• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.11
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• pp.1957-1964
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• 1997

Torsional vibration is to vibrate strongly when the ignition pulses of the engine is excited with natural frequency of driveline. Torsional vibration like this can cause various noises as rattle and booming. For this study multi-degree of freedom analysis model of torsional vibration, which is combined with mass moment of inertia and torsional spring, was developed toward two wheel drive, four wheel drive and torsional vibration characteristics were compared and analyzed through the natural frequences, mode shapes and frequency response characteristics which was acquired by the simulation of it. The pertinence of that model was proved by the field test and the outcome of the simulations coincided with feeling test. Therefore, four wheel drive simulation model is considered to be useful thing for reducing torsional vibration of driveline and developing full-time four wheel drive vehicles.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.119-122
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• 2003

This paper describes characteristics for insertion losses of Isolator have an effect on material parameter. One purpose of the paper is to present insertion loss on this resonator for magnetic loss, dielectric loss, magnetic field and saturation magnetization. Another is to study the effect of propeller resonator on response characteristics. In this paper, the analysis and measurement of the response characteristics were carried out for the isolator prototype. The measurement results agreed on the simulation results and acquire insertion loss $0.18\;{\sim}\;0.24dB$, return loss 27dB, isolation 27dB and bandwidth 500MHz on this condition saturation magnetization 550G, dielectric loss 0.0004, magnetic loss 20 and dielectric constant 14.

• The Journal of the Acoustical Society of Korea
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• v.31 no.3
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• pp.197-204
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• 2012

In this thesis, studied the method to minimize the changes in frequency response and level due to the variation of the distance from the source to the microphone. selecting three microphones (omni directional, cardioid, super cardioid) which are being used generally, frequency responses were measured in accordance with the distance changes. Gotten the difference from the reference as the result of measurement, changed responses for each frequency range were compensated in comparison of the original human vocal source. In low frequency range, the low frequency boost caused by the proximity effect and decrease in accordance with the distance were compensated. The variation in mid-frequency range is comparatively small, however since the mid-range is the most important part of the human vocal signal, were compensated the mid-frequency range in comparison of the reference. The human vocal signal variation in high frequency range is extremely small and the high frequency is compensated close to the original source without difficulty. Understanding the microphone characteristics and compensations, this study showed that the response can be maintain among the change of the distance from the source to the microphone.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.941-944
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• 2005

Asymmetry of rotor systems is an important factor for identification of dynamic characteristics including the stability and response of rotors and for condition monitoring. In this work, asymmetry of rotors is identified by applying curve-fitting method to the directional frequency response functions (dFRFs), which are known as a powerful tool for detecting the presence and degree of asymmetry. This method minimizes least square error between analytical and measured dFRFs by iteratively updating physical parameters associated with rotor asymmetry. The effectiveness of the identification method is demonstrated by experiments with a laboratory test rotor.

• Journal of KSNVE
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• v.7 no.1
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• pp.61-69
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• 1997

Despite of the development in the finite element method, it is difficult to get the finite element model describing the dynamic characteristics of the complex structure exactly. Therefore a number of different methods have been developed in order to update the finite element model of a structure using vibration test data. This paper outlines the basic formulation for the frequency response function based updating method. One important advantage of this method is that the intermediate step of performing an eigensolution extraction is unnecessary. Using simulated experimental data, studies are conducted in the case of 10 DOF discrete system. The solution of noisy and incomplete experimental data is discussed. True measured frequency response function data are used for updating the finite element model of a beam and a plate. Its applicability to the joint identification is also considered.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.11a
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• pp.160-166
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• 1999

Nonlinear characteristics of the hydrodynamic journal bearing with circumferentially groove are analyzed numerically considering cavitation region, when an external sinusoidal shock is given to the system. The oil film force is obtained by solving the finite width universal Reynolds equation at each time step. Frequency response function and journal orbit obtained from both linear and nonlinear bearing simulations are compared with each other. The vibration response of the journal is different from the expectation obtained from the linear analysis as increase the vibration amplitude of external disturbance. Therefore, the linear theory is not adequate, and the nonlinear calculation such as used in this research is needed to design safety rotor systems.

