• Journal of the Korean Geotechnical Society
• /
• v.21 no.6
• /
• pp.67-79
• /
• 2005

The field plate load test has a good potential for determining modulus since it measures both plate pressure and settlement. Conventionally the modulus has been assumed to be a constant secant value defined from the settlement of the plate at a given load intensity. A constant modulus (modulus of subgrade reaction, k), however, may not be a representative value of subgrade soil under working load. Field strain(o. stress)-dependent modulus characteristics of subgrade soils, at relatively low to intermediate strains, are important in the pavement design. In this study, the field strain dependent moduli of subgrade soils were obtained using cyclic plate load test. Testing procedure and data reduction method are proposed. The field crosshole and laboratory resonant column tests were also performed to determine field nonlinear modulus at $0.001\%\;to\;0.1\%$ strains, and the modulus values and nonlinear trends are compared to those obtained by cyclic plate load tests. Both modulus values match relatively well when the different state of stress between two tests was considered, and the applicability of field cyclic plate load test for determining nonlinear modulus values of subgrade soils is verified.

• Journal of the Korean Geosynthetics Society
• /
• v.8 no.2
• /
• pp.47-54
• /
• 2009

The ballast track, the most common type of conventional railroad track in Korea, is deteriorated by abrasion of ballast, it's penetration into roadbed, and rugged surface of roadbed caused by cyclic loading of train. Persistent occurrence of those phenomena lead to insufficient drain capacity, one of major factors in track design, and it increases pore water pressure and decreases of shear strength under rainfall condition leading to unstable roadbed. In this study, cylindrical model tests are executed for 3 types of geotextile applying cyclic loading in order to observe the characteristics of displacement and bearing capacity of geotextile, and undrained condition has been applied for 0 day, 3 days and 7 days to each geotextiles. The results showed that there was about 1% difference at the final displacement rates between reinforced soils and nature soils and the displacement of the ground surface increases along with the degrees of the saturation. And in case that water contents exceeds the threshold, it is also apparent that weight and tensile strength of geotextile influences displacement of the ground surface. And the larger weight of geotextile is, the smaller plastic displacement. It is evaluated that non-woven fabric comes into effect on reducing the bearing capacity but, the weight of geotextile has little influence on it.

• Nuclear Engineering and Technology
• /
• v.52 no.9
• /
• pp.2107-2118
• /
• 2020

The nuclear reactor coupled with supercritical carbon dioxide (S-CO₂) Brayton cycle has good prospects in generation IV reactors. Turbomachineries (turbine and compressor) are important work equipment in circulatory system, whose performances are critical to the efficiency of the energy conversion system. However, the sharp variations of S-CO₂ thermophysical properties make turbomachinery performances more complex than that of traditional working fluids. Meanwhile, almost no systematic analysis has considered the effects of turbomachinery efficiency under different conditions. In this paper, an in-house code was developed to realize the geometric design and performance prediction of S-CO₂ turbomachinery, and was coupled with systematic code for Brayton cycle characteristics analysis. The models and methodology adopted in calculation code were validated by experimental data. The effects of recompressed fraction, pressure and temperature on S-CO₂ recompression Brayton cycle were studied based on detailed design of turbomachinery. The results demonstrate that the recompressed fraction affects the turbomachinery characteristic by changing the mass flow and effects the system performance eventually. By contrast, the turbomachinery efficiency is insensitive to variation in pressure and temperature due to almost constant mass flow. In addition, the S-CO₂ thermophysical properties and the position of minimum temperature difference are significant influential factors of cyclic performance.

• The Korean Journal of Physiology and Pharmacology
• /
• v.3 no.6
• /
• pp.587-595
• /
• 1999

