• Structural Engineering and Mechanics
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• 제25권4호
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• pp.383-403
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• 2007

The contact problem for an elastic layer resting on an elastic half plane is considered according to the theory of elasticity with integral transformation technique. External loads P and Q are transmitted to the layer by means of two dissimilar rigid flat punches. Widths of punches are different and the thickness of the layer is h. All surfaces are frictionless and it is assumed that the layer is subjected to uniform vertical body force due to effect of gravity. The contact along the interface between elastic layer and half plane will be continuous, if the value of load factor, ${\lambda}$, is less than a critical value, ${\lambda}_{cr}$. However, if tensile tractions are not allowed on the interface, for ${\lambda}$ > ${\lambda}_{cr}$ the layer separates from the interface along a certain finite region. First the continuous contact problem is reduced to singular integral equations and solved numerically using appropriate Gauss-Chebyshev integration formulas. Initial separation loads, ${\lambda}_{cr}$, initial separation points, $x_{cr}$, are determined. Also the required distance between the punches to avoid any separation between the punches and the layer is studied and the limit distance between punches that ends interaction of punches, is investigated. Then discontinuous contact problem is formulated in terms of singular integral equations. The numerical results for initial and end points of the separation region, displacements of the region and the contact stress distribution along the interface between elastic layer and half plane is determined for various dimensionless quantities.

• 한국정밀공학회지
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• 제26권10호
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• pp.12-17
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• 2009

• 제어로봇시스템학회논문지
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• 제10권10호
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• pp.855-868
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• 2004

There are several types of singularities in controlling robotic manipulators: kinematic singularity, algorithmic singularity, semi-kinematic singularity, semi-algorithmic singularity, and representation singularity. The kinematic and algorithmic singularities have been investigated intensively because they are not predictable or difficult to avoid. The problem with these singularities is an unnecessary performance reduction in non-singular region and the difficulty in performance tuning. Tn this paper, we propose a method of avoiding kinematic and algorithmic singularities by applying a task reconstruction approach while maximizing the task performance by calculating singularity measures. The proposed method is implemented by removing the component approaching the singularity calculated by using singularity measure in real time. The outstanding feature of the proposed task reconstruction method (TR-method) is that it is based on a local task reconstruction as opposed to the local joint reconstruction of many other approaches. And, this method has dynamic task priority assignment feature which ensures the system stability under singular regions owing to the change of task priority. The TR-method enables us to increase the task controller gain to improve the task performance whereas this increase can destabilize the system for the conventional algorithms in real experiments. In addition, the physical meaning of tuning parameters is very straightforward. Hence, we can maximize task performance even near the singular region while simultaneously obtaining the singularity-free motion. The advantage of the proposed method is experimentally tested by using the 7-dof spatial manipulator, and the result shows that the new method improves the performance several times over the existing algorithms.

• Advances in aircraft and spacecraft science
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• 제7권3호
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• pp.215-228
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• 2020

As is shown in the paper, the Koltunov-Rzhanitsyn singular kernel of heredity (when constructing mathematical models of the dynamics problem of the hereditary theory of viscoelasticity) adequately describes real mechanical processes, best approximates experimental data for a long period of time. A mathematical model of the problem of the flutter of viscoelastic plates moving in a gas with a high supersonic velocity is given. Using the Bubnov-Galerkin method, discrete models of the problem of the flatter of viscoelastic plates flowed over by supersonic gas flow are obtained. A numerical method is developed to solve nonlinear integro-differential equations (IDE) for the problem of the hereditary theory of viscoelasticity with weakly singular kernels. A general computational algorithm and a system of application programs have been developed, which allow one to investigate the nonlinear dynamic problems of the hereditary theory of viscoelasticity with weakly singular kernels. On the basis of the proposed numerical method and algorithm, nonlinear problems of the flutter of viscoelastic plates flowed over in a gas flow at an arbitrary angle are investigated. In a wide range of changes in various parameters of the plate, the critical velocity of the flutter is determined. It is shown that the singularity parameter α affects not only the oscillations of viscoelastic systems, but the critical velocity of the flutter as well.

