Mechanism of Balanced Flow and Frontogenesis

The final balanced state of an initial unbalanced flow is discussed with the same method as Vallis (1992). For the two-dimensional, inviscid, rotating and nonlinear model, the final state of the flow depends on the initial conditions. If the initial potential vortcity of the flow is non-uniform, the final state is not necessarily geostrophic. However, for the zero and uniform potential vorticity flow, the final state will satisfy the thermal wind relation when the length scale of the initial disturbance is large enough. Otherwise, discontinuity will occur in the geostrophic solution. In this case, the final balanced state will not be geostrophic any longer and an extended momentum coordinate is introduced to overcome the mult-value problem. Key words Frontogenesis - Geostrophic adjustment - Thermal wind balance - Extended momentum coordinates The work was supported by the National Natural Science Foundation of China (Grant Nos. 49735180 and 40075011) and the State Key Basic Program: CHERES.

Determination method of load balance ranges for train operation safety under strong wind

The aerodynamic performances of a passenger car and a box car with different heights of windbreak walls under strong wind were studied using the numerical simulations, and the changes of aerodynamic side force, lift force and overturning moment with different wind speeds and wall heights were calculated. According to the principle of static moment balance of vehicles, the overturning coefficients of trains with different wind speeds and wall heights were obtained. Based on the influence of wind speed and wall height on the aerodynamic performance and the overturning stability of trains, a method of determination of the load balance ranges for the train operation safety was proposed, which made the overturning coefficient have nearly closed interval. A min(|A1|+|A2|), s.t. |A1|→|A2|(A1 refers to the downwind overturning coefficient and A2 refers to the upwind overturning coefficient)was found. This minimum value helps to lower the wall height as much as possible, and meanwhile, guarantees the operation safety of various types of trains under strong wind. This method has been used for the construction and improvement of the windbreak walls along the Lanzhou–Xinjiang railway(from Lanzhou to Urumqi, China).

The influences of winds on the salt balance of the Tampa Bay during the fall of 2001

A three-dimensional,high resolution,Finite Volume Coastal Ocean Model（FVCOM） is used to diagnose the influences of winds during the fall of 2001 on the salt balance of the Tampa Bay.To distinguish the wind effecting,two experiments are designed：one is driven by tides and rivers;the other is driven by tides,rivers and winds.First,the salinity change induced by wind is provided.Wind forcing can significantly increase the salinity inside the Tampa Bay,along with decreases of horizontal and vertical salt gradients.Subsequently,the salt balance principles are detailed addressed.The primary salt balance is between the total（horizontal plus vertical）advective salt flux divergence and vertical diffusive salt flux divergence except at the channel bottom where horizontal diffusive salt flux divergence comes into play.At last,the salt balance variation induced by winds is further addressed.Wind forcing does not change the relative importance of salt balance terms.The variations of the salt balance terms influenced by winds are highly dependent on the specific locations.Besides,the variations of the total advective salt flux divergence and the vertical diffusive salt flux divergence are nearly couterbalance,and both of two terms are much greater than that of the horizontal diffusive salt flux divergence.

The Heat Balance in the Western Equatorial Pacific Warm Pool during the Westerly Wind Bursts: A Case Study

The responses of sea surface temperature (SST) in the western equatorial Pacific warm pool to the westerly wind bursts (WWBs) play an important role in the relationship between WWB and ENSO. By using data collected from eight buoys of TOGA (Tropical Ocean-Global Atmosphere)- COARE (Coupled Ocean-Atmosphere Response Experiment), the heat balances of the upper ocean in the western equatorial Pacific around 0 degrees, 156 degreesE during two WWB events were calculated according to Stevenson and Niiler's (1983) method. In both events, SST increased before and after the WWBs, while decreased within the WWBs. The SST amplitudes approximated to 1 degreesC. Although sometimes the horizontal heat advections may become the biggest term in the heat balance, the variation of SST was dominated by the surface heat flux. On the other aspect, some different features of the two events are also revealed. The two cases have different variation of mixed layer depth. The depth of mixed layer is almost double in the first case (35 in to 70 m), which is caused by Ekman convergence, while only 10m increments due to entrainment in the second one, There are also differences in the currents structure. The different variations of thermal and currents structure in the mixing layers accounted for the different variation of the heat balance during the two events, especially the advection and residue terms. The seasonal variation of SST in this area is also investigated simply. The first WWB event happened just during the seasonal transition. So we considered that it is a normal season transition rather than a so-called anomaly. That also suggested that the seasonal distinction of the WWB is worthy of more attention in the researches of its relationship to ENSO.

