• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.47 no.4
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• pp.281-289
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• 2011

The purpose of this study is to identify the flow resistance of the bottom trawl net. The bottom trawl net being used in the training ship of Chonnam National University was selected as a full-scale net, and model nets such as 1/10, 1/25 and 1/50 of the actual net were made. Total resistance of the net part, the height of the net mouth and the flow resistance of components of the net such as wing, bag and cod-end part was measured, converted into full-scale and compared. Additionally, the model rule of Tauti (1934), which has been most frequently used in fishing net modeling experiments, was applied to interpret flow resistance and scale effect of model experiment was investigated. Presumed that the flow resistance R is $R=kS{\upsilon}^2$ against the flow velocity of each net ${\upsilon}$, resistance coefficient k was calculated by substituting R, ${\upsilon}$ and S of the net. From the result, it was found that k decreases exponentially when u increases which makes $k=c{\upsilon}^{-m}$. Whereas m of each net is ranged between 0.13-0.16 and there was not significant difference between nets. c does not show big difference in 1/10 and 1/25 model and the value itself was relatively bigger than in 1/50 model. The height of the net mouth of 1/25 and 1/50 model net h decreases exponentially according as ${\upsilon}$ increases to make $h=d{\upsilon}^{-n}$. Whereas d and n values were almost same in two nets. Additionally, when resistance of cod-end, wing and bag part in 1/25 and 1/50 model nets, both nets showed big resistance in bag part when flow is 1m/s as more than 60%. Wing and cod-end part showed almost same value or wing part had little bit larger value. On the other hand, when reviewing the reasons why both models showed difference in 1/50 model while c value against the resistance coefficient k did not show big difference in 1/10 and 1/25 model, it is inferred that the difference occurred not from material difference but from the difference in net size according to scale. It was judged that they are the scale effects concomitant to the model experiments.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.6
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• pp.794-802
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• 2018

The ice resistance series charts for icebreaking ships were developed through a series of systematic model tests in the ice tank of the Korean Research Institute of Ship and Ocean Engineering (KRISO). Spencer's (1992) component-based scaling system for ship-ice model tests was applied to extend the model ship correlations. Beam to draft ratio (B/T), length to beam ratio (L/B), block coefficient ($C_B$) and stem angle (${\alpha}$) were selected as geometric parameters for hull form development. The basic hull form (S1) of twin pod type with B/T of 3.0, L/B of 6.0, $C_B$ of 0.75 and stem angle of $25^{\circ}$ was generated with a modern hull design concept. A total of 13 hulls were designed varying the geometric parameters; B/T of 2.5 and 3.5, L/B of 5.0 and 7.0, $C_B$ from 0.65 to 0.85 in intervals of 0.05, and 5 stem angles from $15^{\circ}$ to $35^{\circ}$. Ice resistance tests were first carried out with the basic hull form in level ice with suitable speed. Four more tests for $C_B$ variations from 0.65 to 0.85 were conducted and two more for beam to draft and length to beam ratios were also performed to study the effect of the geometric parameters on ice resistance. Ice resistance tests were summarized using the volumetric coefficient, $C_V$ ($={\nabla}/L^3$), instead of L/B and $C_B$ variations. Additional model tests were also carried out to account for the effect of the stem angle, ice thickness and ice strength on ice resistance. In order to develop the ice resistance series charts with a minimum number of experiments, the trends of the ice resistance obtained from the experiments were assumed to be similar for other model ship with different geometric parameters. A total of 18 sheets composed of combinations of three different beam to draft ratios and six block coefficients were developed as a parameter of $C_V$ in the low speed regions. Three correction charts were also developed for stem angles, ice thickness and ice strength respectively. The charts were applied to estimate ice resistance for existing icebreaking ships including ARAON, and the results were satisfactory with reasonable accuracy.

