• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.4
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• pp.489-496
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• 2019

This paper is a study on the evaluation of loss factor of damping treatment materials to reduce the noise and vibration for panels of railway vehicles and automobiles. In order to determine the modal parameters of damping materials, beam excitation tests were carried out using different type PVC coated aluminum and steel base beam specimens. The specimens were excited from 10 Hz to 1000 Hz frequency range using sinusoidal force, and transfer mobility data were measured by using an accelerometer. The loss factors were determined by using integrated program, based on theories of Half Power Method, Minimum Tangent Error Method, Minimum Angle Error Method and Phase Change Method, which enable to evaluate the parameters using modal circle fit and least squares error method. In the case of lower loss factor and data of linear characteristics, any method could be applied for evaluation of parameters, however the case of higher loss factor or data including non-linear characteristics, the minimum angle error method could reduce the loss factor evaluation. The obtained dynamic properties of the coating material could be used for application of Finite Element Method analyzing the noise control effects of complex structures such as carbody or under-floor boxes of rolling stock. The damping material will be very useful to control the structural noise, because the obtained modal loss factors of each mode show very good effect on over $2^{nd}$ mode frequency range.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.7
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• pp.1201-1208
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• 2022

In general, to maximize the supply and efficiency of floating offshore wind power generation energy, the motion caused by wave attenuation of the substructure must be reduced. According to previous studies, the motion response was reduced due to the vortex viscosity generated by the damping plate installed in the lower structure among the waves. In this study, a 5 MW semi-submersible OC5 platform and two platforms with attenuation plates were designed, and free decay experiments and numerical calculations were performed to confirm the effect of reducing motion due to vortex viscosity. As a result of the model test, when the heave free decay tests were conducted at drop heights of 30 mm, 40 mm, and 50 mm, compared with the OC5 platform, the platform with two types of damping plates attached had relatively improved motion damping performance. In the model test and numerical calculation results, the damping plate models, KSNU Plate 1 and KSNU Plate 2, were 1.1 times and 1.3 times lower than OC5, respectively, and the KSNU Plate 2 platform showed about two times better damping performance than OC5. This study shows that the area of the damping plate and the vortex viscosity are closely related to the damping rate of the heave motion.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.04a
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• pp.172-179
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• 2001

비감쇠 혹은 비비례감쇠 시스템의 고유치를 구하기 위한 대부분의 방법들은 저차의 몇 개의 모드만을 사용하여 동적응답을 구하는 경우 누락된 고유치의 존재여부를 검사하기 위해 잘 알려진 Sturm 수열 성질(Sturm sequence property)을 이용한다. 반면 감쇠시스템 즉, 지반-구조물의 진동제어 시스템, 복합재료 구조물과 같은 경우에는 저차 몇 개의 모드만을 사용할 경우 누락 고유치를 검사할 수 있는 효율적인 기법이 아직 확립되지 않은 상태이다. 본 논문에서는 Gleyse의 정리를 이용하여 감쇠스템의 누락된 고유치를 검사하는 기법을 제안하고 이 방법의 효용성을 수치예제를 통하여 검증하였다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1992.04a
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• pp.285-290
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• 1992

기계 구조물의 과도한 진동은 기계의 성능 및 수명에 나쁜 영향을 미치며 기계및 부품의 파괴까지 유발하게 되는 원인이되므로 이를 제진하기위한 각종 방법이 오래전부터 연구되고 있다. 본 연구에서는 현재까지 진행된 충격식 댐퍼의 이론을 기초로 한 사이클당 두번의 충돌이일어난다는 가정하에, 파라메타 의 변화에따른 최적 감쇠특성을 얻기위한 최적간극과 최적 질량비를 쉽게구할 수 있는 식을 유도하였다. 그리고, 실험에 의하여 공진상태에 있어서 불의 충격력에 의한 감쇠특성을 조사하였고, 이론으로구한 식과 비교 검토함으로서, 실제 현장등에서 간편하게 근사식을 이용하여 최적조건을 구하고, 이 자료를 기초로하여 설계, 제작시 보다 간편하게 사용할 수 있도록 하였다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.6
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• pp.907-913
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• 2000

세라믹 강 유전체를 이용한 corrugate 구조의 으 전극으로 마들어지 유전체 칩에 의한 전자파 감쇄기를 설계하고 제작하였다. 이 감쇄기의 감쇠는 corrugate 구조에 의한 전파모드 차단조건으로부터 얻을 수 있도록 설계하였다. 근거리 프로브 측정 및 SAR 측정에 의한 결과는 셀룰라 밴드인 824∼849MHz에서 3.6∼5dB, PCS 밴드인 1750∼1780 MHz에서 4∼5dB의 감쇠를 얻었다. 또한 감쇠 범위는 휴대폰 정면을 중심으로 ±35°이외는 감쇠가 없으므로 통화기 통화품질의 저하가 거의 없음이 나타났다.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.127-132
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• 2001

