• Proceedings of the KSME Conference
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• 2000.11a
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• pp.504-509
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• 2000

In this study, a transfemoral prosthesis system of which stance phase and swing phase are controlled during walking has been developed for the recovery of the biomechanical function of the amputated leg. It consists of a 5 bar link mechanism, a hydraulic-rubber knee damper for stance phase control and a pneumatic cylinder controlled via a microprocessor for stance phase control. The mechanical characteristics and behaviour of the knee damper which absorbs the impact energy generated at the heel contact was investigated. The characteristics of the pneumatic cylinder essential for the speed adaptation of the prosthesis during swing phase was also studied for its mechanical characteristics. The prosthesis was subject to the clinical test ant the gait characteristics obtained were very close to those of normal. The stance and swing controlled prosthesis that were developed in this study showed good stability during the stance phase and showed good controllability during the swing phase.

• Journal of Korea Foundry Society
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• v.4 no.2
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• pp.96-101
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• 1984

The morphologies of eutectic cell formed during solidification affect on the mechanical properties in high Cr cast iron. In order to investigate the influence of Si on the structure, five kinds of specimen containing 16.42% Cr with varying amount of Si (0.51%, 1.17%, 2.22%, 2.71%, 3.56%) were poured into shell mould preheated $330^{\circ}C$ at $1510^{\circ}C$. The effect of Si on matrix in hypo-eutctic Cr cast iron (2.48% C, 16.42%) were studied through its mechanical tests and observation of microstructure using of metallurgical microscope, EPMA, SEM and Image analyzer systematically. The results obtained from the above studies are as follows: 1. Because of ${\Delta}T$ decreasing with increasing Si content, the morpologies of colony change into uniform bar-type carbide from plate-type ones, moreover eutectic colony size (Ew) becomes narrow and spacing of carbide wider. 2. As Si content increases, the amount of carbides also increases and most of Cr were dissolved in carbides while Si in matrix. 3. The hardness, tensile strength and wear resistance were increasing while impact value decreased with increasing Si content. 4. In fracture section, small amount of dimple pattern was observed in less than 1.17% Si but more than 2.22% Si river pattern was presented.

• The Journal of Korean Physical Therapy
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• v.30 no.6
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• pp.218-223
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• 2018

Purpose: The purpose of this study was to evaluate the impact of active vibration exercise on the neck pain, disability index, and muscle activity of patients with forward head posture. Methods: A total of 24 patients were randomly assigned to an experimental group or a control group (n=12 each). The experimental group performed active vibration exercise using a flexi-bar for 20 minutes a day, five times a week for four weeks. The study measured patient neck pain using a visual analog scale, neck pain related disability using the neck disability index, and muscle activity using electromyography. Results: The intragroup comparison showed significant differences in the visual analog scale score, neck disability index score and upper trapezius, lower trapezius and serratus anterior muscle activity values among patients in the experimental group. The intergroup comparison showed that differences in the visual analog scale score, neck disability index score and upper trapezius, lower trapezius and serratus anterior muscle activity values in the control group. Conclusion: This study showed that active vibration exercise was effective in improving the neck pain, disability index, and muscle activity of patients with forward head posture.

• Nuclear Engineering and Technology
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• v.54 no.7
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• pp.2386-2394
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• 2022

In this paper, smooth and notched bar tensile tests of austenitic stainless steel 304 are performed, covering four different multi-axial stress states and six different strain rate conditions, to investigate the effect of the stress triaxiality and strain rate on fracture strain. Test data show that the measured true fracture strain tends to decrease with increasing stress triaxiality and strain rate. The test data are then quantified using the Johnson-Cook (J-C) fracture strain model incorporating combined effects of the stress triaxiality and strain rate. The determined J-C model can predict true fracture strain overall conservatively with the difference less than 20%. The conservatism in the strain-based acceptance criteria in ASME B&PV Code, Section III, Appendix FF is also discussed.

• Journal of Ocean Engineering and Technology
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• v.36 no.4
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• pp.251-269
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• 2022

The process-based XBeach model has numerous empirical parameters because of insufficient understanding of hydrodynamics and sediment transport on the nearshore; hence, it is necessary to calibrate parameters to apply to various study areas and wave conditions. Therefore, the calibration process of parameters is essential for the improvement of model performance. Generally, the trial-and-error method is widely used; however, this method is passive and limited to various and comprehensive parameter ranges. In this study, the Generalized Likelihood Uncertainty Estimation (GLUE) method was used to estimate the optimal range of three parameters (gamma, facua, and gamma2) using morphological field data collected in Maengbang beach during the four typhoons that struck from September to October 2019. The model performance and optimal range of empirical parameters were evaluated using Brier Skill Score (BSS) along with the baseline profiles, sensitivity, and likelihood density analysis of BSS in the GLUE tools. Accordingly, the optimal parameter combinations were derived when facua was less than 0.15 and simulated well the shifting shape, from crescentic sand bar to alongshore uniform sand bars in the surf zone of Maengbang beach after storm impact. However, the erosion and accretion patterns nearby in the surf zone and shoreline remain challenges in the XBeach model.

