Monte Carlo Simulation To Estimate Likelihood of Direct Lightning Strikes
- Friday, 12 September 2008
A software tool has been designed to quantify the lightning exposure at launch sites of the stack at the pads under different configurations. In order to predict lightning strikes to generic structures, this model uses leaders whose origins (in the x–y plane) are obtained from a 2D random, normal distribution. The striking distance is a function of the stroke peak current, which is obtained from a random state machine that extracts the stroke peak current from a lognormal distribution. The height in which the leaders are originated is fixed and chosen to be several “strike distances” greater than the tallest object under study.
The Monte Carlo simulation tool uses several random state machines to generate x–y origin of leaders and peak stroke currents. The structures under study are entered in text files whose names are used as descriptors for report purposes. So, “External_tank.txt” could be the text file that contains all the vertices of the external tank. The lines of the text files contain three points (x, y, and z) that define “points” of lines or “vertices” of polygons. A line composed of three zeros (0 0 0) is used to indicate the end of a line or polygon.
Imaginary spheres (whose diameters are the striking distances) are drawn as the leader descends vertically to ground, and the first object intersected is considered to be struck. Therefore, the last step of the leader can be in any direction. The leaders can move in the z direction only, or in a random xyz direction (software selectable). The leader steps can be either fixed or variable. The length of the study is also software selectable, so the user can perform a study of “n” number of years. A summary report generated by the software indicates the frequency at which objects under study will be struck by lightning.