couple theory for the micro-scale. It is observed that the length scale parameter plays the role of stiffening. The change of porosity ratios also shows that as this ratio increases, the displacement increases and the stable areas decrease. Variations in this ratio lead to uniform changes in buckling load and pull-in instability voltage, and linear relationships are obtained to calculate buckling load and pull-in instability voltage versus porosity ratio. Also, in small values of support load, it is shown that the relationship between the instability voltage and the compressive load of the support is linear, but in the buckling range, this relationship is not linear.Nanocars assembly on surface: coarse-grained molecular dynamics study
https://sjme.journals.sharif.edu/article_23214.html
Using coarse-grained molecular dynamics (CGMD), the simulations of the nanostructures are performed considerably faster and with low computational costs. In the present study, a coarse-grained model is proposed for describing the surface assembly of a molecular machine, called as nanotruck. In this model, we assumed that the interactions of fullerene wheels have the main role in the nanocars interactions. The analysis of the potential energy reveals three stable configurations in the interaction of two nanocars. The stable configuration of nanocars obtained from the coarse-grained model is in agreement with the results of the all-atom molecular dynamics simulations. Simulating the stable configurations at the temperatures of 200, 400 and 600 K, we examined the thermal stability and separation of nanocars. Since each stable configuration shows a specific radius of gyration, we employed this parameter to study the thermal stability of configurations at different temperatures. At 200 K, the nanocars maintain their stable configurations, and at the temperature of 400 K, the nanocars are able to change their relative orientations. The thermal energy supplied at 600 K and higher temperatures is sufficient to break the cluster of two nanocars, and the molecules are separated at this temperature range. The potential energy of the interaction of two molecules finds zero value during the simulation time, which refers to the separation of nanotrucks at this temperature. In the next step, we evaluate the surface arrangement of larger clusters including four and eight nanocars. Considering the relative orientations of each pair of neighboring nanocars it is concluded that, the stable orientations of nanocars are similar to those observed in the cluster of two nanocars. The results of the coarse-grained model on the assembly of nanocars are consistent with the conclusions of the all-atom simulations of nanocars. The proposed coarse-grained model can be employed to study the assembly of other fullerene-based nanocars.Flexibility and Geometric Optimization of a New Structure for a Polymer Stent with the Finite Element Method
https://sjme.journals.sharif.edu/article_23250.html
Cardiovascular diseases cause many problems for patients, and the main reason is associated with arteriosclerosis. According to the American Heart Association, atherosclerosis is a condition caused by the accumulation of a substance called plaque in the walls of arteries. Today, special methods are used to help the patient survive in the event of a heart attack and diagnose the patient's condition. One of the safest methods in medical science is to use a stent. Despite all the innovations in the design of cardiovascular stents, the metal stents that are commonly used cause various problems such as corrosion, infection and restenosis, which lead to physical problems or even death of patients. In order to minimize the problems associated with metal stents, new materials such as polymers are now being developed. On the other hand, the development of polymer-based vascular scaffolds requires a new structural geometry, because these polymeric materials have significantly less radial strength than metal alloys. In this study, the stiffness and flexibility of commercial polymer stents were investigated using analytical relationships and the finite element method, and it was shown that there is a good correlation between these two methods. Then a new design for a zigzag stent is introduced to make it less sensitive to changes in thickness to increase its radial strength. Finally, Taguchi method and analysis of variance were used to design the experiment and determine the effect of stent geometric parameters including strut width, bridge width and stent thickness on the flexibility of this type of stent. The results showed that the width of the bridge and the strut have the greatest effect on the flexibility of the stent, respectively, and the change in stent thickness, which is an effective parameter in the radial strength of the stent, has no significant effect on the flexibility of this type of stent.A design algorithm and numerical investigation of a water-jacket cooling system for a high-altitude simulator diffuser
https://sjme.journals.sharif.edu/article_23251.html
