• Geomechanics and Engineering
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• v.16 no.6
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• pp.643-654
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• 2018

Tunnel excavation leads to a disturbance on the initial stress balance of surrounding soils, which causes convergences around the tunnel and settlements at the ground surface. Considering the effective impact of settlements on the structures at the surface, it is necessary to estimate them, especially in urban areas. In the present study, ground settlements due to the excavation of East-West Line 7 of the Tehran Metro (EWL7) and the Abuzar tunnels are evaluated and the effect of the lateral earth pressure coefficient ($K_0$) on their extension is investigated. The excavation of the tunnels was performed by TBMs (Tunnel Boring Machines). The coefficient of lateral earth pressure ($K_0$) is one of the most important geotechnical parameters for tunnel design and is greatly influenced by the geological characteristics of the surrounding soil mass along the tunnel route. The real (in-situ) settlements of the ground surface were measured experimentally using leveling methods along the studied tunnels and the results were compared with evaluated settlements obtained from both semi-empirical and numerical methods (using the finite difference software FLAC3D). The comparisons permitted to show that the adopted numerical models can effectively be used to predict settlements induced by a tunnel excavation. Then a numerical parametric study was conducted to show the influence of the $K_0$ values on the ground settlements. Numerical investigations also showed that the shapes of settlement trough of the studied tunnels, in a transverse section, are not similar because of their different diameters and depths of the tunnels.

• KIEAE Journal
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• v.12 no.4
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• pp.41-46
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• 2012

In Korea, Apartment houses recently occupy over 80% of all buildings. Ground source system has to be designed to consider feature of apartment house. Most apartment houses use PHC pile to get a bearing power of the soil. Therefore, the purpose of this study is to evaluate performance of ground source heat pump system utilizing energy pile under apartment. Object of experiment is low-energy experiment apartment in Song-do and Energy Pile are applied to 80%, 100% energy reduction model for heat-source. First, performance evaluation of Energy Pile geothermal system was done during summer season. As a result, The COP(coefficient of performance) about geothermal heatpump was approximately 5-6 while cooling. In winter season, Long experiment was performed because it was very important to evaluate ground condition for long time. During heating experiment, Indoor room set temperature was $20^{\circ}C$ and kept constant by heating. Coefficient of performance for heat pump and overall system was calculated. It was 3.5-4.5 for COP and 2.5-3.7 for system COP.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.303-314
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• 2010

This study, as basic research which was intended to develope the surface reinforcement method using reinforcement material which is applicable to very soft ground in Korea, was aimed at proposing the design parameter for the surface ground improvement method. To that end, a wide width tensile test using geotextile, geogrid and steel bar (substitute for bamboo) and 49 kinds of the laboratory model tests were conducted. And the result the study suggested $\beta_s$, the stiffness coefficient to evaluate the stiffness effect of reinforcement materials. Then, it was also found that the stiffness coefficient, $\beta_s$ as the testing constant would be appropriate as high as 1.0, 1.1 and 1.5 for geotextile, geogrid and steel bar, respectively. And It was evaluated that the stiffness effect affecting reinforcement improvement effect would be reduced as the thickness of embeded depth increases and that RFe, the stiffness effect reduction coefficient would have positive correlation with H/B. Finally, it was confirmed that the bearing capacity gained from the method to calculate bearing capacity, which was suggested in the study, would almost correctly estimate the capacity, demonstrating the appropriateness of the proposed bearing capacity calculation method.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.12 no.4
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• pp.33-39
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• 2016

A ground source heat pump (GSHP) system is recommended as a heating and cooling system to solve the pending energy problem in the field of air conditioning, because it has the highest efficiency. However, higher initial construction cost works as a barrier to the promotion and dissemination of GSHP system. In this study, numerical analysis on the characteristics of high density polyethylene (HDPE) pipe with spiral inside was executed. The heat transfer and flow characteristics of it were compared with those of a conventional smooth HDPE pipe. The heat transfer coefficient and pressure drop of the spiral HDPE pipe were higher than those of the smooth HDPE pipes at the same fluid flow rate. By decreasing the flow rate, the spiral HDPE pipe represented similar values of heat transfer coefficient and pressure drop to the smooth HDPE pipe. The lower flow rate of the spiral HDPE pipe comparing with it of the smooth HDPE pipe is estimated to reduce the length of the ground loop heat exchanger.

