• 산업경영시스템학회지
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• 제43권4호
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• pp.161-167
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• 2020

In the process of cutting large aircraft parts, the tool may be abnormally worn or damaged due to various factors such as mechanical vibration, disturbances such as chips, and physical properties of the workpiece, which may result in deterioration of the surface quality of the workpiece. Because workpieces used for large aircrafts parts are expensive and require strict processing quality, a maintenance plan is required to minimize the deterioration of the workpiece quality that can be caused by unexpected abnormalities of the tool and take maintenance measures at an earlier stage that does not adversely affect the machining. In this paper, we propose a method to indirectly monitor the tool condition that can affect the machining quality of large aircraft parts through real-time monitoring of the current signal applied to the spindle motor during machining by comparing whether the monitored current shows an abnormal pattern during actual machining by using this as a reference pattern. First, 30 types of tools are used for machining large aircraft parts, and three tools with relatively frequent breakages among these tools were selected as monitoring targets by reflecting the opinions of processing experts in the field. Second, when creating the CNC machining program, the M code, which is a CNC auxiliary function, is inserted at the starting and ending positions of the tool to be monitored using the editing tool, so that monitoring start and end times can be notified. Third, the monitoring program was run with the M code signal notified from the CNC controller by using the DAQ (Data Acquisition) device, and the machine learning algorithms for detecting abnormality of the current signal received in real time could be used to determine whether there was an abnormality. Fourth, through the implementation of the prototype system, the feasibility of the method proposed in this paper was shown and verified through an actual example.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.491-500
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• 2020

The present study proposes a time domain model for the Vortex-induced Vibration (VIV) simulation of a catenary riser under the combination of the current and oscillatory flow induced by vessel motion. In this model, the hydrodynamic force of VIV comprises excitation force, hydrodynamic damping and added mass, which are taken as functions of the non-dimensional frequency and amplitude ratio. The non-dimensional frequency is related with the response frequency, natural frequency, lock-in range and the fluid velocity. The relatively oscillatory flow induced by vessel motion is taken into account in the fluid velocity. Considering that the added mass coefficient and the non-dimensional frequency can affect each other, an iterative analysis is conducted at each time step to update the added mass coefficient and the natural frequency. This model is in detail validated against the published test models. The results show that the model can reasonably reflect the effect of the added mass coefficient on the VIV, and can well predict the riser's VIV under stationary and oscillatory flow induced by vessel motion. Based on the model, this study carries out the VIV simulation of a catenary riser with harmonic vessel motion. By analyzing the bending moment near the touchdown point, it is found that under the combination of the ocean current and oscillatory flow the vessel motion may decrease the VIV response, while increase the excited frequencies. In addition, the decreasing rate of the VIV under vessel surge is larger than that under vessel heave at small vessel motion velocity, while the situation becomes opposite at large vessel motion velocity.

• 한국군사과학기술학회지
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• 제24권3호
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• pp.264-271
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• 2021

Raman spectroscopy is an equipment that is widely used for classifying chemicals in chemical defense operations. However, the classification performance of Raman spectrum may deteriorate due to dark current noise, background noise, spectral shift by vibration of equipment, spectral shift by pressure change, etc. In this paper, we compare the classification accuracy of various machine learning algorithms including k-nearest neighbor, decision tree, linear discriminant analysis, linear support vector machine, nonlinear support vector machine, and convolutional neural network under noisy and spectral shifted conditions. Experimental results show that convolutional neural network maintains a high classification accuracy of over 95 % despite noise and spectral shift. This implies that convolutional neural network can be an ideal classification algorithm in a real combat situation where there is a lot of noise and spectral shift.

