Search

The control performance of a passive dynamic vibration absorber (DVA) is known to be sensitive to its frequency deviation. This study upgrades the conventional device and proposes an adaptive-passive variable frequency gas-spring DVA (APVF-GSDVA) for controlling the structural seismic response, while an adaptive control algorithm is developed that requires only a single input signal. The DVA’s vibration frequency is precisely modulated by adjusting the gas pressure in the gas-spring, aligning it with the inherent frequency of the multi-degree-of-freedom (MDOF) structure. The working principle and control algorithm of the APVF system is introduced and derived in detail, the corresponding gas-spring DVA and implementation are designed, and the configuration of the entire control system is realized. An adaptive variable frequency test scheme is designed and the frequency retuning function of the prototype APVF-GSDVA device installed on an MDOF structure is experimentally validated. The seismic response control effectiveness of the retuned DVA is demonstrated by comparing the detuned DVA, highlighting the necessity of implementing adaptive frequency adjustment of the gas-spring DVA. Experimental findings demonstrate that APVF-GSDVA accurately identifies the inherent frequency of the MDOF structure in ambient excitation, it then adjusts the pressure of the gas-spring according to the frequency-pressure relationship, optimally retuning the DVA. A retuned GSDVA can effectively suppress the structural seismic responses, compared to a detuned DVA, its control effectiveness on peak and RMS responses can be improved by a maximum of nearly 13.5% and 53.3% at a frequency deviation of 10%. Furthermore, results from two “detuning-retuning” test paths with distinct seismic excitations indicate that the retuned DVA exhibits superior control effectiveness, underscoring the significance of the adaptive frequency adjustment function in passive DVAs. [ABSTRACT FROM AUTHOR]

To maximize vibration reduction efficiency and reduce the risk of detuning, this study proposes a multiobjective optimization design method for shape parameters affecting the nonlinear characteristics of nonlinear gas-spring damper (NGSD) based on the NSGA-II algorithm. A numerical model of a MDOF structure with attached NGSD is developed and optimized under white noise excitation, and the effectiveness of the optimized NGSD in mitigating structural seismic responses is validated through shaking table tests. By comparing with the optimal TMD, the control effectiveness and parameter sensitivity of the optimized NGSD under various near- and far-field seismic excitations are investigated. Results show that the optimization design is carried out with the performance objective of minimizing the RMS of structural displacement and acceleration response, and a set of relatively optimal piston radius and initial volume parameters are obtained, resulting in the control effectiveness of NGSD on the RMS response of MDOF structure’s displacement and acceleration as high as 77% and 39%, respectively. The maximum reduction effectiveness of optimized NGSD on the peak structural acceleration and displacement response under seismic excitation is 18% and 19% respectively, and the RMS reduction ratios are even as high as 56% and 61%, indicating the efficacy of using NSGA-II for parameter optimization. Moreover, the optimized NGSD demonstrates comparable control effectiveness to the optimal TMD with a shorter stroke and stable performance across different seismic excitations, indicating low sensitivity of optimal parameters to excitation frequency. [ABSTRACT FROM AUTHOR]

This work proposes an enhanced particle inerter device (EPID) capable of significantly enhancing the vibration control effect (VCE) of a conventional particle tuned mass damper (PTMD). EPID, an inerter is coupled to the PTMD device, that is, the inerter is attached to the damper cavity on one end and to the ground on the other, mainly using its mass amplification effect. To accomplish the goal, the EPID's mechanical model is established first. Then, the system's governing equation is derived based on the single degree of freedom (SDOF) system, and the EPID's effectiveness is verified via inputting seismic excitation. Finally, the parameter analysis and multi-objective optimization design are carried out for EPID, and the superiority of the proposed multi-objective optimization design method compared with the traditional design method is verified. The results indicate that EPID can effectively minimize the main structure's displacement and acceleration response. In particular, under the El Centro wave's excitation, the vibration reduction rate of the dynamic responses (peak response and root mean square response) is close to 50%, which is over 35% increasing compared to PTMD, and its VCE is better for excitation band changes. At the same time, it is found that the lower the damper's auxiliary mass ratio, the more obvious the enhancement of the inerter system's VCE is, which brings about the lightweight design of the high-control effect of PTMD. [ABSTRACT FROM AUTHOR]

