Experimental Study on Conversion Efficiency of A Floating OWC Pentagonal Backward Bent Duct Buoy Wave Energy Converter

Wave tank tests were carried out to evaluate the total efficiency of a floating OWC Pentagonal Backward Bent Duct Buoy (PBBDB). Two kinds of turbine generators were used in tests. The incident wave power, pneumatic power and electricity were measured. The test results show that the primary efficiency can reach up to 185.98% in regular waves and 85.86% in irregular waves. The total efficiency from wave to wire with Wells turbine-generator set is 33.43% in regular waves and 15.82% in irregular waves. The peak total efficiency of the PBBDB with check valves equipped with the impulse turbine-generator set is 41.68% in regular waves and 27.10% in irregular waves. The efficiency of the turbine-generator set is about 30% in the tests. Obviously, the total efficiency can be further improved with the increasing of turbine efficiency.

Experimental Research on A New Type of Floating Breakwater for Wave-Absorbing and Energy-Capturing

To avoid the damage caused by big wind and wave in cage culture, and to solve the problem of energy supply faced by automatic breeding equipment, a new type of floating breakwater, named as Savonius double buoy breakwater(SDBB), is proposed in the paper. The floating breakwater is composed of HDPE cylindrical double buoys and horizontal axis Savonius rotors, and has the functions of wave-absorbing and energy-capturing. Based on the linear wave theory and energy conservation law, the Fourier Transform was applied to separate the two-dimensional wave frequency domain, and the energy captured by the rotors and absorbed by the floating breakwater were calculated.Experiments were conducted in a two-dimensional wave-making flume, and the transmitted waves at different wave heights and periods, the tension of mooring lines, and the rotational torque exerted on the Savonius rotor were measured. A series of performance comparison tests were also performed on the new floating breakwater and the traditional double-floating breakwater. Results show that the new floating breakwater is better than the traditional one in terms of reducing wave transmittance, and the combination of the floating breakwater with Savonius rotors can provide for marine aquaculture equipments with green power supply to a certain degree of self-sufficiency.

Meta-analysis of CO_(2) conversion,energy efficiency,and other performance data of plasma-catalysis reactors with the open access PIONEER database

This paper brings the comparison of performances of CO_(2)conversion by plasma and plasma-assisted catalysis based on the data collected from literature in this field,organised in an open access online database.This tool is open to all users to carry out their own analyses,but also to contributors who wish to add their data to the database in order to improve the relevance of the comparisons made,and ultimately to improve the efficiency of CO_(2)conversion by plasma-catalysis.The creation of this database and database user interface is motivated by the fact that plasma-catalysis is a fast-growing field for all CO_(2)conversion processes,be it methanation,dry reforming of methane,methanolisation,or others.As a result of this rapid increase,there is a need for a set of standard procedures to rigorously compare performances of different systems.However,this is currently not possible because the fundamental mechanisms of plasma-catalysis are still too poorly understood to define these standard procedures.Fortunately however,the accumulated data within the CO_(2)plasma-catalysis community has become large enough to warrant so-called“big data”studies more familiar in the fields of medicine and the social sciences.To enable comparisons between multiple data sets and make future research more effective,this work proposes the first database on CO_(2)conversion performances by plasma-catalysis open to the whole community.This database has been initiated in the framework of a H_(2)0_(2)0 European project and is called the“PIONEER Data Base”.The database gathers a large amount of CO_(2)conversion performance data such as conversion rate,energy efficiency,and selectivity for numerous plasma sources coupled with or without a catalyst.Each data set is associated with metadata describing the gas mixture,the plasma source,the nature of the catalyst,and the form of coupling with the plasma.Beyond the database itself,a data extraction tool with direct visualisation features or advanced filtering functionalities has been developed and is available online to the public.The simple and fast visualisation of the state of the art puts new results into context,identifies literal gaps in data,and consequently points towards promising research routes.More advanced data extraction illustrates the impact that the database can have in the understanding of plasma-catalyst coupling.Lessons learned from the review of a large amount of literature during the setup of the database lead to best practice advice to increase comparability between future CO_(2)plasma-catalytic studies.Finally,the community is strongly encouraged to contribute to the database not only to increase the visibility of their data but also the relevance of the comparisons allowed by this tool.

