地震及多风况下风力机塔架动力响应

为分析不同风速的湍流风与地震联合作用下大型风力机塔架动力学响应,以美国可再生能源实验室(NREL) 5 MW风力机为研究对象,基于考虑土-构耦合效应的Wolf理论,利用动态入流理论及Prandtl理论修正的叶素动量理论计算气动力,基于FAST软件预留数据接口开发了地震载荷计算模块,建立了湍流风与地震联合作用下的风力机仿真模型;计算了5组风速与30种强度地震耦合共150种工况下的风力机塔架动力学响应。结果显示：额定风速下,塔顶位移响应受地震激励影响明显;低风速下地震作用对塔架加速度响应影响较大,高风速的湍流风会加剧塔架剪切力和弯矩响应;湍流风与地震联合作用时,塔顶位移及剪切力和塔基剪切力及弯矩的临界地面加速度峰值随风速的增大先增大再减小,塔顶加速度的临界地面加速度峰值在高风速下随风速增大而增大。     

超声风速仪与三轴风速仪测风的比较研究

利用1990年8月在中国西北戈壁地区进行的湍流仪器水平比较实验资料，对比分析了超声风速仪与三轴风速仪测风结果。结果表明：超声风速仪和三轴风速仪的水平风速和水平风速脉动方差测量值的相关性在0．99以上，垂直风速脉动方差为0．93．摩擦速度的相关偏差仅为0．78。三轴风速仪的湍流谱曲线在其截止频率前约1个数量级时明显比超声风速仪结果偏低．且高频段谱曲线上翘。     

一种Kaimal谱的修正方法及算法实现

本文发现了脉动风速方差模拟值与设定值存在着误差,分析了引起误差的原因。得到了在不同的湍流尺度与风速比值L/U的情况下,截止频率和初始频率对模拟风速方差的影响,给出了截止频率和初始频率的推荐值,并对Kaimal谱进行了修正。运用修正后的Kaimal谱及平稳随机过程方法,得到了模拟脉动风速时程数据。实例数据表明:模拟脉动风速数据的标准差符合工程应用要求,模拟功率谱与目标风谱吻合得很好。     

低频成分校正的两谱线法

目前已经提出多种频谱校正方法,但是将它们应用于低频成分时其精度显著下降,这是由于相应的校正模型忽略了实信号所包含的负频率分量的影响。给出考虑负频率影响的一种显式校正方法,它仅利用局部谱峰附近的两条谱线。采用数值实验对新方法进行考核。考核算例包括无噪声、弱噪声和强噪声三种情形。研究结果表明:①新方法总体上接近无偏,但当接近整周期采样时偏差变大。②新方法的经验方差与Cramér-Rao bound(CRB)总体局势相符,前者大体为后者的1～3倍。当采样条件接近半周期采样时,方差接近CRB;当记录长度接近整周期采样时,方差反而比较大。     

后台阶流场大涡模拟的入口边界条件研究

对不同入口边界条件下后台阶下游三维流场进行了大涡模拟。讨论了层流及湍流入口流速剖面下边界层厚度及湍流度对台阶下游平均流速剖面、再附长度的影响。模拟结果表明,对于层流入口流速剖面,边界层厚度对再附长度的影响很大,随边界层厚度的增大,再附长度将增大。对于湍流入口流速剖面,边界层厚度对再附长度的影响不大,而入口湍流度则对再附长度有较大影响。随着入口湍流度的增加,再附长度将会变短矗在雷诺数为5000情况下,当采用湍流入口流速剖面并选择湍流度为0．5％时,大涡模拟能得到与直接数值模拟基本一致的结果。     

坡度和风速对跑道限制重量的影响

为了分析跑道坡度和风速分量对最大起飞重量的限制,以某型民用运输机为例,确定了不同特定情况下的修正跑道长度和跑道限制重量,通过线性回归分析得到了跑道坡度和风速分量对修正跑道长度和跑道限制重量的影响规律。研究表明:上坡时修正跑道长度和跑道限制重量均小于无坡度时的数值,且修正跑道长度和跑道限制重量均随坡度增大而线性减小,下坡时结论与上坡相反;上坡时修正跑道长度和跑道限制重量随坡度的变化率明显大于下坡时的情况;顺风对修正跑道长度和跑道限制重量的影响与上坡的影响类似,逆风则与下坡的影响类似。     

