考虑内充气体与外部膜材共同作用的ETFE气枕力学性能及风致响应研究

发布时间：2018-08-25 19:32

【摘要】：ETFE气枕式膜结构是本世纪初才开始大量出现的新型围护结构。目前,有学者针对ETFE气枕的力学性能与分析方法展开研究并取得了一定进展。然而,已有研究仅涉及ETFE气枕的形态分析和荷载分析等静力学内容,尚未触及ETFE气枕的自振特性和风致响应分析等动力学问题。ETFE气枕在风荷载作用下的动力问题涉及两类耦合：一是内充气体与ETFE薄膜的共同作用,二是气枕与外部风场的流固耦合。第一类耦合的实质是如何充分考虑内充气体对ETFE气枕动力特性的影响,而第二类耦合的实质是如何更准确地计算外部流场的附加质量、气动阻尼与气承刚度效应。本文以实现耦合作用下的ETFE气枕风致动力响应分析为出发点,基于理论推导、试验研究及数值模拟等手段对ETFE气枕动力分析中的关键技术问题进行了系统研究,主要内容及创新包括： (1)推导了充气膜结构内充气体与外部膜材的共同作用方程,提出基于共同作用模型的充气膜结构数值分析方法并进行了算例验证。在张拉膜平衡方程中引入内压项得到外部膜材的动力学方程,基于势流假定得到描述内充气体运动的波动方程,然后引入界面协调条件并将结构、流体方程联立得到了充气膜系统的共同作用方程。对两类典型充气膜结构进行了数值模拟,验证了共同作用模型在充气膜结构分析中的准确性和适用性。 (2)提出基于内压和膜面形状测量的气枕形态确定方法并用于ETFE气枕的形态测试和加载测试,测试及分析结果表明该方法有效、可行。提出ETFE气枕共同作用有限元模型的建立方法并进行了静力试验验证。定义了ETFE气枕的破坏模式与承载力确定准则并探讨了尺寸、矢跨比、膜面厚度对承载力-内压曲线的影响。结果表明：ETFE气枕内压对外荷载十分敏感,荷载作用位置对气枕的变形和内压影响明显。在设计内压范围内,存在一个最优气压使得ETFE气枕具有最大承载力；尺寸、矢跨比及膜面厚度等参数变化会显著影响气枕的承载力。 (3)基于非接触视频测试并将峰值法、互谱法与指数拟合法相结合获得了ETFE气枕的模态参数及其随内压和跨度的变化规律,研究了ETFE气枕的自由振动模式、频率分布及阻尼特点。在此基础上进行了ETFE气枕的自振特性参数分析,研究了内压、矢跨比、跨度、膜厚及外部空气对气枕模态参数的影响规律。结果表明：测试气枕的1阶振型均为左右挤压振动,但后续模态的振型有所不同；ETFE气枕在静风环境下属于低阻尼结构,模态阻尼比随内压升高非线性下降；气枕固有频率随着内压升高而非线性增加,随跨度增加而迅速减小,且分布更为密集。内压与跨度变化对气枕的模态振型影响有限；膜材厚度、矢跨比变化对气枕低阶和高阶模态频率的影响效果不同；考虑外部空气影响后的气枕湿模态频率较干模态频率减小,外部空气对气枕动力特性的影响随气枕跨度增加而显著增大。 (4)验证了线性势流单元在ETFE气枕非线性、大变形随机振动分析中的适用性和准确性,为气枕流固耦合动力分析奠定基础。将CFD模拟的刚性气枕表面风压时程加载于共同作用有限元模型进行非线性随机振动分析,研究了ETFE气枕在随机风荷载下的振动模式及膜面响应的分布特点。结果表明：风荷载作用下气枕振动表现出极强的整体性,上、下层膜面在内充气体的联系下呈竖向整体摆动。气枕上层膜的响应峰值向迎风侧偏移,沿风向呈非对称分布；气枕下层膜响应因仅受均布压力作用而近似呈对称分布。 (5)基于结构-流体同步数值建模技术建立了包含整个建筑的ETFE气枕流固耦合分析模型,计算了考虑流固耦合作用的ETFE气枕风致响应,讨论了流固耦合作用对ETFE气枕响应时程、空间分布、功率谱及风振系数的影响。定义了ETFE气枕的流固耦合效应系数,并给出其在工程常见风速、内压、矢跨比和跨度下的变化规律和取值范围。研究表明：ETFE气枕在风荷载下的流固耦合效应主要表现为外流场对气枕动力响应的单向影响,气枕运动引起的流场改变十分微弱。流固耦合作用引起了较大的气动阻尼,抑制了ETFE气枕的风致振动。流固耦合作用下ETFE气枕的响应谱表现为以低频振动为主的宽频带分布,与无耦合结果差异明显,这表明有、无流固耦合作用下气枕的风致振动机制有所区别,前者以风荷载作用下的强迫振动为主,而后者以结构与流场的共振响应为主。ETFE气枕的流固耦合效应系数受风速、内压、矢跨比及跨度影响显著；在工程常见的风速、内压、矢跨比及跨度范围内,气枕流固耦合效应系数的取值范围分别为0.62-0.725、0.6-0.83、0.58-0.87及0.56～0.89。本文以共同作用模型的理论推导和试验验证为基础,并考虑气枕与外部风场间的流固耦合作用实现了ETFE气枕的风致动力响应数值模拟和全过程分析,研究了ETFE气枕的静、动力性能及流固耦合特点,为气枕工程设计提供了有益参考。
[Abstract]:ETFE air-cushion membrane structure is a new type of envelope structure which appeared in large quantities at the beginning of this century. At present, some scholars have made some progress on the mechanical properties and analysis methods of ETFE air-cushion. However, the existing research only involves the static analysis of ETFE air-cushion, such as morphology analysis and load analysis, and has not touched the natural vibration of ETFE air-cushion. The dynamic problems of ETFE air cushion under wind load involve two kinds of coupling: the interaction between the inner air cushion and the ETFE film, and the fluid-solid coupling between the inner air cushion and the external wind field. The essence of the second type of coupling is how to calculate the additional mass, aerodynamic damping and stiffness effect of the external flow field more accurately.
Based on the theoretical derivation, experimental study and numerical simulation, the key technical problems in the dynamic analysis of ETFE air sleepers are systematically studied in this paper. The main contents and innovations are as follows:
(1) The interaction equation between the inflatable membrane and the external membrane is deduced, and a numerical analysis method based on the interaction model is proposed for the inflatable membrane structure. Wave equation is introduced, interface compatibility condition is introduced, and the interaction equation of gas-filled membrane system is obtained by combining structure and fluid equation. Two typical gas-filled membrane structures are numerically simulated to verify the accuracy and applicability of the interaction model in the analysis of gas-filled membrane structures.
(2) A method for determining the shape of the air-cushion based on the measurement of internal pressure and membrane surface shape is proposed and applied to the shape test and loading test of the ETFE air-cushion. The test and analysis results show that the method is effective and feasible. The results show that the internal pressure of ETFE pillow is very sensitive to external load, and the location of load has obvious influence on the deformation and internal pressure of the pillow. Parameters such as size, sagittal span ratio and film thickness will significantly affect the bearing capacity of air cushion.
