• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.553-558
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• 2015

교량의 주탑, 초고층빌딩과 같이 세장비가 큰 대형구조물의 경우 풍하중에 취약한 특성을 지니고 있어서 바람에 의해 직각 방향으로 발산 진동하는 갤로핑(galloping) 현상이 발생하게 된다. 구조물의 진동을 억제하려는 방안으로 단면 형상에 변화를 주어 공기역학적 불안정성을 감소시키는 방법이 사용되고 있다. 본 논문에서는 Edison_CFD를 이용하여 모서리 절단부의 비율과 받음각에 따른 공기력 특성에 대한 전산해석을 수행하였다.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.580-584
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• 2015

수중 식생, 해양 구조물과 같은 복합 구조에 대하여 본 연구에서는 각각의 구조물을 원형 실린더로 가정하고, 구조물 다발 하나를 원형 실린더 패치로 가정하였다. 패치들의 배열을 계산할시 기존의 방법으로는 많은 격자가 필요하기 때문에 좀 더 효율적으로 외력의 특성을 파악할 방법을 살펴보았다. 계산 영역 내에서 평균화된 정보들을 통해서 이용하여 항력계수와 양력계수와 속도, 압력의 관계를 알아내는 모델링 방법을 해보았다.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.575-579
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• 2015

본 연구에서는 스파이럴 보강을 한 원형 실린더 주위의 유동를 분석하였다. 이를 위해 스파이럴 보강 부분을 사각형 부착물로 분리해서 나타내었다. EDISON_CFD의 가상 경계법을 이용하여 원형 실린더와 부착물 주위의 유동 현상을 해석하였다. 부착물의 두께와 각도를 다르게 하여 각각의 공력 계수와 총 합력을 구하고 이에 따른 특성을 분석하였다.

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.614-618
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• 2016

본 논문은 EDISON_CFD를 활용하여 화성에서 운용 가능한 풍력터빈에 대해 실험 및 개선 설계하였다. 본 연구에서는 화성의 중력 및 공기밀도 등 화성의 환경 데이터를 적용함으로써 풍력터빈의 형상을 새롭게 설계 하였다. 개선 설계는 기존의 풍력발전기 형상을 변형시키며 해석을 진행하였으며, 받음각과 형상에 따라 생성되는 토크를 확인하였다. 개선설계한 풍력터빈 모델은 단위 미터 당 약 8 W의 전력생산이 가능한 것을 확인하였다.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.8
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• pp.76-82
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• 1999

The object of this study is to find new evalution index for in-cylinder flow characteristics insteady of current swirl, tumble coefficient using steady flow test rig on intake port system. To this end, port flow rig test was conducted on DOHC head varying intake valve lift respectively. Finally combination angular coefficient and inclination angle were introduced as new evaluation index for in-cylinder angular flow characteristics.

• Ecology and Resilient Infrastructure
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• v.5 no.4
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• pp.246-256
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• 2018

In order to analyze hydraulic characteristics of discharge coefficient, hydraulic jump height, and hydraulic jump length, accompanied sediment transport, in the under-flow type vertical lift gate, the hydraulic model experiment and dimensional analysis were performed. The correlations between Froude number and hydraulic characteristics were schematized according to the presence and absence of sediment transport; the correlation of hydraulic characteristics and non-dimensional parameters was analyzed and multiple regression formulae were developed. In the hydraulic characteristics accompanied the sediment transport, by identifying the aspect different from the case that the sediment transport is absent, we verified that it is necessary to introduce variables that can express the characteristics of sediment transport. The multiple regression equations were suggested and each determination coefficient appeared high as 0.749 for discharge coefficient, 0.896 for hydraulic jump height, and 0.955 for hydraulic jump length. In order to evaluate the applicability of the developed hydraulic characteristic equations, 95% prediction interval analysis was conducted on the measured and the calculated by regression equations, and it was determined that NSE (Nash-Sutcliffe Efficiency), RMSE (root mean square), and MAPE (mean absolute percentage error) are appropriate, for the accuracy analysis related to the prediction on hydraulic characteristics of discharge coefficient, hydraulic jump height and length.