• International Journal of Industrial Entomology and Biomaterials
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• v.9 no.2
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• pp.255-259
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• 2004

Post-infectional biochemical changes due to Xanthomonas campestris pv. mori (Xcm) infection in five elite mulberry varieties viz., $S_1$, $S_{1635}$, $V_1$, RF $S_{175}$ and JRH was studied under inoculated condition. It was revealed that total soluble sugar and protein content was significantly declined in all the varieties due to X. campestris infection. Total phenol content was at par prior to inoculation in all varieties, but it was significantly increased in $S_1$, RF $S_{175}$, $S_{1635}$ and JRH 7 days after inoculation. The correlation coefficient (r) between total soluble sugar and total phenol content was found positive (r = 0.825) and statistically significant. Similarly, correlation coefficient (r) between total soluble protein and phenol content was found positive (r = 0.897) and statistically significant. The present study indicates that X. campestris infected leaves are nutritionally inferior in quality and the duration of phenol production in a mulberry variety play decisive role on disease resistance.nce.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.405-421
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• 2018

In most of cases, the wall friction coefficients applied for local tunnel design are quoted directly from foreign data or local design guideline. In the previous studies, the wall friction coefficient was estimated using the velocity decay method. However, it is difficult to estimate the wall friction coefficient when the convergence wind velocity in the tunnel is negative (-) or if there is a change in the natural wind. Therefore, in this study, the wall friction coefficient is estimated by applying the dynamic simulation technique in addition to the conventional the velocity decay method. As a result of the analysis, the coefficient of wall friction in the tunnels for the total of 9 tunnels (18 tubes both directions) was 0.011~0.025, and the mean value was estimated to be 0.020. In addition, the wall friction coefficient obtained quantitatively through this study was compared with the current design criteria.

• Journal of the Korean Society of Safety
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• v.30 no.4
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• pp.120-127
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• 2015

The aim of the present study is to investigate some characteristics of concrete according to addition of blast furnace slag and alkali-activator dosages. Blast furnace slag was used at 30%, 50% replacement by weight of cement, and liquid sulfur having NaOH additives was chosen as the alkaline activator. In order to evaluate characteristics of blast furnace slag concrete with sulfur alkali activators, compressive strength test, total porosity, chloride ions diffusion coefficient test were performed. The early-compressive strength characteristics of blast furnace slag concrete using a sulufr-alkali activators was compared with those of reference concrete and added 30, 50% blast furnace slag concrete. Also, Blast furnace slag concrete using sulfur-alkali activators enhanced the total porosity, chloride ions diffusion coefficient than two standard concrete. Alkali-activated blast furnace slag concrete was related to total porosity, compressive strength and chloride ions diffusion coefficient each others. As a result, it should be noted that the sulfur-alkali activators can not only solve the demerit of blast furnace slag concrete but also offer the chloride resistance of blast furnace slag concrete using sulfur alkali activators to normal concrete.

• Journal of the Korean Geotechnical Society
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• v.35 no.6
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• pp.17-26
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• 2019

In this study, the statistical characteristics of the resistance bias factors were analyzed using a high-quality field load test database, and the total resistance bias factors were estimated considering the soil uncertainty and construction errors for the application of the limit state design of aggregate pier foundation. The MLR model by Bong and Kim (2017), which has a higher prediction performance than the previous models was used for estimating the resistance bias factors, and its suitability was evaluated. The chi-square goodness of fit test was performed to estimate the probability distribution of the resistance bias factors, and the normal distribution was found to be most suitable. The total variability in the nominal resistance was estimated including the uncertainty of undrained shear strength and construction errors that can occur during the aggregate pier construction. Finally, the probability distribution of the total resistance bias factors is shown to follow a log-normal distribution. The parameters of the probability distribution according to the coefficient of variation of total resistance bias factors were estimated by Monte Carlo simulation, and their regression equations were proposed for simple application.

• Korean Journal of Applied Biomechanics
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• v.18 no.4
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• pp.49-57
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• 2008

The purpose of this study was to determine the effects of 12-week elastic resistance exercise for the elderly on the magnitude of frequency and variability of ground reaction force signals. To this aim, total 12 elderly women aged in their 70 were participated in this study and asked to do a 12-week elastic resistance exercise program. FFT(fast Fourier Transform) was used to analyze the frequency domain analysis of the ground reaction forces's signals and an accumulative PSD (power spectrum density) normalized by support phase of walking was calculated to reconstruct the certain signals. To estimate the gait stability between the before and after exercise, values of variability were determined in a coefficient of variance. The magnitude of frequency and variability analysis for media-lateral signal revealed significantly less after exercise (p<.05). In contrast, variability of this signal's frequency that have used to evaluate the local stability during walking exhibited significantly greater after exercise(p<.05). In summary, magnitude frequency and variability of media-lateral ground reaction force's signal were significantly changed after a 12-week elastic resistance exercise.

