Strong Damping Effect Research Articles

Ultrastretchable hydrogels with strong damping effects

Ultrastretchable hydrogels with strong damping effects

Analytical solutions for hyaluronic acid flow and heat transfer between joints with periodic oscillations under the magnetic field

Osteoarthritis (OA) is a globally prevalent disease that poses significant challenges to the daily work and life of patients. Viscosupplementation is one of the most commonly used drug treatments for OA, which involves injecting hyaluronic acid (HA) into the joint cavity to alleviate synovial inflammation. The current research aims to explore the rheological and thermal behavior of HA between joints by studying the axisymmetric squeezing flow and heat transfer of incompressible Maxwell fluid under the action of static magnetic field between two rigid spheres with partial wall slip. The analytical solutions for velocity and temperature are obtained by using the Laplace integral variational theory. Detailed explanations are provided on the effects of different fluid parameters on velocity and temperature, presented in the form of charts. It can be shown that as the magnetic field intensity increases, the viscosity of HA increases with the increasing of relaxation time, thereby fluid motion is weakened and a strong damping effect is produced. As the frequency of joints motion increases, the velocity distribution becomes more uniform in the central region, and the overall distribution deviates from a parabolic distribution. In addition, as Reynolds number, Prandtl number and squeezing depth increase, the heat transfer capacity of the fluid decreases, resulting in a lower temperature at the top wall and a higher temperature at the bottom wall. This study provides theoretical support for exploring the rheological and thermal behavior characteristics of HA in the treatment of OA.

Vibration damping by periodic additive acoustic black holes

Embedded acoustic black holes (ABHs) have demonstrated significant efficiency in vibration mitigation. However, their practical application is limited due to their inherent low strength. To address this issue, this paper introduces an alternative approach of additive ABHs, which are periodically mounted on the host structure to simultaneously enhance structural rigidity and damping effects. The Gaussian expansion method (GEM) is employed to model the ABH beam and base beam within the framework of Timoshenko beam theory. The coupling between the two substructures is achieved using the nullspace method (NSM) based on the interface coupling condition. Additionally, the wave and Rayleigh–Ritz method (WRRM) is utilized to handle the Bloch-Floquet periodic boundary conditions. The complex dispersion curves are obtained using the k(ω) method, where the imaginary part represents the attenuating waves in space. The accuracy of the proposed model is validated against finite element simulations for the unit cell modes and dispersion curves. The results indicate that local resonance dominates the behavior, overshadowing the Bragg scattering effect. Furthermore, the inclusion of a damping layer results in a strong damping effect across a wide frequency band. Parametric studies reveal that larger lattice constant and increased uniform portion thickness of the ABH contribute to better damping performance, albeit with an associated increase in the added mass of the ABH component. Finally, the damping capability of finite periodic beams with 5 cells is investigated, assessing modal loss factor (MLF), transmissibility, and forced vibration shapes. The findings demonstrate that the proposed additive ABH approach opens up new possibilities for engineering applications.

Nonlinear Analysis of Cross Rolls of Electrically Conducting Fluid under an Applied Magnetic Field with Rotation

The proposed planer layer dynamo physical model has real-world applications, especially in the Earth’s liquid core. Thus, in this paper, an attempt is made to understand the finite amplitude convection when there exists a coupling between the Lorentz force and the Coriolis force. In particular, the effect of a horizontally applied magnetic field is studied on the Rayleigh–Bénard convection (RBC) that contains the electrically conducting fluid and rotates about its vertical axis. Free–free boundary conditions are assumed on the geometry. Attention is focused on the nonlinear convective flow behavior during the occurrence of cross rolls which are perpendicular to the applied magnetic field and parallel to the rotation axis. The visualization of cross rolls is achieved using the Fourier analysis of perturbations up to the O(ε8). The relationship of the Nusselt number (Nu) with respect to the Rayleigh number (R), the Ekman number (E), and the Elsasser number (Λ) is investigated. It is observed that E generates a strong damping effect on the flow velocity and on the heat transfer at high rotation rates. Using the heatline concept, it is observed that the temperature within the central regime is enhanced as the Λ increases. The results show that either E decreases or Λ increases, then the heat transfer rate increases.

