Underwater Acoustic Radiation Research Articles

Contribution Ratio of Excitation Sources to the Underwater Acoustic Radiation of the X-BOW Polar Exploration Cruise Ship

Contribution Ratio of Excitation Sources to the Underwater Acoustic Radiation of the X-BOW Polar Exploration Cruise Ship

Method for vibration and acoustic radiation analysis of underwater stiffened plates with acoustic coatings

Based on the effective medium theory as well as the three-dimensional viscoelastic theory, a semi-analytical model of the three-dimensional underwater vibration and acoustic radiation with cavity-type stiffened plate structures covered with acoustic coatings is established to solve the issues related to underwater vibration and acoustic radiation calculation of the stiffened plate and shell structure with complex acoustic coatings. By comparing the far-field acoustic radiation characteristics of the proposed semi-analytical model and the finite element numerical model, this research verifies the validity and accuracy of the proposed model. On such a basis, this research preliminarily investigates the coupling effect exerted by stiffeners and parent plates in stiffened plates as well as the vibroacoustic characteristics of acoustic coatings, thereby providing a valuable idea for the prediction of vibroacoustic characteristics concerning underwater structures.

The Average Sound Energy Spectrum Produced by a Single Raindrop

The characteristics of underwater acoustic radiation generated by a single raindrop impacting the water surface play a fundamental role in the study of rainfall noise. However, the underwater sound signal generated by a single raindrop has great randomness in the amplitude of sound pressure, frequency range and energy size, so that the uncertainty of the sound energy spectrum curve of a single raindrop is relatively large. In this paper, by generating artificial rainfall containing only one size of raindrop, the acoustic radiation generated by artificial rainfall composed of about 136,000 raindrops with an equivalent diameter of 0.9 mm was measured by reverberation method. A smooth, continuous sound energy spectrum of single raindrop covering the full frequency band is obtained.

Detection of Water Surface Acoustic Waves Using Sinusoidal Phase Modulation Interferometer and Prenormalized PGC-Arctan Algorithm

A sinusoidal phase modulation laser interferometer is proposed to detect water surface acoustic waves excited by underwater acoustic radiation, and an improved PGC-Arctan demodulation algorithm that combines prenormalization and Lissajous ellipse fitting is proposed to demodulate detection signals. In this paper, the effects of phase modulation depth, carrier phase delay, and interference signal visibility on the Lissajous figure formed by quadrature interference components are analyzed. The demodulation algorithm first uses the amplitudes of multiple Fourier spectral components of an interference signal to calculate the phase modulation depth C, and calculation of the carrier phase delay Vc is achieved through the introduction of a quadrature carrier signal. Then, certain coefficients regarding C and Vc are constructed for prenormalization of the two quadrature interference signal components to eliminate the local nonuniform widening phenomenon of Lissajous ellipse. Next, the outer and the inner contours are extracted from a uniformly widened Lissajous ellipse resulting from light intensity disturbance, and the axial ratio of the ellipse is obtained, which is used to correct the ratio of the quadrature interference signal to eliminate the effect of filter gain coefficients. At last, through the combination of an Arctan algorithm and a phase-unwrapping algorithm, high-precision demodulation of the interference signal is realized. A sinusoidal phase modulation interferometer was set up to detect water surface acoustic waves, and a series of detection experiments were carried out. The experiment results show that the detection method and demodulation algorithm described in this paper can accurately realize the measurement of weak water surface acoustic waves. The proposed algorithm shows less distortion in demodulation results, and its signal-to-noise distortion ratio is less than 20 dB at 500 Hz, which is significantly better than traditional algorithms. The experimental results demonstrate the effectiveness and accuracy of water surface acoustic wave detection using sinusoidal phase modulation interferometer.

High-resolution DOA estimation in the hydrophone array shape with uncertainty based on dynamic compressed sensing

Compressed sensing (CS) technology is a popular method for the direction of arrival (DOA) estimation of underwater acoustic radiation noise due to its high resolution. However, in practical applications such as buried arrays and other arrays, uncertainty in the hydrophone array shape can lead to model mismatch which significantly reduces DOA estimation accuracy. This paper focuses on high-resolution wideband DOA estimation in the radiated noise from underwater targets of interest using dynamic compressed sensing. The study introduces phase error into the signal model to simulate the model mismatch, and improves DOA estimation accuracy by jointly estimating both the DOA and phase error. Simulation results demonstrate that the proposed algorithm is effective in improving the accuracy of DOA estimation.