Usually, in a high-altitude test facility, an exhaust diffuser is applied to create and maintain a vacuum condition in the motor test chamber utilizing the energy of the exhaust gases. In this system, the temperature of the exhaust gases, which directly hit the diffuser's inner walls, is much higher than the tolerable temperature of the diffuser metal body. In the current research, a new algorithm has been developed in the design of the cooling system to remove high heat fluxes from the vacuum simulator diffuser walls. In this algorithm, the three parameters of coolant mass flow rate, channel height, and cooling channel length are calculated based on the heat flux distribution along the diffuser, in such a way that, in addition to satisfying the temperature conditions of the metal body and maintaining the ease of implementation of the design, the total pressure drop also is in the desired range. Due to the error of empirical and semi-empirical relationships used to estimate convection heat transfer coefficients in concentric annular flows with large wall surfaces and high heat flux, a numerical simulation technique has been used to find suitable correlations and evaluate the design. The present studies show that the experimental correlations of Meyer and Kaneda are suitable for estimating the Nusselt number (with a maximum error of 3.81 %) and the friction coefficient (with a maximum error of 1.06 %) in the conditions of the present problem, respectively. In the following, the high capability of the algorithm is shown by presenting design results with different heat flux distributions. So, by distributed heat flux attributed to the stable working conditions of the vacuum simulator, a single cooling channel with a height of 3.2 mm and a mass flow rate of 8.025 kg/s has been designed. While for a critical heat flux of about 2.5 MW/m2, a two-channel cooling system with different mass flow rates and channel heights has been designed.Numerical investigation of turbulence models and Stokes number effects on the behavior of nanoparticles in the turbulent flow behind the backward step by Eulerian-Lagrangian method
https://sjme.journals.sharif.edu/article_23256.html
Turbulent backward step flow including air and copper nano particles has been simulated using Computational Fluid Dynamics (CFD) method by Eulerian-Lagrangian method. The simulation was done in two and three-dimensional methods with CFX and FLUENT software. The obtained results were compared with each other and with the experimental results. The two-way coupling discrete phase model (DPM) was used for simulation. The Saffman lift force, pressure gradient and turbulence effects on nano particles are considered. Numerical results obtained with Eulerian-Lagrangian models and single-phase model in steady and transient have been compared with experimantal data. The effect of the turbulence model on the trajectory of particles and in terms of different diameters of 10, 20, 30, 50, 70, 100 and 200 micrometers have been investigated. The effects of particle diameter on the trajectory and behavior of particles and the effect of Stokes number on the presence of particles in the vortex created behind the step have been investigated.The results have been presented as varies contours and graphs for two and three dimensional, steady and transient states. Particles trajectory are shown as contour for different Stokes number and particle diameter. The continues phase velocity variation across the channel for different distance of step present as graphs. Standard, RNG and Realizable k-e and standard and SST k-w models are considered for the modeling of turbulent flow. The results reveal that SST k-w has better accuracy than the experimental. The results show that SST k-w is more accurate compared to the experimental data.Furthermore, simulation has been done with CFX software. Variation of velocity profile are compared with experimental and Fluent data for different distances of step.The results show that the Stokes number and the turbulence model have a significant effect on the trajectory of particles. Three-dimensional modeling of the flow increases the accuracy of the results.Proposing an empirical motion-time pattern for human gaze behavior in different social situations
https://sjme.journals.sharif.edu/article_23300.html
Social robots that are fabricated to interact with humans and to help them in education, healthcare, etc., are required to have an interactive behavior similar to humans. One of the important interactive behaviors of humans is social eye gaze. Eye gaze is significantly more important than other nonverbal signals; it is shown that eyes are special cognitive stimuli with unique hardwired pathways in the brain dedicated to their interpretation. Studying the literature, we found out that in previous researches conducted to control the social robots’ gaze behavior, human gaze behavior was investigated in some limited situations such as two- or three-way conversation in order to extract the pattern of this behavior. Therefore, increasing the variety of studied social situations is a way to fill this gap. In order to design a gaze control system for a social robot, it is required to find out details about the human gaze behavior. The purpose of this research is to propose an empirical motion-time pattern for human gaze behavior in a number of different social situations; these situations include scenes with 2 to 4 people in a prepared video where the people in the scene show the social behaviors of "talking", "waving", "pointing", "entering the scene" and "exiting the scene" in a structured way. Fifteen normal adults (mean age: 24 and std: 3.3 years) watched this movie and their gaze position was recorded by an eye tracker system (SR-Research EyeLink 1000 plus). Next, by using the genetic algorithm (which is an optimization process), we were able to extract the relative coefficient of each of the mentioned social behaviors in our proposed model. The results of reconstructing the participants' gaze on the test data are very similar to the real performance of the subjects. Finally, the ability to implement this model was successfully tested by implementing it on a Nao robot, and its positive performance was confirmed using a survey. The model showed significant differences between the two studied situations in 3 questions out of the whole survey’s 10 questions.Reliability-Based Multidisciplinary Design Optimization Under Uncertainty for Reusable Flexible Launch Vehicle
https://sjme.journals.sharif.edu/article_23301.html
Complex systems design problems entail a suitable structure in which all disciplines including their coupled relationships have been considered and modeled at the same time. These types of design problems involve time and computational cost challenges. Multi-Disciplinary Design Optimization (MDO) methods have been developed to address these issues simultaneously. In this research, a Reusable Flexible Launch Vehicle (RFLV) design problem is presented by Reliability-Based Multi-Disciplinary Design Optimization (RBMDO) approach in the primary design phase. Trajectory, structure, aerodynamics, aeroelasticity, and thermal protection system are considered as involved disciplines in the design problem. The study's purpose will be to obtain an optimal trajectory to meet all the control and structure restrictions while estimating optimal body skin and thermal protection thicknesses based on structural design criteria evaluating in re-entry trajectory are in process. The flexible launch vehicle body has been considered as a free-free Bernoulli-Euler beam for bending variation and D’alembert’s principle for inertia force in static model with the aim of assessing structural design standards. The 3DOF longitudinal dynamic equations plus the first bending mode have been considered. By Chebyshev polynomial interpolation, the angle of attack scope has been achievable and then the trajectory optimization problem has been transformed to a discrete nonlinear programming problem (NLP), which leads to numerical integration of state equation and satisfying all path constraints in Bolza optimal control problem. The design problem formulation has been developed by the single-level MDO framework in which optimization has been implemented by Non-Dominated Sorting Genetic Algorithm (NSGA-II). Finally, epistemic and aleatory uncertainties have been applied through Probability Theory to estimate the reliability of constraints those had been affected by uncertainties. The result shows a significant effect of utilizing the evolutionary multi-objective technique against the gradient-based algorithm in design space optimization. The other conclusion is that the sequential reliability analysis structure modeling efficiency is much better compared to the parallel one.A Comparative Study of the Aerodynamic Performance and Economic Viability of H-Shaped and V-Shaped Wind Turbines in the Climate of Zahedan City
https://sjme.journals.sharif.edu/article_23318.html
In this research, two types of VAWT have been evaluated regarding both the aerodynamic or technical characteristics and also the economic attributes. The baseline turbines selected are a straight blade (H-shaped) turbine and an angled blade (V-shaped) turbine, which both have same dimension and volume. The scale and performance of the turbines are shown to be appropriate for the climatic conditions in Zahedan. The average wind speed distribution of the region has also been investigated. To comparing the power characteristics of these suggested turbines, an aerodynamic method called DMST, double multiple stream tube method, has been presented. Consequently, a MATLAB code has been developed which estimates the forces and moments in both up-wind and down-wind phases. The code is being firstly examined by a validation case, for which experimental data was available. The wind profile has been extracted based on averaging the velocity within 3 recent years. After a validation study on the code results, it was shown the specific trends could be easily drawn by the code. It also can be used for the aerodynamic evaluation of the modified turbines. The results showed that the power produced in the V-type was much less than the H-type, which is due to the reduction of the effective area of the turbine and also the reduction of the torque produced by the rotor. On the other hand, the negative torque during start-up in the V-type is relatively less than H-type machine and this issue will improve the starting phase of the turbine.in spite of lowering the power extracted in V-type system, but the capability of producing wind flow diversion, which can be used in ventilation purpose, is a significant advantage. From the economic point of view, the annual cost of producing regular energy for the V-type turbine is about 10 dollars, which is much lower than the 66-dollar cost of the H-type energy production. It seems using V-type turbines are at least suitable for many dry-weather regions of our country and many other small-scale applications.Developing an Interface Tracking Coupled Solver for Solving two Phase Flow Fields at Low Reynolds Numbers in foam-extend Platform
