Engineering Journal (Faculty of Engineering, Chulalongkorn University, Bangkok)
Not a member yet
1223 research outputs found
Sort by
Spontaneous Ignition of Bagasse Stockpiles in Thailand: A Fire Safety Concern
Get PDFThe sugar industry is confronted with the problem of safe bagasse storage over extended periods. In term of fire safety, there have been many instances that the spontaneous ignition promotes ignition inside a large bagasse stockpile and eventually the spontaneous ignition process develops to a flaming fire. This paper presents a method to determine a safe size for bagasse stockpile from spontaneous ignition. The kinetic parameters for spontaneous ignition of bagasse were estimated based on two methods: the Frank-Kamenetskii method and the crossing point method. The bagasse activation energies experimentally determined were ranged from 89 to 109 kJ/mol. Based on the calculated kinetic parameter values, the bagasse stockpile safe sizes for a sugar factory were estimated in term of graphical solutions. For a fixed surrounding temperature, as the bagasse stockpile radius or length increases, the height of the stockpile that spontaneous ignition does not occur decreases and approaches the asymptotic value as the stockpile radius or length approaches infinity. The graphical solutions showed that a bagasse stockpile with any radius or length stored with height below the asymptotic height for a given surrounding temperature was considered to be safe from spontaneous ignition. Applying the calculated activation energy of 89 kJ/mol, the asymptotic heights for bagasse stockpiles were 10.0 m, 7.8 m, and 6.0 m for surrounding temperatures of 40oC, 45oC and 50oC, respectively.The sugar industry is confronted with the problem of safe bagasse storage over extended periods. In term of fire safety, there have been many instances that the spontaneous ignition promotes ignition inside a large bagasse stockpile and eventually the spontaneous ignition process develops to a flaming fire. This paper presents a method to determine a safe size for bagasse stockpile from spontaneous ignition. The kinetic parameters for spontaneous ignition of bagasse were estimated based on two methods: the Frank-Kamenetskii method and the crossing point method. The bagasse activation energies experimentally determined were ranged from 89 to 109 kJ/mol. Based on the calculated kinetic parameter values, the bagasse stockpile safe sizes for a sugar factory were estimated in term of graphical solutions. For a fixed surrounding temperature, as the bagasse stockpile radius or length increases, the height of the stockpile that spontaneous ignition does not occur decreases and approaches the asymptotic value as the stockpile radius or length approaches infinity. The graphical solutions showed that a bagasse stockpile with any radius or length stored with height below the asymptotic height for a given surrounding temperature was considered to be safe from spontaneous ignition. Applying the calculated activation energy of 89 kJ/mol, the asymptotic heights for bagasse stockpiles were 10.0 m, 7.8 m, and 6.0 m for surrounding temperatures of 40oC, 45oC and 50oC, respectively
Analysis of Fatigue Crack Propagation in Steel I-Beams with Welded Transverse Stiffeners Subjected to In-Plane Loadings
Get PDFFatigue crack propagation represents the mechanical damage that shortens the service life of bridge structures. Most fatigue cracks initiate at the welded details due to geometric discontinuities, residual stresses and initial weld defects. Welded transverse stiffeners have been widely used to increase the shear strength of steel girders. Under cyclic in-plane loadings, however, the fatigue crack initiates at the end of the stiffener in the web gap and propagates into the girder web. The objectives of this study are to (1) numerically simulate the fatigue crack propagation in steel I-girders with welded transverse stiffeners and (2) study the effects of the initial crack size, fillet weld size, stiffener dimension, and web-gap length on the fatigue crack propagation. The FRANC3D software was used to perform the analysis of stress intensity factor, crack propagation, and fatigue life. The numerical results showed that the fatigue life increases as the web-gap length increases, while it decreases as initial crack size and thickness of the transverse stiffener increase. Also, the stress intensity factors of the steel I-beams that include a fillet weld in the finite element models are slightly lower than ones modelled without a fillet weld.For bridge structures, the fatigue crack propagation represents the mechanical damage that shortens the service life of the structures. Most fatigue cracks initiate at the welded details due to geometric discontinuities, residual stresses, and initial weld defects. The welded transverse stiffeners have been widely used to increase shear strength of the steel girders. Under cyclic in-plane loadings, however, the fatigue crack initiates at the end of the stiffener, i.e., in the web gap, and propagates into the girder web. The objectives of this study are to (1) numerically simulate the fatigue crack propagation in steel I-girders with welded transverse stiffeners and (2) study the effects of initial crack size, fillet weld size, stiffener dimension, and web-gap length on the fatigue crack propagation. The FRANC3D software was used to perform the analysis of stress intensity factor, crack propagation, and fatigue life. The numerical results showed that the fatigue life increases as the web-gap length increases, while it decreases as initial crack size and thickness of the transverse stiffener increase. Also, the stress intensity factors of the steel I-beams that include the fillet weld in the finite element models are slightly lower than ones modelled without fillet weld
