Educ6505 assignment 3 taverne

EDUC6505 Assignment 3 CASE STUDIES

Anton Taverne

Abstract: Concepts relevant to fluid mechanics are introduced. A range of applications of hydraulics in transport and lifting devices are

examined. Innovations in braking systems and lifting devices are discussed.

The Use of Fluid Mechanics in Braking Systems

Fluid Mechanics - the study of liquids and gases

Fluid statics Fluid dynamics

At restIn motion

Pneumatics Hydraulics

Pressurised air Pressurised liquid

Fluids can be liquids or gasesLiquids take the

shape of the container

Gases fill the container by

diffusion

Liquids - Hard to compress Gases - Easy to compress

Liquids display capillary action and surface tension

Pressure in fluids

In a static fluid (i.e. gas or liquid), the pressure at any point will, as a result of gravity, depend on the depth.

The more fluid there is above a point, the greater the pressure

Fluids exert pressure in all directions, and perpendicular to walls of container.

Pressure = Force / Area

Pascal’s Principle Any change in pressure, from the application of an external force, results in the same change of

pressure anywhere in an enclosed static fluid. This is Pascal’s Principle and is the basis for hydraulics and pneumatics.

In the hydraulic press shown, the input pressure = the output pressure, so F1 / A1 = F2 / A2

This allows a small force (e.g. a foot on a brake pedal) to become a much larger force (e.g. pushing a brake pad against a brake disc)

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

Basic hydraulic systems include :a fluid (such as oil)a reservoira means of increasing the pressure (such as pushing a pedal)a valve to control the direction of flowa method for relieving any excess pressurean actuator (e.g. the pistons pushing against a brake shoe) filters to remove dust or metal particles

A comparison of Hydraulics and PneumaticsHydraulics (liquids) Pneumatics (gas)

All force is directly transferrable. Liquid does not absorb any supplied energy

Gas absorbs excess force, so less damage by shock. Less maintenance.

Capable of much higher loads

Minimum spring action

More immediate response when effort is applied / removed

Need to bleed off excess pressure

Oil used is flammable, but also protects parts

No fire risk

Compressed gas can be stored. No need for electricity

http://en.wikipedia.org/wiki/Pneumatics

Archimedes principleThe buoyant force on a submerged object is equal to the weight of the liquid displaced by the object. A solid object placed on a liquid will push down on it, displacing it.

The displaced liquid is also pulled down by gravity and will, by pushing other liquid particles, apply an upward force on the solid. The denser of the two will apply the greater force.

As a result, a solid object partially or wholly submerged in a liquid will experience an upward force (the buoyant force) that is equal to the weight of the liquid that the object has displaced. If the object floats, its mass will equal the mass of the liquid displaced by it.

Braking systemsOne purpose of any braking system is to prevent something from moving.The second is to reduce a moving object’s kinetic energy (KE = ½ mv2) by reducing its velocity.

The work done in achieving this is given by W=Fd.

A force F needs to be applied over a distance d (the stopping distance of the object).

Often this force is frictional: the kinetic energy is converted to heat by two surfaces rubbing against each other.

Alternatives include

• electromagnetic braking (the production of eddy currents and hence magnetic fields when metal wheels spin

in an applied magnetic field) used in trains

• regenerative braking (using the kinetic energy to produce electricity to charge a battery) used in hybrid cars

• reversing the direction of spin of propellers or using propellers at the front or sides of ships

• firing retro rockets (space crafts)

• extending the wing flaps of aeroplanes.

Braking Systems

As the Kinetic Energy depends on the mass of the vehicle, the braking force for a bicycle will be much less than that of a train or truck moving at the same speed.

Ideally, a braking system will start to respond instantaneously to the driver’s input, reduce the velocity smoothly over a very short distance, and require minimal physical effort from the driver.

A brake can be applied by squeezing hand-grips, pressing pedals or pushing a button.