• Journal of Platform Technology
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• 제8권1호
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• pp.24-32
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• 2020

본 논문은 SMT라인의 핵심 기술인 칩마운터의 보급을 위해 교육연구용이나 샘플제작을 목적으로 사용이 가능한 3D 프린터 기술기반의 칩마운터를 설계하고 제작하였다. 저가형 구동부 설계를 위해 오픈루프제어가 가능한 스텝모터를 사용하였다. 스텝모터 사용으로 발생하는 모터의 진동, 탈조 등의 특성상 단점은 마이크로스텝제어 방법을 이용하여 보완하였다. 칩마운터 실험은 제작한 소형 칩마운터에 거버파일을 생성하고 실제 크기로 프린트하여 샘플보드 제작과 동일한 방법으로 HASL 처리되어 있는 PCB에 솔더크림을 프린팅한 후 부품을 실장하여 여러 번 반복해서 수행하였다. 실험결과 2012 미소부품과 달리 보정이 필요한 SOIC, TQFP 등의 부품은 부품 실장 시간이 2배정도 길었지만 비교적 정확히 실장되는 것을 확인할 수 있었다. 또한, 초기 위치에 대한 오차를 총 10회에 반복하여 측정한 결과 약 0.110mm의 비교적 적은 오차가 발생함을 확인할 수 있었다.

• 한국전산구조공학회논문집
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• 제34권1호
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• pp.35-42
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• 2021

이 논문에서는 공용중인 구조물의 상시 계측 자료를 사용한 온라인 유한요소 모델 업데이트 방법을 제안한다. 일반적인 최적화 방법에 기반한 기존의 방법은 최적해를 찾기까지 반복적으로 고유치 해석을 수행해야 하므로 상시 업데이트에 사용하기에는 효과적이지 못하다. 제안하는 방법은 별도의 오프라인 작업이나 사용자의 개입이 없이 자동화된 과정으로 계측과 동시에 온라인 유한요소모델 업데이트를 수행할 수 있는 새로운 방법이다. 자동화된 Cov-SSI 알고리즘을 통해 구조물의 진동 계측 신호로부터 고유진동수 및 모드 형상을 식별하고, 이를 다시 역 고유치 신경망에 입력하여 최종적으로 업데이트된 유한요소 모델의 파라미터를 추정한다. 풍하중을 받는 20층 전단 빌딩 구조 모형에 대한 수치예제를 통해 제시한 방법이 자동으로 연속적인 유한요소모델 업데이트를 할 수 있었음을 확인하였다. 또한, 계측 도중 구조물의 특성이 변화하는 시나리오에 대한 예제에서 구조물의 변화가 일어나는 시점과 변화 후 변동된 구조 모델 파라미터 값을 성공적으로 추정할 수 있음을 확인하였다.

• KEPCO Journal on Electric Power and Energy
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• 제7권2호
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• pp.269-275
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• 2021

The turbine rotor, one of the main facilities in a power plant, it generates electricity while rotating at 3600 RPM. Because it rotates at high speed, it requires careful management because high vibration occurs even if it is deformed by only 0.1mm. However, bending occurs due to various causes during turbine operating. If turbine rotor bending occurs, the power plant must be stopped and repaired. In the past, straightening was carried out using a heating torch and furnace in the field. In case of straightening in this way, it is impossible to proceed systematically, so damage to the turbine rotor may occur and take long period for maintenance. Long maintenance period causes excessive cost, so it is necessary to straighten the rotor by minimizing damage to the rotor in a short period of time. To solve this problem, we developed a turbine rotor straightening equipment using high-frequency induction heating equipment. A straightening was validated for 500MW HIP rotor, and the optimal parameters for straightening were selected. In addition, based on the experimental results, finite element analysis was performed to build a database. Using the database, a straightening amount prediction model available for rotor straightening was developed. Using the developed straightening equipment and straightening prediction model, it is possible to straightening the rotor with minimized damage to the rotor in a short period of time.

