Nonlinear energy sink (NES) is an appropriately designed nonlinear oscillator without positive linear stiffness. NES can suppress vibrations over a wide frequency range due to its targeted energy ...transfer characteristics. Thus, investigations on NES have attracted a lot of attention since a NES was proposed. Designs, analysis, and applications of NESs are still active since different configurations are needed in various practical circumstances. The present work provides a comprehensive review of state-of-the-art researches on NESs. The work begins with a survey of the generation of a NES and its important vibration control characteristics. The work highlights possible complex dynamics resulting in a NES coupled to a structure. The work also summarizes some significant design on the implements of optimal damping effects and the offsets of NES shortcomings. Then, the work details the applications of NESs in all engineering fields. The concluding remarks suggest further promising directions, such as NESs for multidirectional vibration reduction, NESs with nonlinearities beyond the cubic, potential deterioration caused by a NES, low-cost NESs, NESs for extremely low frequency range, and NESs integrated into active vibration controls. There are 383 references in the review, including some publications of the authors.
•Vibration of fluid-conveying pipes is isolated by quasi-zero stiffness systems.•Nonlinear solution is obtained via Galerkin method and the finite difference.•The fluid flow can deteriorate the ...performance of vibration isolation.
Fluid-conveying pipes are always subjected to various excitations to cause unwanted vibrations. A quasi-zero stiffness system consisting of three linear springs is adopted as the nonlinear isolator to attenuate the transverse vibrations of fluid-conveying pipes induced by foundation excitations. A dynamic model of nonlinear forced vibration of the fluid-conveying pipe coupled with two nonlinear isolators is established for the nonlinear continuous system and validated by using two methods, Galerkin method and the finite difference method. The influence of the quasi-zero stiffness isolators on the vibration characteristics and vibration transmission of the pipe is investigated by analyzing the natural frequency, vibration mode, and nonlinear vibration response. The effects of flow speed of the fluid and the system parameters of the isolator are studied to evaluate the isolation performance. It is found that the quasi-zero stiffness isolator and fluid flow can shift several natural frequencies of vibration of the pipeline to the low-frequency region. When the linear stiffness of the vibration isolation is zero in the vertical direction, the first two modes of the bending vibration of the fluid-conveying pipe tend to become rigid mode. While achieving high-efficiency vibration isolation in the high-frequency region, the vibration in the low-frequency region is complicated. The flow speed of the fluid can deteriorate the performance of vibration isolation.
Enhancing vibration isolation with locally resonant metamaterials has attracted wide attention due to low-frequency band-gap. Moreover, nonlinear periodic structure could improve the range of ...targeted energy transfer. In this paper, we propose a dual-functional metamaterial for integrated low-frequency vibration isolation and energy harvesting. A periodic array of nonlinear electrical energy harvesters, realized by implanting a rolling-ball with coils into a spherical magnetic cavity, is explored to isolate mechanical wave and simultaneously harvest electrical energy. The dynamical equation is established for a nonlinear dual-functional metamaterial beam under transverse excitation. The Extended Bloch's theorem is applied to give the dispersion relation. Numerical results obtained by finite element method supported the analytical results. Compared to the narrow band-gaps in metamaterials with spherical magnetic cavity, our numerical analysis demonstrates that a cavity mass arrayed beam with a periodic array of nonlinear energy harvesters has more and wider low-frequency band-gaps. Frequency response functions of output power are derived by using finite element analysis. The harvested power is considerable at the local resonant band-gap. Parameter study demonstrates that increasing the cell size and increasing cavity mass could improve elastic waves isolation performance at low frequencies; Increasing the mass of the rolling-ball in the resonator can significantly decrease the frequency of the local resonance band-gap. The existence of multiple band-gaps could be designed for dual-functional vibration attenuation and energy harvesting. Finally, an experimental rig is designed to validate the theoretical results.
