Negative Stiffness Mechanism on An Asymmetric Wave Energy Converter by Using A Weakly Nonlinear Potential Model

Salter's duck,an asymmetrical wave energy converter(WEC)device,showed high efficiency in extracting energy from 2D regular waves in the past;yet,challenges remain for fluctuating wave conditions.These can potentially be addressed by adopting a negative stiffness mechanism(NSM)in WEC devices to enhance system efficiency,even in highly nonlinear and steep 3D waves.A weakly nonlinear model was developed which incorporated a nonlinear restoring moment and NSM into the linear formulations and was applied to an asymmetric WEC using a time domain potential flow model.The model was initially validated by comparing it with published experimental and numerical computational fluid dynamics results.The current results were in good agreement with the published results.It was found that the energy extraction increased in the range of 6%to 17%during the evaluation of the effectiveness of the NSM in regular waves.Under irregular wave conditions,specifically at the design wave conditions for the selected test site,the energy extraction increased by 2.4%,with annual energy production increments of approximately 0.8MWh.The findings highlight the potential of NSM in enhancing the performance of asymmetric WEC devices,indicating more efficient energy extraction under various wave conditions.

Revealing the role of calcium ion intercalation of hydrated vanadium oxides for aqueous zinc-ion batteries

Exploring suitable high-capacity V_(2)O_(5)-based cathode materials is essential for the rapid advancement of aqueous zinc ion batteries(ZIBs).However,the typical problem of slow Zn^(2+)diffusion kinetics has severely limited the feasibility of such materials.In this work,unique hydrated vanadates(CaVO,BaVO)were obtained by intercalation of Ca^(2+)or Ba^(2+)into hydrated vanadium pentoxide.In the CaVO//Zn and BaVO//Zn batteries systems,the former delivered up to a 489.8 mAh g^(-1)discharge specific capacity at 0.1 A g^(-1).Moreover,the remarkable energy density of 370.07 Wh kg^(-1)and favorable cycling stability yard outperform BaVO,pure V_(2)O_(5),and many reported cathodes of similar ionic intercalation compounds.In addition,pseudocapacitance analysis,galvanostatic intermittent titration(GITT)tests,and Trasatti analysis revealed the high capacitance contribution and Zn^(2+)diffusion coefficient of CaVO,while an in-depth investigation based on EIS elucidated the reasons for the better electrochemical performance of CaVO.Notably,ex-situ XRD,XPS,and TEM tests further demonstrated the Zn^(2+)insertion/extraction and Zn-storage mechanism that occurred during the cycle in the CaVO//Zn battery system.This work provides new insights into the intercalation of similar divalent cations in vanadium oxides and offers new solutions for designing cathodes for high-capacity aqueous ZIBs.

Evaluation of the Double Snap-Through Mechanism on the Wave Energy Converter’s Performance

Lower efficiencies induce higher energy costs and pose a barrier to wave energy devices'commercial applications.Therefore,the efficiency enhancement of wave energy converters has received much attention in recent decades.The reported research presents the double snap-through mechanism applied to a hemispheric point absorber type wave energy converter(WEC)to improve the energy absorption perfomance.The double snap-through mechanism comprises four oblique springs mounted in an X-configuration.This provides the WEC with different dynamic stability behaviors depending on the particular geometric and physical parameters employed.The efficiency of these different WEC behaviors(linear,bistable,and tristable)was initially evaluated under the action of regular waves.The results for bistable or tristable responses indicated significant improvements in the WEC's energy capture efficiency.Furthermore,the WEC frequency bandwidth was shown to be significantly enlarged when the tristable mode was in operation.However,the corresponding tristable trajectory showed intra-well behavior in the middle potential well,which induced a more severe low-energy absorption when a small wave amplitude acted on the WEC compared to when the bistable WEC was employed.Nevertheless,positive effects were observed when appropriate initial conditions were imposed.The results also showed that for bistable or tristable responses,a suitable spring stiffness may cause the buoy to oscillate in high energy modes.

