Semi-analytical Vibro-acoustic Analysis of Underwater Stiffened Combined Shells Based on the Energy Variational Principle and Non-negative Acoustic Intensity

ObjectivesTo address the spatial truncation artifacts and near-field reactive interference that often arise when numerical methods are used to compute the acoustic radiation of heavy fluid-loaded structures, an acoustic radiation evaluation method based on the direct coupling of the energy variational principle with non-negative acoustic intensity is proposed.MethodsA continuous-spectrum dynamic model for underwater finite-length stiffened conical, spherical, and cylindrical shells with bulkheads is established via Chebyshev polynomial expansion. The generalized unbounded fluid radiation impedance operator is introduced into the continuous spectral space using the energy equivalence principle. Subsequently, a generalized eigenvalue decomposition is performed on the original three-dimensional physical radiation impedance matrix, and the structural surface velocity field is orthogonally projected onto the subspace of non-negative radiation eigenmodes. Numerical computations and method comparisons are then carried out.ResultsCalculations show that, compared with traditional supersonic acoustic intensity, the proposed method processes the impedance operator containing the actual geometrically truncated boundaries directly in the physical spatial domain, thereby avoiding the Gibbs oscillation phenomenon caused by spatial Fourier transforms and restoring the acoustic radiation characteristics at the structural edges. Compared with traditional active acoustic intensity, the orthogonal projection mechanism onto the radiation eigenmodes filters out the highly oscillatory near-field reactive circulatory interference in the heavy fluid medium, clearly extracting the far-field acoustic radiation region.Conclusions This numerical computation framework provides an approach for analyzing the acoustic characteristics of finite-length structures with complex boundaries that balances computational efficiency and physical fidelity, contributing to improved accuracy in underwater structural radiated noise source localization and performance evaluation.