• 대한수학회지
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• 제40권1호
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• pp.87-107
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• 2003

In this paper, we consider a discrete time queueing system fed by a superposition of an ON and OFF source with heavy tail ON periods and geometric OFF periods and a D-BMAP (Discrete Batch Markovian Arrival Process). We study the tail behavior of the queue length distribution and both infinite and finite buffer systems are considered. In the infinite buffer case, we show that the asymptotic tail behavior of the queue length of the system is equivalent to that of the same queueing system with the D-BMAP being replaced by a batch renewal process. In the finite buffer case (of buffer size K), we derive upper and lower bounds of the asymptotic behavior of the loss probability as $K\;\longrightarrow\;\infty$.

• 한국소음진동공학회논문집
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• 제13권12호
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• pp.938-946
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• 2003

Length of an unconstrained viscoelastic damping layer on beams is determined to maximizeloss factor using a numerical search method. The fractional derivative model can describe damping characteristics of viscoelastic damping materials accurately, and is used to represent nonlinearity of complex modulus with frequencies and temperatures. Equivalent flexural rigidity of the unconstrained beam is obtained using Ross, Ungar, Kelvin[RUK] equation. The loss factors of partially covered unconstrained beam are calculated by a modal strain energy method. Optimal lengths of the unconstrained viscoelastic damping layer of beams are identified with ambient temperatures and thickness ratios of beam and damping layer by using a finite-difference-based steepest descent method.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.665-671
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• 2003

Length of an unconstrained viscoelastic damping layer on beams is determined to maximize loss factor using a numerical search method. The fractional derivative model can describe damping characteristics of the viscoelastic damping material, and is used to represent nonlinearity of complex modulus with frequencies and temperatures. Equivalent flexural rigidity of the unconstrained beam is obtained using Ross, Ungar, Kerwin(RUK) equation. The loss factors of partially covered unconstrained beam are calculated by a modal strain energy method. Optimal lengths of the unconstrained viscoelastic damping layer of beams are obtained with respect to ambient temperatures and thickness ratios of beam and damping layer.

• 소음진동
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• 제4권2호
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• pp.209-219
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• 1994

Classical method calculates the resonance frequency of Helmholtz resonator by postulating that there is a moving mass in neck and a stiffness which expresses the compressibility of cavity. This has been widely accepted as reasonable to determine the resonant frequency, provided that the wave length of interest is longer that any length scale of resonater. Nevertheless, it has been often recognized that this classical method sometimes does not well predict the resonant frequency. This paper decribes the way in which the dynamics of resonator very often does care about the detail geometries of resonator; location of the neck, diameter ratio of the neck to that of cavitty, length of resonator compared with that of neck, etc. This rather unexpected observations have been proved theoretically; 3 dimensional analysis of acoustic wave equation, as well as experimentally by comparing the resonant frequencies, transmission loss, and insertion loss of resonator.

• International Journal of Concrete Structures and Materials
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• 제8권2호
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• pp.99-116
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• 2014

The American Concrete Institute (ACI) 318-11 permits the use of the moment magnifier method for computing the design ultimate strength of slender reinforced concrete columns that are part of braced frames. This computed strength is influenced by the column effective length factor K, the equivalent uniform bending moment diagram factor $C_m$ and the effective flexural stiffness EI among other factors. For this study, 2,960 simple braced frames subjected to short-term loads were simulated to investigate the effect of using different methods of calculating the effective length factor K when computing the strength of columns in these frames. The theoretically computed column ultimate strengths were compared to the ultimate strengths of the same columns computed from the ACI moment magnifier method using different combinations of equations for K and EI. This study shows that for computing the column ultimate strength, the current practice of using the Jackson-Moreland Alignment Chart is the most accurate method for determining the effective length factor. The study also shows that for computing the column ultimate strength, the accuracy of the moment magnifier method can be further improved by replacing the current ACI equation for EI with a nonlinear equation for EI that includes variables affecting the column stiffness and proposed in an earlier investigation.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.449-452
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• 2004

The lap splice lengths of deformed steel reinforcing bars and GFRP bars with two different to surface type were experimentally compared using beam specimens. The purpose was to evaluate the length required of the GFRP bar to develop strength equivalent to the conventional steel reinforcing bar. The main test variable was the lap splice length. Two different GFRP bar surfaces were tested: (1) spiral-type GFRP bars and (2) sand coated GFRP bars. For the conventional steel bars (SD400 grade), strength over 400 MPa in tension was reached using the lap splice length of $30d_b$. Splice failure was observed in the specimen with the lap splice length of $20d_b$. For the spiral-type and sand coated GFRP bars, the tensile strength developed in the GFRP bars decreased with decreasing splice lengths. Development of the cracks on beam surfaces was clearly visible for the beams reinforced with the GFRP bars. Mid-span deflections, however, were significantly smaller than the comparable beams with conventional steel bars indicating potential ductility problem.

