Wavelet Transform to Index Road Vehicle Vibration Mixed Mode Signals

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.

Vibration Control of Variable Thickness Plates With Embedded Acoustic Black Holes and Dynamic Vibration Absorbers

In the past decade, plate-like structures embedded with one or more acoustic black hole (ABH) features have been developed as a promising passive approach for structural sound and vibration control. In this study, the concept of combining dynamic vibration absorbers (DVAs) and the ABH effect is proposed to further improve the vibration control effectiveness of a variable thickness plate. A finite element (FE) model is developed to analyze the vibration response of a plate embedded with both ABHs and DVAs under point force excitations. To demonstrate the effectiveness of different vibration control approaches, the vibration responses of plates of uniform thickness, variable thickness embedded with ABH features, variable thickness embedded with both ABH features and damping layers, and variable thickness embedded with both ABH features and DVAs are compared experimentally. It is shown that, in the frequency range considered in the current study which is up to 6.4 kHz, the uniform plate presents high average velocity response level. On the other hand, although 11.5% lighter, the variable thickness plate integrated with both ABH and DVA features results in the lowest response level. Results in this study demonstrate the potential of combing DVAs and ABHs together as an effective lightweight noise and vibration control approach.

Field Comparison of IEC 61400-11 Wind Turbines — Part 11: Acoustic Noise Measurement Techniques, Edition 3.0 and Edition 2.1

Following the release of Edition 3.0 (2012) of IEC 61400-11 Wind Turbines – Part 11: Acoustic noise measurement techniques, there has been a lot of interest as to how analysis results differ from methods stipulated in Edition 2.1 (2006). This paper provides a detailed review of the differences between Edition 3.0 and Edition 2.1. An analysis is provided on differences in evaluation of the apparent sound power level and tonal audibility between both versions of the measurement standard.

Two-Dimensional Arbitrary Shape Acoustic Cloaks Composed of Homogeneous Parts Realized by Layered Structures

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.

Aeroacoustic Source Separation on a Full Scale Nose Landing Gear Featuring Combinations of Low Noise Technologies

The reduction of noise generated by aircraft at take-off and approach is crucial in the design of new commercial aircraft. Landing gear noise is significant contribution to the total noise sources during approach. The noise is generated by the interaction between the non-aerodynamic components of the landing gear and the flow, which leads to turbulence generated noise. This research presents results from the European Clean Sky funded ALLEGRA project. The project investigated a full-scale Nose Landing Gear (NLG) model featuring the belly fuselage, bay cavity and hydraulic dressing. A number of low noise treatments were applied to the NLG model including a ramp door spoiler, a wheel axel wind shield, wheel hub caps and perforated fairings. Over 250 far field sensors were deployed in a number of microphone arrays. Since technologies were tested both in isolation and in combination the additive effects of the technologies can be assessed. This study describes the different techniques used to quantify the contribution of each technology to the global noise reduction. The noise reduction technologies will be assessed as a function of frequency range and through beamforming techniques such as source deletion.

Determination of the Bearing Quality by Means of Vibroacoustic Response

A signal of mechanical and acoustical vibration generated during a bearing’s quality testing contains variety of useful information about their operational conditions. At defined testing speeds, the bearings generate a periodical and a non-periodical vibroacoustic signal of different intensities, which are dependent on the quality of bearings and/or their damage type. A dynamical response of the tested bearings recorded in time characterizes also the nature of the unwanted noise of bearings. Therefore the dynamical response of the maximum acceleration recorded in time is one of the major criteria of bearing quality evaluation in terms of noisiness. The second criterion is a determination of statistically significant frequency interval for the equivalent acceleration value expressed in decibels. Consequently, from the effective acceleration value, the bearing quality can be determined in terms of its vibration severity, as well as its noise level. This objective methodology substitutes the evaluation bearing quality by means of measurement of the vibration acceleration on the given test device and simultaneously evaluation of the noise quality and its intensity auditorily. Verifying the proposed methodology 100 % conformity was achieved between the methodology currently used and the new methodology, which eliminates the subjective quality evaluation of bearings auditorily.

Study on Driving Point Power Flow as Power Dissipation in Discrete Vibratory Systems

Mechanical power flow into a discrete system is formulated as power dissipation in the system using driving point advantages. Firstly, the complex-valued power flow into a system is defined, and it is shown that the real part (or active power) corresponds to the power dissipation, and the imaginary part (or reactive power) contains the Lagrangian energy. To represent the power dissipation in the system, all the power flows into the system must be counted. Otherwise, the value of power flow may become negative, and its physical interpretation may be troublesome. One of the main advantages of the formulated power flow is that to estimate the power dissipation in the system, only the power flows into the system are necessary. In other words, only the driving point power flows into the system are needed, and no information inside the system is required. Next, to estimate interfacial force/moment for the power flow into a sub-system, the two alternative indirect methods are presented. It is shown that these are exact methods utilizing the responses and the frequency response functions at the driving points only. This is another remarkable characteristic of the driving point. A 7 degree-of-freedom system is employed as an example case, and the presented formulations are confirmed computationally.

Jackhammer Chisel Noise Control

A robust chisel damper for quieting a jackhammer is presented. The noise produced from a jackhammer chisel is dominated by the ringing of the chisel moil resulting from impacts of the internal hammer against the end of the chisel producing airborne radiation of the transverse bending and longitudinal modes. A model steel chisel moil point was constructed with geometric properties similar to a jackhammer chisel and designed so as to not fail during severe acceleration impacts from the reciprocating hammer. Anechoic tests of the maximum overall unweighted sound pressure level for the undamped chisel due to a longitudinal impact was 86.8 dB linear (re. to 20 μ Pa) at 1 meter with the strongest ring tone at 1.37 kHz and harmonics; the overall sound pressure level for the damped chisel with identical axial impacts was reduced by 16.5 dB to 70.3 dB with severe reduction of 40 dB of the dominant chisel ring tone, and the harmonics.

Mixed-Mode Signal Detection of Road Vehicle Vibration Using Hilbert-Huang Transform

The Hilbert-Huang Transform (HHT) is a fully adaptive time-frequency analysis method which is applicable to nonlinear and nonstationary processes. However, this promising method is fairly new and its range of applications is not well known. Furthermore, its mathematical framework is not yet fully developed. So far, the HHT has yielded interesting results for many applications such as biomedical, geophysical, meteorological and health monitoring, but there is no evidence of its application on complex mixed-mode vibration signals. To fill that gap, this paper investigates the application of the HHT to detect the different modes of road vehicle vibration signals. These modes originate from road roughness variation and vehicle speed which create nonstationary random vibration. Other modes are due to road surface aberrations which create transient events and the engine and drive train system of the vehicle which create harmonic vibrations. The energy density/average period significance test based on the HHT is assessed to detect these modes. The results, based on purposefully created synthetic test signals, reveal the limitations and shortcomings of the HHT based technique to detect and separate the various components of the mixed-mode vibration signals such as vehicle vibration signal.