Methylene blue intercalated vanadium oxide with synergistic energy storage mechanism for highly efficient aqueous zinc ion batteries

With the rise of aqueous multivalent rechargeable batteries,inorganic-organic hybrid cathodes have attracted more and more attention due to the complement of each other’s advantages.Herein,a strategy of designing hybrid cathode is adopted for high efficient aqueous zinc-ion batteries(AZIBs).Methylene blue(MB)intercalated vanadium oxide(HVO-MB)was synthesized through sol-gel and ion exchange method.Compared with other organic-inorganic intercalation cathode,not only can the MB intercalation enlarge the HVO interlayer spacing to improve ion mobility,but also provide coordination reactions with the Zn^(2+)to enhance the intrinsic electrochemical reaction kinetics of the hybrid electrode.As a key component for the cathode of AZIBs,HVO-MB contributes a specific capacity of 418 mA h g^(-1) at 0.1 A g^(-1),high rate capability(243 mA h g^(-1) at 5 A g^(-1))and extraordinary stability(88%of capacity retention after 2000cycles at a high current density of 5 A g^(-1))in 3 M Zn(CF_(3)SO_(3))_(2) aqueous electrolyte.The electrochemical kinetics reveals HVO-MB characterized with large pseudocapacitance charge storage behavior due to the fast ion migration provided by the coordination reaction and expanded interlayer distance.Furthermore,a mixed energy storage mechanism involving Zn^(2+)insertion and coordination reaction is confirmed by various ex-situ characterization.Thus,this work opens up a new path for constructing the high performance cathode of AZIBs through organic-inorganic hybridization.

Recent advances in energy storage mechanism of aqueous zinc-ion batteries

Aqueous rechargeable zinc-ion batteries(ZIBs)have recently attracted increasing research interest due to their unparalleled safety,fantastic cost competitiveness and promising capacity advantages compared with the commercial lithium ion batteries.However,the disputed energy storage mechanism has been a confusing issue restraining the development of ZIBs.Although a lot of efforts have been dedicated to the exploration in battery chemistry,a comprehensive review that focuses on summarizing the energy storage mechanisms of ZIBs is needed.Herein,the energy storage mechanisms of aqueous rechargeable ZIBs are systematically reviewed in detail and summarized as four types,which are traditional Zn^(2+)insertion chemistry,dual ions co-insertion,chemical conversion reaction and coordination reaction of Zn^(2+)with organic cathodes.Furthermore,the promising exploration directions and rational prospects are also proposed in this review.

Application of the Latching Control System on the Power Performance of a Wave Energy Converter Characterized by Gearbox,Flywheel,and Electrical GeneratorGustavor

The latching control represents an attractive alternative to increase the power absorption of wave energy converters(WECs)by tuning the phase of oscillator velocity to the wave excitation phase.However,increasing the amplitude of motion of the floating body is not the only challenge to obtain a good performance of the WEC.It also depends on the efficiency of the power take-off system(PTO).This study aims to address the actual power performance and operation of a heaving point absorber with a direct mechanical drive PTO system controlled by latching.The PTO characteristics,such as the gear ratio,the flywheel inertia,and the electric generator,are analyzed in the WEC performance.Three cylindrical point absorbers are also considered in the present study.A wave-to-wire model is developed to simulate the coupled hydro-electro-mechanical system in regular waves.The wave energy converter(WEC)performance is analyzed using the potential linear theory but considering the viscous damping effect according to the Morison equation to avoid the overestimated responses of the linear theory near resonance when the latching control system is applied.The latching control system increases the mean power.However,the increase is not significant if the parameters that characterize the WEC provide a considerable mean power.The performance of the proposed mechanical power take-off depends on the gear ratio and flywheel.However,the gear ratio shows a more significant influence than the flywheel inertia.The operating range of the generator and the diameter/draft ratio of the buoy also influence the PTO performance.

CFD Simulation and Experimental Study of a New Elastic Blade Wave Energy Converter

Small moving vehicles represent an important category of marine engineering tools and devices(equipment)typically used for ocean resource detection and maintenance of marine rights and interests.The lack of efficient power supply modes is one of the technical bottlenecks restricting the effective utilisation of this type of equipment.In this work,the performance characteristics of a new type of elastic-blade/wave-energy converter(EBWEC)and its core energy conversion component(named wave energy absorber)are comprehensively studied.In particular,computational fluid dynamics(CFD)simulations and experiments have been used to analyze the hydrodynamics and performance characteristics of the EBWEC.The pressure cloud diagrams relating to the surface of the elastic blade were obtained through two-way fluid-solid coupling simulations.The influence of blade thickness and relative speed on the performance characteristics of EBWEC was analyzed accordingly.A prototype of the EBWEC and its bucket test platform were also developed.The power characteristics of the EBWEC were analyzed and studied by using the blade thickness and motion cycle as control variables.The present research shows that the EBWEC can effectively overcome the performance disadvantages related to the transmission shaft torque load and power curve fluctuations of rigid blade wave energy converters(RBWEC).

