An optimization method for reverberation room design

2021 ◽  
Vol 263 (4) ◽  
pp. 2360-2371
Author(s):  
Paul Didier ◽  
Cédric Van hoorickx ◽  
Edwin Reynders
Keyword(s):  
Sound Absorption ◽  
Sound Field ◽  
Optimization Procedure ◽  
Optimization Method ◽  
Finite Sample ◽  
Low Frequencies ◽  
Room Design ◽  
Target Values ◽  
Measured Absorption ◽  
Absorption Measurements

The ISO 354:2003 standard relating to sound absorption measurements is currently under revision to improve the reproducibility of the procedure it describes. Round robin tests conducted across various reverberation rooms indeed revealed significant disparities between sound absorption measurements of the same sample. One of the reasons is that, at low frequencies, the sound field in a single laboratory cannot be considered fully diffuse. However, the average sound field across different laboratories may be considered diffuse if the interaction between the finite sample and the diffuse field is duly accounted for and the direct field close to the absorber is disregarded. In this work, a method is developed for optimizing reverberation room design such that measured absorption values are as close as possible to ensemble average diffuse values. The reverberation room is modelled using the finite element method and standardized measurements of an absorptive sample are simulated. The distance between resulting absorption coefficients and diffuse target values is minimized in an optimization procedure having the geometrical characteristics of the model as input parameters. The results are anticipated to participate to the revised ISO 354 as guidelines for the construction of new reverberation rooms or the improvement of existing ones.

Numerical study of the impact of reverberation room design and test parameters on sound absorption measurements

2021 ◽  
Vol 263 (4) ◽  
pp. 2372-2383
Author(s):  
Paul Didier ◽  
Cédric Van hoorickx ◽  
Edwin Reynders
Keyword(s):  
Sound Absorption ◽  
Numerical Study ◽  
Plane Waves ◽  
Sound Field ◽  
Analysis Model ◽  
Absorption Coefficients ◽  
Low Frequencies ◽  
Room Design ◽  
The Impact ◽  
Absorption Measurements

The measurement of sound absorption in reverberation rooms following the ISO 354:2003 standard relies on Sabine's equation to derive absorption coefficients from reverberation times. This equation assumes perfect diffusivity, i.e. the sound field is composed of many statistically independent plane waves with uniformly distributed spatial phases, themselves uncorrelated to the corresponding amplitudes. In this work, both existing and fictitious reverberation rooms are numerically modelled using the finite element method. Finite porous absorbers are introduced in the rooms as equivalent fluid models. Standardized sound absorption measurement are simulated in the rooms through the determination of reverberation times. The respective effects of the sample size, sample placement, source positioning, and presence of finite panel diffusers are investigated. The resulting absorption coefficients are then confronted to the theoretical values in a perfectly diffuse sound field, that interacts with a baffled, finite-sized absorber, as obtained with a hybrid deterministic-statistical energy analysis model. The process notably underlines the strong, yet often disregarded, beneficial effect of panel diffusers at low frequencies in highly regularly-shaped rooms. Another conclusion of this work is that reverberation room design represents a crucial factor that can influence sound absorption measurements at low frequencies.

Effects of Temperature and Humidity on the Sound Absorption of Automotive Sound Absorbing Materials

2008 ◽  
Author(s):  
Edward R. Green ◽  
Andrea L. Zent
Keyword(s):  
Automotive Industry ◽  
Sound Absorption ◽  
Temperature Changes ◽  
Highly Sensitive ◽  
Target Values ◽  
Temperature And Humidity ◽  
Humidity Measurements ◽  
Effects Of Temperature ◽  
Materials Used ◽  
Absorption Measurements

Normally, small differences in day-to-day and laboratory-to-laboratory sound absorption measurements do not have large consequences because most noise control applications are not highly sensitive to small changes in sound absorption. However, in the automotive industry, materials are not purchased unless they meet strict sound absorption targets. As a result, decisions worth millions of U.S. dollars are made based on acoustic measurements. As material sound absorption moves closer to target values, the consequences of small measurement variations, such as those which might be caused by changes in ambient temperature and humidity during the course of a test, become more critical. The purpose of the work presented in this paper is to investigate which materials used for vehicle sound absorption are sensitive to temperature and humidity. Measurements are made using an impedance tube. It is discovered that typical materials used as absorbers in automotive applications are not sensitive to small temperature changes, and only a few materials are sensitive to changes in humidity.

