Acoustic Radiation Characteristics Research Articles

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.

Research on numerical simulation of tandem thrusters flow-induced noise

A tandem propeller is a kind of propulsion device that is installed on the outer axis and the inner axis with the same axis respectively and rotates positively and negatively. Taking DTMB tandem thrusters as an example, which consists of propeller3689 and propeller3849, the hydrodynamic characteristic simulation of the tandem thrusters is completed, using sound analogy theory. The simulation results are consistent with the experimental results. The speed distribution of the tandem thrusters and the hydrodynamic wake of the tandem thrusters are analyzed. Through the analysis of acoustic radiation characteristics, it can be concluded that the noise characteristics of tandem thrusters are more complex than those of ordinary propellers, and there are more line spectrum characteristics in them.

A rapid prediction model for the radiation efficiency of baffled constrained layer damping plate

It’s well-known that constrained layer damping (CLD) can effectively reduce the vibration and radiation noise from the (plate-like or shell-like) thin-walled structures under various of dynamic excitations. As one of the key properties deciding the CLD’s performance, the CLD’s acoustic radiation characteristics has always been a focus of researchers. In this study, an analytical model based on equivalent principle is proposed to predict the acoustic radiation efficiency of the CLD plate. In this model, a laminated CLD plate is equivalent to a single-layer plate and the equivalent stiffness and loss factor are obtained using the strain energy method. The vibration velocity of the plate is calculated using mode-superposition method and the sound pressure on the plate surface is calculated using Rayleigh integral formula. Variable mesh sizes and frequency steps are employed to improve the calculation efficiency. The difference between the base and CLD plates in sound radiation characteristics is investigated using this model. The results indicate that CLD involving a damping layer with a low Young’s modulus can mitigate more vibration at low frequencies. A higher Young’s modulus of the damping layer results in a higher radiation efficiency of the CLD plate between the fundamental and critical frequencies. By increasing the loss factor, the spatially averaged mean square velocity would decrease, more modes would contribute to the response, and the CLD plate can consequently achieve a higher radiation efficiency below the critical frequency. Moreover, the simplified formulae for the average radiation efficiency of the CLD plate is developed to achieve the rapid calculation. Its accuracy is then validated by comparing the results to the more comprehensive model.

Comparison of Acoustic Radiation Characteristics in the Near and Far Fields Due to the Vibration of a Circular Disk Placed on an Infinite Rigid Baffle Using the Rayleigh Integral Method and Lumped Parameter Method

Comparison of Acoustic Radiation Characteristics in the Near and Far Fields Due to the Vibration of a Circular Disk Placed on an Infinite Rigid Baffle Using the Rayleigh Integral Method and Lumped Parameter Method

Smart Blade Count Selection to Align Modal Propagation Angle with Stator Stagger Angle for Low-Noise Ducted Fan Designs

The rotor–stator interaction noise is a major source of fan noise. Especially for low-speed fan stages, the tonal component is typically a dominant noise source. A challenge is to reduce this tonal noise, as it is typically perceived as unpleasant. Therefore, in this paper, we analytically, numerically and experimentally investigate an acoustic effect to lower the tonal noise excitation. Our study on an existing low-speed fan indicates a reduction in tonal interaction noise of more than 9 dB at the source if the excited acoustic modes propagate parallel to the stator leading edge angle. Moreover, a design-to-low-noise approach is demonstrated in order to apply this effect to two new fan stages with fewer stator than rotor blades. The acoustic design of both fans is determined by an appropriate choice of the rotor and stator blade numbers in order to align the modal propagation angle with the stator stagger angle. The blade geometries are obtained from aerodynamic optimization. Both fans provide similar aerodynamic but opposing acoustic radiation characteristics compared to the baseline fan and a significant tonal noise reduction resulting from the impact of the modal propagation angle on noise excitation. To ensure that this effect can also be applied to other low-speed fans, a design rule is derived and validated.

Vibration and acoustic characteristics of acoustic black hole plates with variable elastic modulus

Acoustic black hole (ABH), as a new wave manipulation technique, shows excellent applications in vibration and noise reduction of structures. Nowadays, most ABHs use materials with a fixed elastic modulus, limiting their low-frequency performance. Herein ABH plates with variable elastic modulus (VM-ABH) is designed, and its vibration and acoustic radiation characteristics are investigated by using numerical analysis. The results show that the vibration response of VM-ABH has a decrease of 5–13.2[Formula: see text]dB relative to that of the uniform texture ABH (UT-ABH) in the frequency range of 10–5000[Formula: see text]Hz, and the degree of energy aggregation is significantly improved. Moreover, the sound pressure level was reduced by 3.6 dB. Meanwhile, by linearly varying the elastic modulus in the center region of the VM-ABH, the effects of gradient index and terminal elastic modulus on the damping characteristics and dynamic response are revealed. The research results provide new objects for the study of vibration and noise reduction of ABH.

