• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.2
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• pp.140-149
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• 1985

Fully reversed push-pull low cycle fatigue tests under strain control of trapezoid cyclic mode have been conducted in air at temperature of 550.deg. C and with frequency of 0.5 cpm on the domestic stainless steel STS 316 after solution treatment for 1 hour at 1100.deg. C. As an experimental equipment for high temperature fatigue tests, an electric servo-hydraulic fatigue machine(Instron model 1350) was used. This paper presents the effects of creep hold time and plastic strain range on push-pull high temperature low cycle fatigue life and fracture behavior. The fracture surfaces were observed by means of the scanning electron microscope. The results are as follows. (1) The fatigue life decreases with increase of the plastic strain range equal hold time and also decreases as the hold time is getting longer. (2) The frequency modified damage function can predict fatigue life by incorporating a variation of Coffin's frequency modified approach into damage function. (3) The ratios of creep damage and fatigue damage can be calculated by using he linear accumulation damage concept and the ratio of creep damage increases as the hold time is getting longer. (4) At the creep hold time of 5 minutes and the strain range of 2.0%, the fracture mode was intergranular fracture and striations were hardly observed. In this case, the intergranular cracking was originated in void type('.gamma.' type) cracking.

• Journal of the Korean School Mathematics Society
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• v.15 no.1
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• pp.27-51
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• 2012

This paper analyzed the pedagogical content knowledge (PCK) presented in three novice teachers' mathematics instruction. PCK was analyzed in terms of the knowledge of mathematics content, the knowledge of students' understanding, and the knowledge of teaching methods. Teacher A executed a concept-oriented instruction with manipulative materials because she had difficulties in learning mathematics during her childhood. Teacher B attempted to implement an inquiry-centered instruction in the lesson of looking for the area of a trapezoid. Teacher C focused on the real-life connection to mathematics instruction. There were substantial differences among the teachers' PCK revealed in mathematics teaching, depending on their instructional goals. The detailed analyses of three teachers' teaching in terms of their PCK will give rise to the issues and suggestions of professional development for beginning elementary school teachers in mathematics teaching.

• Education of Primary School Mathematics
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• v.19 no.2
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• pp.113-125
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• 2016

The concept and measuring activities of the height of figures are essential to find the areas or volumes of the corresponding figures. For plane figures, the height of a triangle is defined to be the line segment from a vertex that is perpendicular to the opposite side of the triangle, whereas the height of a parallelogram(trapezoid) is defined to be the distance between two parallel sides. For the solid figures, the height of a prism is defined to be the distance of two parallel bases, whereas the height of a pyramid is defined to be the perpendicular distance from the apex to the base. In addition, the height of a cone is defined to be the length of the line segment from the apex that is perpendicular to the base and the height of a cylinder is defined to be the length of the line segment that is perpendicular to two parallel bases. In this study, we discuss some pedagogical problems on the concepts and measuring activities of the height of figures to provide alternative activities and suggest their educational implications from a teaching and learning point of view.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.1
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• pp.1-18
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• 2007

This study is about an arrangement method of trapezoidal pre-cast segment lining that can be applied in shield tunnel construction. Trapezoidal segment lining is formed by assembling tapered pre-cast concrete segments taking advantage of the tapered shape of pre-cast segments upon delivery on site. By calculating tapering of the segments manufactured in single type and rotating the segments when putting them together, a variety of tunnel alignments can be arranged in the most efficient way. Once the design criteria and tunnel alignment (straight or curved) is analyzed, the sequence of assembling trapezoidal segments in compliance with tunnel alignment will be computed. On site an operator can utilize the softwareto automatically determine sequential arrangement of trapezoidal segments. When the actual arrangement of segmental lining is different from the computed output, the operator can input the actually measured values to coincide the computerized calculation with the real status of assembly. Then the adjustment will be the basis of subsequent arrangement of segments, thus the continuity of work can be guaranteed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.2A
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• pp.117-122
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• 2012

Coastal structures, constructed for preventing coastal slope erosion, often causes the scour on the boundary between the coastal structure and the sea-bed, which might lead to collapse of coastal structures. To prevent the collapse, the usual upright block type coastal structures can be modified to other forms or systems of coastal structures. To validate the performance of the proposed systems, it is necessary to conduct high cost hydraulic experiments. If numerical modeling can be performed prior to the hydraulic experiments and the performance of the proposed systems is analyzed numerically in advance, the expenses can be reduced significantly by optimizing the number of cases for conducting the experiments. In this study, a fluid-structure interaction analysis procedure is proposed for modeling the hydraulic experiments of costal structures using the finite element package, LS-DYNA. As can be found in the usual hydraulic experiments, fluid velocities of potential scour locations are monitored and analyzed in detail for four types of coastal structures, block, step, trapezoid and rubble mound.

