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
Energy Science and Technology
Ahmed F Hasan; Salah N Farhan
Abstract
Phase change materials have attracted a considerable attention in thermal energy storage research field recently due to their thermal characteristic. Composite materials have great potential as one of the best alternative approach that would be utilized to increase the thermal performance of this sort ...
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Phase change materials have attracted a considerable attention in thermal energy storage research field recently due to their thermal characteristic. Composite materials have great potential as one of the best alternative approach that would be utilized to increase the thermal performance of this sort of materials. This piece of work aims to improve the Latent Heat energy Storage Unit (LHSU) in terms of thermal performance during the melting process by utilizing honeycomb metal structures configuration. Experimental work has been carried out to study the thermal behavior of this particular material in honeycomb LHSU. The thermal performance evaluation in terms of melting time of the proposed honeycomb LHSU was conducted in comparison with the normal LHSU. The influences of using different heat transfer fluid temperature on the charging power are considered for the enhanced geometrical configuration. The results showed significant enhancement in the melting time which reached 87%. Also, the melting range in the lower part of the storage unit was improved compared with the normal one. For the propose configuration when increasing the fluid temperature; charging power was accelerated, which in turn reduces the charging time.
Research Paper
Composite Materials
Manoj Kumar Shukla; Kamal Sharma
Abstract
The synergetic effect of Amine Functionalized Multiple Graphene Layers (AMGL) and Multi-Walled Carbon Nanotube (AMWCNT) nano-fillers mixed with epoxy resin has been investigated on the Particle Size Distribution (PSD) and tensile properties of hybrid composites. The hybrid composites with equal ratio ...
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The synergetic effect of Amine Functionalized Multiple Graphene Layers (AMGL) and Multi-Walled Carbon Nanotube (AMWCNT) nano-fillers mixed with epoxy resin has been investigated on the Particle Size Distribution (PSD) and tensile properties of hybrid composites. The hybrid composites with equal ratio of nano-fillers at weight percent of 0.25, 0.50, 1 and 2 wt % are fabricated. The Particle Size Analysis (PSA) is performed by Dynamic Light Scattering (DLS) technique and Image Analysis (IA) method, both methods verified PSD for composites. This is further verified by the analyses of Scanning Electron Microscopy (SEM) images using Image J software. Optimum composite particle size of 6.8 µm and homogeneous mixture with Poly-Dispersity Index (PI) of 0.74 is investigated for sample having filler content of 0.5 wt % Tensile stress and elastic modulus is also found to be maximum at 0.5 wt % which is 49.91 MPa of 2302 MPa respectively. Chemical composition of composite affecting its PSD is characterized by Energy Dispersive X-ray (EDX) process. Dimensional analysis of particle size in the domain of epoxy matrix provides the deep insights to the researchers and may also provide them a direction for selecting an appropriate material for a particular application.
Research Paper
Mahdi Zakyani
Abstract
Large Eddy Simulations of non-reactive Delft II and Sydney bluff body flow are performed using different sub-grid scale models. Simulation of non-reactive burners is useful when studying flow characteristics inside reactive burners. As turbulent combustion simulation is rather an intricate task, it is ...
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Large Eddy Simulations of non-reactive Delft II and Sydney bluff body flow are performed using different sub-grid scale models. Simulation of non-reactive burners is useful when studying flow characteristics inside reactive burners. As turbulent combustion simulation is rather an intricate task, it is helpful to study cold air flow inside the combustion chamber before igniting the chamber. In order to study the flow inside the mentioned test cases, different sub-grid scales model i.e., Constant Smagorinsky, dynamic Smagorinsky and dynamic WALE model are used to model the unresolved small scales. For the numerical simulations, a finite volume in-house code is used. The code adopts the projection method to solve the fluid flow equations. A second order accurate scheme is used for spatial discretization. The time integration is done using second order accurate predictor-corrector scheme. For solving the resultant pressure Poisson equation, TDMA (Tridiagonal Matrix Algorithm) is used with multi-grid convergence acceleration. Generally, the results show good agreement with available experimental data. As expected, the dynamic WALE model performs better than the other models. To further improve the results, a rather realistic type of velocity inlet boundary conditions applied to Sydney bluff body flow i.e., digital filter velocity inflow boundary conditions. The results show drastic improvement using digital filter inflow that is mainly due to turbulent nature of the flow field.
Research Paper
Energy Science and Technology
Jamasb Pirkandi; Amirali Amiralaei; Mohammad Omian
Abstract
In this research, a combined cooling, heating and power system (CCHP) has been analyzed from the perspective of entropy and exergy. The primary driver and the cooling system for this combined system consist of a micro gas turbine and a hot water lithium bromide single-effect absorption chiller, respectively. ...