配重对拓宽无叶片风力机捕能区间的影响研究

为提高无叶片风力机的捕能效率,基于调谐捕能柱固有频率原理,提出采用配重方式拓宽无叶片风力机捕能区间的方法,推导添加配重后捕能柱固有频率的计算式,建立捕能柱涡激振动分析的仿真模型并进行了验证,探讨配重质量占比、配重块移动距离对捕能柱风速锁定区间与捕能效率的影响。所得结果表明,施加配重块后理论计算固有频率接近且大于捕能柱获得最大摆幅所对应的频率;配重块移动与其固定不动相比,捕能柱的捕能功率和风速锁定区间可显著提高,风速锁定区间长度增大了16.3倍;随着配重质量占比值的增大,捕能柱获得最大摆幅的风速锁定区间也增大,且区间长度与配重质量占比之间满足二次函数关系。这意味着当来流风速发生变化时,可通过调整配重块的位置,实现风能捕获最大化。     

扑动幅值角对仿生扑翼气动力特性的影响

通过进行微型扑翼飞行器低速风洞实验,研究了扑动幅值角对扑翼飞行器气动力特性的影响。实验中选择了4种机翼扑动幅值角55°、75°、95°和115°,实验风速从4m/s～10m/s,间隔2m/s,扑动频率从4Hz～8Hz。实验结果表明:在不同风速和扑动频率下,扑动幅值角分别为55°、75°、95°、115°时随着风速的增加升力明显增加,但随着频率的增加升力并未增加。在不同风速和扑动频率下得出扑动幅值角分别为55°、75°、95°、115°时推力随扑动频率的变化曲线,可以看出随着风速的增加推力明显减小,但随着频率的增加推力明显增加。实验结果与自然界中鸟和昆虫的飞行特性相一致。     

基于实测数据的近地层风特性分析研究

根据世界风能技术中心实际测风塔测到的大风天气下近地层不同高度处的风速风向数据,对该风场的平均风速与风向、湍流度、阵风因子、湍流积分尺度和脉动风速功率谱进行分析。结果表明：当平均风速曲线出现较大的尖峰时,平均风向会出现低谷;顺风向湍流强度和湍流积分尺度都明显大于横风向和竖风向相应的湍流强度和湍流积分尺度,各分量比值大致为1∶0.121 3∶0.188 6;文献［1?2］中建议的经验公式均能较好地反映顺风向阵风因子与湍流强度的变化关系,并借助实测数据通过曲线拟合给出了相应的经验公式;顺风向湍流积分尺度有随平均风速的增大而减小的趋势,而竖风向湍流积分尺度随平均风速的增大呈幂指数增长;纵向实测脉动风速功率谱与Von Karman和Kaimal经验谱吻合较差,竖向脉动风速功率谱与Panofsky经验谱在高频段有所偏差,通过拟合得到的经验谱与实测谱更为接近。     

水下捕捞机器人水动力学性能分析

海参捕捞机器人在水下捕捞作业时的性能受姿态变化的影响较大，为了使海参捕捞机器人始终保持最佳性能，需要在实际应用前对不同姿态下的捕捞机器人进行水动力学分析。利用计算流体力学软件 中的RNG 湍流模型作为仿真模型，考虑到仿真计算的精度，对近壁区域的处理进行了研究，在湍流模型的基础上加入了标准壁面函数。应用该模型对水下捕捞机器人水平直航、水平斜航和垂直斜航3种姿态下的水阻力和水阻力矩进行分析。结果表明:不同的姿态将影响水下捕捞机器人所受到的水阻力和水阻力矩的大小；在水平直航时捕捞机器人受到垂直向下的作用力较大，而产生的俯仰力矩较小；在水平斜航时漂角对捕捞机器人的影响较大；在垂直斜航时捕捞机器人的垂向力和俯仰力矩均随着流速和攻角的增大而增加。     

