• Fibers and Polymers
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• 제7권3호
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• pp.317-322
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• 2006

Reduction of yam hairiness by nozzles in ring spinning and winding is a new approach. Simulation of the airflow pattern inside the nozzles provides useful information about actual mechanism of hairiness reduction. The swirling air current inside the nozzles is capable of wrapping the protruding hairs around the yam body, thereby reducing yam hairiness. Since production rate of winding is very high and the process itself increases yarn hairiness any method to reduce the hairiness of yarns at this stage is a novel approach. A CFD (computational fluid dynamics) model has been developed to simulate the airflow pattern inside the nozzles using Fluent 6.1 software. In this study, both S- and Z-type nozzles having an axial angle of 500 and diameter of 2.2 mm were used for simulation studies. To create a swirling effect, four air holes of 0.4 mm diameter are made tangential to the inner walls of the nozzles. S- and Z-twisted yams of 30 tex were spun with and without nozzles and were tested for hairiness, tensile and evenness properties. The total number of hairs equal to or exceeding 3 mm (i.e. the S3 values) for yam spun with nozzle is nearly 49-51 % less than that of ring yams in case of nozzle-ring spinning, and 15 % less in case of nozzle-winding, while both the yarn types show little difference in evenness and tensile properties. Upward airflow gives best results in terms of hairiness reduction for nozzle-ring and nozzle wound yams compared to ring yarns. Yarn passing through the centre of the nozzle shows maximum reduction in S3 values.

• 한국추진공학회지
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• 제17권3호
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• pp.37-46
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• 2013

최근, micro shock tube는 Micro combustion, Micro propulsion, Particle delivery systems 등과 같은 다양한 공학응용분야에서 사용 되고 있다. Micro shock tube 에서 일어나는 유동 특성은 아주 작은 레이놀즈수 와 높은 누센수의 영향으로 인해 잘 알려진 기존의 macro shock tube 유동 특성과 상당한 차이가 나타난다. 또한 기존의 많은 shock tube의 순간적 과정으로 간주되는 격막파막 과정은 micro shock tube의 격막 근처의 유동장과 충격파 형성을 결정하는 중요한 요인이 될 것이다. 본 논문에서는 micro shock tube를 모사하기 위해 축 대칭, Maxwell's 슬립속도 조건과 온도 변화 경계 조건을 적용하여 수치 해석을 수행 하였다. 또한 유동장과 충격파 형성에 대한 유한 파막 과정의 영향을 자세히 조사 하였고, 결과로부터 충격파 강도는 micro shock tube를 통해 전파됨에 따라 급격히 감소하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권5호
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• pp.552-567
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• 2017

The floating crane vessel in waves gives rise to the motion of the lifted object which is connected to the hoisting wire. The dynamic tension induced by the lifted object also affects the motion responses of the floating crane vessel in return. In this study, coupled motion responses of a floating crane vessel and a lifted subsea manifold during deep-water installation operations were investigated by both experiments and numerical calculations. A series of model tests for the deep-water lifting operation were performed at Ocean Engineering Basin of KRISO. For the model test, the vessel with a crane control system and a typical subsea manifold were examined. To validate the experimental results, a frequency-domain motion analysis method is applied. The coupled motion equations of the crane vessel and the lifted object are solved in the frequency domain with an additional linear stiffness matrix due to the hoisting wire. The hydrodynamic coefficients of the lifted object, which is a significant factor to affect the coupled dynamics, are estimated based on the perforation value of the structure and the CFD results. The discussions were made on three main points. First, the motion characteristics of the lifted object as well as the crane vessel were studied by comparing the calculation results. Second, the dynamic tension of the hoisting wire were evaluated under the various wave conditions. Final discussion was made on the effect of passive heave compensator on the motion and tension responses.

