• Structural Engineering and Mechanics
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• v.29 no.3
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• pp.241-258
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• 2008

This paper presents a new identification approach to prestress force. Firstly, a bridge deck is modeled as a prestressed Timoshenko beam. The time domain responses of the beam under sinusoidal excitation are studied based on modal superposition. The prestress force is then identified in the time domain by a system identification approach incorporating with the regularization of the solution. The orthogonal polynomial function is used to improve the noise effect and obtain the derivatives of modal responses of the bridge. Good identification results are obtained from only the first few measured modal data under both sinusoidal and impulsive excitations. It is shown that the proposed method is insensitive to the magnitude of force to be identified and can be successfully applied to indirectly identify the prestress force as well as other physical parameters, such as the flexural rigidity and shearing rigidity of a beam even under noisy environment.

• Bulletin of the Korean Mathematical Society
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• v.59 no.2
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• pp.319-343
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• 2022

We discuss the notions of positive expansivity, chain transitivity, uniform rigidity, chain mixing, weak specification, and pseudo orbital specification in terms of finite open covers for Hausdorff topological spaces and entourages for uniform spaces. We show that the two definitions for each notion are equivalent in compact Hausdorff spaces and further they are equivalent to their standard definitions in compact metric spaces. We show that a homeomorphism on a Hausdorff uniform space has uniform h-shadowing if and only if it has uniform shadowing and its inverse is uniformly equicontinuous. We also show that a Hausdorff positively expansive system with a Hausdorff shadowing property has Hausdorff h-shadowing.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.1117-1120
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• 1999

In this paper, we design the H$\infty$ optimal controller satisfying robust stability and performance in spite of the plant uncertainty for an electro-mechanical actuator system and analyze the controller in frequency domain. H$\infty$ optimal controller K was designed using iteration algorithm suggested by DOYLE. Using the controller in an electro-mechanical actuator system, the joint with very small coupling rigidity coefficient was used to vary the control parameter. The plant unstructured uncertainty was assumed to be a multiplicative type.

• International Journal of High-Rise Buildings
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• v.7 no.3
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• pp.255-264
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• 2018

This paper introduces three distinctive means for the use of a 189-meter high damped structure ensuring safety against earthquake: 1. Realization of L-shaped elevational structural planning: The bottom and top of the tower have belt trusses and hat trusses respectively to restrain the bending deformation. Furthermore, large-capacity oil dampers (damping force 6,000 kN) are installed in the middle part of the tower to restrain the higher-mode deformation. 2. Realization of L-shaped planar structural planning: We devised a means of matching the centers of gravity and rigidity by adjusting planar rigidity. Moreover, viscous damping devices are located at the edges of the L-shaped plan, where torsional deformation tends to be amplified. We call this the "Damping Tail" system. 3. Composite foundation to equalize deformations under different loading conditions: We studied the vertical and horizontal deformations using sway-rocking and 3D FEM models including the ground, and applied multi-stage diameter-enlarged piles to the tower and a mat foundation to the podium to keep the foundations from torsional deformations and ensure structural safety.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.31 no.5
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• pp.24-30
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• 1999

Crosslinked corn starches were prepared to increase their molecular weights and their performance as a component of Compozil system was evaluated and compared with that of potato starches. It was shown that greater improvements in retention and strength properties could be achieved when crosslinded cationic corn starches rather than conventional cationic potato starches were used especially at high conductivity because of their molecular rigidity.

• Structural Engineering and Mechanics
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• v.28 no.2
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• pp.129-152
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• 2008

This paper considers the solution of the stochastic differential equations (SDEs) with random operator and/or random excitation using the spectral SFEM. The random system parameters (involved in the operator) and the random excitations are modeled as second order stochastic processes defined only by their means and covariance functions. All random fields dealt with in this paper are continuous and do not have known explicit forms dependent on the spatial dimension. This fact makes the usage of the finite element (FE) analysis be difficult. Relying on the spectral properties of the covariance function, the Karhunen-Loeve expansion is used to represent these processes to overcome this difficulty. Then, a spectral approximation for the stochastic response (solution) of the SDE is obtained based on the implementation of the concept of generalized inverse defined by the Neumann expansion. This leads to an explicit expression for the solution process as a multivariate polynomial functional of a set of uncorrelated random variables that enables us to compute the statistical moments of the solution vector. To check the validity of this method, two applications are introduced which are, randomly loaded simply supported reinforced concrete beam and reinforced concrete cantilever beam with random bending rigidity. Finally, a more general application, randomly loaded simply supported reinforced concrete beam with random bending rigidity, is presented to illustrate the method.

