• The Journal of the Korean dental association
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• v.57 no.5
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• pp.288-295
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• 2019

Sleep-disordered breathing (SDB) is defined as a disturbed breathing during sleep caused by repetitive upper airway collapse. Complete collapse causes a cessation of breathing, known as obstructive sleep apnea (OSA) and snoring can arise from partial collapse. Undiagnosed and untreated OSA means recurrent intermittent hypoxemia and leads to a variety of cardiovascular disorders, disturbed neurocognition, and excessive daytime sleepiness. Various behavioral modalities have been suggested for treating snoring and sleep apnea including changing the sleep position, avoiding alcohol, and weight loss. Until now continuous positive airway pressure (CPAP) therapy is one of effective treatment for patients with OSA, but its discomfort causes less tolerance and compliance. Therefore, clinical effectiveness and convenience for oral appliance have emerged and the role of dentists has become more important in the management of OSA.

• Journal of Ocean Engineering and Technology
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• v.11 no.2
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• pp.11-17
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• 1997

Simple and efficient way of nonlinear analysis considering elasto-plastic large deformation is introduced to calculate the strength of ring-stiffened cylinears subject to combined load of axial compression and lateral pressure. Parametric study gives various collapse modes according to the combination ratio of axial compression and lateral pressure, interaction between axial compression and lateral pressure and imperfection sensitivity of ultimate strength.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.10
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• pp.1131-1137
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• 2012

Subsea pipelines have been operated with buried depths of 1.2-4m underneath the seabed to prevent buoyancy and external impacts. Therefore, they have to show resistance to both the soil load and the hydrostatic pressure. In this study, the structural integrity of a subsea pipeline subjected to soil load and hydrostatic pressure was evaluated by using FE analyses. A parametric study showed that the internal pressure increased the plastic collapse depth by increasing the resistance to plastic collapse. The hoop stress increased with an increase in the buried depth for the same water depth; however, the hoop stress decreased with an increase in the water depth for the same buried depth.

• Geomechanics and Engineering
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• v.17 no.1
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• pp.97-107
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• 2019

Based on the results of Han et al. (2016), in the failure zone ahead of the tunnel face it can be obviously identified that a shear failure band occurs in the lower part and a pressure arch happens at the upper part, which was often neglected in analyzing the face stability of shield tunnel. In order to better describe the collapse failure feature of the tunnel face, a new improved failure mechanism is proposed to evaluate the face stability of shield tunnel excavated in layered soils in the framework of limit analysis by using spatial discretization technique and linear interpolation method in this study. The developed failure mechanism is composed of two parts: i) the rotational failure mechanism denoting the shear failure band and ii) a uniformly distributed force denoting the pressure arch effect. Followed by the comparison between the results of critical face pressures provided by the developed model and those by the existing works, which indicates that the new developed failure mechanism provides comparatively reasonable results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.8 s.239
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• pp.1070-1077
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• 2005

The $40\%$ of wall thickness criterion which has been used as a plugging rule is applicable only to a single cracked steam generator tubes. In the previous studies performed by authors, several failure prediction models were introduced to estimate the plastic collapse pressures of steam generator tubes containing collinear or parallel two adjacent axial through-wall cracks. The objective of this study is to examine the failure prediction models and propose optimum ones for non-aligned two axial through-wall cracks in steam generator tubes. In order to determine the optimum ones, a series of plastic collapse tests and finite element analyses were carried out for steam generator tubes with two machined non-aligned axial through-wall cracks. Thereby, either the plastic zone contact model or COD based model was selected as the optimum one according to axial distance between two clacks. Finally, the optimum failure prediction model was used to demonstrate the conservatism of flaw characterization rules for various multiple flaws according to ASME code.

• Computers and Concrete
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• v.33 no.5
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• pp.545-557
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• 2024

A real-case incident occurred where a 9-meter-high segment of a pre-fabricated concrete separation wall unexpectedly collapsed. This collapse was triggered by improperly depositing excavated soil against the wall's back, a condition for which the wall segments were not designed to withstand lateral earth pressure, leading to a flexural failure. The event's analysis, integrating technical data and observational insights, revealed that internal forces at the time of failure significantly exceeded the wall's capacity per standard design. The Lattice Discrete Particle Model (LDPM) further replicates the collapse mechanism. Our approach involved defining various parameter sets to replicate the concrete's mechanical response, consistent with the tested compressive strength. Subsequent stages included calibrating these parameters across different scales and conducting full-scale simulations. These simulations carried out with various parameter sets, were thoroughly analyzed to identify the most representative failure mechanism. We developed an equation from this analysis that quickly correlates the parameters to the wall's load-carry capacity, aligned with the simulation. Additionally, our study examined the wall's post-peak behavior, extending up to the point of collapse. This aspect of the analysis was essential for preventing failure, providing crucial time for intervention, and potentially averting a disaster. However, the reinforced concrete residual state is far from being fully understood. While it's impractical for engineers to depend on the residual state of structural elements during the design phase, comprehending this state is essential for effective response and mitigation strategies after initial failure occurs.

