• Tunnel and Underground Space
• /
• v.24 no.5
• /
• pp.344-353
• /
• 2014

In this study, the behavior of rock pillar in the diverging area of road tunnel was assessed by using a three dimensional numerical analysis. Based on parameters affecting the behavior of rock pillar, different safety factors according to pillar width, depth and rock conditions were evaluated. It turned out that as the pillar width increases, the change curve of safety factors in accordance with depth and rock conditions shows more of the nonlinear behavior. By the assessment of the minimum safety factor, a safety factor chart on the behavior of rock pillar in the diverging area of road tunnel was suggested.

• Journal of Environmental Science International
• /
• v.28 no.12
• /
• pp.1133-1145
• /
• 2019

Successful launch requires state-of-the-art launch vehicle technology and constant test operations, However, the meteorological threat to the launch vehicle flight trajectory is also an important factor for launch success. Atmospheric stability above the Naro Space Center at the this time is very important, especially because the initial flight operation can determine the success of the launch. Moreover, during the flight of launch vehicle with rapid pressure and thrust into the atmosphere, convection activity in the atmosphere may create environmental conditions that cause severe weather threats such as thunderstorms. Hence, studies of atmospheric instability characteristics over the Naro Space Center are a necessary part of successful launch missions. Therefore, the main aims of this study were to (1) verify the atmospheric stability index and convection activity characteristics over the Naro Space Center using radiosonde data observed from 2007 to 2018 by the Naro Space Center, (2) analyze changes in the atmospheric stability index according to monthly and seasonal changes, and (3) assess how the calculated atmospheric stability index is related to actual thunderstorm occurrence using statistical analysis. Additionally, we aimed to investigate the atmospheric characteristics above the Naro Space Center through the distribution chart of the atmospheric stability index during summer, when convection activity is highest. Finally, we assessed the relationship between lightning occurrence and unstable atmospheric conditions, through predictability analysis performed using the lightning observation data of the Korea Meteorological Administration.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.12
• /
• pp.2647-2655
• /
• 2002

This research presents an analytical model to investigate the stability due to the ball bearing waviness i n a rotating system supported by two ball bearings. The stiffness of a ball bearing changes periodically due to the waviness in the rolling elements as the rotor rotates, and it can be calculated by differentiating the nonlinear contact forces. The linearized equations of motion can be represented as a parametrically excited system in the form of Mathieu's equation, because the stiffness coefficients have time -varying components due to the waviness. Their solution can be assumed as a Fourier series expansion so that the equations of motion can be rewritten as the simultaneous algebraic equations with respect to the Fourier coefficients. Then, stability can be determined by solving the Hill's infinite determinant of these algebraic equations. The validity of this research is proved by comparing the stability chart with the time responses of the vibration model suggested by prior researches. This research shows that the waviness in the rolling elements of a ball bearing generates the time-varying component of the stiffness coefficient, whose frequency is called the frequency of the parametric excitation. It also shows that the instability takes place from the positions in which the ratio of the natural frequency to the frequency of the parametric excitation corresponds to i/2 (i=1,2,3..).

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.12 no.2
• /
• pp.239-253
• /
• 1992

The masonry walls, having the characters of cheap construction materials and relatively easy construction, have been widely used in supporting slopes. However, the necessity of reinforcing methods to improve the stability of masonry walls has been continuously required due to the collapses taken place quite often. In the present study, a new method to improve the stability of masonry walls was developed based on the soil nailing system proven effective in strengthening the surrounding soils. The developed method could be used in reinforcing the old masonry walls structually unsafe as well as in constructing new masonry walls. The effects of pore water pressures due to heavy rainfalls were included in the developed method and also the chart practically applicable to design was presented, together with a design example.

• Journal of the Korean Geotechnical Society
• /
• v.24 no.6
• /
• pp.5-16
• /
• 2008

This study investigated the existing theoretical backgrounds in order to examine the stability control method of lateral flow caused by the Plasticity of soils when unsymmetrical surcharge works on polluted soils and then compared and analyzed the results measured through model tests. Ultimate bearing power of ML and $ML_{p1}$ and $ML_{p2}$ obtained at surcharge(q)-settlement$(S_v)$ curve showed similar trends to ultimate bearing power obtained from control chart of deflection $(S_v-Y_m)$ by Tominaga.Hashimoto, that of $S_v-(Y_m/S_v)$ by Matsuo.Kawamura and that of $(q/Y_m)-q$ by Shibata.Sekiguchi and so it is considered that it has no problem in actual applicability. ${S_v-(Y_m/S_v)}$ of control chart of $ML_{p1}$ by Matsuo.Kawamura showed smaller value than ultimate bearing capacity value from surcharge-settlement curve $(q-S_v)$. Expression of ML of fracture baseline at stability control charge by Matsuo Kawamura is ${S_v=3.21exp}\{-0.48(Y_m/S_v)\}$ and expression of $ML_{p1}$ is ${S_v=3.26exp}\{-0.96(Y_m/S_v)\}$ and expression of $ML_{p2}$ is ${S_v=6.33exp}\{-0.45(Y_m/S_v)\}$.

