• Journal of KSNVE
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• v.9 no.3
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• pp.577-586
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• 1999

Estimation of damping ratio for vibration signals measured on the passenger car's sear is useful for the objective evaluation of impact harshness in car. The vibratio signal is a transient signal represented by many coupled modes of suspension system. Wavelet transform automatically decouples these modes in the time-frequency domain. Damping ratios for decoupled modes are obtained by logarithmic treatment for the Wavelet transformed signal. The objective evaluation using Wavelet transform has been well corresponded with subjective evaluation done by skilled engineers.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.536-542
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• 2000

The present paper introduces a new fixed interface component mode synthesizing technique based on the notion of higher-order field-consistency. The present technique employs higher-order residual constraint modes in addition to lower fixed interface normal modes while consistency in matching field variables at the substructure interface is maintained. The present field-consistency approach does not increase the size of the synthesized system even if higher-order residual constraint modes are included. A new field-consistent higher-order synthesis technique is first presented and a numerical example is given to verify the present method.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.12
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• pp.956-964
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• 2003

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.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1376-1378
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• 2006

Numerical and experimental study were carried out to characterize sound fields of low frequency in a scaled reverberation chamber for measurement of sound insulation of panels. By using BEM, lower modes of the chamber are identified and then predicted the effect of diffusers in order to destruct lower modes. Compared results with measurements show reasonable agreements, especially at the first end second modes. Based on numerical prediction, the diffuser are installed in order to improve sound fields to be more diffuse than ever. It is found that the diffuser put in nodal line of the chamber destruct evidently the first mode. Consequently, the measuring error at the low frequency can be relatively reduced compare to the case of without diffuser.

• Smart Structures and Systems
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• v.15 no.3
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• pp.831-846
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• 2015

Magneto-Rheological (MR) dampers are being used increasingly because of their adaptability to control algorithms and reliability of passive systems. In this paper, an extensive investigation on performance of MR dampers in semi-active and passive modes has been carried out. It is observed that the overall energy dissipation by MR dampers in passive-on modes is higher than that in semi-active modes for most of the competitive semi-active controllers. Based on the energy dissipation pattern, a novel semi-active controller, termed as "Simple Passive Semi-Active Controller", has been proposed for MR dampers. This controller can be emulated by a simple passive hardware proposed in this paper. The proposed concept of controller "hardware emulation" is innovative and can also be implemented for other semi-active devices for control algorithms of certain form. The effectiveness and reliability of the proposed controller has been investigated extensively through numerical simulations. It has been demonstrated that the proposed controller is competitive to or more effective than other widely used / investigated semi-active controllers.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1370-1375
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• 2001

Substructure coupling or component mode synthesis may be employed in the solution of dynamic problems for structure. The model is partitioned into several subdomains. and a generalized Craig-Bampton representation is derived. In this paper the mode sets(normal modes. constraint modes) have been employed for model reduction. A generalized model reduction procedure has been described. Those reduction methods which adapt constraint modes have been described in detail. As examples. a flexible structure and a 10 DOF damped system are analyzed. Comparison with a conventional reduction method based on a complete model has been made via eigenpairs and dynamic responses.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.83-88
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• 2004

Acoustic modes of internal region of 4-hp scroll compressor are identified by measuring transfer functions between a reference and 84 measuring points. The corresponding acoustic mode-shapes and natural frequencies were calculated by analysis software SYSNOISE. There exist two clearly distinguishable dipole modes of vertical and horizontal direction and a single quadrupole mode in the frequency region of interest. It shows that the natural frequencies of the identified modes are linearly sensitive to suction pressure (Ps) but relatively in sensitive to discharge pressure (Pd) in operating condition.

• Proceedings of the Acoustical Society of Korea Conference
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• 1994.06a
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• pp.770-774
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• 1994

The volume of an acoustic source is important in determining various acoustic parameters. One of the suggested techniques is the internal pressure method incorporating a loudspeaker attached to a chamber wall and a microphone inserted into the cavity. Although the method is easy to handle with a very simple measurement setup, the coupling effects between the dynamic system of the loudspeaker and acoustic field, and the effects of higher order modes introduced by the discontinuities in the acoustic field, and the effects of higher order modes introduced by the discontinuities in the acoustic field should be considered for precise result. In this study, higher order modes due to the discontinuities of loudspeaker and microphone boundaries are included and the electro-acoustic coupling effects are compensated for by using the results of two cylinders with different lengths. The volume velocity of a loudspeaker thus obtained agrees very with that measured by laser sensor.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.3
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• pp.208-213
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• 2004

This paper is concerned with the theoretical estimation of the single-input single-output(SISO) positive position feedback(PPF) controller and the derivation of the stability conditions for the multi-input multi-output (MIMO) PPF controller. Although the stability condition for the SISO PPF controller was derived in the earlier works, the question regarding the performance estimation of the SISO PPF controller has never been studied theoretically. Hence, the SISO PPF controller for the single degree-of-freedom system was first investigated and then control parameters including gain, the filter frequency, and the damping factor of the PPF controller were analyzed in detail thus providing the design methodology for the SISO PPF controller. In the case of real structure. there are infinite number of natural modes so that some modes are to be controlled by a limited number of actuator and sensor. Based on the theoretical results on the SISO PPF controller, the stability condition for the multi-input multi-output PPF controller was derived when only the few number of modes are to be controlled. The control spillover problem is also discussed in detail.

• Journal of the Korean Society of Safety
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• v.17 no.2
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• pp.8-15
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• 2002

In order to investigate the vibration characteristics of fluid-structure interaction problem, we modeled two identical rectangular plates coupled with fluid. A commercial computer code, ANSYS was used to perform finite element analysis and FEM solutions were compared with the experimental results to verify the finite element model. As a result, comparison of FEM and experiment showed good agreement, and the transverse vibration modes, in-phase and out-of-Phase, were observed alternately in the fluid-coupled system. The effect of fluid gap size on the fluid-coupled natural frequency were investigated. It was shown that the mode numbers increased, the normalized natural frequencies monotonically increased. And it was also found that an increase of the fluid gap reduced the coupled natural frequencies for the in-phase modes but increased the coupled natural frequencies for the out-of phase modes, and eventually converged to the results of an infinite fluid gap.