• Current Optics and Photonics
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• v.6 no.1
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• pp.69-78
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• 2022

A high-resolution camera is a precise optical system. Its vibrations during transportation and launch, together with changes in temperature and gravity field in orbit, lead to different degrees of defocus of the camera. Thermal refocusing is one of the solutions to the problems related to in-orbit defocusing, but there are few relevant thermal refocusing mathematical models for systematic analysis and research. Therefore, to further research thermal refocusing systems by using the development of a high-resolution micro-nano satellite (CX6-02) super-resolution camera as an example, we established a thermal refocusing mathematical model based on the thermal elasticity theory on the basis of the secondary mirror position. The detailed design of the thermal refocusing system was carried out under the guidance of the mathematical model. Through optical-mechanical-thermal integration analysis and Zernike polynomial calculation, we found that the data error obtained was about 1%, and deformation in the secondary mirror surface conformed to the optical index, indicating the accuracy and reliability of the thermal refocusing mathematical model. In the final ground test, the thermal vacuum experimental verification data and in-orbit imaging results showed that the thermal refocusing system is consistent with the experimental data, and the performance is stable, which provides theoretical and technical support for the future development of a thermal refocusing space camera.

• Coupled systems mechanics
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• v.12 no.4
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• pp.365-389
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• 2023

Dynamic analysis of a typical concrete gravity dam-reservoir system is formulated by FE-(FE-TE) approach (i.e., Finite Element-(Finite Element-Truncation Element)). In this technique, dam and reservoir are discretized by plane solid and fluid finite elements. Moreover, the H-W (i.e., Hagstrom-Warburton) high-order condition imposed at the reservoir truncation boundary. This task is formulated by employing a truncation element at that boundary. It is emphasized that reservoir far-field is excluded from the discretized model. The formulation is initially reviewed which was originally proposed in a previous study. Thereafter, the response of Pine Flat dam-reservoir system is studied due to horizontal and vertical ground motions for two types of reservoir bottom conditions of full reflective and absorptive. It should be emphasized that study is carried out under high order of H-W condition applied on the truncation boundary. The initial part of study is focused on the time harmonic analysis. In this part, it is possible to compare the transfer functions against corresponding responses obtained by FE-(FE-HE) approach (referred to as exact method). Subsequently, the transient analysis is carried out. In that part, it is only possible to compare the results for low and high normalized reservoir length cases. Therefore, the sensitivity of results is controlled due to normalized reservoir length values.

• Journal of the Korean Geotechnical Society
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• v.24 no.11
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• pp.5-16
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• 2008

Field monitoring data of nine sites were investigated to suggest an evaluation method on lateral movement of the quaywall on soft grounds. It was found that in order to evaluate the lateral movement of quaywalls with foundation piles such as the landing pier, the safety factor of slope should be applied with consideration of the stabilizing effect of the piles. If the required safety factor of slope is greater than 1.6 in slope stability analysis with consideration of the stabilizing effect of the piles, the quaywalls are considered to be safe against lateral movement. On the other hand, for the gravity-type quaywalls such as the caisson type quaywall, the required safety factor of slope should be greater than 1.3.

• Journal of the Korean earth science society
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• v.37 no.7
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• pp.465-475
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• 2016

The diurnal and semidiurnal tides in the global atmosphere are examined using 3-hourly geopotential height field of the state-of-the-art reanalysis data. Unlike the previous studies, the spatial structure and seasonality of those tides are analyzed from the surface of the earth to the stratosphere. It is found that, at most levels, diurnal tide is strong in the midlatitudes while semidiurnal tide is predominant in the tropics. The former shows strong seasonal cycle with a larger amplitude in summer than in winter in both hemispheres. This is different from the semidiurnal tide which has essentially no seasonal cycle. In term of the vertical structure, while semidiurnal tide has a barotropic structure, diurnal tide exhibits a distinct vertical structure with increased amplitude and height. Especially tropical diurnal tide exhibits a nearly opposite phase from the surface to the free troposphere, and to the upper stratosphere. Its amplitude also varies nonlinearly with height, possibly influenced by water vapor, ozone, gravity waves and solar radiation.

• Journal of the Korean Geotechnical Society
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• v.33 no.1
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• pp.17-30
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• 2017

There are many limitations for ensuring structural stability of retaining wall. Especially, L-shaped retaining wall and gravity retaining wall need large space, and massive concrete, respectively. Assembled Earth Retailing (AER) wall was developed to overcome the shortcomings. In this paper, stability of AER wall is verified by field model tests and the 3D-numerical analysis. The results show that horizontal displacement of AER wall was reduced by maximum 67.84% for conventional retaining walls, and earth pressure acting on the retaining wall was reduced by maximum 73.19%.

