• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.337-345
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• 2002

The present study addresses a computational result of unsteady gas flow through a critical nozzle. The axisymmetric, unsteady, compressible, Wavier-Stokes equations are solved using a finite volume method that makes use of the second order upwind scheme for spatial derivatives and the multi-stage Runge-Kutta integral scheme for time derivatives. The steady solutions of the governing equation system are validated with the previous experimental data to ensure that the present computational method is valid to predict the critical nozzle flows. In order to simulate the effects of back pressure fluctuations on the critical nozzle flows, an excited pressure oscillation with an amplitude and frequency is assumed downstream of the exit of the critical nozzle. The results obtained show that for low Reynolds numbers, the unsteady effects of the pressure fluctuations can propagate upstream of the throat of critical nozzle, and thus giving rise to the applicable fluctuations in mass flow rate through the critical nozzle, while for high Reynolds numbers, the pressure signals occurring at the exit of the critical nozzle do not propagate upstream beyond the nozzle throat. For very low Reynolds number, it is found that the sonic line near the throat of the critical nozzle remarkably fluctuateswith time, providing an important mechanism for pressure signals to propagate upstream of the nozzle throat, even in choked flow conditions. The present study is the first investigation to clarify the unsteady effects on the critical nozzle flows.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.2127-2132
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• 2003

A computational study is performed to better understand the choke phenomenon of unsteady gas flow through a critical nozzle. The axisymmetric, unsteady, compressible, Navier-Stokes equations are solved using a finite volume method. In order to simulate the effects of back pressure fluctuations on the critical nozzle flow, a forced sinusoidal pressure wave is assumed downstream the exit of the critical nozzle. It's frequency is 20kHz and amplitude is varied below 15% of time-mean back pressure. The results obtained show that for low Reynolds numbers, the unsteady effects of the pressure fluctuations can propagate upstream of the throat of critical nozzle, and thereby giving rise to applicable fluctuations of mass flow through the critical nozzle. The effect of the amplitude of the excited pressure fluctuations on the choke phenomenon is discussed in details.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1915-1920
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• 2004

An edge tone is the discrete tone or narrow-band sound produced by an oscillating free shear layer impinging on a rigid surface. In this paper we present a two-dimensional edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle by the finite difference lattice Boltzmann method. We use a new lattice BGK compressible fluid model that has an additional term and allow larger time increment comparing a conventional FDLB model, and also use a boundary fitted coordinates. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of ${\alpha}=23^{\circ}$ . At a stand-off distance ${\omega}$ , the edge is inserted along the centreline of the jet, and a sinuous instability wave with real frequency f is assumed to be created in the vicinity of the nozzle and to propagate towards the downstream. We have succeeded in capturing very small pressure fluctuations result from periodically oscillation of jet around the edge. That pressure fluctuations propagate with the sound speed. Its interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips.

• Journal of Ship and Ocean Technology
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• v.12 no.1
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• pp.1-15
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• 2008

An edgetone is the discrete tone or narrow-band sound produced by an oscillating free shear layer, impinging on a rigid surface. In this paper, 2-dimensional edgetone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle is presented using lattice Boltmznan model with 21 bits, which is introduced a flexible specific heat ratio y to simulate diatomic gases like air. The blown jet is given a parabolic inflow profile for the velocity, and the edges consist of wedges with angle 20 degree (for symmetric wedge) and 23 degree (for inclined wedge), respectively. At a stand-off distance w, the edge is inserted along the centerline of the jet, and a sinuous instability wave with real frequency is assumed to be created in the vicinity of the nozzle exit and to propagate towards the downward. Present results presented have shown in capturing small pressure fluctuating resulting from periodic oscillation of the jet around the edge. The pressure fluctuations propagate with the speed of sound. Their interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips. It is found that, as the numerical example, satisfactory simulation results on the edgetone can be obtained for the complex flow-edge interaction mechanism, demonstrating the capability of the lattice Boltzmann model with flexible specific heat ratio to predict flow-induced noises in the ventilating systems of ship.

