Wavenumber-frequency Analysis Research Articles

Interior noise prediction of inter-coach space of high-speed maglev trains based on wavenumber decomposition on aerodynamic excitation

Current research on noise and vibration control of high-speed maglev trains pays more attention to far-field noise, while the level of interior noise has a direct impact on the ride comfort and should be placed equal weight on. In this paper, inter-coach space, one of the main pressure fluctuation sources of a specific type of high-speed maglev train with a design speed of 600 km·h−1, is taken as the research object. The turbulent and acoustic components of wall pressure fluctuations (WPF) are separated based on a wavenumber-frequency analysis approach, and then each component is applied as different forms of source input to the vibroacoustic model, namely, finite element method-boundary element method (FEM-BEM) and statistical energy analysis (SEA) for low- and high-frequency ranges respectively, to investigate the contribution of both components to interior acoustic cavity in all frequency range. It can be seen quantitatively from the results that the amplitude of turbulent component is generally much higher than that of the acoustic one, but it can be vice versa when it comes to the interior response. The conclusion drawn in this paper are able to provide guidance for future researches on more targeted interior noise control of high-speed maglev trains.

Evaluation of Welded Lap Joints Using Ultrasonic Guided Waves.

Welded lap joints play a vital role in a wide range of engineering structures such as pipelines, storage tanks, pressure vessels, and ship hulls. This study aims to investigate the propagation of ultrasonic guided waves in steel welded lap joints for the baseline-free inspection of joint defects using the mode conversion of Lamb waves. The finite element method was used to simulate a single lap joint with common defects such as corrosion and disbonding. To identify the propagating wave modes, a wavenumber-frequency analysis was conducted using the 2D fast Fourier transform. The power loss of the transmitted modes was also determined to identify damage in the lap joints. The results indicate that the A0 incident in pristine conditions experienced significant transmission losses of about 9.5 dB compared to an attenuation of 2.8 dB for the S0 incident. The presence of corrosion was found to reduce these transmission losses by more than 28%. In contrast, introducing disbonding in the lap joint increased the transmission loss of the S0 incident, while a negligible loss was observed for the A0 incident. The mode-converted S0 (MC-S) and mode-converted A0 (MC-A0) incidents were found to exhibit a unique sensitivity to the presence of corrosion and disbonding. The results indicate that MC-S0 and MC-A0 as well as Lamb mode incidents interact differently in terms of corrosion and disbonding, providing a means to identify damage without relying on baseline signals.

Collinear nonlinear guided wave mixing for debonding detection in reinforced concrete beam using longitudinal and torsional wave modes

Nonlinear guided wave (GW) mixing of longitudinal wave is proposed to detect and locate debonding damage between rebar and concrete in the reinforced concrete beam. Two wave mode pairs are chosen based on phase matching and synchronism conditions for observing sum combinational harmonics, and longitudinal GW as the excitation signal while the longitudinal and torsional wave as the receiving signal. The study is carried out numerically and experimentally for bonded and debonded reinforced concrete specimens. For bonded specimens, second-order combinational harmonics are absent in all bonded cases. The contact effect due to debonding can generate second and higher-order combination harmonics. The indication of debonding damage is determined in debonded specimens by the presence of sum combinational harmonics. The use of the phase reversal approach in this study clearly observes the increase in the amplitude of the sum combinational harmonics in the debonded cases. By utilizing the phase reversal approach and wavenumber frequency analysis, the dominant longitudinal GW modes can be used to accurately determine the location of debonding. The amplitude of the nonlinear parameter of longitudinal and torsional GW modes increases with debonding length. In this study, the results show that the torsional GW modes have better performance than longitudinal GW modes for debonding detection because the torsional GW modes have larger amplitudes than the longitudinal GW modes.

Development and validation of a global 1∕32° surface-wave–tide–circulation coupled ocean model: FIO-COM32