Nonlinear dynamic analysis of a vertical rotor-bearing system

Nonlinear dynamic model of a vertical rotor-bearing system is developed based on nonlinear bearing forces. Nonlinear dynamic behaviors are studied comprehensively through numerical analyses, such as bifurcation diagrams, waterfall diagrams, rotor center orbits, Poincare maps, and frequency spectrums. Factors which affect those behaviors, including structural arrangement, rotor mass unbalance, clearance and length of bearing, are investigated as well. Analytical results show that, in vertical arrangement, period doubling bifurcation occurs in advance and the system stability decreases dramatically. When the rotor motion becomes unstable, vertical rotor-bearing system generates sub-synchronous vibrations that are much lower than half-frequency component (0.5x). The stability of vertical rotor-bearing system increases with the increases in rotor mass unbalance and bearing length, but it decreases with the increase in bearing clearance.     

双层翼叶片几何参数对水平轴风力机气动性能影响研究

为了提高风力机的气动性能，基于NREL Phase Ⅵ水平轴风力机叶片，设计出的一种双层翼叶片。通过计算流体力学的方法，在不同来流风速下，对比分析了双层翼叶片与按比例缩放各叶高处弦长的NREL Phase Ⅵ水平轴风力机叶片的扭矩与弯矩，研究了叶片实度的影响，发现实度增加并不是双层翼叶片的气动性能优于原始NREL Phase Ⅵ风力机叶片的主要原因。对不同弦长比、垂直距离及水平距离的大小叶片所组成的双层翼结构进行数值模拟研究，利用流线图着重分析了大小叶片水平距离对风力机气动性能的影响，总结了气动性能随双层翼叶片几何参数的变化规律，发现在15 m/s至25 m/s的风速下，选择较大弦长比、较大垂直距离或者较小水平距离的双层翼叶片可得到较高的扭矩值，但弯矩值也会随之增加。     

垂直轴风力机三维气动性能研究及优化设计

建立了五叶片垂直风力机三维模型,采用滑移网格技术对五叶片垂直风力机的气动性能进行分析。研究结果表明,叶片的半径和高度会对风力机外围的速度场及湍动能分布产生明显影响,进而影响风力机的风能利用率。不同转速的风力机随着叶片宽度的增加其风能利用率呈现先增加后减小的趋势,同时在风力机转速一定情况下,风力机的风能利用系数随着叶片高度的增加也呈现明显的先增加后减少趋势。     

Optimization of a subsonic wind tunnel nozzle with low contraction ratio via ball-spine inverse design method

The goal of wind tunnel design is to generate a uniform air flow with minimum turbulence intensity and low flow angle. The nozzle is the main component of wind tunnels to create a uniform flow with minimal turbulence. Pressure distribution along nozzle walls directly affects the boundary layer thickness, pressure losses and non-uniformity of flow velocity through the test section. Although reduction of flow turbulences and non-uniformity through the test section can be carried out by nozzles with high contraction ratio, it increases the construction cost of the wind tunnel. For decreasing the construction cost of nozzle with constant test section size and mass flow rate, the contraction ratio and length of nozzle should be decreased; that causes the non-uniformity of outlet velocity to increase. In this study, first, three types of nozzle are numerically investigated to compare their performance. Then, Sargison nozzle with contraction ratio of 12.25 and length of 7 m is scaled down to decrease its weight and construction cost. Having scaled and changed to a nozzle with contraction ratio of 9 and length of 5 m, its numerical solution reveals that the non-uniformity of outlet velocity increases by 21%. By using the Ballspine inverse design method, the pressure distribution of the original Sargison nozzle is first scaled and set as the target pressure of the scaled down nozzle and geometry correction is done. Having reached the target nozzle, numerical solution of flow inside the optimized nozzle shows that the non-uniformity just increases by 5% in comparison with the original Sargison nozzle.     