Review of vanadium-based electrode materials for rechargeable aqueous zinc ion batteries

In recent years,rechargeable aqueous zinc ion batteries(ZIBs),as emerging energy storage devices,stand out from numerous metal ion batteries.Due to the advantages of low cost,environmentally friendly characteristic and safety,ZIBs can be considered as alternatives to lithium-ion batteries(LIBs).Vanadiumbased compounds with various structures and large layer spacings are considered as suitable cathode candidates for ZIBs.In this review,the recent research advances of vanadium-based electrode materials are systematically summarized.The electrode design strategy,electrochemical performances and energy storage mechanisms are emphasized.Finally,we point out the limitation of vanadium-based materials at present and the future prospect.

Redox Charge Transfer Kinetics and Reversibility of VO_(2) in Aqueous and Non-Aqueous Electrolytes of Na-Ion Storage

The deep understanding about the electrochemical behavior of the nanostructured electrode in electrolytes provides crucial insights for the rational design of electrode for sodium(Na)-ion storage system(NIS).Here,we report redox charge transfer kinetics and reversibility of VO_(2)(B) nanorod electrodes in both aqueous and organic electrolytes for NIS.The assynthesized VO_(2)(B) nanorods show the reversible redox reaction with the higher specific and rate capacitances at high current density in aqueous electrolytes than in organic electrolytes.Temperature-dependent impedance measurements demonstrate the more facile interfacial charge transfer of Na ions into VO_(2)(B) nanorods in aqueous electrolytes.The reversible evolution in oxidation state and chemical composition of VO_(2)(B) nanorods is observed in aqueous electrolytes,as confirmed by ex situ XRD and ex situ X-ray photoelectron spectroscopy analyses.Given by the facile and reversible pseudocapacitive feature,the electrochemical performances of VO_(2)(B) nanorods are further improved by constructing the hierarchical structure of the reduced graphene oxide-VO_(2) composite for aqueous Na+ion storage.

A novel improvement strategy and a comprehensive mechanism insight for α-MnO_(2) energy storage in rechargeable aqueous zinc-ion batteries

Aqueous zinc-ion batteries have been regarded as the most potential candidate to substitute lithium-ion batteries.However,many serious challenges such as suppressing zinc dendrite growth and undesirable reactions,and achieving fully accepted mechanism also have not been solved.Herein,the commensal composite microspheres withα-MnO_(2) nano-wires and carbon nanotubes were achieved and could effectively suppress ZnSO_(4)·3Zn(OH)_(2)·nH_(2)O rampant crystallization.The electrode assembled with the microspheres delivered a high initial capacity at a current density of 0.05 A g^(-1) and maintained a significantly prominent capacity retention of 88%over 2500 cycles.Furthermore,a novel energy-storage mechanism,in which multivalent manganese oxides play a synergistic effect,was comprehen-sively investigated by the quantitative and qualitative analysis for ZnSO_(4)·3Zn(OH)_(2)·nH_(2)O.The capacity contribution of multivalent manganese oxides and the crystal structure dissection in the transformed processes were completely identified.Therefore,our research could provide a novel strategy for designing improved electrode structure and a comprehensive understanding of the energy storage mechanism of α-MnO_(2) cathodes.

基于小波能量占比与时序预测的换流变压器机械状态智能诊断技术

换流变压器运行过程中其内部绕组承受交直流电压的共同作用,导致振源振动响应非常复杂。为关注换流变压器在长期振动作用下的机械状态变化,文中首先基于换流变压器绕组振动机理及其振动特性开发了振动在线监测系统,针对现场某换流变压器的振动信号进行了长期带电监测,并提取了不同时刻下振动信号的小波能量占比,最后以小波能量占比等振动特征组成的时间序列作为数据样本,结合时间序列预测模型提出了适用于现场换流变压器的机械状态智能诊断技术。分析结果表明,振动在线监测系统在现场能够对换流变进行长期带电监测,小波能量占比特征量可以在一定程度上反映换流变压器的运行规律和内部机械状态。通过时间序列预测模型对小波能量占比序列的处理,最终得到的预测值与期望值达到了较高的相似度,为现场换流变压器的状态评估和潜在缺陷诊断提供了更加及时、有效的技术途径。

