• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.5
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• pp.470-474
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• 2014

This study proposes an improved synchronization control scheme for a low-cost 400Hz power supply for a no-break power transfer system. In the case of aircraft applications, the 400Hz power supply called ground power units is accepted and used as the external electrical power system during stopovers on ground. A momentary break in the supply occurs when shifting from one power source to another. To allow shifting without a break in the supply, the two power sources are momentarily connected in parallel. The proposed synchronization control is achieved by connecting an existing synchronization bus to the voltage zero-crossing signal of a generator power with discrete logic ICs and analog circuits. Therefore, unlike expensive controllers, such as DSP and CAN, the proposed control scheme is rather simple and may decrease operational cost. The practical feasibility of the proposed control scheme is proven by experimental results.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.619-626
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• 2002

In this study, a correlation among pressure, time and quantity of injection was organized from the laboratory tests, which were executed many times representing in-situ soil conditions carefully and then it would be applied to the in-situ soil injection simulator which will be developed for optimal injection into the ground. The sort of sample soils were both sand(A specimen) and silty sand(B specimen). Injection tests were gone into operation by compaction state, injection velocity and the depth individually. In the ground improved with permeation Infection, the relation among injection pressure of the same depth, the injected quantities and time were systematic by the depth. By defining the limit range of injection pressure and quantity about the variety of a linear equation obtained from lining each of their trend, the application of laboratory injection monitoring program and the data to evaluate its realization were produced. In the ground improved with root type injection, the relation between injection pressure and the injected quantities was irregular because fracture state occurred quickly.

• Korean Journal of Remote Sensing
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• v.40 no.2
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• pp.141-150
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• 2024

Ground subsidence in urban areas is mainly caused by anthropogenic factors such as excessive groundwater extraction and underground infrastructure development in the subsurface composed of soft materials. Global Navigation Satellite System data with high temporal resolution have been widely used to measure surface displacements accurately. However, these point-based terrestrial measurements with the low spatial resolution are somewhat limited in observing two-dimensional continuous surface displacements over large areas. The synthetic aperture radar interferometry (InSAR) technique can construct relatively high spatial resolution surface displacement information with accuracy ranging from millimeters to centimeters. Although constellation operations of SAR satellites have improved the revisit cycle, the temporal resolution of space-based observations is still low compared to in-situ observations. In this study, we evaluate the extraction of a time-series of surface displacement in Incheon Metropolitan City, South Korea, using the small baseline subset technique implemented using the commercial software, Gamma. For this purpose, 24 COSMO-SkyMed X-band SAR observations were collected from July 12, 2011, to August 27, 2012. The time-series surface displacement results were improved by reducing random phase noise, correcting residual phase due to satellite orbit errors, and mitigating nonlinear atmospheric phase artifacts. The perpendicular baseline of the collected COSMO-SkyMed SAR images was set to approximately 2-300 m. The surface displacement related to the ground subsidence was detected approximately 1 cm annually around a few Incheon Subway Line 2 route stations. The sufficient coherence indicates that the satellite orbit has been precisely managed for the interferometric processing.

• New & Renewable Energy
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• v.20 no.1
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• pp.61-69
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• 2024

This study investigates the barriers to the deployment of solar thermal and ground source heat pump (GSHP) from the perspective of consumers and businesses, as well as evaluates priorities for improving the barriers via expert AHP evaluation. From a consumer's perspective, the overall satisfaction with solar thermal is significantly lower than that with PV and needs to be improved at the installation and use stages. GSHP needs to be improved at the prior-information search stage. From a business perspective, the non-distinction between heat and electricity in mandatory installations in public buildings, the difficulty in assessing the value of heat, and high initial costs impede the deployment. Based on the result of AHP analysis, the priorities for improving the barriers to the wide utilization of solar thermal are evaluated in the order of economic feasibility, policy, acceptability, and technology, where high installation cost is shown to be the greatest barrier. Barriers for GSHP are evaluated in the order of policy, acceptability, economic feasibility, and technology, where policy means improvement is evaluated as the most important factor in promoting the deployment of GSHP.

