Final Flashcards
why did the airport in China collapse?
because of strong winds
Describe a direct and indirect impact of wind
Direct: strong wind blowing roof off a building
Indirect: strong wind creating larger shore waves that contribute to coastal erosion.
How is water able to destroy culverts and highways?
Once soil has reached saturation, it becomes surface runoff, at 1kg per L, it can become a heavy force of potential and kinetic energy acting on a surface.
what is a load?
a load is a force: can have wind loading, rain loading, snow loading…
Why is it a good idea to open your windows when there is a tornado?
Depending on where the wind load is acting on the building, low pressure from tornados cause either a positive or negative pressure inside the home causing the walls to collapse.
what is the relationship between wind speed and pressure?
exponential
How does wind positively pressurize a structure?
Wind blowing against an opening in a structure creates a positive internal pressure and wind blowing against an opposite wall to an opening creates negative internal pressure and suction through the opening.
where is pressure strongest on a wind bearing structure?
at its corners (airfoil effect)
what do irregularities in a structure cause when it comes to wind?
local eddies. this means rocks on roof can be displaced. Flow around building accelerates around edges, can pull off roofing material, gutters.
types of wind + building interactions:
- Exposure (wind pushing on wall)
- Internal Pressurization (seen with tornado)
- Aerodynamic Pressure (air foil example)
- Topography
- building height
types of winds
- straight line wind
- downslope wind
- thunderstorm
- downburst
straight line wind reoccurrence interval
Design for the 50 year recurrence interval
100 year recurrence for larger buildings
static vs dynamic loading
static: structure supporting its own weight
dynamic: for supporting additional weight (patrons)
role of climate change in the relationship between wind and engineering
Shifts baseline frequencies and probabilities.
More thunderstorms
More ice storms in eastern states
name the 5 weather parameters that impact wildfire
- wind speed and direction
- humidity
- precipitation
- temperature
- pressure
how does wind speed + direction impact wildfire
○ Enhances spread: spotting via carrying embers to other parts of the
forest
○ More oxygen as fuel for the fire
○ Can dry out an area to enhance its burning effect
○ Direction of wind can determine fate of the fire (if it pushes it to a lake
it’ll be terminal vs into more wooded area)
how does humidity impact forest fires?
○ Relative is compared to amount air needs to saturate
○ Absolute is the actual amount of moisture in air
○ if air is really dry it’ll take moisture from other things (skin or
from forest materials) drying
how does precipitation impact wildfire
it wets the fuel and can slow the fire
how does temperature impact forest fire
○ Impacts dew point, relative humidity. Relative humidity throughout the day decreases because temp rises.
○ RH=e/es x100 (impacts denominator)
how does pressure impact forest fire
○ 2nd order effect- can influence wind speed and direction. Don’t need to measure this at the fire site, its over a large scale that will impact the fire large scale.
What does the USA use to forecast fire?
uses NOAA (National Oceanic and Atmospheric Administration) storm prediction center
what parameters does NOAA storm prediction center measure?
-Cloud cover
- Precip type
- Probability of Precip
- Temperature
- Relative humidity
- winds at 20ft (10m * 0.8)
morning
afternoon forecast
8-pt compass used
- Lightning potential
- “Haines Index”
Snow vs rain on fire
snow requires more energy to melt to water therefore is more restrictive to fire development
what is Haines Index (HI)
an atmospheric index used to indicate the potential for wildfire growth by measuring the stability and dryness of air.
○ HI numbers are computed for 3 different elevations using the following parameters:
HI=stability term A + moisture term B.
Haines Index classifications take values 2 - 6 (2=very low, 6=High)