Sharif Journal of Mechanical Engineering
https://sjme.journals.sharif.edu/
Sharif Journal of Mechanical Engineeringendaily1Thu, 20 Jun 2024 00:00:00 +0330Thu, 20 Jun 2024 00:00:00 +0330-
https://sjme.journals.sharif.edu/article_23631.html
-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 research 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, details about human gaze behavior must be found. 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 positions were recorded using 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.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 and increase its radial strength. Finally, the 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 to design 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. Furthermore, 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.Nanocars assembly on a 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 a 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 temperatures of , and, 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 K, the nanocars maintain their stable configurations, and at the temperature of K, the nanocars are able to change their relative orientations. The thermal energy supplied at 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.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 nanoparticles, has been simulated using the Computational Fluid Dynamics (CFD) method by the Eulerian-Lagrangian method. The simulation was done using 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 nanoparticles are considered. Numerical results obtained with Eulerian-Lagrangian models and single-phase models in steady and transient have been compared with experimental 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 various contours and graphs for two- and three- dimensional, steady, and transient states. Particle trajectories are shown as contours for different Stokes numbers and particle diameters. The continuous phase velocity variation across the channel for different distances of step are presented 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 show that SST k-w is more accurate than the experimental data. Furthermore, simulation was done using CFX software. Variations of velocity profile are compared with experimental and Fluent data. 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. The maximum error in the single-phase method is equal to 25% and for the Eulerian-Lagrangian method is equal to 19%. Particles with a Stokes number smaller than 1.2 (equivalent to a diameter of 35 micrometers in this study) sense the presence of the vortex and enter the vortex. Among the turbulence models, the lowest error for the sst model is equal to 6.25, and the highest error for the standard Kε model is equal to 18.75.Reliability-Based Multidisciplinary Design Optimization Under Uncertainty for Reusable Flexible Space Launcher utilizing NSGA-II
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. This article aims to provide a proper design structure for an uncertainty-based re-entry trajectory design optimization problem under the control restrictions and structural constraints of a Reusable Flexible Space Launch Vehicle (RFSLV) alongside the determination of optimal skin thickness and thermal protection system thickness concerning the design criteria of the flexible structure in such a way that the final design would meet the desired reliability. Trajectory, structure, aerodynamics, aeroelasticity, and thermal protection systems are considered to be 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 the re-entry trajectory, which is in process. The flexible space launcher 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. All highly nonlinear uncertainty-based constraints in the model have led to taking advantage of the evolutionary optimization algorithm that has been implemented here 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 that had been affected by uncertainties. The result shows a 75 percent decrease through utilizing the evolutionary multi-objective technique against the gradient-based algorithm in design space optimization regarding computational cost in recalling objective functions. The other conclusion is that the sequential reliability analysis structure modeling efficiency is much better compared to the parallel one.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 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 numerical 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 classical 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.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. Microchannels are used to control the temperature of equipment and components that generate a high amount of heat flux. Heat transfer can be further increased by dispersing particles (nano-sized particles) with a low volume fraction into the base fluid (nanofluid). A nanofluid can change the thermophysical properties of a base fluid and improve its thermal performance. The purpose of this study was to examine the heat transfer characteristics of oil-based nanofluid within wavy microchannels in series and parallel arrangements of microchannels. In order to examine the performance of each microchannel separately and to make it easier to draw their diagrams, they are named 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 a 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.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 the present study, for the first time, a finite volume coupled solver is developed for the simultaneous numerical solving of two-phase incompressible fluid flow equations at low Reynolds numbers, and for solving the the interface position equation by applying interface boundary conditions using the foam-extend platform. The studied flows with interface and mesh motion are considered to be laminar and in the range of Reynolds numbers less than 100. The Foam-extend is a fork of OpenFOAM, an opensource 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 removes the distance effect for the cell adjacent to the interface, and the interface is modeled with zero thickness cells. The main advantage of the present coupled solver compared to the previously developed solvers is that in this solver, all the equations in both phases are coupled with each other by cells adjacent to the interface and with an the interface position equation. All the governing equations and the interface position equation are assembled in a single 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 an implicit manner and in the same block matrix system. The movement of the interface was done separately, and in another step. For this purpose, the kinematic condition was implemented. The computational performance of the coupled solver was evaluated by solving the equations of two-phase fluid flow inside a channel and on a backward-facing step. In the beginning, a preliminary investigation was done for the case, where both phases were completely independent and decoupled. Matching the interface with the streamlines, as well as the reasonable and justifiable movement of the surface, has been observed from the physical point of view. 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.A Comparative Study of the Aerodynamic Performance and Economic Viability of H-Shape and V-Shape Wind Turbines in the Climate of Zahedan City
https://sjme.journals.sharif.edu/article_23318.html
This research evaluates two types of vertical axis turbines from both an aerodynamic and economic perspective. The turbines used in this study have straight (H-shaped) and angled (V-shaped) blades, with equivalent dimensional characteristics that are suitable for the climatic conditions and average wind speed distribution in Zahedan city. The aerodynamic evaluation of the turbines was conducted using the semi-analytical DMST method. The results indicate that the V-shaped turbine generates significantly less power than the H-shaped turbine due to the reduction of the effective area of the turbine and the torque produced by its rotor. However, during startup, the V-shaped turbine exhibits about seven times less negative power than the H-shaped turbine, which improves the overall startup process. Economically, the cost of energy production per kWh for a V-shaped turbine is approximately 20% lower than that of an H-shaped one. This makes the V-shaped turbine a more suitable option for urban and small-scale applications.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, was to calculate 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 plots the force-displacement diagram during the impact test, was used. Then, by dividing the area under the force-displacement diagram into two parts, both 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 was in agreement with the total energy calculated from the area under the force-displacement curve. Characteristic forces were also determined from the force-displacement curve as described in the BS 14556 standard. After that, power law expressions with high accuracy were extracted to describe the behavior of the tested steel against variations of the Charpy sample thickness for crack initiation energy, crack propagation energy, and characteristic forces. Additionally, the average correction factor, which is used 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 in the literature. It was shown that by increasing the thickness, due to the transition from plain stress to plain strain condition, the correction factor changed from 1.26 to 1.3 in 8 to 10 mm thicknesses, while it did not change so much from 4 to 8 mm thicknesses. By examining the characteristic forces and plotting the ratio of the yield force to the maximum force versus thickness variation, it was also found that increasing the thickness leads to decreasing the work hardening of the steel.ABSTRACT OF PAPERS IN ENGLISH
https://sjme.journals.sharif.edu/article_23624.html
-List of Articles and Journal Info
https://sjme.journals.sharif.edu/article_23623.html
-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.