• Nuclear Engineering and Technology
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• v.54 no.3
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• pp.860-866
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• 2022

An accurate prediction of the pressure drop along the flow paths is crucial in the design of advanced passive systems cooled by heavy liquid metal coolants. To date, a generic pressure drop correlation over spacer grids by Rehme has been applied extensively, which was obtained from substantial experimental data with multiple types of components. However, a few experimental studies have reported that the correlation may give large discrepancies. To provide a more reliable correlation for ring-type spacer grids, the current numerical study aims at figuring out the most critical factor among four hypothetical parameters, namely the flow area blockage ratio, number of fuel rods, type of fluid, and thickness of the spacer grid in the flow direction. Through a set of computational fluid dynamics simulations, we observed that the flow area blockage ratio dominantly influences the pressure loss characteristics, and thus its dependence should be more emphasized, whereas the other parameters have little impact. Hence, we suggest a new correlation for the drag coefficient as C_B = C_ν,m/ε^2.7, where C_ν,m is formulated by a nonlinear fit of simulation data such that C_ν,m = -11.33 ln(0.02 ln(Re_b)).

• Journal of the Society of Naval Architects of Korea
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• v.59 no.6
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• pp.385-392
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• 2022

Naval ship could face a variety of threats in isolated seas. In particular, fires and flooding are defined as disasters that are very likely to cause irreparable damage to ships. These disasters have a very high risk of personal injury as well. Therefore, when a disaster occurs, it must be quickly suppressed, but if there are people in the disaster area, the protection of life must be given priority. In order to quickly evacuate the ship crew in case of a disaster, we would like to propose a plan to quickly explore the evacuation route even in urgent situations. Using commercial escape simulation software, we obtain the data for deep neural network learning with simulations according to aisle characteristics and the properties and number of evacuation person. Using the obtained data, the passage prediction model is trained with a deep learning, and the passage time is predicted through the learned model. Construct a numerical map of a naval ship and construct a distance matrix of the vessel using predicted passage time data. The distance matrix configured in one of the path search algorithms, the Dijkstra algorithm, is applied to explore the evacuation path of naval ship.

• The Journal of the Korea institute of electronic communication sciences
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• v.17 no.3
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• pp.473-482
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• 2022

Wearing a mask is also necessary to limit the risk of infection in today's era of COVID-19 and wearing a helmet is inevitable for the safety of personnel who works in a dangerous working environment such as construction sites. This paper proposes an effective deep learning model, HelmetMask-Net, to classify both Helmet and Mask. The proposed HelmetMask-Net is based on CNN which consists of data processing, convolution layers, max pooling layers and fully connected layers with four output classifications, and 4 classes for Helmet, Mask, Helmet & Mask, and no Helmet & no Mask are classified. The proposed HelmatMask-Net has been chosen with 2 convolutional layers and AdaGrad optimizer by various simulations for accuracy, optimizer and the number of hyperparameters. Simulation results show the accuracy of 99% and the best performance compared to other models. The results of this paper would enhance the safety of personnel in this era of COVID-19.

• Nuclear Engineering and Technology
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• v.53 no.12
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• pp.3879-3891
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• 2021

A heat pipe residual heat removal system is proposed to be incorporated into the reactor driven subcritical (RDS) facility, which has been proposed by MIT Nuclear Reactor Laboratory for testing and demonstrating the Fluoride-salt-cooled High-temperature Reactor (FHR). It aims to reduce the risk of the system operation after the shutdown of the facility. One of the main components of the system is an air-cooled heat pipe heat exchanger. The alkali-metal high-temperature heat pipe was designed to meet the operation temperature and residual heat removal requirement of the facility. The heat pipe model developed in the previous work was adopted to simulate the designed heat pipe and assess the heat transport capability. 3D numerical simulation of the subcritical facility active zone was performed by the commercial CFD software STAR CCM + to investigate the operation characteristics of this proposed system. The thermal resistance network of the heat pipe was built and incorporated into the CFD model. The nominal condition, partial loss of air flow accident and partial heat pipe failure accident were simulated and analyzed. The results show that the residual heat removal system can provide sufficient cooling of the subcritical facility with a remarkable safety margin. The heat pipe can work under the recommended operation temperature range and the heat flux is below all thermal limits. The facility peak temperature is also lower than the safety limits.

• Earthquakes and Structures
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• v.22 no.1
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• pp.25-38
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• 2022

The RC private constructions represent a large part of the housing stock in the north part of Algeria. For various reasons, they are mostly built without any seismic considerations and their seismic vulnerability remains unknown for different levels of seismic intensity possible in the region. To support future seismic risk mitigation efforts in northern Algeria, this document assesses the seismic vulnerability of typical private RC constructions built after the Boumerdes earthquake (May 21, 2003) without considering existing seismic regulation, through the development of analytical fragility curves. The fragility curves are developed for four representative RC frames in terms of slight, moderate, extensive, and complete damage states suggested in HAZUS-MH 2.1, using nonlinear time history analyses. The numerical simulation of the nonlinear seismic response of the structures is performed using the SeismoStruct software. An original intensity measure (IM) is proposed and used in this study. It is the zone acceleration coefficient "A", through which the seismic hazard level is represented in the Algerian Seismic Regulations. The efficiency, practicality, and proficiency of the choice of IM are demonstrated. Incremental dynamic analyses are conducted under fifteen ground motion accelerograms compatible with the elastic target spectrum of the Algerian Seismic Regulations. In order to cover all the seismic zones of northern Algeria, the accelerograms are scaled from 0.1 to 2.5 in increments of 0.1. The results mainly indicate that private constructions built after the Boumerdes earthquake in the moderate and high seismic zones with four (04) or more storeys are highly vulnerable.

