Due to the significantly low-frequency tonal noise generated by the flow holes of underwater vehicles at high-speed operation, which can degrade the accuracy and reliability of onboard detection systems, the Leading-Edge Flow Splitter (LEFS) models for noise control are proposed. LEFS models reduce noise through lifting the incoming boundary layer away from the cavity mouth and generating secondary flow directed into the cavity. The influence of secondary flow characteristics on noise suppression is examined using three LEFS configurations: the straight Separate-Flow model (SF), SF-Concave, and SF-Convex. Results show that the SF and SF-Concave models replace coherent transverse Rossiter-mode oscillations with asymmetric longitudinal perturbations, achieving significant tonal and broadband noise reduction, modifying the acoustic directivity, and accelerating the attenuation rate of acoustic waves propagating perpendicular to the cavity opening surface. In contrast, the SF-Convex model exhibits limited downstream control, leading to the emergence of a new transverse self-sustained oscillation and a corresponding higher-frequency tonal acoustic. In summary, this paper proposes effective passive control strategies that serve as a useful reference for the low-noise design of underwater vehicles.

Blade structures in rotating machinery, such as aircraft engines and gas turbines, are subjected to multifarious excitations including centrifugal load and aerodynamic load. Blade material optimization is an effective way to make blades resistant to complex excitations. In this work, an isogeometric flutter optimization model for sandwich functionally graded (SFG) material distribution of the rotating blades is developed. With Non-Uniform Rational B-Splines (NURBS) basis functions and material parameters at limited control points, the model can achieve continuous variation in blade materials, addressing parameter jumps between optimization elements in conventional optimization techniques. The vibrational solution model of blades considers the variable thickness shape characteristics and temperature-dependent materials. The direct stress integration method is used to calculate the rotating centrifugal force, and the first-order piston theory is employed to obtain the aerodynamic work. The critical flutter pressure is increased through research on optimizing the distribution of sandwich materials in the thickness direction, with material compositions at the control points as design variables. To demonstrate the effectiveness of the current model, the obtained optimization results are compared with those from traditional models. On this basis, the effects of thermal conditions, airflow parameters and rotation speed on the optimal material profiles of the rotating variable thickness blades are investigated.

Offshore wind turbines are subjected to complex wind-wave coupling, yet most laboratory model tests still rely on simplified equivalent static or quasi-static loads. This study presents the first experimentally investigation of the discrepancies in monopile strain between wind-wave fluid loading and the conventional equivalent approach. A 1:100-scale NREL 5 MW monopile offshore wind turbine model was tested in the Wind Tunnel Flume - Seabed integrated experimental system basin under (1) realistic coupled fluid loading and (2) equivalent static wind plus quasi-static cyclic wave loading. The equivalent method under-predicted peak strain by up to 24.3 % near the mudline, while over-predicting by 13.7 % at the monopile top. These discrepancies increased nonlinearly with load intensity and were most pronounced at crucial elevations. Moreover, the equivalent loading approach failed to capture the mutual coupling between the deformations of the aerodynamic components and support structure and the fluid loads acting upon them, along with the randomness and transient nature of realistic two-phase flow fields. The findings highlight the limitations of traditional equivalent loading in scale-model tests and provide guidance for refining design codes, recalibrating location-specific partial safety factors, and improving numerical modeling practices for OWT foundations.

Vibro-acoustic coupling systems between closed acoustic cavities with complex geometric shapes and elastic structures are commonly encountered in engineering applications. In the mid-frequency range, their dynamic characteristics are quite complex, and accurate deterministic analysis poses significant challenges. In this study, an improved wavelet finite element method is developed for complex cavity-plate coupling systems, aiming to maintain high precision for complex acoustic geometries while broadening the applicable frequency range and improving computational efficiency. The proposed method adopts the interval B-spline wavelet scaling functions as basis functions to formulate the discrete governing equations of the coupled acoustic-plate system, while enforcing physically consistent fluid-structure coupling conditions. The performance of this method is evaluated using a numerical validation example consisting of a semi-ellipsoidal acoustic cavity coupled with a fixed circular plate. Under different excitations, the results obtained using this method are systematically compared with reference finite element solutions. The results show good agreement within the studied frequency range, including regions with relatively high modal density. Furthermore, the relative error analysis indicates that the improved method significantly outperforms the traditional finite element method in terms of the accuracy per degree of freedom. These results demonstrate that the proposed method provides an effective and reliable alternative tool for deterministic mid-frequency vibro-acoustic analysis of coupled systems with complex geometric acoustic cavities.

