• Nuclear Engineering and Technology
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• v.49 no.4
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• pp.855-864
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• 2017

The control rod assembly controls reactor power by adjusting its position during normal operation and shuts down chain reactions by its free drop under scram conditions. Therefore, the drop performance of the control rod assembly is important for the safety of a nuclear reactor. In this study, the drop performance of the conceptually designed control rod assembly for the prototype generation IV sodium-cooled fast reactor that is being developed at the Korea Atomic Energy Research Institute as a next-generation nuclear reactor was experimentally investigated. For the performance test, the test facility and test procedure were established first, and several free drop performance tests of the control rod assembly under different flow rate conditions were then carried out. Moreover, performance tests under several types and magnitudes of seismic loading conditions were also conducted to investigate the effects of seismic loading on the drop performance of the control rod assembly. The drop time of the conceptually designed control rod assembly for 0% of the tentatively designed flow rate was measured to be 1.527 seconds, and this agrees well with the analytically calculated drop time. It was also observed that the effect of seismic loading on the drop time was not significant.

• Korean Journal of Metals and Materials
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• v.48 no.6
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• pp.477-488
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• 2010

Zr-based amorphous alloy matrix composites reinforced with stainless steel (STS) and tantalum continuous fibers were fabricated without pores or defects by a liquid pressing process, and their quasi-static and dynamic deformation behaviors were investigated by using a universal testing machine and a Split Hopkinson pressure bar, respectively. The quasi-static compressive test results indicated that the fiberreinforced composites showed amaximum strength of about 1050~1300 MPa, and its strength maintained over 700 MPa until reaching astrain of 40%. Under dynamic loading, the maximum stresses of the composites were considerably higher than those under quasi-static loading because of the strain-rate hardening effect, whereas the fracture strains were considerably lower than those under quasi-static loading because of the decreased resistance to fracture. The STS-fiber-reinforced composite showed a greater compressive strength and ductility under dynamic loading than the tantalum-fiber-reinforced composite because of the excellent resistance to fracture of STS fibers.

• Korean Journal of Applied Biomechanics
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• v.26 no.2
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• pp.143-151
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• 2016

Objective: The purpose of this study was to investigate the effect of fatigue induction on ground reaction force (GRF) components, postural stability, and vertical jump performance in Taekwondo athletes. Method: Ten Taekwondo athletes (5 men, 5 women; mean age, $22.30{\pm}2.62years$; mean height, $174.21{\pm}9.20cm$; mean body weight, $67.28{\pm}12.56kg$) participated in this study. Fatigue was induced by a short period of strenuous exercise performed on a motorized treadmill. The analyzed variables included vertical jump performance, static stability (mediolateral [ML], center of pressure [COP], anteroposterior [AP] COP, ${\Delta}COPx$, ${\Delta}COPy$, and COP area), postural stability index values (ML stability index [MLSI], AP stability index [APSI], vertical stability index [VSI], dynamic postural stability index [DPSI]), and GRF components (ML force, AP force, peak vertical force [PVF], and loading rate). To analyze the variables measured in this study, PASW version 22.0 was used to calculate the mean and standard deviation, while a paired t-test was used to evaluate the pre- versus post-fatigue results. Pearson's correlation coefficients among variables were also analyzed. The statistical significance level was set at ${\alpha}$ = .05. Results: Vertical jump performance decreased significantly after the induction of fatigue, while AP COP, ${\Delta}COPx$, COP area, APSI, VSI, and DPSI increased significantly. PVF and loading rate increased significantly after the induction of fatigue, while the postural stability variables (AP COP, ${\Delta}COPy$, COP area, APSI, VSI, DPSI) were similarly correlated with GRF components (PVF, loading rate) after fatigue was achieved (r = .600, $R^2$ = 37%). Conclusion: These results suggest that the induction of fatigue can decrease postural stability and exercise performance of Taekwondo athletes during training and competition sessions.

