• 대한기계학회논문집B
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• 제27권6호
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• pp.766-772
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• 2003

The pseudospectral method for stability analysis was used to find the most influential disturbance mode for transition of plane channel flows and Blasius flow at their critical Reynolds numbers. A number of various oblique disturbance waves were investigated for their pseudospectra and resolvent norm contours in each flow, and an exhaustive search method was employed to find the disturbing waves to which the flows become most unstable. In plane Poiseuille flow an oblique disturbance with a wavelength of 3.59h (where h is the half channel width) at an angle $28.7^{\circ}$ was found to be the most influential for the flow transition to turbulence, and in plane Couette flow it is an oblique wave with a wavelength of 3.49h at an angle of $19.4^{\circ}$. But in Blasius flow it was found that the most influential mode is a normal wave with a wavelength of $3.44{\delta}_{999}$. These results imply that the most influential disturbance mode is closely related to the fundamental acoustic wave with a certain shear sheltering in the respective flow geometry.

• 제어로봇시스템학회논문지
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• 제4권1호
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• pp.45-55
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• 1998

In this paper, a robust path tracker and depth controller of Autonomous Underwater Vehicle based on sliding mode control is presented. We have also designed augmented equivalent control inputs by analyzing the sliding mode with the reaching mode. This can enhance the reaching rate, and improve chattering problems, that is, noise caused by the control plane actuator of the vehicle, which is one of the problems that occur when sliding mode control is used. Also to resolve the steady state error generated in the path tracker under current effect, a modified sliding plane is constructed. Also a redesigned sliding plane and control input using transformation matrix is proposed to do easy design of MIMO depth controller. For state variables that cannot be measured directly, reduced order sliding mode control is used to design an observer. The performance of designed path tracker and depth controller is investigated by computer simulation. The results show that the proposed control system has robust performance to parameter variation, modelling error and disturbance.

• 한국해양공학회지
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• 제17권4호
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• pp.59-65
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• 2003

In order to achieve the desired lightweight and robust design of a structure, it is preferable to design a structure and its control system, simultaneously, which is termed the combined optimal design. A constant-cross-sectional area cantilever beam was chosen as the optimum design method, An initial load and a time-varying disturbance were applied at the free end of the beam. Sliding mode control was selected, due to its insensitivity to the disturbance, compared with other modes. It is known that the sliding mode control is robust to the disturbance and is uncertain, only if a matching condition is met, after giving a switching hyper plane. In this study, the optimum method was used for the design of the switching hyper plane, and the objective function of the optimum switching hyper plane was assumed to be the objective of the control system. The total weight of the structure was treated as a constraint, and the cross sectional areas of the beam were considered as design variables, the result being a nonlinear programming problem. To solve it, the sequential linear programming method was applied. As a result of the optimum design, the effect of attenuating vibrations has been substantially improved. Moreover, the lightweight design of the structure became possible as a result of the relationship of the weight of the structure to the control objective function.

• 소성∙가공
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• 제11권8호
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• pp.668-675
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• 2002

The circles deform into various shape during deformation, the major and minor axes of which indicate the direction of the major and minor principal strains. Likewise, the measured dimensions are used to determine the major and minor principal strain magnitudes. This circular grid technique of measuring strains can be used to diagnose the causes of necking and fracture in industrial practice and to investigate whether these defects were caused by material property variation, changes in lubrication, of incorrect press settings. In non-axisymmetric deep drawing, three modes of forming regimes are found: draw, stretch, plane strain. The stretch mode for non-axisymmetric deep drawing could be defined when the major and minor strains are positive. The draw mode could be defined when the major strain is positive and minor strain is negative, and plane strain mode could be defined when the major strain is positive and minor strain is zero. Through experiments the draw mode was shown on the wall and flange are one of a drawn cup, while the plane strain and the stretch mode were on the punch head and the punch corner area respectively, We observed that the punch load of elliptical deep drawing was decreased according to increase of die corner radius and the thickness deformation of minor side was more large than major side.

