• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.8
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• pp.684-694
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• 2004

Presented in this dissertation is a new method of identifying the critical speed of rotor-bearing systems without actually reaching at the critical speed itself. Using the method, it is possible to calculate the critical speed by measuring a series of rotor responses at much lower rotating speeds away from and without reaching at the critical speed of the system. In the course of the procedures illustrated, not only the critical speed but also the damping ratio and the eccentricity of the system can be identified at the same time. Test rotor was tested on the Rotor Dynamics Test Facility at the Korea Institute of Machinery ＆ Materials. Korea, and the theory has been confirmed experimentally. The method can be adopted to monitor changes of the dynamic characteristics of critical rotating machinery before and after overhauls, repairs, exchanges of various parts, or to detect trends or direction of subtle changes in the dynamic characteristic parameters over a long periods of time.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1149-1149
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• 2006

The leakage characteristic is an important factor in power plant. However, most of power plant have efficiency problem which is occurred leaking between high pressure steam turbine axle and stator. The labyrinth seal which is used between the main turbine axle and stator in the power plant. Because it is able to be non-contact seal and it is minimize clearance to decrease the leakage. But its actual system is too huge to experiment. Therefore, most steam turbine seal performance tests were conducted by air similarity test. This paper described a test facility and program for air similarity test of high pressure steam turbine seal. A test facility has been designed and built to evaluate leakage verification of labyrinth seal. The test facility consist of air compressor, anti-swirl labyrinth seal for 1/3 air similarity model, pressure transducer, air flow measure system, instrumentation and auxiliary system. For evaluation of steam turbine seal performance, the air similarity test of labyrinth seal leakage verification was conducted and we compared experiment data and analysis result.

• Journal of the Society of Naval Architects of Korea
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• v.49 no.6
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• pp.498-503
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• 2012

Independent component analysis (ICA) technique based on statistical independency of the signals is known as suitable to identify the source signals by measuring and separating mixed signals through transfer paths and has successfully applied in the field of medical care, communications and so forth. In this study, the ICA technique is introduced for the identification of excitation sources from measured vibration signals of structures, which can be done by evaluating negentropy of centered and whitened vibration signals and correlation of separated signals. To validate the method, numerical analyses are carried out for a plate and a cylinder structure. The results show that the method can be applied efficiently to source identification of complex structures. Nevertheless, additional studies would be required to complement problems of occasional inaccuracy.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.3
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• pp.263-271
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• 2010

A reaction wheel is commonly used, as an important actuator, to control the attitude of a satellite. Operation of the reaction wheel plays a role of an excitation source to loading equipment inside the satellite. As requirements for environmental vibration to manifest the performance of precision equipment are getting more stringent, the research for analysis or reduction of unwanted action force in high frequency range when operating the reaction wheel is necessary. In this paper, the procedure to extract input forces and damping of a rotor system of reaction wheel is suggested. The analysis for measured action forces of reaction wheel is accomplished and important higher harmonics of action forces are determined. The input forces and damping of the rotor system are, then, extracted by curve-fitting and a particular solution for input force.

• Journal of the Korean Geotechnical Society
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• v.21 no.5
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• pp.33-43
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• 2005

This work reports results of our study on the dynamic responses of the buried pipelines both along the axial and the transverse directions under various boundary end conditions. In order to investigate the effect of the boundary end conditions for the dynamic responses of the buried pipeline, we have devised a computer program to find the solutions of the formulae on the dynamic responses (displacements, axial strains, and bending strains) under the various boundary end conditions considered in this study, The dynamic behavior of the buried pipelines for the forced vibration is found to exhibit two different forms, a transient response and a steady state response, depending on the time before and after the transfer of a seismic wave on the end of the buried pipeline. We have observed a resonance when the mode wavelength matches the wavelength of the seismic wave, where the mode number(k) of resonance f3r the axial direction. On the other hand, we have not been able to observe a resonance in the analysis of the transverse direction, because the dynamic responses are found to vanish after the seventh mode. From the results of the dynamic responses at many points of the pipeline, we have found that the responses appeared to be dependent critically on the boundary end conditions. Such effects are found to be most prominent especially for the maximum values of the displacement, the strain and its position.

