A DC-side energy dissipation device and control method for offshore wind power generation systems have been proposed, which effectively solves the energy imbalance caused by the AC voltage drop at ...the receiving end. The proposed circuit structure uses IGBT and metal oxide varistor (MOV) to form a switching module, effectively avoiding the overvoltage problem caused by the IGBT series structure during the turn-off process, while significantly reducing the overall equipment volume. The proposed structure connects the energy dissipation resistor with the main circuit through a coupling transformer, which reduces the voltage at both ends of the energy dissipation resistor, thus reducing the cost of high-voltage wall bushings in the system. The proposed DC voltage and energy dissipation resistor current dual-loop control method can flexibly adjust the dissipation power of the energy dissipation arm. When a single switch in the arm fails, the proposed multi-equipment coordinated control method can realize Fault Ride Through (FRT) at the AC side of the receiving end converter (REC). Simulation and experimental results confirm that the proposed hardware structure and control method can safely and stably handle the DC voltage increase caused by the AC voltage drop at the receiving end.
This paper explored the seismic behaviour of self-centring hybrid-steel-frame (SC-HSF) employing energy dissipation sequences and the corresponding inelastic seismic demand model. The SC-HSF ...employing energy dissipation sequences was composed of the self-centring main frame (SCMF) and energy dissipation bays (EDBs). Two prototype structures were designed and developed using modelling techniques validated by experimental data. Nonlinear cyclic pushover analyses and nonlinear dynamic analyses were conducted to examine the seismic behaviour of the prototype structures. The seismic response of prototype structures including peak interstorey drifts and post-earthquake residual interstorey drifts were examined in detail. After verifying the promise of the SC-HSF structures, the energy factor for quantifying the inelastic seismic demand was developed by nonlinear spectral analyses based on the equivalent single-degree-of-freedom (SDOF) systems assigned with the structural hysteretic model. The effects of the structural hysteretic parameters on the mean and probabilistic features of the energy factors were discussed in detail. In addition, the lognormal distribution was selected to develop a probabilistic spectral seismic demand model based on a comparative study, and the prediction equations were developed to simulate the probabilistic features of the energy factors. Finally, the probabilistic spectral seismic demand model was used for evaluating the behaviour of the prototype structures, and the sufficiency of the model was justified.
•Self-centring hybrid-steel-frame employing energy dissipation sequences was proposed.•The seismic behaviour of the novel structure was examined.•A probabilistic spectral seismic demand model was developed.
Soft fiber‐reinforced polymers (FRPs), consisting of rubbery matrices and rigid fabrics, are widely utilized in industry because they possess high specific strength in tension while allowing flexural ...deformation under bending or twisting. Nevertheless, existing soft FRPs are relatively weak against crack propagation due to interfacial delamination, which substantially increases their risk of failure during use. In this work, a class of soft FRPs that possess high specific strength while simultaneously showing extraordinary crack resistance are developed. The strategy is to synthesize tough viscoelastic matrices from acrylate monomers in the presence of woven fabrics, which generates soft composites with a strong interface and interlocking structure. Such composites exhibit fracture energy, Γ, of up to 2500 kJ m−2, exceeding the toughest existing materials. Experimental elucidation shows that the fracture energy obeys a simple relation, Γ = W · lT, where W is the volume‐weighted average of work of extension at fracture of the two components and lT is the force transfer length that scales with the square root of fiber/matrix modulus ratio. Superior Γ is achieved through a combination of extraordinarily large lT (10–100 mm), resulting from the extremely high fiber/matrix modulus ratios (104–105), and the maximized energy dissipation density, W. The elucidated quantitative relationship provides guidance toward the design of extremely tough soft composites.
Novel soft fiber‐reinforced polymers (FRPs) are developed by using viscoelastic polymers that are adhesive, soft, and tough as matrices. The unique combination of these properties in the matrices ensures a strong component interface, which consequently maximizes the energy dissipation density and gives rise to a large force transfer length enabled by the extremely high fiber/matrix modulus ratio. As a result, the soft FRPs can achieve toughness of up to 2500 kJ m−2, exceeding any existing best‐in‐class materials.
