Young-Wann Kim

Vibration Analysis of Trapezoidally Corrugated Plates

In this paper, the vibration characteristics of the trapezoidally corrugated plate are investigated by the analytical method. The corrugated plate is widely used as the structural elements because of its high stiffness and light weight. Because the corrugated plate is flexible in the corrugation direction and stiff in the transverse direction, it is treated as an equivalent orthotropic plate to analyze the corrugated plate simply. This equivalent plate must include both extensional and flexural effect to obtain the precise solution. The effective extensional and flexural stiffness of the equivalent plate are derived to consider these effects in the analysis. To demonstrate the validity of the proposed approach, the comparison is made with the previously published results and ANSYS solutions. Some numerical results are presented to check the effect of the geometric properties.

Mode Separation in Torsional Guided Waves Using Chirplet Transform

ABSTRACT The sensor configuration of the magnetostrictive guided wave system can be described as a single continuous transducing element which makes it difficult to separate the individual modes from the reflected signal. In this work we develop the mode decomposition technique employing chirplet trans-form based on the maximum likelihood estimation, which is able to separate the individual modes from dispersive and multimodal waveform measured with the magnetostrictive sensor, and estimate the time-frequency centers and individual energies of the reflection, which would be used to locate and characterize defects. Simulation results on a carbon steel pipe are presented, which show the ac-curate mode separation and more discernible time-frequency representation could become enabled us-ing the proposed technique. * 1. 서 론 초음속 유도파(ultrasonic guided waves)는 현재 비파괴검사의 중요한 수단으로 자리 잡게 되었으며, 많은 기술적 진보에 힘입어 석유화학, 철강 산업에 쓰이는 배관 검사에 자주 이용되고 있다 (1) . 유도파 시험에는 종파(longitudinal wave)나 비틀림 모드(torsional mode)와 같은 축대칭 모드를 배관에 인가하는데, 종파 가진을 위해서는 다채널 시간지연 기능을 갖는 신호변환기 배열(transducer array)

Vibration Analysis of Trapezoidal Corrugated Plates with Stiffeners and Lumped Masses

ABSTRACT In this paper, the vibration characteristics of the trapezoidal corrugated plate with axial stiffeners and lumped masses are investigated by the analytical method. The corrugated plate can be treated as an equivalent orthotropic plate as this plate has different flexure properties in two perpendicular direc-tions; flexible in the corrugation direction and stiff in the transverse direction. The effective extensional and flexural stiffness of the equivalent plate are considered to obtain the precise solution in the analysis. The plate is stiffened by concentric stiffeners horizontally to the corrugation direction. The discrete stiffener theory is adopted to consider the position of stiffener. To demonstrate the validity of the proposed approach, the comparison is made with the results of 3D ANSYS finite element solutions. Some numerical results are presented to check the effect of the geometric properties. * 1. 서 론 일반적으로 주름판은 한 방향으로 주름을 잡기 때문에 주름방향으로는 유연하고 횡방향으로는 고강성을 갖는 구조적 특성을 갖고 있기 때문에 한 방향으로 하중이 작용하는 경우에 유용하게 사용할 수 있다. 최근에는 비행기의 모핑 날개 및 유연 터빈 블레이드 등과 같은 유연 구조물에 적용되고 있는 실정이다

Free Vibrations of Fluid-filled Cylindrical Shells on Partial Elastic Foundations

The free vibration characteristics of fluid-filled cylindrical shells on partial elastic foundations are investigated by an analytical method. The cylindrical shell is fully or partially surrounded by the elastic foundations, these are represented by the Winkler or Pasternak model. The motion of shell is represented by the first order shear deformation theory to account for rotary inertia and transverse shear strains. The steady flow of fluid is described by the classical potential flow theory. The fluid-structure interaction is considered in the analysis. The effect of internal fluid can be considered by imposing a relation between the fluid pressure and the radial displacement of the structure at the interface. To validate the present method, the numerical example is presented and compared with the available existing results.

Critical Fluid Velocity of Fluid-conveying Cantilevered Cylindrical Shells with Intermediate Support

The critical fluid velocity of cantilevered cylindrical shells subjected to internal fluid flow is investigated in this study. The fluid-structure interaction is considered in the analysis. The cantilevered cylindrical shell is supported intermediately at an arbitrary axial position. The intermediate support is simulated by two types of artificial springs: translational and rotational spring. It is assumed that the artificial springs are placed continuously and uniformly on the middle surface of an intermediate support along the circumferential direction. The steady flow of fluid is described by the classical potential flow theory. The motion of shell is represented by the first order shear deformation theory (FSDT) to account for rotary inertia and transverse shear strains. The effect of internal fluid can be considered by imposing a relation between the fluid pressure and the radial displacement of the structure at the interface. Numerical examples are presented and compared with existing results.

