• 비파괴검사학회지
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• 제13권3호
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• pp.24-30
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• 1993

원자력발전소 터빈 계통의 손상중에서 blade의 파손에 따른 원전의 불시 정지가 발생함에 따라 blade 균열 검출을 위한 초음파 검사의 필요성이 증가하고 있다. 그러나 터빈 blade root부 결함 탐지를 위한 초음파검사 방법은 그 형상의 복잡성으로 인하여 검사 기술이 아직 확립되지 자아 검사의 신뢰성 확보에 대한 많은 연구가 요망되고 있다. 본 연구에서는 터빈 blade에 인공 결함을 가공한 다음 초음파 검사시 복잡한 형상을 가진 blade root부 구멍 주위의 결함 검출 능력, skew angle 영향, 실제 결함과 기하학적 신호사이의 신호 구분에 대한 내용를 조사하였으며, 또한 RF 신호수집, 해석을 통하여 신호 분류 특성에 대한 연구도 병행하였다. 실험 결과 pin hole 주위의 초음파 균열 탐지를 위하여 인공 결함이 있는 blade 시편을 이용함으로 결함 검출을 위한 최적 검사조건의 도출이 가능하였고, blade의 복잡형상에 기인한 기하학적 영향을 줄이기 위해서는 skew angle 이 필수적인 것으로 나타났다. 따라서 본 연구 결과를 적용하면 blade root부위의 내부 균열 탐지를 위해 blade 를 해체함이 없이 현장 검사의 신뢰도를 제고할 수 있다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표논문집(II)
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• pp.553-558
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• 1998

Since the mid of the 20th century in the world, it has been observed that the number of minor or moderate earthquake motions tend to be increased year by year. Owing to the topographical condition, moreover, large numbers of skew bridges have been constructed for the requirements of more than DB18 ton bridge in Korea. It has been also observed from foreign countries that lots of superstructures collapse in bridge were occurred in previous earthquakes, inclusive of 1995 Kobe earthquake. This is caused by a relative displacement between the upper and lower structure of bridge by the earthquake and the rotation with respect to the vertical axis of skew bridges, which were subjected to and earthquake motion. In this study, the probabilistic analysis of unseating failure of skew bridges under scenario earthquake has been carried out by evaluating the longitudinal displacement of skew bridges.

• 비파괴검사학회지
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• 제26권3호
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• pp.198-205
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• 2006

The necessity of nondestructively inspecting austenitic steels, fiber-reinforced composites, and other inherently anisotropic materials has stimulated considerable interest in developing beam models for anisotropic media. The properties of slowness surface playa key role in the beam models based on the paraxial approximation. In this paper, we apply a modular multi-Gaussian beam (MMGB) model to study the effects of material anisotropy on ultrasonic beam profile. It is shown that the anisotropic effects of beam skew and excess beam divergence enter into the MMGB model through parameters defining the slope and curvature of the slowness surface. The overall beam profile is found when the quasilongitudinal(qL) beam propagates in the symmetry plane of transversely isotropic austenitic steels. Simulation results are presented to illustrate the effects of these parameters on ultrasonic beam diffraction and beam skew. The MMGB calculations are also checked by comparing the anisotropy factor and beam skew angle with other analytical solutions.

• Structural Engineering and Mechanics
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• 제70권1호
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• pp.125-131
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• 2019

A nine node isoparametric plate bending element is used for bending analysis of laminated composite skew cylindrical shell panels. Both thick and thin shell panels are solved. Rotary inertia and shear deformation are incorporated by considering first order shear deformation theory. The analysis is performed considering shallow shell theory. Both shallow and moderately deep skew cylindrical shells are investigated. Skew cylindrical shell panels having different thickness ratios (h/a), radius to length ratios (R/a), ply angle orientations, number of layers, aspect ratio (b/a), boundary conditions and various loading (concentrated, uniformly distributed, linear varying and doubly sinusoidal varying) conditions are analysed. Various new results are presented.

• Wind and Structures
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• 제38권1호
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• pp.43-58
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• 2024

To ensure the flutter stability of three-tower suspension bridges under skew wind, by using the computational procedure of 3D refined flutter analysis of long-span bridges under skew wind, in which structural nonlinearity, the static wind action(also known as the aerostatic effect) and the full-mode coupling effect etc., are fully considered, the flutter stability of a three-tower suspension bridge-the Taizhou Bridge over the Yangtze River in completion and during the deck erection is numerically investigated under the constant uniform skew wind, and the influences of skew wind and aerostatic effects on the flutter stability of the bridge under the service and construction conditions are assessed. The results show that the flutter critical wind speeds of three-tower suspension bridge under service and construction conditions fluctuate with the increase of wind yaw angle instead of a monotonous cosine rule as the decomposition method proposed, and reach the minimum mostly in the case of skew wind. Both the skew wind and aerostatic effects significantly reduce the flutter stability of three-tower suspension bridge under the service and construction conditions, and the combined skew wind and aerostatic effects further deteriorate the flutter stability. Both the skew wind and aerostatic effects do not change the evolution of flutter stability of the bridge during the deck erection, and compared to the service condition, they lead to a greater decrease of flutter critical wind speed of the bridge during deck erection, and the influence of the combined skew wind and aerostatic effects is more prominent. Therefore, the skew wind and aerostatic effects must be considered accurately in the flutter analysis of three-tower suspension bridges.

