Search results

Motivated by the acoustics of motor vehicles, a coupled fluid–solid system is considered. The air pressure is modeled by the Helmholtz equation, and the structure displacement is described by elastodynamic equations. The acoustic–structure interaction is modeled by coupling conditions on the common interface. First, the existence and uniqueness of solutions are investigated, and then, after recalling fundamental notions of shape optimization, the tensor form of the distributed shape derivative is obtained for the coupled problem. It is then applied to the minimization of the sound pressure by variation of the structure shape through the positioning of beads.

The existence and uniqueness of solutions up to eigenfrequencies are shown by the Fredholm–Riesz–Schauder theory using a novel decomposition into an isomorphism and a compact operator. For the design optimization, the distributed shape derivative is obtained using the averaged adjoint method. It is then used in a closed 3D optimization process of the position of a bead for noise reduction. In this process, the C++ library concepts are used to solve the differential equations on hexahedral meshes with the finite element method of higher order.

The existence and uniqueness of solutions have been shown for the case without absorption, where the given proof allows for extension to the case with absorption in the domain or via boundary conditions. The theoretical results show that the averaged adjoint can be applied to compute distributed shape derivatives in the context of acoustic–structure interaction. The numerical results show that the distributed shape derivative can be used to reduce the sound pressure at a chosen frequency via rigid motions of a nonsmooth shape.

The proof of shape differentiability and the calculation of the distributed shape derivative in tensor form allows to consider nonsmooth shapes for the optimization, which is particularly relevant for the optimal placement of beads or stampings in a structural-acoustic system.

A torque ripple minimization technique for switched reluctance motors is shown in this paper. Precalculated current shapes are applied to reduce torque ripple and to raise the degrees of freedom of the application in the commutation region. The optimization criteria for this region can be chosen freely. Therefore, it is possible to take positive effect to some motor characteristics like power losses, mechanical vibrations or acoustic noise.

The purpose of this paper is to present experimental studies on the designed muffler which contains ceramic foam and has the integration function of purification and noise elimination.

Comparative tests were done on a diesel engine with no muffler, the original muffler and the purification muffler. The soot index (light absorption coefficient), A-weighted sound pressure level and fuel consumption rate, which were collected by the partial flow opacity method, the insertion loss measurement of spatial five points and the load characteristics tests, respectively, and the effects of purification and noise elimination were studied.

The results of this paper state that the purification muffler shows great improvement on exhaust soot purification and noise elimination. The variation in diesel fuel consumption rate was small, the sound pressure level of purification muffler was reduced by 6 to 10 dB, the insertion loss of the purification muffler was increased by 6.41 dB and the average light absorption coefficient decreased by 57.8 percent compared with the original muffler.

The value of this study is that it supplies a purification muffler which contains a ceramic foam. Under the prerequisite of little effect on the fuel economy of diesel engine, the purification muffler shows great improvement in exhaust soot purification and noise elimination.

Informed by acoustic design standards, the built environments are designed with single reverberation times (RTs), a trade-off between long and short RTs needed for different space functions. A range of RTs should be achievable in spaces to optimise the acoustic comfort in different aural situations. This paper proclaims a novel concept: Intelligent passive room acoustic technology (IPRAT), which achieves real-time room acoustic optimisation through the integration of passive variable acoustic technology (PVAT) and acoustic scene classification (ASC). ASC can intelligently identify changing aural situations, and PVAT can physically vary the RT.

A qualitative best-evidence synthesis method is used to review the available literature on PVAT and ASC.

First, it is highlighted that dynamic spaces should be designed with varying RTs. The review then exposes a gap of intelligently adjusting RT according to changing building function. A solution is found: IPRAT, which integrates PVAT and ASC to uniquely fill this literature gap.

The development, functionality, benefits and challenges of IPRAT offer a holistic understanding of the state-of-the-art IPRAT, and a use case example is provided. Going forward, it is concluded that IPRAT can be prototyped and its impact on acoustic comfort can be quantified.

Informed by acoustic design standards, the built environments are designed with single reverberation times (RTs), a trade-off between long and short RTs needed for different space functions. The novel intelligent passive room acoustic technology (IPRAT) has the potential to revolutionise room acoustics, thus, it is imperative to analyse and quantify its effect. IPRAT achieves real-time room acoustic improvement by integrating passive variable acoustic technology (PVAT) and acoustic scene classification (ASC). This paper aims to compare IPRAT simulation results with the AS/NZS 2107:2016 Australian/New Zealand recommended design acoustic standards.

