Goods and products transported by road are subjected to vehicle vibration which, without proper protective packaging, can suffer damage. To reduce shipment costs, protection has to be optimised to limit product damage occurrence while keeping packaging weight and size to a minimum. Optimisation is realized by simulating the vibration of transport vehicles. To achieve an accurate simulation, each vehicle vibration mode has to be modelled. These include: the nonstationary random vibration induced by road roughness and speed variations, the transient vibration created by road surface aberrations and the harmonic vibration created by the vehicle engine and drive train. Identifying and indexing these mixed-modes within complex road vehicle vibration signals is essential to define the severity and occurrence of the different modes in order to develop an accurate model. This paper shows that indexing can be performed using the orthogonal wavelet transform such as Daubechies 10. Assuming that each mode is preponderant in different analysis scales, the wavelet coefficients can be used to perform the indexing. This allows more sensitive mode detection and a more precise time indexing thanks to the multi-resolution nature of the wavelet transform compared to other time-frequency analysis methods.

Reducing tire noise has been a topic of increased focus in the recent years in industrial countries in order to decrease road traffic noise. Computational fluid dynamics (CFD) simulations conducted using ANSYS FLUENT are presented here to provide a better understanding of the small-scale noise generation mechanisms due to air-pumping at the tire-road interface. The CFD model employs a large eddy simulation (LES) turbulence modeling approach, where the filtered compressible Navier-Stokes equations are solved for simple groove geometries with a moving bottom wall that represents the deformation due to the tire movement along the road surface. A horizontally moving wall is used to represent the motion of the tire groove in and out of the contact patch while the deformation of the groove is prescribed. Temporal and spatially accurate pressure fluctuations are utilized to determine sound pressure levels and dominant frequencies. In addition to an understanding of noise generation mechanisms in such grooves, the CFD model developed here can potentially provide a series of control parameters that can help optimize the tire performance in terms of tire acoustics.

Acoustic cloaking is an important application of metamaterials and has received much attention since it was first proposed. Due to the extreme properties of the cloaks produced by previous methods, they are difficult to fabricate. In addition, cloaks with arbitrary shapes are more favorable in applications but are difficult to realize. Therefore, it is important to present a method for designing arbitrary shaped cloak with attainable properties. In this paper, a technique for realizing cloaks with arbitrary shapes is presented by dividing the cloak into finite parts. Transformation acoustics is used to derive the properties of each part of the cloak. With appropriate mapping relationships, the properties of each part are anisotropic but homogeneous. Layered structures are adopted to approximate the anisotropic properties within each part. Full wave simulations are conducted to validate this technique. The method can be used to design cloaks with arbitrary shapes, which perform well within certain frequency limits. It provides an easier way to fabricate cloaks with arbitrary shapes.

It is well known that the performance of open field acoustic sensors is affected by complex sound propagation phenomena occurring in outdoor settings, such as ground effects, noise from atmospheric turbulence, refraction by wind and temperature gradients, diffraction over buildings and hills, and acoustic sensors on moving platforms. In addition, the behavior of sound propagation changes at the interface of different media. We have developed a time-domain simulation that enables the numerical simulation of all the mentioned factors. This capability provides information on the effect of sound waves once they reach a sensor or a target. We are implementing this algorithm for 3D, long-distance propagations. The challenge is three-fold: a) efficient parallelization; b) moving frame capability in 3D for long-distance propagation simulation; c) accurately implementing the perfectly match layer (PML) methods to represent the free boundaries. In this paper, we have selected cylinders as the objects for sound wave to propagate through. Both 2D and 3D simulations were conducted. The results are compared with available measurement data in the literature. The phenomena are discussed in the context of 2D and 3D propagation behaviors.

Brake squeal is a ubiquitous disturbance in automotive systems. Facing the complexity and the cost of experimental tests, simulations of brake squeal have become essential as well as to provide a predictive numerical method. Two major approaches exist in the numerical analysis of this phenomenon, the transient analysis and the complex eigenvalue analysis. In this study, the Constrained Harmonic Balance Method is applied on an industrial finite element system in order to estimate the nonlinear stationary responses due to friction induced vibration. This paper aims at explaining how a finite element system was adapted to the CHBM and at analyzing the results. First of all, the method used to reduce a finite element brake system is examined and the contact issue is particularly emphasized. Then, a brief summary of the CHBM is made. Finally, limit cycles are obtained close to the Hopf bifurcation.

