外文翻译-风洞效应结构舞动的研究和分析.doc

外文翻译 译文风工程与工业空气动力学杂志7476 (1998) 967976风洞效应结构舞动的研究和分析O. Chabart, J.L. Lilien摘要：舞动是一个大振幅，低频率，架空电线的风致振动。在绝大多数情况下，输电导线上存在覆冰：这使导线的截面形状发生改变，从而使其发生空气动力学失稳。本文通过在架空导线上形成一个典型的覆冰形状并进行研究风洞试验中产生的舞动。文章的第一部分已测得在不同风速作用下舞动准静态空气动力学系数。第二部分在风洞实验中用弹簧悬挂模型，使得实验系统尽可能地接近真实的架空导线（允许纵向，横向和旋转运动）。在适当的攻角下导线就会发生舞动。对电力工作人员来说，有两种舞动：邓哈托舞动和颤振。前者是一个空气动力学不稳定问题，因为引起这个问题的主要因素是覆冰的空气动力学特性。颤振是一个气动弹性问题，因为对这种失稳来说，导线的结构特性显得同样重要。同时它存在至少两个自由度之间振动的相互耦合。它们都被试验记录。这些试验提供一套完整的数据并在舞动过程中记录极限环。这些测量结果可用于数值模型验证和防舞动措施的效率评价（失谐，增加垂直、扭转阻尼，转动惯量的改变等）。关键词：振动；风洞；架空导线；舞动1. 引言架空导线舞动会带来相位间闪络并对导线、装置或输电塔造成损害。它影响到能源传输的可靠性。此外，建造费用必须增加，以减少闪络的概率。文献9-11中总结了许多实际观察结果，主要在单导线方面。目前尽管有许多有关风洞方法的论文2，3，6，13，但据笔者所知，除了一篇研究单条导线有部分结果的论文外14，仍未发表有关架空导线完全实验数据的论文。这块领域有很多录像资料，但无法取得导线或风速或覆冰形状的数据，而且（但非常明显）在已观察的事件中没有覆冰的空气动力学特性的数据。最近一些足尺测试将会在不久的将来取得一些非常吸引人的结果17。实际上，过去有人曾对容易导致邓哈托舞动的人工D形覆冰进行了一些实地测试1。在我们看来，这种测试不能重现架空导线真实的舞动，或者说仅仅是异常的重现。架空导线上覆着的湿雪，霜或冰都不会形成D字形截面15。只有当很薄的偏心覆着层受到迎风作用时才会导致偏离偏心覆着层原始位置的 Den-Hartog舞动。但大多数覆冰情况下并不是这样的。获得完整数据的一个简单廉价的方法是进行实验测试。因为把整个架空导线放入风洞中是不可能的，而减小规模尺寸又模拟不出真实现象。于是我们在实验中采用一系列小线段的悬浮模型。导线、人工覆冰和风保持与外界一致，给模型适当的频率振荡来模拟跨度和跨与跨之间的相互作用。如他人一样4，6-8，考虑三频率（水平、竖向和扭转）的基本影响因素，进行适当的测试安装。我们还没获得有关索中张力改变的反应，但是这种现象很容易通过模拟来实现，而且它不是评价舞动的稳定性和一些参数的影响（像失谐、驰振等等）的基本参数。我们的风洞试验将通过全面完整的一组数据来验证一个数值计算模型。此外，一个好的试验装置可以测试许多参数，如各个自由度下的振动频率（包括失谐的影响），分裂导线舞动的伴流影响（将二分裂导线放入风洞中），阻尼效应（在测试中加入适当的阻尼器）等。数值模型验证后12，17，18，同样的模型可以用来进行足尺模拟，包括张力的变化，完整的跨越效应，间隔的影响，跨阶段间隔效应等。2. 试验模型本文只限于一种覆冰形状，偏心非常严重（见图1）。其他稍有偏心的形状也在我们的试验中加以了研究。该架空电缆是一个用于比利时400千伏网络的架空导线：所有铝合金线，直径，截面积。导线的外层用一个适当直径的铝管包裹，以保持大约一米长的直线试验导线。选用接近麦克滕斯托尔（Mike tunstall）形状的人工覆冰形状，与我们的外部直径相适应。覆在索上的“覆冰”（ 密度1.13）通过表面粗糙的木模具用硅树脂做成（见图2）。这种试验导线已从原来的试验导线（自身得到实际覆冰）中复制而来。人工覆冰的长度为0.8米，离心率（覆冰厚度和导线半径的比值）为1.32。覆冰重心与电缆截面中心的距离为。图 1 覆冰的形状 图 2 覆冰样本图3. 风洞设施我们大学的风洞是小型的，最初是为航空系设计和使用的。46千瓦的电动引擎允许风速60m/s，但是最小风速约为8m/s。这是一个有开放部分的环闭试验区。有效圆形截面的直径为0.8米。湍流强度约为1%。该系统用刚性杆架成悬空结构，用三个测力计（最大负载10公斤， 0.1 的偏差的全尺实测）来测量气动力系数。两个垂直测力计（放在图5中的1和2位置）用来测量垂直力（L）和力矩（M）。第三个（放在3位置）用来测量拉力（D）。在五种不同风速作用下（在820m/s），对每个风攻角测量三次（时距超过一分种）得到各个力的平均值。风攻角的增量为，覆盖了范围内的风攻角。图3显示了特定风速下的实验测量值。 图 3 风速为了15米/秒下的系数值为了获得有用的曲线,我们采用了不同的数据处理方式(平均，样条或傅立叶插值)。图4是最后结果的一个说明。这个数字表明，对大多数风攻角来说，风速对升力系数的影响是有限的。这同样也适用于其它系数。实际上，系数变化作为风速的函数对每一个风攻角来说是不同的。 图 4 不同风速下的升力系数4. 风洞中的舞动试验模型用四根垂直的弹簧悬挂在风洞中（图5）。四根横向弹簧允许系统水平振动。所有的弹簧具有相同的刚度（14N/m），但竖向的施加预应力，以限制由于结构自重（2.99千克）引起的静态变形。为了防止风吹到弹簧及部分没有覆冰的结构上，在覆冰样本的末端放置了两个垂直板（图中未画出）。风洞的收敛和发散已略作修改，以加入这些板块。两个圆形（外径0.2米）开口允许样本运动，但限制了其最大振幅。结构的阻尼非常低，垂直方向和水平方向运动的临界阻尼为0.08%，旋转的临界阻尼约为0.3%（呈对数递减）。垂直运动频率和扭转频率通常是用以避免舞动的一个因素，可通过增加惯性或增加扭转刚度（在架空导线上增加垂直质量）。在这种情况下，很容易通过改变垂直弹簧之间的距离来改变扭转刚度。框架内的锚固点可以在弹簧方向上移动来保证当风吹来时试验导线在板块开口的中心（如果没有考虑不稳定问题）。试验导线的竖向和水平位移和扭转用工作频率为50Hz像素为520万的CCD照相机记录。一排发光二级管放在管的最后，使电脑处理时实信号更加容易。 图 5 风洞动力系统图覆冰与水平方向的角度用表示（如图1）。结构水平时，初始积冰角（）就是角度。针对不同的速度对不同的积冰角和频率比进行试验。首先把竖向弹簧放置在离样本中心0.12米处。这样的布置在无风的情况下测得垂直频率（），扭转频率（）和水平频率分别为0.845 ，0.865和0.995Hz。对一个实际的架空分裂导线来说，垂直频率和扭转频率之间的比值约为1。对不同的积冰角度进行了测试：典型的上面象限迎风（0）和下面象限背风（）9。试验过程中，即使在风洞试验允许的最小风速下我们观察到的舞动振幅也经常超过垂直板上限制的0.2米开口。