• Journal of the Korean Society for Nondestructive Testing
• /
• v.13 no.3
• /
• pp.24-30
• /
• 1993

The necessity of ultrasonic inspection to detect the cracks in turbine blade is being increased as the forced outage of nuclear power plants have been occurred due to blade failure in turbine components. However, the complex blade root geometry causes the ultrasonic inspection technique not to be established yet and much effort is required to set up a more reliable inspection. In this paper, the ultrasonic inspection technique for flaw detectability, skew angle effect, identification of flaw and geometric signal have been investigated with a test block and discussed the interpretation of ultrasonic signal through the acquisition and analysis of RF waveform. The experimental results show that the proper examination procedure can be established. It is required that the skew angle is essential to decrease the effect of signals from the complex blade geometry. The present results of this study can be applied to the site inspection without blade disassembly.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1998.10a
• /
• pp.553-558
• /
• 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.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.26 no.3
• /
• pp.198-205
• /
• 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
• /
• v.70 no.1
• /
• pp.125-131
• /
• 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
• /
• v.38 no.1
• /
• pp.43-58
• /
• 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
• /
• v.10 no.6
• /
• pp.1467-1486
• /
• 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
• /
• v.25 no.2
• /
• pp.161-180
• /
• 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
• /
• v.6 no.3
• /
• pp.179-196
• /
• 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.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.9 no.1
• /
• pp.159-170
• /
• 2005

The grid structure is parallel main girders intersected with crossgirder. It distribute the loads to adjoining main girder through the crossgirder when a girder is subjected to a load. grillage girder bridge has high load-carrying capacity, it can save materials and become more economical type of bridge. In this paper, the grillage girder bridge analysis program developed by using the transfer matrix method deals with following problems: the comparision with Leonhardt, Szabo, FEM yang and jung in the analysis of grillage girder bridges, quality of straight and curved bridges with skew angle, forces of straight and curved bridges according to skew angle and bending stiffness/torsional stiffness ratio.

• Proceedings of the KIEE Conference
• /
• 1989.11a
• /
• pp.10-14
• /
• 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.