Bong-Jo Ryu

Eigenvalue branches and modes for flutter of cantilevered pipes conveying fluid

This paper describes the relationship between the eigenvalue branches and the corresponding unstable modes associated with flutter of cantilevered pipes conveying fluid. The order of branches in root locus diagrams is clearly defined. The flutter configuration of the pipes at the critical flow velocities are drawn graphically at every 12th period to define the order of quasi-mode of flutter configuration. The transferences of flutter-type instability from one eigenvalue branch to another are thoroughly investigated and discussed in case of continuous pipes conveying fluid. The critical mass ratios, at which the transference of the eigenvalue branches related to flutter take place, are definitely determined.

A Modeling of Impact Dynamics and its Application to Impact Force Prediction

In this paper, the contact force between two colliding bodies is modeled by using Hertz’s force-displacement law and nonlinear damping function In order to verify the appropriateness of the proposed contact force model, the drop type impact test is carried out for different impact velocities and different materials of the impacting body, such as rubber, plastic and steel In the drop type impact experiment, six photo interrupters in series close to the collision location are installed to measure the velocity before impact more accurately The characteristics of contact force model are investigated through experiments The parameters of the contact force model are estimated using the optimization technique Finally the estimated parameters are used to predict the impact force between two colliding bodies in opening action of the magnetic contactor, a kind of switch mechanism for switching electric circuits

A modular torsional actuator using shape memory alloy wires

In this study, novel modular shape memory alloy wire–based torsional actuators were designed and fabricated. These shape memory alloy–based actuators provide rotational displacements. The mechanical and thermal properties of a single module shape memory alloy torsional actuator were characterized. Next, a modular shape memory alloy torsional actuator was configured by connecting single actuator modules in series. This modular actuator can be used directly as a soft or biologically inspired robot. Finally, the rolling motion and shape transformation of the modular shape memory alloy torsional actuator (soft robot) were demonstrated with a simple open-loop-based control scheme experimentally validating the novel mobility and actuation of the proposed actuator. For a control input, sequentially coordinated square waves of electric current were supplied to the shape memory alloy actuating units.

Dynamic behaviors of an elastically restrained beam carrying a moving mass

Dynamic responses of a simply supported beam with a translational spring carrying a moving mass are studied. Governing equations of motion including all the inertia effects of a moving mass are derived by employing the Galerkin’s mode summation method, and solved by using the Runge-Kutta integral method. Numerical solutions for dynamic responses of a beam are obtained for various cases by changing parameters of the spring stiffness, the spring position, the mass ratio and the velocity ratio of a moving mass. Some experiments are conducted to verify the numerical results obtained. Experimental results for the dynamic responses of the test beam have a good agreement with numerical ones.

Dynamic Responses and Active Vibration Control of Beam Structures Under a Travelling Mass

© 2012 Ryu and Kong, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Dynamic Responses and Active Vibration Control of Beam Structures Under a Travelling Mass

Experimental Study on Railway Vibration Isolation of a Large Structure using Isolation Materials

The paper deals with the vibration isolation of a large structure using an experimental technology. In the case of vibration isolation for the vicinity of a subway or a railroad station, most of vibration isolation techniques using isolation materials with high isolation efficiency only, have been applied. Therefore, the quantitative evaluation and design technologies are required for a vibration isolation of large structures. In this study, firstly, vibration characteristics due to train or subway are analyzed. Secondly, the performance of existing vibration isolation materials such as precision isolation material, elastomer is estimated through the experiments. Thirdly, the performance of a tire isolation material and its frame is tested and evaluated. Finally, it is shown that tire isolation materials can be applied to the vibration isolation or vibration reduction of large structures.

Structural Analysis and Vibration Characteristics of Scaffolding Structures

This paper deals with structural analysis and vibration characteristics of scaffolding structures with a hoist according to payloads. In order to analyze the vibrational and structural characteristics for 20-step scaffolding structure, structural and vibrational characteristics for 2-step scaffolding structure were compared with some experimental results. The numerical results for natural frequencies of scaffolding structures have a good agreement with experimental ones. Through the numerical analysis, firstly, it is shown that the maximum stress of scaffolding structures is lower than von-mises yield criteria when four persons with total weight of 280 kgf are working at the top of the scaffolding structures. Secondly, vibration characteristics including natural frequencies and modes for scaffolding structures are shown in case of various kinds of moving masses.

Effect of External Damping and Tip Mass on Dynamic Stability of Pipes Conveying Fluid

ABSTRACT The paper presents the influences of the external damping and the tip mass on dynamic stability of a vertical cantilevered pipe conveying fluid. In general, real pipe systems may have some valves and attached mechanical parts, which can be regarded as attached lumped masses and support-dampers. The support-dampers can be assumed as viscous dampers. The equations of motion are derived by energy expressions using extended Hamiltons principle, and some numerical results using Galerkins method are presented. Critical flow velocities and stability maps of the pipe with external dampers and tip mass are obtained for various tip mass ratios, external damping coefficients and positions of the viscous dampers. * 1. 서 론 내부에 유동유체가 흐르는 파이프의 동적안정성 및 진동에 관한 연구는 Ashley 와 Haviland (1) 에 의한 연구를 초기연구의 시초로 일컫는데, 이들은 Trans-Arabian 송유관의 진동문제를 연구하는 시도를 하였다. Feodos’ev (2) 는 유동유체가 내부에 흐르는 파이프에 대한 정확한 선형 운동방정식을 유도하고 , 파이프의 동역학적 문제를 병행하여 연구하였다. 이와 같이 초기의 연구들은 파이프 외부에 어떤 것도 부착되지 않은 파이프만의 운동방정식의 유도나 임계유속을 구하는 수치해석적 및 실험적 연구들이 대부분 이었다†교신저자;정회원, 한밭대학교 기계공학부E-mail : bjryu701@hanbat.ac.krTel : (042)821-1159, Fax : (042)821-1587* 정회원, 강원대학교 기계자동차공학부** 정회원, 한국원자력연구소그 후, 내부 유동유체에 의한 파이프의 동역학과 진동에 관한 이론 및 실험의 병행 연구는 Benjamin

Eigenvalue Branches and Flutter Modes of a Cantilevered Pipe Conveying Fluid and Having a Tip Mass

The paper describes the relationship between the eigenvalue branches and the corresponding flutter modes of cantilevered pipes with a tip mass conveying fluid. Governing equations of motion are derived by extended Hamilton`s principle, and the numerical scheme using finite element method is applied to obtain the discretized equations. The flutter configurations of the pipes at the critical flow velocities are drawn graphically at every twelfth period to define the order of quasi-mode of flutter configuration. The critical mass ratios, at which the transference of the eigenvalue branches related to flutter takes place. are definitely determined. Also, in the case of haying internal damping, the critical tip mass ratios, at which the consistency between eigenvalue braches and quasi-modes occurs. are thoroughly obtained.

Dynamic Stability of a Vertical Cantilevered Pipe Conveying Fluid with Additional Spring Supports

The paper presents the dynamic stability of a vertical cantilevered pipe conveying fluid and haying translational linear spring supports. Real pipe systems may have some elastic hanger supports or other mechanical attached parts. which can be regarded as attached spring supports. Governing equations are derived by energy expressions, and numerical technique using Galerkin`s method is applied to the equations of small motion of the pipe. Effects of spring supports on the dynamic stability of a vortical cantilevered pipe conveying fluid are fully investigated for various locations and spring constants of elastic supports.