• Earthquakes and Structures
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• 제10권6호
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• pp.1467-1486
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• 2016

This research focuses on seismic performance of a class of single pier skewed bridges with three different pier-deck connections; skew angles vary from $0^{\circ}$ to $60^{\circ}$. A well-documented four span continuous deck bridge has been modeled and verified. Seat-type connections with fixed and sliding bearings plus monolithic pier-deck connections are studied. Shear keys are considered either fully operational or ineffective. Seismic performances of the bridges and the structural components are investigated conducting bidirectional nonlinear time history analysis in OpenSees. Several global and intermediate engineering demand parameters (EDP) have been studied. On the basis of results, the values of demand parameters of skewed bridges, such as displacement and rotation of the deck plus plastic deformation and torsional demand of the piers, increase as the skew angle increases. In order to eliminate the deck collapse probability, the threshold skew angle is considered as $30^{\circ}$ in seat-type bridges. For bridges with skew angles greater than $30^{\circ}$, monolithic pier-deck connections should be applied. The functionality of shear keys is critical in preventing large displacements in the bearings. Pinned piers experience considerable ductility demand at the bottom.

• Structural Engineering and Mechanics
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• 제25권2호
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• pp.161-180
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• 2007

A first endeavor is made to exploit the differential quadrature method (DQM) as a simple, accurate, and computationally efficient numerical tool for the large deformation analysis of thin laminated composite skew plates, which has very strong singularity at the obtuse vertex. The geometrical nonlinearity is modeled by using Green's strain and von Karman assumption. A recently developed DQ methodology is used to exactly implement the multiple boundary conditions at the edges of skew plates, which is a major draw back of conventional DQM. Using oblique coordinate system and the DQ methodology, a mapping-DQ discretization rule is developed to simultaneously transform and discretize the equilibrium equations and the related boundary conditions. The effects of skew angle, aspect ratio and different types of boundary conditions on the convergence and accuracy of the presented method are studied. Comparing the results with the available results from other numerical or analytical methods, it is shown that accurate results are obtained even when using only small number of grid points. Finally, numerical results for large deflection behavior of antisymmetric cross ply skew plates with different geometrical parameters and boundary conditions are presented.

• Wind and Structures
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• 제6권3호
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• pp.179-196
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• 2003

A long suspension bridge is often located within a unique wind environment, and strong winds at the site seldom attack the bridge at a right angle to its long axis. This paper thus investigates the buffeting response of long suspension bridges to skew winds. The conventional buffeting analysis in the frequency domain is first improved to take into account skew winds based on the quasi-steady theory and the oblique strip theory in conjunction with the finite element method and the pseudo-excitation method. The aerodynamic coefficients and flutter derivatives of the Tsing Ma suspension bridge deck under skew winds, which are required in the improved buffeting analysis, are then measured in a wind tunnel using specially designed test rigs. The field measurement data, which were recorded during Typhoon Sam in 1999 by the Wind And Structural Health Monitoring System (WASHMS) installed on the Tsing Ma Bridge, are analyzed to obtain both wind characteristics and buffeting responses. Finally, the field measured buffeting responses of the Tsing Ma Bridge are compared with those from the computer simulation using the improved method and the aerodynamic coefficients and flutter derivatives measured under skew winds. The comparison is found satisfactory in general.

• 한국구조물진단유지관리공학회 논문집
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• 제9권1호
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• pp.159-170
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• 2005

격자구조는 병렬하는 주거더에 횡거더로 접합된 구조를 말하며 집중하중이 재하될 때 하중이 주거더만 부담하지 않고 횡거더를 통하여 다른 주거더로 하중이 일부를 부담하게 된다. 격자형의 교량은 과다한 집중하중을 분산시켜 내하력이 높은 특성을 갖고 있으며 사용재료를 절약할 수 있어 경제적이다. 본 연구에서는 해석절차가 간단하고 이해가 쉬운 전달행렬법을 이용하여 격자교의 프로그램을 작성하여 Leonhardt, Szabo, FEM, 양창현 및 정진환의 해석결과와 비교하였다. 또한, 경사각을 갖는 직선격자교와 곡선격자교의 특성을 분석하였고, 경사각과 휨강도/비틀림강도의 비에 따른 직선격자교와 곡선격자교의 단면력을 분석하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1989년도 추계학술대회 논문집 학회본부
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• pp.10-14
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• 1989

This paper shows an experimental study of home appliance motor noise, also represents some relations between skew-types and skew-angles. Frequency analysis was made for stator and rotor harmonic fluxes. making use of searching coils. Besides electrical analysis, mechanical noise trans mission analysis are studied to lee how they affected on the noise of the motor. Finally, we proved the noise sources of the motor using sound intensity method.