Nonlinear Response Characteristics Research Articles

Performance of geotechnical seismic isolation system using rubber‐soil mixtures in centrifuge testing

ABSTRACTGeotechnical seismic isolation (GSI) system involves the dynamic interaction between structure and low‐modulus foundation material, such as rubber‐soil mixtures (RSM). Whilst numerical studies have been carried out to demonstrate the potential benefits of GSI‐RSM system, experimental research is indispensable for confirming its isolation mechanism and effectiveness in reducing structural demand. In this regard, centrifuge modelling with an earthquake shaker under an acceleration field of 50 g adopted in this study can mimic the actual nonlinear dynamic response characteristics of RSM and subsoil in a coupled soil‐foundation‐structure system. This is the first time the performance of GSI‐RSM system was examined in a geotechnical centrifuge. It was found that an average of 40‐50% reduction of structural demand can be achieved. The increase in both the horizontal and rotation responses of the foundation was also evidenced. The unique augmented rocking mechanism with reversible foundation rotation was highlighted.

Structural optimization of optoelectronic components in millimeter-wave radio-transmitting modules

The paper analyzes the effect of structure inherent to optoelectronic radio-transmitting modules of a phased array antenna (PAA) on the noise characteristics in the millimeter range (MMR) of waves. Considered are promising structures of MMR modules for generating radiation with a phased array for communication systems based on optoelectronic technologies. The promising types of photodiodes that are used to form MMR radio signals as well as the distance and physical limitations for photodetectors associated with a limited bandwidth and nonlinear response characteristics have been analyzed. Mathematical modeling of the oscillation of the output current after the optoelectronic conversion of the signal and noise characteristics of the radio-transmitting modules capable to form MMR radiation in PAA has been carried out. The analysis of the nonlinearity of the sensitivity of photodiodes in the high-frequency regions of formation of radio signals has been carried out. The necessity to structurally optimize optoelectronic components in the MMR transmission module has been shown depending on the noise characteristics of the output signal. It has been shown that fundamental studies of nonlinear characteristics and factors limiting the band of photodetectors are important tasks for further developing MMR telecommunications of the next generations.

Course-keeping with roll damping control for ships using rudder and fin

To resolve the severe wear problems of steering engine and fin stabilizer, the nonlinear response characteristics of steering engine and fin stabilizer are studied by analyzing sea trial data of ship Yukun. The nonlinear response characteristics are summarized and applied to a rudder and fin hybrid control system. Decoupling, $$\hbox {H}_\infty$$ and $${\rm H}_2$$ controllers are designed to achieve low control frequency for it. Simulations show that all the three controllers can achieve excellent course-keeping and roll damping performances, and their control frequencies and amplitudes are consistent with those of nautical practice. It can be found that $$\hbox {H}_2$$ controller achieves the best response performance of course-keeping and energy saving performance for rudder engine; $$\hbox {H}_\infty$$ controller achieves the best response performance for roll damping; Decoupling controller has the best energy saving performance for fin stabilizer. When the Beaufort wind force scale is increased from 6 to 8 and model perturbation is involved, $$\hbox {H}_2$$ controller shows the best robustness of control performance and control input. In addition, the designed low-order controllers can reduce hardware cost for autopilot realization in nautical field.

Dynamic features of a non-polarized Erbium-doped fiber ring laser subjected to external cavity-loss modulation

An experimental study of an Erbium-doped fiber ring laser subjected to external cavity-loss modulation using a loudspeaker as the modulator has been carried out and analyzed via modulation of the driving amplitude and frequency in the range of 1–20 kHz. The linear and non-linear (chaotic) dynamical behaviors have been observed from the bifurcation, time domain and frequency domain diagrams presented. The bifurcation diagram showed that the loss modulated laser is more sensitive to the acoustic wave generated from the loudspeaker when the driving amplitude is < 200 mV and < 1000 mV (< 16.5 mW and < 82.5 mW optical power). At driving amplitudes of 500 mV – 1000 mV (41.25 mW – 82.5 mW optical power), the ring laser system behaves like a damped non-linear oscillator. Optical bi-stability was also observed in the bifurcation diagrams near or exactly at the fundamental resonance frequency and first super harmonic resonance frequency. The availability of different control parameters during external cavity-loss modulation in an Erbium doped fiber laser makes the study of its non-linear response features easy in a very precise way. The control parameters considered in this paper are the driving amplitude and the modulation frequency.