• 설비공학논문집
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• 제17권3호
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• pp.268-276
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• 2005

The aim of this paper is to suggest one efficient method for the various requirements of performance during the process designing and producing an impeller. The study considers that the revisions of a pitch angle of an impeller at an axial turbo fan affect an air flow rates and a static pressure rise. The axial turbo fan specified with the 250 Pa maximum static pressure and 1300 CMH fan air flow rates was tested and analyzed by CFD. The Numerical results show that the air flow rates are calculated to 1,175 CMH, 1,223 CMH, 1,270 CMH, 1,340 CMH and 800 CMH in cases that the pitch angles are $44^{\circ},\;49^{\circ},\;54^{\circ},\;59^{\circ},\;and\;64^{\circ}$ respectively. Also the static pressure rises are shown to 108 Pa, 122Pa, 141 Pa, 188 Pa and 63 Pa at the same cases. The air flow rate is increased linearly according to the changes of the pitch angle from $44^{\circ}\;to\;59^{\circ}$ and the maximum air flow rate passing the impeller is increased to $13\%$ over at the case of $59^{\circ}$ pitch angle compared with the reference case of $54^{\circ}$ pitch angle. The static pressure rise is increased linearly according to the changes of the pitch angle from $44^{\circ}\;to\;54^{\circ}$, too. The static pressure rise at the $59^{\circ}$ pitch angle is increased to $33\%$ over compared with the $54^{\circ}$ pitch angle. The result shows that the revisions of pitch angle make the static pressure rise increase widely. However the air flow rates and the static pressure rise at the $64^{\circ}$ pitch angle are suddenly decreased because of over-changed pitch angle.

• 설비공학논문집
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• 제30권3호
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• pp.123-129
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• 2018

In this study, CFD is used to compare and analyze the flow characteristics using reflected pressure wave during the intersection of two trains in straight tunnel. Two tunnels of different lengths; 600 m and 3,400 m were designed and numerical analysis of the flow characteristics of two tunnels carried out by setting the crossing state of the two trains at a constant velocity of 27 m/s form the center of the tunnel. The simulation model was designed using the actual tunnel and subway dimensions The train motion was achieved by using the moving mesh method. For the numerical analysis, $k-{\omega}$ standard turbulence model and an ideal gas were used to set the flow conditions of three-dimensional, compressible and unsteady state. In the analysis results, it was observed that the inside of the long tunnel without interference of the reflected pressure wave was maintained at a pressure lower than the atmospheric pressure and that the flow direction was determined by the pressure gradient and shear flow. On the other hand, the flow velocity in the short tunnel was faster and the pressure fluctuation was noted to have increased due to the reflected pressure wave, with more vortices formed. In addition, the flow velocity was noted to have changed more irregularly.

• 한국화재소방학회논문지
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• 제23권5호
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• pp.110-116
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• 2009

본 연구는 Double Skin System의 화재 전파 위험성을 전산유체역학모델인 FDS를 이용하여 평가하였다. 화재모델링을 구현하기 위해 오피스 용도의 단위 구획공간을 화재지역으로 선정하였으며, 화재시나리오는 외창으로의 연소확대 위험 분석을 위하여 일반적으로 많이 설치되는 시스템조건들을 Case로 선정하여 분석하였다. 본 연구의 목적은 일반적으로 많이 사용되는 Double Skin System의 설치 간격에 따른 건물상층부로의 화재확대 위험성을 평가하고, 이에 따른 방화대책 등을 수립하는데 있다. 해석 결과, 더블스킨 중간층 간격이 넓을수록 상부층으로 연소확대 영향이 작은 것을 확인할 수 있었으며, 중간층 간격이 1m 미만인 경우는 발화층 상부 2개층으로 연소확대가 예상되므로 층간연소 확대 방지 시스템이 요구됨을 알 수 있다.

