• 한국정밀공학회지
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• 제22권6호
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• pp.152-158
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• 2005

The stress conditions acting on the practical structure are complex, and thus most cracks existing in the practical structures are under mixed-mode loading conditions. The effect of shear load component of mixed-mode loading acts more greatly in the stage of crack initiation and initial propagation than crack propagation stage. Hence, research on the behavior in the stage of crack initiation and initial propagation need to be examined in order to evaluate behavior of mixed-mode fatigue cracks. In this study, the crack tip displacement(CTD) was measured by using the direct measuring method(DMM). We examined the behavior at crack tip by determining crack opening load$(P_{op})$. From the test results, the propagation behavior of mixed-mode fatigue cracks was evaluated by considering mixed-mode crack closure. Also, we examined the characteristic of crack propagation under mixed-mode loading with crack propagation direction.

• 대한기계학회논문집A
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• 제24권5호
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• pp.1133-1145
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• 2000

It is necessary to develop an efficient analysis method to identify the dynamic characteristics of a large mechanical structure and update its finite element model. That is because these processes need the huge computation of a large structure and iterative estimation due to the use of the first- order sensitivity. To efficiently carry out these processes, a new method, called the generalized free-interface mode sensitivity method, has been proposed in the authors' preceeding paper. This method is based on substructuring approach such as a free-interface method and a generalized synthesis algorithm. In this paper, the proposed method is applied to the model updating of a car body structure to verify its accuracy and reliability for a large mechanical structure.

• 한국유체기계학회 논문집
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• 제18권1호
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• pp.20-28
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• 2015

The pump-turbine impeller is the key component of pumped storage power plant. Current design methods of pump-turbine impeller are private and protected from public viewing. Generally, the design proceeds in two steps: the initial hydraulic design and optimization design to achieve a balanced performance between pump mode and turbine mode. In this study, the 3D inverse design method is used for the initial hydraulic impeller design. However, due to the special demand of high performance in both pump and reverse mode, the design method is insufficient. This study is carried out by modifying the geometrical parameters of the blade which have great influence and need special consideration in obtaining the high performance on the both modes, such as blade shape type at low pressure side (inlet of pump mode, outlet of turbine mode) and the blade lean at blade high pressure side (outlet of pump mode, inlet of turbine mode). The influence of the geometrical parameters on the performance characteristic is evaluated by CFD analysis which presents the efficiency and internal flow results. After these investigations of the geometrical parameters, the criteria of designing pump-turbine impeller blade low and high sides shape is achieved.

• Structural Engineering and Mechanics
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• 제20권2호
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• pp.143-160
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• 2005

Modal analysis of cracked cantilever composite beams, made of graphite-fibre reinforced polyamide, is studied. By using the finite element and component mode synthesis methods, a numeric model applicable to investigate the vibration of cracked composite beams is developed. In this new approach, from the crack section, the composite beam separated into two parts coupled by a flexibility matrix taking into account the interaction forces. These forces are derived from the fracture mechanics theory as the inverse of the compliance matrix calculated with the proper stress intensity factors and strain energy release rate expressions. Numerical results are obtained for modal analysis of composite beams with a transverse non-propagating open crack, addressing the effects of the location and depth of the crack, and the volume fraction and orientation of the fibre on the natural frequencies and mode shapes. By means of modal data, the position and dimension of the defect can be found. The results of the study confirmed that presented method is suitable for the vibration analysis of cracked cantilever composite beams. Present technique can be easily extended to composite plates and shells.

• Journal of the Optical Society of Korea
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• 제8권3호
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• pp.137-146
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• 2004

A new method of obtaining the eigenmode of an anisotropic planar waveguide is studied. The planar waveguide can be composed of an arbitrary number of isotropic or uniaxially anisotropic layers, provided all the optical axes arc lying in the incidence plane. Since the equation of motion for the TE mode is not different from that for the TE mode in an isotropic planar waveguide, only the equation of motion for the TM mode is of any concern. For this kind of device structure, the Maxwell's equations can be solved for one component of the electric field and one component of the magnetic field. The resulting coupled set of equations is linear in the propagation constant and the eigenmode can be easily obtained using canned numerical routines.

