• Nuclear Engineering and Technology
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• v.54 no.7
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• pp.2359-2366
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• 2022

Selecting graphite grades with superior irradiation characteristics is important task for designers of graphite moderation reactors. To provide reference information and data for graphite selection, the effects of irradiation on three fine-grained, iso-molded nuclear grade graphites, ETU-10, IG-110, and NBG-25, were compared based on irradiation-induced changes in volume, thermal conductivity, dynamic Young's modulus, and coefficient of thermal expansion. Data employed in this study were obtained from reported irradiation test results in the high flux isotope reactor (HFIR)(ORNL) (ETU-10, IG-110) and high flux reactor (HFR)(NRL) (IG-110, NBG-25). Comparisons were made based on the irradiation dose and irradiation temperature. Overall, the three grades showed similar irradiation-induced property change behaviors, which followed the historic data. More or less grade-sensitive behaviors were observed for the changes in volume and thermal conductivity, and, in contrast, grade-insensitive behaviors were observed for dynamic Young's modulus and coefficient of thermal expansion changes. The ETU-10 of the smallest grain size appeared to show a relatively smaller VC to IG-110 and NBG-25. Drastic decrease in the difference in thermal conductivity was observed for ETU-10 and IG-110 after irradiation. The similar irradiation-induced properties changing behaviors observed in this study especially in the DYM and CTE may be attributed to the assumed similar microstructures that evolved from the similar size coke particles and the same forming method.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.543-546
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• 2000

Static and dynamic experiments were done to study on the restitution behaviors of strings. The elastic and viscoelastic model were compared. To apply a linear viscoelastic model (Kelvin model) to longitudinal behaviors of strings, static and dynamic tensile tests were done. Using their results, it should be intended to acquire damped stress (Stress related to velocity), and to calculate the viscoelastic coefficient. Fixing both ends, string was pushed by the loadcell attached to the tensile tester. The experimental results were in accordance with the calculated results using the Kelvin model acquired from the results of longitudinal tensile test. But the results of falling mass experiments, the behaviors of strings were near to elastic model. The clamping condition of strings in both sides has an effected on the value of COR. The smaller contact area, the grower the value of COR.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.11
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• pp.1069-1076
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• 2007

The purpose of this study is to improve the performance of a linear feeder that can transport grains uniformly. In order to analyze the dynamic behaviors of a linear feeder, the displacements of the feeder are measured by several accelerometers when it is in an operating condition. After the signal data from the accelerometers are captured in the time domain, the feeder motion in the space is visualized by using graphic computer software. In addition, a dynamic model of the feeder is established for a multi-body dynamics simulation. For the dynamic simulation, RecurDyn, which is a commercial multi-body dynamic package, is used. From the experimental and the computational approaches, an optimal dynamic motion is obtained for uniform transportation of grains. Furthermore, we also consider the determination of design parameters for optimal dynamic motion such as centroid, stiffness, and damping coefficient of the feeder system.

• Macromolecular Research
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• v.17 no.10
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• pp.785-790
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• 2009

In this paper, the relaxation behavior of the regenerated silk fibroin (SF) films was investigated using dielectric thermal analysis (DETA), and compared with the dynamic mechanical behavior obtained from dynamic mechanical thermal analysis (DMTA), in order to gain a better understanding of the characteristics of dielectric behavior of SF film and identify the differences between the two analyses. Compared to DMTA, DETA exhibited a higher sensitivity on the molecular relaxation behaviors at low temperature ranges that showed a high $\gamma$-relaxation peak intensity without noise. However, it was not effective to examine the relaxation behaviors at high temperatures such as $\alpha-$ and ${\alpha}_c$-relaxations that showed a shoulder peak shape. On the contrary, DMTA provided more information regarding the relaxation behaviors at high temperatures, by exhibiting the changes in width, intensity and temperature shift of the $\alpha$-relaxation peak according to various crystallinities. Conclusively, DETA and DMTA can be utilized in a complementary manner to study the relaxation behavior of SF over a wide temperature range, due to the different sensitivity of each technique at different temperatures.