• Structural Engineering and Mechanics
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• v.88 no.6
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• pp.599-608
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• 2023

The present study is focused on instigation of the nonlinear mechanical behavior of reinforced concrete beams considering different types of FRP bars through nonlinear finite element simulations. To explore the impact of the FRP reinforcement type and geometry on the nonlinear mechanical behavior of reinforced beam, intensive parametric studies are carried out and discussed. Twenty models were carried out based on the finite element software (ABAQUS). The concrete damage plasticity model was considered. Four types of fiber polymer bars, CFRP, GFRP, AFRP and BFRP as longitudinal reinforcement for concrete beam were used. The validation of numerical results was confirmed by experimental as well as numerical results, then the parametric study was conducted to evaluate the effect of change in different parameters, such as bar diameter size, type of FRP bars and shear span length. All results were analyzed and discussed through, load-deflection diagram. The results showed that the use of FRP bars in rebar concrete beam improves the beam stiffness and enhance the ultimate load capacity. The load capacity enhanced in the range of (20.44-244.47%) when using different types of FRP bars. The load-carrying capacity of beams reinforced with CFRP is the highest one, beams reinforced with AFRP is higher than that reinforced with BFRP but beams reinforced with GFRP recorded the lowest load of capacity compered with other beams reinforced with FRP Bars.

• Nuclear Engineering and Technology
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• v.55 no.12
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• pp.4431-4446
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• 2023

A Multiphysics coupling framework, MPCORE, has been developed to analyze safety parameters using the best estimate codes. The framework contains neutron kinetics (NK), thermal hydraulics (TH), and fuel performance (FP) codes to analyze fuel burnup, radial power distribution, and coolant temperature (T_bc). Shuffling and rotation capabilities have been verified on the Watts Bar reactor for three cycles. This study focuses on two coupling approaches for TH and FP modules. The one-way coupling approach involves coupling the FP code with the NK code, providing no data to the TH modules but getting T_bc as boundary condition from TH module. The two-way coupling approach exchanges information from FP to TH modules, so that the simplified heat conduction solver of the TH module is not used. The power profile in both approaches does not differ significantly, but there is an impact on coolant and cladding parameters. The one-way coupling approach tends to over-predict the cladding hydrogen concentration (CHC). This research highlights the difference between one-way and two-way coupling on critical boron concentration, T_bc, CHC, oxide surface temperature, and pellet centerline temperature. Overall, MPCORE framework with two-way coupling provides a more accurate and reliable analysis of safety parameters for nuclear reactors.

• Journal of Environmental Impact Assessment
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• v.24 no.3
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• pp.287-299
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• 2015

If the Nakdong River estuary is to be sustainable, land use management practices need to consider bird habitat requirements, especially given that the area serves as an important migratory bird sanctuary. In this study, bird habitats found in the Nakdong River estuary were classified into 11 different types including Phragmites australiss, mud flat, farmland, open surface in freshwater, sand bar, riparian forest, Scirpus planiculmis, waterway, construction, grasslands, and open surface in sea or brackish water. Taking into consideration the regional characteristics, habitat properties, and landscape indices, a total of 12 study sites were analyzed. Mud flat, construction, farmland, and P. australis account for 80% of the total land area. The high area ratio of construction and farmland to other types of habitat revealed a high amount of historical human activity and intervention in the area. Both patch numbers as well as patch density were high in West Nakdong River, Samrak Waterfront, Maekdo River, and Daejeo Floodgate, with these areas showing the greatest fragmentation as well. Total numbers of species and individuals had a positive correlation with the area and the number of habitat types. Findings suggest that protecting the habitat area, especially in S. planiculmis, is the most important factor for bird habitat management and that future development could result in habitat loss, having a profoundly adverse impact on bird populations. Therefore, it is important that the total area should be carefully protected by land use regulations in order to ensure that the Nakdong River estuary maintains its functional integrity as a migratory bird sanctuary.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.47-56
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• 2009

Rock bolts and shotcrete play a crucial role as a main support system in the underground space. Thus, the safety of the underground space may be affected by the defect of rock bolts. In order to evaluate the rock bolt integrity by using non-destructive technique, the transmission method of the guided ultrasonic waves, which are generated by using the piezo disk elements has been successfully performed. The energy generated by the piezo disk elements, however, is not enough for the rock bolts in the field. In addition, the piezo disk elements should be installed at the end of the steel bar during construction of the rock bolts. The purpose of this study is the devolvement of the reflection method, which may generate enough energy, and the application in the field rock bolts. Both laboratory and field tests are carried out. The guided ultrasonic waves with high energy are generated by the hammer impact with the center punch, and the AE sensor is used to measure the reflected guided waves. The received guided waves are analyzed by the wavelet transform. The peak value of the wavelet transform produces the energy velocity, which is used for the evaluation of the rock bolt integrity. The energy velocity increases with an increase in the defect ratio in both laboratory and field rock bolts. This study demonstrates that the hammer-impact reflection method may be a suitable method for the evaluation of the rock bolt in the field.

• Journal of the Korean Institute of Gas
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• v.16 no.6
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• pp.87-101
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• 2012

In gas industries, the potential risks of serious accidents have been increased due to high technology application and process complexities. Especially, in case of gas-related accidents, the extent of demage is out of control since gas plants handle and produce combustible, flammable, explosive and toxic materials in large amounts. The characteristics of this kind of disaster is that accident frequency is low, while the impact of damage is high, extending to the neighboring residents, environment and related industries as well as employees involved. The hydrogen gases treated important things and it used the basic material of chemical plants and industries. Since 2000, this gas stood in the spotlight the substitution energy for reduction of the global warming in particular however it need to compress high pressure(more than 150 bar.g) and store by using the special cylinders due to their low molecular weight. And this gas led to many times the fire and explosion due to leak of it. To reduce these kinds of risks and accidents, it is necessary to improve the new safety management system through a risk management after technically evaluating potential hazards in this process. This study is to carry out the quantitative risk assesment for hydrogen filling plant which are very dangerous(fire and explosive) and using a basic materials of general industries. As a results of this risk assessment, identified the elements important for safety(EIS) and suggested the practical management tools and verified the reliability of this risk assessment model through case study of accident.