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Nonlinear self-excited forces pose a significant role in wind-induced aeroelasticity of long-span bridges, predominantly characterized by the flutter derivatives. As in other works already in the literature, the flutter derivatives are extended here to the nonlinear case by introducing amplitude dependence. At that point, accurately describing the nonlinearity of aerodynamic damping as a function of amplitude, etc., is crucial for the precise identification of flutter derivatives, while the nonlinearity of amplitude-dependent structural damping should also be considered. Therefore, this study aims to develop a time-domain method, that simultaneously accounts for the structural and aerodynamic nonlinearities in calculating the wind-induce responses of a double-deck truss girder. First, wind tunnel tests were performed to measure the time histories of displacement responses for the section model accounting for various damping ratio levels, from which the corresponding structural and aerodynamic damping was extracted. Next, the generalized Van der Pol oscillator (GVPO) model was employed to characterize the nonlinear structural and aerodynamic damping, and the accuracy was validated by comparing the computed displacement histories by the GVPO model with the experimental results. Subsequently, the nonlinear flutter derivatives at lower damping level are determined, with the nonlinear characteristics captured through the GVPO model. Finally, both the heaving and torsional responses at higher damping levels are predicted using the nonlinear flutter derivatives identified from the responses measured at lower damping levels, and the predicted results align with the experimental results. The time-domain method developed in this study incorporates both the aeroelastic and structural nonlinearities.

The slow coherent groups recognition method is one of the dynamic equivalence techniques, which is based on the singular perturbation principle. Its algorithm performance is widely recognized. In order to reduce the solving difficulty and time consuming, this method ignores the generator stator damping effect. But during a fault, the generator stator damping effect directly affects the oscillation amplitude and frequency of the rotor angular curve. If the damping characteristics of the original system are ignored, when the damping torque coefficients of each generator vary greatly, the coherence between generators will be affected, and the accuracy of the simplified equivalent system will inevitably decrease. This paper proposes a new method based on the traditional slow coherent groups’ recognition method. The new method, which is based on the second-order model of the generator, can consider the generator stator damping effect without increasing the algorithm complexity. The active and reactive power of the system are decoupled. The eigenvalues of the system model and the general solution of the second-order differential equations are obtained through rigorous derivation. It also proposes a two-scale coherent groups recognition criterion. Finally, the effectiveness of the new method is verified based on the IEEE-39-Bus system.

The dissipation behavior of granular balls in a Q-2D closed container subjected to vertical vibration is investigated by means of Discrete Element Method (DEM). Damping contour and phase diagram of vibrated granular balls in the interested excitation amplitude-frequency plane are obtained respectively, revealing ten different granular motion patterns where density inversion, wave-solid state and Leidenfrost effect demonstrate relatively higher damping effect. Uncertainty of vibrated granular balls in dissipation behavior under the same excitation parameters is indicated. Moreover, the influence of cavity dimension (i.e., height, width and aspect ratio) of granular container on dissipation behavior of vibrated granular balls is further explored based on the three high damping granular phases, which not only lays a foundation for the optimal design of Q-2D granular damping structure based on dissipation behavior of vibrated granular materials, but also further verifies the existence of granular wave-solid state as a newly revealed high damping granular phase.

Solar Arrays (SA’s) of a satellite are typically folded within the launcher. After the satellite is inserted into its orbit, SA’s are unfolded (or deployed) and locked. The deployment is a critical operation as its failure translates to catastrophic satellite mission failure. Therefore, the design of the SA Deployment Mechanism (DM) must be robust. The design must additionally ensure smooth deployment and gentle locking not to damage the SA’s nor the satellite structure. This work demonstrates designing a SADM having reasonable deployment speed yet smooth locking. This design is verified by simulation using transient Finite Element Analysis (FEA) employing implicit time-stepping scheme. Deployment large rotations, complex contacts and rapid locking, however, caused challenging convergence difficulties. This work demonstrates design, optimization, simulation and difficulties overcoming for a typical SADM. This also extends to any relatively slow mechanism.

