Transient wave behaviour over an underwater sliding hump from experiments and analytical and numerical modelling

Callaghan, David P., Ahmadi, Afshin and Nielsen, Peter (2011) Transient wave behaviour over an underwater sliding hump from experiments and analytical and numerical modelling. Experiments in Fluids: experimental methods and their applications to fluid flow, 51 6: 1657-1671. doi:10.1007/s00348-011-1183-2


Author Callaghan, David P.
Ahmadi, Afshin
Nielsen, Peter
Title Transient wave behaviour over an underwater sliding hump from experiments and analytical and numerical modelling
Journal name Experiments in Fluids: experimental methods and their applications to fluid flow   Check publisher's open access policy
ISSN 0723-4864
1432-1114
Publication date 2011-12-01
Sub-type Article (original research)
DOI 10.1007/s00348-011-1183-2
Volume 51
Issue 6
Start page 1657
End page 1671
Total pages 15
Place of publication Heidelberg, Germany
Publisher Springer
Collection year 2012
Language eng
Abstract Flume measurements of a one-dimensional sliding hump starting from rest in quiescence fresh water indicate that when the hump travels at speed less than the shallow-water wave celerity, three waves emerge, travelling in two directions. One wave travels in the opposite direction to the sliding hump at approximately the shallow-water wave celerity (backward free wave). Another wave travels approximately in step with the hump (forced wave), and the remaining wave travels in the direction of the hump at approximately the shallow-water wave celerity (forward free wave). These experiments were completed for a range of sliding hump speed relative to the shallow-water wave celerity, up to unity of this ratio, to investigate possible derivation from solutions of the Euler equation with non-linear and non-hydrostatic terms being included or excluded. For the experimental arrangements tested, the forced waves were negative (depression or reduced water surface elevation) waves while the free waves were positive (bulges or increased water surface elevation). For experiments where the sliding hump travelled at less than 80% of the shallow-water wave celerity did not include transient behaviour measurements (i.e. when the three waves still overlapped). The three wave framework was partially supported by these measurements in that the separated forward and forced waves were compared to measurements. For the laboratory scale experiments, the forward free wave height was predicted reasonably by the long-wave equation (ignoring non-linear and non-hydrostatic terms) when the sliding hump speed was less than 80% of the shallow-water wave celerity. The forced wave depression magnitude required the Euler equations for all hump speed tested. The long-wave solution, while being valid in a limited parameter range, does predict the existence of the three waves as found in these experiments (forward travelling waves measured quantitatively while the backward travelling waves visually by video). Nevertheless, the forced wave transient development required non-linear and non-hydrostatic terms for higher sliding hump speeds. The forward free wave, controversially, does not need non-linear and non-hydrostatic terms until much higher hump speeds, suggesting that the forward free wave falls in the parameter space where long-wave equations apply whereas the forced wave more often falls into the parameter space requiring non-linear and non-hydrostatic terms. It does raise the question of why the forced wave transient dynamics does not impact on the initial transient dynamics where the forward free wave is in the long-wave theory, escaping the forced wave (at least for speeds less than 80% of the shallow-water wave celerity).
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Civil Engineering Publications
Official 2012 Collection
 
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Created: Tue, 18 Oct 2011, 02:47:49 EST by Jeannette Watson on behalf of School of Civil Engineering