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Engineering Education Studies 1

DATESTAMPHERE

Insert

this

way

Donald

E D U C 6 5 0 5

HEATHER

Intro to UniversityA B C D 1 2 3 4

D. HEATHER - C2008809

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PRINCIPLES OF FLUID MECHANICS

ARCHIMEDES PRINCIPLE

Archimedes principle explains buoyancy. If an object is placed in water and “weighted” it will register a

smaller value than if weighted in air. (Copeland, 2005) The upward force of the water partially balances

the weight force. The force exerted by the water on the object is the buoyancy force, and is dependent

on the density of the fluid and the volume of the submerged object. The buoyancy force is equal in value

to the weight of displaced fluid by the object.

Archimedes principle is used to calculate the specific gravity of objects.

The formula: Specific Gravity: weight of object in air_______________________________ Weight loss when submerged in water

PASCAL’S PRINCIPLE

Pressure at the bottom of a container is greater than the top, and is independent of the shape of the

container. Pressure is also the same at all points at the same depth. Increasing pressure at the surface

with a piston, forcing it into the liquid will increase the pressure throughout the liquid.

This situation is known as Pascal’s principle and is stated as follows: Pressure applied to an enclosed liquid

is transmitted undiminished to every point in

the fluid and to all the walls of the container.

(Copeland, 2005)

An example of Pascal’s principle

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HISTORY OF BRAKES

The early braking systems were used to stop vehicles with steel rimmed wheels. A curved block made out

of wood was manipulated against the wheel by leverage systems. The brake shoe was the normal way of

braking in a steam locomotive or a horse drawn vehicle.

External spoon brake

In 1895 the Michelin brothers replaced the steel rim with pneumatic rubber tyres. A new method was to

apply the force to the axle or to a drum on the axle. This was operated by the driver depressing a pedal.

The band and the drum had to be continuously replaced due to poor friction quality which led to a

replacement friction material. Herbert Frood processed an asbestos fabric in 1908 which was used as a

replacement.

The next development in 1902 was drum brakes by Louis Renault who designed an internal expanding

brake shoe. This design principle remained for the next 50 years.

Cams were used to force the shoes onto the drum with one having a pivot pin at the bottom to increase

the servo-assistance of the brakes. Equalising the brake pressure on both wheels was a problem

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Left, a leading/trailing shoe hydraulic brake; right the twin wheel cylinders create two leading

shoes for the use on front brakes

This was solved by the introduction of the hydraulic system, using fluid to transfer the force applied to the

brake pedal. One of the biggest developments of recent years has been the development of braking

systems that inhibit the tendance of a car to skid under braking. (Copeland, 2005)

The Anti-lock braking system works by using a sensor that detects the wheel when it begins to lock up, it

then releases the hydraulic pressure at the brake calliper to allow the wheel to spin again. The brake can

be reapplied and if the wheel locks again the process will be repeated.

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Anti –lock braking systems

PUBLIC TRANSPORT BRAKES

The rocket train design expanded rail transport as it offered speedier transport. Mechanical brakes were

difficult to use, in 1869 George Westinghouse developed an air brake that was held off by air pressure.

When air pressure was lost the brakes were applied which made it safer if the train lost air pressure.

Electric trains have an advantage as they can have regenerative braking systems. The application of the

brakes on a train results in the electric motor switching to an electric generator which generates

electricity to power other items in the train such as lights or air-conditioning.

REGENERATIVE BRAKING SYSTEM

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When disc brakes are applied the energy is wasted. Physics tells us that energy cannot be destroyed, it

has to go somewhere with most dissipating as heat and is wasted. The braking systems on cars waste

energy and the driver can do nothing to stop this. Regenerative braking systems can recapture much of

the cars kinetic energy and convert it into electricity. These brakes are primarily found in hybrid vehicles.

Hybrid vehicles place a high degree of importance being able to keep the battery charged. Regenerative

brakes utilise the system that drives the vehicle to do the majority of the braking. When the brakes are

applied in an electric or hybrid vehicle the vehicles electric motor goes into reverse mode, causing it to

run backwards thus slowing the cars wheels. When the motor runs backwards it acts as an electric

generator, producing electricity that can be transferred to the vehicles batteries. This is best utilised in

city or stop start traffic when the brakes are used constantly. The vehicles momentum is used to get the

motor to run backwards as the mechanical energy puts the motor in reverse. Momentum is the property

that keeps the vehicle moving once it is up to speed. When the motor is reversed the electricity

generated by the motor is fed back into the batteries where it can be used to accelerate the vehicle again.

