Experimental reconstruction of the hull sectional forces under slamming events

An analysis of the slamming load distribution along a slender floating body on the basis of experimental measurements is presented. The dataset is provided by the (lumped) vertical forces measured on the hull portions of a segmented scaled model in seakeeping tests. Using the proper orthogonal decomposition the vector time-history of the hydrodynamic forces is first decomposed into the summation of few terms, each one retaining separately time and space information. This decomposition allows highlighting interesting features regarding variations in the load distribution under different test conditions. The analysis has exploited also the use of pre-filtering for separating the load components at different frequencies to be further decomposed with POD. Then, a polynomial spline approximation under integral constraints is used to approximate the shape functions and then to obtain the continuous distribution of the sectional force. The considered tests were carried out in both irregular sea and regular waves with a choice of model speed and wave parameters so as slamming occurs. The identified distribution of force per unit length over the impacting hull segments is then compared with a modified Von-Karman model (with 3D correction) which accounts for the water uprise in the expression of the slamming force and variable entry velocity.