Hydrodynamic Performance Study of Wave Energy-Type Floating Breakwaters

The integration of wave energy converters(WECs) with floating breakwaters has become common recently due to the benefits of both cost-sharing and providing offshore power supply. In this study, based on viscous computational fluid dynamics(CFD) theory, we investigated the hydrodynamic performances of the floating box and Berkeley Wedge breakwaters, both of which can also serve as WECs. A numerical wave flume model is constructed using Star-CCM+software and applied to investigate the interaction between waves and wave energy converters while completing the verification of the convergence study of time and space steps. The effects of wave length on motion response and transmission coefficient of the floating box breakwater model are studied. Comparisons of our numerical results and published experimental data indicate that Star-CCM+ is very capable of accurately modeling the nonlinear wave interaction of floating structures, while the analytical potential theory overrates the results especially around the resonant frequency. Optimal damping can be readily predicted using potential flow theory and can then be verified by CFD numerical results. Next, we investigated the relationship between wave frequencies and various coefficients using the CFD model under optimal damping, including the motion response, transmission coefficient, reflection coefficient,dissipation coefficient, and wave energy conversion efficiency. We then compared the power generation efficiencies and wave dissipation performances of the floating box and Berkeley Wedge breakwaters. The results show that the power generation efficiency of the Berkeley Wedge breakwater is always much higher than that of the floating box breakwater. Besides, the wave dissipation performance of the Berkeley Wedge breakwater is much better than that of the floating box breakwater at lower frequency.

Oscillation and Conversion Performance of Double-Float Wave Energy Converter

In this study, we investigated the hydrodynamic and energy conversion performance of a double-float wave energy converter(WEC) based on the linear theory of water waves. The generator power take-off(PTO) system is modeled as a combination of a linear viscous damping and a linear spring. Using the frequency domain method, the optimal damping coefficient of the generator PTO system is derived to achieve the optimal conversion efficiency(capture width ratio).Based on the potential flow theory and the higher-order boundary element method(HOBEM), we constructed a threedimensional model of double-float WEC to study its hydrodynamic performance and response in the time domain. Only the heave motion of the two-body system is considered and a virtual function is introduced to decouple the motions of the floats. The energy conversion character of the double-float WEC is also evaluated. The investigation is carried out over a wide range of incident wave frequency. By analyzing the effects of the incident wave frequency, we derive the PTO's damping coefficient for the double-float WEC's capture width ratio and the relationships between the capture width ratio and the natural frequencies of the lower and upper floats. In addition, it is capable to modify the natural frequencies of the two floats by changing the stiffness coefficients of the PTO and mooring systems. We found that the natural frequencies of the device can directly influence the peak frequency of the capture width, which may provide an important reference for the design of WECs.

Study on Performance of Savonius Rotor Type Wave Energy Converter Used in Conjunction with Floating Breakwater

In the present study,the performance characteristics of a Savonius rotor type wave energy converter used in conjunction with a conventional double-buoy floating breakwater is investigated using physical model studies.The Savonius rotor type converter is suspended under the double-buoy floating breakwater to achieve wave attenuation while generating electricity,thereby enhancing the overall wave-elimination effect of the combination.The Savonius rotor is tested with different water submergence depths,and a reasonable relative submergence depth is determined within the scope of the research parameters.The hydrodynamics and energy capture performance of the combined breakwater with four different sizes of Savonius rotor under different wave conditions are studied,and the transmission coefficient of the experimental device is analyzed.The results show that when the optimal relative submergence depth is 0.65D,where D is the impeller diameter,there is a correspondence between the optimal performance of Savonius rotor with different rotor sizes and the wave period and wave height.The optimal energy capture efficiency of the wave energy converter reaches 17%−20.5%,and the transmission coefficient is reduced by 35%−45%compared with the conventional double-buoy breakwater.

