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      • KCI등재

        집속체 유동계의 안정성 해석

        김종성,허유,Kim, Jong-S.,Huh, You 한국섬유공학회 2008 한국섬유공학회지 Vol.45 No.2

        Bundle flow occurs in the processes where material with long shape in comparison with its cross-section is used and the process products often undergo thickness fluctuation due to the flow dynamics. This study deals with investigating the stability of a bundle flow by means of theoretical simulation. Introducing perturbation in the flow state demonstrated that the eigenvalues of the linearized flow dynamic system, determining the stability of the flow state, were dependent on the model parameters and the draft ratios. The stability diagram revealed that the stable area of the parameters became narrower as the draft ratio increased, which indicates that the state of the bundle flow is sensitive to the input bundle properties. As the fiber cohesion of the bundle or the draft ratio increased, the flow was apt to change to an unstable state. Especially there existed a specific value of the draft ratio that represented a characteristic measure, addressing the criterion of the bundle flow stability. The bundle flow dynamics was insistently stable under the condition of the draft ratio less than the characteristic value, no matter what values of the parameters were given.

      • 롤 에너지 다이어그램을 이용한 롤오버 저감에 관한 연구

        이재천(J. C. Lee),류하오(Hao Liu),윤권수(G. S. Yun),김현찬(H. C. Kim) 유공압건설기계학회 2014 유공압건설기계학회 학술대회논문집 Vol.2014 No.9

        The rollover accident of vehicle is fatal. so it is necessary to avoid rollover for a vehicle. In this paper, the vehicle roll motion mitigate by using energy diagram. This paper focuses on how to determine the rollover stiffness threshold in a RSC system. In the paper, the equilibrium states of vehicle’s roll motion are analyzed firstly, and then the roll energy diagram is plotted to show how roll energy varies with the lateral acceleration. Thus, the rollover stiffness threshold is determined. The required minimal torque for the motor in the RSC system is calculated.

      • 초장폭 로타리 작업기 수평제어 안정성 분석

        이현우 ( Hyun Woo Lee ),이종원 ( Jong Won Lee ),유찬희 ( Chan Hee Yu ),이충호 ( Choong Ho Lee ) 한국농업기계학회 2023 한국농업기계학회 학술발표논문집 Vol.28 No.1

        제어 시스템 설계는 시스템이 불안정할 때 출력이 발산하게 되고 제어 목표를 수행할 수 없기 때문에 안정성을 확인하는 것이 제어 시스템 설계 시 중요하다. 본 연구는 Matlab Simulink를 활용하여 로터리 작업기의 수평 제어 알고리즘을 설계하고 주파수 영역 분석을 통해 제어 시스템의 안정성을 해석하였다. Fig. 1과 같이 피드백에 의하여 출력신호를 감지하여 목푯값과 비교하여 입력과 출력의 오차를 줄이는 폐루프 제어 시스템 구조의 알고리즘을 설계하였다. 또한 입력 변화량의 범위를 조절해주는 Dead Zone 블록과 G(s)=y(s)/x(s) 와 같은 형태로 입력값에 대해 출력값을 변환시켜주는 전달함수 등을 연결하여 블록선도로 표현하고 입출력 조건을 ±11 기준으로 안정성 분석을 하였다. 안정성 분석 결과, Fig. 2의 좌측은 Nyquist Diagram을 나타낸 것으로 피드백 제어계의 블록선도인 Y(s)=G(s)/1+G(s)H(s) ㆍX(s)인 특정 방정식을 기준으로 안정도를 판별한 결과 벡터 궤적이 (-1,0)의 점을 기준으로 우측에 위치하고, 그림 의 우측은 Bode Plot을 나타낸 것으로 위상여유 및 이득여유를 통해 안전 여유값을 추정하기 위해 사용하였다. 0dB에서 측정된 PM(Phase margin)은 155°, -180°에서 측정된 GM(Gain margin)은 106dB로 도출되었고 위상마진의 일반적인 목표는 최소 45°도 이상을 유지하고, GM 및 PM이 높게 도출되어 안정한 제어 결과가 도출되었다. 향후, 실제 노면에서 수평 제어시스템이 안정적으로 도출되는지 Recurdyn과 연동한 Co-Simulation을 진행 후, 실증 테스트를 진행할 예정이다.