This study was designed to investigate effects of calcium antagonists on endothelial and neuronal dysfunction of right coronary artery (RCA) induced by ischemia- reperfusion in anesthetized, open-chest pigs. After reperfusion, pigs were sacrificed and the RCA was rapidly dissected for in vitro experiments. Experimental groups were divided into 4 groups: control (C-RCA), ischemia-reperfusion only (I-RCA), verapamil infusion (VI-RCA) and nifedipine infusion (NI-RCA) group, respectively. The ischemia did not affect hemodynamics, mean arterial pressure, heart rate, LVdP/dtmax, and decreased RCA flow. Arterial pressure and heart rate during ischemia-reperfusion were decreased in VI-RCA and NI-RCA, and RCA flow during reperfusion was increased in NI-RCA. 5-Hydroxytryptamine (5-HT) produced concentration-dependent contractions in C-RCA. The 5-HT-induced contractions were potentiated in I-RCA and VI-RCA, but not in NI-RCA. Endothelium-dependent relaxation by calcium ionophore A23187 was inhibited in I-RCA and VI-RCA, and recovered in NI-RCA. Cyclic GMP contents were decreased in I-RCA group alone. Electrical field stimulation in C-RCA produced transient and frequency-dependent contractions and at 50 Hz caused biphasic contractions. The transient contractions were not affected by pretreatment with phentolamine and atropine, but the biphasic contraction was altered by the pretreatment. Both contractions were inhibited in I-RCA, and were partially recovered in VI-RCA and NI-RCA. Ischemia-reperfusion of RCA in pigs causes endothelial and neuronal dysfunctions, and calcium antagonists partially prevent both.

• Transactions of the Korean hydrogen and new energy society
• /
• v.19 no.1
• /
• pp.49-55
• /
• 2008

The feasibility of ionic liquid as a novel absorbent of $SO_2$ for the separation of $SO_2$ from $SO_2/O_2$ mixture in the thermochemical IS(Iodine-Sulfur) cycle was investigated. 1,3-dimethylimidazolium methylsulfate ([DMIm]$MeSO_4$) had shown twenty five times higher solubility of $SO_2$ than that of $O_2$. The dependence of $SO_2$ solubility by [DMIm]$MeSO_4$ on temperature and $SO_2$ partial pressure was examined, which confirmed the possibility of temperature and pressure swing for the separation process. Through cyclic absorption and desorption with temperature swing the stability of [DMIm]$MeSO_4$ in the separation process was also demonstrated. As a result of the experiments carried out, $SO_2$ separation from $SO_2/O_2$ mixture with ionic liquid([DMIm]$MeSO_4$) can be applied to the thermochemical IS cycle.

• Proceedings of the Ginseng society Conference
• /
• 1993.09a
• /
• pp.40-48
• /
• 1993

Intravenous administration of saponin extracted from the root of Panax ginseng lowered the blood pressure dose-dependently (10-200 mg/kg, B.W) in anesthetized rats. Therefore, experiments were designed to study the hypothesis that the lowering of blood pressure is associated with the release of endothelium-derived relaxing factor and the accumulation of guanosine 3, 5-cyclic monophosphate (cGMP). Rings of thoracic aorta with and without endothelium were suspended for the measurement of isometric tension in organ chamber and the tissue content of cGMP was measured by radioimmunoassay. All experiments were performed in the presence of $indomethacin(10^{-5}M).$ Ginseng saponin $(10^{-5}-3{\times}10^{-6}g/ml)$ relaxed contractions induced by phenylephrine $10^{-6}M)$ in the aorta with endothelium but not in that without endothelium. Treatment of aortic rings with $N^G$ monomethyl-L-arginine (L-NMMA, $10^{-4}M$ for 30 min), a competitive inhibitor of nitric oxide synthase, and methylene blue $(MB,\;3{\times}10^{-7}M$ for 30 min). an inhibitor of soluble guanylate cyclase, diminished the relaxation induced by Ginseng saponin. Ginseng saponin $10^{-4}g/ml$ for 2 min) increased the accumulation of cGMP in rings with endothelium. L-NMMA and MB inhibited the accumulation of cGMP induced by Ginseng saponin. These data suggest that vascular relaxations induced by Ginseng saponin are mediated by release of endothelium-derived relaxing factor and the accumulation of cGMP. The effect of Ginseng saponin on endothelial function in hypercholesterolemic rabbits was examined. In hypercholesterolemic rabbits fed with $2\%$ cholesterol for 8 weeks, relaxation of aortic rings to acetylcholine was impaired. The impaired relaxations of aortic rings in hypercholesterolemic rabbits were improved by dietary supplementation of Ginseng saponin, probably because of an improved release of endothelium - derived relaxing factor.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.8
• /
• pp.1575-1582
• /
• 1992

