Response analysis of sand ripple form to wave elements
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Abstract:
Sand ripple movement widely exists in the impinged river and coastal zone,and the ripple shape leads to the obvious change of bed surface roughness,which has a significant influence on the total resistance of the bottom bed.For ripple height and ripple length calculation methods,many scholars did comprehensive research,but due to the diversity of each factor affect the ripple scale and the complexity of interconnected,the different research methods,and the differences between the source and water features,lead to the existing formula of ripple shape structure that is diversiform,and the calculation formula lack universality due to an error in the formula under different hydraulic conditions. The general expression for calculating ripple height and ripple length was established based on adapting wave conditions to ripple shape.A total of 385 groups of field measured data and flume experimental data were used for fitting analysis from 1957 to 2018,and the calculation formula for ripple height and ripple length based on the mobility number of near-bottom wave water quality point was obtained.Compared with the existing ripple calculation models,the influence rules of the mobility number on the ripple shape and the advantages and disadvantages of each model were analyzed and demonstrated.Two statistical error parameters RMSE and MAE were used to evaluate the degree of concordance [JP3]between the predicted ripple height and ripple length of each prediction model and the actual value,and the accuracy of the formula was measured according to the calculation error.At the same time,the calculation formulas of ripple height and ripple length were applied to calculate the bottom rough height of the bed.The variation characteristics of ripple surface roughness under wave action and the rationality of the ripple formula were discussed by comparing with the existing models,and the parameters in the formula were calibrated using measured data.The formula of ripple shape and bottom roughness were introduced into the calculation of the bottom friction coefficient of waves,and the influence of the calculation method on the calculation result of the bottom friction coefficient was discussed. The Eq.(12) and Eq.(13) for the ripple height and the ripple length were obtained by fitting analysis of measured data.The analysis showed that the dimensionless ripple height and ripple length were related to the mobility number,and decrease with the increase of the mobility number.Based on measured data,compared with Ni81 regular wave model,Ni81 irregular wave model,VR89 model,and GK04 model,the calculated values of Eq.(12) and Eq.(13) had higher accuracy,which could be applied to the prediction of the ripple height and the ripple length in both field flow and flume experiment,and the expression form of the formula was more general.The bottom roughness had a high sensitivity to wave parameters.According to the measured value,the parameter α in the bottom roughness formula was calibrated,and α was set as 245.The ripple scale formula was substituted into the bottom friction coefficient under wave action,and the calculated results were in good agreement with the representative experimental data,indicating that the newly obtained ripple scale formula could be applied for bottom friction coefficient calculation.The shape of the bed surface and the ripple scale affect the energy dissipation and flow state of the wave bottom boundary layer,and the ripple scale had a significant effect on the roughness of the bed surface.However,there were some differences in the calculation methods of the ripple height and the ripple length.The new formula for calculating the shape of the ripple was more accurate and could better reflect the influence of the ripple scale on the friction coefficient of wave bottom.The new formula is more general in expression form and easy to be applied in engineering.This paper provides an effective basis for analyzing the shape resistance of bed surface under wave action and also provides a reference for further studying the total resistance of bed surface and sediment transport.
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