• Wind and Structures
• /
• v.16 no.6
• /
• pp.561-577
• /
• 2013

Rational Functions are used to express the self-excited aerodynamic forces acting on a flexible structure for use in time-domain flutter analysis. The Rational Function Approximation (RFA) approach involves obtaining of these Rational Functions from the frequency-dependent flutter derivatives by using an approximation. In the past, an algorithm was developed to directly extract these Rational Functions from wind tunnel section model tests in free vibration. In this paper, an algorithm is presented for direct extraction of these Rational Functions from section model tests in forced vibration. The motivation for using forced-vibration method came from the potential use of these Rational Functions to predict aerodynamic loads and response of flexible structures at high wind speeds and in turbulent wind environment. Numerical tests were performed to verify the robustness and performance of the algorithm under different noise levels that are expected in wind tunnel data. Wind tunnel tests in one degree-of-freedom (vertical/torsional) forced vibration were performed on a streamlined bridge deck section model whose Rational Functions were compared with those obtained by free vibration for the same model.

• Wind and Structures
• /
• v.27 no.6
• /
• pp.357-368
• /
• 2018

For a long cable-stayed bridge, stay cables are its most important load-carrying components. In this paper, long-term monitoring of super-long stay cables of Sutong Bridge is introduced. A comprehensive data analysis procedure is presented, in which time domain and frequency domain based analyses are carried out. In time domain, the vibration data of several long stay cables are firstly analyzed and the standard deviation of the acceleration of stay cables, and its variation with time are obtained, as well as the relationship between in-plane vibration and out-plane vibration. Meanwhile, some vibrations such as wind and rain induced vibration are detected. Through frequency domain analysis, the basic frequencies of the stay cables are identified. Furthermore, the axial forces and their statistical parameters are acquired. To investigate the vibration deflection, an FFT-based decomposition method is used to get the modal deflection. In the end, the relationship between the vibration amplitude of stay cables and the wind speed is investigated based on correlation analysis. Through the adopted procedure, some structural parameters of the stay cables have been derived, which can be used for evaluating the component performance and corresponding management of stay cables.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.3 no.2
• /
• pp.147-154
• /
• 1999

A new approach to conducting the vibration parameters identification algorithm is proposed. The approach employs the concept of modal amplitude ratio implemented in a mode shape estimation. The accuracy of the improved Ibrahim Time Domain identification algorithm in extracting structural modal parameters from free response functions has been studied using computer simulated data for 9 stations on the two-span continuous beam. Simulated responses from the lumped and distributed parameter system demonstrate that this algorithm produces excellent results, even in the 300% noise response.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.16 no.11 s.116
• /
• pp.1100-1107
• /
• 2006

As environmental vibration requirements on precision equipment become more stringent, use of pneumatic isolators has become more popular and their performance is subsequently required to be further improved. Performance of passive pneumatic isolators is related to various design parameters in a complicated manner and, hence, is very limited especially in low frequency range by chamber volume. In this study, transmissibility behavior of the pneumatic isolators depending on frequency and dynamic amplitude are presented. Then, an active control technique, time delay control, which is adequate for a low frequency nonlinear system, is applied. A procedure of applying the time delay control law to a pneumatic isolator is presented and it's effectiveness in the transmissibility performance is shown. Comparison between passive and active pneumatic isolators is made based on simulation.

• Proceedings of the KIEE Conference
• /
• 2015.07a
• /
• pp.1517-1518
• /
• 2015

The paper deals with the real time sensing of a chatter vibration in grinding machine line of automobile bearings using machine black box. The chatter vibration plays bad role in machining quality such as high roughness as well as tool life and machine failure. In this paper, the vibration signals of the automobile hub bearing in the grinding process are shown in the time domain and frequency domain. Through the vibrational signals, chatter vibration badness is detected using machine black box. Therefore, machine black box can be applied to the real time detection of the grinding process in engineering fields.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2006.05a
• /
• pp.837-843
• /
• 2006

As environmental vibration requirements on precision equipment become more stringent, use of pneumatic isolators has become more popular and their performance is subsequently required to be further improved. Performance of passive pneumatic isolators is related to various design parameters in a complicated manner and, hence, is very limited especially in low frequency range by chamber volume. In this study, transmissibility behavior of the pneumatic isolators depending on frequency and dynamic amplitude are presented. Then, an active control technique, time delay control, which is adequate for a low frequency nonlinear system, is applied. A procedure of applying the time delay control law to a pneumatic isolator is presented and it's effectiveness in the transmissibility performance is shown. Comparison between passive and active pneumatic isolators is made based on simulation.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1996.05a
• /
• pp.587-593
• /
• 1996

Vibration analysis is one of the most powerful tools available for the detection and isolation of incipient faults in mechanical systems. The methods of vibration analysis in use today and under continuous study are broad band vibration monitoring, time domain analysis, and frequency domain analysis. In recent years, great interest has been generated concerning the use of time-frequency representation and its application for a machinery diagnostics and condition monitoring system. The objective of the research described in this paper was to develop a new diagnostic tool for the rotating machinery. This paper introduces a new time-frequency representation, Directional Wigner-Ville Distribution, which analyses the time- frequency structure of the rotating machinery vibration.

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

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2003.05a
• /
• pp.973-978
• /
• 2003

Vibration and Noise of air conditioner are entirely determined by compressor vibration. Compressor vibration transmitted to the enclosure of air conditioner or Pipes connected compressor with heat exchanger. Enclosure generated noise and vibration. Therefore, the analysis of compressor vibration analysis is considered significant technical issue. For the reduction of vibration of compressor, it is necessary to grasp correctly vibration transmission paths and excitation sources in the compressor shell. Because, shell (Surface of compressor) shows whole vibration characteristic of compressor mechanism. In this paper, vibration intensity was applied to measure vibration energy flow on the shell. From this technique, it is possible to catch the path of vibration propagation along the one cycle and the location of vibration energy sources may change with time on the shell.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2010.05a
• /
• pp.612-613
• /
• 2010