• Transactions of the Korean hydrogen and new energy society
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• v.29 no.2
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• pp.205-211
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• 2018

Performance evaluation of a regenerative pump has been compared with a conventional open channel impeller and a S-shaped continuous impeller designed newly. To analyze flow field for both pumps, analysis code, CFX, is employed. Unstructured grids are used to represent a composite geometryincluding blade, casing and ducts. Throughout the comparisons between numerical simulation and experiments, the predicted efficiency has a good agreement with the experimental one. It is noted that the pump having a S-shaped continuous impeller is about 4.8 percent more efficient than conventional one, which is due to the relatively large pressure increase. Detailed flow field inside the pump is also analyzed and compared.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.17-22
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• 2009

Reliability analyses were performed to quantify the risk in axially loaded large-scale pile foundations in consideration of pile-soil interaction and uncertainties on various design variables. The finite difference method based on an equivalent soil spring model and a load transfer method and Monte Carlo simulation method are integrated in the framework of reliabilty analysis. The applicability and efficiency of the proposed method in the safety assessment of axially loaded pile-soil system was verified using a realistic example. Since the proposed method can explicitly consider uncertainties in various design variables, and quantify failure probability of a pile foundation, it can be used to estimate risk, to obtain basic informations for life cycle cost analysis, and to develop code requirements for a reliability-based design of pile foundations.

• Journal of Korean Association for Spatial Structures
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• v.17 no.1
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• pp.69-75
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• 2017

In fire design for floors, the three criteria of stability, integrity and insulation are required for the specified fire resistance duration. Among these, stability is not easy to confirm. For solid prestressed concrete slabs of uniform thickness, Eurocode 2 provides tabulated data and specifies an axis distance to the centroid of strands to achieve particular fire resistance ratings, but it is not clear if this data can be used for a wide range of different prestressed slab profiles. In order to verify the current code-fire ratings for precast prestressed slabs, both simple and advanced calculation methods are investigated. This paper examines the use of calculation methods, accounting for the real behaviour of unprotected simply supported prestressed concrete slabs exposed to the standard ISO 834 fire. The calculated fire resistance of each prestressed concrete slab is compared with tabulated data in Eurocode part 1.2, with detailed discussion.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.1
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• pp.121-126
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• 2016

Hydraulic performance of a micro-bubble pump has been analyzed by numerical simulation and experimental measurements. Flow recirculation apparatus between the pump inlet and outlet reserviors has been adopted to measure pump performance according to flow conditions sequentially. To analyze three-dimensional flow field in the micro-bubble pump, general analysis code, CFX, is employed. SST turbulence model is employed to estimate the eddy viscosity and compared the pump performance to k-${\varepsilon}$ model. Unstructured grids are used to represent a composite grid system including blade, casing and inlet casing. It is found that the numerical model used in the present study is effective to evaluate the pump performance. From the numerical simulation, low velocity region due to pressure loss is decreased where pump efficiency has maximum value. Detailed flow field inside the micro-bubble pump is also analyzed and compared.

• The Korean Society of Law and Medicine
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• v.16 no.2
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• pp.131-157
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• 2015

NHIS claimed for damages to doctors that by doing the treatment breaching medical insurance criteria caused by doctors, NHIS paid for medicine cost to pharmacy; as a result, the doctors caused the tort to NHIS. Following consecutive rulings afterwards, NHIS also argued that the medicine cost violating medical law or medical treatment expense paid to medical organizations are both the tort in civil law. NHIS claimed for all the damages, and the Supreme Court confirmed this judgment. However, within our national health insurance system, the subject of insurance payment is NHIS and the subject of medical treatment expense are also NHIS since the treatment expense is also insurance payment by asking the treatment to medical organizations. Further, national health insurance law is not made to control the violation of medical treatment cases; therefore, the breach of medical law cannot be covered by illegality of tort in civil law regarding NHIS. If that is the case, in the case that if the patients are treated according to treatment criteria via the doctors delegated the doctors' permission by Health and Welfare minister, NHIS acquired the benefits to remove the duty to give treatment payment to doctors in civil law; thus, even though the doctors have breached the medical law, NHIS does not have any damages. The fact that supreme court confirmed the ruling that the treatment is the tort in civil law towards NHIS is the judgment not counting the benefits of insurance payment as the subject but only considering the fact that NHIS paid to the doctors and this ruling have gone against the principle under civil code section 750. If the doctors have breached the medical law, the case should be sanctioned by medical law not national health insurance law, and the ruling of supreme court is assumed that they have confused both with the principle of national health insurance law and civil law.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.2
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• pp.43-54
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• 1989