In this paper 20 classroom environments are virtually configured for the simulation, multiplying 5 classrooms with 4 aural situations typical to New Zealand classrooms. The acoustic parameters RT, sound clarity (C50) and sound strength (G) are considered and analysed in the simulation. These parameters can be used to determine the effects of improved acoustics for both teacher vocal relief and student comprehension. The IPRAT was assumed to vary RT and was represented in the simulation by six different absorption coefficient spectrums.

The optimised acoustic parameters were derived from relationships between C50, RT and G. These relationships and optimal RTs contribute a unique database to literature. IPRAT’s advantages were discerned from a comparison of “current,” “attainable” and “optimised” acoustic parameters.

By quantifying the effect of IPRAT, it is understood that IPRAT has the potential to satisfy the key recommendations of professional industry standards (for New Zealand namely; AS/NZS 2107:2016 recommended design acoustic standards).

This paper aims to give an overview on four empirical studies which explored the impact of background speech on cognitive performance and subjectively perceived disturbance. Background speech is the most serious noise problem in shared-room and open-plan offices for employees who are supposed to do silent, concentrated work. Different measures of acoustic office optimization, as well as the outstanding role of the intelligibility of background speech for its disturbance impact, are empirically evaluated.

The article provides a synopsis describing the core empirical results of four of our empirical studies. A survey study among office employees (n = 659) explored the subjective importance of office acoustics. Three experimental studies (n1 = 20; n2 = 30; n3 = 24) evaluated the effects of reduced background speech level, play-back of partial maskers and reduced speech intelligibility on cognitive performance and subjective ratings.

Background speech is subjectively perceived as a severe problem, and the different noise abatement measures affect objective performance and subjective ratings differently. Speech intelligibility is – besides level – a key determinant for the acoustic optimization regarding these two dimensions.

Practitioners are encouraged to apply the findings and described measures when planning and/or evaluating open-plan offices.

It is concluded that different acoustically efficient measures need to be combined to minimize the negative effects of background speech on cognitive performance and subjectively perceived disturbance. The aspired set value for open-office concepts is the lowest possible sound level with a bad intelligibility of the background speech at the same time.

The synopsis of several empirical studies allows deriving comprehensive and well-founded information for practitioners involved in the evaluation and/or design of offices environments.

Introduces papers from this area of expertise from the ISEF 1999 Proceedings. States the goal herein is one of identifying devices or systems able to provide prescribed performance. Notes that 18 papers from the Symposium are grouped in the area of automated optimal design. Describes the main challenges that condition computational electromagnetism’s future development. Concludes by itemizing the range of applications from small activators to optimization of induction heating systems in this third chapter.

This paper presents a shape optimization problem under acoustic, aerodynamic and geometric constraints. The acoustic specification concerns the generated sonic boom. The aim is to see the validity of incomplete sensitivities when a nonlinear CFD model is coupled with a nonlinear wave transport model to define pressure rise on the ground.

The purpose of this paper is to revisit the recursive computation of closed-form expressions for the topological derivative of shape functionals in the context of time-harmonic acoustic waves scattering by sound-soft (Dirichlet condition), sound-hard (Neumann condition) and isotropic inclusions (transmission conditions).

The elliptic boundary value problems in the singularly perturbed domains are equivalently reduced to couples of boundary integral equations with unknown densities given by boundary traces. In the case of circular or spherical holes, the spectral Fourier and Mie series expansions of the potential operators are used to derive the first-order term in the asymptotic expansion of the boundary traces for the solution to the two- and three-dimensional perturbed problems.

As the shape gradients of shape functionals are expressed in terms of boundary integrals involving the boundary traces of the state and the associated adjoint field, then the topological gradient formulae follow readily.

The authors exhibit singular perturbation asymptotics that can be reused in the derivation of the topological gradient function in the iterated numerical solution of any shape optimization or imaging problem relying on time-harmonic acoustic waves propagation. When coupled with converging Gauss−Newton iterations for the search of optimal boundary parametrizations, it generates fully automatic algorithms.

Disturbing vibrations and noise of electrical machines are gaining impact. The paper aims to focus on the necessity of estimating the electromagnetic, structure‐dynamical, and acoustic behaviour of the machine during designing and before proto‐typing.

An adequate tool is numerical simulation applying the finite‐element method (FEM) and the boundary‐element method (BEM) allowing for the structured analysis and evaluation of audible noise also caused by manufacturing tolerances.

The simulated results show good accordance to measurement results. The methods and simulation tools allow the analysis and evaluation of every type of energy converter with respect to its electromagnetic, structure‐dynamical and acoustic behaviour.

The methods developed and proved can be applied to any electromagnetic device in general.