Vibro-acoustic 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.

Active feedback control on acoustic radiation of metastructure shell with low-frequency and broadband characteristics

Due to the tunable characteristics of elastic waves, the vibroacoustic coupling behavior of a mechanical metastructure is a hot topic of underwater vehicles. In this work, a metastructure shell with active feedback control is presented and fabricated. The dynamic effective density and sound pressure level are derived to find the influences of acceleration and displacement feedback control. Different from a single cylinder, a double cylinder structure has both in-phase and anti-phase modes. Numerical results are obtained by Fourier transform and harmonic series expansion. With the introduction of an active feedback control system, the reduction of acoustic radiation shows low-frequency and broadband characteristics. In addition, finite element simulation is applied to support numerical results and present vibroacoustic characteristics. Finally, an experiment is performed in the anechoic chamber to illustrate the quiet metastructure shell, which can be applied to new designs of underwater vehicles.

Vibroacoustic analysis of submerged fluid-filled cylindrical shell

This study presents a comprehensive Chebyshev-Fourier spectral method for analyzing the free and forced vibroacoustic characteristics of submerged fluid-filled cylindrical shells in heavy fluids. The vibroacoustic interaction system of submerged cylindrical shells consists of three discrete regions: The Sanders shell theory is applied for the shell structure, whereas the wave equation is used to determine the fluid inside. The external fluid pressure on the shell is described using the Helmholtz boundary integral equation. The governing equations for the shell's motion, the formulation of the external fluid pressure on the fluid-structure-interaction (FSI) surface using first-class Chebyshev polynomial and Fourier series expansions, and the internal sound pressure employing two-dimensional Chebyshev polynomial and Fourier series expansions, are seamlessly integrated with Gauss-Chebyshev-Lobatto sampling techniques. Artificial springs are implemented to replicate the boundary conditions of the cylindrical shell. The precision of the proposed methodology is corroborated by comparisons with existing literature and finite element method (FEM) results. Furthermore, the research examines how the properties of the acoustical medium on the vibroacoustic responses of the cylindrical shell. Results indicate that the presence of air inside the shell slightly influence on its acoustic radiation. However, replacing the internal medium with water significantly alters the shell's original radiation characteristics.

Визначення параметрів вібрацій космічного апарата на активній ділянці польоту ракети-носія на основі вогневих випробувань рiдинного ракетного двигуна

In orbital injection, the launch vehicle (LV) structure and the spacecraft are subjected to extreme dynamic loads, in particular to vibroacoustic loads (from rocket engine thrust oscillations and aerodynamic loads), which may cause spacecraft instrumentation malfunction and damage spacecraft light-weight thin-walled structures. This paper is dedicated to the development of an approach to predicting dynamic loads on spacecraft in orbital injection by LVs of various layouts under propulsion system thrust oscillations in active flight. The paper presents an approach to predicting dynamic loads on spacecraft in orbital injection by LVs of various layouts. The approach makes it possible to evaluate dynamic loads (spectral densities of vibration accelerations) on spacecraft under propulsion system thrust oscillations acting on the liquid-propellant LV structure in active flight. The approach includes a mathematical simulation of the spatial oscillations of the LV structure according to its structural layout scheme and the experimental pre-determination of the spectral density of the rocket engine power. The workability of the proposed approach in predicting the spacecraft dynamic loads is demonstrated by the example of a computational analysis of the spectral densities of spacecraft oscillations in orbital injection by LVs of various structural layouts. It is shown that the approach allows one to predict, as early as at the initial LV design stage, the spacecraft vibratory load parameters at different times of the LV first-stage liquid-propellant rocket engine operation accounting for the rocket layout (with the spacecraft) and design features and using the vibroacoustic characteristics of the liquid-propellant rocket engine (known from the results of its fire tests).