• Journal of Navigation and Port Research
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• v.33 no.1
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• pp.27-33
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• 2009

Estimation of the buckling and ultimate strength of a continuous stiffened plate subjected to combined transverse compression and lateral pressure is of high importance to ensure the safety of ship structures, particularly for the bottom plating under a deep draft condition For example, bottom plating of bulk carriers is subjected to transverse thrust caused by the bending of double bottom structure and the direct action of pressure on the side shells. Most of experimental tests, theoretical approach and numerical researches have been performed on the buckling and ultimate strength behaviour of plates or stiffened plates under combined compression and lateral pressure. With regard to stiffened panels, however, most of studies have been concerned with the load conditions of combined longitudinal thrust and lateral pressure, while fewer studies have been performed for the combined transverse thrust and lateral pressure. In addition, the previous researches are mainly concerned with an isolated rectangular plate simply supported along the all edges, whereas actual ship plating is continuous across the transverse frames and heavy girders. In the present paper, a series of elastoplastic large deflection FEA on a continuous stiffened plate is performed and then clarify the characteristic of collapse mode and explain the effect of transverse compression.

• Korean Chemical Engineering Research
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• v.56 no.6
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• pp.864-870
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• 2018

The effect of lower bed height on the collapse velocity was investigated for a two-stage bubbling fluidizedbed (0.1 m in diameter, 1.2 m high) connected with a standpipe (0.025 m in diameter) for solid transport. Air was used as fluidizing gas and mixture of coarse (< $1000{\mu}m$ in diameter and $3625kg/m^3$ in apparent density) and fine (< $147{\mu}m$ in diameter and $4079kg/m^3$ in apparent density) particles as solid particles. Mixing ratio of fine particles, height of the lower bed and the distributor of the upper bed were considered as experimental variables. The collapse velocity increased with static height of the lower bed. However, the effect decreased as the mixing ratio of fine particles increased. The effect seemed to be attributed to the increase in height of the dense layer of coarse particles that prevented the gas from flowing into the standpipe, not in pressure drop for the standpipe, as the bed height increased. The collapse velocity decreased a little as the pressure drop of the distributor of the upper bed increased. An improved correlation was proposed for predicting the collapse velocity.

• Journal of the Korean Geophysical Society
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• v.6 no.2
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• pp.107-119
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• 2003

The behavior of pore pressure and effective stress in a highly saturated sand bed under variations in the water pressure in its surface were investigated to determine the mechanism of the collapse of hydraulic structures during flooding or when attacked by storm waves. The vertical, one-dimensional model was used as a basic model to clarify the effect of water pressure variation on only to the vertical direction. The theoretical results show that a sand bed under variations of water pressure is weakened by an increase in excess pore pressure and that under certain conditions the sand bed will liquefy. Although many factors related to water pressure variation and property of the material determine this phenomenon, the mist important factor seems to be the small amount of air present in the sand bed. The theoretical results reported are verified by experiments.

• Journal of the Korean Geotechnical Society
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• v.31 no.12
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• pp.71-76
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• 2015

Recently, people are increasingly interested in horizontal directional drilling (HDD) to construct oil and gas pipeline and utility pipeline in the urban area as one of trenchless methods. One of major issues during the HDD is the collapse of borehole, which may be the potential causes of ground collapse. This study investigated the effect of mud pressure on the borehole stability, using finite element analysis. Since the borehole is being drilled with a certain angle, three dimensional analysis should be performed. The borehole stability was examined by applying two different types of mud pressures, i.e., uniform and non-uniform, to the exterior surface of borehole. The results show that the high mud pressure at the beginning of drilling, i.e., at shallow depth, causes the borehole collapse, whereas the borehole was stable even at high mud pressure as the drilling depth increases. It can be said that the determination of maximum mud pressure is strongly related to the drilling depth.