MechanismsMethods for transferring the force (or signal) from the driver to the braking mechanism include:Mechanical linkagesBowden cables Hydraulic cablesElectrical cables

Brake Types

Air BrakesHeavy vehicles such as trucks and buses typically use air brakes. The high pressures needed to stop such heavy vehicles with hydraulics-based braking can lead to catastrophic leaking.

The slide valve controls which way the pressure is directed.

Safer BrakingABSTo brake effectively, the brake should not lock. If the wheels stop turning while the vehicle is still in motion, the driver loses control over the steering as the tyres glide over the road. Anti-lock Braking Systems adjust the pressure on each brake so that the wheels stop quickly but smoothly. Prior to the introduction of ABS, good drivers knew to “pump the brakes”.

ESPTo calculate how much braking force is needed, a vehicle needs to be equipped with an Electronic Stability Program (ESP). The ESP maintains the stability of the car during braking with the aid of different sensors integrated into a vehicle.An Electronic Stability Program maintains the stability of a car during braking. A range of sensors in the vehicle provide data which is used to adjust the braking effect of each wheel.

Vacuum BoostersBraking can be assisted by making use of the partial vacuum in the exhaust manifold of petrol-driven cars (or a vacuum pump in diesel-driven buses).

When the brake pedal is pressed, air at atmospheric pressure is let into the booster unit by a valve.

http://auto.howstuffworks.com/auto-parts/brakes/brake-types/power-brake2.htm>

INNOVATION

Innovations in brake technology aim to facilitate one or more of the following:

Brake energy recuperationLighter vehiclesEfficient, controlled braking on increasingly crowded roads

One such innovation combines “brake by wire” (using electronic signals) with Electronic Wedge Braking (EWB)

Electronic Wedge Braking

http://www.zigwheels.com/news-features/auto-insight/brakebywire-technology-the-future-of-automobile-braking-system/10519/1>

Every 10 milliseconds a set of sensors measure the speed of the wheel, the forces on the brake and the wedge’s position.

Under software control, the electric motors then adjust the position of the brake pad.

Electric motors (3, 4) move the brake pad (2) using a series of rollers (5) that move along wedge-shaped surfaces (6). This immediately brakes the rotating disk (1).

Electronic Wedge Braking

Pressure from the wedge on the disk applies the brake. The disk’s rotation drags the wedge with it, enhancing the braking, so the EWB needs less energy than hydraulic braking systems. A common drawback of vacuum boosted brakes is the ease with which locking can occur. This locking is considered an advantage in EWBs, as the wedge’s position can be so finely adjusted. The wedge is pulled in just enough to achieve the desired braking. It is prevented from being fully dragged in and locking the wheel.

http://www.zigwheels.com/news-features/auto-insight/brakebywire-technology-the-future-of-automobile-braking-system/10519/1

Advantages over conventional hydraulic braking systems As the activation of the brake is done within the wheel assembly itself, the system is a bolt-on and plug-in assembly without the need for vacuum boosters and brake fluid reservoirs (freeing up space in the engine compartment) or the hydraulic connection between the brake pedal and individual wheel brakes. It allows a quicker response – it can take up to a second for the brake signal to reach a rear trailer in trucks fitted with air brakes. (Aschenbrenner)

Conventional ABS typically take around 150 ms to generate full braking power. The EWB only needs around 100 ms. ( Aschenbrenner) It is “less expensive and more efficient than conventional hydraulic systems.” (Aschenbrenner) It has smaller dimensions and therefore reduces total vehicle weight. The EWB’s software can help bring the vehicle to a smooth halt by reducing the braking force just before it stops, and can prevent the vehicle from reversing while pulling away up a hill.

The concept of using a wedge is not new.

The ability to control its movement to the nearest micrometer (using sophisticated sensors and electric motors precisely controlled by software)

is new.

Fluid mechanics in lifting devices

Usually the task of a lifting device is to raise an object with minimal effort.

This can result from changing the direction of a force e.g. single pulley first-order lever

or by reducing the force needed by applying it through a greater distancee.g. inclined plane

Car jacks and car hoists

They do not allow much working space under the car and are not considered safe for that purpose.