• Journal of Biosystems Engineering
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• v.15 no.3
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• pp.207-218
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• 1990

Grains display characteristics of both elastic bodies and viscous fluids when they are subjected to mechanical treatments in harvesting, handling, and processing. This viscoelastic behavior of grains when mechanically stressed must be fully understood to establish maximum machine efficiency and have a minimum degree of grain damage and the highest quality of the final product. The studies were conducted to examine the effect of the moisture content, the loading rate and the initial deformation on the stress relaxation behavior of whole kernel of rough rice, and develop the rheological model to represent its stress relaxation behavior. The following results were obtained from the study. 1. Moisture content had the greatest influence on the initial portion of the relaxation curve. With elapsing time the lower moisture content resulted in the lower residual stress for the Japonica-type rough rice and vice versa for the Indica-type rough rice. But within the ranges of moisture content tested, the degree of stress relaxation per unit strain on the Indica-type rough rice was a little higher than those on the Japonica-type rough rice. 2. The slower loading rate resulted in less initial stress. The decreasing trend of residual stress for all the samples tested with increasing loading rate was shown. 3. The higher initial deformation for all the samples resulted in less initial stress. The increasing of amount of stress relaxation per unit strain with increase of initial stress indicated that viscoelastic properties of rough rice depended not only upon duration of load applied but also initial stress applied. This means that rough rice is nonlinear viscoelastic material. 4. The compression stress relaxation properties of rough rice kernel can be described by a generalized Maxwell model representing by the Maxwell elements.

• Magazine of the Korean Society of Agricultural Engineers
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• v.39 no.5
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• pp.97-108
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• 1997

Natural wastewater treatment systems using the constructed wetland system were evaluated for the wastewater from the industrial complex in rural areas. For the treatment of wastewater from the industrial complex in rural area, a pilot plant of the constructed wetland system was installed at Baeksuk agri-industrial complex in ChunahnCity, Chunchungnam-Do. The experiment with this pilot plants was performed for 1996 and 1997. Results of the study were summarized as follows. For the BOD and COD, when the pollutant loading of them was about 1 3.8g/$m^2$. day (the concentration was l24.0mg/${\ell}$) arid 24.4g/$m^2$.day(the concentration was 220.Omg/${\ell}$), the removal rate of them was high, 90.2% and 93.4%, respectively. For the SS, the effluent concentration was consistently lower than the water quality standard even though the influent concentration varied significantly, which showed that SS was removed by the system effectively which consist of soil and plants. For the T-N and T-P, when the influent pollutant loading of them were moderately high, 2.8g/$m^2$.day to 7.4g/$m^2$. day(concentration 25.0mg/${\ell}$ to 49.7mg/${\ell}$) for T-N and 1.0g/$m^2$.day to 2.6g /$m^2$.day(concentration 8.6mg/${\ell}$ to 14.7mg/${\ell}$) for T-P, the removal rate of them were 86.5% and 94.0%, respectively. The removal rate by the flow distance increased rapidly in the first 4m from the inlet zone, and gradually there after. The width of system was 2m. Overall, the result showed that constructed wetland system is a feasible alternative for the treatment of wastewater from industrial complex in rural areas. Compared to existing systems, this system is quite competitive because it requires low capital cost, almost no energy and maintenance, and therefore, very cost effective.

• Journal of Periodontal and Implant Science
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• v.52 no.6
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• pp.496-508
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• 2022

Purpose: This study aimed to compare the long-term survival rate and peri-implant marginal bone loss between different types of dental implant-abutment connections. Methods: Implants with external or internal abutment connections, which were fitted at Gangneung-Wonju National University Dental Hospital from November 2011 to December 2015 and followed up for >5 years, were retrospectively investigated. Cumulative survival rates were evaluated for >5 years, and peri-implant marginal bone loss was evaluated at 1- and 5-year follow-up examinations after functional loading. Results: The 8-year cumulative survival rates were 93.3% and 90.7% in the external and internal connection types, respectively (P=0.353). The mean values of marginal bone loss were 1.23 mm (external) and 0.72 mm (internal) (P<0.001) after 1 year of loading, and 1.20 mm and 1.00 mm for external and internal abutment connections, respectively (P=0.137) after 5 years. Implant length (longer, P=0.018), smoking status (heavy, P=0.001), and prosthetic type (bridge, P=0.004) were associated with significantly greater marginal bone loss, and the use of screw-cement-retained prosthesis was significantly associated (P=0.027) with less marginal bone loss. Conclusions: There was no significant difference in the cumulative survival rate between implants with external and internal abutment connections. After 1 year of loading, marginal bone loss was greater around the implants with an external abutment connection. However, no significant difference between the external and internal connection groups was found after 5 years. Both types of abutment connections are viable treatment options for the reconstruction of partially edentulous ridges.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.05a
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• pp.214-215
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• 2017

