Binomial's pilot study
Olivier Antibi & Eric Valette

 I . Introduction II . Optimization of the profile of the reef III . Sedimentary transport

I . Introduction

This binomial's work is the analysis of two particular points that are relatively connected and with the binomial 1 's project. Its aim is the optimization of the profile of the reef and influences of sedimentary transport. Construction of a recreationnal reef is to produce the best and most consistent surfing conditions for a particular location. Binomial 1 has to describe this "ideal wave" and to locate it. We will use the previous results to shape the reef and to optimize it. The main problem is setting up an artificial reef and especially in environmental consequences. Thus a study of the sedimentary transport will be necessary; data about sandbank in the bay will be used with existing dyke and reef model.

II . Optimization of the profile of the reef ( in collaboration with binomial 1 )

Breaking of waves is conditionned by many parameters - see the following picture. The goal is to predict what shape waves are according to bathymetry i.e. profile of the reef.

At this point of the study, we can use two distinct methods. Using an existing code that could model wave breaking seems to be the easiest one. The second method is based on swell modelling code but that is unable to give results in wave breaking; this could provide us quite relevant figures.

Particle code SPH

At present, SPH is an experimental code develloped at the INSA ; it uses particle method that enables the visualisation of wave breaking. The limits of this code as well as installation troubles are the setting of boundary conditions. As it is a particle method, the required definition of ghost particles  makes processing of any bathymetry difficult. At the moment only the influences of the height of a step and the angle of a dihedral could be studied.

"Télémac2D" method

At the ENSEEIHT, a course about this industrial code is given. Morover any bathymetry can be used. The main limit is kind of results given - see the following picture. Post-processing for this data is required.

Thanks to data processing and Iribaren number defined by

where m is slope of banks, H height and L legth of the wave.

The following table gives the profile expected acoording to the previous parameters.

With this method, complex geometry of reef can be modelled ( examples of reefs ).

III . Sedimentary transport

This work aims to sudy the influence of the dyke and the reef on erosion and sandbank of the bay. Thsi study is divided into two part :

• Influence of dyke : With this we could compare our results and reality and thus lock our numerical model. We process a first mesh of the bay without dykes to bring to the fore erosion of the site. After dykes will be integrated to simulations. For this we will use an unit of Telemac 2D.
• Influence of the reef i.e. sedimentary transport. We will try to foretell sandbank of the bay.