Daniele Dessi

Reconstruction of the Experimental Slamming Force Distribution Based on POD

A new technique for determining the continuous hydrodynamic load distribution along a slender floating body on the basis of a small set of force data is presented. This technique is based on a combination of proper orthogonal decomposition and polynomial spline approximation under integral constraints. The input data are provided by the time-histories of the lumped vertical forces acting on several longitudinal portions (segments) of a segmented-hull model. The set of force data, obtained by subtracting from the total force the Froude-Krylov force, defines the vector process to which POD is applied. The tests are carried out in 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.Copyright

Experimental Investigation vs Numerical Simulation of the Dynamic Response of a Moored Floating Structure to Waves

A combined experimental/numerical investigation of a moored floating structure response to incoming waves to incoming waves is proposed. The floating structure consists of three bodies, equipped with fenders, joined by elastic cables. The system is also moored to the seabed with eight mooring lines. This corresponds to an actual configuration of a floating structure used for ships and submarines in special docking operations. The dynamic wave response is investigated by performing experiments in a towing tank equipped with a wave maker. Experimental results are compared with numerical simulations in regular and irregular waves, showing a good agreement. In regular waves the predicted time histories of pitch, heave and surge motions of the three-body structure and of the mooring line forces, bear very satisfactorily the experimental results. The case of irregular waves is also encouraging, since the statistics of the response is correctly kept up to the fourth order statistical moments. This confirms that the theoretical model proposed in this paper is a suitable tool to predict the actual behaviour of a complex moored structure at sea.

Preliminary Design of an Amphibious Aircraft by the Multidisciplinary Design Optimization Approach

In the past few decades, besides the important progress that the aeronautical and aerospace engineering have achieved, the requirement of improving aircrafts performances and features, and the need of devising crafts performing special missions were growing meanwhile. Nevertheless, developing unconventional or innovative conflgurations the reference data extrapolated by known standard conflgurations are useless. Thus, the concept of Multidisciplinary Design Optimization, MDO, for the preliminary design of aeronautical and aerospace structures is the natural answer to the challenge that aeronautical and aerospace structures represent especially if new conflgurations of crafts are requested. Hence, the aim of this paper is to present an MDO procedure and an associated overview of the work code called MAGIC, (Multidisciplinary Aircraft desiGn of Innovative Conflgurations), for conceptual design of non-conventional aircraft conflgurations in civil aviation. Accordingly, the relevance of an adequate modeling is an essential issue in order to obtain meaningful designing results. Thus, the intimate link between MDO, modeling, and simulations flelds is evident. The algorithms used in MAGIC for modeling structures, aerodynamics, and aeroelasticity are flrst-principles based, since for innovative conflgurations the designer cannot rely upon past experience. In addition, we emphasize the conceptual design: thus, the algorithms used must be accurate and e‐cient, so as to produce accurate predictions with a relatively small computational efiort. In the paper presented the structural analysis (statics -including the buckling analysis- and dynamics) has been performed using an external commercial FEM code. Furthermore, since the special condition of ground efiect ∞ight is considered, we have adopted the speciflc methodology introduced by Keldysh-Lavrentiev (KL) and available in the steady aerodynamic case for airfoils in bounded domain in order to evaluate the aerodynamic loads. The e‐ciency of the proposed methodology is illustrated by applications to speciflc conflgurations.

Limit Cycle Stability Reversal via Singular Perturbation and Wing-Flap Flutter

A three degrees of freedom aeroelastic typical section with control surface is theoretically modeled including nonlinear springs and augmented states for linear unsteady aerodynamic description. The system response is determined by time marching of the governing equations by using a standard Runge-Kutta algorithm in conjunction with a ‘shooting method’ to find out stable and unstable limit cycles along with stability reversal in the neighborhood of the Hopf bifurcation. Furthermore, the equations of motion are analyzed by a singular perturbation technique, specifically, by using a normal form method. Approximate analytical expressions for amplitudes and frequencies of limit cycles are obtained and the terms which are responsible of the nonlinear system behavior are identified.Copyright

Statistical hydroelasticity of a wing in a random flow: A stochastic perturbation approach

The problem of an elastic lifting body in a randomly perturbed flow is considered. It appears that the phenomenon of hydro-elastic induced vibrations is controlled by a stochastic differential operator. By using the theory of stochastic perturbation, a new technique of solution for this class of problems is proposed leading to a very effective numerical solution.