자기유변유체감쇠기를 이용한 반능동 제어 시스템은 최근에 개발되어 승용차의 승차감 향상을 위한 진동제어에 사용되고 있다. 본 연구에서는 바람, 지진, 파랑 등에 대한 대형구조물의 진동제어를 위한 MR 감쇠기의 적용성을 분석하기 위하여, 미국 토목학회에서 제안한 76층 건물의 풍하중에 대한 진동제어에 관한 Benchmark Problem에 대하여 수치모의 해석을 수행하였다. 연구결과로부터, 풍하중에 대한 고층 건물의 진동제어를 위하여 MR 감쇠기를 이용한 반능동 제어의 성능은 능동형 동조질량 감쇠기의 성능과 유사함을 확인할 수 있었다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.11a
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• pp.640-643
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• 2002

본 연구에서는 위성통신을 이용한 방송 및 멀티미디어 서비스의 확대를 앞두고 20[GHz] 이상의 높은 주파수 대역의 강우에 의한 전파 손실 예측 모델을 제안하고 강우량에 따른 감쇠 정도를 기존의 모델과 비교 분석하였다. 특히 위성 방송대역으로 이용될 Ka 대역에서 강우 감쇠에 의한 전파 손실을 제시하고 Ka 대역 위성통신 링크 설계를 위한 기본 자료를 제공하고 강우 감쇠 극복 대책을 제시하고자 한다.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.22-23
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• 2003

광섬유 가변 감쇠기는 광증폭기, add／drop 모듈, Mux／Demux, 광송수신기 등 중요한 광통신 시스템의 입력 및 출력 광신호 레벨을 적절하게 제어하기 위해 요구되는 중요한 소자이다. 가변 감쇠기는 높은 신뢰성, 높은 해상도, 작은 삽입손실, 낮은 편광 및 파장 의존성 손실 등이 요구되어 진다. 가변 광감쇠기는 평면 기판에 형성된 도파로 의 열광학 효과나 전기광학 효과를 이용하는 기법과 MEMS 기술에 기초한 방법이 잘 알려져 있다. (중략)

• Progress in Medical Physics
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• v.9 no.3
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• pp.163-173
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• 1998

Nuclear medicine emission computed tomography(ECT) can be very useful to diagnose early stage of neuronal diseases and to measure theraputic results objectively, if we can quantitate energy metabolism, blood flow, biochemical processes, or dopamine receptor and transporter using ECT. However, physical factors including attenuation, scatter, partial volume effect, noise, and reconstruction algorithm make it very difficult to quantitate independent of type of SPECT. In this study, we quantitated the effects of attenuation and scatter using brain SPECT and three-dimensional brain phantom with and without applying their correction methods. Dual energy window method was applied for scatter correction. The photopeak energy window and scatter energy window were set to 140ke${\pm}$10% and 119ke${\pm}$6% and 100% of scatter window data were subtracted from the photopeak window prior to reconstruction. The projection data were reconstructed using Butterworth filter with cutoff frequency of 0.95cycles/cm and order of 10. Attenuation correction was done by Chang's method with attenuation coefficients of 0.12/cm and 0.15/cm for the reconstruction data without scatter correction and with scatter correction, respectively. For quantitation, regions of interest (ROIs) were drawn on the three slices selected at the level of the basal ganglia. Without scatter correction, the ratios of ROI average values between basal ganglia and background with attenuation correction and without attenuation correction were 2.2 and 2.1, respectively. However, the ratios between basal ganglia and background were very similar for with and without attenuation correction. With scatter correction, the ratios of ROI average values between basal ganglia and background with attenuation correction and without attenuation correction were 2.69 and 2.64, respectively. These results indicate that the attenuation correction is necessary for the quantitation. When true ratios between basal ganglia and background were 6.58, 4.68, 1.86, the measured ratios with scatter and attenuation correction were 76%, 80%, 82% of their true ratios, respectively. The approximate 20% underestimation could be partially due to the effect of partial volume and reconstruction algorithm which we have not investigated in this study, and partially due to imperfect scatter and attenuation correction methods that we have applied in consideration of clinical applications.

• Journal of Korean Society of Steel Construction
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• v.22 no.6
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• pp.553-561
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• 2010

The purpose of this paper is to analytically find the approximate supplement damping ratio of the viscous damper installed in self-centering (SC) single-degree-of-freedom (SDOF) systems with maximum displacements that are similar to those of elasto-plastic (EP) SDOF systems. The behavior of an SC SDOF system under harmonic cyclic loading was first described. Then an analytical model that can capture the behavior of the viscously damped SC SDOF system was introduced. Analysis parameters that characterize the hysteresis of the EP and SC SDOF systems were chosen, and nonlinear time-history analyses were performed using 20 historical accelerograms. Most of the SC SDOF systems with viscous dampers with approximately 10-15% damping ratios presented mean maximum displacement values that were similar to those of the EP SDOF systems. To investigate in detail the seismic performance of both systems, three EP SDOF systems and six corresponding SC SDOF systems were selected. The analyses showed that all the SC SDOF systems eliminated the residual displacements after the end of their shaking, and that the SC SDOF systems with 15% damping ratios performed better than the EP SDOF systems in terms of maximum displacement and acceleration response.