Generalised maximum scour depth prediction on 2D jet scour and 3D jet scour

• Main Author: Wang, Xinyao
• Other Authors: Lim Siow Yong
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Civil engineering
• Online Access: https://hdl.handle.net/10356/145065
• Institution: Nanyang Technological University

Local scour caused by water jets has been extensively investigated in the past. As the understanding on the jet scour processes improved the study area has transformed from the basic understanding on the 2D jet scour to the formulation on the scour prediction. Since there is much similarity between 2D and 3D jet scour, generalizing the 2D and 3D jet scour is possible for the purpose of convenient formulation and spreading technical and physical application. A thorough literature review was carried out to firstly understand the nature of scour that are identified up to date. In this study, the jet scour analysis is limited to the horizontal jet scour in non-cohesive sediment under full-flowing condition. Most previous researchers used the complete similarity in the jet scour analysis. These researches concurred that the densimetric Froude number is the key parameter to correlate the scour hole dimensions. However, since the jet scour analysis has the speciality that other parameters such as the relative tailwater depth or sediment size should not be easily ignored, the incomplete self-similarity approach will be introduced on the application nature and working mechanism, then applied through the analysis of this study. The multiple regression model by excel tools are conducted on the data analysis, coupled with the computed Standard Error, SE and coefficient of determination,R2 which are helpful on the relative influence of the characteristic parameters affecting the scour processes. No experiments are conducted in this study. A total of 518 data sets were used and all are generated by previous researchers and used to propose a prediction model on the maximum scour depth. The effects of several parameters are evaluated in the aspect of observation and interpretation on the plot and multiple regression elements, as well as by comparison. The analysis shows that the densimetric Froude number based on the sediment size of d84, Fo,d84 is observed to be the better representative in the prediction model than the densimetric Froude number based on median sediment size,Fo,d50. The effect of the relative tailwater depth with the hydraulic radius of the jet, H/Rh is also important and is considered as a weighted parameter separately in specific study by previous researchers, and cannot be ignored in the prediction model. The strong relationship between the relative sediment size, d50/Rh and the maximum scour depth dse/Rh is also included in the prediction model. Finally, the proposed maximum scour equation is compared with the prediction models of Lim (2019) and Chiang (2019). The proposed equation agrees reasonably well with the 2D and 3D jet scour database used, and is recommended to predict the maximum scour depth for horizontal 2D and 3D jet scour under a wide range of varying sediment sizes and submerged tailwater conditions under full-flowing condition.