Strong Nonlinear Conditions Research Articles

Nonlinear dynamic characteristics and stability analysis of energy storage flywheel rotor with shape memory alloy damper

In this paper, the nonlinear dynamic characteristics and stability of an energy storage flywheel rotor with shape memory alloys (SMA) damper are studied. A new type of SMA constitutive model is proposed to express SMA's hysteresis properties, and the nonlinear dynamic model of an energy storage flywheel rotor with SMA damper is established. A developed multi-scale method is proposed to obtain the natural frequency of the system with high accuracy in strong nonlinear condition, and the nonlinear dynamic characteristics of the system are analyzed. To a cracked flywheel rotor, a time-varying function is proposed to express the effect of the crack depth on the system's stiffness, and the variation of the system's area with different parameters is discussed. Simulation results show that the nonlinearity and crack will both affect the stable area of the system. To a flywheel rotor subjected to stochastic excitation, a developed analysis method for the stability is proposed to obtain the global stability of the system. Finally, the conditions on stochastic bifurcation are determined. Simulation results show that the stochastic system's motion will change from balance point to periodic orbit, and will also jump from one orbit to another in special cases. The results of this paper are helpful for the design of energy storage flywheel rotor.

A new type of nonlinear hysteretic model for magnetorheological elastomer and its application

In this paper, a new type of nonlinear hysteretic model for MRE is proposed. Natural frequency is introduced to the hysteretic model to offset the influence of the loading rate on the hysteresis loop. A kind of developed multi-scale method is proposed to solve the natural frequency under strong nonlinear conditions. Based the new hysteretic model, the dynamic characteristics of a MRE sandwich plate with four sides simply supported and by the in-plane stochastic load are discussed. The simulation results show that the new hysteretic model is hardly affected by the loading rate and should be an ideal model for viscoelastic materials; there are abundant types of stochastic bifurcation in the system.

Prediction Method of Ocean Wave Spectrum Based on an Echo State Network

Zhang, X.; Yang, B.; Sun, H., and Zhang, S., 2020. Prediction method of ocean wave spectrum based on an echo state network. In: Zheng, C.W.; Wang, Q.; Zhan, C., and Yang, S.B. (eds.), Air-Sea Interaction and Coastal Environments of the Maritime and Polar Silk Roads. Journal of Coastal Research, Special Issue No. 99, pp. 319–323. Coconut Creek (Florida), ISSN 0749-0208.In order to realize the prediction of ocean wave spectrum under strong nonlinear conditions, a new method combining the empirical mode decomposition (EMD) and an echo state neural network (ESN) is proposed based on ocean wave spectral data measured by shipborne X-band radar. The proposed method uses empirical mode decomposition to decompose the time series of the strongly nonlinear wavelet spectral density values so that the nonlinearity and nonstationarity of the obtained subsequence is greatly reduced compared with the original sequence, and the echo state neural network can be applied separately. By superimposing the prediction results, the predicted values of the wavelet spectral density can be obtained, and the entire ocean wave spectral information can be further combined. The results show that the method can effectively solve the problem of poor prediction effects under strong nonlinear conditions. The method can provide a certain basis for ships to obtain wave spectral information in real time and improve the practicability of shipborne wave radar systems.

The performance improvement of visible light communication systems under strong nonlinearities based on Gaussian mixture model

AbstractNonlinearity is a major problem in visible light communication (VLC). In recent years, machine learning has emerged and has been widely used in many fields. Among them, the nonlinear algorithms have gradually become a powerful tool to solve the nonlinearity in VLC. In this article, we compare the performance of two main clustering algorithms—Gaussian mixture model (GMM) and K‐means under strong nonlinear conditions. Experimental results show that the signal peak‐to‐peak voltage (Vpp)r range is approximately 0.25 V that meets the BER threshold of forward error correction when using GMM and is larger than the range using K‐means under the data rate is 1.5 Gbps.

Nonlinear theory for axisymmetric self-similar two-dimensional oscillations of electrons in cold plasma with constant proton background

We consider simultaneous oscillations of electrons moving both along the axis of symmetry and also in the direction perpendicular to the axis. We derive a system of three nonlinear ordinary differential equations which describe self-similar oscillations of cold electrons in a constant proton density background (np = n0 = constant). These three equations represent an exact class of solutions. For weak nonlinear conditions, the frequency spectra of electric field oscillations exhibit split frequency behavior at the Langmuir frequency ωp0 and its harmonics, as well as presence of difference frequencies at low spectral values. For strong nonlinear conditions, the spectra contain peaks at frequencies with values ωp0(n+m2), where n and m are integer numbers (positive and negative). We predict that both spectral types (weak and strong) should be observed in plasmas where axial symmetry may exist. To illustrate possible applications of our theory, we present a spectrum of electric field oscillations observed in situ in the solar wind by the WAVES experiment on the Wind spacecraft during the passage of a type III solar radio burst.

Modeling Rapid Flood Propagation Over Natural Terrains Using a Well-Balanced Scheme

AbstractThe consequences of rapid and extreme flooding events, such as tsunamis, riverine flooding, and dam breaks show the necessity of developing efficient and accurate tools for studying these flow fields and devising appropriate mitigation plans for threatened sites. Two-dimensional simulations of these flows can provide information about the temporal evolution of water depth and velocities, but the accurate prediction of the arrival time of floods and the extent of inundated areas still poses a significant challenge for numerical models of rapid flows over rough and variable topographies. Careful numerical treatments are required to reproduce the sudden changes in velocities and water depths, evolving under strong nonlinear conditions that often lead to breaking waves or bores. In addition, new controlled experiments of flood propagation in complex geometries are also needed to provide data for testing the models and evaluating their performance in more realistic conditions. This work implements a ro...

Research on Nonlinear Dynamical Behaviors of Mine Hoist Transmission System under External Excitation

For the research on dynamical behaviors of mine hoist transmission system under strong nonlinear condition, the dynamic equation with nonlinear stiffness, nonlinear damping and external excitation is established. With the method of modified Lindstedt-Poincare, the influence of system parameters on amplitude-frequency characteristic is analyzed. Last, the complex dynamical behaviors caused by the change of excitation amplitude is studied through numerical simulation, and the evolution process from stability to chaos is described by the use of bifurcation diagram, maximum Lyapunov index figure and Poincare section graph. This provides a theoretical basis for further research of mine hoist transmission system.