Philippe Sergent

3-D NUMERICAL SIMULATION OF CONVOY-GENERATED WAVES IN A RESTRICTED WATERWAY

We consider waves generated by the passing of convoys in a restricted waterway. The magnitude of these waves depends mainly on the geometrical and kinematical parameters of the convoy, such as the speed and the hull geometry. The objective of this study is to predict the relationship between these geometrical and kinematical parameters and the amplitude of ship-generated waves as well as the water plane drawdown. Numerical simulations are conducted by solving the 3-D Navier-Stokes equations along with the standard k-ε model for turbulent processes. The results are compared first with the empirical model and second with experimental measurements performed by the French company Compagnie National du Rhône (CNR).

Modelling of Non-Linear Waves by An Extended Boussinesq Model

Abstract The main limitation of the most common form of the equations of Boussinesq is that they are valid only for relatively shallow depth of water. In the present study, an innovative approach (h − s) based on the finite elements method is presented to improve the dispersion relationship. This approach, based on the so-called extended Boussinesq model, reproduces with a high degree of accuracy the propagation of waves processes on a greater range of depths than the standard Boussinesq models.

Chapter 3 – Innovative Engineering Solutions and Best Practices to Mitigate Coastal Risk

Engineering solutions are widely used for the mitigation of flood and erosion risks and have new challenges because of the expected effects induced by climate change in particular sea level rise and increase of storminess. n nThis chapter describes both active methods of mitigation based on the reduction of the incident wave energy, such as the use of wave energy converters, floating breakwaters and artificial reefs, and passive methods, consisting of increase in overtopping resistance of dikes, improvement of resilience of breakwaters against failures, and the use of beach nourishment as well as tailored dredging operations.Existing coastal management and defense approaches are not well suited to meet the challenges of climate change and related uncertanities. Professionals in this field need a more dynamic, systematic and multidisciplinary approach. Written by an international group of experts, Coastal Risk Management in a Changing Climate provides innovative, multidisciplinary best practices for mitigating the effects of climate change on coastal structures. Based on the Theseus program, the book includes eight study sites across Europe, with specific attention to the most vulnerable coastal environments such as deltas, estuaries and wetlands, where many large cities and industrial areas are located. * Integrated risk assessment tools for considering the effects of climate change and related uncertainties* Presents latest insights on coastal engineering defenses* Provides integrated guidelines for setting up optimal mitigation measures* Provides directly applicable tools for the design of mitigation measures* Highlights socio-economic perspectives in coastal mitigation

Uncertainty Quantification for the Gironde Estuary Hydrodynamics with TELEMAC2D

In a context of development and implementation of data assimilation techniques in Gironde estuary for flood forecasting, a TELEMAC2D model is used to compute water depth and velocity fields at each node of an unstructured mesh. Upstream, the model boundaries are, respectively, La Reole and Pessac on the Garonne and Dordogne rivers. The maritime boundary is 32 km off the mouth of Gironde estuary, located in Le Verdon. This model, which contains 7351 nodes and 12,838 finite elements, does not take into account overflows. This paper presents a global SA study in the context of flood forecasting in the Gironde estuary. It aims at identifying which input variables should be better described for water levels to be better simulated and forecasted in the estuary. On the one hand, a propagation and quantification of uncertainties by a unidirectional analysis method was carried out. On the other hand, a variance sensitivity study (ANOVA) was carried out, by calculating the total and partial sensitivity Sobol’ indices for all numerical parameters (wind influence coefficient, Strickler friction coefficients for four zones) and time-dependent forcings of the model (rivers discharges and maritime boundary conditions). It led to the identification of parameters and forcings to which the model is most sensitive for each area of the estuary, as well as the identification of very low interdependencies, in order to choose the variables to assimilate later. The standardized variation coefficients for 1981 event as well as Sobol’ indices for 2003 event show a predominance of the influence of the maritime boundary conditions all along the estuary and of the Strickler coefficient corresponding to the zone considered for the estuarine part and the confluence, to which must be added the Garonne discharge as a predominant parameter for the latter. Unsurprisingly, the upstream part of river zones is influenced primarily by the friction coefficient and the respective river flows of Garonne and Dordogne rivers.

