In the present paper combining the relationship between wave steepness andwave age with the significant wave energy balance equation for wind wave, a new wind wave growthrelation is presented. Comparisons with the oth...In the present paper combining the relationship between wave steepness andwave age with the significant wave energy balance equation for wind wave, a new wind wave growthrelation is presented. Comparisons with the other existing wind wave growth relations show that theresults in present paper accord better with the wind wave growth process.展开更多
Background： Forests are a key component of the global carbon cycle, and research is needed into the effects of human-driven and natural processes on their carbon pools. Airborne laser scanning （ALS） produces detail...Background： Forests are a key component of the global carbon cycle, and research is needed into the effects of human-driven and natural processes on their carbon pools. Airborne laser scanning （ALS） produces detailed 3D maps of forest canopy structure from which aboveground carbon density can be estimated. Working with a ALS dataset collected over the 8049-km2 Wellington Region of New Zealand we create maps of indigenous forest carbon and evaluate the influence of wind by examining how carbon storage varies with aspect. Storms flowing from the west are a common cause of disturbance in this region, and we hypothesised that west-facing forests exposed to these winds would be shorter than those in sheltered east-facing sites. Methods： The aboveground carbon density of 31 forest inventory plots located within the ALS survey region were used to develop estimation models relating carbon density to ALS information. Power-law models using rasters of top-of-the-canopy height were compared with models using tree-level information extracted from the ALS dataset. A forest carbon map with spatial resolution of 25 m was generated from ALS maps of forest height and the estimation models. The map was used to evaluate the influences of wind on forests. Results： Power-law models were slightly less accurate than tree-centric models （RMSE 35% vs 32%） but were selected for map generation for computational efficiency. The carbon map comprised 4.5 million natural forest pixels within which canopy height had been measured by ALS, providing an unprecedented dataset with which to examine drivers of carbon density. Forests facing in the direction of westerly storms stored less carbon, as hypothesised. They had much greater above-ground carbon density for a given height than any of 14 tropical forests previously analysed by the same approach, and had exceptionally high basal areas for their height. We speculate that strong winds have kept forests short without impeding basal area growth. Conclusion： Simple estimation models based on top-of-the canopy height are almost as accurate as state-of-the-art tree-centric approaches, which require more computing power. High-resolution carbon maps produced by ALS provide powerful datasets for evaluating the environmental drivers of forest structure, such as wind.展开更多
The local scour around a new pile-group foundation of offshore wind turbine subjected to a bi-directional current was physically modeled with a bi-directional flow flume. In a series of experiments, the flow velocity ...The local scour around a new pile-group foundation of offshore wind turbine subjected to a bi-directional current was physically modeled with a bi-directional flow flume. In a series of experiments, the flow velocity and topography of the seabed were measured based on a system composed of plane positioning equipment and an ADV.Experimental results indicate that the development of the scour hole was fast at the beginning, but then the scour rate decreased until reaching equilibrium. Erosion would occur around each pile of the foundation. In most cases, the scour pits were connected in pairs and the outside widths of the scour holes were larger than the inner widths. The maximum scour depth occurred at the side pile of the foundation for each test. In addition, a preliminary investigation shows that the larger the flow velocity, the larger the scour hole dimensions but the shorter equilibrium time. The field maximum scour depth around the foundation was obtained based on the physical experiments with the geometric length scales of 1:27.0, 1:42.5 and 1:68.0, and it agrees with the scour depth estimated by the HEC-18 equation.展开更多
A new sound alloy, abbreviated to S, has been developed by the General Research Institutefor Non-ferrous Metals, Beijing. The alloy is very suitable for making trumpets, trombones, tenorhorns, saxaphones and other kin...A new sound alloy, abbreviated to S, has been developed by the General Research Institutefor Non-ferrous Metals, Beijing. The alloy is very suitable for making trumpets, trombones, tenorhorns, saxaphones and other kinds of wind instruments. Beijing Wind Instrument Factory, which is the largest one in China, has used Salloy formanufacturing 5200 type trompets, the sound performance of which has been examined with fre-quency analysis and experimented by famous musical experts. The results show that the 5200 typetrumpets made of Salloy have excellent quality, accurate intonation and ease of response at展开更多
【目的】电网电压跌落故障会引起风电机组载荷的剧烈变化,严重影响风电机组的安全稳定运行。随着风电机组的大型化,风电叶片长度不断增加,塔筒增高,其载荷特性对系统参数波动变得敏感。因此,需要研究电网电压跌落过程中关键部件的载荷...【目的】电网电压跌落故障会引起风电机组载荷的剧烈变化,严重影响风电机组的安全稳定运行。随着风电机组的大型化,风电叶片长度不断增加,塔筒增高,其载荷特性对系统参数波动变得敏感。因此,需要研究电网电压跌落过程中关键部件的载荷与振动特性。【方法】提出了基于动态链接库和Socket通信的数据交互方式,建立了Simulink与Bladed的联合仿真方法。基于某3.4 MW风电机组模型,采用给定风速变化的工况对联合仿真平台进行验证。研究了低电压穿越(low voltage ride through,LVRT)过程中机组总体性能与叶片、塔筒载荷的变化关系。【结果】电网电压跌落幅值对电机功率影响较大,对风轮的调节参数影响较小。低电压穿越过程中风轮的桨矩角调节和转速有较长时间的波动,叶片外叶展处载荷的变化大于内叶展处,叶尖位移增加。塔架的振动频率与固有频率接近,存在潜在风险,需要在机组设计中考虑。【结论】联合仿真平台可以很好地模拟风电机组的气动性能与部件载荷的暂态特性,为机组的优化控制提供参考。展开更多
文摘In the present paper combining the relationship between wave steepness andwave age with the significant wave energy balance equation for wind wave, a new wind wave growthrelation is presented. Comparisons with the other existing wind wave growth relations show that theresults in present paper accord better with the wind wave growth process.
