• 한국수소및신에너지학회논문집
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• 제34권3호
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• pp.274-282
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• 2023

This study conducted direct numerical simulations of the natural convection phenomena of gaseous hydrogen in a physical storage container containing four circular cylinders. Rayleigh numbers (Ra) in the range of 10⁴≤Ra≤10⁶ and a Prandtl number (Pr)=0.69 (gaseous hydrogen) were considered. The main parameter is a horizontal distance of four circular cylinders and the values of ε_h=0.1, 0.2, 0.3, 0.4, and 0.5 are considered. The flow and thermal structures and corresponding heat transfer characteristics are investigated with respect to the transition of the flow regime. The time- and surface-averaged Nusselt number on the cylinder surface and the wall of physical storage container increased by about 57% and 69% according to the Ra and ε_h, respectively. Thus, the horizontal distance has an influence on the heat transfer characteristics on natural convection of gaseous hydrogen.

• The Journal of Korean Physical Therapy
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• 제35권5호
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• pp.156-161
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• 2023

Purpose: This study examined the effects of subjective visual vertical perception and head orientation on static balance control. Methods: The subjects were 25 young and healthy adults. The vertical perception was measured using a subjective visual vertical (SVV), and the Center of pressure (COP) parameter was analyzed by continuously measuring the movement of the COP to determine the changes in static postural control. The group was divided based on a deviation of 3° in SVV (11 of SVV≥3°, 14 of SVV<3°) and measured with different head orientations: front, up, down, left, and right in the upright and tandem positions, respectively. Results: In the upright position, the SVV≥3° group had significantly larger values for all COP parameters (Sway length, Surface, Delta X, Delta Y, and Average speed) compared to the SVV<3° group (p<0.05). In the tandem stance, only the Ellipse Surface value was significantly larger among the COP parameters in the group with SVV≥3° compared to the group with SVV<3°(p<0.05). In contrast, the other COP parameters were not significantly different (p>0.05). The effects of static balance control on the head orientation were not statistically significant (p>0.05), and the interactions between the subjective vertical perception and head orientation were not significant (p>0.05). Conclusion: These results suggest that pathological deviations in SVV are associated with impaired static balance performance. This study can provide a therapeutic rationale for using visuospatial cognitive feedback training to improve the static balance.

• 지구물리와물리탐사
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• 제9권4호
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• pp.299-303
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• 2006

지질잡음, 특히 이들이 천부에 위치할 경우 물리탐사자료의 해석에 상당한 문제가 된다. 따라서 이들 지질잡음을 효과적으로 억제해야만 조사지역내의 주된 이상체를 정확하게 탐지해 낼 수 있다. 물리탐사자료의 역산에서 천부에 존재하는 물성대비가 크지 않은 소규모 이상체는 지질잡음의 하나로 생각할 수 있다. 현재 물리탐사 자료의 역산에는 평활화 제한 최소자승법이 널리 사용되고 있다. 이 방법은 물성대비가 큰 모델변수에는 강한 제한을 가하고, 작은 모델변수에는 약한 제한을 가한다. 따라서 천부에 존재하는 소규모 이상체(지질잡음)를 제거하는 데는 한계가 있다. 본 연구에서는 큰 모델변수에는 작은 제한을, 작은 모델변수에는 강한 제한을 가하는 새로운 MTE 역산법을 개발하였으며, 이 방법은 천부의 소규모 이상체의 억제에 효과적이다. 개발된 역산 방법을 소형루프 전자탐사자료의 2.5차원 역산에 적용한 결과 천부의 소규모 이상체를 효과적으로 억제하고 주 대상체를 보다 선명하게 나타내는 영상을 얻을 수 있었다.

• 한국해안해양공학회지
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• 제9권2호
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• pp.86-96
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• 1997

진해만에서 천해전선의 형성 및 전선과 수질분포와의 관계를 해석하기 위해 해양학적인 조사가 수행 되었으며, 또한 Simpson-Hunter의 성층계수 log(H/U$^3$)을 수치계산하였다.인공위성 자료와 현지조사결과에 의하면, 진해만의 천해전선은 가덕수로 북쪽해역 부근에서 형성되며, 전선부근에서 성층계수 값은 2.0~2.5이다. 전선이 셩성되는 위치를 기준으로 했을 때 만의 외해역과 진해만 서부해역에서는 COD 농도가 2.0 mg/l 이하로 낮으나, 전선역의 북쪽 내해에 위치한 마산만에서는 3.0~5.5 mg/l로써 높다. COD 농도는 마산만에서 외해로 갈수록 강한 해수교환으로 인해 점차 감소한다. 하계 저층 무산소 및 저산소 수괴는 진해만 서부해역과 마산만에서 일어나며, DO 농도는 성층계수가 증감함에 따라 감소한다. DO 농도는 전선이 형성되는 해역을 기준으로 만외에서는 약 4.0 mg/l 이상으로 높으나, 만내에서는 낮다. 천해전선은 연안에서 외해로의 물질수송에 대해 중요한 역하을 하며, 또한 전선의 형성지역은 물리적 및 화학적으로 중요한 경계를 이루는 것 같다.

