• Journal of the Korean Society for Precision Engineering
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• v.14 no.3
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• pp.147-155
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• 1997

Optimal trajectory for a robot manipulator minimizing actuator torques or energy consumptions ina fixed traveling time is obtained in the presence of obstacles. All joint displacements are represented in finite terms of Fourier cosine series and the coefficients of the series are obtained optimally by nonlinear programming. Thus, the geometric path need not be prespecified and the full dynamic model is employed. To avoid the obstacles, the concept of the penalty area is newly introduced and this penalty area is includ- ed in the performance index with an appropriate weighting coefficient. This optimal trajectory will be useful as a geometric path in the minimum-time trajectory planning problem.

• Bulletin of the Korean Mathematical Society
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• v.49 no.4
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• pp.875-883
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• 2012

Let $\mathbb{F}_q$ be a finite field with q elements and $\mathbb{F}_q((X^{-1}))$ be the field of all formal Laurent series with coefficients lying in $\mathbb{F}_q$. This paper concerns with the size of the set of points $x{\in}\mathbb{F}_q((X^{-1}))$ with their partial quotients $A_n(x)$ both lying in a given subset $\mathbb{B}$ of polynomials in $\mathbb{F}_q[X]$ ($\mathbb{F}_q[X]$ denotes the ring of polynomials with coefficients in $\mathbb{F}_q$) and deg $A_n(x)$ tends to infinity at least with some given speed. Write $E_{\mathbb{B}}=\{x:A_n(x){\in}\mathbb{B},\;deg\;A_n(x){\rightarrow}{\infty}\;as\;n{\rightarrow}{\infty}\}$. It was shown in [8] that the Hausdorff dimension of $E_{\mathbb{B}}$ is inf{$s:{\sum}_{b{\in}\mathbb{B}}(q^{-2\;deg\;b})^s$ < ${\infty}$}. In this note, we will show that the above result is sharp. Moreover, we also attempt to give conditions under which the above dimensional formula still valid if we require the given speed of deg $A_n(x)$ tends to infinity.

• The Journal of Korean Academy of Prosthodontics
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• v.25 no.1
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• pp.161-179
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• 1987

To study the mechanical behaviors of the margins of porcelain-fused-to-metal crown on the posterior teeth, 5 types of margins on the lower first molar were chosen, and then the finite element models were constructed. 50kg forces were applied to the porcelain on the axial wall supported by the metal vertically. The displacements and stresses of the porcelain-fused-to-metal crown were analyzed to investigate the influence of the type of margins. The results were as follows; 1. High tensile stresses were exhibited on the porcelain of the portion of the coronal line angle insufficient metallic support. 2. In case metal coping had a good supporting form to vertical force, uniform compressive stresses were exhibited on their supporting form. 3. Tensile stresses in the inframetallic margin on the series of the shoulder with a bevel margins were decreased in the bevel portion. 4. Principal stresses on the metal of the chamfer marginal portion were decreased comparing with the series of the shoulder margins. 5. The noticeable compressive stress gradients were exhibited between axial cement layer and metal on the series of the shoulder margins. 6. The principal stresses on the marginal cement layer were higher than that of the occlusal surface and axial wall.

• Proceedings of the KIEE Conference
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• 1987.11a
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• pp.469-473
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• 1987

This paper presents a method to estimate p.d.f.(probability density function) of harmonic phasor voltage. Because the quantity of harmonics is not fixed, stochastic analysis of harmonics is needed. Because it is impossible to obtain p.d.f. of voltage from p.d.f. of current directly, the moments of voltage and current are used. Firstly, the moments of current is calculated from p.d.f. of current. Secondly, the moments of voltage are calculated from the moments of current using the linearity of the moments. Finally, p.d.f. of voltage is estimated from the moments of voltage using Gram-Charlier Type A Series. [1] The moments of the p.d.f. obtained by the series and of the true p.d.f. is same up to given finite moments. Because current and voltage of harmonics are represented as not instantaneous values but phasors, the estimated value can be compared with the measured value and harmonic phasor voltage can be analyzed when the p.d.f. of phase is nonuniform as well as uniform.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.2 s.140
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• pp.129-135
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• 2005