Numerical study of the high-intensity heat conduction effect on turbulence induced by the ablative Rayleigh–Taylor instability

By adopting heat conduction of the Spitzer form in implicit large eddy simulations, the effect of high-intensity heat conduction on turbulence induced by the ablative Rayleigh–Taylor instability is studied in this paper. The height of the spike and bubble exhibit self-similar evolution with t2 dependence by the late stage of simulations, while heat conduction suppresses the coefficient of spike αs and slightly enhances that of the bubble αb. Heat conduction displays a strong damping effect for small-scale fluctuations of the temperature and density field, resulting in a much steeper slope for energy spectra in intermediate scales. The diffusion effect is responsible for the suppression of temperature fluctuations, and velocity dilatation is shown to be a possible route for heat conduction to affect density fluctuations. The impact of heat conduction on the velocity field is relatively weak, with vertical velocity spectra exhibiting classical Kolmogorov inertial range in intermediate scales. By comparing enstrophy profiles, it is found that vorticity tends to peak at the bubble side in cases with high-intensity heat conduction.

On the collisional damping of plasma velocity space instabilities

For plasma velocity space instabilities driven by particle distributions significantly deviated from a Maxwellian, weak collisions can damp the instabilities by an amount that is significantly beyond the collisional rate itself. This is attributed to the dual role of collisions that tend to relax the plasma distribution toward a Maxwellian and to suppress the linearly perturbed distribution function. The former effect can dominate in cases where the unstable non-Maxwellian distribution is driven by collisionless transport on a timescale much shorter than that of collisions, and the growth rate of the ideal instability has a sensitive dependence on the distribution function. The whistler instability driven by electrostatically trapped electrons is used as an example to elucidate such a strong collisional damping effect of plasma velocity space instabilities, which is confirmed by first-principles kinetic simulations.

Recent progress of gold nanostructures and their applications.

For noble metals, such as gold (Au) and silver (Ag), it is well-known that surface plasmons of their nanocrystals have significant spatial confinement and propagation loss due to the strong damping effect and the scattering between the plasmons and phonons. Noble metal nanostructures are usually referred to as "plasmonic nanostructures" in many studies. Based on the resonance effect of surface plasmons, the electromagnetic field can be localized on the subwavelength scale, which induces a booming new field of nanophotonics. Among the various nanostructures, Au nanostructures have received extensive attention both in fundamental research and technological fields due to their unique localized surface plasmon characteristics. These characteristics include strong optical extinction, near-field enhancement, and far-field scattering. By changing either the morphological parameters or the surrounding medium of nanostructures, the localized surface plasmon resonance (SPR) of Au nanostructures can be tuned in a large spectral region from visible to near infrared (Vis-NIR) wavelength. Corresponding to the experimental research, there are several numerical techniques that enable modeling the optical characteristics of Au nanostructures in different shapes and assemblies. The most popular technique is the finite-difference time-domain (FDTD) method for modeling various nanostructures and nanoscale optical devices. The accuracy of the computational models has been proven by reliable experimental data. In this review, we focused on Au nanostructures of different morphologies, such as nanorods, nanocubes, nanobipyramids and nanostars. Then combined with FDTD simulations, we described the effect of morphological parameters and the surrounding medium on the SPR properties of Au nanostructures. More and more achievements indicate that the surface plasmon effect is promising in many technical fields. In the last part, we summarize some typical applications of plasmonic Au nanostructures, such as high sensitivity sensors, photothermal conversion with hot electron effects and photoelectric devices, as well as plasmonic nanolasers.

Experimental and performance analysis of the combined damping system with a TMD and a multiple unidirectional single-particle damper

Although the tuned mass damper (TMD) is characterized by simple construction, a definite damping mechanism, and a strong damping effect, a narrow damping frequency band, a detuning effect, and large occupied space limit its application in practical engineering. Particle dampers have the advantages of damping frequency bandwidth and small space, but the damping effect is unsatisfactory. Therefore, a new combined damping system (CTP) containing a TMD and a multiple unidirectional single-particle damper (MUSPD) was developed. A series of shaking table tests for a controlled and uncontrolled structure were conducted to investigate the performance of the system, and the damping effects of a TMD, MUSPD and CTP subjected to harmonic excitation, normal ground motions, rock ground motions, and soft ground motions were compared and analyzed. Finally, a mechanical model of the CTP and corresponding numerical simulation method were developed based on its damping mechanism. The results indicate that a CTP can effectively integrate the advantages of a TMD and MUSPD, and exhibits a better damping effect, wider damping frequency band, and stronger robustness. The shaking table test demonstrates the rationality and feasibility of a simulation method for a CTP.

