Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

IB Engineering > 2P8 Mechanical Engineering > Flashcards

2P8 Mechanical Engineering Flashcards

(66 cards)

Start Studying
1
Q

What are the rules of thumb for placement of wind turbines?

A

Top of smooth hill, good

At least 10H from obstacles, H is height of tower

Don’t put near sharp cliffs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How does pressure vary along the axis of a wind turbine?

A

Free stream, pa, increases to p just befiore rotor then p-Δp just after the wind turbine, then returns to pa father away.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Define axial induction factor?

A

u = (1-a)V0

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the three steps to deriving Betz limit in broad terms?

A

Use bernoulli to find Δp

Use SFME to find N (reaction force in wind)

Write power as a function of a, V0, ρ, A

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the two equations for thrust of a wind turbine?

A

N=ΔpA

Ν = mdot (V0-u1)

Use this to find u1 = (1-2a)V0

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Equation for power?

A

P=Nu

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the coefficient of power?

A

power from wind turbine/ max available power from the wind.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Key values of a, axial induction factor?

A

a>0.5 is impossible (flow completely stops)
a = 1/3 leads to maximum power
a=1/2 leads to maximum force

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Define capacity factor.

A

The total energy generated in a year compared to the max possible if the installation if it was to run at full output all year

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What does the graph of CL and Cd against angle of attack look like?

A

Drag remains constant at around 0.02, lift increases linearly until stall.

At stall, drag increases significantly

keep α<15 to avoid stall

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Where do lift and drag point?

A

Lift - perpendicular to the oncoming wind direction

Drag - parallel to the oncoming wind direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is θ in BEM?

A

Angle of blade twist relative to the tangential velocity direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the components of the velocity relative to an aerofoil section of the blade?

A

Tangential component is ωr(1+a’) where a’ is the angular induction factor.

In the axial direction the velocity is V0(1-a)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How do you find φ, the relative wind direction?

A

tan φ = V0(1-a)/ωr(1+a’)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How do you find the angle of attack?

A

α = φ-θ

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Eq for normal and tangential component of Force on blade?

A

FN = FL cos φ + FD sin φ
FT = FL sin φ - FD cos φ

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How do you find axial and angular momentum change in annular control volume?

A

Use an annular control volume, and look at the rate of change of momentum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How do you find flapwise or tangential bending moment at root of blade?

A

Integrating FN (r-rmin)dr
Integrating FT(r-rmin)dr

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How do you find deflection of a blade?

A

Split inot elements, determine bending stiffness for each element, bending moment, rotation and delta

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How does aerodynamic loading intensity scale?

A

FN scales as 1

total load scales as 2

root bending moment scales as 3 integral (Fn r dr)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What becomes critical with bigger size?

A

Self-weight
Tip deflection

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

How to find material indicies?

A

eliminating free variable and finding equation for mass or cost…

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Advantages of composites?

A

High specific stiffness and strength

Complex shapes are possible

Corrosion resistance

Smooth surface

Low maintenance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

How can you optimise blade design?

