• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.8 s.113
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• pp.886-892
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• 2006

Hot spot phenomenon is caused by non-uniform contact area between brake pad and disk frequent braking. Brake disk deformed by locally concentrated heat increases magnitude of frictional vibration. And this deformation can highly influence the judder vibration. In this experimental study, vibration and hot spot was measured in accordance with rotation of disk and pressure of master cylinder for finding the factors that causes hot spot phenomena. For comparing hot spot aspects with mode shapes of disk, mode shapes were measured by conducting modal test, and analyzed by using finite element analysis. Relation between hot spot phenomenon, and mode shape, pressure of master cylinder and rotation speed of disk respectively, was achieved by hot spot measurement and frequency analysis.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.27 no.2
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• pp.204-212
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• 2017

The rotor dynamics and balancing technic for rotating equipment during engineering and manufacture stage are to be carefully considered in order to minimize the operation troubles regarding vibration during commissioning stage. In this paper, the test rig, which includes the disks as balancing plane, is designed and manufactured, so that the characteristic of rotor dynamics can be analyzed such as critical speed and mode shape. The critical speed predicted through natural frequency analysis is verified by the actual measurement on bearing housing vibration during start-up condition of test rig. The low speed balancing and the operating speed balancing test are performed respectively with consideration of first critical speed, and the residual unbalance amounts are estimated in accordance with the relevant method described in API standard. In addition, the single and dual plane balancing are carried out on main disk and trim disk depended on phase information at each balancing step.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.381-384
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• 2005

The purpose of this study is to develop a prediction model for evaluating heavy-weight floor impact sounds in a test building. Three rooms in the test building (slab thickness In and 240mm), which consist of frame concrete structures were tested and modeled. First, the SPL distribution in the receiving room was analyzed by measuring SPL at 90 positions using a bang machine. Then, a vibration model using finite element method is proposed considering the material properties and boundary conditions. In addition, the result of transient analysis was compared with field measurements using a standard heavy-weight impact source. Through a vibro-acoustic simulation program, an acoustic model evaluating the building elements (reflected wall, nor, window and door) was proposed. Finally, validation of the prediction model was conducted by vibro-acoustic analysis with field measurements of noise radiation characteristics in receiving rooms.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1162-1165
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• 2001

Operational Modal Analysis also known as Output Only Modal Analysis has in the recent years been used for extracting modal parameters of civil engineering structures and is now becoming popular for mechanical structures. The advantage of the method is that no artificial excitation need to be applied to the structure or force signals to be measured. All the parameter estimation is based upon the response signals, thereby minimising the work of preparation for the test. This test case is a controlled lab set-up enabling different parameter estimation methods techniques to be used and compared to the Operational Modal Analysis. For Operational Modal Analysis two different estimation techniques are used： a non-parametric technique based on Frequency Domain Decomposition (FDD), and a parametric technique working on the raw data in time domain, a data driven Stochastic Subspace Identification (SS!) algorithm. These are compared to other methods such as traditional Modal Analysis.

• Structural Engineering and Mechanics
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• v.84 no.6
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• pp.823-829
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• 2022

This study considered the experimental parameters (Nano-graphene oxide reinforced polycarbonate, GFRP) under low-velocity impact load and vibration analysis. The effect of nano-graphene oxide (NGO) on a polycarbonate-based composite was studied. Two test procedures were adopted to obtain experimental results, vibration analysis. The mechanical tests were performed on damaged and non-damaged specimens to determine the damaging effect on the composite specimens. After the test was carried out, the effect of NGO was measured and damping factors were ascertained experimentally. 0. 2 wt% NGO was determined as the optimum amount that best affected the Vibration Analysis. The experiments revealed that the composite's damping properties were increased by adding the nanoparticles to 0.25 wt% and decreased slightly for the specimens with the highest nanoparticles content. Cyclic sinus loading was applied at a frequency of 3.5 Hz. This paper study the frequency effect of 3.5khz frequency damage on mechanical results. Found that high frequency will worthlessly affect the fatigue life in NGO/polycarbonate composite. In 3.5 Hz frequency, it was chosen to decrease the heat by frequency. Transmission electron microscopy (TEM) micrographs were used to investigate the distribution of NGO on the polycarbonate matrix and revealed a homogeneous mixture of nano-composites and strong bonding between NGO and the polycarbonate which increased the damping properties and decreased vibration. Finally, experimental modal analysis was conducted after the high-velocity impact damage process to investigate the defect on the NGO polycarbonate composites.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.376-379
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• 2006

