Influence Of Nonlinear Effects Research Articles

A nonlinear instability theory for a wave system inducing transition in spiral Poiseuille flow

This paper is on the transition scenario of the class of spiral Poiseuille flows that results from the onset, propagation and evolution of disturbances according to mechanisms of Tollmien-Schlichting, and Taylor, acting simultaneously. The problem is approached from the fundamental point of view of following the growth of initially infinitesimally small disturbances into their nonlinear stage when the effect of Reynolds stresses makes itself felt. To this end a set of Generalised Nonlinear Orr–Sommerfeld, Squire and Continuity Equations is set up that enables accounting for effects of growth of initially infinitesimally small disturbances into nonlinearities through a rational iteration scheme. The present proposal closely follows the method put forth for this pupose in 1971 by Stuart and Stewartson in their seminal papers on the influence of nonlinear effects during transition in the bench-mark flows of the class of spiral Poiseuille flows; which are the plane-walled channel flow and the flow in the gap between concentric circular cylinders (Taylor instability).The basic feature of the proposed method is the introduction of an Amplitude Parameter and of a slow/long- scale variable through which the effects of growing disturbances are accounted for within the framework of a rational iteration scheme. It is shown that the effect of amplified disturbances is capturable, as in the bench-mark flows, by a Ginzburg–Landau type differential equation for an Amplitude Function in terms of suitably defined slow/long-scale variables. However, the coefficients in this equation are numbers that depend upon the flow parameters of the spiral Poiseuille flow, which are a suitably defined Reynolds Number, the Swirl Number, and the geometric parameter of transverse curvature inherent in the flow geometry. The Ginzburg–Landau equation derived hints at the drastic changes in flow pattern that the spiral Poiseuille flow in transition may undergo, as its Swirl Number is taken from very small to very large values.

Measurement of the absorption cross-sections of sulfur compounds in the 180-270 nm region considering nonlinear effects.

Sulfur compounds (SO2, CS2, H2S and OCS) are common toxic pollutants in the atmospheric environment, and the absorption spectroscopy technique can indeed help to realize online monitoring of their concentrations. However, nonlinear effects that occur during absorption spectroscopy measurements have a serious impact on the measurement of the absorption cross-sections (ACSs) of sulfur compounds, leading to serious deviations in both the substance absorption properties and concentrations obtained based on ACS analysis. In this paper, the maximum effective ACSs of sulfur compounds in the linear region are obtained by considering the influence of nonlinear effects and eliminating interference factors such as oxygen and photolysis. In addition, the nonlinear effects are found to be greatly attenuated in spectra with broad band absorption characteristics by comparing the oscillatory absorption spectra before and after the differential treatment and by comparing the change in the oscillatory ACS with the broad band ACS. The experimental results show that the effective ACSs of SO2, CS2, H2S, and OCS with a resolution of 0.23 nm are 14.15 × 10-18 cm2 per molecule, 5.61 × 10-16 cm2 per molecule, 7.09 × 10-18 cm2 per molecule, and 3.20 × 10-19 cm2 per molecule, respectively. So far, it is the largest ACS obtained at room temperature and atmospheric pressure, which is of great significance for online measurement of sulfur compounds.

Nonlinear effects at the deformation of amorphous polymers in warm and frozen states

One of the important problems of the modern rheology of polymer materials, namely, the possibility of describing the deformation of amorphous polymers within the framework of linear rheological relationships between relative deformation and deforming stress or the need to use nonlinear rheological equations is considered. The criteria for distinguishing these approaches, namely, the determination of the corresponding critical values of the macro- and microphysical characteristics of the material and the conditions for carrying out the mechanical tests are also discussed. In particular, the difference between the influence of kinetic and thermodynamic nonlinear effects on the regularities of deformation processes of amorphous polymers in warm and frozen states was noted. The influence of nonlinear effects on the general shape and characteristics of individual stages of the “relative strain - deforming stress” diagram at deformation of polymer samples with specified values of strain rate and temperature is analyzed in detail. The results of the theoretical analysis were used for the physical interpretation of the general form and features of individual stages of the tensile test diagrams of amorphous polyimide films (V. D. Natsik, H. V. Rusakova, S. V. Lubenets, V. A. Lototskaya, and L. F. Yakovenko, Fiz. Nyzk. Temp. 49, 569 (2023) [Low Temp. Phys. 49, 521 (2023)]), empirical estimates for the rheological characteristics of this polymer were obtained.

