scholarly journals SEDIMENT RESPONSES TO NATURAL WAVES

1984 ◽  
Vol 1 (19) ◽  
pp. 121 ◽  
Author(s):  
Alexander F. Nielsen ◽  
Angus D. Gordon

This paper is concerned with wave-induced seabed forcing functions and sediment responses on the Australian South East Continental Shelf. The transfer of surface displacement energy to near-bed oscillatory water movement energy is examined with respect to linear and second order wave theories. Seabed sediment responses are examined by comparing field bedform size data to laboratory data with a view to determining characteristic spectral parameters that may be applied with existing theories to predict sediment responses under natural wave spectra. A rippled bed incipient motion criterion incorporating the contribution to boundary shear stress made by the presence of bedforms as well as particle size is developed empirically from field data using dimensional analysis techniques.

1995 ◽  
Vol 299 ◽  
pp. 267-288 ◽  
Author(s):  
K. T. Shum

The role of wave-induced separated flow in solute transport above a rippled bed is studied from numerical solutions to the two-dimensional Navier–Strokes equations and the advection-diffusion equation. A horizontal ambient flow that varies sinusoidally in time is imposed far above the bed, and a constant concentration difference between the upper and lower boundaries of computation is assumed. The computed flow field is the sum of an oscillatory rectilinear flow and a vortical flow which is periodic both in time and in the horizontal. Poincaré sections of this flow suggest chaotic mixing. Vertical lines of fluid particles above the crest and above the trough deform into whorls and tendrils, respectively, in just one wave period. Horizontal lines near the bottom deform into Smale horseshoe patterns. The combination of high shear and vortex-induced normal velocity close to the sediment surface results in large net displacements of fluid particles in a period. The resulting advective transport normal to the bed can be higher than molecular diffusion from well within the viscous boundary layer up to a few ripple heights above the bed. When this flow field is applied to the transport equation of a passive scalar, two distinct features – regular temporal oscillations in concentration and a linear time-averaged vertical concentration profile – are found immediately above the bed. These features have also been observed previously in field measurements on oxygen concentration. Advective transport is shown to be dominant even in the region where the time-averaged concentration profile is linear, a region where vertical solute transport has often been estimated using diffusion-type models in many field studies.


2015 ◽  
Vol 4 ◽  
pp. 812-818 ◽  
Author(s):  
Sovan Sankalp ◽  
Kishanjit. K. Khatua ◽  
Arpan Pradhan

2016 ◽  
Vol 78 (9-4) ◽  
Author(s):  
Zulkiflee Ibrahim ◽  
Zulhilmi Ismail ◽  
Sobri Harun ◽  
Koji Shiono ◽  
Nazirah Mohd. Zuki ◽  
...  

Frequent floods around the globe including recent events in several states in Malaysia have damaged the residential properties, infrastructures and crops or even deaths. Clearing vegetations or trees on the floodplain has been pointed out as a contributing factor to the damages. Thus, the influence of floodplain vegetation on the river hydraulics during flooding must be better understood. The hydraulics of flood flows in non-erodible vegetated meandering channel was experimented in the laboratory where two-lined steel rods were installed along a riparian zone to simulate as trees. The stage-discharge relationship, flow resistance, depth-averaged velocity, streamwise vorticity and boundary shear stress patterns during shallow and deep flood inundations were studied. The findings showed that floodplain vegetation had increased the channel flow depth by 32% and its flow resistance. The velocity in vegetated zone was lowered and the shear stress reduced by 86.5% to 91% along the river meander. In addition, the trees also limit flow interaction between main channel and floodplain


2013 ◽  
Vol 20 (2) ◽  
pp. 161-168 ◽  
Author(s):  
M. Patnaik ◽  
K.C. Patra ◽  
K.K. Khatua ◽  
L. Mohanty

2005 ◽  
Vol 110 (F4) ◽  
pp. n/a-n/a ◽  
Author(s):  
E. R. Griffin ◽  
J. W. Kean ◽  
K. R. Vincent ◽  
J. D. Smith ◽  
J. M. Friedman

1968 ◽  
Vol 72 (696) ◽  
pp. 1059-1060 ◽  
Author(s):  
N. Rajaratnam ◽  
D. Muralidhar

Summary In this note it is suggested that the three-tube yaw probe be placed on the boundary and used as a Preston tube to measure the boundary shear stress when both its magnitude and direction are unknown. The calibration results necessary for this method are also presented herein.


2022 ◽  
Author(s):  
Bandita Naik ◽  
Vijay Kaushik ◽  
Munendra Kumar

Abstract The computation of the boundary shear stress distribution in an open channel flow is required for a variety of applications, including the flow resistance relationship and the construction of stable channels. The river breaches the main channel and spills across the floodplain during overbank flow conditions on both sides. Due to the momentum shift between the primary channel and adjacent floodplains, the flow structure in such compound channels becomes complicated. This has a profound impact on the shear stress distribution in the floodplain and main channel subsections. In addition, agriculture and development activities have occurred in floodplain parts of a river system. As a consequence, the geometry of the floodplain changes over the length of the flow, resulting in a converging compound channel. Traditional formulas, which rely heavily on empirical approaches, are ineffective in predicting shear force distribution with high precision. As a result, innovative and precise approaches are still in great demand. The boundary shear force carried by floodplains is estimated by gene expression programming (GEP) in this paper. In terms of non-dimensional geometric and flow variables, a novel equation is constructed to forecast boundary shear force distribution. The proposed GEP-based method is found to be best when compared to conventional methods. The findings indicate that the predicted percentage shear force carried by floodplains determined using GEP is in good agreement with the experimental data compared to the conventional formulas (R2 = 0.96 and RMSE = 3.395 for the training data and R2 = 0.95 and RMSE = 4.022 for the testing data).


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