Journal of Sound and Vibration最新文献

This paper proposes an efficient wavenumber dynamic stiffness method (WDSM) for exact dispersion analysis of plate built-up waveguides. Firstly, the wavenumber dynamic stiffness (WDS) matrices for inplane and out-of-plane wave motions of a plate waveguide element are developed by using the general solutions of the governing differential equations as the exact shape functions. The Wittrick–Williams (WW) algorithm is used as the eigen-solution technique to calculate dispersion relations. Furthermore, the explicit expression for the $J_0$ term in the WW algorithm is derived, which enables the proposed method to conduct dispersion analysis of complex plate built-up waveguides with very few elements and eliminates the need for mesh refinement throughout the entire frequency range. The proposed WDSM is then applied to several examples including individual plate strip and complex plate built-up waveguides. Results are compared with existing exact solutions and those obtained by using the wave finite element method (WFEM) and the semi-analytical finite element method (SAFEM), which demonstrate the exactness and the significantly improved computational efficiency of the proposed WDSM. In conclusion, this paper presents an exact and efficient dispersion analysis method for complex plate built-up waveguides, which can be considered as a competitive alternative to numerical methods such as SAFEM and WFEM.

This paper explores spatial discretization within finite element simulations of laser-induced elastic waves within the context of Laser Ultrasonic Testing (LUT). Motivated by discrepancies and oscillations detected in temperature and displacement results in the literature, we traced these issues back to spatial discretization challenges. These challenges originate from rapid localized heating and the generation and propagation of high-frequency waves across a relatively large domain. This study effectively addresses and rectifies these inaccuracies, offering guidance for selecting the appropriate element size and type. We examined two element types: four-node quadrilaterals (Q4) employing first-order Lagrange and nine-node quadrilaterals (Q9) using second-order Lagrange shape functions. Our analysis encompasses mesh refinement strategies, exploration of time and frequency domain plots for temperature and displacement, as well as an evaluation of different pulse durations. Our findings demonstrate that Q9 elements attain accuracy with grids four times larger than Q4 elements for temperature and wave propagation analyses. Furthermore, we observe that lower frequency waves exhibit reduced sensitivity to element size, emphasizing the relationship between element size and elastic wave frequency. Pulse durations in the 6 to 30 ns range affect the required element size in the heat-affected zone but exert minimal influence on wave frequency and spatial discretization in the remainder of the domain. Finally, we present a new formula for element size selection based on the dominant frequency. This study provides a comprehensive guideline for selecting element size and type, enabling the attainment of accurate results while effectively managing computational costs.

In the present paper, we present a Cell-Centered Implicit Finite Difference (CCIFD) operator-based numerical scheme for the propagation of acoustic waves that is very effective, accurate, and small in size. This scheme requires fewer estimation points than the traditional central difference derivative operator. Any numerical simulation is significantly impacted by the precision of a numerical derivative. Long stencils can deliver excellent accuracy while also minimizing numerical anisotropy error. However, a long stencil requires a lot of computational resources, and as these derivatives get bigger, they could start to look physically unrealistic due to contributions from nodes located extremely far, wherein the derivative is local in nature. Furthermore, using such lengthy stencils at boundary nodes may result in errors. The present article investigates a cell-centered fourth order finite difference scheme to model acoustic wave propagation which utilizes a lesser number of nodes in comparison to the traditional Central Difference (CD) operator. However, in general the implicit derivative operator has high computational cost and therefore despite its significant advantages it is generally avoided to be implemented in applications. This serves as a motivation for the present paper to explore a technique called CCIFD that significantly decreases the computational expense by nearly fifty percent. Additionally, spectral characterization of the CCIFD derivative operator has been analyzed and discussed. Finally, the wave propagation has been numerically simulated in 2-dimensional homogeneous and Marmousi model using CCIFD scheme to validate the applicability and stability of the scheme.

