• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.450-455
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• 2001

The time-dependent behavior of nonequilibrium condensation of moist air through the Ludwieg tube is investigated with a computational fluid dynamics(CFD) method. The two-dimensional, compressible, Navier-Stokes equations, fully coupled with the condensate droplet growth equations, are numerically solved by a third-order MUSCL type TVD finite-difference scheme, with a second-order fractional time step. Baldwin-Lomax turbulence model is employed to close the governing equations. The computational results are compared with the previous experiments using the Ludwieg tube with a downstream diaphragm. The results clearly show that for an initial relative humidity below 30% there is no periodic oscillation of the condensation shock wave, but for an initial relative humidity over 40% the periodic excursions of the condensation shock occurs in the Ludwieg tube, and the frequency increases with the initial relative humidity. It is also found that total pressure loss due to nonequilibrium condensation in the Ludwieg tube should not be ignored even for a very low initial relative humidity, and the periodic excursions of the condensation shock wave are responsible for the total pressure loss.

• 한국전산유체공학회지
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• 제16권4호
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• pp.21-27
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• 2011

In this paper, the diagonal implicit harmonic balance method is applied to analyze helicopter rotor blade flow. The periodic boundary condition for Fourier coefficients is also applied in hover and forward flight conditions. It is available enough to simulate the forward flight problem with only one rotor blade using the periodic boundary condition in the frequency domain. In order to demonstrate the present method, Caradonna & Tung's rotor blades were used and the results were compared to the time-accurate method and experimental data.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.543-549
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• 2011

In this paper, diagonal implicit harmonic balance method is applied to analyze helicopter rotor blade flow. Periodic boundary condition for Fourier coefficients is also applied in hover and forward flight condition. It is available enough to simulate the forward flight problem with only one rotor blade using the periodic boundary condition in frequency domain. In order to demonstrate present method Carodonna & Tung's rotor blades are used and the results are compared to time-accurate method and experimental data.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2007년도 The 1st International Symposium on Advanced Magnetic Materials
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• pp.261.2-261.2
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• 2007

• 대한산업공학회지
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• 제23권1호
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• pp.23-37
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• 1997

In this paper, performance analysis of video traffic shaper for Motion Picture Experts Group (MPEG) video traffic in on ATM network are investigated. Traffic shaping for MPEG video traffic is proposed as a traffic control function in ATM networks. The proposed shaper smoothes video traffics by controling the output rate of the buffer, which is placed in an MPEG source, according to I,B,P frame sequences of MPEG. In performance analysis of an video traffic shaper, a periodic botch arrival model is suggested to describe cell streams in a frame of MPEG video traffic. The queueing model which has periodic independent botch arrival and periodic deterministic service time is used to obtain the cell loss ratio, the mean cell delay, and the measure of smoothing effect. Simulation results are used to validate this queueing model. The cell loss performance of ATM multiplexer is measured by simulation study with real MPEG-1 data. From the viewpoint of traffic load, the cell loss ratio is observed to be considerably high, which is considered to result from the burstiness of MPEG video traffic. As a result, it is shown that the shaping decreases cell loss ratio of multiplexer. The results of this paper can be employed to establish a basic guideline in the implementation of a traffic control scheme and the design of ATM multiplexer for MPEG video traffic.

• 한국농공학회지
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• 제6권1호
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• pp.737-749
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• 1964

This is an attempt to find out the periodicity of the natural hydrological phenomena by the function of vibration periodicity, under the assumption that the phenomena are periodic. The result of this study at Suwon is as foIlows: 1. Annual precipitation and tota1 precipitation during summer season have the periodicity of five years. 2. Annual temperature and tota1 temperature during winter season have the periodicity of seven years. 3. The regulation curve equations of the above vibration phenomena are as foIlows: a Annual precipitation. Y = 1149-250cos2/5${\PI}$t-33 sin 2/5 t b. Total precipitation during summer season. Y=212'.9+33.06sin (2/5${\PI}$t+$88^{\circ}$13') c. Annual temperature. Y= 140.3+3.3 sin (2/7${\PI}$t+ $154^{\circ}C$55')

