• 소성∙가공
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• 제15권2호
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• pp.148-152
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• 2006

In this study, the experiments of warm deep drawing were done with heated die, and with heated die, and blankholder, and cooled punch in order to investigate the formability of AZ31 magnesium alloy sheet in warm deep drawing. For this, warm deep drawing experiments were executed under various temperatures and punch velocities. The results of warm deep drawing with heated die showed that fracture occurred around the punch part at punch velocity of 75mm/min and punch stroke of 10mm under temperature range of 373-523K, but did not occur under temperature range of 548-673K even punch stroke of 25mm. And fracture at the punch stroke of 25mm and the temperature of 523K did not occur under the punch velocity of 30mm/min, but occurred under punch velocity of 75 and 125mm/min. Also warm deep drawing with heated die and blankholder, and cooled punch showed that the temperature range happening maximum height under punch velocity of 10-100mm/min was around 498-523K. Finally, with heating and cooling technique necking of AZ31 magnesium alloy occurred at punch shoulder part under the temperature range of 293-423K, but at die wall part under the temperature range of 473-573K.

• 설비공학논문집
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• 제24권10호
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• pp.745-749
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• 2012

Heating pipes burst was occurred in the apartment complex that was applied floor radiant heating system. There were two opinions for the cause of the bursted heating pipes that was the flaw during construction and defects in the product and also there were conflicting among them. Officials analyzed it in order to investigate the cause of the rupture. Tensile test results showed different tensile strength between the lower part of heating pipe and the upper part of heating pipes. The lower tensile strength is maintained while the top was not secured. The reason why rupture heating pipes is that flow velocity isn't secured and then the air get stagnant. Stagnant air makes hardening. It is caused rupturing. The proper flow rate was confirmed 0.166 m/sec after experiment. It isn't make stagnant air inside heating pipes.

• 대한조선학회논문집
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• 제41권4호
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• pp.68-76
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• 2004

Inherent strain method for analyzing deformation of line-heating is substituting experiments of high cost, because of its high accuracy and quickness. Nowadays, the progressing forms of line-heating are not straight moving motions used to traditional studies, but weaving motions which can diversely input heat source. In shipyard, reasons of weaving motions are induction of a special characteristic by water cooling, maximum temperature limitation for keeping plates from melting, and rhythm for workman's maintaining velocity. On this study, a method which can obtain optimal weaving heating condition was presented, some examples were introduced, and the results corresponded to works of shipyard. Lastly, what the specifications of plates on efficiency are is presented, through the quality standard of shipyard and FEM heat transfer simulation. The ultimate purpose of line heating is the automation, so in case of plates which need weaving heating, the optimal heating condition suggested by this study can be used well in designing coil specifications of induction heaters which are heat input sources of new generation.

• KIEAE Journal
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• 제7권5호
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• pp.65-71
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• 2007

The purpose of this study was to analyze the difference of thermal sensation by radiant floor heating as ecological design element. The experimental investigations were carried out in climate chamber, and subjects were 34 college-age females in good health. The experimental variable was radiant heat by floor heating, and experimental controlled conditions were indoor temperature, relative humidity, and air velocity in climate chamber and clothing value and activity of subjects. The results are as follows. (1) Indoor temperature($21{\pm}0.5^{\circ}C$) in climate chamber were maintained as controlling. Clothing values of the subjects were controlled as average 0.73 clo. In the floor heating-off, globe temperature was average $23.2^{\circ}C$(22.4~24.1), but in the floor heating-on, globe temperature was average $24.8^{\circ}C$(23.0~25.5). (2) In the floor heating-off, thermal sensation rating was average -1.03(slightly cool), in the floor heating-on, thermal sensation rating was average +1.03(slightly warm). (3) There were the differences of thermal sensation by radiant floor heating although indoor temperatures were maintained in an equal state. (4) The thermal sensation rating was tending upward according as the globe temperature was getting higher.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.915-918
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• 2008

수화열 및 자기수축은 동일한 수화반응에 의해 필연적으로 발생되는 현상으로서 여러 연구자들에의해 수화온도와 자기수축의 깊은 상관성은 언급되어 왔으나, 아직까지 수화온도와 자기수축의 구체적인 관계에 대한 연구보고는 거의 없는 실정이다. 이에 본 연구에서는 시험체의 단면크기를 달리하여 초기 수화발열 및 자기수축의 특성을 구체적으로 분석한 후, 내부 수화온도와 자기수축의 상관성을 검토하였다. 그 결과, 시험체 단면이 증가할수록 전체적인 내부온도와 자기수축은 증가하였으며, 수화발열상승구간 및 자기수축증가구간에서 발생하는 수화온도 상승량 및 상승률, 자기수축 증가량 및 증가율은 증가하였다. 수화발열상승속도 및 자기수축증가속도가 증가할수록 구간에서 발생하는 수화온도상승량과 자기수축증가량은 증가한 반면, 수화온도상승률과 자기수축증가율은 유사하게 나타났으며, 수화발열상승 속도가 증가할수록 자기수축증가구간의 자기수축증가량과 자기수축증가속도는 증가하였다.