The Boundary Layer Ingestion (BLI) configuration is a promising installed propulsion arrangement for aircraft owing to its potential to boost aerodynamic efficiency. However, it is prone to generate additional noise as the inflow to the propulsion system is non-uniform and turbulent due to the ingested boundary layer. Nevertheless, the acoustic characteristics of the BLI configuration and its sensitivity to different operating parameters (e.g., boundary layer thickness, turbulence contents and propeller rotational speeds) are not well understood. Thus, the present study reports a detailed experimental campaign to investigate the aerodynamic thrust, far-field acoustics and plate surface pressure of a two-bladed propeller ingesting distinct turbulent boundary layers (TBL) for a range of advance ratios. All results were compared against a reference ‘No BLI’ case. It was found that BLI noise comprises mostly broadband noise that is directed predominantly in the downstream direction parallel to the plate, whilst orthogonal to the plate, the noise signature is mostly tonal. When increasing thrust, the effect of BLI on noise is reduced. Scaling of the acoustic spectra with tip Mach number identifies that leading-edge-turbulence interaction was the main source of broadband noise in the BLI configuration and more importantly, showed two distinct operating regimes based on thrust conditions. Lastly, phase-averaged acoustic results showed marked noise variations over a rotation with an increase when the propeller begins to ingest the boundary layer, particularly for the thicker and more turbulent boundary layer, indicating that the broadband components became dominant during TBL interaction and were partly responsible for the modulation of the emitted noise.

In this paper the authors investigate the free vibration of a two-length-scale nonlocal micromorphic Timoshenko beam, which is shown to overlap with the nonlocal strain gradient Timoshenko beam under certain conditions. Hamilton’s principle is utilized to obtain a system of two coupled fourth-order equations of motion governing the eigen-deflection and the eigen-rotation of the beam. Uncoupling both equations leads to two eight-order differential equations. Using Ferrari’s method, exact solutions are derived for the eigenfrequencies for various boundary conditions, including simply supported, clamped-clamped, clamped-free, and clamped-hinged boundary conditions. The obtained results are compared with those published in the literature using similar nonlocal strain gradient cases. A detailed parametric study is then performed to emphasize the role of the variationally-derived higher-order boundary conditions (natural higher-order boundary conditions or mixed higher-order boundary conditions). It is noted that when the difference in length-scales is large, the effect of the slenderness of the beam on the frequencies is amplified. Finally, the hardening or the softening effect of the beam model can be achieved through a choice of the ratio between the two length-scales.

Sound attenuation along a waveguide is intensively studied for applications ranging from heating and air-conditioning ventilation systems, to aircraft turbofan engines. In particular, the new generation of Ultra-High-By-Pass-Ratio turbofan requires higher attenuation at low frequencies, in less space for liner treatment. This demands to go beyond the classical acoustic liner concepts and overcome their limitations. In this paper, we discuss an unconventional boundary operator, called Advection Boundary Law, which can be artificially synthesized by electroactive means, such as Electroacoustic Resonators. This boundary condition entails nonreciprocal propagation, meanwhile enhancing noise transmission attenuation with respect to purely locally-reacting boundaries, along one sense of propagation. Because of its artificial nature though, its acoustical passivity limits are yet to be defined. A thorough numerical study is provided to assess the performances of the Advection Boundary Law, in absence of mean flow. An experimental test-bench validates the numerical outcomes in terms of passivity limits, non-reciprocal propagation and enhanced isolation with respect to local impedance operators. Guidelines are outlined to properly implement the Advection Boundary Law for optimal noise transmission attenuation. Moreover, the tools and criteria provided here can also be employed for the design and characterization of other innovative liners.

Bridge health monitoring has been a prominent focus within the global engineering community. Bridge owners, stakeholders, and engineers face the formidable tasks of ensuring efficient monitoring, conducting reliable data analysis, interpreting data logically, and making timely decisions. With the increasing global infrastructure deficit, there is an ever-increasing need to develop reliable and economical bridge monitoring solutions. In this paper, a bridge condition assessment technique is proposed that can utilize the vibration data collected from the instrumented sensors and provide reliable system identification results. The proposed method develops a hybrid approach by integrating the Natural Excitation Technique (NExT) and Empirical Fourier Decomposition (EFD) to analyze ambient bridge vibration data and determine the modal parameters of the bridge. First, NExT is formulated to determine the cross-correlation functions of the bridge measurements, and then EFD is explored to decompose the signals into their monocomponents to identify the bridge modal parameters. The proposed methodology can overcome mode mixing and perform modal identification of a system with closely spaced frequencies and low energy modes. The estimated modal parameters such as bridge frequencies, mode shapes, and damping ratio are used for condition assessment of numerical, experimental and full-scale structures, including a short-span steel bridge located in Ontario, Canada. The results demonstrate that the proposed methodology can provide accurate and robust estimates of bridge modal parameters. Future research is reserved for real-time implementation of the proposed methodology for a wide range of civil structures.