To address flow noise reduction in piping systems, this study develops a method for reducing flow noise based on surfactant solutions. A surfactant solution was prepared with dodecyl trimethyl ammonium bromide and sodium salicylate as solutes in water. The flow noise of surfactant solutions was measured within a recirculating water piping system. The noise reduction effectiveness of surfactant solutions was verified, and the flow noise characteristics were systematically analyzed under varying volume flow rates and concentrations. Experimental results demonstrate that the surfactant solutions exhibit significant noise reduction effectiveness, particularly in the mid-to-high frequency range, with maximum noise reduction exceeding 30 dB. The noise reduction capability of surfactant solutions is characterized by an initial enhancement, followed by intermediate attenuation, and subsequent secondary enhancement with increasing concentration. As the volume flow rate increases, the noise suppression capability of surfactant solutions improves across the entire frequency spectrum. Both the required concentration and the achieved noise reduction at the limit increase with higher flow rates.

This paper introductions a Chebyshev spectral method for the vibroacoustic analysis of fluid-loaded rectangular plates incorporating nonlinear energy sinks (NES). The proposed method employs Chebyshev polynomials for the spatial discretization of both structural displacements and the radiated acoustic pressure, achieving high accuracy with relatively few degrees of freedom. An iterative approach is used to solve for the eigenpairs of a rectangular plate submerged in a heavy fluid medium, and the obtained modal components are then incorporated into the reduced-order model of the fluid-loaded rectangular plate with NES. The harmonic balance method (HBM) is employed to efficiently determine the forced nonlinear response of the system. To validate the accuracy of the proposed approach, the model is first verified for fluid-loaded baffled rectangular plates equipped with a tuned mass damper (TMD) by comparing the results with reference solutions from the literature. For NES-equipped plates, Runge-Kutta methods combined with the Rayleigh integral formula are used as a benchmark for comparison. The results demonstrate the effectiveness of the proposed methodology in capturing the vibroacoustic behavior of NES-equipped fluid-loaded plates. Results indicate that the NES effectively suppresses vibration and reduces radiated sound pressure, without introducing additional resonance peaks. However, excessive NES stiffness can weaken noise reduction despite enhanced local vibration control. These findings confirm the method’s accuracy and computational efficiency, providing a powerful tool for nonlinear vibroacoustic analysis in heavy fluid environments.

Cylindrical members of offshore platforms and sea-crossing bridges are continuously exposed to traveling-wave-induced hydrodynamic loads, where rapid prediction and mechanistic interpretation of free-surface gas-liquid flow are both desirable. Conventional finite-volume simulations for complex two-phase configurations remain expensive and are difficult to reuse across boundary or geometric changes. To address these issues, we develop a physics-informed neural network framework that combines a residual-connected convolutional neural network geometric encoder with a Transformer attention mechanism in a transfer-learning architecture, termed the physics-informed residual-connected convolutional transformer network (PRCT-Net). High-fidelity reference solutions are generated using the Reynolds-averaged Navier-Stokes equations coupled with the volume of fluid method and the shear stress transport turbulence model and are used to validate traveling-wave-driven two-phase flow past two cylinders under multiple operating conditions. PRCT-Net achieves high-fidelity reconstruction of the free surface and the associated velocity and pressure fields while substantially accelerating inference; under the baseline condition, the maximum relative error of wave height is about 3.2%, velocity errors remain below 4% at all sampled instants, and the overall error is within 3.5%. A hierarchical freeze-unfreeze fine-tuning strategy further enables efficient cross-condition adaptation, reaching the target accuracy within 119 epochs while preserving a stable geometric-temporal latent space. From a mechanistic perspective, an overlapping V-shaped free-surface wake forms downstream at the steady stage and gradually decouples as cylinder spacing increases. The Omega field reveals V-shaped downstream vortex bands whose trajectory angles closely match those extracted from the free-surface wake. Leveraging PRCT-Net for rapid sampling over operating conditions, an empirical correlation for the wake-vortex trajectory angles is fitted, providing a quantitative and efficient tool for characterizing wake interference and vortex-band dynamics in free-surface flow past two cylinders.