Abstract. Model resolution and the included physical processes are two of the most important factors that determine the realism or performance of ocean model simulations. In this study, a new global surface-wave–tide–circulation coupled ocean model FIO-COM32 with a resolution of 1/32∘ × 1/32∘ is developed and validated. Promotion of the horizontal resolution from 1/10 to 1/32∘ leads to significant improvements in the simulations of surface eddy kinetic energy (EKE), the main paths of the Kuroshio and Gulf Stream, and the global tides. We propose the integrated circulation route error (ICRE) as a quantitative criteria to evaluate the simulated main paths of the Kuroshio and Gulf Stream. The non-breaking surface-wave-induced mixing (BV) is proven to still be an important contributor that improves the agreement of the simulated summer mixed-layer depth (MLD) against the Argo observations even with a very high horizontal resolution of 1/32∘. The mean error in the simulated mid-latitude summer MLD is reduced from −4.8 m in the numerical experiment without BV to −0.6 m in the experiment with BV. By including the global tide, the global distributions of internal tide can be explicitly simulated in this new model and are comparable to the satellite observations. Based on Jason-3 along-track sea surface height (SSH), wavenumber spectral slopes of mesoscale ranges and wavenumber frequency analysis show that the unbalanced motions, mainly internal tides and inertia-gravity waves, induced SSH undulation and are a key factor for the substantially improved agreement between model and satellite observations in the low latitudes and low-EKE regions. For the ocean model community, surface waves, tidal currents and ocean general circulations have been separated into different streams for more than half a century. This paper demonstrates that it is time to merge these three streams for a new generation of ocean model development.

Progress in understanding seismic wind noise

Previous work at NCPA on predicting and measuring wind noise in the ground used a quasistatic calculation employing Shield’s wind noise correlation function. This method predicted the vertical displacements at the surface well, but under predicted the horizontal displacement and predicted a rapid decay of levels with depth that was not observed in the measurements. A new measurement of the wind noise correlation coefficients using flush mount microphones was presented at the Seattle Meeting (2aPa1). In this talk additional measurements and improved methods for evaluating the coefficients are described. An improved calculation of the seismic levels due to wind induced pressures at the ground has been developed based on the wavenumber-frequency analysis developed for studying airframe noise due to turbulence. This calculation correctly predicts the surface vertical component and the near constant seismic level in the first 40cm of the ground. It still under predicts the horizontal component, but the under prediction is smaller than that predicted by the quasistatic calculation. [This research was sponsored by the Department of the Navy, Office of Naval Research under ONR Award No. N00014-18-2489.]

Comparative Analysis of Surface Pressure Fluctuations of High-Speed Train Running in Open-Field and Tunnel Using LES and Wavenumber-Frequency Analysis

The interior noise of a high-speed train due to the external flow disturbance is more than ever a major problem for product developers to consider during a design state. Since the external surface pressure field induces wall panel vibration of a high-speed train, which in turn generates the interior sound, the first step for low interior noise design is to characterize the surface pressure fluctuations due to external disturbance. In this study, the external flow field of a high-speed train cruising at a speed of 300 km/h in open-field and tunnel are numerically investigated using high-resolution compressible LES (large eddy simulation) techniques, with a focus on characterizing fluctuating surface pressure field according to surrounding conditions of the cruising train, i.e., open-field and tunnel. First, compressible LES schemes with high-resolution grids were employed to accurately predict the exterior flow and acoustic fields around a high-speed train simultaneously. Then, the predicted fluctuating pressure field on the wall panel surface of a train was decomposed into incompressible and compressible ones using the wavenumber-frequency transform, given that the incompressible pressure wave induced by the turbulent eddies within the boundary layer is transported approximately at the mean flow and the compressible pressure wave propagated at the vector sum of the sound speed and the mean flow velocity. Lastly, the power levels due to each pressure field were computed and compared between open-field and tunnel. It was found that there is no significant difference in the power levels of incompressible surface pressure fluctuations between the two cases. However, the decomposed compressible one in the tunnel case is higher by about 2~10 dB than in the open-field case. This result reveals that the increased interior sound of the high-speed train running in a tunnel is due to the compressible surface pressure field.

Experimental validation of the applicability of effective spring boundary conditions for modelling damaged interfaces in laminate structures

The paper presents the experimental validation of the applicability of the effective spring boundary conditions (ESBC), where spring stiffness is expressed in terms of material properties and damage characteristics, for modelling the dynamic behaviour of laminates with damaged interfaces. For this purpose, several intact and defected multi-layered samples manufactured from aluminium plates adhesively bonded with two-sided epoxy tape have been considered. To simulate imperfect interfaces, either a particular surface of one of the adherents or of the adhesive has been mechanically damaged with varying severity before the bonding. Elastodynamic motion excited in the samples by thin surface-mounted piezoelectric transducers has been acquired with laser Doppler vibrometer in the form of B-scans of the specimen’s top surface. The wavenumber-frequency analysis of the measured data is performed to extract information on dispersion curves of guided waves propagating in the investigated laminates. It is demonstrated that changes in the properties of guided waves caused due to damaged interfaces are adequately described by the ESBC, and spring stiffness expressed via material and damage characteristics in ESBC allows to characterize properly the severity of the interface degradation in multi-layered structures.

