• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.21 no.3
• /
• pp.481-487
• /
• 2020

This study examined the behavior change of river levees during an earthquake by numerical analysis. Unlike conventional research using artificial earthquake waves, earthquake analysis was performed using real earthquake waves. The behavior of a river levee before and after an earthquake was compared and analyzed quantitatively. Studies show that the river levee has a safety factor of approximately 28.5% due to an earthquake. On the other hand, the minimum standard safety factor is satisfied. Vertical effective stress has decreased by 81.8% due to excess pore-water pressure generated by the earthquake. In addition, liquefaction occurs in most of the foundation soil. An examination of the stress-displacement behavior due to the earthquake revealed a large amount of settlement in the backfill layer. Most of the foundation soil yielded. Therefore, the target river levee is quite vulnerable to earthquakes. Through the results of this study, the necessity of refreshing the seismic design standards for river levees is required. This study can be used as basic data for estimating the approximate damage level and vulnerable areas.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.29 no.6
• /
• pp.672-680
• /
• 2023

Weight is a critical factor in the ship design process given that it has a substantial impact on the hydrodynamic performance of ships. Typically, ships are optimally designed for specific conditions with a fixed draft and displacement. However, in reality, weight and draft can vary within a certain range owing to operational activities, such as fuel consumption, ballast adjustments, and loading conditions . Therefore, we investigated how resistance changes under three different loading conditions, namely overload, design-load, and lightship, for small craft, using both model experiments and numerical simulations. Additionally, we examined the sensitivity of weight changes to resistance to enhance the performance of ships, ultimately reducing power requirements in support of the International Maritime Organization's (IMO) goal of reducing CO2 emissions by 50% by 2050. We found that weight changes have a more significant impact at low Froude Numbers. Operating under overload conditions, which correspond to a 5% increase in draft and an 11.1% increase in displacement, can lead to a relatively substantial increase in total resistance, up to 15.97% and 14.31% in towing tests and CFD simulations, respectively.

• Journal of the Korean Society for Railway
• /
• v.13 no.4
• /
• pp.363-370
• /
• 2010

This paper describes the evaluation of structural integrity and dynamic characteristic of inertial load test equipments for performance test of railway vehicle propulsion control system. The propulsion control system of railway vehicle has to be confirmed of safety and reliability prior to its application. Therefore, inertial load test equipments were designed through theoretical equation for performance test of propulsion control system. The structural analysis of inertial load test equipments was conducted using Ansys v11.0 and the dynamic characteristic was evaluated using Adams. The results showed that the structural integrity of inertial load test equipment was satisfied with a safety factor of 10.2 on the bearing part under combined load. Also, the structural stability of flywheel according to dynamic simulation was secured by the maximum oscillation displacement within 0.83mm.

• Journal of the Korean Geotechnical Society
• /
• v.39 no.7
• /
• pp.57-67
• /
• 2023

Slope failures during rainfall have been observed in mountainous areas of South Korea as a result of the presence of solar power facilities. The seepage behavior and pore pressure distribution differ from typical slopes due to the presence of impermeable solar panels, and the load imposed by the solar power structures also affects the slope behavior. This study aims to develop a method for evaluating the stability of slopes with solar power facilities and to analyze vulnerable points by considering the maximum slope displacement. To assess the slope stability and predict behavior while considering rainfall seepage, a combined seepage analysis and finite difference method numerical analysis were employed. For the selected site, various variables were assumed, including parameters related to the Soil Water Characteristic Curve, strength parameters that satisfy the Mohr-Coulomb failure criterion, soil properties, and topographic factors such as slope angle and bedrock depth. The factors with the most significant influence on the factor of safety (FOS) were identified. The presence of solar power facilities was found to affect the seepage distribution and FOS, resulting in a decreasing trend due to rainfall seepage. The maximum displacement points were concentrated near the upper (crest) and lower (toe) sections of the slope.

• Journal of the Korean Geotechnical Society
• /
• v.39 no.9
• /
• pp.13-24
• /
• 2023

To investigate the stability of temporary retaining walls during excavation, it is essential to develop reverse analysis technologies capable of precisely evaluating the properties of the ground and a learning model that can assess stability by analyzing real-time data. In this study, we targeted excavation sites where the C.I.P method was applied. We developed a Deep Neural Network (DNN) model capable of evaluating the stability of the retaining wall, and estimated the physical properties of the ground being excavated using a Differential Evolution Algorithm. We performed reverse analysis on a model composed of a two-layer ground for the applicability analysis of the Differential Evolution Algorithm. The results from this analysis allowed us to predict the properties of the ground, such as the elastic modulus, cohesion, and internal friction angle, with an accuracy of 97%. We analyzed 30,000 cases to construct the training data for the DNN model. We proposed stability evaluation grades for each assessment factor, including anchor axial force, uneven subsidence, wall displacement, and structural stability of the wall, and trained the data based on these factors. The application analysis of the trained DNN model showed that the model could predict the stability of the retaining wall with an average accuracy of over 94%, considering factors such as the axial force of the anchor, uneven subsidence, displacement of the wall, and structural stability of the wall.