Optimizing CO Reductions in a Diesel Oxidation Catalyst under Diesel Dual Fuel Exhaust Conditions
Get PDFA Diesel Dual Fuel (DDF) engine is an adapted diesel engine that uses natural gas and diesel fuel as the energy source at the same time. Natural gas is mixed with air at the intake manifold while diesel fuel is injected into the combustion chamber directly to initiate the combustion process. Based on the past DDF literatures, they are indicated that Carbon Monoxide (CO) emissions were more substantial at low load conditions than those when running in diesel engine modes. The Diesel Oxidation Catalyst (DOC) that is installed to this diesel engine is, therefore, not capable to reduce CO emissions abide by to the emission regulation. Literatures also indicate that the exhaust temperature, mass flow rate, Oxygen (O2) concentration, CO concentration, as well as Propane (C3H8) concentration may affect CO conversion efficiency of the catalytic converter. In the present work, Design of Experiments (DOE) is employed to explore the behavior of various factors that affect CO reductions in the catalytic converter. Once the knowledge is founded, the optimization of CO reductions in the catalytic converter at 90% is studied extensively. Using Fractional Factorial Design for screening factors on CO conversions, it is found that the exhaust temperature, mass flow rate, O2 concentration, and CO concentration affect CO conversions of the catalytic converter significantly. Optimization of these factors, by using Box-Behnken Design, for reducing CO concentration of 6200 ppm which is the maximum CO amount emitted from the tested engine shows that 90% of CO conversion can be reached at the exhaust temperature of 2000C, the mass flow rate of 25 kg/h, and the oxygen concentration of 16%.A Diesel Dual Fuel (DDF) engine is an adapted diesel engine that uses natural gas and diesel fuel as the energy source at the same time. Natural gas is mixed with air at the intake manifold while diesel fuel is injected into the combustion chamber directly to initiate the combustion process. Based on the past DDF literatures, they are indicated that Carbon Monoxide (CO) emissions were more substantial at low load conditions than those when running in diesel engine modes. The Diesel Oxidation Catalyst (DOC) that is installed to this diesel engine is, therefore, not capable to reduce CO emissions abide by to the emission regulation. Literatures also indicate that the exhaust temperature, mass flow rate, Oxygen (O2) concentration, CO concentration, as well as Propane (C3H8) concentration may affect CO conversion efficiency of the catalytic converter. In the present work, Design of Experiments (DOE) is employed to explore the behavior of various factors that affect CO reductions in the catalytic converter. Once the knowledge is founded, the optimization of CO reductions in the catalytic converter at 90% is studied extensively. Using Fractional Factorial Design for screening factors on CO conversions, it is found that the exhaust temperature, mass flow rate, O2 concentration, and CO concentration affect CO conversions of the catalytic converter significantly. Optimization of these factors, by using Box-Behnken Design, for reducing CO concentration of 6200 ppm which is the maximum CO amount emitted from the tested engine shows that 90% of CO conversion can be reached at the exhaust temperature of 200oC, the mass flow rate of 25 kg/h, and the oxygen concentration of 16%
A Novel Approach for Centralized 3D Radio Resource Allocation and Scheduling in Dense HetNets for 5G Control-/User-plane Separation Architectures
Get PDFThis paper presents a centralized 3-dimensional radio resources (namely, time, frequency, and power) allocation and scheduling approach for control-plane and user-plane (C-/U-plane) separation architectures for fifth generation mobile networks. A central station is considered where schedulers of all base stations (BSs) are located. We consider a multi-tier network that comprises of a macrocell BS (MCBS), several outdoor picocell BSs, and a number of indoor femtocell BSs (FCBSs) deployed in a number of multi-storage buildings. The system bandwidth is reused in FCBSs within each building orthogonally. In contrast to the conventional almost blank subframe, we consider a fully blank subframe based time-domain enhanced intercell interference coordination to split completely C-/U-plane traffic such that the control-plane can be served only by the MCBS and the user-plane of user equipments by their respective BSs. We propose two power management schemes for FCBSs based on whether or not the coordinated multi-point communication with joint transmission (JT CoMP) is employed during off-state of a FCBS and develop a power control mechanism for both a single user and multi-user per FCBS scenarios. An optimal value of average activation factor (OAF) for a FCBS is derived to trade-off its serving capacity and transmit power saving factor. It is shown that in order to improve the network capacity, a FCBS needs to operate at an average activation factor (AAF) greater than its OAF using JT CoMP to serve neighboring on-state FCBSs during its normal off-state, whereas at an AAF less than the OAF to improve the energy efficiency. With a system level simulation, we show that the capacity of a FCBS increases, whereas its power saving factor decreases linearly with an increase in its AAF because of serving increased traffic, and an OAF of 0.5 for the capacity scaling factor and greater than 0.5 for are found.This paper presents a