• Explosives and Blasting
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• v.40 no.3
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• pp.1-18
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• 2022

Due to the advent of the hydrogen economy era, various studies are being conducted to transport and store hydrogen, and the risk of hydrogen explosion is emerging. In order to figure out the new technology related to hydrogen energy, it is necessary to figure out the overall research trends related to various hydrogen energy at home and abroad. In this study, a bibliometric analysis using VOSViewer for the papers published in the international journal was conducted. From the analysis in different time period using the keywords including hydrogen explosion, hydrogen pipeline, and hydrogen storage, it was found that there were frequent paper publications using numerical analysis simulation. It is also found that more and more researches on safety and hydrogen explosion in hydrogen storage and hydrogen pipeline transportation have been conducted in 2011-2022 compared to those in 2000-2010.

• The Journal of the Korea institute of electronic communication sciences
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• v.17 no.5
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• pp.905-912
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• 2022

Virtual reality, one of the core technologies of the 4th industrial revolution, is entering a new phase with the spread of low-cost wearable devices represented by Oculus. In the case of disaster evacuation drills, where practical training is almost impossible due to the risk of accidents, virtual reality is becoming a new alternative that enables effective training. In this paper, we propose a smoke modeling method that can be applied to fire evacuation drills implemented with virtual reality technology. In the event of a fire, smoke spreads along the aisle, and the density of the smoke changes over time. The proposed method models the smoke by applying a procedural function that can reflect the density of smoke calculated through simulation to the model in real-time. Implementation results in the background of the factory show that the proposed method produces models that can express the smoke according to the user's movement.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.28 no.2
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• pp.143-149
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• 2022

PCS needs to freely switch AC and DC to connect the battery, external AC loads and renewable energy in both directions for energy efficiency. Whenever converting happens, power loss inevitably occurs. Minimization of the power loss to save electricity and convert it for usage is a very critical function in PCS. PCS plays an important role in the ESS(Energy Storage System) but the importance of stabilizing semiconductors on PCB(Printed Circuit Board) should be empathized with a risk of failure such as a fire explosion. In this study, the temperature variation inside PCS was reviewed by cooling fan on top of PCS, and the vibration characteristics of PCS were analyzed during truck transportation for reliability of the product. In most cases, a cooling fan is mounted to control the inner temperature at the upper part of the PCS and components generating the heat placed on the internal aluminum cooling plate to apply the primary cooling and the secondary cooling system with inlet fans for the external air. Results of CFD showed slightly lack of circulating capacity but simulated temperatures were durable for components. The resonance points of PCS were various due to the complexity of components. Although they were less than 40 Hz which mostly occurs breakage, it was analyzed that the vibration displacement in the resonance frequency band was very insufficient. As a result of random-vibration simulation, the lower part was analyzed as the stress-concentrated point but no breakage was shown. The steel sheet could be stable for now, but for long-term domestic transportation, structural coupling may occur due to accumulation of fatigue strength. After the test completed, output voltage of the product had lost so that extra packaging such as bubble wrap should be considered.

• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.1949-1958
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• 2023

The International Commission on Radiological Protection (ICRP) Publication 116 was released to provide a comprehensive dataset of the dose coefficients (DCs) for external exposures produced with the adult reference voxel phantoms of ICRP Publication 110. Although an advanced skeletal dosimetry method for photons and neutrons using fluence-to-dose response functions (DRFs) was introduced in ICRP Publication 116, the ICRP-116 skeletal DCs were calculated by using the simple method conventionally used (i.e., doses to red bone marrow and endosteum approximated by doses to spongiosa and/or medullary cavities). In the present study, the photon and neutron DRFs were used to produce skeletal DCs of the ICRP-110 reference phantoms, which were then compared with the ICRP-116 DCs. For photons, there were significant differences by up to ~2.8 times especially at energies <0.3 MeV. For neutrons, the differences were generally small over the entire energy region (mostly <20%). The general impact of the DRF-based skeletal DCs on the effective dose calculations was negligibly small, supporting the validity of the ICRP-116 effective DCs despite their skeletal DCs derived from the simple method. Meanwhile, we believe that the DRF-based skeletal DCs could be beneficial in better estimates of skeletal doses of individuals for risk assessments.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1B
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• pp.99-106
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• 2006

Due to both global warming and constructions of seadike/seawalls, continuously or abruptly rising tendencies of extreme high water levels have been detected at Kunsan and Mokpo harbors. This paper deals firstly with the separation of each effect, namely global warming effect and construction effect, on increases of water level quantitatively by a linear regression method. And then, it can be explained why and how the extreme high water levels had been risen just after constructions at both harbors. A numerical simulation of $M_2$ tidal constituent at Mokpo coastal zone shows that the tidal amplification by constructions is mainly due to the extinguishment of TCE at Mokpogu. The tidal flat effect makes the amplification more deepen at spring tide or extreme high tide, which results in the increase of inundation risk at Mokpo harbor. A frequency analysis method is applied, which is shown to be effective at such a site of having non-homogeneous tidal data due to constructions as Mokpo harbor.