      • KCI등재후보

        주축 모터를 이용한 포터블 자동 면취기의 가공 안정성 진단

        김태영 ( Tae Young Kim ),안병훈 ( Byeong Hun An ),김화영 ( Hwa Young Kim ) 한국센서학회 2022 센서학회지 Vol.31 No.1

        This study describes a system that monitors the tool and cutting state of automatic beveling operation in real time. As a signal for cutting state monitoring, a motor current detected from the spindle drive system of the automatic beveling machine is used to monitor abnormal state. Because automatic beveling is processed using a face milling cutter, the cutting force mechanism is the same as the milling process. The predicted cutting torque is obtained using a cutting force model based on specific cutting resistance. Then, the predicted cutting torque is converted into the spindle motor current value, and cutting state stability is diagnosed by comparing it with the motor current value detected during beveling operation. The experimental results show that the spindle motor current can detect abnormal cutting state such as overload and tool wear during beveling operation, and can diagnose the cutting stability using the proposed equipcurrent line diagram.

      • KCI등재

        주파수응답함수(FRF)를 이용한 자기 애자의 손상평가

        최인혁,손주암,오태근,윤영근 한국전기전자재료학회 2019 전기전자재료학회논문지 Vol.32 No.2

        Porcelain insulators have been used mainly for power line fixing and electrical insulation in transmissiontowers. Porcelain insulators have generally a 30 years desired life, but over 50% exceed their life expectancy. Since thedamage to porcelain insulators is usually accompanied by enormous loss of human resource material, their efficientmaintenance has emerged as an important issue. In this regard, this study applied a frequency response function (FRF)for integrity assessment of the insulator. The characteristics of the FRF according to damage types were identified andanalyzed by the change in natural frequencies, curve shape, attenuation, and Nyquist diagram stability. The resultsshowed significant differences in the FRF according to damage types, which can be used as basic data for the effectiveintegrity assessment of porcelain insulators. 자기애자는 송전탑의 전력선 고정 및 전기적 절연을 위해 사용된다. 자기애자는 사용수명이 30년으로 제작되었지만, 현재 제작수명을 넘어선 애자는 전체의 50%를 상회한다. 자기애자의 손상으로 발생되는 손실은 막대한 인적, 물적 피해를 동반하기 때문에 자기애자의 건전성을 평가하는 방법이 중요한 쟁점으로 떠오르고 있다. 이에 따라 비파괴 검사기법 중 FRF를 활용하여 자기애자의 건전성을 평가하기 위한 방법으로 적용하였다. 본 연구에서는 자기애자의 고유모드 주파수, 곡선 형상, 감쇠 및 나이퀴스트 선도 안정성 분석을 통해 손상유형에 따른 특성을 분석하였다. 본 연구결과를 통해 자기애자의 건전성 평가를 위한 기초자료로 쓰일 수 있기를 기대한다.

      • 에너지 다이어그램을 이용한 롤오버 안정성 해석

        윤권수(GwonSoo Yun),류하오(Hao Liu),이재천(Jae-Cheon Lee) 한국자동차공학회 2014 한국자동차공학회 부문종합 학술대회 Vol.2014 No.5

        The rollover accident of vehicle is fatal. so it is necessary to avoid rollover for a vehicle. In this paper, the vehicle rollover stability is analysis by using energy diagram. Sensitivity can analysis is performed through spring stiffness, active roll bar length, vehicle body mass and height of roll center. The results show how these parameters influence steady state and dynamic rollover threshold.