Characterization of Axial Defects in Pipeline Using Torsional Guided Wave

ABSTRACT In this work we use the mode decomposition technique employing chirplet transform, which is able to separate the individual modes from dispersive and multimodal waveform measured with the magnetostrictive sensor. The mode decomposition technique is also used to estimate the time-fre-quency centers and individual energies of the reflection, which would be used to locate and charac-terize axial defects. The arrival times of the separated modes are calculated and the axial defect lengths can be evaluated by using the estimated arrival time. Results from an experiment on a car-bon steel pipe are presented and it is shown that the accurate and quantitative defect characterization could become enabled using the proposed technique. * 1. 서 론 유도파(guided waves)는 현재 비파괴검사의 중요한 수단으로 자리 잡게 되었으며, 많은 기술적 진보에 힘입어 석유화학, 철강, 발전설비에 쓰이는 배관의 검사에 자주 이용되고 있다 (1∼4) . 그러나 결함을 발견해도 그 크기를 정량적으로 평가하거나 이로 인한 배관의 위험성을 파악하는 것은 아직도 많은 연구가 필요한 분야라고 할 수 있는데, 그 이유는 결함에서 반사된 신호는 여러 신호들이 혼재되어 존재하는 매우 복잡한 양상을 갖기 때문이다

Free Vibrations of Cylindrical Shells on Inclined Partial Elastic Foundation

The free vibration characteristics of cylindrical shells on inclined partial elastic foundations are investigated by an analytical method. The cylindrical shell is partially surrounded by the elastic foundations, these are represented by the Winkler or Pasternak model. The area of elastic foundation is not uniform and varies along the axial direction of the shell. The motion of shell is represented by first-order shear deformation theory(FSDT) to account for rotary inertia and transverse shear strains. The governing equation is obtained using the Rayleigh-Ritz method and a variation approach. To validate the present method, the numerical example is presented and compared with the present FEA results. The numerical results reveal that the elastic foundation has significant effect on vibration characteristics.

Transient Response Analysis of Trapezoidal Corrugated Plates with Stiffeners

In this paper, the transient response analysis of the trapezoidal corrugated plate subjected to the pulse load is investigated by the theoretical method. Three types of pulse loads are considered: step- ped, isosceles triangular and right triangular pulse loads. The corrugated plates can be represented as an orthotropic plate. Both the effective extensional and flexural stiffness of this equivalent orthotropic plate are considered in the analysis. The plate is stiffened by concentric stiffeners perpendicular to the corrugation direction. The stiffening effect is represented by the discrete stiffener theory. This theoretical results are validated by those obtained from 3D finite element analysis based on shell elements. Some numerical results are presented to check the effect of the geometric properties.

Coupled Vibration of Functionally Graded Cylindrical Shells Conveying Fluid

The coupled fluid-structure interaction problem is analyzed using the theoretical method to investigate the coupled vibration characteristics of functionally graded material(FGM) cylindrical shells conveying an incompressible, inviscid fluid. Material properties are assumed to vary continuously through the thickness according to a power law distribution in terms of the volume fraction of the constituents. The steady flow of fluid is described by the classical potential flow theory. The motion of shell represented by the first order shear deformation theory(FSDT) to account for rotary inertia and transverse shear strains. The effect of internal fluid can be taken into consideration by imposing a relation between the fluid pressure and the radial displacement of the structure at the interface. Numerical examples are presented and compared with exiting results.

Coupled Vibration Analysis of Cylindrical Fluid-storage Tanks with a Baffle

The coupled vibration characteristics for the fluid-structure interaction systems are investigated through the finite element method. The present paper is focused on vibration characteristics of the cylindrical fluid-storage tank with a baffle. The tank is partially filled with an inviscid and irrotational fluid having a free surface. A baffle is assumed here to have the shape of a thin annular plate and a conical shell, attached to the cylindrical tank and positioned below the fluid surface. The liquid domain is limited by a rigid flat bottom. As the effect of free surface waves is taken into account in the analysis, the bulging and sloshing modes are studied. To demonstrate the validity of present results, they are compared with the published ones. The effect of positions and inner-to-outer radius ratio of annular baffle and setting angles of conical baffle on coupled vibration characteristics is investigated.