• 한국자동차공학회논문집
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• 제1권1호
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• pp.59-65
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• 1993

In a spark ignition engine, in order to make research on flame propagation, attentive concentration should be paid on initial combustion stage about the formation and development of flame. In addition, the initial stage of combustion governs overall combustion period in a spark ignition engine. With the increase of the size of flame kernel, it could reach initial flame stage easily, and the mixture could proceed to the combustion of stabilized state. Therefore, we must study the theoretical calculation of minimum flame kernel radius which effects on the formation and development of kernel. To calculate the minimum flame kernel radius, we must know the thermal conductivity, flame temperature, laminar burning velocity and etc. The thermal conductivity is derived from the molecular kinetic theory, the flame temperature from the chemical reaction equations and the laminar burning velocity from the D.K.Kuehl's formula. In order to estimate the correctness of the theoretically calculated minimum flame kernel radius, the researcheres compared it with the RMaly's experimental values.

• 소성∙가공
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• 제13권1호
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• pp.90-101
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• 2004

An inverse mosaic method has been proposed to generate an initial blank shape from the final product shape. Differently from the geometric mapping method, the method can handle triangular patches. However, the generated blank shape is strongly dependent on the order of determination of nodes. In order to compensate the dependency error smoothing technique has been also developed. Although the accuracy has been improved greatly compared with the geometrical mapping method, the method has limitation, due to the no incorporation of plasticity theory. Even though the accuracy of the radius vector method is already proved. the method requires initial guess to start the method. In order to compromise the limitation of the present method and the radius vector method, the method has been connected to the radius vector method. The efficiency of the present optimal blank design method has been verified with some chosen examples.

• 대한기계학회논문집
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• 제11권5호
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• pp.740-745
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• 1987

본 연구에서는 파괴조건(4)와 유사하게 임계 스트레인 조건을 사용하나 기존 스트레인이 없는 재료의 날카로운 균열선단을 가진 시편의 파괴인성실험치(.delta.$_{IC}$)로 부터 재료의 고유상수인 특성길이를 결정하는 방법이 제안되었다.이 파괴조건을 이 용하여 처음노치선단의 유한한 반경과 재료의 기존 스트레인이 시편의 파괴개시에 미 치는 영향을 예측하고자 한다.

• 한국항행학회논문지
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• 제10권4호
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• pp.371-376
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• 2006

스피어 디코더의 초기 반지름 결정 문제는 비트 오율 (bit error rate)과 복잡도에 있어서 많은 영향을 미친다. 이런 초기 반지름은 채널의 통계적 특성을 고려함으로 설정되거나, MMSE 결정 값을 이용하여 설정할 수 있다. 채널의 통계적 특성을 이용한 방법은 초기 반지름이 송신 신호에 해당하는 격자점을 매우 높은 확률로 포함한다. MMSE 결정 값을 이용하는 방법은 먼저 수신 신호에서 MMSE 연 판정 부호(soft output information)을 얻은 후, 경 판정(hard decision)을 내린 다음, 수신 신호 공간에서 경 판정 부호에 해당하는 격자점을 찾는다. 그리고 수신 신호와 경 판정 부호에 해당하는 격자점 사이의 유클리디안 거리(Euclidean distance)를 초기 반지름으로 설정한다. 본 논문에서는 채널의 통계적 특성을 이용한 방법에 있어서 기존의 복잡한 수식에 비해 간단한 새로운 식을 유도하고, MMSE 결정값을 이용한 방법과 비교 연구 하였다. 비교를 위해 'Tightness'라는 새로운 측도를 이용하였다. 전산 실험 결과, 낮은 SNR 영역과 중간 정도의 SNR 영역에서는 MMSE를 이용한 방법의 더 많이 디코딩 복잡도 감소를 보였고, 높은 SNR 영역에서는 채널의 통계적 특성을 이용한 방법이 더 낮은 디코딩 복잡도를 보였다.

• 천문학회보
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• 제35권2호
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• pp.35.1-35.1
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• 2010

Unlike the initial mass function, the initial size distribution of globular cluster (GC) systems is not well known. We calculate the evolution of the mass function (MF), radial distribution (RD), and size distribution (SD) of the Galactic GC system. By comparing the results from this calculation and the present-day MF, RD, and SD of the Galactic GC system, we infer the initial SD of the GC system. We find that a Gaussian distribution of the half-mass radius and a Gaussian distribution of the half-mass to Jacobi radius ratio are the best-fit initial SDs of the Galactic GC system.