Thermo-elastostatic analyzes of new dampers made of polymer springs with negative thermal expansion

The article presents original results of research of the dampers with passive and semi-active damping using polymer springs (also artificial muscles or nylon springs) with negative thermal expansion. Passive damping can be ensured by the strong damping effects of polymer springs. Semi-active damping can be provided by heating the springs from an additional heat source. According to design such dampers, mathematical models for analytical elastostatic and thermoelastostatic analyzes of dampers for selected load cases are processed in the paper. The permissible values of mechanical and thermal load of the dampers are determined. The obtained results are verified by numerical analysis using the finite element method. The elastostatics of the passive damper and its damping functionality have been verified on a real model of the damper. The compiled mathematical models can be used in the design of polymer dampers as well as in their automatic control. Designed and analysed dampers can be used in smaller mobile or stationary systems such as scooters, small car kits and the like. The elastodynamic functionality of the dampers with passive and semiactive damping will be presented and discussed in our further paper.

Strong damping effect of chemo-repulsion prevents blow-up

In this paper, we study Keller–Segel type chemotaxis systems with power-like nonlinear sensitivity, production of signals, and switching chemotaxis mechanism. We establish explicit relations to ensure local- and global-in-time boundedness of classical solutions. In the chemo-attractive setting, our results cover and unify separate cases and they are critical to the quite known blow-up results in the existing literature, while, in the chemo-repulsive setting, we find that much wider regimes compared to the attraction case can ensure global existence and boundedness. In comparison to the known results on the dichotomy between global solvability and blow-up for the associated chemo-attraction system, our findings reveal that the strong damping effect of chemo-repulsion prevents blow-up. Furthermore, our 3D local-in-time boundedness moves one step further toward the yet-to-be-proven popular saying that no blow-up would occur in the 3D minimal chemo-repulsion model.

Spin waves in metallic iron and nickel measured by soft x-ray resonant inelastic scattering

The spin-wave dispersions in iron and nickel along the [111] direction are determined using soft x-ray resonant inelastic x-ray scattering (RIXS). For iron, a 10-nm thin film was studied and, over the limited $q$ range accessible, the peaks disperse as expected for a spin wave and in agreement with inelastic neutron scattering (INS) results. At the higher $q$ values damping is observed with the peaks weakening and broadening. This damping is less pronounced than in the INS studies. The RIXS results are also compared with ab initio spin fluctuation calculations. The calculations slightly underestimate the energy dispersion and the damping is larger than in the measurement. Nevertheless, the agreement between the RIXS results, INS studies, and the theory is quite satisfactory. For the single crystal of nickel, the measured $q$ dispersion flattens out rapidly and the peaks broaden. The strong damping effect is reproduced by the spin fluctuation calculations but the energy of the peaks is largely overestimated. Nevertheless, the flattening of the dispersion is not reproduced by the calculations and, although similar effects were observed in early INS experiments, they are not seen in more recent work. Possible reasons for this are discussed. These measurements show that using soft x-ray RIXS to study spin fluctuations in metallic systems, which are in general very challenging for the technique, has much promise. More interestingly, since the iron measurements were performed on a 10-nm thin film, the study opens the possibility to study tailor-made thin-film samples, which cannot be easily studied by other techniques. Combining these studies with state-of-the-art ab initio calculations opens up interesting prospects for testing our understanding of spin waves in metallic systems.

Influence of vibration frequency variation on poroelastic response of intervertebral disc of lumbar spine

Long-time working under whole body vibration might accelerate the degeneration of spine and lead to low back pain and other spinal diseases. A poroelastic finite element model of L4-L5 disc segment was generated to investigate the biomechanical response of lumbar spine under different frequency vibration loads. The results show that the change of the deformation, pore pressure, stress and fluid flow under 8 Hz and 11.5 Hz vibration loads appears periodic; however, the change under lower frequency vibration loads (1 Hz and 4 Hz) is relatively gentle. With increasing time, the axial displacement of disc increases, the liquid gradually flows away and the pore pressure and effective stress in nucleus all show an upward trend. The deformation, stress and fluid flow of the L4-L5 disc segment present a periodicity under higher-frequency vibration loads; however, the fluctuation period is larger than the load frequency, which means that the poroelastic characteristic of intervertebral disc presents a strong damping effect. The effective stress and pore pressure of the nucleus show a rising trend under vibration loads. The findings of this study exhibited the poroelastic performance of the spine under different frequency vibration loads.

