• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.6
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• pp.678-685
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• 2012

The objective of this study is to monitor the health status of harbor caissons which have potential foundation damage. To obtain the objective, the following approaches are performed. Firstly, a structural damage monitoring(SDM) method is designed for interlocked multiple-caisson structures. The SDM method utilizes the change in modal strain energy to monitor the foundation damage in a target caisson unit. Secondly, a finite element model of a caisson system which consists of three caisson units is established to verify the feasibility of the proposed method. In the finite element simulation, the caisson units are constrained each other by shear-key connections. The health status of the caisson system against various levels of foundation damage is monitored by measuring relative modal displacements between the adjacent caissons.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.215-217
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• 2008

This paper deals with the structural vibration characteristics for an outdoor units support of an air-conditioner. Even though main noise sources are compressor noise and fluid noise which is caused by the fan, the structural modification of the outdoor units support may affect vibration and noise. In this paper, damping ratios for two kinds of an outdoor units support of an air-conditioner are measured through the modal testing. In order to reduce the structural borne noise due to an outdoor units support of an air-conditioner, four kinds of rubber materials are selected and tested.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.719-724
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• 2002

Impact hammer is widely used as a convenient excitation tool in structural modal testing though, little is known about the dynamic characteristics of its impulse mechanism. Transmission of the impulsive force to the structure depends m the dynamic properties of the impact hammer as well as the stiffness of the tip. In this study an improved dynamic model of the impact hammer is proposed with the consideration of structure to be tested. The deformation masses of hammer tip and structure are as well as their contact stiffness. Numerical results show that this model is useful for the prediction of the impulse duration and the condition of rebounce..

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.3
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• pp.110-115
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• 2010

This paper studies the vibration characteristics of a vehicle seat on several driving conditions. Modal test for a vehicle seat is conducted for the three different boundary conditions: on the rigid jig, BIW and the full vehicle. In driving on various road conditions and speeds, vibration level is measured at several locations including seat mounting and seat-back. The vibration pattern for each driving condition is found where the suspension mode and the 1st bending and torsion modes of the seat make the major contribution on it.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.401.1-401
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• 2002

The state core of a motor/generator was modeled using dynamic model updating technique based on the modal testing work. In order to take into account the orthotropic effect of laminated structure the axial, radial and circumferential properties of the solid element were separately varied to match the primary modes of the stator core which were extracted from the modal testing. Comparison of the results after model tuning showed fairly good coincidence with measured data.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1513-1520
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• 2000

Complex modal testing method for rotating disks with support motion is introduced which handles the pairs of two point excitation and responses of the disk as complex input and output, respectively. This method utilizes the directivity information and the separation over the rotational speed of forward and backward traveling wave modes or bending coupled modes in the directional frequency response functions(dFRFs). This method synthesizes the normal/reverse dFRFs and complex wave dFRF, which were originally applied to rotating shaft and rotating disk, respectively, and is applied to complex system with dynamically coupled rotating disks and shaft. Experiments with a commercial hard disk drive spindle system demonstrate the validity of this method.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1660-1665
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• 2003

On this study, we improved the efficiency applying algorithm that is repeatedly using orthogonal array in discrete design space and filling a defect of gradient method in continuous design space. we showed optimal ply angle that maximized 1st natural frequency of CFRP laminated composite cantilever plate by each aspect ratio. A finite element analysis on the CFRP laminated composite cantilever plate using orthogonal array is carried out, and the results are compared with those obtained by modal testing.

• Journal of KSNVE
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• v.9 no.6
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• pp.1234-1239
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• 1999

This research investigates the characteristicsw of NRRO in a 2.5" HDD by using FEM, modal testing and runout analysis, and reduces NRRO using visco-elastic damping material. Most frequency components of NRRO are generated by the defects of ball and rotating race, and they can be determined by the kinematic analysis of ball bearing. It also proposes the novel design of a spindle motor that can reduce NRRO effectively by inserting the visco-elastic damping material to one of the transmission path of NRRO, i.e., where the strain energy is highly concentrate. By this technique, NRRO is reduced by 27%. 27%.

• Journal of Industrial Technology
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• v.27 no.A
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• pp.47-53
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• 2007

A theoretical model based on Rayleigh-Ritz method is proposed to predict the resonance frequency of a W/T(Wind Turbine) tower structure supported by guy cables. In order to verify the validity of the theoretical model, a reduced W/T tower system is manufactured and tested. Frequency response and mode data are determined by modal testing and finite element analysis is performed to calculate the natural frequency of the tower model. Numerical and experimental results are compared with those by the theoretical analysis. Parametric study by the theoretical model shows how the cable tension and cable elasticity influence the resonance frequency of the W/T tower structure. Finally, vibration response under various rotating speed is investigated to examine the possibility of severe resonance.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.397-403
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• 1989

A slight asymmetry exists in Korean beslls due to decorative sculptures, carved figures and casting irregularities. In this study, the influence of the asymmetry on the bell's best frequencies and mode shapes is studied by using finite element method and modal testing. Also measurement techniques of nodal lines and damping ratios of bells with very small beat frequencies are discussed.