6505, assign3, case studies, part 1

Fluid Mechanics and Braking Systems

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Fluid Mechanics in Braking SystemsCase studies, Part 1

A version of PDF version of this presentation is available at SlideShare

http://www.slideshare.net

http://www.slideshare.net


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Definition of a fluid

Properties of fluids• Unable to support shear stresses• Take on the shape of the container

A continuous, amorphous substance whose molecules move freely past one another and that has the tendency to assume the shape of its container; a liquid or gas.http://www.thefreedictionary.com/fluid


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Principles of Fluid Mechanics

• Hydrostatic pressure• Pressure Principle• Archimedes' Principles


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Hydrostatic Pressure

• When an object placed in a fluid, the fluid exerts a pressure over the entire surface of the object• The pressure acts at 90o to the surface of the object at any point

Pressure, P (Pa) = F = Force (N) A Area (m2)


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Hydrostatic Pressure and Depth

Rule: The deeper an object is submerged, the greater the hydrostatic pressure

Hydrostatic Pressure Depth RelationshipGiven the pressure at the surface, Po (in Pa), the pressure (in Pa) at depth, h ( in m) is:

P = Po + ρghwhere

ρ = density of the fluid (a constant - kgm-3)g = acceleration due to gravity (ms-2)


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Additional References

http://celebrate.digitalbrain.com/celebrate/accounts/takacs/web/Hydrostatica/membr/

• http://www.youtube.com/watch?v=GdAuzpYLOsc

http://celebrate.digitalbrain.com/celebrate/accounts/takacs/web/hydrostatica/membr/


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Pascal's Principle• Pressure applied to an enclosed liquid is transmitted undiminished to every point in the fluid and to the walls of the container

• Commonly used in sealed hydraulic systems, e.g. automotive braking systems


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Pascal's Principle


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Additional References• http://hyperphysics.phy-astr.gsu.edu/hbase/pasc.html

• http://en.wikipedia.org/wiki/Pascal's_law

• http://www.grc.nasa.gov/WWW/k-12/WindTunnel/Activities/Pascals_principle.html


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Archimedes Principle• When immersed in water an object will weigh less than in air

• Water provides an upward force (buoyancy) that partially counteracts the weight force

• If the upward force by the water on an object is greater than the weight force, the object floats

Factors that effect buoyancy• The density of the fluid

• The volume of the submerged object


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A body wholly or partially submerged in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the body

As Archimedes put it ....

This is independent of the composition or shape of the object


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Specific Gravity

Using Archimedes Principle, an object's specific gravity can be calculated

Specific Gravity = Weight of object in air Weight of object when submerged in water


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Additional References

• http://en.wikipedia.org/wiki/Buoyancy

• http://library.thinkquest.org/27948/archimede.html


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Use of Hydraulic Principles in Braking Systems

To find out about:

• the basic principles of a braking system, use the linkhttp://auto.howstuffworks.com/auto-parts/brakes/brake-types/brake.htm

• Drum brakes in cars, use the linkhttp://auto.howstuffworks.com/auto-parts/brakes/brake-types/drum-brake.htm

• Disk brakes in cars, use the linkhttp://auto.howstuffworks.com/auto-parts/brakes/brake-types/disc-brake.htm


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How hydraulic disk brakes work in cars

http://www.youtube.com/watch?v=LYetGatzWjM


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How hydraulic drum brakes work

http://www.youtube.com/watch?v=LX4mqzoe3BY


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Brakes used on Trains• The braking systems on trains are based on a different "fluid" - namely compressed air

• In 1869, George Westinghouse developed a braking system that used compressed air to hold the brake shoe off the wheels of the carriages

• To apply the brake the air is released, (or the pressure fails), and the bakes are immediately activated

• The method of braking is used with trains as a safety feature and is still used today

For more information on train brakes see:

• http://en.wikipedia.org/wiki/Railway_air_brake


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http://www.railway-technical.com/airbra-app.gif


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Innovation in Braking Systems - ABS or Anti-lock

Braking System

Why was it developed?

• When a vehicle brakes suddenly, the wheels typically lock and the vehicle skids

• A skidding vehicle has less traction than a turning wheel and as a result the driver has less control of the vehicle

• If the wheels can be prevented from skidding, the driver will be able to:

• Stop faster

• Have some control over the vehicle when the brakes are applied


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ABS or Anti-lock Braking SystemComponents of ABS ?

• Speed sensors - located in wheels. Detect when the wheels are about to lock

• ABS Controlled Valve - located in the brake line. The valve has three possible positions:

1. Open - pressure from the master cylinder is passed directly to the brake2. Closed - The brake line is closed off from the master cylinder. Prevents increase in brake pressure if the brake is pressed harder3. Release - some (not all) pressure is released from the brake

• Pump - Restores pressure in the brake line sfter the valve has been activated

• Controller - a computer that monitors the speed sensors and controls the valves


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http://auto.howstuffworks.com/auto-parts/brakes/brake-types/anti-lock-brake4.htm


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How do the speed sensors work - Step 1ABS speed sensors, mounted in the vehicle's wheel hubs constantly monitor the rotation of each wheel to determine if the ABS needs to override manual braking of the vehicle.The speed sensors calculate

* revolutions of wheels as well as * evaluating the continuity between all wheels.

If any differences are detected in rotation, the ABS is activated to control braking.


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How do the speed sensors work - Step 2Generating the Speed Sensor SignalSpeed sensors are made of:

A magnet wrapped in a coil and A toothed sensor ring mounted around the CV joint hub.

When contact is made between the toothed ring and magnet, an electrical field is given off forming a signal. The signal includes measurements of the number of pulses per second created by the electrical field existing between the magnet coil and sensor ring. After conversion into digital form the signal is transmitted to the ABS controller.


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How do the speed sensors work - Step 3Sending Messages to the ABS ControllerThis signal is passed along to the controller which counts the number of pulses. This is used to determine wheel speed.The ABS uses this data to determine whether it should intercede to control braking

http://sciencealerts.blogspot.com.au/2011/07/how-to-replace-abs-wheel-speed-sensor.html


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ABS or Anti-lock Braking SystemHow does ABS work?

http://www.youtube.com/watch?v=ngKSirE7zJA


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Additional Resources

• http://en.wikipedia.org/wiki/Anti-lock_braking_system

• http://www.tc.gc.ca/eng/roadsafety/tp-tp13082-absind_e-127.htm


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BibliographyCopeland, P. Engineering Studies, The Definitive Guide, Volume 1: The Preliminary Course, 2002, Anno Domini 2000 Pty Ltd

TutorVista.com, Pascal's Law and Hydraulic Brake System, http://www.youtube.com/watch?v=VxLTDtaRCZk, Accessed 18/5/12

KeepVid, http://keepvid.com/?url=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DVxLTDtaRCZk, Accessed 18/5/12

The Free Dictionary by Farlex, http://www.thefreedictionary.com/fluid, Accessed 19/5/12, 2012, Farlex Inc


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Bibliography

Nice K., How Anti-Lock Brakes Work, http://auto.howstuffworks.com/auto-parts/brakes/brake-types/anti-lock-brake.htm, Accessed 20/5/12


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End of Part 1


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6505, assign3, case studies, part 1

Technology

cars http

link http

law http

orgwikibuoyancy http

submerged object

point pressure

pressure acts

open pressure