• 한국철도학회논문집
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• 제13권4호
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• pp.404-411
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• 2010

철도차량용 선형유도전동기(Linear Induction Motor, LIM) 축소-회전형 모델의 기본 설계 결과를 검증하기 위하여 LIM의 자기등가회로법을 이용한 파라미터 도출 및 특성 계산을 수행하였다. LIM의 경우, 자기등가회로상의 파라미터는 LIM의 전기자 코어와 2차측 알루미늄 도체판의 형상 및 공극에 대한 함수로써 표현이 가능하다. 즉 전기자 코어와 2차측 알루미늄 도체판의 형상 및 공극 변경에 의해 LIM의 특성이 크게 달라질 수 있다는 것을 의미한다. 따라서 본 연구에서는 철도차량용 LIM 축소-회전형 모델의 공극, 2차측 AL-Plate의 두께, 오버행 길이, 형상 변경에 따른 LIM 축소-회전형 모델의 자기등가회로 파라미터 및 특성의 변화 추세를 분석하여, 철도차량용 실모델 LIM 개발을 위한 기초 연구를 수행하였다.

• 한국소음진동공학회논문집
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• 제22권12호
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• pp.1213-1219
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• 2012

The purpose of this study is to present a guideline to design a short-term manual measurement of environmental noise level, which is more economical and flexible, but less representative than long-term automatic measurement. The proposed guideline can provide the number of measurement times and the length of measurement term required to secure the extent of the representativeness. The data was collected at 4 sites located in Seoul and at 4 sites located outside of Seoul. The probabilities for five-minute equivalent noise levels, Leq, 5min, to stay in an error range from the quarterly representative noise level were used to evaluate sampling techniques. The probability analysis of the daytime period showed that the noise levels measured between 10 am and 2 pm and between 9 pm and 10 pm have the probabilities higher than 60 %. On the other hand, even for the same length of total measurement time, increasing the number of random samplings results in higher probabilities than increasing the length of measurement term.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권3호
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• pp.315-325
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• 2017

The design dimension may not be satisfactory at the final stage due to the welding during the assembly stage, leading to cutting or adding the components in large structure constructions. The productivity is depend on accuracy of the welding quality especially at assembly stage. Therefore, it is of utmost importance to decide the component dimension during each assembly stage considering the above situations during the designing stage by exactly predicting welding deformation before the welding is done. Further, if the system that predicts whether welding deformation is equipped, it is possible to take measures to reduce deformation through FE analysis, helping in saving time for correcting work by arresting the parts which are prone to having welding deformation. For the FE analysis to predict the deformation of a large steel structure, calculation time, modeling, constraints in each assembly stage and critical welding length have to be considered. In case of fillet welding deformation, around 300 mm is sufficient as a critical welding length of the specimen as proposed by the existing researches. However, the critical length in case of butt welding is around 1000 mm, which is far longer than that suggested in the existing researches. For the external constraint, which occurs as the geometry of structure is changed according to the assembly stage, constraint factor is drawn from the elastic FE analysis and test results, and the magnitude of equivalent force according to constraint is decided. The comparison study for the elastic FE analysis result and measurement for the large steel structure based on the above results reveals that the analysis results are in the range of 80-118% against measurement values, both matching each other well. Further, the deformation of fillet welding in the main plate among the total block occupies 66-89%, making welding deformation in the main plate far larger than the welding deformation in the longitudinal and transverse girders.

• 한국화재소방학회논문지
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• 제27권3호
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• pp.52-59
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• 2013

본 연구에서는 화재현장에서 사용하는 소방호스에 대하여 사용압력과 방수량 변화에 따른 마찰손실을 실측하였다. 소방호스의 종류, 수량, 사용압력 등 소방호스의 사용 실태를 분석하여 그 결과를 토대로 실측한 결과 화재현장에서 소방공무원이 사용하는 조건에서 소방호스의 마찰손실은 무려 56.8%까지 측정되었다. 옥내 외 소화전설비에서 펌프양정 계산시 사용하는 소방호스의 등가 길이와도 많은 차이가 난다. 관련규정조차 마찰손실에 대한 제한 규정이 없고, 소방호스를 생산하는 업체에서도 마찰손실을 측정한 자료가 없으며, 화재현장에서는 마찰손실을 고려하지 않고 소방호스를 전개함으로써 호스의 사용량이 많아지고 소방펌프차에서 고압으로 방수하게 되는 원인이 되므로 본 연구를 통하여 소방호스 마찰손실에 대한 등가길이 기준을 정립하고 화재현장에서 소방호스의 마찰손실을 고려한 전개 방법을 제안하고자 한다.