Numerical study of generation mechanisms of narrow spectral modes, emerging in a raman fiber laser with randomly distributed feedback

The present paper discusses possible influence of nonlinear effects, namely – the degenerate four-wave mixing process – upon the build-up and attenuation of narrow spectral modes, emerging in radiation of a Raman fiber laser with randomly distributed feedback.

Comparative Analysis of the Silver Nanoparticle's Yield for Pico-Femto-Nanosecond Laser Generation.

Comparative analysis of different laser regimes of silver nanoparticle generation in water was performed for laser pulsewidth in the range of 300 fs-100 ns. Optical spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and method of dynamic light scattering were used for nanoparticle characterization. Different laser regimes of generation were used with varying pulse duration, pulse energy and scanning velocity. The proposed universal quantitative criteria as productivity and ergonomicity of the obtained colloidal solutions of nanoparticles were investigated to compare different laser regimes of production. The efficiency per unit energy for picosecond generation of nanoparticles, free from the influence of nonlinear effects, turns out to be higher by 1-2 orders of magnitude than for nanosecond generation.

Experimental and theoretical investigations on dry gas seal transient performance and its disparity with steady performance

Through high-speed dry gas seal test rig, the real-time film thickness and leakage rate of spiral grooved dry gas seal have been monitored under different closing forces which are changed by adjusting spring compression. Under the conditions of different spring pressures and seal face deflection rates, the change rules of transient opening force and leakage rate are obtained by solving the transient-state Reynolds equation based on the measured real-time film thickness. Meanwhile, the steady opening force and leakage rate are figured out by solving the steady-state Reynolds equation using the average value of the real-time film thickness. Results show that the variation trends of calculated results based on steady-state or transient-state theory coincide well with experimental results. But with the influence of nonlinear effect, the average value of transient opening force and leakage rate are larger than steady opening force and leakage rate calculated with the average value of real-time film thickness, and compared with the value of steady leakage rate, the average value of transient leakage rate considered seal face deflection is closer to the experimental monitoring results.

Influence of nonlinear effects on forward stimulated Brillouin scattering distributed sensing

The influences of nonlinear effects on sensing performance of forward stimulated Brillouin scattering (FSBS) are investigated using opto-mechanical time-domain analysis sensor, which is taken for example. The excitation of FSBS often requires high pulse power (at Watt level) because of the lower gain coefficient. Owing to the co-propagation of reading pulse and scattered light, high-power activation pulses will induce various nonlinear effects in an FSBS sensing system. Using the reported method based on activation-reading time-domain separation, the influences of nonlinear effects due to activation pulses can be effectively avoided. However, the nonlinear effects of reading pulses directly affect the sensing performance. Based on this consideration, we study the influences of nonlinear effects on FSBS sensing and their physical mechanisms under different values of peak power of reading pulses; the variation process of the 1st- and 2nd-order FSBS spectrums along ～4.7 km standard single-mode fiber are revealed in detail. Finally, the optimal region is found, in which a perfect FSBS local spectrum is obtained, and the sensing distance can be extended.

Classical nonlinear simulation of low-order modes of Lamb waves in plate

For the classical nonlinear research of low-order modes of Lamb waves, this paper firstly introduces the classical nonlinearity derived from the intrinsic nonlinear induced low-order Lamb waves (S0 and A0 modes). Theoretical and numerical calculations are studied in two aspects. The influence of nonlinear effects on the nonlinear effects of classical nonlinear low-order Lamb waves and the cumulative growth effect are analyzed by finite element simulation. The results show that the nonlinear effect produced by the superelastic material model is greater than the geometric nonlinearity, and the linear elastic material model does not produce nonlinear effects. In addition, as the third-order elasticity increases in the material, the amplitude of the second harmonic gradually increases. The second harmonic generated by the A0 mode with phase velocity mismatch is the S0 mode. It can be seen that the group velocity matching is not a necessary condition for generating the second harmonic. Since the phase velocity matching is not satisfied, there is no cumulative growth effect; The higher the S0 mode phase velocity matching degree, the more obvious the cumulative growth effect, and the second harmonic is the S0 mode.

