An Introduction to
Mechanical Engineering
Dr. Drew Landman
Professor and Associate Chair
Department of Mechanical
and
Aerospace Engineering
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Classical definition: An engineering discipline that encompasses the generation and
application of heat and mechanical power and the design, production, and use of
machines.
A machine is an apparatus using or applying mechanical power and having several
parts, each with a definite function and together performing a particular task.
Pumps, compressors, internal combustion engines, wind turbines
Piping systems and pressure vessels, reactors, heat exchangers
Consumer goods and products: everything from coffee grinders to toothbrushes
Material handling equipment - conveyers, robots, production assembly lines
Vehicles - cars, trucks, heavy equipment, buses, aircraft, ships
Power generation equipment: wind power, hydroelectric, nuclear, geothermal
What is Mechanical Engineering ?
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We have discussed classical mechanical
engineering applications but will now look at
some new topics
In engineering, boundaries between
mechanical, electrical, and software engineers
are increasingly blurry
As a new mechanical engineer you will need
some knowledge in other fields
Mechanical engineering now has undergraduate
courses called Electro-Mechanical Systems or
Mechatronics
As modern engineering becomes more precise
both with measurements and computer
simulations, understanding the error
associated with solutions has become a focus
An undergraduate course of study should
include Probability and Statistics
The Modern Era and Mechanical Engineering
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Product Design:
Designing products ranging from knee replacements to internal
combustion engines to self driving cars, aircraft, bicycles, robots,
drones and appliances
Research and Development:
Researching new ideas and solutions that satisfy society’s demands or
improving or expanding older ideas and solutions
Manufacturing:
Designing and building the machines and processes used for mass
production of consumer products
Systems Management:
Managing the operations of a large system, such as a manufacturing
facility or a power plant
Energy
Planning how energy is created, stored and moved in industries that
produce and deliver electrical power, such as natural gas, oil and
alternative energy
Typical Jobs of A Mechanical Engineer
Wind Power Example
In the next slides we will examine the role mechanical engineers
play in the design, manufacture and management of systems for
energy generation using wind
Tex t in BOLD identifies relevant coursework from the
undergraduate curriculum
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A wind turbine extracts energy from the movement of air in the atmosphere
Here is the basic concept of operation:
Mechanical Engineering of the Wind Turbine
Turbine
Blades
Generator
Transformer
Distribution
Home &
Business
Wind Turbine
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At a given location, wind velocity
over the earth increases with
height near the surface
The change in velocity is due to
skin friction from the air being in
contact with the surface of the
earth
At the ground, the wind velocity is
zero
This layer where velocity changes
is called the boundary layer and
you will learn about it in Fluid
Mechanics
This is the reason wind turbines
are mounted high above the earth
They generate more electricity in
higher winds
Wind Turbine Aerodynamics
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The rotor blades spin a main shaft at low speed that is supported by bearings
The low-speed shaft drives gears in a gear box which in turn drives the
generator; all have bearings
The blades can be rotated on their
axes to adjust pitch and are supported
by their own bearings
The whole assembly can be turned
into the wind via the yaw bearing
All of these devices have
to be analyzed and designed
to withstand the given loads
over a long lifetime
The design of these
components requires
courses like Dynamics,
Mechanics of Materials,
and Mechanical Design
Wind Turbine Machine Element Design
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To understand the loads on the structure we first need predictions for the forces
generated by the airflow over the blades
The wind and blade rotation cause forces of Lift and Drag which you can learn
about in Fluid Mechanics and Aerodynamics coursework
Blade Aerodynamics
A Section of a Blade
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If we know what loads are applied to the blade we can now investigate which
materials are best to resist the loads
Coursework in Materials Science and Mechanics of Materials will help us here
Computer knowledge is essential in modern design; here is an image from a blade
that was designed using a Computer Aided Drafting program then analyzed using
a Finite Element Method, both courses in the undergraduate curriculum at ODU
The image shows the deflection of the blade under wind loads
Blade Structure
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Now that the blade is designed, its time to
manufacture it
The mechanical engineer will design a blade mold
that serves as the outer form
Layers of composite fabric and resin will make up the
structure and be laid into the mold to cure
Expertise here comes from knowledge of Composite
Materials
Composite Blade Manufacturing
Nuclear Power Example
In the next slides we will examine the role mechanical engineers
