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Superposition principle in bridge aerodynamics: Modelling of self-excited forces for bridge decks in random vibrations

机译：桥梁空气动力学中的叠加原理：随机振动中桥面板的自激力建模

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摘要

The modeling of self-excited forces in modern bridge aerodynamics traditionally involves the assumption of superposition. The use of a linear load model allows to perform sophisticated buffeting analyses, where the response consists of multiple frequency components, even though the aerodynamic derivatives have been determined by single harmonic forced vibration test. The principle of superposition is also of crucial importance when assessing the critical flutter velocity, since the flutter motion is dissimilar to the motion considered in the standard wind tunnel tests. In this study, a recently-developed forced vibration setup that can force arbitrary motions is used to examine the linearity of the load model for self-excited forces considering several frequency components. The section model is first forced into bi-harmonic motions to be able to determine the aerodynamic derivatives for two different reduced velocities at the time. The results correspond in an excellent manner to aerodynamic derivatives from standard forced vibration tests. Further, the aeroelastic forces are measured during broad-banded motions and compared in time and frequency domains with self-excited forces predicted using rational functions. The experimental results confirm that the principle of superposition is valid for lift and pitch for the wedged-shape box cross-section considered. Significant nonlinearities are, however, observed for the self-excited drag, which implies that the principle of superposition does not apply.
机译：现代桥梁空气动力学中的自激力建模通常涉及叠加的假设。线性负载模型的使用允许执行复杂的抖振分析，其中响应由多个频率分量组成，即使空气动力学导数已通过单次谐波强制振动测试确定。在评估临界颤振速度时，叠加原理也至关重要，因为颤振运动与标准风洞测试中考虑的运动不同。在这项研究中，最近开发的可以强迫任意运动的强迫振动装置被用来检查考虑了多个频率分量的自激力载荷模型的线性。首先将截面模型强制为双谐波运动，以便能够确定当时两种不同速度的空气动力学导数。结果与标准强制振动测试的空气动力学衍生结果非常吻合。此外，在宽频带运动期间测量气动弹性力，并在时域和频域中与使用有理函数预测的自激力进行比较。实验结果证实，叠加原理对于所考虑的楔形箱形截面的升力和俯仰有效。但是，对于自激阻力观察到了显着的非线性，这意味着叠加原理不适用。

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