Analysis of the vibro-acoustic behavior of a submarine hull on a wide frequency range using experimental and numerical approaches

Valentin Meyer (1) , Laurent Maxit (2)

1 Naval Group Research [Bouguenais]
2 LVA - Laboratoire Vibrations Acoustique

Acoustic stealth is one of the main operational capabilities for a submarine vehicle. To meet always stricter requirements in terms of radiated noise, it is important for the shipbuilder to be able to predict the noise at the early design stages. One of the key elements is the transfer function between a mechanical excitation on the pressure hull of the submarine vehicle and the far-field pressure radiated into water. This transfer function is commonly called p/F. A dedicated numerical method, called the Condensed Transfer Function (CTF) method, has been developed to calculate the vibro-acoustic behavior of a submarine hull. The method is based on a substructuring approach, where a model of an infinite fluid-loaded cylindrical shell is coupled to models of internal structures such as stiffeners and bulkheads. The fluid-loaded cylindrical shell is described analytically, while the internal structures are modeled by the finite element method (FEM). For each uncoupled subsystem, mechanical admittances are calculated at the junctions between the subsystems, and approximated with a set of functions called condensation functions. The interactions between the subsystems are estimated using the superposition principle, the force equilibrium and the displacements continuity. Compared to fully analytical models, the CTF method has more flexibility on the geometry of the internal frames. Compared to models completely described by the FEM, the present approach has lower calculation cost. Consequently, transfer functions can be calculated on a wide frequency range (from some Hz to several kHz) with limited calculation costs. Besides, an experimental campaign has been conducted to measure the transfer function p/F of a scaled model of the pressure hull. Based on laser vibrometer measurements on a model in air, the radial acceleration are measured at the surface of the shell. The far-field radiated pressure is calculated through the stationary phase theorem to deduce the transfer function p/F. This approach has two main advantages. First, no microphones are needed to estimate the radiated noise from the shell and second, the directivity of the radiated pressure can be studied. In this paper, the principle of both the numerical and the experimental approaches are described. A test case is presented and the results using both approaches are compared. The directivity pattern and some physical features of the vibro-acoustic behavior of the hull are discussed.

Domaines: Acoustique [physics.class-ph]

Valentin Meyer, Laurent Maxit. Analysis of the vibro-acoustic behavior of a submarine hull on a wide frequency range using experimental and numerical approaches. UDT 2019, May 2019, Stockholm, Sweden. ⟨hal-02414570⟩