Paolo Veltri

Assessment of dynamic pressures at vertical and perforated breakwaters through diffusive SPH schemes

This paper deals with the development of a 2D weakly compressible SPH model to simulate wave pressures acting on vertical and slotted coastal structures. Attention is devoted to investigate the diffusive term in the continuity equation in order to smooth out the high-frequency numerical noise in the pressure field. A hybrid formulation based on two literature diffusive models is proposed. The interaction between regular waves with vertical and perforated breakwaters is analyzed in time, space, and frequency domain. Numerical results are compared with laboratory experiments and other diffusive SPH formulations, varying the magnitude of the adopted diffusive term. On the basis of an error analysis, the results show that the hybrid formulation gives a better agreement with the experimental data for the majority of the investigated cases. Moreover, SPH simulations highlight nonlinear trends of dynamic pressures in correspondence with geometrical singularities, such as the holes of slotted walls, due to strong pressure drops induced by the flow motion.

Full-scale experiments on a beach drainage system: hydrodynamic effects inside beach

An extensive full-scale laboratory investigation on a two-dimensional physical model of a beach drainage system (BDS) was performed at “Grosser Wellen-Kanal” of Hannover, Germany. This research deals with the hydrodynamic aspects of a beach equipped with a BDS, while the morphodynamic aspects of the study are discussed in a companion paper. Knowledge of both the hydrodynamic and the morphodynamic behaviours of a drained beach allows the definition of the main design criteria. The adopted BDS was constituted by four corrugated pipes. Several drain configurations in static and dynamic conditions were considered, paying attention to water table oscillations, drains and groundwater regime and drainage discharge induced by the system start-up. The main results indicate a rise in the unsaturated beach and the presence of a hydraulic disconnection in the groundwater–drain system. The analyses yield useful hydrodynamic information influencing the general system efficiency.

Laboratory study on the open channel flow reaeration: a dimensional approach

Results of laboratory experiments on open channel flow reaeration are presented and commented on. The tests were designed on the basis of the classical dimensional analysis. They were carried out using three 15 m long channels with different cross-sections: 1) 0.5 m wide semi-circular cross-section; 2) 0.4 m wide rectangular cross section; 3) 0.2 m wide rectangular cross-section. The longitudinal bottom slope, the roughness and the flow discharge were varied independently. The disturbed equilibrium approach was adopted within an innovative experimental procedure, i.e. comparing the dissolved oxygen measures acquired in tests without de-oxygenation agent (hereinafter ‘white tests’) with those performed in runs with de-oxygenation agent (‘reaeration tests’). A new relationship between the reaeration coefficient and the hydrodynamic characteristics of an open channel is proposed. The relationship is applicable to a wide range of values of hydraulic characteristics not previously analysed in the literature and typical of small rivers.

Modelling of Periodic and Random Wave Forces on Submarine Pipelines

A numerical model for the prediction of the time variation of the flow field and the hydrodynamic forces on bottom submarine pipelines is proposed. The model is an extension for periodic and random waves of the Wake II hydrodynamic forces model (Soedigdo et al., 1999), originally proposed for sinusoidal waves. An extensive laboratory investigation has been carried out in order to calibrate the model. The numerical model is based on an analysis of the time history of the velocity field at each wave semi-cycle. A modified relationship of the wake velocity is introduced and the time history of the drag and lift hydrodynamic coefficients are obtained using a Gauss integration of the start-up function. The laboratory investigation was performed at the large wave flume of the Centro Sperimentale per Modelli Idraulici at Voltabarozzo (Padua, Italy). The tests were carried out by measuring the pressure values at 8 transducers mounted on a cylinder subjected to different periodic and random waves. The experiments refer to the range 4 ÷ 12 of the Keulegan-Carpenter number for periodic waves and to the range 4 ÷ 9 for random waves. The empirical parameters involved in the extended Wake II and in the classical Morison models were calibrated using the results of the sampled velocities and force time histories under different wave conditions. The comparisons between the experimental and numerical results indicate that the extended Wake II model allows an accurate evaluation of the peaks and of the phase shifts of the horizontal and vertical forces and is more accurate than the Morison model.Copyright