张拉膜结构气弹失稳机理研究

发布时间：2018-04-20 13:23

本文选题：张拉膜结构 + 气弹模型试验　；参考：《哈尔滨工业大学》2015年博士论文

【摘要】：膜结构因其轻柔特性,在风荷载作用下会产生较大的变形和振动,这种变形和振动反过来又影响到结构周围的流场,形成所谓的“流固耦合效应”。特定条件下,流固耦合效应会导致结构振幅随风速增加急剧增大,产生类似桥梁和机翼的气弹失稳现象。由于气弹失稳对结构抗风安全威胁很大,因而对其作用机理的研究一直是结构风工程领域的重要课题之一。但这方面的工作以往多集中于桥梁结构,对膜结构的研究很少。其中的一个重要原因在于,膜结构的动力特性十分复杂,难以像桥梁那样简化为仅具有平动和转动自由度的节段模型。近年来,国内外大型膜结构在强风作用下的破坏事件时有发生,说明现阶段的膜结构抗风设计理论还存在一定的不足,需要进一步探索膜结构的风致动力灾变的机理,探讨气弹失稳发生的可能性及应对措施。基于上述背景,本文开展了系列膜结构气弹模型风洞试验研究,通过对结构多种响应特征参数随风速变化规律的探讨,明确了结构与风场间的相互作用机制,揭示了膜结构的气弹失稳机理,建立了考虑气弹失稳的膜结构抗风设计方法。本文主要工作包括如下几方面:1.建立了基于全荷载域和多响应特征的膜结构气弹失稳研究方法。鉴于膜结构风振响应具有几何非线性明显和多阶模态参振等特点,传统的结构气弹失稳研究方法不再适用,需建立适用于多自由度柔性体系的气弹失稳研究方法。为此,提出了基于全荷载域和多响应特征的膜结构气弹失稳综合研究方法。该方法是以气弹模型风洞试验为主,联合运用数值模拟和解析方法,从结构响应特征和流场变化规律两方面入手,通过考察不同风速(全荷载域)下结构响应与流场风速之间的相关性,以及结构振幅、主导振型和系统阻尼比等特征参数的变化规律,来揭示膜结构的气弹失稳机理。在建立总体研究框架的基础上,对若干关键技术问题,如模态识别方法、阻尼识别方法和基于动边界技术的CFD数值模拟方法等进行了探讨,并验证了其有效性。2.设计并完成了系列典型膜结构气弹模型风洞试验。气弹模型风洞试验一直是结构风工程领域的一个难题,尤其是膜结构的气弹模型风洞试验,如何选择合适的模型材料以及如何避免测量装置对风场和结构振动的干扰,都是需要解决的关键问题。基于对气弹模型相似理论、非接触测量技术和预张力施加方法等问题的探讨,设计并完成了开敞式单向张拉膜结构、封闭式单向张拉膜结构和鞍形张拉膜结构气弹模型风洞试验,获得了不同风速下的结构风振响应及其表面风场变化数据。通过对结构振幅和主导振型在不同风速下的变化规律分析,发现存在振幅急剧增大和主导振型跳跃等现象,初步判断该现象与结构气弹失稳有关。3.联合运用多种研究手段,揭示了膜结构的气弹失稳机理。通过对全荷载域下结构的位移响应和流场风速相关性分析,确定发生气弹失稳的风速区间;结合频谱分析进一步考察了结构位移主导频率与风速主导频率,发现气弹失稳时风速主导频率出现了类似涡激共振的锁定现象。为验证该现象,分别开展了考虑结构平均变形和受迫振动的CFD数值模拟研究,发现随着结构平衡构形的改变,结构表面的漩涡脱落频率也发生了变化,当其与结构某阶自振频率相接近时,就会引发结构的大幅振荡,而这种大幅振荡又反过来控制了漩涡脱落频率,从而出现锁定现象。此外,还分析了系统总阻尼比随风速的变化,发现其随风速增加呈现先增大后减小的特征,峰值点恰好对应出现气弹失稳时的前一个风速;该现象可解释为由于气动阻尼作用导致结构主导振型的阻尼比迅速增大,迫使结构跳跃到阻尼比较低的另一阶振型上振动,从而揭示了振型跳跃的内在原因。基于上述分析,可认为膜结构的气弹失稳是一种由旋涡脱落诱发的涡激共振现象,具有振幅突然增大、主导振型出现跳跃、总阻尼迅速衰减等特征。4.采用解析方法推导了膜结构的附加质量和气动阻尼计算公式。基于气动声学理论和拟静态理论,推导了均匀流中开敞式单向张拉膜结构的附加质量及气动阻尼解析公式。该方法将作用在膜面的风荷载简化为气动声压和拟静态风压两部分,前者由膜面振动对空气的挤压作用引起,与来流风速无关,可采用气动声学方法确定;后者与来流作用下膜面的拟静态风压有关,反映了膜面振动过程中形状变化对风荷载的影响,可通过对一个振动周期内不同时刻结构形状的风荷载CFD数值模拟来确定。与气弹模型风洞试验结果对比表明,附加质量解析公式的误差不超过9.0%,气动阻尼解析公式的误差也基本可以控制在20%以内。进一步分析表明:附加质量和气动阻尼均随着风速的增大而增大,附加质量可达结构质量的5倍左右,气动阻尼可达结构阻尼的10倍左右,因而在膜结构风振分析中附加气动力作用不可忽视。5.提出了考虑气弹失稳的膜结构抗风设计方法。在现有膜结构抗风设计流程的基础上,增加了临界风速判定和附加气动力评估环节,以考虑气弹失稳和流固耦合的影响。在此基础上,给出了气弹失稳临界风速的定义和一些典型工况下的取值建议,以及附加气动力的确定方法。此外,还结合气弹模型风洞试验结果探讨了预张力对结构临界风速的影响,提出通过改变预张力来改善结构气动稳定性的建议。
[Abstract]:Because of its soft characteristics, membrane structure will produce larger deformation and vibration under wind load. This deformation and vibration, in turn, affect the flow field around the structure, forming a so-called "fluid solid coupling effect". Under specific conditions, the fluid solid coupling effect will lead to a sharp increase in structural amplitude with wind speed, which produces similar bridges and wings. The study of the mechanism of its action has been one of the most important topics in the field of structural wind engineering. However, the work in this field is mostly concentrated on the structure of the bridge, and the study of the membrane structure is very few. One of the important reasons is the dynamic characteristics of the membrane structure. It is very complicated that it is difficult to simplify the segment model as a bridge, which only has translational and rotational degrees of freedom. In recent years, the damage events of large membrane structures at home and abroad have occurred in strong wind, which indicates that the theory of wind resistant design for membrane structures at the present stage still has some shortcomings. It is necessary to further explore the wind induced dynamic catastrophe of membrane structure. On the basis of the above background, the wind tunnel test of a series of membrane structures is carried out in this paper. The mechanism of the interaction between the structure and the wind field is clarified, and the mechanism of the aeroelastic instability of the membrane