• Journal of the Korean Society of Industry Convergence
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• v.7 no.2
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• pp.153-159
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• 2004

The purpose of this research is to investigate the performance of swirl combustion chamber diesel engine by changing the jet passage area, the depth and shape of the piston top cavity (main chamber). The performance of diesel engine with newly changed swirl combustion chamber was tested through the experimental conditions as engine speed, load and injection timing etc. The test results were compared and analyzed. And another purpose of this research is to make a new diesel engine that is satisfied fuel consumption and regulation value of exhaust gas. 1. The rate of fuel consumption was affected significantly by the jet passage area at the high speed and load than low speed and low load. The influence of jet passage large area was proven to decrease the rate of fuel consumption. 2. Smoke was affected significantly by the depth of the piston top cavity, but exhaust temperature and the rate of fuel consumption wasn't affected. The rate of fuel consumption was affected by changing injection timing. 3. The rate of fuel consumption, exhaust temperature and Smoke were affected significantly by the shape of the piston top cavity from rectangular to trapezoid. That is we have all high value. The exhaust smoke density and exhaust gas temperature depended sensitively on variation of the injection timing rather than the shape of the combustion chamber within the experimental conditions. 4. We made a new diesel engine that is satisfied design target values(sfc=190 g/hr, NOx + THC=6.0 g/KWh, PM=0.3 KWh), the rate of fuel consumption and emission standard etc., through changing injection timing at the maximum torque point and rated power point. Although we have a little high NOx value.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.10
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• pp.1318-1326
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• 2001

The evaporation heat transfer coefficient and pressure drop for refrigerant R-22 flowing in the plate and shell heat exchanger were investigated experimentally in this study. Two vertical counterflow channels were farmed in the exchanger by three plates of commercial geometry with a corrugated trapezoid shape of a chevron angel of 45 ° Upflow boiling of refrigerant R-22 in one channel receives heat from the hot downf1ow of water in the other channel. The effects of the mean vapor quality, mass flux, heat flux and pressure of R-22 on the evaporation heat transfer and pressure drop were explored. The quality change of R-22 between the inlet and outlet of the refrigerant channel ranges from 0.03 to 0.05. The present data showed that both the evaporation heat transfer coefficient and pressure drop increase with the vapor quality. At a higher mass flux, the evaporation heat transfer coefficient and pressure drop are higher for the entire range of the vapor quality Raising the imposed wall heat flux was found to slightly improve the heat transfer, while at a higher refrigerant pressure, both the heat transfer and pressure drop are slightly lower.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.4
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• pp.2868-2875
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• 2015

Both the friction velocity and the friction coefficient have to be estimated to determine flow characteristic in an open channel. In spite of the importances in an open channel, the complete interpretation is highly difficult because of free water surface, the complex of cross section and the various hydraulic parameters. The researches related to the friction factor are based on empirical outcome. Therefore, the equations are difficult to be generally applied. For that reason, the new friction factor estimation equation using the entropy concept was proposed in the present study, and the data measured in rectangular and trapezoid cross sections was used to verify the accuracy of equation. The advantage of the proposed equation dose not use the energy slope term which is difficult to be measured and to be estimated in an open channel. In addition, the proposed method showed that the accurate friction factor f can be estimated on the Basis of theoretical background.

• Journal of Fashion Business
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• v.11 no.2
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• pp.58-75
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• 2007

This study held human measurement for 200 male subjects in their twenties in full age living in Ningbo City, Zhejiang Province in China. Their lower body types were classified and grouped according to shapes and sizes. Consequently, representative body type reflecting shapes, sizes, and characteristics were chosen and presented with their measurement values to be used as the basic data for slacks pattern making and fitness evaluation. The following are the results of the analysis: 1. Homogeneity analysis was given to determine the correspondence relationships among index types, indirect types, and size types. Index Type 1 (H-Round), Indirect Type 2 (Adjacent Straight Legs & Slight Slant of Lateral Lower Body), and Size Type 1 (Medium-Thick) were correlated; Index Type 2 (A-Trapezoid), Indirect Type 1 (Bow Legs & Slight Slant of Lateral Lower Body), and Size Type 3 (Small-Slim) were corresponded; Index Type 3 (A-Balance), Indirect Type 3 (Balance Legs & Large Slant of Lateral Lower Body), and Size Type 2 (Tall-Normal) were mutually related. 2. Mahalanobis distance based on each shape factor (index or indirect) and size factor (absolute) was obtained, while an index-absolute representative body type group (47 people, 24.4%) and an indirect-absolute representative body type group (45 people, 23.7%) were chosen, each reflecting shapes, sizes, and characteristics. 3. The representative body type group of lower body shapes of Chinese males in their 20s had average measurement values, such as 169.15cm (stature), 73.32cm (waist circumference), 75.76cm (omphalion waist circumference), 91.08cm (hip circumference), 106.02cm (outside leg length), 53.96cm (thigh circumference), and 74.42cm (crotch length).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.5
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• pp.516-524
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• 1997

The propagation properties of various pulse signal types(square pulse, Gaussian pulse, trapezoid pulse, RF pulse) on coupled microstrip lines are investigated. Numerical integration technique which has its accuracy and is easily simulated, is used to obtain the time domain response of pulse signals. Frequency-dependent characteristics of coupled microstrip line is obtained using Jansen's approximate equation. The propagation properties of pulse signal on coupled microstrip lines is analyzed regarding to its geometric structure (relative permittivity ${varepsilon}_r$ substrate height h, strip width w of the microstrip line) and pulse width ${\tau}$ of signal pulse. The simulation results show that space between two lines is very significant parameter in pulse distortion in comparison of any other parameters. The results of this paper are compatible to the trade-off determination of relative permittivity, substrate height, strip width and pulse width of signal pulse when a design of MIC and MMIC is necessary.