DURCWAVE ‘amending the Design criteria of URban defences in LECZs through Composite-modelling of WAVE overtopping under climate change scenarios’

The main scientific objective of DURCWAVE project is to define new design criteria for wave action by modelling wave overtopping and post-overtopping processes of these urban defences.Postprint (published version

Overtopping formula for vertical tiers-headed breakwaters

The semi-empirical methods are useful tools to understand the wave overtopping phenomena, but uncertainty remains on their applicability. It’s necessary to carry out campaign surveys or laboratory tests to support them. In this paper we apply the methods proposed in the European Overtopping Manual (2007) in order to assess the flows over a vertical breakwater, marking the need to calibrate those methodologies to take into account the peculiar geometry of the structural system. This was done by introducing appropriate correction factors. The results show an improved accuracy, among numerical results and physical ones.Postprint (published version

Determination of semi-empirical models for mean wave overtopping using an evolutionary polynomial paradigm

The present work employs the so-called Evolutionary Polynomial Regression (EPR) algorithm to build up a formula for the assessment of mean wave overtopping discharge for smooth sea dikes and vertical walls. EPR is a data-mining tool that combines and integrates numerical regression and genetic programming. This technique is here employed to dig into the relationship between the mean discharge and main hydraulic and structural parameters that characterize the problem under study. The parameters are chosen based on the existing and most used semi-empirical formulas for wave overtopping assessment. Besides the structural freeboard or local wave height, the unified models highlight the importance of local water depth and wave period in combination with foreshore slope and dike slope on the overtopping phenomena, which are combined in a unique parameter that is defined either as equivalent or imaginary slope. The obtained models aim to represent a trade-off between accuracy and parsimony. The final formula is simple but can be employed for a preliminary assessment of overtopping rates, covering the full range of dike slopes, from mild to vertical walls, and of water depths from the shoreline to deep water, including structures with emergent toes.This research was funded by European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No.: 792370.Peer ReviewedPostprint (published version

Study of the efflux velocity induced by two propellers

Present analysis is related with seabed erosion caused during docking and undocking maneuvering. Twin propellers without rudder were studied using a physical model with a fixed clearance distance and three different rotating velocities. Experimental results were compared to theoretical expressions of the efflux velocity, axial velocity and finally maximum bed velocity. Efflux velocity equations overestimate the experimental results, whereas axial velocity computed using the Dutch method fits reasonably well the experimental data. However, when maximum bed velocity expressions are compared to experimental results, German method behaves better with an over estimation if a quadratic superposition of the single jets is used.Postprint (published version

Experimental set-up and calibration errors for mapping wave-breaking pressures on marine structures

Capturing the detailed spatial variation of pressures induced by breaking waves on physical model structures has become possible using a high resolution mapping system. It can provide data with 4 measuring points/cm2, whereas the denser pressure measurements reported so far, for wave-structure interaction experiments, were limited to 0.4 pressure transducers/cm2. The paper explores the main parameters affecting the accuracy and errors of pressure data induced by laboratory set-up and system calibration. The quality of pressure maps deteriorates due to cushioning effects associated to air trapped in the sensor during manufacturing. The sensor's response is also shown to depend on the loading conditions. Non-calibrated outputs returned for impact pressures induced by impinging water-jets are more than three times smaller than the outputs recorded for static pressures, and/or for pressures developed when a material less compliant than water comes forcibly in contact with the sensor. Therefore, the calibration settings must be similar to the conditions anticipated in the experiments. To this end, a set-up and calibration methodology, designed specifically for hydraulic model tests with waves breaking on structures, are proposed and discussed in the paper.Peer ReviewedPostprint (author's final draft

Erosion caused by propeller jets in a low energy harbour basin

This is an Accepted Manuscript of an article published by Taylor & Francis Group in Journal of Hydraulic Research on January, 2017, available online at: http://www.tandfonline.com/10.1080/00221686.2016.1252801Field 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.Peer ReviewedPostprint (author's final draft

Impulsive wave loads on rigid structure, an experimental approach

Within the European project ‘Hydralab IV’, HyRes we aim to improve the characterization of wave loads on rigid structures and the associated response by carrying out some laboratory experiments. Wave loads on rigid structures are divided into quasi static loads and impact loads. If the physics of quasi-static loads due to waves is well known, this cannot be said the same for wave impact loads. A comprehensive method to design maritime rigid structures under impact loads does not exist yet and the actual design method suggests avoiding scenarios where impact loads can take place. In the last decade, some laboratory experiments have been carried out; however some questions remain still unanswered. The use of different sensors can lead to significant changes in the results and an “exhaustive comparison” between dissimilar types of sensors has not been done yet. Even the magnitude of these forces can be underestimated during a laboratory test just for the choice of sample frequencies which are too low. This paper describes the experiments performed on a small scale flume at UPC on a scaled vertical breakwater in order to compare the results of pressure transducers and force load cells. Moreover, a high frequency sampler (up to 20 KHz) was used in order to understand the importance of sample frequency on the magnitude of the results. A simplified scenario has been set up in order to make the data analysis easier.Postprint (published version

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.Peer ReviewedPostprint (published version

Tools for evaluation quay toe scouring induced by vessel propellers in harbour basins during the docking and undocking manoeuvring

The evolution of the shipping industry (increased capacity and size of ships, power and self-propulsion), the increased productivity and rearrangement of spaces (port calls increased in number and frequency, changes in use of docks), the intensification of the use not only of stern main propellers (conventional or azimuthal) but also lateral bow and stern ones, are the leading causes of injury to the toe of the docks. Scouring processes due to manoeuvring actions can produce big consequences on the stability of harbour structures such as docks and protecting dikes. As a consequence, the sedimentation of the eroded sediment reduces the total depth of the harbour basin and navigation channel. At the same time, contaminants settled at the bed of the harbour basins may be resuspended by the effect of vessel’s propellers and produce an important environmental problem to harbour authorities. One of the main problems is the interpretation of parameters related to propellers, but also the fact of not considering important aspects such as different types of propeller, manoeuvring practices for docking and undocking, propulsion system orientation or the confinement effect generated by the dock itself and the shelter of the vessel. This contribution aims to assess docking and undocking manoeuvres which can produce erosion generated by the propulsion of ships. This methodology will analyse manoeuvres patterns and will allow understanding the effects of the sedimentation of the eroded sediment on docking and undocking manoeuvres.Postprint (author's final draft

Stern twin-propeller effects on harbor infrastructures. Experimental analysis

The growth of marine traffic in harbors, and the subsequent increase in vessel and propulsion system sizes, produces three linked problems at the harbor basin area: (i) higher erosion rates damaging docking structures; (ii) sedimentation areas reducing the total depth; (iii) resuspension of contaminated materials deposited at the seabed. The published literature demonstrates that there are no formulations for twin stern propellers to compute the maximum scouring depth. Another important limitation is the fact that the formulations proposed only use one type of maneuvering during the experimental campaign, assuming that vessels are constantly being undocked. Trying to reproduce the real arrival and departure maneuvers, 24 different tests were conducted at an experimental laboratory in a medium-scale water tank using a twin propeller model to estimate the consequences and the maximum scouring depth produced by stern propellers during the backward/docking and forward/undocking scenarios. Results confirm that the combination of backward and forward scenario differs substantially from the experiments performed so far in the literature using only an accumulative forward scenario, yielding deeper scouring holes at the harbor basin area. The results presented in this paper can be used as guidelines to estimate the effects of regular vessels at their particular docking location.Postprint (published version