• Title/Summary/Keyword: Numerical Calculation

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Proposal of Approximation Analysis Method for GI/G/1 Queueing System

  • Kong, Fangfang;Nakase, Ippei;Arizono, Ikuo;Takemoto, Yasuhiko
    • Industrial Engineering and Management Systems
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    • v.7 no.2
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    • pp.143-149
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    • 2008
  • There have been some approximation analysis methods for a GI/G/1 queueing system. As one of them, an approximation technique for the steady-state probability in the GI/G/1 queueing system based on the iteration numerical calculation has been proposed. As another one, an approximation formula of the average queue length in the GI/G/1 queueing system by using the diffusion approximation or the heuristics extended diffusion approximation has been developed. In this article, an approximation technique in order to analyze the GI/G/1 queueing system is considered and then the formulae of both the steady-state probability and the average queue length in the GI/G/1 queueing system are proposed. Through some numerical examples by the proposed technique, the existing approximation methods, and the Monte Carlo simulation, the effectiveness of the proposed approximation technique is verified.

A Study on the Prediction Method of Propulsive Energy Loss Related to Automatic Steering of Ships (자동조타로써 항행하는 선박의 추진 에너지 손실량 평가법에 관한 연구)

  • 손경호;이경우;황승욱;배정철
    • Journal of the Korean Institute of Navigation
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    • v.19 no.3
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    • pp.11-19
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    • 1995
  • When an automatic course keeping is introduced, as is quite popular in modern navigation, the closed-loop control system consists of autopilot device, power unit, steering gear, ship dynamics, and magnetic or gyrocompass. We derive mathematical models of each element of the automatic steering system. We provide a method of theoretical analysis on the propulsive energy loss related to automatic steering of ships in the open seas, taking account of the on-off(non-linear) characteristics of power unit. Also we paid attention to non-linear element installed in autopilot device, which is normally called weather adjuster. Next we make numerical calculation of the effects of autopilot control constants on the propulsive energy loss for two kinds of ship, a fishing boat and an ore carrier. Realistic sea and wind disturbances are employed in the calculation.

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Limit Analysis of Axisymmetric Forward Extrusion (축 대칭 전방 압출의 극한 해석)

  • Kim, Byung-Min;Choi, In-Keun;Choi, Jae-Chan;Lee, Jong-Soo
    • Journal of the Korean Society for Precision Engineering
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    • v.8 no.3
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    • pp.93-104
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    • 1991
  • Limit analysis is based on the duality theorem which equates the least upper bound to the greatest lower bound. In this study, limit analysis of axisymmetric forming problem with workhardening materials is formulated by minimizing the upper bound functional and finite element program is developed for forward estrusion. Limit loads, velocity and flow line fields are directly obtained under various process conditions and deformation characteristics such as strains, strain rates and grid distortion are obtained from the optimum velocity components by numerical calculation. The experimental observation was carried out for extrusion and compared with computed results. The good agreement between theoretical and experimental results is shown that the developed programming is very effective for the analysis of axisymmetric extrusion.

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Design of automobile body shape by using panel method (파넬법을 이용한 자동차의 외형설계)

  • 이동호;강신영
    • Journal of the korean Society of Automotive Engineers
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    • v.6 no.4
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    • pp.54-61
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    • 1984
  • Numerical calculation of the flow field past a passenger car was carried out by using a panel method with a small computer of 5Mbyte memory size. The shape of car body was simplified and reconstructed by 2180 panels on which a constant strength sink (or source) was distributed. The separation of flow from the surface and the wake flow were not considered in the calculation because of the computer memory limitation. All of the results of calculation were presented by using a 3-dimensional computer graphics. In spite of small memory size of computer, generally good agreements were obtained, except the separated region, from the comparison of pressure distribution between numerical analysis and wind tunnel experiment with 1/5 scaled model.

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Numerical Calculation of High Pressure Compaction for Porous Materials (높은 압력을 받는 다공질재료의 압축에 대한 수치해석적 연구)

  • 박종관
    • Geotechnical Engineering
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    • v.3 no.3
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    • pp.63-74
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    • 1987
  • A practical constitutive equation with sufficient generality is proposed for porous materials to deal with plastic pore compaction and pore related strain-hardening. With an application of this proposed model, finite element calculations are executed for the compaction of a porous material. Results show powerful potential of finite element method in a quantitative investigation of the process of the compaction. Special attention is given to the process of unloading during which the development of tensile principal stress may lead to phenomena such as lamination and end-capping.

