A generalized computational approach to predict high-frequency acoustic pressure response of cavity structures for structural health monitoring of wind turbine blades

This paper details the development of a generalized computational approach that enables prediction of cavity-internal sound pressure distribution due to flow-generated noise at high frequencies. The outcomes of this research is of particular interest for development of an acoustics-based structural health monitoring system for wind turbine blades. The methodology builds from existing reduced-order aeroacoustic modeling techniques and ray tracing based geometrical acoustics and is demonstrated on the model NREL 5 MW wind turbine blade as a case study. The computational predictions demonstrated that damage could be successfully detected in the first half of the blade cavity near the root and that the change in frequency content may be indicative of the type of damage that has occurred. This study provides a foundation to analyze specific blades and likely damage cases for determining key factors of system design such as number and placement of sensors as well as for hardware selection.

3D sound spatialization with game engines: the virtual acoustics performance of a game engine and a middleware for interactive audio design

This study analyses one of the most popular game engines and an audio middleware to reproduce sound according to sound propagation physics. The analysis focuses on the transmission path between the sound source and the receiver. Even if there are several ready-to-use real-time auralization platforms and software, game engines' use with this aim is a recent study area for acousticians. However, audio design needs with game engines and the limits of their basic releases require additional tools (plugins and middleware) to improve both the quality and realism of sound in virtual environments. The paper discusses the use of Unreal Engine 4 and Wwise's 3D audio production methods in a set of different test environments. It assesses their performance in regard to a commercial geometrical acoustics software. The results show that the investigated version of the game engine and its sound assets are insufficient to simulate real-world cases and that significant improvements can be achieved with use of the middleware.

ABOUT HEAD WAVES AND UNDER-SURFACE LONGITUDINAL WAVES, RADIATED BY THE NORMAL PROBE WHICH IS TAKING PLACE ON A FREE FLAT SURFACE OF THE ELASTIC ENVIRONMENT

On the basis of integrated representations Fourier–Bessel a component of displacement of elastic waves, radiating by the normal converter which is taking place on a free flat surface of the elastic environment, receives analytical estimations of displacement a under-surface longitudinal and head (it is surface-longitudinal) waves. Components of displacement a under-surface longitudinal wave are the sum a component in approximation of geometrical acoustics (GA), the diffraction amendments to this approximation and the amendments which are taking into account influence of feature when the parameter of integrated representation is equal to wave number of a longitudinal wave. Components of displacement of a head wave are defined as the sum appropriate diffraction amendments for a component of displacement of a volumetric longitudinal wave in approximation GA and a component of displacement of a lateral wave. The maximum of amplitude of displacement a under-surface longitudinal wave in angular area of a direction of distribution near to a free surface of environment is caused by one of local maxima of the directivity characteristic of the normal probe. Thus dependence of change of amplitude of this wave of distance wave from the centre of the probe practically corresponds to similar dependence for displacement of a volumetric longitudinal wave in GA approximation. Quantitative estimations of maxima of amplitude of displacement under-surface longitudinal and head waves concerning the greatest amplitude, radiated by the normal probe of a volumetric longitudinal wave.

An Archaeoacoustics Analysis of Cistercian Architecture: The Case of the Beaulieu Abbey

The Cistercian order is of acoustic interest because previous research has hypothesized that Cistercian architectural structures were designed for longer reverberation times in order to reinforce Gregorian chants. The presented study focused on an archaeoacacoustics analysis of the Cistercian Beaulieu Abbey (Hampshire, England, UK), using Geometrical Acoustics (GA) to recreate and investigate the acoustical properties of the original structure. To construct an acoustic model of the Abbey, the building’s dimensions and layout were retrieved from published archaeology research and comparison with equivalent structures. Absorption and scattering coefficients were assigned to emulate the original room surface materials’ acoustics properties. CATT-Acoustics was then used to perform the acoustics analysis of the simplified building structure. Shorter reverberation time (RTs) was generally observed at higher frequencies for all the simulated scenarios. Low speech intelligibility index (STI) and speech clarity (C50) values were observed across Abbey’s nave section. Despite limitations given by the impossibility to calibrate the model according to in situ measurements conducted in the original structure, the simulated acoustics performance suggested how the Abbey could have been designed to promote sacral music and chants, rather than preserve high speech intelligibility.