Extreme loads such as impact and explosion have higher strain rate than static loading condition. Therefore, it is necessary to evaluate mechanical properties at high strain rate in order to apply fiber reinforced cement composites to ensure safety performance against impact and explosion. In this study, the compressive properties of fiber reinforced cement composites by strain rate were evaluated.

• Korean Journal of Applied Biomechanics
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• v.18 no.1
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• pp.235-243
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• 2008

The purpose of this study is to find out the effect of Growth Hormone promotin and kinetic factors on Growth Hormone Activated Shoes. The results of the present study were as follows; First, there was a significient difference between a normal shoes and the Growth Hormone activated shoes in the student's GH secretion with running test, and there was a significant interaction effect between shoes and distance. therefore it can be assumed that there is a significant effect of GH secretion in student at growth period during running with Growth Hormine Activated Shoes. Second, Within 4km walking, Growth Hormone secretion was in creased averagely in student. Third, Growth Hormone Activated Shoes make a large load for light motion as walking. For heavy motion as running, it make a large impulsion but good pressure distribution and small loading rate.

• Korean Journal of Applied Biomechanics
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• v.15 no.3
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• pp.1-7
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• 2005

Excessive pronation and impact force during running are related to various running injuries. To prevent these injuries, three type of running shoes are used, such as cushioning, stability, and motion control. Although there were may studies about the effect of midsole hardness on impact force, no study to investigate biomechanical effect of motion control running shoes. The purpose of this study was to determine biomechanical difference between cushioning and motion control shoes during treadmill running. Specifically, plantar and rearfoot motion, impact force and loading rate, and insole pressure distribution were quantified and compared. Twenty male healthy runners experienced at treadmill running participated in this study. When they ran on treadmill at 3.83 m/s. Kinematic data were collected using a Motion Analysis eight video camera system at 240 Hz. Impact force and pressure distribution data under the heel of right foot were collected with a Pedar pressure insole system with 26 sensors at 360 Hz. Mean value of ten consecutive steps was calculated for kinematics and kinetics. A dependent paired t-test was used to compare the running shoes effect (p=0.05). For most kinematics, motion control running shoes reduced the range of rearfoot motion compared to cushioning shoes. Runners wearing motion control shoe showed less eversion angle during standing less inversion angle at heel strike, and slower eversion velocity. For kinetics, cushioning shoes has the effect to reduce impact on foot obviously. Runners wearing cushioning shoes showed less impact force and loading rate, and less peak insole pressure. For both shoes, there was greater load on the medial part of heel compared to lateral part. For pressure distribution, runners with cushioning shoes showed lower, especially on the medial heel.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.4
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• pp.571-580
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• 2015

In this paper, a computational study was conducted in order to investigate the rotor blade sweep effect on the aerodynamics of a small axial supersonic impulse turbine stage. For this purpose, three-dimensional unsteady RANS simulations have been performed with three different rotor blade sweep angles ($-15^{\circ}$, $0^{\circ}$, $+15^{\circ}$) and the results were compared with each other. Both NTG (No tip gap) and WTG (With tip gap) models were applied to examine the effect on tip leakage flow. As a result of the simulation, the positive sweep model ($+15^{\circ}$) showed better performance in relative flow angle, Mach number distribution, entropy rise, and tip leakage mass flow rate compared with no sweep model. With the blade static pressure distribution result, the positive sweep model showed that hub and tip loading was increased and midspan loading was reduced compared with no sweep model while the negative sweep model ($-15^{\circ}$) showed the opposite result. The positive sweep model also showed a good aerodynamic performance around the hub region compared with other models. Overall, the positive sweep angle enhanced the turbine efficiency.