centralized 3-dimensional radio resources (namely, time, frequency, and power) allocation and scheduling approach for control-plane and user-plane (C-/U-plane) separation architectures for fifth generation mobile networks. A central station is considered where schedulers of all base stations (BSs) are located. We consider a multi-tier network that comprises of a macrocell BS (MCBS), several outdoor picocell BSs, and a number of indoor femtocell BSs (FCBSs) deployed in a number of multi-storage buildings. The system bandwidth is reused in FCBSs within each building orthogonally. In contrast to the conventional almost blank subframe, we consider a fully blank subframe based time-domain enhanced intercell interference coordination to split completely C-/U-plane traffic such that the control-plane can be served only by the MCBS and the user-plane of user equipments by their respective BSs. We propose two power management schemes for FCBSs based on whether or not the coordinated multi-point communication with joint transmission (JT CoMP) is employed during off-state of a FCBS and develop a power control mechanism for both a single user and multi-user per FCBS scenarios. An optimal value of average activation factor (OAF) for a FCBS is derived to trade-off its serving capacity and transmit power saving factor. It is shown that in order to improve the network capacity, a FCBS needs to operate at an average activation factor (AAF) greater than its OAF using JT CoMP to serve neighboring on-state FCBSs during its normal off-state, whereas at an AAF less than the OAF to improve the energy efficiency. With a system level simulation, we show that the capacity of a FCBS increases, whereas its power saving factor decreases linearly with an increase in its AAF because of serving increased traffic, and an OAF of 0.5 for the capacity scaling factor k = 1/2 and greater than 0.5 for k < 1 are found. 
A Novel Design and Implementation of a 4-DOF Upper Limb Exoskeleton for Stroke Rehabilitation with Active Assistive Control Strategy
Get PDFWe developed a robot, CUREs (Chulalongkorn University Rehabilitation Robotic Exoskeleton system), for upper extremity rehabilitation. The active assistive control strategy based on the impedance force control is developed and implemented to obtain assistive-resistive paths tracking for rehabilitation activities. The desired trajectory or rehabilitated training pattern for each specific patient need to be assigned first by a medical doctor and a physical therapy. The therapist can program the desired trajectory by guiding the patient arm based on the assigned path pattern and the set of via points will be stored and used for generating the desired trajectory. The desired trajectory will be stored specific for the patient and can be called back anytime. During the rehabilitation, the robot can assist and resist the patient’s arm to follow the desired trajectory. If the patient has difficulty moving his arm to track the desired path, the robot will help by adding more torque to help the patient to move his arm to reduce the error between the desired path and the actual posture. And if the patient himself can move his arm tracking the desired path, the robot will not apply any more force to assist or resist. The necessary state variables such as angular position and torque can be recorded during the training. The main purpose of the experiment, follow the medical ethic, is to assure that there is no side effect for using this rehabilitation robot. Five subacute stroke patients participated in this pilot study. All patients have severe upper extremity weakness. The medical doctor will assign the training pattern based on patient condition. The result showed that the Fugl-Meyer Assessment Upper Extremity Scale was improved after 10 days of training in all participants without any sign of side effect.We developed a robot, CUREs (Chulalongkorn University Rehabilitation Robotic Exoskeleton system), for upper extremity rehabilitation. The active assistive control strategy based on the impedance force control is developed and implemented to obtain assistive-resistive paths tracking for rehabilitation activities. The desired trajectory or rehabilitated training pattern for each specific patient need to be assigned first by a medical doctor and a physical therapy. The therapist can program the desired trajectory by guiding the patient arm based on the assigned path pattern and the set of via points will be stored and used for generating the desired trajectory. The desired trajectory will be stored specific for the patient and can be called back anytime. During the rehabilitation, the robot can assist and resist the patient’s arm to follow the desired trajectory. If the patient has difficulty moving his arm to track the desired path, the robot will help by adding more torque to help the patient to move his arm to reduce the error between the desired path and the actual posture. And if the patient himself can move his arm tracking the desired path, the robot will not apply any more force to assist or resist. The necessary state variables such as angular position and torque can be recorded during the training. The main purpose of the experiment, follow the medical ethic, is to assure that there is no side effect for using this rehabilitation robot. Five subacute stroke patients participated in this pilot study. All patients have severe upper extremity weakness. The medical doctor will assign the training pattern based on patient condition. The result showed that the Fugl-Meyer Assessment Upper Extremity Scale was improved after 10 days of training in all participants without any sign of side effect