Numerical simulations are presented on a feedback active control strategy for flow-induced off-track vibration of the head gimbals assembly (HGA) supporting the slider in hard disk drives, through suppressing pressure fluctuations around the HGA. A virtual sensing method is employed to enable the feedback signal changeable from pressure fluctuations at the physical sensor position to those at single “virtual sensor” positions closely around the HGA or a spatial average of pressure fluctuations along an HGA surface. Based on a linear control methodology, performance of the proposed active control strategy with different feedback signals has been investigated in two-dimensional simulations, where a physical pressure sensor and a pressure actuator are assumed on the inner-surface of the HDD cover to detect the pressure fluctuations and to actuate active pressure oscillations into HDD space respectively. The results show effective control on the HGA off-track vibration when the feedback signal is configured to minimize pressure fluctuations at specific positions closely around the HGA, such as the wake region. It is also shown that satisfying control effect can be achieved on the HGA off-track vibration in the global spectrum when the feedback signal is configured to minimize the spatial average of pressure fluctuations along the upper surface of the HGA.

The acoustic characterization of fluid machines, e.g., internal combustion engines, compressors, or fans is of great importance when designing the connected duct systems and its silencers. For machines connected to large ducts where also the non-plane wave range is important, for instance large diesels and gas turbines, a suitable way to characterize the source is to determine the sound power under reflection free conditions. For the low frequency plane wave range in-duct sound power can be measured with the widely used two microphone method. The goal of this study is to investigate how, starting from the two-microphone approach, a suitable wall mounted microphone configuration can be defined and used to estimate the propagating in-duct sound power also beyond the plane wave range. For this purpose an acoustic source test-rig was built and numerical simulations were also conducted. The in-duct sound power from monopole, dipole, and quadrupole source types was determined using twelve wall mounted microphones and cross-spectra averaging methods. The in-duct results were compared against sound power measured using the reverberation room method (ISO 3741). Based on the simulations and the experimental results the best microphone positions and weighting factors were determined.

The utilization of guided waves generated and sensed by an array of phased sensors allows steering the wave-front in a specific direction (beamforming technique). In this work a linear array of sensors is used to generate an ultrasonic wavefront steered in a specific direction. Numerical simulations are carried out with the LS-DYNA, an explicit Finite Element (FE) code, on a CFRP plate. The damage to be identified is a delamination produced by an impact (BVID). The array of sensors consists of a number of disk-shaped piezo patches. From the echo reflected and returning back to the array, it’s possible to evaluate the time of flight of the signal (TOF) from which the distance of the damage from the sensors array can be determined, and the angular position of the crack by evaluating the time shift of the signal received by each sensor in the array. The experimental tests are carried out in a 0.5m × 0.5m ×2.2 mm CFRP plate with the same sensor array and delamination used in the simulation. A number of receivers located along the panel edges have been also used to detect the damage direction in pitch-catch mode.

Most of the room acoustics evaluation parameters are calculated from the energy decay curve obtained from the room impulse response. Schroeder’s backwards integration method is one of the most commonly used methods to obtain room impulse response. Although, the method holds its validity since 1964 and used extensively, obtaining room impulse response with sufficient length to observe total energy decay requires high computational cost especially in highly reverberant rooms. In such cases, present acoustical analysis and simulation tools either use data extrapolation and linear fitting methods or they fail to provide any reliable output. Hence, in order to provide reliable data based on such an impulse response, high computational cost and effort are required. In this context, a modification for acoustical analysis methods based on impulse response is proposed, comprising a linear fitting algorithm and extrapolation together with data culling. Proposed method is based on the linear energy decay assumption of Schroeder and ideal energy decay according to global reverberation time estimates. Method is proposed for diffuse field conditions regardless of the length of room impulse response. Validity of the proposed method is checked via a developed room acoustics tool, namely RAT, and case studies conducted with the mentioned tool.

In this work, we study the effects of the width of the sound source in several acoustical virtual room models with different topologies, sizes and uses, calibrated with commercial software. To achieve this aim, a square distribution of sound sources with variable side length has been considered. We have auralized four channels of speech signal and musical signal in three different locations in each room. By using signal processing techniques, a comparison of multisource auralizations with the ones obtained from a single source in the middle of the stage is made. Also, the variations between the usual room parameters obtained from these simulations are analyzed, in order to show the effect of the hall in the objective evaluation according to the source width. Paper NCAD2012-72001 is available online only.

In this study, effects of windscreen material property on wind noise reduction are investigated at different frequencies of incoming wind turbulence. The properties of porous materials used for the windscreen are represented by flow resistivity. Computational techniques are developed to study the detailed flow around the windscreen as well as flow inside the windscreen that uses a porous material as the medium. The coupled simulation shows that for low-frequency turbulence, the windscreens with low flow resistivity are more effective in noise reduction. Contrarily, for high-frequency turbulence, the windscreens with high flow resistivity are more effective.

This paper proposed an approach to construct the acoustic cloak by a network of subwavelength Helmholtz resonators. Based on transmission line model to describe the acoustic wave propagation inside such effective anisotropic medium, we derived the acoustic parameters such as effective density and compressibility. Our simulation demonstrates the propagation of acoustic waves can be bent and excluded from an object inside the cloak with no perturbation of exterior field, which may have great potential application in ultrasound noise control.