• Journal of Yeungnam Medical Science
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• 제24권2호
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• pp.197-205
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• 2007

Background : The occurrence of atrial fibrillation after ablation of atrial flutter is clinically important. We investigated variables predicting this evolution in ablated patients without a previous atrial fibrillation history. Materials and Methods : Thirty-six patients (Male=28) who were diagnosed as atrial flutter without previous atrial fibrillation history were enrolled in this study. Group 1 (n=11) was defined as those who developed atrial fibrillation after atrial flutter ablation during 1 year follow-up. Group 2 (n=25) was defined as those who has not occurred atrial fibrillation during same follow-up term. Echocardiogram was performed to all patients. We measured left atrial size, left ventricle end diastolic and systolic dimension, ejection fraction and left atrial volume index before and after ablation of atrial flutter. The differences of each variables were compared and analyzed between two groups. Results : The preablation left ventricular ejection fraction (preLVEF) and postablation left ventricular ejection fraction (postLVEF) are $54{\pm}14%$, $56{\pm}13%$ in group 1 and $47{\pm}16%$, $52{\pm}13%$ in group 2. The differences between each two groups are statistically insignificant ($2.2{\pm}1.5$ in group 1 vs $5.4{\pm}9.8$ in group 2, p=0.53). The preablation left atrial size (preLA) and postablation left atrial size (postLA) are $40{\pm}4mm$, $41{\pm}4mm$ in group1 and $44{\pm}8mm$, $41{\pm}4mm$ in group 2. The atrial sizes of both groups were increased but, the differences of left atrial size between two groups before and after flutter ablation were statistically insignificant ($0.6{\pm}0.9mm$ in group 1 vs $-3.8{\pm}7.4mm$ in group 2, p=0.149). The left atrial volume index before flutter ablation was significantly reduced in group 1 than group 2 ($32{\pm}10mm^3/m^2$, $35{\pm}10mm^3/m^2$ in group 1 and $32{\pm}10mm^3/m^2$, $29{\pm}8mm^3/m^2$ in group 2, p<0.05). Conclusion : The difference between left atrial volume index before and after atrial flutter ablation is the robust predictor of occurrence of atrial fibrillation after atrial flutter ablation without previous atrial fibrillation.

• 한국항행학회논문지
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• 제3권1호
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• pp.20-31
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• 1999

본 논문에서는 김포국제공항 주변지역을 프랏터(flutter) 장애 분석 대상지역으로 선정하여 프랏터 장애를 분석하였다. 프랏터 장애 분석을 위해 김포국제공항 주변 25지점에 대한 현장 측정을 실시하고 컴퓨터 시뮬레이션을 수행하였다. 프랏터 장애 분석 함수로서 직접파 수신 전계강도, 송 수신점 안테나 높이, 송신점 ERP, 송신주파수, 항공기의 반사계수, 송 수신점 좌표 등을 고려하였다. 결과로부터, 항공기 운항에 따른 프랏터 장애는 항공기의 항로 주변지역에서 심각하게 나타났고 항공기의 고도가 낮을 때(항공기 고도 : 40~240m) 주로 발생하였다. 또한, 프랏터 장애는 항공기와 방송 송신점 간의 거리, 앙각 및 항공기의 반사계수에 따라 장애 정도가 달라짐을 알 수 있었다.

• 한국항공우주학회지
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• 제34권1호
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• pp.18-23
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• 2006

본 연구에서는 Gurney 플랩이 달린 NACA 0012 익형에 대한 플러터 해석을 시간 영역에서 수행하였다. 2차원 비정상 압축성 Navier-Stokes 방정식과 Lagrange 방정식으로 부터 유도한 2계 자유도 plunge & pitch 모델을 지배방정식으로 하여 연성 결합 기법을 통해 플러터 해석을 수행하였다. 계산 결과 Gurney 플랩을 장착할 경우 NACA 0012에 비해 플러터가 발생하는 속도가 낮아졌고, 마하수가 0.85보다 작은 영역에서는 Gurney 플랩의 플러터 경계 곡선은 안전 여유를 상회하는 영역에 위치하였다. 그러나, 마하수가 0.85에서 0.9사이일 경우에는 안전 여유에 근접하게 되므로 이러한 운용 영역에서는 Gurney 플랩의 사용에 주의를 요한다.

