• Nuclear Engineering and Technology
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• v.48 no.4
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• pp.941-951
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• 2016

The aim of this work is to simulate the thermohydraulic consequences of a main steam line break and to compare the obtained results with Rossendorf Coolant Mixing Model (ROCOM) 1.1 experimental results. The objective is to utilize data from steady-state mixing experiments and computational fluid dynamics (CFD) calculations to determine the flow distribution and the effect of thermal mixing phenomena in the primary loops for the improvement of normal operation conditions and structural integrity assessment of pressurized water reactors. The numerical model of ROCOM was developed using the FLUENT code. The positions of the inlet and outlet boundary conditions and the distribution of detailed velocity/turbulence parameters were determined by preliminary calculations. The temperature fields of transient calculation were averaged in time and compared with time-averaged experimental data. The perforated barrel under the core inlet homogenizes the flow, and therefore, a uniform temperature distribution is formed in the pressure vessel bottom. The calculated and measured values of lowest temperature were equal. The inlet temperature is an essential parameter for safety assessment. The calculation predicts precisely the experimental results at the core inlet central region. CFD results showed a good agreement (both qualitatively and quantitatively) with experimental results.

• Nuclear Engineering and Technology
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• v.45 no.5
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• pp.625-636
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• 2013

Pressing demands of economic competitiveness, the need for large-scale deployment, minimizing the need of human intervention, and experience from the past events and incidents at operating reactors have guided the evolution and innovations in reactor technologies. Indian innovative reactor 'AHWR' is a pressure-tube type natural circulation based boiling water reactor that is designed to meet such requirements, which essentially reflect the needs of next generation reactors. The reactor employs various passive features to prevent and mitigate accidental conditions, like a slightly negative void reactivity coefficient, passive poison injection to scram the reactor in event of failure of the wired shutdown systems, a large elevated pool of water as a heat sink inside the containment, passive decay heat removal based on natural circulation and passive valves, passive ECC injection, etc. It is designed to meet the fundamental safety requirements of safe shutdown, safe decay heat removal and confinement of activity with no impact in public domain, and hence, no need for emergency planning under all conceivable scenarios. This paper examines the role of the various passive safety systems in prevention and mitigation of severe plant conditions that may arise in event of multiple failures. For the purpose of demonstration of the effectiveness of its passive features, postulated scenarios on the lines of three major severe accidents in the history of nuclear power reactors are considered, namely; the Three Mile Island (TMI), Chernobyl and Fukushima accidents. Severe plant conditions along the lines of these scenarios are postulated to the extent conceivable in the reactor under consideration and analyzed using best estimate system thermal-hydraulics code RELAP5/Mod3.2. It is found that the various passive systems incorporated enable the reactor to tolerate the postulated accident conditions without causing severe plant conditions and core degradation.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.5
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• pp.380-387
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• 2014

Piper Alpha disaster drew attention to the damage likely to arise from explosions and fires on an offshore platform. And great concerns have been increased to prevent these hazards. Blast wall is one of the passive safety systems; it plays a key part of minimizing the consequences. However, a buckling due to explosion loads is a factor which can reduce the strength of blast wall. The buckling often occurs between web and flange at the center of blast wall. This study aims to find a solution for reinforcing its strength by installing a flat plate at the spot where the buckling occurs. First of all, ANSYS finite element method is adopted to numerically compute the structural resistance characteristic of blast wall by using a quasi-static approach. Sequentially, the impact response characteristics of blast wall are investigated the effect on thickness of flat plate by using ANSYS/LS-DYNA. Finally, pressure-impulse diagrams (P-I diagram) are presented to permit easy assessment of structural response characteristics of stiffened blast wall. In this study, effective use is made to increase structural intensity. of blast wall and acquired important insights have been documented.

• Korean Circulation Journal
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• v.52 no.3
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• pp.198-204
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• 2022

Blood pressure measurement (BPM) is an essential part of medical examination, and therefore accuracy of BPM devices is crucial. Over the past few years, there has been a rise in new BPM techniques using photoplethysmographic (PPG) signals and complex algorithms for blood pressure estimation. Especially the combination of a mobile device or a smartphone with a camera using PPG may potentially revolutionize BPM in the future. The first-ever BPM application to be approved as a medical device was one by the Korean Ministry of Food and Drug Safety in 2020, despite the lack of robust scientific evidence proving its validity. While the prospect of using these novel BPM devices is an opportunity, there are also some critical issues around calibration and utility in different patient groups that need to be resolved before they can be incorporated into daily clinical practice.