A

Align fibres with loading direcion, using multidirectional laminates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
What is wet hand lay-up?
Layup on mould, dry or pre-preg material vacuum bag to consolidate Curing - room temp with heaters
26
What is resin transfer moulding?
Closed mould process Charge mould with dry fabric Inject thermoset resin at relatively low pressure
27
How does vacuum injectino moulding work?
Open or closed mould Use vacuum bag with open mould vacuum forces resin through reinforcement.,
28
What is a carpet plot?
Balance of 0o, 90o, 45o fibres.
29
What rules are used for fatigue failure?
S-N curve, N = (S/S0)^-M Miner's Rule sum (Ni/Nfi) = 1 Goodman's rule Δσ = Δσ0 ( 1- σm/σts)
30
How to do rainfall plots?
Rainflow intiates at each peak and trough and drops down, flow stops if the opposite trough is more negative than at the start of the path under consideration If rain intercepts a previous path, the present path is stopped Half cycles of loading are projected distances onto stress axis.
31
What tip speed ratio is typical?
λ=8
32
What are three types of gears?
Spur - simplest Helical - gradual contact, less noise, but axial thrust Herringbone - no axial thrust
33
What are three gear arrangements?
Parallel shaft spur gears Bevel gears worm gears
34
Why do we like epicyclic gearbox?
Load shearing => compact
35
How does angular speed relate to tooth number?
ωΑ/ωB = NB/NA
36
Why is planetary gear good?
Load sharing, hence compact Hard to dissipate heat, noisy, hard to achieve theoretically load sharing
37
How does radii relate to tooth numbers?
radii proportional to tooth numbers
38
What is the input and output of planetary gearbox?
Sun is output, carrier is input, ring is held to get speed increase.
39
Define module.
m = d/N d= 2r (pitch circle diameter.
40
what is pitch?
Tooth spacing around the pitch circle πd/N = πm
41
What is Contact stress?
Where gears meet, elasticity calculation, depends on tooth shape. Independent of module for gear size.
42
What's the cantilever model of teeth?
2m high, 2.4m wide, force F at the top.
43
How to reduce noise?
prime number of teeth, to avoid common factors Use helical gears.
44
What are the key frequencies of vibration for wind turbines?
1P is rotational frequency, 3P is blade passing ferquency. Also consider key harmonics.
45
Sources of non-steady loading on a wind turbine?
Unsteady flow (turbluence), varying wind load at different heights. Wind shear - 1P loading on blades (3P ont ower) Out of balance in mass (1P on tower) Self weight (1P on blade) Tower shadow (1P on blade, 3P on tower + harmonics) Aeroelastic and flutter effects Vortex shedding
46
How can you derive equation of motion of cantilevered beam?
Consider D'alambert acceleration mdx d^2y/dt^2 Leads to wave equation d^2M/dx^2 = -m d^2y/dt^2 = EI d^4y/dx^4 which has analytical solution/
47
What are the mode frequencies of the cantilever proportaionl to?
(EI/mL^4) ^0.5 When substituted in with eq for tower, it is independent of the thickness of the tower.
48
What's the equivalent mass for a cantilever?
α=0.24
49
What is the torsional spring constant?
EI/l
50
Torsional model of blade vibration?
Blades as rigid with bending stiffness k, and tip accelerations and angular acceleration.
51
What's power, wind speed charactersitic of a typical wind turbine?
Low speed cut in speed, below which it is not connected to grid (as losses would likely exceed generation) Medium speed --> increasing power extraction, maintained at optimum tip speed ratio, facing into the wind. Higher speed -> produces at rated power (even though more could be extracted), will not operate at optimum tip speed ratio, furling blades, to make it less efficient. Very high speed -> storm conditions with gusts expected. Damag likely due to instability, therefore turbine is stalled. (passive stall is where the force is zero above a certain wind pspeed). Active stall - blades are furled and then yaw is used to twist nacelle out the wind .
52
What are limiting factors for generators?
Flux density is limited by saturation of iron magnetic circuit, 0.4-0.8T Max current before overheating due to resistance of windings. Leads to VA rating, which is proportional to volume of generator and angular speed. Faster is smaller
53
How can you have a direct drive turbine, and why would it be implemented?
Leads to much greater reliability, Can have 100 poles, salient pole generator.
54
What is a typically compromise between high pole numbers and low gearing ratio?
Have a 8 pole generator with 50:1 gearing (2 or 3 stage gearbox)
55
Why is fixed speed wind power bad (when using a synchronous generator)?
Peremnenatn magent exciter, allows for reliable operation, but doesn't make good use of power avaialebl.
56
How can vaiable speed wind power be achieved?
Synchronous generators with power electronic convertor. Variable speed can be used without need for a gearbox. But extra cost of power electronics. OFten use permanent magnet synchronous generators. ( no slip rings needed - which are maintenance problem). HV DC is often used for far offshore, so it doesn't matter the frequency. Induction motors can operate at variable speeds but only over a limited range. Using power electronics this can be expanded. Slip energy recovery system.
57
Whats the effect of increasing rotor resistance?
flattens out the torque speed curve, increasing speed of peak torque generator Vary by around 10% But this leads to extra power losses in the roto resistance.
58
What is slip energy recovery?
Instead of the rotor resistance just dissipating power, use its power to feed into the grid, but its frequency is at 50Hz * s, so need power electronic
59
What does it mean for development to be sustainable?
Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.
60
What is the methodology for analysising the sustainability of a project?
1. Define objectives, scales and metrics 2. Stakeholder analysis 3. Fact-finding 4. Synthesis 5. Reflection
61
What are some objectives for wind turbines>
Decarbonize electricity supply, increase energy security Metrics, materials supply, energy and cost payback, emissions and land use
62
What is a stakeholder plot?
Influence against interest.
63
Who are stakeholders in wind turbine development?
Energy providers Turbine makers Green activisits Government Public Local Communities
64
What areas does fact finding need?
Materials, environment, society, economics, legislation, energy
65
What is a critical material?
A material which access could be limited due to geopolitics, but essential for security/economy.
66
How do emissions per kWhr compare to gas and coal?
10x better than gas 30x better than coal

IB Engineering (9 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions