Xavier Gironella

Submerged Breakwaters and Bars — From Hydrodynamics to Functional Design

This paper deals with the functional design of submerged breakwaters and the associated hydro-morphodynamic impact. After presenting the advantages and difficulties of submerged structures it summarises the state of art on the hydrodynamic impact/effect for such a type of structure. The next pages describe the experimental set-up used to construct a number of large-scale mobile bed tests to further advance the knowledge on the hydrodynamics and morphodynamics associated to this structural type. The next section presents the corresponding numerical analyses, which supplement the findings of the laboratory work. The final section presents on-going work on the effect of these structures on beach profile dynamics.

Simulation of Wave Overtopping of Maritime Structures in a Numerical Wave Flume

A numerical wave flume based on the particle finite element method (PFEM) is applied to simulate wave overtopping for impermeable maritime structures. An assessment of the performance and robustness of the numerical wave flume is carried out for two different cases comparing numerical results with experimental data. In the first case, a well-defined benchmark test of a simple low-crested structure overtopped by regular nonbreaking waves is presented, tested in the lab, and simulated in the numerical wave flume. In the second case, state-of-the-art physical experiments of a trapezoidal structure placed on a sloping beach overtopped by regular breaking waves are simulated in the numerical wave flume. For both cases, main overtopping events are well detected by the numerical wave flume. However, nonlinear processes controlling the tests proposed, such as nonlinear wave generation, energy losses along the wave propagation track, wave reflection, and overtopping events, are reproduced with more accuracy in the first case. Results indicate that a numerical wave flume based on the PFEM can be applied as an efficient tool to supplement physical models, semiempirical formulations, and other numerical techniques to deal with overtopping of maritime structures.

Short communication: Numerical model for wave overtopping and transmission through permeable coastal structures

In this paper, an energetic wave propagation model that reproduces shoaling, refraction, diffraction, wave-current interaction, bottom friction and wave breaking is modified to simulate also the processes of overtopping and wave transmission over and through permeable coastal structures. This enhances the capabilities of the model and allows to obtain, at a low computational cost, a better reproduction of the wave field (and as a consequence currents and beach response) behind a coastal structure, especially if it is permeable and/or low crested. Model results are compared with laboratory data, showing a good agreement and the suitability of the followed approach.

On the generation of regular long waves in numerical wave flumes based on the particle finite element method

ABSTRACT Most of the coastal hydraulic studies in physical and numerical wave flumes (NWF) require the correct generation of nonlinear, long period waves at intermediate and shallow water conditions. In this paper, the ability to generate such long waves in an NWF based on the particle finite element method (PFEM) is analysed. Wavemaker theories based on the Stokes second-order wave theory, cnoidal wave theory and solitary wave theory are implemented in the NWF through piston type paddle boundary conditions. An assessment of the capability and robustness of generation and propagation of long waves in the NWF is carried out. Numerical results are compared to theoretical results and the data from physical tests. Results indicate that regular long waves of permanent form can be generated in an NWF based on the PFEM using the implemented wavemaker theories. However, when choosing a wavemaker theory a compromise has to be made between the target wave conditions and the validity range of each wavemaker theory.

Erosion caused by propeller jets in a low energy harbour basin

ABSTRACT Field data of a harbour basin are compared with analytical formulations for predicting maximum scouring depth due to propeller jets. Spatial data analysis of seven-year biannual bathymetries quantifies the evolution of the scouring hole along with the sedimentation process within a harbour basin. The maximum scouring depth is found to be of the order of the propeller diameter with a maximum scouring rate within the first six months of docking manoeuvring. Three of the analysed expressions yielded realistic results while observed discrepancies between the theoretical predictions and field data are related to scaling factors. The outcomes of this analysis can be extrapolated to other harbours to improve their management. The obtained results highlight the importance of field data in developing combined physical and numerical models.

Experimental RAO’s Analysis of a Monolithic Concrete SPAR Structure for Offshore Floating Wind Turbines

Nowadays the offshore wind energy market is clearly oriented to be extended around the world. Bottom fixed solutions for supporting offshore wind turbines are useful in shallow waters which are available in a limited extent unless a continental shelf exists. Considering the Oil & Gas background knowledge, move from bottom fixed solutions to floating solutions is not a technical challenge, but the cost of each structure in terms of industry profit is currently the main issue for its commercial implementation. That point has induced huge research efforts on the topic.Recently, a new concept consisting of a monolithic concrete SPAR platform was experimentally and numerically studied in the framework of the AFOSP KIC-InnoEnergy project (Alternative Floating Platform Designs for Offshore Wind Towers using Low Cost Materials) [1] [2]. The studies comprised a set of hydrodynamic tests performed in the CIEM wave flume facility at UPC, with a 1:100 scaled model assuming Froude similitude.The whole test campaign includes free decay tests, RAO’s determination, regular and irregular waves with and without wind mean force. For the determination of the platform RAO’s, a set of 21 regular waves trains with periods ranging from 0.8s up to 4.8s were applied. The 6 DOF motions of the platform were measured with an infrared stereoscopic vision system.In this paper, a summary of pitch and heave RAO’s tests will be presented with the main objective to calibrate and validate the accuracy of the Morison-based numerical model for floating wind turbine platforms developed at the Universitat Politecnica de Catalunya.Because the wave flume spatial constraints, both Airy and Stokes wave theories are necessary to reproduce the correct wave kinematics. The numerical model includes both theories and a comparison between them has been done, checking the validity range of each one.The simulations revealed a reasonable good agreement with the experimental results, as well with the computed RAO’s in commercial software.Copyright

Study of the bed velocity induced by twin propellers

Twin propellers without a rudder were studied using a physical model with a fixed clearance distance and three different rotating velocities. Experimental results were compared with results from theoretical expressions developed over the past 50 years for the efflux velocity, axial velocity, and maximum bed velocity. It was found that the efflux velocity equations overestimated the experimental results, whereas the computed axial velocities matched the experimental data reasonably well. However, when maximum bed velocity expressions were compared with experimental results, only one method was found to behave better; overestimation resulted if a quadratic superposition of single jets was used.

Effects of ultra-porous 3D printed reefs on wave kinematics

ABSTRACT Frau, L.; Marzeddu, A.; Dini, E; Gracia, V.; Gironella, X.; Erioli A.; Zomparelli, A., and Sánchez-Arcilla, A., 2016. Effects of ultra-porous 3D printed reefs on wave kinematics. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 851–855. Coconut Creek (Florida), ISSN 0749-0208. Present 3D printing technology allows the efficient design and construction of structures with complex shapes and high porosity satisfying biological and coastal protection demands. In this case, an array of ultra-porous tetrahedron-shaped 3D printed artificial reef (UPTSAR) is proposed to be used as a submerged breakwater for both environmental enhancement and wave protection. The aim of this study is to analyse the wave-structure interaction effects and the resulting velocity and wave height fields. For this, two-dimensional small scale tests (1:15) using irregular waves were carried out in a wave flume facility at BarcelonaTech. The influence of wave steepness, relative freeboard, relative water depth and the porosity on wave Kinematics have been analysed. The paper will describe in detail the results obtained for the different tests. These results are used to evaluate the functionality of the UPTSAR as coastal protection structures.