The introduction of hydraulic car hoists, typically electrically operated, provided a more rapid and higher lift of the entire car, and a safer, more comfortable work space for mechanics.

(Oten: Lifting Devices)

(Oten: Lifting Devices)

When a car has a flat tyre, a simple mechanical car jack is used to raise one corner of a car. Although such jacks have a significant mechanical advantage, there is still significant effort involved.

ElevatorsAs buildings have become taller, there has been a greater need for elevators. Hydraulic elevators such as that show diagrammatically have a number of advantages.

(OTEN Lifting Devices p. 46)

There is no need for cables, pulleys or motors above the elevator itself and there is no need for a counterweight.

The telescopic, hydraulically controlled piston takes up little space.

The pumping unit need not be near the shaft.

They are fairly cheap to install and run, but their use is limited to low-rise buildings and relatively slow speeds

Cherry PickersSpecial platforms, lifted hydraulically, provide a safe working space for working with power lines, or changing light bulbs in high places. It reduces the risks associated with setting up and climbing ladders, and, when not in use, take up limited space.

To build modern skyscrapers, building materials need to be lifted high into the air and moved across floors. It would be very difficult to manoeuvre large cranes safely in our crowded cities, so the cranes used for this are built on-site.

Tower Cranes

A Derrick crane sits on top of a tower.As construction of the next building level begins, the derrick crane is lifted on its hydraulic legs, the crane is used to lift materials to build the next layer to support it, and the legs are retracted. The crane’s tower can be strapped to the existing building for safety. On completion of the building, the tower is dismantled in a similar fashion.

Innovation:Problems with the use of tower cranes include the wind affecting the operation of the jib, and torsion forces occurring in the tower. These limit the possible size of the jib.

www.ggcrane.com/press/crane2-spring2010-lo.pdf

Cranes with two jibs were first patented in Gaspard Gillis in 1968, and were redesigned in 2008 by his son, in response to a greater number of large construction projects.

Two-Jib CraneA central tower has two jibs, one on each side. Rotation of the jibs around the tower is achieved with propellers (driven by electric motors) on the ends of the jibs. These propellers also provide braking. The force to turn the jibs is not applied at the tower, and less force is needed, saving energy.

Areas in which the two-jib tower crane represent an improvement on existing cranes include:

Longer jibsHigher rotation speedsBetter braking powerWind has less effectTorsion is minimisedImproved work efficiencyEnergy savings

Computer modelling studies conducted at the University of Alberta indicate the two-jib crane can complete the same task as two separate cranes, but at half the cost.

www.ggcrane.com/press/crane2-spring2010-lo.pdf

Hydraulics in the aeronautical industry

Ailerons trailing edge sections near the ends of the wing that

help control roll (turning about the longitudinal axis).

Elevators hinged sections on the horizontal stabiliser (or tail plane) that can lift or lower the tail, thereby controlling the pitch (turning about the lateral axis).

A rudder the trailing edge section on the fin at the rear of the

plane. It controls yaw, the sideways movement of the tail and nose (turning about the vertical axis).

Flaps trailing edge sections of the wings, closer to the

fuselage. These help control the lift and also help slow down a plane after landing.

The most important use of hydraulics in aircraft is moving the various control surfaces in response to pilot input, to control the plane’s speed, orientation and direction.

Hydraulics in the aeronautical industry

In large commercial jets, flying at speed, the forces required to move these surfaces are enormous.

The hydraulic system’s components must therefore be able to withstand very high pressures.

At the same time they should be light weight (to maximize payload) and very reliable, as failure can be catastrophic. Usually there are redundant systems in case of failure.