scholarly journals THE INFLUENCE OF ADDITIONAL ABSORPTION ON THE ACOUSTICAL INDICATORS OF A HALL/PAPILDOMOS ABSORBCIJOS ĮTAKA SALĖS MODELIO AKUSTINIAMS RODIKLIAMS

1998 ◽  
Vol 4 (1) ◽  
pp. 86-90
Author(s):  
Vytautas Stauskis
Keyword(s):  
Sound Source ◽  
Sound Absorption ◽  
Sound Field ◽  
Reverberation Time ◽  
Frequency Range ◽  
Time Intervals ◽  
Scaled Model ◽  
Additional Absorption ◽  
Low Frequencies ◽  
Sound Energy

The influence of the slits between the walls and the floor of the model upon the objective acoustical indicators was examined in a scaled model of a hall. The Small Hall of the Lithuanian National Philharmonic Society was selected for the investigations. The hall is of rectangular form, 13.6 m in length, 10.7 m in width and 7 m in height. The hall model was scaled 1:25. The floor and the ceiling of the model were made of cloth-based laminate, while the walls of plywood 8 mm thick, with three layers of varnish. Thus, all materials employed in the model were similar to those of the real hall by their sound-absorption properties. There were 1 to 3 mm slits between the floor and the walls of the model. Their overall length was about 10–12 m (converted to real values). A spark sound source was used for the radiation of signals within the required spectrum. The sound source was put through a hole in the floor in order to improve the directivity diagram of the radiation. The positions of both the source and the ¼ microphone coincided in all cases. The frequencies examined fell in the range between 1250 Hz and 50000 Hz. The frequency of quantization of the signal was 166.6 kHz and the quantization time was 6 mcs. All frequencies were converted into real ones in the diagrams. A 2000 Hz upper limit was established to ensure that the Nyquist frequency exceeds 3. The experiments showed that the slits in the model influenced the muffling of the sound energy starting from 200 ms. With the slits present, the muffling occurs faster and the greatest difference of 2–3 dB is observed in the interval of 1000—2500 ms. Given small slit dimensions and overall slit length, the change of 2-3 dB is quite significant. The muffling of the sound field of the model is not exponent in character. The muffling varies on differently in different time intervals. Then the reverberation times of a non-filtered signal must be different when the muffling is approximated every 10 dB. The investigation showed that, with the slits present, the reverberation time values were reduced by 0.4–0.8 s throughout the interval when the muffling was approximated every 10 dB, starting from 0 to—30 dB and from—5 to—35 dB. This means that the slits absorb the sound energy on all intervals of the muffling of the sound field. The largest sound absorption is reached when the muffling of the sound field is approximated every 10 dB from 0 to—30 dB and amounts to as much as 3-6 m2. The influence of the slits is weaker when the muffling is approximated on other intervals. The slits also produce effect upon subjective acoustical indicators of a non-filtered signal, which vary between 1 to 2 dB. This shows that the intensity of reflections is changed in various time intervals by the slits. The influence exerted by the slits over the early reverberation time manifests itself both at the low and high frequencies. The greatest difference of about 0.8 s is observed at 100 Hz and 160 Hz. Within the frequency range from 500 Hz to 1000 Hz, the difference is not so marked and amounts to about 0.5 s. Within the range from 200 Hz to 400 Hz, the early reverberation time is only slightly influenced by the slits. The effect produced by the slits on the standard reverberation time, as compared with the early reverberation time, is not significant up to 160 Hz, while in the frequency range of 200—2,000 Hz the standard reverberation time is cut by about 0.4–0.6 s. The smallest sound absorption brought about by the slits is observed at low frequencies (around 1 m2). In the frequency range of 200—500 Hz, the sound absorption amounts to 3–4 m2, and at the frequencies exceeding 630 Hz to 2–7 m2. At low frequencies, the music sound clarity index is increased by the slits by about 0.5 dB. From 200 Hz and on, the clarity index is increased by 2 to 4 dB. These results show that the slits in the model alter the intensity of the early sound reflections. Beginning with 250 Hz, the sound absorption amounts to 3.2–9.0 m2. Such absorption is already significant, therefore the slit factor must be taken into consideration while conducting investigations in the hall model.

