• Nuclear Engineering and Technology
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• 제54권3호
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• pp.860-866
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• 2022

An accurate prediction of the pressure drop along the flow paths is crucial in the design of advanced passive systems cooled by heavy liquid metal coolants. To date, a generic pressure drop correlation over spacer grids by Rehme has been applied extensively, which was obtained from substantial experimental data with multiple types of components. However, a few experimental studies have reported that the correlation may give large discrepancies. To provide a more reliable correlation for ring-type spacer grids, the current numerical study aims at figuring out the most critical factor among four hypothetical parameters, namely the flow area blockage ratio, number of fuel rods, type of fluid, and thickness of the spacer grid in the flow direction. Through a set of computational fluid dynamics simulations, we observed that the flow area blockage ratio dominantly influences the pressure loss characteristics, and thus its dependence should be more emphasized, whereas the other parameters have little impact. Hence, we suggest a new correlation for the drag coefficient as C_B = C_ν,m/ε^2.7, where C_ν,m is formulated by a nonlinear fit of simulation data such that C_ν,m = -11.33 ln(0.02 ln(Re_b)).

• 한국가시화정보학회지
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• 제15권2호
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• pp.41-47
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• 2017

Microring/nanoring structure has high applicability for nano-antenna and biosensor thanks to its superior optical characteristics. Although coiling nanowires manufactured using immiscible emulsion droplets have an advantage in mass production, this process also forms nanowire bundles. In this study, we solved the nanowire bundle problem by size-selective sorting of the emulsion droplets in a pinched flow fractionation microchannel. Utilizing silver nanowires and immiscible emsulsion droplets, we investigated the correlation between the size of ring droplets and bundle droplet. We visualized the sorting process for glass particles and microring-containing emulsion droplets. Droplets were sorted based on their size, and the ratio of bundle droplets in solution decreased. This droplet-sorting strategy has potential to help the printing and coating process for manufacturing of ring structure patterns and developing of functional materials.

• 자원환경지질
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• 제54권1호
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• pp.35-48
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• 2021

구미분지는 영남육괴의 남동 중간부에 있으며 하부로부터 백악기의 구미층, 안산암질암류(영암산응회암, 부상리안산암), 유문암질암류(오봉리응회암, 도선굴유문암, 금오산응회암)와 관입암류(환상암맥, 기타 암맥)로 구성된다. 금오산응회암은 거의 대부분 회류응회암으로 구성되며 환상암맥과 함께 금오산 칼데라와 연관되어있다. 칼데라는 직경이 3.5 × 5.6 km이고 환상암맥과 단층으로 둘러싸인다. 칼데라 내부 화산암층은 유상 및 용결엽리가 대체로 칼데라 연변부에서 안쪽으로 경사되는 하향자루 구조를 나타낸다. 칼데라 블록은 북변부에서 350m, 남변부에서 600m 내려앉은 비대칭 침하를 나타낸다. 이 자료들에 의하면 금오산 칼데라는 하나의 칼데라윤회를 암시하는 기하학적으로 비대칭 피스톤 침하 칼데라로 분류된다. 이 칼데라는 챔버로부터 마그마의 대규모 분출에 뒤따라 외측경사 환상단층으로 경계되는 칼데라 블록의 피스톤 침하를 지시한다. 칼데라 블록에서 하향자루는 경계 단층의 완전한 발달과 동시에 초기 침하동안 하향자루운동을 의미한다. 이 운동에 의한 벌어진 환상열극에는 침하에 따른 마그마 과압으로 인해 마그마가 주입되어 환상암맥을 형성하였다.

