• Title/Summary/Keyword: Time Domain Numerical Simulation

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Analysis of Density Wave Oscillation in Boiler Furnace Wall Tubes with Parallel Channel Modeling (평행관 모델링을 통한 보일러 화로벽관 내 밀도파 불안정의 해석)

  • Kim, Jinil;Choi, Sangmin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.37 no.2
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    • pp.187-196
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    • 2013
  • A numerical model was developed to predict the density wave oscillation (DWO) in the furnace wall tubes of a fossil-fired once-through boiler. The transient flow fields in the tubes were obtained using a 1D finite volume method in the time domain. A header model was also implemented to simulate the parallel tube connection of the wall tubes. The inlet and outlet mass flow variation in one of the parallel tubes was examined after a heat perturbation to find the DWO. After successful verification with experimental results reported in literature, the developed model was applied to the wall tubes of a 700-MW boiler furnace. In contrast to the simulation of Takitani's experiment, in which the unstable power thresholds tended to rise in the reduced bypass channel flow, no remarkable changes were observed in the power thresholds in the parallel channel modeling of the wall tubes of the boiler furnace.

An Implementation of Inverse Filter Using SVD for Multi-channel Sound Reproduction (SVD를 이용한 다중 채널상에서의 음재생을 위한 역변환 필터의 구현)

  • 이상권;노경래
    • The Journal of the Acoustical Society of Korea
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    • v.20 no.8
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    • pp.3-11
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    • 2001
  • This paper describes an implementation of inverse filter using SVD in order to recover the input in multi-channel system. The matrix formulation in SISO system is extended to MIMO system. In time and frequency domain we investigates the inversion of minimum phase system and non-minimum phase system. To execute an effective inversion of non-minimum phase system, SVD is introduced. First of all we computes singular values of system matrix and then investigates the phase property of system. In case of overall system is non-minimum phase, system matrix has one (or more) very small singular value (s). The very small singular value (s) carries information about phase properties of system. Using this property, approximate inverse filter of overall system is founded. The numerical simulation shows potentials in use of the inverse filter.

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Transient Effects of Wind-wave Hybrid Platform in Mooring Line Broken Condition (부유식 파력-해상풍력 복합발전 구조물의 계류선 손상 시 과도 응답 해석)

  • Bae, Yoon Hyeok;Lee, Hyebin
    • Journal of the Korean Society for Marine Environment & Energy
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    • v.19 no.2
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    • pp.129-136
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    • 2016
  • Floating offshore structures keep its position by a mooring system against various kind of environmental loadings. For this reason, a reliable design of the mooring system is a key factor for initial design stage of a floating structure. However, there exists possibility of mooring failure, even the system is designed with enough safety margin, due to the unexpected extreme environmental conditions or long-term fatigue loadings. The breaking of one of the mooring lines may change the tension level of the other mooring lines, which can potentially result in a progressive failure of the entire structure. In this study, time domain numerical simulation of 10MW class wind-wave hybrid platform was carried out with partially broken mooring line. Overall platform responses and variations of the mooring line tension were numerically evaluated.

Comparison of Fragility Using Natural Frequency and Damping Parameter in System (고유주파수와 감쇠비에 대한 시스템 손상도 비교)

  • Lee, Seok-Min;Jung, Beom-Seok
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.22 no.1
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    • pp.48-55
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    • 2018
  • The purpose of the present study is to compare the reduction rate of natural frequency and the increase rate of damping parameter with structural damage in system. For this purpose, experiment and numerical simulation analysis are performed for the 2-span H-Beam with lower natural frequency and higher damping parameter from free vibration in structure. The response signal by impact load before and after damage is analyzed at 14 locations. The response signals for all locations are performed fast fourier transform to estimate the natural frequency reduction rate and wavelet transform to estimate the damping parameter increase rate. The time domain function corresponding to each scale(frequency) is separated from the response signal by wavelet parameter. The estimation of damping parameter increase rate using wavelet transform is more sensitive than the estimation of natural frequency reduction rate in structure.

