• Tribology and Lubricants
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• 제27권6호
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• pp.338-343
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• 2011

Laser surface texturing (LST) methods are widely applied now to reduce friction and improve reliability of machine components such as thrust bearings, mechanical face seals and piston rings, etc. In this paper, the effect of dimple shapes on the lubrication characteristics of parallel thrust bearing are studied using a commercial computational fluid dynamics (CFD) code, FLUENT. Pressure and streamline distributions, variations of supporting load, leakage flow rate and friction force, are compared for three different dimple sectional shapes such as circle, pyramid and rectangle type. The lubrication characteristics are highly affected by dimple shapes and number of dimples. The pyramid type dimple shape can support the highest load while the rectangle type is the best in friction reduction.

• 한국금형공학회:학술대회논문집
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• 한국금형공학회 2008년도 하계 학술대회
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• pp.31-34
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• 2008

The L-bending of inner-structure bonded sandwich sheet metal is examined to reduce springback and defects of bent parts. The specimen is composed of top and bottom layers and a middle layer with dimple type-inner-structure and each layer is bonded by resistance welding. This specimen with hollow type-inner-structure shows different bending characteristics from the conventional sandwich sheet metals with solid type-inner-structure. The experiments were conducted for two kinds of working conditions, that is, clearance and movement of first bent specimen for second bending. The deformed profile, bend angle and springback were investigated and compared and then the proper working conditions for L-bending of sandwich sheet metal were prosed.

• 설비공학논문집
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• 제22권3호
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• pp.149-155
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• 2010

In the present study, the characteristics on the internal flow and heat transfer of the dimple-type plate heat exchanger were numerically investigated. For the numerical analysis, the conjugate heat transfer analysis between hot fluid-separating plate-cold fluid was performed using the periodic boundary condition at the center area of the plate and appropriate inlet and outlet conditions for the two streams. The numerical results were validated by the comparison with the experimental data. From these results, the correlations of the Colburn j-factor for the heat transfer and the Fanning f-factor for the flow friction were obtained. The present results could be applicable for the optimal design of dimple-type plate heat exchanger.

• Tribology and Lubricants
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• 제25권4호
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• pp.217-224
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• 2009

In this study, friction tests were carried out in order to investigate the friction behavior of textured surface in unlubricated state using ball-on-disk type apparatus. Test specimens were SUJ2 bearing steel ball and SM45C steel disk. Square arrays of circular micro-dimples were created on the surface of disk specimen by Nd:YAG Laser. Friction tests were performed for the disk specimen with various micro-dimple parameters and was also conducted for the variation of normal loads and relative velocities. The results showed that fiction coefficient of textured surface was lower than that of non-textured surface and the deeper depth of micro-dimple was, the lower friction coefficient obtained at the same diameter of micro-dimple in unlubricated state. Area density of micro-dimple had an effect on the friction coefficient. It was also found that friction coefficient generally decreased with the increase of normal load and relative velocity.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.39-44
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• 2008

In this paper, heat transfer coefficients were measured in a channel with one side dimpled surface. The sphere type dimples were fabricated and the diameter and depth of dimple was 16mm and 4mm, respectively. Two channel heights of about 0.6 and 1.2 time of the dimple diameter, two dimple configuration were tested. The Reynolds numbers based on the channel hydraulic diameter was varied from 30000 to 50000. The improved hue detection based transient liquid crystal technique was used in the heat transfer measurement. Heat transfer measurement results showed that high heat transfer was induced downstream of dimples due to flow reattachment. Due to the flow recirculation on the upstream side in the dimple, the heat transfer coefficient was very low. As the Reynolds increased, the overall heat transfer coefficients also increased. With same dimple arrangement, the heat transfer coefficients and the thermal performance factor were higher for the lower channel height. As the distance between dimples became smaller, the overall heat transfer coefficient and the thermal performance factor were increased.

• 대한기계학회논문집A
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• 제33권2호
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• pp.153-161
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• 2009

Three-dimensional finite-element methods(FEM) have been used to analyze the thermal stress of an exhaust gas recirculation(EGR) cooler due to thermal and pressure load. Since efficiency and capability of the heat exchanger are mainly dependent on net heat transferring area of the EGR cooler system, the tube inside the system has a numerous dimples on the surface. Thus for finite element analysis, firstly the dimple-typed tube is modeled as a plain element without the dimple, and then the equivalent thermal conductivities and elastic modulus are calculated. This work describes the numerical homogenization procedure of the dimple-typed tube and verifies the equivalent material properties by comparison of a single unit and the actual full model. Finally, the homogenization scheme presented in this study can be efficiently applied to finite element analyses for the thermal stress and deformation behavior of the EGR cooler system with the dimple-typed tube.