Industrial Progress:New Energy-Efficient Absorbents for the CO_(2) Separation from Natural Gas,Syngas and Flue Gas

The CO2 separation from natural gas, syngas or flue gas represents an important industrial field of applications. An economic and energy-efficient CO2 separation from these gas streams is a prerequisite for sustainable industry contributions to the megatrends resource efficiency and globalization of technologies. One way of reducing operational expenditure for these separation processes is the development of better performing CO2 absorbents. Although a number of absorbents for the separation of CO2 from process gas streams exist, the need for the development of CO2 absorbents with an improved absorption performance, less corrosion and foaming, no nitrosamine formation, lower energy requirement and therefore less operational expenditure remains. Recent industrial activities have led to the development of novel high-performance CO2 scrubbing agents that can be employed in numerous industrial processes such as natural gas treatment, purification of syngas and the scrubbing of flue gas. The objective of this paper is to introduce these new high-performance scrubbing agents and to compare their performance with other state-of-the-art absorbents. It turned out, that the evaluated absorbents offer high cyclic capacities in the range of 2.4 to 2.6 mol CO2/kg absorbent and low absorption enthalpies (–30 kJ/mol) allowing for distinctive savings in the regeneration energy of the absorbent. Calculations with the modified Kremser model resulted in a reduction of the specific reboiler heat duty of 55%. Furthermore, the absorbents are less corrosive than standard amines as indicated by the measured corrosion rates of 0.21 mm/y versus 1.18 mm/y for a piperazine/methyldiethanolamine mixture. Based on new experimental results it is shown how substantial savings in operational and capital expenditure can be realized due to favorable absorbent properties. The novel high-performance CO2 system solutions meet recent industrial absorbent requirements and allow for more efficient or new CO2 separation processes.

Sustainable Cement Production with Improved Energy Efficiency and Emerging CO₂Mitigation

This paper studies the current strategies of energy efficiency improvement, CO2 capture in cement production and fly ash blended cement and concrete. Application of updated technology in newly industrialized countries (especially China) has improved energy efficiency due to their (its) dominant global cement production shares. Waste heat recovery (WHR) increases its energy efficiency. CO2 capture from cement plants will be more efficient than that from pulverized coal fired power plant. This paper might serve as a guide for the technology improvement, energy policy making and environmental protection in cement production.

Floating Wind Turbine Motion Suppression Using an Active Wave Energy Converter

This paper proposes a new concept of an actively-controlled wave energy converter for suppressing the pitch and roll motions of floating offshore wind turbines.The wave energy converter consists of several floating bodies that receive the wave energy,actuators that convert the wave energy into electrical energy and generate the mechanical forces,and rigid bars that connect the floating bodies and the wind turbine platform and deliver the actuator forces to the platform.The rotational torques that are required to minimize the platform pitch and roll motions are determined using a linear quadratic regulator.The torques determined in this manner are realized through the actuator forces that maximize the wave power capture as well.The performance of the proposed wave energy converter in simultaneously suppressing the platform pitch and roll motions and extracting the wave energy is validated through simulations.

Experimental Study on Conversion Characteristics of Dual-Mode OWC Models Appropriate for Voyaging

Freely movable wave energy converters(WECs) will greatly improve their adaptability to the marine environment.In this paper, a dual-mode oscillating water column(OWC) WEC with potential sailing capability is proposed. By opening and closing a gate on the side facing the waves, the WEC converts wave energy in the vertical duct(called VD mode) with low sailing resistance or in the backward bend duct(called BBD mode) with high sailing resistance.A small model and a medium model were designed and manufactured. The capture width ratio(CWR) of the small model in the two modes was experimentally studied. The CWR under bidirectional airflow and conversion characteristics under unidirectional airflow of the medium model in the BBD mode were obtained. Tests of the small model show that the peak CWR is 145.2% under regular waves and 90.1% under random waves in BBD mode, and in VD mode the peak CWR is about 60% of that in the BBD mode. Tests of the medium model show that the peak CWR is 228.96% under regular waves, the maximum wave-to-battery efficiency is 63.36% under regular waves and 30.17%under random waves, respectively.

