• 터널과지하공간
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• 제25권3호
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• pp.284-292
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• 2015

일반화된 Hoek-Brown 파괴함수는 GSI 지수를 이용하여 현장 암반의 강도정수를 결정하는 경험적 비선형 파괴조건식으로서 오늘날 다양한 암반공학적 설계에 널리 활용되고 있다. 그러나 여전히 많은 암반공학 전문가들이 암반의 강도를 마찰각과 점착력으로 표현하는 것에 익숙하다. 또한 거의 대부분의 암반안정성해석 수치해석 프로그램이 간편한 선형 Mohr-Coulomb 파괴조건식을 채택하고 있다. 이에 따라 Hoek-Brown 파괴함수를 Mohr-Coulomb 파괴함수 틀에서 이해하는 방법의 제시가 필요하다. 이 연구에서는 한계해석 상계정리를 적용하여 유도된 줄기초의 지지력 공식을 활용하여 Hoek-Brown 파괴조건을 따르는 천부 암반의 등가마찰각과 등가점착력을 계산하는 방법을 제안하였다. 일반화된 Hoek-Brown 파괴함수가 내포하는 접선점착력-접선마찰각 관계식을 이용하여 지지력 상계해를 마찰각의 함수로 표현한 후 최소 지지력 조건의 마찰각을 탐색하여 이를 등가마찰각으로 간주하였다. 제안된 방법을 활용하여 GSI, $m_i$, 교란계수 D가 등가마찰각과 등가점착력에 미치는 영향을 분석하였다.

• 한국통신학회논문지
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• 제26권8A호
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• pp.1437-1440
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• 2001

We present a modification method for runlength limited codes based on convolutional codes. This method is based on cosets of convolutional codes and can be applied to any convolutional code without degradation of error control performance of the codes. The upper bound of maximum zero and/or one runlength are provided. Some convolutional codes which have the shortest maximum runlength for given coding parameters are tabulated.

• 대한수학회지
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• 제56권4호
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• pp.1001-1016
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• 2019

We are concerned with optimization methods for the $L^2$-Wasserstein least squares problem of Gaussian measures (alternatively the n-coupling problem). Based on its equivalent form on the convex cone of positive definite matrices of fixed size and the strict convexity of the variance function, we are able to present an implementable (accelerated) gradient method for finding the unique minimizer. Its global convergence rate analysis is provided according to the derived upper bound of Lipschitz constants of the gradient function.

• 한국지반공학회논문집
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• 제20권3호
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• pp.85-96
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• 2004

본 연구는 점토층위의 모래지반에 위치하는 표면기초의 극한지지력에 대해 이론적으로 조사하였다. 실용적인 적용을 위하여 표면기초의 지지력에 관한 연구들에 대한 검토와 논의가 제시되며, 한계해석(Limit Analysis)의 운동학적 접근방법을 이용하여 정해의 극한 지지력이 계산되었다. 운동학적 해는 상한값이며 해의 정확성은 파괴메카니즘의 형상에 달려 있다. 이러한 방법은 설계도표를 만드는데 편리할 뿐만 아니라 물성치의 영향을 추정할 수 있다. 본 연구에서는 범용 유한요소해석 프로그램인 ABAQUS를 사용하여 탄소성 이론에 근거하여 극한지지력을 계산하였다. 운동학적 방범으로 계산된 결과와 유한요소 해석, 한계평형론에 근거한 몇몇 알려진 식들(Yamaguchi, Meyerhof와 Okamura 등)에 의한 결과를 비교하였다. 아울러, 운동학적 방법에 의한 제안식과 유한요소해석 결과와 한계평형해석 결과의 유효성에 대하여 검증하였다.

• 한국기계가공학회지
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• 제19권9호
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• pp.15-23
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• 2020

Spline is a machine component using transmits rotating energy with grooves on internal of boss and external periphery of shaft. Internal spline is generally produced by machining process. However, to reduce manufacturing cost and save time, plastic deformation process such as backward extrusion is gradually adapted for spline production. In plastic deformation process, forming load, stress on tools and flow flaws should be taken into account to have sound products. For this purpose, kinematically admissible velocity fields for Upper Bound Method in backward extrusion of internal spline has been suggested, then forming load and relative pressure have been calculated. Internal spline forming experiments have been con-ucted under hydraulic press and the calculated forming load well predicts the load of experiment.