Evolution of Surge Levels Inside Harbour Basins: The Case of Le Havre Harbour

Within the Technical Commission for the Study and Evaluation of Maritime Submersions in the Seine Estuary (CTeeSMES), whose aim is to improve the collective knowledge on physical processes linked to maritime surge levels, a numerical model of the Seine estuary based on TELEMAC2D has been used to study the evolution of surge levels from the ocean to the harbour area of Le Havre and, in particular, evaluate the amplification of the global signal and the apparition of seiches inside Rene Coty’s basin. The bathymetry of the model was partially provided by Le Havre and Rouen Harbours for the north-eastern part of the model. For the rest of the area, EMODNET was used. The numerical model was calibrated on the Johanna (March 2008) and Xynthia (February 2010) storm events. The global signal (tide + surge levels) was calibrated using measurements available on seven outputs of the Seine Estuary and provided by ports of Le Havre and Rouen to optimize the friction coefficient and the coefficient for wind influence. Winds and pressure fields came from CFSR data. Once the numerical model of the Seine Bay had been calibrated, it was possible to draw the evolution of surge levels from the ocean to Le Havre (quai Meunier) and then compare the signal obtained inside Rene Coty harbour basin. As shown by measurements, numerical results stress out the apparition of an oscillating signal which is added to the signal at the entry of the harbour. The process of amplification of seiche inside the port near the Rene Coty harbour basin is still underestimated by the model and further investigations must be realised.

Modelling Wave Energy Conversion of a Semi-submerged Heaving Cylinder

In the current paper, a numerical model for simulating the ocean wave energy conversion of a semi-submerged heaving cylinder is presented. Contrary to the convectional potential flow theory, our solution is based on the full three-dimensional viscous Navier-Stokes equations. An efficient numerical wave tank is established to generate waves according to the wave theory. The coupling between the fluid equations with the rigid body dynamics are also taken into consideration in the present study.

Numerical Modelling of the Sediment Re-Suspension Induced by Boat Traffic

Fluvial transport in inland waterways is used in France and Europe since millennia. It was the most effective transport mode for goods and merchandizes before the development of the terrestrial alternatives. As an illustration, the French network of the inland waterways counted 12800 km of both, rivers and channels, at the beginning of the twentieth century. The huge development of highways and railways encountered in France has progressively decreased the use of fluvial transport. By considering the duration for the transport, the terrestrial mode looks more attractive than the fluvial one. But, the actual context of climate change and the international or European commitments to strongly diminish CO2 emissions are pleading for the reverse modal transfer, i.e. from highways and/or railways to waterways. Rebalancing the different transport modes are indeed compatible with the sustainable development concepts facing against road saturation, CO2 emissions, visual or noise pollutions while ensuring a better safety. Even through the shared awareness and the common efforts to increase the river traffic, this transport mode is still considered under-developed in the white paper of the European commission of 2001. For example, the fluvial transport in France has increased by 30% in ten years (1997− 2007), but it only represents 3% of the means of transport. And the recent recommendations in Grenelle de l’environnement initiated by the Frenchministry of ecology may accelerate the rebalance between rails, roads and rivers, carrying the ambition of a 25% report from the road down to the river by 2020. However, the development of this transport mode will certainly have economical and ecological consequences on the river management. The intensification of the river traffic by increasing the size and/or the frequency of passing boats will impact the actual management plan of the river. The waves induced by navigation could become stronger and bank erosion more frequent. The induced currents may be more intense and the resulting sediment transport more problematic. Indeed, it is accepted in aquatic environment that erosion Numerical Modelling of the Sediment Re-Suspension Induced by Boat Traffic 3

Modélisation numérique des processus de transport des sédiments et de l'évolution des fonds

ABSTRACT We propose a new mixing length profile, based on an extension of von Kármán similarity hypothesis, as well as the associated mixing velocity profile. This profile was compared with other profiles and was tested on three academic and experimental tests. The validation of the model was made by considering two reference examples. The first example concerns the erosion of a bottom of sand in a uniform flow, and the second concerns the filling of an extraction pit resulting from the tests presented in the European project SANDPIT.

Simulations numériques de l’évolution des fonds et effet du mélange turbulent sur le transport sédimentaire : Application au remplissage d’une fosse d’extraction

The linear mixing length profile lm = κz classically used, does not allow to obtain the logarithmic profile of the velocity observed in experiments, and its validity is limited to the fields of low roughness (boundary conditions of the type ’ smooth bed ’). In the present paper, we propose three types of mixing length profiles lm(z) as well the associated mixing velocities. The obtained results are tested on academic cases and compared with experimental results of filling of an extraction pit resulting from the tests presented in the European project Sandpit.