To mitigate the adverse structural responses, an improved version of the traditional tuned vibration absorber has been proposed based on the shape memory alloy spring, referred as the shape memory alloy-spring tuned vibration absorber. The finite element numerical models of the multi-degree-of-freedom structure (e.g., transmission tower) and shape memory alloy-spring tuned vibration absorber are developed by using the commercial software ANSYS, and the nonlinear behavior of the shape memory alloy spring is validated based on a previous experimental study. The damping mechanism of the shape memory alloy-spring tuned vibration absorber attached to a multi-degree-of-freedom structure under seismic excitations is investigated, and the nonlinear hysteretic behavior of the shape memory alloy spring is also discussed. The results show that the proposed damper has a two-stage damping mechanism, and its control performance is remarkable. Because the coupled system response is sensitive to the amplitude level, the optimal configuration of the shape memory alloy-spring tuned vibration absorber can be obtained by parametric analysis. Particularly, because of the nonlinear target energy transfer and transient resonance capture mechanism, the shape memory alloy-spring tuned vibration absorber exhibits stable control ability under different seismic waves, indicating a good stability in vibration control of a multi-degree-of-freedom system. [ABSTRACT FROM AUTHOR]

Statistics from past strong earthquakes revealed that electricity transmission towers were vulnerable to earthquake excitations. It is necessary to mitigate the seismic responses of power transmission towers to ensure the safety of such structures. In this research, a novel shape memory alloy-tuned mass damper is proposed, and seismic vibration control of power transmission tower using shape memory alloy-tuned mass damper based on three types of shape memory alloy materials (i.e. NiTi, M-CuAlBe, P-CuAlBe) is analyzed. The detailed three-dimensional finite element model of a power transmission tower incorporated with shape memory alloy-tuned mass damper is developed using numerical simulation software ANSYS. The control effects of shape memory alloy-tuned mass damper on the seismic vibration of power transmission tower are assessed using nonlinear time history analysis method. The interested seismic performance indices include displacement, acceleration, and base shear force. In addition to the shape memory alloy materials, the influence of seismic intensity and frequency ratio are conducted for the optimal design. It is shown that installing shape memory alloy-tuned mass damper well reduced the seismic responses of power transmission tower. The comparison between different shape memory alloys indicated that the damping of the shape memory alloy-tuned mass damper is beneficial to mitigate the vibrations. [ABSTRACT FROM AUTHOR]

Melanoma is derived from melanocytes and accounts for ~80% of skin cancer-associated fatalities worldwide. The dysregulation of microRNAs (miRNAs/miRs) is involved in the development and progression of melanoma. Therefore, miRNAs may be novel diagnostic or prognostic biomarkers and promising therapeutic targets in the treatment of patients with melanoma. miR-675 is differentially expressed in several types of human cancer and has important roles in the pathogenesis of several diseases. However, the expression levels and the biological roles of miR-675 in melanoma remain unclear. Therefore, the present study aimed to assess the expression of miR-675 in melanoma, explore the effects of miR-675 on melanoma cells and investigate the underlying molecular mechanisms that may be involved in the actions of miR-675. The present study indicated that miR-675 expression was downregulated in melanoma tissues and cell lines. Functional assays demonstrated that the upregulation of miR-675 impaired cell proliferation and invasion in melanoma. Bioinformatics analysis, luciferase reporter assay, reverse transcription-quantitative polymerase chain reaction and western blot analysis demonstrated that metadherin (MTDH) was a direct target of miR-675 in melanoma. The MTDH levels were upregulated in melanoma tissues and inversely correlated with the miR-675 expression. Furthermore, restored MTDH expression rescued the inhibition effects in melanoma cells caused by miR-675 overexpression. Thus, miR-675 may be a potential therapeutic target for melanoma. [ABSTRACT FROM AUTHOR]