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Simulering av exteriört bussljud: Undersökande av en Ray Tracing metod för ljudsimuleringar
Karlstad University, Faculty of Health, Science and Technology (starting 2013).
2014 (Swedish)Independent thesis Basic level (university diploma), 15 credits / 22,5 HE creditsStudent thesisAlternative title
Simulation of Exterior Bus Noise : Testing of a Ray Tracing Method For Simulation of Exterior Bus Noise (English)
Abstract [sv]

En metod för att simulera exteriört bussljud med hjälp utav Ray Tracing har testats och utvärderats. En modell av en buss har byggts upp i ett CAD program. Dominerande ljudkällor i bussen samt materialkoefficienter har tagits fram för de material som ingår i bussen. Bussen har sedan förts in i simuleringsprogrammet Odeon, där ett antal simuleringar har utförts. Olika pass-by simulering har utförts och jämförts med mätningar. Olika grader inkapsling av motorrummet har simulerats. Ett grid response har tagits fram för att se vart det lönar sig att placera absorbenter. Ett beräkningsfel har hittats i den använda programvaran Odeon 10.13 vilket ledde till att en jämförelse mellan Odeon 10.13 och demoversionen av Odeon 12.

Resultatet visar att simuleringsmetoden i dagsläget fungerar bäst då ingen ljudtransmission tas hänsyn till, detta kräver dock att det finns öppningar i bussen eftersom detta annars leder till ett antal problem ifall bussen simuleras med alltför hög grad av inkapsling. Inga strålar skulle i detta fall kunna nå någon mottagare. Anledningen till att transmissionen inte kan tas i hänsyn beror på de fel som hittats i Odeon 10.13. Programmet räknar fel och överskattar transmissionen samt transmitterar strålar även i de fall där en yta är definierad att inte transmittera några strålar alls, något som Odeon 12 räknar rätt på. Metoden kan tills detta är löst med fördel användas för att se energifördelning mellan frekvensbanden, optimal placering av absorbenter samt i viss mån även den totala ljudnivån för bussen.

Abstract [en]

A method to simulate exterior bus sound with the help of ray tracing has been tested and evaluated. To do this a model of a bus has been built up using CAD software. Dominant noise sources in the bus and material coefficients for the materials included in the bus have been researched. The bus has been imported into the simulation program Odeon where a number of simulations have been performed. Different pass-by simulations have been performed and compared with physical measurements. Different degrees of encapsulation of the engine compartment have been simulated. A grid response has been formulated to optimize the positioning of the absorbers. A calculation error has been found in release 10.13 of the Odeon Software which led to a comparison between Odeon 10.13 and a demonstration version of Odeon 12.

The results show that the simulation method in its current state performs best when no sound transmission is taken into account. This requires that there are openings in the bus as problems will arise if the bus is simulated with too high a level of encapsulation. Theoretically, no rays would in this case be able to reach any receiver outside the engine compartment. The reason that the transmission loss cannot be taken into account depends on the errors found in Odeon 10.13. The software incorrectly overestimates the sound transmission and transmits rays even in cases where an area is defined to not transmit any rays at all, something that Odeon 12 calculates correctly. Until this is resolved, the simulation method can be used to estimate the energy distribution between the octave bands, the optimal placement of absorbers and to some extent the overall sound level of the bus.

Place, publisher, year, edition, pages
2014. , 45 p.
Keyword [en]
ray tracing, acoustics, noise, sound, odeon
Keyword [sv]
ray tracing, akustik, ljud, odeon
National Category
Other Engineering and Technologies
Identifiers
URN: urn:nbn:se:kau:diva-33037OAI: oai:DiVA.org:kau-33037DiVA: diva2:730863
External cooperation
Volvo Bussar AB
Educational program
Music and Sound Engineering, 180 hp
Supervisors
Examiners
Available from: 2014-08-25 Created: 2014-06-30 Last updated: 2014-08-25Bibliographically approved

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