Experimental and numerical investigation on vibro-acoustic performance of a submerged stiffened cylindrical shell under multiple excitations

The underwater vibro-acoustic characteristics of a stiffened cylindrical shell have been investigated using experimental and numerical methods. A numerical analysis model is developed to capture the behavior of the cylindrical shell structure, and the validity of the model is verified based on experimental data. Experimental measurements are conducted in an anechoic tank to assess the vibration and acoustic radiation characteristics of the stiffened cylindrical shell under white noise excitations. Additionally, the disparities in underwater vibration noise characteristics of the stiffened cylindrical shell under both single excitation and multiple excitations are explored by numerical method. The experimental and numerical findings reveal that, within the frequency range of 10–2000 Hz, the stiffened cylindrical shell exhibits a rapid augmentation of low-frequency vibration noise followed by a gradual stabilization trend. This behavior can be attributed to the high density of low-frequency modes embedded within the structure. Furthermore, it is noteworthy that the underwater vibration noise of the cylindrical shell under multiple excitations arises not solely as a result of individual excitations being superimposed, but rather as a consequence of the intricate coupling effects induced by multiple excitations.

Research on wheel-rail noise in rail corrugation road of urban rail transit

As an efficient, fast, green and environmentally friendly means of transportation, subway vehicles account for the largest proportion of urban rail transit, and in large and medium-sized cities, the construction of subway is still in rapid development, but with the subway noise radiation problem, subway noise plagued by passengers, related operators and residents along the subway. In this study, the finite element analysis software ABAQUS is used to establish the coupled dynamics model of subway B-type vehicle-rail, and the acoustic radiation characteristics of wheels and rails are calculated based on the FE-BE and FE-SEA method, respectively, with the aim of analyzing the effects of different wavelength and depth parameters on the dynamics of vehicle response and wheel-rail noise radiation pattern when the vehicle is running on the rail corrugation road. The results of the study show that the effect of rail corrugation parameters on the power level of wheel and rail sound radiation is more significant in the low-frequency range, and the wheel-rail noise is mainly radiated by the wheel in the low-frequency range, while in the high-frequency range, it is mainly radiated by the rail.

Vibro-Acoustic Analysis of an Underwater Cylindrical Shell with Internal Structures and a Comparison with Experiment

Abstract: In this work, the low-frequency vibration response and full-band acoustic radiation characteristics of an underwater reinforced cylindrical shell with internal structures are studied by combining the FEM with SEA. The stiffened cylindrical shell contains internal structures such as the F-shape plates and the support valve frames. The exciting sources have two different exciting forces corresponding to two experimental conditions. In the low-frequency band, the FEM was employed, and in the medium and high-frequency bands, the SEA was used. A comparison of the numerical results and the experiment shows that they agree well. The FEM and SEA give better results at [1,1k] Hz and [1k,10k] Hz, respectively. Due to mesh quality limitations, the FEM is not favorable for medium and high-frequency calculations. The SEA focuses on the structural mean power flow but cannot obtain position-specific vibrational responses. The results show that the internal excitation source mainly causes the structural vibration and sound radiation and are closely related to the free vibration characteristics of the structure. In addition, with the increase in frequency, the circumferential sound pressure level of the underwater structure has more substantial directivity.

Quasi-real-time estimation of a loudspeaker direction from sound pressure level ratio among four channels

This paper describes a quasi-real-time estimation method of loudspeaker direction under Gaussian noise environment. Our estimation method is based on sound pressure level ratio among four channels when the loudspeaker is surrounded by four microphones. Performance of our method tends to be better when acoustic spatial radiation characteristics of sound source is skewed. Preliminary experiments show that an offline processing version of our method is more than 99% accurate in acoustically clean environments. In this paper, we discuss the noise robustness of our method through simulation experiments. Loudspeaker direction is estimated from 0.34s segments of Japanese sentences every 0.01s, that is quasi-real-time processing. Those segments are contaminated by Gaussian noise at 0dB, 10dB, 20dB. We demonstrate that the proposed method is robust to Gaussian noise. The results show that accuracies of proposed method (Prop2) are 96.9%, 98.2%, 98.4% at the band the center frequency of which is 2000Hz.

Complex modal analysis of structural vibration and acoustic radiation of plates

Inhomogeneous damping distribution leads to the occurrence of complex modes of structures. Complex modes' vibration and acoustic radiation characteristics are different from real modes. This paper studies the complex modal characteristics of inhomogeneously damped plates for forced vibration. We used the state space method to obtain the complex eigenvalues and eigenvectors of the vibration system and calculated the relationship between modal coordinates and frequency under unit force. The results show that the absolute values of the modal coordinates of two conjugate complex eigenvectors are different, and the structure's vibration is dominated by the eigenvectors corresponding to eigenvalues with positive imaginary parts near natural frequencies. When investigating the structural sound radiation in the vibration mode space, each mode's acoustic radiation is not independent but coupled with each other. The influence of the coupling between complex modes on the calculation results of the acoustic radiation power of the plate is studied in this paper. The results show that the coupling effect between modes cannot be ignored when calculating the acoustic radiation power based on complex modes. Finally, the error of calculating acoustic power using the decoupling approximation instead of the complex mode method is analyzed.