An ultrasonic visualization system using a fiber-optic Bragg grating sensor and its application to damage detection at a temperature of 1000 °C

Structural health monitoring (SHM) techniques are required to evaluate the reliability of aging heat-resistant structures. To build a method of high-temperature in situ damage diagnosis, the authors developed a laser ultrasonic visualization system with a heat-resistant fiber-optic Bragg grating (FBG) sensing configuration. In this system, an ultrasonic wave is excited by laser irradiation on the surface of a material and then received by a remotely installed FBG sensor. Because both the wave excitation and wave sensing parts have excellent heat resistance, the proposed sensing system enables a stable ultrasonic measurement at a temperature of 1000 °C. In this research, a wavenumber-frequency analysis shows that the proposed sensing system was able to visualize the correct laser ultrasonic wavefield in a planar structure. The ultrasonic visualization performance was then verified for a plate of heat-resistant material at temperatures of 200 and 1000 °C. A wavenumber-frequency analysis based on a three-dimensional Fourier transform was also conducted to extract the wave components corresponding to the reflection caused by an artificial defect in the plate. As a result, the developed method enabled clear damage identification at temperatures as high as 1000 °C.

Numerical Analysis and Characterization of Surface Pressure Fluctuations of High-Speed Trains Using Wavenumber–Frequency Analysis

The high-speed train interior noise induced by the exterior flow field is one of the critical issues for product developers to consider during design. The reliable numerical prediction of noise in a passenger cabin due to exterior flow requires the decomposition of surface pressure fluctuations into the hydrodynamic (incompressible) and the acoustic (compressible) components, as well as the accurate computation of the near aeroacoustic field, since the transmission characteristics of incompressible and compressible pressure waves through the wall panel of the cabin are quite different from each other. In this paper, a systematic numerical methodology is presented to obtain separate incompressible and compressible surface pressure fields in the wavenumber–frequency and space–time domains. First, large eddy simulation techniques were employed to predict the exterior flow field, including a highly-resolved acoustic near-field, around a high-speed train running at the speed of 300 km/h in an open field. Pressure fluctuations on the train surface were then decomposed into incompressible and compressible fluctuations using the wavenumber–frequency analysis. Finally, the separated incompressible and compressible surface pressure fields were obtained from the inverse Fourier transform of the wavenumber–frequency spectrum. The current method was illustratively applied to the high-speed train HEMU-430X running at a speed of 300 km/h in an open field. The results showed that the separate incompressible and compressible surface pressure fields in the time–space domain could be obtained together with the associated aerodynamic source mechanism. The power levels due to each pressure field were also estimated, and these can be directly used for interior noise prediction.

Experimental observation of theoretically predicted spectrum of edge waves in a thick elastic plate with facets

The existence of the edge waves spectrum predicted in a series of recent theoretical studies is investigated and confirmed experimentally. Wave motion in 20 mm thickness aluminium rectangular plate with two facets is generated by a circular piezoelectric transducer and measured by laser Doppler vibrometry. Eight edge modes (four symmetric and four antisymmetric) are clearly observed by means of wavenumber-frequency analysis applied to out-of-plane velocities measured at the edge. The semi-analytical method used by the authors in previous theoretical studies is modified to take into account the facets. By the numerical investigations of edge waves in the plate with facets, the sensitivity of attenuation of higher order edge waves to the form of edge profile is revealed. A good agreement between experimental data and theoretical predictions is demonstrated for dispersion curves and the waveforms of individual modes extracted by means of 2D bandpass filters.

고속열차의 바람소리에 따른 실내소음 예측을 위한 표면압력 섭동의 파수-주파수 분석

고속열차의 바람소리에 따른 실내소음 예측을 위한 표면압력 섭동의 파수-주파수 분석

Linear thermal-acoustic responses of a composite panel in progressive wave tube based on wavenumber-frequency analysis