• 한국항공우주학회지
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• 제33권2호
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• pp.54-59
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• 2005

구동기의 백래쉬와 동강성을 고려한 미사일 조종날개의 비선형 공탄성 해석이 수행되었다. 아음속 비정상 공기력 계산을 위해 DHM을 사용하였고 최소상태접근법을 사용하여 근사하였다. 비선형 플러터 해석을 위해 백래쉬는 유격으로 모델하고 기술 함수법을 사용하여 선형화하였다. 또한, 동강성은 주파수의 함수로 모터의 운동방정식으로부터 계산하였다. 선형 및 비선형 플러터 해석 결과들은 공력탄성학적 특성들이 백래쉬와 동강성에 중요한 영향을 받는다는 것을 보여준다. 비선형 플러터 해석에서 다양한 제한 주기 운동이 선형플러터 속도 이하에서 관측되었다. 또한 플러터 특성과 응답을 시간영역에서도 조사하였다.

• 한국항공우주학회지
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• 제34권1호
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• pp.24-31
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• 2006

본 연구에서는 완전 내재적 기법을 이용한 2계 자유도 모델에 대한 플러터 해석을 수행하였다. 유동해석을 위하여 2차원 Navier-Stokes 지배방정식을 ε-SST 난류모델과 DP-SGS 병렬화 기법을 이용해 구성하였다. 구조해석을 위하여 피치 와 플런지의 2계 자유도를 갖는 모델을 구성하였으며 시간영역에서의 해석을 위하여 유동해석과 마찬가지로 이중 시간 전진 기법을 이용하였다. 가상 시간 전진에서 유체-구조 결합을 통해서 강성결합을 구현하였으며 이를 천음속 플러터 예측에 적용하였다. 플러터 해석의 전형적인 응답인 감쇠응답, 중립응답, 발산응답 및 limit cycle oscillation (LCO) 등을 계산하였으며, 더불어 플러터 속도 경계곡선을 작성하였다. 천음속 플러터 해석은 난류모델 뿐만 아니라 유체-구조 결합 방법에 따라 다른 특성을 보임을 확인하였다.

• Structural Engineering and Mechanics
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• 제84권4호
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• pp.437-452
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• 2022

For the first time, the higher-order shear and normal deformable plate theory (HOSNDPT) is used for the vibration and flutter analyses of the multilayer functionally graded graphene platelets reinforced composite (FG-GPLRC) plates under supersonic airflow. For modeling the supersonic airflow, the linear piston theory is adopted. In HOSNDPT, Legendre polynomials are used to approximate the components of the displacement field in the thickness direction. So, all stress and strain components are encountered. Either uniform or three kinds of non-uniform distribution of graphene platelets (GPLs) into polymer matrix are considered. The Young modulus of the FG-GPLRC plate is estimated by the modified Halpin-Tsai model, while the Poisson ratio and mass density are determined by the rule of mixtures. The Hamilton's principle is used to obtain the governing equations of motion and the associated boundary conditions of the plate. For solving the plate's equations of motion, the Galerkin approach is applied. A comparison for the natural frequencies obtained based on the present investigation and those of three-dimensional elasticity theory shows a very good agreement. The flutter boundaries for FG-GPLRC plates based on HOSNDPT are described and the effects of GPL distribution patterns, the geometrical parameters and the weight fraction of GPLs on the flutter frequencies and flutter aerodynamic pressure of the plate are studied in detail. The obtained results show that by increasing 0.5% of GPLs into polymer matrix, the flutter aerodynamic pressure increases approximately 117%, 145%, 166% and 196% for FG-O, FG-A, UD and FG-X distribution patterns, respectively.

