• Journal of Korean Association for Spatial Structures
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• v.14 no.1
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• pp.61-68
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• 2014

The design of foot-bridge is often influenced by natural frequency. Consequently, vibration frequency becomes important. The empirical expressions used to quantify this parameter at the design phase have not been developed enough to give guideline to Korean foot-bridge. This paper is concerned with the vertical natural frequency of steel foot-bridges. It describes the vibration measurement methods employed for testing structures and presents reliable methods of assessing natural frequency from jumping vibration tests. Data from measurements on 16 structures in Seoul are given. Regression formulas of natural frequency for steel-framed foot-bridges are suggested. Finally, obtained formula are compared with empirical expressions of Seoul City's guideline.

• Journal of international Conference on Electrical Machines and Systems
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• v.3 no.4
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• pp.389-393
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• 2014

This paper presents one of the methods for design to reduce the noise and vibration of 200kW motor for electric propulsion ship. One of the important factors affecting vibration of the motor is the resonance. The natural frequency and natural mode of the 200kW motor is analyzed by using FEM tool and impact test equipment to avoid the resonance. Also, compare FEM result with impact test result to make a reliable FE model of 200kW motor. In order to find out the effect of the noise and vibration of the motor by electromagnetic excitation force, conduct electromagnetic-structure coupled analysis. These characteristics are much useful to design 200kW motor for electric propulsion ship.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.9 s.114
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• pp.912-918
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• 2006

A modeling method for the vibration analysis of rotating multi-blade systems considering the coupling stiffness effect is presented in this paper. Blades are assumed as cantilever beams and the coupling stiffness effect originates from disc or shroud between blades. As the angular speed, hub radius ratio, and the coupling stiffness vary, the natural frequencies of the system vary. Numerical results show that the coupling stiffness is very important to estimate the natural frequencies. Along with the natural frequencies, associated mode shapes, critical angular speed, and critical hub radius ratio are obtained through the analysis.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.963-968
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• 2004

Free vibration analysis of helical spring with crack was studied. Natural frequency changes due to the crack was analyzed with respect to crack locations. The effect of crack on natural frequency was decreased as crack location is further from the fixed end of a spring. The frequency change was larger in rectangular-shaped spring than that in circular-shaped spring. It was found that experiment may not be appropriate to determine the presence of crack because no significant natural frequency change can be shown by experiment.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.919-922
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• 2003

The correlation between noise and vibration by a heavy-weight floor impact was studied. The triggering technique was used for increasing the reliability and stability to measure the level of sound pressure, sound intensity and vibration acceleration. The simple finite element and rigid body analysis method were suggested to calculate the natural frequencies of the multi-layer floor system. The result show that the isolation material adapted to reduce the light-weight floor impact noise, causing the natural frequency lower, make resonance with dominant driving frequency, and increase the noise level very sharply. Therefore the noise level Peak in the region of low frequency, below 63Hz, would be related with the natural frequencies of the floor system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1354-1359
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• 2006

A modeling method for the vibration analysis of rotating multi-blade systems considering the coupling stiffness effect is presented in this paper. Blades are assumed as cantilever beams and the coupling stiffness effect originates from disc or shroud between blades. As the angular speed, hub radius ratio, and the coupling stiffness vary, the natural frequencies of the system vary. Numerical results show that the coupling stiffness is very important to estimate the natural frequencies. Along with the natural frequencies, associated mode shapes, critical angular speed, and critical hub radius ratio are obtained through the analysis.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1040-1043
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• 2006

Every mechanical system has a series of natural frequencies at which it will vibrate and to which it will respond if an external stimulus or excitation at this frequency is applied. Vibration is not of itself dangerous, and is always anticipated in an operating unit. However, if the frequency of operation is coincidental with one of the natural frequency of the blade system or the blade has a natural frequency near coincide with the exciting stimulus, then the amplitude of vibration of the blade may increase to the destructive damage can result. In this paper We investigated damage of blade when turbine operated.

• Structural Engineering and Mechanics
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• v.33 no.6
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• pp.747-763
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• 2009

In this work, the linear vibration characteristics of $90^{\circ}$ pipe bends and their cylindrical and toroidal shell components are studied. The finite element method, based on shear-deformation shell elements, is used to carry out a vibration analysis of metallic multiple $90^{\circ}$ mitred pipe bends. Single, double, and triple mitred bends are considered, as well as a smooth bend. Sample natural frequencies and mode shapes are given. To validate the procedure, comparison of the natural frequencies is made with existing results for cylindrical and toroidal shells. The influence of the multiplicity of the bend, the boundary conditions, and the various geometric parameters on the natural frequency is described. The differential quadrature method, based on classical shell theory, is used to study the vibration of components of these bends. Regression formulas are derived for cylindrical shells (straight pipes) with one or two oblique edges, and for sectorial toroidal shells (curved pipes, pipe elbows). Two types of support are considered for each case. The results given provide information about the vibration characteristics of pipe bends over a wide range of the geometric parameters.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.8 s.101
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• pp.988-995
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• 2005

Vibration has been severly increased at the branch pipe of main steam header since the commercial operation of nuclear power plant. Intense broad band disturbance flow at the discontinuous region such as elbow, valve, and header generates the acoustical pulsation which is propagated through the piping system. The pulsation becomes the source of low frequency vibration at piping system. If it coincide with natural frequency of the pipe system, excessive vibration is made. High level vibration due to the pressure pulsation related to high dynamic stress, and ultimately, to failure probability affects fatally the reliability and confidence of plant piping system. This paper discusses vibration effect for the branch pipe system due to acoustical pulsations by broad band disturbance flow at the large main steam header in 700 MW nuclear power plant. The exciting sources and response of the piping system are investigated by using on-site measurements and analytical approaches. It is identified that excessive vibration is caused by acoustical pulsations of 1.3 Hz, 4.4 Hz and 6.6 Hz transmitted from main steam balance header, which are coincided with fundamental natural frequencies of the piping structure. The energy absorbing restraints with additional stiffness and damping factor were installed to reduce excessive vibration.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.780-785
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• 2005

Vibration has been severly increased at the branch pipe of main steam header since the commercial operation of a nuclear power plant. Intense broad band disturbance flow at the discontinuous region such as elbow, valve or heather generates the acoustical pulsation which is propagated through the piping system. The pulsation becomes the source of low frequency vibration at piping system. If it coincide with natural frequency of the pipe system, excessive vibration is made. High level vibration due to the pressure pulsation related to high dynamic stress, and ultimately, to failure probability affects fatally the reliability and confidence of plant piping system. This paper discusses vibration effect for the branch pipe system due to acoustical pulsations by broad band disturbance flow at the large main steam header in 7nn nuclear power plant. The exciting sources and response or the piping system are investigated by using on site measurements and analytical approaches. It is identified that excessive vibration is caused by acoustical pulsations of 1.3Hz, 4.4Hz and 6.6Hz transferred from main steam header, which are coincided with fundamental natural frequencies of the piping structure. The energy absorbing restraints with additional stiffness were installed to reduce excessive vibration.