AN ORIGINAL METHOD FOR URBAN TRAFFIC NOISE PREDICTION

Transcription

1 AN ORIGINA METHOD FOR URBAN TRAFFIC NOISE REDICTION Federico Rossi 1, Uberto Di Mtteo, Sofi Sioni 3 1 University of erugi Industril Engineering Deprtent oc. enti Bss 1, 05100, Terni, Itly frossi@unipg.it Università Teletic Guglielo Mrconi Vi Nzrio Suro 4, 00195, Roe, Itly ditteo@unirconi.it 3 University of erugi Industril Engineering Deprtent oc. enti Bss 1, 05100, Terni, Itly sioni.unipg@cirif.it ABSTRACT A new ethod for urbn rod noise prediction is here proposed which is bsed on originl source nd propgtion odels. The proposed ethod is suitble for urbn situtions which involve sei-reverberting propgtion nd source-receivers jed scenrios. A esureent cpign hs been crried out in typicl urbn res to vlidte the proposed ethod which sees to fit ech sitution with strong ccurcy. Further ethod tests re ctully on progress. 1

2 Euronoise 006, Tpere, Finlnd 1 INTRODUCTION Itlin urbn res re inly constituted by ncient settleent with nrrow streets nd buildings fcdes very close to trffic lnes; in such scenrios reverbertion y significntly contributes to noise level. However, clssicl reverbertion theory (sttisticl coustic) cnnot be pplied becuse ny preters re introduced exclusively for indoor conditions. It is here proposed ethod to evlute trffic noise in which odifictions to soe clssicl preters re introduced king the suitble for sei reverberting conditions. A esureent cpign nd coercil code siultion llowed to vlidte the proposed ethod which sees to be suitble to estite trffic noise levels on urbn Itlin scenrios. The ethod is very siple nd it is ctully going to be iproved. NOISE REDICTION METHOD In urbn scenrios noise level is deterined by the overlpping of direct nd sei reverberting sound fields. Reverberting contribute is due to wve reflections on building fcdes nd other s; the proposed ethod introduces new odelliztion for both rod noise sources nd sei reverberting field which tkes into ccount open s s well s rod ceiling. The ethod is bsed on the following hypotheses: 1. trffic lnes re considered s liner source t the center of the rod, in which ech segent eits ccording to bert lw (diffusive eission);. open s (i.e. rod ceiling) re tken into ccount in order to introduce odified verge be length. The ethod introduces two originl reltions respectively for the liner source nd for sei reverberting propgtion:.1 iner source According to hypothesis 1, sound intensity produced by the rod segent dx [1] t generic point (see Fig. 1) y be found by eq.(1): dj W cosα ω dx = (1) π S n W is the rod sound power per unit of length nd cos y be rewritten s follows: H H cosα = = R () x + y + H is given by: S ω = n (3) R

3 Euronoise 006, Tpere, Finlnd At point ech rod segent gives different contribution to direct field. h Y H Sn y r R α Z dx X Rod Fig. 1. Source nd propgtion odels reference schee. Substituting Eq., 3 into Eq. 1 nd integrting long rod length, sound intensity t point is found: J W H W = dx = 0 π π H ( x + y + H ) 3 ( H + y ) + y + H (4) Sound pressure level d in, due to direct sound field, is given by Eq. 5: J p = = d 10 log 10 log (5) 0 J 0. Sei reverberting field For sei reverberting sound field prediction, noise propgtion volue hs been ssued s prllelepiped in which lower is the rod pveent, side s re the building fcdes nd upper is the rod ceiling. The overll power which supplies sei reverberting field is given by: W rev ( α ) = W 1 (6) According to Sbine theory [], reverberting cousticl energy density is unifor within the entire propgtion volue: 3

