The Linear and Nonlinear Ultrasound Field of Convex Arrays Operating in a Diverging Wave Mode

2018 ◽  
Author(s):  
Ting-Yu Lai ◽  
Michalakis A. Averkiou
Keyword(s):  
Wave Mode ◽  
Nonlinear Ultrasound ◽  
Ultrasound Field ◽  
Linear And Nonlinear

Linear and nonlinear ultrasound simulations using the discontinuous Galerkin method

2018 ◽  
Vol 143 (4) ◽  
pp. 2438-2448 ◽  
Author(s):  
James F. Kelly ◽  
Simone Marras ◽  
Xiaofeng Zhao ◽  
Robert J. McGough
Keyword(s):  
Galerkin Method ◽  
Discontinuous Galerkin ◽  
Discontinuous Galerkin Method ◽  
Nonlinear Ultrasound ◽  
Linear And Nonlinear

IWSHM 2017: Structural health monitoring of the loosening in a multi-bolt structure using linear and modulated nonlinear ultrasound acoustic moments approach

2018 ◽  
Vol 17 (6) ◽  
pp. 1349-1364 ◽  
Author(s):  
Gian Piero Malfense Fierro ◽  
Michele Meo
Keyword(s):  
Structural Health Monitoring ◽  
Health Monitoring ◽  
Correlation Method ◽  
Detection Accuracy ◽  
Monitoring Method ◽  
Nonlinear Ultrasound ◽  
Structural Health ◽  
Repair Costs ◽  
Linear And Nonlinear ◽  
Bolt Loosening

Applying highly accurate clamp loads in bolted joints during assembly and inspections is essential for estimation of the integrity of a joint and reduction of disastrous failures. Non-destructive post-assembly and in-service inspections of joint integrity are vital and significantly reduce maintenance and associated repair costs. Therefore, a bolt control technology able to provide precise direct measurement of bolt loosening state during assembly and in-service is needed. This work proposes an in situ structural health monitoring approach based on the evaluation of linear and nonlinear modulated acoustic moments for the assessment of the loosened state of bolts in a multi-bolted structure. Linear and nonlinear ultrasound methods’ detection accuracy and robustness can be highly dependent on correct frequency selection. The structural health monitoring method suggested uses material resonance and a frequency sweep methodology coupled with a cross-correlation method which identifies significant frequency pairs or higher harmonics used to determine bolt loosening. The proposed approach was tested and successfully validated on three different bolted structures showing that loosening of the structure can be identified accurately with a limited number of transducers. The solution provides a qualitative solution, which identifies degradation in the torque of a bolted structure; furthermore, the developed structural health monitoring method has the potential to become an automatic tool for monitoring the loosened state of bolts in critical complex structural components.

scholarly journals Interplay of Linear and Nonlinear Localization Mechanisms in Spin-Torque Oscillators with a Field Well

2019 ◽  
Vol 64 (10) ◽  
pp. 947 ◽  
Author(s):  
R. V. Verba
Keyword(s):  
Wave Mode ◽  
Spin Torque ◽  
Nonlinear Frequency ◽  
Magnetization Dynamics ◽  
Nonlinear Localization ◽  
Generation Mode ◽  
Spin Wave Mode ◽  
Linear And Nonlinear ◽  
Generation Power ◽  
Nonlinear Frequency Shift

The magnetization dynamics in a spin-torque oscillator with nonuniform profile of a static magnetic field creating a field well is studied by analytic calculations and numerical simulations. It is demonstrated that, in the case of sufficiently deep and narrow field well, the linear localization in the field well dominates the nonlinear self-localization, despite a negative nonlinear frequency shift. A change of the localization mechanism results in a qualitatively different dependence of the generation power on the driving current. For the dominant linear localization, the soft generation mode is realized, while, for the nonlinear self-localization, we observe a hard mode of auto-oscillator excitation. Simultaneously, a difference in the profiles of the excited spin-wave mode can become evident and distinguishable in experiments only in the case of a nonsymmetric field well.

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