Grid-forming （GFM） converters， known for their superior inertia damping characteristics， have emerged as a center research focus in the renewable energy sector. As a result， the damping ...characteristics of GFM wind power converters are first examined. The analysis centers on their equivalent external characteristics from an impedance standpoint， and the Bode stability criterion is utilized to study their stability during grid connection. Subsequently， the frequency support characteristics of GFM wind power converters are examined in terms of inertia. A comparative investigation is undertaken via simulation analysis to gauge the supportive capability of GFM and grid-following （GFL） wind power converters during alterations in grid frequency and power fluctuation on the wind turbine side. The findings reveal that the external impedance characteristics of GFM wind power converters not only display inductive properties but also maintain commendable stability throughout grid integration. In response to a grid malfun
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•A refined neural network model of hydro-turbine is established and verified.•An accurate quantitative evaluation of system damping is proposed.•The effect of operating condition on ...the hydraulic-mechanical damping is studied.•The relation between the control stability and damping is revealed.•The hydraulic-mechanical damping is decomposed.
Hydropower is a renewable energy source with flexible and rapid regulation. Its efficient utilization is of significance in improving the stability of the electric power grid and its ability to absorb renewable energy. The current day power grid is facing security challenges due to its composition and structural changes. To understand the damping mechanism of the hydropower unit on the power grid, a new quantitative evaluation method is proposed for the analysis of the damping characteristics of the hydropower unit under full operating conditions and control parameters. In order to improve the simulation accuracy, firstly a hydro-turbine regulation system simulation platform for quantitative analysis is built and a refined hydro-turbine model using a polynomial correction neural network is proposed. Secondly, to realize the damping analysis of the hydropower unit, an accurate quantitative evaluation method based on gradient-descent algorithm is proposed. Finally, taking a large hydropower station in China as an example, damping of the hydropower unit under full operating conditions (FOC) and control parameters is computed and analyzed considering two control modes. The results show that the damping of the hydropower unit on the power grid changes from −1.1415 to 0.4402 with a certain regularity under FOC and increases with the increase of control parameters. The damping under power control mode is generally better than that under opening control mode. Conclusions drawn from an in-depth analysis of the damping mechanism of hydropower units can provide necessary theoretical guidance and application value for optimizing the operation mode of the units.
The suspension vibration energy generated by high-speed tracked vehicles under off-road driving conditions is huge, but the power density of existing regenerative suspension cannot meet its kilowatt ...level energy recovery needs. Therefore, a novel mechanical-electrical-hydraulic regenerative suspension system (MEH-RSS) is proposed with high-power density in this paper. The hydraulic motor-generator (HMG) is used as the core component of hydraulic-electrical energy conversion to realize the conversion and recovery of high-power energy in limited space. Specifically, the bidirectional energy management control strategy is studied based on the energy conversion transfer path, and the fluid-solid-thermal-magnetic multiphysics coupling simulation model is established to analyze the influence of external excitation characteristics on the damping and energy recovery characteristics. The test proves that the energy recovery module can effectively realize energy conversion and recovery, and the maximum hydraulic-electrical energy conversion efficiency can reach 40.4% under the external resistance of 5 Ω. Further, the simulation results show that the MEH-RSS can achieve kilowatt level energy recovery with high efficiency under different road excitation characteristics, and the energy recovery characteristics are superior. The analysis also indicates that the damping force can be adjusted by changing the external resistance, which is the basis of semi-active control.
•A novel high-power density regenerative suspension is proposed for tracked vehicles.•The energy transfer and dissipation paths are analyzed.•The multiphysics coupled simulation model is proposed.•The damping and regenerative characteristics are analyzed via simulation and test.•The power density of suspension system is studied.
A great number of waste tires are discarded in landfills, occupying land resources, and severely endangering the ecosystem. Upcycling these wastes as aggregates to partially substitute natural sand ...and develop structure-function integration in concrete structures is a desirable solution. In this study, a sustainable fiber-reinforced rubberized mortar with superior material damping and moderate strength is developed by combined use of waste crumb rubber (WCR) incorporated at 0, 30%, and 60%, by volume of sand, and polyvinyl alcohol (PVA) fiber added at 0, 0.5%, and 1%, by volume, in a high-volume fly ash binder system. Low-temperature plasma (LTP) pre-treatment of the WCR was applied to compensate for strength loss resulting from the incorporation of a large portion of the WCR, which increases the recycling efficiency of the WCR. The macro tests of static and dynamic mechanical properties were used to characterize the material damping and energy dissipation capacity, followed by microstructural tests to evaluate the enhanced damping mechanisms. Test results show that the combination of 60% LTP pre-treated WCR and 1% PVA fiber can secure the highest damping capacity and energy dissipation ratio without a significant strength drop. The use of discarded WCR is therefore promising to substitute conventional sand and design functionalized intrinsic viscoelastic cement composites that can be adopted in anti-vibrational technology applications.
•Green fiber-reinforced rubber mortar with superior damping capacity is developed.•Waste rubber with low-temperature plasma serves as fine aggregate, up to 60 vol%.•High-volume fly ash system can improve toughness.•Damping capacity is evaluated by dynamic analyzer coupled with micro tests.•Damping mechanism related to viscous hysteresis, Coulomb friction, porosity and ITZ.