A hybrid wave and finite element/boundary element method for predicting the vibroacoustic characteristics of finite-width complex structures

This paper presents a hybrid wave and finite element/boundary element method for predicting the vibroacoustic characteristics of complex panels characterised by an irregular cross-sectional shape with a non-flat upper surface. In this approach, the panels are treated as waveguides and only a small segment of the panel is modelled using finite elements. The mass and stiffness matrices of the segment are then post-processed to project the motion onto its cross-sectional boundaries interfacing with the surrounding fluids. The acoustic pressures in the fluids are modelled by applying Fourier transforms to the Helmholtz boundary integral equations in the wavenumber domain. For each wavenumber component, the pressures acting on the segment are transformed into external nodal forces by evaluating the virtual work performed by the surface pressure on the segment. The wave and finite element formulations are subsequently coupled to the discretised boundary integral equations to determine the response of the panel to acoustic wave excitation. The hybrid method for predicting dispersion curves and sound transmission is validated through comparisons with predictions obtained from both an analytical model and a wave-based method found in the literature. To demonstrate the practical utility of the approach, the hybrid method is employed to predict sound transmission through a corrugated sandwich panel, where developing an analytical model is difficult. The method provides accurate predictions at a low computational cost.

Integrated CFD-FEM approach for external gear pump vibroacoustic field prediction

In this work, a three-dimensional fluid-structural and vibro-acoustics coupled model of a gear pump is presented. Gear pumps represent the majority of the positive displacement machines used for flow generation in fluid power systems. Typically, the dynamics of gear pumps are dependent on the characteristics of the fluid dynamics inside the pump, which translates into vibrations to the housing. These vibrations then propagate to the surrounding medium and emit sound. The purpose of this study is to propose a three-dimensional fully integrated computational model to simulate the complete gear pump behaviour from the fluid dynamics to the structural vibrations, up to the vibroacoustic response. In this hybrid configuration, a transient CFD (Computational Fluid Dynamics) model is first developed to simulate the 3D flow field with a deforming and re-meshing approach to take into account the variation of the volume between the gears. Second, the internal pressure field calculated at each time step is then used as a loading into a structural FEM (Finite Element Method) model of the gear pump to compute the actual stresses and deformations of the housing. Third, the results of the structural response are used as excitation in a vibroacoustic sub-model to simulate the radiated noise using a high-order FEM technique. The comparison between the numerical and experimental flow curves validates the CFD model. The sound power calculations from the vibroacoustic model show good comparison with the sound intensity measurements around the pump casing, confirming the validity of the proposed coupled model. The described CFD-FEM approach proves to be a powerful gear pump design tool: it provides a reliable estimate of gear pump working parameters such as fluid power and vibroacoustic characteristics, starting from the CAD (Computer-Aided Design) geometry of the components. Furthermore, being one of the first multi-domain simulation models of a gear pump, this work can be useful to researchers as a starting point to correlate the noise emitted with the internal flow in full 3D conditions.

Analysis of vibro-acoustic characteristics of functionally graded sandwich microplates under thermal-electric effects

Based on the hyperbolic tangent parabola mixed shear deformation theory, the paper studied the sound radiation and the sound insulation of the functionally graded (FG) sandwich microplates under thermal-electric effects. The sandwich plate is composed of piezoelectric skin layers and FGM core layer. By using Hamilton’s principle, a size-dependent model considering the thermal-piezoelectric effects are established. The acoustic response and sound insulation are calculated with Rayleigh integral and solid-fluid coupling conditions. The accuracy of the presented method is verified by the numerical simulations. Then the effects of various parameters on the vibro-acoustic characteristics are analyzed and discussed. Numerical results show that the temperature variations, the length scale parameter to thickness ratio and the gradient index have great impacts on the FG sandwich microplates.

Probabilistic and Statistical Methods for Identifying Defects in Diesel Fuel Equipment Using Vibroacoustic Spectra

The article deals with the practical results of technical diagnostics of diesel fuel equipment using vibroacoustic characteristics. The authors used given diagnostic matrix, Bayesian methods and sequential analysis to calculate the effect of reducing the elasticity of the injector spring on the performance of the fuel injector and the connection of the diagnosis “increased injector spring tension” with the sign “high amplitude at a frequency of 115 Hz”.