Within the frames of this study, the synthesis of a permalloy to be used as a filler for magnetoactive and magnetorheological elastomers (MAEs and MREs) was carried out. By means of the mechanochemical method, an alloy with the composition 75 wt.% of Fe and 25 wt.% of Ni was obtained. The powder of the product was utilized in the synthesis of MAEs. Study of the magnetorheological (MR) properties of the elastomer showed that in a ~400 mT magnetic field the shear modulus of the MAE increased by a factor of ~200, exhibiting an absolute value of ~8 MPa. Furthermore, we obtained experimentally a relative high loss factor for the studied composite; this relates to the size and morphology of the synthesized powder. The composite with such properties is a very perspective material for magnetocontrollable damping devices. Under the action of an external magnetic field, chain-like structures are formed inside the elastomeric matrix, which is the main determining factor for obtaining a high MR effect. The effect of chain-like structures formation is most pronounced in the region of small strains, since structures are partially destroyed at large strains. A proposed theoretical model based on chain formation sufficiently well describes the experimentally observed MR effect. The peculiarity of the model is that chains of aggregates of particles, instead of individual particles, are considered.

To improve the safety and functional retention of masonry structures under moderate to severe earthquakes, a systematic study of the mechanical properties of lead rubber bearings (LRBs) and shaking table tests of seismic isolation masonry models was conducted. Firstly, based on the characteristics of low-rise masonry structure houses and common wall sizes, five small-diameter lead-rubber isolation bearings were designed, and vertical performance and horizontal stiffness tests were carried out. The mechanical performance parameters such as equivalent horizontal stiffness, post-yield stiffness, equivalent damping ratio, and vertical stiffness were obtained. The relationship curve and fitting formula between horizontal displacement, shock absorption coefficient and their influencing factors were calculated. Subsequently, a typical two-story brick structure house without structural columns in a village was selected as the test prototype. A vibration table comparison test with and without seismic isolation layer was designed at a 1:2 scale and full counterweight. Using response spectrum analysis and numerical simulation, three seismic waves were selected for both isolated and non-isolated structures, and sensor placement and loading schemes were designed. Based on the comparison of isolation and non-isolation test phenomena, especially the structural damage of the isolation layer, combined with the dynamic characteristics of white noise sweep frequency, acceleration, displacement, interlayer shear force and interlayer displacement angle, the isolation effect is analyzed and the isolation layer model design is verified. The results show that the vertical compression stiffness of LRB No. 4 is relatively stable, the hysteresis curve is full, the horizontal displacement is less than 60.5 mm, the damping coefficient is less than 0.4, the post-yield stiffness is 149.7 N/mm-167.8 N/mm, and the equivalent horizontal stiffness is 193.9 N/mm-218.65 N/mm. The first two periods of the isolation model are longer and the natural frequency is low, about 25% of the non-isolation model. When the peak acceleration is 0.4 g, the reduction rate of the top layer increases to about 48%, and the reduction rate of the first layer increases to about 40%. The displacement reduction rate of the top floor is about 24% under the action of Tangshan waves, about 36% under the action of Jiangyou waves, and up to 40% under the action of artificial waves. The test results verified the rationality of the low masonry isolation model structure and the isolation effect of lead core rubber bearing(LRB) + Frictionless sliding bearing(FSB).

Hard coatings are widely employed on blades to enhance impact resistance and mitigate fatigue failure caused by vibration. While previous studies have focused on the dynamic characteristics of beams and plates, research on real blades remains limited. Specifically, there is a lack of investigation into the dynamic characteristics of hard-coated blades under base excitation. In this paper, the finite element model (FEM) of blade-hard coating (BHC) composite structure is established based on finite element methods in which the hard coating (HC) material and the substrate are considered as the isotropic material. Harmonic response analysis is conducted to calculate the resonance amplitude of the composite under base excitation. Numerical simulations and experimental tests are performed to examine the effects of various HC parameters, including energy storage modulus, loss factors, coating thickness, and coating positions, on the dynamic characteristics and vibration reduction of the hard-coated blade composite structures. The results indicate that the difference in natural frequency and modal loss factor of blades increases with higher storage modulus and HC thickness. Moreover, the vibration response of the BHC decreases with higher storage modulus, loss factor, and coating thickness of the HC material. Blades with a complete coating exhibit superior damping effects compared to other coating distributions. These findings are significant for establishing accurate dynamic models of HC composite structures, assessing the effectiveness of HC vibration suppression, and guiding the selection and preparation of HC materials.

