• International Journal of Aeronautical and Space Sciences
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• 제18권2호
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• pp.279-289
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• 2017

In this study, a series of conjugate heat transfer (CHT) analyses are conducted for a stage of a fully cooled high-pressure turbine (HPT) at elevated levels of free stream turbulence (Tu = 5% and 25.7%). The goal of the analyses is to investigate the influence of high turbulence intensity on the fluid-thermal characteristics of a nozzle guide vane (NGV). The turbine inlet temperature is defined by considering a typical radial temperature distribution factor (RTDF). The Unsteady Reynolds Average Navier-Stokes (URANS) CHT simulations are carried out using CFX 15.0, a commercial CFD package. The presented CFD modeling approach for high turbulence intensity is verified with the experimental data from two types of NASA C3X NGVs with films. The computation grid is generated for both the fluid and solid domains. The fluid domain grid is created using a tetrahedral grid system with prism layers because of its complex geometry, and the solid domain grid is composed of only tetrahedral elements. The analytical results are compared to understand the effect of turbulence on flow characteristics and metal temperature distributions. The results obtained in this study provide useful insights on the effects of high free stream turbulence and unsteadiness. The results also lead to the proposal of meaningful turbine design guidelines.

• 농촌계획
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• 제1권1호
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• pp.65-74
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• 1995

As a initial methodological approach to rational land use planning in the county-level area, three types of land suitability classification techniques were examined from the viewpoint of their practical applicability through the case study of Seungju-gun area, Chonnam-province, Korea : major factors' criteria(method I ), principal component analysis( I ), and local monitoring( R( ). Each method has its strong and weak points as shown in Tab.-5. Therefore, when its practical application, there seem to be wide-range methodological selectivities from exclusive use of the best one to intermethodological combination of related ones In the beginning stage, intermethodological combination of all three types were tried to formulate the best solution possible. However, because of reliability problem of method R accrued from non- uniformity of evaluators'quality, only two methods( 1 , E ) were combined into a new evaluation method The applied results of the new combined method to case study area are shown in Fig.-2, 3 and 4.

• 한국전산유체공학회지
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• 제17권1호
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• pp.61-69
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• 2012

In this paper, the shape design process is briefly discussed emphasizing the use of topology optimization in the conceptual design stage. The basic idea is to view feasible domains for sensitivity region concepts. In this method, the main process consists of two steps: as the design moves further inside the feasible domain using Taguchi method, and thus becoming more successful topology optimization, the sensitivity region becomes larger. In designing a double-eccentric butterfly valve, related to hydrodynamic performance and disc structure, are discussed where the use of topology optimization has proven to dramatically improve an existing design and significantly decrease the development time of a shape design. CFD analysis results demonstrate the validity of this approach.

• 한국정밀공학회지
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• 제27권3호
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• pp.41-49
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• 2010

Two promising control candidates have been selected to test the sinusoidal reference tracking performance for a brush-type polishing machine having strong nonlinearities and disturbances. The controlled target system is an oscillating mechanism consisting of a common positioning stage of one degree-of-freedom with a screw and a ball nut driven by a servo motor those can be obtained commercially. Beside the strong nonlinearity such as stick-slip friction, the periodic contact of the polishing brush and the work piece adds an external disturbance. Selected control candidates are a Sliding Mode Control (SMC) and a variant of a feedback linearization control called Smooth Robust Nonlinear Control (SRNC). A SMC and SRNC are selected since they have good theoretical backgrounds, are suitable to be implemented in a digital environment and show good disturbance and modeling uncertainty rejection performance. It should be also noted that SRNC has a nobel approach in that it uses the position information to compensate the stickslip friction. For both controllers analytical and experimental studies have been conducted to show control design approaches and to compare the performance against the strong nonlinearity and the disturbances.

• 한국해양공학회지
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• 제34권4호
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• pp.237-244
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• 2020

In this study, we investigate surge force, heave force, and pitch moment, which are vertical plane hydrodynamics acting on Manta-type unmanned underwater vehicles (UUVs), using a model test and computational fluid dynamics (CFD) simulation. Assessing the maneuvering hydrodynamic characteristic of an underwater glider in the initial design stage is crucial. Although a model test is the best approach for obtaining the maneuvering hydrodynamic derivatives for underwater vehicles, numerical methods, such as Reynolds averaged Navier-Stokes (RANS) equations, have been used owing to their efficiency in terms of time and cost. Therefore, we conducted an RANS-based CFD calculation and a model test for Manta-type UUVs. In addition, we conducted a validation study through a comparison with a model test conducted at a circular water channel (CWC) in Korea Maritime & Ocean University Furthermore, two RANS solvers (Star-CCM+ and OpenFOAM) were used and compared. Finally, the maneuvering hydrodynamic forces obtained from the static drift and resistance tests for a Manta-type UUV were presented.

• 한국지반공학회지:지반
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• 제12권2호
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• pp.43-58
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• 1996

지하구조물에 대한 설계 및 시공기술의 많은 발전에도 불구하고 아직도 상당부분 그간의 경험에 의존하며, 또한 많은 불확정성 요소들을 내포하고 있다. 그 중 가장 대표되는 것이 지반계수로서, 이를 설계단계에서 정확히 산정하는 데는 많은 어려움이 따른다. 본 논문의 주된 목적은 지하공간의 설계와 시공을 유기적으로 연결할 수 있는 지반공학적 접근의 일환으로 최적의 지반계수를 산정하는 데 있다. 이를 위하여 초기예측치와 계측치로부터 예측된 간을 합리적으로 조합할 수 있는 Extended Bayesian Method(EBM)을 적용하였으며, 이를 유한요소해석으로부터 구할 수 있도록 하였다. 또한 부산 지하철 현장과 캐나다의 Darlington취수터널에 대한 예제해석을 수행하여 제안된 방법의 효용성을 검증하였다.