Linear thermal-acoustic responses of a composite panel in a progressive wave tube are studied based on wavenumber-frequency analysis in both pre- and post-buckling ranges. The coupled finite element method/boundary element method (FEM/BEM) is developed to study the modal behavior of the panel under thermal environment. The effects of temperature-dependent material property, thermal stresses and initial deflection on the modal behavior are investigated. Wavenumber-frequency analysis is performed to predict the thermal-acoustic responses of the thermally loaded panel under the excitation of a travelling pressure wave. Both unstiffened and stiffened panel have been investigated. As temperature rose, modal frequencies decrease to the minimum values in sequence due to the softening effect of thermal stresses, and then turn to increase mainly due to the stiffening effect of initial deflection, which provides additional stiffness to prevent the minimal modal frequencies drop to zero. Wavenumber-frequency analysis is able to offer a physical explanation of interaction between the excitation and the dynamic behavior of the panel, especially in terms of a filtering effect in the wavenumber domain. The dynamic characteristics of the unstiffened and the stiffened panel under combined thermal and travelling pressure wave excitations are different. Finally, an experiment is carried out to partially validate wavenumber-frequency analysis under ambient temperature in a progressive wave tube. It is demonstrated that the proposed method is of reasonable accuracy for the test article. However, it is limited to predicting linear responses and will over predict the thermal-acoustic responses in a conservative way.

Wavenumber-frequency analysis of river surface texture to improve accuracy of image-based velocimetry

In the unseeded image-based techniques for river surface flow measurements, advection speed of surface textures composed of surface ripples or floating objects is measured by image analysis. However, the methods would yield erroneous information when the surface texture is affected by gravity waves propagating in all directions. In order to improve the measurement accuracy, such wave effects have to be subtracted in the image analysis. For that purpose, a wavenumber-frequency analysis was applied to a space-time image (STI) generated in the space-time image velocimetry (STIV) analysis and succeeded in eliminating the wavegenerated pattern contained in the texture in STI. It was made clear that turbulence-generated texture propagates at the speed of surface flow.

Wavenumber-Frequency Analysis of Internal Aerodynamic Noise in Constriction-Expansion Pipe

High-pressure gas is produced during the oil production process at offshore plants, and pressure relief devices, such as valves, are widely used to protect related systems from it. The high-pressure gas in the pipes connected to the flare head is burned at the flare stack, or, if it is nontoxic, is vented to the atmosphere. During this process, excessive noise is generated by the pressure relief valves that are used to quickly discharge the high-pressure gas to the atmosphere. This noise sometimes causes severe acoustic-induced vibration in the pipe wall. This study estimated the internal aerodynamic noise due to valve flow in a simple constriction-expansion pipe, by combining the large eddy simulation technique with a wavenumber-frequency analysis, which made it possible to decompose the fluctuating pressure into the incompressible hydrodynamic pressure and compressible acoustic pressure. First, the steady-state flow was numerically simulated, and the result was compared with a quasi-one-dimensional theoretical solution, which confirmed the validity of the current numerical method. Then, an unsteady simulation analysis was performed to predict the fluctuating pressure inside a pipe. Finally, the acoustic pressure modes in a pipe were extracted by applying the wavenumber-frequency transform to the total pressure field. The results showed that the acoustic pressure fluctuations in a pipe could be separated from the incompressible ones. This made it possible to obtain accurate information about the acoustic power, which could be used to assess the likelihood of a piping system failure due to acoustic-induced vibration, along with information about the acoustic power spectrum of each acoustic mode, which could be used to facilitate the systematic mitigation of the potential acoustic-induced vibration in piping systems.

Wavenumber-frequency analysis of single-layer shallow-water beta-plane quasi-geostrophic turbulence

We numerically investigate single-layer shallow-water beta-plane quasi-geostrophic turbulence in a doubly periodic domain with emphasis on wavenumber-frequency spectra. We conduct a broad parameter sweep, varying the deformation radius (Ld), the narrow-band forcing wavenumber (kf), and the meridional gradient of the Coriolis parameter (β). Out of 54 simulations we present ten in detail spanning slowly propagating vortices to strong jets. We define a nondimensional parameter γβ in terms of β, Ld, and the energy injection rate. The moderately low γβ case is characterized by westward propagating coherent vortices and zonal wavenumber-frequency spectra dominated by a nondispersive line (NDL) corresponding to uniform propagation at or near the long-wave Rossby speed. The moderately high γβ case is characterized by jets, and the NDL persists even when there are no coherent vortices. The jets have large meridional excursions (meanders) that propagate westward nearly uniformly at a speed slower than the long-wave Rossby speed. Also at moderately high γβ, a second dispersion relation appears, roughly corresponding to linear waves on a zonal potential vorticity (PV) staircase. At very high γβ, during the slow evolution to a PV staircase, the structure of the linear waves is altered by the small perturbations to a constant potential vorticity gradient. A simple model treating the small perturbation as a sinusoid accurately predicts the meridional wavenumber-frequency spectra in the very high γβ simulations.