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Time-dependent Characteristics of Pulse Modulated rf Plasma (펄스모듈레이션 된 고주파 플라즈마의 시변특성)

  • Lee Sun-Hong;Park Chung-Hoo;Lee Ho-Jun
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.53 no.11
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    • pp.566-571
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    • 2004
  • Pulse modulation technique provide additional controling method for electron temperature and density in rf and microwave processing plasma. Transient characteristics of electron density and temperature have been measured in pulse modulated rf inductively coupled argon plasma using simple probe circuit. Electron temperature relaxation is clearly identified in the after glow stage. Controllability of average electron temperature and density depends on the modulation frequency and duty ratio. Numerical calculation of time-dependent electron density and temperature have been performed based on the global model. It has been shown that simple langmuir probe measurement method used for continuous plasma is also applicable to time-dependent measurement of pulse modulated plasma.

A Study on Position and Induced Voltage of ADSS Using CSM (CSM을 이용한 ADSS유도전압 해석 및 위치선정에 관한 연구)

  • Myung, S.H.;Lee, B.Y.;Lee, G.C.;Lee, J.B.;Ha, T.H.;Joo, M.N.
    • Proceedings of the KIEE Conference
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    • 1997.07e
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    • pp.1654-1656
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    • 1997
  • Tracking currents related to field exposure for ADSS in T/L is of importance. At phase-ta-phase voltage in excess of 100 kV self-supporting aerial cables with solid insulation tend to suffer damage in regions close to the tower. The damage can be put down to surface tracking currents resulting from different degrees of surface contamination and moisture. Main characteristic of this exposure is the induced voltage analysis and position of ADSS. For complicated calculation of induced voltage on ADSS, this paper described an effective numerical calculation method based on CSM. The proposed methods are applied to 275 kV T/L of Malaysia.

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Evaluation of Tip Leakage Loss and Reduction of Efficiency of Axial Turbomachinery Using Numerical Calculation (수치계산에 의한 축류터보기계의 회전차 익말단의 누설손실과 효율저하에 대한 평가)

  • Ro, Soo-Hyuk;Cho, Kang-Rae
    • The KSFM Journal of Fluid Machinery
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    • v.2 no.1 s.2
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    • pp.73-80
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    • 1999
  • Leakage vortices formed new blade tip causes an increase of total pressure loss near the casing endwall region and as a result, the efficiency of rotor decreases. The reduction of rotor efficiency is related to the size of the tip clearance. In this study, the three-dimensional flowfields in an axial flow rotor were calculated by varying the tip clearance under various flow rates, and the numerical results were compared with experimental ones. The effects of tip clearance and attack angle on the leakage vortex and overall performance, and the loss distributions were investigated through numerical calculations. In this study, tip leakage flow rate and total pressure loss by tip clearance were evaluated using numerical results and approximate equations were presented to evaluate the reduction of rotor efficiency by tip leakage flow.

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Design Technology and Performance Characteristics of Small Scale Two-Dimensional Centrifugal Compressor (초소형 2차원 원심압축기의 설계 및 성능특성)

  • Cho, Hyung-Hee;Choi, Hang-Cheol;Kim, Kwang-Ho;Chung, Jin Taek
    • 유체기계공업학회:학술대회논문집
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    • 2004.12a
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    • pp.405-410
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    • 2004
  • 2-dimensional impeller's distinctive feature is expected to have an influence on performance and flow characteristics of centrifugal compressor. And new design method is required for 2-dimensional impeller, because the unique geometry cannot be designed using conventional theories. The objective of this study is to advance new design technology for 2-dimensional impeller and to investigate the performance characteristics of designed 2-dimensional centrifugal compressor. The performance test for 2-dimensional impeller is conducted at 35000, 40000 and 45000rpm. Also numerical calculation is applied by using commercial CFD code, FLUENT, and the results are compared with experimental results.

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Diffraction of Electromagnetic Waves by a Dielectric Wedge, Part III: Correction by Neumann-Expanded Source (쇄기형 유전체에 의한 전자파의 회절, III부: Neumann 전개된 전원에 의한 수정)

  • 김세윤;라정웅;신상영
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.25 no.9
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    • pp.1027-1038
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    • 1988
  • This paper, the last part of these three companion papers treated the electromagnetic diffraction by a dielectric wedge, presents the correction to the physical optics approcomation by the sheet currents of the Neumann expansion. Those expansion coefficients obtained by solving dual series equation amenable to simple numerical calculation may provide the asymprotically corrected solution. The validity of this result, satisfying both the edge condition near the tip of the dielectric wedge and the boundary condition along dielectric interfaces, is assured by approach of the corrected diffraction pattern to that of a perfectly conducting wedge for large permittivity of dielectric wedge.

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