• Korean Journal of Radiology
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• 제22권11호
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• pp.1834-1840
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• 2021

Objective: To analyze the computational fluid dynamics (CFD) of femoral artery pseudoaneurysm (FAP), identify a suitable location and timing for percutaneous thrombin injection (PTI) based on this analysis, and report our clinical experience with the procedure. Materials and Methods: CFD can be used to analyze the hemodynamics of the human body. An analysis using CFD recommended that the suitable location of the needle tip for PTI is at the center of the aneurysm sac and the optimal timing for starting PTI is during the early inflow phase of blood into the sac. Since 2011, seven patients (three male and four female; median age, 60 years [range, 43-75 years]) with FAP were treated with PTI based on the devised suitable location and time. Prior to the procedure, color Doppler ultrasonography was performed to determine the location and timing of the thrombin injection. Results: The technical success rate of the PTI was 100%. The amount of thrombin used for the procedure ranged from 200 IU to 1000 IU (median, 500 IU). None of the patients experienced any symptoms or signs of embolic complications during the procedure. Follow-up CT images did not reveal any embolism in the lower extremities and showed complete thrombosis of the pseudoaneurysm. Conclusion: Based on our study of CFD, PTI administered centrally in the FAP during early inflow, as seen on color Doppler, can be an effective technique.

• Nuclear Engineering and Technology
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• 제44권3호
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• pp.283-296
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• 2012

The natural convection in a horizontal enclosure heated from the bottom wall, cooled at the top wall, and having a square adiabatic body in the center is studied. Three different Prandtl numbers (0.01, 0.7 and 7) are considered for the investigation of the effect of the Prandtl number on natural convection. Adiabatic boundary conditions are employed for the side walls. A two-dimensional solution for unsteady natural convection is obtained, using an accurate and efficient Chebyshev spectral methodology for different Rayleigh numbers varying over the range of $10_3$ to $10_6$. It had been experimentally reported that the heat transfer mode becomes oscillatory when Pr is out of a specific Pr band beyond the critical Ra. In this study, we reproduced this phenomenon numerically. It was found that when Ra=$10_6$, only the case for intermediate Pr (=0.7) reached a non-changing steady state and the low and high Pr number cases (Pr=0.01 and 7) showed a periodically oscillatory fashion hydrodynamically and thermally. The variation of time- and surface-averaged Nusselt numbers on the hot and cold walls for different Rayleigh numbers and Prandtl numbers are presented to show the overall heat transfer characteristics in the system. Further, the isotherms and streamline distributions are presented in detail to compare the physics related to their thermal behavior.

• 한국자동차공학회논문집
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• 제7권9호
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• pp.36-47
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• 1999

Three-way catalyst converter, cleaning up the exhaust gas contamination of SI engine, has the best efficiency when A/F ratio is near the stoichiometry . The feedback control using oxygen sensors in the exhaust manifold has limits caused by the system delays. So the accurate measurement of air flow rate to an engine is essential to control the fuel injection rate especially on transient condition like the rapid throttle opening and closing. To measure the rapid change of flow rates. the air flow meter for the engine requires quick response, flow reversal detection, and linearity . Tjhe proposed integration type air flow meter (IFM), composed of an ultrasonic flow meter with an integration circuit, has significantly improved the measurement accuracy of air mass inducted through the throttle body. The proposed control method estimated the air mass at the cylinder port using the measured air mass at the throttle . For the fuel dynamic model, the two constant fuel model is introduced . The control parameters from air and fuel dynamics are tuned to minimize the excursion of the air fuel ratio. As a result A/F ratio excursion can be reduced within 5% when throttle rapidly opens and closes at the various engine conditions.

• 한국산학기술학회논문지
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• 제7권3호
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• pp.308-313
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• 2006

포탄의 탄착점은 대포의 형상, 제작공차, 제어시스템 그리고 발사체의 제작공차 등 여러 변수의 함수이다. 본 논문에서는 포탄의 탄두를 본체와 분리, 움직임이 가능한 형태로 부착하여 탄착점의 정확도를 향상시키는 가능성에 대하여 검토하였다. 기존의 포탄이 갖는 6 개의 자유도에 탄두의 3 개의 자유도를 더한 9 자유도의 동역학 식을 유도하였고 시뮬레이션을 통하여 가변탄두를 갖는 발사체가 탄두부분의 피치(pitch)와 요(yaw) 회전운동을 통하여 발사 초기의 불확실성을 흡수할 수 있음을 확인하였다.

• Journal of Astronomy and Space Sciences
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• 제15권1호
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• pp.251-260
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• 1998

통신위성의 임무 및 위성 체 동역 화 해석 시스템은 서브 시스템별로 몸체를 분류하고 이들 몸체각각의 운동뿐 아니라 위성 체 전체의 운동을 고려하여 정해진 임무에 대하여 위성 체의 자세제어와 궤도조정을 할 수 있도록 다 몸체 동역 학 모델 링 방법을 채택하였다. 따라서 본 시스템은 어느 특정한 통신위성에만 적용되는 것이 아니라 일반적인 통신위성에 적용할 수 있는 통신위성 임무 및 위성 체 동역 학 해석 시스템이다. 시뮬레이션 결과를 2차원 그래픽 및 3차원 동화상으로 파악할 수 있도록 하였으며 또한 사용자 친화방식을 채택하여 누구든지 본 시스템을 쉽게 사용할 수 있도록 하였다. 개발된 시스템의 성능을 검증하기 위하여 현재 운용 중에 있는 정지궤도 통신위성인 무궁화위성 1,2호의 시나리오에 대하여 시뮬레이션을 수행하였다.