Research on Feature Extraction of Underwater Acoustic Target Radiation Noise Based on Machine Learning Algorithm

Underwater acoustic target recognition is a very important technology in the field of underwater acoustics, with great economic and military value. Feature extraction technology for underwater acoustic target radiation noise signals is the key to achieving acoustic target recognition. This study aims at the feature extraction task of acoustic targets and extracts 10 types of 252-dimensional feature vectors from three domains: time domain, frequency domain, and auditory domain. Through 7 machine learning algorithms for classification and recognition experiments, the experimental results show that the recognition performance of the ensemble classifier is much better than that of a single classifier. For different types of features, this study combines three ensemble learning algorithms and feature selection algorithms to select the original 252-dimensional features. The feature selection experiment shows that the wrapper feature selection algorithm has the best effect, and the feature vector dimension can be reduced to 40 dimensions. The recognition accuracy rate is not less than 92.8%, which provides feature extraction guidance for acoustic target recognition based on feature extraction.

An efficient hybrid collocation scheme for vibro-acoustic analysis of the underwater functionally graded structures in the shallow ocean

In this paper, a novel hybrid collocation scheme based on the generalized finite difference method (GFDM) and the Burton–Miller singular boundary method (BMSBM) is developed to study the vibration and acoustic radiation characteristics of an underwater functionally graded (FG) structure immersed in the shallow ocean. By utilizing the individual strengths of both methods, the GFDM is adopted for the vibration analysis of the FG structures, while the BMSBM is applied for the acoustic wave radiation analysis. Numerical examples verify the accuracy and efficiency of the proposed hybrid collocation scheme for the natural frequency and acoustic radiation behavior of the underwater structures consisting of the functionally graded materials (FGMs). The influences of the material parameters, structural geometries and shallow ocean environment on the natural frequencies of the structural vibration and the underwater acoustic wave radiation field are investigated in detail. Numerical study shows that the variation trend of the natural frequencies of the structural vibration is consistent with that of the resonance peak frequencies of the underwater acoustic radiation field. The present results may provide valuable references for the design and application of underwater marine structures consisting of the FGMs.

Numerical Modeling of the Low-Medium Frequency Vibration and Acoustic Radiation of Underwater Vehicles

_ Considering the main structures of typical underwater vehicles, three types of numerical model are established, including the beam model, the shell-beam model, and the whole shell model. The results of the three models are compared during the analyses of global vibration, local vibration of cabins, and underwater acoustic radiation. Giving consideration to both the computational cost and accuracy, the proposed shell-beam model is appropriate for the calculation of low-medium frequency acoustic radiation of the main structures of underwater vehicles. The rationality and the frequency range of application of the shell-beam model are verified by calculating the fluid-structure coupling vibration response and the underwater acoustic radiation of the hull subjected to the transverse load excitation, which also demonstrate the significance of this model in engineering practice. Introduction The calculation research on the acoustic radiation of typical underwater vehicle structures can be generally divided into three types based on the calculation methods: analytical methods (Caresta & Kessissoglou 2009), numerical methods, and analytical-numerical hybrid methods (Zhu et al. 2014; Meyer et al. 2016; Qu et al. 2017). The analytical methods can be used for the study of basic laws and mechanisms, and can also be treated as benchmarks for numerical algorithms. However, when it comes to real ships with complex structures, it is difficult to accurately predict the forced vibration and underwater acoustic radiation characteristics by analytical methods. Previously, due to the limitation of the computer hardware, a whole ship was usually simplified as a free–free beam of variable cross section (the hull beam) when conducting the analysis of global vibration. In recent years, with the development of computer technology, whole shell models are usually established during analyses of the low-medium frequency vibration and acoustic radiation of underwater vehicles.

Applicability and reliability of an experimental method measuring underwater acoustic radiation efficiency of floating box-type plate structures in a reverberant water tank

This paper aims to investigate the applicability and reliability of an experimental method measuring the underwater acoustic radiation efficiencies of floating plate structures in a reverberant water tank. For the purpose, an experimental method for estimating the acoustic power of a source in a reverberant sound field has been introduced and applied to measure the acoustic radiation efficiencies of two floating box-type plate structures excited by a logarithmic sine sweeping force in a water tank. The validity of the adopted experimental method has been examined by the comparison with numerical results obtained by a fully coupled vibroacoustic analysis with an infinite radiation boundary condition for the structures. From the results, it is confirmed that the experimental method for measuring the underwater acoustic radiation efficiency of floating plate structures in a reverberant water tank is reliably applicable for high-frequency ranges above the Schroeder frequency of the water tank.

