• Journal of Advanced Marine Engineering and Technology
• /
• v.28 no.5
• /
• pp.728-734
• /
• 2004

Environmentally friendly refrigerants with zero ozone layer depletion potential are required to be used in refrigerators and air conditioners due to the difficulties related to ozone layer depletion and global warming. A rigorous study for the system performance with new refrigerants having zero ozone layer depletion potential is inevitable before adopting that as a new fluid. The HFC(Hydrofluorocarbon) potential has been recommended as alternatives. In this paper. system performance in the heat pump facilities were studied using R-290, R-600a. R-1270 as an environment friendly refrigerant. R-22 as a HCFC's refrigerant. The experimental apparatus has been set-up as a conventional vapor compression type heat Pump system. The test section is a horizontal double pipe heat exchanger. A tube diameter of 12.70mm with 1.315mm wall thickness is used for this investigation. The test results showed that the COP of hydrocarbon refrigerants were superior to that of R-22 and the maximum increasing rate of COP was found in R-1270. The refrigeration capacity of hydrocarbon refrigerants were higher than that of R-22. The compressor work was obtained with the maximum value in R-1270 and the minimum one in R-22.

• Structural Engineering and Mechanics
• /
• v.58 no.5
• /
• pp.799-823
• /
• 2016

A finite element model for the non-linear dynamic analysis of a reinforced concrete (RC) containment shell of a nuclear power plant subjected to extreme loads such as impact and earthquake is presented in this work. The impact is modeled by using an uncoupled approach in which a load function is applied at the impact zone. The earthquake load is modeled by prescribing ground accelerations at the base of the structure. The nuclear containment is discretized spatially by using 20-node brick finite elements. The concrete in compression is modeled by using a modified $Dr{\ddot{u}}cker$-Prager elasto-plastic constitutive law where strain rate effects are considered. Cracking of concrete is modeled by using a smeared cracking approach where the tension-stiffening effect is included via a strain-softening rule. A model based on fracture mechanics, using the concept of constant fracture energy release, is used to relate the strain softening effect to the element size in order to guaranty mesh independency in the numerical prediction. The reinforcing bars are represented by incorporated membrane elements with a von Mises elasto-plastic law. Two benchmarks are used to verify the numerical implementation of the present model. Results are presented graphically in terms of displacement histories and cracking patterns. Finally, the influence of the shear transfer model used for cracked concrete as well as the effect due to a base slab incorporation in the numerical modeling are analyzed.

• Journal of Electrochemical Science and Technology
• /
• v.12 no.4
• /
• pp.440-452
• /
• 2021

Enhancement of durability and reduction of maintenance cost of concrete, with the implementation of various approaches, has always been a matter of concern to researchers. The integration of pozzolans as a substitute for cement into the concrete is one of the most desirable technique. Silica fume (SF) and colloidal nanosilica (CS) have received a great deal of interest from researchers with their significant performance in improving the durability of concrete. The synergistic role of the micro and nano-silica particles in improving the main characteristics of cemented materials needs to be investigated. This work aims to examine the utility of partial substitution of cement by SF and CS in binary and ternary blends in the improvement of the durability characteristics linked to resistance for electrochemical corrosion using electrical resistivity and half-cell potential analysis and chloride penetration trough rapid chloride penetration test. Furthermore, the effects of this silica mixture on the compressive strength of concrete under normal and aggressive environment have also been investigated. Based on the maximum compression strength of the concrete, the optimal cement substituent ratios have been obtained as 12% SF and 1.5% CS for binary blends. The optimal CS and SF combination mixing ratios has been obtained as 1.0% and 12% respectively for ternary blends. The ternary blends with substitution of cement by optimal percentage of CS and SF exhibited decreased rate for electrochemical corrosion. The strength and durability studies were found in consistence with the microstructural analysis signifying the beneficiary role of CS and SF in upgrading the performance of concrete.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.10 no.7
• /
• pp.1237-1245
• /
• 2006

This paper presented a hardware implementation of ARIA, which is a Korean standard l28-bit block cryptography algorithm. In this work, ARIA was designed technology-independently for application such as ASIC or core-based designs. ARIA algorithm was fitted in FPGA without additional components of hardware or software. It was confirmed that the rate of resource usage is about 19% in Altera EPXAl0F1020CI and the resulting design operates stably in a clock frequency of 36.35MHz, whose encryption/decryption rate was 310.3Mbps. Consequently, the proposed hardware implementation of ARIA is expected to have a lot of application fields which need high speed process such as electronic commerce, mobile communication, network security and the fields requiring lots of data storing where many users need processing large amount of data simultaneously.

• Korean Journal of Materials Research
• /
• v.20 no.11
• /
• pp.559-569
• /
• 2010

The liquid-phase sintering method was used to prepare a glass lens forming core composed of SiC-$Al_2O_3-Y_2O_3$. Spark plasma sintering was used to obtain dense sintered bodies. The sintering characteristics of different SiC sources and compositions of additives were studied. Results revealed that, owing to its initial larger surface area, $\alpha$-SiC offers sinterability that is superior to that of $\beta$-SiC. A maximum density of $3.32\;g/cm^3$ (theoretical density [TD] of 99.7%) was obtained in $\alpha$-SiC-10 wt% ($6Al_2O_3-4Y_2O_3$) sintered at $1850^{\circ}C$ without high-energy ball milling. The maximum hardness and compression stress of the sintered body reached 2870 Hv and 1110 MPa, respectively. The optimum ultra-precision machining parameters were a grinding speed of 1243 m/min, work spindle rotation rate of 100 rpm, feed rate of 0.5 mm/min, and depth of cut of $0.2\;{\mu}m$. The surface roughnesses of the thus prepared final products were Ra = 4.3 nm and Rt = 55.3 nm for the aspheric lens forming core and Ra = 4.4 nm and Rt = 41.9 for the spherical lens forming core. These values were found to be sufficiently low, and the cores showed good compatibility between SiC and the diamond-like carbon (DLC) coating material. Thus, these glass lens forming cores have great potential for application in the lens industry.