• Explosives and Blasting
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• v.32 no.2
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• pp.1-8
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• 2014

In this study, 16 test blastings had been carried out with different spacings, burdens, drilling lengths, and charges per delay for investigating the characteristics of ground vibration propagation, which depends on the delay time. From the tests, it was possible to derive a ground vibration equation. Using the equation, the characteristics of ground vibration could be investigated by analyzing the nomogram and predicting the Peak Particle Velocity (PPV), which are influenced by the delay time and the priming location. The trend of ground vibration change depending on the delay time was analyzed for the standards charges of 0.5, 1.6, 5, and 15 kg, which were suggested in "Blasting design and construction guidelines to road construction" by the Ministry of Land, Infrastructure and Transport. From the study, it would be possible to suggest a favorable vibration control method, which depends on the charge.

• Explosives and Blasting
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• v.30 no.1
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• pp.29-36
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• 2012

In this study, the influence of priming location inside a blast hole on the ground vibration has been studied. In most of the previous studies dealing with the ground vibration, the effect of priming location in a blast hole was usually considered in a limited way. Thus, it seems that the results of the studies can be applicable only to the relevant sites. Considering the fact that the mechanism of ground vibration caused by blasting is quite complex, the priming location can have a considerable effect on the ground vibration in certain situations and be an important parameter in a blasting design. To identify the characteristics of the wave propagation according to priming locations, total 72 test blasts were carried out with different spacing, burden, drilling length, and charge, and prediction equations were derived. The characteristics of ground vibration, which was changed according to the priming location, was analyzed by using the nomogram of peak particle velocity (PPV) record. Attenuation relations, which were also dependent on the priming location, were analyzed. In this case, four different amounts of charge, that is, 0.5, 1.6, 5, and 15 kg, were used for the test. This criterion of charge amount is specified in the "Blasting design and construction guidelines to road construction" by the Ministry of Land, Transport and Maritime Affairs of Korea.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.1
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• pp.55-60
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• 2012

This experimental study investigated the characteristics of flow-induced vibration of two elastically supported circular cylinders in a side-by-side arrangement. In particular, the characteristics of the flow-induced vibration of the two cylinders are investigated by changing the flow speed at each spacing ratio L/D (L is the space between two cylinders and D is the diameter of the cylinder). To clarify the mechanism generating the flow-induced vibration of the cylinders, the flow patterns around the two vibrating cylinders are also investigated using a flow visualization test that reproduces the flow-induced vibration of the cylinders with a forced vibration apparatus. As a result, it is clarified that the flow-induced vibration characteristics of the two cylinders arranged side-by-side switch among four patterns as the flow between the two cylinders is switched. Among the three arrangements considered (tandem, staggered, and side-by-side), the arrangement that generates flow-induced vibration of the two cylinders most easily is the side-by-side arrangement.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.4
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• pp.47-55
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• 2009

The purpose of this study is to verify the transfer function of input acceleration and output control force by linearizing a velocity-dependent damping term of Liquid Column Vibration Absorber (LCVA). Analytical and experimental research is conducted to identify natural frequency, damping ratio and participated mass ratio of LCVA with various section ratios of vertical and horizontal areas. Findings obtained experimentally by the shaking table test are compared with analytical findings using optimization technique with constraints. The results indicate that the level of liquid and section ratio of LCVA affect the characteristics of damping ratio and mass ratio. Damping and mass ratio increase as the section of vertical column of LCVA decreases, due to turbulence in the elbow of LCVA.

• Tunnel and Underground Space
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• v.24 no.1
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• pp.97-109
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• 2014

In order to identify the characteristics of the propagation depending on delay time (20, 25 ms) and priming location (top priming, middle priming, bottom priming), test blasts were carried out a total of 4 times using different spacing, burden, drilling length, charge per delay and was derived the formula to predict blast vibration. This study investigated the characteristics of vibration by analysis of the nomogram and prediction of Peak Particle Velocity (PPV) from delay time and priming location by the formula to predict ground vibration. And it analyzed the trends of vibration increase by standards charge 0.5, 1.6, 5, 15 kg. Standards charge is "Blasting design and construction guidelines to road construction" by the Ministry of Land, Infrastructure and Transport. Depending on the charge in favor of vibration control method is proposed. Thus, when the design was to be used as a variable.