Exam Flashcards
1
Q
What do level 1 and level 2 responders do
A
Level 1:
- local authorities
- government
- emergency services
Level 2:
- utilities
- transport
- government
2
Q
What are tropical, extra tropical cyclones and local wind systems?
A
- tropical when surface temperature in tropical regions increased due to solar radiation and near surface air is also heated. When sea surfaces exceeds this temp hot air saturated with water rises. As is does it cools and some of the water is carries comes out of the vapour and falls as rain. Large upward moving masses of air are then acted on by the corollas forces caused by the earths rotation
- extra tropical caused by large scale instabilities in the atmosphere at the boundaries between different climate zones. Result in peaks and troughs in atmospheric pressure known as anti-cyclones
- Tornadoes, moist air rises and becomes trapped under a layer of cloud forming a culumus-nimbus cloud. Results in a strong downdraft in the centre of these clouds and the resulting two way flow of air intensifies the rotational flow.
- Or thunderstorms, caused by strong downwards flows
- microburst: caused by strong downwards flows with radial outwards flows
- frontal wind: two winds at different temps meet and wind
3
Q
What is the Monin-Obukov Length?
A
- describes the stability of the atmosphere
- mainly affected by the velocity as the velocity is cubed, at higher wind speeds there is a lower Lmo
- affected by the temperature
- Lower Lmo indicated a less stable atmosphere
- defined as that height at which turbulence is generated more by buoyancy than by wind shear. e.g. from rising thermals from the earth’s surface.
- quantifies atmospheric stability
- very boldly, at any one height, the mean velocity is decreased in unstable in unstable flows and turbulence level increases, and in stable flows the mean velocity is is increased and turbulence decreased
4
Q
What is the Van Der Hoven Spectrum?
A
- Shows the energy within the wind over a wide range of frequencies
- major peaks at 0.01 cycles/hour and 50 cycles per hour
- low frequency/ high period peak indicates the energy in the macro - meteorological winds whilst high frequency / peak show the energy in micro-meteorological winds
- Between two peaks there is a spectral gap where there is little energy at a frequency of 2 cycles/hour or duration. This shows that the macro and micro meteorological winds did not interact and can be considered as independent
- smaller peaks at 0.08 cycles/hour which shows the day/night variations in wind
5
Q
Define:
- Average wind speed
- gust wind speed
- Atmospheric Boundary Layer
A
- Average wind speed: wind speed averaged over 1 hour
- low frequency sine waves represent fluctuations
- gust wind speed: fluctuations around the hourly mean wind speed
- high frequency sine wave represent gusts
-Atmospheric Boundary Layer: typical turbulent boundary layer mean velocity and fluctuations about the mean
6
Q
What does the weibull distribution show?
A
- the probability that the wind speed will be below a value
- at a particular site the frequency of occurrence of the parent wind speed
7
Q
What does the Grumbel Extreme Value Distribution?
A
-the probability of a parent wind speed being exceeded at least once in a particular time period with particular probability
8
Q
What three layers can flow over and within urban creased be divided into?
A
- logarithmic layer are the max and min building heights
- a roughness layer between zero displacement height
- a canopy layer below the displacement height
9
Q
What categorises are micro-meteorological divided into?
A
- the average magnitudes of the fluctuations
- the frequency and duration of the fluctuations
- the maximum values of the fluctuations
10
Q
What is the Von Karman Spectrum?
A
- extensive measurements have shown that a genera; spectrum can be defined that is valid for a wide range of heights, roughness ect.
- L is the turbulence length scale and gives an indication of size of gust
- for low frequency’s denominator = 0
- high frequency x is huge
- for peak frequency dy/dx
11
Q
What do the values of Reynolds value show?
A
- less than 10, dominated by viscous effects and remains attached to the surface of the cylinder
- around 40 the wake becomes unstable and vortices are periodically shed downstream
- around 2000 the boundary layer on the surface of the cylinder undergoes transition from laminar to turbulent
12
Q
What can be said about the flow around a cylinder?
A
- flow around bluff bodies is sensitive to reynolds number
- this sensitivity is due to the nature of the boundary layer on the surface
- laminar boundary layers will separate more easily than turbulent boundary layers
- the variation of the flow pattern is best discussed in terms of dimensionless pressures and forces
- vortex shedding in wakes can produce unsteady flow patterns, which may lead to structural oscillations
13
Q
What are the two types of unsteady forces?
A
- vortex shredding which results in oscillating crosswind forces
- turbulent buffeting which is when flow around buildings is in general turbulent
14
Q
What are large scale predictions of weather systems?
A
- tools used by meteorological organisations to make predictions
- on large scale are global climate models
- used to investigate long term effects of climate change on physical parameters
- locally offer high to reasonable forecasting accuracies over 3 to 5 day period
15
Q
What are the 4 types of structure?
A
- static: do not move significantly in the wind
- mildly dynamic structure: allow for dynamic effects
- dynamic structure : high significant wind induced movements
- aeroelastic structures : exhibit different types of wind induced oscillation
