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11 noise

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Information about 11 noise
Education

Published on February 26, 2008

Author: Nathaniel

Source: authorstream.com

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CE 453 Lecture 11:  CE 453 Lecture 11 Noise Analysis See: http://www.nonoise.org/library/highway/probresp.htm and http://www.fhwa.dot.gov/environment/noise/index.htm and http://www.fhwa.dot.gov/environment/audible/contents.htm Noise:  2 Noise What is noise? Who decides? news.bbc.co.uk www.stedmundsbury.gov.uk sprott.physics.wisc.edu/fractals/chaos www.plu.edu/scene/issue/1999/summer/img Noise:  3 Noise Undesirable or unwanted sound Subjective Impacts Annoyance, disturbance Stress Physical and psychological damage Transportation Noise:  4 Transportation Noise Decreases with increasing distance – a corridor problem Generated by: Engine Exhaust Aerodynamic friction Interaction between tire-pavement Control of Transportation Noise:  5 Control of Transportation Noise Federal -- Noise control act of 1972 Recognized noise as a major degrader of urban living Encourage use of noise standards State and local governments Also institute noise control Noise Measurement:  6 Noise Measurement Intensity of a single sound is measured on a relative of logarithmic scale Uses a unit called a bel (B) or subunit – decibel (dB, 1/10 of a bel) At 14 bels, sound is painful to human ear Common Sounds:  7 Common Sounds Noise Propagation:  8 Noise Propagation Noise is generated at source and spreads spherically away from source Intensity diminishes with distance Losses also occur from sound energy being dissipated as sound is transferred by air particles Bending and diffraction occurs as sound waves encounter natural and manufactured solid objects Noise Control Strategies:  9 Noise Control Strategies Minimize noise levels Source controls Vehicle control devices – maintenance, traffic and highway design controls Path controls Sound barriers that reflect and diffuse noise Buffer zones Receiver-side controls insulation Noise abatement measures:  10 Noise abatement measures Traffic management (see next slide) Buffer zones Vegetation Noise insulation Relocating the highway Traffic management measures:  11 Traffic management measures Prohibit trucks Truck routes Prohibit daytime (or night-time) use Traffic signal timing Speed limits Will all these work? Slide12:  12 http://www.nonoise.org/library/highway/traffic/traffic.htm Noise Source Slide13:  13 http://www.nonoise.org/library/highway/traffic/traffic.htm Slide14:  14 Slide15:  15 http://www.nonoise.org/library/highway/traffic/traffic.htm Paths: Effects of distance And adding sources Slide16:  16 http://www.nonoise.org/library/highway/traffic/traffic.htm Receivers: Perceptions of noise Slide17:  17 Number of people annoyed At different sound levels Slide18:  18 http://www.nonoise.org/library/highway/policy.htm Slide19:  19 Slide20:  20 Noise Measurement:  21 Noise Measurement Significant variability in noises from transportation sources Lp: noise level at a particular receptor that is exceeded p percent of the time i.e. Noise that exceeds 100 db 90% of the time A-weighted noise level (equivalent “irritation” level – has to do with mix of frequencies DNL (day/night level – weights nighttime noises) What are L10 and Leq?:  22 http://www.nonoise.org/library/highway/policy.htm#II What are L10 and Leq? The equivalent sound level is the steady- state, A-weighted sound level which contains the same amount of acoustic energy as the actual time-varying, A-weighted sound level over a specified period of time. If the time period is 1 hour, the descriptor is the hourly equivalent sound level, Leq(h), which is widely used by SHAs as a descriptor of traffic noise. An additional descriptor, which is sometimes used, is the L10. This is simply the A-weighted sound level that is exceeded 10 percent of the time. What are L10 and Leq?:  23 http://www.nonoise.org/library/highway/traffic/traffic.htm What are L10 and Leq? L10 is usually about 3dB greater than Leq Mathematical Model:  24 Mathematical Model Simple model L50 = 68 + 8.5 log V – 20 log D (db) Where: V = traffic volume (veh/hour) D = distance from traffic to observer in feet Also use nomographs, relate noise to speed, volume, distance, etc. State of the Art is FHWA’s Traffic Noise Model (TNM):  25 State of the Art is FHWA’s Traffic Noise Model (TNM) Modeling of five standard vehicle types, including automobiles, medium trucks, heavy trucks, buses, and motorcycles, as well as user-defined vehicles. Modeling of both constant-flow and interrupted-flow traffic using a 1994/1995 field-measured data base. Modeling of the effects of different pavement types, as well as the effects of graded roadways. Sound level computations based on a one-third octave-band data base and algorithms. Graphically-interactive noise barrier design and optimization. Attenuation over/through rows of buildings and dense vegetation. Multiple diffraction analysis. Parallel barrier analysis. Contour analysis, including sound level contours, barrier insertion loss contours, and sound-level difference contours. Slide26:  26 2280 120 60 Problem: Find dBA L10 500 ft from road 2 lane road 2400 vehicles per hour 5 percent trucks 60 mph #cars = .95x2400=2280 Example Problem Slide27:  27 Problem: Find dBA L10 at 500 ft From a 2 lane road carrying: 2400 vehicles per hour 5 percent trucks, at 60 mph … cars = .95x2400=2280 L50 dBA for cars at 100’ = 68 dBA Slide28:  28 68 2280 120 60 Slide29:  29 Problem: Find dBA L10 at 500 ft From a 2 lane road carrying: 2400 vehicles per hour 5 percent trucks, at 60 mph … trucks = .05x2400=120 L50 dBA for trucks at 100’ = 62 dBA 20 30 40 50 60 70 Slide30:  30 68 62 2280 120 60 Slide31:  31 Problem: Find dBA L10 at 500 ft From a 2 lane road carrying: 2400 vehicles per hour 5 percent trucks, at 60 mph … O-ELD = 500’ Slide32:  32 Problem: Find dBA L10 at 500 ft From a road carrying: 2400 vehicles per hour 5 percent trucks, at 60 mph … Adjustment from 100ft ref = -10 dB Slide33:  33 68 62 -10 -10 2280 120 60 Slide34:  34 Problem: Find dBA L10 at 500 ft From a road carrying: 2400 vehicles per hour 5 percent trucks, at 60 mph … (vol/speed)*ELD = 19,000 for cars, 1,000 for trucks L10 - L50 = 2 dBA cars, 6.5 dBA trucks Slide35:  35 68 62 -10 -10 2 6.5 60 58.5 60 58.5 2280 120 60 Slide36:  36 Adding 2 sources Heavy trucks 58.5 db Passenger vehicles 60 db Slide37:  37 Difference = 60 – 58.5 = 1.5 Add 2.3 db to higher 60 + 2.3 = 62.3 db due to both sources Slide38:  38 68 62 -10 -10 2 6.5 60 58.5 60 58.5 62.3 2280 120 60 Slide39:  39 Slide40:  40 Slide41:  41 Noise Barriers:  42 Noise Barriers Other Adjustments:  43 Other Adjustments Grade (trucks) +/- 3-4% = +2 +/- 5-6% = +3 +/- >7 = +5 Surface very smooth = -5 (auto only) very rough = +5 (auto, or truck>60mph) Interrupted flow (L10) auto = +2 Truck = +4 Foliage -5 for each 100’ >15’ -10 max Rows of houses -5 for each -10 max Noise Barriers (how they work):  44 Noise Barriers (how they work) Noise is "diffracted" over the barrier, this increases the distance it travel to the listener, thus decreasing the noise A + B > C Source:http://www.urbislighting.com/uap1.html Slide45:  45 Source: FHWA, “Keeping the Noise Down, Highway Traffic Noise Barriers” Noise Barriers (how they work):  46 Noise Barriers (how they work) Noise is also reflected and/or absorbed Source:http://www.urbislighting.com/uap1.html Possible barriers:  47 http://www.nonoise.org/library/highway/traffic/traffic.htm Possible barriers Slide48:  48 http://www.nonoise.org/library/highway/traffic/traffic.htm Slide49:  49 Source: FHWA, “Keeping the Noise Down, Highway Traffic Noise Barriers” Slide50:  50 Source: FHWA, “Keeping the Noise Down, Highway Traffic Noise Barriers” Slide51:  51 Source: FHWA, “Keeping the Noise Down, Highway Traffic Noise Barriers” Slide52:  52 Source: FHWA, “Keeping the Noise Down, Highway Traffic Noise Barriers” Slide53:  53 Source: FHWA, “Keeping the Noise Down, Highway Traffic Noise Barriers” Slide54:  54 Source: FHWA, “Keeping the Noise Down, Highway Traffic Noise Barriers”

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