This study presents a modeling approach for analyzing the aero-thermo-elastic vibration characteristics of porous functionally graded (FG) cracked plates. An extended Chebyshev spectral method is proposed to accurately capture the effects of cracks on the dynamic response by introducing supplementary functions that address local discontinuities while preserving the rapid convergence of Chebyshev polynomials. A thermo-dynamic analysis under steady-state temperature conditions is conducted to determine the internal non-uniform temperature distribution of the plate. The first-order shear deformation theory and supersonic piston theory are integrated to derive the strain energy and kinetic energy expressions for FG cracked plates with non-uniform porosity. Hamilton’s principle is employed to systematically formulate the stiffness, damping, and mass matrices. The proposed method enables high-fidelity modeling of crack-induced discontinuities and effectively captures the coupling between aerodynamic, thermal, and elastic fields. A comprehensive convergence study verifies the stability of the proposed spectral method, and comparisons with published studies and FEM results confirm its accuracy. Finally, a detailed parametric analysis investigates the influence of cracks on the aero-thermo-elastic vibration characteristics of porous FG plates, providing valuable insights into their dynamic behavior under combined aerodynamic and thermal loads.

This study presents a coarse-mesh Chebyshev spectral element method (CSEM) for the free-vibration analysis of Reissner-Mindlin shell structures of arbitrary geometry. The main novelty lies in integrating high-order Chebyshev spectral approximation, C0 patch wise shell assembly and logicaL-quadrilateral geometric mapping into a unified coarse-mesh framework for general curved shell geometries. Shell geometry is defined using a set of non-overlapping logical quadrilaterals, enabling an efficient representation of complex surfaces while significantly reducing the number of degrees of freedom (DOFs). Within each element, field variables are discretised using high-order Chebyshev polynomial expansions at Chebyshev-Gauss-Lobatto collocation points, allowing high-order modal accuracy to be achieved without dense low-order finite element meshes. The accuracy, convergence, and computational efficiency of the proposed method are demonstrated through a series of numerical experiments. Both h-refinement (mesh subdivision) and p-refinement (increasing polynomial order) convergence studies are conducted, revealing that the method achieves exponential convergence rates with a markedly small number of DOFs. Comparisons with finite element results, reference solutions and experimental measurements confirm the validity of the CSEM, particularly in capturing higher-order modes and complex vibration behaviours. The results reveal that the proposed formulation remains accurate for shells with arbitrary curvature and geometric discontinuities while maintaining favourable computational efficiency on comparatively coarse meshes.

This study develops a semi-analytical reduced-order modeling framework for the underwater vibro-acoustic analysis of acoustic black hole-piezoelectric shunt damping (ABH-PSD) composite plates submerged in a semi-infinite heavy fluid. A variable-fidelity projection-based model order reduction (MOR) strategy is proposed by exploiting the intrinsic difference between the highly localized structural response induced by the ABH and the spatially smooth acoustic field, enabling efficient and accurate fluid-structure coupling. The partition collocation points method (PCPM) is incorporated to avoid the direct evaluation of frequency-dependent singular quadruple integrals arising from the Rayleigh radiation formulation. The model is validated against finite element method (FEM) simulations and available experimental data, demonstrating excellent accuracy while achieving an approximate 90% reduction in the computational cost of the acoustic subproblem. Based on this framework, systematic underwater parametric investigations of ABH plates are conducted, revealing the dominant role of the ABH indentation radius in modal redistribution and the associated low-frequency mode clustering under heavy fluid loading. Furthermore, the integration of PSD, particularly through parallel and series negative-capacitance resistive-inductive (PNCRL and SNCRL) circuits, provides substantial low-frequency vibro-acoustic suppression, with maximum reductions of 18.4 dB in mean-square velocity level (MVL) and 18.1 dB in sound pressure level (SPL) at the fundamental mode. Comparison with equal-areal-density plates reveals a clear synergistic vibro-acoustic suppression mechanism, in which the ABH concentrates vibrational energy into the piezoelectric region, while the shunt circuit efficiently dissipates the concentrated energy, offering an effective strategy for lightweight underwater structures with enhanced low-frequency vibro-acoustic stealth performance.