• 전산구조공학
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• 제9권4호
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• pp.165-172
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• 1996

들보나 아치, 판재 그리고 쉘과 같은 박판구조물의 경계부근의 매우 좁은 영역에는 경계층이 존재하는데, 이 영역에서 해는 급격하게 변화하는 특이 거동을 나타낸다. 유한요소법을 이용하여 이러한 물체의 거동을 해석하는 경우, 이런 특이성을 묘사하기 위해 유한요소 체눈패턴이 대단히 중요한 역할을 한다. 이 논문은 경계층에 대한 이론적 해석과 최적의 체눈패턴을 형성하기 위한 가이드를 제시한다. 또한 이론적인 결과를 입증하는 예제도 소개하고자 한다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1988년도 한국자동제어학술회의논문집(국내학술편); 한국전력공사연수원, 서울; 21-22 Oct. 1988
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• pp.37-40
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• 1988

It is well-known that the redundancy can be exploited to avoid the singular regions of the redundant manipulator by increasing the manipulability. The method, however, requires exprecessive energy and gives rather large tracking errors since the manipulability is increased repidly so that the manipulator avoid the singular region quickly. In this paper, a new method is proposed in which the increasing speed of the manipulability is confined to a certain bound. Therefore, in the proposed method, the movement energy and the tracking errors are reduced. The computer simulation studies are performed to show the validity of the method.

• 대한기계학회논문집
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• 제18권4호
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• pp.887-902
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• 1994

Within the framework of anisotropic thermoelasticity, the problem of an interlaminar crack in a laminated fiber-reinforced composite subjected to a uniform heat flow is investigated. Under a state of generalized plane deformation, dissimilar anisotropic half-spaces with different fiber orientations are considered to be bound together by a matrix interlayer containing the crack. The interlayer models the matrix-rich interlaminar region of the fibrous composite laminate. Based on the flexibility/stiffness matrix approach, formulation of the current crack problem results in having to solve two sets of singular integral equations for temperature and thermal stress analyses. Numerical results are obtained, illustrating the parametric effects of laminate stacking sequence, relative crack size, crack location, crack surface partial insulation, and fiber volume fraction on the values of mixed mode thermal stress intensity factors.

• 항공우주시스템공학회지
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• 제1권1호
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• pp.25-35
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• 2007

In this paper, the interlaminar crack problems of a fiber metal laminate (FML) under generalized plane deformation are studied using the theory of anisotropic elasticity. The crack is considered to be embedded in the matrix interlaminar region (including adhesive zone and resin rich zone) of the FML. Based on Fourier integral transformation and the stress matrix formulation, the current mixed boundary value problem is reduced to solving a system of Cauchy-type singular integral equations of the 1st kind. Within the theory of linear fracture mechanics, the stress intensity factors are defined on terms of the solutions of integral equations and numerical results are obtained for in-plane normal (mode I) crack surface loading. The effects of location and length of crack in the 3/2 and 2/1 ARALL, GLARE or CARE type FML's on the stress intensity factors are illustrated.

• 한국안전학회지
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• 제15권2호
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• pp.13-21
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• 2000

Under the mixed mode loading, it has been known that the influence of non-singular terms in the stress fields is serious, because the critical distance, ${\gamma}_o$ - the distance of nonlinear elastic region near the crack tip has no negligible value. In this paper, it has been studied on the influence of non-singular terms, T-stress, and the case of T=0, ${\sigma}cos^2{\beta}$, ${\sigma}cos(2{\beta})$ and $0.05{\sigma}cos(2{\beta})$, under uniaxial tension and compression. It has been seen that the T-stress of ${\sigma}cos(2{\beta})$ has better than others as comparing to the experimental data.

• 대한기계학회논문집A
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• 제20권4호
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• pp.1186-1193
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• 1996

The analytic solution of the stress field at creep crack in the presence of grain boundary caviation is to be obtained by solving the governing equation which was derived through the previous paper. The complex integral technique is used to slove the singular integral equation. under the help of the information about stress behaviors at the ends of integral region know by numerical solution. The resultant stress disstribution obtained shows the relaxed crack-tip singularity of $r^{1/2+\theta}$ due to the intervention of cavitation effect, otherwise, it should assumed to be $r^{1/2}$ singularity of linear elastic fracture mechanics with no cavitation.