新能源基地经LCC-HVDC送出系统振荡机理分析与抑制策略(二):阻抗特性与振荡机理分析

该文基于系列文章1建立的电网换相换流器型高压直流(line commutated converter-based high voltage direct current,LCC-HVDC)阻抗模型,开展新能源基地经LCC-HVDC送出系统阻抗特性和振荡机理分析。首先,研究LCC-HVDC送端交流端口阻抗与阀本体交流阻抗、交流滤波器阻抗间的构成关系,分析直流线路、受端换流站、受端电网强度对送端换流站阀本体交流阻抗的主导影响;然后,研究送端换流站直流电流环对阀本体交流阻抗的重叠效应,分析送端换流站交流端口阻抗次/超同步频段负阻尼特性形成机理,并论述受端换流站和受端电网强度对送端交流端口阻抗特性的交互影响;接下来,建立新能源基地经LCC-HVDC送出系统等值模型,研究送端系统振荡边界条件,阐明LCC-HVDC对新能源并网点阻抗特性影响的变化规律,揭示直驱风机(permanent magnet synchronous generator,PMSG)、双馈风机(doubly-fed induction generator,DFIG)、光伏(photovoltaic,PV)不同类型新能源基地经LCC-HVDC送出系统次/超同步振荡机理;最后,不同类型新能源基地经LCC-HVDC送出系统仿真结果验证了该文提出的次/超同步振荡机理的正确性和通用性。

In-situ construction of MnCO_(3)@CNTs nanosheets for high-capacity aqueous zinc ion batteries

Owing to severe agglomeration of manganese carbonate(MnCO_(3))during its synthesis,it exhibits rapid decay cycle performance when used as a cathode material in aqueous zinc ion batteries.To overcome this drawback,we synthesized a MnCO_(3)material with carbon nanotubes(CNTs)(i.e.,MnCO_(3)@CNTs)via a one-step solvothermal method using a hybrid modification strategy.MnCO_(3)nanospheres were grown in-situ on a two-dimensional(2D)plane that was orderly interwoven by tubular single fibers of carbon to form a leaf-like nanosheet structure.The surface area of the MnCO_(3)@CNTs material was enlarged enormously through the special nanosheet structure,and its stability was improved by the supporting structure of the CNTs.As a result,the MnCO_(3)@CNTs exhibited a discharge capacity of 247.6 mAh g^(-1)at a current density of 0.1 A g^(-1).The energy storage mechanism of MnCO_(3)@CNTs was further explored using a series of electrochemical kinetic analyses and ex-situ characterization tests.This modification method not only broadens the application field of MnCO_(3),but also provides the possibility of modifying more cathode materials.

Identifying Heteroatomic and Defective Sites in Carbon with Dual-Ion Adsorption Capability for High Energy and Power Zinc Ion Capacitor

Aqueous zinc-based batteries(AZB s)attract tremendous attention due to the abundant and rechargeable zinc anode.Nonetheless,the requirement of high energy and power densities raises great challenge for the cathode development.Herein we construct an aqueous zinc ion capacitor possessing an unrivaled combination of high energy and power characteristics by employing a unique dual-ion adsorption mechanism in the cathode side.Through a templating/activating co-assisted carbonization procedure,a routine protein-rich biomass transforms into defect-rich carbon with immense surface area of 3657.5 m^(2) g^(-1) and electrochemically active heteroatom content of 8.0 at%.Comprehensive characterization and DFT calculations reveal that the obtained carbon cathode exhibits capacitive charge adsorptions toward both the cations and anions,which regularly occur at the specific sites of heteroatom moieties and lattice defects upon different depths of discharge/charge.The dual-ion adsorption mechanism endows the assembled cells with maximum capacity of 257 mAh g^(-1) and retention of72 mAh g^(-1) at ultrahigh current density of 100 A g^(-1)(400 C),corresponding to the outstanding energy and power of 168 Wh kg^(-1)and 61,700 W kg^(-1).Furthermore,practical battery configurations of solid-state pouch and cable-type cells display excellent reliability in electrochemistry as flexible and knittable power sources.

含机械整流动力输出之多自由度波能转换装置的水动力性能

为提高波能俘获效率,提出了一种由固定平台、垂直轴对称浮体、管状结构和三个动力输出(PTO)机构组成的多自由度波能转换装置,其中管状结构与固定平台之间采用万向接头连接,浮体与管状结构间采用运动导向机构连接使两者具有相同的纵摇和横摇运动,浮体沿管状结构滑动的能量俘获采用机械整流PTO系统使与之连接的发电机实现单向旋转,其余两个PTO安装在铰接轴处;利用势流理论建立了该装置水动力分析的时域计算模型,其中静水力和Froude-Krylov力采用沿浮体静浮时湿表面积分的线性和沿瞬时湿表面积分的非线性两种方法分别计算;为考虑可能出现的大幅纵/横摇运动的影响,垂向机械整流PTO负载力分解到纵荡、横荡和垂荡方向时不作线性化处理;分析了随浪规则波作用下,波高、垂向PTO和纵摇PTO阻尼系数的影响。结果表明:在相同参数下采用非线性方法所得垂向PTO的波能浮获效率及装置总效率均小于线性方法所得结果,而纵摇PTO的波能浮获效率则大于线性方法结果;波高越大,两种方法所得结果之间的差值越大。