图6-9显示了振幅被限制情况下的结果。无量纲风速定义为，其中代表风速，f表示舞动频率，d为导线的直径。对这个冰积角（-）来说，当风速小于9m/s或大于12.5m/s时，由于不稳定性太高以至难以获得极限环（实际上，或多或少有稳定的反应）。当风速在这两个限值之间时，可得到以下结果。变化角度的位置保持不变（图8），但是扭转最大点之间的幅度差随着风速的增加而增加（ 到）。垂直和水平振幅随着时间的变化而变化（见图6和图7）。三个运动方向的振动频率是相同的，都为0.89 Hz,这是舞动频率（无量纲风速为335）。试验导线上的一点在xy坐标系下的运动轨迹被称为舞动椭圆。这个椭圆的形状和大小对防止舞动作用十分重要。这可被输电塔设计者用以防止舞动的一个被动的对策。对这个冰积角来说，在不同的风速下（即使是微弱的变化），舞动椭圆的外表变化很大（图9）。 图 6 水平位移 图 7 垂直位移 图 8 积冰角的位置 图 9不同风速下的舞动椭圆，在这种情况下，旋转对垂直振幅的影响减小，对垂直振幅的影响主要为不断变化的舞动椭圆的斜率。但在其他情况下可能会有相反的结果。事实上，更加重要的是迎风角的变化。迎风角的变化和垂直运动之间相位的转变也会影响竖向振幅。图10显示了积冰初始角为的结果（对应反向风）。这个角下的舞动行为与前述角度下的不同。当风速小于20m/s时，振幅保持在限制值之下，且三个方向运动的振幅都是稳定的。在不同的风速下，舞动椭圆的形状保持不变。在12m/s的风速下，峰值扭转幅度差为，舞动频率为0.86Hz。在这个频率比下()，该系统除了在-之间是稳定的,其它情况下显得十分不稳定。在之间，系统显得十分不稳定以至在风洞允许的最小风速下舞动就发生了。所以临界风速不能通过测量得到。有时系统自然条件下是不稳定的，无论是小幅的转动还是垂直方向小的位移，有时必须会有扰动。对一些积冰角，观察到了特别不稳定现象。它是一个在水平面上绕覆冰中心的旋转，像一个飞机的偏航运动。Den-Hartog舞动的特点是垂直运动和缺乏显著的扭转运动。但是对频率比约为1的情况下，有可能存在这样一个积冰角，它既遵循Den-Hartog 准则,又很容易发生颤振。在覆冰形状气动力曲线中运用的Den-Hartog准则表明有两个不稳定区（），其中一个在附近（实际覆冰的典型形状），另一个在附近。因此，该系统第二次形成了垂直和扭转频率的最大可用失谐。竖向的弹簧放置在离中心0.36米处。这样的布局，在无风的条件下测得垂直、扭转和水平方向的频率分别为0.85、1.54和0.96Hz（）。这也同样适用于证实失谐对颤振的影响。试验中观察了与Den-Hartog不稳定相应的两个积冰角区域。图11显示了积冰角为的舞动。这不是极限环（振幅太大，导线碰到了开孔的平板），但很显然舞动的椭圆是垂直方向的，而且非常薄。结束时记录的旋转幅度峰值差小于。各个运动方向的频率是不同的，垂直方向的频率为0.85HZ，水平频率为1.27Hz，扭转频率为1.71Hz。图10竖向位移和舞动椭圆，图11竖向位移和舞动椭圆，5. 结论这个试验表明，用悬挂的弹簧的模型来模拟舞动的装置是合理的。试验中观察到的（风的影响，失谐率，舞动椭圆，扰动的影响）跟数值模拟真实架空导线十分吻合。无论是对稳定性还是三维极限环来说，这是用来验证数值模拟的一个很好的工具。 在不久的将来，将进行用来评估分裂导线在尾流效应下的气动力系数的试验。这将带来一个与单导线相当的更加适合的分裂导线模型。还将进行其它的试验，以更好的确定阻尼对舞动稳定性和振幅的影响（在三个自由度上）。还将进行不同失谐率下的单导线和分裂导线的测试。不幸的是，我们的风洞不能方便评价湍流的影响，这也是一个极大的关注点。致谢 作者非常感谢”la Communaut Francaise de Belgique”在这个项目中提供的经济支持。感谢“cblerise de Dour”为我们提供导线试样。特别感谢来自全国高压电线路网的Mike Tunstall为我们提供接近自然覆冰的人工覆冰试样。7中南大学学士学位论文 外文翻译 原文Journal of Wind Engineeringand Industrial Aerodynamics 7476 (1998) 967976Galloping of electrical lines in wind tunnel facilitiesO. Chabart, J.L. Lilien*AbstractGalloping is a large amplitude, low frequency, wind-induced oscillation of overhead electrical lines. In the vast majority of cases, an ice accretion is present on the conductor: this has the effect of modifying the conductors cross-sectional shape such that it becomes aerodynamically and/or aeroelastically unstable. This paper deals with galloping generated during wind tunnel testing. A typical eccentric ice shape has been reproduced on a classical stranded overhead line conductor. In the first part, the quasi-static aerodynamic coefficients have been measured for different wind speeds in the range of galloping observations. In the second part the same sample has been suspended in the wind tunnel by springs in order to obtain a system as close as possible to an overhead line (vertical, horizontal and rotational movements are allowed). For appropriate angles of attack, galloping has been obtained. For an electrical engineer, there are two kinds of galloping: Den-Hartog galloping and flutter galloping. The first one is