Study on Rigid-Flexible Coupling Effects of Floating Offshore Wind Turbines

In order to account for rigid-flexible coupling effects of floating offshore wind turbines, a nonlinear rigid-flexible coupled dynamic model is proposed in this paper. The proposed nonlinear coupled model takes the higher-order axial displacements into account, which are usually neglected in the conventional linear dynamic model. Subsequently,investigations on the dynamic differences between the proposed nonlinear dynamic model and the linear one are conducted. The results demonstrate that the stiffness of the turbine blades in the proposed nonlinear dynamic model increases with larger overall motions but that in the linear dynamic model declines with larger overall motions.Deformation of the blades in the nonlinear dynamic model is more reasonable than that in the linear model as well.Additionally, more distinct coupling effects are observed in the proposed nonlinear model than those in the linear model. Finally, it shows that the aerodynamic loads, the structural loads and global dynamic responses of floating offshore wind turbines using the nonlinear dynamic model are slightly smaller than those using the linear dynamic model. In summary, compared with the conventional linear dynamic model, the proposed nonlinear coupling dynamic model is a higher-order dynamic model in consideration of the rigid-flexible coupling effects of floating offshore wind turbines, and accord more perfectly with the engineering facts.

Evaluating and correcting rain effects on dual-frequency altimeter Jason-1 wind measurements

Rain is one of the main sources of error in dual-frequency altimeter Jason-1 wind measurement. In this study, a new radar altimeter backscatter model is proposed and validated to eliminate rain effects. The model takes into account attenuation, volume backscattering, and sea surface perturbation by raindrops under rain conditions. A match-up dataset is built to evaluate rain effects, in combination with the Jason-1 normalized radar cross section, precipitation radar data from the Tropical Rainfall Measuring Mission, and sea surface wind reanalysis data from the European Centre for Medium-Range Weather Forecasts. The results show that rain-induced surface perturbation backscatter increases with rain rate at Ku-band, but their correlation at C-band is poor. In addition, rain surface perturbation and attenuation have major effects on radar altimeter wind measurements. Finally, a rain correction model for Jason-1 winds is developed and validation results prove its ability to reduce rain-induced inaccuracies in wind retrievals.

Dynamic Response of Sea-Crossing Rail-cum-Road Cable-Stayed Bridge Influenced by Random Wind–Wave–Undercurrent Coupling

Sea-crossing bridges are affected by random wind–wave–undercurrent coupling loads, due to the complex marine environment. The dynamic response of long-span Rail-cum-Road cable-stayed bridges is particularly severe under their influence, potentially leading to safety problems. In this paper, a fluid–structure separation solution method is implemented using Ansys–Midas co-simulation, in order to solve the above issues effectively while using less computational resources. The feasibility of the method is verified by comparing the tower top displacement response with relevant experimental data. From time and frequency domain perspectives, the displacement and acceleration responses of the sea-crossing Rail-cum-Road cable-stayed bridge influenced by wave-only, wind–wave, and wind–wave–undercurrent coupling are comparatively studied. The results indicate that the displacement and acceleration of the front bearing platform top are more significant than those of the rear bearing platform. The dominant frequency under wind–wave–undercurrent coupling is close to the natural vibration frequencies of several bridge modes,such that wind–wave–undercurrent coupling is more likely to cause a resonance effect in the bridge. Compared with the wave-only and wind–wave coupling, wind–wave–undercurrent coupling can excite bridges to produce larger displacement and acceleration responses: at the middle of the main girder span, compared with the wave-only case, the maximum displacement in the transverse bridge direction increases by 23.58% and 46.95% in the wind–wave and wind–wave–undercurrent coupling cases, respectively;at the tower top, the variation in the amplitude of the displacement and acceleration responses of wind–wave and wind–wave–undercurrent coupling are larger than those in the wave-only case, where the acceleration change amplitude of the tower top is from-0.93 to 0.86 m/s^(2) in the waveonly case, from-2.2 to 2.1 m/s^(2) under wind–wave coupling effect, and from-2.6 to 2.65 m/s^(2) under wind–wave–undercurrent coupling effect, indicating that the tower top is mainly affected by wind loads, but wave and undercurrent loads cannot be neglected.