Propagation and Crosstalk Characteristic Analysis of Pulse Shaped Signals on the Coupled Microstrip Lines (결합 마이크로스트립 선로상의 펄스형태 신호의 전파 및 누화 특성 해석)

  • Park, Sun-Keun;Kim, Nam;Rhee, Sung-Yup;Jang, Woo-Hyun
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.8 no.5
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    • pp.516-524
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    • 1997
  • The propagation properties of various pulse signal types(square pulse, Gaussian pulse, trapezoid pulse, RF pulse) on coupled microstrip lines are investigated. Numerical integration technique which has its accuracy and is easily simulated, is used to obtain the time domain response of pulse signals. Frequency-dependent characteristics of coupled microstrip line is obtained using Jansen's approximate equation. The propagation properties of pulse signal on coupled microstrip lines is analyzed regarding to its geometric structure (relative permittivity ${varepsilon}_r$ substrate height h, strip width w of the microstrip line) and pulse width ${\tau}$ of signal pulse. The simulation results show that space between two lines is very significant parameter in pulse distortion in comparison of any other parameters. The results of this paper are compatible to the trade-off determination of relative permittivity, substrate height, strip width and pulse width of signal pulse when a design of MIC and MMIC is necessary.

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FLUID-STRUCTURE INTERACTION IN A U-TUBE WITH SURFACE ROUGHNESS AND PRESSURE DROP

  • Gim, Gyun-Ho;Chang, Se-Myoung;Lee, Sinyoung;Jang, Gangwon
    • Nuclear Engineering and Technology
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    • v.46 no.5
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    • pp.633-640
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    • 2014
  • In this research, the surface roughness affecting the pressure drop in a pipe used as the steam generator of a PWR was studied. Based on the CFD (Computational Fluid Dynamics) technique using a commercial code named ANSYS-FLUENT, a straight pipe was modeled to obtain the Darcy frictional coefficient, changed with a range of various surface roughness ratios as well as Reynolds numbers. The result is validated by the comparison with a Moody chart to set the appropriate size of grids at the wall for the correct consideration of surface roughness. The pressure drop in a full-scale U-shaped pipe is measured with the same code, correlated with the surface roughness ratio. In the next stage, we studied a reduced scale model of a U-shaped heat pipe with experiment and analysis of the investigation into fluid-structure interaction (FSI). The material of the pipe was cut from the real heat pipe of a material named Inconel 690 alloy, now used in steam generators. The accelerations at the fixed stations on the outer surface of the pipe model are measured in the series of time history, and Fourier transformed to the frequency domain. The natural frequency of three leading modes were traced from the FFT data, and compared with the result of a numerical analysis for unsteady, incompressible flow. The corresponding mode shapes and maximum displacement are obtained numerically from the FSI simulation with the coupling of the commercial codes, ANSYS-FLUENT and TRANSIENT_STRUCTURAL. The primary frequencies for the model system consist of three parts: structural vibration, BPF(blade pass frequency) of pump, and fluid-structure interaction.

Wet Drop Impact Response Analysis of CCS in Membrane Type LNG Carriers -I : Development of Numerical Simulation Analysis Technique through Validation- (멤브레인형 LNG선 화물창 단열시스템의 수면낙하 내충격 응답해석 -I : 검증을 통한 수치해석 기법 개발-)

  • Lee, Sang-Gab;Hwang, Jeong-Oh;Kim, Wha-Soo
    • Journal of the Society of Naval Architects of Korea
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    • v.45 no.6
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    • pp.726-734
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    • 2008
  • While the structural safety assessment of Cargo Containment System(CCS) in membrane type LNG carriers has to be carried out in consideration of sloshing impact pressure, it is very difficult to figure out its dynamic response behaviors due to its very complex structural arrangements/materials and complicated phenomena of sloshing impact loading. For the development of its original technique, it is necessary to understand the characteristics of dynamic response behavior of CCS structure under sloshing impact pressure. In this study, for the exact understanding of dynamic response behavior of CCS structure in membrane Mark III type LNG carriers under sloshing impact pressure, its wet drop impact response analyses were carried out by using Fluid-Structure Interaction(FSI) analysis technique of LS-DYNA code, and were also validated through a series of wet drop experiments for the enhancement of more accurate shock response analysis technique. It might be thought that the structural response behaviors of impact response analysis, such as impact pressure impulses and resulted strain time histories, generally showed very good agreement with experimental ones with very appropriate use of FSI analysis technique of LS-DYNA code, finite element modeling and material properties of CCS structure, finite element modeling and equation of state(EOS) of fluid domain.