• Wind and Structures
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• 제14권5호
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• pp.413-434
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• 2011

Without output covariance estimation, one reference-based Stochastic Subspace Technique (SST) for extracting modal parameters and flutter derivatives of bridge deck is developed and programmed. Compared with the covariance-driven SST and the oscillation signals incurred by oncoming or signature turbulence that adopted by previous investigators, the newly-presented identification scheme is less time-consuming in computation and a more desired accuracy should be contributed to high-quality free oscillated signals excited by specific initial displacement. The reliability and identification precision of this technique are confirmed by a numerical example. For the 3-DOF sectional models of Sutong Bridge deck (streamlined) and Suramadu Bridge deck (bluff) in wind tunnel tests, with different wind velocities, the lateral bending, vertical bending, torsional frequencies and damping ratios as well as 18 flutter derivatives are extracted by using SST. The flutter derivatives of two kinds of typical decks are compared with the pseudo-steady theoretical values, and the performance of $H_1{^*}$, $H_3{^*}$, $A_1{^*}$, $A_3{^*}$ is very stable and well-matched with each other, respectively. The lateral direct flutter derivatives $P_5{^*}$, $P_6{^*}$ are comparatively more accurate than other relevant lateral components. Experimental procedure seems to be more critical than identification technique for refining the estimation precision.

• Wind and Structures
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• 제9권6호
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• pp.441-455
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• 2006

A more applicable optimization model for extracting flutter derivatives of bridge decks is presented, which is suitable for time-varying weights for fitting errors and different lengths of vertical bending and torsional free vibration data. A stochastic search technique for searching the optimal solution of optimization problem is developed, which is more convenient in understanding and programming than the alternate iteration technique, and testified to be a valid and efficient method using two numerical examples. On the basis of the section model test of Sutong Bridge deck, the flutter derivatives are extracted by the stochastic search technique, and compared with the identification results using the modified least-square method. The Empirical Mode Decomposition method is employed to eliminate noise, trends and zero excursion of the collected free vibration data of vertical bending and torsional motion, by which the identification precision of flutter derivatives is improved.

• Wind and Structures
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• 제21권1호
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• pp.41-61
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• 2015

The flutter stability of long-span suspension bridges during erection can be more problematic and more susceptible to be influenced by many factors than in the final state. As described in this paper, numerical flutter stability analyses were performed for the construction process of Zhongdu Bridge over Yangtze River using the commercial FE package ANSYS. The effect of the initial wind attack angle, the sequence of deck erection, the stiffness reduction of stiffening girders, the structural damping, and the cross cables are discussed in detail. It was found that the non-symmetrical sequence of deck erection was confirmed to be aerodynamically favourable for the deck erection of long-span suspension bridges and the best erection sequence should be investigated in the design phase. While the initial wind attack angle of $-3^{\circ}$ is advantageous for the aerodynamic stability, $+3^{\circ}$ is disadvantageous compared with the initial wind attack angle of $0^{\circ}$ during the deck erection. The stiffness reduction of the stiffening girders has a slight effect on the flutter wind speed of the suspension bridge during erection, but structural damping has a great impact on it, especially for the early erection stages.

• 항공우주기술
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• 제7권2호
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• pp.205-212
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• 2008

본 논문에서는 스마트무인기 로터시스템의 공진, 로터 공탄성 안정성 및 휠플러터 안정성 해석을 위한 모델링 데이터와 최종 해석결과를 기술하였다 향후 날개구조 설계변경 가능성을 고려하여 날개 빔, 코드 및 비틀림 강성이 훨플러터 안정성에 미치는 영향이 분석되었다. 파라메트릭 분석 결과 날개의 비틀림 강성 및 빔강성의 변화가 코드방향 강성에 비하여 빔모드 댐핑값에 훨씬 큰 영향을 미치는 것으로 분석되었다. 최종 설계된 로터시스템은 공진가능성이 없고, 스마트무인기 TR-S4 로터/파일론/날개에 대하여 로터 공탄성 안정성 및 훨플러터 안정성이 보장됨을 해석적으로 확인하였다.