• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.5
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• pp.510-521
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• 2008

In the study, experiments are performed in the interaction region combined with wave and current to investigate the characteristics of local scour around submarine pipelines. Wave generator and current generator are used for the experiments and two current directions were used; co-direction and counter direction to the wave. The local scour depths around the pipeline are obtained according to the various pipe diameters(D), wave periods(T), wave heights(H), and current velocities(V). The experiments show that the maximum equilibrium local scour depth increases with pipe diameter, wave period, wave height, and current velocity. Using the experimental results, the correlations of scour depth and parameters such as Shields parameter($\theta$), Froude number(Fr), period parameter, Keulegan-Carpenter number(KC), Ursell number($U_R$), modified Ursell number($U_{RP}$) and ratio of velocities($U_{c}/(U_{c}+U_{m})$) are analyzed. In the interaction region combined with waves and currents, Froude number and Shields parameter are found the main parameters to cause the local scour around the submarine pipelines and this means that current governs the scour within any limits of the currents.

• Ecology and Resilient Infrastructure
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• v.6 no.4
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• pp.314-327
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• 2019

This study investigates channel stabilities with groynes by developing the assessment of it and applying a 2-dimensional numerical model, which simulates flow and sediment transport with various flows in the channel. Evaluation inventories are composed of five items, which are width to depth ratio, sinuosity, bed slopes, velocities in the flow flied, Shields number with discharges and geomorphic characteristics in the study reach. The channel stability is evaluated by applying the evaluation indicators to the channel with and without groynes in the study reach between Dalseong-weir and Gangjeonggoryeong-weir in the Nakdong river. Width to depth ratio, sinuosity, and bed slopes, which are index of river characteristics, little affect the channel stability. However, velocities in the flow flied, and Shields number, which is dimensionless tractive, near the banks of the channel strongly affect the stability. The evaluation values of the stability in the channel on the left and right banks decrease as the number of groynes increase in both the left and right banks, which means that the bank stability increases with the groynes.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.6
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• pp.405-414
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• 2010

In the study, experiments are performed in the mixing region combined wave and current to investigate the characteristics of local scour around a slender pile. Wave generator and current generator are used for the experiments and currents are co-directions with the waves. The local scour depths around the pipeline are obtained according to the various pipe diameters, wave periods, wave heights, and current velocities. The experiments show that the maximum equilibrium local scour depth increases with pipe diameter, wave period, wave height, and current velocity. Using the experimental results, the correlations of scour depth and parameters such as Shields parameter ($\theta$), Froude number (Fr), Keulegan-Carpenter number (KC), Ursell number ($U_R$), modified Ursell number ($U_{RP}$) and ratio of velocities ($U_c/U_c+U_m$) are analyzed. In the mixing region combined with waves and currents, The Froude number of single parameters is the main parameter to cause the local scour around a slender pile due to waves and current and this means that current governs the scour within any limits of the currents.

• Journal of Appropriate Technology
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• v.6 no.2
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• pp.226-237
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• 2020

As the number of reported COVID-19 cases rises around the world, regions affected by the virus are taking serious measures to contain its spread. Face shields are one of the highest-need personal protective equipment (PPE) during COVID-19 pandemic. Beyond traditional face masks, as known cases of the coronavirus soar, currently there is a significant shortage of face shields around the world. In response, the protective face shields were designed and fabricated with open-source 3D modelling software and 3D printing technology, respectively. Our face shield consisted of two parts only; a reusable 3D printed headband and a visor made of transparent plastic sheet, as barrier. The resulting 3D printed face shields are affordable, lightweight, one-size-fits-most and ready-to-wear with minimal assemblies, and go on easily over glass, goggle and face mask. To ensure being donated to the healthcare professionals without risk infected by any pathogens, the 3D printed face shields were successfully be disinfected with ultraviolet germicidal irradiation (UVGI dosage of 1000 mJ/cm²) and 70% alcohol. For routine disinfection a UVGI chamber was designed and optimized to provide uniform UV-C illumination with an appreciated fluence for complete decontamination. More than 1,000 face shields were produced already and donated to the special hospitals for COVID-19 patients, quarantines, government and medical agencies in Ethiopia as well as in East-African countries. With certainty, our intention goes beyond the hospitals and other first responders, but not limited for all those who have to stay in the service or be in contact with many other people in the time of COVID-19 pandemic.

• Journal of Ocean Engineering and Technology
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• v.15 no.3
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• pp.28-34
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• 2001

The experimental studies for the artificial reef (AFR) subsidence characteristics in the unsteady flow field and in the unsteady flow-wave field were carried out. The difference of scou $r_sidence characteristics between in the steady flow field and in the unsteady flow field wad discussed and also the long-term subsidence characteristics in the unsteady flow field were investigated. AFR subsidence characteristics was discussed with Keulegan - Carpenter number(KC), Reynolds number (Re),. Shields number (Sn) and dimensionless time (t/Tt). And the difference of subsidence characteristics between in the unsteady flow and in the unsteady flow-wave field was discussed.ed.