Dimensioning a recovery boiler furnace using mathematical optimization

TAPPI Journal ◽  
2015 ◽  
Vol 14 (2) ◽  
pp. 119-129 ◽  
Author(s):  
VILJAMI MAAKALA ◽  
PASI MIIKKULAINEN
Keyword(s):  
Radial Basis Function Network ◽  
High Capacity ◽  
Mathematical Optimization ◽  
Optimization Procedure ◽  
Optimization Method ◽  
Performance Criteria ◽  
Boiler Furnace ◽  
Starting Point ◽  
Recovery Boiler ◽  
Base Design

Capacities of the largest new recovery boilers are steadily rising, and there is every reason to expect this trend to continue. However, the furnace designs for these large boilers have not been optimized and, in general, are based on semiheuristic rules and experience with smaller boilers. We present a multiobjective optimization code suitable for diverse optimization tasks and use it to dimension a high-capacity recovery boiler furnace. The objective was to find the furnace dimensions (width, depth, and height) that optimize eight performance criteria while satisfying additional inequality constraints. The optimization procedure was carried out in a fully automatic manner by means of the code, which is based on a genetic algorithm optimization method and a radial basis function network surrogate model. The code was coupled with a recovery boiler furnace computational fluid dynamics model that was used to obtain performance information on the individual furnace designs considered. The optimization code found numerous furnace geometries that deliver better performance than the base design, which was taken as a starting point. We propose one of these as a better design for the high-capacity recovery boiler. In particular, the proposed design reduces the number of liquor particles landing on the walls by 37%, the average carbon monoxide (CO) content at nose level by 81%, and the regions of high CO content at nose level by 78% from the values obtained with the base design. We show that optimizing the furnace design can significantly improve recovery boiler performance.

scholarly journals Semiparametric likelihood inference for heterogeneous survival data under double truncation based on a Poisson birth process

2021 ◽  
Author(s):  
Achim Dörre
Keyword(s):  
Survival Data ◽  
Process Model ◽  
Optimization Method ◽  
Finite Sample ◽  
Birth Process ◽  
Dimensional Parameter ◽  
Lifetime Distributions ◽  
Computational Performance ◽  
Semiparametric Likelihood ◽  
Double Truncation

AbstractWe study a selective sampling scheme in which survival data are observed during a data collection period if and only if a specific failure event is experienced. Individual units belong to one of a finite number of subpopulations, which may exhibit different survival behaviour, and thus cause heterogeneity. Based on a Poisson process model for individual emergence of population units, we derive a semiparametric likelihood model, in which the birth distribution is modeled nonparametrically and the lifetime distributions parametrically, and define maximum likelihood estimators. We propose a Newton–Raphson-type optimization method to address numerical challenges caused by the high-dimensional parameter space. The finite-sample properties and computational performance of the proposed algorithms are assessed in a simulation study. Personal insolvencies are studied as a special case of double truncation and we fit the semiparametric model to a medium-sized dataset to estimate the mean age at insolvency and the birth distribution of the underlying population.

scholarly journals Dual UV-Thermal Curing of Biobased Resorcinol Epoxy Resin-Diatomite Composites with Improved Acoustic Performance and Attractive Flame Retardancy Behavior

2021 ◽  
Vol 2 (1) ◽  
pp. 24-48
Author(s):  
Quoc-Bao Nguyen ◽  
Henri Vahabi ◽  
Agustín Rios de Anda ◽  
Davy-Louis Versace ◽  
Valérie Langlois ◽  
...  
Keyword(s):  
Heat Release ◽  
Flame Retardant ◽  
Epoxy Resin ◽  
Flame Retardancy ◽  
Sound Absorption ◽  
Flexural Modulus ◽  
Construction Materials ◽  
Acoustic Properties ◽  
Low Frequencies ◽  
Compacting Pressure