This study describes the response performances of actual engine speed, turbocharger speed, air mass flow rate through engine, boost pressure ratio, exhaust temperature and combustion efficiency for a six-cylinder four-stroke turbocharged diesel engine during the change in operating conditions by using the computer simulation with test bed. In order to obtain the transient conditions, a suddenly large load was applied to the simulation engine with the several kinds of inertia moment in turbocharger and engine, and engine set speed. From the results of this study, the following conclusions were summarized The inferior response performances was mainly caused by turbocharger lag, and air mass flow rate and boost pressure ratio were closely related to the turbocharger speed. A reduced moment of turbocharger inertia resulted in less transient speed drop and much faster recovery to the steady state of the engine. The increase of moment of engine inertia reduced cyclic variation of engine speed. When a large load was applied to the engine at high speed, the engine could be fastly recovered. However, when the same load was applied to the engine at low speed, the engine was stalled.

• Korean Chemical Engineering Research
• /
• v.43 no.6
• /
• pp.728-739
• /
• 2005

An experiment and simulation were performed for hydrogen separation of mixtures by PSA (pressure swing adsorption) process on activated carbon. The binary ($H_2/Ar$; 80％/ 20％) and ternary ($H_2/Ar/CH_4$; 60％/ 20％/ 20％) mixtures were used to study the effects of feed composition. The cyclic performances such as purity, recovery, and productivity of 2bed-6step PSA process were experimentally and theoretically compared under non-isothermal and non-adiabatic conditions. The develped process produced the hydrogen with 99％ purity and 75％ recovery from both processes. Therefore, optimal separation condition was referred multicomponent gas mixtures.

• Transactions of the Korean Society of Pressure Vessels and Piping
• /
• v.15 no.2
• /
• pp.19-30
• /
• 2019

In this study, to evaluate conservatism of various fatigue life evaluation procedures, fatigue tests were conducted using compact tension (CT) specimens with a round notch, made of A516 Gr.70 carbon steel and A240 TP304 stainless steel, under load-controlled cyclic condition. Experimental fatigue failure cycles were measured and compared with predicted fatigue lives using two different life evaluation methods; (1) Design-By-Analysis (DBA) procedure given in ASME B&PV Code, Sec. III, Div. 1, Subsec. NB-3200 and (2) structural stress-based approach provided in ASME B&PV Code, Sec. VIII, Div. 2, Part 5. To predict fatigue failure cycles, three-dimensional elastic finite element analysis was conducted. Fatigue lives were predicted by both design fatigue curve given in ASME B&PV Code, Sec. III, Div. 1, Appendices and best-fit fatigue curve suggested in NUREG/CR-6815 for the DBA procedure. Finally, fatigue lives evaluated by various methods were compared with test results, and then conservatism between each evaluation procedure was discussed.

• Corrosion Science and Technology
• /
• v.3 no.5
• /
• pp.216-221
• /
• 2004

The operating experience showed that the fatigue is one of the major piping failure mechanisms in nuclear power plants (NPPs). The pressure and/or temperature loading transients, the vibration, and the mechanical cyclic loading during the plant operation may induce the fatigue failure in the nuclear piping. Recently, many fatigue piping failure occurred at the socket weld area have been widely reported. Many failure cases showed that the gap requirement between the pipe and fitting in the socket weld was not satisfied though the ASME Code Sec. III requires 1/16 inch gap in the socket weld. The ASME Code OM also limits the vibration level of the piping system, but some failure cases showed the limitation was not satisfied during the plant operation. In this paper, the fatigue behavior of the socket weld in the nuclear piping was estimated by using the three dimensional finite element method. The results are as follows. (1) The socket weld is susceptible to the vibration if the vibration levels exceed the requirement in the ASME Code OM. (2) The effect of the pressure or temperature transient load on the socket weld in NPPs is not significant because of the very low frequency of the transient during the plant lifetime operation. (3) 'No gap' is very risky to the socket weld integrity for the specific systems having the vibration condition to exceed the requirement in the ASME OM Code and/or the transient loading condition. (4) The reduction of the weld leg size from $1.09*t_1$ to $0.75*t_1$ can affect severely on the socket weld integrity.