A study of the dissipation of energy in the helmet due to a blast on a helmet–skull–brain assembly

We present a mathematical model to study the dissipation of energy in a composite helmet that is subjected to blast loading. In addition to assuming a constitutive relation for the material of the helmet, we also assume models for the skull, and brain, all of them being treated as homogeneous isotropic bodies. A rate type model with non-linear dissipative response characteristics is assumed within the context of a thermodynamic framework for the helmet, as well as the skull, and brain. We study the effect of orientation, the region of impact, the dissipative materials used in the helmet, and the interface condition between the helmet and head assembly. We present a numerical simulation corresponding to different dissipative mechanisms that lead to multiple wave transmissions and reflections that could be detrimental to the brain, highlighting the necessity to pick the materials for the helmet with great care.

Morphing of symmetric cross-ply cylindrical shells by minimising the Brazier moment: Optimised hinge folding

Aerospace and industries where both localised compliance and weight savings play a central role in design can benefit from using flexible hinges. These morphing structures use no mechanical hinges for folding. They fold by exploiting the limit point, i.e. the Brazier moment, of a geometrically nonlinear structural response characteristic of thin-walled beams under bending. Therefore, a smaller Brazier moment induces smaller non-classical stresses in the hinge during folding.Two aspects make cross-ply laminates attractive for designing flexible hinges. Firstly, the difference between the Brazier moment of an optimal symmetric generic laminate and that of an optimal symmetric cross-ply is relatively small. Secondly, cross-ply laminates do not exhibit extension-shear or bend-twist couplings which can induce complex deformations which can present challenges during design, especially considering that available analytical solutions of the Brazier moment neglect their effects. Driven by these premises, this work contributes to the preliminary design of flexible hinges by offering an analytical solution of the optimum symmetric cross-ply laminate for minimising the Brazier moment, which is subsequently validated through geometrically nonlinear finite element analysis. Moreover, this work provides insights into the prediction of the folding load considering the effects of local buckling instabilities.

Modeling and nonlinear dynamics of thermomechanically coupled composite plates

An overview of extended research recently pursued on unified continuous/reduced-order modeling and nonlinear dynamics of thermomechanical composite plates of interest in aerospace, mechanical and civil engineering is presented. Reduced models exhibit the fundamental features of geometrical nonlinearity and thermomechanical coupling of the underlying continua. The role of multiphysics coupling and the main features of nonlinear response obtained with variably refined minimal models is highlighted. Besides transverse mechanical excitation and mechanically or thermally-induced buckling, a variety of active thermal excitations, of body or boundary nature, are considered. Features of thermal response obtained with variably refined thermal assumptions are compared, in view of detecting cheap, yet reliable, models to be used for systematic numerical investigations. The effects of two-way thermomechanical coupling on local and global nonlinear dynamics are addressed through bifurcation diagrams, phase portraits and planar cross sections of 4D basins of attraction, highlighting the important role played by the slow transient thermal dynamics solely detectable with coupled models in the steady outcome of the swifter mechanical response. Conditions allowing to utilize partially coupled models or even the uncoupled mechanical one with prescribed steady temperature are discussed.

Synthesis, growth, optical and third-order nonlinear optical properties of glycine sodium nitrate single crystal for photonic device applications

Glycine and its related compounds play a prominent role in the field of nonlinear optical studies and of fibre optical communication. In the present work, glycine sodium nitrate (GSN) crystal was grown using the method of slow evaporation method. The GSN crystal belongs to space group Cc in the monoclinic system. Using the FTIR spectrophotometer, the different functional groups have been qualitatively identified. A UV–Vis–NIR spectroscopy was used to record the optical absorption spectra, and the optical energy bandgap of GSN crystal is reported. The SHG conversion efficiency of GSN is determined by Kurtz and Perry technique. The Z-scan experiment was conducted to analyze GSN crystal for third-order NLO behavior and it is used to calculate the values of the nonlinear absorption coefficient, nonlinear refractive index, and third-order nonlinear susceptibility. Third-generation harmonic studies reveal that GSN is an excellent material useful in the fabrication of NLO devices due to its nonlinear response characteristics. The thermal stability of the grown crystal was determined through TG/DTA examination. Also photoconductivity studies confirm the negative photoconductive behavior of GSN and I–V characteristics measurement that have been carried out. The dielectric loss is significantly low and this supports defect-free growth of the crystal. These properties of GSN make it a good candidate in the fabrication of NLO devices.

