Outputs of Rothermels Models
spread direction [degree] - the direction of the spread in degrees
effective wind speed [m/s] - As an intermediate step in obtaining solutions
to the fire spread model, effective windspeed is determined. This value integrates
the additive effects of slope steepness with a wind that is moving across or
up a slope.
rate of spread [m/s] - The spread model calculates the rate of spread at the head of fire when the fire reaches its full, steady state speed. It predicts the speed of a fire burning in surface fuels, spreading on a single, unified front, that is not influenced by other ignitions. Rate of spread is generally stated in chains per hour, feet per minute, or meters per minute.
flame residence time [s] - describes how long flaming combustion continues at a certain point.
heat release per unit area [kJ/m2] - It is the total amount of heat released
in each square foot of the flaming fire front, usually expressed as Btu per
square foot. All of the heat given off in the flaming front is included in this
value, regardless of the length of time that the flaming front persists. For
a given area with a specific amount and distribution of fuel, heat per unit
area is inversely related to fuel moisture content. Heat released in flaming
combustion that occurs as fuels burn out after the flaming front has passed
is not included in the heat per unit area value.
fire line intensity [kW/m] - Fireline intensity is the amount of heat given off by a fire along each foot of the leading edge of the fire each second, usually expressed as Btu per lineal foot of fireline per second.
flame length [m] - length of the flames when the fire has reached its full, forward rate of spread.
How the wildfire was simulated\
First the.corect parameters are intailized according to the scenetype. The the correct scale for the enviromental agent container is set distributing the rate of spread equally to the x and y coordinates of the container. This rate of spread from Rothermels model is stated in meters per sec which matchs the way distances in VRML are measured (meters). Then the flame height of the the fire is applied to the agent container in the Z direction. This flame height is also measured in meters (usually a small number). Orginally the flame residence time, which is measured in measured in seconds was applied to a sensor that timed the movement of the wildfire (remember this is the time the flame sits before it moves on). In this simulator it was found that this caused events to happen to quickly for the observer so timer was set to move every ten seconds. Finally the new point that the fire was travelling to was found. This new point is calculated by obtaining the orginal point, speed the wildfire is traveling at, and the direction it is traveling and performing some simple trig to obtain a new point. In this move function the direction was first converted to radians, which was needed for the calculation, then the x coordinate was the orginal point * speed * COS(direction). The y coordinate was simple the orginal y coordinate * speed * SIN(direction). The Z coordinate was left the same since we are dealing with flat terrain. The fire would not continue to burn if it left contact with combustible material.