• Tribology and Lubricants
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• 제31권6호
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• pp.287-293
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• 2015

Laser surface texturing (LST), a surface engineering modification, has been considered as one of the new processes used to improve tribological characteristics of materials by creating artificially patterned microstructure on the contact surface of mechanical components. In LST technology, the laser is optimized to obtain or manufacture the dimples with maximum precision. The micro-dimples reduce the coefficients of friction and also improve the wear resistance of materials. This study investigates the effect of dimple density is investigated. For this purpose, a ball-on-disc type tester is used with AISI 52100 bearing steel as the test material. Discs are textured with a 5% and 10% dimple density. Experimental work is performed with normal loads of 5 N, 10 N, and 15 N under a fixed speed of 150 rpm at room temperature. The effect of the textured surface is compared to that of the untextured one. Experimental results show that the textured surface yields lower friction coefficients compared to those of untextured surfaces. Specifically, the 10% dimple density textured surface shows better friction reduction behavior than the 5% dimple density textured sample, and has an 18% improvement in friction reduction compared with the untextured samples. Microscopic observation using a scanning electron microscope (SEM) shows that the major friction mechanisms of the AISI 52100 bearing steel are adhesion, plastic deformation, and ploughing.

• Tribology and Lubricants
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• 제28권3호
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• pp.136-141
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• 2012

In this paper, we investigated the friction characteristics of $W100^{\circ}{\o}L25m$ ellipse type surface pattern, on bearing steel. These characteristics are researched by utilizing a pin-on-disk wear test machine, under various velocities and other conditions. The reduction of friction is a necessary requirement for the improved efficiency of industrial parts. As the speed increases, there is a decrease in the effect of the dimple of friction characteristic in low velocity, with substantially little change to density. Conversely, as the load increases, the test direction of ellipse type dimple pattern, resulting in a difference in the texture of these two components. At a dimple density of 7.5% the friction characteristic is easily demonstrated, with a consistent change in both speed and load.

• 한국초등과학교육학회지:초등과학교육
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• 제38권1호
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• pp.73-86
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• 2019

The purpose of this study is to investigate the characteristics of problem solving strategies that gifted students use in science inquiry problem. The subjects of the study are the notes and presentation materials that the 15 team of elementary and junior high school students have solved the problem. They are a team consisting of 27 elementary gifted and 29 middle gifted children who voluntarily selected topics related to dimple among the various inquiry themes. The analysis data are the observations of the subjects' inquiry process, the notes recorded in the inquiry process, and the results of the presentations. In this process, the knowledge related to dimple is classified into the declarative knowledge level and the process knowledge level, and the strategies used by the gifted students are divided into general strategy and supplementary strategy. The results of this study are as follows. First, as a result of categorizing gifted students into knowledge level, six types of AA, AB, BA, BB, BC, and CB were found among the 9 types of knowledge level. Therefore, gifted students did not have a high declarative knowledge level (AC type) or very low level of procedural knowledge level (CA type). Second, the general strategy that gifted students used to solve the dimple problem was using deductive reasoning, inductive reasoning, finding the rule, solving the problem in reverse, building similar problems, and guessing & reviewing strategies. The supplementary strategies used to solve the dimple problem was finding clues, recording important information, using tables and graphs, making tools, using pictures, and thinking experiment strategies. Third, the higher the knowledge level of gifted students, the more common type of strategies they use. In the case of supplementary strategy, it was not related to each type according to knowledge level. Knowledge-based learning related to problem situations can be helpful in understanding, interpreting, and representing problems. In a new problem situation, more problem solving strategies can be used to solve problems in various ways.

• 화훼연구
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• 제19권4호
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• pp.259-263
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• 2011

'Dimple' 품종은 경남농업기술원 화훼연구소에서 황색 홑꽃인 'Champy'를 모본, 황색 홑꽃의 'SP05-135'를 부본으로 인공교배를 실시하여 2005에서 2009년에 걸쳐서 계통선발을 통해 육성하였다. 품종의 특성검정은 2007년부터 2009년까지 촉성재배와 억제재배, 자연재배 조건 아래서 3회에 걸쳐 조사하였다. 'Dimple' 품종의 자연개화기는 10월 30일경이며, 일장조절에 의해 주년재배가 가능하다. 초장은 105.1 cm 정도이며, 생장유형은 단일줄기형이다. 꽃 크기가 4.7 cm, 설상화 길이 2.7 cm, 설상화 너비 0.8 cm인 스프레이국화로 착화수는 20.3개이다. 화색은 선명한 황색이며, 화서형태는 산방화서이다. 봄의 단일상태에서 'Dimple' 품종의 개화소요일수는 50일 정도인 7주 품종이며, 가을 절화수명 검정에서 21.3일로 긴 편이다.