• Journal of Mechanical Science and Technology
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• 제17권1호
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• pp.146-156
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• 2003

A numerical algorithm is developed to analyze the performance of a Unit-injector (UI) System for a diesel engine. The fundamental theory of the algorithm is based on the continuity equation of fluid dynamics. The loss factors that should be seriously regarded on the continuity equation are the compressibility effect of liquid fuel, the wall friction loss in high-pressure fuel lines of the system, the kinetic energy loss of fuel in the system, and the leakage of fuel out of the control volume. For an evaluation of the developed simulation algorithm, the calculation results are compared with the experimental outputs provided by the Technical Research Center of Doowon Precision Industry Co. (DPICO) ； the maximum pressure in the plunger chamber (P$\_$p/) and total amount of fuel injected into a cylinder per cycle (Q$\_$f/) at each operational condition. The result shows that the average error rate (%) of P$\_$p/ and Q$\_$f/ are 2.90% and 4.87%, respectively, in the specified operational conditions. Hence, it can be concluded that the analytical simulation algorithm developed in this study can be reasonably applied to the performance prediction of newly designed UI system.

• 대한기계학회논문집A
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• 제39권6호
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• pp.589-596
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• 2015

횡등방성 압전재료에 대한 모서리경사균열 문제를 해석하였다. 두 기계적 집중 면외하중과 전기적 집중 면내하중이 표면과 균열면에 각각 작용하고, 균열면은 절연균열면이다. 일반화된 변위벡터를 도입하고 Mellin 변환을 사용하여 문제를 수식화하고, 이로부터 Wiener-Hopf 식을 유도하였다. 이식을 풀므로써 폐형으로 주어지는 해를 얻었다. 임의의 균열길이나 경사각에 대해서도 적용이 되는 응력 및 전기변위 강도계수와 에너지 방출율을 구하였다. 이 해는 중첩에 의하여 임의로 분포하는 전기기계하중 문제에 대한 해를 제공하는 기본해로 사용될 수 있다.

• 한국수학사학회지
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• 제25권1호
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• pp.15-27
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• 2012

16세기 후반과 17세기 전반에 활동했던 영국의 과학자이자 수학자인 Thomas Harriot은 대수기호를 독창적으로 만들어 사용하였고 일부는 오늘날에도 사용하고 있다. 또한 방정식에서 음수근 뿐만 아니라 복소수근도 받아들였는데 그의 이러한 관점은 당시로는 혁신적이었으며 나아가 방정식의 형태의 일반화에도 진일보한 모습을 보여주었다. 사후 유작 외에는 생전에 수학 저서가 한 권도 없는 탓에 Harriot 개인이나 그가 이루어 놓은 수학이 수학적 성취에 비하여 수학사나 수학교육에서 그에 대하여 소홀히 다루어진 감이 있다. 이 논문에서는 동시대 유명한 수학자였던 비에타와 데카르트의 대수기호와 방정식론을 비교함으로써 Harriot이 이루어놓은 수학을 알리고자 한다.

• 한국측량학회지
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• 제25권6_1호
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• pp.529-536
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• 2007

Registration between image and object space is a fundamental step in photogrammetry and computer vision. Along with rapid development of sensors - multi/hyper spectral sensor, laser scanning sensor, radar sensor etc., the needs for registration between different sensors are ever increasing. There are two important considerations on different sensor registration. They are sensor invariant feature extraction and correspondence between them. Since point to point correspondence does not exist in image and laser scanning data, it is necessary to have higher entities for extraction and correspondence. This leads to modify first, existing mathematical and geometrical model which was suitable for point measurement to line measurements, second, matching scheme. In this research, linear feature is selected for sensor invariant features and matching entity. Linear features are incorporated into mathematical equation in the form of extended collinearity equation for registration problem known as photo resection which calculates exterior orientation parameters. The other emphasis is on the scheme of finding matched entities in the aide of RANSAC (RANdom SAmple Consensus) in the absence of correspondences. To relieve computational load which is a common problem in sampling theorem, deterministic sampling technique and selecting 4 line features from 4 sectors are applied.

• Advances in aircraft and spacecraft science
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• 제7권1호
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• pp.79-90
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• 2020

The dynamic coupling between shaker and test-article has been investigated by recent research through the so called Virtual Shaker Testing (VST) approach. Basically a VST model includes the mathematical models of the test-item, of the shaker body, of the seismic mass and the facility vibration control algorithm. The subsequent coupled dynamic simulation even if more complex than the classical hard-mounted sine test-prediction, is a closer representation of the reality and is expected to be more accurate. One of the most remarkable benefits of VST is the accurate quantification of the frequency down-shift (with respect to the hard-mounted value), typically affecting the first lateral resonance of heavy test-items, like medium or large size Spacecraft (S/Cs), once mounted on the shaker. In this work, starting from previous successful VST experiences, the parameters having impact on the frequency shift are identified and discussed one by one. A simplified analytical system is thus defined to propose an efficient and effective way of calculating the lower bound frequency shift through a simple equation. Such equation can be useful to correct the S/C lateral natural frequency measured during the test, in order to remove the contribution attributable to the shaker in use. The so-corrected frequency value becomes relevant when verifying the compliance of the S/C w.r.t. the frequency requirement from the Launcher Authority. Moreover, it allows to perform a consistent post-test correlation of the first lateral natural frequency of S/C FE model.