• 한국주조공학회지
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• 제35권2호
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• pp.29-35
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• 2015

In this study, potential defects of ring-type cast products during the mold-filling stage of the casting process were investigated using computer simulation. The main focus was on the effects of runner extension and ingates. During the mold filling the molten metal flowed from the bottom to the top of the mold in two curved paths along the ring-type cavity. The fluid fronts in the two paths did not show the identical velocity during the mold filling stage. This difference in the filling speeds may cause defects such as voids and local contractions. The present model contained virtual fluid detectors at various positions inside the mold. When the molten metal passed those points, the volume of fluid jumped up from zero to one. The moments were measured to compare the speeds of the fluid fronts. We attempted various combinations of runner extensions and ingates to stabilize the flow and then to optimize the casting mold design.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.1494-1498
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• 2007

Impulsive shooting noise is basically complex phenomenon which contains the linear and non-linear characteristics. For those reasons, numerical analysis of impulsive shooting noise has the difficulties in control of the numerical stability and accuracy on the simulation. In this research, Wave-number Extended Finite Volume Scheme (WEFVS) is applied to the numerical analysis of impulsive shooting noise. In the muzzle blast flow simulation, the generation of the precursor wave and the induced vortex ring are observed. Consequently, blast wave. vortex ring interaction and vortex ring. bow shock wave interaction are evaluated on the shooting process using the accurate and stable scheme. The sound generation in the interactions can be explained by the vorticity transport theorem. The shear layer is evolved behind the projectiles due to the jet flow. In these computations, the impulsive shooting noise is generated by the complex interaction with shooting process and is propagated to the far-field boundary. The impulsive shooting noise generation can be observed by the applications of WEFVS and analyzed by the physical phenomena.

• 드라이브 ㆍ 컨트롤
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• 제12권2호
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• pp.21-26
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• 2015

In order to design a swash plate type pump for electro-hydrostatic actuators the performance of the hydrostatic piston shoe bearings in the low speed range needs to be examined, since the pump operates frequently at low speeds, compensating for position control errors as a control element. As a common practice, piston shoes are equipped with inner rings as an auxiliary element to enhance their tribological performance. In this paper, the effects of the inner rings of the piston shoes on the frictional loss and leakage flow rate were investigated, where three piston shoe models, with different inner ring shapes and different inlet orifice sizes, were integrated. The test results showed that a large inner ring and small inlet orifice were advantageous for reducing both the frictional loss and leakage flow rate; this could also be confirmed by computational analyses.

• 한국의류산업학회지
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• 제17권6호
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• pp.1020-1029
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• 2015

This paper investigated the wearing performance of knitted fabrics made of air vortex yarns using PTT/tencel/cotton fibres in comparison with ring and compact yarns for emotional garment. Wicking property of knitted fabric made of MVS yarns was worse than those by ring and compact yarns, however, drying property of knitted fabric made of MVS yarns was better than those by ring and compact yarns, which was explained as more water vapor transport due to larger openness between fibres in the MVS yarns than those in the ring and compact yarns. Thermal conductivity of knitted fabric made of MVS was lower than those of ring and compact yarns and maximum heat flow(Q_max) at the transient state of MVS knitted fabric was lower than those of ring and compact yarns, which may be attributed to MVS yarn structure that has parallel fibres in the core part of the yarn and fasciated fibre bundles on the sheath part with roughness on the yarn surface. However, pilling of MVS knitted fabric was better than those by ring and compact yarns, which was caused by less and shorter hairy fibres protruded from MVS yarn surface than those of ring and compact yarns. It was observed that tactile hand of MVS yarn knitted fabrics was stiffer than those of ring and compact yarns knitted fabrics. It was explained by low extensibility and compressibility and high bending and shear rigidities of the MVS yarn knitted fabrics, which resulted in bad wearing performance of MVS knitted fabric.