The constant vibrations in aircraft can lead to fatigue in materials, which must also be able to withstand harsh operating conditions. Hydraulic systems can also be found in:

the operation of external doors

dropping and raising the landing gear

shock absorbing struts

Part of an aircraft’s hydraulic system

Available from http://www.gen-aircraft-hardware.com/store.asp

Sources and references

Aschenbrenner, N(2005): “Pictures of the Future Fall 2005” retrieved on May 16th, 2012 from http://www.siemens.com/innovation/en/publikationen/publications_pof/pof_fall_2005/auto_electronics/braking_systems.htm

Copeland, P. L. (2005) Engineering Studies: The definitive Guide Volume 2 . (2nd ed.). Helensburgh, NSW: Anno Domini 2000 Pty Ltd

Copeland, P. L. (2000) Engineering Studies: The definitive Guide Volume 1. Helensburgh, NSW: Anno Domini 2000 Pty Lt

Course Notes 2011: “1. Engineering Materials and Applications” EDUC6505 Engineering Education Studies 2 University of Newcastle

Gillis,P, Al-Hussein, M & Hasan, S (2010): “An Innovative Tower Crane: Tower Crane with Two Jibs” CRANE AND HOIST CANADA, Vol 22, SPRING 2010 retrieved retrieved on May 27th, 2012 from www.ggcrane.com/press/crane2-spring2010-lo.pdf

Metcalfe, P. & Metcalfe, R. (2009) Excel Senior High School Engineering Studies. (2nd ed.). Glebe, NSW: Pascal Press

Sources and references

OTEN “Aeronautical Engineering” (2000) Published by Learning Materials Production, Open Training and Education Network – Distance Education, NSW Department of Education and Training, 2000. 51 Wentworth Rd. Strathfield NSW 2135. Retrieved on May 4th , 2012 from http://www.tale.edu.au/tale/components/includes/trap.html?uid=MzA2NkBUYUxFXzIwMDVfREVUTFJNX1Yy

OTEN “Braking Systems” (2000) Published by Learning Materials Production, Open Training and Education Network – Distance Education, NSW Department of Education and Training, 2000. 51 Wentworth Rd. Strathfield NSW 2135. Retrieved on May 4th , 2012 from http://www.tale.edu.au/tale/components/includes/trap.html?uid=MjkzNEBUYUxFXzIwMDVfREVUTFJNX1Yy

OTEN “Lifting Devices” (2000) Published by Learning Materials Production, Open Training and Education Network – Distance Education, NSW Department of Education and Training, 2000. 51 Wentworth Rd. Strathfield NSW 2135. Retrieved on May 4th , 2012 from http://www.tale.edu.au/tale/components/includes/trap.html?uid=MzA1OUBUYUxFXzIwMDVfREVUTFJNX1Yy

OTEN “Personal and PublicTransport” (2000) Published by Learning Materials Production, Open Training and Education Network – Distance Education, NSW Department of Education and Training, 2000. 51 Wentworth Rd. Strathfield NSW 2135. Retrieved on May 4th , 2012 from http://www.tale.edu.au/tale/components/includes/trap.html?uid=Mjk3MEBUYUxFXzIwMDVfREVUTFJNX1Yy

http://hyperphysics.phy-astr.gsu.edu/hbase/pbuoy.html http://en.wikipedia.org/wiki/Pneumatics

Additional images:

Bicycle – brake padshttp://www.google.com.au/imgres?q=images+bicycles&hl=en&sa=X&rls=com.microsoft:en-au:IE-SearchBox&rlz=1I7ADFA_enAU475&biw=892&bih=549&tbm=isch&prmd=imvns&tbnid=LC3teuOR7IvPTM:&imgrefurl=http://www.pedalpushersonline.com/%3FCID%3D753&docid=Z8kM5IVQELf_yM&imgurl=http://www.pedalpushersonline.com/images/bicycles_landing.jpg&w=420&h=296&ei=4nHBT8n-K-miiAfN18ySCg&zoom=1&iact=hc&vpx=577&vpy=242&dur=1313&hovh=188&hovw=268&tx=139&ty=154&sig=107158942787319641740&page=10&tbnh=157&tbnw=223&start=88&ndsp=9&ved=1t:429,r:5,s:88,i:295> Bicycle – disc brakes http://www.tale.edu.au/tale/components/includes/trap.html?uid=Mjk3MEBUYUxFXzIwMDVfREVUTFJNX1Yy Drum brakes - carhttp://www.google.com.au/imgres?q=images+car+brakes&hl=en&rls=com.microsoft:en-au:IE-SearchBox&rlz=1I7ADFA_enAU475&biw=995&bih=549&tbm=isch&tbnid=LkhHuWv1B7MEtM:&imgrefurl=http://www.geddesautomotive.co.nz/brake-repairs-car-van-truck-auckland-01.html&docid=WBVvkEe79XSESM&imgurl=http://www.geddesautomotive.co.nz/Images/brake_lining01.jpg&w=640&h=480&ei=UHPBT97IBMegiQeiqPSNCg&zoom=1&iact=hc&vpx=515&vpy=145&dur=3329&hovh=194&hovw=259&tx=73&ty=216&sig=107158942787319641740&page=2&tbnh=155&tbnw=191&start=18&ndsp=12&ved=1t:429,r:2,s:18,i:114Disc brakes - carhttp://www.google.com.au/imgres?q=images+car+brakes&hl=en&rls=com.microsoft:en-au:IE-SearchBox&rlz=1I7ADFA_enAU475&biw=995&bih=549&tbm=isch&tbnid=29cGvdEXmAKVfM:&imgrefurl=http://hillsidetireauto.blogspot.com/2011/06/your-car-brakes-and-vehicle-braking.html&docid=fO0pViH2yMe9iM&imgurl=http://1.bp.blogspot.com/-sqj4r_VMhFY/TgzhL4bf5JI/AAAAAAAAABg/sYic89u0YIM/s1600/brakes%252B3.gif&w=406&h=336&ei=UHPBT97IBMegiQeiqPSNCg&zoom=1&iact=hc&vpx=107&vpy=109&dur=234&hovh=204&hovw=247&tx=101&ty=83&sig=107158942787319641740&page=2&tbnh=152&tbnw=184&start=18&ndsp=12&ved=1t:429,r:4,s:18,i:119 Hydraulics diagramhttp://www.google.com.au/imgres?q=images+car+brakes&hl=en&rls=com.microsoft:en-au:IE-SearchBox&rlz=1I7ADFA_enAU475&biw=995&bih=549&tbm=isch&tbnid=BWFhi6090E0YmM:&imgrefurl=http://www.carbibles.com/brake_bible.html&docid=XI9qN2rOfYwg-M&imgurl=http://www.carbibles.com/images/singlecircuitactuator.gif&w=466&h=300&ei=UHPBT97IBMegiQeiqPSNCg&zoom=1&iact=hc&vpx=277&vpy=148&dur=28703&hovh=180&hovw=280&tx=147&ty=123&sig=107158942787319641740&page=3&tbnh=138&tbnw=215&start=30&ndsp=12&ved=1t:429,r:9,s:30,i:158 Air-brake schematichttp://www.google.com.au/imgres?q=images+air+brakes&hl=en&rls=com.microsoft:en-au:IE-SearchBox&rlz=1I7ADFA_enAU475&biw=1028&bih=502&tbm=isch&tbnid=mvgtmircrE0w8M:&imgrefurl=http://www.railway-technical.com/air-brakes.shtml&docid=lWuvZJqPqnQL9M&imgurl=http://www.railway-technical.com/airbra-app.gif&w=714&h=418&ei=2HTBT8rACamSiQemzf3ACg&zoom=1&iact=hc&vpx=265&vpy=195&dur=9672&hovh=172&hovw=294&tx=170&ty=99&sig=107158942787319641740&page=2&tbnh=117&tbnw=199&start=9&ndsp=13&ved=1t:429,r:5,s:9,i:102Servo brakeshttp://auto.howstuffworks.com/auto-parts/brakes/brake-types/power-brake2.htm Hydraulic aircraft componenthttp://www.gen-aircraft-hardware.com/store.asp