• 대한전자공학회논문지
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• 제22권5호
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• pp.93-101
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• 1985

다양한 채널 길이와 임의의 인가전압하의 MOS 트랜지스터를 2차원적으로 시뮬레이션 하기 위한 프로그램(SOMOS)을 제작하였다. Poisson의 방정식에 대하여는 Newton방법을, 연속방정식에 대하여는 발산정리를 이용하여 기본 수식들에 대한 유한차등법(FDM)에 따른 수식을 전개하였으며, 선형화된 수식의 해는 SOR 방법과 Cummel의 알고리즘을 이용하여 구했다. 하난의 동작상태의 소자를 시뮬레이션 하기 위한 시간은 VAX 11/780 컴퓨터를 사용했을때 인가전압 상태에 따라 30초 내지 4분 정도가 소요되었다. 인가전압과 전위분포에 따라 자동적으로 생성되는 그리드는 비균일한 간격을 가지며 필요에 따라 자동적으로 개선된다.

• 대한기계학회논문집
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• 제16권12호
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• pp.2306-2314
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• 1992

본 연구에서는 Lagrangian 방정식을 이용해 알루미늄, CFRP, GFRP, BFRP 등으 로 혼합적층된 cross-ply 사각판에 대해 굽힘-신장연성을 고려하여 Runge-Kutta Gill 법을 적용하여 수치적으로 비선형진동해석을 수행하였다.그리고 여러가지 적층방법 에 따라 비선형 진동에 어떠한 영향이 미치는가를 검토하였으며, 형상비(a/b), 모우드 의 변화 그리고 탄성계수비에 따른 비선형진동 거동을 규명하였다. 한편, 기본진동 수에 대해서는 상용 유한요소프로그램인 ABAQUS의 결과와 비교하였으며, 단일 적층된 판의 비선형진동거동에 대해서는 Singh의 결과와 비교 검토하였다.

• Structural Engineering and Mechanics
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• 제11권4호
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• pp.357-372
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• 2001

In this paper, cantilevered tall structures are treated as cantilever bars with varying cross-section for the analysis of their free longitudinal (or axial) vibrations. Using appropriate transformations, exact analytical solutions to determine the longitudinal natural frequencies and mode shapes for a one step non-uniform bar are derived by selecting suitable expressions, such as exponential functions, for the distributions of mass and axial stiffness. The frequency equation of a multi-step bar is established using the approach that combines the transfer matrix procedure or the recurrence formula and the closed-form solutions of one step bars, leading to a single frequency equation for any number of steps. The Ritz method is also applied to determine the natural frequencies and mode shapes in the vertical direction for cantilevered tall structures with variably distributed stiffness and mass. The formulae proposed in this paper are simple and convenient for engineering applications. Numerical example shows that the fundamental longitudinal natural frequency and mode shape of a 27-storey building determined by the proposed methods are in good agreement with the corresponding measured data. It is also shown that the selected expressions are suitable for describing the distributions of axial stiffness and mass of typical tall buildings.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2006년도 춘계학술대회 논문집
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• pp.298-301
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• 2006

This paper describes the electron energy distribution function characteristics in $SF_6-Ar$ gas calculated for range of E/N values from $50\sim700[Td]$ by the Monte Carlo simulation(MCS) and Boltzmann equation(BE) method using a set of electron collision cross sections determined by the authors and the values of electron swarm parameters are obtained by time of flight(TOF) method. In this dissertation the results of the combined experimental and theoretical studies designed to understand and predict the spatial growth and transport coefficients for electrons in $SF_6$ and $SF_6-Ar$ mixtures have described. The ionization and attachment coefficients in pure $SF_6$ and $SF_6-Ar$ mixtures have been calculated over the range of 10$SF_6$ molecule and for Ar atom proposed by other authors. The results obtained in this work will provide valuable information on the fundamental behaviors of electrons in weakly ionized gases and the role of electron attachment in the choice of better gases and unitary gas dielectrics or electro negative components in dielectric gas mixtures.

• 한국가스학회지
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• 제13권5호
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• pp.20-25
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• 2009

혼합물의 폭발하한계는 Raoult의 법칙, Dalton의 법칙, Le Chatelier 법칙 그리고 활동도계수 모델식을 이용하여 예측될 수 있다. 본 연구에서는 ethylacetate-ethanol 계와 ethanol+toluene 계의 폭발하한계를 예측하기 위해 Raoult의 법칙 그리고 활동도계수 모델식인 van Laar 식과 Wilson 식을 이용하였다. 계산값과 문헌값을 비교한 결과, Raoult의 법칙에 의한 계산값이 활동도 모델식에 의한 계산값 보다 모사성이 뛰어남을 확인하였다.