This study has developed novel fully bio-based resorcinol epoxy resin–diatomite composites by a green two-stage process based on the living character of the cationic polymerization. This process comprises the photoinitiation and subsequently the thermal dark curing, enabling the obtaining of thick and non-transparent epoxy-diatomite composites without any solvent and amine-based hardeners. The effects of the diatomite content and the compacting pressure on microstructural, thermal, mechanical, acoustic properties, as well as the flame behavior of such composites have been thoroughly investigated. Towards the development of sound absorbing and flame-retardant construction materials, a compromise among mechanical, acoustic and flame-retardant properties was considered. Consequently, the composite obtained with 50 wt.% diatomite and 3.9 MPa compacting pressure is considered the optimal composite in the present work. Such composite exhibits the enhanced flexural modulus of 2.9 MPa, a satisfying sound absorption performance at low frequencies with Modified Sound Absorption Average (MSAA) of 0.08 (for a sample thickness of only 5 mm), and an outstanding flame retardancy behavior with the peak of heat release rate (pHRR) of 109 W/g and the total heat release of 5 kJ/g in the pyrolysis combustion flow calorimeter (PCFC) analysis.

Structural Topology Optimization Using Frame Elements Based on the Complementary Strain Energy Concept for Eigen-Frequency Maximization

2005 ◽  
Author(s):  
Akihiro Takezawa ◽  
Shinji Nishiwaki ◽  
Kazuhiro Izui ◽  
Masataka Yoshimura
Keyword(s):  
Topology Optimization ◽  
Cross Sections ◽  
Strain Energy ◽  
Optimization Procedure ◽  
Optimization Method ◽  
Structural Topology ◽  
Energy Concept ◽  
Conceptual Design Phase ◽  
Complementary Strain ◽  
Topology Optimization Method

This paper discuses a new topology optimization method using frame elements for the design of mechanical structures at the conceptual design phase. The optimal configurations are determined by maximizing multiple eigen-frequencies in order to obtain the most stable structures for dynamic problems. The optimization problem is formulated using frame elements having ellipsoidal cross-sections, as the simplest case. Construction of the optimization procedure is based on CONLIN and the complementary strain energy concept. Finally, several examples are presented to confirm that the proposed method is useful for the topology optimization method discussed here.

Sound absorption measurements at 10–60 kHz in near‐freezing sea water

1975 ◽  
Vol 58 (3) ◽  
pp. 608-619 ◽  
Author(s):  
G. R. Garrison ◽  
R. E. Francois ◽  
E. A. Pence
Keyword(s):  
Sound Absorption ◽  
Sea Water ◽  
Absorption Measurements

Structural Optimization of Composite Panel with Lamination Parameters and Equivalent Stiffness Laminate Method

2014 ◽  
Vol 496-500 ◽  
pp. 429-435
Author(s):  
Xiao Ping Zhong ◽  
Peng Jin
Keyword(s):  
Genetic Algorithm ◽  
Structural Optimization ◽  
Composite Structure ◽  
Optimization Procedure ◽  
Optimization Method ◽  
Composite Panel ◽  
Analysis Tool ◽  
Equivalent Stiffness ◽  
Lamination Parameters ◽  
Design Variables

Firstly, a two-level optimization procedure for composite structure is investigated with lamination parameters as design variables and MSC.Nastran as analysis tool. The details using lamination parameters as MSC.Nastran input parameters are presented. Secondly, with a proper equivalent stiffness laminate built to substitute for the lamination parameters, a two-level optimization method based on the equivalent stiffness laminate is proposed. Compared with the lamination parameters-based method, the layer thicknesses of the equivalent stiffness laminate are adopted as continuous design variables at the first level. The corresponding lamination parameters are calculated from the optimal layer thicknesses. At the second level, genetic algorithm (GA) is applied to identify an optimal laminate configuration to target the lamination parameters obtained. The numerical example shows that the proposed method without considering constraints of lamination parameters can obtain better optimal results.

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