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Kuai, Le,Haan, Fred L. Jr.,Gallus, William A. Jr.,Sarkar, Partha P. Techno-Press 2008 Wind and Structures, An International Journal (WAS Vol.11 No.2
A better understanding of tornado-induced wind loads is needed to improve the design of typical structures to resist these winds. An accurate understanding of the loads requires knowledge of near-ground tornado winds, but observations in this region are lacking. The first goal of this study was to verify how well a CFD model, when driven by far field radar observations and laboratory measurements, could capture the flow characteristics of both full scale and laboratory-simulated tornadoes. A second goal was to use the model to examine the sensitivity of the simulations to various parameters that might affect the laboratory simulator tornado. An understanding of near-ground winds in tornadoes will require coordinated efforts in both computational and physical simulation. The sensitivity of computational simulations of a tornado to geometric parameters and surface roughness within a domain based on the Iowa State University laboratory tornado simulator was investigated. In this study, CFD simulations of the flow field in a model domain that represents a laboratory tornado simulator were conducted using Doppler radar and laboratory velocity measurements as boundary conditions. The tornado was found to be sensitive to a variety of geometric parameters used in the numerical model. Increased surface roughness was found to reduce the tangential speed in the vortex near the ground and enlarge the core radius of the vortex. The core radius was a function of the swirl ratio while the peak tangential flow was a function of the magnitude of the total inflow velocity. The CFD simulations showed that it is possible to numerically simulate the surface winds of a tornado and control certain parameters of the laboratory simulator to influence the tornado characteristics of interest to engineers and match those of the field.
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Variable Coefficient Inductance Model-Based Four-Quadrant Sensorless Control of SRM
Kuai, Song-Yan,Li, Xue-Feng,Li, Xing-Hong,Ma, Jinyang The Korean Institute of Power Electronics 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.6
The phase inductance of a switch reluctance motor (SRM) is significantly nonlinear. With different saturation conditions, the phase inductance shape is clearly changed. This study focuses on the relationship between coefficient and current in an inductance model with ignored harmonics above the order of 3. A position estimation method based on the variable coefficient inductance model is proposed in this paper. A four-quadrant sensorless control system of the SRM drive is constructed based on the relationship between variable coefficient inductance and rotor position. The proposed algorithms are implemented in an experimental SRM test setup. Experimental results show that the proposed method estimates position accurately in operating two/four-quadrants. The entire system also has good static and dynamic performance.
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Top-Down Crack Modeling of Asphalt Concrete based on a Viscoelastic Fracture Mechanics
Kuai Hai Dong,LeeHyunJong,ZiGoangSeup,MunSungHo 한국도로학회 2008 한국도로학회 학술대회 발표논문 초록집 Vol.2008 No.10
An energy based crack growth model is developed in this study to simulate the propagation of top-down cracking in asphalt pavements. A viscoelastic fracture mechanics approach, generalized J integral, is employed to model the crack growth of asphalt concrete. Laboratory fatigue crack propagation tests for three different asphalt mixtures are performed at various load levels, frequencies and temperatures. Disk-shaped specimens with a proper loading fixture and crack growth monitoring system are selected for the tests. It is observed from the tests that the crack propagation model based on the generalized J integral is independent of load levels and frequencies, while the traditional Paris’ law model based on stress intensity factor is dependent of loading frequencies. However, both models are unable to take care of the temperature dependence of the mixtures. The fatigue crack propagation model proposed in this study has a good agreement between experimental and predicted crack growth lives, which implies that the energy based J integral could be a better parameter to describe fatigue crack propagation of viscoelastic materials such as asphalt mixtures.
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Principal Component Analysis of BGP Update Streams
Kuai Xu,Jaideep Chandrashekar,Zhi-Li Zhang 한국통신학회 2010 Journal of communications and networks Vol.12 No.2
In this paper, we propose a novel methodology to identify border gateway protocol (BGP) updates associated with major events—affecting network reachability to multiple ASes—and separate them (statistically) from those attributable to minor events,which individually generate few updates, but collectively form the persistent background noise observed at BGP vantage points. Our methodology is based on principal component analysis, which enables us to transform and reduce the BGP updates into different AS clusters that are likely affected by distinct major events. We demonstrate the accuracy and effectiveness of our methodology through simulations and real BGP data.
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Principal Component Analysis of BGP Update Streams
Xu, Kuai,Chandrashekar, Jaideep,Zhang, Zhi-Li The Korea Institute of Information and Commucation 2010 Journal of communications and networks Vol.12 No.2
In this paper, we propose a novel methodology to identify border gateway protocol (BGP) updates associated with major events - affecting network reachability to multiple ASes - and separate them (statistically) from those attributable to minor events, which individually generate few updates, but collectively form the persistent background noise observed at BGP vantage points. Our methodology is based on principal component analysis, which enables us to transform and reduce the BGP updates into different AS clusters that are likely affected by distinct major events. We demonstrate the accuracy and effectiveness of our methodology through simulations and real BGP data.
