Noise Pollution Flashcards
Noise
sound that is unwanted because it causes disturbance or damage
Sources of noise pollution
Aircraft, Road traffic, Railway, Industrial, Domestic
Effects of noise pollution on non-living objects
Acoustic fatigue, vibration damage, Shock impacts
Acoustic fatigue
Stress cracking of a material caused by repetitive vibrations induced by sound.
Effects of noise pollution on humans
Hearing damage/loss, stress, ulcers, high blood pressure, heart disease, irritability, aggression, accidents due to lack of concentration, communication problems
Effects of noise pollution on other organisms
Livestock panic, injuries, breeding failure, disturbance of birds, reduced feeding success, hearing damage and behavioural change
Controls of air traffic noise through airport design
Locate away for major population centres, Taxi areas away for residential areas, Engine test areas away from residentials areas, acoustic insulation and triple glazing for nearby buildings, restriction on house building close to the airport, acoustic barriers and baffle mounds, multiple runways for slower and quieter landings
Reverse thrusters
A method used on most aircraft to slow down after landing.
Cowling
A cowling is the removable covering of a vehicle’s engine. On airplanes, cowlings are used to reduce drag and to cool the engine
Controls of air traffic noise through aircraft design
High bypass-ratio engine, chevron nozzles, engine hush kits, engine acoustic liners, blended wing design, improved aerodynamics, liter materials
High bypass-ratio engine
Have a second cowling (second layer around the engine). Air is passed around the engine as well as through it. Bypass air smooths the flow of exhaust air and reduces noise, the higher the ratio of bypass air to engine exhaust air, the quieter the engine
Chevron nozzles
A serrated edge on the cowling that mixes exiting bypass and engine exhaust air with the surrounding air more smoothly and reduces noise
Engine hush kits
Can be retrofitted to older low bypass ratio engines to increase mixing of exiting exhaust air to reduce noise
Engine acoustic liners
liners inside the outer engine cowling to absorb noise
Blended wing design
A plane where there is no clear dividing line between the wings and the main body of the craft. The engine is located on top of and within the main body of the aircraft reducing noise. The design also reduces drag and therefore noise.
Improved airplane aerodynamics -
The addition of fairings (smooth coverings) in particular around landing gear reduces turbulence. Welded construction gives a smoother aerodynamic structure that rivets.
Aerodynamics
The study of airflow over surfaces to allow the design of surfaces that reduce wind resistance, turbulence, friction and noise generation.
Lighter airplane materials
The use of alternative lighter materials eg aluminium replacing steel and the use of composite high strength materials such carbon fibre reduce mass and the power required from the engine.
Controls of air traffic noise through pilot behaviour
Steep take-off angle, flight paths over less populated areas, changing flight paths, constant angle of descent, night flight restrictions
Constant descent angle
A method of approaching an airport where the aircraft descends at a constant angle, usually 3° reducing periods of high thrust
Steep take-off angle
this is noisier as the engines are running at higher power however the aircraft climbs rapidly to an altitude where it cannot be heard on the ground
Controls of noisier aircraft
Noise limits at some airports, higher charges for noisier aircraft, control of supersonic flights, Quota count systems
Supersonic flights
Aircraft that fly faster than the speed of sound, currently no civil aircraft in this category although some are in development, supersonic speeds are banned over most countries due to the supersonic boom (shock impact)
Quota count system
Points system for airports, aircraft noise at landing and takeoff is measured and allocated points. The total point score of an airport must not exceed their allocation. The system encourages the airport to accept many quieter takeoffs and landings rather than noisy ones
Sources of road noise pollution
wheel noise, vehicle air turbulence, engine noise
Controls of road noise pollution
noise absorbing materials in such as porous asphalt and shredded tyres in road surfaces, improved aerodynamics, acoustic insulation around the engine, designated routes for heavy goods, fences, embankments and tree planting, double/triple glazing, traffic management to maintain speed and reduce acceleration and braking
Sources of rail noise pollution
Wheel vibration, engine noise, pantograph turbulence, wheel squeal on corners, brake squeal, wheel noise
Controls of rail noise pollution
Track polishing, sound absorbing ballast around rails and sleepers, sound absorbing suspension, aerodynamic fairing for pantographs, lubrication of wheels and track, use of composite materials for brakes to reduce metal on metal noise
Baffle mounds
Embankments that absorb and deflect noise, especially around mines, airports and major roads.
Industrial noise sources
Air compressors, stamping machines, metal conveyors, mine blasting, pile-driving, marine seismic surveys, military sonar
Industrial noise controls
Silences on air compressors reducing the explosive expansion of air, pressing or moulding instead of stamping, reducing the use of metal in conveyors, restricted timing and baffle mounds for mine blasting, drilling instead of pile driving on land, air bubble curtains when pile driving at sea, acoustic surveys before seismic surveys at sea to check for the presence of cetaceans.
Acoustic monitoring
Monitoring environmental sounds e.g. to detect the presence of dolphins and whales or bats.
Domestic noise sources
Domestic appliances, music equipment, garden machinery, power tools, dogs
Domestic noise controls
Absorbers and liners on appliances, use of ear defenders, volume limiters on musical equipment, dog control
dB scale
A logarithmic scale used to measure sound levels.
0dB
The threshold of human hearing, there is still sound below the level but it cannot be detected by human hearing
How the dB scale works
an increase in 10 dB is a 10x increase in sound volume
dB(A) scale
decibel scale adjusted for the range of human hearing
Measuring road traffic noise LA10
measures noise exceeded for 10% of the time period, measures the noisiest periods of time
Measuring road traffic noise LA90
measures noise level exceeded for 90% of the time period, measures quieter background noise.
Measuring road traffic noise Traffic Noise Index TNI
Uses both LA10 and LA90 and provides a more representative measure of road traffic noise.
Measuring road traffic noise L10(18h)
This is an LA10 measurement over the busiest 18 hour period of road use form 6am until midnight
Measuring aircraft noise - effective perceived noise levels EPNL
an estimate of perceived loudness of a particular aircraft at takeoff, overflight and landing
Measuring aircraft noise - Noise and Number Index NNI
combines the number of flights and the noise levels above 80dB
Measuring aircraft noise - Leq 57dB
Has replaced NNI. A measure of the average noise level at an airport between 7am and 11pm. Average levels above 57dB are considered an annoyance
Sonograms
A graph showing the volumes of sounds at different frequencies.
