Giorgio Bellotti

Application of wavelet transform analysis to landslide generated waves

The aim of this paper is to illustrate the results of a preliminary study on aerial landslide-generated waves, which has been mainly intended to establish a method for analyzing water surface records. Some simple physical experiments, reproducing the Scott Russells wave generator, were carried out in a small two-dimensional wave flume; the Wavelet Transform (WT) is applied to analyze wave measurements and it is shown that useful information can be obtained by means of this technique. The celerity of impulsively generated waves, reflection by an overflow structure and seiching phenomena of the flume are studied. A discussion of the results along with some remarks about ongoing research is also given.

A comparison of two different types of shoreline boundary conditions

Two different types of shoreline boundary conditions which can be used in either wave-resolving or wave-averaging models of waves and currents propagation in the nearshore are compared here. The two techniques are essentially different: in the first case the velocity of the shoreline is obtained by the momentum equation and the shoreline position is tracked by changing the grid position, while in the other case the velocity of the shoreline is obtained by a modified Riemann solver and the shoreline is defined as an interface between dry and wet fixed grid points. A number of test cases are described to compare the performance of the two techniques.

Internal generation of waves in 2D fully elliptic mild-slope equation FEM models

Abstract This paper looks at an alternative approach for the treatment of open boundaries in linear wave field simulations by means of fully elliptic mild-slope equation (MSE) finite elements models. In these kinds of models, the domain of investigation is traditionally contoured both by reflecting–absorbing boundaries, which simulate the coastline or the structures that emerge from the sea, and by an ‘open’ or ‘artificial’ boundary, which separates the sea region included in the domain from the semi-infinite region that extends outward to infinity. The approach presented here assumes the domain to be completely contoured by reflecting–absorbing boundaries. A total absorbing boundary is, in particular, assumed to separate the inner (finite) from the outer (semi-infinite) sea region. Sources of energy, which generate waves of specified height and period, are located within the domain along a line in the proximity of the inner–outer sea region boundary. Reflected and scattered waves can propagate over the generation line and are absorbed at the open boundary. Numerical tests have been carried out to simulate progressive and stationary waves in a channel and long waves around a fully reflecting circular island on a parabolic shoal, and to evaluate the amplification factors of a long and narrow bay. All these validation tests show a very good agreement with the available analytical solutions. A discussion is finally carried out on the advantages and disadvantages of the presented approach with respect to traditional ones.

Hydro‐acoustic and tsunami waves generated by the 2012 Haida Gwaii earthquake: Modeling and in situ measurements

Detection of low-frequency hydro-acoustic waves as precursor components of destructive tsunamis can enhance the promptness and the accuracy of Tsunami Early Warning Systems (TEWS). We reconstruct the hydro-acoustic wave field generated by the 2012 Haida Gwaii tsunamigenic earthquake using a 2-D horizontal numerical model based on the integration over the depth of the compressible fluid wave equation and considering a mild sloped rigid seabed. Spectral analysis of the wave field obtained at different water depths and distances from the source revealed the frequency range of low-frequency elastic oscillations of sea water. The resulting 2-D numerical model gave us the opportunity to study the hydro-acoustic wave propagation in a large-scale domain with available computers and to support the idea of deep-sea observatory and data interpretation. The model provides satisfactory results, compared with in situ measurements, in the reproduction of the long-gravitational waves. Differences between numerical results and field data are probably due to the lack of exact knowledge of sea bottom motion and to the rigid seabed approximation, indicating the need for further study of poro-elastic bottom effects.

Integral flow properties of the swash zone and averaging. Part 2. Shoreline boundary conditions for wave-averaged models

Shoreline boundary conditions for nearshore hydrodynamic models are discussed on the basis of the swash zone equations of Brocchini & Peregrine (1996). Swash zone flows are investigated further using the shallow water equations. Results from numerical computations are used to guide approximation to provide more practical boundary conditions for wave-averaged flows. Approximate boundary conditions, valid for small values of the rate of change of the mean water volume in the swash zone, are found which allow explicit computation of a non-zero mean water depth at the mean shoreline. This is computed in terms of the local height of the short waves. Implementation issues are also discussed.

On using Boussinesq-type equations near the shoreline: a note of caution

We briefly analyze some characteristics of the behavior in very shallow waters i.e. near the shoreline of high-order (dispersive-nonlinear) Boussinesq-type equations. By using the Carrier and Greenspan (1958) solution as test flow conditions we illustrate the behavior of both purely dispersive and dispersive-nonlinear contributions near the shoreline. It is also shown that Boussinesq-type equations can be more usefully handled in the swash zone if written in terms of the total water depth.

Tsunamis generated by landslides at the coast of conical islands: experimental benchmark dataset for mathematical model validation

This paper presents a new experimental campaign aimed at reproducing tsunamis generated by landslides at the flank of conical islands. In order to describe in high details the wave field around the island a special acquisition system, which consists of both fixed and movable wave gauges, has been employed. Indeed, each experiment has been repeated several times by changing the configuration of the movable gauges, then obtaining a single virtual experiment with high spatial resolution measurements. Fixed run-up gauges measure the waves at fixed locations to statistically quantify the repeatability of the experiments. Selected experimental results are illustrated within the paper that is mainly aimed at defining a benchmark dataset, available on request, for the development/calibration/validation of analytical and numerical models of tsunamis generated by landslides.

Tsunami and shelf resonance on the northern Chile coast

This work presents the analysis of long waves resonance in two of the main cities along the northern coast of Chile, Arica, and Iquique, where a large tsunamigenic potential remains despite recent earthquakes. By combining a modal analysis solving the equation of free surface oscillations, with the analysis of background spectra derived from in situ measurements, the spatial and temporal structures of the modes are recovered. Comparison with spectra from three tsunamis of different characteristics shows that the modes found have been excited by past events. Moreover, the two locations show different response patterns. Arica is more sensitive to the characteristics of the tsunami source, whereas Iquique shows a smaller dependency and similar response for different tsunami events. Results are further compared with other methodologies with good agreement. These findings are relevant in characterizing the tsunami hazard in the area, and the methodology can be further extended to other regions along the Chilean coast.

Full-Scale Measurement of Wave Overtopping at Ostia-Rome Yacht Harbour Breakwater

This paper describes new wave overtopping field measurements at Ostia yacht harbor breakwater (Rome, Italy). The structure, the measurement strategy and the equipment are described in some details. Preliminary results of a recently measured overtopping storm, which are occurred in October of 2003, are presented in the paper. The activities are carried out within the framework of the European Union research project CLASH, aimed at studying model scale effects in overtopping studies and at providing scientific and professional communities with reliable crest level design criteria for coastal structures.

On the Resonant Behavior of a Weakly Compressible Water Layer During Tsunamigenic Earthquakes

Tsunamigenic earthquakes trigger pressure waves in the ocean, given the weak compressibility of the sea water. For particular conditions, a resonant behavior of the water layer can occur, which influences the energy transfer from the sea-bed motion to the ocean. In this paper, the resonance conditions are explained and analyzed, focusing on the hydro-acoustic waves in the proximity of the earthquake area. A preliminary estimation of the generation parameters (sea-bed rising time, velocity) is given, by means of parametric numerical simulations for simplified conditions. The results confirm the importance of measuring, modeling, and interpreting such waves for tsunami early detection and warning.