• The Journal of the Korea Contents Association
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• v.8 no.1
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• pp.143-151
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• 2008

In this paper, we have implemented a ubiquitous healthcare system that can measure and check human's health in anytime and anywhere. The implemented prototype are composed of both front-end and back-end. The front-end have several groups: environment sensor group such as temperature, humidity, photo, voice sensor, health sensor group such as blood pressure, heart beat, electrocardiogram, spo2 sensor, gateway for wired/wireless communication, and RFID reader to identify personal. The back-end has a serial forwarder to propagate measurment results, monitor program, and medical information server The implemented sensor node constructs a sensor network using the Zigbee protocol and is ported the tinyOS. The data gathering base node is linux-based terminal that can transfer a sensed medial data through wireless LAN. And, the medical information server stores the processed medical data and can promptly notify the urgent status to the connected medical team. Through our experiments, we've confirmed the possibility of ubiquitous healthcare system based on sensor network using the Zigbee.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.921-924
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• 2007

In this paper, we have implemented a ubiquitous healthcare system that can measure and check human's health in anytime and anywhere. The implemented prototype are composed of both front-end and back-end. The front-end have several groups: environment sensor group such as temperature, humidity, photo, voice sensor, health sensor group such as blood pressure, heart beat, electrocardiogram, spo2 sensor, gateway for wired/wireless communication, and RFlD reader to identify personal. The back-end has a serial forwarder to propagate measurment results, monitor program, and medical information server. The implemented sensor node constructs a sensor network using the Zigbee protocol and is ported the TinyOS. The data gathering base node is linux-based terminal that can transfer a sensed medial data through wireless LAN. And, the medical information server stores the processed medical data and can promptly notify the urgent status to the connected medical team. Through our experiments, we've confirmed the possibility of ubiquitous healthcare system based on sensor network using the Zigbee.

• The Journal of the Korea institute of electronic communication sciences
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• v.2 no.4
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• pp.209-214
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• 2007

This paper effectively suppress the mutual interference simbologan has proposed algorithm using a combination of multi-tier peosepteuron the tab so that the weight update can be done more efficiently. Simulation of the convergence characteristics superior to the average square error, that is research.

• International Journal of Ocean System Engineering
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• v.2 no.1
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• pp.50-56
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• 2012

This study investigates flow fields and energy dissipation due to regular wave interaction with a perforated vertical breakwater, through velocity data measurement in a two-dimensional wave tank. As the waves propagate through the perforated breakwater, the incoming wave energy is reflected back to the ocean, dissipated due to very turbulent flows near the perforations and inside the chamber, and transmitted through the perforations of the breakwater. This transmitted energy is further reduced due to the presence of the perforated back wall. Hence most of the energy is either reflected or dissipated in the vicinity of the structure, and only a small amount of the incoming wave energy is transmitted through the structure. In this study, particle image velocimetry (PIV) technique was employed to measure two-dimensional instantaneous velocity fields in the vicinity of the structure. Measured velocity data was treated statistically, and used to calculate mean flow fields, turbulence intensity and turbulent kinetic energy. For investigation of the flow pattern, time-averaged mean velocity fields were examined, and discussed using the cross-sections through slot and wall for comparison. Flow fields were obtained and compared for various cases with different regular wave conditions. In addition, turbulent kinetic energy was estimated as an approach to understand energy dissipation near the perforated breakwater. The turbulent kinetic energy was distributed against wave height and wave period to see the dependence on wave conditions.

• Journal of the Korea Society of Computer and Information
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• v.6 no.2
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• pp.48-57
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• 2001

In a fuzzy connectionist expert system(FCES), the knowledge base can be constructed of neural logic networks to represent fuzzy rules and their relationship, We call it fuzzy rule inference network. To find out the belief value of a conclusion, the traditional inference strategy in a FCES will back-propagate from a rule term of the conclusion and follow through the entire network sequentially This sequential search strategy is very inefficient. In this paper, to improve the above search strategy, we proposed fuzzy rule inference rule used in a FCES was modified. The proposed adaptive search strategy in fuzzy rule inference network searches the network according to the search priorities.

• 제어로봇시스템학회:학술대회논문집
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• 1999.10a
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• pp.226-229
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• 1999

We have been developing a method to build models for time series using Genetic Programming. The proposed method has been applied to various kinds of time series e.g. computer-generated chaos, natural phenomena, and financial market indices etc. Now we apply the prediction method to time histories of seismic ground motion i.e. one-step-ahead prediction of seismographic amplitude. Waves of earthquakes are composed of P-waves and S-waves. They propagate in different speeds and have different characteristics. It is believed that P-waves arrive firstly and S-waves arrive secondly. Simulations were performed based on real data of Hyuganada earthquake which broke out at southern part of Kyushuu Island in Japan. To our surprise, prediction model built using the earthquake waves in early time can enough precisely predict main huge waves in later time. Lots of experiments lead us to conclude that every slice of data involves P-wave and S-wave. The simulation results suggest the GP-based prediction method can be utilized in alarm systems or dispatch systems in an emergency.