Hydrodynamic response of a pitching elastic hydrofoil in the wake of a circular body

A hydrofoil with a classic cylinder–hydrofoil structure is adopted for study in this paper. The hydrofoil is invented by National Advisory Committee for Aeronautics (NACA) and so-called NACA0012.The hydrofoil is placed in an unsteady turbulent environment by positioning a cylinder in front of the hydrofoil. The simulation includes a solid stress model to calculate the hydrofoil's elastic deformation. Large-eddy simulation is used to simulate the effects of different materials on the hydrodynamic performance and noise characteristics. Researching the hydrodynamic performance and acoustic radiation characteristics of the pitching hydrofoil in a turbulent flow provides a reference basis for its design and manufacture. It was found that different material properties have limited effects on the hydrodynamic performance of pitching hydrofoils, and the generated lift is similar for each case. An analysis of stress changes shows that the stress increases with increasing elastic modulus and as the fixed rod is approached. In contrast, the displacement decreases as the elastic modulus increases. The displacement increases with the distance from the fixed rod. In addition, the noise component results show that thickness noise dominates, and an elastic material hydrofoil has better noise performance.

Flow-Induced Noise Characteristics Analysis of a Pipeline Structure in a Cabin Rigid Corner

The acoustic radiation characteristics of pipeline structures caused by turbulent fluctuating pressure are among the most important acoustic radiation sources in vessel cabins. Studying the vibro-acoustic characteristics of pipeline structures is of great relevance to engineering. The turbulence fluctuation pressure of pipeline structures’ inner surfaces was numerically analyzed by using the large eddy simulation (LES) method. At first, the vibro-acoustic differential equation of the pipeline structure system was derived by defining the fluctuation pressure as the excitation loading. According to the acoustic radiation characteristic in the quarter-infinite space, which had a combination of two rigid wall interfaces at the same time for the pipeline structures in the vessel cabins, the double reflection method, mirror image method and elastic wave Graf addition principle were applied, and the analytical function of the acoustic radiation for the cylindrical shell was derived. For the pipeline structures in the quarter-infinite acoustic space, for example, the numerical calculation for the acoustic radiation of cylindrical shell was carried out, which was excited by the turbulent pulsating pressure. Finally, the influence of inner flow velocity, frequency, and pipeline installation position were compared using numerical analysis. The results can provide technical support for the acoustic design of pipeline structure systems with complex acoustic boundaries.

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.

Acoustic radiation characteristics according to the vibration area of OLED panel speakers

Previous studies have introduced the potential of flat OLED panels to be utilized as multiple-channel speakers. Subsequent research has also focused on improving sound quality and implementing multi-channel audio system in OLED TV. For personal displays using OLED panels find diverse applications, offering comfortable and accessible viewing for OTT services with top-notch video and audio quality. Moreover, they excel in delivering crucial audio information during various gaming experiences. In this study, we present a film-based Cinematic Sound OLED (CSO) technology, directly vibrating a single flat OLED panel, which extends the vibrational area compared to previous studies and can reproduce two or more independent sounds. In particular, the proposed method transmits information by generating sound directly on the screen. This method is as sophisticated, accurate, and realistic as the method using headphones. Headphones or earphones generate sound close to the human auditory system, potentially harming auditory health. However, the proposed method aligns the focus of the display and sound, maintaining a certain distance from the user's auditory system. In this paper introduced the advantages of the proposing method and discuss a personal high-performance display device and an appropriate advanced audio generation method.

Propeller-shaft-hull coupling acoustic radiation characteristics induced by friction self-excitation of the stern bearing

This paper focuses on the practical engineering problem of excessive propeller-shaft-hull coupling vibration noise, which is caused by poor lubrication contact of water-lubricated stern bearings in the ship propulsion shaft system. Firstly, based on the three-dimensional sono-elasticity theory of ships, calculation models for the propeller-shaft-hull coupling acoustic radiation transfer function are established separately, considering the propeller excitation and friction excitation of the stern bearing. Secondly, by analyzing the acoustic radiation contribution of each mode, the vibration mode with the highest contribution to the typical acoustic radiation transfer function peaks of the propeller-shaft-hull coupling under the friction excitation of the stern bearing is separated. The spatial distribution and pointing characteristics of the sound field corresponding to the propeller-shaft-hull coupling acoustic under friction excitation of the stern bearing are given. Finally, a quantitative evaluation model of propeller-shaft-hull coupling acoustic radiation caused by friction self-excitation of the stern bearing is established. The mechanism behind the typical acoustic radiation peaks of propeller-shaft-hull coupling under friction excitation of the stern bearing is revealed, which provides methodological guidance for the quantitative evaluation of friction vibration noise and the separation of vibration noise components in ship stern structures.