https://sjme.journals.sharif.edu/article_23363.html
In present study, for the first time, a finite volume coupled solver is developed for simultaneous numerical solution of two-phase incompressible fluid flow equations at low Reynolds numbers and the equation for the interface position by applying interface boundary conditions using foam-extend platform. The studied flows with interface and mesh motion are considered to be laminar and in the rage of Reynolds numbers less than 100. The Foam-extend is a fork of OpenFOAM, an open-source object-oriented C++ library for computational continuum mechanics. This solver is based on the interface tracking algorithm, which is developed using an innovative technique called zero-thickness cell. This technique causes the distance effect to be removed for the cell adjacent to the interface and the interface is modeled with zero thickness. The main advantage of present coupled solver compared to the previously developed solvers is that in this solver, all the equations governing both phases are coupled with each other by cells adjacent to the interface and with an equation for the interface position. All the governing equations and the equation for the interface position are assembled in a linear system of equations and simultaneously solved. In fact, unlike the usual segregated procedure of solving two-phase flows, where the phases are solved with lagged value boundary conditions, in the present solver, the phases are solved simultaneously with the interface conditions in implicit manner and a same block matrix system. The movement of the interface has been done separately and, in another step, using kinematic condition. Computational performance of coupled solver will be evaluated by solving the equations of two-phase fluid flow inside a channel and on a backward facing step. At beginning, a preliminary investigation has been done for the case where both phases are completely independent and decoupled. Matching the interface with the streamlines as well as reasonable and justifiable movement of the surface has been observed from the physical point. Also, the damping of the numerical oscillations generated on the interface and changing the flow variables will be investigated. The present results are in excellent agreement with other results reported in the literature.Experimental determination of correction factors from Charpy impact testing of API X65 steel with varying specimen thickness
https://sjme.journals.sharif.edu/article_23398.html
The purpose of this research, in addition to determining the characteristic forces including the yield force and maximum force, is to determine the correction factors to predict the onset of failure in the energy transmission pipelines with high toughness under dynamic (impact) loading. To achieve this goal, an instrumented Charpy impact machine, which plot the force-displacement diagram during the impact test, was used. Then, by dividing the area under the force-displacement diagram into two part, the initiation energy and crack growth energy in API X65 steel were calculated. The results showed that the total energy provided by the machine dial had good agreement with the total energy calculated from the area under the force-displacement curve. Characteristic forces, also, was determined from force-displacement curve as is described in the BS 14556 standard. After that, Power law expressions with high accuracy for describing the behavior of the tested steel against variation of the Charpy sample thickness for crack initiation energy, crack propagation energy and characteristic forces were extracted. Additionally, the average correction factor, which is use in prediction models of energy transmission steel pipelines, was found to be 1.26, which is in good agreement with the available results for the current steel. It was shown that by increasing the thickness, due to transition from plain stress to plain strain condition, the correction factor change from 1.26 to 1.3 once the thickness reaches to 10 mm, while it had not been changed so much from 4 to 9 mm thicknesses. By examining the characteristic forces and drawing the ratio of the yield force to the maximum force versus thickness variation, it was also found that increase in thickness led to a decrease in the work hardening of the steel. Finally, by comparing the results of 450 and 750 Joule Charpy impact testing machines, it was concluded that the use of Charpy impact testing machine with the capacity of less than 750 Joules for steels with a fracture energy of less than 250 Joules gave the same result.Experimental study of the effect of oil-based nanofluid on heat transfer characteristics in different arrangements of wavy microchannels
https://sjme.journals.sharif.edu/article_23399.html
