• 대한기계학회논문집A
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• 제21권12호
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• pp.1984-1991
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• 1997

Recently burr technology is rising in the fields of the precision manufacturing and the high quality machining, deburring has treated as a difficult problem on going to the high efficiency, automation in the FMS. Removal of burr with various shapes, dimensions and properties couldn't be standardized and has depended on manual treatment. Especially, deburring for cross hole inside owing to passing through out perpendicular to a main hole is more difficult, the electrochemical method is proper as its solution at practical aspects. Burr elimination in the cross hole drilling of governor shaft used in the automobile engine so far has been worked by a manual post-processing by a skillful worker, which becomes a factor of productivity-down and cost-up so that improvement of machining process is needed. Therefore, for the high efficiency and automation of internal deburring in the cross hole, development of electrochemical deburring technology is needed. So, the new process in the burr treatment is supposed. In this study, characteristics of electrochemical deburring through experiments were identified and factors such as electrolytic gap and electorlytic fluid contributed to removal burr height were analyzed. Also, deburring efficiency and electrolytic performance for cross hole were examined according to electrolytic current and electrochemical deburring condition corresponding to acquired edge quality was found out.

• Journal of the Korean Physical Society
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• 제73권10호
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• pp.1420-1430
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• 2018

We investigate an entangled system, which is analogous to a composite system of a black hole and Hawking radiation. If Hawking radiation is well approximated by an outgoing particle generated from pair creation around the black hole, such a pair creation increases the total number of states. There should be a unitary mechanism to reduce the number of states inside the horizon for black hole evaporation. Because the infalling antiparticle has negative energy, as long as the infalling antiparticle finds its partner such that the two particles form a separable state, one can trace out such a zero energy system by maintaining unitarity. In this paper, based on some toy model calculations, we show that such a unitary tracing-out process is only possible before the Page time while it is impossible after the Page time. Hence, after the Page time, if we assume that the process is unitary and the Hawking pair forms a separable state, the internal number of states will monotonically increase, which is supported by the Almheiri-Marolf-Polchinski-Sully (AMPS) argument. In addition, the Hawking particles cannot generate randomness of the entire system; hence, the entanglement entropy cannot reach its maximum. Based on these results, we modify the correct form of the Page curve for the remnant picture. The most important conclusion is this: if we assume unitarity, semi-classical quantum field theory, and general relativity, then the black hole should violate the Bekenstein-Hawking entropy bound around the Page time at the latest; hence, the infinite production arguments for remnants might be applied for semi-classical black holes, which seems very problematic.

• 한국자동차공학회논문집
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• 제15권2호
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• pp.1-7
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• 2007

The effect of injector geometries including the injection angle and number of nozzle holes on homogeneous charge compression ignition (HCCI) engine combustion has been investigated in an automotive-size single-cylinder diesel engine. The HCCI engine has advantages of simultaneous reduction of PM and NOx emissions by achieving the spatially homogenous distribution of diesel fuel and air mixture, which results in no fuel-rich zones and low combustion temperature. To make homogeneous mixture in a direct-injection diesel engine, the fuel is injected at early timing. The early injection guarantees long ignition delay period resulting in long mixing period to form a homogeneous mixture. The wall-impingement of the diesel spray is a serious problem in this type of application. The impingement occurs due to the low in-cylinder density and temperature as the spray penetrates too deep into the combustion chamber. A hole-type injector (5 holes) with smaller angle ($100^{\circ}$) than the conventional one ($150^{\circ}$) was applied to resolve this problem. The multi-hole injector (14 holes) was also tested to maximize the atomization of diesel fuel. The macroscopic spray structure was visualized in a spray chamber, and the spray penetration was analyzed. Moreover, the effect of injector geometries on the power output and exhaust gases was tested in a single-cylinder diesel engine. Results showed that the small injection angle minimizes the wall-impingement of diesel fuel that results in high power output and low PM emission. The multi-hole injector could not decrease the spray penetration at low in-cylinder pressure and temperature, but still showed the advantages in atomization and premixing.

• Steel and Composite Structures
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• 제18권1호
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• pp.135-148
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• 2015

The cutout hole locating at the place of rib-to-diaphragm welded connection is adopted to minimize the restraint, which is caused by the floor-beam web to rib rotation at the support due to the unsymmetrical loads in orthotropic deck. In practice, an inevitable problem is that there is a large number of welding joint's cracks formed at the edge of cutout hole. In this study, a comparative experiment is carried out with two types of cutout hole, the circular arc transition and the vertical transition. The fatigue life estimation of specimens is investigated with the application of the structural hot spot stress approach by finite element analyses. The results are compared with the ones of the fatigue tests which are carried out on these full-scale specimens. Factors affecting the stress range are also studied.