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Le Kuai,Fred L. Haan, Jr.,William A. Gallus, Jr.,Partha P. Sarkar 한국풍공학회 2008 Wind and Structures, An International Journal (WAS Vol.11 No.2
A better understanding of tornado-induced wind loads is needed to improve the design of typical structures to resist these winds. An accurate understanding of the loads requires knowledge of near-ground tornado winds, but observations in this region are lacking. The first goal of this study was to verify how well a CFD model, when driven by far field radar observations and laboratory measurements, could capture the flow characteristics of both full scale and laboratory-simulated tornadoes. A second goal was to use the model to examine the sensitivity of the simulations to various parameters that might affect the laboratory simulator tornado. An understanding of near-ground winds in tornadoes will require coordinated efforts in both computational and physical simulation. The sensitivity of computational simulations of a tornado to geometric parameters and surface roughness within a domain based on the Iowa State University laboratory tornado simulator was investigated. In this study, CFD simulations of the flow field in a model domain that represents a laboratory tornado simulator were conducted using Doppler radar and laboratory velocity measurements as boundary conditions. The tornado was found to be sensitive to a variety of geometric parameters used in the numerical model. Increased surface roughness was found to reduce the tangential speed in the vortex near the ground and enlarge the core radius of the vortex. The core radius was a function of the swirl ratio while the peak tangential flow was a function of the magnitude of the total inflow velocity. The CFD simulations showed that it is possible to numerically simulate the surface winds of a tornado and control certain parameters of the laboratory simulator to influence the tornado characteristics of interest to engineers and match those of the field.
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Variable Coefficient Inductance Model-Based Four-Quadrant Sensorless Control of SRM
Song-Yan Kuai,Xue-Feng Li,Xing-Hong Li,Jinyang Ma 전력전자학회 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.6
The phase inductance of a switch reluctance motor (SRM) is significantly nonlinear. With different saturation conditions, the phase inductance shape is clearly changed. This study focuses on the relationship between coefficient and current in an inductance model with ignored harmonics above the order of 3. A position estimation method based on the variable coefficient inductance model is proposed in this paper. A four-quadrant sensorless control system of the SRM drive is constructed based on the relationship between variable coefficient inductance and rotor position. The proposed algorithms are implemented in an experimental SRM test setup. Experimental results show that the proposed method estimates position accurately in operating two/four-quadrants. The entire system also has good static and dynamic performance.
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Acoustic Effect on Induction of Cerium Carbonate in Reaction Crystallization
He, Xin-Kuai,Kim, Rayoung,Shin, Dongmin,Kim, Woo-Sik The Society of Chemical Engineers, Japan 2012 Journal of chemical engineering of Japan Vol.45 No.4
<P>The influence of ultrasonication and agitation on the induction of nucleation in the reaction crystallization of cerium carbonate has been investigated in a semi-batch crystallizer. When the cerium chloride and sodium carbonate reactants are constantly injected, the induction time depends significantly on ultrasonication and agitation. Due to the acoustic cavitation of ultrasonication promoting micromixing of the reactants, the induction time of cerium carbonate is markedly reduced. Simultaneously, the acoustic cavitation appears to reduce the energy barrier of nucleation, inducing nucleation at a lower supersaturation level than with the turbulent fluid motion of agitation. However, the acoustic stream of ultrasonication does not promote the induction of nucleation. Meanwhile, agitation also facilitates the induction of nucleation due to turbulent mixing of the reactants. The micromixing resulting from agitation meant the supersaturation in the solution increases rapidly when increasing the agitation speed, thereby reducing the induction time. The influence of ultrasonication and agitation on the induction of nucleation has also been compared in terms of the energy dissipation. With the same energy dissipation, ultrasonication is much more effective than agitation for induction, possibly due to its unique feature of acoustic cavitation.</P>
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Synthesis of nanocrystals of gadolinium carbonate by reaction crystallization.
He, Xin-Kuai,Shin, Dongmin,Kim, Woo-Sik American Scientific Publishers 2012 Journal of nanoscience and nanotechnology Vol.12 No.3
<P>The formation of nano-sized crystals of gadolinium carbonate via reaction crystallization was studied in a semi-batch crystallizer using gadolinium chloride and ammonium hydrogen carbonate as the reactants. The gadolinium carbonate crystals were formed by the aggregation of primary particles sized about 5 nm. Thereby, the crystallization parameters acting directly on the aggregation of the primary particles, such as the reactant concentrations, non-stoichiometry of the reactants, solution pH, acoustic energy, and agitation speed, were mechanistically investigated. As such, increasing the reactant concentrations enhanced the crystal size due to higher nucleation of the primary particles for the aggregation. Non-stoichiometric reactant concentrations resulted in a significant reduction of the crystal size, due to the adsorption of the excess species on the primary particles. Similarly, the surface charge of the primary particles depended on the solution pH. Thus, the crystal size was reduced when the pH deviated from the neutral point. The acoustic cavitation of the ultrasound was much more effective than the turbulent fluid motion of the agitation in inhibiting the primary particle aggregation. Thus, the crystal size was remarkably reduced, even at a low acoustic energy of 6 watts.</P>
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