Modeling and calculation of acoustic radiation of underwater stiffened cylindrical shells treated with local damping

Damping materials are widely used and playing an essential role in reducing the vibration and noise of various ships and underwater vehicles. In practical engineering, damping materials are often applied over the structural surface of ships and underwater vehicles. They are generally distributed not evenly in the whole area, but locally in some vital regions. The stiffened cylindrical shell is the most representative configuration for the main structure of underwater vehicles. Therefore, research on modeling and calculation of underwater acoustic radiation from stiffened cylindrical shells locally treated with damping has high practical value. This paper introduces a mixed analytical-numerical acoustic-vibration interaction method to achieve efficient calculation of the vibration and acoustic radiation from a locally damped cylindrical shell immersed in water. Two kinds of vibration and noise reduction measures are proposed for the damping treatment of a large-scale stiffened cylindrical shell structure. Calculation and analysis are carried out for both measures. The results can provide reference for developing the technology of reducing vibration and noise from ships and underwater vehicles via damping treatment.

A review of computational models for underwater acoustic radiation induced by structural vibration in the shallowmarine environment

<p indent="0mm">The vibration and acoustic performance of underwater structures have always been a research hotspot in the field of ocean engineering. The acoustic stealth technology of submarines and the marine hydroacoustic detection technology are based on the accurate prediction and effective control of the underwater structural vibration and acoustic behavior in the marine environment. For vibration and acoustic analysis in the marine environment, most of the early studies regarded the marine environment as an infinite fluid region, or a semi-infinite fluid region with a free sea surface. These two marine models simplify the simulation process of underwater acoustic radiation and propagation by ignoring the impact of the seabed. Underwater acoustic radiation and propagation caused by structural vibrations in the shallow marine environment will be greatly affected by the reflection and refraction effects at the sea surface and seabed. Moreover, the sound velocity in the shallow marine environment usually shows different profiles due to the influences of the water pressure and temperature, which affects the vibration and acoustic behavior of underwater structures. To accurately characterize the coupling effect of underwater structures and shallow marine environments, many researchers have devoted their particular efforts to the analysis of vibration and acoustic radiation of underwater structures in the shallow marine environment, and have developed a variety of numerical computational models, such as the finite element method, finite element-boundary element method, finite element-wave superposition method, finite element-singular boundary method, finite element-parabolic equation method and finite element-normal mode method, and so on. This paper focuses on deterministic computational models for vibration and acoustic analysis of underwater structures in the mid-low frequency range, and discusses two analytical schemes: Wet modal analysis and dry modal analysis. The development and application status of the computational models for the vibration and acoustics of underwater structures in the shallow marine environment are reviewed from the aspects of underwater acoustic models and numerical algorithms. Among those computational models, the finite element method combined with absorbing boundary layers is a common and efficient computational model, which is suitable for the analysis of near-field acoustic radiation induced by structural vibrations in the shallow marine environment. By contrast, the boundary discretization schemes, such as the boundary element method, wave superposition method and singular boundary method, avoid the special truncated treatment of marine domains by using the Green’s function derived from the mirror virtual source method and the normal mode model. Therefore, the hybrid computational solvers, such as the finite element-boundary element method, finite element-wave superposition method and finite element-singular boundary method, can be applied to the analysis of vibration and acoustic behaviors of the near- and far-field vibration and acoustic analysis. On the other hand, based on the wet modal analysis, the finite element-wave superposition method, finite element-parabolic equation method and finite element-normal mode method have higher computational efficiency in far-field acoustic propagation problems induced by vibration of underwater structures. Finally, the future development and application prospect of computational models for vibration and acoustic analysis of underwater structures in the shallow marine environment are discussed. Most of the existing computational models are based on the shallow marine environment of the horizontal sea surface and seabed. In future development, it is necessary to broaden the application scope of computational models, improve the computational efficiency of numerical algorithms, introduce the efficient optimization algorithm to develop a high-performance computational model for the optimal design of vibration and noise reduction of underwater structures in the typical and complex shallow marine environment.

Computational method of underwater acoustic radiation from a spherical shell coupled with nonlinear systems

