• Journal of the Korean Chemical Society
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• v.23 no.4
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• pp.206-209
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• 1979

Empirical force-field calculations have been applied to eight 1,6-anhydropyra-noses, the crystal structures$^{13{\sim}21}$ of which have been studied by single crystal X-ray or neutron diffraction analysis. The theoretical calculations reproduce closely the variations in conformation between $^1C_4$ and $E_0$, which are observed in the pyranose rings. The smaller conformational differences in the five-membered anhydro ring are not so well predicted. The calculated C-C bond lengths agree with those observed within 0.012${\AA}$ with one exception. The C-O bond lengths show a larger deviation, 0.027${\AA}$. The non-hydrogen atom valence angles agree within 1.9$^{\circ}$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.8 s.179
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• pp.2074-2082
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• 2000

In this study, to investigate and to predict the crack growth behavior under variable amplitude loading, crack growth tests are conducted on 7075-T6 aluminum alloy. The loading wave forms are generated by normal random number generator. All wave forms have same average and RMS(root mean square) value, but different standard deviation, which is to vary the maximum load in each wave. The modified Forman's equation is used as crack growth equation. Using the retardation coefficient D defined in previous study, the load interaction effect is considered. The variability in crack growth process is described by the random variable Z which was obtained from crack growth tests under constant amplitude loading in previous work. From these, a statistical model is developed. The curves predicted by the proposed model well describe the crack growth behavior under variable amplitude loading and agree with experimental data. In addition, this model well predicts the variability in crack growth process under variable amplitude loading.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.804-809
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• 2009

The present study measured frost pattern on a cylinder to propose empirical correlation equations for the local and average frost thickness, frost density and frost mass. The key parameters were diameter of the cylinders (7mm, 20mm), cooling surface temperature of the circular tube, absolute humidity of air, air temperature and air velocity. A 50% ethylene glycol aqueous solution was applied as a coolant. The frost thicknesses at both front and rear were larger than those at the other parts, while they were increased as diameter of the cylinder was increased. The local frost thicknesses at high air velocity were more uniform than those at low air velocity. The values predicted by Kim et al. under the freezer condition showed larger by the maximum of $30{\sim}50%$ than the measured data under heat pump condition. The empirical correlations for the local and average frost thickness and frost mass were proposed. The correlation equations for the frost thickness and frost mass under the heat pump condition in the present study might predict more accurate than the other correlation equations. The proposed correlations might be applied for the freezer condition within the maximum 15% deviation from the previous correlations under freezer condition.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.11
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• pp.1171-1177
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• 2013

In this study, the torque transmitting capability of a flexible disk coupling was investigated. Flexible disc coupling is used to transmit power between two axes, and there exist mis-alignments such as angle of deviation and end play between two shafts. A disk is an important part in the flexible disk coupling because the disk has to transmit power between two mis-aligned shafts. To investigate the effect of mis-alignment on load carrying capacity, finite element analyses were carried out. Analyses were carried out for two types of disk; i.e., circular and square disks. The rotational and bending stiffness of disk plates was predicted to investigate the effect of mis-alignment on stress. As a result, it was shown that the mis-alignment can cause severe decrease in load-carrying capacity. And, the square disk showed better performance than the circular disk.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.17 no.1
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• pp.19-28
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• 1981

Accuracy of the position fix obtained by navigation with Omega in the capacity of worldwide navigation depends on the predicted propagation correction. The authors observe continuously the phase differences of the A-C pair and the A-E pair from April 17 to October 14, 1980, at Busan(35\ulcorner07'. 9N, 129\ulcorner06'. 3E), and analyze the characteristic of daily variation the relation between the theoretical PPC and the measu red PPC to study the accuracy of the position fix. The results are as follows: 1. The results of fourier's analysis for the theoretical PPC and the measured PPC are positive correlation in the coefficients ao, a2, a3 with A-C pair and in the coefficients aO-a3 with A-E pair, and those PPC are apparent to daily periodicity during all measured time. The initial phase is around to 280\ulcorner with A-C pair and 1800 with A-E pair. 2. Daily variatons of the phase difference tend to decrease and the time width to narrow from April toward July, but these variations are opposed to those from July toward October. 3. Mean value of total errors of the position fix by theoretical PPC is 2.67 miles and its standard deviationis O.90miles. 4. Mean value of total errors of the position fix by the measured PPC is 0.63 miles and its standard deviation is 0.217 miles.

