Hydrodynamic characterisation of a body-like shape: a contribution to guide the search for victims of drowning in rivers

Abstract

This thesis is a contribution towards model-based guidance for the search of victims of drowning in rivers. It includes two parts: (i) an experimental study aiming at characterizing the hydrodynamic properties of a human-body shape, and (ii) the setup of a preliminary computational tool designed to simulate the drift of a human body in an open channel. Literature on the prediction of the motion of floating objects and bodies in water was first reviewed. For the case of a human body, a lack of knowledge on the parameters influencing controlling the drift was highlighted. Next, two complementary series of laboratory experiments were undertaken, one in a 20-m long glass flume and the second one in a 100-m long towing tank. The former involves rigid body models (dummies) at a scale of approximately 1:6, the covered range of relative velocity is 0.09 and 0.2 m/s and the particulate Reynolds number spans between 2.8*104 and 5.2*104. In the towing tank, a prototype-scale rigid body model was used, with a velocity of 0.1 to 0.5 m/s, and a particulate Reynolds number varying between 105 and 8*105. The experiments enabled estimating the drag coefficient of the body models, and the results were compared to a reference shape (cylinder). A systematic analysis of parameters such as the body shape, its orientation with respect to the approaching flow, and its submersion depth was undertaken. Additional parameters were also explored, including the presence of hair and clothes. Based on a combination of backwater profile calculation and parametrized cross-sectional velocity distribution, a 3D computational model of the flow field in the laboratory flume was set up. Simple drift computations were performed, which focused on the body motion in the streamwise direction. This enabled sensitivity analysis regarding the relative importance of the drag and added mass coefficients. Finally, limitations of the study are discussed and future research directions are proposed.