Marco Petti

Turbulence experiments in the swash zone

Abstract Turbulence and water surface elevation measurements were carried out in the swash zone which was induced by plunging and collapsing breakers in a wave flume. Three different period regular waves were generated on a 1/10 smooth impermeable concrete beach and the water surface elevations were collected by a number of wave gauges and a run-up meter lying on the bottom. Velocity measurements were carried out by a Laser Doppler velocimeter system, at spatial steps of 1 mm from the bottom, along three vertical sections in the swash zone. The data have been used to describe the wave front dynamics, to derive the length and velocity macro and micro scales and the Eulerian frequency spectrum. In some points, it shows a double structure. The results add to and expand on similar results obtained by other researchers in the surf zone.

Turbulence in the swash and surf zones: a review

This paper reviews mainly conceptual models and experimental work, in the field and in the laboratory, dedicated during the last decades to studying turbulence of breaking waves and bores moving in very shallow water and in the swash zone. The phenomena associated with vorticity and turbulence structures measured are summarised, including the measurement techniques and the laboratory generation of breaking waves or of flow fields sharing several characteristics with breaking waves. The effect of air entrapment during breaking is discussed. The limits of the present knowledge, especially in modelling a two- or three-phase system, with air and sediment entrapped at high turbulence level, and perspectives of future research are discussed.

Shallow water numerical model of the wave generated by the Vajont landslide

On October 9th 1963 a huge landslide fell into the Vajont artificial reservoir in Northern Italy, and displaced the water which overtopped the dam and produced a destructive wave that inundated the valley causing about 2000 casualties and complete devastation. The landslide has been the subject of many geological studies, and is one of the largest ever documented in literature. Nevertheless, only a small number of hydraulic analyses have been conducted relating the sliding motion to the consequent water waves and describing the formation of different waves and how they interfered with each other. A numerical model, capable of doing so, has not yet been presented.In this paper, a horizontal bi-dimensional finite volume model is proposed in order to study the wave generated by the Vajont landslide. We hereby introduce a moving wall reproducing the effects of the landslide.

Simulation of wave breaking over complex bathymetries by a Boussinesq model

A Boussinesq-type model is applied herein to study wave propagation and wave breaking over complex bathymetries reproducing common coastal features, namely plane and barred beaches, submerged bars and rip channels. A hybrid finite volume–finite difference numerical scheme solves a set of, in the horizontal plane, two-dimensional extended Boussinesq equations where both nonlinear and dispersive effects are relevant and nonlinear shallow water equations where nonlinearity prevails over dispersion. The shock-capturing features of the finite volume method enable an intrinsic representation of spilling wave breaking and runup. Comparisons with experimental data indicate that the numerical model adequately simulates wave transformation over submerged bars, correctly capturing wave breaking onset and termination including the related energy dissipation. The development of breaking-induced currents and their interaction with wave propagation are also well represented within the applicability range of the governing equations.

Bottom Stress in Non Stationary Free Surface Flow

This paper describes studies of the bed friction factor in nonstationary free surface flow, for the specific case of bores moving in shallow water and breaking waves on beaches. Data from a set of experiments carried out in a laboratory flume, including measurements of water level displacement and fluid velocity through LDV, are used to evaluate the bottom stress and the mean flow velocity. The results of other measurement techniques in similar conditions are used to critically assess our results. It is found that the friction factor is higher and the transition from laminar to turbulent boundary layer takes place at higher Re numbers than values obtained in separate studies of turbulent bottom boundary layer including an additional source of turbulence. INTRODUCTION Bottom friction and boundary layer dynamics play a major role in many nonstationary flee surface physical flows such as roll waves and bores in shallow water and over beaches. This subject is of interest because the stability analysis of free surface flows aiming to detect the presence of roll waves is sensitive to the friction, and also, bore dynamics in shallow water and the maximum run-up of waves over beaches depends on the bottom friction. Flow resistance is usually expressed through a friction factor. The friction factor is an integral expression of the efficiency in fluid momentum transport and is useful in modeling stream processes without resolving the detail in the turbulence and the velocity distribution. In general, in stationary flows the resisting force per unit length acting on a control volume is the product of the wetted perimeter of the section and the mean intensity of the boundary stress. If the flow is accelerating there are forces working Assistant Professor, Department of Civil Engineering, University of Parma, Parco Area delle Scienze, 181/A, 1-43100 Parma, Italy. slongo@unipr.it Professor, Department of Georisorse e Territorio, University of Udine, Via Cotonificio, 114, 133100 Udine, Italy. petti@uniud.it Research Scientist, Department of Georisorse e Territorio, University of Udine, Via Cotonificio, 114, 1-33100 Udine, Italy.

Morphodynamic Model Suitable for River Flow and Wave-Current Interaction

Morphodynamic models are a great support in water environment management and decision-making, as well as in integrated coastal zone planning. In the present paper, a 2DH model is presented, able to deal with both currents, waves and their mutual interaction. The model is briefly presented and the results of its application to some benchmark tests are discussed.

VELOCITY MEASUREMENTS UNDER BROKEN WAVES AND BORES

1. ABSTRACT The dynamics of waves after breaking is widely investigated because it controls several phenomena in the surf zone and swash zone. Several numerical models based essentially on non-linear shallow water equations (NLSWE) have been developed, but all of them fail to model turbulence in the bore. Many authors have measured fluid velocity in bores using Laser Doppler Velocimetry (LDV), Hot Wire and Hot Film anemometry, and Particle Image Velocimetry (PIV) with good results, though such studies possess several limitations imposed mainly by the presence of air bubbles. In order to overcome such limitations, a set of experiments was carried out in a flume using the Doppler Ultrasonic Technique for fluid velocity measurements. The instrument, a DOP1000, works essentially as a radar and utilizes ultrasound in the range 1 MHz-8 MHz as a carrier. This instrument is able to measure fluid velocity in several points along the US beam with negligible time delay. The maximum data rate obtained is ≈30 profiles per second for each probe, with three probes being employed and a maximum of 255 points per profile. The generated waves have a period of T=2.0, 2.5 and 3.0 s, and break as spilling on a 1:20 bottom. UDVP velocity profiles have been collected in three sections: one at the breaking point and two in the bore region after breaking.