During the continuous research and practical application of nonlinear vibration isolation systems, new problems arise for the vibro-acoustic calculation of underwater targets. The present frequency-domain analysis method can only deal with linear problems, so the acoustic radiation calculation of underwater targets coupled with nonlinear systems can only be performed in the time domain. When it comes to the real-time calculation, the huge computation cost will definitely bring challenges to the practical application. To solve this problem, a new calculation method is established for the underwater vibro-acoustic problems of structures coupled with nonlinear systems, taking elastic spherical shells as research objects in this paper. This method realizes the time-frequency domain conversion of the fluid-structure coupled vibration equation of an elastic spherical shell through the Fourier transform. The explicit difference method is further used to calculate the vibration response of the spherical shell, while the Newmark method is used to calculate the vibration response of the internal nonlinear system. An efficient integrated calculation of the two coupling parts is then achieved by considering boundary conditions at the connection point. Without the time-domain acoustic field solution, this method is able to calculate the vibration response of both the internal nonlinear system and the spherical shell, as well as the radiated acoustic power generated by the spherical shell vibration in real time. The calculation complexity and efficiency are radically improved. The nonlinear system discussed in this paper is a nonlinear mass-spring oscillator system installed at the bottom of a spherical shell. Finally, the correctness of the method described in this paper is verified through specific numerical examples, and a series of calculations and analyzes are carried out to explore the influence of nonlinear effects on the acoustic radiation of underwater structures. The calculation method described in this article is not limited to spherical shells, and is still applicable to general underwater targets.

Analysis of Viscoelastic Damping Effect on the Underwater Acoustic Radiation of a Ring-Stiffened Conical Shell

Hydroacoustic radiation from submarine power compartments has been the focus of research for many years. In this work, a ring-stiffened conical shell with bases is employed as the target model. The self-factors of viscoelastic damping, such as the damping thickness and damping location, are selected to study their effect on the underwater acoustic radiation, which will give a better understanding of the optimal scheme for applying damping. Firstly, based on a combination of finite element method (FEM) and boundary element method (BEM), the underwater vibration and acoustic radiation of the whole structure are analyzed. Secondly, taking a clamped-free sandwich beam as an example, through comparison with the published numerical data, the present damping application method and mesh density are verified. Finally, the influence of viscoelastic damping parameters on acoustic radiation is studied. The results show that the viscoelastic damping thickness has a significant influence on the amplitude of radiated noise but does not change the distribution of the acoustic field. Furthermore, the damping on the web may achieve the best vibration damping effect in this work.

Structure-Acoustic Coupling Analysis of Vibration and Underwater Acoustic Radiation of a Ring-Stiffened Conical Shell

The underwater acoustic radiation of the submarine power cabin has recently become a hot topic in the industry and also in the academia. In this article, the vibration and underwater acoustic radiation of a ring-stiffened conical shell with bases are investigated numerically by means of the combination of the finite element method and boundary element method. The acoustic radiation field is obtained by the traditional acoustic field model and ISO acoustic field model, respectively. A series of numerical examples are given, and the results are compared. Besides, the sound pressure at different positions with frequency is further studied. It is shown that the sound radiated by the structure mainly propagates to the side directions of the shell and propagates relatively less to the front side and the rear side.

A weak-form interpolation meshfree method for computing underwater acoustic radiation

An improved interpolating element-free Galerkin (IIEFG) method coupled with Modified Dirichlet-to-Neumann (MDtN) boundary condition is presented in this paper for use in computing underwater acoustic radiation. In the scheme of the IIEFG-MDtN approach, the improved interpolating moving least-square technology is employed to construct the shape function with the aim of improving the interpolation accuracy, and the MDtN boundary condition is used to meet the Sommerfeld radiation condition required at infinity and remove the difficulties arisen as the truncated DtN boundary condition is employed in computation. It is the key feature of this weak-form meshfree method that no connectivity of nodes or mesh is required for acoustic field variable interpolations while the prediction accuracy is significantly improved. The factors including the size of the influence domain, shape parameters and the number of terms used in the MDtN map, which affect the performance of this proposed method, are studied numerically. Typical numerical examples are presented to test the properties of the IIEFG-MDtN approach. The results indicate the devised method is outstanding to cope with underwater acoustic radiation prediction and can achieve higher accuracy and faster convergency compared to the finite element method.

On near- and far-field acoustic radiation characteristics of ships in finite-depth water environment

A simplified calculation model is established to evaluate the acoustic radiation of the single-shell underwater ship structure considering typical ship mechanical excitation. The three-dimensional sono-elastic method of ships in Pekeris ocean-acoustic waveguide environment is used to calculate the acoustic radiation of the ship structure in three water environments. Variation of the ship's acoustic radiation, from the near field to the far field, is analyzed. In the near field, the value of the radiated acoustic pressure varies greatly with the changing of spatial coordinates (near-field acoustic waves exist). When evaluating underwater acoustic radiation of the ship quantitatively in the engineering, the locations of observation points (where the radiated noise is measured under water) are usually close to the ship. The distance of the observation point away from the hull is even smaller than the length of the ship taking into account the requirement of a sufficient SNR (Signal-to-Noise Ratio). At such a distance, it cannot guarantee that the converted acoustic source levels are basically stable and can effectively reflect the acoustic radiation magnitude in the far-field, that is, the condition of far-field investigation is not satisfied. This study will be helpful in answering two issues of concern in engineering: (1) How much near-field acoustic disturbance will be introduced if the distance from the hull to the observation point is less than the length of the ship? (2) How far does the observation point need to be away from the hull in order to exclude the near-field acoustic disturbance effectively?