RETRACTED ARTICLE: Dynamic boundary of floating platform and its influence on the deepwater testing tube

ABSTRACT The motion of the floating platform is one of the important factors influencing the safety of testing string. The allowable motion limits of various floating drilling platforms are discussed and their calculation formulas are presented, based on which the nonlinear dynamic response characteristics of the testing tube are investigated through ABAQUS software. Results show that an excessive offset of floating platform will cause many problems to testing tube, such as operation difficulty in rising and landing pipe string, disconnection difficulty of testing tree in case of emergency. Under heave motion and slow drift motion condition, the maximum Mises stress appears in the part closed to the upper end. The heave and horizontal motions of the platform have a superposition influence on the axial force of the pipe. So, a more precise dynamic theoretical model should be developed to study the longitudinal-transverse coupled vibration of testing string in the future.

Nonlinear dynamics analysis on intermediate bearing-dual rotor system for a marine gas turbine

In this paper, a marine dual-rotor gas turbine is taken as the research object, and a dual-rotor system model with a simplified structure and supported by intermediary bearings is established based on its structural characteristics and nonlinear characteristics of bearings. The Lagrange equation of motion is used to derive the differential equations of motion of the system, and the fourth-order Runge-Kutta method is used to solve the equations. The nonlinear dynamic response and bifurcation chaotic characteristics of the dual-rotor system with speed changes are studied. The results show that when the speed is low, the system is in a single-cycle motion. As the rotational speed increases, the system exhibits multiplicative bifurcation, Hopf bifurcation and chaotic behaviour. This result provides theoretical guidance for the design and safe and stable operation of the rotor system.

On the Nonlinear Seismic Responses of Shock Absorber-Equipped Porcelain Electrical Components

Porcelain electrical equipment is prone to brittle failure due to resonance under seismic effects. To improve its seismic resistance, some researchers have conducted research on shock absorption technology for porcelain electrical equipment. However, extant research fails to provide a detailed and systematic study of the effect of the nonlinear characteristics of these shock absorbers on the performance of equipment under seismic effects. This paper provides a theoretical analysis, verified by shaking table testing, of the performance of a 1000 kV pillar-type porcelain lightning arrester. The Bouc–Wen model is fitted to the force-displacement curve of hysteretic nonlinear metal shock absorbers, and a dynamic model of, and equations for, pillar-type porcelain electrical components are derived, taking into account their nonlinear characteristics. This reveals the influence of the nonlinear characteristics of shock absorbers on the nonlinear seismic response characteristics of these components. Our results indicate that the seismic responses of pillar-type porcelain components can be effectively suppressed by hysteretic nonlinear shock absorbers and that the greater the intensity of the seismic waves, the more obvious the efficiency of shock absorption. However, as the installation radius and yield force of the installed shock absorbers increase, their shock absorption efficiency gradually decreases.

Simulation of nonlinear vibration responses of cab system subject to suspension damper complete failure for trucks

The strong vibration responses of the cab system can be restrained by the damper force and the friction of the suspensions for trucks. After the failures of dampers, especially in the case of the complete failure, the anti vibration effect of the friction is prominent. However, the nonlinear vibration response characteristics of the cab subject to the damper complete failure have not been revealed. In order to reveal the nonlinear vibration response characteristics, a dynamic model of the cab system was established and its vibration equations were given. The friction forces existing in the suspensions were determined by the bench test. The influences of the friction forces on the cab vibration under different amplitude harmonic inputs were investigated when the dampers completely fail. The cab vertical displacement changes with the excitation amplitude and the vibration represents various motion states, including the periodic motion, the quasi-periodic motion, and the chaotic motion. The simulation results show that when the dampers fail, the proper friction forces help to suppress the quasi-periodic motion and the chaotic motion of the cab and to reduce the amplitude of the periodic motion. The proper friction forces can make the cab movement far away from the chaos area. They also help to avoid the fatigue damage of the cab floor and suspension parts to improve the service life of the suspension parts and to reduce the maintenance cost of the cab suspensions.