• Wind and Structures
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• 제36권3호
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• pp.215-220
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• 2023

We study the progressive full-scale wind tunnel tests on a high solidity vertical axis wind turbine (VAWT) for various tip speeds and pitch angles to understand the VAWT shaft system's dynamics using 0-1 Test for chaos. We identify that while varying rotor speed (tip speed) of the turbine, the system's dynamics change from periodic to chaotic through quasiperiodic and strange non-chaotic (SNA) states. The present study is the first experimental evidence for the existence of these states in the VAWT shaft system to the best of our knowledge. Using the asymptotic growth value Kc in 0-1 test, when the turbine operates at the low tip speeds and high pitch angles for low incoming wind speeds, the system behaves periodic (Kc ≈ 0). However, when the incoming wind speed increases further the system's dynamics shift from periodic to chaotic vibrations through quasi-periodic and SNA. This phenomenon is due to the dynamic stalling of blades which induces chaotic vibration in the VAWT shaft system. Further, the singular continuous spectrum method validates the presence of SNA and differentiates the SNA from chaotic vibrations.

• Kyungpook Mathematical Journal
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• 제56권2호
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• pp.507-516
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• 2016

In this paper, we introduce an explicit formula for the solutions and discuss the global behavior of solutions of the difference equation $$x_{n+1}={\frac{ax_{n-3}}{b-cx_{n-1}x_{n-3}}}$$, $n=0,1,{\ldots}$ where a, b, c are positive real numbers and the initial conditions $x_{-3}$, $x_{-2}$, $x_{-1}$, $x_0$ are real numbers.

• 한국수학교육학회지시리즈B:순수및응용수학
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• 제2권2호
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• pp.157-162
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• 1995

Let I be the interval, $S^1$ the circle and let X be a compact metric space. And let $C^{circ}(X,\;X)$ denote the set of continuous maps from X into itself. For any f$f\in\;C\circ(X,\;X),\;let\;P(f),\;R(f),\;\Gamma(f),\;\Lambda(f)\;and\;\Omega(f)$ denote the collection of the periodic points, recurrent points, ${\gamma}-limit{\;}points,{\;}{\omega}-limit$ points and nonwandering points, respectively.(omitted)

• 한국산업보건학회지
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• 제4권1호
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• pp.33-42
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• 1994

This study was carried out to assess worker exposure to vinyl chloride monomer (VCM) and to present control measures in the factories processing and producing polyvinyl chloride (PVC) resin. The conclusion remarks are as follows. Only two personal samples in the factory ("E") processing polyvinyl chloride resin were analysed to be 27.6 ppm and 12.6 ppm, respectively. But, these concentration exceed 1 ppm, Permissible Exposure Limits (PEL) of OSHA. So, worker's exposure to VCM at "E" factory should be reevaluated. In "A", "B" and "C" factory producing polyvinyl chloride resin, the average worker's exposures to VCM were 0.12 ppm, 0.86 ppm and 1.23 ppm, respectivery. Worker exposure to VCM at distillation and dry process was higer than other processes at "A" factory. The average exposure concentration of worker at polymerization process of "B" and "C" factory was 1.23 ppm, and 1.46 ppm respcetively. These concentration exceed 1 ppm, Permissible Exposure Limits of OSHA. Control room of "B" and "C" factory had 0.91 ppm and 0.65 ppm of worker's exposure concentration respectively. "A" factory was evaluated to be "acceptable", but "B" and "C" factories were evaluated to be "not acceptable", by the workplace exposure assessment program of AIHA. Process other than bagging and control room of "A" factory was evaluated to "not acceptable". Immediate correction measures for preventing workers from exposure to VCM should be performed in the factories or process that were evaluated to be "not acceptable". After these control measures are taken, worker exposure to VCM must be reevaluated through personal air monitoring. Control measures presented by this study are complete sealing of connecting pipe lines, flanging, packing, bolting and nutting. Periodic leak test for leak parts is also required. And positive pressure facility should be constructed at control room of "B" and "C" factory. Fresh air through cleaner such as HEPA filter should be supplied to control room. In addition to these control measures, periodic personal monitoring for evaluating worker exposure to VCM should be performed.