• Journal of the Korean institute of surface engineering
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• v.50 no.6
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• pp.480-485
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• 2017

Soft mold imprinting method that uses nanostructured polymer mold was investigated for anti-reflection film fabrication. The nanostructured soft mold was polyethylene terephthalate(PET) irradiated by oxygen ion beams. The collisional energy transfer between oxygen ion and the polymer surface induced cross-linking and scission reactions, resulting in self-organized nanostructures with regular patterns of the wavenumber of $5{\mu}m^{-1}$. Post processes including ultra-violet curable resin coating and delamination fabricated anti-reflection films. The imprinted resin surface also showed the consistent wavenumber, $5{\mu}m^{-1}$. Pristine PET, oxygen ion beam treated PET, and imprinted replica sample showed total transmittance of 91.04, 93.25, and 93.57-93.88%, respectively.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.4
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• pp.199-208
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• 2019

Regular waves were generated in a wave flume under perfect reflection condition to evaluate performance of three CFD models of CADMAS-SURF, olaFlow, and KIOSTFOAM. The experiments and numerical simulations were carried out for three different conditions of non-breaking, breaking of standing waves, and breaking of incident waves. Among the three CFD models, KIOSTFOAM showed best performance in reproducing the experimental results. Although the run time was reduced by using CADMAS-SURF, its computational accuracy was worse than KIOSTFOAM. olaFlow was the fastest model, but active wave absorption at the wave generation boundary was not satisfactory. In addition, the model excessively dissipated wave energy when wave breaking occurred.

• Journal of The Korean Association For Science Education
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• v.35 no.3
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• pp.523-536
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• 2015

In this study, we analyzed the co-reflection of pre-service teacher community in three years of post-class discussions (PCD) on the basis of cultural historical activity theory in the case of an biological laboratory class program. We figured out the sociocultural elements of co-reflection of community using activity system suggested by $Engestr{\ddot{o}}m$. We also analyzed the aspect of reflection in terms of both 'the diversity of reflection subjects' and 'the practicality of reflection.' Finally, limitations of co-reflection were sought in a process of continuos circulation of reflection and practice. The results show that the sociocultural factors of 3-year-PCD changed, and in these changes, 'regular PCD,' 'introduction of tools for facilitating reflection,' 'transition of the subject in PCD from researcher to pre-service teachers' are remarkable. And in these process, co-reflection made positive progress since the content of reflection became diverse and practical. However, in some subjects such as 'managing time,' 'participation of students,' 'mentor's role (a kind of teaching manual),' reflective practice have not developed and similar patterns of discussion were repeated. From these results, we suggested ways of facilitating pre-service teacher community's co-reflection from the viewpoint of an activity system.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.4
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• pp.263-272
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• 2001

Recently, some attempts to construct slit caisson-type breakwaters are made in Korea. Since slit caisson-type breakwaters are suitable for relatively deep sea areas, a lot of theoretical and experimental researches have been performed. In this study, the reflection characteristics of vertical slit caisson breakwaters are investigated based on the measured data in two-dimensional hydraulic model tests with irregular waves. The experiments were conducted for various cases; variation of porosity of perforated-wall, width of wave chamber, number of slits for single-and double-chamber, respectively. It is found that in the case when the wave steepness (H/L$_{s}$ ) is small, the reflection coefficients are large. The existing researches have shown that the wave reflection is minimized when the nondimensional width of wave chamber B/L is about 0.2~0.25 for the regular waves. However, for the irregular waves the reflection is lowest when $B/L_2$, is 0.13~0.15. For a same porosity condition, the wave dissipation is stronger as the width of s1it is larger. The double-chamber caisson is superior to single- chamber caisson in the wave dissipating effects.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.49 no.2
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• pp.144-152
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• 2013

In an effort to find the optimum porous of Taewoo through the mathematical model 2 - dimensional tank water experiment among the approached to a problem related to ocean engineering, this study analyzed the porosity by dividing it into 9 cases. As the wave penetrates through the longitudinal porous of the Taewoo model, it was found that there is a wave energy loss because of the phenomenon of the separation of the porous due to the eddy. Looking into the general tendency based on the wave-height meter (probe) data, it was found that the shorter wavelength and higher frequency area, the more reflection coefficients increased, but in contrast, the longer wavelength and lower frequency area, the transmission coefficients showed the increasing trend and energy dissipation was in a similar way with reflection coefficients. In addition, it was found that the bigger the porosity was, the narrower distribution range of reflection coefficients was, and the more its average value decreased. On the other hand the transmission coefficients in direct opposition to reflection was found to show the wider range and the more gradual increase in the average value as porosity was the bigger around the average value. In contrast, energy dissipation rate was found to increase linearly as porosity increased the more around the porosity of 0.2518 but it decreased gradually around the peak point. Through the above results, it is judged that the porous of optimum in the longitudinal direction of the Taewoo model perforated plate was about 2.6cm because it was found that the porosity which produced the lowest reflection and transmission coefficient and the highest energy dissipation. As a result of comparing this to the case where there was no porosity at all, it showed the function of wave absorbing about 31.60%.