The Vibro-Acoustic Characteristics Analysis of the Coupled System between Composite Laminated Rotationally Stiffened Plate and Acoustic Cavities

In order to study vibro-acoustic characteristics between composite laminated rotationally stiffened plate and acoustic cavities in the coupled system, first-order shear deformation theory (FSDT) and modified Fourier series are used to construct a unified analysis model. The involved coupled systems primarily encompass three types: the coupled system between composite laminated rotationally stiffened plate and cylindrical-cylindrical cavities, spherical-cylindrical cavities, and conical-cylindrical cavities. First, the first-order shear deformation theory and the modified Fourier series are applied to construct the allowable displacement function of the composite laminated rotationally stiffened plate and the allowable sound pressure function of the acoustic cavities. Second, the energy functionals for the structural domain and the acoustic field domain are established, respectively. According to the continuity condition of the particle vibration velocity at the coupling boundary between the composite, laminated cylindrical shell and the enclosed cavity, the coupling potential energy between the stiffened plate and two acoustic cavities is introduced to obtain the energy functional of the coupled system. Third, the Rayleigh-Ritz method is utilized to solve the energy functional and, when combined with artificial virtual spring technology, the suggested theory may be used to study the vibro-acoustic characteristics of a coupled system with arbitrary elastic boundary conditions. Finally, based on validating the fast convergence and correctness of the model, this paper will analyze the impact of crucial parameters on vibro-acoustic characteristics. Furthermore, by incorporating internal point forces and point-sound source stimulation, a steady-state response analysis of the coupled system will be conducted. This research can give a theoretical foundation for the vibration and noise reduction of a vibro-acoustic coupling system.

Dynamic investigation of the influence of propeller on the vibro-acoustic characteristics of marine propulsion systems

Dynamic investigation of the influence of propeller on the vibro-acoustic characteristics of marine propulsion systems

The acoustic radiation analysis of SFGP conical shell

The shell of revolution made of sandwich functionally graded material (SFGM) has broad applications in engineering. Pores are inevitable in processing SFGM, making it complex for the vibro-acoustic characteristics of the structure. To analyze the acoustic radiation mechanism of sandwich functional gradient porous materials (SFGP) shells deeply, a theoretical model for vibro-acoustic coupling of SFGP shells based on a semi-analytical approach is proposed. The spectral boundary element approach is used to simulate the sound field while the energy method is utilized for representing the structural field. The substructure scheme is introduced, resulting in a uniform division of both the structural field and the sound field into several segments. Similarly, both the displacement and sound pressure are depicted in an identical manner, with the meridional direction expanded using the Legendre series and the circumferential direction expanded using the Fourier series. By introducing the virtual work done by the sound pressure, the structural and sound fields are coupled to form the vibro-acoustic coupling equation, which is solved using the strong coupling approach. The present method exhibits outstanding convergence and precision, showcasing a strong agreement in vibro-acoustic response results when compared to prior research. Since the conical shell is one of the most widely applicable shells of revolution, this paper takes the conical shell as the research object to study. Following the proposed methodology, we delve into the examination of the roles played by various circumferential wave number modes in influencing the vibro-acoustic response of SFGP conical shells. Building upon this groundwork, an investigation is conducted into the influence of factors such as material gradient index, porosity, and pore distribution on the vibro-acoustic characteristics of SFGP conical shells.

Analysis and prediction of vibro-acoustic characteristics of parallel propulsion systems for large-scale marine ships

The parallel power propulsion system is the preferred option for large-scale ships. The improper configuration of multidimensional power parameters is a significant factor contributing to the vibration and noise generated by the system. This study examines the sensitivity and dependence of the vibro-acoustic characteristics of the system on various power parameters through theoretical and experimental methods, and reveals the evolution mechanism of the dynamic behaviors under the coupling effect of multidimensional power parameters. Firstly, the nonlinear dynamic model considering the lateral–torsional–axial coupling of the propulsion system is established and the effects of different combinations of power parameters on the vibration response and system stability are investigated. Secondly, an experimental platform of the parallel propulsion system is constructed, and the comprehensive description of the effects of multidimensional power parameters on the vibration and noise of the system under asymmetrical input power is further provided. Finally, the radial basis function (RBF) neural network is innovatively employed to predict and approximate the vibro-acoustic characteristics of the system under the combined influence of rotating speed, torque ratio, and drag current. The research results are of significant theoretical and practical importance in breaking through the technical bottleneck related to reducing the vibration and noise of such parallel propulsion systems.