Wavenumber-frequency analysis of landslide-generated tsunamis at a conical island. Part II: EOF and modal analysis

In this paper the Empirical Orthogonal Function (EOF) method is applied to extract from the experimental data, related to landslide-tsunamis around the coast of a conical island, the spatial modes that contribute to the wave field. For each mode the wavenumber and the frequency are calculated by analyzing the shape along the coast and the time function. The relevant modes are then compared with those obtained through numerical eigenanalysis of the long wave equation around the considered island. It was possible to associate each EOF mode with some eigenvectors and the corresponding eigenfrequencies, both on the basis of the spatial shape, the wavenumber calculated along the coast and the frequency. Results confirm that landslide-generated waves propagate along the coast as trapped edge waves and the zero-th order mode is the most important. Further of exploring the physics, it is believed that this paper can be of use as some of the most relevant and straightforward techniques for modal identification are applied to the same problem and dataset.

A Guided Wave Sensor Enabling Simultaneous Wavenumber-Frequency Analysis for Both Lamb and Shear-Horizontal Waves.

Guided waves in plate-like structures have been widely investigated for structural health monitoring. Lamb waves and shear horizontal (SH) waves, two commonly used types of waves in plates, provide different benefits for the detection of various types of defects and material degradation. However, there are few sensors that can detect both Lamb and SH waves and also resolve their modal content, namely the wavenumber-frequency spectrum. A sensor that can detect both waves is desirable to take full advantage of both types of waves in order to improve sensitivity to different discontinuity geometries. We demonstrate that polyvinylidene difluoride (PVDF) film provides the basis for a multi-element array sensor that detects both Lamb and SH waves and also measures their modal content, i.e., the wavenumber-frequency spectrum.

Numerical investigation into flow noise source of a convergent-divergent nozzle in high pressure pipe system using wavenumber-frequency analysis

Numerical investigation into flow noise source of a convergent-divergent nozzle in high pressure pipe system using wavenumber-frequency analysis

Decomposition of Atmospheric Disturbances into Standing and Traveling Components, with Application to Northern Hemisphere Planetary Waves and Stratosphere–Troposphere Coupling

Abstract This study updates a body of literature that aims to separate atmospheric disturbances into standing and traveling zonal wave components. Classical wavenumber–frequency analysis decomposes longitude- and time-dependent signals into contributions from distinct spatial and temporal scales. Here, an additional decomposition of the spectrum into standing and traveling components is described. Previous methods decompose the power spectrum into standing and traveling parts with no explicit allowance for covariance between the two. This study provides a simple method to calculate the variance of each of these components and the covariance between them. It is shown that this covariance is typically a significant portion of the variance of the total signal. The approach also preserves phase information and allows for the reconstruction of the real-space standing and traveling components. The technique is applied to reanalysis wintertime geopotential height anomalies in the Northern Hemisphere in order to investigate planetary wave interference effects in stratosphere–troposphere coupling. The results show that for planetary waves 1–3, standing waves explain the largest portion of the variance at low frequencies. An exception is for wave 1 in the high-latitude troposphere, where there is a strong westward-traveling wave. Furthermore, the antinodes of the standing waves have preferred longitudes that tend to align with the extremes of the climatological wave, suggesting that standing waves contribute to a linear interference effect that has been shown to be an important part of stratosphere–troposphere interactions.

Wavenumber–frequency analysis of the landslide-generated tsunamis at a conical island

In this paper we investigate the propagation of tsunamis generated by landslides around the coast of an island to understand the propagation and trapping mechanisms of the waves. Records of shoreline displacement have been processed using the wavenumber–frequency analysis (k–f). We identify the dispersion relation followed by the waves that propagate alongshore. It appears that the 0th-order edge wave mode is the only one relevant for shoreline run-up. Furthermore, it is shown that the edge wave dispersion relation is a quantitative tool to estimate the phase and group wave celerities. A very good agreement is found when comparing the wave celerities as calculated from the experimental records, against those predicted by the edge wave theory. Furthermore the analysis of the tsunami around the island has been carried out by means of the two-dimensional k–f. Using as input data a high-space resolution dataset of free surface elevations it is found that other modes, both trapped (1st-order edge waves) and non-trapped (free radiating waves), occur during the propagation.