• 대한기계학회논문집A
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• 제21권11호
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• pp.1827-1836
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• 1997

In this paper, the clamping type forging of helical gears has been investigated. Clamping type forging is an operation in which the product is constrained to extrude sideways through an orifice in the container wall. Punch is cylindrical shaped. The punch compresses a cylindrical bilet placed in a die insetr. As a consequence the material flows in a direction perpendicular to that of punch movement. The forging has been analysed by using the upper-bound method. A kinematically admissible velocity field has been developed, wherein, an involute curve has been introduce to re4present tooth profile of the gear. Numerical calculations have been carried out to investigate the effects of various parameters, such as module, number of teeth, helix angle, friction factor and initial height of billet on the forging of helical gears. Some firgiing experiments were catrried out with aluminium alloy to show the validity of the analysis. Good agreement was found between the predicted values of the forging load and obtained from the experimental results.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2002년도 제7회 단조 심포지엄
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• pp.85-91
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• 2002

Of all the many types of machine elements which exist today, gears are among the most commonly used. Many researches have been done to manufacture helical gears by cold forging and extrusion. Although cold forging and extrusion were applied to some bevel, spur, and helical gears, problems in connection with reducing forming load and tool life still make it difficult for the related methods to be commercialized. In this study, focusing on reducing load in forming helical gears, extrusion of helical gears by a two-step process is proposed. The process is composed of an extrusion step of spur gears used as preform and a torsion step of the preform to make helical gears. Upper-bound analysis for the two-step process is performed and compared with results of experiments. The newly proposed method can be used as an advanced forming technique to remarkably reduce the forming load and replace the conventional forming process of helical gears.

• Journal of applied mathematics & informatics
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• 제30권5_6호
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• pp.699-717
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• 2012

In this paper, we deal with the robust mixed $H_2/H_{\infty}$ guaranteed-cost control problem involving uncertain neutral stochastic distributed delay systems. More precisely, the aim of this problem is to design a robust mixed $H_2/H_{\infty}$ guaranteed-cost controller such that the close-loop system is stochastic mean-square exponentially stable, and an $H_2$ performance measure upper bound is guaranteed, for a prescribed $H_{\infty}$ attenuation level ${\gamma}$. Therefore, the fast convergence can be fulfilled and the proposed controller is more appealing in engineering practice. Based on the Lyapunov-Krasovskii functional theory, new delay-dependent sufficient criteria are proposed to guarantee the existence of a desired robust mixed $H_2/H_{\infty}$ guaranteed cost controller, which are derived in terms of linear matrix inequalities(LMIs). Furthermore, the design problem of the optimal robust mixed $H_2/H_{\infty}$ guaranteed cost controller, which minimized an $H_2$ performance measure upper bound, is transformed into a convex optimization problem with LMIs constraints. Finally, two simulation examples illustrate the design procedure and verify the expected control performance.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.824-828
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• 2002

Of all the many types of machine elements which exist today, gears are among the most commonly used. Many researches have been done to manufacture helical gears by cold forging and extrusion. Although cold forging and extrusion were applied to some bevel, spur, and helical gears, problems in connection with reducing forming load and tool life still make it difficult for the related methods to be commercialized. In this study, focusing on reducing load in forming helical gears, extrusion of helical gears by a two-step process is proposed. The process is composed of an extrusion step of spur gears used as preform and a torsion step of the preform to make helical gears. Upper-bound analysis for the two-step process is performed and compared with results of experiments. The newly proposed method can be used as an advanced forming technique to remarkably reduce the forming load and replace the conventional forming process of helical gears.

• International Journal of Control, Automation, and Systems
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• 제6권2호
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• pp.269-277
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• 2008

This paper proposes a necessary and sufficient condition of convergence in the $L_2$-norm sense for a feedback-based iterative learning control (ILC) system including a multi-input multi-output (MIMO) linear time-invariant (LTI) plant. It is shown that the convergence conditions for a nominal plant and an uncertain plant are equal to the nominal performance condition and the robust performance condition in the feedback control theory, respectively. Moreover, no additional effort is required to design an iterative learning controller because the performance weighting matrix is used as an iterative learning controller. By proving that the least upper bound of the $L_2$-norm of the remaining tracking error is less than that of the initial tracking error, this paper shows that the iterative learning controller combined with the feedback controller is more effective to reduce the tracking error than only the feedback controller. The validity of the proposed method is verified through computer simulations.