• Wind and Structures
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• 제17권2호
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• pp.203-225
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• 2013

An analysis framework for vehicle-bridge dynamic interaction system under turbulent wind is proposed based on the relevant theory of wind engineering and dynamics. Considering the fluctuating properties of wind field, the stochastic wind velocity time history is simulated by the Auto-Regressive method in terms of power spectral density function of wind field. The bridge is represented by three-dimensional finite element model and the vehicle by a multi-rigid-body system connected by springs and dashpots. The detailed calculation formulas of unsteady aerodynamic forces on bridge and vehicle are derived. In addition, the form selection of wind barriers, which are applied as the windbreak measures of newly-built railways in northwest China, is studied based on the suggested evaluation index, and the suitable values about height and porosity rate of wind barriers are studied. By taking a multi-span simply-supported box-girder bridge as a case study, the dynamic response of the bridge and the running safety indices of the train traveling on the bridge with and without wind barriers are calculated. The limit values of train speed with respect to different wind velocities are proposed according to the allowance values in the design code.

• 한국정밀공학회지
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• 제32권5호
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• pp.491-496
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• 2015

Electric handbike can be easily detachable to various sizes of manual wheelchair and the elderly and people with disabilities can use them easily. Therefore, connectors used for coupling between the handbike and manual wheelchair must secure structural stability for occupant safety. However, related research is rare. The aim of this study is to find the connector with highly structural stability by comparing static and dynamic mechanical characteristics among three typical connectors(a snatch lock, a slide latch, and a fastener) by computational simulations. To perform static and dynamic simulation, we referred to durability test based on Korean Standards and then calculated mechanical stresses in connectors. The results showed that the snatch lock addressed the lowest von-mises stress under the same mechanical condition. Therefore when using the combination of a handbike and a wheelchair, we concluded that the snatch lock is considered as the structurally stable connector to structural stability and usability.

• 한국군사과학기술학회지
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• 제20권3호
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• pp.405-412
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• 2017

In the present study, two phase flows around a projectile vertically launched from an underwater platform have been numerically investigated by using a three dimensional multi-phase RANS flow solver based on pseudo-compressibility and a homogeneous mixture model on unstructured meshes. The relative motion between the platform and projectile was described by six degrees of freedom(6DOF) equations of motion with Euler angles and a chimera technique. The propulsive power of the projectile was modeled as the fluid force acting on the lower surface of the body by the compressed air emitted from the platform. Qualitative analysis was conducted for the time history of vapor volume fraction distributions. Uncorking pressure around the projectile and platform was analyzed to predict impact force acting on the surfaces. The results of 6DOF analysis presented similar tendency with the surficial pressure distributions.

• International Journal of Aeronautical and Space Sciences
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• 제14권4호
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• pp.356-368
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• 2013

The Korea Aerospace Research Institute plans to launch a lunar module by 2025, and so is carrying out a preliminary study. Landing stability on the lunar surface is a key design factor of a lunar module. In this paper, a 1/6 scale model of a lunar module is investigated, for its landing stability on non-level surfaces. The lunar module has four tripod legs, with aluminum honeycomb shock absorbers in each leg strut. ADAMS$^{TM}$, the most widely used multi-body dynamics and motion analysis software, is used to simulate the module's lunar landing. Three types of dampers in the struts (rigid, viscous, and aluminum honeycomb dampers), and two types of lunar surfaces (rigid and elastic) are considered. The Sforce function is adopted, to model the aluminum honeycomb dampers. Details on the modeling and analysis of the landing stability of the 1/6 scale lunar module and the simulation results are provided in this paper.

• 한국철도학회논문집
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• 제10권4호
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• pp.444-450
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• 2007

The bi-modal tram guided by the magnetic guidance system has two car-bodies and three axles. Each axle of the vehicle has an independent suspension to lower the floor of the car and improve ride quality. The turning radius of the vehicle may increase as a consequence of the long wheel base. Therefore, the vehicle is equipped with the All-Wheel-Steering(AWS) system for safe driving on a curved road. Front and rear axles should be steered in opposite directions, which means a negative mode, to minimize the turning radius. On the other hand, they also should be steered in the same direction, which means a positive mode, for the stopping mode. Moreover, only the front axle is steered for stability of the vehicle upon high-speed driving. In summary, steering angles and directions of the each axle should be changed according to the driving environment and steering mode. This paper proposes an appropriate AWS control algorithm for stable driving of the bi-modal tram. Furthermore, a multi-body model of the vehicle is simulated to verify the suitability of the algorithm. This model can also analyze the different dynamic characteristics between 2WS and AWS.