Research Paper
Nonlinear Solution
Wah Yen Tey; Yu Maan Kong
Abstract
The theory of superposition of waves has been widely deployed in many engineering applications such as medical imaging, engineering measurements, and wave propagation in structures. However, these applications are prone to the interference of unwanted waves. The root cause of the weakness could be ascribable ...
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The theory of superposition of waves has been widely deployed in many engineering applications such as medical imaging, engineering measurements, and wave propagation in structures. However, these applications are prone to the interference of unwanted waves. The root cause of the weakness could be ascribable to the wave propagation pattern, which is not actively controlled. A new concept of imposing a time-lagging effect on the source of the wave as an active wave emission strategy is introduced and discussed in this paper. A numerical solver has been developed based on the finite volume Euler explicit method to investigate the wave propagation pattern when there is a time-lagged effect and frequency difference at the source of the wave. Our results reveal that time-lagged wave propagation will be more immune to the disturbance of other waves. The larger the time lag, the more resilient the wave is to resist the interference of other waves, even at a higher frequency. Time-lagged waves can be regarded as a promising active wave emission method that has many potential and robust engineering applications to be explored in the future.
Research Paper
Production Methods
Mohammad Ali Farsi
Abstract
Manufacturing systems are one of the complex systems for modelling and analysis, different types of structures may be utilized for this. Their behaviour is similar to Multi-state systems. Multi-state system configurations, possibly with load sharing and other structural dependencies are designed to provide ...
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Manufacturing systems are one of the complex systems for modelling and analysis, different types of structures may be utilized for this. Their behaviour is similar to Multi-state systems. Multi-state system configurations, possibly with load sharing and other structural dependencies are designed to provide high reliability/availability. Consequently, this scheme can help companies to improve efficiency and reduce operation cost. During operation and utilization, maintenance and part replacement contribute to keeping their performance. Decision-making about spares ordering is difficult because of the interconnection between spare parts inventory and maintenance strategy. In this paper, the characteristic parameters of spare parts inventory management and maintenance policies are jointly considered for multi-machines systems (manufacturing systems) with different types of dependencies among them (economic, load-sharing, and multi-state configuration). Two maintenance policies are considered: condition-based and preventive maintenance. The interactions among maintenance policies and spare parts management are considered for determining system cost and availability of a manufacturing system. These factors influences are investigated. load sharing factor and ordering time are more important and their influence are higher then others.
Research Paper
Computational Fluid Dynamics (CFD)
Golchehreh Shajari; Morteza Abbasi; Mehran Khaki Jamei
Abstract
AbstractIn this study, comprehensive numerical simulations were conducted to examine laminar pulsatile developing flows through flat channels. The developing velocity fields and the hydrodynamic entry length were explored for the Reynolds numbers from 20 to 200, and the low and intermediate non-dimensional ...
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AbstractIn this study, comprehensive numerical simulations were conducted to examine laminar pulsatile developing flows through flat channels. The developing velocity fields and the hydrodynamic entry length were explored for the Reynolds numbers from 20 to 200, and the low and intermediate non-dimensional pulsation frequency or the Womersley number, (1.08 ≤Wo≤ 8.86). For all simulations, the pulsating amplification factor was considered from zero to one, (0 ≤A≤ 1), and to achieve more practical and relevant outcomes, time-dependent parabolic inlet velocity profiles were applied. The outcomes reveal for the higher values of the pulsation frequency or the Womersley number (6 ≤ Wo ≤ 8.66), the maximum pulsatile entrance length during a cycle is close to the inlet length of the mean component of the flow. On the other hand, for the rest of the Womersley number range (1.08 ≤ Wo < 6), and high amplification factor (0.5 ≤ A), the value of the entrance length increases and is significantly different from the development length of the steady component. Moreover, the results demonstrate the entry length correlates with the Womersley number through a power-law function, whilst it has linear correlations with the Reynolds number and the amplification factor. Further, using the result of the accomplished numerical study, a practical correlation of the entrance length is offered to use in the design phase for any type of pulsatile flow through the flat channels.Keywords: Entrance Length, Pulsatile Flow, Numerical Simulation, Flat Channel.
Research Paper
Energy Science and Technology
Hamed Khoshkam; Kazem Atashkari; Mehdi Borji
Abstract
Carbon deposition has a serious effect on failure mechanism of solid oxide fuel cells. A comprehensive investigation based on a two-dimensional model of solid oxide fuel cell with detailed electrochemical model is presented to study the mechanism and the effects of carbon deposition and unsteady state ...
