• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.593-597
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• 2016

항공기의 비행 안정성을 판별하기 위해서는 정적(static)안정성과 동적(dynamic)안정성을 모두 고려해야 한다. 본 연구는 EDISON_CFD의 KFLOW_EDISON_2D3DOF, 2D_Com_P해석자를 이용해 2차원익형의 정적(static)계수와 동적(dynamic)계수를 구해 항공기 전체형상의 정적 안정성 및 동적 안정성을 분석하였다. 그 중 2015년도 인간 동력 항공기대회 건국대학교 참가 기체를 예시로 연구를 진행하였다. 주익 익형 SG6043과 미익 익형 NACA0012을 EDISON_CFD를 이용하여 각 익형의 모멘트계수를 구하고 그 결과값을 이용하여 기체의 무게중심에 대한 각 익형의 감쇠계수를 계산하였다. 그리고 주익과 미익의 면적비율과 코드길이의 비율을 고려해 전체 항공기형상의 안정성과 비행 형태를 분석하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.5
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• pp.10-17
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• 2003

Dynamic stability is critically required to stabilize an airship which is statically unstable. Numerical computations were performed in order to support and confirm the foced oscillation wind tunnel tests. To analyze the low-speed flow filed around the airship, a low-Mach number preconditioned method was applied. Using two computation methods, variations of the dynamic damping coefficients were examined. Numerical results show that it is dynamically stable for three directional moments, but unstable for normal or side force. It is revealed that the damping coefficients are more sensitive to the direction of the angular rate than the angle of attack or the magnitude og angular rate.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.11
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• pp.1-8
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• 2006

A steady prediction method is presented to compute dynamic damping coefficients for axisymmetric projectiles. Viscous flow analysis is essential to the steady method using a zero-spin coning motion in the inertial coordinate frame. The present method is applied to compute the pitching moment and the pitch-damping moment coefficients for the Army-Navy Spinning Rocket. The results are in good agreement with the parabolized Navier-Stokes data, range data, and unsteady prediction data. Predictions for Secant-Ogive-Cylinder configurations are performed to investigate effects of afterbody geometries. To investigate the geometrical effect and flow physics, the longitudinal developments of the coefficients are examined in detail.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.265-268
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• 1999

감쇠가 큰 고분자 복합재료에서 초음파 다중반사파를 이용한 Pulse Echo법, 공진주파수에서 내부마찰계수 측정법과 Rheometer를 이용한 동적탄성계수 측정법을 사용하여 음향감쇠계수를 측정하고 각각의 측정자료를 비교하는 연구를 수행하였다. Pulse Echo법을 이용하여 0.5, 1.0, 2.25MHz에서 음향감쇠계수를 측정하였고, 이때 폴리에틸렌기지 복합재료의 음향감쇠계수는 강화재의 부피분율에 따라 3-15dB/cm 정도로 큰 값을 나타내었다. 폴리에틸렌기지 복합재료를 600kHz 근처에서 공진주파수를 가지도록 시편을 만든 후에 내부마찰계수를 측정한 결과로 계산된 음향감쇠계수는 Pulse Echo 실험에서 구한 값과 잘 일치하는 결과를 얻을 수 있었다. Rheometer를 이용한 동적탄성계수 측정법은 0.1-100Hz의 주파수에서 측정한 자료를 TTSP 이론을 이용하여 1MHz의 결과와 비교하였는데, 단일 고분자 재료에서는 다른 측정방법과 음향감쇠계수가 일치하였지만 복합재료에서는 음향감쇠계수값이 일치하지 않는 결과를 나타내었다.

• Journal of the Korean GEO-environmental Society
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• v.12 no.5
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• pp.59-63
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• 2011

Ground dynamic parameter such as shear elastic modulus and damping ratio is a very important variable in design of ground-structure with repeated load and dynamic load. Shear elastic modulus and damping ratio on small strain below linear limit strain is constant regardless of strain. Shear elastic modulus as the maximum shear elastic modulus and damping ratio as the minimum damping ratio were considered. As a lot of experiment related to the maximum shear elastic modulus, which is in dynamic deformation characteristics, have been conducted, many factors including voiding ratio, over consolidation ratio(OCR), confining pressure, geology time, PI, and the number of load cycle affect to dynamic soil characteristic. However, the research of ground dynamic characteristic improved with grout is absent such as underground continuous wall construction, deep mixing method, umbrella arch method. In order to investigate the dynamic soil characteristics improved with grout, in this study, resonant column tests were performed with changing water content(20%, 25%, 30%) and injection ratio of grout(5%, 10%, 15%), cure time(7th day, 28th day) As a result, shear elastic modulus and damping ratio, which are ground dynamic parameter, are affected by the injection ratio of milk grout, cure time and water content.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.8
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• pp.19-26
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• 2003