• 한국화재소방학회논문지
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• 제33권4호
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• pp.77-82
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• 2019

소화설비는 예상치 못한 화재를 진압하는 설비이며, 방호대상과 장소에 따라 부합한 소화약제를 사용해야한다. 이 중 가스계 소화설비는 물에 취약한 전자장비 등을 방호하기 위하여 사용되는데, 이 때문에 화학적 반응이 없는 불활성 기체가 주로 적용된다. 하지만 최근 전자장비들의 고집적화로 인하여 가스계 소화설비로부터 발생하는 소음이 전자장비에 손상을 주는 사례가 대두되고 있다. 이에 본 연구에서는 가스계 소화설비를 개선하고자, 노즐 수축각에 따른 유동소음을 수치적으로 계산 및 분석하였다. ANSYS FLUENT ver. 18.1을 사용하여 수치해석을 수행하였으며, 스월 분포를 고찰하여 유동소음에 대한 원인을 분석하였다. 개선된 모델은 기본 모델 대비 약 6 dB가 감소된 것을 확인하였으며, 이는 가스계 소화시스템 노즐 수축각이 방출소음 저감에 영향력 있는 인자임을 확인하였다.

• 한국자동차공학회논문집
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• 제12권6호
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• pp.111-118
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• 2004

The work presented in this paper concerns the aerodynamic characteristics and compression wave generated in a tunnel when a high speed train enters it. A large number of solutions have been proposed to reduce the amplitude of the pressure gradient in tunnels and some of the most efficient solutions consist of (a) addition ofa blind hood, (b) addition of inclined part at the entrance, and (c) holes in the ceiling of the tunnel. These are numerically studied by using the three-dimensional unsteady compressible Euler equation solver with ALE, CFD code, based on FEM method. Computational results showed that the smaller inclined angle leads to the lower pressure gradient of compression wave front. This study indicated that the most efficient slant angle is in the range from $30^{\circ}$ to $50^{\circ}$. The maximum pressure gradient is reduced by $26.81\%$ for the inclined angle of $30^{\circ}$ as compared to vertical entry. Results also showed that maximum pressure gradient can be reduced by $15.94\%$ in blind hood entry as compared to $30^{\circ}$ inclined tunnel entry. Furthermore, the present analysis showed that inclined slant angle has little effect on aerodynamic drag. Comparison of the pressure gradient between the inclined tunnel hood and the vertical entry with air vent holes indicated that the optimum inclined tunnel hood is much more effective way in reducing pressure gradient and increasing the pressure rise time.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.833-837
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• 2010

본 연구는 최소 압력 모사로 엔진 배기가스를 배출시키기 위한 최적 이젝터 크기를 결정하기 위한 것을 목적으로 한다. 실험 챔버로 유입되는 2차 냉각 공기는 유량제어 밸브들과 진공펌프가 장착된 배출구를 통해 엔진배기가스는 분리되어 배출된다. 기존 고도시험 장치와 달리, 본 연구에 제안한 형상은 기존 이젝터의 압력 회복을 개선한 좀 더 작은 포획 면적을 가진 배기 이젝트를 사용하면 가스에 스텔링 챔버로 부터 20% 냉각 공기를 부가하여 배출시키도록 크기가 정해진다. 제안된 형상은 벨마우스 이젝터와 엔진배기 출구의 면적비가 이론적으로 약 1.2를 갖는다. 제안된 형상의 혼합 공기 모사결과에 따르면 큰 에너지는 기존 시스템 비해 좀 더 개선된 압력 회복과 감소된 전력 소모를 같음을 확인하였다.

• 대한기계학회논문집B
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• 제39권5호
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• pp.405-414
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• 2015

유체이송 기술은 마이크로 유체시스템 개발에서 핵심문제로 인식되고 있다. 최근 명(2014)은 외부 동력을 사용하지 않고 액적을 이동시킬 수 있는 새로운 개념을 제안하고, 초기에 반원통형 형상을 가지는 가상의 2차원 액적에 대한 수치해석을 통해 이 개념이 성립함을 보였다. 본 논문에서는 친수성/소수성 표면위에서 초기 3차원 반구형상의 실제 물 액적이 가지는 움직임을 상용소프트웨어 Fluent의 VOF 방법을 사용하여 수치해석하였다. 해석결과는 명(2014)의 2차원 수치해석 결과와 비교하였으며, 또한 물 액적이송의 메커니즘을 시간에 따른 액적형상과 액적 내부의 운동에너지, 중력에너지, 표면자유에너지 및 압력에너지의 수치해석 결과를 통해 규명하였다.