• Wind and Structures
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• v.25 no.5
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• pp.475-492
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• 2017

Inclined and yawed circular cylinder is an essential element in the widespread range of structures. As one of the applications, cables on bridges were reported to have the possibility of suffering a kind of large amplitude vibration called dry galloping. In order to have a detailed understanding of the aerodynamics related to dry galloping, this study carried out a set of wind tunnel tests for the inclined and yawed circular cylinders. The aerodynamic coefficients of circular cylinders with three surface configurations, including smooth, dimpled pattern and helical fillet are tested using the force balance under a wide range of inclination and yaw angles in the wind tunnel. The Reynolds number ranges from $2{\times}10^5$ to $7{\times}10^5$ during the test. The influence of turbulence intensity on the drag and lift coefficients is corrected. The effects of inclination angle yaw angle and surface configurations on the aerodynamic coefficients are discussed. Adopting the existed the quasi-steady model, the nondimensional aerodynamic damping parameters for the cylinders with three kinds of surface configurations are evaluated. It is found that surface with helical fillet or dimpled pattern have the potential to suppress the dry galloping, while the latter one is more effective.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.3
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• pp.285-295
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• 2016

A contact strip shape of a high speed train pantograph system was optimized with CFD to increase the aerodynamic performance and stability of contact force, and the results were validated by a wind tunnel test. For design of the optimal contact strip shape, a Kriging model and genetic algorithm were used to ensure the global search of the optimal point and reduce the computational cost. To enhance the performance and robustness of the contact strip for high speed pantograph, the drag coefficient and the fluctuation of the lift coefficient along the angle of attack were selected as design objectives. Aerodynamic forces were measured by a load cell and HWA (Hot Wire Anemometer) was used to measure the Strouhal number of wake flow. PIV (Particle Image Velocimetry) was adopted to visualize the flow fields. The optimized contact strip shape was shown a lower drag with smaller fluctuation of vertical lift force than the general shaped contact strip. And the acoustic noise source strength of the optimized contact strip was also reduced. Finally, the reduction amount of drag and noise was assessed when the optimized contact strip was applied to three dimensional pantograph system.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.447-449
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• 2004

The purpose of this study is measured surface acoustic wave(SAW) characteristics to confirm utilization possibility as SAW sensor using new Pb(Mg$_{1}$3/Nb$_{2}$3/) $O_3$-PbTiO$_3$ (PMN-PT) piezoelectric substrate. We have tried to see if the material can be practically available as a new surface acoustic wave (SAW) biosensor to detect protein. The experimental results clarified that the frequency filtering of the central frequency of the PMN-PT substrate is a superior result to that of the LiTaO$_3$ (LT) substrate, but the result was not completely satisfactory. We know there is a problem in the design of inter-digital transducer (IDT) pattern. The waves transferred through the input terminal forms SAW which is sure to be transferred to the direction of the output terminal and the backward direction of the input terminal. This reflected wave is reiterated with SAW, which is transferred to the output direction, and so the frequency filtering gives a not good result. The electromechanical coupling coefficient of the PMN-PT substrate is excellent, and we can use it as a SAW sensor, in the near future, provided that there will be a new IDT design to increase the frequency filtering.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.921-927
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• 2001

Steady flow bench test is a practical, powerful and widely used test in most engine manufacturers to give a design concept of a new engine. In order to use steady data as a performance index, it is necessary to build some database, which can correlate the port characteristics with engine data. However, it is very hard to investigate all port and valve shapes with experimental tools. The steady flow scheme is relatively simple and its results are bulk ones such as flow rate and momentum of flow. Therefore a CFD code can be easily applied to the port evaluation. In this study, the steady flow test was simulated through two and three-dimensional analysis on intake port design for comparing with experimental data and confirming the feasibility of applying analytic method. For this purpose, the effect of valve curvature on flow rate was estimated by a CFD code. There results were compared with those of real steady flow tests. As a result, the 2-D analysis described the phenomena qualitatively well, and also the results of 3-D analysis were almost consistent with experimental data.