• Structural Engineering and Mechanics
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• v.75 no.3
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• pp.339-356
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• 2020

In this article, a developed bond-based peridynamic model for functionally graded materials (FGMs) is proposed to simulate the dynamic fracture behaviors in FGMs. In the developed bond-based peridynamic model for FGMs, bonds are categorized into three different types, including transverse directionally peridynamic bond, gradient directionally peridynamic bond and arbitrary directionally peridynamic bond, according to the geometrical relationship between directions of peridynamic bonds and gradient bonds in FGMs. The peridynamic micromodulus in the gradient directionally and arbitrary directionally peridynamic bonds can be determined using the weighted projection method. Firstly, the standard bond-based peridynamic simulations of crack propagation and branching in the homogeneous PMMA plate are performed for validations, and the results are in good agreement with the previous experimental observations and the previous phase-field numerical results. Then, the numerical study of crack initiation, propagation and branching in FGMs are conducted using the developed bond-based peridynamic model, and the influence of gradient direction on the dynamic fracture behaviors, such as crack patterns and crack tip propagation speed, in FGMs is systematically studied. Finally, numerical results reveal that crack branching in FGMs under dynamic loading conditions is easier to occur as the gradient angle decreases, which is measured by the gradient direction and direction of the initial crack.

• Journal of the Korean Society for Railway
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• v.9 no.2 s.33
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• pp.160-168
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• 2006

The major objective of this study is to investigate the effects and application of external post-tensioning method far steel plate girder bridge. It analyzed the mechanical behaviors of steel plate girder bridge with applying external post-tensioning on the finite element analysis, field test and laboratory test fur the lateral dynamic characteristics. As a result, the reinforcement of steel plate girder bridge the external post-tensioning method are obviously effective for the lateral dynamic response which is non-reinforced. The analytical and experimental study are carried out to investigate the post-tension force decrease lateral acceleration and deflection on steel plate girder bridge for serviceability. And the external post-tensioning method reduce dynamic maximum displacement(about $10{\sim}24%$), the increase of dynamic safety is predicted by adopting external post-tensioning method. From the dynamic test results of the servicing steel plate girder bridge, it is investigated that the change degree of natural frequency is very low with applying the external post-tensioning method The servicing steel plate girder bridge with external post-tensioning has need of the reasonable reinforcement measures which could be reducing the effect of lateral dynamic behavior that degradation phenomenon of structure by an unusual response characteristic and a drop durability.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.10a
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• pp.216-222
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• 1998

Effects of translational and rotational motions of the foundation on the dynamic behaviors of a bridge under seismic excitations are examined by utilizing a simplified 3 degree-of-freedom of system. To consider the nonlinear characteristics of the RC pier, a hysteresis model is adapted, which can simulate the inelastic motion of the pier with the stiffness degradation. From results, the portion of the total displacement due to rotational motion of the foundation becomes larger as applied seismic excitation increases.

• Bulletin of the Korean Chemical Society
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• v.16 no.11
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• pp.1113-1118
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• 1995

The Schlo'gl model with the first order transition for a photochemical reaction is considered to study the dynamic behaviors in the neighborhood of the Gaussian white noise by obtaining the explicit results of the time-dependent variance and time correlation function with the aid of approximate methods based on the stationary properties of the system. Then, we discuss the effect of external noise strength on the stability of the model at steady states in detail.

• Journal of Korean Society of Steel Construction
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• v.10 no.1 s.34
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• pp.73-83
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• 1998

Considering dynamic behaviors according to initial tension forces, geometric nonlinearity and the effect of higher eigen modes to participate in dynamic behaviors increase as initial tension forces decrease, and from phase portrait we can realize that period attractors are produced in many area with complexity. If initial tension forxes increase, difference between linear and nonlinear solutions will decrease and the first eigen mode dominate the dynamic behaviors and observing phase portrait, period attractors appear in certain area regularly. These results may offer meaningful informations to nonlinear dynamic analysis using modal reduction methods such as Lanczos modal analysis. And actually nonlinear dynamic analysis needs very large computational efforts. So, if we determine the number of eigen modes to take part in modal analysis corresponding to initial tension forces we will get more accurate data close to exact nonlinear dynamic solutions.

• Journal of Electrical Engineering and Technology
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• v.1 no.2
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• pp.161-169
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• 2006

Load representation has a significant impact on power system analysis and control results. In this paper, composite load models are developed based on on-line measurement data from a practical power system. Three types of static-dynamic load models are derived: general ZIP-induction motor model, Exponential-induction motor model and Z-induction motor model. For the dynamic induction motor model, two different third-order induction motor models are studied. The performances in modeling real and reactive power behaviors by composite load models are compared with other dynamic load models in terms of relative mismatch error. In addition, numerical consideration of ill-conditioned parameters is addressed based on trajectory sensitivity. Numerical studies indicate that the developed composite load models can accurately capture the dynamic behaviors of loads during disturbance.