Issues and strategies of cathode materials for mild aqueous static zinc-ion batteries

Researchers prefer mild aqueous static zinc-ion batteries(ASZIBs)for their distinct benefits of excellent safety,abundant zinc resources,low cost,and high energy density.However,at the moment there are some issues with the cathode materials of mild ASZIBs,including dissolution,by-products,poor conductivity,and a contentious energy storage system.Consequently,there are numerous difficulties in the development of high-performance mild ASZIBs cathode materials.This overview examines the mechanisms for storing energy and the de-velopments in inorganic,organic,and other novel cathode materials that have emerged in recent years.At the same time,three solutions—structural engineering,interface engineering,and reaction pathway engineering—as well as the difficulties now faced by the cathode materials of mild ASZIBs are forcefully introduced.Finally,a prospect is made regarding the evolution of cathode materials in the future.

新型浮力摆式波浪能发电装置波-电动力学建模和时域特性分析

主动共振浮力摆式波浪能发电装置通过调节内部配重位置实现共振发电。本文以基于机械式动力输出系统(Power Take-off,PTO)的主动共振浮力摆式波浪能发电装置为研究对象,构建波-电时域动力学模型并验证模型可行性,该模型的非线性特征主要体现在正弦函数形式的静水回复力矩及止动力矩中。进一步,研究自振周期同不规则波能量周期一致的共振状态下,不同负载形式及取值大小对装置时域响应曲线、时均功率和效率的影响。研究结果表明:不同负载设置对俘获宽度比的影响大于PTO传动效率。阻性负载值过大或过小均会削弱俘获宽度比,使有功时均值和发电效率下降,共振状态下,负载的感性或容性成分会使发电机产生大量无功,且无功有正有负,感性或容性成分能有效削弱俘获宽度比、有功时均值和发电效率。

Development of organic redox-active materials in aqueous flow batteries: Current strategies and future perspectives

Aqueous redox flow batteries,by using redox-active molecules dissolved in nonflammable water solutions as electrolytes,are a promising technology for grid-scale energy storage.Organic redox-active materials offer a new opportunity for the construction of advanced flow batteries due to their advantages of potentially low cost,extensive structural diversity,tunable electrochemical properties,and high natural abundance.In this review,we present the emergence and development of organic redox-active materials for aqueous organic redox flow batteries(AORFBs),in particular,molecular engineering concepts and strategies of organic redox-active molecules.The typical design strategies based on organic redox species for high-capacity,high-stability,and high-voltage AORFBs are outlined and discussed.Molecular engineering of organic redox-active molecules for high aqueous solubility,high chemical/electrochemical stability,and multiple electron numbers as well as satisfactory redox potential gap between the redox pair is essential to realizing high-performance AORFBs.Beyond molecular engineering,the redoxtargeting strategy is an effective way to obtain high-capacity AORFBs.We further discuss and analyze the redox reaction mechanisms of organic redox species based on a series of electrochemical and spectroscopic approaches,and succinctly summarize the capacity degradation mechanisms of AORFBs.Furthermore,the current challenges,opportunities,and future directions of organic redox-active materials for AORFBs are presented in detail.

小型斯特林发动机不同外加热工况下运行的探索性实验

该文就其微型化可能产生的一系列问题,如:输出频率过高、产生转矩过小、冷热端差过小等进行了分析。提出自由活塞式斯特林发动机比热声式更具微型化的优势。并对一台长12cm、直径2.5cm 的小型活塞式斯特林发动机进行了实验。实验中发动机热端温度范围64～626℃,通过测量其外壁面温度和声信号随时间的变化,得到发动机的稳定性和输出功率随外加热功率变化规律。该发动机的理论最高功率密度为102kW/m^3。

刮板输送机用隔爆兼本质安全型交流变频器研发

针对刮板输送机在轻载、空载运行时整机效率低、电网功率因数低、多机拖动存在功率不平衡、启动力矩不足难启动、启动时存在机械冲击和电网冲击等问题,探讨了刮板输送机的工况特点及其对变频器的特殊要求;阐述了刮板输送机用隔爆兼本质安全型交流变频器的组成、工作原理及主要技术参数;研究了直接转矩控制、过载能力解决、节能运行控制、多机驱动功率平衡、变频器电磁干扰的途径及抑制措施等特殊控制技术;介绍了刮板输送机隔爆兼本安型交流变频器在西铭煤矿、樟村煤矿等4个煤矿的井下典型应用情况,结果表明:该设备使用可靠,运行稳定,节能降耗优势明显,可以满足井下1 140 V供电的刮板输送机使用要求。