• Applied Chemistry for Engineering
• /
• v.10 no.2
• /
• pp.201-205
• /
• 1999

Hydroxypropylmethylcelluloses (HPMC) are cellulose ethers which may be used as the basis for hydrophilic matrices for controlled release oral delivery and offer the advantages of being non-toxic and relatively inexpensive. In this work, we designed new drug release system using HPMC as matrix, manufactured by direct compression technology and have investigated the effects of the controlling factors on drug release from a swellable hydrophillic delivery system. It was found that the release rate of the drug decreased with increasing the polymer molecular weight and the polymer content in tablets, and was independent of compaction pressure and pH of dissolution fluids. Especially, the ability of the anionic surfactant, sodium laurylsulfate, to retard the release of pseudoephedrine hydrochloride from HPMC was characterised. With increasing the concentration of the sodium laurylsulfate within the matrix, drug release rate decreased. It is believed that, provided the pseudoephedrine hydrochloride and the sodium laurylsulfate are oppositely charged, they will bind together in situ within the HPMC matrix, leading to reduced drug release rates.

• Journal of ILASS-Korea
• /
• v.16 no.3
• /
• pp.119-125
• /
• 2011

Due to the oxygen contents in biodiesel, application of the fuel to compression ignition engines has significant advantages in terms of lowering PM formation in the combustion chamber. In recent days, considerable studies have been performed to extend the low temperature combustion regime in diesel engines by applying biodiesel fuel. In this work, low temperature combustion characteristics of biodiesel blends in dilution controlled regime were investigated at a fixed engine operating condition in a single cylinder diesel engine, and the comparisons of engine performances and emission characteristics between biodiesel and conventional diesel fuel were carried out. Results show that low temperature combustion can be achieved at $O_2$ concentration of around 7~8% for both biodiesel and diesel fuels. Especially, by use of biodiesel, noticeable reduction (maximum 50% of smoke was observed at low and middle loads compared to conventional diesel fuel. In addition, THC(total hydrocarbon) and CO(Carbon monoxide) emissions decreased by substantial amounts for biodiesel fuel. Results also indicate that even though about 10% loss of engine power as well as 14% increase of fuel consumption rate was observed due to lower LHV(lower heating value) of biodiesel, thermal efficiencies for biodiesel fuel were slightly elevated because of power recovery phenomenon.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.8 no.9
• /
• pp.1325-1332
• /
• 2013

The first frame of a GOP, an I frame, is encoded in intra mode which generates a larger number of bits. In addition, the I frame is used for the inter mode encoding of the following frames. Thus the intial QP for the I frame affects the first frame as well as the following frames. In our previous work, we analyzed the number of bits for an I frame and showed that the ratio of the number of bits which maximizes the PSNR of a GOP maintains similar value regardless of GOP's. In this paper, we propose a R-Q model which can be used for the calculation of the initial QP given the amount of bits for an I frame. The proposed model is simple and adaptively modifies model parameters, so it can be applicable to the real-time application. It is shown by experimental results that the proposed model captures initial QP characteristics effectively and the proposed method for model parameters accurately estimates the real values.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.24 no.2
• /
• pp.211-218
• /
• 2021

This paper deals with the computational work to characterize the formation and pinching of a plasma in an X-pinch configuration. A resistive magnetohydrodynamic model of a single fluid and two temperature is adopted assuming a hollow conical structure in the (r,z) domain. The model includes the thermodynamic parameter of tungsten from the corrected Thomas-Fermi EOS(equation of state), determining the average ionization charge, pressure, and internal energy. The transport coefficients, resistivity and thermal conductivity, are obtained by the corrected Lee & More model and a simple radiation loss rate by recombination process is considered in the simulation. The simulation demonstrated the formation of a core-corona plasma and intense compression process near the central region which agrees with the experimental observation in the X-pinch device at Seoul National University. In addition, it confirmed the increase in radiation loss rate with the density and temperature of the core plasma.

• Analytical Science and Technology
• /
• v.9 no.2
• /
• pp.179-191
• /
• 1996

In order to understand the high temperature deformation behavior of superalloy 718, a rotating grade 718 alloy has been compression tested to about 0.7 upset ratio at $927{\sim}1066^{\circ}C$ temperature range and $5{\times}10^{-4}{\sim}5{\times}10^0sec^{-1}$ strain rate. The maximum flow stress was increased with increasing strain rate, and similar behavior was observed with decreasing temperature. At low temperature and high strain rates other than $5{\times}10^{-1}sec^{-1}$, strain softening was occurred mainly by dynamic recovery and deformation twinning processes, while at high temperature and low strain rates strain softening was offseted by dynamic recrystallization. At $5{\times}10^{-1}sec^{-1}$, strain hardening was occurred due to work hardening of the dynamic recrystallized grains. Strain rate sensitivity, m, was varied with strain rates. In the case of lower strain rate tests, m was measured as 0.3 and it was observed that the deformation was mainly controlled by dynamic recrystallization. At higher strain rate, m was lowered to 0.1 and the deformation was controlled by the dynamic recovery and the deformation twinning processes.