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The power flow analysis approach is applied for quantitatively evaluating the dynamic performance of a nonlinear energy sink in the frequency domain. A two-degree-of-freedom model of the whole-spacecraft coupled to a nonlinear energy sink is considered. Analytical approximations and numerical integrations are performed for the integrated system. The time-averaged input and dissipated and absorbed powers of the system are formulated. Power absorption ratio is proposed as the vibration reduction performance indicator of the nonlinear energy sink and is compared with kinetic energy of the oscillator. Results show that the power absorption ratio of nonlinear energy sink is high at all frequencies except at an antiresonance region. The effects of varying nonlinear energy sink parameters on its vibration absorption performance are discussed. As observed, the nonlinear energy sink performs well with the increase in viscous damping of nonlinear energy sink in the high-frequency range. However, the nonlinear energy sink performs poorly in the low-frequency range in the same case. Therefore, power flow analysis can provide great insight for nonlinear energy sink design in frequency domain and is suitable for practical engineering application.

In nanoscale structure sizes, the surface-to-bulk energy ratio is high and the surface effects must be taken into account. Surface effect plays a key role in accurately predicting the vibration behavior of nanostructures. In this paper, the wave behaviors of a single-walled carbon nanotube (CNT) conveying fluid are studied. The nonlocal Timoshenko beam theory is used and the surface effect is taken into account. It is found that the fluid can flow at a very high flow velocity and the wave propagates in the terahertz frequency range. The surface effects can significantly enhance the propagating frequency. This finding is different from the classical model where the surface effect is neglected.

In traditional active flutter control, piezoelectric materials are used to increase the stiffness of the aeroelastic structure by providing an active stiffness, and usually the active stiffness matrix is symmetric. That is to say that the active stiffness not only cannot offset the influence of the aerodynamic stiffness which is an asymmetric matrix, but also will affect the natural frequency of the structural system. In other words, by traditional active flutter control method, the flutter bound can just be moved backward but cannot be eliminated. In this investigation, a new active flutter control method which can suppress the flutter effectively and without affecting the natural frequency of the structural system is proposed by exerting active control forces on some discrete points of the structure. In the structural modeling, the Kirchhoff plate theory and supersonic piston theory are applied. From the numerical results, it can be noted that the present control method is effective on the flutter suppression, and the control effects will be better if more active control forces are exerted. After being controlled by the present control method, the natural frequency of the structure remains unchanged. [ABSTRACT FROM AUTHOR]

A nonlinear energy sink (NES) approach is proposed for whole-spacecraft vibration reduction. Frequency sweeping tests are conducted on a scaled whole-spacecraft structure without or with a NES attached. The experimental transmissibility results demonstrate the significant reduction of the whole-spacecraft structure vibration over a broad spectrum of excitation frequency. The NES attachment hardly changes the natural frequencies of the structure. A finite element model is developed, and the model is verified by the experimental results. A two degrees-of-freedom (DOF) equivalent model of the scaled whole-spacecraft is proposed with the two same natural frequencies as those obtained via the finite element model. The experiment, the finite element model, and the equivalent model predict the same trends that the NES vibration reduction performance becomes better for the increasing NES mass, the increasing NES viscous damping, and the decreasing nonlinear stiffness. The energy absorption measure and the energy transition measure calculated based on the equivalent model reveals that an appropriately designed NES can efficiently absorb and dissipate broadband-frequency energy via nonlinear beats, irreversible targeted energy transfer (TET), or both for different parameters. [ABSTRACT FROM AUTHOR]

Thermal metamaterials have been proposed to manipulate heat flux as a new way to cloak or camouflage objects in the infrared world. To date, however, thermal metamaterials only operate in the steady-state and exhibit detectable, transient heat signatures. In this letter, the theoretical basis for a thermal camouflaging technique with controlled transient diffusion is presented. This technique renders an object invisible in real time. More importantly, the thermal camouflaging device instantaneously generates a pre-designed heat signature and behaves as a perfect thermal illusion device. A metamaterial coating with homogeneous and isotropic thermal conductivity, density, and volumetric heat capacity was fabricated and very good camouflaging performance was achieved. [ABSTRACT FROM AUTHOR]

Nonlinear parametric vibration of an axially accelerating viscoelastic string is investigated. The string is constituted by the fractional Kelvin model. The principal parametric resonance is analyzed by using an asymptotic approach. The modulation equation is derived from the solvability condition. Closed-form expressions of the amplitudes and the existence conditions of steady-state responses are obtained from the modulation equation. Numerical examples are presented to highlight the effects of fractional order and other system parameters on the responses. [ABSTRACT FROM AUTHOR]

Nonlinear targeted energy transfer (TET) is applied to suppress the excessive vibration of an axially moving string with transverse wind loads. The coupling dynamic equations used are modeled by a nonlinear energy sink (NES) attached to the string to absorb vibrational energy. By a two-term Galerkin procedure, the equations are discretized, and the effects of vibration suppression by numerical methods are demonstrated. Results show that the NES can effectively suppress the vibration of the axially moving string with transverse wind loadings, thereby protecting the string from excessive movement. [ABSTRACT FROM AUTHOR]

This paper applies the multistage homotopy-perturbation method (MHPM) to the Lii system, which bridges the gap between the Lorenz system and the Chen system. Approximate closed-form expressions of the chaotic attractor are derived. Numerical comparison between the MPHM and the fourth-order Runge-Kutta method is carried out, revealing that the method is a powerful tool for analyzing and understanding chaos. [ABSTRACT FROM AUTHOR]

The propagation characteristics of the longitudinal wave in a piezoelectric nanoplate were investigated in this study. The nonlocal elasticity theory was used and the surface effects were taken into account. In addition, the group velocity and phase velocity were derived and investigated, respectively. The dispersion relation was analyzed with different scale coefficients, wavenumbers, and voltages. The results showed that the dispersion degree can be strengthened by increasing the wavenumber and scale coefficient. [ABSTRACT FROM AUTHOR]