Effects of Size and Permittivity of Rat Brain on SAR Values at 900 MHz and 1,800 MHz

  • Hyun Jong-Chul;Oh Yi-Sok
    • Journal of electromagnetic engineering and science
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    • v.6 no.1
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    • pp.47-52
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    • 2006
  • The objective of this study is to evaluate the effects of size and permittivity on the specific absorption rate(SAR) values of rat brains during microwave exposure at mobile phone frequency bands. A finite difference time domain (FDTD) technique with perfect matching layer(PML) absorbing boundaries is used for this evaluation process. A color coded digital image of the Sprague Dawley(SD) rat based on magnetic resonance imaging(MRI) is used in FDTD calculation with appropriate permittivity values corresponding to different tissues for 3, 4, 7, and 10 week old rats. This study is comprised of three major parts. First, the rat model structure is scaled uniformly, i.e., the rat size is increased without change in permittivity. The simulated SAR values are compared with other experimental and numerical results. Second, the effect of permittivity on SAR values is examined by simulating the microwave exposure on rat brains with various permittivity values for a fixed rat size. Finally, the SAR distributions in depth, and the brain-averaged SAR and brain 1 voxel peak SAR values are computed during the microwave exposure on a rat model structure when both size and permittivity have varied corresponding to different ages ranging from 3 to 10 weeks. At 900 MHz, the simulation results show that the brain-averaged SAR values decreased by about 54 % for size variation from the 3 week to the 10 week-old rat model, while the SAR values decreased only by about 16 % for permittivity variation. It is found that the brain averaged SAR values decreased by about 63 % when the variations in size and permittivity are taken together. At 1,800 MHz, the brain-averaged SAR value is decreased by 200 % for size variation, 9.7 % for permittivity variation, and 207 % for both size and permittivity variations.

Evaluation of the Effect of Riser Support System on Global Spar Motion by Time-domain Nonlinear Hull/Mooring/Riser Coupled Analysis

  • KOO BON-JUN;KIM MOO-HYUN
    • Journal of Ocean Engineering and Technology
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    • v.19 no.5 s.66
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    • pp.16-25
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    • 2005
  • The effect of vertical riser support system on the dynamic behaviour of a classical spar platform is investigated. Spar platform generally uses buoyancy-can riser support system, but as water depth gets deeper the alternative riser support system is required due to safety and cost issues. The alternative riser support system is to hang risers off the spar platform using pneumatic cylinders rather than the buoyancy-can. The existing numerical model for hull/mooring/riser coupled dynamics analysis treats riser as an elastic rod truncated at the keel (truncated riser model), thus, in this model, the effect of riser support system can not be modeled correctly. Due to this reason, the truncated riser model tends to overestimate the spar pitch and heave motion. To evaluate more realistic global spar motion, mechanical coupling among risers, guide frames and support cylinders inside of spar moon-pool should be modeled. In the newly developed model, the risers are extended through the moon-pool by using nonlinear finite element methods with realistic boundary condition at multiple guide frames. In the simulation, the vertical tension from pneumatic cylinders is modeled by using ideal-gas equation and the vertical tension from buoyancy-cans is modeled as constant top tension. The different dynamic characteristics between buoyancy-can riser support system and pneumatic riser support system are extensively studied. The alternative riser support system tends to increase spar heave motion and needs damper system to reduce the spar heave motion.

Comparisons between UPML and Liao's ABC in the FDTD method for 2D Cylindrical Coordinates (2D 원통형 좌표계를 위한 FDTD 방법에서 UPML과 Liao 흡수경계조건의 비교)

  • Hong, Ic-Pyo
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.11 no.6
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    • pp.1054-1061
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    • 2007
  • In this paper, the comparison between UPML and Liao's absorbing boundary condition in the FDTD(Finite-Difference Time-Domain) method was performed for the analysis of the 2D cylindrical coordinate system. Generally, it is known as the absorbing characteristics of the UPML is bro than Liao's absorbing boundary condition in the 2D rectangular coordinate. The simulation results in this paper showed that Liao's original absorbing boundary condition is better than other two absorbing boundary conditions, Liao's modified condition and UPML. We concluded that more numerical, theoretical studies, simulations and verifications for various absorbing boundary conditions will be needed to get more accurate results for the design of useful 2D cylindrical microwave circuits.