• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.778-781
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• 1995

In this paper, sound radiation of a rotary compressor used in room air-conditioner is investigated. structural eigenmodes are identified through modal test. Since accumulator is found important factor of sound radiation, damping material was added around accumulator to reduce sound radiation level of rotary compressor. As result, sound radiation was reduced to 3 dB.

• Journal of Biomedical Engineering Research
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• v.11 no.1
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• pp.179-186
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• 1990

A numerical analysis of crutch walking cycle has been performed to determine the transmissibility of a single-degree-of-freedom crutch system when a non-harmonic periodic forcing function is acting on the spring-damping-mass system. The results indicate that the damping factor which can reduce the forces transmitted to the human body plays an important role. In crutch walking, the stride angle of dynamic crutches must be limited for the comfortable walking.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.592-596
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• 2012

This paper presents numerical analysis result of rotor-bearing system of a multi-stage high pressure pump. Especially resonance possibility, stability and damping factor are estimated for a selected commercial multi-stage high pressure pump. The result shows that it is not easy to avoid resonance of rotor-bearing system against main excitation forces which are residual unbalance force and pressure pulsation. This makes damping effect be more important.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.2 s.107
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• pp.163-168
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• 2006

The PWR Nuclear Fuel assembly consists of more than 250 fuel rods that are supported by leaf springs in the cells of more than 10 Spacer Grids (SG) along the rod length. Since it is not easy to conduct mechanical tests on a full-scale model basis, the small-scaled rod bundle $(5\times5)$ which is called partial fuel assembly is generally used for various performance tests during the development stage. As one of the small-scaled tests, a flow test should be carried out in order to verify the performance of the spacer grid to obtain the Flow-Induced Vibration (FIV) characteristics of the scaled fuel assembly over the specified flow range. A vibration test should be also performed to obtain the modal parameters of the assembly prior to the flow test. In this study, we want to develop the estimation procedure of the damping ratio for the scaled test assembly. For the damping factor of the partial fuel assembly and the grid cage at the first vibration mode, as one of the vibration tests, a so-called pluck testing has been performed in air as a preliminary test prior to in-flow damping measurement test. Logarithmic decrement method is used for calculation of the damping ratio. Estimated damping ratio of the partial fuel assembly is about $0.7\%$ with reasonable error of $2\%$ for the previous results. Nonlinear behavior of the partial fuel assembly might be stem mainly from the rod-grid support configuration.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.1
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• pp.1-8
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• 2006

A linear acoustic analysis is conducted to examine bituning of acoustic resonators for acoustic damping in a combustion chamber of liquid rocket engine. Bituned resonators are tuned to the two principal modes, the first tangential(1T) and the first radial(1R) modes. First, the acoustic-damping effect of monotuned resonators is investigated. The damping capacity is quantified by damping factor as a function of the number of the resonators monotuned to 1T or 1R mode. Next, the damping characteristics of the bituned resonators are investigated. From the numerical data, the number of resonators, to be tuned to 1T and 1R modes, respectively, can be selected properly. Furthermore, the concept of resonator bituning is applied to reduce the degradation of damping effect caused by the mode split and thereby, optimal bituning frequencies are found.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.503-506
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• 2005

The PWR Nuclear Fuel assembly consists of more than 250 fuel rods that are supported by leaf springs in the cells of more than 10 Spacer Grids (SG) along the rod length. Since it is not easy to conduct mechanical tests on a full-scale model basis, the small-scaled rod bundle (5$\times$5) is generally used for various performance tests during the development stage. As one of the small-scaled tests, a flow test should be carried out in order to verify the performance of the spacer grid like the coolant mixing performance and to obtain the Flow-Induced Vibration (FIV) characteristics of the rod bundle over the specified flow range. A vibration test should be also performed to obtain the modal parameters of the bundle prior to the flow test. In this study, we want to develop the estimation procedure of the damping ratio for the small scaled test bundle. For the damping factor of the rod bundle and the grid case at the first vibration mode, as one of the vibration tests, a so-called pluck testing has been performed in air as a preliminary test prior to in-flow damping measurement test. Logarithmic decrement method is used for calculation of the damping ratio. Estimated damping ratio of the rod bundle is about 0.7% with reasonable error of 2% for the previous results. Nonlinear behavior of the rod bundle might be stem mainly Iron the rod-grid support configuration.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.12
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• pp.24-29
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• 2021

Recently, owing to the high demand for eco-friendly cars in the automotive industry, noise and vibrations have become major challenges. The use of laminated damping steel is increasing in response to these demands. Laminated damping steel is primarily used in sound insulation plates. The vibration energy is converted into thermal energy due to the viscoelastic resin being located between two steel sheets and being able to damp the vibrations when an external force, such as, noise or vibration is applied to the steel plate. Laminated damping steel is chiefly applied to dash panels in automotive body parts, and because of its structure, junction technology for bonding with other components is necessary. However, there has not been sufficient research conducted on junctions. In this study, regardless of the electrode shape, in the range of 4.0 ~ 8.0 kA welding current, the same welding force and welding time were applied which were 2.8 kN and 200 m/s (12 cycles) and the tensile shear load and nugget size were analyzed after the resistance spot welding between different materials of laminated damping steel with a thickness of 1.035 mm. The results show that in the range of 5 ~ 8 kA welding current, 1.035 mm laminated damping steel meets the MS181-15 standard, which is the technical standard of Hyundai-Kia Motors.

• Journal of the Korea Society of Computer and Information
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• v.4 no.1
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• pp.76-84
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• 1999

For FH/SS communication, We discussed the method of indirect frequency synthesizer in several methods. The problem of sing1e frequency synthesizer using with PLL is a varied coefficient value of damping factor in frequency hopping time, which is caused unstable frequency. So. for stable frequency synthesizer, a coefficient of damping factor must be optimized and synthesized to be removed excessive response time. In this paper, we studied FH using with double loop frequency synthesizer which takes stable frequency. We made up a simulator and had a good performance(real time speed).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.721-724
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• 2005

With the advantages of large vibration energy dissipation of structures, the granular materials are used as vibration and acoustic treatments. In this case of vibro acoustic controls, a finite dynamic strength of the solid component (frame) is an important design factor. The dynamic stiffness of hollow cylindrical beams containing porous and granular materials as damping treatment was measured. Using the Rayleigh-Ritz method, the effects of damping materials on the dynamic characteristics of beams were investigated. The results suggested that the acoustic structure Interaction between the frame and the structure enhances the dissipation of the vibration energy significantly. The same methods were applied also to vibration control of sandwich panels. By filling the cavities of honeycomb cores using unconsolidated granular materials, its sound transmission toss was improved significantly.

• Korean Journal of Optics and Photonics
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• v.8 no.2
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• pp.88-94
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• 1997

Photographic lenses and an aspheric optical pickup-lens are designed by using damped least-squares(DLS) method. We start optimization with arbitrary initial damping factor. To improve the rate of convergence and the stability in optimization, we apply the special procedure that estimates numerical adequacy of derivative increments of variables to the DLS method. When the initial damping factor is almost equal to the median of series of eigenvalues, the convergence and the stability of the method significantly are improved. Optimized lenses have the performance of each target.