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2003

University of Beira Interior. Overview of IST Group Results on the Sediment Benchmark. João Leal (UBI) Rui Ferreira (IST) António Cardoso (IST) António Almeida (IST). 3 rd IMPACT Workshop Louvain-la-Neuve. 2003. Overview of IST Group Results on the Sediment Benchmark.

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2003

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  1. University of Beira Interior Overview of IST Group Results on the Sediment Benchmark João Leal (UBI) Rui Ferreira (IST) António Cardoso (IST) António Almeida (IST) 3rd IMPACT Workshop Louvain-la-Neuve 2003

  2. Overview of IST Group Results on the Sediment Benchmark Comment the IST numerical results Perform a sensitivity analysis on the empirical coefficients in order to improve the results University of Beira Interior OBJECTIVES:

  3. Overview of IST Group Results on the Sediment Benchmark bed shear stress (Chézy equation) depth of the sheet-flow layer (Sumer et al. 1996; Pugh & Wilson 1999) EMPIRICAL COEFFICIENTS velocity in the sheet-flow layer (Sumer et al. 1996) sediment transport rate (Bagnold 1966) University of Beira Interior CONCEPTUAL MODEL Closure equations

  4. Overview of IST Group Results on the Sediment Benchmark University of Beira Interior CONCEPTUAL MODEL Coefficients evaluation: using Sumer et al. (1996) results and the non-dimensional fall velocity as the measure of similitude between the sediment used by those authors and the PVC cylinders used in the UCL test Wilson’s (1987) theoretical relation

  5. Overview of IST Group Results on the Sediment Benchmark University of Beira Interior RESULTS GOOD AGREEMENT

  6. Overview of IST Group Results on the Sediment Benchmark University of Beira Interior RESULTS GOOD AGREEMENT

  7. Overview of IST Group Results on the Sediment Benchmark University of Beira Interior RESULTS BAD AGREEMENT (the numerical model underestimates the scour hole)

  8. Overview of IST Group Results on the Sediment Benchmark University of Beira Interior RESULTS BAD AGREEMENT (the numerical model underestimates the scour hole)

  9. Overview of IST Group Results on the Sediment Benchmark University of Beira Interior RESULTS BAD AGREEMENT (the numerical model predicts no scour)

  10. Overview of IST Group Results on the Sediment Benchmark University of Beira Interior RESULTS BAD AGREEMENT (the numerical model predicts no scour)

  11. Overview of IST Group Results on the Sediment Benchmark University of Beira Interior RESULTS BAD AGREEMENT (the numerical wave-front celerity is faster than the experimental one)

  12. Overview of IST Group Results on the Sediment Benchmark In the sections near the dam the scour is underestimated by the numerical model POSSIBLE SOLUTION: increase the coefficient of Bagnold’s sediment transport formula The numerical wave-front celerity is faster than the experimental one POSSIBLE SOLUTION: increase the friction coefficient University of Beira Interior COMMENTS Two major discrepancies were found between the UCL experimental data and the IST numerical results NOTE: should the initial water depth downstream the gate be non negligible and the wave-front celerity would be slowed down

  13. Overview of IST Group Results on the Sediment Benchmark University of Beira Interior Influence hd The increase of hd increases the wave-front height

  14. Overview of IST Group Results on the Sediment Benchmark In order to increase friction (Cf) we will need to use smaller values of University of Beira Interior Limitation imposed by the closure equations (value adopted in the blind test) The experimental sheet-flow data by Sumer et al. (1996) and by Pugh & Wilson (1999) indicate that which implies a new limit

  15. Overview of IST Group Results on the Sediment Benchmark University of Beira Interior Influence As  increases, the water levels increase in the wave-front region while the sheet-flow height decreases. The celerity is not influenced by 

  16. Overview of IST Group Results on the Sediment Benchmark University of Beira Interior Influence  = 2 overestimates the erosion, affecting the water level for higher times

  17. Overview of IST Group Results on the Sediment Benchmark University of Beira Interior Influence  = 2 gives better bed levels but worst water levels

  18. Overview of IST Group Results on the Sediment Benchmark University of Beira Interior Influence The increase of Cf increases the scour hole, but the numerical bed level is still much higher than the experimental one

  19. Overview of IST Group Results on the Sediment Benchmark University of Beira Interior Influence The increase of Cf allows the approximation between the numerical and the experimental wave-fronts

  20. Overview of IST Group Results on the Sediment Benchmark University of Beira Interior Influence For higher Cf values the numerical wave-front celerity is reduced and approximates the experimental celerity

  21. Overview of IST Group Results on the Sediment Benchmark University of Beira Interior Final Results

  22. Overview of IST Group Results on the Sediment Benchmark University of Beira Interior Final Results

  23. Overview of IST Group Results on the Sediment Benchmark University of Beira Interior Final Results

  24. Overview of IST Group Results on the Sediment Benchmark The IST numerical results are generally in good agreement with the benchmark data The model always underestimate the scour hole that is observed downstream the dam in the experiments The major discrepancies between numerical and experimental results can be attenuated by changing the value of some parameters of the closure equations University of Beira Interior CONCLUSIONS

  25. END

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