• Journal of the Korean GEO-environmental Society
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• v.13 no.6
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• pp.83-90
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• 2012

Generally, the effect of the cement deep mixing method on the improvement of clay ground is far greater than the effect of physical improvement. Although it leads to great improvement strength in the initial stage, there are not many constructional precedents in Korea and it is hard to manage quality according to the cement-clay mixing method. In order to figure out the strength characteristics according to the mixing ratio of cement, sand, and clay and the improvement characteristics of weak ground according to the forms of the specimens to be improved, marine clay was used in this study to conduct the uniaxial compression test and soil bin model test. The test piece specimens for the uniaxial compression test were mixed with sand in a fixed ratio with the criterion of the water cement ratio. The cement was mixed with clay in the ratios of 10%, 20%, 30%, and 40% to the clay weight. The moisture content of the soil ground was made in the ratios of 40%, 60%, and 80%. The test piece specimens went through curing by moistening for 7, 14, and 28 days and underwent the uniaxial compression test according to the curing period. For the bearing test, the soil bin models were made and the ground improved in the Mat type was formed. After that, the bearing strength was compared in this study according to the improvement ratio and analyzed the intervening effect between the walls of the improved specimens.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.264-271
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• 2005

Sand pile method, such as sand drain method and sand compaction pile method, has been popularly used as an improvement method for soft clay grounds. The effect of accelerating consolidation of soft clay grounds has been evaluated with Barron's solution. By the way, the consolidation behavior of soft clay ground with sand piles strongly depends on both the nonlinear mechanical interaction between sand piles and surrounding clays and the degradation permeability of clays. In this paper, the method for determining consolidation parameters of soft clay ground with sand drains by using Barron's solution was proposed, through a series of numerical simulations. Through the method, the change in both volume compressibility and permeability during consolidation was reasonably evaluated.

• Journal of The Korean Society of Agricultural Engineers
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• v.52 no.3
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• pp.89-95
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• 2010

There is the freezing method as one of the ground improvement methods for excavating an underground tunnel, and due to its improved reliability, recently construction cases of applying this method into sandy soil grounds as well as cohesive soil grounds of cities have been reported. But, applying the freezing method into cohesive soil grounds could bring concerns of the expansion of the whole ground and the settlements from thawing of ground. In this study, the deformation strength characteristics of cohesive soil which received freezing and thawing hysteresis were examined using the sample collected from the site of cohesive soil ground applied with the freezing method and its structural characteristics were analyzed using an electronic microscope. And, the test with cohesive soil reconstituted from cohesive soil which received freezing and thawing hysteresis was carried out and its result was analyzed comparatively. The result of this test showed that the structure of natural clay was significantly changed due to freezing and thawing hysteresis.

• Journal of the Korean Geosynthetics Society
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• v.8 no.1
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• pp.19-24
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• 2009

In this paper, a series of numerical analyses on soft clay ground improved by PVD were carried out, in order to investigate the consolidation promotion effect considering PVD width and surcharge pressure. In the numerical analyses, an elasto-viscoplastic three-dimensional consolidation finite element method was applied, in which the applicability of numerical analyses could be confirmed comparing with consolidation behavior simulated at the laboratory. And, through the results of the numerical analyses, consolidation behaviors of soft clay ground with elapsed time was elucidated, together with the effects of PVD width and surcharge pressure.

• Proceedings of the Korean Geotechical Society Conference
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• 1995.10a
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• pp.41.1-44
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• 1995

The JV method is an epochal civil engineering style that boasts of significant pile driving power through low-vibration works by ideally combining the high pressure water injected from the water jet cutter and the vibrations combining from the vibratory pile driver extractors. As a result, you are ensured stable and safe pile driving and extraction in bedrocks that were previously impossible with conventional machines and methods. The other advantage is its high performance and a low-pollution characteristis that is ensured by suppressing ground vibrations. This is a very important factor since it often becomes an issue upon civil engineering in the city. With the addition of this method. the range of steel pipe pile, steel sheet pile and other steel pile use has been drastically expanded. Other advantages of this method incldes accurate works, shortening of the construction period and improved work performance. Since the minimun amount of high pressure water is used to drill the ground, it not only loosens the ground, but also cuts the ground at the tip of the pile to improve driving works.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1678-1688
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• 2008

In this study, dredging reclamation ground were performed to evaluate the ground improvement and liquefaction reduction effect with the result that standard penetration test(SPT) and piezo penetration test(CPT) before and after of improvement. Especially, the estimate center of the pile and factor of liquefaction safety to the position of ground around with the pile presented improvement of compaction for improved compaction of dredging reclamation ground.