Counter-Wind Deep Current in the Northern Beibu Gulf in Boreal Winter

The Beibu Gulf is at an important geographical location and rich in gas, oil and biological resources. The observed currents showed that the current in the upper layer was opposite to that in the lower layer in boreal winter in the northern Beibu Gulf and it was northeastward in the lower layer. This northeastward current was reproduced by a 3 D baroclinic model in this study. It's found that the counter-wind deep current(referred to as ‘CWDC' hereinafter) strengthened from September to November but weakened from December to the following February. A closed meridional circulation in vertical direction was found in the northern Beibu Gulf, including CWDC, surface southwestward current, an upwelling, and a downwelling. The temporal variation process of the meridional circulation was similar to that of CWDC, with strength and range stronger in November and December than in other four months. Similar to the variation process of CWDC, the monsoon wind changed from weak easterly wind in September to strong northeasterly wind in November and December, and it was transformed into weak southeasterly wind in February again. The sensitive experiments showed that CWDC and the meridional circulation were controlled by the monsoon wind and were adjusted by heat flux-and tide-induced mixing, respectively. According to the momentum balance equation, it can be revealed the counter-wind deep current is a compensation current which is induced by the surface elevation gradient balanced by the Coriolis force, vertical diffusion and baroclinic pressure gradient.

DEVELOPMENT FOR HIGH PRECISION SIX COMPONENT STRAIN GAUGE BALANCE

The measurement accuracy of a wind tunnel balance is the key factor to improve the measurement accuracy for a test model in the wind tunnel. In order to improve the measurement accuracy of the wind tunnel balance, a great deal of investigation is carried out in China. This paper summarizes a program to improve the measurement accuracy of wind tunnel balances. In the program, the investigation is carried out in three aspects (1) designing a drag component of the balance in low interactions (2) choosing high quality foil strain gauges with temperature self-compensation (3) choosing the excellent gauges and mounting them meticulously. As an example, these research achievements are applied in a φ18 six component balance. The measurement accuracy of a GB-04 standard model in a transonic wind tunnel with the φ18 six component balance comes up to the advanced world standard.

On the Variation of Divergent Flow： An Eddy-flux Form Equation Based on the Quasi-geostrophic Balance and Its Application

Based on basic equations in isobaric coordinates and the quasi-geostrophic balance,an eddy-flux form budget equation of the divergent wind has been derived. This newly derived budget equation has evident physical significance. It can show the intensity of a weather system,the variation of its flow pattern,and the feedback effects from smaller-scale systems(eddy flows). The usefulness of this new budget equation is examined by calculating budgets for the strong divergent-wind centers associated with the South Asian high,and the strong divergence centers over the Tibetan Plateau,during summer(June–August) 2010. The results indicate that the South Asian high significantly interacts with eddy flows. Compared with effects from the mean flow(background circulation),the eddy flows’ feedback influences are of greater importance in determining the flow pattern of the South Asian high. Although the positive divergence centers over the Tibetan Plateau intensify through different mechanisms,certain similarities are also obvious. First,the effects from mean flow are dominant in the rapid intensification process of the positive divergence center. Second,an intense offsetting mechanism exists between the effects associated with the eddy flows’ horizontal component and the effects related to the eddy flows’ convection activities,which weakens the total effects of the eddy flows significantly. Finally,compared with the effects associated with the convection activities of the mean flow,the accumulated effects of the eddy flows’ convection activities may be more favorable for the enhancement of the positive-divergence centers.

Lift Force at Equatorial Sea Level Due to Compressed Air Dynamics of the Trade Wind’s Boundary Layer

Starting with a recent unconventional explanation of the lift force on a wing, featuring compressibility of the air, an application of the same concept is made to the lift force on the equatorial sea surface due to the Trade Winds, by greatly increasing the spatial scales. If the equatorial sea level does rise up, the northward slope to the sea level should facilitate the poleward flux of summer heat in both the North Pacific and North Atlantic Oceans, as two examples, in accordance with the heat budget requirements of these oceans. Compressed air dynamics consists of Bernoulli’s law applied to the streamlines of the Trade Winds, the force balance between the upward centrifugal force of the curved streamlines at the earth’s surface and a downward pressure force, and the perfect gas law for air.