A Chebyshev spectral approach is developed for the vibroacoustic analysis of revolving shell structures submerged in an acoustic half-space. The method couples dynamic modeling of shell vibrations with the Helmholtz boundary integral formulation, employing the half-space Green's function to evaluate radiated sound pressure for both soft and rigid boundary conditions. To address the higher accuracy requirements for singular integrals introduced by high-order Chebyshev polynomials, an adaptive numerical integration strategy is implemented. The approach is validated through numerical examples involving a single spherical shell, a cylindrical shell, and a coupled conical-cylindrical-spherical shell, with results compared against analytical solutions, literature data, and commercial software. Detailed convergence, accuracy, and computational efficiency studies using the spherical shell benchmark confirm the effectiveness of the proposed method. This framework provides an efficient and robust tool for vibroacoustic analysis of complex shell structures in underwater acoustic environments. In addition, the study reveals that significant circumferential modal coupling occurs at shallow submersion depths, leading to pronounced frequency shifts and energy redistribution among modes. These effects manifest as distinct changes in both the displacement and radiated sound pressure spectra, especially for lower circumferential wavenumber modes.

Accurate characterization of acoustic radiation from submerged structures is crucial for underwater noise assessment and vibro-acoustic analysis. In practical engineering, acoustic measurements are often confined to limited near-field regions and contaminated by noise, rendering sound field reconstruction an ill-posed inverse problem. The conventional Equivalent Source Method (ESM), employing Tikhonov regularization, typically yields over-smoothed solutions prone to spurious artifacts. In contrast, compressive sensing approaches using [Formula: see text]-norm regularization often suffer from amplitude bias in source strength estimation. To address these limitations, this study proposes a physically consistent reconstruction framework for underwater structural acoustic radiation. The non-convex Generalized Minimax-Concave (GMC) penalty is utilized to promote sparsity while mitigating the amplitude bias inherent in convex regularization. To overcome the inherent non-sparsity of submerged elastic structures in the spatial domain, acoustic radiation modes are employed. This transformation maps the dense source distribution into a sparse modal domain, inducing the requisite sparsity. The resulting optimization problem is solved within the framework of the Alternating Direction Method of Multipliers (ADMM). Numerical investigations on a complex cone-cylinder-sphere assembly demonstrate that the proposed method yields superior reconstruction accuracy and robustness compared to conventional techniques. The method suppresses spatial aliasing artifacts, especially in sparse measurement scenarios. Furthermore, a sparsity analysis is conducted to validate the effectiveness of the proposed sparse representation strategy.

To address the lack of unified quantitative guidelines for numerical modeling and absence of engineering design thresholds for the frame-type floating raft structure (FRS) as well as to satisfy the integrated vibration isolation requirements for equipment in underwater vehicle cabins, this study systematically analyzes a small irregular frame-type FRS using a combination of finite element simulations and modal hammer tests. The results show that the mode shapes and natural frequencies yielded by the two element models agree well, with Pearson correlation coefficients of 0.99 (shell element) and 0.95 (beam element), respectively. The maximum calculation errors for the first six natural frequencies are 14% (beam element) and 7% (shell element). Moreover, under the same mesh size, the beam element model enables a reduction in the number of elements by approximately 87%, reduction in the calculation time by 84%, and a 6.25-fold improvement in computational efficiency. This clarifies the feasible engineering application scenarios: shell elements are suitable for high-precision quantitative analyses, whereas beam elements are appropriate for rapid iteration in preliminary design. On the basis of experimental and simulation data as well as standard requirements, this study first proposes a design threshold for small frame-type FRSs: namely, the deviation between the calculated frequencies of the first two elastic modes and the main disturbance frequencies of the power equipment must exceed 3%. This threshold applies to similar structures with masses of 400–1000 kg and dimensions not exceeding 3 m × 2 m × 2 m. Overall, this study quantifies the applicability of boundaries of different modeling methods and provides a practical engineering threshold for the design of FRSs.