Electronic control in a regenerative braking system allows the driver to select certain presets that

determine how the vehicle will apply the brakes and when. Regenerative brake controllers are electronic

devices that control brakes remotely, deciding when the braking starts, ends and how quickly the brakes

need to be applied.

The brake controller may decide if motor capability is capable of handling the force necessary to stop the

car. If it is not capable it will turn the braking to the friction brakes averting a catastrophe.

The efficiency of regenerative braking system is the reason it has been developed. Conventional cars

efficiency is 20%, with the remaining 80% of its energy being converted to heat through friction.

Regenerative braking could capture as much as half that wasted energy and put it back to work.

http://auto.howstuffworks.com/auto-parts/brakes/brake-types/regenerative-braking7.htm

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Regenerative braking system

IMPACT OF HYDRAULIC LIFTING DEVICES

Hydraulic systems have the following advantages over power systems.

• Equal forces are applied to each output cylinder

• Higher efficiency than other systems

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• Less maintenance and more reliability

• Low inertia of moving parts allows hydraulic systems to start and stop quickly. (Rochford, 2011)

Hydraulic lifting devices contribute to safety in the workforce by reducing the human effort required to

raise materials or supply a safe working platform. Hydraulic lifting devices greatly reduce the chance of

back injuries in construction workers.

Hydraulic elevators are used in low-rise building up to 5 storeys. The elevator is pushed up the shaft by

hydraulically controlled pistons or a telescopic piston to save space. The advantage of this system is it

does not need overhead mounted equipment to lift the elevator. The pump can be located away from

the shaft and installation and running costs are less than an electric elevator.

Specialised work platforms that are hydraulically operated can lift workers up to heights quickly with

minimum effort. They allow workers to move freely and work safely while high off the ground.

Components of a hydraulic elevator

RECENT INNOVATIONS

Hydraulic Jack

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The hydraulic jack forces compressible fluid into a cylinder by a plunger. Oil is used because it is a stable

fluid and is self- lubricating which minimises maintenance.

A Scottish machinist named Richard Dudjeon invented the hydraulic jack. Hydraulic cylinders have not

changed much over the years. The tolerances of the parts are tighter and the jack is still the hard working

push-pull tools they have always been.

Hydraulic jacks are easy to use, portable and lift loads from 1.5 to 3 tonnes. Hydraulic jacks have different

functions. Floor jacks are used to lift loads from the floor and in small areas bottle jacks are used. Ram

jacks have long arms and are used in the construction industry.

Jacks are utilised to make lifting and high pressure moving easy for industries. Hydraulic jacks are used by

service stations, storage establishments, automotive industries for a range of high pressure and heavy

duty lifting procedures.

The significance of jacks is that they make lifting and moving items or equipment easy for industries. The

hydraulic jack is easy to use and the process is accomplished quickly.

Bottle Jack

AERO INDUSTRY

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Hydraulic systems in aircraft have multiple uses depending on the aircraft. Hydraulics is used to operate

wheel brakes, landing gear and some constant speed propellers in small aircraft. Larger planes utilise

hydraulics for flight control surfaces, spoilers, wing flaps and other systems.

The hydraulic system compromises a reservoir, pump, filter, selector valve to control the direction of the

flow, relief valve and an actuator.

The fluid is pumped to an actuator. An actuator is a cylinder with a piston inside that converts fluid power

into work which creates the power needed to move an aircraft system. Cylinders can be single or double

acting depending on the systems requirements. A selector valve allows the control of the fluid direction.

This system operates the extension and retraction of the landing gear during which the fluid needs to

work in different directions. If the pressure within the system is excessive the relief valve provides an

outlet to reduce fluid pressure.

The hydraulic fluid most widely used for aircraft has a mineral base. This fluid, a kerosene-like petroleum

product has good lubricating properties. The fluid has additives to inhibit foaming and prevents the

formation of corrosion. The fluid is chemically stable and changes viscosity very little with temperature

and is dyed for identification.

Aircraft landing gear.

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An example of a double acting

cylinder

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The gland is screwed into one end of the cylinder and the rod passes through it, a pressure seal and wiper

seal are fitted to the gland to resist oil pressure and clean rod when it is moving in and out of the cylinder.

Bibliography

Copeland.P.L. (2005). Engineering studies The Definitive Guide V2.Helensburg N.S.W. Anno Domini

2000PtyLty.

Rochford. J. (2011). Stage 6 Engineering Studies. [ed 2011]. Tumbi Umbi; KJS Publications.

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