• Journal of The Korean Society of Integrative Medicine
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• v.4 no.3
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• pp.61-68
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• 2016

Purpose : The purpose of this study was to examine the differences in sit-to-stand movement and static standing balance between young adults and older adults Methods : Thirty young adults and thirty older adults participated in this study. The Good Balance System was used to assess participants' sit-to-stand movement and static standing balance. The sit-to-stand movement was measured as mediolateral and anterioposterior displacement of the centre of pressure (mm/s) while sit-to-stand on a force platform, and time required to complete a sit-to-stand movement on a force platform. The static standing balance was measured as mediolateral and anterioposterior displacement of the center of pressure (mm/s) and velocity moment (mm2/s) while standing on a force platform with opened eyes and with closed eyes. Result : A significant difference was found in the mediolateral and anterioposterior center of pressure displacement and the time required to complete a sit-to-stand movement of the two groups (p<.05). A significant difference between the groups was found as to mediolateral centre of pressure displacement and the velocity moment when standing with opened eyes and with closed eyes (p<.05). Conclusion : In conclusion, older adults showed decreased sit-to-stand movement and static standing balance ability compared to the young adult. Clinicians should consider sit-to-stand and balance training for older adult.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.10a
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• pp.273-274
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• 2012

• International Journal of Air-Conditioning and Refrigeration
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• v.13 no.1
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• pp.11-21
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• 2005

The present paper investigates the heat transfer characteristics in a cylinder packed with porous medium of solid spheres for various parameters such as mass flow rate, sphere diameter, length of the porous medium, and gas temperatures. Pressures and temperatures at the inlet and outlet regions were measured by using static pressure gages and R-type thermocouples. The modified relationship based on the Ergun equation is suggested for the estimation of pressure drops. In addition, the useful empirical correlation for thermal efficiency is obtained in the current study. Thermal efficiency is expressed in terms of non-dimensional time, sphere diameter, porosity, and pressure drops. It is also found that the pressure drop through the cylinder becomes larger as the gas temperature does higher at the inlet region, whereas it substantially decreases when the inlet flow rate decreases.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.46-47
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• 2003

Direct numerical simulations are performed for a turbulent flow subjected to a sudden change in pressure gradient. The calculations are started from a fully-developed turbulent channel flow at $Re_{\tau}=180$. The pressure gradient of the channel flow is then changed abruptly. The responses of the turbulence quantities (e.g., turbulence intensities, Reynolds shear stress, and vorticity fluctuations) and the near-wall turbulence structure to the pressure gradient change are investigated. It is found that there are two different relaxations: a fast relaxation at the early stage and a slow one at the later stage. The early response of the velocity fluctuations shows an anisotropic response of the near-wall turbulence.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.2
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• pp.153-160
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• 2015

Pipelines are one of the most important structures in subsea equipment. It is the main equipment for transportation of crude oil and natural gas to the downstream facilities. Crude oil and natural gas leak will be carry out not only political and financial issues but also pollution to the environment. Inaccurate predictions of corrosion behavior will make hazardous consequences. The serviceability assessment of corroded structures is essential especially for subsea pipelines. As corrosion is concerned, the effects of failure due to significant reduction will make it hard to the pipeline operator to maintain the serviceability of pipelines. In this paper, the serviceability assessment of corroded crude oil pipeline is performed using the industry design code (Shell92, DNV RP F101, ASME B31G, BS 7910, PCORRC) and FEA depending on corrosion area. In last step, the future integrity of the subsea crude oil pipeline is assessed to predict the remaining year in service of crude oil pipelines.

• Corrosion Science and Technology
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• v.20 no.1
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• pp.26-36
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• 2021

Pipes operating in the seawater environment faces cavitation degradation and corrosion of the metallic component, as well as a negative synergistic effect. Cavitation degradation shows the mechanism by which materials deteriorate by causing rapid change of pressure or high-frequency vibration in the solution, and introducing the formation and explosion of bubbles. In order to rate the cavitation resistance of materials, constant conditions have been used. However, while a dynamic cavitation condition can be generated in a real system, there has been little reported on the effect of ultrasonic amplitude on the cavitation resistance and mechanism of composites. In this work, 3 kinds of epoxy coatings were used, and the cavitation resistance of the epoxy coatings was evaluated in 3.5% NaCl at 15 ℃ using an indirect ultrasonic cavitation method. Eleven kinds of mechanical properties were obtained, namely compressive strength, flexural strength and modulus, tensile strength and elongation, Shore D hardness, water absorptivity, impact test, wear test for coating only and pull-off strength for epoxy coating/carbon steel or epoxy coating/rubber/carbon steel. The cavitation erosion mechanism of epoxy coatings was discussed on the basis of the mechanical properties and the effect of ultrasonic amplitude on the degradation of coatings.