• Structural Engineering and Mechanics
• /
• v.80 no.5
• /
• pp.523-538
• /
• 2021

The mechanical behaviour and stability of coal mining engineering underground is significantly affected by ground water. In this study, nuclear magnetic resonance imaging (NMRI) technique was employed to determine the water distribution characteristics in coal specimens during saturation process, based on which the functional rule for water distribution was proposed. Then, using discrete element method (DEM), an innovative numerical modelling method was developed to simulate water-weakening effect on coal behaviour considering moisture content and water distribution. Three water distribution numerical models, namely surface-wetting model, core-wetting model and uniform-wetting model, were established to explore the water distribution influences. The feasibility and validity of the surface-wetting model were further demonstrated by comparing the simulation results with laboratory results. The investigation reveals that coal mechanical properties are affected by both water saturation coefficient and water distribution condition. For all water distribution models, micro-cracks always initiate and nucleate in the water-rich area and thus lead to distinct macro fracture characteristics. With the increase of water saturation coefficient, the failure of coal tends to be less violent with less cracks and ejected fragments. In addition, the core-wetting specimen is more sensitive to water than specimens with other water distribution models.

• BMB Reports
• /
• v.44 no.2
• /
• pp.102-106
• /
• 2011

Thermodynamic stability and refolding kinetics of firefly luciferase and three representative mutants with depletion of negative charge on a flexible loop via substitution of Glu by Arg (ER mutant) or Lys (EK mutant) as well as insertion of another Arg in ER mutants (ERR mutant) was investigated. According to thermodynamic studies, structural stability of ERR and ER mutants are enhanced compared to WT protein, whereas, these mutants become prone to aggregation at higher temperatures. Accordingly, it was concluded that enhanced structural stability of mutants depends on more compactness of folded state, whereas aggregation at higher temperatures in mutants is due to weakening of intermolecular repulsive electrostatic interactions and increase of intermolecular hydrophobic interactions. Kinetic results indicate that early events of protein folding are accelerated in mutants.

• Journal of the Korean Society for Precision Engineering
• /
• v.20 no.6
• /
• pp.197-204
• /
• 2003

This paper presents an efficient modeling and dynamic analysis method for open cracked beam structures. An equivalent bending spring model is introduced to represent the structural weakening effect in the presence of cracks. The proposed method adopts the exact dynamic element method (EDEM) to avoid the inconvenience and numerical errors in association with re-meshing the structural model with the crack position changed. The proposed modeling method is validated through a series of simulation and experiments. First, the proposed method is rigorously compared with a commercial finite element code. Then, two kinds of experiments are performed to validate the proposed modeling method. Finally, a diagnostic scheme fur open cracked beam structures is proposed and demonstrated through a numerical example.

• Nuclear Engineering and Technology
• /
• v.49 no.1
• /
• pp.254-266
• /
• 2017

Finite-element analysis based on elastic-perfectly plastic material was conducted to examine the influence of structural deformations on collapse loads of circumferential through-wall critically cracked $90^{\circ}$ pipe bends undergoing in-plane closing bending and internal pressure. The critical crack is defined for a through-wall circumferential crack at the extrados with a subtended angle below which there is no weakening effect on collapse moment of elbows subjected to in-plane closing bending. Elliptical and semioval cross sections were postulated at the bend regions and compared. Twice-elastic-slope method was utilized to obtain the collapse loads. Structural deformations, namely, ovality and thinning, were each varied from 0% to 20% in steps of 5% and the normalized internal pressure was varied from 0.2 to 0.6. Results indicate that elliptic cross sections were suitable for pipe ratios 5 and 10, whereas for pipe ratio 20, semioval cross sections gave satisfactory solutions. The effect of ovality on collapse loads is significant, although it cancelled out at a certain value of applied internal pressure. Thinning had a negligible effect on collapse loads of bends with crack geometries considered.

• Smart Structures and Systems
• /
• v.14 no.2
• /
• pp.159-189
• /
• 2014

One of the most important requirements in the evaluation of existing structural systems and ensuring a safe performance during their service life is damage assessment. Damage can be defined as a weakening of the structure that adversely affects its current or future performance which may cause undesirable displacements, stresses or vibrations to the structure. The mass and stiffness of a structure will change due to the damage, which in turn changes the measured dynamic response of the system. Damage detection can increase safety, reduce maintenance costs and increase serviceability of the structures. Artificial Neural Networks (ANNs) are simplified models of the human brain and evolved as one of the most useful mathematical concepts used in almost all branches of science and engineering. ANNs have been applied increasingly due to its powerful computational and excellent pattern recognition ability for detecting damage in structural engineering. This paper presents and reviews the technical literature for past two decades on structural damage detection using ANNs with modal parameters such as natural frequencies and mode shapes as inputs.