Research of magnetic self-balance used in a repetitive high voltage rectangular waveform pulse adder

Compared with a sinusoidal operation, pulsed operation has more homogeneity and more efficiency in dielectric barrier discharge. In this paper, an improved pulse adder is designed and assembled to create repetitive high voltage rectangular pulses when resistive loads or capacitive loads exist. Beyond the normal pulse adder based on solid-state switches, additional metal- oxide-semiconductor field effect transistors are used in each stage for a faster falling edge. Further, the voltage difference between stages is eliminated by balancing windings. In this paper, we represent our theoretical derivation, software simulations and hardware experiments on magnetic self-balance. The experiments show that the voltage difference between stages is eliminated by balancing windings, which matches the result of simulations with almost identical circuits and parameters.

Wind Power Potential in Interior Alaska from a Micrometeorological Perspective

The wind power potential in Interior Alaska is evaluated from a micrometeorological perspective. Based on the local balance equation of momentum and the equation of continuity we derive the local balance equation of kinetic energy for macroscopic and turbulent systems, and in a further step, Bernoulli’s equation and integral equations that customarily serve as the key equations in momentum theory and blade-element analysis, where the Lanchester-Betz-Joukowsky limit, Glauert’s optimum actuator disk, and the results of the blade-element analysis by Okulov and Sorensen are exemplarily illustrated. The wind power potential at three different sites in Interior Alaska (Delta Junction, Eva Creek, and Poker Flat) is assessed by considering the results of wind field predictions for the winter period from October 1, 2008, to April 1, 2009 provided by the Weather Research and Forecasting (WRF) model to avoid time-consuming and expensive tall-tower observations in Interior Alaska which is characterized by a relatively low degree of infrastructure outside of the city of Fairbanks. To predict the average power output we use the Weibull distributions derived from the predicted wind fields for these three different sites and the power curves of five different propeller-type wind turbines with rated powers ranging from 2 MW to 2.5 MW. These power curves are represented by general logistic functions. The predicted power capacity for the Eva Creek site is compared with that of the Eva Creek wind farm established in 2012. The results of our predictions for the winter period 2008/2009 are nearly 20 percent lower than those of the Eva Creek wind farm for the period from January to September 2013.

Contrasting Trend of Wintertime Wind Speed Between Near-surface and Upper Air in China During 1979-2021

The long-term height-resolved wind trend in China under global warming still needs to be discovered.To fill this gap,in this paper we examined the climatology and long-term(1979-2021)trends of the wintertime wind speed at the near-surface and upper atmosphere in China based on long-term radiosonde measurements.At 700,500,and 400 hPa,much higher wind speed was found over eastern China,compared with western China.At 300,200,and 100 hPa,maximum wind speed was observed in the latitude zone of around 25-35°N.Furthermore,westerly winds dominated most parts of China between 20°N and 50°N at altitudes from 700 hPa to 100 hPa.A stilling was revealed for the near-surface wind from 1979-2003.From 2004 onward,the near-surface wind speed reversed from decreasing to increasing.This could be largely due to the joint impact of reduced surface roughness length,aerosol optical depth(AOD),and increased sensible heat flux in the ground surface.The decrease of AOD tended to reduce aerosol radiative forcing,thereby destabilizing the planetary boundary layer(PBL).By comparison,the wintertime wind in the upper atmosphere exhibited a significant monotonic upward trend,albeit with varying magnitude for different altitudes.In the upper troposphere,the wintertime maximum wind was observed along a westerly jet stream,with a pronounced upward trend within the zone approximately bounded by latitudes of 25-50°N,particularly above 500 hPa.This accelerating wind observed in the upper troposphere and lower stratosphere could be closely associated with the large planetary-scale meridional temperature trend gradient.Besides,the direction for the wind at the near-surface and lower troposphere(925 and 850 hPa)exhibited a larger variance over the period 1979-2021,which could be associated with the strong turbulence of PBL caused by the heterogeneous land surface.For those pressure levels higher than 850 hPa,large wind directional variance was merely found to the south of 25°N.The findings from long-term radiosonde measurements in winter over China shed light on the changes in wind speed on the ground and upper atmosphere under global warming from an observational perspective.

