High‐frequency nonlinear acoustic beams and wave packets

1992 ◽  
Vol 92 (4) ◽  
pp. 2186-2194
Author(s):  
Andrew N. Norris
Keyword(s):  
High Frequency ◽  
Wave Packets ◽  
Acoustic Beams ◽  
Nonlinear Acoustic

Landslide Characteristics Revealed by High-Frequency Seismic Waves from the 2017 Landslide in Central Japan

2020 ◽  
Vol 91 (5) ◽  
pp. 2719-2729
Author(s):  
Issei Doi ◽  
Takuto Maeda
Keyword(s):  
High Frequency ◽  
Seismic Waves ◽  
Wave Packets ◽  
Impulsive Phase ◽  
Frequency Component ◽  
Source Location ◽  
High Frequency Component ◽  
Central Japan ◽  
Location Determination ◽  
High Frequency Seismic Waves

Abstract The recent development of advanced seismograph networks offers us a chance to remotely detect landslide occurrences with high-frequency (>∼1  Hz) components. This study examined a landslide in central Japan that produced clearly detectable seismic signals at multiple seismic stations in a permanent network. Wave packets propagated with a group velocity of 3  km/s from the landslide area. Using a source location determination method with amplitude information from the high-frequency component, the source location of the wave packets was shown to be in the vicinity of the landslide with an error of 5 km. Moreover, seismograms specific to this landslide also contained a distinct impulsive phase with a source located in the vicinity of the landslide. The study demonstrated that seismic waves with a high-frequency component from landslides can be used to estimate their mechanisms as well as their locations when they are recognized by a routine seismic network.

On the spatio-temporal stability of primary and secondary crossflow vortices in a three-dimensional boundary layer

2002 ◽  
Vol 456 ◽  
pp. 85-111 ◽  
Author(s):  
WERNER KOCH
Keyword(s):  
Saddle Point ◽  
High Frequency ◽  
Wave Packets ◽  
Temporal Stability ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Dimensional Boundary ◽  
Spatio Temporal ◽  
Secondary Instabilities ◽  
Dimensional Wave

To examine possible links between a global instability and laminar–turbulent breakdown in a three-dimensional boundary layer, the spatio-temporal stability of primary and secondary crossflow vortices has been investigated for the DLR swept-plate experiment. In the absence of any available procedure for the direct verification of pinching for three-dimensional wave packets the alternative saddle-point continuation method has been applied. This procedure is known to give reliable results only in a certain vicinity of the most unstable ray. Therefore, finding no absolute instability by this method does not prove that the flow is absolutely stable. Accordingly, our results obtained this way need to be confirmed experimentally or by numerical simulations. A geometric interpretation of the time-asymptotic saddle-point result explains certain convergence and continuation problems encountered in the numerical wave packet analysis. Similar to previous results, all our three-dimensional wave packets for primary crossflow vortices were found to be convectively unstable.Due to prohibitive CPU time requirements the existing procedure for the verification of pinching for two-dimensional wave packets of secondary high-frequency instabilities could not be implemented. Again saddle-point continuation was used. Surprisingly, all two-dimensional wave packets of high-frequency secondary instabilities investigated were also found to be convectively unstable. This finding was corroborated by recent spatial direct numerical simulations of Wassermann & Kloker (2001) for a similar problem. This suggests that laminar–turbulent breakdown occurs after the high-frequency secondary instabilities enter the nonlinear stage, and spatial marching techniques, such as the parabolized stability equation method, should be applicable for the computation of these nonlinear states.

Tidally generated high-frequency internal wave packets and their effects on plankton in Massachusetts Bay

1983 ◽  
Vol 41 (1) ◽  
pp. 65-112 ◽  
Author(s):  
Loren R. Haury ◽  
Peter H. Wiebe ◽  
Marshall H. Orr ◽  
Melbourne G. Briscoe
Keyword(s):  
Internal Wave ◽  
High Frequency ◽  
Wave Packets ◽  
Massachusetts Bay
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