4 Euronoise 006, Tpere, Finlnd D R W = ( 1 α ) t V α (7) It is here proposed n originl verge be length t in which issing reflections on open s re not tken into ccount; observing Fig. 1 t becoes [3]: t = c 4 V ( S h) (8) Averge bsorption coefficient hs been clculted by supposing coplete bsorption on open s (i.e. ceiling). Sound pressure level r t point, due to reverberting field is given by Eq. 9 where D r is given by Eq. 7: D r = = r 10 log 10 log (9) 0 D0 Overll sound pressure level is given by the contribution of direct level given by Eq. 5 nd reverberting level of Eq. 9: d r = 10 log TOT (10) 3 VAIDATION Vlidtion of the proposed ethod hs been ttined by esureent cpign in which three typicl Itlin urbn scenrios hve been considered; in ech scenrio, three different icrophone positions hve been chosen. Such positions corresponds to eningful points: point 1 represents typicl people position on sidewlk, point represents the icrophone position stted by Itlin lw for rod noise esureents, point 3 represents the verge position of top floor receiver. First scenrio (see Fig. ) is nrrow street between se height buildings. Second scenrio (see Fig. 3) is nrrow street between different height buildings. The third scenrio (see Fig. 4) is nrrow street with buildings long only one side. Noise levels hve been evluted by clssicl theory reltions [4] nd coercil code SoundAN in which ech scenrio chrcteristic hve been introduced nd clibrted; SoundAN clibrtion hs been crried out dopting the verge nuber of trnsits during esureent cpign s trffic volue. In tble 1 noise levels provided by clssicl theory [4], by SoundAN, by the proposed ethod nd by esureents cpign re represented. For ech scenrio, the proposed ethod gives noise levels very close to esureents ones. 4

5 Euronoise 006, Tpere, Finlnd 3 h h1 1 b Rod x Fig.. Mesureent points positions in the scenrio 1. 3 h1 1 b Rod x h Fig. 3. Mesureent points positions in the scenrio. 3 h1 1 b Rod x Fig. 4. Mesureent points positions in the scenrio 3. Coprison shows tht the highest difference between the esured vlues nd those chieved by the proposed ethod is dba. Such difference hs been verified in scenrio 3 t the ost distnt point fro the source. 5

6 Euronoise 006, Tpere, Finlnd Tble 1. Coprison between the results provided by the clssicl ethod, the proposed ethod, SoundAN odel nd the esureents cpign for three different scenrios nd icrophone positions. Scenrio 1 Scenrio Scenrio 3 oints Distnce Sound pressure level (dba) Height fro centre H () Clssicl roposed SoundAN line y () Mesured ethod ethod odel 1 1,5 4,0 58,7 59,5 60,0 60,6 4,0 3,0 55,5 57,0 56,7 57,5 3 0,0 4,0 5, 54,1 51,6 53, 1 1,5 4,0 58,7 59,5 59,9 59, 4,0 3,0 55,4 56,9 56,7 56,5 3 0,0 4,0 51,4 53,0 50, 5,3 1 1,5 4,0 58,5 59,4 59,8 59,0 4,0 3,0 55,0 56,1 55,9 56,0 3 0,0 4,0 50,8 5, 49,6 50, Noise levels provided by proposed ethod in points 1 nd re both very close to SoundAN s nd to the esured ones. In 3, for ech scenrios, such vlues re lower thn esured noise levels but higher thn SoundAN ones. For greter distnces the proposed ethod fits esureents results with better ccurcy thn the other ethods tken into ccount. 4 CONCUSIONS In this pper new ethod for noise estition on urbn res is proposed. The ethod is bsed on two originl reltions respectively for liner source nd for sei reverberting propgtion. Method vlidtion hs been chieved tking into ccount three typicl Itlin urbn scenrios; for ech scenrio esureent cpign hs been crried out nd noise levels hve been evluted by clssicl theory reltions, by coercil code nd by proposed ethod. Coprison between esured nd predicted vlues shows tht results provided by the proposed ethod fit esured sound pressure levels with better ccurcy thn other literture ethods. The proposed ethod is ctully going to be iproved nd furtherore tested. REFERENCES [1] R. Spgnolo, Mnule di custic pplict, UTET ibreri, Torino 001. [].. Bernek, Noise nd vibrtion control, McGrw-Hill, Revised Edition, [3] G. Moncd o Giudice, S. Sntoboni, Acustic, Msson Editorile ESA, Milno, [4] Mlcol J. Crocker, Hndbook of Acoustics, John Wiley & Sons, New York, USA,