• Proceedings of the Korean Institute of Building Construction Conference
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• v.y2004m10
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• pp.71-76
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• 2004

This paper investigate that the effect of the concrete containing mineral admixtures(pozzolanic materials such as fly-ash, ground granulated blast-furnace slag, silica fume and meta kaolin) on the resistance properties to chloride ion invasion. The purposed testing procedure was applied to the concrete added mineral admixtures for $3\sim4$ replacement ratios under W/B ratios ranged from 0.40 to 0.55. Specimens were immersed in $3.6\%$ NaCl solution for 330 days, and penetration depth, water soluble chloride contents and acid soluble chloride contents were measured in 28, 91, 182 and 330 days. Then, diffusion coefficient were calculated using total chloride contents. As a results. the kinds of mineral admixture and replacement ratios had a great effect on the resistance property of the concrete to chloride ion invasion compared with the plain concrete. And the optimal replacement ratios of mineral admixture had a limitation for each admixtures. The amount of acid soluble chloride ions and water soluble chloride ions were varied with the kinds of mineral admixtures and the penetration depth from the concrete skin. Chloride diffusion coefficient of each concretes decreased with the time elapsed. and the diffusion coefficients of the concrete immersed salt water for 330 days had a establishment with the compressive strength measured before immersing.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.30 no.5
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• pp.700-707
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• 1997

In order to express exactly the total resistance of bottom trawl nets subjected simultaneously to the water flow and the bottom friction, the influence of frictional force was added to the formular for the flow resistance of trawl nets obtained by previous papev and the experimental data obtained by other investigators were analyzed by the formula. The analyzation produced the total resistance R (kg) expressed as $$R=4.5(\frac{S_n}{S_m})^{1.2}S\;v^{-1.8}+20(Bv)^{1.1}$$ where $S(m^2)$ was the wall area of nets, $S_m\;(m^2)$ the cross-sectional area of net mouths, $S_n\;(m^2)$ the area of nets projected to the plane perpendicular to the water flow, B (m) the made-up circumference at the fore edge of bag parts, and v(m/sec) the dragging velocity. From the viewpoint that expressing R in the form of $R=kSv^2$ was a usual practice, however, the resistant coefficient $k(kg{\cdot}sec^2/m^4)$ was compared with the factors influencing it by reusing the experimental data. The comparison gave that the coefficient k might be expressed approximately as a function of BL only and so the resistance R (kg) as $$R=18{\alpha}B^{0.5}L\;v^{1.5}$$ where L (m) was the made-up total length of nets and $\alpha=S/BL$. But the values of a in the nets did not deviate largely from their mean, 0.48, for all the nets and so the general expression of R (kg) for all the bottom trawl nets could be written as $$R=9\;B^{0.5}\;L\;v^{1.5}$$.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.615-618
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• 2002

Turbo-fan for ceiling cassette type air conditioner doesn't operate in general volute. It is operated by porous material, heat exchanger. Heat exchanger increases resistance of air conditioning system and disturbs exit-flow of impeller. Therefore it has some influences on impeller capacity. In this study, we want to how that influence of exchanger on impeller capacity for ceiling cassette type air conditioner. To research, we made circular case that didn't have asymmetric part unlike rectangular case. With and without heat exchanger we measured total pressure and static pressure of impeller and three-dimensional rear flow field From the result, a turbo fan , installed in the 35mm back of fan and operated in heat exchanger, experienced $2{\%}{\~}5{\%}$% total pressure loss over all flow rate. With heat exchanger impeller efficiency decrease as flow rate decrease when flow rate coefficient was below 0.18. Especially when flow rate coefficient was below 0.12, there was $20{\%}{\~}30{\%}$ decrease of impeller efficiency.