Analysis of Vibration and Acoustic Radiation Characteristics of Reinforced Laminated Cylindrical Shell Structure

This paper investigates the acoustic radiation characteristics of reinforced laminated cylindrical shell structures in the medium-low frequency range (1~1000 Hz) of aircrafts, submarines, and deepwater thrusters by combining simulation analysis and experimental testing. The research focuses on reinforced laminated plates, where experimental setup is established to measure structural modal parameters and structural acoustic power, and a finite element model is developed to verify the reliability of the finite element modeling method through comparison with experimental and simulation results. Simultaneously, a finite element model of the reinforced laminated cylindrical shell structure is established, and finite element simulation analysis is conducted to investigate the effects of different reinforcement methods, reinforcement quantities, reinforcement lengths, and reinforcement thicknesses on the acoustic radiation characteristics of the structure. The results indicate that in the frequency range of 1~1000 Hz, ribbed reinforcement exhibits better performance in reducing structural noise radiation compared to longitudinal reinforcement. With the increase in reinforcement quantity and thickness, the structural acoustic radiation decreases. Meanwhile, with the increase in reinforcement length, the overall sound power level of the structure shows a trend of first increasing and then decreasing.

Case study: Acoustic radiation characteristics and mechanism of high-speed railway box-girder bridge

The proportion of box-girder bridges in high-speed railways in China is high. The noise caused by trains passing a box-girder bridge is more intense than the noise in other sections of the railway because it is radiated by the bridge. This study investigates the acoustic radiation characteristics and mechanism of the box-girder bridge including low-frequency vibrations below the hearing threshold. The foregoing is examined in terms of natural vibration characteristics, vibration responses of the bridge under nonlinear train–track dynamic interactions, and structural noise radiation principle. The results show that the structural resonance, acoustic radiation efficiency, acoustic–vibration coupling in the bridge cavity, and severe train-induced vibrations play important roles in the acoustic radiation of the box-girder bridge. Under moving train loads, bridge vibrations are mainly in the 80- to 100-Hz frequency range and cause distinct noise radiation. Moreover, the low-frequency (20 Hz) train-induced vibrations of the bridge can generate distinct low-frequency noise. Additionally, the box-girder bridge cavity induces acoustic–vibration coupling, which can aggravate the noise radiation on both sides of the box-girder bridge.

Analysis of acoustic radiation characteristic of laminated paraboloidal shell based on Jacobi-Ritz-spectral BEM

This research presents a semi-analytical method to investigate the acoustic characteristics of a composite laminated paraboloidal shell in a light fluid. First of all, the mathematical model of a paraboloidal shell structure is constructed based on the Ritz method and multi-section partition technique. Secondly, Jacobian polynomial and Fourier series are innovatively used to expand displacement tolerance functions of a paraboloidal shell structure, and the external acoustic fluid is modeled using Helmholtz integral formula. Lastly, artificial spring technology is employed to effectively realize complex boundary conditions such as stiff fixing and basic support of paraboloidal shell structures. The validity and dependability of Jacobi-Ritz-spectral BEM are verified by comparing it with the results of the coupled FEM/BEM. In the meantime, this research also discusses the effects of boundary conditions, structural parameters, and fiber ply angle on acoustic radiation characteristics.

Study on interior noise control of minibus based on structural acoustic radiation

Aiming at the problem of excessive low-frequency noise inside a minibus, the interior noise control scheme was studied to improve the NVH (Noise, Vibration, and Harshness) performance of the vehicle based on the characteristics of the structural acoustic radiation. With acoustic contribution as the evaluation index, the ability of the structure to radiate noise to the vehicle was studied from the perspective of modal participation and panel contribution. In this study, the legacy finite element model of the vehicle was firstly established, and the model was validated through the modal test of the BIW (Body in White), and the noise transfer function analysis was carried out to identify the critical frequency points. Furthermore, the improved super element method (SEM) was used to establish the super element simulation model of the vehicle, the simulation analysis of the modal contribution and panel contribution was carried out for the critical frequency points, and the panels that provide the main contribution were determined. In addition, a single-factor experimental study was carried out on the position of the critical panel by using the dynamic vibration absorbers with different performance parameters, so as to verify the accuracy of the simulation results of the panel acoustic contribution for the critical frequency. Finally, the structural optimization schemes of the critical panels were designed and verified by experiments. It was indicated that optimizing the acoustic radiation characteristics of the structure by improving the body panel structure to reduce interior noise was feasible.