Variations of on-axis average intensity along the propagation path in turbulent atmosphere for plane wave excitation limited by a circular aperture

2006 ◽  
Vol 267 (1) ◽  
pp. 32-35 ◽  
Author(s):  
Xiuxiang Chu ◽  
Guoquan Zhou ◽  
Yongzhou Ni
Keyword(s):  
Plane Wave ◽  
Turbulent Atmosphere ◽  
Propagation Path ◽  
Average Intensity ◽  
Circular Aperture ◽  
Wave Excitation

Finding the boom: Phased array processing applied to sonic boom direction of arrival estimation

2017 ◽  
Vol 16 (4-5) ◽  
pp. 230-254
Author(s):  
Todd Schultz ◽  
James R Underbrink ◽  
LC Hunting ◽  
James Giannakis ◽  
Matthew D Moore ◽  
...  
Keyword(s):  
Wave Front ◽  
Phased Array ◽  
Array Processing ◽  
Time Estimation ◽  
Direction Of Arrival ◽  
Test Point ◽  
Propagation Path ◽  
Sonic Boom ◽  
Circular Aperture ◽  
Aperture Diameter

From 29 October 2012 to 7 November 2012, 73 supersonic passes of an F-18 aircraft were observed over a dry lake bed at Edwards Air Force Base as part of NASA’s Farfield Investigation of No-boom Thresholds project, which was conceived to measure the characteristics of sonic booms at the boundaries of their decay, where overpressure is exceptionally low, thereby stretching the limits of current prediction methods. Each pass was recorded by a 55-microphone phased array sensor system with a circular aperture diameter of 2000 ft (609.6 m). The data were processed using a novel time domain array processing algorithm to estimate the direction of arrival and trace speed of the sonic boom wave front along the plane of the phased array. The results from the phased array processing are consistent with the known location of the test aircraft for each processed flight and are consistent with expectations for direction of arrival due to atmospheric refraction. Near real-time estimation of the sonic boom direction of arrival, trace speed along the ground, and visualization of the propagation of the sonic boom wave front are possible. This could allow the test team to assess the data and determine if the target of the test point has been met while the test aircraft is still in flight. This would enable improved test efficiency and efficacy, ultimately improving the value of the test campaign. The measured direction of arrival also provides sonic boom propagation numerical prediction code validation. Most sonic boom prediction codes provide the propagation path of the sonic boom and thus the direction of arrival of the sonic boom at a point on the ground. Thus for predictions made using the actual flight data measured at the time of the test, the predicted direction of arrival and measured direction of arrival can be directly compared to help validate the prediction codes.

Efficient Plane Wave Excitation for 3-D Laguerre-Based FDTD Method

2014 ◽  
Vol 556-562 ◽  
pp. 4542-4546
Author(s):  
Zheng Chen ◽  
Yan Tao Duan ◽  
Ye Rong Zhang ◽  
Cheng Gao
Keyword(s):  
Plane Wave ◽  
Electric Fields ◽  
Laguerre Polynomials ◽  
Fdtd Method ◽  
Three Dimensional ◽  
Field Variable ◽  
Wave Excitation ◽  
Computationally Efficient ◽  
Scattering Problems ◽  
Scatter Field

In the three-dimensional (3-D) Laguerre-based finite-difference time-domain method, each electric field variable has the relationship with the adjacent twelve electric fields. This results in the tedious modification of field components adjacent to the total-field/scatter-field boundary in analyzing scattering problems. In addition, the plane wave excitation requires much time in evaluating the expansion coefficient of incident field which involves integral of the weighted Laguerre polynomials with respect to time. In this letter, the plane wave is introduced by defining a set of equivalent currents on a closed Huygen's surface and a computationally efficient one-dimensional auxiliary propagator is presented to speed up the plane wave excitation. Numerical results indicated that the proposed method is valid.

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