an aerodynamic instability because the main factor at the origin of this problem is the aerodynamic properties of the ice deposit. The flutter galloping is an aeroelastic problem. For this type of instability, the structural properties of the line are also important and there is a coupling between at least two degrees of freedom. Both of them were recorded. These tests make available a full set of data and recordings of limit cycles during galloping events. Such measurements can be used for numerical model validation and for efficiency evaluation of some anti-galloping means (detuning, increase of damping in vertical, torsion, modification of rotational inertia, etc.).Keywords:Overhead lines; Vibrations; Galloping; Wind tunnel1. IntroductionOverhead lines galloping may bring flashover between phases and cause damage to the conductors, the fittings or the towers. It affects the reliability of energy transmission; moreover, construction costs must be increased to reduce the flashover probability. Numerous practical observations have been summarized in the literature 911, mainly on single conductors.Despite some nice papers on the wind tunnel approach 2,3,6,13, there are no published papers, known to the authors, on the full experimental set of data of galloping, except for one case on a single conductor with partial results 14. On the field there are many videos, but no access to the data on the conductor lines and/or the wind speed and/or the ice shape, and of course (but obviously) no aerodynamic properties of the ice coating during an observed event! Some recent tests on a full-scale site will give access in the near future to some extraordinary attractive results 17.In fact in the past some field tests were performed with an artificial D shape which easily causes Den-Hartog galloping 1. From our point of view such tests do not reproduce actual galloping on an overhead line, or only exceptionally. None of the wet snow, rime or glaze ice on overhead line conductors could reproduce a D shape 15. Only a very thin eccentric layer could induce Den-Hartog galloping for the natural position of the ice eccentricity facing the wind 2,5,13,16. But most of the deposits would not be like that.A simple and cheap way to get a full data set is a laboratory test. As it is impossible to put overhead lines in a wind tunnel and as a reduced scale model will not simulate the true phenomenon, we decided to experiment a string suspended model of a small section of the line. The conductor, the artificial ice and the wind remain as in the field but the span and interaction between spans in a line is replaced by giving to the model the appropriate frequencies of oscillations. As we were convinced like others 4,68 of the fundamental influence of the three frequencies (horizontal, vertical and torsion), appropriate test arrangements were installed. We have not obtained