•The variation in energy density with the number of cycles and upper stress limit was investigated.•The energy storage and dissipation laws were revealed.•The fact that larger crack angles lead to ...larger bearing capacity was verified from a perspective of energy.
In order to obtain influence laws of crack angles on energy characteristics of sandstones in complex stress environment, this study performed a cyclic loading and unloading test under stress gradients with a constant lower limit of stress on sandstone samples with cracks at different angles. By utilizing the integral method for area, total energy density, elastic energy density and dissipated energy density of the sandstone samples with cracks at different angles were derived. Moreover, this study explored the increase laws of the three energy densities with the number of cyclic loading and the upper limit of stress in each cyclic loading. The results demonstrate that during the whole cyclic loading process, the three energy densities increase with the increase of the number of cyclic loads, and the growth rate of elastic energy density is obviously larger than that of dissipated energy density. In addition, In the whole cyclic loading and unloading process, the energy densities of the sandstones with cracks at different angles show obvious growth relationships in the form of a quadratic function with upper limit of stress in single cyclic loading and unloading. The index that characterizes the storage energy capability and dissipated energy capability of the rock, namely the energy storage coefficient and the energy dissipation coefficient, is defined. By analyzing the relationships of energy storage coefficient and energy dissipation coefficient of rocks with crack angles in rocks, it is found that the larger the crack angle, the larger the energy storage coefficient of rocks while the smaller the energy dissipation coefficient. This explains the phenomenon that the larger the crack angle, the stronger the bearing capacity of rocks from the perspective of energy.
•Experimental study of a new steel beam-to-CFST column connection was conducted.•The new connection consists of unequal depth beams and CFST column.•Seismic shear behavior of the irregular panel ...zones was investigated.•Complex failure modes were distinguished in various panel locations.
This paper presents an experimental investigation on the seismic behavior of a novel steel-concrete composite beam-to-column connections reinforced by outer-annular-stiffener. This type of connection consists of beams with varying depths in opposite sides, and a concrete filled steel tubular (CFST) column. Four cruciform connection specimens with varying beam depth ratios (1, 0.75 and 0.5) were tested under monotonic and cyclic loading protocols to investigate shear capacity, hysteretic behavior, deformation capacity and failure modes within the irregular joint panel zone. From the test results, two types of failure modes were identified as global shear failure occurred in the panel zones 1 and 2 on the side of large depth beam when subjected to positive loading direction, and partial shear failure only in the panel zone 1 under the negative loading direction. The global shear failure was characterized by plastic deformation in the panel zones 1 and 2 prior to out-of-plane instability arose in the column flange near the outer-annular-stiffener. On the other hand, shear failure of panel zone under negative direction loading, the deformation of steel part was similar to that under the positive loading direction. While, the concrete panel zone located in the web of column only connecting with small depth beam, showed an arch mechanism. There was no fatigue fracture throughout the test, and all the specimens behaved in a ductile manner. All the tested specimens demonstrated good plastic deformation and energy dissipation capacity.
One‐for‐all phototheranostics, referring to a single component simultaneously exhibiting multiple optical imaging and therapeutic modalities, has attracted significant attention due to its excellent ...performance in cancer treatment. Benefitting from the superiority in balancing the diverse competing energy dissipation pathways, aggregation‐induced emission luminogens (AIEgens) are proven to be ideal templates for constructing one‐for‐all multimodal phototheranostic agents. However, to this knowledge, the all‐round AIEgens that can be triggered by a second near‐infrared (NIR‐II, 1000–1700 nm) light have not been reported. Given the deep tissue penetration and high maximum permissible exposure of the NIR‐II excitation light, herein, this work reports for the first time an NIR‐II laser excitable AIE small molecule (named BETT‐2) with multimodal phototheranostic features by taking full use of the advantage of AIEgens in single molecule‐facilitated versatility as well as synchronously maximizing the molecular donor‐acceptor strength and conformational distortion. As formulated into nanoparticles (NPs), the high performance of BETT‐2 NPs in NIR‐II light‐driven fluorescence‐photoacoustic‐photothermal trimodal imaging‐guided photodynamic‐photothermal synergistic therapy of orthotopic mouse breast tumors is fully demonstrated by the systematic in vitro and in vivo evaluations. This work offers valuable insights for developing NIR‐II laser activatable one‐for‐all phototheranostic systems.