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.

СОВЕРШЕНСТВОВАНИЕ АКУСТИЧЕСКОГО ПОВЕДЕНИЯ КОРПУСА АВТОМАТИЧЕСКОЙ КОРОБКИ ПЕРЕДАЧ АВТОМОБИЛЯ КАТЕГОРИИ N2 НА ОСНОВЕ МЕТОДА МОДАЛЬНОГО ПРЕДСТАВЛЕНИЯ ДИНАМИЧЕСКОЙ СИСТЕМЫ

There is a global tendency nowadays in the development of transport vehicles to ensure high safety, energy efficiency and comfort, characterized primarily by ergonomic and vibroacoustic indicators. This forces engineers and scientists to constantly strive to reduce a noise level emitted by both the vehicle as a whole and individual units and systems. The paper is a continuation of a series of articles devoted to the development of a verified mathematical model of a promising automatic transmission (AT) for a N2 category vehicle, reliably characterizing its vibroacoustic behavior. The article represents the results of a computational and experimental study of the AT vibroacoustic behavior, including the stages of testing, processing and analysis of their results, verification of the computational model created in the Simcenter 3D software product, identification of the main sources of acoustic radiation and the development of proposals for its reduction. The vibroacoustic characteristics of the object of study are obtained, namely frequencies and corresponding acoustic pressure values, their localization on the AT housing is performed. The developed and verified AT model makes it possible to predict the level of vibration and acoustic radiation with satisfactory accuracy. Based on comparative evaluation modeling of various design modification options, the best ones are determined, which allow to obtain the minimum acoustic pressure level at the measurement points and neutralize the most significant forms of vibrations. The introduction of the developed scientifically-based technical solutions into the design made it possible to reduce the integral level of acoustic pressure in the entire range from 2 to 10 dBA.

Vibro-acoustic responses of coupled pump-jet-hull model under duct excitation and the influence of shafting support modes

The vibro-acoustic characteristics of coupled pump-jet-hull system under excitations on the wall of duct are investigated. The fluid excitation of duct is simulated using computational fluid dynamics. The different vibro-acoustic characteristics for excitations on inner and outer wall of duct are contrastively investigated through establishing a finite element model and boundary element model of coupled pump-jet-hull system. Meanwhile, the influence of shafting support modes on vibro-acoustic responses is discussed. The results show that the source of excitation forces on inner and outer wall is different. The force spectra of inner wall exhibit a line spectrum characteristic, reflected in blade passing frequency, while the force spectra of outer wall show a broadband characteristic. The vibration response as well as sound radiation are mainly contributed by hull modes. The acoustic radiation power excited by forces on inner wall is slightly dominant in the low frequency range. The duct excitation can cause a coupling resonance of the shafting system and it is insensitive to the shafting support modes.

Vibro-acoustic characteristics of a rail transit viaduct paved with trapezoidal sleeper track