• Nuclear Engineering and Technology
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• v.52 no.6
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• pp.1297-1303
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• 2020

In this study, nuclear radiation shielding and rigidity parameters of Y (0.1-x)B0.6Bi1.8O3La2x glassy system were investigated in order to determine it's suitability for use as nuclear radiation shielding materials. Therefore, a group of bismuth borate glass samples with La₂O₃ additive were synthesized using the technique of melt quenching. According to the results, the increase of the La₂O₃ additive increases the density of the glass samples and the mass attenuation coefficient (μ_m) values, whereas the half-value layer (HVL) and mean free path (MFP) values decrease. The effective atomic number (Z_eff) is also enhanced with an increment of both mass removal cross section for neutron (Σ_R) and absorption neutron scattering cross section (σ_abs). In addition to the other parameters, rigidity parameter values were theoretically examined. The increase of La₂O₃ causes some other important magnitudes to increase. These are the average crosslink density, the number of bonds per unit volume, as well as the stretching force constant values of these glass samples. These results are in concordance with the increase of elastic moduli in terms of the Makishima-Mackenzie model. This model showed an increase in the rigidity of the glass samples as a function of La₂O₃.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2000.11b
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• pp.287-294
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• 2000

Calculation of the flexural rigidity value (EI) is indispensable for prescription of deflection characteristics of crop stalks in harvesting□Conventionally□EI has been determined by either average EI of the whole stalk or average EI of each stems divided into node through the calculation method of cantilever with homogeneous section□However□deflection characteristics of crop stalks caused by mechanical operation such as combine harvester were not exactly presumed by these conventional EI through the experiment by authors. Further, actual EI of a stalk changes in company with a change of moisture contents as time passes during the experiment. Finally, efficient calculation method for determining EI is needed in order to improve these problems. In this study, mechanical model based on actual structure of the crop stalk with variety sectional area was proposed. This mechanical model is calculated by the theory of cantilever with continuous stages. Therefore, improvement of both calculating accuracy on EI and efficiency of measuring system was tried. At first, this calculation method was applied to piano wire of which EI was recognized in advance. As a result, EI calculated from this new method coincided approximately with piano wire's EI. Next, applying to crop stalks as same as piano wire, relationship between loads acting on crop stalks and deflection values calculated by EI using this new calculation method was exactly presumed in comparison with conventional method. Further, measuring time of deflection test was greatly reduced. Finally, new calculation method of EI will be available for estimating mechanical characteristics of so many kinds of crop stalks in harvesting operation. Further, in this study, new deflection test using image-processing apparatus by computer will be introduced.

• Journal of Fashion Business
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• v.12 no.6
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• pp.61-72
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• 2008

The UV-protection effect of green-tea dyed fabrics was reported in our previous studies. The chitosan was used as a natural mordant of cellulose fiber for green tea extract because chitosan is a natural bio-polymer. The increase in the UV protection property of summer cellulose fabrics, cotton and linen, upon the repetition of chitosan mordanting and green tea dyeing was observed. However, the physical property change would be followed by this repeated wet processing of the cellulose fabric. Therefore, the physical changes of the chitosan mordanted and green tea dyed cotton and linen fabrics were evaluated by KES-FB system. Tensile, shear, bending, compression, and surface characteristics were tested upon the repetition of mordanting and dyeing treatments. Linearity of tensile force increased in the treated cotton and linen samples. Tensile energy and resilience decreased in all treated fabrics. Shear stiffness increased in the treated cotton and linen in general. Shear hysteresis was increased in all cotton samples and some linen samples. In cotton, the bending rigidity in all treated cottons increased except C3G3. As the chitosan mordanting numbers increased, the bending rigidity tended to decrease. In linen, the bending rigidity and hysteresis increased in all treated samples. Compressional energy and resilience increased as the number of chitosan mordanting increased both in cotton and linen. This could be the result of the increase in thickness upon chitosan mordanting. Surface coefficient of friction increased in the treated cotton and linen in general. Surface roughness tended to increase in cotton.

• Korean Journal of Materials Research
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• v.7 no.12
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• pp.1089-1096
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• 1997

본 연구에서는 에폭시/산무수물계에 화학양론비(r=산무수물/에폭시)를 0.5, 0.7,0.9,1.1로 변화시켜 서로 다른 두종류의 경화촉진제 1-cyanoethy1-2-ethy1-4-methy1 imidazole(2E4MZ-CN)과 N,N-dimethy1 benzy1 amine(BDMZ)을 첨가한 시료에 대한 경화거동과 경화 후 물성을 관찰하였다. 이 시료의 등온 경화거동은 동역학 측정기(dynamic mechanical analyzer, DMA)와 시차주사 열량분석기(differential scanning calorimeter, DSC)를 이용하여 조사하였다. DMA로부터 구해진 결과를 보면 경화시 상대저장강성을 (relative storage rigidity, RSR)과 상대손실강성율(relative loss rigidity, RSR)과 상대손실강성율(relative loss rigidity, RLR)의 변화가 r값과 경화촉진제의 종류에 영향을 받았다. 그리고 DSC결과는 r값이 감소함에 따라 경화가 촉진되는 것으로 나타났다. 경화물의 성질을 조사하기 위하여 사용된 DMA로부터 얻어진 유리전이온도(glass transition temperature, T$_{g}$)와 가교결합간의 평균분자량(average molecular weigh between crosslinks, M$_{c}$은 사용한 두 경화촉진제에 대하여 r값의 영향이 다르게 나타났다. BDMA의 경우는 T$_{g}$가 1:1화학양론비인 r=0.9에서 최고치를 보였으나, 2E4MZ-CN은 r이 감소함에 따라 계속 증가하는 양상을 보였다. 이와 같은 경향은 2E4MZ-CN을 경화촉진제로 사용하였을 때 에폭시가 과량으로 될수록 잔류 에폭시기들간의 에케르반응이 추가적으로 일어나 M$_{c}$가 감소하기 때문이다.