Dynamic Response of Tensile Membrane Structure under Coupling Effect of Wind and Rain

Because of the small stiffness and high flexibility, the tension membrane structure is easy to relax and damage or even destroy under the action of external load, which leads to the occurrence of engineering accidents. In this paper, the damped nonlinear vibration of tensioned membrane structure under the coupling action of wind and rain is approximately solved, considering the geometric nonlinearity of membrane surface deformation and the influence of air damping. Applying von Karman’s large deflection theory and D’Alembert’s principle, the governing equations are established for an analytical solution, and the experimental results are compared with the analytical results. The feasibility of this method is verified, which provides some theoretical reference for practical membrane structure engineering design and maintenance.

Application of Tikhonov regularization method to wind retrieval from scatterometer data Ⅱ: cyclone wind retrieval with consideration of rain

According to the conclusion of the simulation experiments in paper I, the Tikhonov regularization method is applied to cyclone wind retrieval with a rain-effect-considering geophysical model function （called CMF＋Rain）. The CMF＋Rain model which is based on the NASA scatterometer-2 （NSCAT2） GMF is presented to compensate for the effects of rain on cyclone wind retrieval. With the multiple solution scheme （MSS）, the noise of wind retrieval is effectively suppressed, but the influence of the background increases. It will cause a large wind direction error in ambiguity removal when the background error is large. However, this can be mitigated by the new ambiguity removal method of Tikhonov regularization as proved in the simulation experiments. A case study on an extratropical cyclone of hurricane observed with SeaWinds at 25-km resolution shows that the retrieved wind speed for areas with rain is in better agreement with that derived from the best track analysis for the GMF＋Rain model, but the wind direction obtained with the two-dimensional variational （2DVAR） ambiguity removal is incorrect. The new method of Tikhonov regularization effectively improves the performance of wind direction ambiguity removal through choosing appropriate regularization parameters and the retrieved wind speed is almost the same as that obtained from the 2DVAR.

THE IMPACT OF INITIAL FORCED WIND ON THE PREDICTABILITY OF THE ZEBIAK-CANE COUPLED OCEAN-ATMOSPHERE MODEL

With simultaneous observed sea surface temperature anomaly （SSTA）, the difference between NCEP/NCAR 925hPa reanalysis wind stress anomaly （NCEPWSA） and FSU wind stress anomaly （FSUWSA） is analyzed, and the prediction abilities of Zebiak-Cane coupled ocean-atmosphere model （ZC coupled model） with NCEPWSA and FSUWSA serving respectively as initialization wind are compared. The results are as follows. The distribution feature of NCEPWSA matches better with that of the observed SSTA than counterpart of FSUWSA both in 1980s and in 1990s; The ZC ocean model has a better skill under the forcing of NCEPWSA than that of FSUWSA, especially in 1990s. Meanwhile, the forecast abilities of the ZC coupled model in 1990s as well as in 1980s have been improved employing NCEPWSA as initialization wind instead of FSUWSA. Particularly, it succeeded in predicting 1997/1998 E1 Nino 6 to 8 months ahead, further analysis shows that on the antecedent and onset stages of the 1997/1998 E1 Nino event, the horizontal cold and warm distribution characteristics of the simulated SSTA from ZC ocean model, with NCEPWSA forcing compared to FSUWSA forcing, match better with counterparts of the corresponding observed SSTA, whereby providing better predication initialization conditions for ZC coupled model, which, in turn, is favorable to improve the forecast ability of the coupled model.

