Enio Paris

SPH modeling of fast muddy debris flow: numerical and experimental comparison of certain commonly utilized approaches

SPH (Smoothed Particle Hydrodynamics) is a particle, purely mesh-free Lagrangian method, proposed by different authors, well suited to the computing of highly transitory free surface flows of complex fluids in complex geometries. Different approaches have been proposed in order to better simulate the mutual interaction between particles and their interactions with boundaries. Therefore, the main target of this article is to discuss and explore the numerical performance of certain commonly utilized SPH approaches, based essentially on mass and momentum balances, in the simulation of a 2D fast mudflow in fast motion, composed of fluid and solid material, assumed to be just one equivalent phase (fluid-solid). The “Herschel-Bulkley”, non Newtonian constitutive equations, describing a viscoplastic material suitable to reproduce the rheological behaviour of mudflows, has been selected. Hence, a laboratory experimental test, already proposed in literature and, after properly scaling, representative of a real fast flow phenomenon, was considered for comparison with numerical outcomes carried out by a research code that has already been tested and discussed in previous papers. A simple but effective statistical approach was developed and applied in order to identify and utilize a numerical index suitable for the quantitative measurement of the degree of matching between numerical results and measurement data affected by experimental errors. More than thirty numerical experiments were performed, of which the most significant eleven simulations are discussed. Satisfactory results were achieved. As outcomes, it was verified that, in particular for the selected experimental test, Rusanov flux addition within the continuity equation with the proper choice of both the viscosity term of momentum and the SPH boundary conditions, is suited to enhancing the performance of this type of numerical simulation of a fast flow.

Applicability of the De Marchi Hypothesis for Side Weir Flow in the Case of Movable Beds

Side weirs are widely used hydraulic structures typically designed and studied in the case of fixed bed conditions. In the case of subcritical flows, the hydraulics of side weirs can be modelled by using the classical De Marchi hypothesis. In the present work, a generalization of this hypothesis is developed for the case of side weirs over movable beds. Experiments showing the effects and feedbacks between the spilling discharge and the bed morphodynamics are presented. The application of the experimental observations to the generalized De Marchi hypothesis clearly show that the functioning of side weirs on a movable bed can be modelled by using this hypothesis. These findings could be instrumental for the design and verification of these structures. DOI: 10.1061/(ASCE)HY.1943-7900.0000566.

The effects induced by a new embankment at the confluence between two rivers: TELEMAC results compared with a physical model

With the aim of evaluating the hydraulic risks connected with the construction of a new embankment at the confluence of the Magra River and the Bagnone Torrent, an experimental analysis was conducted using an undistorted 1 : 55 scale physical model. A parallel study using the software TELEMAC-2D applied to the same domain as the physical model and with the same boundary conditions was also carried out. The use of a numerical model enabled comparison of the results obtained from the physical model and a test of the reliability of the numerical model itself in terms of accuracy, stability and instability. In order to estimate the effects induced by the construction of a new embankment, two sets of experiments were carried out; in the first set bed and bank topography before construction were modelled, and in the second set the actual situation with the embankment was considered. Comparison of data obtained from numerical simulations with measurements from the physical model showed a good agreement from a qualitative point of view, However, some differences were noticed in terms of local values, particularly in the bed morphology evolution where estimation of bed level variations are strongly dependent on the local sediment transport dynamics.

On the vulnerability of river levees induced by seepage

Seepage through earthen levees is a mechanism often observed during floods and can lead to levee failure if combined with internal erosion. This notwithstanding, hazard maps for levee failure are often elaborated solely considering the mechanism of overtopping. In this work, the assessment of levee vulnerability relative to seepage is investigated by considering the characteristic time scales of the phenomena and the main factors upon which they depend. In particular, the persistence of hydrological load is compared with the critical time of seepage associated to the emergence of the phreatic line along the landside of levees. The results can easily be applied to long river reaches, elaborating of through seepage-hazard maps and locating the levees that are more vulnerable to seepage failure.

Side Weir Flow on a Movable Bed

AbstractSide weirs are hydraulic structures widely used for flow control in rivers and canals. Whenever the water level rises above the side weir crest elevation, a fraction of the main flow is diverted so that the water discharge flowing downstream in the main channel is reduced. In movable bed channels, the lateral outflow may have significant interactions with the sediment transport processes affecting the side weir flow. The spilled discharge creates a reduction of the downstream sediment transport capacity with a consequent deposition in the side weir proximity. In addition, sediment in the main channel can be diverted into the lateral branch. To investigate these interactions, experimental data at the laboratory scale have been collected and analyzed. The increase of the spilled discharge induced by the local sediment deposition is described according to the classical De Marchi hypothesis. Furthermore, the sediment transport leaving the main channel through the lateral structure is modeled in terms ...

Monitoring Sediment Transport During Floods in Tuscany

This work describes the monitoring activity of flow and sediment discharges carried out in four river stations on four different rivers in Tuscany: Arno, Serchio, Magra and Versilia characterized by a large difference in the drainage areas ranging from about 100 km2 to about 4,100 km2. From December 2006 to November 2012, 43 floods events were monitored and measured in these stations, with the aim of deriving flow-sediment rating curves. Field measurements include more than 150 samples of bed load and suspended load and flow discharges up to about 700 m3/s. Laboratory analyses of collected samples show that bed load was mostly composed by gravel in the case of the Versilia and Magra rivers, while Arno and Serchio showed a dominant sand transport. The measured data constitute a precious and unique dataset at the regional scale for calibrating sediment budget model and morphodynamic model, and for predicting the sand and gravel volume fractions annually conveyed to the sea.

On the erosion due to inclined jets

On the erosion due to inclined jets Some preliminary experiments and studies regarding scour processes on a mobile bed caused by inclined jets issuing from a sluice gate are presented. Tests with submerged tailwater conditions have been carried out using different flow and geometric conditions. The investigated experimental conditions included different jet Froude numbers, inclinations and tailwater conditions. The bed configuration has been measured during the whole scour hole evolution process until the achievement of a dynamic steady state, where sediment motion was still possible even though it did not allow for any persistent change in the scour and ridge shapes anymore. On the basis of the observed sediment motion, two different patterns of flow seem to develop under the investigated conditions: one where the main flow remains attached to the bottom of the channel and another where it oscillates between the aforementioned configuration and a surface jet. Some relevant parameters have been identified and used to plot graphs showing their correlation and trends. O erozji wywołanej wypływem spod zasuwy W referacie przedstawiono wstępne doświadczenia i badania dotyczące procesów wyboju w rozmywalnym podłożu wywołane przez nachylone strumienie wypływające spod zasuwy. Przeprowadzono doświadczenia dla zatopionej wody dolnej dla różnych przepływów i warunków geometrycznych. Badane warunki doświadczalne zawierały różne liczby Frouda strumienia, nachylenia strumienia i warunki wody dolnej. Konfiguracja dna była rejestrowana w czasie całego procesu ewolucji wyboju aż do osiągnięcia dynamicznego stanu ustalonego, gdzie ruch rumowiska był nadal możliwy, mimo że nie wywoływał dalszej stałej zmiany wyboju ani odkładu rumowiska. Na bazie obserwowanego ruchu rumowiska dwa różne układy przepływu mogą się tworzyć w badanych warunkach: jeden - gdy główny strumień pozostaje przyczepiony do dna kanału i inny - gdzie strumień oscyluje między poprzednio wymienionym i strumieniem powierzchniowym. Pewne parametry zostały zidentyfikowane i wykorzystane przy wykonaniu wykresów wykazujących ich korelacje i trendy.