• International Journal of Fluid Machinery and Systems
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• v.3 no.4
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• pp.332-341
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• 2010

Standard dimensionless parameters cannot simultaneously represent all operation modes of a pump-turbine. They either have singularities at E=0 and multiple values in the 'unstable' areas, or else get singular at n=0. P. Suter (1966) introduced an alternative set of variables which avoids singularity and always remains unique-valued. This works for non-regulated pumps but not so well for regulated machines. A modification by C.S. Martin avoids distortion at low load. The present paper describes further improvements for the representation of torque, and for closed gate (where Suter's concept does not work). The possibility to interpolate across all operation modes is likewise useful for representing other mechanical parameters of the machine. Practical application for guide vane torque and pressure pulsation data is demonstrated by examples.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.12 no.2
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• pp.131-136
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• 2012

If one can find a control Lyapunov function (CLF) for a given nonlinear system, the control input stabilizing the system can be easily obtained. To find a CLF, the time derivative of an energy function should be negative definite. This procedure frequently requires a control input which is a rational function or includes an inverse function. The control input is not defined on the specific state-space where the denominator of the rational function is equal to 0 or the inverse function does not exist. In this region with singularities, the trajectory of the control system cannot be generated, which is one of the most important reasons why it is hard to make the origin of a nonlinear system be globally asymptotically stable. In this paper, we propose a smooth control law ensuring the globally asymptotic stability by means of cancelling the singularity in the control input.

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• v.3 no.1
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• pp.8-13
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• 2000

The singularity system to represent two circular cylinders poised under different ambient flow fields is considered in the present research. The singularity system, being composed of a series of singularities, has to be truncated for numerical calculations. A rational criterion to determine how many terms of this series should be retained to maintain the prescribed accuracy is provided through analysis of the converging property of the series. A particular emphasis is put to how to deal with the discrete vortex model of a boundary layer, this possibility being the basis for the development of a tool to simulate vortex shedding from a structure composed of two circular cylinders. The principle to obtain the present singularity system can be applied to more-than-cylinders structure. Only th series become much more complex with increase of the number of cylinders.

• Journal of the Korea institute for structural maintenance and inspection
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• v.2 no.4
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• pp.217-223
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• 1998

본 논문에서는 원형연단이 단순지지 되어 있을 때 단순과 자유의 방사연단 조건을 갖는 부채꼴형 평판의 휨진동에 대한 엄밀한 해석방법을 제시한다. Ritz방법을 이용하여 수직진동변위를 두가지 적합 함수식으로 가정하였다. 이러한 두가지의 적합 함수식은 (1) 수학적으로 완전한 대수삼각다항함수와, (2) 둔각 모서리에서의 휨모멘트 특이도를 고려하는 모서리함수로 구성되어있다. 본 연구에서는 방사연단의 둔각 모서리를 이루는 부채꼴형 각도의 범위에 따른 엄밀한 진동수 및 수직진동 변위의 전형적인 등고선을 제시하였다.

• Proceedings of the KIEE Conference
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• 1993.07a
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• pp.399-402
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• 1993

In this paper, an inverse kinematics of redundant manipulators is proposed. Optimality-constraint based inverse kinematic algorithms have some problems because those algorithms are based on necessary conditions for optimality. Among the problems, switching from a maximum value to a minimum value may occur and make an inverse kinematic solution unstable while performing a given task. An inverse kinematic solution for protecting from the switchings is suggested. By sufficient conditions for optimality, the configuration space is defined as a set of regions, potentially good configuration region and potentially bad configuration region. Inverse kinematics solution within potentially good configuration region can provide joint trajectories without both singularities and switchings. Through a simulation of tracing a circle, we show the effectiveness of this inverse kinematics.

• Proceedings of the KIEE Conference
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• 2001.07d
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• pp.1938-1939
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• 2001

시스템을 입력과 출력간의 함수관계로 볼 때 출력에 대한 상대차수가 정의되지 않는 점을 특이점이라고 정의할 수 있다. 본 논문에서는 적절한 기하학적 조건을 만족하는 해석적인 시스템(analytic system)에 대하여 그러한 특이점의 성질을 살펴본다. 특이점을 지나는 궤적은 특이점의 특이도와 그에 관련된 함수 값의 부호에 의해서 특이점의 주변에서는 특이 매니폴드를 기준으로 한 영역에서 나머지 다른 영역으로 통과하거나 혹은 그를 기준으로 어느 한 쪽의 영역에만 머물러 있게 됨을 보임으로써 특이점과 이를 지나는 궤적의 상관관계를 명확히 규명하였다.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.11
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• pp.129-139
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• 2000

The problem of eigenvalue and eigenvector is obtained from a V-notched crack in pseudo-isotropic dissimilar materials by the traction free boundary and the perfect bonded interface conditions. The complex stress function is assumed as the two-term William's type. The eigenvalue is solved by a commercial numerical program, MATHEMATICA to discuss stress singularities for V-notched cracks in pseudo-isotropic dissimilar materials. The RWCIM(Reciprocal Work Contour Integral Method) is applied to the determination to eigenvector coefficients associated with eigenvalues. The RWCIM algorithm is also coded by the MATHEMATICA.

• Multiscale and Multiphysics Mechanics
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• v.1 no.1
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• pp.35-51
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• 2016

In this paper, a mixed-mode cohesive law for an interface crack between epoxy and TR (transparent thermoplastic) resin is inversely estimated by the field projection method using numerical solutions and experimentally measured displacements. Displacements in a region far away from the crack tip are measured by digital image correlation technique. An inverse analysis, the field projection method formulated from the interaction J- and M-integrals with numerical auxiliary fields, is carried out to estimate a mixed-mode cohesive law for an interface crack between dissimilar materials. In the present approach, nonlinear deformations and damage near the crack tip are converted into the relationships of tractions and separations on crack surfaces behind the crack tip. The phase angle of mixed-mode singularities of the interface crack is also obtained from measured displacements in this study.

• Bulletin of the Society of Naval Architects of Korea
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• v.13 no.3
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• pp.1-9
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• 1976

A numerical method for solving the boundary-value problem related to potential flows with a free surface and an experimental work are introduced in this paper. The forced heaving motion of cylinders with arbitrary shapes in water of finite depth are Considered here. The Fredholm integral equation of the first kind is employed in determining strengths of singularities distributed on the body surface. And the results obtained by the present method for the case of a heaving circular cylinder on water of finite depth agree well with existing results of earlier investigators.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.2
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• pp.162-171
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• 2012

A method of hydrodynamic discrete sources is applied for two-dimensional modeling of stepped planing surfaces. The water surface deformations, wetted hull lengths, and pressure distribution are calculated at given hull attitude and Froude number. Pressurized air cavities that improve hydrodynamic performance can also be modeled with the current method. Presented results include validation examples, parametric calculations of a single-step hull, effect of trim tabs, and performance of an infinite series of periodic stepped surfaces. It is shown that transverse steps can lead to higher lift-drag ratio, although at reduced lift capability, in comparison with a stepless hull. Performance of a multi-step configuration is sensitive to the wave pattern between hulls, which depends on Froude number and relative hull spacing.