Numerical Analysis of a Floating Offshore Wind Turbine by Coupled Aero-Hydrodynamic Simulation

The exploration for renewable and clean energies has become crucial due to environmental issues such as global warming and the energy crisis. In recent years,floating offshore wind turbines(FOWTs) have attracted a considerable amount of attention as a means to exploit steady and strong wind sources available in deep-sea areas. In this study, the coupled aero-hydrodynamic characteristics of a spar-type 5-MW wind turbine are analyzed. An unsteady actuator line model(UALM) coupled with a twophase computational fluid dynamics solver naoe-FOAM-SJTU is applied to solve three-dimensional Reynolds-averaged NavierStokes equations. Simulations with different complexities are performed. First, the wind turbine is parked. Second, the impact of the wind turbine is simplified into equivalent forces and moments. Third, fully coupled dynamic analysis with wind and wave excitation is conducted by utilizing the UALM. From the simulation, aerodynamic forces, including the unsteady aerodynamic power and thrust, can be obtained, and hydrodynamic responses such as the six-degrees-of-freedom motions of the floating platform and the mooring tensions are also available. The coupled responses of the FOWT for cases of different complexities are analyzed based on the simulation results. Findings indicate that the coupling effects between the aerodynamics of the wind turbine and the hydrodynamics of the floating platform are obvious. The aerodynamic loads have a significant effect on the dynamic responses of the floating platform, and the aerodynamic performance of the wind turbine has highly unsteady characteristics due to the motions of the floating platform. A spar-type FOWT consisting of NREL-5-MW baseline wind turbine and OC3-Hywind platform system is investigated. The aerodynamic forces can be obtained by the UALM. The 6 DoF motions and mooring tensions are predicted by the naoe-FOAM-SJTU. To research the coupling effects between the aerodynamics of the wind turbine and the hydrodynamics of the floating platform, simulations with different complexities are performed. Fully coupled aero-hydrodynamic characteristics of FOWTs, including aerodynamic loads, wake vortex, motion responses, and mooring tensions, are compared and analyzed.

The Physical Principles Elucidate Numerous Atmospheric Behaviors and Human-Induced Climatic Consequences

The principles that govern the operation of an open and a closed evaporator are relevant for the understanding of the open and “closed” Earth’s atmospheric behaviors, and are thus described. In these greenhouses, the water is included, otherwise the heat and mass balances do not match. It is incorrect to consider the radiation as the only energy transfer factor for an atmospheric warming. Demonstrations show that when the greenhouse effect and the cloud cover increase, the evaporation and the wind naturally decrease. Researchers did not understand why reductions in surface solar radiation and pan evaporation have been simultaneous with increased air temperature, cloudiness and precipitation for the last decades. It is an error to state that the evaporation increases based solely on the water and/or air temperatures increase. Also, researchers did not comprehend why in the last 50 years the clouds and the precipitation increased while the evaporation decreased and they named such understanding as the “evaporation paradox”, while others “found” “the cause” violating the laws of thermodynamics, but more precipitation is naturally conciliatory with less evaporation. The same principle that increases the formation of clouds may cause less rainfall. Several measurements confirm the working principles of greenhouses described in this paper. The hydrological cycle is analyzed and it was also put in form of equation, which analyses have never been done before. The human influence alters the velocity of the natural cycles as well as the atmospheric heat and mass balances, and the evaporation has not been the only source for the cloud formation. It is demonstrated that the Earth’s greenhouse effect has increased in some places and this proof is not based only on temperatures.

Wind-induced response analysis of a wind turbine tower including the blade-tower coupling effect

To analyze wind-induced response characteristics of a wind turbine tower more accurately, the blade-tower coupling effect was investigated. The mean wind velocity of the rotating blades and tower was simulated according to wind shear effects, and the fluctuating wind velocity time series of the wind turbine were simulated by a harmony superposition method. A dynamic finite element method (FEM) was used to calculate the wind-induced response of the blades and tower. Wind-induced responses of the tower were calculated in two cases (one included the blade-tower coupling effect, and the other only added the mass of blades and the hub at the top of the tower), and then the maximal displacements at the top of the tower of the tow cases were compared with each other. As a result of the influence of the blade-tower coupling effect and the total base shear of the blades, the maximal displacement of the first case increased nearly by 300% compared to the second case. To obtain more precise analysis, the blade-tower coupling effect and the total base shear of the blades should be considered simultaneously in the design of wind turbine towers.