To investigate the effects of a trapezoidal sleeper track (TST) on the vibration and noise of rail transit viaducts, the wheel–rail interaction model was first built according to the vehicle–track coupling dynamics theory. Subsequently, the vibration responses of the viaduct were analyzed using the beam–slab finite element method, and its radiated noise was calculated using the acoustic boundary element method. The modeling method was verified based on the test data of a 3 × 40 m continuous rigid frame bridge. Taking the Jialing River Bridge of Chongqing Rail Transit Line 9 as the background, the control effects of the TST on the vibration and noise of the viaduct and the effective laws of different track parameters on the bridge noise were analyzed. Results show that the simulated and measured values are in good agreement; for example, the modeling methods are reliable; the radiated noise of the viaduct is influenced by the vibration responses under the action of train load, which are jointly determined by dynamic wheel–rail force (external excitation) and displacement admittance (self-vibration characteristics); compared with embedded sleeper track (EST), the TST can reduce the overall vibration acceleration level and sound pressure level of the box girder web plate by 13.9 dB and 7.8 dB, respectively; the stiffness of the damping path is the primary factor influencing the noise of the elevated box girder, followed by the sleeper thickness and the fastener stiffness; taking the bottom plate as an example, the stiffness of the damping pad is reduced by 1 and the overall sound pressure level can be reduced by approximately 3 dB; the sleeper thickness is increased by 1, and the overall sound pressure level can be reduced by 1–2 dB; and the fastener stiffness is reduced by 1, and the noise reduction is within 1 dB.

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.

Investigation of alternative methods for measuring and evaluating airborne sound insulation

The reproducibility of airborne noise insulation testing is poor, as documented by various interlaboratory studies. This is compounded by the definition of Sound Transmission Class (STC), the dominant single-number rating used in North America, which over-emphasizes the wall performance at and around the 125 Hz third-octave band. Small variations in performance at these frequencies can result in substantial changes in STC rating. To address these concerns, changes to both the measurement method and the single number ratings may be appropriate. For the former, the authors have begun an investigation of measuring the vibro-acoustic characteristics of walls, including measuring the vibration on the surfaces of the separating assembly and the flanking assemblies. This may result in increased precision of sound insulation measurements. For the latter issue, the authors have performed statistical evaluation of published wall sound insulation tests to clarify the effects of idiosyncrasies in the definition of STC and investigated whether different rating methods may better describe the performance of wall assemblies.

Free Vibration and Sound Insulation of FG-CNTRC Sandwich Plates with Different Cores

The core layer is very important in studying the vibration and noise problems of sandwich structures. The present paper studied the free vibration and sound insulation characteristics of FG-CNTRC sandwich plates with FG-CNT face sheets and different cores including the soft core (epoxy), hard core (aluminum) and porous metal foam core with different porosity distributions. By Hamilton’s principle the dynamic equations of FG-CNTRC sandwich plates are formulated based on the third-order shear deformation theory (TSDT), and the sound insulation expression is given under the excitation of the sound pressure. The theoretical solution of natural frequency and sound insulation are compared with the finite element simulation results and validated. The natural frequency of the square sandwich plate are compared with the rectangular case. The free vibration and sound insulation performance of FG-CNTRC sandwich plates are analyzed and discussed, and parametric studies are performed to evaluate the effects of CNT volume fraction, CNT distribution patterns, CNT orientation angles, porosity coefficient and incident angles on the vibro-acoustic characteristics of the sandwich plate. Some new results are presented to be used as references for the further research.

Effect of Support Stiffness Nonlinearity on the Low-Frequency Vibro-Acoustic Characteristics for a Mechanical Equipment—Floating Raft—Underwater Cylindrical Shell Coupled System

The low-frequency vibro-acoustic characteristics of a mechanical equipment—floating raft—cylindrical shell—underwater acoustic field coupled system with nonlinear supports are studied in this paper. Firstly, the state space equations were established by a modal superposition theory for the coupled system, and a modal parameter identification method was deduced and verified for the cylindrical shell—underwater acoustic field coupled subsystem. On this basis, the formulas were derived for transmitted power flow in the coupled system, and the nonlinear stiffness constitutive relation of the vibration isolation supports was expressed by softening and hardening characteristics. Finally, dynamic simulations were carried out by the Runge—Kutta method to analyze the effect of nonlinear stiffness characteristic parameters on the low-frequency vibration modes and vibro-acoustic transfer characteristics in the coupled system. The research shows that a superharmonic phenomenon is common in the steady vibration mode of the coupled system with a nonlinear softening (or hardening) stiffness characteristic under harmonic excitation. The stronger the softening (or hardening) stiffness characteristic is, the more complex the vibration form is, and the smaller (or larger) the low-frequency vibro-acoustic transfer level in resonance regions is.