Effects of heave plate on dynamic response of floating wind turbine Spar platform under the coupling effect of wind and wave

Stability of the platform is the most fundamental guarantee for floating offshore wind turbines. In order to explore hydrodynamics of floating wind turbine Spar platform under the coupling effect of wind and wave, whole model of floating wind turbine is established based on the OC3-Hywind Spar Buoy platform and the NREL 5 MW wind turbine. Taking the research experiences of traditional marine engineering, this work proposed the structural design method of installing heave plate on main body of Spar. Based on the Bladed Element Momentum theory, this paper adopts FORTRAN language to accomplish the secondary development of hydrodynamic software AQWA to establish the coupled aerodynamic - hydrodynamic - mooring line system model. The amplitude-frequency curves of the added mass, radiation damping, wave exciting force and response amplitude operators (RAO) were obtained based on radiation/diffraction theory to investigate the hydrodynamic performance of floating wind turbine Spar platform in frequency domain. In the time-domain analysis, the three kinds of working conditions include wave-only, non-coupling effect of wind-wave and coupling effect of wind-wave were conducted comparatively to verify the importance of wind load and wind - wave interaction. In addition, the actual motions of original Spar and Spar with heave plates were analyzed to explore the effects of the heave plate and its installation position on the nonlinear dynamic response characteristics of Spar under the coupling effect of wind and wave. The research results indicated that the installation position of the heave plate has little influence on the surge response. In view of the actual heave motion, the heave plate can play a positive effect no matter where the heave plate is installed. When the heave plate is located on the upper part of the platform, the pitch response and the intensity of the fluctuation of the platform will be greatly reduced. Finally, time domain mooring analysis for Spar platform with and without heave plate is performed to illustrate the feasibility of the present approach for mooring modeling.

Nonlinear analysis of a geared rotor system supported by fluid film journal bearings

This paper presents a novel approach for modeling and analyzing a geared rotor-bearing system including nonlinear forces in the gear set and the supporting fluid film journal bearings. The rotordynamics system model has five degrees of freedom that define the transverse displacements of the shaft-gear centerlines and the relative displacement of the gear tooth contact point. The journal bearing nonlinear forces are obtained via a solution of Reynolds equation for lubricant film pressure utilizing the finite element method. Co-existing, steady-state, autonomous and non-autonomous responses are obtained in an accurate and computationally efficient manner utilizing the multiple shooting and continuation algorithms. This yields the full manifolds of the multiple bifurcation system. Chaos is identified with maximum Lyapunov exponents, frequency spectra, Poincaré attractors, etc. The results reveal a dependence of the gear set contact conditions and system nonlinear response characteristics, i.e. jump, co-existing responses, subharmonic resonances and chaos on the choice of journal bearing parameters. The results also show that Hopf bifurcations, which occur along with oil whirl in a journal bearing system, can be attenuated by increasing the gear torque.

Optical and Nonlinear Properties of Photonic Polymer Nanocomposites and Holographic Gratings Modified with Noble Metal Nanoparticles.

Nanocomposites based on transparent polymer matrices containing nanoparticles (NPs) of noble metals are modern-day materials that can be specially designed for photonics, linear and nonlinear optics, laser physics and sensing applications. We present the improved photosensitive nanocomposites doped with Au and Ag NPs allowing fabrication of high effective submicrometer dimensional diffraction structures using holographic method. A general approach for the fabrication of holographic structures using a two-component mixture of the monomers of different reactivity was developed. Two different methods, ex situ and in situ, were studied to introduce Au and Ag NPs in the polymer matrix. The diffusion model of the grating formation upon holographic exposure as well as the process of Ag NP synthesis in a polymer matrix is considered. The influence of the NP size on the polymerization process, material dynamic range and nonlinear properties were investigated. The mechanisms and characteristics of the nanocomposite nonlinear optical response are discussed.

MXene Nanosheets: Harmonic Mode‐Locked Er‐Doped Fiber Laser by Evanescent Field‐Based MXene Ti3C2Tx (T = F, O, or OH) Saturable Absorber (Ann. Phys. 1/2020)

MXenes, as a legendary family of two-dimensional (2D) van der Waals nanosheets materials, have been extensively studied due to their unique characteristics of broadband nonlinear optical response. In article number 1900437, Xiaohui Li, Han Zhang, and co-workers characterize MXene nanosheets systemically, and successfully apply MXene nanosheets in an Er-doped fiber laser to achieve harmonic mode-locking with a repetition frequency of 218.4 MHz.