• Journal of Ocean Engineering and Technology
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• v.15 no.3
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• pp.29-29
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• 2001

The experimental studies for the artificial reef (AFR) subsidence characteristics in the unsteady flow field and in the unsteady flow-wave field were carried out. The difference of scour/subsidence characteristics between in the steady flow field and in the unsteady flow field wad discussed and also the long-term subsidence characteristics in the unsteady flow field were investigated. AFR subsidence characteristics was discussed with Keulegan - Carpenter number(KC), Reynolds number (Re),. Shields number (Sn) and dimensionless time (t/Tt). And the difference of subsidence characteristics between in the unsteady flow and in the unsteady flow-wave field was discussed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.6
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• pp.470-479
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• 2009

The local scour in waves can be thought of as very complex synthetic processes which is influenced by geology of bed material, bed flow in the sea and hydraulics condition. The most research until now be targeted at the scour depth and therefore the local scour width in waves has not been investigated as well. The size of wave or bottom velocity at the bed is direct cause of the local scour among lots of the scour effect factors, and the scour depth and width can be estimated through interrelationship analysis with scour area to use the dimensionless parameters including these such as Keulegan-Carpenter number, Ursell number etc. In this paper, to find out closely relation with the dimensionless parameters and scour width, performed an experiment with the variations of pipe diameters, wave heights and wave periods and then analyzed it. As the result, while Reynolds number and period parameter were seen to disperse local scour width largely, Shields number, KC number and Ursell number appeared good interrelationship. Specially, Shields number doesn't much affect the scour depth but has good relation for the scour width.

• Journal of Advanced Research in Ocean Engineering
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• v.2 no.2
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• pp.86-98
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• 2016

In this study, after the installation of a subsea pipeline, backfilling was performed in the trenched area. During these operations, a stability problem in the subsea pipeline occurred. The pipeline was directly impacted by environmental loading such as waves and currents that were caused by backfill material when scouring or sediment transport and siltation was carried out. Therefore, this study reviewed whether trenching was necessary, and conducted research into an indigenous seabed property that contains granular soil. A study of cohesive soil was also conducted in order to cross-correlate after calculating the values of the critical Shields parameter relevant to elements of the external environment such as waves and current, and the shear Shields parameter that depends on the actual shearing stress. In case of 1), sedimentation or erosion does not occur. In the case of 2), partial sedimentation or erosion occurs. If the case is 3), full sedimentation or erosion occurs. Therefore, in the cases of 1) or 2), problems in structural subsea pipeline stability will not occur even if partial sedimentation or erosion occurs. This should be reflected particularly in cases with granular and cohesive soil when a reduction in shear strength occurs by cyclic currents and waves. In addition, since backfilling material does not affect the original seabed shear strength, a set-up factor should be considered to use a reduced of the shear strength in the original seabed.

• Journal of the Korean Wood Science and Technology
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• v.49 no.2
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• pp.154-168
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• 2021

Various types of wooden relics are being unearthed following the full-scale excavation in Wolseong palace site, Gyeongju in Korea. In particular, a large number of relics were found in the moat surrounding the Wolseong Fortress. This study attempted to secure basic data on the shields of the Silla era through species identification, radiocarbon dating, and shape analysis of the two wooden shields excavated from the Wolseong moat. As a result of the radiocarbon dating, it was confirmed that the shields were made of wood procured in the period between the mid-4th century and the early 5th century. The species identification confirmed that the body of the relic was made with Pinus soft pine group and the handle with Zelkova serrata. It was also confirmed that the excavated wooden shield was made by first marking a thin line on a flat grain board, then marking double concentric circles and perforating small holes. The distance between the division lines is constant at about 6cm, and spaces between them are colored in red and black. The shape analysis estimated that two artifacts were more than 50cm and 36cm in width, respectively.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1564-1569
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• 2004

Insulating a heat from the environment is the most important in cryogenic applications like HTS cable system. Vacuum and MLI(Multi-Layer Insulation) have been widely used to get highly efficient cryogenic insulation. In this study, experiment on annular cylinder regarded as basic model of HTS cable cryostat has been performed to measure the heat loads. To investigate the effectiveness of radiation shields in cryogenic insulation system, the experiments are carried out to various number of the shields. The measured values are compared with the results estimated theoretically. The heat loads invaded from the environment was determined by liquid nitrogen boil-off calorimetry.