Different Scenarios of FDS Modeling - Assignment Example

1,728,000 cells can be formed from the above compartment.

The domain was split into 3 meshes along the x-axis where the central mesh had a uniform cell size of 0.1m while the x and y direction had a  cell size of 0.2m i and 0.1m in the z-direction for the two neighboring meshes. Meshes should be given approximately equal physical dimensions.

The model involves the division of the compartment into numerous cells and through the application of the model it is possible to calculate the heat and fluid flow occurring between each cell through the use of fundamental physics equations. The number of cells which is used has a considerable effect on the results obtained. It is always desirable to have a large number of cells but this would call for more computer resources which will translate to high expenses.

Halving the size of the grid cells in each direction will result in the doubling of the run time for each dimension in space and time. Changing the dimensions of a mesh from a resolution will mean better results, however, the reduction in cell size will take sixteen times longer to run.

Studies which were carried out by these authors’ indicated a correlation that, size and geometry contribute the largest in the determination of the growth pattern of any ignition fire. They agree that, once a fire ignition occurs in a room, there will be the production of hot gases, which will then rise due to buoyancy until when they hit the ceiling of the room and then form a hot layer underneath the ceiling. If heat radiated from fire is increased it will increase the temperature of the hot layer, which in turn increases the temperature levels of the surrounding boundaries.

This is done by varying cell sizes from smallest to largest and the results of the parameter are checked for changes. The cell is involved in absorbing thermal radiation and has a net rate of heat flow due to thermal radiation given by Þnet = Þemitted -Þabsorbed. Suppose an object with surface area A and temperature T is bathed in thermal radiation coming from its surrounding in all directions that are at a uniform temperature Ts.

A body emits energy even if it is at the same temperature as its surroundings; it just emits at the same rate that it absorbs, so Þnet = 0. if T>Ts, the object emits more thermal radiation than it absorbs. If T>Ts, the object absorbs more thermal radiation than it emits.

The other parameters to be analyzed for sensitivity are fuel size and cell size. The cel size and geometry contribute the largest to the determination of the growth pattern of any ignition fire. ventilation sizes is also another parameter to be considered for sensitivity, ventilation sizes affect temperatures, smoke behavior, time taken to burn out, and heat release rate. Another is the speed of wind is increased, oxygen entry increased thus increasing the combustion rate which in turn increases the heat release rate and the temperature measured from the experiment.