• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.4C
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• pp.193-200
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• 2010

This study suggests a method predicting at-rest coefficient of earth pressure ($K_0$) in order to evaluate the effect of stress history of granular soil. The method is based on the relation $K_D/K_0={\chi}(E_D/{\sigma}_m{^{\prime}})^{\delta}$, which is developed by combining two previously published relations such as $E_D/{\sigma}_m{^{\prime}}-{\psi}$ and $K_D/K_0-{\psi}$. As $K_D$ and $E_D$ are observed to be sensitive to the pre-stress, both indices are adopted for the estimation of $K_0$ value of granular soil. It is shown that the proposed $K_D/K_0-E_D/{\sigma}_m{^{\prime}}$ relation is insignificantly affected by the stress history. It is concluded from the comparative study that the proposed method, which uses only dilatometer test results to predict the $K_0$ of granular soil, provides more convenient and reliable prediction than other methods which use both CPT and DMT results.

• Journal of the Korean Society for Railway
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• v.15 no.6
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• pp.558-565
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• 2012

Abnormal climate or weather is more frequently reported nowadays due to the global climate change. Especially, extremely low temperature in winter season may cause bad thermal discomfort of passengers. In this study, the effect of car heating modes on cabin temperature change and distribution was studied by using a real-scale environmental chamber for passenger cabin. It was found that the cabin temperature rose quickly at the initial stage of heating system operation, but it stopped increasing after certain point. And, temperature was higher when the height from the floor was higher. Based on the obtained result, the way to minimize the decrease of passengers' thermal comfort was suggested.

• Journal of computational fluids engineering
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• v.20 no.3
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• pp.8-14
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• 2015

More and more, spaces are decreasing which satisfy multiple requirements for wind power plants. However, areas which have excellent wind resources and are free to civil complaints occupy a large space, although they are exposed to the cryogenic environment. This study conducted a thermal-fluid analysis of a cryogenic chamber for testing large wind turbine parts exposed to the cryogenic environment. The position of supply air is placed to the upper area to compare each cooling performance for each location of various outlets in mixing ventilated conditions. The study carried out CFD analysis for the chamber both with and without a test object. For the cases without the test object, the air temperature of the upper supply and down extract type chamber was cooled faster by 5-100% than the others. However, for the cases with the test object, the object temperature of upper supply and center extract on the opposite side type chamber was cooled faster by 33-132% than the others. The cooling performance by the air inside the chamber and the test object did not show the same pattern, which implicates the need to consider the cooling performance by not only the air but also the test object in the large cryogenic chamber design for testing large parts.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.6
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• pp.53-59
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• 2010

This research aims in finding a more optimal ejector size for evacuating engine exhaust gasses and 20% of the cell cooling air. The remaining 80% of cell cooling air pumped into the test chamber is separately exhausted from the test chamber via a discharge port fitted with flow control valves and vacuum pump. Unlike its predecessor this configuration utilizes a smaller capture area to improve pressure recovery. The modified ejector size has a diameter of 1100mm enough to evacuate 66kg/s jet engine exhaust in addition to about 20%, 24kg/s of the cell cooling air tapped from the sterling chamber. This configurations has an area ratio of the engine exit and ejector inlet of about 1.2. Simulation results of the proposed ejector configuration, indicates improved pressure recovery.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.627-630
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• 2009

Ejector system can induce the secondary flow or affect the secondary chamber pressure by both shear stress and pressure drop which are generated in the primary jet boundary. Ejectors are widely used in a range of applications such as a turbine-based combined-cycle propulsion system and a high altitude test facility for rocket engine, pressure recovery system, desalination plant and ejector ramjet etc. The primary interest of this study is to set up an configuration and operating conditions for an ejector in the condition of sonic and subsonic. Experimental and theoretical investigation on the sonic and subsonic ejectors with a converging-diverging diffuser was carried out. Numerical simulation was adopted for an optimal geometry design and satisfying the required performance. Also, some ejectors with a various of nozzle throat and mixing chamber diameter were manufactured precisely and tested for the comparison with the calculation results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.3
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• pp.291-300
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• 2004