The development of microchannel manufacturing technology has led to a growing interest in using them as heat exchangers. Devices like microchannel are used to control the temperature of equipment and components that generate high heat flux. Use of microchannels can be explored in various applications i.e. turbine blades, rocket engine, hybrid vehicle, hydrogen storage, refrigeration cooling, thermal control in microgravity and capillary pump loops. Another method for increasing heat transfer is to disperse nanoparticles with a low volume fraction into the base fluid. Nanofluids have been found to possess enhanced thermophysical properties such as thermal conductivity, thermal diffusivity, viscosity, and convective heat transfer coefficients compared to those of base fluids like oil or water. It has demonstrated great potential applications in many fields. In this research, an experimental study on the heat transfer characteristics of oil-based nanofluid inside wavy microchannels with series and parallel arrangement has been carried out. In order to examine the performance of each microchannel separately and to make it easier to draw their diagrams, they are named as 1 and 2. Experiments were performed on TiO2 and SiO2 oil-based nanofluids in volume fractions of 0.05 and 0.1, flow rates of 0.5, 1.0 and 1.5 lit/min and inlet temperatures of 40°C, 45°C, 50°C, 55°C. The results show an increase in the Nusselt number of the base fluid up to 41.8% in the series arrangement and also a decrease in the surface temperature in the series arrangement compared to the parallel arrangement. Also, TiO2 and SiO2 nanofluids with volume fraction of 0.1 caused the highest increase in heat transfer up to 56% and 52.7% in parallel arrangement and up to 45.8% and 42% in series arrangement compared to the base fluid, respectively. The pressure drop of the test section in series arrangement was up to 82.1% higher than parallel.Fractional Order Sliding Mode Controller (FOSMC) Design for Attitude
Control of a Satellite with
Coupled Rigid–Flexible Structures Using Fractional Order Transfer Function
https://sjme.journals.sharif.edu/article_23433.html
One of the important problems in controlling mechanical systems is the structural interactions. Obviously, all of the bodies have elastic behavior and rigidity is assumed for reducing the modeling complexity which is not applicable for many situations. For example, gravity gradient booms and solar panels used in satellites have considerable large deflections relative to their basements. These such systems are recognized as Coupled Rigid-Flexible structures. In these cases it is possible to consider the more flexible part of the structure as the elastic one and the other as the rigid part. With the development of fractional order calculus and more accurately modeling of physical phenomena, the problem of controlling these systems, by considering the uncertainties in the system, will become necessary and inevitable. In this thesis, the fractional order transfer function model of a satellite with Coupled rigid-flexible structures is used as the reference work of the research. To control this dynamical system, sliding mode control method, which is one of the robust control methods, has been used. It is clear that it is not possible to directly design a sliding mode controller for a transfer function. For this reason, a fractional order pseudo-state space model is first obtained from the fractional order transfer function model. Then a controller is designed for it. On the other hand, considering the dynamics of the system is used in the design process of sliding mode controller and proving its stability. Since the state space model is fractional, it is clear that the integer order sliding surface cannot be used. Therefore, the fractional sliding surface has been used for this purpose. The results show that in the presence of considerable uncertainties in each of the four parameters of the dynamical system, and considering the effects of sensor noise and the saturation element for the control signal, this controller can overcome it and follow the reference signal.Investigating the effect of Texture Intensity on the Forming Limit Diagram of Magnesium Microtubes used in Stents using Crystal Plasticity Finite Element Modeling
https://sjme.journals.sharif.edu/article_23434.html
Metal microtubes are usually made using the extrusion method, which eventually creates a special texture in the tube. The way of creating tissue in the microtube has a great effect on its mechanical properties, which is very effective in the quality of the fabricated stents. In this research, the effect of texture intensity caused by the extrusion process to make magnesium microtubes is extracted using the crystal plasticity finite element simulation process. First, in order to validate the modeling, the hydroforming process for aluminum has been simulated in Abaqus finite element software and compared with similar results in the literature. After confirming the modeling process, using the criterion of the second derivative of the maximum large strain for the hydroforming process, the forming limit diagram is drawn for magnesium without texture intensity. In order to confirm the modeling of crystal plasticity, the representative volume element was subjected to tension and compression and the strain stress curve in tension and compression was compared with the experimental strain stress curve. Then, the representative volumetric