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Time-Line Interpolation Errors in Pipe Networks

J. Hydraul. Eng. 132, 294 (2006); http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(294) (13 pages)

Masashi Shimada1, Jim Brown2, Della Leslie3, and Alan Vardy, F.ASCE4

1Professor, Dept. of Biological and Environmental Engineering, Univ. of Tokyo, Tokyo, Japan.
2Research Fellow, Civil Engineering Division, Univ. of Dundee, Dundee, Scotland DD1 4HN.
3Formerly, Civil Engineering Division, Univ. of Dundee, Dundee, Scotland DD1 4HN.
4Research Professor, Civil Engineering Division, Univ. of Dundee, Dundee, Scotland DD1 4HN.

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(Submitted 30 December 2003; accepted 19 May 2005)

An exact method of assessing numerical errors in analyses of unsteady flows in pipe networks is introduced. The assessment is valid for fixed-grid method of characteristics analyses using time-line interpolations. A pipe polynomial transfer matrix is developed and is analogous to transfer function matrices used in free oscillation theory. The influence of reachback is assessed by comparing exact numerical predictions using a polynomial transfer matrix with exact analytical predictions obtained using free oscillation theory. The investigation is part of a long-term project aimed at automating the selection of numerical grid sizes in unsteady flow analyses. The eventual goal is to enable users of unsteady flow software to prescribe required degrees of accuracy instead of specifying the numerical grid itself. This paper is only a first step toward the long-term aim, but it is a big step toward an intermediate objective of providing exact benchmarking data for the assessment of approximate methods of automatic grid selection.

© 2006 ASCE

Article Outline

  1. Introduction
    1. Numerical Responses in Transient Flows
    2. Outline of Paper
  2. MOC with Time-Line Interpolation
    1. Reachback and Interpolation Parameters ( m and ξ )
    2. MOC Equations
    3. Standing Waves
    4. Properties of the MOC Response
    5. Polynomial Transfer Matrix
  3. Application to Single Pipes
    1. Grid Size Dependence
    2. Influence of the Reachback Factor, m
    3. Influence of the Interpolation Factor, ξ
  4. Application to Networks
    1. Pipe End Conditions
    2. Polynomial Transfer Matrix—Pipes in Series
    3. Polynomial Transfer Matrix—Branches
  5. Free-Oscillation Theory
  6. Three-Pipe Branch
  7. Four-Pipe Loop
  8. Multibranch Network
  9. High versus Low Frequencies
  10. Future Use of the Polynomial Transfer Method
  11. Conclusions

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0733-9429 (print)  
1943-7900 (online)

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