• Geomechanics and Engineering
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• 제19권2호
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• pp.141-151
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• 2019

A novel theoretical solution is presented for created (zero initial radius) cavity expansion problem based on CamClay model and considers the effect of initial anisotropic in-situ stress and drained conditions. Here the strain of this theoretical solution is small deformation in elastic region and large deformation in plastic region. The works for cylindrical and spherical cavities expanding in drained condition from zero initial radius are investigated. Most of the conventional solutions were based on the isotropic and undrained condition, however, the initial stress state of natural soil mass is anisotropy by soil deposition history, and drained cavity expansion calculation is closer to actual engineering in permeable soil mass. Finally, the parametric study is presented in order to the engineering significance of this work.

• 한국연소학회지
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• 제4권2호
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• pp.1-10
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• 1999

Pulverized coal is widely used as the source of electrical power generation and industrial processes. Numerical analysis on the transient ignition process of the cloud of pulverized coal particles in various cases is carried out. Particle radius, initial particle temperature, number density are chosen as major parameters that influence the characteristics of ignition and combustion. The result can be summarized as follow. The ignition occurs at the position that is closed to the surface of the cloud. Maximum temperature and velocity appear at ignition point, and the concentrations of gaseous fuel and oxidizer decrease rapidly near the ignition point. The chemical reaction takes place in wider zone as number density and particle radius decrease. The ignition delay is shortest when particle radius is about $50\;{\mu}m$, and tends to be shorter as number density and initial ambient temperature increase.

• 소성∙가공
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• 제17권1호
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• pp.52-58
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• 2008

Tube hydroforming process is generally consisted with pre-bending, preforming and hydroforming processes. Among forming defects which may occur in tube hydroforming such as buckling, wrinkling and bursting, the wrinkling and bursting by local instability under excessive tensile stress mode were mainly caused by thinning phenomenon in the manufacturing process. Thus the accurate prediction and suitable evaluation of the thinning phenomenon play an important role in designing and producing the successfully hydroformed parts without any failures. In this work, the formability on hydroformed part for automobile, i.e. engine cradle, was evaluated using finite element analysis. The initial tube radius, loading path with axial feeding force and internal pressure, and preformed configuration after preforming process were considered as the dominant process parameters in total tube hydroforming process. The effects on these process parameters could be confirmed through the numerical experiments with respect to several kinds of finite element simulation conditions. The degree of enhancement on formability with each process parameters such as initial tube radius, loading path and preform configuration were also compared. Therefore, it is noted that the evaluation approach of the formability on hydroformed parts for lots of industrial fields proposed in this study will provide one of feasible methods to satisfy the increasing practical demands for the improvement of the formability in tube hydroforming processes.

• 대한기계학회논문집A
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• 제33권4호
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• pp.296-309
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• 2009

Thick-walled cylinder with high pressure have had wide application in the armament industry. In the thick-walled cylinder, fatigue crack is generated at inner radius and developed toward the outer radius. To prevent generation of fatigue crack, the autofrettage process had been used. The compressive residual stress induced by the autofrettage process extends loading pressure and fatigue life of the thick-walled cylinder. In this study, the residual stress of single and compound cylinder by the autofrettage process was evaluated. The analytical compressive residual stress of single cylinder was good agreement with experimental result at inner radius. The analysis on the residual stress of compound cylinder was conducted. The compressive residual stress at inner radius was increased with the overstrain level. And fatigue life of the compound cylinder with initial crack was evaluated. The considered initial crack shape was straight and semi-elliptical. The fatigue life was extended with the overstrain level. The fatigue life of the compound cylinder with semi-elliptical crack was longer than straight crack. The suitable way to extend fatigue life of the compound cylinder was proposed.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 추계학술발표대회 논문집
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• pp.163-169
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• 2001

The solution of two-dimensional deflection of circular wavy reinforcing fiber elastics was obtained for one end clamped boundary under concentrated load condition. The fiber was regarded as a linear elastic material. Wavy shape was described as a combination of half-circular arc smoothly connected each other with constant curvature of all the same magnitude and alternative sign. Also load direction was taken into account. As a result, the solution was expressed in terms of a series of elliptic integrals. These elliptic integrals had two different transformed parameters involved with load value and initial radius of curvature. While we found the exact solutions and expressed them in terms of elliptic integrals, the recursive ignition formulae about the displacement and arc length at each segment of circular section were obtained. Algorithm of determining unknown parameters was established and the profile curve of deflected beam was shown in comparison with initial shape.