An improved wind speed algorithm for “Jason-1” altimeter under tropical cyclone conditions

Rain effect and lack of in situ validation data are two main causes of tropical cyclone wind retrieval errors. The National Oceanic and Atmospheric Administration＇s Climate Prediction Center Morphing technique （CMORPH） rain rate is introduced to a match-up dataset and then put into a rain correction model to remove rain effects on ＂Jason-1＂ normalized radar cross section （NRCS）; Hurricane Research Division （HRD） wind sPeed, which integrates all available surface weather observations, is used to substitute in situ data for establishing this relationship with ＂Jason-l＂ NRCS. Then, an improved ＂Jason-l＂ wind retrieval algorithm under tropical cyclone conditions is proposed. Seven tropical cyclones from 2003 to 2010 are studied to validate the new algorithm. The experimental results indicate that the standard deviation of this algorithm at C-band and Ku-band is 1.99 and 2.75 m/s respectively, which is better than the existing algorithms. In addition, the C-band algorithm is more suitable for sea surface wind retrieval than Ku-band under tropical cyclone conditions.

Climate Changes: How the Atmosphere Really Works

Top concepts adopted by the current science on climate changes or atmospheric warming are not in agreement with the first principles of the physics. This paper presents a new understanding on the atmospheric behaviors. For example, the radiation is not the only factor that influences the air temperature, as the law of conservation of energy defines and as shown physically and mathematically in this article. The Sun is not the only heat source for the atmosphere because there is generation of heat at the Earth’s surface by human activities. It is also shown that the water vapor is not a null effect and that the water vapor cannot be removed from the atmosphere for air temperature, greenhouse effect and climate changes considerations, in contrast to the current literature beliefs. The “feedback” concept is unfounded and invalid. The literature also says that “water vapor increases as the Earth’s atmosphere warms”, but this is also incorrect. The above equivocated understanding is accompanied by another one which believes that more water evaporates if the air temperature increases, but it is not in this way. These demonstrations and other authors’ surveys showing that in the last decades the planet became wetter eliminate the literature concept that the water vapor does not have influence on the atmospheric warming/cooling. The conventional water cycle is related to the mass of water (mass of evaporation mass of precipitation) and then the physical and mathematical principles of the new hydrological cycle that includes the direct human influence are shown. The same is done for the carbon cycle. It is solved the problem on why the wind speed on Venus is very high above the cloud deck while it is stagnant below it, being this the same physical principle valid for the Earth’s cloud cover. In the atmosphere, all the corresponding principles are the same, only their amounts change. It is demonstrated that the CO2 is not decisive for building and changing the temperatures of Venus, Mars, Mercury, Jupiter and Earth. Ice cores are not valid for “determining” “past” temperatures of the planet, because the mass of their air bubbles may be old, but the corresponding temperatures are not.

基于流固耦合的单轴跟踪式光伏结构风致扭转研究

以某跟踪式光伏发电系统为研究对象,通过编写自定义程序代码UDF对Fluent进行二次开发,建立单轴跟踪式光伏结构的二维模型,研究其在风荷载作用下的扭转振动问题。研究结果表明:风速达到某一特值后,结构出现等幅周期性振动,发生软颤振现象,而其阻尼比对抑制扭转振动有一定的作用,这同实际情况较吻合;光伏组件倾角在0°~20°范围内时,倾角越大,扭转振动的临界风速越低。

浮式风机风载荷与浮式基础运动相互影响研究

本文定量研究浮式风机系统风载荷与浮式基础运动间的相互影响。建立了浮式风力机系统一体化耦合动力学分析模型,对比分析了风载荷对系缆力、浮式基础运动、机舱加速度的影响及浮式基础运动对叶片相对流速、叶片推力和发电功率的影响。结果表明,风载荷显著影响浮式基础纵荡/纵摇平均值,对其标准差影响较小;风载荷对系缆力的平均值和标准差都有一定影响,而机舱加速度受风载荷的影响并不大;浮式基础运动对叶片相对风速的标准差有显著影响,离轮毂越远位置的相对风速受基础运动影响越大,这导致浮式风机叶片推力和发电功率有很大波动。为保证平稳发电,对浮式风机控制设计时,需考虑浮式基础运动的影响。

