• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.50.3-50.3
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• 2009

지구관측용 광학탑재체를 탑재한 저궤도위성은 내부부품보호를 위해 표면처리와 같은 수동적 기법과 히터동작과 같은 능동적 기법을 함께 사용을 한다. 내부열손실을 막기 위해 위성외부의 거의 모든 부분을 단열재(MLI)로 감싸게 되며, 각 단열재는 견고하게 고정이 된다. 광학탑재체는 구성품의 보호와 최적성능의 영상획득을 위해 다수의 히터가 장착되는데, 각 히터는 가열대상물의 온도를 실시간으로 측정하여 미리 설정된 On/Off 온도를 기준으로 제어가 된다. 궤도상에서 탑재체가 겪게 되는 다양한 궤도열환경 시나리오에 대한 열해석결과를 이용하여 히터의 위치, 용량 및 제어온도가 결정된다. 궤도상 운용 중, 위성을 보호하는 단열재 사이에 미세한 틈이 발생한 가상적인 상황을 가정하여, 탑재체 히터의 임무주기변화와 탑재체 운용에의 영향을 분석한다.

• 한국방재학회:학술대회논문집
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• 2010.02a
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• pp.89.1-89.1
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• 2010

본 연구는 토양의 함수비를 측정하기 위하여 TDR(Time Domain Reflectometry, 시간영역 광전자파 분석기) 방식의 함수센서(CS616)에 대한 올바른 보정시험을 제안하기 위하여 피복두께, 센서간 간섭 영향, 온도의 영향 및 다짐율 변화에 대한 실내 시험을 수행하였다. 시험 결과 피복두께, 센서간 간섭 영향 및 온도의 영향은 체적함수비의 크기에 미치는 영향은 크지 않은 것으로 나타났으며, 오히려 보정시험시 정확한 체적함수비 조건을 유지하는 것이 중요할 것으로 사료된다. 또한 보정시험을 수행할 때 다짐율까지 고려한 시험을 수행하는 노력에 비하여 얻어지는 체적함수비의 정확도의 크기는 다짐율과 주기를 고려하여 얻어진 회귀식을 살펴보면 주기에 비하여 상대적으로 영향이 작은 것으로 사료된다.

• Journal of computational fluids engineering
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• v.16 no.3
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• pp.52-58
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• 2011

This study investigates the bifurcation sequence to chaos in a horizontal annulus with a constant heat flux wall. After the first Hopf bifurcation from a steady to a simple time-periodic flow with a fundamental frequency, quasi-periodic flows with two or three incommensurable frequencies appear. A reverse transition from a quasi-periodic flow to a simple periodic flow is observed with increase of Rayleigh number. And finally, chaotic convection is established after appearance of three incommensurable frequencies at a high Rayleigh number. Simple periodic flows exist between quasi periodic flows. The transition route to chaos of the present simulations follows the Ruelle-Takens route.

• Journal of Korea Water Resources Association
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• v.32 no.6
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• pp.649-655
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• 1999

The maximum run-up heights of periodic waves are numerically investigated in this study. Incident waves are sinusoidal and enoidal waves. The maximum run-up height of enoidal wave approaches that of sinusoidal wave as the wave length decreases, while it approaches that of solitary wave as the wave length increases. If wave height is fixed, the maximum run up heights of enoidal waves are always greater than those of sinusoidal waves but smaller than those of solitary waves.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.2
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• pp.88-95
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• 2001

Transition to chaotic convection is investigated for natural convection of a fluid with Pr=0.1 in a wide-gap horizontal annuls. The unsteady two-dimensional stream-function-vorticity equation is solved with finite difference method. As the Rayleigh number is increased, the steady 'downward flow' bifurcates to a time-periodic flow with a fundamental frequency, and afterwards a period-doubling bifurcation occurs. As the Rayleigh number is increased further, the chaotic flow regime is reached after a sequence of successive Hopf bifurcation to quasi-periodic and chaotic flow regimes. The route to chaos shows the Ruelle-Takens-Newhouse scenario. The flow of chaotic regime displays complex coalescence and separation of eddies in the side and lower region of the annulus.

• Journal of Chest Surgery
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• v.36 no.12
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• pp.952-960
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• 2003

It has been reported that p53 regulates the G2-M checkpoint transition through cyclin Bl, and it has been suggested that p53 plays an important role in the development and progression of various malignancies. The aim of this study is to clarify the role of the cell cycle regulators, cyclin B1 and p53 in patients with esophageal squamous cell carcinoma (ESCC). Material and Method: Tissue samples from 46 patients with ESCC were included in this study. Expression levels of cyclin Bl and p53 in samples of normal squamous epithelium, dysplasia, and tumor cells from patients with ESCC were analyzed by immunohistochemical study Result: Several cells in the basement layer of normal epithelium expressed cyclin B1. The number of cyclin B1 positive cells tended to increase as the degree of dysplasia increased from low grade to high grade. More than 10% of tumor cells were cyclin B1 positive in 19 patients (41.3%). Several clinicopathologic parameters, including tumor stage (p<0.05), pathologic Iymph node status (p<0.05) and invasion of Iymphatic vessels (p<0.05), were correlated with the overexpression of cyclin B1. Elevated expression levels of cyclin B1 also correlated with a poor prognosis in patient with ESCC in univariate analysis (p<0.05) and multivariate analysis (p<0.05), In contrast, p53 expression exhibited significant correlation with the level of cyclin B1 expression, but was not associated with prognostic parameters in patients with ESCC. Conclusion: These findings suggest that cyclin B1 is involved in the pathogenesis of carcinoma of the esophagus and that elevated levels of cyclin B1 expression, but not p53 expression, may indicate a poor prognosis for patients with ESCC.