• 산경연구논집
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• 제11권3호
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• pp.7-17
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• 2020

Purpose: This study reexamines the test on the pricing of accruals quality. Theory suggests that information risk is a priced risk factor. Using accruals quality as the proxy for information risk, researchers have tested the pricing of information risk. The results are inconsistent potentially because of the information shock in the realized returns that are used as the proxy for expected returns. Based on this argument, this study revisits this issue excluding information-shock-free measure of expected returns. Research design, data and methodology: This study estimates expected returns using the vector autoregression model. This method extracts information shocks more thoroughly than the methods in prior studies; therefore, the concern regarding information shock is minimized. As risk premiums are larger in recession periods than in expansion periods, recession and expansion subsamples were used to confirm the robustness of the main findings. For the pricing test, this study uses two-stage cross-sectional regression. Results: Empirical results find evidence that accruals quality is a priced risk factor. Furthermore, this study finds that the pricing of accruals quality is observed only in recession periods. Conclusions: This study supports the argument that accruals quality, as well as the pricing of information risk, is a priced risk factor.

• 정보처리학회논문지D
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• 제18D권6호
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• pp.443-450
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• 2011

모델 중심 컴포넌트 기반 개발 방법은 개발 대상 시스템을 하나의 추상컴포넌트로 보고, 재귀적인 컴포넌트의 분화(decomposition)와 정제(refinement) 과정을 통하여 물리적인 컴포넌트를 도출해내는 하향식 개발방식이다. 본 연구에서는 모델 기반 컴포넌트 개발기법을 근간으로 한 컴포넌트 정제 과정에서 정제 전 후의 추상컴포넌트들 간의 행위 일관성을 정형분석하기 위한 모델 변환기를 개발하였다. 이 모델변환기는 컴포넌트의 분화와 정제 전 과정에 걸쳐 사용되어 정제 전 후 컴포넌트 간의 상호작용 오류로 인한 잠재적인 결함을 조기에 발견하고 해결하는데 기여할 수 있다. 본 논문은 추상컴포넌트의 각 구성요소들을 정형검증기 SPIN의 구성요소로 변환하기 위해 사용된 변환방법들과 변환기의 구성요소들을 소개한다. 개발된 변환기는 자동차 거울조종시스템, 무선센서네트워크를 위한 운영체제 등의 사례연구에 적용되어 그 효용성을 입증하였다.

• Ocean and Polar Research
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• 제23권2호
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• pp.195-203
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• 2001

A fine-grid (3 km ${\times}$ 3 km), three-dimensional nowcast system of sea levels, currents, temperature, and salinity is being developed for the Taiwan Strait. The project takes a balanced approach relying equally on models and observations, will have the capacity of real-time data assimilation, and is aimed at both practical and scientific applications. To determine boundary conditions and verify model results, eight coastal tide-gauge stations were first established along both sides of the strait. Strait-wide hydrographic surveys were conducted by research vessels. Currents are being measured using bottom-mounted ADCP moorings in a meridional deep channel off southwest Taiwan and along a traverse section in the central part of the strait. In addition to a fine-resolution three-dimensional model of the Taiwan Strait, an adjoint model and a larger-domain two-dimensional model were used to better determine boundary conditions in the northern and southern boundaries of the strait. In the first stage of model development, barotropic tides were successfully simulated in a hindcast mode. The protocol product has been released to general public, including government agencies, universities and general users.

• Journal of Chest Surgery
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• 제5권1호
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• pp.29-34
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• 1972

Interventricular Septal Defect is probably the most common congenital cardiac lesion. Despite rapid technical advances and increasing surgical experience the risk of surgical intervention for correction of Ventricular Septal Defect in infants with pulmonary hypertension remains formidable. Since Sirak et al [1959] reported a succesful case of two stage approach to their surgical correction, it has led to a policy of primary palliation,followed by complete correction as a secondary procedure, after age 3 to 4 years. Most surgeon prefer to perform complete correction of Ventricular Septal Defect when body weight exceeds 30 Lbs. and before development of so-called Eisenmengers complex, for the good postoperative results. Authors report 2 cases of Ventricular Septal Defect with pulmonary hupertenslon, who was underwent pulmonary artery banding as a palliative procedure in the Department of Surgery,Severance Hospital Yonsei University. Case 1:4 year old male, initially a complete correction of Ventricular Septal Defect was attempted by the help of mild hypothermia and extracorporeal circulation. During the procedure of a construction of an extracorporeal by- pass, a sudden cardiac arrest developed. After resuscitation of the heart,pulmonary artery banding was performed as a palliation. On the first postoperative day the patient developed generalized tonic convulsion, cyanosis, vomiting and eventually shock. Patient discharged home after a full recovery. Case 2.: 9 month old female, the pulmonary artery constricted with Teflon patch successfully. After the patients first postoperative day several cyanotic spells developed followed by 3 cardiac arrests. This repeated until when she expired with respiratory failure.