element was subjected to tension in three directions of extrusion, perpendicular to extrusion and forty-five degrees, and by calculating the ratio of transverse strain to thickness strain, the anisotropy coefficient for the random state in these three directions was obtained. In the following, the anisotropy coefficient was obtained in three different tissue intensities as in the random state. The results show that the relative activity range of hard slip systems such as pyramidal slip and prismatic slip is greater in the direction of extrusion than in other directions, so the anisotropy coefficient obtained in the direction of extrusion is greater than in other directions. As the texture intensity decreases, the anisotropy coefficients approach one and the formation limit curve increases, and as the texture intensity increases, the formation limit curve shows a lower safe zone.Numerical simulation of film pool boiling of ethanol based nanofluids
https://sjme.journals.sharif.edu/article_23454.html
In recent decades, considerable efforts have been made by thermal fluid specialists to investigate the boiling heat transfer process. Pool boiling of pure liquids and nanofluids has been widely studied in the last decade, but the existing knowledge on modeling of nanofluids pool boiling process is still limited. The boiling of fluids containing tinny solid particles is very complicated due to the interaction between the existing phases, their interface and the heating surface Some new research shows that many factors are effective in pool boiling of nanofluids. Among these factors, we can mention particle size, concentration, the structure of the boiling surface, and the dynamics of bubbles. In this research, the film pool boiling process of pure ethanol was numerically simulated. Then, the film pool boiling of nanofluids including two types of nanoparticles 〖Al〗_2 O_3, SiO_2 and ethanol base fluid with two volumetric concentrations of 0.1% and 0.3% have been simulated. The results show that in film boiling, the presence of nanoparticles in the base fluid has increased the heat transfer coefficient. The highest value coefficient for alumina and silica nanofluids with a volumetric concentration of 0.3% was obtained, respectively 0.32 (kW/m2°C) and 0.3 (kW/m2°C). In addition, the presence of nanoparticles in the boiling process has significantly increased the minimum heat flux. According to the results of numerical simulation, the minimum heat flux value in boiling of pure ethanol is 28.99 (kW/m2), in boiling of alumina-ethanol nanofluid with volumetric concentrations of 0.1% and 0.3%, is 37.11 (kW/m2) and 38.84 (kW/m2), respectively and in boiling of silica-ethanol nanofluid with volumetric concentrations of 0.1% and 0.3%, is 35.81 (kW/m2) and 38.31 (kW/m2), respectively. The highest heat transfer coefficient is achieved by alumina nanofluid with 0.3% concentration, while the highest minimum heat flux is achieved by silica nanofluid with 0.3% concentration. The numerical results are in good agreement with the experimental results. By comparing these values with the experimental results, there is a good consistency between the results.Intelligent Fault Detection of Rolling Element Bearing under Variable Operating Conditions by Convolutional Neural Network using Time and Frequency Domain Signals
https://sjme.journals.sharif.edu/article_23547.html
Intelligent detection of rolling element bearing faults is a critical aspect of rotating equipment condition monitoring. Early detection of faults holds significant economic value for industrial units in terms of maintenance and planning. Traditional intelligent fault detection algorithms, which rely on a combination of feature extraction and signal classification, are time-consuming and require a high level of expertise to define appropriate inputs that are the most relevant to the desired output. In comparison to traditional methods, Convolutional Neural Networks (CNNs) can process a large volume of data with high accuracy and automatically extract features from vibration signals. Therefore, in this research, an attempt has been made to use a simple and shallow CNN to determine the health state of rolling element bearings and identify the defective element, which can be inner race, outer race, or rolling element bearing. For this purpose, a CNN model has been employed to investigate three common faults in rolling element bearings. In order to achieve the best performance, various inputs, including time waveform, frequency spectrum, and envelope spectrum, have been utilized and the results are compared to select the best and appropriate input. CNN requires a large amount of data to be trained. So, a laboratory setup has been designed and constructed to collect the required data for training the models and verifying them. After creating artificial faults on the bearings, experiments were conducted under 36 different operating conditions, comprising 9 different speeds, each at 4 different loads, encompassing four healthy states, including healthy, inner race fault, outer race fault, and rolling element fault. The obtained results have illustrated that the fault detector model with the frequency spectrum input is more accurate with an accuracy of 95% than the models receiving the other two inputs.