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Carbon deposition has a serious effect on failure mechanism of solid oxide fuel cells. A comprehensive investigation based on a two-dimensional model of solid oxide fuel cell with detailed electrochemical model is presented to study the mechanism and the effects of carbon deposition and unsteady state porosity variation. The studies of this kind can be an aid to identify the SOFC optimal working conditions and providing an approximate fuel cell life time. It has been revealed that, due to carbon deposition, the porosity coefficient of the fuel cell decreases. Consequently, a reduction in the amount of fuel consumption along the fuel cell and the chemical and electrochemical reaction rates are resulted which can be clearly seen in the off-gases molar ratio. The percentage of output fuel changes in the timeframe is a useful information for optimizing CHP systems including fuel cells. The percentage of output water vapor, which usually increases compared to the input, decreases by 17% at the end of the working period. Also, unreacted methane in the output of the fuel cell increased by 12%, in other words, it is wasted. The other consequence of carbon deposition, reduced electrochemical and chemical reaction rates and the reduction of temperature difference along the cell. The study shows that after 145 working days, the temperature difference along the cell varies from 117 C for the starting time to 7 C. Also, by reducing current density, the cell output power density decreases by 72% after 145 working days.
Research Paper
Machining
Amith H Gadagi; Chandrashekar Adake
Abstract
In any machining process, it is important to predict and select the appropriate process parameters to get the proper Surface roughness (Ra) of a component. In this paper, the prediction of Ra through Multiple regression Analysis (mra), Artificial neural network (ann) and Random forest method (Machine ...
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In any machining process, it is important to predict and select the appropriate process parameters to get the proper Surface roughness (Ra) of a component. In this paper, the prediction of Ra through Multiple regression Analysis (mra), Artificial neural network (ann) and Random forest method (Machine Learning) are done and compared. Using the process parameters namely spindle speed, feed and depth of cut, the turning of the GFRP composites was carried out on a conventional lathe using single point HSS cutting tool with brazed carbide tip. Surface Roughness of the turned components is measured experimentally using Talysurf method. By employing the Taguchi's L27 array (3 Level), the experiments were conducted and the experimental results were utilized in the development of mra, ann and Random forest method models for the prediction of Surface roughness (Ra). It is observed that Mean Absolute Error (MAE) of mra, ann and Random forest for the training cases are found to be 39.33%, 0.56% and 24.88% respectively whereas for the test cases MAE are 54.34%, 2.59% and 24.88% for mra, ann and Random forest respectively.
Research Paper
Computational Fluid Dynamics (CFD)
DEVESH KUMAR BAGHEL; Sobha Lata Sinha; SATISH KUMAR DEWANGAN
Abstract
Neonatal incubators provide an artificial thermal environment to maintain the thermoregulation of premature babies. Several studies revealed the dry and latent heat exchange estimation between newborn's body and surrounding environment. Heat transfer due to convection is leading over the thermal radiation ...
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Neonatal incubators provide an artificial thermal environment to maintain the thermoregulation of premature babies. Several studies revealed the dry and latent heat exchange estimation between newborn's body and surrounding environment. Heat transfer due to convection is leading over the thermal radiation in incubators. The aim of this article is to study the air flow modeling and estimation of heat transfer coefficient over an infant body inside incubator. For this purpose, an experiment and numerical simulation is carried out to develop the methodology and subsequently computational fluid dynamics (CFD) analysis is accomplished to evaluate the heat transfer coefficient of a preterm infant. By means of shear stress transport (SST K-ω) turbulence model, 3-D computational models are numerically studied using commercial CFD tool StarCCM+. Flow visualization reveal that large-scale flow circulation pattern is produced in mean region of enclosed chamber, and small scale eddies are generated at corners and close to the walls. The numerical results obtained for heat transfer assessment in present study is validated with experimental and numerical results available in biomedical open literature.
Research Paper
Fluid Mechanics
Rasoul Talebian; Mansour Talebi
Abstract
In the present study, the pressure-drop of the nanofluid flow of carbon-water nanotubes (CNT/water) in a helical three-tube heat exchanger with constant fluid physical properties has been experimentally evaluated. For this purpose, first the experimental device was designed and manufactured and then ...
