• Journal of Ocean Engineering and Technology
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• v.21 no.4
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• pp.1-7
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• 2007

Based on the eigenfunction expansion method, the wave-absorbing performance of a square or circular pile breakwater was investigated. Flow separation resulting from sudden contraction and expansion is generated and is the main cause of significant energy loss. Therefore, evaluation of an exact energy loss coefficient is critical to enhancing the reliability of the mathematical model. To obtain the energy loss coefficient, 2-dimensional turbulent flow is analyzed using the FLUENT commercial code, and the energy loss coefficient can be obtained from the pressure difference between upstream and downstream. It was found that energy loss coefficient of circular pile is 20% that of a square pile. To validate the fitting equation for the energy loss coefficient, comparison between the analytical results and the experimental results (Kakuno and Liu, 1993) was made for square and circular piles with good agreement. The array of square piles also provides better wave-absorbing efficiency than the circular piles, and the optimal porosity value is near P=0.1.

• International Journal of Fluid Machinery and Systems
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• v.10 no.2
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• pp.176-188
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• 2017

The nozzle-flapper valves are widely applied as a pilot stage in aerospace and military system. A subject of the analysis presented in this work is to find out a reasonable range of null clearance between the nozzle and flapper. This paper has presented a numerical flow coefficient simulation. In every design point, a parameterized model is created for flow coefficient simulation and cavitation under different conditions with varying gap width and inlet pressure. Moreover, a new test device has been designed to measure the flow coefficient and for visualized cavitation. The numerical simulation and test results both indicate that cavitation intensity gets fierce initially and shrinks finally as the gap width varies from small to large. From the curve, the flow coefficient mostly has experienced three stages: linear throttle section, transition section and saturation section. The appropriate deflection of flapper is recommended to make the gap width drop into the linear throttle section. The flapper-nozzle null clearance is optionally recommended near the range of $D_N/16$. Finally through simulation it is also concluded that the inlet pressure plays a little role in the influence on the flow coefficient.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.983-986
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• 2007

The absorption power of a surface depends on the surface irregularity which has been known as an important factor in determining scattering coefficient. This study investigates the effect of increase in surface area on the absorption and scattering coefficients of a diffuse surface. The surface irregularity or surface pattern can be compared to the wavelengths and the random-incidence scattering coefficient of surface is measured by ISO 17497-1. The scattering coefficients of increasing the surface area in linear pattern of v-cut groove on rubber plate were measured in 1:10 scale model reverberation chamber. It is found that the scattering and absorption coefficients increase with increasing surface area. At 60% of increased surface area the spacing between the hemisphere diffuser and the v-cut groove acts similar with results of absorption coefficient. The results show that absorption coefficient depends on surface area and the spacing where as scattering coefficient depends on surface area and texture.

• Transactions of Materials Processing
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• v.20 no.3
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• pp.243-249
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• 2011

In this study, an approach designed to compute high temperature friction coefficients for SCM 435 steel through a pilot hot rolling test and a finite element analysis, is proposed. Single pass pilot hot flat rolling tests with reduction ratios varying from 20 to 40% were carried out at temperatures ranging from 900 to $1200^{\circ}C$. In the proposed approach, the friction coefficient is calculated by comparing the measured strip spread and the roll force with the simulation results. This study showed that the temperature and reduction ratio had a significant influence on the friction coefficient. As both material temperature and reduction ratio become higher, the friction coefficient increases monotonically. This finding is not in agreement with the Ekelund model, which is widely used in the analysis of the hot rolling process. In the present work, the friction coefficient at a reduction ratio of 40% was found to be 1.2 times greater than that at a reduction of 30%. This higher friction coefficient means that an increment of the roll thrust force is expected at the next stand. Therefore, a roll pass designer must understand this phenomenon in order to adjust the reduction ratio at the stands while keeping the driving power, the roll housing structure and the work roll strength within the allowable range.

• Journal of the Korean Wood Science and Technology
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• v.17 no.2
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• pp.26-33
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• 1989

The acoustic absorption coefficient and acoustic impedance of 5 species of softwood(sonamoo, sam namoo, gusang namoo, hwaback, sitka spruce) and 5 species of hardwood (Mulgusul namoo, Italian popular, white meranti, red meranti, kalantas) were measured by the standing wave method. which is simple in the setup and gives more accurate result than does any other measuring method. The dependence of the absorption coefficient and complex acoustic impedance on the wood sections. thickness of the sample itself and the back air gap was investigated experimentally in the frequency range from 200Hz to 1800Hz, and the result are as follows: 1. The acoustic absorption coefficient of wood sections was higher on the cross section than radial and tangential sections. 2) The acoustic absorption coefficient were higher in the frequency range from 400Hz to 600Hz, but decreased in the frequency above 600Hz. 3. The genenal tendency of the variation of the normal acoustic impedance was increased according to the frequency. 4. The acoustic absortion coefficient was increased in the to 7mm-thick sample and decreased in 9mm-thick sample. 5. The higher acoustic absorption coefficient was shown in the case with the backing an gap than in the case without the gap.