structure is revealed, and the mechanism of the aeroelastic instability is revealed. The main work includes the following aspects: 1. the aerodynamic instability research method of membrane structure based on the full load domain and multiple response characteristics is established. In view of the characteristics of the geometrically nonlinear and multi order modal parameters of the wind vibration response of the membrane structure, the traditional structural aeroelastic instability research is studied. The method is no longer applicable. It is necessary to establish an aeroelastic instability study method suitable for the flexible system with multiple degrees of freedom. Therefore, a comprehensive study method of aerodynamic instability of membrane structures based on the full load domain and multiple response characteristics is proposed. The method is based on the wind tunnel test of the aeroelastic model, and the structure response characteristics and the flow are combined with the numerical simulation and analytical method. In the two aspects of the law of field change, by investigating the correlation between the structure response and the flow velocity of the flow field under the different wind speed (full load field), and the variation of the characteristic parameters such as the structure amplitude, the dominant vibration and the damping ratio of the system, the mechanism of the aeroelastic instability of the membrane structure is revealed. On the basis of the establishment of the overall research framework, some key technologies are set up. The problem, such as modal identification method, damping identification method and CFD numerical simulation method based on dynamic boundary technology, has been discussed, and its effectiveness.2. is verified and a series of typical membrane structure aeroelastic model wind tunnel tests have been completed. The wind tunnel test of aeroelastic model has always been a difficult problem in the field of structural wind engineering, especially the gas of membrane structure. It is the key problem to solve the problem of how to choose the suitable model material and how to avoid the interference between the wind field and the structural vibration of the measuring device. Based on the similarity theory of the aeroelastic model, the non-contact measurement technology and the pretension method, the open type unidirectional tensioned membrane structure is designed and completed. In the wind tunnel test of closed one-way tensioned membrane structure and saddle shaped membrane structure aeroelastic model, the wind vibration response and the change data of the surface wind field under different wind speeds are obtained. Through the analysis of the variation of the structure amplitude and the dominant mode at different wind speeds, it is found that there is a sharp increase in the amplitude of the vibration amplitude and the leading mode of the mode jump. In order to judge the phenomenon and the structural gas elastic instability,.3. combined with a variety of research means to reveal the mechanism of aeroelastic instability of the membrane structure. Through the analysis of the displacement response and wind velocity correlation of the structure under the full load domain, the wind velocity interval of the aeroelastic instability is determined, and the dominant frequency and wind of the structural displacement are further investigated by the spectrum analysis. In order to verify this phenomenon, the CFD numerical simulation of the average structure and forced vibration is carried out to verify this phenomenon. It is found that the vortex shedding frequency of the structure surface changes with