Keywords: Condition Monitoring, Intelligent Fault Diagnosis, Convolutional Neural Network, Rolling Element Bearing, Variable Operating Conditions, Vibration Analysis.Experimental Investigation of the Pre-evacuation Effect on Starting Performance of a Vacuum Simulator Diffuser with different Expansion Ratio Conical Nozzle
https://sjme.journals.sharif.edu/article_23595.html
Starting time of a high-altitude exhaust diffuser is one of the most important parameters in engine unsteady performance evaluations. Pre-evacuating vacuum chamber and a part or all of the inside of the diffuser is one of the frequent methods of reducing the starting time. In this study, the effect of pre-evacuation on the unsteady performance of a diffuser has been investigated using four different diffuser inlet to nozzle outlet area ratios of 1.27, 1.91, 4.1, and 7.81 with compressed air and rapid nozzle pressure rises. These area ratios have been constructed considering four conical nozzles with different expansion ratios of 45, 30, 15, and 7.5. Experiments have been conducted by measuring wall pressures along the diffuser and vacuum chamber with 13 pressure transducers, both with and without pre-evacuation. Pre-evacuation tests have been conducted using a vacuum pump and placing a removable obstruct at the end of the subsonic diffuser before the pressure loading stage. The investigation of the diffuser's starting performance under rapid pressure loading showed that at area ratio of 1.91 and above, harmonic pressure oscillations appear along the diffuser and the vacuum chamber. It was also observed that pre-evacuation of whole space of the diffuser, vacuum chamber, and nozzle does not eliminate the pressure oscillations, but reduces the beginning time of oscillations and diffuser starting time specially for ratio of 1.27. Because in the ratio of 1.27, due to small annular gap, the diffuser starting time is relatively long without pre-evacuation process. Calculating the mass flow rate of the vacuum chamber also showed that during pressure oscillations, it alternately fills and empties. According to the frequency analysis of oscillations using fast Fourier transform, the pressure oscillation frequency remains constant along the diffuser and elevates with an increase in the area ratio, while the amplitude of the oscillations decreases.Experimental acoustic study of small horizontal axis wind turbines based on computational fluid dynamics and artificial intelligence approaches
https://sjme.journals.sharif.edu/article_23603.html
In modern wind turbine design, two significant challenges arise: achieving optimal aerodynamic performance while minimizing acoustic noise emissions. However, the extensive numerical computations required for accurate evaluation often hinder the implementation of multi-objective optimization strategies. This paper introduces an innovative approach to address this issue, leveraging a combination of neural network-based reduced order modeling and a multi-objective genetic algorithm. This methodology aims to optimize the aerodynamic and aero-acoustic characteristics of an S8xx-series airfoil, including the trailing edge serration geometry. Utilizing Class-Shape Transformation to parameterize various serrated airfoil geometries, the method minimizes the need for costly computational fluid dynamics (CFD) simulations. Instead, a feed-forward neural network (NN) is trained with a minimal dataset to predict airfoil behavior within a specified range. Comparisons between CFD results and NN predictions validate the accuracy of the neural network. Significantly, this approach substantially reduces optimization time by approximately 95%, maintaining high levels of accuracy. In conducting multi-objective optimization for both the airfoil and serration shapes, the study demonstrates notable improvements: a 5 to 7% enhancement in aerodynamic performance alongside a simultaneous 1-4% reduction in noise compared to benchmark airfoils. Then in the second step, experimental methodology is employed to investigate the aeroacoustic attributes of a small horizontal axis wind turbine with optimized blades. Conducted within a semi-anechoic chamber, this investigation meticulously positions both original and optimized geometry models to measure sound pressure levels (SPL) across various rotational speeds and positions. The results reveal subtle enhancements in aerodynamic performance with the optimized serrated blade configuration, accompanied by a remarkable reduction in noise levels across the frequency spectrum, culminating in an impressive overall sound pressure reduction of approximately 10 dB. Additionally, intriguing observations highlight the impact of turbine rotational speed on noise production, particularly in the downstream domain. Notably, the noise emission reduction for the serrated optimized blade is more dispersed in the plane of rotation compared to the original blade, which exhibited nearly uniform noise distribution. Overall, these findings offer valuable insights into the intricate interplay between aerodynamics and aeroacoustics in the context of small wind turbines with optimized blades.