• Journal of the Korean Society of Safety
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• v.27 no.5
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• pp.30-34
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• 2012

A safety helmet is a personal protective equipment to protect the head from falling and flying objects. A safety helmet has the maximum delivered impact force as shock absorption performance, the lower delivered impact force the better performance, which was not a controlled variety during manufacturing safety helmet. Accordingly there were some difficulties in establishing the standard for improved performance as there was not a clear controllable impact force for improved performance. In this study the shock absorption performance was intended to be found as coefficient of restitution related to impulse. As a research method, a coefficient of restitution during the absorption of shock was calculated using the impulse transferred to pharynx utilizing the safety helmet shock absorption performance testing device based on the theory of momentum and impulse. The estimated impulsive force curve was derived assuming that shock was not absorbed using the measured data. The sample was selected as tested goods of ABS material for safety certification available mainly in the market. As a result of study, the maximum delivered impact force of safety helmet made by a domestic safety certified a company was 735 N, and its coefficient of restitution proved to be 0.64. The smaller coefficient of restitution is, the lower maximum delivered impact force and the higher shock absorption performance. The coefficient of restitution can be used as a performance index of safety helmet.

• Journal of Astronomy and Space Sciences
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• v.34 no.2
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• pp.99-103
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• 2017

The sun is not equally bright over the whole sphere, but rather is darkened toward the limb. This effect is well-known as limb darkening. The limb darkening coefficient is defined by the ratio of the center intensity to limb intensity. In this study, we calculate the limb darkening coefficient using the photospheric intensity estimated from solar images taken by solar and helispheric observatory (SOHO) and solar dynamics observatory (SDO). The photospheric intensity data cover almost two solar cycles from May 1996 to December 2016. The limb darkening coefficient for a size of 0.9 diameter is about 0.69 and this value is consistent with solar limb darkening. The limb darkening coefficient estimated from SOHO shows a temporal increase at solar maximum and a gradual increase since the solar minimum of 2008. The limb darkening coefficient estimated from SDO shows a constant value of about 0.65 and a decreasing trend since 2014. The increase in the coefficient reflects the effect of weakened solar activity. However, the decrease since 2014 is caused by the aging effect.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.122-126
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• 2004

The temperature difference between die and workpiece has been frequently caused to various surface defects. The distribution and change fur the temperature of forged part should be analyzed to prevent the generation of various defects related with the temperature. The surface temperature changes were affected with the interface heat transfer coefficient. Therefore, the coefficient is necessary to predict the temperature changes of die and workpiece. In this study, the experimental and FE analysis were performed to evaluate the coefficient with a function of pressure, temperature, material, and etc. The sealed die upsetting was used to measure the coefficient on pressure over the flow stress. AISI1045, Al6XXX, and Pure-Cupper were used to analyze effects according to the material. The coefficient was increased with step-up of pressure between die and workpiece. And, Al6XXX was larger than the AISI1045 and Pure-Cupper up to the five times.

• Journal of the Korean Home Economics Association
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• v.11 no.1
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• pp.14-25
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• 1973

The measurements includings 22 items such as height, weight, body width were carried out for Korean male and female students, one hundred each, from 18 to 24 years old. The correlation coefficient was calculated for every two items. The values are basic for the Clothing construction and the Pattern grading. The results are as follows : 1) The measuring values are as shown in Table 1 and the index are as shown in Table 2. 2) The correlation coefficient of length to length is larger than that of length to girth and that of length to width. The correlation coefficient of girth to girth is larger than girth to length and that of girth to width. The correlation coefficient of width to width does not show remarkable difference from those of others. 3) The correlation coefficient values of weight to lengths, weight to lengths, weight to girths and weight to width are larger. Among these, the correlation coefficient of weight to girths is the largest. 4) The correlation coefficient in general shows almost positive values except a few exception showing negative values. 5) No meaning differences are found between males and females.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.5
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• pp.1951-1966
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• 2020

Recent advancements in mobile device technology have enabled real-time positioning so that mobile patterns of people and favorable locations can be identified and related researches have become plentiful. One of the fields of research is the relationship between the object properties and the favored location to visit. The object properties of a person include personality, which is a major property jobs, income, gender, and age. In this study, we analyzed the relationship between the human personality and the preference of the location to visit. We used Spearman's Rank correlation coefficient, one of the many methods that can be used to determine the correlation between two variables. Instead of using actual data values, Spearman's Rank correlation coefficient deals with the ranks of the two data sets. In our research, the personality and the location data sets are used. Our personality data is ranked in five ranks and the location data is ranked in 8 ranks. Spearman's Rank correlation coefficient showed better results compared to Pearson linear correlation coefficient and Kendall rank correlation coefficient. Using Spearman's correlation coefficient, the degree of the relationship between the personality and the location preference is found to be 43%.