Today's topics

• Discussion of lab
• Wind phenomena and case studies

Wind phenomena and case studies

Global Patterns

[Simiu 1986, fig 1.3.2]

Mean hurricane tracks

[Simiu 1986, fig 1.3.4]

Hurricanes

Hurricane form, locations, and behavior

Links to resources from NOAA

• Saffir-Simpson Hurricane Scale
• Costliest Hurricanes
• Deadliest Hurricanes

Properties of wind and their code representation

Boundary layer flow

[Gupta 1993, fig 3.3.2]

• A fluid flowing over a surface tends to adhere to the surface.
• The flow velocity increases at greater distances from the surface.
• The variation in flow velocity increases with the roughness of the surface.

Wind forces on buildings

Contours of pressure under a steady boundary flow

[Simiu 1986, fig 4.6.6b]

• An object placed in the path of a flowing fluid diverts the path of the fluid's moving mass: i.e. it changes the velocity vector of the mass.
• Changing velocity means acceleration, so the object must exert a force as it changes the velocity of the fluid's mass.
• There is a counteracting force exerted on the object by the fluid in the form of pressure on the surface of the object.
• The magnitude and distribution of this force depends on the density and velocity of the fluid, and the shape of the object.
• There is a relationship between fluid pressure and velocity determined by fundamental physics: the Bernoulli equation:

  (1/2) ro v² + p = constant

  Where:
  ro = mass density of the fluid
  v = fluid velocity
  p = fluid pressure
  

• There are two important consequences of the Bernoulli equation:
  1. The pressure in a fluid increases as it slows down.
  2. The pressure in a fluid decreases as it speeds up.

• The stagnation pressure is defined as the change in pressure that occurs when the flow is brought to a complete stop.

• The stagnation pressure increases with the square of the velocity. (e.g. 80 MPH winds create four times the pressure of 40 MPH winds).

Wind flow and buildings

Internal and external pressure

Wind-borne missles

Roof forms

Details and Building practices

Storm Surge