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# 6505, assign3, case studies, part 1

## on May 27, 2012

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How hydraulics is used with Elevators

How hydraulics is used with Elevators

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## 6505, assign3, case studies, part 1Document Transcript

• Fluid Mechanics and Braking Systems 27/5/12 Fluid Mechanics in Braking Systems Case studies, Part 1 A version of PDF version of this presentation is available at SlideShare http://www.slideshare.net 1
• Fluid Mechanics and Braking Systems 27/5/12 Definition of a fluid 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 Properties of fluids • Unable to support shear stresses • Take on the shape of the container 2
• Fluid Mechanics and Braking Systems 27/5/12 Principles of Fluid Mechanics • Hydrostatic pressure • Pressure Principle • Archimedes Principles 3
• Fluid Mechanics and Braking Systems 27/5/12 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) 4
• Fluid Mechanics and Braking Systems 27/5/12 Hydrostatic Pressure and Depth Rule: The deeper an object is submerged, the greater the hydrostatic pressure Hydrostatic Pressure Depth Relationship Given the pressure at the surface, Po (in Pa), the pressure (in Pa) at depth, h ( in m) is: P = Po + ρgh where -3 ρ = density of the fluid (a constant - kgm ) -2 g = acceleration due to gravity (ms ) 5
• Fluid Mechanics and Braking Systems 27/5/12 Additional References http://celebrate.digitalbrain.com/celebrate/accounts/tak acs/web/Hydrostatica/membr/ • http://www.youtube.com/watch?v=GdAuzpYLOsc 6
• Fluid Mechanics and Braking Systems 27/5/12 Pascals 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 7
• Fluid Mechanics and Braking Systems 27/5/12 Pascals Principle 8
• Fluid Mechanics and Braking Systems 27/5/12 Additional References • http://hyperphysics.phy-astr.gsu.edu/hbase/pasc.html • http://en.wikipedia.org/wiki/Pascals_law • http://www.grc.nasa.gov/WWW/k- 12/WindTunnel/Activities/Pascals_principle.html 9
• Fluid Mechanics and Braking Systems 27/5/12 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 10
• Fluid Mechanics and Braking Systems 27/5/12 As Archimedes put it .... A body wholly or partially submerged in a fluid is buoyed up This is independent of the by a force equal to the weight of composition or shape of the the fluid displaced by the body object 11
• Fluid Mechanics and Braking Systems 27/5/12 Specific Gravity Using Archimedes Principle, an objects specific gravity can be calculated Specific Gravity = Weight of object in air Weight of object when submerged in water 12
• Fluid Mechanics and Braking Systems 27/5/12 Additional References • http://en.wikipedia.org/wiki/Buoyancy • http://library.thinkquest.org/27948/archimede.html 13
• Fluid Mechanics and Braking Systems 27/5/12 Use of Hydraulic Principles in Braking Systems To find out about: • the basic principles of a braking system, use the link http://auto.howstuffworks.com/auto-parts/brakes/brake-types/brake.htm • Drum brakes in cars, use the link http://auto.howstuffworks.com/auto-parts/brakes/brake-types/drum-brake.htm • Disk brakes in cars, use the link http://auto.howstuffworks.com/auto-parts/brakes/brake-types/disc-brake.htm 14
• Fluid Mechanics and Braking Systems 27/5/12 How hydraulic disk brakes work in cars http://www.youtube.com/watch?v=LYetGatzWjM 15
• Fluid Mechanics and Braking Systems 27/5/12 How hydraulic drum brakes work http://www.youtube.com/watch?v=LX4mqzoe3BY 16
• Fluid Mechanics and Braking Systems 27/5/12 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 17
• Fluid Mechanics and Braking Systems 27/5/12 http://www.railway-technical.com/airbra-app.gif 18
• Fluid Mechanics and Braking Systems 27/5/12 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 19
• Fluid Mechanics and Braking Systems 27/5/12 ABS or Anti-lock Braking System Components 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 brake 2. Closed - The brake line is closed off from the master cylinder. Prevents increase in brake pressure if the brake is pressed harder 3. 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 20
• Fluid Mechanics and Braking Systems 27/5/12 http://auto.howstuffworks.com/auto- parts/brakes/brake-types/anti-lock- brake4.htm 21
• Fluid Mechanics and Braking Systems 27/5/12 How do the speed sensors work - Step 1 ABS speed sensors, mounted in the vehicles 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. 22
• Fluid Mechanics and Braking Systems 27/5/12 How do the speed sensors work - Step 2 Generating the Speed Sensor Signal Speed 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. 23
• Fluid Mechanics and Braking Systems 27/5/12 How do the speed sensors work - Step 3 Sending Messages to the ABS Controller This 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 24
• Fluid Mechanics and Braking Systems 27/5/12 ABS or Anti-lock Braking System How does ABS work? http://www.youtube.com/watch?v=ngKSirE7zJA 25
• Fluid Mechanics and Braking Systems 27/5/12 Additional Resources • http://en.wikipedia.org/wiki/Anti-lock_braking_system • http://www.tc.gc.ca/eng/roadsafety/tp-tp13082-absind_e-127.htm 26
• Fluid Mechanics and Braking Systems 27/5/12 Bibliography Copeland, P. Engineering Studies, The Definitive Guide, Volume 1: The Preliminary Course, 2002, Anno Domini 2000 Pty Ltd TutorVista.com, Pascals 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 27
• Fluid Mechanics and Braking Systems 27/5/12 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 28
• Fluid Mechanics and Braking Systems 27/5/12 End of Part 1 29
• Fluid Mechanics and Braking Systems 27/5/12 30