At present, fatigue design of welded structures is primarily based on a nominal stress or hot spot stress approach with a series of classified weld S-N curves. Although well accepted by major industries, the nominal stress based fatigue design approach is cumbersome in terms of securing a series of S-N curves corresponding to each class of joint types and loading modes. The hot spot stress based fatigue design has a difficulty of finding a proper stress through the global model, the midium size model, and the detail model of ship structure. Also, it is difficult to link proper displacements within three different mesh size models. Recently, the structural stress is proposed as a mesh-size insensitive structural stress definition that gives a stress state at weld toe with relatively large mesh size. However, this method requires an experimental validation in obtaining the fatigue strength of weldments. Therefore, in this study, a series of experiment is performed for various sizes of weldments.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.336-339
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• 2007

In order to investigate the cause of fluting in tangential bending of low carbon steel sheet, an analytic analysis, an experiment and a series of finite element analysis for bending process were done. The fluting in bended sheet was due to the yield point elongation of material. Due to the yield point elongation, unstable plastic hinge was occurred in course of bending of elastic perfectly plastic sheet. According to the analysis and computational results, lower yield point elongation than 5% was required to prevent fluting in $0.5{\sim}0.6t$ sheet in $15{\sim}20mm$ radius bending.

• Corrosion Science and Technology
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• v.4 no.4
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• pp.164-170
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• 2005

Pipelines have the highest capacity and are the safest and the least environmentally disruptive means for transmitting gas or oil. Recently, failures due to corrosion defects have become a major concern in maintaining pipeline integrity. A number of solutions have been developed for the assessment of remaining strength of corroded pipelines. In this paper, a Fitness-For-Purpose(FFP) type limit load solution for corroded city gas pipelines is proposed. For this purpose, a series of burst tests with various types of machined defects were performed. Finite element simulations were carried out to derive an appropriate failure criterion. Based on such solution along with existing solutions, an integrity evaluation program for corroded city gas pipeline, COPAP-CITY, has been developed.

• Structural Engineering and Mechanics
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• v.11 no.6
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• pp.651-662
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• 2001

In order to investigate the seismic behavior and seismic design methods in the transverse direction of a shield tunnel, a series of model shaking table tests and a two-dimensional finite element dynamic analysis on the tests are carried out. Two kinds of static analytical methods based on ground-tunnel composite finite element model and beam-spring element model are proposed, and the validity of the static analyses is verified by model shaking table tests. The investigation concerns the dynamic response behavior of a tunnel and the ground, the interaction between the tunnel and ground, and an evaluation of different seismic design methods. Results of the investigation indicate that the shield tunnel follows the surrounding ground in displacement and dynamic characteristics in the transverse direction; also, the static analytical methods proposed by the authors can be used directly as the seismic design methods in the transverse direction of a shield tunnel.

• Interaction and multiscale mechanics
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• v.6 no.4
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• pp.357-375
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• 2013

In this paper, the forced vibration problem of an Euler-Bernoulli beam that is joined with a semi-infinite field of a compressible fluid is considered as a boundary value problem (BVP). This BVP includes two partial differential equations (PDE) and some boundary conditions (BC), which are introduced comprehensively. After that, the closed-form solution of this fluid-structure interaction problem is obtained in the frequency domain. Some mathematical techniques are utilized, and two unknown functions of the BVP, including the beam displacement at each section and the fluid dynamic pressure at all points, are attained. These functions are expressed as an infinite series and evaluated quantitatively for a real example in the results section. In addition, finite element analysis is carried out for comparison.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1995.04a
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• pp.53-56
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• 1995

Despite the recent development of structural analysis programs for the CRCP pavements over Westergaard's equations and finite element techniques, the Winkler foundations which are modelled by series of vertical springs at the nodes are generally used for the computer modelling of subbases under the concrete slab. Herewith, two parameter of soil foundation model is adopted as the most convenient mathematical model to enable deflections outside the loaded area to be effected and to upgrade the Winkler foundations. This paper highlights the derivations of finite element method for the two-parameter soil foundation model in the concrete pavements.