• Journal of the Korean Geotechnical Society
• /
• v.15 no.3
• /
• pp.41-70
• /
• 1999

The benefits of utilizing internal reinforced members, such as soil nails and ground anchors, in maintaining stable excavations and slopes have been known among geotechnical engineers to be very effective. Occasionally, however, both soil nails and ground anchors are simultaneously used in one excavation site. In the present study, a method of limit equilibrium stability analysis of the excavation zone reinforced with the vertically or horizontally mixed nail-anchor system is proposed to evaluate the global safety factor with respect to a sliding failure. The postulated failure wedges are determined based on the results of the $FLAC^{2D}\; 및\; FLAC^{3D}$ program analyses. This study also deals with a determination of the required thickness of the shotcrete facing. An excessive facing thickness may be required due to both the stress concentration and the relative displacement at the interface zone between the soil nailing system and the ground anchor system. A simple finite element method of analysis is presented to estimate the corresponding relative displacement at the interface zone between two different support systems. As an efficient resolution to reduce the facing thickness, the modified bearing plate system is also proposed. Finally with various analysis related to the effects of design parameters, the predicted displacements are compared with the results of the $FLAC^{2D}$ program analyses.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.20 no.6
• /
• pp.106-112
• /
• 2016

In this study, circular concrete column specimens confined by carbon sheet tube with different winding angles and different number of carbon sheet plies(3T, 5T and 7T) were tested to propose design equations and a strength reduction factor. Specimens were designed by 300 mm diameter and 600 mm height with $90^{\circ}{\pm}0^{\circ}$, $90^{\circ}{\pm}30^{\circ}$, $90^{\circ}{\pm}45^{\circ}$, $90^{\circ}{\pm}60^{\circ}$, $90^{\circ}{\pm}75^{\circ}$ and $90^{\circ}{\pm}90^{\circ}$ carbon fiber angles. A 10,000 kN UTM was used for compressive strength test of specimens by displacement control method with 0.01 mm/sec velocity. Estimation equations of compressive strength and ultimate strain of circular concrete column specimens confined by carbon sheet tube using a regression analysis and a strength reduction factor to apply ultimate strength design method of concrete were proposed. The strength reduction factor(${\phi}$) of circular concrete columns confined by carbon sheet tube was estimated as 0.64 by the Monte Carlo Analysis Method. Manufacture and construction process have to be perfectly managed by construction managers because the structural capacities of carbon tubes were depends on construction abilities of manufacturing operators.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.27 no.3
• /
• pp.12-20
• /
• 2023

This study presents basic data on how to secure stability by analyzing the change in tensile force of steel rod and the inclination characteristics of PSC BOX in the "Temporary fixation system using internal prestressing tendon", which is mainly applied to construction of superstructures by FCM. To date, it has been difficult to confirm the changes in tension force of the steel rod and the inclination of the PSC BOX because the steel rod was installed vertically inside the pier and the PSC BOX. Therefore, measurement of the change in length of the steel rod and the displacement of PSC BOX were performed using a micro-measured FBG sensor. Comparisons of the calculated tensile force and the residual tensile force of the steel rod revealed that the safety factor decreased in all bridges. The cause was mainly identified to be the loss of tensile force in fixation~1segment, and countermeasures are suggested. The analysis of the inclination characteristics showed that the inclination increased with the segment progresses even in bridges with sufficient safety factor, and the difference before and after the segment was confirmed. In addition, the increase in inclination was related to the loss of tension force in the steel rod, and the stress on the opposite sides of the inclination was further reduced. It is believed that upward tensile force is generated in the steel rod on the opposite side of the inclined side due to the unbalanced moment, causing the difference in stress of the steel rod between the two sides.

• Proceedings of the Korean Geotechical Society Conference
• /
• 1991.10a
• /
• pp.87-102
• /
• 1991

It has been reported that the failure of Carsington Dam in Eng1and occured due to the existence of a thin yellow clay layer which was not identified during the design work, and due to pre-existing shears of the clay layer. The slope stability analyses during the design work, which utilized traditional circular arc type failure method and neglected the existence of the clay layer, showed a safety factor of 1.4. However, the post-failure analyses which utilized translational failure mode considering the clay layer and the pre-existing shear deformation revealed the reduction of safety factor to unity. The post-failure analysis assumed 10。 inclination of the horizontal forces onto each slice based on the results of finite element analyses. In this paper, Bishop's simplified method, Janbu method, and Morgenstern-Price method were used for the comparison of both circular and translational failure analysis methods. The effects of the pre-existing shears and subsquent movement were also considered by varying the soil strength parameters and the pore pressure ratio according to the given soi1 parameters. The results showed factor of safefy 1.387 by Bishop's simplified method(STABL) which assumed circular arc failure surface and disregarding yellow clay layer and pre-failure material properties. Also the results showed factor of safety 1.093 by Janbu method(STABL) and 0.969 by Morgenstern-Price method(MALE) which assumed wedge failure surface and considerd yellow clay layer using post failure material properties. In addition, dam behavior was simulated by Cam-Clay model FEM program. The effects of pore pressure changes with loading and consolidation, and strength reduction near or at failure were also considered based on properly assumed stress-strain relationship and pore pressure characteristics. The results showed that the failure was initiated at the yellow clay layer and propagated through other zones by showing that stress and displacement were concentrated at the yel1ow clay layer.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.22 no.2
• /
• pp.593-601
• /
• 2021

The axial fan is an element of a blower used for ventilation in various industrial fields. Many studies on aerodynamic performance have been conducted to assess axial fans using fluid dynamics. The subject was a large axial fan size, 1800 mm in diameter with 100 horsepower. The blower's axial fan consisted of blades, hubs, hub caps, and bosses are important components. The blade design has a great influence on the aerodynamic performance. 3D point data is extracted using an aerodynamic performance prediction program, and a 3D modeling shape is generated. The blades and hubs, which are important components, can be easily modified if processed by cutting owing to the environment in which blades and hubs are manufactured through die casting or gravity casting. In this study, the structural safety of components and the analysis results of weak areas at the rated operating speed of the axial fan were verified using the maximum stress and safety factor. The tip clearance reflected in the design was the rotation of the blade. To check whether there is interference with other components, the displacement result was derived to verify the structural safety of the axial fan.