基金supported by Ministry of Business, Innovation and Employment core funding to Crown Research Institutes
文摘Background： Forests are a key component of the global carbon cycle, and research is needed into the effects of human-driven and natural processes on their carbon pools. Airborne laser scanning （ALS） produces detailed 3D maps of forest canopy structure from which aboveground carbon density can be estimated. Working with a ALS dataset collected over the 8049-km2 Wellington Region of New Zealand we create maps of indigenous forest carbon and evaluate the influence of wind by examining how carbon storage varies with aspect. Storms flowing from the west are a common cause of disturbance in this region, and we hypothesised that west-facing forests exposed to these winds would be shorter than those in sheltered east-facing sites. Methods： The aboveground carbon density of 31 forest inventory plots located within the ALS survey region were used to develop estimation models relating carbon density to ALS information. Power-law models using rasters of top-of-the-canopy height were compared with models using tree-level information extracted from the ALS dataset. A forest carbon map with spatial resolution of 25 m was generated from ALS maps of forest height and the estimation models. The map was used to evaluate the influences of wind on forests. Results： Power-law models were slightly less accurate than tree-centric models （RMSE 35% vs 32%） but were selected for map generation for computational efficiency. The carbon map comprised 4.5 million natural forest pixels within which canopy height had been measured by ALS, providing an unprecedented dataset with which to examine drivers of carbon density. Forests facing in the direction of westerly storms stored less carbon, as hypothesised. They had much greater above-ground carbon density for a given height than any of 14 tropical forests previously analysed by the same approach, and had exceptionally high basal areas for their height. We speculate that strong winds have kept forests short without impeding basal area growth. Conclusion： Simple estimation models based on top-of-the canopy height are almost as accurate as state-of-the-art tree-centric approaches, which require more computing power. High-resolution carbon maps produced by ALS provide powerful datasets for evaluating the environmental drivers of forest structure, such as wind.
基金financially supported by the National Key Research and Development Program of China(Grant No.2017YFC1404200)the Tianjin Key Program of Applied Foundation and Advanced-Tech Research,China(Grant No.18JCZDJC40200)+1 种基金the National High Technology Research and Development Program of China(863 Program,Grant No.2012AA051709)the National Natural Science Foundation of China(Grant No.51509183)
文摘The local scour around a new pile-group foundation of offshore wind turbine subjected to a bi-directional current was physically modeled with a bi-directional flow flume. In a series of experiments, the flow velocity and topography of the seabed were measured based on a system composed of plane positioning equipment and an ADV.Experimental results indicate that the development of the scour hole was fast at the beginning, but then the scour rate decreased until reaching equilibrium. Erosion would occur around each pile of the foundation. In most cases, the scour pits were connected in pairs and the outside widths of the scour holes were larger than the inner widths. The maximum scour depth occurred at the side pile of the foundation for each test. In addition, a preliminary investigation shows that the larger the flow velocity, the larger the scour hole dimensions but the shorter equilibrium time. The field maximum scour depth around the foundation was obtained based on the physical experiments with the geometric length scales of 1:27.0, 1:42.5 and 1:68.0, and it agrees with the scour depth estimated by the HEC-18 equation.
文摘A new sound alloy, abbreviated to S, has been developed by the General Research Institutefor Non-ferrous Metals, Beijing. The alloy is very suitable for making trumpets, trombones, tenorhorns, saxaphones and other kinds of wind instruments. Beijing Wind Instrument Factory, which is the largest one in China, has used Salloy formanufacturing 5200 type trompets, the sound performance of which has been examined with fre-quency analysis and experimented by famous musical experts. The results show that the 5200 typetrumpets made of Salloy have excellent quality, accurate intonation and ease of response at
文摘【目的】电网电压跌落故障会引起风电机组载荷的剧烈变化,严重影响风电机组的安全稳定运行。随着风电机组的大型化,风电叶片长度不断增加,塔筒增高,其载荷特性对系统参数波动变得敏感。因此,需要研究电网电压跌落过程中关键部件的载荷与振动特性。【方法】提出了基于动态链接库和Socket通信的数据交互方式,建立了Simulink与Bladed的联合仿真方法。基于某3.4 MW风电机组模型,采用给定风速变化的工况对联合仿真平台进行验证。研究了低电压穿越(low voltage ride through,LVRT)过程中机组总体性能与叶片、塔筒载荷的变化关系。【结果】电网电压跌落幅值对电机功率影响较大,对风轮的调节参数影响较小。低电压穿越过程中风轮的桨矩角调节和转速有较长时间的波动,叶片外叶展处载荷的变化大于内叶展处,叶尖位移增加。塔架的振动频率与固有频率接近,存在潜在风险,需要在机组设计中考虑。【结论】联合仿真平台可以很好地模拟风电机组的气动性能与部件载荷的暂态特性,为机组的优化控制提供参考。