• The Journal of the Acoustical Society of Korea
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• v.18 no.4E
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• pp.31-36
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• 1999

Circulant Feedback Delay Networks (CFDN's), whose feedback matrix is circulant to control the stability of system and time-frequency response easier than unitary one, were recently proposed. However, the drawback of this structure is that the flatness of the frequency response of CFDN's is not enough and it is difficult to adjust the placement of zeros to decrease this problem. Therefore, we propose Modified CFDN's (MCFDN's) consisted of a general recursive filter and CFDN's to maintain maximally the impulse response of CFDN's and improve the flatness of frequency response without adjusting the placement of zeros. The delay unit of a general recursive filter's feedback loop is replaced by CFDN's, are omitted the direct path. We represent the usefulness of MCFDN's to build artificial reverberators and the main parameter to determine characteristics of MCFDN's in this paper.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.5
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• pp.123-130
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• 2001

The purpose of this paper is to reduce the level of idling vibration on a steering wheel. In some cases, vibration on steering wheel is amplified due to the resonance between the first natural frequency of T-beam and engine idling speed. Using SDM(structural dynamic modification) technique, T-beam is redesigned to reduce its vibration. This paper used FRF(frequency response function) synthesis technique which is entirely dependent on experiment. But this method requires lots of test efforts to enhance its reliability of design. While combining this method with an analytic method. the experimental burden, the major drawback of FRP synthesis method, can be considerably relieved. Using ana1ytic sensitivity analysis, some effective modification regions are preliminarily chosen as candidate Positions where SDM can be applied to modify T-beam\`s dynamic characteristics.

• Wind and Structures
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• v.30 no.1
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• pp.85-97
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• 2020

The accurate estimation of the buffeting response of a bridge pylon is related to the quality of the bridge construction. To evaluate the influence of wind field characteristics on the buffeting response of a pylon in a trumpet-shaped mountain pass, this paper deduced a multimodal coupled buffeting frequency domain calculation method for a variable-section bridge tower under the twisted wind profile condition based on quasi-steady theory. Through the long-term measurement of the wind field of the trumpet-shaped mountain pass, the wind characteristics were studied systematically. The effects of the wind characteristics, wind yaw angles, mean wind speeds, and wind profiles on the buffeting response were discussed. The results show that the mean wind characteristics are affected by the terrain and that the wind profile is severely twisted. The optimal fit distribution of the monthly and annual maximum wind speeds is the log-logistic distribution, and the generalized extreme value I distribution may underestimate the return wind speed. The design wind characteristics will overestimate the buffeting response of the pylon. The buffeting response of the pylon is obviously affected by the wind yaw angle and mean wind speed. To accurately estimate the buffeting response of the pylon in an actual construction, it is necessary to consider the twisted effect of the wind profile.

• Earthquakes and Structures
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• v.3 no.2
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• pp.169-180
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• 2012

The performance of pure friction isolation system with respect to the frequency bandwidth of excitation and the predominant frequency is investigated. A set of earthquake ground motions (artificial as well as recorded [with different combinations of magnitude-distance and local site geology]) is considered for investigating effectiveness of pure friction isolators. The results indicate the performance of pure friction base isolated system does not only depend upon coefficient of friction and mass ratio but the stick-slip behaviour depends upon the frequency content of the excitation as well. Slippage prevails if the excitation frequency lies in a suitable frequency range. This range widens with increasing mass ratio. For larger mass ratios, the sliding effect is more pronounced and the maximum acceleration response is further reduced in the neighbourhood of frequency ratio (${\omega}/{\omega}_n$) of unity. The pure friction isolation system is effective in the case of broadband excitations only and that too, in the acceleration sensitive range of periods. The pure friction system is not effective for protection against narrow band motions for which the system response is quasi-periodic.