• 한국유체기계학회 논문집
• /
• 제11권1호
• /
• pp.9-17
• /
• 2008

A numerical study for three-dimensional laminar flow in the entrance region of helical tubes connected with straight ones is carried out to investigate the effects of Reynolds number, pitch and curvature ratio on the oscillation periods of the flow. The fully elliptic governing equations were solved by means of a finite volume method. The fully developed laminar flow boundary condition was applied at the straight tube inlet. This results cover a curvature ratio range of 1/10${\sim}$1/320, a pitch range of 0.0${\sim}$3.2, and a Reynolds number range of 62.5${\sim}$2000. A comparison is made with previous experimental correlations and numerical data. The developments of velocity, local and average friction factors are discussed. The average friction factors are oscillatory in the entrance region of helical pipes. It has been found that the angle required for the flow to be similarly developed is most affected by the curvature ratio. The pitch and Reynolds number do not have any significant effect on the angle. The characteristic angle ${\phi}_c(={\phi}/sqrt{\delta})$, or the characteristic length to diameter ratio $s_c(=l\sqrt{\delta} cos(atan{\lambda})/d)$, can be useful to represent the development of flow in helical tubes. As the pitch increases and as the curvature ratio and Reynolds number decrease, the amplitude and the number of flow oscillations along the main streamwise direction decrease.

• 한국세라믹학회지
• /
• 제41권8호
• /
• pp.588-592
• /
• 2004

Dynamic Milling (DM) 방법에 의한 $UO_2$ 분말의 특성 변화가 밀도에 미치는 영향을 조사하였다 분쇄시간(0∼8시간)의 증가에 따라 분말입자의 크기는 감소하며 둥근 형태를 지녔으며, 비표면적과 O/U 비는 증가하였다. 이러한 특성 변화에 의해 성형밀도는 증가한 반면에, 소결밀도는 감소하는 경향을 보였다. 소결밀도의 감소는 분말 분쇄과정에서 야기된 $UO_2$ 분말의 O/U 비의 증가가 주된 영향을 미친 것으로 사료된다.

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2002년도 춘계학술발표대회 논문집
• /
• pp.9-12
• /
• 2002

A parametric study has been conducted to investigate the effect of the geometry on the strength of an unidirectional and fabric hybrid laminated composite joint. Tests are conducted for the specimens with nine different edge-to-hole diameter or width-to-hole diameter ratios. For the finite element analysis, the characteristic length method is used, and the tests for determining the characteristic length are performed additionally. Nonlinear contact problem between the pin and laminate is modeled by the gap element in MSC/NASTRAN. Tsai-Wu failure criteria is applied to the stress on the characteristic curve. The finite element and experimental results shows good agreement in strength of composite joint. Results of the parametric study shows the effect of the geometry is remarkable in the specimens with width-to-hole diameter ratio less than 2.8 and edge-to-hole diameter ratio less than 1.4.

• 아동학회지
• /
• 제22권4호
• /
• pp.189-199
• /
• 2001

The purpose of this study was to explore the relationship between caregivers' characteristic variables and quality of child care and to investigate the magnitude of the association between variables and quality of child care according to children's age. The following factors were suggested as the caregivers' characteristic variables: Total years of caregiving experience, educational level, job satisfaction, amounts of turnover, time for commuting, salary, pay step, years of work in charge of current children, perception on the recommended caregiver/child ratio. The results of the study were as follows : First, it was found that caregivers' salary, total years of caregiving experience, pay step, perception on the recommended caregiver/child ratio, age, and amounts of in-service program were significant among caregivers' variables. Second, when the caregivers' characteristic variables were examined in terms of children's age respectively, the effects of teacher-related variables to influence the child-care quality were significantly different according to children's age group.

• 대한의용생체공학회:의공학회지
• /
• 제30권6호
• /
• pp.510-515
• /
• 2009

In this paper, variable characteristic ratio algorithm based on oscillometric method is proposed to enhance the accuracy of blood pressure measurement. We combined the slope-based approach and fuzzy inference technique to change the characteristic ratios of height-based method. The proposed algorithm was assessed on 255 measurements from 85 subjects and compared with the conventional height-based algorithm. The testing results showed that the developed algorithm achieved an overall grade A for both systolic and diastolic blood pressures according to the BHS protocol. And, mean standard deviation between the observers and the developed algorithm were 5.71mmHg and 6.29mmHg for systolic and diastolic pressures respectively, which also fulfilled the AAMI criteria. In conclusion, this algorithm was successfully developed and recommended for further clinical trials with the wider adult population.