• 한국수자원학회논문집
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• 제55권11호
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• pp.887-901
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• 2022

개별 강우-유출 사상을 대상으로 최적 매개변수를 산정하는 경우 사상별로 매개변수가 서로 다르며 물리적인 범위를 중심으로 변동성이 커 유역의 대표 매개변수를 결정하는데 어려움이 있다. 매개변수 추정 시 변동성 증가는 강우의 시공간적 변동성과 함께, 유역 내 일부 홍수량 산정지점 기준으로 강우-유출 자료만이 이용 가능하여 매개변수의 식별성(identifiability)이 매우 낮다. 추정되는 매개변수의 변동성 확대에 따른 문제점을 개선하기 위하여, 본 연구에서는 다수의 사상들을 동시에 고려한 매개변수 최적화 방법을 제안하였으며, NSE를 목적함수로 하여 매개변수를 최적화하였다. 개별 사상들을 통합적으로 고려하여 최적매개변수를 산정하는 경우 매개변수의 물리적인 특성을 유지함과 동시에 유역의 공동 매개변수 효율적으로 추정이 가능하였다. 개별 매개변수와 공통 매개변수 NSE의 차이가 최대 0.08 정도를 나타내며, 홍수량 재현 측면에서도 개별적으로 최적화를 수행한 경우와 유사하거나 보다 개선된 결과를 확인할 수 있었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 D
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• pp.1614-1616
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• 1999

Epoxy resin has been used as matrix resin of advanced composites owing to ideally suitable properties and inherent physical and chemical properties for electrical and electronic insulation. In this paper, in order to evaluate the performance of epoxy composites for out door insulation, variations of tracking resistance were investigated on the complex ageing parameter. Also, IPN methods were introduced in order to improve performance for out door use. As a result, it was confirmed that tracking resistance were degraded with complex ageing parameters. But, it was confirmed that specimen of IPN structure have the better tracking resistance properties than SIN structure by moisture absorption aging.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2006년도 제33회 KOSCO SYMPOSIUM 논문집
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• pp.46-49
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• 2006

Extinction limits and combustion temperatures in heat-recirculating excess enthalpy reactors employing both gas-phase and catalytic reaction have been examined previously, with and emphasis Reynolds number (Re) effects and possible application to microscale combustion devices. However, Re is not the only parameter needed to characterize reactor operation. In particular, the use of a fixed reactor size implies that residence time and Re cannot be adjusted independently. To remedy this situation, in this work geometrically similar reactors of different physical sizes were tested with the aim of independently determining the effects of Re and Da. It is found that the difference between catalytic and non-catalytic combustion limits narrow as scale decreases. Moreover, to assess the importance of wall thermal conductivity, reactors of varying wall thickness were studied. From these results the effect of scale on microscale reactor performance and implications for practical microcombustion devices are discussed.

• 한국측량학회:학술대회논문집
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• 한국측량학회 2007년도 춘계학술발표회 논문집
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• pp.85-88
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• 2007

Sea level fluctuation present a direct influence to those who live near the coast. The importance of monitoring sea level is evident. Therefore, various techniques have been employed for sea level measurements such as the coastal water level gauges, satellite altimetry and GPS buoy. Especially, GPS buoys have been used to measure water levels, atmospheric parameter and other physical conditions in sea, tide correction, the altimeter range calibration, ocean environment. In this paper, we will mainly concentrate on the kinematic technique for GPS buoy to measure the sea level. A test was carried out to test the method proposed in this paper, which made use of a GPS buoy equipped to monitor the sea level in Busan. We have executed to analysis about applications of GPS buoy.

• Structural Engineering and Mechanics
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• 제42권2호
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• pp.269-289
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• 2012

Free vibration and dynamic responses of piles semi-rigidly connected with the superstructures are investigated. Timoshenko beam theory is employed to characterize the pile partially embedded in a two-parameter elastic foundation. The formulations for the method of reverberation-ray matrix (MRRM) are then derived to investigate the dynamics of the pile with surface cracks, which are modeled as massless rotational springs. Comparison with existent numerical and experimental results indicates the proposed method is very effective and accurate for dynamic analysis, especially in the high frequency range. Finally, the effects of some physical parameters on the natural frequencies, frequency responses and transient responses of the piles are studied.

• 천문학회보
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• 제40권1호
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• pp.49.3-50
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• 2015

Synchrotron radiation of relativistic electrons is an important radiation mechanism in many astrophysical sources. In the sources where the synchrotron cooling timescale is shorter than the dynamical timescale, electrons are cooled down below the minimum injection energy. It has been believed that such fast-cooling electrons have a power-law distribution in energy with an index -2, and their synchrotron radiation has a photon spectral index -1.5. On the other hand, in a transient expanding astrophysical source, such as a gamma-ray burst (GRB), the magnetic field strength in the emission region continuously decreases with radius. Here we study such a system, and find that in a certain parameter regime, the fast-cooling electrons can have a harder energy spectrum. We apply this new physical regime to GRBs, and suggest that the GRB prompt emission spectra whose low-energy photon spectral index has a typical value -1 could be due to synchrotron radiation in this moderately fast-cooling regime.