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Author:Haapaniemi, Aki
Title:Simulation of Acoustic Wall Reflections Using the Finite-Difference Time-Domain Method
Seinärakenteiden akustisten heijastusten simulointi FDTD-menetelmällä
Publication type:Master's thesis
Publication year:2012
Pages:[8] + 66      Language:   eng
Department/School:Signaalinkäsittelyn ja akustiikan laitos
Main subject:Akustiikka ja äänenkäsittelytekniikka   (S-89)
Supervisor:Lokki, Tapio
Instructor:Southern, Alex
Electronic version URL: http://urn.fi/URN:NBN:fi:aalto-201210313331
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  717   | Archive
Keywords:FDTD
room acoustics
sound reflection
wave propagation visualization
diffusion measurement
FDTD
huoneakustiikka
äänen heijastuminen
ääniaallon visualisointi
diffuusiomittaus
Abstract (eng): In this thesis, the reflection characteristics of layered wall structures are studied using the standard rectilinear (SRL) finite-difference time-domain (FDTD) method for modeling sound wave propagation.

The structures consist of a panel with slats combined with a back wall, forming a cavity in between.
Outwardly similar structures are known to have resonant properties and are generally known as resonant absorbers or distributed Helmholtz resonators.
The structures studied in this thesis, however, are in a different parameter range and do not include absorptive material.
They are found in practical use in, e.g., the Helsinki Music Centre Concert Hall.
The various features of the structure are varied to establish how the reflection responses change with the features.

The relevant background in acoustics - including wave phenomena, measurement methods and acoustic modeling methods - is briefly reviewed.
The basics of the SRL FDTD method is introduced in the context of the 3-D method.
Introductory simulations are done to explore the nature of the 2-D and 3-D methods, and issues regarding the simulation setup are addressed.
A comparison case of the 2-D and 3-D methods shows that the results can be qualitatively equivalent for structures having one axis of symmetry.
The 2-D method is deemed a better suited choice for the work in this thesis.

The investigation was conducted through frequency- and time-domain analysis, diffusion measurements and visualizations.
The studied structures were found to exhibit various degrees of comb filtering effects and frequency-dependent spatial and temporal spreading.
Abstract (fin): Tässä diplomityössä tutkitaan kerrosteisten seinärakenteiden akustisia ominaisuuksia simuloimalla ääniaallon etenemistä SRL FDTD -menetelmällä.

Tutkittavat rakenteet koostuvat säleisestä paneelista ja takaseinästä, joiden väliin muodostuu ilmatila.
Ulkoisesti samankaltaiset rakenteet tunnetaan alan kirjallisuudessa yleisesti resonoivina vaimentimina.
Tässä opinnäytetyössä tutkitut rakenteet ovat kuitenkin mitoiltaan eri luokassa, eivätkä sisällä vaimentavaa materiaalia.
Rakenteita löytyy esim.
Helsingin Musiikkitalon konserttisalista.

Aiheen kannalta olennainen taustatieto, liittyen ääniaallon ominaisuuksiin, mittausmenetelmiin ja mallinnusmenetelmiin, käsitellään lyhyesti.
SRL FDTD -simulaatiomenetelmän perusteet esitellään 3-D menetelmän muodossa.
Alustavat simulaatiot toimivat johdantona 2-D ja 3-D menetelmien ominaisuuksiin ja lisäksi käsitellään simulaatioiden toteutukseen liittyviä asioita. 2-D ja 3-D menetelmiä vertaileva tapaus osoittaa, että saatavat tulokset ovat laadullisesti vastaavia, kun tutkittavassa rakenteessa on yksi symmetria-akseli ja toteutukset vastaavat toisiaan.
Näin 2-D menetelmä osoittautuu sopivammaksi tätä opinnäytetyötä varten.

Tutkimus toteutettiin taajuus- ja aika-tason analyysillä, diffuusiomittauksilla ja visualisaatioilla.
Rakenteiden todettiin aiheuttavan kampasuodatusta sekä taajuudesta riippuvaa äänienergian paikallista ja ajallista leviämistä.
ED:2012-10-08
INSSI record number: 45341
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