The service life of concrete structures is often threatened by unfavorable dynamic loads. Optimizing the material damping can improve the vibration damping of the structure. In this study, a ...polyvinyl alcohol fiber-reinforced high-volume fly ash (PVA-HVFA) cementitious composite was developed with high damping characteristics and moderate mechanical properties. The coupling effects of frequency and temperature on the damping were further clarified. Experiments combined with MIP and SEM tests were performed to analyze the pore structure distribution, fiber–matrix morphology, and enhanced damping mechanism. The results showed that the large amount of FA adversely affected strengths of the PVA-HVFA but significantly improved the damping and energy dissipation capacity. Meanwhile, the PVA fibers enhanced both strengths and damping characteristics. Vibration damping and energy dissipation were hypothesized to be affected by the matrix, fibers, and fiber–matrix interface. PVA-HVFA is expected to be applicable to beam–column plastic hinges and other vibrational damping fields.
•Novel PVA fiber-reinforced composite with superior damping property is developed.•Damping performance characterized by fiber content and fly ash substitution rate.•Coupling effects of excitation frequency and temperature are clarified.•Pore structure and distribution significantly affect the damping of PVA-HVFA.•Damping mechanism explained in terms of matrix, fibers, and fiber–matrix interface.
This paper aims to study the nonlinear damping characteristic of hydro-turbine governing systems (HTGS) in various frequency bands and improve the reliability of nonlinear damping quantification. ...Firstly, an HTGS model including multiple hydraulic-mechanical nonlinearities is established using an actual hydropower system as the object. Then, a trajectory quantification method is proposed to enhance the accuracy and stability of the damping calculation. On this basis, the influence of the hydraulic and controller parameters on the HTGS damping in the ultra-low and low frequency band is analyzed. Finally, a deviation indicator is defined to analyze the contribution level of each nonlinear factor to the damping characteristics, and the action mechanism of dominant nonlinearity on damping is further investigated. The results show that increasing the controller parameter and hydraulic parameter decreases the minimum damping of the HTGS. The total deviation of damping under the influence of nonlinearity reaches 1.31 times. Among them, water system nonlinearity and governor delay are two major nonlinearities, and their influence on damping characteristics accounts for 41.4% and 34.4% of the total nonlinear influence, respectively. This paper provides a powerful tool to quantify the damping of nonlinear HTGS and potentially supports the regulation performance enhancement of HTGS.
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Abstract This paper focuses on the effect of granite-micro-filler on static mechanical properties, damping behavior, and physical characteristics of silk-sisal hybrid composite. The composites ...structures are fabricated by using three layers of plain weaves mat with varying weight percentages (2, 4, and 6 wt%) of granite-micro-filler by hand layer process. The effect of granite-micro-filler on silk-sisal is analyzed and results are compared with pure silk-sisal (without granite-Micro-filler) hybrid composite. The results infer that; the tensile strength and flexural strength value of the developed silk-sisal hybrid composites are increased with the increase in wt% of granite-micro-filler content than pure silk–sisal, approximately 5% and 9% improved value in order by adding 6 wt% granite-micro-filler on silk–sisal. The tensile and flexural fracture morphology analysis indicated that composed plain weave of silk–sisal fiber mat with two (longitudinal and transverse) directions possesses higher mechanical properties and also observed that, granite-micro-filler dispersed on silk–sisal fiber mat and resin with closely packed. The improved damping factor is obtained by adding 6 wt% of granite-micro-filler content, which is approximately 75.8% higher than pure silk–sisal. The physical properties of silk–sisal hybrid composite have also been analyzed and well discussed in this paper.
Long-span suspension bridges are susceptible to wind loads due to their lightweight, low stiffness, and small structural damping. Recently, two large-span suspension bridges in China that closed for ...several months due to COVID-2019 experienced large-scale and continuous vortex-induced vibration shortly after reopening to traffic, and the traffic was closed again for safety consideration, which has aroused widespread concerns in society. To provide a reference for owners and related decision-making departments whether to restore the traffic, this article intends to explore the impact mechanism of traffic loads on the dynamic behavior of suspension bridges. First, two mechanical models for suspension bridges considering traffic loads and structural damping are proposed in this article. Then, based on the extended dynamic stiffness method, the explicit expressions of modal damping ratio in the two models are derived for the first time. Subsequently, Wittrick–Williams algorithm is employed to solve the frequency equation to obtain the modal frequency of the structure that considers the effect of traffic loads. A numerical case is studied to inspect the influence of traffic loads on the structural dynamic characteristics. Moreover, field monitoring data of accelerations of a suspension bridge are utilized to demonstrate the reasonability and accuracy of the approach proposed. Analysis shows that the theoretical results are consistent well with the measured ones, which indicates the traffic loads will affect the dynamic characteristics of the suspension bridge, thus reducing the modal frequency and increasing the modal damping ratio. Besides, the measured results further explain that the contribution of traffic loads to the structural damping is significant, which has a positive effect on preventing and eliminating vortex-induced vibration response. Some interesting and enlightening conclusions are also obtained in this article.