中心管振荡水柱式波浪能装置外形设计性能试验

为了探索中心管振荡水柱式波浪能装置的结构外形对其性能的影响,本文进行了装置外形结构设计,通过入射波要素、浮筒吃水深度、尾管高度、水下结构比例等类型的多种工况的物理模型试验,验证不同参数对装置性能的影响。试验结果表明:设计的模型对入射波周期变化敏感,对特定入射波高响应较优越,且在波高为65 mm,周期为1.1 s时,获得最大俘获宽度比为67.64%;模型浮筒吃水深度越大,则俘获宽度比越小,通频带越窄;锥形尾管高度值对模型的俘获宽度比和通频带宽影响较小;不同水下结构比例的模型之间俘获宽度比数值差距较小,比例为0.3时,模型的俘获宽度比通频带最宽。模型试验结果对装置的进一步优化具有理论指导意义。

浮球覆盖下水面能量平衡再建与蒸发模型研究

针对干旱区平原水库蒸发强烈导致水资源利用率低的问题,选用黑色高密度聚乙烯(HDPE)浮球作为干旱区平原水库节水材料。通过理论分析、建模与室外试验三者结合,对完整非冰冻期内浮球覆盖下水面蒸发、水体能量平衡组分变化分布的响应机理进行研究,并在此基础上建立相应的水面蒸发量计算模型。结果显示:相较于自由水面,73%的浮球覆盖率下的整体水面净辐射吸收率减小约12.6%,其月均蒸发所需潜热通量减少了61.8%,约为148.73 W/m^(2),水体的感热通量和蓄热通量也有较大的变化。通过对彭曼模型的能量项和空气动力项进行修正,建立的覆盖条件下的水面蒸发量计算模型具有较高的精度。

基于非线性摆杆刚度机构的点吸式波能转换器

为了稳定捕获海洋低频波能,设计了一种基于非线性摆杆刚度机构的点吸式波能转换器.通过在摆杆间添加简单的拉伸弹性元件,制作了紧凑的摆杆刚度装置.对非线性刚度结构进行了受力分析,结合Cummins方程,建立了非线性波能转换器的时域动力学模型,并分析了规则波作用下点吸式波能转换器的波能转换特性.数值仿真结果表明,引入合适的非线性摆杆刚度机构可以提升系统在波浪激励下的运动响应,降低系统在波浪激励下运动响应峰值对应的频率,从而提高系统对于低频能量的捕获效率.

基于TLP浮式风机的分块垂荡点吸式波浪能装置的实验研究

面对海洋中庞大的波浪能资源,如何对其高效利用是目前仍需解决的一大难题。针对中国南海海域周期短、波高小的海况特点,本文提出一种与张力腿式平台(TLP)相结合的分块垂荡点吸收式波浪能装置模型。通过物理水池试验,测量分析分块浮子的水动力特性和波能捕获效率,同时与传统浮子的性能进行对比,探讨浮子分块后波浪能装置获能的优化效果。结果表明,分块浮子呈现出新的水动力特性,在低海况下装置对短周期波的能量捕获效率得到大幅提升,但在特定浪向角下会显著增大依附平台的纵摇运动,需要进一步优化张紧式系泊系统。

面向能效设计指数的LNG燃料船CO_(2)捕集系统设计及性能分析

为满足国际海事组织(International Maritime Organization,IMO)第三阶段船舶能效设计指数(energy efficiency design index,EEDI)的要求,提出一种液化天然气(liquefied natural gas,LNG)燃料船船载碳捕集系统(onboard carbon capture system,OCCS)。OCCS通过醇胺溶液对主机烟气中的CO_(2)进行富集,并回收主机烟气余热用于醇胺溶液再生,再利用LNG汽化过程中释放的冷能对解吸出的CO_(2)进行液化。以一艘Kamsarmax型船为例,构建基于冷热能综合利用的OCCS模型,分析烟气质量流量、溶剂质量流量和吸收塔进口处的贫液温度对CO_(2)捕集量及比热耗的影响。结果表明:提高贫液温度能够有效减少热量消耗,烟气和溶剂质量流量对CO_(2)捕集量影响显著,当溶剂质量流量大于18000 kg/h时,OCCS能满足IMO第三阶段的CO_(2)减排要求。该船通过所设计的OCCS可以满足IMO第三阶段EEDI的要求,其比热耗在10.9~12.2 GJ/t范围内。

阵列式直驱波浪发电系统集中式模型预测控制方法

将多个波浪能发电装置组成阵列是大规模开发波浪能的发展趋势。对于阵列式直驱波浪发电系统,采取合适的能量优化控制方法能显著提升波浪能捕获效率。然而,由于阵列式系统存在浮子间的相互辐射作用,已有的集中式模型预测控制(MPC)面临在线计算量大、难以工程应用的困难,而将各浮子视作独立系统的分布式MPC则存在能量捕获效率的损失。对此,文中提出一种改进的集中式MPC方法,将优化区间与约束区间进行解耦,可在保障系统整体能量捕获效率的同时,大幅减少计算开销,提升系统的实时控制性能。通过仿真研究分析了约束区间解耦方法的性能,并在多种波浪工况条件下验证了所提出方法的有效性。

