• Wind and Structures
• /
• 제20권5호
• /
• pp.643-660
• /
• 2015

The wind tunnel test of large-scale sectional model and computational fluid dynamics (CFD) are employed for the purpose of studying the aerodynamic appendices and mechanism on suppression for the vortex-induced vibration (VIV). This paper takes the HongKong-Zhuhai-Macao Bridge as an example to conduct the wind tunnel test of large-scale sectional model. The results of wind tunnel test show that it is the crash barrier that induces the vertical VIV. CFD numerical simulation results show that the distance between the curb and crash barrier is not long enough to accelerate the flow velocity between them, resulting in an approximate stagnation region forming behind those two, where the continuous vortex-shedding occurs, giving rise to the vertical VIV in the end. According to the above, 3 types of wind fairing (trapezoidal, airfoil and smaller airfoil) are proposed to accelerate the flow velocity between the crash barrier and curb in order to avoid the continuous vortex-shedding. Both of the CFD numerical simulation and the velocity field measurement show that the flow velocity of all the measuring points in case of the section with airfoil wind fairing, can be increased greatly compared to the results of original section, and the energy is reduced considerably at the natural frequency, indicating that the wind fairing do accelerate the flow velocity behind the crash barrier. Wind tunnel tests in case of the sections with three different countermeasures mentioned above are conducted and the results compared with the original section show that all the three different countermeasures can be used to control VIV to varying degrees.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 1998년도 가을 학술발표회 논문집
• /
• pp.305-312
• /
• 1998

• 대한치과보철학회지
• /
• 제44권4호
• /
• pp.421-431
• /
• 2006

Statement of problem : Accurate impression is essential to success of implant prostheses. But there have been few studies about the accuracy of fixture-level impression technique in internal connection implant system. Purpose: This study evaluated the accuracy of splinted fixture-level impression technique using clinical methods and the effect of internal hex on fit of superstructure in internal connection implant system (Astra Tech). Material and method : Two metal master frameworks made from two abutments (Cast-to Abutment ST) each for parallel and divergent conditions and a corresponding. passively fitting, dental stone master cast with four future replicas (Fixture Replica ST) were fabricated. Ten dental stone casts were made with vinyl polysiloxane impressions from the master cast by acrylic resin splinted fixture-level impression technique. To evaluate the accuracy of impression technique, the fit of master frameworks for test models was evaluated using screw resistance test (SRT) and one-screw test. The results of SRT were recorded as SRT values from grade 1 to grade 5 by 1/4 turn. And to evaluate the effect of hex on fit of superstructure, the same tests were performed after removing hexes of master frameworks. Results: 1. There was only one case (2.5%) showing SRT value of test model below ade 2 in total before and after removing hexes of master frameworks. And, by removing hexes. SRT values decreased in only one test model (5%) and did not change in 17 test models (85%). 2. SRT values of the 1$^{st}$ screws were grade 2 in 80% of cases before, and grade 1 in 80% of cases after removing hexes. And, by removing hexes, SRT values decreased in 72.5% of cases. 3. SRT values of the 2$^{nd}$ screws were grade 3 in 85% of cases before, and grade 3 in 95% of cases after removing hexes. And, by removing hexes, SRT values did not change in 85% of cases. 4. There were only 2 cases regarded as acceptable fit by one-screw test, and SRT values of 2$^{nd}$ screws of both cases were grade 2. Conclusion. Within the limitations of this study, future-level impression of internal connection implant system is considered to obtain inaccurate working cast, even using acrylic resin splinted impression technique. And, it is considered to be unable improve the fit to remove the hexes of implant restoration.

• 한국정보과학회논문지:소프트웨어및응용
• /
• 제36권5호
• /
• pp.361-375
• /
• 2009

사전 제조된 컴포넌트들을 재사용하여 애플리케이션을 개발하는 컴포넌트 사용자의 관심사는 사용자의 요구사항에 따라 적절히 다른 컴포넌트들과 협동하는지 여부를 확인하는 것이다. 따라서 컴포넌트 기반 소프트웨어의 경우 개발 환경이 아닌 새로운 환경에서 소프트웨어를 구성하는 컴포넌트들이 잘 연동되는지를 테스트할 수 있는 상호운용성 테스트에 관련된 연구가 중요시되고 있다. 본 논문에서는 컴포넌트 기반 소프트웨어의 상호운용성 테스트를 위한 테스트 모델을 정의하고, 유스케이스 명세로부터 테스트 모델을 생성한 후 생성된 모델로부터 테스트 케이스를 생성하는 기법을 제안한다. 또한 테스트 모델로부터 테스트 시퀀스를 생성하는 프로시저를 구현한 도구를 소개한다.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2012년도 제38회 춘계학술대회논문집
• /
• pp.498-501
• /
• 2012