A steady prediction method of dynamic stability derivatives is presented in the unified framework of the unsteady Euler equations. New approach does not require any modification of the governing equations except addition of non-inertial force terms. The present methods are applied to compute the pitch-damping coefficients using the lunar coning and the lunar helical motions in the Cartesian coordinate frame. The results for the ANSR and the Basic Finner are in good agreement with the PNS data, range data, and the results using the unsteady prediction method. The results show that the steady approach using the unified governing equations in the Cartesian coordinate frame can be successfully applied to predict the pitch-damping coefficients.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.253-259
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• 1997

씨일의 마모에 따른 터빈펌프의 동적거동을 고찰하기 위해서 10단 터빈펌프를 대상으로 유한요소법에 의한 동특성 해석을 수행하였다. 베어링과 씨일의 동적계수를 회전속도의 하수로 계산하였으며, 이를 동적거동해석에 적용하였다. 해석결과 씨일들은 그 간극이 커질수록 강성 및 감쇠계수가 크게 떨어지고 누설량이 급격히 늘어남을 확인하였다. 따라서 1차 위험속도(1st Critical Speed) 이하에서 충분한 분리여유(Seperation Margine)를 가지고 정상운전되도록 설계된 터빈펌프라 할지라도 장기적 사용시 마모가 진전됨에 따라 계의 1차 위험속도가 변하여 운전속도에 접근할 수 있으며, 아울러 이 때 씨일의 감쇠가 크게 줄어들어 급격한 진동의 증가를 가져올 수 있음을 보였다.

• Magazine of the Korea Concrete Institute
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• v.11 no.2
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• pp.261-270
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• 1999

In these days, construction activities have caused civil petitions associated with vibration-induced damages or nuisances. Therefore, it is strongly needed to develop a remedial technique to mitigate unfavorable effects. The objective of this experimental research is to investigate material and structural dynamic characteristics of vibration-controlled concretes which have been proportionally mixed with various vibration reducing material, such as latex, rubber powder, plastic resin, polystyrofoams and etc. Normal and high strength concrete specimens are also prepared for corresponding comparison. As part of the recycling research for obsolete rubber and plastic materials, 32 concrete cylinders and 10 concrete flexural beams have been made for material and structural dynamic properties, respectively. In accordance with the resonance test on concrete cylinders, it can be concluded that concrete with vibration-reducing material have relatively larger material damping ration than normal or high strength concrete. Styrofoam is determined to be very effective vibration-reducing mixtures. From the vibration test on 10 concrete flexural beams, meamwhile, of importance observations was that material damping ratio is very smaller than structural damping ratio of corresponding specimen. But further vibration test on more flexural beams should be strongly needed by varying support conditions.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.1
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• pp.108-115
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• 1995

An efficient model for the dynamic analysis of caisson breakwaters under impulsive wave loadings is presented. The caisson structure is. regarded as a rigid body, and the rubble mound foundation is idealized as virtual added masses, springs, and dampers using the elastic half-space theory. The frequency-dependent hydrodynamic added mass and damping coefficients are considered by using the time memory functions and added mass at infinite frequency. To simulate the permanent sliding phenomenon of the caisson, the horizontal spring is modeled as a nonlinear spring with plastic behaviors. Comparisons with experimental results show that the present model gives fairly good results. Sensitivity analysis is performed for the relevant parameters affecting the dynamic responses of a caisson breakwater. Numerical experiments are also carried out to investigate the applicability to the prediction of permanent sliding distance and critical weight of the caisson.

• The Journal of the Acoustical Society of Korea
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• v.28 no.1
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• pp.25-31
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• 2009

This paper introduces a spectrally formulated element method (SEM) for the beams treated with passive constrained layer damping (PCLD). The viscoelastic core of the beams has a complex modulus that varies with frequency. The SEM is formulated in the frequency domain using dynamic shape functions based on the exact displacement solutions from progressive wave methods, which implicitly account for the frequency-dependent complex modulus of the viscoelastic core. The frequency response function and dynamic responses obtained by the SEM and the conventional finite element method (CFEM) are compared to evaluate the validity and accuracy of the present spectral PCLD beam element model. The spectral PCLD beam element model is found to provide very reliable results when compared with the conventional finite element model.