考虑冲刷效应的大跨桥梁地震-风-车-桥耦合振动分析

为研究冲刷效应对地震与风联合作用下大跨桥梁动力响应的影响,在已建立的地震-风-车-桥耦合振动分析模型基础上,利用p-y曲线(p为土阻力,y为变形)折减法考虑不同冲刷深度的桩土荷载-位移关系,根据桩土荷载-位移关系和冲刷深度更新桩基的侧向支撑刚度和长度,从而考虑了冲刷效应对大跨桥梁动力响应的影响,并将模型应用到江顺大桥冲刷效应的分析研究中.研究结果表明:基础冲刷减弱了地基土对结构的侧向约束,从而降低结构的自振频率,侧向振型的自振频率最大降低6.01%;在运营车辆和风荷载作用下,基础冲刷对结构的振动响应影响很小;在地震发生后,基础冲刷会增大结构的横向振动,结构的横向位移响应极值最大增大9.1%,横向位移响应谱也相应增大,而对结构的竖向振动影响很小;基础冲刷可能减小车辆横向加速度的响应,车辆的横向加速度响应极值最大降低7.7%,对车辆的竖向振动影响很小.

横风环境下方形建筑迎风面雨滴收集率特性分析

现有建筑风驱雨研究主要关注不同环境和建筑外形条件下,建筑表面风驱雨量的分布结果,但缺乏对风驱雨量分布产生原因的分析。利用有限区域计算方法,对典型条件下方形建筑迎风面收集率分布进行计算,分析了雨滴轨迹包络区域的变化规律,说明了收集率分布的产生原因。结果表明,从轨迹起点平面至终点平面,轨迹包络区域存在拉伸和扭转2种效应。在风向角为0°、参考风速为10 m/s时,高度和宽度方向拉伸率均呈现“上小下大”、“两侧小中间大”的特点。高度方向边界扭转角呈现从中间到两侧逐渐增大的趋势,宽度方向边界扭转角呈现从角点到中间区域逐渐减小的趋势。随参考风速增大,高度方向拉伸率由正变负,宽度方向拉伸率逐渐减小,高度方向扭转角在靠近地面区域逐渐增大、在建筑上部逐渐减小,宽度方向扭转角在靠近建筑顶部区域逐渐增大、在建筑下部逐渐减小。风向角为30°时,从上风侧到下风侧,高度方向拉伸率、高度和宽度边界扭转角均逐渐增大,宽度方向拉伸率则从两侧到中间逐渐增大。研究结果为分析建筑外形对收集率分布的影响和建筑防雨结构设计提供了进一步的理论依据。

风浪流单独及耦合作用下15 MW级浮式基础动力特性研究

了解风浪流等环境荷载效应对浮式基础设计及优化至关重要,为此,以15 MW级漂浮式基础为研究对象,系统性定量分析风浪流环境荷载单独及耦合作用下对浮式基础运动及系泊系统受力的影响。首先,以INOWINDMOOR 12 MW和TaiDa 15 MW浮式基础为原型设计新的15 MW级浮式基础,并在ANSYS-AQWA建立水动力分析模型,风力荷载及海流荷载通过风力系数、流力系数添加;其次,针对风浪流等环境荷载单独及耦合作用下浮式基础运动和系泊受力等特征开展分析。结果表明:浮式基础运动及系泊受力主要受风力和流力的影响,波浪会加剧浮式基础运动及系泊受力的往复性,并加大运动幅度及系泊受力;流荷载对浮式基础运动及系泊受力影响较大,特别是风、浪与流耦合作用时会导致系泊受力明显增加,实际工程设计时,流荷载应给与重点关注。