한국형발사체개발을 위하여 소형연소시험장을 개량하였다. 개량된 시험설비는 7톤급 연소기 개발에 활용될 예정이며, 이를 통해 획득한 자료와 시험평가 절차와 시험기법을 토대로 고성능 로켓엔진 개발에 활용될 것이다. 본 논문에서는 7톤급 축소형 연소기 시험을 위해 개량된 시험설비에 대해 기술하였다.

• 항공우주기술
• /
• 제4권1호
• /
• pp.39-44
• /
• 2005

로터의 성능 예측 검증을 위해 tilt rotor aeroacoustic model(TRAM)에 대한 3차원 CFD 해석을 수행하였고 로터 파워 효과에 의한 영향을 분석하기 위해 수치해석을 행하였다. 수치 기법은 multiple reference method(MRF)와 sliding mesh technique을 사용하였다. TRAM 실험치와 비교 결과 정지 비행시에는 수치해석이 실험보다 적은 추력을 예측하였고 전진 비행시에는 실험결과와 매우 유사한 결과를 예측하였다. 로터효과를 고려한 비행체의 양력은 감소하고 항력 및 피칭 모멘트는 거의 변화가 없는 것으로 판단된다.

• International Journal of Automotive Technology
• /
• 제3권2호
• /
• pp.57-62
• /
• 2002

It is well known that the entrained air in oil causes appreciable reduction in the stiffness of hydraulic systems. It makes the response delay of the systems and sometimes destroys the stability. Because the hydraulic systems of automatic transmissions are operated in relatively low pressure and high temperature, it is very important to analyze the effects of the air included in automatic transmission fluid. However, it is difficult to derive the generalized model to describe the effective bulk modulus theoretically or measure it in actual operating conditions of automatic transmissions. This paper reviews previous studies of the air effects in hydraulic systems and the measurement techniques of the effective bulk modulus in operating conditions. Based on this work, the theoretical model with moderate complexity and the measurement technique of the effective bulk modulus considering entrained air effect at real operating conditions are suggested. Our paper also shows that the quantity of the entrained air in the automatic transmission fluid can be estimated from the experimental results.

• 한국자동차공학회논문집
• /
• 제5권5호
• /
• pp.170-177
• /
• 1997

In this study, an analysis technique using simple beam model for predicting structure crashworthiness of the passenger car side impacted with an angle by another passenger car was investigated. The simple model was composed of major beam-like side structure which carry almost all side impact load. A procedure of component collapse test, calculation of load carrying capability and dynamic simulation was carryed out sequentially. Transient dynamic algorithms and a computer program to simulate deformations and motions of the impacted car was developed. The developed procedure was applied to a 3 door passenger car side impacted with an angle of 75 degree and the analysis results show good agreements with the actual test results.

• 대한조선학회논문집
• /
• 제48권4호
• /
• pp.363-367
• /
• 2011

In this paper, friction coefficients between ices and model ship were studied in order to predict the resistance of ice. The friction coefficient is a dimensionless scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together. The coefficient of friction depends on the materials, roughness on surface, lubrication, etc. We tested and analyzed the friction coefficient for the development of the test methodology. The friction coefficient for ice model test is very dominant to predict the ship performance, so every ice tank uses their own painting technique. In this study, the friction coefficient with changing the moving speed of ice was studies by using a flat plates which were made by the MOERI's paining technique and the basic research for the developing the paining methodology in the MOERI ice model basin was carried out.

• 한국군사과학기술학회지
• /
• 제3권2호
• /
• pp.81-87
• /
• 2000

This paper presents an application of forced oscillation technique to measure pitch dynamic stability derivatives of a missile model in the low speed wind tunnel. The missile model is oscillated by D.C. electric servomotor with constant amplitudes and frequencies. Phase shift is determined as the difference of peak values between input and output signals from the dynamic stability balance installed at the center of gravity of the model. Stability derivatives were calculated by using phase shifts, amplitudes, forcing moments and input frequencies. Test results show the proper usage of the force oscillation technique with good damping effects.