Modified multiple time scale method for solving strongly nonlinear damped forced vibration systems

Abstract In this paper, modified multiple time scale (MTS) method is employed to solve strongly nonlinear forced vibration systems. The first-order approximation is only considered in order to avoid complexicity. The formulations and the determination of the solution procedure are very easy and straightforward. The classical multiple time scale (MS) and multiple scales Lindstedt-Poincare method (MSLP) do not give desire result for the strongly damped forced vibration systems with strong damping effects. The main aim of this paper is to remove these limitations. Two examples are considered to illustrate the effectiveness and convenience of the present procedure. The approximate external frequencies and the corresponding approximate solutions are determined by the present method. The results give good coincidence with corresponding numerical solution (considered to be exact) and also provide better result than other existing results. For weak nonlinearities with weak damping effect, the absolute relative error measures (first-order approximate external frequency) in this paper is only 0.07% when amplitude A = 1.5 , while the relative error gives MSLP method is surprisingly 28.81%. Furthermore, for strong nonlinearities with strong damping effect, the absolute relative error found in this article is only 0.02%, whereas the relative error obtained by MSLP method is 24.18%. Therefore, the present method is not only valid for weakly nonlinear damped forced systems, but also gives better result for strongly nonlinear systems with both small and strong damping effect.

Vertical Structure and Energetics of the Western Pacific Teleconnection Pattern

AbstractThe western Pacific (WP) pattern, characterized by north–south dipolar anomalies in pressure over the Far East and western North Pacific, is known as one of the dominant teleconnection patterns in the wintertime Northern Hemisphere. Composite analysis reveals that monthly height anomalies exhibit baroclinic structure with their phase lines tilting southwestward with height in the lower troposphere. The anomalies can thus yield not only a poleward heat flux across the climatological thermal gradient across the strong Pacific jet but also a westward heat flux across the climatological thermal gradient between the North Pacific and the cooler Asian continent. The resultant baroclinic conversion of available potential energy (APE) from the climatological-mean flow contributes most efficiently to the APE maintenance of the monthly WP pattern, acting against strong thermal damping effects by anomalous heat exchanges with the underlying ocean and anomalous precipitation in the subtropics and by the effect of anomalous eddy heat flux under modulated storm-track activity. Kinetic energy (KE) of the pattern is maintained through barotropic feedback forcing associated with modulated activity of transient eddies and the conversion from the climatological-mean westerlies, both of which act against frictional damping. The net feedback forcing by transient eddies is therefore not particularly efficient. The present study suggests that the WP pattern has a characteristic of a dynamical mode that can maintain itself through efficient energy conversion from the climatological-mean fields even without external forcing, including remote influence from the tropics.

Kinetic study of ion acoustic twisted waves with kappa distributed electrons

The kinetic theory of Landau damping of ion acoustic twisted modes is developed in the presence of orbital angular momentum of the helical (twisted) electric field in plasmas with kappa distributed electrons and Maxwellian ions. The perturbed distribution function and helical electric field are considered to be decomposed by Laguerre-Gaussian mode function defined in cylindrical geometry. The Vlasov-Poisson equation is obtained and solved analytically to obtain the weak damping rates of the ion acoustic twisted waves in a non-thermal plasma. The strong damping effects of ion acoustic twisted waves at low values of temperature ratio of electrons and ions are also obtained by using exact numerical method and illustrated graphically, where the weak damping wave theory fails to explain the phenomenon properly. The obtained results of Landau damping rates of the twisted ion acoustic wave are discussed at different values of azimuthal wave number and non-thermal parameter kappa for electrons.