An NIR‐II light activatable AIE small molecule with multimodal phototheranostic features is constructed for the first time by taking full use of the advantage of AIEgens in single molecule‐facilitated versatility, as well as synchronously maximizing the molecular donor‐acceptor strength and conformational distortion. This molecule actualizes prominent NIR‐II FLI‐PAI‐PTI trimodal imaging‐guided PDT‐PTT synergistic therapy of orthotopic mouse breast tumors.
Low-density compressible materials enable various applications but are often hindered by structure-derived fatigue failure, weak elasticity with slow recovery speed and large energy dissipation. Here ...we demonstrate a carbon material with microstructure-derived super-elasticity and high fatigue resistance achieved by designing a hierarchical lamellar architecture composed of thousands of microscale arches that serve as elastic units. The obtained monolithic carbon material can rebound a steel ball in spring-like fashion with fast recovery speed (∼580 mm s
), and demonstrates complete recovery and small energy dissipation (∼0.2) in each compress-release cycle, even under 90% strain. Particularly, the material can maintain structural integrity after more than 10
cycles at 20% strain and 2.5 × 10
cycles at 50% strain. This structural material, although constructed using an intrinsically brittle carbon constituent, is simultaneously super-elastic, highly compressible and fatigue resistant to a degree even greater than that of previously reported compressible foams mainly made from more robust constituents.
The damage and failure of rock under triaxial stress is an irreversible process of energy dissipation, which mainly includes plastic energy dissipation and damage energy dissipation. However, it is ...difficult and rare to separate plastic energy dissipation and damage energy dissipation and to conduct relevant research on this basis. In this work, a loading control method with a combination of load (0.5 kN/s) and circumferential deformation (0.01 mm/min) was used, and triaxial cyclic loading and unloading tests under five different confining pressures were performed on granite from the Beishan site area of China's high-level radioactive waste repository. The results indicate that the angle between the main fracture surface and the longitudinal axis increases with the increase of confining pressure. According to the characteristics of the stress–strain curve and energy dissipation, the test process can be divided into five stages: the initial compaction and elastic stage, the stable crack growth stage, the unstable crack growth stage, the postpeak unstable fracture stage and the residual stress stage. Importantly, a separate determination method of plastic energy dissipation and damage energy dissipation was proposed, and the evolution characteristics of plastic energy dissipation and damage energy dissipation were revealed. The ratio of plastic energy dissipation to input energy decreases slightly in the initial compaction and elastic stage, stabilizes at a low level in the stable and unstable crack growth stages, increases significantly in the postpeak unstable fracture stage and remains at a high level in the residual stress stage. Meanwhile, the ratio of damage energy dissipation to input energy increases slightly before the unstable crack growth stage, increases abruptly at the end of the unstable crack growth stage and the initial part of the postpeak unstable fracture stage, then declines rapidly, and finally remains at a low level. Furthermore, the qualitative and quantitative research results of damage evolution show that the plastic shear strain and damage variable established by damage energy dissipation can qualitatively and quantitatively describe the damage evolution of Beishan granite respectively. Finally, the verification results of Beishan granite and two other rock types show that the separation method for calculating plastic energy dissipation and damage energy dissipation proposed in this work has good adaptability, and the qualitative damage development analysis based on plastic shear strain can be verified and supplemented with the quantitative damage development analysis based on energy theory.
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