Due to the rapid growth of mobile communication services, many studies have been performed on the biological effects of EMF(Electromagnetic field) exposure. However, it is not easy to create the field uniformity in radio frequency. To overcome this difficulty, the electric field and SAR(Specific Absorption Rate) distribution is developed to measure the whole body exposure system. In this paper, we developed the whole body exposure system for in-vivo study utilizing reverberation chamber which has a high possibility of practical use by substituting previous the EMC chamber. The field uniformity in the test area of the designed reverberation chamber was satisfied by the simulation and measurement data. In animal study of the whole body exposure for a mouse, the results of FDTD simulation were compared with those of measurement to confirm SAR under the electromagnetic exposure. We analyze the electric field distribution in the interior of the reverberation chamber and treat these results in statistical manner. In the CDMA frequency band(PCS ＆ Cellular band), an average value of the whole body SAR and local peak value for a experimental mouse were presented for various input power.

• The KSFM Journal of Fluid Machinery
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• v.15 no.6
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• pp.70-76
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• 2012

Recently, because people are taking a great interest in the water supply system and the related facilities are getting larger, the surge suppression is very important problem. The waterhammer occurs when the pumps are started or stoped for operation or tripped due to the power failure. As the waterhammer problems as a result of the pump power failure were very serious, these situations were carefully investigated. Accordingly, we carried out both numerical simulations and field tests to confirm the safety of Juam intake pumping station in which had the in-line pumps. In this paper, it was reviewed that the water supply system has the reliability on the pressure surge, in case the air chambers were installed at both the inlet and the oulet of the in-line pumping station. From the numerical simulations, we found that negative pressure occurred at the inlet disappeared and high pressure occurred at the outlet reduced due to the air chambers. And these results of numerical simulations verified by the field tests. The field tests carried out in case of normal start, normal stop, one and two of pumps emergency stop. By results of simulations and field tests, we are sure that Juam intake pumping station in which have the air chambers is safe for the waterhammer. In addition, we suggested the operation methods of facilities for safe maintenance of the pumping station.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.2
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• pp.81-88
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• 2016

There are many types of national and international standards for low temperature tests depending on the products. This study conducted CFD analysis and estimation of the energy efficiency of the chamber both with and without a test object by considering variations of COP and specific volume according to temperature. The supply air was located in the upper area to compare the cooling performance for each location using various outlets in mixed ventilated conditions. For cases without the test object, the air temperature of the upper supply and center extract on the opposite side type chamber cooled faster than other areas by 4.3~29.8%. However, for cases with the test object, the object temperature of the upper supply and lower extract type chamber cooled faster than the other areas by 7.2~31.5%. The cooling efficiency of the air inside the chamber and the test object did not show the same pattern, which indicates the need to consider the cooling performance by not only the air but also the test object in the cryogenic chamber design for testing.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.833-837
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• 2010

This study aims at finding an optimal exhaust diffuser design of a high altitude testing chamber for a low bypass turbofan engine (F404-402) with thrust pound force of 17,700 and air mass flow rate of 66kg/s ejecting at a speed of Mach 1.66. The final proposed ejector size has better pressure recovery characteristics and targets to reduce operational cost at engine performance testing. Conventional high altitude test chamber layout was adopted and first drawn in two dimensions using Autocad software so as to determine the gas path, the ejector frontal size was then determined from gas dynamics equations considering traditional gas ejection method where both the engine exhaust and cell cooling air are exhausted via the ejector. Modification to a smaller ejector with an alternative secondary cell cooling exhaust port was then performed and modelled in 3D using Solid Works software.

• Journal of IKEEE
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• v.21 no.1
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• pp.30-38
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• 2017

It is necessary to check the fault of phased array antenna, when the active phased array radar installed in the site is suspected performance degradation due to external impact or long-term operation. However, the near-field test should be performed in anechoic chamber in order to measure the phased array antenna, so that much time and cost must be applied for radar disassembly and transportation, and the operational availability of the radar system is deteriorates. Therefore, we propose a near-field scanner with mobility to check the fault of the phased array antenna at the site, and the effectiveness of the proposed scanner was verified with ${\pm}0.5dB$ magnitude and ${\pm}1.5^{\circ}$ phase in comparison with measured data in anechoic chamber.