Evaluation of the influence of a dimensionless threshold pressure gradient on deviation of filtration from classical filtration law

Depletion of hydrocarbon reserves in reservoirs with high and medium permeability increases the proportion of low permeability reservoirs in which nonlinear filtration effects are observed: at low pressure gradients, filtration does not obey the classical filtration law (Darcy’s law). One of the methods to describe the nonlinear filtration effects is to apply the filtration law with a threshold pressure gradient (TPG). The influence of this parameter on the deviation of filtration from Darcy's law has not been previously analyzed. The aim of this work is to evaluate this effect of the TPG. Piezoconductivity equations are nondimensionalized and solved according to the classical filtration law and the filtration law with TPG for plane radial flow and constant well pressure. In the framework of the classical filtration law, the piezoconductivity equation is solved by applying a self-simulated variable. Using the filtration law with TPG, the conductivity equation solution is solved by the method of integral relations. Relations between dimensionless production rate and dimensionless time for both filtration laws are found from the solved piezoconductivity equations. To prove the identity of the obtained solutions, a comparative analysis is performed for a threshold pressure gradient equal to zero. Comparison of production decline curves for classical filtration law and filtration law with TPG at various values TPG is carried out. The relation between the shapes of the production decline curves shape and various dimensionless TPG values is analyzed. With increasing dimensionless TPG, the influence of nonlinear effects on filtration increases: the nonlinear filtration effects become apparent earlier, and the production decline curves for the filtration law with TPG deviate greater from the production decline curve for the classical filtration law.

Nonlinear states and dynamics in a synthetic frequency dimension

Recent advances in the study of synthetic dimensions revealed a possibility to employ the frequency space as an additional degree of freedom which allows for investigating and exploiting higher-dimensional phenomena in a priori low-dimensional systems. However, the influence of nonlinear effects on the synthetic frequency dimensions was studied only under significant restrictions. In the present paper, we develop a generalized mean-field model for the optical field envelope inside a single driven-dissipative resonator with quadratic and cubic nonlinearities, whose frequencies are coupled via an electro-optical resonant temporal modulation. The leading-order equation takes the form of a driven Gross-Pitaevskii equation with a cosine potential. We numerically investigate the nonlinear dynamics in such a microring resonator with a synthetic frequency dimension in the regime where parametric frequency conversion occurs. We observe that the modulation brings additional control to the system, enabling one to readily create and manipulate bright and dark dissipative solitons inside the cavity. In the case of anomalous dispersion, we find that the presence of electro-optical mode coupling confines and stabilizes the chaotic modulation instability region. This leads to the appearance of an unconventional type of stable coherent structure which emerges in the synthetic space with restored translational symmetry, in a region of parameters where conventionally only chaotic modulation instability states exist. This structure appears in the center of the synthetic band and, therefore, is referred to as the band soliton. Finally, we extend our results to the case of multiple modulation frequencies with controllable relative phases creating synthetic lattices with nontrivial geometry. We show that an asymmetric synthetic band leads to the coexistence of chaotic and coherent states of the electromagnetic field inside the cavity, i.e., dynamics that can be interpreted as chimeralike states. Recently developed ${\ensuremath{\chi}}^{(2)}$ microresonators can open the way to experimentally exploring our findings.

Nonlinear effect measurement based on high‐speed optical transmission communication system

AbstractThe problem of nonlinear effect in high‐speed optical transmission communication systems limits the performance of systems; therefore, it needs to be measured and suppressed. In this article, the influence of nonlinear effect was illustrated taking signal phase as an example. Then an Xcross phase modulation (XPM) measurement model was established. It was found through simulation experiment that XPM effect tended to theoretical value with the increase of frequency of radio frequency signal and strengthened with the decrease of dispersion effect. The effectiveness of the measurement method is illustrated and relevant influence factors were verified, providing a reference for the study of nonlinear effect of communication technology.