the change of the structure balance structure, and it is found that the vortex shedding frequency of the structure surface changes as the structure balance structure changes. The large oscillation of the structure will be triggered when the structure of a certain order of vibration frequency is close, and this large oscillation also controls the vortex shedding frequency, which leads to the locking phenomenon. In addition, the change of the total damping ratio of the system with the wind speed is also analyzed, and it is found that the increase of the wind speed increases first and then decreases with the wind speed, and the peak point coincide with the occurrence of the wind velocity. This phenomenon can be interpreted as a rapid increase in damping ratio of the dominant structure caused by aerodynamic damping, which forces the structure to jump to the other order of the lower damping vibration, and thus reveals the internal cause of the mode jump. Based on the above analysis, it is considered that the aerodynamic instability of the membrane structure is a kind of cause. The vortex induced vortex induced resonance phenomenon, which has a sudden increase in amplitude, a jump in the dominant mode and the rapid attenuation of the total damping, is used to deduce the additional mass and aerodynamic damping formula of the membrane structure by analytic method. Based on the theory of aeroacoustics and quasi-static theory, the open type unidirectional tensile membrane structure in the uniform flow is derived. The analytical formula of additional mass and aerodynamic damping is formulated. This method simplifies the wind load acting on the membrane surface as two parts of the aerodynamic pressure and the pseudo static pressure. The former is caused by the extrusion of the membrane surface vibration to the air, and is independent of the wind velocity. The latter is determined by the aerodynamic acoustics. The latter is related to the pseudo static pressure of the membrane surface. The influence of the shape change on the wind load during the film surface vibration can be determined by the CFD numerical simulation of the wind load at different moments in the vibration period. The error of the analytical formula of the added mass is not more than 9%, and the error of the analytical formula of the aerodynamic damping can also be basically controlled. The further analysis shows that the additional mass and aerodynamic damping increase with the increase of wind speed, the additional mass can reach about 5 times of the structure mass, and the aerodynamic damping can reach about 10 times of the structural damping, so the addition of aerodynamic force to the wind vibration analysis of the membrane structure can not be ignored by.5. to consider the wind resistance of the membrane structure to resist the wind. On the basis of the current wind resistance design flow of the membrane structure, the critical wind speed determination and the additional aerodynamic evaluation link are added to consider the influence of the aeroelastic instability and the fluid solid coupling. On this basis, the definition of the critical wind speed of the aeroelastic instability and some suggestions on the value under typical conditions, as well as the determination of the additional aerodynamic force are given. In addition, the effect of pretension on the critical wind speed of the structure is discussed in combination with the wind tunnel test results of the aeroelastic model, and a proposal to improve the aerodynamic stability of the structure by changing the pretension is proposed.

【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU383;TU352.2

【参考文献】