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In the present study, the pressure-drop of the nanofluid flow of carbon-water nanotubes (CNT/water) in a helical three-tube heat exchanger with constant fluid physical properties has been experimentally evaluated. For this purpose, first the experimental device was designed and manufactured and then the carbon-water nanotube nanofluid with volume percentages of 0.01%, 0.1% and 0.5% was prepared and stabilized. For the experiment, two triple-tube helical heat exchanger with different geometries are considered, in which the diameter of the middle pipe varies in two geometries. The pitch of the helical coil is 100mm and the helix radius is 9.235mm. The experiment was performed on Dean numbers between 1000 and 5000. The measured and calculated data were according to the available correlation in the literature with an error less than 4%. It is found that at low volumetric percentages of CNT, the pressure-drop is almost equal to that of the base fluid, and with increasing volumetric percentage of nanoparticles, the pressure-drop also increases. By changing the geometry of the tube (decreasing the middle diameter of the tube), the pressure-drop decreases.
Research Paper
Sarallah Abbasi
Abstract
The purpose of this paper is to investigate the effect of aspect ratio on vortex on vortex shedding and transient flow induced noise over a rectangular cylinder is presented. The freestream velocity is assumed 50 m/s. URANS equations with turbulence model k-ω-SST are employed to flow analysis. Aerodynamic ...
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The purpose of this paper is to investigate the effect of aspect ratio on vortex on vortex shedding and transient flow induced noise over a rectangular cylinder is presented. The freestream velocity is assumed 50 m/s. URANS equations with turbulence model k-ω-SST are employed to flow analysis. Aerodynamic noise calculations are performed using FW-H analogy. The rectangular cross-section with various lengths and widths is considered. Comparison of the results extracted in the present study with the experimental results of other reference indicates the accuracy of the present research. In this study, the aspect ratios from 0.6 to 6 (equivalent to Reynolds numbers from 2.5×10^4 to 5.6×10^4) is studied. The simulations can be divided into two categories. In the first category, the ratio of length to width (R=B/H) is less than one, and in the second one, this ratio is greater than one. In the first case, noise is reduced by a relatively low slope. But in the second condition, the behavior of noise is different in various ratios and the slope of noise variations is high. The flow structure is also discussed in this paper. It is founded that for the first category, by increasing aspect ratio both the fluctuations and aerodynamic forces are reduced and the longitudinal wake zone is increased. But in the second category, fluctuations of flow may be increased or decreased in various aspect ratios.
Research Paper
Micro and Nano Systems
Aylar Khooshehmehri; Abdollah Eslami Majd; Elham Arabsheybani
Abstract
The hemispherical resonator gyro (HRG) is a type of precision inertial sensor that has the advantages of direct angle measurement and unlimited dynamic range. The overall accuracy of the HRG is due to the quality of its resonator shell and Improving the performance of resonators requires a proper understanding ...
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The hemispherical resonator gyro (HRG) is a type of precision inertial sensor that has the advantages of direct angle measurement and unlimited dynamic range. The overall accuracy of the HRG is due to the quality of its resonator shell and Improving the performance of resonators requires a proper understanding of processes of energy damping in each resonance cycle, which has a significant impact on sensor performance. In this paper, in order to investigate the losses in the hemisphere shell resonator, first, the equations governing the shell are studied and three-dimensional modeling is performed in COMSOL software. By performing mechanical simulations, the resonance modes and the natural frequency of the shell are investigated and finally, the second and third resonance modes are selected as the optimal operating mode of the gyroscope. Also, by performing thermal simulations, the dominant energy damping processes such as thermo-elastic damping and anchor loss were analyzed and simulated and the effect of shell material on damping was investigated. Then the quality factor of the resonator was evaluated based on its geometry and material. In this way, according to the scope of work of the gyroscope, this process can be used to design the specifications of the shell to achieve a resonator with the desired quality factor.
Research Paper
Dynamic Response
J. Akbari; H. Valaei; M. F. Sepahvand
Abstract
Finite-element modeling of structures using elements without rotational degrees of freedom (DOFs) is usually stiffer than their physical behavior. Therefore, the stiffness of a structural system will be smoothed by adding rotational DOFs in the numerical model. In the traditional displacement-based finite-element ...
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Finite-element modeling of structures using elements without rotational degrees of freedom (DOFs) is usually stiffer than their physical behavior. Therefore, the stiffness of a structural system will be smoothed by adding rotational DOFs in the numerical model. In the traditional displacement-based finite-element method, adding drilling rotations is not easy. The main contribution of this paper is performing dynamic analyses using the finite strip element with added drilling rotations to the elements. For this purpose, any quadrilateral area is divided into two independent sets of orthogonal strips comprising truss and Bernoulli-Euler beam elements. Then by using new shape functions, mass, damping, stiffness matrices, and equivalent nodal forces are derived. Finally, time history analysis for plane stress or strain type problems for direct earthquake records is performed using the developed formulations. The numerical studies show that the results of the finite strip method using coarse meshes are competitive with the results of the finite-element method using fine meshes. This advantage is valuable in time-consuming computational problems, e.g., dynamic or nonlinear analyses.
