• Solar Energy
• /
• v.10 no.3
• /
• pp.13-18
• /
• 1990

When nonuniform thermal boundary conditions are imposed on the surface of a circular cylinder in crossflow, the heat transfer characteristics can be quite different compared to what is found for isothermal or constant heat flux boundary conditions. In the present analysis, two kinds of nonuniform boundary conditions along the circumference of the cylinder are considered in a uniform stream of air: step changes and linear profiles. Step changes in temperature can arise on the surface of an external, cylindrical, solar central receiver. As the working fluid(water) flows through the vertical tubes that ring the circumference of Solar One(a solar central receiver in Barstow, California), the solar flux on the receiver heats the water from a liquid to a superheated state. In this process, portions of the receiver panels, and thus portions of the circumference of the cylinder, function as a preheater, boiler, or superheater. Hence the surface temperature can vary significantly around the cylinder. Common engineering practice has been to use an average wall temperature with an isothermal cylinder heat transfer coefficient when estimating the convective loss in these kinds of situations.

• 보존과학연구
• /
• s.35
• /
• pp.73-86
• /
• 2014

The Seosanmaaesamjonbulsang (national treasure 84) is carved has a quite developed tectonic line in a precipitous wall of stratified rock to the vertical and horizontal directions. The main buddha and the left part of it have got the biological weathering and the efflorescence has been detected on the shoulder part of the right buddha. It has been caused by the raindrops from upper rock after the dismantling of the protection shelter in 2007. Two proper measures have been taken in order to reduce the weathering and protect it from some damages. The one is removing the contaminant by dry/wet cleaning not to get any damage on the rock. The other is the isolation by the construction of a new waterway used L-30 on the upper part of the rock not to contaminate the surface of Rock-carved triad buddha with the raindrops from upper rock. Moreover, the sunlight for buddha has been increased and good ventilation has been made by cutting down the trees around the Rock-carved triad buddha.

• Journal of The Korea Institute of Healthcare Architecture
• /
• v.18 no.4
• /
• pp.7-16
• /
• 2012

Purpose : The purpose of this study is to look into the change of area and space organization percentage of wards in main general hospitals in Busan and Gyeongnam. Method : Patient area, nursing area, service area, training area, common area were classified for functional space organization. Patient area was reclassified to bedroom and comfort area, and common area was reclassified into vertical circulation, horizontal circulation and facility area. Also, method of area calculation was chosen standard to wall center-lines following building act 911 and functional space area of each hospital was estimated and comparatively analyzed. Result : For hospitals completed before 2000, area ratio by functional space for patient area, nursing area, service area and common area showed 53.6%, 10.2%, 0.8%, and 35.3% respectively. For hospitals completed after 2000, area ratio by functional space for patient area, nursing area, service space, and common area showed 49.2%, 12.6%, 1.1%, and 37.2% respectively. Implications : Through this study, change of percentage of space organization of main general hospitals in Busan Gyeongnam can be understood. Also because most studies on area organization of general hospital wards were focused on the capital area, this study provides basic material for future studies related to area of general hospital wards in Busan Gyeongnam.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.29 no.2
• /
• pp.149-159
• /
• 2016

In this study, the solitary wave-induced tsunami force acting on an onshore bridges in coastal area was numerically modelled by means of TWOPM-3D based on Navier-Stokes solver and VOF method which can track free surface effectively. The validity of numerical analysis was verified by comparing the experimental tsunami bore force acting on vertical wall and column structure. In particular, the characteristics of tsunami force with the changing tsunami intensity were surveyed through numerical experiments. The availability of 3-dimensional numerical analysis was reviewed through the comparison between the existing numerical results and design criteria for each drag force coefficient by applying Morison equation considering only drag force. As reasonable and high-precision estimation method of tsunami force, it was suggested to apply the estimation method taking drag and inertial force into consideration at the same time.

• Geomechanics and Engineering
• /
• v.13 no.1
• /
• pp.43-61
• /
• 2017

The inverted T-type abutments are generally used in highway bridges constructed in Korea. This type of abutment is used because it has greater stability, with more pile foundations embedded in the bedrock, while simultaneously providing support for lateral earth pressure and vertical loads of superstructures. However, the cross section of inverted T-type abutments is large compared with the piers, which makes them more expensive. In addition, a differential settlement between the abutment and embankment, as well as the expansion joints, causes driving discomfort. This study evaluated the driving comfort of several types of abutments to improve driving comfort on the abutment. To achieve this objective, a traditional T-type abutment and three types of candidate abutments, namely, mechanically stabilized earth wall (MSEW) abutment supported by a shallow foundation (called "true MSEW abutment"), MSEW abutment supported by piles (called "mixed MSEW abutment"), and pile bent and integral abutment with MSEW (called "MIP abutment"), were selected to consider their design and economic feasibility. Finite element analysis was performed using the design section of the candidate abutments. Subsequently, the settlements of each candidate abutment, approach slabs, and paved surfaces of the bridges were reviewed. Finally, the driving comfort on each candidate abutment was evaluated using a vehicle dynamic simulation. The true MSEW abutment demonstrated the most excellent driving comfort. However, this abutment can cause problems with respect to serviceability and maintenance due to excessive settlements. After our overall review, we determined that the mixed MSEW and the MIP abutments are the most appropriate abutment types to improve driving comfort by taking the highway conditions in Korea into consideration.