play in the design, and management of systems for energy
generation using nuclear power
Tex t in BOLD identifies relevant coursework from the
undergraduate curriculum
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The basic operation of a nuclear power plant involves many systems
designed by mechanical engineers
Here is how it works:
An atomic fission reactor heats water
Steam is generated and flows to a turbine
The turbine drives a generator
Steam condenses to water
after passing through
the turbine
Water is returned to a steam
generator by pumps
for reheating
Nuclear Power Plant
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The theory behind the thermal cycle water undergoes is a topic in two
courses in Thermodynamics
The course Heat Transfer discusses the design of
heat exchangers such as the one
used to transfer heat from high
pressure water lines to steam in
the steam generator vessel
Fluid Mechanics will cover
the sizing of pumps
The pump shown at the right
features staged impellers to
increase pressure
Nuclear Power Plant
Propeller Performance
Measurement Example
In the next slides we will examine the role mechanical engineers
play in the design, manufacture and use of instruments for
aerodynamic measurements on propellers
Tex t in BOLD identifies relevant coursework from the
undergraduate curriculum
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An example that illustrates the multi-dimensional nature of modern mechanical
engineering. Several years ago ODU developed a measurement capability to
determine propeller performance
for the NASA unmanned aerial
vehicle called the
Greased Lightning
This aircraft features a
tilting wing and tail to
allow vertical takeoff
and landing (VTOL)
It uses 10 electric motors
and propellers for VTOL
For forward flight, it uses
as few as two motors on
the wing tips for
maximum efficiency
Aircraft Propeller Performance
Forward Flight
Takeoff &
Landing
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To understand propeller
performance we need to
measure:
The force of thrust and torque
The rotation rate of the prop
(revolutions per second)
The airspeed of the airplane
We do this in a wind tunnel – a
closed duct with known wind
speed
Propeller Performance
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Here is a CAD model of the test stand designed at
ODU with student engineering help
Relevant courses: CAD, Mechanics of Materials, Electromechanical Systems
The Propeller Test Stand
Thrust and Torque
Measurement
Load Cell
Composite Shield
(keeps wind out)
Copper Springs
Bulkhead
Support Strut
(streamlined)
Bulkhead
Motor
Bulkhead
(thermal
isolation
of motor)
Propeller
Shaft
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The load cell is an electro-mechanical sensor – a transducer
Loads (Thrust and Torque) are sensed by small beams that deflect
Relevant courses here are Mechanics of Materials and Finite Element Methods
The Thrust-Torque Load Cell Design
Beam sensitive to Thrust
Beams sensitive to Torque
Deflection is Exaggerated
Beams sensitive to Torque
Beam sensitive to Thrust
Computer model - torque and thrust load
Picture of finished transducer
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How do we design an instrument to measure force and torque ?
One popular method is to use strain gages with mechanical elements like beams
A strain gage is a piece of thin film with a very
thin wire arranged in a long serpentine shape called a grid
The strain gage is bonded to a metal surface
As the metal is under load, the gage wire length changes and so does the resistance
Relevant courses here are Mechanics of Materials, Electromechanical Systems
Instrumentation Design: Electro-Mechanical Devices
Strain Gage
Electrical
Connection
Wire Grid
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Glue the strain gage to the beams that bend most with applied Thrust and Torque
Connect them to a special circuit and now: Thrust is proportional to Voltage
Instrumentation Design: Electro-Mechanical Devices
Connection
Wire Grid
Voltage to Computer
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To record the propeller torque and thrust, we use a computer
Voltages are digitized in an Analog to Digital converter
A program is written to display and file all the quantities measured
Using the Computer
Thrust and Torque
Displayed
Propeller Rotational Speed
Control for Propeller Speed
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Here is a plot showing thrust of a propeller from data recorded in the wind tunnel
We build a mathematical model that fits the data and graph the curve
We use statistics to compute error or uncertainty in our results – helps us compare
Here the blue line is the first trial, orange the second
The dashed lines indicate the uncertainty – Trials 1 & 2 are identical from a statistical test
Reporting Results
Thrust
Relative Air Velocity
0
0
Increasing
Increasing
Uncertainty
For Second
Trial
Relevant Courses:
Flight Vehicle Aerodynamics
Propulsion
Probability and Statistics
First Trial
Second Trial
Expectations
2019 ODU SAE Aero Design Team
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National average salary in the USA for a new graduate of Mechanical Engineering
New Mechanical Engineering Graduate Salaries
Source: Ziprecruiter.com
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Average Mechanical Engineering Salaries in USA
Source: US Bureau of Labor Statistics
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Mechanical Engineering Employment in the USA
Source: US Bureau of Labor Statistics