Hybrid optical CDMA and DWDM system implemented under the influence of Non-linear effects

<span>A hybrid optical CDMA-DWDM system accommodating 12 optical CDMA users carried by 5 DWDM wavelengths at a data rate of 60Gb/s/wavelength with channel spacing of 0.4nm is implemented under the effect of four-wave mixing (FWM). It was found that the FWM effect could be minimized by the use of CDMA technology, where the energy of each bit is spread over the optical sequence code. Over a distance of 105.075km, significant performance of all optical CDMA users in terms of the BER is achieved. The results reveal that the inter-symbol interference (ISI) can be mitigated when the interval of optical signature sequence code is squeezed into 25% of the bit duration. </span>

Strain study of epitaxial Al1−xGaxN based on first-principles theory

The mechanical properties of Al1−xGaxN epitaxial layers grown on GaN and AlN substrates were studied by using density functional theory and anharmonic elastic calculation method. Accurate theoretical calculation of nonlinear elastic responses is a basic and important scientific question, which is the key to understand and further explore the potential synthesis and design of new solids. In this paper, detailed numerical calculations were carried out for the nonlinear mechanical properties of würtzite GaN and AlN compounds. The variation of strain energy and stress of disordered Al1−xGaxN epitaxial layer with gallium composition was analyzed. We found that in the epitaxial structure of AlN substrate, with the increase of gallium content, the influence of nonlinear effect on internal stress reached 29.4%, which proved the great influence of nonlinear mechanical response on semiconductor alloy material and heterostructure.

Interactions between M-typed solitons based on nonlinear optimization in dispersion management systems

Investigations on soliton interactions in dispersion management systems are beneficial to improving the communication capacity. In this paper, the variable-coefficient fifth-order nonlinear Schrödinger equation, which can be used to describe the soliton interactions in dispersion management systems, is studied analytically. M-typed soliton interactions are presented based on the obtained soliton solutions. Influences of nonlinear effects on M-typed soliton interactions are analyzed. Results indicate that we can effectively control soliton interactions by means of nonlinear optimization of dispersion management systems.

Modelling of vibration-damping properties of elastic-viscoplastic layers of the roadbed. Problem statement 2

The present article is a continuation of the article [1], where was considered a model of the vibration damping properties of the subgrade at the main area of the sole of a ballast prism of normalized thickness, a protective sand cushion and clay soils under conditions of harmonic vibrations on the basis of physical and chemical mechanics. It was noted that the Kelvin-Vogt model, currently used for modeling, is not applicable for layered systems that do not have, in principle, concentrated masses. For the occurrence of oscillations in the clay layer, it is necessary that under it there would be a medium reflecting the vertical longitudinal wave. Otherwise, the reverse half-wave will not form, and the compression wave will go deep into the ground and turn into heat in the end. Such problems can be solved only using the theory of wave processes. On the basis of the harmonic analysis of wave processes in layered systems for the ballast track, it is shown that the displacement amplitude at the sand-loam boundary decreases 26 times in the frequency range 1-250 Hz. Along the sleeper, secondary longitudinal and transverse waves arise due to the “transfer” of the energy of the main longitudinal wave into the transverse along the sleepers. As a result, circulation flows along the length of the sleeper occurred as well as irreversible deformation of the prism and the accumulation of defects in the subgrade, the porosity and the probability of splashes of ballast are increased. The best damping and cost properties have constructions with crushed stone in comparison with a ballastless design. However, the stability of the motion on the ballast prism and its inter-repair period depends on the correct organization of drains, especially in spring and autumn. Developed apparatus for determining the degree of stress damping in the structure of the track subgrade and the superstructure can be used to develop a normative document for selecting the design of the subgrade structure of the track, depending on the geological, climatic conditions and the average annual groundwater level. The use of the apparatus of linear harmonic analysis is explained by the fact that the influence of nonlinear effects of wave propagation in dispersed materials does not have time to appear because of the extremely small thicknesses of materials constituting the subgrade.

