NASA Scientific and Technical Aerospace Reports

flux focusing lens is incorporated such that in the absence of any inhomogeneities in the material under test only a minimal
magnetic field will reach the interior of the probe. A magnetometer (pickup coil) located in the center of the probe therefore
registers a null voltage in the absence of material defects. When a fatigue crack or other discontinuity is present in the test
article the path of the eddy currents in the material is changed. The magnetic field associated with these eddy currents then
enter into the interior of the probe, producing a large output voltage across the pickup coil leads. Further
Author
Eddy Currents; Cracks; Rivets; Electric Potential; Detection
20040120885 Wichita State Univ., Wichita, KS, USA
THERMOD Composite Airframe Termperature Prediction Tool Evaluation, Validation, and Enhancement with Initial
Steady-State Temperature Data
Miller, L. S.; Waltner, J.; Mazmudar, T.; Merchant, M.; Tomblin, J.; Sep. 2004; 32 pp.; In English
Report No.(s): PB2004-107309; DOT/FAA/AR-04/30; No Copyright; Avail: CASI; A03, Hardcopy
General aviation aircraft airframe temperatures can reach extreme levels while parked on the ground, depending on
ambient conditions (e.g., temperature and solar radiation) and airframe construction (e.g., material types, geometry, and paint
color). The implications of this situation are extremely important to understand since composite aircraft structural limits are
dependent on the airframe temperatures. The THERMOD computer code predicts both steady-state and transient airframe
temperatures based on a comprehensive range of factors, including those mentioned above. Unfortunately, however, the
THERMOD program has not been fully validated. Previous experimental investigations, conducted at Wichita State
University, suggest that THERMOD code predictions for convective cooling effects are reasonable, typically conservative.
However, a few key questions surfaced, specifically (1) What is the impact of input variable uncertainties. (2) What is the
accuracy of THERMOD in predicting steady-state or initial temperatures. and (3) Are there ways to improve THERMODs
utility or ease of use. These issues became the goals for the current work. A sensitivity study, using the THERMOD code itself,
showed that the impact of input variable uncertainties is typically small, depending most on the obvious geometry and material
properties. Atmospheric testing, using solar radiation to heat test panels, suggests that THERMOD steady-state predictions are
reasonable. The temperature data generated will be useful for design and certification. However, the code can underpredict
temperatures in some cases, perhaps due to the fact that THERMOD assumes a constant 10-mph wind in its analysis. A
Windows style interface, called the THERMOD Analysis Assistant (TAA), was developed and is undergoing initial user
evaluations. TAA is composed of two parts, an input file generation interface and an output file viewer. Each element offers
a more familiar user environment incorporating graphics and controls to ease THERMOD code use. A brief TAA introduction
and overview is included in this report.
NTIS
Airframes; Aircraft Structures; Composite Materials
20040120949 Akron Univ., Akron, OH, USA
BASS Code Development
Sawyer, Scott; August 04, 2004; 25 pp.; In English
Contract(s)/Grant(s): NAG3-2537; No Copyright; Avail: CASI; A03, Hardcopy
The BASS computational aeroacoustic code solves the fully nonlinear Euler equations in the time domain in
two-dimensions. The acoustic response of the stator is determined simultaneously for the first three harmonics of the convected
vortical gust of the rotor. The spatial mode generation, propagation and decay characteristics are predicted by assuming the
acoustic field away from the stator can be represented as a uniform flow with small harmonic perturbations superimposed. The
computed field is then decomposed using a joint temporal-spatial transform to determine the wave amplitudes as a function
of rotor harmonic and spatial mode order. This report details the following technical aspects of the computations and analysis.
1) the BASS computational technique; 2) the application of periodic time shifted boundary conditions; 3) the linear theory
aspects unique to rotor-stator interactions; and 4) the joint spatial-temporal transform. The computational results presented
herein are twofold. In each case, the acoustic response of the stator is determined simultaneously for the first three harmonics
of the convected vortical gust of the rotor. The fan under consideration here like modern fans is cut-off at +, and propagating
acoustic waves are only expected at 2BPF and 3BPF. In the first case, the computations showed excellent agreement with
linear theory predictions. The frequency and spatial mode order of acoustic field was computed and found consistent with
linear theory. Further, the propagation of the generated modes was also correctly predicted. The upstream going waves
propagated from the domain without reflection from the in ow boundary. However, reflections from the out ow boundary were
noticed. The amplitude of the reflected wave was approximately 5% of the incident wave. The second set of computations were
used to determine the influence of steady loading on the generated noise. Toward this end, the acoustic response was
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