In this paper, measured and calculated responses are compared in order to give how the static and dynamic responses occurred in steel railway bridges due to train loads could be calculated appropriately. From this, it is investigated how the impact factors are varied by changing the train speed above 100km/h Field measurement is carried out by the steel strain gages and displacement transducers at the main design points, and then the static and dynamic response, fundamental frequencies, damping ratios and impact factors of the bridges are obtained. Static analysis is done using the computer program developed according to three dimensional matrix structural analysis in which the trains and bridges are modelled as 1,2 and 3 dimensions. Dynamic analysis is done according to 2 approaches, the moving force and mass problem. In moving force problem, the solutions are obtained by the modesuperposition-method and in moving mass problem by the direct integration method. From this study, it is known that in order to obtain the static response in the railway bridges, the bridge could be modelled by 1 or 2 dimension as in the highway bridge, however the response ratio(measured/calculaled) is high comparing to the highway bridges. By the way, the dynamic response should be obtained by the moving mass problem. And by comparing the measured and code specified impact factors, it is known that the factors specified in the present railway bridge code are very safe under the present service speed below 100km/h. However, because the factors become very high under the speed above 100km/h, especially in the simple plate girder bridge, it is thought that the code specification on impact factor should be discussed enough under the rapid transit system.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.3
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• pp.299-309
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• 2022

This paper presents a new class of the vehicular live load factor for a reliability-based bridge design code. The significance of the current vehicular live load factor of 1.8 is investigated based on the return period of the vehicular live load and the design life of a bridge. It is shown that the current vehicular live load factor corresponds to a return period of 6.7 million years for a 100-year design life, which seems to be unrealistic in an engineering sense, and that the target reliability of 3.72 is set to too high without any reasoning for the gravitational load-governed limit state compared with that of the other limit states. In case the same return period as the design wind velocity or the ground acceleration is employed for the vehicular live load, the corresponding vehicular live load factor becomes around 1.15, and the target reliability index for the return period may be selected as 2.0 or 2.5 depending on the governing load effect. The complete sets of the load-resistance factors for the proposed target reliability indices are evaluated through optimization.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.6
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• pp.335-349
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• 2017

Submerged breakwaters installed under the water surface are a representative coastal structure to prevent coastal erosion, and various types of submerged breakwaters have been proposed and discussed so far. Generally, submerged breakwaters make the complex wave fields due to abrupt change in water depth at the crown of the breakwater. In this study, wave heights and mean water level formed around a breakwater are examined numerically for three-dimensional permeable submerged breakwaters. OLAFOAM, CFD open source code, is applied in the numerical analysis, and the comparisons are made with available experimental results on the permeable upright wall and the impermeable submerged breakwater to verify its applicability to the three-dimensional numerical analysis. Based on the applicability of OLAFOAM numerical code, the wave height and mean water level distribution formed around the permeable submerged breakwaters are investigated under the formation condition of salient. The numerical results show that as the gap width between breakwaters decreases, the wave height in the center of the gap increases, while it decreases behind the gap, and the installing position of the breakwater from the shoreline has little influence on the change of the wave height. Furthermore, it is found that the decrease of the mean water level near the gap between breakwaters increases with decreasing of the gap width.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.6
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• pp.242-252
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• 2018

It is well known that an Oscillating Water Column Wave Energy Converter (OWC-WEC) is one of the most efficient wave absorber equipment. This device transforms the vertical motion of water column in the air chamber into the air flow velocity and produces electricity from the driving force of turbine as represented by the Wells turbine. Therefore, in order to obtain high electric energy, it is necessary to amplify the water surface vibration by inducing resonance of the piston mode in the water surface fluctuation in the air chamber. In this study, a new type of OWC-WEC with a seawater channel is used, and the wave deformation by the structure, water surface fluctuation in the air chamber, air outflow velocity from the nozzle and seawater flow velocity in the seawater channel are evaluated by numerical analysis in detail. The numerical analysis model uses open CFD code OLAFLOW model based on multi-phase analysis technique of Navier-Stokes solver. To validate model, numerical results and existing experimental results are compared and discussed. It is revealed within the scope of this study that the air flow velocity at nozzle increases as the Ursell number becomes larger, and the air velocity that flows out from the inside of the air chamber is larger than the velocity of incoming air into the air chamber.

• Journal of the Korean Geotechnical Society
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• v.25 no.10
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• pp.87-97
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• 2009

The seismic site coefficients are often used with the seismic hazard maps to develop the design response spectrum at the surface. The site coefficients are most commonly developed deterministically, while the seismic hazarde maps are derived probabilistically. There is, hence, an inherent incompatibility between the two approaches. However, they are used together in the seismic design codes without a clear rational basis. To resolve the fundamental imcompatibility between the site coefficients and hazard maps, this study uses a novel probabilistic seismic hazard analysis (PSHA) technique that simulates the results of a standard PSHA at a rock outcrop, but integrates the site response analysis function to capture the site amplification effects within the PSHA platform. Another important advantage of the method is its ability to model the uncertainty, variability, and randomness of the soil properties. The new PSHA was used to develop fully probabilistic site coefficients for site classes of the seismic design code and another sets of site classes proposed in Korea. Comparisons highlight the pronounced discrepancy between the site coefficients of the seismic design code and the proposed coefficients, while another set of site coefficients show differences only at selected site classes.