Differences In Frequency Response Research Articles

Nonlinear response of conical flame to dual-frequency excitation

This work investigates the nonlinear response of a conical premixed flame to dual-frequency excitation through experiments and G-equation analysis. In addition to the responses at excitation frequencies, f1 and f2, a notable flame response can also be identified at the difference frequency, fd. The fd response is particularly significant in the high-frequency regime, characterized by multiple wavelengths of both f1 and f2 on the flame front. This distinct behavior of difference-frequency response can be attributed to the spatial superposition of the intensified flame fluctuation waves at the two forcing frequencies. As the excitation enhances at either f1 or f2, the nonlinear effect suppresses the responses of the upper-part flame at both f1 and f2 while promoting the bulk flame response at fd. Based on a third-order expansion of the G-equation, it is shown that the nonlinear flame dynamics necessarily generate the observed interaction component when the flame is perturbed by dual-frequency excitations. The present results emphasize the importance of nonlinear flame dynamics in inducing flame responses at interaction frequencies, offering insights into thermoacoustic oscillations of multiple frequencies.

Statistical Analysis of Nonlinear Response of Moored Vessels in Random Seas

This paper presents statistical analyses for second-order responses of tension-leg platform.Second-order responses of moored vessels in random seas include two kinds of elements, difference-frequency response and sum-frequency response. It is well known that difference-frequency response leads to slow drift oscillation. Sum-frequency response is generally eliminated for an analysis of slack mooring.In the case of heaving motion of tension-leg platform, sum-frequency response is large because of its high natural frequency, and it leads to springing response. Non-normality of two kinds of responses are investigated, and compared these two responses for surging, heaving and pitching modes.Main results are as follows :1) Sum-frequency response of exciting force is a little larger than difference frequency response of it. Both of them have large non-normality.2) Sum-frequency response of heaving and pitching motions are much larger than difference, and surging shows opposite result. These three large responses have behavior similar to normal distribution.3) Gamma-distribution approximation and DVI method can be applied to sum-frequency response.4) Non-normality increases and standard deviation becomes small as damping increases.

Dynamic frequency response for InGaAs/InAlAs multiple quantum well optical modulators

The frequency response of InGaAs/InAlAs multiple-quantum-well (MQW) optical modulators and their dependence on incident light power are described. No decrease in small-signal modulation bandwidth was observed up to ten times the initial value of 1 mW. The mechanism of the frequency-response difference between InGaAs/InAlAs MQW modulators and InGaAs/InP modulators is discussed. >