Challenges of Power Delivery from Jiuquan Wind Power Base

The 10-GW-class Jiuquan Wind Power Base in Gansu Province is to get its Phase I Project completed soon, and will further expand and become the world largest wind power base in the future. Whether electricity from the wind power base can be delivered on such a large scale becomes the focus of attention of the world. This paper analyzes four challenges facing the wind power base, including transmission capability, peak regulation and frequency modulation, capacity balance and generation accommodation, as well as system stability.

On the Maximum of Wind Power Efficiency

In our paper we demonstrate that the filtration equation used by Gorban’ et al. for determining the maximum efficiency of plane propellers of about 30 percent for free fluids plays no role in describing the flows in the atmospheric boundary layer (ABL) because the ABL is mainly governed by turbulent motions. We also demonstrate that the stream tube model customarily applied to derive the Rankine-Froude theorem must be corrected in the sense of Glauert to provide an appropriate value for the axial velocity at the rotor area. Including this correction leads to the Betz-Joukowsky limit, the maximum efficiency of 59.3 percent. Thus, Gorban’ et al.’s 30% value may be valid in water, but it has to be discarded for the atmosphere. We also show that Joukowsky’s constant circulation model leads to values of the maximum efficiency which are higher than the Betz-Jow-kowsky limit if the tip speed ratio is very low. Some of these values, however, have to be rejected for physical reasons. Based on Glauert’s optimum actuator disk, and the results of the blade-element analysis by Okulov and S&oslashrensen we also illustrate that the maximum efficiency of propeller-type wind turbines depends on tip-speed ratio and the number of blades.

脉冲风洞天平基础动力特征的简化计算方法

为了研究脉冲风洞天平基础在脉冲气动荷载作用下的动力响应特征,以某脉冲风洞为例,选择某典型气动荷载作用形式,建立了脉冲风洞天平基础在气动荷载作用下竖直方向、水平方向位移以及回转角度等动力特征的简化计算方法,并采用数值模拟的方法验证其可靠性.研究结果表明:天平基础在典型气动荷载作用下,竖直向最大振幅0.00175 mm,频率7.94 Hz,水平向最大振幅0.00283 mm,频率7.94 Hz,回转角度最大振幅0.00034°,频率7.94 Hz,典型气动荷载对天平基础振动影响较小,也未产生共振现象;基础振动最大振幅随气动荷载增大而增大,基础振动频率随气动荷载频率增大而增大;在气动荷载不变的条件下,基础振动的最大振幅与频率随尺寸的变大而变小,基础振动的最大振幅也随地基土性质的增强而减小,但地基土性质的变化对基础振动频率无影响.

Five Major Concerns about China’s Wind Power Development

Economic issue is the very focus of China's wind power development.Although all the security problems can be dealt with through technical measures,the compensation for supportive thermal power units and the subsidy from economically developed regions to resource-outputting regions would require a higher level of strategic considerations.The core purpose of developing wind energy is to reduce pollutant emissions,so planners should take into account the overall cost of all sides,without touching the bottom of social affordability.

风压平衡关系对高分辨率区域模式地面资料同化的影响分析

随着模式分辨率的提高,数值模式可分辨的短波信息增加,以地转平衡为基础的风压平衡约束关系不能完全满足低纬度地区及对流尺度高分辨率模式资料同化的需求。提出了基于多重网格方法构建1 km分辨率数值模式变分同化风压平衡约束关系的方案,基于CMA-MESO (China Meteorological Administration Mesoscale Model)三维变分(Three-Dimensional Variational Data Assimilation,简称3DVAR)和1 km分辨率中尺度区域模式开展了单点同化试验和典型个例分析。单点同化试验表明,气压和风的同化结果在没有平衡约束关系条件下比线性平衡约束下更接近观测。地面自动气象站观测资料同化试验表明新风压平衡约束关系将明显增加模式低层几十千米尺度的分析增量,其次是增加100—200 km尺度的分析增量。新风压平衡约束试验的同化分析增量相对于线性平衡约束的对照试验可以给出更多的增量中心位置,更好描述低层水汽辐合,对模式初始0—3 h降水、0—6 h地面10 m风和地面气压的模拟有改进。研究表明在大尺度风压平衡约束的基础上增加局地无风压平衡约束的订正,可以提高对流尺度天气系统地面短波信息的同化能力,改进高分辨率模式短时临近预报。