the feedback related to tension changes in the cable, but this phenomena is very easily reproduced by simulation, and is not a fundamental parameter to evaluate galloping instabilities and influences of some parameters (like detuning, damping, etc.).Our wind tunnel tests will give access to a full complete set of data for the validation of a numerical model. Moreover, a nice experimental set is available to test many parameters, like different frequencies for each degree of freedom (including the effect of detuning), the wake effect on galloping for a bundle conductor (2 conductors will be put in the tunnel), damping effects (appropriate dampers will be inserted in the test arrangement), etc.After validation of a numerical model 12,17,18, the same model can then be used for full-scale simulations, including tension variation, full inter-spans effects, spacers effects, inter-phase spacers effects, etc.2. Test sampleThis paper will be restricted to one kind of ice shape, very eccentric (Fig. 1). Other slightly eccentric shape has also been studied during our tests.The overhead line conductor is the one used in Belgium for 400 kV networks: AMS(all aluminum alloy conductor) 620;10 m(diameter 32.5;10 m). The outside layer of a conductor was placed on an aluminum tube of appropriate diameter in order to maintain a straight line of the sample for approximately one meter. Artificial ice has been chosen close to Mike Tunstall shape C1 13 and adapted to our outside diameter. The ice in silicone (density 1.13) has been modeled on the cable with a wooden mold on which the roughness pattern has been printed (Fig. 2). This pattern has been copied from the original sample (itself obtained from a sample of real ice accretion). The length of the artificial ice is 0.8 m and its eccentricity, the ratio between the ice thickness and the radius of the conductor, is 1.32. The distance between the center of gravity of the ice and the center of the cable is . Fig.1.Ice shape and sign convention.Fig. 2. View of the ice sampleFig. 2. View of the ice sample. 3. Wind tunnel facilitiesThe wind tunnel of our university is small and originally designed and used by the aeronautical department. The 46 kW electrical engine allows a wind speed of 60 m/s, but the minimum wind speed is about 8 m/s. It is a close loop with an open section for the testing area. The diameter of the useful circular cross-section is 0.8 m. The turbulence intensity is about 1%.The sample is suspended by a rigid rod to a frame and 3 dynamometers (10 kg maximal load, 0.1% of deviation on full-scale measurement) are used to measure the aerodynamic coefficients. Two vertical dynamometers (set at 1 and 2 in Fig. 5) measure the vertical force () and the moment (M). The last one (set at 3) measures the drag (D). The average of the forces over 1 min is taken three times for each angle of attack and this for five