• Journal of Ocean Engineering and Technology
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• v.27 no.4
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• pp.83-89
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• 2013

A numerical scheme based on a mode superposition method is presented for the dynamic response analysis of a top-tensioned riser (TTR) under sheared current loads. The natural frequencies and mode shapes of the TTR have been calculated analytically for a beam with a slowly varying tension and pinned-pinned boundary conditions at the top and bottom ends. The lift coefficients and corresponding amplitudes used to estimate the vortex-induced modal force and damping for each mode were predicted via iterative calculations based on the input and output power balancing concept. Here, the power-in regions were controlled by the normal distribution function, for which the center was coincident with the lock -in location by local vortex-shedding, and the range was defined by the constant standard deviation for the reduced velocity by the local current speed. Finally, dynamic responses such as root-mean-squared displacement and stress were calculated using the mode superposition technique. In order to verify the presented scheme, a numerical calculation was performed for a TTR under an arbitrary linearly sheared current and linearly varying tension. A comparison with the results of the existing software showed that the presented scheme could give reliable and feasible solutions. Case studies were performed to investigate the effects of various current loads and tensions.

• Journal of Mechanical Science and Technology
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• v.19 no.10
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• pp.1957-1963
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• 2005

In this study, external condensation heat transfer coefficients (HTCs) of six flammable refrigerants of propylene (RI270), propane (R290), isobutane (R600a), butane (R600), dimethylether (RE170), and HFC32 were measured at the vapor temperature of $39^{\circ}C$ on a 1023 fpm low fin and Turbo-C tubes. All data were taken under the heat flux of $32\~116\;and\;42\~142kW/m^2$ for the low fin and Turbo-C tubes respectively. Flammable refrigerants' data obtained on enhanced tubes showed a typical trend that external condensation HTCs decrease with increasing wall subcooling. HFC32 and DME showed up to $30\%$ higher HTCs than those of HCFC22 due to their excellent thermophysical properties. Propylene, propane, isobutane, and butane showed similar or lower HTCs than those of HCFC22. Beatty and Katz' correlation predicted the HTCs of the flammable refrigerants obtained on a low fin tube within a mean deviation of $7.3\%$. Turbo-C tube showed the best performance due to its 3 dimensional surface geometry for fast removal of condensate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.3
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• pp.381-388
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• 2003

An experimental study was carried out to measure the heat transfer coefficient in flow boiling to mixtures of HFC-l34a and HCFC-123 in a uniformly heated horizontal tube. Tests were run at a pressure of 0.6 MPa and in the ranges of heat flux 1-50 kw/$m^2$, vapor quality 0-100 % and mass velocity 150-600 kg/$m^2$s. Heat transfer coefficients of mixture were less than the interpolated values between pure fluids both in the low quality region where the nucleate boiling is dominant and in the high quality region where the convective evaporation is dominant. Measured data of heat transfer are compared to a few available correlations proposed for mixtures. The correlation of Jung et. al. satisfactorily predicted the present data, but the data in lower quality was overpredicted and underpredicted the high quality data. The correlation of Kandlikar considerably underpredicted most of the data. and showed the mean deviation of 35.1%.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.11a
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• pp.28-35
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• 2001

The heat transfer and pressure drop characteristics of R718 flowing in smooth horizontal copper tubes with inner diameter of 3.36 mm, 5.35 mm, 6.54 mm and 8.12 mm were investigated. The test section is a counterflow heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. Experiments were peformed for the flowing range of variables : Reynolds number (1000 to 20000), mass flow rate of brine (450 kg/h) and refrigerant temperature (5$0^{\circ}C$). The main results were summarized as follows : (1) The heat transfer coefficient of 3.36 mm ID was about 10% to 30% higher than that of 5.35 mm, 6.54 mm and 8.12 mm ID, and the heat transfer coefficients for small diameter. tubes are about 20% to 27% higher than these predicted by Gnielinski. The new correlation is proposed to predict the experimental data. (2) As a result of comparison with correlation prosed by Blasius. the deviation of the experimental data slightly increased as the tube diameter decreased. (3) The ratio of heat transfer to friction factor (j/f) correlated by all experimental data increased as the tube diameter decreased.

• Journal of ILASS-Korea
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• v.14 no.3
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• pp.131-138
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• 2009

In the present study, spread-recoil behavior of a drop of shear-thinning liquid (xanthan solution) on a dry wall (polished stainless-steel plate) was examined and compared with that of Newtonian liquid (glycerin solution). Nine different kinds of xanthan and glycerin solutions were tested, including three pairs of xanthan and glycerin solutions, each having the same viscosity in low shear rate region ($10^{-2}-10^0\;l/s$). The drop behavior was visualized and recorded using a CCD camera. The maximum diameter and the spreading velocity of the xanthan drops turned out to be significantly larger and the time to reach their final shape was much shorter compared to the cases with the glycerin solutions, due to the smaller viscous dissipation resulted from lower viscosity in the higher shear rate region (>$10^0\;l/s$). As a result, the maximum diameters were measured to be larger than the predicted values based on the model proposed for Newtonian liquids, and the deviation was more pronounced with the solution with the larger viscosity variation. Consequently, viscosity variation with the shear rate was found to be a dominant factor governing the spread-recoil behavior of shear-thinning drops.