层状地基对脉冲风洞天平基础振动特征影响分析

由于脉冲风洞天平基础在飞行器风洞试验中起支撑作用,为深入研究层状地基对天平基础振动特性的影响,推导了层状地基上天平基础在脉冲载荷作用下的阻抗函数,利用简化模型建立基础的动态响应方程,并将简化模型的动态阻抗函数与基础-地基系统的动态阻抗函数进行等效处理,求得层状地基上天平基础在脉冲风洞载荷作用下的动力响应,并通过数值模拟进行验证。研究结果表明:随着载荷频率的增大,基础的竖向振幅、水平向振幅和回转角度逐渐减小;荷载幅值的增大导致基础振动最大振幅增大,振动频率保持不变;地基剪切模量的增大导致基础振动最大振幅递减;基础尺寸的增大引起基础振动最大振幅和振动频率的明显下降。另外,基础的竖向振幅随基础层深比的减小而增大,而水平向振幅和回转角度随层深比的减小而减小;地基剪切波速的增大对竖向振幅的影响较小,而对水平振幅和回转角度的影响更为显著。

基于微型数据采集器的一体化天平研制及应用

针对传统应变天平模拟信号传输方式存在抗干扰能力弱、传输距离短、线缆复杂等问题,开展了基于微型高精度数据采集器的一体化数字天平研制及应用。通过将微型高精度数据采集器嵌入测力天平,并且在微型高精度数据采集器中集成具有浮点运算能力的微控制单元,结合天平静态校准公式实现了天平实际力/力矩的实时解算和输出,并且实现了天平测量信号由模拟方式传输向数字方式传输的转变,提高测试系统的抗干扰能力。通过风洞内抗干扰测试表明,在常规高超声速风洞较为复杂的电磁环境下一体化天平信号传输几乎零干扰;通过开展高超升力体标模风洞试验验证表明,一体化天平试验重复性好(精度高),数据规律与常规天平测量结果一致,轴向力系数、法向力系数和俯仰力矩系数最大偏差分别为2.1%、1.8%和3.6%。

考虑储能充放电均衡度的风储联合调频控制策略

针对储能分组调频的充放电不均衡问题,提出一种考虑储能均衡度的风储联合一次调频控制策略。基于充放电任务分组执行的储能调频原理,建立了最佳放电深度下的储能分组调频充放电数学模型。为改善储能充放电不均衡问题,以储能均衡度构建2组储能的充放电综合下垂控制系数,并设计风储协同控制策略,在储能均衡度偏差较大时通过风机转子动能调频弥补储能功率不足,提升一次调频效果。最后以频率差偏移量及储能均衡度偏移量等作为评价指标进行仿真分析,结果表明所提风储联合调频控制策略有效改善了储能均衡度,降低了其对储能使用寿命的损害程度,同时提升了调频效果。

模块化多电平矩阵换流器接入下的工频故障特性分析

基于模块化多电平矩阵换流器(M3C)的柔性低频输电系统在中远海风电外送、异步电网互联等方面优势突出。然而,有别于模块化多电平换流器(MMC)等其他电力电子换流设备,M3C的控制策略将导致系统故障特性发生显著变化。现有将电力电子设备负序部分等效为开路的故障等值与响应特性计算方法无法适用。文中计及M3C正序定电容电压总平均值控制、负序电流注入控制以及环流控制分层构成的桥臂电容电压均衡策略,推导了工频侧线路故障以后,M3C输入输出功率均衡、桥臂功率均衡(电容电压均衡的必要条件)与正负序电压电流间的映射关系,由此构建了工频侧线路故障(不对称、对称)后的M3C输出电压电流响应特性的等效模型。在此基础上,提出了M3C接入下工频侧线路故障后电压电流响应特性的精确计算方法。最后,基于PSCAD/EMTDC仿真平台,搭建了海上风电柔性低频送出系统仿真模型,通过大量仿真算例充分验证了所提故障特性分析方法的正确性和精确性。