Parallel-Axis Gear Design Methodology for Minimization of Power Loss and Its Effect on Vibration Characteristics
Get PDFGear tooth strength is mainly considered in gear design to ensure the ability to transmit power. With the design process, various sets of gear parameters are probably selected to meet the tooth strength. However the efficiencies of various designed gears are different. Improper gear parameter selection probably makes the gear power loss increase significantly. In this paper, the design methodology to minimize gear power loss is presented. A spur gear selected from a catalogue is used as the reference gear. Then several gears with various parameters but having the ability to transmit the same load are designed. The power losses of the designed and the reference gears are estimated by the sliding loss model, hence the minimum power loss gear is able to choose from the various designed gear set.s Both analytical and experimental results show that to minimize gear power loss along with keeping loading capacity, pressure angle should be increased and module should be reduced. The effect of this design methodology on vibration characteristics is also investigated by measuring the vibration attributed to the sample gear sets. It is found that the helical gear having large pressure angle, wide face width and having helix angle about 10° to 20° is favorable, since it has more capability to transmit load, lower power loss and also lower vibration than the reference spur gear
Printed Thai Character Recognition using Shape Classification in Video Sequence along a Line
Get PDFThis paper presents a novel method for recognition of 68 printed Thai characters in image sequences captured along a line of characters, based on their shape appearance such as the height and width, the top, bottom, and right edges, the numbers and positions of the circles (head of Thai characters) and the end points. Since each character appears in more than one frame of the image sequence that moves along the line, an algorithm to identify the arrangement of the characters in each line is necessary for accurate recognition results. We tested our system on image sequences with four different Thai fonts. The recognition rate is about 85.64% correct
Managing Real Power Loss of Distribution System Connected with Distributed Generator Using Least Square Quadratic Approximation
Get PDFThis paper compared two scenarios for managing real power loss of a distribution feeder connected with a Distributed Generator (DG). Under planning scenario, the objective is to obtain the optimal purchasing contract, which is a constant power injected from DG to minimize loss of a feeder. In real time operating scenario, the optimal scheduled power of DG to minimize loss for each hour is calculated. These two scenarios are formulated as optimization problems and solved with the proposed Least Square Quadratic Approximation (LSQA) technique. This technique is formulated based on a quadratic nature of a real power loss versus its real power output injected from DG. In term of the obtained results, it is reliable and has high accuracy. A 93-bus radial distribution system connected with a synchronous based DG sizes 7.5 MW under North-Eastern region 2 of Provincial Electricity of Thailand (PEA) is adopted as a tested system. The obtained results shown that managing loss under both scenarios bring benefits to a tested feeder. Moreover, the proposed LSQA technique is easy to understand, thereby can be used alternatively with others present optimization techniques
A Reduced Complexity of Vahedi's Tag Estimation Method for DFSA
Get PDFIn order to calculate the number of tags in a radio frequency identification (RFID) system, several tag estimation methods have been investigated in literature and most of the available estimation methods need the overall knowledge of idle, success and collision slots of the previous frame to carry out the tag estimation process. In this article, we present three techniques to reduce the complexity of Vahedi’s tag estimation for tag collision resolution in RFID systems using dynamic frame slotted ALOHA. Our modified and useful approach considers the information about only the number of empty, successful or colliding slots in the previous frame for the tag estimation. Three decision rules were obtained by maximizing the likelihood of success, idle and collision which helps in the reduction of complexity substantially. However, the accuracy of estimation decreases for success-only and idle-only methods while the collision-only method gives a consistent and lower estimate error when the frame sizes and the number of tags increase
Photocatalytic Degradation of Phenol over Highly Visible-Light Active BiOI/TiO2 Nanocomposite Photocatalyst
Get PDFBiOI/TiO2 nanocomposites were successfully prepared by the two-step method, co-precipitation/solvothermal method. The amount of BiOI in the composites were varied as 0, 5.0, 7.5, 10.0 and 12.5 mol%. XRD results exhibited sharp and narrow diffraction peaks of both BiOI and TiO2 in all composite samples. Morphologies of as-prepared samples consisted of spherical shapes of TiO2 and nanosheets of BiOI. Difuse Reflectance UV-visible (DR-UV-vis) spectra of composites drastically shifted into the visible range and the reduced band gap energies were observed. The composits obviously showed an enhanced phenol degradation of ca. 6 times higher than that of pure BiOI, pure TiO2 and Degussa P25. The maximum photocatalytic activity of ca. 68% was found for 10.0 mol% BiOI/TiO2 nanocomposite because of its increased visible-light-harvesting ability and its efficient electron-hole separation efficiency as observed from DR-UV-vis and PL spectra results