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W. Wu et al.
40.3 Sound Wave Transmission and Measurement
of Sound Velocity in Steel Bifurcated Pipe
The location accuracy of AE sources in location of TDOA is directly affected by
the sound velocity, as well as the structure shape which result in the uncertainty and
complication of sound transmission paths.
Sound velocity is affected by material type, anisotropy, structure shape and size,
AE source property, distance between the AE sources and receiving sensor, gate
threshold, container medium and other factors.
The modes of sound waves received by the sensors may be longitudinal, shear,
surface, lamb waves (symmetric or asymmetric)etc., therefore, sound velocity variation is often encountered, as well as dispersion phenomenon under which the sound
velocity is a function of the frequency of the sound wave.
At present, the mainstream AE detection system can’t deal with the condition
of variable sound velocity. If the true sound velocity in the detected component is
constant but different from the value entered in the location calculation software,
the location error will depend on the measured time difference of arrival. If the AE
source is in the middle of the sensor array, TDOA of the sensors is very small and it
is not easy to detect the difference in sound velocity. Nevertheless, the closer the AE
source is to the sensor, the greater the time difference is, and the greater the error of
AE source location is due to velocity error.
40.3.1 Diversity of Acoustic Transmission Paths
in Thick-Wall Plate of Bifurcated Pipe
The welds and obstacles (the crescent rib protrudes from the weld, and the K-shaped
groove angle of rib changes gradually) result in the interface reflection of the wave,
and each reflection generates wave model conversion besides superposition due to
the complicated acoustic transmission paths.
The possible acoustic transmission paths in a cylinder of thick-wall plate are very
complicated [3, 4], shown as Figs. 40.2 and 40.3.
Fig. 40.2 Possible propagation paths of the wave in the bifurcated pipe
W. Wu et al.
40.3 Sound Wave Transmission and Measurement
of Sound Velocity in Steel Bifurcated Pipe
The location accuracy of AE sources in location of TDOA is directly affected by
the sound velocity, as well as the structure shape which result in the uncertainty and
complication of sound transmission paths.
Sound velocity is affected by material type, anisotropy, structure shape and size,
AE source property, distance between the AE sources and receiving sensor, gate
threshold, container medium and other factors.
The modes of sound waves received by the sensors may be longitudinal, shear,
surface, lamb waves (symmetric or asymmetric)etc., therefore, sound velocity variation is often encountered, as well as dispersion phenomenon under which the sound
velocity is a function of the frequency of the sound wave.
At present, the mainstream AE detection system can’t deal with the condition
of variable sound velocity. If the true sound velocity in the detected component is
constant but different from the value entered in the location calculation software,
the location error will depend on the measured time difference of arrival. If the AE
source is in the middle of the sensor array, TDOA of the sensors is very small and it
is not easy to detect the difference in sound velocity. Nevertheless, the closer the AE
source is to the sensor, the greater the time difference is, and the greater the error of
AE source location is due to velocity error.
40.3.1 Diversity of Acoustic Transmission Paths
in Thick-Wall Plate of Bifurcated Pipe
The welds and obstacles (the crescent rib protrudes from the weld, and the K-shaped
groove angle of rib changes gradually) result in the interface reflection of the wave,
and each reflection generates wave model conversion besides superposition due to
the complicated acoustic transmission paths.
The possible acoustic transmission paths in a cylinder of thick-wall plate are very
complicated [3, 4], shown as Figs. 40.2 and 40.3.
Fig. 40.2 Possible propagation paths of the wave in the bifurcated pipe