Structural fatigue assessment of a fixed mono-pile platform

Fatigue assessment of fixed offshore platforms is essentially important to ensure their structural safety. Because of the small-scale leg diameter, these structures are often drag dominated, and linearized wave force is often utilized for the fatigue estimation. To evaluate the influence of nonlinear effect on fatigue damage, the nonlinear drag force is directly incorporated into the computation of the wave force spectrum based on autocorrelation function. The features and the contributions of nonlinear wave force are first investigated in the frequency domain. Then, structural fatigue damage associated with the linear and nonlinear wave forces is compared using a time-domain fatigue assessment method. Investigation indicates that the influence of nonlinear drag force is closely related to the characteristic diameter of the structure. The nonlinear drag force can contribute up to 10% of the total wave force and lead to about 10% structural fatigue life reduction when the characteristic diameter is small.

Thickness and power dependence of the spin-pumping effect inY3Fe5O12/Pt heterostructures measured by the inverse spin Hall effect

The dependence of the spin-pumping effect on the yttrium iron garnet (Y3Fe5O12, YIG) thickness detected by the inverse spin Hall effect (ISHE) has been investigated quantitatively. Due to the spin-pumping effect driven by the magnetization precession in the ferrimagnetic insulator YIG film a spin-polarized electron current is injected into the Pt layer. This spin current is transformed into electrical charge current by means of the ISHE. An increase of the ISHE-voltage with increasing film thickness is observed and compared to the theoretically expected behavior. The effective damping parameter of the YIG/Pt samples is found to be enhanced with decreasing YIG film thickness. The investigated samples exhibit a spin mixing conductance of g=(7.43 \pm 0.36) \times 10^{18} m^{-2} and a spin Hall angle of theta_{ISHE} = 0.009 \pm 0.0008. Furthermore, the influence of nonlinear effects on the generated voltage and on the Gilbert damping parameter at high excitation powers are revealed. It is shown that for small YIG film thicknesses a broadening of the linewidth due to nonlinear effects at high excitation powers is suppressed because of a lack of nonlinear multi-magnon scattering channels. We have found that the variation of the spin-pumping efficiency for thick YIG samples exhibiting pronounced nonlinear effects is much smaller than the nonlinear enhancement of the damping.

Influence of nonlinear effects on the efficiency of a thermoelectric generator

We propose a nonlinear model for thermoelectric coupling which is based on the thermomass theory for heat conduction. We show that in this model, the second Kelvin relation and the classical Onsager relations are no longer satisfied simultaneously, namely, if one holds, then the other one breaks down, and viceversa. As a function of the different breaking, we evaluate the efficiency of a thermoelectric generator. The influence of the electric-charge gradient on the efficiency of thermoelectric coupling is investigated as well.

Review of Research Progresses in Unsteady Aerodynamic Model

Based on the analysis of the flight stability, the research progress of the unsteady aerodynamic model was comprehensively introduced. Bryan, first of all, the aerodynamic load of traditional dynamic derivative model is put forward, still used today in some engineering issues. However, Bryan state parameters of the model is not complete, not exactly reflect the unsteady aerodynamic force time history effect and nonlinear effect. Etkin models, by retaining the item of high order Taylor expansion, including the influence of nonlinear effect. Improved Etkin model can explain the actual flight of some of the common transient response, including due to stall the mutation and aerodynamic force/torque caused by unsteady flow dynamic bifurcation and chaos of the aerodynamic force/torque value and uncertain phenomenon. Finally, the unsteady flow field of a reduced order model development trends and application prospect were analyzed, and pointing out that the CFD simulation is still accurately predict the plane stability and handling the most important method.

Influence of nonlinear effects on the three-photon excitation of L-Tryptophan in water using phase-shaped pulses

We show that nonlinear effects like self-phase modulation in a sample have to be considered for phase control of three-photon excitations. Furthermore, we demonstrate the control of three-photon excitation of L-Tryptophan in water using a pulse-shaping setup. Simulations of the propagation of the laser pulses in the cuvette exhibit good agreement with the experimental fluorescence scans at different laser intensities and show large discrepancies when neglecting nonlinear effects prior to the three-photon process. This can lead to improvements in selective excitation of amino acids by a near-infrared femtosecond laser source.