• Journal of Advanced Navigation Technology
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• v.27 no.1
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• pp.111-118
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• 2023

For the implementation of a smart factory, it is necessary to collect data by connecting various sensors and devices in the manufacturing environment and to diagnose or predict failures in production facilities through data analysis. In this paper, to predict the residual useful lifetime of milling insert used for machining products in CNC machine, weight k-NN algorithm, Decision Tree, SVR, XGBoost, Random forest, 1D-CNN, and frequency spectrum based on vibration signal are investigated. As the results of the paper, the frequency spectrum does not provide a reliable criterion for an accurate prediction of the residual useful lifetime of an insert. And the weighted k-nearest neighbor algorithm performed best with an MAE of 0.0013, MSE of 0.004, and RMSE of 0.0192. This is an error of 0.001 seconds of the remaining useful lifetime of the insert predicted by the weighted-nearest neighbor algorithm, and it is considered to be a level that can be applied to actual industrial sites.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.11a
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• pp.71-72
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• 2022

In this paper, the performance evaluation of the vibration damping ratio according to the polymer mixing ratio of the polymer modified mortar used as the floor finishing material of the apartment building structure was evaluated. To compare the vibration damping rate, ordinary potland cement (OPC) mortar and polymer modified mortar (PMM) were prepared. In addition, the mixed polymer was mixed with Styrene Butadiene Rubber (SBR) liquid polymer with a solid content of about 49%. Accordingly, the W/C of the test specimen was adjusted and compounded, and the experiment was conducted by mixing 5 types of the test specimen: OPC-60, PMM-5%, PMM-10%, PMM-15%, and PMM-20%. In addition, in order to adjust the W/C of the specimen, the fluidity of each specimen was set as 210 (±5) mm. The specimens measured density and flow in fresh mortar and after curing for 28 days, flexural strength, compressive strength and ultrasonic pulse were measured. The attenuation rate was shown. The experimental results showed that the density increased according to the mixing of the polymer, the flexural strength increased as the mixing rate of the polymer increased, and the compressive strength was decreased. In addition, it was shown that the vibration damping rate increases with the increase in the amount of polymer incorporated.

• The Journal of the Acoustical Society of Korea
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• v.43 no.3
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• pp.270-276
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• 2024

In this study, we analyzed the stick slip characteristics through friction experiments on materials used in mechanical and electronic products, and propose improvements to reduce abnormal noise generated inside refrigerators. To analyze the stick slip phenomenon of the materials, we fabricated a friction testing device and conducted friction experiments. Additionally, we measured the vibration and noise levels of internal components to analyze the occurrence and location of abnormal noise inside the refrigerator. By comparing the results of the refrigerator's phenomenon analysis and friction experiment, we confirm that the abnormal noise occurring inside the refrigerator is caused by the stick slip phenomenon of internal components. Finally, to propose improvements for abnormal noise reduction, we performed friction experiments using the Taguchi method and validated the performance of the proposed improvements by applying them to refrigerators.

• Journal of the Korean Society for Railway
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• v.12 no.1
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• pp.129-134
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• 2009

To ensure the safety and functionality of a railroad bridge, maintaining the integrity of the bridge via continuous structural health monitoring is important. However, most structural integrity monitoring methods proposed to date are based on modal responses which require the extracting process and have limited availability. In this paper, the applicability of the existing damage identification method based on free-vibration reponses to time-domain deflection shapes due to moving train load is investigated. Since the proposed method directly utilizes the time-domain responses of the structure due to the moving vehicles, the extracting process for modal responses can be avoided, and the applicability of structural health evaluation can be enhanced. The feasibility of the presented method is verified via a numerical example of a simple plate girder bridge.

• Journal of the Korea Convergence Society
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• v.11 no.11
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• pp.249-255
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• 2020

This study developed the health monitoring method of press process using the acoustic emission (AE) sensor and high-pass filter. Also, the AE parameters such as ring-down count and peak amplitude are used. Based on this AE signal, the AE parameters were acquired and was utilized to detect the crack of the specimen. Since the defect detection is difficult due to noise and low magnitude of signal, the signal noise and press operation frequency were checked through the Short Time Fourier Transform(STFT) and damped. High-pass Filtering data was applied to AE parameters to select effective parameters. By using this signal processing techniques, the proposed AE parameters could improve the performance of defect detection in the press process.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.2 s.54
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• pp.172-180
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• 2009

Normally in order to build a semi-active control system equipped with MR damper, the dynamic modeling of the damper is required to numerically predict its dynamic damping force and also its behavioral characteristics. For the dynamic modeling of the MR damper, this paper attempts to predict and evaluate its dynamic behavior by applying specifically both a power model and a Bingham model. Dynamic loading tests were performed on the squeeze type of damper specially designed for this research, and force-displacement hysteresis loops confirmed the effectiveness of the damper as a semi-active control device. In the meantime, in order to evaluate the effectiveness of each model applied, the model parameter for each model was identified. On the basis of the parameter, we derived the error ratio of the force-velocity relationship curve and the dynamic damping force, which was contrasted and compared with the experimental results of the squeeze type of damper. Finally, the squeeze type of MR damper developed in this research was proved to be valid as a semi-active control device, and also the evaluation of the two dynamic models showed they were working fine so that they were likely to be easily utilized to numerically predict the dynamic characteristics of any dampers with MR fluid as well as the squeeze type of MR damper.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2A
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• pp.93-102
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• 2010