• 한국소음진동공학회논문집
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• 제16권8호
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• pp.814-821
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• 2006

A structural coupling method is developed for the dynamic analysis of a nonlinear structure with concentrated nonlinear hinge joints or sliding lines. The component mode synthesis method is extended to couple substructures and the nonlinear models. In order to verify the improved coupling method, a numerical plate model consisting of two substructures and torsional springs, is synthesized by using the proposed method and its modal parameters are compare with analysis data. Then the coupling method is applied to a three-substructure-model with the nonlinearity of sliding lines between the substructures. The coupled structural model is verified from its dynamic analysis. The analysis results show that the improved coupling method is adequate for the structural nonlinear analyses with the nonlinear hinge and sliding mode condition.

• 전력전자학회논문지
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• 제17권4호
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• pp.359-367
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• 2012

In this paper, the input split type series-parallel hybrid electric vehicle (SPHEV) is established and the interpretation of the dynamic characteristics in four kinds of HEV modes, such as electric vehicle mode, engine mode, hybrid mode, and regeneration mode, is described. For this research, the forward-facing approach simulation method is chosen, which is useful for vehicle dynamic analysis. The rating of each powertrain component is designed based on energy-based concept and electrical peaking hybrid (ELPH) method. Finally, the designed powertrain is evaluated with the developed PSiM simulator and simulation results are shown.

• Journal of Advanced Marine Engineering and Technology
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• 제30권2호
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• pp.239-246
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• 2006

This paper describes the scheme of sliding mode control (SMC) to adopt the conventional slip frequency vector drives. The purpose of sliding mode control is to achieve an accurate, robustness of response for ac servomotor speed control. A sliding mode control design method is proposed for a speed control of an induction servomotor. The control law is composed of the variable structure component and the suppressed coefficients to suppress load disturbance and variation of external parameters. The proposed control scheme is simulated by the computer which is installed in an ideal ac servomotor. The simulation results show that the proposed design method has robustness and accuracy in the speed response by adjusting the suppressed coefficients for load disturbance and the motor mechanical parameter variation.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.561-565
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• 2005

Sliding mode control (SMC) is an effective method of controlling systems with uncertainties which satisfy the so-called matching condition. However, how to effectively handle mismatched uncertainties of systems is still an ongoing research issue in SMC. Several methods have been proposed to design a stable sliding surface even if mismatched uncertainties exist in a system. Especially, it is presented that robustness and efficiency of SMC for linear systems with mismatched uncertainties can be improved by reducing mismatched uncertainties in the reduced-order system. The reduction method needs a new sliding surface with an additional component based on Lyapunov redesign technique. In this paper, a stable sliding surface which contains additional component to reduce the influence of mismatched uncertainties, is introduced. It is designed by using linear matrix inequalities that guarantees the stability of the system. A numerical example demonstrates the validity of the proposed scheme.

• 한국가스학회지
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• 제23권4호
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• pp.19-27
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• 2019

세계 환경규제가 강화되면서 액화천연가스의 사용량이 지속해서 증가하고 있다. 안정적이고 효율적인 액화천연가스 생산을 위해서는 운전 조건을 세분화하여 감시하는 시스템 구축이 필수적이다. 본 연구에서는 천연가스 액화플랜트 성분 분리공정을 해석하여 구축한 동적 모델 데이터를 대상으로 다중 모드 감시시스템 개발 방법을 제안하였다. 먼저 전체 정상 데이터를 주성분분석과 k-평균 군집화 방법론을 사용하여 다중 정상 운전 모델로 구분하였다. 그 다음, 새로운 데이터 값을 k-최근접 알고리즘으로 구축된 다중 정상 모드와 매칭하였다. 마지막으로, 다중 모드 주성분분석 감시 기법을 통해 공정 데이터의 이상 여부를 판별하였다. 제시된 방법론은 45가지 이상경우에 적용하였고, 기본 주성분분석 방법론과 단변수 감시 방법론과의 비교를 통해 속도와 정확도 지표에서 평균 약 5~10%이상 우수함을 입증하였다.