• Journal of Energy Engineering
• /
• v.23 no.3
• /
• pp.51-57
• /
• 2014

A MILD(Moderate and Intense Low oxygen Dilution) combustion, which is effective in the reduction of NOx, is considerably affected by the recirculation flow position of hot exhaust gas to the combustion furnace. A numerical analysis was accomplished to elucidate the flow characteristics in the MILD combustion incinerator for several cases with or without exhaust gas recirculation. It could be seen from the result of the present numerical study that the flow recirculation could be observed in the upper region over the vertical dividing wall for the case without exhaust gas recirculation. The optimal position of exhaust gas recirculation position was derived by the comparison of %RMS of x directional velocity for the cases with exhaust gas recirculation. The case with the exhaust gas recirculation position at the upper right of free board was the most effective with the smallest value of 57.4% RMS.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.10 no.5
• /
• pp.545-565
• /
• 2018

A numerical code is developed based on potential flow theory to investigate nonlinear sloshing in rectangular Liquefied Natural Gas (LNG) tanks under forced excitation. Using this code, internal free-surface elevation and sloshing loads on liquid tanks can be obtained both in time domain and frequency domain. In the mathematical model, acceleration potential is solved in the calculation of pressure on tanks and the artificial damping model is adopted to account for energy dissipation during sloshing. The Boundary Element Method (BEM) is used to solve boundary value problems of both velocity potential and acceleration potential. Numerical calculation results are compared with published results to determine the efficiency and accuracy of the numerical code. Sloshing properties in partially filled rectangular and membrane tank under translational and rotational excitations are investigated. It is found that sloshing under horizontal and rotational excitations share similar properties. The first resonant mode and excitation frequency are the dominant response frequencies. Resonant sloshing will be excited when vertical excitation lies in the instability region. For liquid tank under rotational excitation, sloshing responses including amplitude and phase are sensitive to the location of the center of rotation. Moreover, experimental tests were conducted to analyze viscous effects on sloshing and to validate the feasibility of artificial damping models. The results show that the artificial damping model with modifying wall boundary conditions has better applicability in simulating sloshing under different fill levels and excitations.

• Maxillofacial Plastic and Reconstructive Surgery
• /
• v.38
• /
• pp.1.1-1.4
• /
• 2016

Background: This study aimed to investigate the distribution and prevalence of intraosseous loop (anastomosis between posterior superior alveolar artery and infraorbital artery) in Koreans detected on computed tomography (CT) images taken prior to sinus augmentation surgery. Methods: From the 177 patients who underwent sinus augmentation with lateral approach at Ewha Womans University Department of Implant Dentistry, 284 CT scans were evaluated. The canal height (CH), ridge height (RH), and canal height from the sinus floor (CHS) were measured on para-axial views at the first premolar, first molar, and second molar. The horizontal positions of the bony canals in the lateral wall were also classified. One-way analysis of variance (ANOVA) and t test were used to estimate the statistical differences (p < 0.05). Results: The intraosseous loops were detected in 92 CT scans (32 %). The mean vertical height of the bony canals from the alveolar crest (CH) was $23.45{\pm}2.81$, $15.92{\pm}2.65$, and $16.61{\pm}2.92mm$ at the second premolar, first molar, and second molar, respectively. In the horizontal positions of the bony canals, intraosseous type was the most predominant. The canal heights more than 15 mm and less than 17 mm were most prevalent (33.7 %) and those under 13 mm were 12.0 %. Conclusions: The radiographic findings in this study could be used to decide the lateral osteotomy line avoiding potential vascular complication. However, only one third of the canals could be detected in CT scans; a precaution should be taken for the possibility of severe bleeding during lateral osteotomy.

• Journal of Hydrogen and New Energy
• /
• v.13 no.1
• /
• pp.90-99
• /
• 2002

In order to utilize hydrogen energy in a large-scale in the future, development of effective hydrogen storage method is essentially required as well as that of efficient hydrogen production method. The hydrogen storage method using metal hydrides has been holding the spotlight as a safer and higher-density hydrogen storage method than conventional hydrogen storage methods such as liquid hydrogen or compressed hydrogen storage method. However when metals react with hydrogen to store hydrogen as metal hydrides, they undergo exothermic reactions, while metal hydrides evolve hydrogen by endothermic reaction. Therefore, hydrogen storage tank should have such structure that it can absorb or release reaction heat rapidly and efficiently. In this study, a review on the improvement of the heat release and absorption structure in the hydrogen storage tank was conducted, and as a result, a new type of hydrogen storage tank with the structure of vertical-type wall was designed and manufactured. Experimental results showed that this new type of tank could be used as an efficient hydrogen storage tank because its structure is simpler and manufacture is easier than cup-type hydrogen storage tank with the structure of packed horizontal cup.

• Journal of Advanced Marine Engineering and Technology
• /
• v.41 no.1
• /
• pp.50-55
• /
• 2017

Foamed aluminum is an eco-friendly material that is reusable and safe against fire. These superior characteristics have many advantages in the field of building and construction and in cruise ships as sound absorbers. So far, the research on foamed aluminum has been focused on the sound absorption performance using the foaming ratio. Foamed aluminum, when compared with the existing sound absorbers such as glass wool or rock wool, has a better structural performance, and it can be installed on walls in many different ways. This study conducted experiments on the sound absorption characteristics considering the various applications of foamed aluminum. The effects of painting surfaces with the finishing material were compared to that of the normal surface, and the effects of vertical installation and hanging from the ceiling was compared with the effects of installing on the floor.