斜置方柱气动力特性试验研究

土木工程结构中有很多方形断面的细长结构,常常受到斜向风作用,其风荷载可以简化为斜置方柱的气动力,与垂直风向作用不同,目前尚没有明确的气动力估算方法。针对此问题,采用刚性节段模型测压风洞试验,分析了风偏角对方柱的静态气动力特性的影响规律。结果表明:采用传统风速分解法仅可以有效地估计在分离点之前的风压,并不适用于斜置方柱完整气动力的估算;由于背风面风压的减弱,斜置方柱的平均和脉动气动力系数小于垂直方柱的对应值;斜置方柱的旋涡脱落频率小,强度弱,频带宽。因此,采用垂直方柱的平均气动力作为方柱抗风设计的平均风荷载是偏于安全的,但是由于旋涡脱落频率及带宽的变化,斜置方柱的风致振动与垂直方柱会有明显的差别。     

基于变采样长度相关滤波的不平衡信号提取法

根据相关滤波提取信号幅值和相位的原理,定义了不平衡信号的近频噪声干扰度的概念,并构建了近频噪声干扰度模型,揭示了干扰度随频率差变化的分布规律;进而提出了一种基于变采样长度相关滤波的不平衡信号提取法,在短数据情况下根据MUSIC谱确定幅值最大的近频干扰信号频率,结合近频干扰度分布规律合理选择采样长度提取不平衡信号幅值和相位。电主轴动平衡测量实验和仿真结果表明：与传统定采样长度相关滤波相比,所提方法受信噪比波动影响小,抗近频干扰能力强,在采样长度更短时提取的不平衡信号幅值和相位的方差更小。     

基于双通道可调F-P干涉仪的机载测风激光雷达系统的鉴频器

利用双通道可调Fabry-Perot干涉仪作为机载测风激光雷达系统的鉴频器。该鉴频器可以克服现有测风雷达测速范围小的缺点,能够根据相对风速变化调整干涉仪的腔长,从而达到调整干涉仪透射谱中心频率的目的,从而间接实现测速范围动态可调,扩大测速范围的目的。采用此鉴频器可以实时测量飞行器与大气的相对风速。文中详述了测速原理和鉴频器结构,并给出机载雷达的系统参数,分析了系统的测量误差,结果表明:探测累积时间1s,测速范围为0~1000m/s时,探测高度可达30km,系统测量误差小于5m/s。     

Study of the sensitivity of the first four flexural modes of an AFM cantilever with a sidewall probe

The resonant frequency and sensitivity of flexural vibration for an atomic force microscope (AFM) cantilever with a sidewall probe have been analyzed. A closed-form expression for the sensitivity of vibration modes has been obtained using the relationship between the resonant frequency and contact stiffness of cantilever and sample. The results show that a sidewall scanning AFM is more sensitive when the contact stiffness is lower and that the first mode is the most sensitive. However, the high-order modes become more sensitive than the low-order modes as the contact stiffness increases. The resonance frequency of an AFM cantilever is low when contact stiffness is small. However, the frequency rapidly increases as contact stiffness increases. In addition, it can be found that the effects of the vertical extension on the sensitivity and the resonant frequency of an AFM cantilever are significant. Decreasing the length of vertical extension can increase the resonance frequency and sensitivity of mode 1 when the contact stiffness is small. However, the situation is reverse when the contact stiffness becomes large.     

Trajectory analyses of uncontrolled circular parachutes in random spatial wind fields

The present paper explores the trajectories of two uncontrolled circular parachute models which differ in size and mass in random spatial wind fields. The wind velocity components were generated through three-dimensional inverse fast Fourier transforms; and the correlations of the simulation data compared with the theoretical functions to confirm the accuracy of the wind model. The parachute systems are modelled as six-degrees-of-freedom rigid bodies, on which the aerodynamic forces and moments are applied. The dynamics model was validated before being used to study the drop trajectories of the parachute systems in spatial wind fields. Analyzing the drop trajectories and the impact point dispersion characteristics of the two parachute systems, the paper shows that the smaller one oscillates at a higher frequency and is affected more strongly by the wind. While descending at low altitude, there could be resonance between the dynamics of the larger parachute model and the wind turbulence. Moreover, it is found that the use of simplified vertical wind profiles, which include only the variation of the wind velocity against the altitude, may cause significant error in the simulation results.