Carbon nanotube-reinforced (CNTR) composites, as advanced materials with high strength and low density, exhibit significant potential for application in the lightweight design and performance optimization of rotating blades. The properties of the matrix material significantly influence the overall mechanical performance of carbon nanotube-reinforced composites. This paper assumes that the matrix material exhibits power-law gradient variations along both the spanwise and thickness directions of the blade, investigating the vibration characteristics of MDFG-CNTR variable cross-section blades. The three-dimensional geometry of pre-twisted blades with variable cross-sections is constructed through isogeometric approach (IGA), and material distributions in various blade orientations are also characterized by geometric control points and spline functions. The centrifugal force work is solved using a step-by-step centrifugal force solution method, obtaining the vibration characteristics of rotating MDFG-CNTR blades under operational conditions. Through comparisons with published literature, numerical simulations, and experimental results, the convergence and accuracy of the proposed modeling approach are verified. Based on the validated model, the coupled effects of rotational speed, geometric parameters, and material variation parameters on the vibration behavior of variable-section blades are systematically investigated, providing a theoretical foundation for the application of CNTR composites in rotating machinery blades.

The identification of crack parameters in blades is crucial for the operational safety of rotating machinery. This paper presents a boundary determination and XIGA-based multiple crack type identification method for the rotating functionally graded (FG) blades. Assuming that the material varies in the thickness direction, the first-order shear deformation shell theory is used to describe the displacement of the FG blade with a pre-twisted angle. The XIGA method utilizing a level set approach is applied to consider the crack effects, with distinct enrichment functions capturing the displacement fields at the crack tip and along the crack faces. Taking the modal parameters as input, DE algorithm minimizes the objective function through multiple iterations to achieve intelligent quantitative identification of boundary penalty stiffness and crack parameters. Convergence and accuracy verifications of the cracked blade model with various types of cracks are performed by using data from experiments and software simulations. The parameter analysis reveals that different combinations of crack length and location induce distinct variation in the natural frequencies of the blade model. It is evident from the comparative analysis that the optimization technique with XIGA model exhibits comparable precision in detecting the targeted crack information. The developed method demonstrates applicability across multiple crack types, allowing for the effective identification of a wide range of crack parameter combinations.

To address the need for dynamic analysis of complex coupled plate structures in practical engineering, this study proposes a modelling method for the vibration analysis of coupled plates with arbitrary-angle rotation about three independent axes. The core novelty of the study lies in overcoming the limitations of conventional models on the number of coupling rotational axes and rotation angles, enabling rapid modelling of coupled plates with arbitrary spatial rotation angles and arbitrary translation positions, and offering stronger engineering generality. Based on spatial parametric equations, the proposed method determines the coordinate information of the endpoints of the coupling edges, discretizes the coupling edges using the point collocation method, introduces penalty coupling springs to impose coupling constraints, and establishes the coupling energy formulation of arbitrary-angle coupled plates. On the basis of the Chebyshev spectral method and the Rayleigh-Ritz method, the proposed method adopts Chebyshev-Gauss-Lobatto collocation sampling to achieve high-accuracy discretization of the structural displacement field and performs vibration-characteristic analysis of the coupled plates. Through comparisons with refined finite-element simulation results and experimental measurement data, the correctness and computational accuracy of the proposed method are verified. Parametric analysis is conducted to reveal the effects of the coupling angle and coupling position on the structural vibration characteristics.