• 한국환경복원기술학회지
• /
• 제7권6호
• /
• pp.39-48
• /
• 2004

The purpose of this paper was to confirm the application of the equation of the soil-water characteristic curve on an unsaturated soil. To this ends, a series of suction test was conducted on the selected 4 kinds of soil which is located in Korea, using the modified pressure extractor apparatus. And it was carried out to analyze the experimental parameters which can describe the soil-water characteristics, were determined by using the data obtained from the experiment. From the results, it was found that the matric suction was varied according to the grain size distribution, amount of fine grain particle and void ratio. Also it was found that the residual volumetric water content was decreased with the void ratio, but the index related air entry value, the soil parameter related water content and the parameter with residual water content were increased with the void ratio. And the application of equation of the soil-water characteristic curve was confirmed for the various conditions and the various state by the comparison between the volumetric water content measured by the experiment and the predicted values.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1994년도 추계학술대회 논문집
• /
• pp.288-297
• /
• 1994

The sewing machine is one of the oldest machine that has ever used, which is related with clothes' life. Modern sewing machines are divided into three groups by the sititch character, which are the lock stitch sewing machine group, the over lock sewing machine group and the specical sewing machine group. The lock stitch sewing machine have being used more than any others, which is also good model to study. This work is part of the improvement of an industrial lock stitch(ILS) sewing machine's design. The research objectives are the kinematic analysis and evaluations of stitch performance. The feed dog and the needle extreme's motion, which are important two part's motion in the sewing machine, are characterized by the stitch process and the needle trace. The needle trace is formulated as the stitch spacing, the stitch spacing's ratio(the static characteristic), and the stitch's phase difference(the dynamic characteristic). The tested ILS sewing machine is evaluated as a good static characteristic and a bad dynamic characteristic. Namely, a stitch spacing's ratio is 0.01~0.063(mm/mm) and a stitch's phase difference ratio is 0.06~0.13(mm/mm).

• 한국농공학회논문집
• /
• 제46권6호
• /
• pp.61-69
• /
• 2004

The aim of the work described in this paper was to confirm the application of the equation of the soil-water characteristic curves on an unsaturated soil. A series of suction test for unsaturated soils was conducted on the selected 4 kinds of soil using modified pressure extractor apparatus. And it was carried out to analyse The experimental parameters which can be describe the soil-water characteristics, were determined by using the data obtained from the experiment. From the results, it was found that The matric suction varied according to the grain size distribution, amount of fine grain particles and void ratio. Also it was found that the residual degree of saturation was decreased with in crease of the void ratio, but the pore size distribution index and air entry value were increased with in crease of the void ratio. And The application of the soil-water characteristic curve equation was confirmed for the various conditions and the various state by the comparison between the measured degree of saturation and the predicted degree of saturation.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
• /
• pp.546-549
• /
• 2003

This paper was shown removal characteristic of escherichia coli for discharge tube with globular $SiO_2$. At the result of the removal characteristic experiments of escherichia coli using the discharge tube with globular $SiO_2$, because the electric field is also increased when input voltage is increased, the removal characteristic of escherichia coli was appeared relation connection to input voltage. If a passing number of test water in discharge tube is increased, the removal ratio of escherichia coli is increased because passing number of electric field section is increased. When diameter of globular $SiO_2$ is increased, the removal time of escherichia coli is to be decreased because dielectric polalization of globular dielectric($SiO_2$), Also, the removal ratio of escherichia coli of the discharge tube with globular dielectric($SiO_2$) is appeared higher than the removal ratio of the discharge tube without globular dielectric($SiO_2$).

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
• /
• pp.550-553
• /
• 2003

This paper was shown water properly conversion and removal characteristic of escherichia coli for discharge tube with $ZrO_2$ beads. At the result of the removal characteristic experiments of escherichia coli using the discharge tube with $ZrO_2$ beads, because the electric field is also increased when input voltage is increased, the removal characteristic of escherichia coli was appeared relation connection to input voltage. And if a passing number of test water in discharge tube with $ZrO_2$ beads is increased, the removal ratio of escherichia coli is to be increased because passing number of electric field section is increased. And if diameter of $ZrO_2$ beads is increased, the removal time of escherichia coli is to be decreased because dielectric polalization of $ZrO_2$ beads. Also, the removal ratio of escherichia coli of the discharge tube with $ZrO_2$ beads. is appeared higher than the removal ratio of the discharge tube without $ZrO_2$ beads. And a salutation point of ozone and $H_2O_2$ generation density inner water was appeared near 60[min].