Landau damping of Langmuir twisted waves with kappa distributed electrons

The kinetic theory of Landau damping of Langmuir twisted modes is investigated in the presence of orbital angular momentum of the helical (twisted) electric field in plasmas with kappa distributed electrons. The perturbed distribution function and helical electric field are considered to be decomposed by Laguerre-Gaussian mode function defined in cylindrical geometry. The Vlasov-Poisson equation is obtained and solved analytically to obtain the weak damping rates of the Langmuir twisted waves in a nonthermal plasma. The strong damping effects of the Langmuir twisted waves at wavelengths approaching Debye length are also obtained by using an exact numerical method and are illustrated graphically. The damping rates of the planar Langmuir waves are found to be larger than the twisted Langmuir waves in plasmas which shows opposite behavior as depicted in Fig. 3 by J. T. Mendoça [Phys. Plasmas 19, 112113 (2012)].

Impact of relative phase shift on inward turbulent spreading

The relative cross-phase between density, temperature, and potential perturbations plays a major role in turbulent spreading and transport. Nonlinear Landau-Fluid simulations show that the electron wave-particle resonances provide a relatively strong parallel damping effect on the electron temperature perturbation and can induce a relative cross-phase shift of smaller than π∕2 angle between E × B velocity and the electron temperature perturbation for large electron temperature gradient, which yields a large spreading for electron. The relative phase for ions is about π∕2 and has no turbulent spreading effect on it. The inward turbulent spreading stops at the position where the radial turbulent correlation length is shorter than the magnetic surface spacing. The temperature pedestal height determines the energy loss due to the turbulent spreading.

Mode complexity in a harmonically forced string with a local spring–damper and transitions from vibrations to waves

We numerically and analytically investigate the dynamics of a linear, uniform, homogeneous, undamped string coupled to a linear spring–dashpot system at its center and fixed to ground at its ends. Both ends of the string are excited through identical and synchronous harmonic motion, and the steady-state dynamics of the system is analytically studied. The localized damping introduces mode complexity, which results in spatial shifting of the peak resonance amplitudes to different locations of the string and highly nontrivial phase variations confined to certain predictable boundary layers of the string. We find that there exists a unique combination of system parameters such that mode complexity reaches an absolute maximum: in such an optimal case, damping destroys all the normal modes of vibration, and instead, traveling waves are formed. This peak in complexity marks the transition between very weak and very strong damping effects and provides a direct mode complexity-induced transition from vibrations (standing waves) to traveling waves.

Plasmon–Interband Coupling in Nickel Nanoantennas

Plasmonic excitations are usually attributed to the free electron response at visible frequencies in the classic plasmonic metals Au and Ag. However, the vast majority of metals exhibit spectrally localized interband transitions or broad interband transition backgrounds in the energy range of interest for nanoplasmonics. Nevertheless, the interaction of interband transitions with localized plasmons in optical nanoantennas has hitherto received relatively little attention, probably because interband transitions are regarded as highly unwanted due to their strong damping effect on the localized plasmons. However, with an increasing number of metals (beyond Au and Ag) being considered for nanoplasmonic applications such as hydrogen sensing (Pd), UV-SERS (Al), or magnetoplasmonics (Ni, Fe, Co), a deeper conceptual understanding of the interactions between a localized plasmon mode and an interband transition is very important. Here, as a generic example, we examine the interaction of a localized (in energy space) interband transition with spectrally tunable localized plasmonic excitations and unearth the underlying physics in a phenomenological approach for the case of Ni disk nanoantennas. We find that plasmon–interband interactions can be understood in the classical picture of two coupled harmonic oscillators, exhibiting the typical energy anticrossing fingerprint of a coupled system approaching the strong-coupling regime.

Dynamical density and spin response functions of two-dimensional correlated fermion systems: Self-consistent second-order perturbation theory

Dynamical density and spin responses of a two-dimensional fermion system are studied with the self-consistent second-order perturbation theory using a model Hamiltonian. Special attention is paid to the density response at a large wave vector, where it was reported that a sharp mode develops below the particle-hole continuum in two-dimensional liquid ${}^{3}$He. We find that at a large wave vector, a peak in the dynamical density structure factor shifts to lower energy as interaction sets in, but it is not sharp enough to represent a well-defined mode because of the strong damping effect of the quasiparticles. We point out that it is necessary to treat the large damping effect properly in explaining the propagating mode found in two-dimensional liquid ${}^{3}$He.