Coplanar built-up plates coupled by plate elements have wide applicability in engineering fields. Their diverse geometries pose a challenge to vibro-acoustic coupling modeling. Therefore, a discrete collocation point method is proposed for the first time to establish a semi-analytical vibro-acoustic coupling model for such structures. Based on the infinitely rigid baffle assumption, one side of coplanar built-up plates is in contact with a semiinfinite heavy fluid domain. Motivated by the element discretization, the coplanar built-up plates are discretized into several elements, the boundary conditions and coupling conditions are implemented using virtual springs. All energy expressions are derived via the first-order shear deformation theory. When considering the sound pressure loading effect, the vibration and acoustic fields of each element are expanded in Chebyshev polynomials. Relying on sound pressure continuity, the vibro-acoustic coupling relationships among the elements are established. Finally, a complete vibro-acoustic coupling equation is derived using the Rayleigh-Ritz method. This paper takes cross-shaped, T-shaped, Z-shaped and L-shaped built-up plates as examples to validate the convergence and accuracy of the proposed method. Furthermore, the underwater vibro-acoustic characteristics of the above-mentioned structures are analyzed. This work is expected to be a valuable and dependable reference for future research of such structures.

This study investigates flow-induced vibration characteristics in a plate-double open cavity model for the first time by conducting experiments in a low-noise gravity water tunnel to assess vibration responses. By appropriately designing the opening size and structural dimensions, flow-induced resonance can be effectively suppressed, thereby reducing the vibration response of the open cavity system. The results indicate that the amplitude of vibration acceleration increases significantly with rising inflow velocity. Monitoring points farther from the clamped boundary exhibit higher vibration amplitudes than those closer to the fixed edge. Moreover, within the 0-100 Hz frequency range, the peak frequencies of vibration acceleration gradually shift toward higher values as the flow velocity increases, which is attributed to resonance induced by coupling between the shear layer's self-sustained oscillation and the structural modal frequencies. Further analysis reveals that the coupled wet structural modes are notably influenced by cavity depth, which highlights the complex FSI mechanisms involved. In the absence of coupling resonance, the shallow cavity, being closer to the boundary layer vortex shedding region, experiences stronger vortex-induced excitation, resulting in more pronounced flow-induced vibration responses.

The impact and underlying mechanisms of bionic blade optimization on the hydraulic performances of the underwater propulsion pump are investigated for the first time. Inspired by the morphology of shark fin leading edges and eagle wing trailing edges, bionic optimization strategies for the three-dimensional twisted blade in the outlet chamber of the pump are proposed. Three types of bionic designs are developed: Leading Edge (LE), Trailing Edge (TE), and Leading and Trailing Edge (LTE) bionic structures. The computational results are validated against experimental data and show deviations of less than 5.0 %. The bionic blade optimization significantly improves the propulsion pump's efficiency and head, with the LTE optimization achieving a 3.73 % increase in propulsion efficiency and a 7.45 m rise in head. A comparative analysis of flow characteristics confirms that the bionic designs effectively suppress unsteady disturbances and decrease energy losses, thereby enhancing hydraulic performance. Additionally, distinct mechanisms for the LE and TE bionic optimization designs are revealed. The LE design induces a spanwise flow that mitigates the impact of the incoming flow and promotes near-wall attachment, thereby delaying boundary layer separation. But the TE design creates lowpressure zones between the serrated protrusions, generating edge vortices that suppress flow separation.

A wavelet-based Galerkin weak form is developed in this paper to investigate the vibro-acoustic responses of a coupled panel-cavity system. The structural and acoustic models of the coupled panel-cavity system are constructed via the scaling function of a B-spline wavelet with multi-resolution analysis. Semi-orthogonal and compact support wavelet-based shape functions are employed as the wholly unknown displacement and sound pressure field variables in the vibro-acoustic systems. The similarity between the two-dimensional B-spline wavelet and three-dimensional (3D) B-spline wavelet on a bounded interval (BSWI) theory provides the potential for their integration and model at the fluid-structure interface. The panel is modeled according to both Kirchhoff and Mindlin theory using B-spline wavelets, with distinct coupling formulations derived by combining these plate theories with the 3D acoustic theory. In numerical examples, a parametric study, a convergence study, and an L-shaped panel-cavity system study are conducted using the proposed method and the standard finite-element method. The results demonstrate that the wavelet finite-element method effectively reduces the pollution error at a high wavenumber due to high order and multi-resolution of the B-spline wavelet and reveal that the coupled BSWI element is less sensitive to the irregular mesh, indicating that the proposed method provides more stable solutions for vibro-acoustic problems.