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In this research, a combined cooling, heating and power system (CCHP) has been analyzed from the perspective of entropy and exergy. The primary driver and the cooling system for this combined system consist of a micro gas turbine and a hot water lithium bromide single-effect absorption chiller, respectively. The effects of compressor pressure ratio, micro turbine inlet gas temperature and chiller cooling capacity on important system efficiencies and other operational parameters (e.g. electrical efficiency, thermal efficiency, combined heating and power cogeneration efficiency, and combined cooling, heating and power cogeneration efficiency) have been investigated. The findings indicate that the system has its highest electrical efficiency at a compressor pressure ratio of 5. Also at this pressure ratio, the cogeneration efficiency (combined heating, cooling and power) and the exergy efficiency are about 48% and 24%, respectively. Moreover, the increase of turbine inlet gas temperature has had a positive effect on the investigated parameters. The results show that the increase of cooling capacity reduces the cogeneration efficiencies, but has no effect on the exergy efficiency. Also, by considering specific values for the studied parameters, the amounts of generated entropy and destroyed exergy in various parts of the system have been calculated. The results indicate that the highest amounts of entropy and exergy have been generated and destroyed in the combustion chamber. Parts of the results indicate a system state in which the overall efficiency (combined heating, cooling and power cogeneration efficiency) of the system has increased 13% relative to the system’s initial state.
Research Paper
Vibration
Henry Ogbemudia Omoregbee; Modestus O. Okwu; Mabel U. Olanipekun; Bright A Edward
Abstract
This paper presents detection of fault prognostics in bearings with the application of extended takagi-sugeno fuzzy recursive least square algorithms (extsfrlsa). The nonlinear system is decomposed into a multi-model structure consisting of linear models that are not inherently independent, due to the ...
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This paper presents detection of fault prognostics in bearings with the application of extended takagi-sugeno fuzzy recursive least square algorithms (extsfrlsa). The nonlinear system is decomposed into a multi-model structure consisting of linear models that are not inherently independent, due to the fuzzy regions defined in extsfrlsa. The extsfrlsa was developed to tune, adjust and adapt the parameters involved in the propagation model, as it tends to update itself with the availability of new data. This method is suitable for on-line identification of systems because of its unsupervised learning pattern which dwells on mechanism centred on rule-based evolution. Scenarios considered for the rule-based modification and upgrade are quite diverse, thereby ensuring effective comparism of measured and predicted defect size. An estimation of the remaining useful life was determined successfully with the proposed method, showing that the system performance health indicator reflects bearing degradation and it was concluded that extsfrlsa can be used for fault prediction of bearing where rolling element are involved, especially while its operation is associated with fluctuating speed and load conditions.
Research Paper
Computational Fluid Dynamics (CFD)
Tamil Chandran A; Suthakar T; Balasubramanian KR; Rammohan S; Jacob Chandapillai
Abstract
Abstract Numerical analysis of Drag coefficient of three-dimensional bluff bodies such as flat plates, cylinder, triangular prism, semicircular profiles located in the flow path of the pipe was performed. Bluff bodies of various lengths are analysed using a turbulence model. The effect of bluff body ...
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Abstract Numerical analysis of Drag coefficient of three-dimensional bluff bodies such as flat plates, cylinder, triangular prism, semicircular profiles located in the flow path of the pipe was performed. Bluff bodies of various lengths are analysed using a turbulence model. The effect of bluff body thickness on drag coefficient was analysed. A significant observation of the study was reduction in drag coefficient with increase in thickness. Effect of pressure coefficient, on drag coefficient was evaluated. The study confirms that frictional coefficient has negligible effect on drag coefficient in the studied Reynolds number range. Change in drag coefficient over a wide range of Reynolds number was studied and is reported. Irrespective of geometry and length, the study indicates that there is a significant difference in drag coefficient between two dimensional and three dimensional simulation studies. It is also brought out that for a bluff body, in a confined domain; its length has a significant effect on its drag coefficient.
Research Paper
Machining
Jayasimha SLN; Ganapathy Bawge; Raju H.P.
Abstract
Traditional methods of finishing like grinding, lapping and honing are limited to finishing of vital shape such as flat and circular. These conventional methods are lagging for processing components that are fabricated by hard materials involving complicated profiles in particular. Hence, it is essential ...
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Traditional methods of finishing like grinding, lapping and honing are limited to finishing of vital shape such as flat and circular. These conventional methods are lagging for processing components that are fabricated by hard materials involving complicated profiles in particular. Hence, it is essential to explore a finishing process which address wide applications, better accuracy, efficient, consistent quality and economy in finishing complex shaped parts. So, a new precision finishing process like extrusion honing has been implemented for polishing from several microns to nano level. The aim of the work is to assess the influence of number of abrasive media passes on surface integrity of aluminium, copper and titanium grade-2 materials. The study has been performed by adopting abrasive 36 mesh size with concentration 40 % followed by 10 abrasive media passes. The influence of these process parameters has been studied in analyzing the roughness characteristics Ra, Rmax, Rz and Rmax/Ra and the nature of surface induced by SEM characterization for the metals of consideration using extrusion honing process.
