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Nonlinear Ultrasonic Techniques for Nondestructive Evaluation
Published in Kundu Tribikram, Mechanics of Elastic Waves and Ultrasonic Nondestructive Evaluation, 2019
For nonlinear materials the resonance frequency and attenuation depend on the excitation amplitude, unlike linear materials for which these two parameters are independent of the excitation amplitude. The resonance frequency shift and attenuation variations with increasing amplitude of excitation are monitored in the nonlinear resonance techniques. A downward resonance peak shift and increase of attenuation with increasing excitation amplitude are observed in nonlinear materials. The resonance frequencies of a specimen can be determined by hitting the specimen with an impactor which can be, for example, an instrumented hammer. Multiple resonance spectra are recorded by continuously increasing the excitation amplitude in consecutive strikes. This technique is known as Nonlinear Impact Resonance Acoustic Spectroscopy, or NIRAS (Van Den Abeele et al., 2000).
Nonlinear dynamic characteristics analysis of the surge motion of a tender-assisted drilling operation system
Published in Ships and Offshore Structures, 2023
Zhuang Kang, Rui Chang, Shangmao Ai
As shown in Figure 17, there is a linear relationship between the wave frequency response of the TLP surge and the wave amplitude. In contrast, an apparent nonlinear relationship exists in the high frequency and low frequency responses. The amplitude changes of these two responses show a trend of increasing first and then decreasing gradually with increasing incident wave amplitude. The trend at the high-frequency and the low-frequency in the TLP surge coincides with that in the TAD surge and the relative surge motion, as shown in Figure 18 and 19. It is worth mentioning that the RAO of the low-frequency component is usually much larger than that of the wave frequency component, which can lead to unexpected large amplitude oscillations. For example, the low-frequency RAO will reach 5.5 under the regular wave with a small amplitude A = 0.2 m when T = 19 s. This nonlinear resonance phenomenon may cause unexpected resonance risk, which must be carefully considered in the design.
Multi-jump resonance systems
Published in International Journal of Control, 2020
Arturo Buscarino, Carlo Famoso, Luigi Fortuna, Mattia Frasca
Jump resonance, also called nonlinear resonance, is a phenomenon that occurs in nonlinear non-autonomous systems. The peculiarity of jump resonance is that there exists a range of frequencies for which the system frequency response is a multi-valued function that, therefore, leads to an hysteretic behaviour. The occurrence of this behaviour depends on both the linear and nonlinear part of the system and the span of the hysteresis window is influenced also by the amplitude of the forcing signal. The presence of a frequency multi-valued function leads to a response in which abrupt jumps down/up in the magnitude of the output signal are retrieved, as long as the frequency of the driving signal is increased or decreased, thus generating an hysteretic behaviour in the sense that the value of the output amplitude switches at two different frequency thresholds, depending on the way in which the input frequency has been varied (decreasing it or increasing it). An example of frequency response with jump resonance is shown in Figure 1(a). The two frequencies (up) and (down) correspond to the jumps occurring in the output magnitude for decreasing and increasing frequency of the input, respectively. In this case . A curve dual to that shown in Figure 1(a) is reported in Figure 1(b), where on the contrary.