Research Paper
Forming
Amir Hossein Rabiee; Ehsan Sherkatghanad; Ali Zeinolabedin Beygi; Hassan Moslemi Naeini; Lihui Lang
Abstract
In this paper, by considering the processing parameters including Blank Holder Force, Blank Holder Gap, and Cavity Pressure as the most important input factors in the hydroforming process, an experimental design is performed and an adaptive neural-fuzzy inference system (ANFIS) are applied to model and ...
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In this paper, by considering the processing parameters including Blank Holder Force, Blank Holder Gap, and Cavity Pressure as the most important input factors in the hydroforming process, an experimental design is performed and an adaptive neural-fuzzy inference system (ANFIS) are applied to model and predict the behavior of aluminum thinning rate (upper layer and lower layer), the height of wrinkles and achieved depths that are extracted in hydroforming process. Also, the optimal constraints of the network structure are obtained by the gray wolf optimization algorithm. Accordingly, the results of experimental tests have been utilized for training and testing of the ANFIS. The accurateness of the attained network has been examined using graphs and also based on the statistical criteria of root mean square error, mean absolute error, and correlation coefficient. The results show that the attained model has been very effective in approximating the aluminum thinning rate (upper layer and lower layer), the height of wrinkles, and achieved depth in the hydroforming process. Finally, it can be seen that the root means square error of aluminum thinning rate (upper layer and lower layer), the height of wrinkles, and achieved depth respectively) of the test section, are 1.67, 2.25, 0.05, and 2.67. It is also observed that the correlation coefficient for the test data is very close to 1, which demonstrates the high precision of the ANFIS in predicting the outputs of the hydroforming procedure.
Research Paper
Energy Systems
Armin Emamifar
Abstract
In this research, the thermodynamic analysis of a two-stage absorption compression refrigeration system employing a flash tank with indirect subcooler is presented. The absorption cycle uses LiBr-water solution as working fluid and prepares the high temperature medium for the bottoming cycle, which is ...
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In this research, the thermodynamic analysis of a two-stage absorption compression refrigeration system employing a flash tank with indirect subcooler is presented. The absorption cycle uses LiBr-water solution as working fluid and prepares the high temperature medium for the bottoming cycle, which is a two-stage compression refrigeration system with R744 refrigerant. The thermodynamic analysis indicates that the proposed system decreases the required electrical work and the total exergy destruction rate which result in improvement of the overall COP and total exergy efficiency. The results are compared with the same system without subcooler and a simple cascade absorption compression refrigeration system. It was found that the overall COP and the total exergy efficiency of the proposed system are 7.86% and 11.21% higher than the system without subcooler. This enhancements are 11.42% and 16.48% in comparison with the simple cascade absorption compression refrigeration system. Moreover, the effect of generator temperature, condenser temperature, cascade condenser temperature, evaporator temperature, and the intermediate pressure of the compression section on the system electrical work, overall COP, total exergy destruction rate, and the total exergy efficiency of the proposed system is also discussed.
Research Paper
Optimization
ehsanolah Assareh; Iman poultangari; Afshin ghanbarzadeh
Abstract
A common method utilized in wind turbines is pitch angle control whereby via varying the angle of wind turbine blades around their own axis, power generated at high speeds of wind is held around maximum amount and is kept away from the severe mechanical stress on wind turbine. In current study, in order ...
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A common method utilized in wind turbines is pitch angle control whereby via varying the angle of wind turbine blades around their own axis, power generated at high speeds of wind is held around maximum amount and is kept away from the severe mechanical stress on wind turbine. In current study, in order to control pitch angle, a control method based on using PI controller is suggested. Therefore, gains of the PI controller are regulated through combining the Firefly evolutionary algorithm and MLP neural network in such a way that the controller at its output sends a suitable controlling signal to the pitch actuator to set the pitch angle and so by varying the blades pitch angle suitably at high speeds of wind, the produced generator power remains around its nominal value. A wind turbine 5MW made by NREL (National Renewable Energy Laboratory) has been utilized based on FAST software code to simulate and analyze the results. The simulation results show that proposed method has a good performance.
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