Nonlinear dynamic simulation of a tethered aerostat: A fidelity study

Full-scale Right tests of an instrumented TCOM 71M(TM) tethered aerostat co nducted by the U.S. Army provide a database for determining the fidelity of the TCOM nonlinear dynamic simulation. Six global position system sensors, accurate to +/-5 cm, determined the position and attitude of the aerostat, and winds were measured using a three-axis anemometer mounted on the aeros tat's fin near the tip. A 32-min window of data was selected for comparison with the simulation, using the recorded winds to derive a turbulence table . This required correcting the winds for aerostat velocity and transforming to an Earth-fixed coordinate system aligned with the mean aerostat heading . Best results were obtained when the turbulence was propagated through the reference point with uniform flow over the aerostat, rather than the segme nted hull with nonuniform Row This is shown clearly by comparing standard d eviations of the flight parameters. This unexpected result is attributed to the strong influence of aerostat velocity in reconstructing the true wind. Graphical comparisons are made in the time domain of the aerostat's positi on and orientation as well as tether tension. Qualitatively, the comparison s are very good, generally showing the same patterns of motion and order of magnitude as the standard deviations. Tether tension in particular showed a remarkable duplication by the simulation. Frequency spectra based on fast Fourier transformation of the time histories are also compared.