different wind speeds (between 8 and 20 m/s). The 360 range of angle of attack has been covered with an increment of 5. Fig. 3 shows the experimental measurements for a specific wind speed.In order to obtain usable curves, we apply different data processing (average, spine or Fourier interpolation). Fig. 4 is an illustration of the final result. Fig. 3. Measured values of the coecient Fig. 4. Lift coefficient for different wind speedsThis figure shows that the effect of wind speed on the lift coefficient is limited for the majority of the angles of attack. This is also true for the other coefficients. The evolution of the coefficients as a function of the wind speed is in fact different for each angle of attack.4. Galloping in wind tunnelThe sample is suspended by four vertical springs in the wind tunnel (Fig. 5). The four horizontal springs allow the horizontal oscillation of the system. All the springs have the same stiffness (14 N/m) but the vertical ones are prestressed in order to limit the static deformation due to the weight of the structure (2.99 kg). To prevent the wind from blowing on the springs and the part of the structure without ice, two vertical plates (not drawn in the figure) are placed just at the extremities of the ice sample. The convergent and the convergent and the divergent of the wind tunnel have been slightly modified to join these plates. Two circular (diameter 0.2 m) openings allow the movement of the sample but limit the maximum amplitude. The damping in the structure is very low, about 0.08% of critical damping for the vertical and horizontal movement and about 0.3% for the rotation (measured by logarithmic decrement). The ratio between vertical and torsional frequencies is a factor often used to avoid galloping, either by increasing the inertia or by increasing the torsional stiffness (addition of pendula on the overhead line). In this case, it is easier to change the torsional stiffness, simply by modifying the distance between the vertical springs. The frame anchoring points can be moved in the spring direction to keep the sample at the center of the plate openings when the wind blows (if no instabilities are considered). The vertical and horizontal displacements of the sample and its rotation are recorded by means of a CCD camera working at 50 Hz and with a resolution of 520 pixels. A row of LEDs is placed at the end of the tube to make the processing (in real time) of the signal by a PC easier.Fig. 5. Diagram of the dynamic system in the wind tunnelThe angular position of the ice with regard to the horizontal is denoted by (Fig. 1). The ice accretion angle() is the angle when the structure is horizontal. Different ice accretion angles and frequency ratios have been tested, and for different wind speeds. First the vertical springs have been placed at 0.12 m from the center of the sample. For this configuratio