• Explosives and Blasting
• /
• v.31 no.1
• /
• pp.1-10
• /
• 2013

In blasting demolition, a method would be chosen among many depends on shape and system of a structure and its surround. To demolish using explosives a structure, which is asymmetric and with high aspect ratio, pre-weakening, explosive locations, detonating delay, and surround conditions are needed to be considered in front to design blasting demolition plan. In this study, to over turn asymmetric and high aspect ratio structure in safe, a simulation using a software named Extreme Loadings for Structures, ELS, had performed. In results, it is achieved optimized pre-weakening shapes and locations, which prevent kick back motion of the structure when it collapse, by analyzing moment distribution caused by pre-weakening. And of structural collapse and by minimizing asymmetric structure's torsional moment. Also, after the demolition, simulation results are also compared with actual collapse behavior. In results, it is confirmed the accuracy of collapse behaviour simulation results, and in blasting demolition, kick back motion can be controled by adjusting pre-weakening shape and location, and the torsional moment of an asymmetric structure also can be solved by optimizing detonation locations and its time intervals.

• Journal of the Economic Geographical Society of Korea
• /
• v.17 no.2
• /
• pp.321-334
• /
• 2014

This study is planned to discover the behavior of Korean peasants cope with the changes of structure last 30 years. So, I have surveyed the activists of Jindo Peasants Association through questionnaire. The outcome of survey are as follows; First, Peasants movement have been become weakened and the hope of future have disappeared. Although they have resisted the pressure of structural changes zealously, their life conditions have worsened. So, Peasants movement have been become weakened and they have no alternative choice. Second, The economic situations of all activist those who surveyed have worsened and there is no exits. If looking only at the surface of things, the socio-economic situations of Jindo peasants activists show a tendency to polarization. But, to tell the truth, overall immiseration have occurred at Jindo area. Third, confusion of their sense of values and weakening of self-esteem have occurred among the Jindo peasants activists. It is because that farming which is evaluated high in respect to cultural and industrial perspective, have been eliminated and disregarded. Especially, worsening of earnings and expenses make the peasants to be in the worse situations.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.13 no.4
• /
• pp.290-299
• /
• 2003

This paper presents an efficient modeling and dynamic analysis method for open cracked rotor bearing systems. An equivalent bending spring model is introduced to represent the structural weakening effect in the presence of cracks. The proposed modeling method is validated through a series of simulations and experiments. First, the proposed method Is rigorously compared with a commercial finite element code. Then, an experiment is performed to validate the proposed modeling method. Finally, a numerical example is introduced to demonstrate the possible application of the proposed method in the crack diagnosis for rotor systems.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.30 no.11
• /
• pp.693-698
• /
• 2017

In this study, the thermal degradation properties of polyethylene terephthalate film has been examined by the capacitance, Tan ${\delta}$, thermography, FTIR, and SEM results at temperatures of $90{\sim}170^{\circ}C$ and frequencies of 0.3~3,000 kHz. It was found that the capacitance decreased with increasing thermal imaging temperature, probably caused by weakening of chemical bond with increasing temperature. Tan ${\delta}$ decreased upon increasing temperature from $90^{\circ}C$ to $170^{\circ}C$, probably due to the molecular motion of COOH radical or OH radical. The FT-IR measurement reveals that no structural change of the material occurs upon thermal radiation. The SEM measurement shows that the material is stabilized by thermal decomposition with increasing temperature; however, excessive thermal degradation obstructs the stabilization of the material.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.11b
• /
• pp.725-730
• /
• 2002

This paper presents an efficient modeling method for open cracked beam structures. An equivalent bending spring model is introduced to represent the structural weakening effect in the presence of open cracks. The proposed method adopts the exact dynamic element method (EDEM) to avoid the difficulty and numerical errors in association with re-meshing the structure. The proposed method is rigorously compared with a commercial finite element code. Experiments are also performed to validate the proposed modeling method. Finally, a diagnostic scheme for open cracked beam structures is proposed and demonstrated through a numerical example.