相交圆柱摆式波能装置俘获效率数值分析

摆式波能装置具有结构简单和转化效率高等特点,本文应用AQWA软件基于势流理论对相交圆柱摆式波能装置进行了数值模拟研究,分析了轴间距比、结构阻尼、净浮力比、水深、波浪特性及吃水深度等主要参数对相交圆柱摆式波能装置俘获效率的影响,并与直板摆式波能装置的俘获效率进行了对比。结果表明:同样条件下,相交圆柱摆式波能装置往往比直板摆式波能装置的俘获效率更高;在研究范围内,轴间距比越大俘获效率越高;潮汐导致的水深变化对底铰摆式波能装置的俘获效率具有明显的影响,在工程应用中应采取适当的措施进行处理。

燃煤电厂CO_(2)捕集的减排效率研究与展望

为了客观评价不同CO_(2)捕集技术的能耗水平,判别CO_(2)捕集技术的有效性和经济性,提出减排效率概念和计算模型。CO_(2)减排效率表示某种CO_(2)捕集技术的有效减排能力,即捕集单位CO_(2)所发生的CO_(2)有效减排量,减排效率模型对CO_(2)捕集技术的能耗进行归集和平准化计算,其值越大表明减排效果越佳。利用减排效率模型测算,目前我国燃煤电厂CO_(2)捕集技术的减排效率理论极值为98%,燃烧前、燃烧中和燃烧后捕集技术的减排效率分别达到80%、70%和58%~68%。经工程应用实践验证,减排效率模型能满足评价要求。最后对CO_(2)捕集技术的发展进行了展望,认为未来随着捕集技术的不断进步和创新,CO_(2)减排效率将超过90%。

不同动力输出系统下多浮体波浪能转换装置性能研究

[目的]旨在对一种兼具防波效果的多浮体波浪能转换装置(MBFWEC)进行动力输出系统控制优化。[方法]应用OpenFOAM程序构建数值波浪水槽,模拟5种不同PTO阻尼(线性阻尼、定常阻尼、线性弹簧阻尼、速度平方阻尼、跳跃阻尼)作用下多浮体波浪能转换装置与波浪的相互作用。同时,比较不同PTO阻尼作用下波能转换装置的能量俘获效率和消波性能。[结果]结果表明,多浮体波浪能转换装置的波浪能俘获效率最高可达52.6%,线性弹簧阻尼和跳跃阻尼作为基于线性阻尼的优化,对波浪能装置的波浪能俘获和防浪消波效果有一定程度的影响。综合考虑波浪能俘获和防浪消波作用,线性阻尼相比线性弹簧阻尼和跳跃阻尼更有优势。[结论]通过研究,找到了定常阻尼、速度平方阻尼等PTO的优势波浪区间,对多浮体的PTO阻尼设置优化有一定参考意义。

振荡水翼弦向主动变形提高获能效率的机理研究

为探明振荡水翼弦向主动变形对获能效率的影响机理,应用结构变形方程结合动网格方法对水翼弦向变形进行主动控制,并通过求解雷诺平均纳维-斯托克斯(Reynolds-averaged Navier-Stokes, RANS)方程和Spalart-Allmaras(S-A)湍流模型,对具有不同变形程度的振荡水翼获能过程进行数值模拟。分析了振荡水翼弦向主动变形对获能效率的影响规律,提出了考虑水翼运动和弦向柔性变形的有效攻角计算公式,并从一个周期内不同时刻漩涡同水翼相互作用、弦向压力分布以及有效攻角变化等角度对水翼获能差异进行分析,探讨水翼弦向主动变形影响下获能效率变化的根本原因。研究结果表明:相较于刚性水翼,振荡水翼弦向主动变形可以显著提高效率,可达19%,由结构变形引起的漩涡强度变化是获能效率提升的原因之一,但其作用比较有限,由结构变形导致有效攻角增大是效率提升的主要原因。