• 한국화재소방학회논문지
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• 제18권1호
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• pp.31-36
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• 2004

본 연구는 잔골재 및 혼화재 종류, W/C에 따른 콘크리트의 폭열성상 및 압축강도 초음파속도 등의 공학적 특성을 검토함으로서 폭열 방지 및 화재 피해를 입은 콘크리트 구조물의 재사용과 보수보강, 안전도평가 등에 기초적인 자료를 제시하고자 한다. 폭열성상을 살펴보면, 잔골재에 따라서는 바다모래를 사용한 경우 폭열이 발생하지 않았거나 약간의 폭열이 나타나는 정도이나 재생잔골재나 부순모래를 사용한 경우에는 폭열이 심하게 나타났다. 또한 혼화재 종류에 따라서는 대체로 유사한 폭열성상을 나타내었다. 한편, W/C 30.5%의 고강도 영역에서는 대부분 폭열하였으나 W/C 55%의 보통강도 영역에서는 대부분 폭열하지 않았다. 잔존 압축강도는 W/C 55%의 경우 평균 45%로 나타났으며, W/C 30.5%의 경우에는 평균 64％로 나타났다. 초음파속도는 잔골재 종류 및 W/C, 가열시간에 따라 다르게 나타났으며, 가열 후 3개월이 가열 후 1개월보다 약 1.3∼8.4%의 초음파속도 회복을 보였다.

• 설비공학논문집
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• 제17권4호
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• pp.370-376
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• 2005

For the purpose of investigating the effective removal of heating/cooling load from light-weighted building envelope, two air-conditioning systems, conventional parameter air-conditioning system and air-barrier system, are evaluated and compared by both experiment and simulation with six different cases during heating and cooling season. In addition, the characteristics of window-side building thermal load are assessed by varying supply air velocity in order to seek the optimal system operation condition. The results are as follows. 1) Air-barrier system is more effective to remove heating/cooling load at perimeter zone than conventional parameter air-conditioning system. Moreover, the better effectiveness appears during cooling season than during heating season. 2) The experiment during cooling season provides that indoor temperature of air-barrier system shows $1^{\circ}C$ less than that of the conventional system with similar outdoor air temperature profile, and indoor temperature distribution is more uniform throughout the experimented model space. It concludes that air-barrier system can achieve energy saving comparing to the conventional system. 3) The capturing efficiency of air-barrier system is 0.47 on heating season and 0.2 on cooling season with the same supply air volume. It results that the system performs effectively to remove building thermal load, moreover demonstrates high efficiency during cooling season. 4) The simulation results provide that capturing efficiency to evaluate the effective removal of building load from perimeter zone shows high value when supply air velocity is 1 m/s.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 동계학술발표대회 논문집
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• pp.552-557
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• 2007

Due to the recent improvement of living standard of residential buildings, the requirements of the thermal comfort and energy saving in heating system have been raised. The radiant floor heating system has been widely used as a residential heating method, which has been modernized to use hot water running into the tubes embedded in the floor structure. The uniform flow distribution is very important factor for a radiant floor heating system such as a blood vessel system in human body. Therefore, it is necessary to investigate the operating characteristics to develop an optimal radiant floor heating system. In this study, numerical analyses were carried out, using a commercial CFD code, FLUENT, to obtain the velocity distribution under steady, three-dimensional, standard k-$\varepsilon$ model and no-slip condition. Results are graphically depicted with various parameters.

• 지구물리와물리탐사
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• 제23권1호
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• pp.1-12
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• 2020

섭입 및 열개와 같이 대변형을 수반하는 지구동역학적 현상 발생은 암석권의 국지적인 약대의 발달이 필요하다. 이러한 약화 기작 중 하나인 전단열은 암석권의 온도를 국부적으로 높여 강도를 낮추는 역할을 하여 암석권 파괴를 촉진시킬 수 있다. 본 연구에서는 전단열에 대한 정량적인 분석을 위하여 2차원 탄소성 인장 분지 모형을 제작하여 기존 수치 모사 연구를 벤치마크하였다. 암석권의 항복강도, 인장 속도, 변형량- 및 온도-의존성 약화 현상 등을 조절하여 전단열 발생량에 미치는 영향을 분석하였다. 실험 결과, 약화를 고려하지 않은 경우 전단열의 발생량은 암석권의 항복강도 및 인장 속도와 양의 상관관계가 있는 것으로 나타났다. 기준 모형인 항복강도 100 MPa, 인장 속도 2 cm/yr로 설정된 경우, 총 20 km 인장된 시점(0.025의 변형률)에서 ~ 50 K의 온도 상승을 보여주었다. 소성 변형 및 온도에 따른 약화가 포함된 경우에는, 더 효율적인 약화 기작이 더 강한 전단열의 생성으로 이어지는데 이러한 현상은 약화 기작과 전단열 발생 사이에 양성되먹임이 작용함을 지시한다. 또한 변형 초기에 급격한 전단열 발생량을 보여주지만, 변형이 지속되어 암석권의 강도가 약화되면 전단열 발생 속도가 최대 ~ 80% 감소했다. 이는 약화 기작이 포함된 경우 전단열은 비교적 손상되지 않은 상태인 암석권의 강도에 큰 영향을 미침을 시사한다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.434-437
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• 2006

Due to the shape of spindle with small diameter and heavy section, rapid cooling is difficult. It is difficult to fabricate the tapered wheel bearings with fine microstructure. Thus, their mechanical characteristics, such as yield strength and fatigue resistance, decrease. Producing the tapered wheel bearings with good workability during orbital forming after hot forging, hot forging process with several process parameters was optimized by means of statistical technique of Six-Sigma scheme. As a result, the lower heating temperature is, the lower the hardness and yield strength of forgings are. Also, the faster conveyer velocity is, the lower the hardness and yield strength of forgings are. To avoid therefore occurrence of the surface rupture during orbital forming, the heating temperature should be controlled as low as possible and the conveyer velocity should be controlled as fast as possible.