Research Paper
Nhu-Tung Nguyen; Dong Van Pham; Dung Tien Hoang; Cuong Duc Pham
Abstract
Cutting force coefficients (CFCs) are the most important factors in prediction of CFs (CFs) and other machining characteristics (MCs). This study was conducted to model the CFs and MCs in milling process based on the calculated values of CFCs. From the relationship of average values of CFs and feed rate, ...
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Cutting force coefficients (CFCs) are the most important factors in prediction of CFs (CFs) and other machining characteristics (MCs). This study was conducted to model the CFs and MCs in milling process based on the calculated values of CFCs. From the relationship of average values of CFs and feed rate, CFCs were determined and used to predict of dynamic CFs (DCFs) in flat milling process. In static models, the average values of CFs were presented as a linear regression of feed rate. The DCFs and other MCs were modeled depending on the cutting parameters, cutter geometry, CFCs, and structure parameters of machine-tool system. By performing the flat-milling process of gray cast iron GG25 using HSS-Co solid tool, the average CFs were modeled as the linear regression of feed rate with large determination coefficients (R2 > 93%). Besides, all CFCs of a pair of tool and workpiece for each cutting type were successfully determined based on the measured data of CFs from experimental process. Moreover, the proposed models of DCFs were successfully verified based on the compared results between the predicted CFs and measured CFs in several cutting tests with different cutting parameters. The proposed models of cutting force in this study were successfully used to predict the DCFs and several MCs in milling processes using flat milling tool. And can be used to design and develop the tool and machine in industrial manufacturing.
Research Paper
Heat and Mass Transfer
Javad Zareei; Seyyed Hissein Hoseyni; marischa Elveny
Abstract
In this paper, the effect of boundary layer excitation on increasing the heat transfer coefficient of water/carbon nanotube (CNT) nanofluid and water/aluminum oxide (Al2O3) nanoparticles has been investigated. The turbulent flow equations inside the pipe with RNG K-ε turbulence model are solved ...
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In this paper, the effect of boundary layer excitation on increasing the heat transfer coefficient of water/carbon nanotube (CNT) nanofluid and water/aluminum oxide (Al2O3) nanoparticles has been investigated. The turbulent flow equations inside the pipe with RNG K-ε turbulence model are solved employing fluent software. The results show that the use of water/CNT nanofluid significantly increases the heat transfer coefficient of convection. There is no such increase for water-aluminum oxide nanoparticles. If the volumetric percentage of carbon nanotube increases, the rate of increase in the heat transfer coefficient and the flow pressure drop will increase. Therefore, the use of water/CNT nanofluid with lower volumetric percentages is better for improving the convective heat transfer. Also, by placing the barrier on the inner wall of the tube and stimulating the boundary layer, the heat transfer coefficient and then thereafter increases in the excitement area. In the present study, the use of three obstacles behind each other has increased the average heat transfer coefficient by 16.7%.
Research Paper
Optimization
Meraj Rajaee; Mina Jalali
Abstract
The solar tree is a combination of technology and art that is considered as the application of solar energy in the art of urban architecture. This study aims to combine solar technology with architectural style and art, help urban beautification and investigate the increase in solar panels' efficiency ...
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The solar tree is a combination of technology and art that is considered as the application of solar energy in the art of urban architecture. This study aims to combine solar technology with architectural style and art, help urban beautification and investigate the increase in solar panels' efficiency by focusing on the optimal slope and no shading in the form of a new solar tree structure. In this paper, the best angle for placing panels on tree branches to increase Shiraz's maximum efficiency has been calculated. The best angle is done with the help of the NRI mathematical model. Also, the Fibonacci sequence, which originates from nature and real trees, has been used to minimize shadows on this tree. The panels' optimal slope calculations are performed using MATLAB software. Also, the monthly efficiency changes resulting from the optimal slope have been calculated and displayed. By analyzing the computational relationships and their implementation by PVsyst simulator, the optimal annual slope of solar panels obtained 30 degrees. By implementing it in the solar tree structure, the proposed model's annual efficiency has increased by 12% compared to the fixed state. This article examines the technical methods of using solar systems in urban architecture with emphasis on integration methods. In the proposed and implemented solar tree model with the ability to adjust the optimal angle and beautify passages, parks and recreation centers, it is possible to charge electronic equipment such as mobile phones, tablets, and electric bicycles through clean solar energy.
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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