• The Journal of the Petrological Society of Korea
• /
• v.27 no.4
• /
• pp.207-222
• /
• 2018

Celestial Chart Stones (original and reproduction) in the National Palace Museum are representative scientific cultural heritage of Korea. Material analysis and nondestructive deterioration assessment were conducted for long-term preservation of these stones. Material analysis revealed that the original was composed of slate and the reproduction was made of dolostone. The original consists of quartz, mica, dolomite minerals, while the reproduction was made up of dolomite, calcite and forsterite. Major deterioration factors of the original stone were cracks and breakouts. In case of the reproduction, scratches and artificial materials were mainly observed. The green and black surface contaminants present at the sides and back of the two celestial chart stones were interpreted as resin-based paint materials. The physical property evaluation using ultrasonic velocity showed a low velocity in the upper left side of the original, while the front right side of the reproduction showed a weak property. Meanwhile, the To-Tc method using ultrasonic velocity was applied to major cracks that impede stability of the original. As a result, it has been calculated that the beginning and the center of the crack are the deepest.

• Tunnel and Underground Space
• /
• v.17 no.1 s.66
• /
• pp.9-16
• /
• 2007

The influence of round length on the tunnel stability and construction cost is well acknowledged by many researchers and engineers but the coherent procedure is not available for its determination. In this study, the behaviour modes of the face and unsupported span was investigated for weak rock tunnel by a small scale model test, PFC3D and FDM analyses in consideration of the round length. Total five types of behaviour modes are defined and quantitative estimation of the behaviour modes was established in terms of the safety factor for the face stability and the conditional chart. Although the proposed method has some restrictions, this method can provide useful information for the optimization of the round length and excavation, especially in design stage.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2007.04a
• /
• pp.369-374
• /
• 2007

For a stability design of steel frames, AISC-LRFD specification recommend to use Alignment Chart and story-based methods in order to determine an effective budding length. Recently, elastic buckling analysis, which is the method that calculate the effective length of members using eigenvalue of the overall structure, has been widely used in practical design of steel frames because this method can be performed effectively and automatically by computers. However, it can in some cases lead to unexpectedly large effective length in column having small axial forces. Therefore, this paper propose a method using elastic buckling analysis, which estimate a proper effective buckling length for all members having a small axial force. For verification of proposed method, it is compared with system based approach and stiffness distribution factor method. As a result, proposed method can rationally solve a problem in some case of column having small axial force. Also, adoption range for proposed method is established.

• Journal of Ocean Engineering and Technology
• /
• v.7 no.1
• /
• pp.73-80
• /
• 1993

본 연구에서는 장주형 해양구조물의 횡방향 진동에 대한 파라메트릭 가진 효과를 고찰하였다. 먼저, 장주형 해양구조물의 횡방향 운동에 대한 4계 편미방지배방정식을 비선형 Mathieu 방정식으로 유도하였다. 비선형 mathieu 방정식의 해를 구하여 장주형 해양구조물의 동적 반응 특성을 해석하였다. 유체 비선형 감쇠력은 불안정 조건하에 있는 파라메트릭 진동의 반응크기를 제한 하는데 중요한 역활을 한다. 파라메트릭 진동의 경우 가장 큰 반응크기는 Mathieu 안정차트의 첫번째 불안정 구간에서 일어난다. 반면에, 파라메트릭 진동과 강제진동의 결합 진동인 경우, 가장 큰 반응 크기는 두번째 불안정 구간에서 발생된다. 파라메트릭 가진으로 인한 장주형 해양구조물의 횡방향 운동은 동적조건에 따라 subharmonic, superharmonic 또는 chaotic 운동이 되기도 한다.

• Journal of Information Technology Applications and Management
• /
• v.29 no.2
• /
• pp.17-25
• /
• 2022

Although the two types of currencies compete, the possibility of a virtual currency price bubble is diagnosed by assuming an economic model with currencies (won, virtual currency) that are intrinsically worthless. The won is supplied by the central bank to achieve the price stability target, while the supply of virtual currency increases by a fixed number. According to the basic price theory equation, as a simple proposition, cryptocurrency prices form a Martin Gale process [Schilling and Uhlig, 2019, p.20]. Based on the existing theoretical proposition, we applied the variance ratio verification method [Linton and Smetanina, 2016] and a simple technical chart method for empirical analysis. For the purpose of this study, the possibility of a bubble was empirically analyzed by analyzing the price volatility formed in the Korean virtual currency market over the past year, and brief policy implications for this were presented.