The application of ORSA2D_WT on the 2017 event on the Piave River

Massive accumulations of large wood (LW), especially when transported during floods, can cause several damages into urban areas such as Belluno (Italy). Bridges and weirs are vulnerable to LW accumulations around the world, which might lead to the failure of the structure. Although LW is transported and deposited during floods via numerous processes, it is difficult to predict where and how these accumulations may affect communities. Consequently, reducing LW-related risk is challenging. This research contributes to the application of an appropriate numerical model ORSA2D_WT for simulating the flood wave propagation incorporating the motion of floating rigid bodies to the real case study. Considering the two-dimensional movement of floating objects, this model forecasts their trajectories, orientation, and interactions with other bodies and structures. Due to the focus on large bodies, each object in the model was treated as an independent entity which is reflected in the Lagrangian approach of the Discrete Element Method, one-way coupled with Eulerian solution of the Shallow Water Equations. As result of the flow, the translation and rotation of the bodies are controlled by the forces exerted by the flow. The movement of singular and grouped rigid bodies floating on water surface was analyzed by flume experiments for obtaining an adequate dataset. The cylindrical samples were released under steady conditions in rectangular channels in two-dimensional configurations (2D) with two rectangular smooth obstacles. Planar displacement and rotation of the samples are the results of the experiments, which are related to the flow field in the various configurations. Numerical models simulating floating bodies transport can be calibrated by analyzing the detailed experimental analysis of floating body motion. Thus, the Eulerian-Lagrangian model ORSA2D_WT is validated with this dataset. The dataset highlights the strength and areas where it can be used in these applications. The main limitations of floating bodies simulation are related to the high degree of unpredictability of the transport process since both the initial conditions and log shape are uncertain. It is difficult to replicate exactly wood-wood or wood-riverbank interactions, and there is also an unexpected effect of surface turbulence that is not accounted for in the 2D SWE model. The thesis is organized in the five chapters: the first chapter introduces the problem associated with large wood transport, the characteristics of floating transportation, the strategies that can be adopted to deal with this problem and the state of the art of large wood modelling. Chapter two presents the mathematical model for entrainment, rigid body transport and collisions. Chapter three reports the numerical model implementation of ORSA2D_WT. Chapter four presents the application of ORSA2D_WT to the laboratory experiment of log transport: hydraulic simulation results of log transport in the flume, Chapter five highlight the application of ORSA2D_WT to the real case study and discuss the obtained results.