A ferrofluid-based sensor to measure bottom shear stresses under currents and waves

This is an Accepted Manuscript of an article published by Taylor & Francis Group in Journal of Hydraulic Research on 2018, available online at: http://www.tandfonline.com/10.1080/00221686.2017.1397779The measurement of the near-bottom flow characteristics is crucial to correctly understand coastal processes. To overcome some of the limits of present state-of-the-art measuring instruments, we propose a novel approach to measure bottom shear stress under currents and waves based on the exploitation of magneto-rheological fluids, named ferrofluids. In particular, the deformation of a magnetically controlled ferrofluid drop O(0.01 ml) is transformed by a conditioning circuit into an output voltage which is proportional to the bottom shear stress. Calibration curves are presented for both steady-current and regular wave conditions, over fixed and weakly mobile beds, showing that the behaviour of the proposed measuring system can be assumed linear. In the range of the investigated parameters, it is shown that the working range is comprised between 0.08 N m-2 and an upper limit which is a function of the controlling magnetic field and the flow type.Peer ReviewedPostprint (author's final draft

A nonlinear rotational, quasi-2DH, numerical model for spilling wave propagation

The propagation of spilling waves interacting with complex bathymetries was studied by means of a new two-dimensional weakly dispersive, fully nonlinear Boussinesq-type of model. In particular, the governing equations were derived assuming the flow as rotational, and the effects of vorticity due to breaking were included through the surface roller concept, which was defined and implemented on the basis of a new algorithm developed for the purpose. The propagation of vorticity, due to wave breaking, is estimated under the assumption that the effect of convection is leading order with respect to the effect of vorticity-stretching and that the breaking phenomenon does not show high curvature on the horizontal plane. In particular, the dynamic problem is decoupled in a lateral direction considering a series of separated sections in which vorticity is solved. In this way it is possible to obtain rotational information along the domain to a reasonable computational cost. The numerical model was validated in a simple one-dimensional case and then applied to the study of breaking-generated vorticity due to wave motion over a submerged shoal

Wave-induced loads on a lock gate provided with an opening through the ballast tank

AbstractThe wave loads on a navigation lock gate provided with an opening in the ballast tank are analyzed using a mathematical model based on the linear wave theory. The analysis focuses on the influence of the wave number and the geometrical characteristics of the structure on the applied load. It is shown that the maximum value of the vertical force mainly depends on the height of the ballast tank and on the width of the opening. The wave number for which the maximum load occurs significantly depends on the geometric characteristics of the structure except for the water depth above the ballast tank which has a negligible effect. An increase in the height of the ballast tank causes an increase in the wave load while an increase in the width of the opening causes a decrease in the wave load. Based on the results of the mathematical model an easy to use regression model has been developed which can be employed to evaluate the wave load

wave current interaction over seabeds with different roughness a statistical analysis

Wave-current flow over seabeds covered with different roughness has been studied in order to deepen the knowledge on the statistical properties of the near-bed velocity. The results of three different experimental campaigns performed in the presence of a sandy bed, a gravel bed and a rippled bed, carried out superimposing a steady current onto an orthogonal wave, have been analysed. The statistics of the current velocity, including the wave effects on the steady current have been investigated. It has been observed that in the absence of waves, the fluctuations of the near-bed velocities closely follow a Gaussian distribution. When waves are also present, in order to obtain consistent near-bed velocity statistics, it is necessary to decouple the velocity events in the current direction by taking into account the sign of the wave velocities. In the latter case, the nature of the distribution functions is influenced by the mass conservation principle. A Gaussian distribution well describes the turbulent fluctuations obtained by removing the phase averaged velocity from the current velocity

Risk Assessment of Transport Linear Infrastructures to Debris Flow

For the assessment of debris flow risk, it is essential to consider not only the triggering and propagation stages but also to perform analyses of its effects and consequences. The study aims at developing a procedure based on a quantitative risk assessments able to estimate the different levels of risk with reference to transport linear infrastructures. This includes numerical modelling for debris flows to determine the zones where the elements at risk could suffer an impact. A detailed comparison between the performances of two different approaches to debris flow modelling was carried out. In particular, the results of a mono-phase Bingham model (FLO-2D) and that of a single-phase model (RASH-3D) with reference to the Enna area (Sicily). The results can be applied for the risk calculations. The purpose is to define a priority of intervention for the identification of the infrastructures exposed at risk, leading to the choice of safety measures

experimental investigations on full depth buoyancy flows in the presenceof surface waves

The propagation of density currents in the presence of waves is experimentally investigated by considering a lock exchange schematization. In particular, we perform experiments considering the classical lock release, where the only driving force is buoyancy, as well as lock-exchange experiments with superimposed periodic surface waves, where the driving forces are both buoyancy and the wave-induced orbital motion. The application of an image processing technique is used for the detection of the main features of the front propagation (i.e depth, height, velocity etc.). All experiments are in full-depth conditions. The propagation of the waves is in intermediate water depth conditions. The presence of surface waves induces an orbital motion along the water column able to modify the dynamics of the density current propagation. Results show that the oscillation of the front advancement, as well as the oscillation of the gravity current depth observed in the presence of waves, are directly correlated with the wave period

CATANIA HARBOR BREAKWATER: PHYSICAL MODELLING OF THE UPGRADED STRUCTURE

Most of the worldwide historical coastal and harbor structures have been severely damaged by extreme sea storms during their lifetime and hence need to be upgraded, also considering the effects of climate change (Hughes, 2014). Physical modelling is identified as the only feasible approach for the optimization of the upgraded structures, because of the existence of few studies concerning such an issue and the lack of specific design formulae (Burcharth et al. 2014; Croeneveld et al. 1984; Lara et al. 2019; Foti et al. 2020). Therefore, a novel general methodology for the design of upgrading solutions for existing breakwaters based on physical modelling is presented, considering the case study of the Catania Harbor breakwater. The results of the systematic extensive experimental campaign on possible solutions for upgrading the Catania harbor breakwater led to some general practical findings, which can be useful for the design of restoration options for existing breakwater at end of their lifetime