• 동의생리병리학회지
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• 제22권3호
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• pp.593-599
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• 2008

This research was aimed to examine the effect of Polygoni Multiflori Radix extract on the blood pressure in spontaneous hypertensive rat (SHR) and norepinephrine - induced arterial contraction in rabbit. In order to investigate the effect of Polygoni Multiflori Radix on rabbit's contracted vascular ring detached from common carotid artery, vascular ring with intact or damaged endothelium was used for the experiment using organ bath. To analyze the mechanism of Polygoni Multiflori Radix-induced relaxation, Polygoni Multiflori Radix extract was infused into contracted vascular ring which had been pretreated by $N{\omega}$-nitro-L-arginine(L-NNA), Methylene blue(MB), and $Ca^{2+}$ was infused into contracted vascular ring induced by NE after treatment of Polygoni Multiflori Radix extract in $Ca^{2+}$-free solution. The results were as follows: Systolic blood pressure was significantly attenuated by administration of Polygoni Multiflori Radix. Blood flow and aldosterone were significantly decreased, but velocity and renin were not affected by Polygoni Multiflori Radix. Polygoni Multiflori Radix had an effective relaxation to the contracted vascular ring by NE in 0.03 mg/ml, 0.1 mg/ml and 0.3 mg/ml level. Polygoni Multiflori Radix had an effective relaxation to the intact endothelium vascular ring, but when endothelium was removed, vascular ring did not relax. Polygoni Multiflori Radix-induced relaxation was inhibited by the pretreatment of L-NNA and MB. Pretreatment of Polygoni Multiflori Radix extract inhibit the contraction by influx of extra-$Ca^{2+}$ in contracted vascular ring induced by NE in $Ca^{2+}$-free solution. As mentioned above, we suggest that Polygoni Multiflori Radix relaxes vascular ring through suppress influx of extra-cellular $Ca^{2+}$ by the action of nitric oxide from endothelium.

• 암석학회지
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• 제8권3호
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• pp.171-182
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• 1999

면봉산 칼데라는 경상북도 청송군 남부에서 백악기 퇴적암류와 중성 화산암류 속에 직경 10.2$\times$8.0km 의 크기로 존재한다. 면봉산 칼데라 지역은 하부의 중성 화산암류, 중부의 응회질 퇴적암과 상부의 면봉산응회암으로 구성된다. 칼데라를 형성케 한 면봉산응회암은 하부 회류응회암, 층리응회암과 상부 회류응회암으로 나누어지며, 칼데라 북동부에서 최고 1,030m의 두께이고 남서부로 갈수록 얇아진다. 면봉산 칼데라는 칼데라 북측에서 최고 820m 내려앉았고 남서측에서 함몰되지 않은 비대칭 칼데라로 분류된다. 본 칼데라는 면봉산 지역에서 폭발적인 회류 분출로 인해 마그마챔버의 지붕이 갑자기 함몰됨으로서 형성되었다. 칼데라 연변부의 환상단열대는 유문암이 맥상으로 관입되고 칼데라 중앙부는 유문암이 플러그상으로 관입되었다. 그리고 환상단열대의 남부와 북서부는 심성암류의 관입에 의해 잘려 있다. 이와 같은 증거들을 종합하면, 면봉산 칼데라는 기하학상 뚜컹문형 칼데라로 분류되고 하나의 칼데라 윤회를 따르는 진화를 밟았다.

• 한국의류학회지
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• 제40권2호
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• pp.305-314
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• 2016

This paper investigated the applicable possibility of PTT and wool staple fibers to the air vortex system as high quality yarns for a high emotional and comfort garment. It was found that the tactile hand of vortex yarn knitted fabrics was harsher than ring and compact yarns knitted fabrics. It was observed that formability and sewability of air vortex yarn knitted fabrics seemed worse than ring and compact yarns due to low tensile and compressional resilience and high bending and shear hysteresis of air vortex yarn knitted fabrics. It revealed that wicking and drying rates of air vortex yarn knitted fabric were better than ring and compact yarns; in addition, the heat keepability of vortex yarn knitted fabric was higher than ring and compact yarns due to low thermal conductivity and max heat flow rate ($Q_{max}$). Any difference of thermal shrinkage between air vortex and ring yarn knitted fabrics was not shown, but pilling characteristic of air vortex yarn knitted fabric was superior. However, it was shown that wicking, drying, thermal property and pilling characteristics of air vortex yarn knitted fabric were superior due to air vortex yarn structure with parallel fibers in the core part and periodical and fasciated twists in the sheath part of the yarns.