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Title: The impacts of geometrical configuration changes in wave overtopping reduction, spatial distribution and loadings
Author: Dong, Shudi
ISNI:       0000 0005 0292 9101
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2019
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With changing climatic conditions, and ageing infrastructure, existing coastal defences need to be updated to create improved resilience in coastal regions. Retrofitting existing structures, can be a promising solution to improve the resilience of coastal infrastructure. The reliability of coastal defences can principally be assessed based on three aspects: overtopping results, hazardous zone and structural safety. A comprehensive physical model study was undertaken in a 1:50 scale wave flume, to investigate: • Wave overtopping reduction provided by four retrofitting prototypes, • Landward spatial distributions of overtopping water behind vertical seawall and recurve walls, • The applied wave loads on the vertical seawall and recurve walls. The physical modelling experiments were conducted in a research grade laboratory study. The tests were performed in a wave flume of 22m (l) × 0.6m (w) × 1m (h), with a 1:20 smooth impermeable beach slope, with an approximate 1:50 scale. The flume was equipped with a piston-type wave generator with an active absorption system. Each test case consisted of approximately 1000 pseudo-random waves based on the JONSWAP spectrum. The overtopping discharge and proportion were measured by a system consisting of an overtopping detector, collection tank and load-cell, behind the vertical seawall. When measuring the spatial distribution, the collection tank and load-cell were replaced with a multi chamber container. The wave loads applied on the structure were measured by 10 equally distributed pressure transducers with the sampling frequency of 1.28kHz. Effectiveness of recurve walls in reducing overtopping volumes (e.g. overtopping discharge, proportion) were evaluated against three other structural retrofitting options, including i) reef breakwater, ii) diffraction pillars and iii) model vegetation. By comparing overtopping results (e.g. overtopping discharge, overtopping proportion) measured on tested retrofits, recurve walls were evaluated as the most promising retrofitting approach within the tested structure, with over 63% reduction measured in mean overtopping discharge. It was observed that wave overtopping reduction increased significantly with the relative freeboard at the vertical seawall. The influence of structural dimensions on wave overtopping reduction were analysed through the submerged depth on reef breakwater, packing density of vegetation, overhang and height of the recurve walls. Considering the recurve dimensions and wave characteristics, a new version of an equation is proposed for better estimation on mean overtopping discharges on recurve walls. Phase II of this study investigated the spatial distribution of overtopping water landward of the recurve wall. It was observed that the affected range of overtopping events reduced with a recurve wall on the crest of coastal defences, for all tested conditions. Three recurve walls provide favourable reductions (approximate to 45%) to the hazardous zone under non-impulsive conditions. Therefore, empirical equations are advised for each configuration. Difficulties were found when predicting the spatial distribution behind the recurve wall under impulsive wave conditions. However, a methodology was postulated based on the mean overtopping discharge reduction along the landward distance from the seawall. The addition of a recurve parapet was found to increase the applied wave loads on the whole structure, while contributing to the reduction in overtopping volumes. All horizontal wave loads become 1.4 times higher on average, and recurve walls additionally cause extra uplift loads which do not exit on the plain vertical seawall. The magnitude of both wave loads increased with different overhang length and height of the recurve wall. A longer overhang amplifies the uplift loads more significantly (around 1.7), while an increased recurve height is more likely to increase horizontal wave loads (around 1.5). Outcomes from this study give new understanding for wave overtopping on recurve walls. New equations are developed for estimating overtopping discharges and the hazardous zone behind tested recurve walls. Influences of recurve wall to the wave loads applied on the structure were also evaluated. These new results will benefit coastal engineers in further applications of recurve walls.
Supervisor: Not available Sponsor: University of Warwick ; China Scholarship Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: GC Oceanography ; TC Hydraulic engineering. Ocean engineering