Reaction Wheel Assembly (RWA) is one of the major disturbance sources that have influence upon the Line of Sight (LOS) of payload. A micro-vibration induced by RWA is propagated through the satellite structure and decrease the LOS stability performance of payload. This effect shall be analyzed through the jitter analysis. If a requirement or specification of payload jitter level is found to be not satisfied according to the jitter analysis campaign, some modification or redesign should be done on the satellite structure or a couple of isolator should be attached on the RWA interface in order to reduce the transmitted vibration level of RWA. The purpose of ???RWA isolator test? is to roughly evaluate the performance of vibration suppression level with a passive RWA isolator made of rubber. For this test, actual RWA is used as a vibration source and a couple of cube-shaped rubber mount designed for satellite is used as a passive isolator. There may be several considerations in order to accommodate RWA isolator to spacecraft such as not only vibration reduction performance but also thermal conduction problem, mechanical size, RWA alignment problem, etc. But in this report the feasibility of RWA isolator is analyzed only in a vibration suppression point of view. As a result, high frequency vibration of RWA above 50Hz is perfectly attenuated with isolators, however, first harmonic components below 50Hz became larger due to the additional low frequency resonance modes of roll, pitch, yaw rigid body motion of RWA+bracket.

• Journal of Korean Association for Spatial Structures
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• v.15 no.4
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• pp.107-114
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• 2015

Large spatial structures can not easily predict the dynamic behavior due to the lack of construction and design practices. The spatial structures are generally analyzed through the numerical simulation and experimental test in order to investigate the seismic response of large spatial structures. In the case of analysis for seismic response of large spatial structure, the many studies by the numerical analysis was carried out, researches by the shaking table test are very rare. In this study, a shaking table test of a small-scale arch structure was conducted and the dynamic characteristics of arch structure are analyzed. And the dynamic characteristics of arch structures are investigated according to the various column cross-section and length. It is found that the natural vibration periods of the small-scaled arch structure that have large column stiffness are very similar to the natural vibration period of the non-column arch structure. And in case of arch structure with large column stiffness, primary natural frequency period by numerical analysis is very similar to the primary natural frequency period of by shaking table test. These are because the dynamic characteristics of the roof structure are affected by the column stiffness of the spatial structure.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.911-916
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• 2012

It is important to identify dynamic characteristics of nuclear fuel components. Since the fuel always exposed to turbulent flow, the dynamic contact between grids and rods is one of the fuel failure modes. The dynamic behavior of grids in nuclear fuels is quite complex, since two pairs of spring support are placed in the limited space. The strap in a cell has single spring and double dimples and this paper focuses on investigation of the grid strap(Test Fuel Strap, TFS) vibration in one cell. To identify the grid strap vibration, modal analysis of the strap is performed using Finite Element Method (FEM). Modal testing on a $5{\times}5$ grid structure without rods is performed. The modal testing results are compared to analytic results. In addition, random test considering rod effect is performed about a $5{\times}5$ grid with rods under real contact condition in the air. Finally, the strap vibration of a $5{\times}5$ fuel bundle in INvestigation of Flow INduced vIbraTion(INFINIT) facility is measured in real fluid velocity condition without heating. It is shown that modal frequencies from the test are almost equal to those peak frequencies in the INFINIT test.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.13-18
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• 2001

This paper deals with finite element analysis for free vibration and forced sine vibration of Ka- and Ku- bend antenna structures using MSC/PATRAN/NASTRAN. The structures are designed to satisfy minimum resonance frequency requirement in order to decouple the dynamic interaction of the satellite with the spacecraft bus structure. From the forced sinusoidal vibration, we have observed output acceleration versus input in X-,Y- and Z- direction, based on base excitation using large mass method. The results of finite elements analysis can be used as the reference data for the experimental test of satellite antenna, resulting in the reduction of cost and time by predicting and complementing experimental data.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.232-237
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• 2006

Operation deflection shapes(ODS) is defined as a motion of structure at particular frequency. The ODS is eligible to show any types of structural motions while the modes supply solutions only to linear and stationary motion. The principal vibration source of an auto teller machine(ATM) case was occurred due to resonance which was found by modal analysis. To reduce the vibration of ATM case, the motion of the case was visualized using ODS analysis, which can suggest how to modify the structure. As a result the vibration of the ATM case was greatly reduced with a stiffening bar between the opposite plates.