• Journal of Navigation and Port Research
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• v.48 no.3
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• pp.155-163
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• 2024

As the demand for reducing carbon emissions increases, efforts to reduce the usage of fossil fuels and research on renewable energy are also increasing. Among the various renewable energy harvesting techniques, the floating offshore wind turbine has several advantages. Compared to other technologies, it has fewer installation limitations due to interference with human activity. Additionally, a large wind turbine farm can be constructed in the open ocean. Therefore, it is important to conduct motion analysis of floating offshore wind turbines in waves during the initial stage of conceptual design. In this study, a frequency motion analysis was conducted on a semi-submersible type floating offshore wind turbine. The analysis focused on the effects of varying trim on the motion characteristics. Specifically, motion response analysis was performed on heave, roll, and pitch. Natural period analysis confirmed that changing the trim angle did not significantly affect the heave and pitch motions, but it did have a regular impact on the roll motion.

• Journal of Korean Society of Forest Science
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• v.86 no.2
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• pp.135-145
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• 1997

This study aimed at evaluating one curvilinear equation and nine non-linear equations for estimating stand growth characteristics(mean dbh, mean height and volume per ha) for the plantations of Pinus koraiensis and the natural stands of Quercus mongolica. The data were collected from 92 plots in Pines koraiensis stands and 83 plots in Quercus mongolica stands, and the site index of all the stands is 14. The curvilinear equation, $Y=at^be^{-c/t}$, used in preparing the yield tables was well fitted within the range of data, but was likely to give overestimates when extrapolating in old stage due to the tendency of linear increase. Among the non-linear equations, logistic equation and Sloboda equation gave overestimates in young stands and reached the asymptotic status early which means underestimates in old stage. Extrapolating in old stage, Hossfeld equation generally gave larger values than others due to its large estimates of parameter a, the maximum value. On the other hand, Bertalanffy equation gave underestimates in young and old stands and overestimates in middle-aged stands. The estimates with Korf equation was relatively low for Pinus koraiensis stands, and this tendency was more obvious in dbh growth of Quercus mongolica stands. Ueno-Ohzaki equation was liable to give over or underestimates depending on the value of parameter b when extrapolating in old stands. Considering the accuracy of estimates and the biological base of the growth equations, Gompertz equation, Chapman-Richards equation and Weibull equation were generally applicable for estimating the stand growth characteristics of both species in the whole range of stand ages including extrapolated range. To get more accurate and precise parameter estimates, more data, especially in old stands, should be required in further study.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.71-76
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• 2017

The roll damping problem in the design of ships and offshore structures remains a challenge to many researchers due to the fluid viscosity and nonlinearity of the phenomenon itself. In this paper, the study on viscous roll damping of a circular cylinder was carried out using forced oscillations. The roll moment generated by forced oscillation using a torque sensor was measured for each forced oscillation period and compared with the empirical formula. Although the magnitude of the measured torque from the shear force was relatively small, the results were qualitatively similar to those obtained from the empirical formula, and showed good agreement with the quantitative results in some oscillation periods. In addition, the flow around the circular cylinder wall was observed closely through the PIV measurements. Owing to the fluid viscosity, a boundary layer was formed near the wall of the circular cylinder, and a minute wave was generated by periodical forced oscillations at the free surface through the PIV measurement. In this study, the suitability of the empirical formula for the roll moment caused by viscous roll damping was verified by model tests. The wave making phenomenon due to the fluid viscosity around the wall of a circular cylinder was testified by PIV measurements.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.6
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• pp.561-568
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• 2020

Wave measurements using X-band radar have many advantages compared to other wave gauges including wave-rider buoy, P-u-v gauge and Acoustic Doppler Current Profiler (ADCP), etc.. For example, radar system has no risk of loss/damage in bad weather conditions, low maintenance cost, and provides spatial distribution of waves from deep to shallow water. This paper presents new methods for estimating significant wave heights of X-band marine radar images using Artificial Neural Network (ANN). We compared the time series of estimated significant wave heights (Hs) using various estimation methods, such as signal-to-noise ratio (${\sqrt{SNR}}$), both and ${\sqrt{SNR}}$ the peak period (TP), and ANN with 3 parameters (${\sqrt{SNR}}$, TP, and Rval > k). The estimated significant wave heights of the X-band images were compared with wave measurement using ADCP(AWC: Acoustic Wave and Current Profiler) at Hujeong Beach, Uljin, Korea. Estimation of Hs using ANN with 3 parameters (${\sqrt{SNR}}$, TP, and Rval > k) yields best result.