Phononic crystal (PnC) sensors are recognized for their capability to control acoustic wave propagation through periodic structures, presenting considerable potential across various applications. Despite advancements, the effects of fluid viscosity on PnC performance remain intricate and inadequately understood. This study theoretically investigates the influence of shear (dynamic) and bulk viscosity on acoustic wave damping in defective one-dimensional phononic crystal (1D PnC) sensors designed for detecting liquid analytes. Acetic acid with varying viscosities is considered to fill a cavity layer intermediated by a multilayer stack of lead and epoxy. The effects of dynamic and bulk viscosity on the resonance characteristics of the defective mode were analyzed. Numerical results reveal that increased dynamic viscosity leads to substantial broadening and decreased intensity of resonance peaks, accompanied by a shift to higher frequencies due to enhanced elastic wave attenuation and damping. At low dynamic viscosity (η = 0.2 η d ), numerous resonance peaks with varying intensities are observed. However, at higher viscosities (η = 2.0 η d to η = 10.0 η d ), only one prominent peak appears in the spectrum. The intensity of this resonant peak starts at 98% for η = 2 η d and decreases to 58.8% as the dynamic viscosity increases to η = 10 η d . Additionally, the combined effect of dynamic and bulk viscosity introduces further damping, causing a strong shift of the resonance peak to higher frequencies, along with an increase in the full width at half maximum (FWHM) and a decrease in the quality factor (QF). These findings emphasize the necessity of incorporating both shear and bulk viscosity in the design of PnC sensors to enhance their sensitivity and accuracy in practical applications. This theoretical framework provides critical insights for optimizing sensor performance and bridging gaps between theoretical predictions and experimental observations, especially in 1D PnCs, offering potential solutions to challenges in real-world PnC sensor applications.

The fuel sloshing in the vehicle fuel tank can cause adverse consequences, especially under resonance conditions, and the vertical baffle may efficiently restrain the fuel sloshing. The current work couples mesh motion and volume of fluid to investigate the effect of baffle height on the liquid sloshing damping effect at different filling levels under resonance conditions. The aim  is to explore the optimal baffle height at different fuel filling levels. The results indicate that the best damping performance can be obtained when using baffles with the same height as the fluid height. To reduce the impact pressure on the tank walls, a baffle slightly higher than the free surface height should be used at low filling levels, and a baffle slightly lower than the free surface height should be used at medium filling levels. Compared with high filling level, the baffle is more effective in reducing the sloshing force and moment at low and medium filling levels. A new formula for calculating the energy damping ratio is proposed. At 20% fuel filling level, the energy damping ratio increases continuously as the baffle height increases, and reaches the maximum value of 85.31% when h b / h w  = 1.2. At 50% and 80% fuel filling level, the damping ratio reaches the maximum when h b / h w  = 1, which is 79.79% and 56.39% respectively. This study provides important theoretical support for the anti-sloshing design of a vehicle fuel tank.

Tuned mass-high damping rubber damper (TM-HDR-D), as a high-efficiency damper, has great practical feasibility and good application prospect for cable vibration mitigation. To investigate the effect of TM-HDR-D on the cable dynamics, a refined model which considers the cable sag effect is established via complex modal method. Then, based on this model, the influence of cable sag and the stiffness, location, loss factor, and mass of the TM-HDR-D on the cable dynamics is systematically investigated. Meanwhile, the multi-mode damping effect of TM-HDR-D is also analyzed. Results show that TM-HDR-D can significantly increase the additional damping of the system. The cable sag only affects the first-order modal damping, and the effect of TM-HDR-D is significantly affected by its frequency, loss factor, and installation position. Improving the mass of the damper can improve the damping effect. Reasonable selection of damper tuning frequency can achieve multi-order modal damping enhancement.