      • KCI등재

        A novel recursive stochastic subspace identification algorithm with its application in long-term structural health monitoring of office buildings

        Wen-Hwa Wu,Jhe-Wei Jhou,Chien-Chou Chen,Gwolong Lai 국제구조공학회 2019 Smart Structures and Systems, An International Jou Vol.24 No.4

        This study develops a novel recursive algorithm to significantly enhance the computation efficiency of a recently proposed stochastic subspace identification (SSI) methodology based on an alternative stabilization diagram. Exemplified by the measurements taken from the two investigated office buildings, it is first demonstrated that merely one sixth of computation time and one fifth of computer memory are required with the new recursive algorithm. Such a progress would enable the realization of on-line and almost real-time monitoring for these two steel framed structures. This recursive SSI algorithm is further applied to analyze 20 months of monitoring data and comprehensively assess the environmental effects. It is certified that the root-mean-square (RMS) response can be utilized as an excellent index to represent most of the environmental effects and its variation strongly correlates with that of the modal frequency. More detailed examination by comparing the monthly correlation coefficient discloses that larger variations in modal frequency induced by greater RMS responses would typically lead to a higher correlation.

      • KCI등재

        Frequency-domain approach for the parametric identification of structures with modal interference

        Chang-Sheng Lin 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.9

        This study aims to improve the accuracy of the parametric estimation of systems with modal interference in the frequency domain. The theory of modal identification states that the frequency response function can be expressed as a rational function form by using the curve fitting technique, and the modal parameters can then be estimated from rational fractional coefficients. The conventional common denominator model only indicates the frequency response function of a single-degree-of-freedom system; thus, it cannot acquire the mode shape information. In this paper, we propose the matrix-fractional coefficient model constructed by the frequency response functions of a multiple-degree-of-freedom system for modal identification. To avoid the phenomenon of omitted modes caused by the distortion from modal interference among the vibration modes of systems during modal estimation, we use a system model with higher-order matrixfractional coefficients, but fictitious modes may be caused by numerical computation. Structural and fictitious modes can be effectively separated by using a different-order constructed stabilization diagram. Modal identification can be implemented by solving the eigenproblem of the companion matrix yielded from least-square estimation. Numerical simulations, including a full model of sedan and onehalf railway vehicle in the form of a linear 2D model, as well as the experimental testing of an actual plate, confirm the validity and robustness of the proposed parametric-estimation method for a system with modal interference under noisy conditions.

      • KCI등재

        Spurious mode distinguish by eigensystem realization algorithm with improved stabilization diagram

        Chun-Xu Qu,Ting-Hua Yi,Xiao-Mei Yang,Hong-Nan Li 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.63 No.6

        Modal parameter identification plays a key role in the structural health monitoring (SHM) for civil engineering. Eigensystem realization algorithm (ERA) is one of the most popular identification methods. However, the complex environment around civil structures can introduce the noises into the measurement from SHM system. The spurious modes would be generated due to the noises during ERA process, which are usually ignored and be recognized as physical modes. This paper proposes an improved stabilization diagram method in ERA to distinguish the spurious modes. First, it is proved that the ERA can be performed by any two Hankel matrices with one time step shift. The effect of noises on the eigenvalues of structure is illustrated when the choice of two Hankel matrices with one time step shift is different. Then, a moving data diagram is proposed to combine the traditional stabilization diagram to form the improved stabilization diagram method. The moving data diagram shows the mode variation along the different choice of Hankel matrices, which indicates whether the mode is spurious or not. The traditional stabilization diagram helps to determine the concerned truncated order before moving data diagram is implemented. Finally, the proposed method is proved through a numerical example. The results show that the proposed method can distinguish the spurious modes.

      • SCIEKCI등재

        An Integrated Approach to the Improvement of Stability Lobes

        Mohan, Sekar,Jonnalagadda, Srinivas,Kang, Nam-Cheol,Yang, Seung-Han Korean Society for Precision Engineering 2008 International Journal of Precision Engineering and Vol.9 No.4

        Redundant spurious loops and overlapping segments in stability lobe diagrams cannot be removed easily by regular methods. A programmatic approach is presented to detect multiple spurious loops occurring within the lobes. They are identified by reorganizing the numerical lobe data into speed-depth corners for subsequent removal. The same principle is then extended to remove overlapping segments of adjacent lobes to obtain a final continuous stability map. Unlike existing methods, the proposed methodology requires no interface with additional editing software, and can also yield stability lobe diagrams more quickly. The methodology is presented with lobe diagrams constructed using milling and turning models.

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