Nationwide nonpharmaceutical interventions (NPIs) have been effective at mitigating the spread of the novel coronavirus disease (COVID-19), but their broad impact on other diseases remains ...under-investigated. Here we report an ecological analysis comparing the incidence of 31 major notifiable infectious diseases in China in 2020 to the average level during 2014-2019, controlling for temporal phases defined by NPI intensity levels. Respiratory diseases and gastrointestinal or enteroviral diseases declined more than sexually transmitted or bloodborne diseases and vector-borne or zoonotic diseases. Early pandemic phases with more stringent NPIs were associated with greater reductions in disease incidence. Non-respiratory diseases, such as hand, foot and mouth disease, rebounded substantially towards the end of the year 2020 as the NPIs were relaxed. Statistical modeling analyses confirm that strong NPIs were associated with a broad mitigation effect on communicable diseases, but resurgence of non-respiratory diseases should be expected when the NPIs, especially restrictions of human movement and gathering, become less stringent.
Bending vibration of isolated structures has always been neglected when the vibration isolation was studied. Isolated structures have usually been treated as discrete systems. In this study, dynamics ...of a slightly curved beam supported by quasi-zero-stiffness systems are firstly presented. In order to achieve quasi-zero-stiffness, a nonlinear isolation system is implemented via three linear springs. A nonlinear dynamic model of the slightly curved beam with nonlinear isolations is established. It includes square nonlinearity, cubic nonlinearity, and nonlinear boundaries. Then, the mode functions and the frequencies of the curved beam with elastic boundaries are derived. The schemes of the finite difference method (FDM) and the Galerkin truncation method (GTM) are, respectively, proposed to obtain nonlinear responses of the curved beam with nonlinear boundaries. Numerical results demonstrate that both the GTM and the FDM yield accurate solutions for the nonlinear dynamics of curved structures with nonsimple boundaries. The multi-mode resonance characteristics of the curved beam affect the vibration isolation efficiency. The quasi-zero-stiffness isolators reduce the transmissibility of modal resonances and provide a promising future for isolating the bending vibration of the flexible structure. However, the initial curvature significantly increases the resonant frequency of the flexible structure, and thus the frequency range of the effective vibration isolation is narrower. Furthermore, the quadratic nonlinear terms in the curved beam make the dynamic phenomenon more complicated. Therefore, it is more challenging and necessary to investigate the isolation of the bending vibration of the initial curved structure.
Portal vein tumor thrombus (PVTT) is a significant poor prognostic factor for hepatocellular carcinoma (HCC). Patients with PVTT limited to a first‐order branch of the main portal vein (MPV) or above ...could benefit from negative margin (R0) liver resection (LR). An Eastern Hepatobiliary Surgery Hospital (EHBH)/PVTT scoring system was established to predict the prognosis of HCC patients with PVTT after R0 LR and guide selection of subgroups of patients that could benefit from LR. HCC patients with PVTT limited to a first‐order branch of the MPV or above who underwent R0 LR as an initial therapy were included. The EHBH‐PVTT score was developed from a retrospective cohort in the training cohort using a Cox regression model and validated in a prospective internal validation cohort and three external validation cohorts. There were 432 patients in the training cohort, 285 in the prospective internal validation cohort, and 286, 189, and 135 in three external validation cohorts, respectively. The score was calculated using total bilirubin, α‐fetoprotein (AFP), tumor diameter, and satellite lesions. The EHBH‐PVTT score differentiated two groups of patients (≤/>3 points) with distinct long‐term prognoses (median overall survival OS, 17.0 vs. 7.9 months; P < 0.001). Predictive accuracy, as determined by the area under the time‐dependent receiver operating characteristic curves (AUCs; 0.680‐0.721), was greater than that of the other commonly used staging systems for HCC and PVTT. Conclusion: The EHBH‐PVTT scoring system was more accurate in predicting the prognosis of HCC patients with PVTT than other staging systems after LR. It selected appropriate HCC patients with PVTT limited to a first‐order branch of the MPV or above for LR. It can be used to supplement the other HCC staging systems.