(3) Based on the non-contact video test and the peak value method, the cross-spectrum method and the exponential fitting method are combined to obtain the modal parameters of the ETFE air cushion and their variation with internal pressure and span. The free vibration mode, frequency distribution and damping characteristics of the ETFE air cushion are studied. The results show that the first mode shapes of the test sleepers are left-right extrusion vibration, but the subsequent mode shapes are different; the ETFE sleepers belong to low damping structure in static wind environment, and the modal damping ratio decreases nonlinearly with the increase of internal pressure. With the increase of internal pressure and span, the influence of the change of internal pressure and span on the modal vibration mode of the air sleeper is limited; the effect of the change of membrane thickness and rise-span ratio on the low-order and high-order modal frequencies of the air sleeper is different; the wet modal frequencies of the air sleeper considering the influence of external air are higher than that of the dry mode. When the state frequency decreases, the influence of external air on the dynamic characteristics of air cushion increases significantly with the increase of air cushion span.
(4) The applicability and accuracy of the linear potential flow element in the nonlinear and large deformation random vibration analysis of the ETFE air cushion are verified, which lays the foundation for the fluid-structure coupling dynamic analysis of the air cushion. The results show that the vibration of the air cushion under wind load shows a strong integrity, and that the upper and lower membrane surfaces oscillate vertically and wholly under the connection of the inner inflatable. The response peak value of the upper membrane of the air cushion shifts to the windward side and distributes asymmetrically along the wind direction. It is symmetrical distribution only under uniform pressure.
(5) Based on the structure-fluid synchronous numerical modeling technique, a fluid-structure coupling analysis model of ETFE air-cushion is established, and the wind-induced response of ETFE air-cushion considering fluid-structure coupling is calculated. The influence of fluid-structure coupling on response time history, spatial distribution, power spectrum and wind-induced vibration coefficient of ETFE air-cushion is discussed. The results show that the fluid-structure coupling effect of ETFE air-cushion under wind load is mainly manifested by the unidirectional influence of the external flow field on the dynamic response of the air-cushion, and the fluid-structure coupling effect caused by the movement of the air-cushion is very weak. The response spectrum of the ETFE sleeper under the fluid-solid coupling is broadband with low-frequency vibration as the dominant component, which is obviously different from that without coupling. This shows that the mechanism of the wind-induced vibration of the sleeper under the fluid-solid coupling is different, and the former is strong under the wind load. The fluid-structure coupling effect coefficients of ETFE gas sleepers are significantly affected by wind speed, internal pressure, rise-span ratio and span. In the common Wind speed, internal pressure, rise-span ratio and span range, the fluid-structure coupling effect coefficients of ETFE gas sleepers are 0.62-0.725, 0.6-0.83, 0.58-0.87 and 0.58-0.87 respectively. .56 ~ 0.89.
Based on the theoretical derivation and experimental verification of the interaction model and considering the fluid-structure interaction between the air cushion and the external wind field, the wind-induced dynamic response of the ETFE air cushion is numerically simulated and analyzed. The static, dynamic and fluid-structure coupling characteristics of the ETFE air cushion are studied, which provides a useful reference for the engineering design of the air cushion.
【学位授予单位】：北京交通大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU383

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