• 한국항공우주학회지
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• 제50권8호
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• pp.523-530
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• 2022

다양한 임무에서 활용 가능한 무인기 다개체 시스템은 단일 무인기보다 복잡하므로 효율적인 대형 제어방식이 요구된다. 특히 광역 탐색임무에 있어 통신량 및 연산량 부담이 적으며, 무인기간 자율적인 대형 형성이 가능한 분산 제어형의 유동적인 대형 형성이 필요하다. 본 연구는 스캔 면적의 확장 및 탐색 성능향상을 위해 Swarm 대형과 뱅크 정렬 대형, 대형 전체 운동을 고려한 대형 형성 알고리즘을 제안한다. 본 알고리즘은 상대거리에 대해서 2차 진동 특성을 가지며 parameter tuning을 통해 알고리즘을 설계할 수 있다. 또한 통상적인 무인기 시스템에 적합하도록 제어명령을 변환하였고, 시뮬레이션을 통해 알고리즘의 대형 형성 및 운동에 대한 성능을 입증하였다.

• Advances in nano research
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• 제13권3호
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• pp.207-216
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• 2022

In this paper, a novel model is developed for frequency behavior of single walled carbon nanotubes. The governing equation of motion is constructed method based on the Sander theory using Rayleigh-Ritz's method The frequencies enhances on increasing the power law index using simply supported, clamped and clamped free end conditions. The frequency curve for C-F is less than other conditions. It is due to the physical constraints which are applied on the edge of the CNT. It is observed that the C-F boundary condition have less frequencies from the other two conditions. The frequency phenomena for zigzag are insignificant throughout the aspect ratio. Moreover when index of power law is increased then frequencies increases for all boundary conditions. The natural frequency mechanism for the armchair (10, 10) for various values of power law index with different boundary conditions is investigated. Here frequencies decrease on increases the aspect ratio for all boundary conditions. The frequency curves of SS-SS edge condition is composed between the C-C and C-F conditions. The curves of frequency are less significant from small aspect ratio (L/d = 4.86 ~ 8.47) and decreases fast for greater ratios. It is found that the frequencies via aspect ratios, armchair (10, 10) have higher values from zigzag (10, 0). It is due to the material structure which is made by the carbon nanotubes. The power law index have momentous effect on the vibration of single walled carbon nanotubes. The present frequency result is also compared numerically experimentally with Raman Spectroscopy.

• 대한조선학회논문집
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• 제59권1호
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• pp.39-45
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• 2022

Normal strategy of structure optimization procedure has been minimum cost or weight design. Minimum weight design satisfying an allowable stress has been used for the ship and offshore structure, but minimum cost design could be used for the case of high human cost. Natural frequency analysis and forced vibration one have been used for the strength estimation of marine structures. For the case of high precision experiment facilities in marine field, the structure has normally enough margin in allowable stress aspect and sometimes needs high natural frequency of structure to obtain very high precise experiment results. It is not easy to obtain a structure design with high natural frequency, since the natural frequency depend on the stiffness to mass ratio of the structure and increase of structural stiffness ordinary accompanies the increase of mass. It is further difficult at the grillage structure design using the profiles, because the properties of profiles are not continuous but discrete, and resource of profiles are limited at the design of grillage structure. In this paper, the grillage structure design system under the constraint of high natural frequency is introduced. The design system adopted genetic algorithm to realize optimization procedure and can be used at the design of the experimental facilities of marine field such as a towing carriage, PMM, test frame, measuring frame and rotating arm.

• 한국구조물진단유지관리공학회 논문집
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• 제26권5호
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• pp.49-56
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• 2022

본 연구에서는 능동소음제어(ANC, Active Noise Control) 기술을 이용하여 공동주택의 층간소음을 저감시키는 시뮬레이션 기반 연구를 수행하였다. ANC의 층간소음 저감 활용 가능성을 검토하기 위하여 층간소음시험시설에서 가속도계와 소음 수집용 마이크로폰을 설치하여 임팩트볼 낙하에 의한 소음진동을 측정하여 Fx-LMS 알고리즘 기반의 능동소음제어 시뮬레이션을 수행하였다. 이 과정에서 적응제어 수렴계수 등의 최적 시뮬레이션 조건을 도출한 후 가속도계와 스피커 수량을 변수로 하는 수치 시뮬레이션을 통해 소음저감효과를 분석하여 제한된 조건에서 층간소음을 저감시킬 수 있는 것을 확인하였다.