In this paper, a nonlinear Timoshenko model of the coupled vibration of a pipe conveying fluid is established to distinguish it from the Euler-Bernoulli coupled model and the Timoshenko model of the ...transverse vibration in terms of application scope and accuracy. The generalized Hamilton’s principle is utilized to derive the coupled Timoshenko model. The coupled Timoshenko model can be degenerated into three other models, namely the integro-partial differential Timoshenko transverse model, the partial differential Timoshenko transverse model, and the Euler-Bernoulli coupled model. The finite difference method (FDM) is developed to calculate the time history of the free vibration of the pipe. Based on the time history, the nonlinear frequency is obtained by using the discrete Fourier transform method (DFT). Furthermore, the amplitude-frequency curves of the forced vibration of the viscoelastic pipe are studied. The necessity for the Timoshenko coupled pipe model is shown by comparing with the other three models. Through extremely time-consuming calculations, comparisons show that these nonlinear models agree well at a low flow velocity and slight vibration. However, when the flow velocity or the initial displacement amplitude is large, the relative error of the nonlinear frequencies of the free vibration may exceed 30%. Moreover, the results indicate that the nonlinear coefficient has great influence on the nonlinear frequency when the flow velocity or the initial amplitude is large. Interestingly, the shear coefficient has a significant impact on the nonlinear frequency when the initial amplitude is small. In general, this paper shows that a large flow velocity, a large vibration amplitude or a shorter pipe length makes the coupled Timoshenko theory more necessary for modeling pipes conveying fluid.
Bacterial infections remain a leading threat to global health because of the misuse of antibiotics and the rise in drug‐resistant pathogens. Although several strategies such as photothermal therapy ...and magneto‐thermal therapy can suppress bacterial infections, excessive heat often damages host cells and lengthens the healing time. Here, a localized thermal managing strategy, thermal‐disrupting interface induced mitigation (TRIM), is reported, to minimize intercellular cohesion loss for accurate antibacterial therapy. The TRIM dressing film is composed of alternative microscale arrangement of heat‐responsive hydrogel regions and mechanical support regions, which enables the surface microtopography to have a significant effect on disrupting bacterial colonization upon infrared irradiation. The regulation of the interfacial contact to the attached skin confines the produced heat and minimizes the risk of skin damage during thermoablation. Quantitative mechanobiology studies demonstrate the TRIM dressing film with a critical dimension for surface features plays a critical role in maintaining intercellular cohesion of the epidermis during photothermal therapy. Finally, endowing wound dressing with the TRIM effect via in vivo studies in S. aureus infected mice demonstrates a promising strategy for mitigating the side effects of photothermal therapy against a wide spectrum of bacterial infections, promoting future biointerface design for antibacterial therapy.
A localized thermal‐management strategy from thermal‐disrupting interface induced mitigation (TRIM) is developed to maintain intercellular cohesion and reduce function loss of epidermis tissue for topical antibacterial therapy. A dressing film with the TRIM effect inhibits aggregation of bacteria, promotes selective elimination of pathogens, and shortens the healing process.
Double-function stewart platform designed for both vibration isolation and energy harvesting.•Vibration isolation efficiency of the 6-dofs enhanced by the stiffness nonlinearity.•Using a shorter ...initial distance d between magnets leads to higher power output and wider isolation range.•Varying the resistance r produces the opposite effect between vibration isolation.
An electromagnetic Stewart platform with high static and low dynamic stiffness is explored to reduce the vibration in six degrees of freedom (6-dofs) and simultaneously harvest energy. Each strut in the Stewart platform contains a moving electromagnet suspended between two fixed permanent magnets that are configured so that the magnet spring has both negative stiffness and soft nonlinearity. The use of stiffness nonlinearity improves vibration isolation efficiency. To obtain the frequency-response function for transmissibility and the power output in the first primary resonance, we apply the harmonic balance method, which is based on rigid-body dynamics and nonlinear elastic theory. The frequency response curves of the 6-dofs have peaks that redshift and bend leftward (toward lower frequencies), and a bubble-shaped resonance curve appears around the first resonance frequency. The numerical simulations support the analytical results. For various mechanical and electrical parameters, the analytical and numerical results both demonstrate that the frequency band of vibration isolation extends to lower frequencies and produces considerable power output. Moreover, the increase in energy harvesting leads to reduced vibration transmissibility under varying some parameters.
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