• 한국생산제조학회지
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• 제26권3호
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• pp.292-298
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• 2017

Numerical analysis for various design parameters should be preceded by optimal design of composite materials. Numerous studies have been conducted on the bolting of interconnecting beams. In this study, the response surface method was applied to optimize the design of bolted joints connected by laminated wood composite beams. The response surface was created by combining the FEA code for composite analysis and the algorithm for forming the response surface. Optimization on this response surface was performed with a genetic algorithm to derive the results. The determination of the optimum bolt-hole position for the connection of composite beams is an optimization problem. Tsai-Wu composite failure index, maximum deflection, and simple von Mises stress are set as the objective functions. It has been proved that the design results of the optimized bolt-hole are superior to the design performance of the existing conventional bolt-hole position.

• 한국자동차공학회논문집
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• 제9권4호
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• pp.112-120
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• 2001

Poor fuel vaporization in gasoline engines causes the problem of HC emission during the cold start and warm-up period. This paper presents a strategy to improve fuel atomization during the warm-up phase. In this experiment, the heated fuel-rail system is constructed to investigate the effects of fuel heating on the average size of fuel droplets. The fuel atomization effects are examined by measuring Sauter Mean Diameter (SMD) of the fuel droplets from the three different types (two-hole, pintle, and six-hole) of injectors based upon a returnless heated fuel-rail system. The results show that the six-hole type injector is the most sensitive to fuel heating in terms of SMD among three different types of injectors.

• 한국자동차공학회논문집
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• 제9권4호
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• pp.204-213
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• 2001

This paper develops the compliance approach to the problem of load sharing between a cracked plate and a cover plate used to bridge the crack. The theory is validated by using calculated stress intensity factors for the covered and uncovered cases and by using stop hole method to reduce experimentally observed growth rates to a common base. Calculations are then made on the effect of cover plate width on fatigue crack retardation in order to demonstrate the predictive capability of the technique.

• 천문학회지
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• 제29권2호
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• pp.195-205
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• 1996

The evolution of the stellar debris after tidal disruption due to the super massive black hole's tidal force is difficult to solve numerically because of the large dynamical range of the problem. We developed an SPH (Smoothed Particle Hydrodynamics) - TVD (Total Variation Diminishing) hybrid code in which the SPH is used to cover a widely spread debris and the TVD is used to compute the stream collision more accurately. While the code in the present form is not sufficient to obtain desired resoultion, it could provide a useful tool in studying the aftermath of the stellar disruption by a massive black hole.

• 산업공학
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• 제12권2호
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• pp.346-353
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• 1999

In this paper, the optimum drilling operation sequence which results into the minimum overall machining time required to produce a (multi-diameter) hole is identified. The operation sequence is defined as the set of ordered operations used for producing a (multi-diameter) hole. The overall machining time is derived by summing the minimum machining times of each operation assigned to a sequence. The operations represent the drilling actions of certain sizes to produce the related holes. The minimum machining time of each operation is obtained by solving the optimization problem. Finally, this paper will identify the effects of machining constraints on the overall machining times and their relationships to sequence selection.

• 정보처리학회논문지C
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• 제16C권4호
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• pp.535-542
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• 2009

무선센서네트워크는, 다수의 센서노드가 넓은 지역에 배치되어 자신의 전원에 의해 동작하고 다른 센서노드와 협력하여 환경검침 또는 물리량 검침을 수행하는 무선네트워크로 정의한다. 각각의 센서노드들은 자신의 배터리전원소모를 최소화하여, 장기간 사용할 수 있어야 하며, 센서 노드를 적절하게 배치하여 전체 네트워크 커버리지를 제공할 수 있어야 무선센서네트워크의 수명을 늘일 수 있다. 초기 센서노드의 배치로는 센서들의 배터리 수명 등의 이유로 제약이 있으며, 모바일센서노드는 센서가 이동하여 새로운 커버리지를 제공함으로써, 이러한 제약조건을 완화할 수 있다. 본 논문에서는 perimeter coverage property를 만족하는 모바일 센서들의 단계적인 이동을 통한 커버리지 제공기법을 제안한다. 각각의 모바일 센서노드들은 이웃한 센서노드들이 dead 노드인지 판단하게 되며, dead 노드인 경우, 센서네트워크의 커버리지 hole을 만드는지 여부를 판단한 후, 각각의 모바일 센서노드들은 hole의 중심점을 계산하고, 관련된 센서노드들이 협동하여, 단계적으로이동하여, 최종 hole을 커버하는 새로운 센서네트워크를 형성하게 된다. 본 제안기법을 시뮬레이션하여 DCM 기법과 비교한 결과, 에너지 효율을 결정하는 전체 움직임거리 측면에서 최소 50% 이상의 성능향상을 보임을 확인하였다.