The image edge model

Noise from traffic, industry and neighborhood is a prominent feature in urban environments. In these environments, sound reaches receiver points through reflections and diffractions. Real-time auralization of outdoor scenarios is a common goal for presenting sound characteristics in a realistic and intuitive fashion. Challenges in this attempt can be identified on many levels, however the most prominent part is sound propagation simulation. Geometrical acoustics has become the de-facto standard for the prediction of acoustic propagation in a virtual scenario. A considerable difficulty is the determination of the diffracted sound field component, because it is a wave effect that must be be explicitly integrated into the search algorithm of valid propagation paths. A deterministic solution to this problem is implemented that establishes propagation paths with an arbitrary constellation of far-field interactions at geometrical boundaries, i.e. reflecting surfaces and diffracting edges in large distance to each other. The result is an open-source code algorithm for propagation paths that follows the wave front normal and assembles metadata required for further acoustic modelling, such as incoming and outgoing angles, reflection material and geometrical details for the construction of the diffracting wedge. Calculation times are outlined and a proof of concept is presented that describes the employment of the propagation algorithm as well as the determination of an acoustic transfer function based on the input of the intermediate path representation. Future research will focus on prioritization of path contributions according to physical and psychoacoustical culling schemes.

Interaction of waves in one-dimensional dusty gas flow

The present study uses the theory of weakly nonlinear geometrical acoustics to derive the high-frequency small amplitude asymptotic solution of the one-dimensional quasilinear hyperbolic system of partial differential equations characterizing compressible, unsteady flow with generalized geometry in ideal gas flow with dust particles. The method of multiple time scales is applied to derive the transport equations for the amplitude of resonantly interacting high-frequency waves in a dusty gas. These transport equations are used for the qualitative analysis of nonlinear wave interaction process and self-interaction of nonlinear waves which exist in the system under study. Further, the evolutionary behavior of weak shock waves propagating in ideal gas flow with dust particles is examined here. The progressive wave nature of nonresonant waves terminating into the shock wave and its location is also studied. Further, we analyze the effect of the small solid particles on the propagation of shock wave.

Acoustic optimization of curved architecture in practice: The new Strait Cultural Arts Center in Fuzhou

Curved surfaces are increasingly part of the architectural language used in buildings for the performing arts, yet have known challenges both in reality and in ray-tracing-based computer simulations. The designs of the 1000-seat symphony hall, the 1600-seat opera house and the 800-seat multi-purpose hall in Fuzhou, China, were all based on curved surfaces, both convex and concave, often covered with local ceramic tiles. Providing the right amount, distribution and quality of early reflections thus required a precise analysis of the acoustic behavior of curved surfaces. The acoustic design interacted with the architecture in precisely shaping those curves in 3D. In order to explore the acoustic potential and detect problems related to the architectural concept of both rooms, novel geometrical acoustics analysis algorithms were developed within NURBS modeling software rather than relying on commercial ray-tracing algorithms. Optimization of the curved surfaces is obtained when the output of these algorithms, the interpretation of the acoustic consultant, and the required integration of acoustic solutions within the global architectural concept are all aligned – a “meeting of minds” between acoustics and architecture. The analysis procedure and geometrical acoustics algorithms used will be presented in detail, as well as the related decision-making process, the acoustic predictions and the measurement results of the three built halls.

Computer Modeling of Barrel-Vaulted Sanctuary Exhibiting Flutter Echo with Comparison to Measurements

Computer modeling in acoustics allows for the prediction of acoustical defects and the evaluation of potential remediations. In this article, computer modeling is applied to the case of a barrel-vaulted sanctuary whose architectural design and construction led to severe flutter echoes along the main aisle, which was later mitigated through acoustical remediations. State-of-the-art geometrical acoustics and wave-based simulations are carried out to analyze the acoustics of this space, with a particular focus on the flutter echoes along the main aisle, before and after remediations. Multi-resolution wavelet and spectrogram analyses are carried out to isolate and characterize flutter echoes within measurements and computer-simulated room impulse responses. Comparisons of simulated responses to measurements are also made in terms of decay times and curves. Simulated room impulse responses from both geometrical acoustics and wave-based methods show evidence of flutter echoes matching measurements, to varying degrees. Time-frequency analyses isolating flutter echoes demonstrate better matches to measurements from wave-based simulated responses, at the cost of longer simulation times than geometrical acoustics simulations. This case study highlights the importance of computer modeling of acoustics in early design phases of architectural planning of worship spaces.