The numerical analysis and safety assessment by construction stages were considered the essential examination particular in order to solving the unstability of long-span bridges in the middle a construction. When estimating structural response characteristics by the construction stage analysis of long-span bridges, the influence of the near-field ground motion (NFGM) would be evaluated as a critical factor for the seismic design because it indicates clearly different aspects from the existing input earthquake motion data. Therefore, this study re-examined the response aspect of long-span bridges considering NFGM characteristics based on the response spectrum result, and advanced the presented numerical analysis program by the related research for conducting the construction stage analysis and reliability assessment of long-span bridges efficiently. The excellency of various construction schemes was assessed using the time history analysis result of critical member considering NFGM characteristics. For evaluating quantitative safety level, the reliability analysis was conducted considering the influence of external uncertainties included in random variables, and presented the safety index and failure probability of the critical construction stage by NFGM characteristics. In addition, the reliability result was examined the influence of internal uncertainties using monte carlo simulation (MCS), and assessed the distribution aspect of the essential analysis result. It is expected that this study will provide the basic information for the construction safety improvement when performing seismic design of long-span bridges considering NFGM characteristics.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.101-101
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• 2009

압전 세라믹스는 진동, 변형, 압력 등의 기계적 에너지를 전기적 에너지로 혹은 전기적 에너지를 기계적 에너지로 변환시키는 소자로서의 기능을 가지며 조성의 개선 및 제조 기술의 진보가 계속되어 큰 관심을 받고 있다. 최근 audio의 고급화 및 자동차, 평면 TV, 고성능 통신기기, 디지털방송, 홈시어터 등 스피커의 성능이 크게 부각되면서 대기업에서부터 중소기업에 이르기까지 고성능 스피커의 개발에 박차를 가하고 있다. 압전 세라믹을 이용하여 음압을 변조하는 압전 스피커는 디스크 형상의 압전 프레이트를 단층 또는 다층으로 형성하여 기존의 마그네틱 스피커와는 차별되는 형태를 가진 스피커로서 응용하는 것이다. PSN-PZT계 조성을 개발하여 $d_{33}$, 전기기계결합계수($k_p$), 온도안정성 및 내구성 향상 및 특성향상을 위한 입경 조절 및 공정을 연구하고자 한다. 디스크 형태의 압전 세라믹을 이용하여 2, 3, 4 layer 이상의 멀티레이어 시편을 제작하였고, 여러 시편에서 크기 및 형상, 접합 방법 등에 따른 특성을 최적화하여 스피커의 특성을 향상 시키고자 한다.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.443-450
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• 2002

본 논문에서는 미국토목학회(ASCE)의 사장교에 대한 첫번째 벤치마크 문제를 이용하여 제어-구조물 상호작용을 고려한 새로운 반능동 제어 기법을 제안하였다. 이 벤치마크 문제에서는 2003년 완공 예정으로 미국 Missouri 주에 건설 중인 Cape Girardeau 교를 대상 구조물로 고려하였다. Cape Girardeau 교는 New Madrid 지진구역에 위치하고, Mississippi 강을 횡단하는 주요 교량이라는 점 때문에 설계단계에서부터 내진 문제에 대하여 자세하게 고려되었다. 상세 설계 도면을 기반으로 하여 교량의 전체적인 거동 특성을 정확하게 나타낼 수 있는 3차원 모델이 만들어졌고, 사장교의 제어 성능에 관련된 평가 기준이 수립되었다. 본 연구에서는 제어 가능한 유체 감쇠기에 속하는 MR 유체 감쇠기를 제어 장치로 제안하였고, 기존 연구에서 MR 유체 감쇠기를 포함한 구조물의 제어에 효율적이라고 검증된 clipped-optimal 알고리듬을 제어 알고리듬으로 사용하였다. 또한, 실제 규모의 MR 유체 감쇠기 실험 결과를 이용하여 수치해석에 이용할 수 있는 동적 모델을 개발하였다. MR 유체 감쇠기는 제어 가능한 에너지 소산장치이며 구조물에 에너지를 가하지 않기 때문에 제안된 제어 기법은 한정입출력 안정성이 보장된다. 수치해석을 통해, MR 유체 감쇠기를 이용한 반능동 제어 기법이 사장교의 응답 감소에 효과적인 방법임을 증명하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.2 s.173
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• pp.370-377
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• 2000

This paper presents a mixed-mode type ER(electro-rheological) engine mount, and its vibration control performance for a passenger vehicle is presented. The field-dependent yield stress of a transfo rmer oil-based ER fluid is empirically distilled in both shear and flow modes. This is then incorporated with the governing equation of motion of the proposed mixed-mode(shear mode plus flow mode) type engine mount. The damping force is analyzed with respect to the intensity of the electric field and design parameters such as electrode gap. Subsequently, the ER engine mount which is equivalent to the conventional hydraulic engine mount in terms of the damping level is designed and manufactured. Both computer simulation and experimental test are undertaken in order to evaluate vibration isolation performance. In addition, this performance is compared with that of the conventional hydraulic engine mount.