• Journal of Technologic Dentistry
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• v.31 no.4
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• pp.45-52
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• 2009

This study is analyzed to conduct better on-site practices with recognizing importance of the clinical practice of Dept. of dental technology and use it as a basic material in the clinical practice. Target people who are students studying dental technology in D college in Daegu were questioned by survey. Study results below 1. Average score of the survey about satisfaction of the operating method of clinical practice shows 3.26. In detail elements, 'credit assignment(10 credits)' is 3.65 as the highest score, 'execution period(vacation)' is 3.50, 'choice of the clinical practice organization' is 3.25, 'measures after practice' is 2.98 and 'pre-education' is 2.98 as the lowest score. 2. Through the real clinical practice, 'experience of new equipments and technology' is 3.64 as the highest score, 'choice of lecturer' is 3.61, 'guidance way' is 3.49, 'contents properness' is 3.44, 'environment of practice organization' is 3.36, 'evaluation way' is 3.35 and 'practical use of the evaluation material' is 3.18 as the lowest score. 3. The average score of survey about satisfaction after clinical practice of the participated students is 3.46 that is higher than both 'satisfaction about operating method(3.26)' about clinical practice of college and 'satisfaction about organization(3.44)' about environment of dental craft organizations and labs, guidance way of lecturer and evaluation. 4. In the improvement of distribution of the clinical practice evaluation, in the 'practice organization: college' viewpoint, '7:3' is 35.77% as the highest response, '6:4' is 25.20%, '8:2' is 22.76% and '4:6' is 16.26 in regular sequence. 5. In site evaluation reflection of clinical practice, 50% reflection is 32.93% as the highest percentage, 60% reflection is 26.83%, 20% reflection is 20.73% and 80% reflection is 6.10% in regular sequence. In attendance score, it shows percentage of reflecting 50% and 40% is 26.98%, students wanting to reflect 30% is 25.40%, reflecting 10% is 20.63% and no reflecting is 0%. In result of the analyzed data, clinical practice has to be studied more in considering that clinical practice is important point in education of Dept. of Dental Technology and also problems in college and on-site practice need improvements.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.3
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• pp.612-623
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• 1994

Shock-wave focusing from a two-dimensional parabolic reflector was simulated using an explicit finite volume upwind TVD scheme. Computations were performed for three different incident shock speeds of $M_s$ = 1.1, 1.2 and 1.3, corresponding to the relatively weak, intermediate, and strong shock waves, respectively. Numerical solutions nicely resolved all the waves evolving through the focusing process. As the incident shock strength increase, a transition was observed in the shock-fronts geometry that was caused by the change in the reflection type of converging shock fronts on the axis of symmetry, from regular-type to Mach-type reflection. The computed maximum on-axis pressure amplification and the trajectories of three-wave intersections showed good agreement with experimental results. The strong nonlinear effect near the focal region which determines the shock-fronts geometries at and behind the focus and at the same time confines the pressure amplification at the focus was clearly revealed from the present numerical simulation.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.357-361
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• 2010

When high-pressure gas is exhausted through nozzle exit to the atmosphere, expanded supersonic jet is formed with the Mach disk at a specific condition. In two-dimensional supersonic jets, the hysteresis phenomenon of the reflected shock waves is found to occur under quasi-steady flow conditions. Transitional pressure ratio between the regular reflection and Mach reflection in the jet is affected by this phenomenon. In the present study, experiments are carried out on internal flow in a supersonic nozzle to clarify the hysteresis phenomena for the shock waves and to discuss its interdependence on the rate of the change of pressure ratio with time. Flow visualization is carried out separately on the straight and divergent channels downstream of the nozzle throat section. The influence that the hysteresis phenomena have on the location of shock wave in a supersonic nozzle is also investigated experimentally.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 1999.10a
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• pp.235-242
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• 1999

Wave which propagate from the offshore cause transformation of diffraction, refraction, and reflection etc. in coming in the coastal by depth change. Especially, Wave strongly show the charcateristics of rancom wave in the coastal zone. Developed wave model until a recent date analysed regular waves with height and period equal to those of the significant wave, In case of Monochromatic wave, it can be analysed fine in the offshore, but differ from in coastal zone. In this study, form of governing equation is parabolic mild slope equation. This model calculated random wave for using frequency spectrum and directional spectrum from input data condition of wave. This model is applied to Vincent shoal and compared with laboratory experimental data. The results agreed well with laboratory data.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.573-574
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• 2006

This research deals with the wave transmission and dissipation problems for two dimensional regular waves and s vertical circular cylindersr. Using the unsteady mild slope equation, a numerical model has been developed to calculate the reflection and transmission of regular waves from a multiple-row vertical circular cylinders. In addition hydraulic model experiments have been conducted with different values of properties between the cylinders and opening ratio (distances) between the rows of the cylinders. It is found that the transmission coefficients decrease with decreasing the opening ratio and increasing the rows of vertical cylinders. Comparison between hydralic and numerical experiments results shows resonable agreement.