Nonlinear response characteristics of neural networks and single neurons undergoing optogenetic excitation

Optogenetic stimulation has become the method of choice for investigating neural computation in populations of neurons. Optogenetic experiments often aim to elicit a network response by stimulating specific groups of neurons. However, this is complicated by the fact that optogenetic stimulation is nonlinear, more light does not always equal to more spikes, and neurons that are not directly but indirectly stimulated could have a major impact on how networks respond to optogenetic stimulation. To clarify how optogenetic excitation of some neurons alters the network dynamics, we studied the temporal and spatial response of individual neurons and recurrent neural networks. In individual neurons, we find that neurons show a monotonic, saturating rate response to increasing light intensity and a nonmonotonic rate response to increasing pulse frequency. At the network level, we find that Gaussian light beams elicit spatial firing rate responses that are substantially broader than the stimulus profile. In summary, our analysis and our network simulation code allow us to predict the outcome of an optogenetic experiment and to assess whether the observed effects can be attributed to direct or indirect stimulation of neurons.

Excitation states of metabolic networks predict dose-response fingerprinting and ligand pulse phase signalling

With a computational model of energy metabolism in an astrocyte, we show how a system of enzymes in a cascade can act as a functional unit of interdependent reactions, rather than merely a series of independent reactions. These systems may exist in multiple states, depending on the level of stimulation, and the effects of substrates at any point will depend on those states. Response trajectories of metabolites downstream from cAMP-stimulated glycogenolysis exhibit a host of non-linear dynamical response characteristics including hysteresis and response envelopes. Dose-dependent phase transitions predict a novel intracellular signalling mechanism and suggest a theoretical framework that could be relevant to single cell information processing, drug discovery or synthetic biology. Ligands may produce unique dose-response fingerprints depending on the state of the system, allowing selective output tuning. We conclude with the observation that state- and dose-dependent phase transitions, what we dub “ligand pulses” (LPs), may carry information and resemble action potentials (APs) generated from excitatory postsynaptic potentials. In our model, the relevant information from a cAMP-dependent glycolytic cascade in astrocytes could reflect the level of neuromodulatory input that signals an energy demand threshold. We propose that both APs and LPs represent specialized cases of molecular phase signalling with a common evolutionary root.

Harmonic Mode‐Locked Er‐Doped Fiber Laser by Evanescent Field‐Based MXene Ti3C2Tx (T = F, O, or OH) Saturable Absorber

AbstractMXenes, as a legendary family of 2D van der Waals nanosheets materials, are extensively studied due to their unique characteristics of broadband nonlinear optical response. In particular, MXenes have excellent nonlinear optical properties of very large nonlinear absorption coefficients and very large nonlinear refractive indexes, which have attracted people's great attentions to study the application of MXenes in photonics, electronics, and optoelectronics in recent years. However, the high‐repetition‐rate (HRR) ultrafast pulses are not explored based on these kinds of materials. MXene Ti3C2Tx saturable absorber (SA) based on micro‐fiber is fabricated by optical deposition method. Here, MXene Ti3C2Tx SA is used to achieve 36th harmonic mode‐locking with a repetition rate of 218.4 MHz, a central wavelength of 1566.9 nm, the pulse width of 850 fs, and the spectral width of 3.51 nm. The maximum average output power and pulse energy are 6.95 mW and 0.032 nJ, respectively. This research based on MXene Ti3C2Tx light modulator opens a bright avenue for advanced nonlinear photonics.

Constrained inference in sparse coding reproduces contextual effects and predicts laminar neural dynamics.

When probed with complex stimuli that extend beyond their classical receptive field, neurons in primary visual cortex display complex and non-linear response characteristics. Sparse coding models reproduce some of the observed contextual effects, but still fail to provide a satisfactory explanation in terms of realistic neural structures and cortical mechanisms, since the connection scheme they propose consists only of interactions among neurons with overlapping input fields. Here we propose an extended generative model for visual scenes that includes spatial dependencies among different features. We derive a neurophysiologically realistic inference scheme under the constraint that neurons have direct access only to local image information. The scheme can be interpreted as a network in primary visual cortex where two neural populations are organized in different layers within orientation hypercolumns that are connected by local, short-range and long-range recurrent interactions. When trained with natural images, the model predicts a connectivity structure linking neurons with similar orientation preferences matching the typical patterns found for long-ranging horizontal axons and feedback projections in visual cortex. Subjected to contextual stimuli typically used in empirical studies, our model replicates several hallmark effects of contextual processing and predicts characteristic differences for surround modulation between the two model populations. In summary, our model provides a novel framework for contextual processing in the visual system proposing a well-defined functional role for horizontal axons and feedback projections.