A novel model-based method for railway Crossing Panel Condition Monitoring (CPCM) is presented. Based on sleeper accelerations measured during wheel crossing transitions and knowledge of the crossing panel design, it is shown that it is possible to identify the ballast stiffness properties, vertical wheel–rail contact forces and vertical relative wheel–rail displacement trajectories (crossing irregularities) in the crossing panel. The method uses a multibody dynamics simulation model with a finite element representation of the track structure for evaluation of the dynamic interaction between vehicle and crossing panel. Considering the low-frequency domain where the sleeper response is not significantly affected by the influence of the irregularity due to the designed (and current state of the) crossing and wing rail geometry, the ballast condition is identified via a calibration of the distribution of ballast stiffness in the finite element model. This enables ballast stiffness identification without a priori knowledge of the crossing geometry. From the reconstructed track displacements, the wheel–rail contact forces are identified by solving an inverse problem formulated using the Green's Kernel Function Method (GKFM) that provides a direct link between the track excitation forces and the track response. Further, the irregularity induced by the crossing and wing rail geometry is estimated by taking the difference between the wheel and rail displacements during the crossing transition computed from the identified wheel–rail contact forces. By monitoring the evolving irregularity, the degradation of the crossing rails over time can be assessed. The method is verified and validated using concurrently measured sleeper accelerations and laser scanned crossing geometries from six crossing panels in situ.

Minimum Actuation Power (MAP) is a novel active vibration control strategy that minimizes the total input power into the structure by monitoring the input power from the secondary source. In a previous paper, we presented the theory for MAP for a single primary source controlled by a single secondary source and demonstrated the application of MAP for rotorcraft interior noise control. In this paper, we extend the theoretical framework for MAP for multiple primary sources (excitation) controlled by multiple secondary sources (control). We show that the input power from the secondary sources is zero only when the secondary sources are located such that the phase of the cross-mobility term for each primary–secondary pair is same. This condition puts a constraint on the location of the secondary sources with respect to the primary sources so that the input power from the secondary sources is zero. We present simulations for a simply supported plate excited by two primary sources and controlled by a single secondary source that validate the theoretical findings. We also study the effect of phasing between the primary sources on MAP control performance and show that the maximum power reduction is obtained when the phase difference between the primary sources is zero. Experimental results are provided that demonstrate the feasibility of the MAP theory.

Novel 2D tri-chiral metastructures with mass inclusion are proposed in this work. Compared to conventional 2D honeycomb metastructures, these superior metastructures have a wide in-plane low-frequency bandgap (BG) and single Dirac cone (DC) simultaneously. Ligament width and inclusion density are both key factors for tuning the DC and low-frequency BGs. Due to the superior dispersion properties, metamolecules analog of quantum spin Hall effects (QSHEs) are built by the band folding method, and topological phase transition is obtained by shrinking/expanding distance between the mass inclusion and metamolecule center. Topological interface states (TISs) are observed between the two domains with distinct topological properties. To further enhance energy capacity of in-plane elastic wave transport, a 2D heterostructure is constructed by doping waveguiding layer at the topological interface. As expected, robust high capacity in-plane elastic wave transport is realized, named as topological waveguide states (TWSs). While TWS velocity remains unaffected, an increasing number of waveguiding layers additionally leads to a reduced bandgap width and transition from TWSs to conventional edge states (CESs). Average transmitted energy is also observed to increase almost linearly with the thickness of waveguide layer. By virtue of the robust high-capacity wave transport, two potential applications for energy focusing and beam splitting are clearly demonstrated. Besides, the temperature field is introduced into the 2D topological heterostructure to widen the operating frequency of TWSs. Fortunately, TWSs can be tuned to the lower frequency range by increasing temperature, and retain gapless and high-capacity characteristics. Last but not least, we demonstrate that temperature can be used as a switch for in-plane topological wave transport. The proposed 2D chiral metastructures have great potentials to serve as building blocks for multifunctional topological devices.