Show simple item record Hettiarachchi, SSL Mirihagalla, PD 2019-05-24T08:02:56Z 2019-05-24T08:02:56Z
dc.description.abstract The wave field in the vicinity of a coastal structure may be treated in terms of dissipated, reflected and transmitted components. These structures are designed to dissipate a significant proportion of the incident wave energy and will' reflect or transmit the remainder. The transmitted energy has two components namely transmission through the structure and transmission by over topping. The need to absorb or dissipate wave energy demands that coastal structures offer some significant degree of porosity. Most armoured slopes are constructed with voids between and sometimes within the armour units in order to increase wave energy dissipation. The voids matrix offers a conducive configuration for wave energy dissipation arising from wave structure interaction. The ability to predict the levels of reflection, transmission, run-up and run-down for various types of coastal structures play an important role in the assessment of their hydraulic performance. These design parameters together with the hydraulic, geotechnical and structural stability of the individual components and of the structure as a whole determine the overall performance of the structure. The porosity and permeability of the structure too has a significant influence on the hydraulic performance and the economies of construction. The failure in the last two decades, of several large rubble mound breakwaters led to the careful examination of physical processes of wave-structure interaction. It is established that the interaction of waves with a rubble mound breakwater results in a complex flow pattern involving unsteady, two-phase flow. Such flow generates equally complex flow fields. Basic research findings have highlighted some of the related factors which have contributed to the failure of rubble mounds. Such findings have contributed to • better understanding of wave-structure interaction • review of design procedures • development of new concepts and further examination of alternative design practices. • improved investigative techniques, in particular for physical modelling. . The mechanics of wave-structure interaction in the context of a porous coastal structure is a complex phenomenon. When a progressive wave collides with the structure, reflection and transmission of the wave takes place on and across the interface and the resultant flow is often non-Darcy and may be single or two phase. Two phase flow occur due to external or internal wave breaking. These flow conditions in combination and within voids matrix generate a complicated flow system which influence the effective conductivity of the structure contributing to the reduction in wave transmission and an increase in wave reflection. The constituent elements of the structure are subjected to unsteady wave forces. The findings on mechanics of wave-structure interaction have clearly identified the importance of porosity and permeability in the context of wave reflection, transmission and dissipation and the overall hydraulic stability. With respect to development of new concepts and further examination of alternative design practices research have been carried out on both rock armoured and concrete armoured rubble mound breakwaters. Once such alternative in rock armoured breakwaters is the application of naturally reshaping mass armoured breakwaters which work in harmony with the flow field. This in practice is to construct a structure with a geometry and armour stone weight gradation which results in natural profile adjustment and subsequent minimisation of the applied hydrodynamic loadings. These structures are often called berm breakwaters due to the presence of a large berm of armour stones. Berm breakwaters can be classified in many ways based on dynamic/static stability, classes of stone in mass armour etc. Investigations arising from failure of breakwaters have established that wave action on the structure, wave induced flow within the breakwater and the related hydro-geotechnical behaviour of the rubble mound fill have significant impacts on the overall stability. The complex phenomena associated with this type of hydraulic regime cannot be simulated at small scale, without leading to major scale effects. Therefore, large-scale model studies which measure important external and internal hydraulic parameters are required for reliable information on the overall hydraulic performance of the structure. The fact that the actual permeability of the prototype rubble mound fill cannot be predicted due to factors such as segregation, settlement, variation in grading, supports the use of large scale physical models for these types of investigations. It is required that large scale hydraulic model investigations be used to study critical aspects of wave-structure interaction. Hydraulic model studies having scale ratios of the order of 1:10 to 1:20 and designed to obtain a complex profile of the hydraulic performance are necessary for this purpose
dc.description.sponsorship Senate Research Grant en_US
dc.language.iso en en_US
dc.subject Research Report en_US
dc.subject Coastal Engineering en_US
dc.subject Breakwaters en_US
dc.title Investigation of hydraulic design parameters of coastal structures en_US
dc.type SRC-Report en_US
dc.identifier.department Department of Civil Engineering en_US
dc.identifier.accno 72257 en_US
dc.identifier.year 2000 en_US

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