• 한국정밀공학회지
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• 제19권10호
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• pp.45-51
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• 2002

To achieve the lightweight and robust design of a structure, it is requested to design a structure and its control system simultaneously, which is called as the combined optimal design. A constant-cross-sectional area cantilever beam was chosen as an example for the applying the optimum design method. An initial load and a time varying disturbance were applied at the free end of the beam. Sliding mode control was selected due to its insensitiveness to the disturbance compared with other modes. It is known that the sliding mode control is robust to the disturbance and the uncertainty only if a matching condition is met, after giving a switching hyper plane. In this study, the optimum method was used for the design of the switching hyper plane and the objective function of the optimum switching hyper plane was assumed to be the objective one of the control system. The total weight of the structure was treated as a constraint and the cross sectional areas of the beam were considered as design variables, which means a nonlinear programming problem. The sequential linear programming method was applied to solve it. As a result of the optimum design, the effect of attenuating vibrations has been improved obviously. Moreover, lightweight design of the structure became possible from the relationship of the weight of the structure and the control objective function.

• 대한기계학회논문집
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• 제13권5호
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• pp.911-920
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• 1989

본 연구에서는 층간균열면에서의 보 두께비를 달리함에 따라 다양한 혼합 모우드 층간파괴인성을 평가할 수 있는 Fig.1과 같은 층간균열 시편에 대해 3점 굽힘하중 하중이 작용될 때의 전체어너지방출률을 전단변형을 고려한 보이론에 의해 유도하고 이를 층간균열면에서의 보 두께비에 따라 모우드I 성분과 모우드II 성분의 분리된 형태로 나타내었다. 또 한 여러가지 시편두께에 대해 전체에너지방출률을 구해 전단변형에 의한 에너지방출률이 전체에너지방출률에 미치는 영향도 조사하였다. 그리고 층간 균열면에서의 보 두께비가 0.3, 0.5, 0.6, 0.7, 그리고 0.9인 경우의 층간균열시편에 대해 실험적으로 혼합모우드 층간 파괴인성을 평가하고 혼합 모우드 변형을 받을 때의 층간파괴 거동도 조사하였다.

• 한국광학회지
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• 제13권2호
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• pp.162-165
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• 2002

본 논문에서는 반투과 반사판과 22.5$^{\circ}$의 in-plane tilt각을 가지며 λ/2로 설계된 반강유전성 액정 셀을 이용하여 새로운 형태의 반투과형 LCD모드의 구조를 제시하였다. 제안된 구조에서, 투과형 모드뿐만 아니라 광대역 λ/4 필름을 사용한 반사형 모드에서도 높은 밝기와 명암대비비를 구현해 낼 수 있었다.

• 전자공학회논문지A
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• 제30A권11호
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• pp.80-87
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• 1993

In this paper, the fields of double-plane steps in rectangular waveduides are analyzed using the modified TE$_{mn}$$^{x}$ mode-matching method. The characteristics of rectangular waveguide having double-plane steps are investigated with accomdating the effects of higher-order modes generated by discontinuities. In comparison with the generalized TE$_{mn}$-TM$_{mn}$ mode analysis, the modified TE$_{mn}$$^{x}$ mode-matching method consumes less memory and CPU time and provides improved convergence behavior. The results obtained in this manner coinside with that of the TE$_{mn}$-TM$_{mn}$ mode-matching method.

• 한국음향학회지
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• 제21권4호
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• pp.183-183
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• 2002

In this paper, the strong in-plane vibration has been experimentally observed at the end of a finite cylindrical shell. The strong in-plane vibration was generated by the evanescent wave field, which was excited along about half the length of the shell. The evanescent waves were generated due to mode conversion of elastic waves at the ends of the cylindrical shells.

• Structural Engineering and Mechanics
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• 제36권5호
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• pp.575-598
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• 2010

The shape and size of the plastic zone around the crack tip are analyzed under pure mode I, pure mode II and mixed mode (I+II) loading for small scale yielding and for both plane stress and plane strain conditions. A new analytical formulation is presented to determine the radius of the plastic zone in a non-dimensional form. In particular, the effect of T-stress on the plastic zone around the crack tip is studied. The results of this investigation indicate that the stress field with a T-stress always yields a larger plastic zone than the field without a T-stress. It is found that under predominantly mode I loading, the effect of a negative T-stress on the size of the plastic zone is more dramatic than a positive T-stress. However, when mode II portion of loading is dominating the effect of both positive and negative T-stresses on the size of the plastic zone is almost equal. For validating the analytical results, several finite element analyses were performed. It is shown that the results obtained by the proposed analytical formulation are in very good agreements with those obtained from the finite element analyses.