• Korean Journal of Food Science and Technology
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• v.21 no.6
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• pp.735-741
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• 1989

For the accurate prediction of freezing time, probably the most difficult factor to measure and major error source is the surface heat transfer coefficient. In this work, surface heat transfer coefficient were determined for still air freezing and immersion freezing methods by theory of the transient temperature method and confirmed by using a modification of plank's equation to predict the freezing time of ground lean beef. The results showed the cooling rate of immersion freezing was about 11 times faster than that of still air freezing method. A comparison of surface heat transfer coefficient of copper plate and ground lean beef resulted an difference of 25-30% because the food sample surface is not smooth as copper plate. Also, when h-values measured by ground lean beef were applicated to modified model, the accuracy of its results is very high as difference of about 8%.

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.513-515
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• 2016

There are various walking devices based on Theo Jansen mechanism. And these systems controlled by complicate equations. So we decided to optimize the design of walking device with two points of view. The device is required to ensure stability while maintaining the high speed. To simplify the control system, we applied trigonometric ratio with ideal Jansen trajectory. As a result, we were able to draw the connection between height of barrier and Ground Length (GL). Also we could change traveling distance and Ground Angle Coefficient (GAC) by shifting the position of the joints. Through controlling these parameter, we can analyze stability and speed of the device. Ultimately, we develop the device that can walk more efficiently by the optimization process.

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.443-454
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• 2016

This study focus to make 8 legs robot based on Jansen's mechanism. In the process of making, we found GL(Ground length),GAC(Ground Angle Coefficient) and the height difference of tract and compare Several models with M.Sketch to find link's Length ratio Optimised simple walking and crossing of obstacles. In the process, our team Analyzed the difference ideal tract (Jansen holy number model's track) contrived by Jansen and our final model tract. As a result, we found optimal link's length ratio to over the obstacles and some features that our model differ from Jansen holy number model. It means that optimal link's length ratio depends on certain circumstances, perfect length ratio is nonexistent.

• Journal of the Korean GEO-environmental Society
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• v.11 no.11
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• pp.19-26
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• 2010

An influence factors for soundness evaluation of river levee include consisting embankment in case piping, permeability coefficient of ground, height of embankment, the width of crest, material characteristics of embankment and foundation ground, shape of embankment slope, an influence for penetration of rainfall or river water in case slope stability. In this study, it was operated a feasibility investigation of existing design result, stability evaluation for permeability coefficient use and permeability coefficient change of foundation ground to investigate an influence in line with permeability coefficient change for result of river levee penetration analysis. The evaluation results of influence factors, the permeability coefficient was used in design and it was evaluated influence in safety factor of piping. After the evaluation of influence factors, the permeability coefficient used in the design appears with the fact that differs in a design report about same soil.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.249-252
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• 2004

Chloride ion diffusion is the most important thing of occuring deterioration in RC structure. According to establish data, the curing time in concrete reduce the chloride ion diffusion coefficient. The purpose of this study is to make clear through experience on the effect of curing time on the chloride ion diffusion coefficient in concrete with Portland cement and ground granulated blast-furnance slag and a propose the standard of chloride ion diffusion coefficient in concrete.

• 한국전산유체공학회:학술대회논문집
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• 1999.11a
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• pp.174-180
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• 1999

Aerodynamic characteristics of tandem airfoil under ground effect is investigated numerically. Some numerical results for NACA 6409 tandem airfoil are presented. The numerical results show that as being decreased distance between airfoils, the lift coefficient of leading airfoil is increased and that of trailing airfoil is decreased. Drag coefficient shows opposite property, At the same distance between leading airfoil and trailing airfoil, lower position of trailing airfoil give better tandem airfoil effect.