• Journal of the Korea Furniture Society
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• v.21 no.6
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• pp.479-485
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• 2010

The anatomical characteristics, green moisture content, inorganic element concentration, and black heartwood percentage were compared between the Japanese cedar (Cryptomeria japonica) planted in a general mountain forest and in a windbreak forest for a mandarin orange field in Jeju island. The results obtained were as follows: 1. Black heartwood percentage was found to be much higher in the trees of windbreak forest than in those of general mountain forest. 2. Green moisture content of wood appeared to increase with the color change of heartwood from reddish brown to black. 3. Inorganic elements of $K_2O$ and CaO in the ray cells of black heartwood were thought to be one of the important factors for black heartwood formation. 4. Wood specific gravity and strength properties were comparatively lower in the trees of Jeju island than in those of southern part of the Korean peninsula. These properties, however, were found to be not significantly different between the trees of windbreak forest and general mountain forest in Jeju island.

• Economic and Environmental Geology
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• v.45 no.1
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• pp.59-68
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• 2012

With the decline in discoveries of new oil fields and increasing demand from developing countries it is believed that enhanced oil recovery (EOR) technologies will play a key role to meet the energy demand in years to come. Based on the recently-published data, this paper discusses current status of global EOR market and technical development trends. The EOR market includes oil produced through various EOR recovery methods, such as thermal recovery, gas injection, chemical injection. Also, EOR methods are addressed screening criteria by reservoir and fluid characteristics including lithology, depth, thickness, and oil properties such as composition and gravity. Finally, the examples of field applied by various EOR methods are discussed with respect to reservoir characteristics and performance.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.551-554
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• 2001

A necessity of remote control robots or various searching robots etc. that accomplish works given instead of human under long distance and extreme environment such as volcano, universe, deep-sea exploration and nuclear power plant etc. is increasing, and so the development and the research regarding these mobile robots are actively progressing. The wheel mobile robot or the track mobile robot have a sufficient energy efficiency under this en, but also have a lot of limits to accomplish works given which are caused from the restriction of mobile ability. Therefore, recently many researches for the walking robot with superior mobility and energy efficiency on the terrain, which is uneven or where obstacles, inclination and stairways exist, have been doing. The research for these walking robots is separated into fields of mechanism and control system, gait research, circumference environment and system condition recognition etc. greatly. It is a research field that the gait research among these is the centralist in actual implementation of walking robot unlike different mobile robots. A research field for gait of walking robot is classified into two parts according to the nature of the stability and the walking speed, static gait or dynamic gait. While the speed of a static gait is lower than that of a dynamic gait, a static gait which moves the robot to maintain a static stability guarantees a superior stability relatively. A dynamic gait, which make the robot walk controlling the instability caused by the gravity during the two leg supporting period and so maintaining the stability of the robot body spontaneously, is suitable for high speed walking but has a relatively low stability and a difficulty in implementation compared with a static gait. The quadruped walking robot has a strong point that can embody these gaits together. In this research, we will develope an autonomous quadruped robot with an asaptibility to the environment by selectry appropriate gait, element such as duty factor, stride, trajectory, etc.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.47 no.3
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• pp.226-235
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• 2002

This experiment was to evaluate lodging characteristics of 35 recommended rice varieties of Kyonggi-do at normal (110 kg N/ha) and hen (220 kg N/ha) nitrogen application rates during 1999 to 2000. At heavy N fertilization rate, varieties that were highly resistant to lodging were Obongbyeo, Daejinbyeo, Naepoongbyeo, Nonganbyeo and Ilpumbyeo. Fourteen varieties including Daeanbyeo were moderately resistant and 11 varieties including Jinbubyeo were susceptible to lodging. The lodging-related characters which showed the highest effect on lodging at lodging degree of 9 were culm length and height of center gravity, culm length at lodging degree of 5, and culm length and the third internode length at lodging degree of 3 or below. The difference in rice yield between normal and heavy nitrogen fertilization rate was within 5% in early-maturing varieties but there was great yield difference in mid- and late-maturing varieties depending on the degree of lodging. Consequently, stable rice yield could be obtained by selecting lodging-resistant varieties and lowering fertilization rate, specially in the paddy field where lodging occurrence is common.

• Geotechnical Engineering
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• v.4 no.2
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• pp.33-44
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• 1988

The Taechong Dam completed in 1980 is a composite dam at which a junction was formed partly by butting the core against the end face of the concrete gravity section and partly by the core overlapping the upstream face of the concrete. In order to evaluate the performance of the junction, the interfaces between the concrete dam and core of the embankment dam were well instrumented with total pressure cells and piezometers. A nonlinear incremental finite element analysis simulating its construction behaviour was carried out under plane strain conditions. Material parameters for the core are determined from triaxial tests on the specimens, sampled in the quarry site and compacted to the field dry density at the field moisture content. Material parameters for the filter, transition materials and the rockfill are estimated from literature. When compared with the earth pressures measured at the interfaces, the analytical results show good agreement in the core, however, there are some discrepancy in the shell. A nonlinear model for pore pressure response is used successfully to predict the pore pressures at the interface in the core.