Hybrid FEM–SBM solver for structural vibration induced underwater acoustic radiation in shallow marine environment

This study focuses on the efficient computational model for predicting the structural vibration induced underwater acoustic radiation in shallow marine environment. In the proposed model, the finite element method (FEM) is used to calculate the vibration response of the shell structures and the singular boundary method (SBM) with near-field and far-field Green’s functions is used to simulate the underwater acoustic radiation excited by shell structural vibration in shallow water marine environment, namely, the hybrid FEM–SBM solver. For axisymmetric shell structures, the axisymmetric numerical formulation of the FEM–SBM solver is derived to save the computational cost. For general shell structures, the fast direct solver based on the recursive skeletonization factorization is introduced into the FEM–SBM solver to accelerate the computation of the underwater acoustic field. Numerical results demonstrate that the proposed FEM–SBM solver provides more efficient and reliable solutions in comparison with the coupled FEM/FEM solver (COMSOL software). The effect of the sound velocity profiles on the underwater acoustic radiation field in shallow water marine environment is numerically investigated.

A Hybrid GFDM–SBM Solver for Acoustic Radiation and Propagation of Thin Plate Structure Under Shallow Sea Environment

This paper makes the first attempt to propose a novel hybrid collocation solver based on the generalized finite difference method (GFDM) and singular boundary method (SBM) to analyze underwater acoustic radiation and propagation around the thin plate structures excited by simple harmonic force under shallow sea environment. In the proposed hybrid solver, the meshless GFDM is employed to obtain the fluid–structure coupling vibration response of thin plate structure, and then the SBM with Pekeris waveguide Green function is used to calculate the external acoustic field of thin plate structure. The simplified Price–Wu boundary condition is adopted on the surface of plate structure to connect the computational domains between the GFDM and SBM. Three benchmark examples are carried out to demonstrate the accuracy and efficiency of the proposed hybrid GFDM–SBM solver in comparison with the COMSOL simulation for computing underwater acoustic wave fields around the thin plate structures under shallow sea environment.

An Experimental and Modeling Study on Vibro-Acoustic Response of Double-Walled Steel Cylindrical Shells

Based on precise transfer matrix method (PTMM), the analytical model of the double-walled steel cylindrical shell was setup by taking into account of the annular plate and interlayer water. Under the linear sweep frequency excitation or the fixed frequency excitation, an experimental model of the double-walled steel cylindrical shell has been designed, which is performed to gain the natural frequencies, forced vibration in air and water, underwater acoustic radiation. The analytical model was established to calculate natural frequencies, vibration acceleration level and sound pressure level and compare with the relevant experimental results. The compared results show that analytical results coincide with the experimental value and prove that the analytical model established by PTMM is reliable and credible. Meanwhile, the forced vibration behaviour of measuring positions at inner and outer shells was investigated both theoretically and experimentally. Effects of different types of external excitations on the vibration and sound radiation of the double-walled cylindrical shell are discussed. As to acoustic radiation, the acoustic excitation plays a leading role in the low-frequency range. The force excitation is a major contributor in middle-high frequency range conversely.

Simulation and investigations on the vibro-acoustic behavior of cylindrical shells in ice-covered water

Vibro-acoustic responses of cylindrical shells immersed in ice-covered water are typical acoustic-structure coupling problems. The dynamic model of the immersed cylindrical shell was established by Finite Element Method (FEM) to obtain the vibration response. The elastic constitutive material was adopted to simulate the ice model. The acoustic model of cylindrical shells was constructed by Boundary Element Method (BEM) to gain the underwater acoustic radiation. A series of boundary conditions were defined to tackle dynamic accurate contact interactions of the cylindrical shell, fluid field and ice model. Comparative analysis with the vibro-acoustic results of numerical model was proceeded to show the practicality and effectiveness of the numerical method. Both models of fully immersed and partially immersed cylindrical shells were calculated to analyze the vibration and underwater acoustic radiation. The effect of immersion depth, ice thickness, temperature and brine volume on vibro-acoustic responses of the immersed cylindrical shells were also discussed. It provides a way to evaluate the vibro-acoustic performance of underwater vehicles in polar ice area.