实际风况下萨沃纽斯风力机集群性能及布局规律研究

为探究风况条件对萨沃纽斯风力机集群功率输出和安装方向的影响,基于变转速控制策略和计算流体力学仿真结果,获得了集群在我国8个典型站点不同安装方向下的输出功率,分析了集群在实际风况下的最佳布局规律,并验证了规律的普适性。仿真结果表明:在沈阳、厦门、昆明、呼和浩特、青岛、喀什、大连以及郑州8个站点合理安装集群,可使单台机组的输出功率分别提升至原来的1.14、1.23、1.31、1.20、1.21、1.24、1.12、1.11倍;对于有明显单一主风能风向的地区,集群应正对此方向摆放;对于两个主风能风向相位差较大的地区,需选择两者中周围风能更丰富的方向排布集群;对于有3个主风能风向、主风能风向不明显或风能分布比较均匀的地区,应先使机组相互格挡的方位避开风能相对集中区,再选择风能资源较丰富的方向排布集群。该研究可使实际风况下萨沃纽斯风力机集群耦合增益最大化,并为复杂风场条件下集群安装方向的选择提供参考。

风力机叶片预弯状态颤振效应分析

风力机叶片预弯设计大多采用静气弹分析方法,忽略了叶片气动力、惯性力和弹性力三者相互作用而引发的气弹耦合失稳问题,而预弯对百米量级超长柔性叶片的颤振性能影响尤为显著。为对比分析不同预弯尺寸对叶片颤振临界状态的影响,基于主梁刚度等效原则进行叶片气弹模型设计,通过风洞试验发现了15 MW两种预弯叶片颤振区间及其临界风速的差异;进一步基于修正的叶素动量理论和几何精确梁理论(Blade Element Momentum Theory-Geometrically Exact Beam Theory,BEM-GEBT)耦合计算方法对4种预弯叶片进行分析,对比了不同预弯尺寸叶片的颤振临界风速、气动力分布和位移频谱特性,并揭示了颤振耦合模态机理。研究表明:BEM-GEBT耦合计算方法结果与风洞试验结果吻合较好;随着预弯尺寸的增大,挥舞-摆振耦合颤振临界风速提高,颤振区间范围基本一致;不同预弯尺寸叶片升力系数和俯仰力矩系数发散速率与位移发散速率呈正相关,平均风压曲线在预弯3~4 m范围内出现显著变化,挥舞-摆振耦合效应大于挥舞-扭转耦合效应,其颤振耦合频率由一阶挥舞频率主导。

海上风电基础阴极保护技术研究

目的 探究外加单一电流阴极保护(Impressed Current Catholic Protection,ICCP)系统、单一牺牲阳极保护(Sacrificial Anode Cathodic Protection,SACP)系统以及SACP与ICCP系统联合保护3种工况下对海上风电基础的最优保护方案。方法 通过对3种工况进行数值模拟计算,对比不同工况下阴极保护系统对风电基础的保护效果。确定最优工况后,构建大比尺模型对最佳工况进行该工况下的实海测试实验。结果 单一SACP、单一ICCP系统以及SACP与ICCP系统联合保护3种工况下,风电基础保护电位区间分别为–926~–881 mV、–1 018~–985 mV和–984~–963 mV。实海测试实验中,导管架电位分布为–1 029~–912 mV。数值模拟结果与实验结果基本一致。结论 当SACP与ICCP系统联合保护时,保护效果最好。随着输出电流的逐步增大,风电基础模型逐步趋于过保护状态。

Multi-hazard joint probability distribution model for wind speed,wind direction and rain intensity

Multiple disasters such as strong wind and torrential rain pose great threats to civil infrastructures.However,most existing studies ignored the dependence structure between them,as well as the effect of wind direction.From the dimension of the engineering sector,this paper introduces the vine copula to model the joint probability distribution(JPD)of wind speed,wind direction and rain intensity based on the field data in Yangjiang,China during 1971–2020.First,the profiles of wind and rain in the studied area are statistically analyzed,and the original rainfall amounts are converted into short-term rain intensity.Then,the marginal distributions of individual variables and their pairwise dependence structures are built,followed by the development of the trivariate joint distribution model.The results show that the constructed vine copula-based model can well characterize the dependence structure between wind speed,wind direction and rain intensity.Meanwhile,the JPD characteristics of wind speed and rain intensity show significant variations depending on wind direction,thus the effect of wind direction cannot be neglected.The proposed JPD model will be conducive for reasonable and precise performance assessment of structures subjected to multiple hazards of wind and rain actions.