A spectrum analyzer is necessary for quantitative monitoring of low-frequency noise, but there are currently no national testing standards or engineering norms regarding low-frequency railway noise in China or several other countries. Individuals subjected to environments characterized by chronic low-frequency noise can suffer from insomnia, headache, tinnitus, discomfort, chest tightness, abdominal pressure, and other psychological and physical symptoms. Low-frequency railway noise can easily pass through walls, windows, and other obstacles and can harm people’s physical and mental health. Compared with high-frequency noise (such as wheel–rail noise), low-frequency noise has slower energy attenuation upon environmental radiation and is thus transmitted over longer distances. īridges vary significantly in design and construction: those constructed from steel radiate mid- to high-frequency noise (200–1,000 Hz), while concrete bridge-borne noise is generally low-frequency noise (<200 Hz). The magnitude of such bridge-borne noise can typically be 10 dB or more for common railway networks. These vibrations cause the wheels and track to radiate noise and transfer energy directly to each component of the bridge, causing the beams, piers, and other components to vibrate, thus forming secondary noise radiation. When a train passes over a bridge, vibrations are generated owing to irregularities in the wheels and the track. Finally, according to the results of the current review, the main factors affecting bridge-borne noise are analyzed, several noise reduction measures are proposed for different types of bridges, and their effectiveness is demonstrated. Several case studies are reviewed, and their results are discussed. Second, this paper reviews existing theoretical prediction models of noise emanating from bridges: the semianalytical method, the Rayleigh integral method, the boundary element method, and statistical energy analysis. This review paper first analyzes the space distribution, spectral characteristics, and sound pressure levels of noise radiated by all -concrete, steel–concrete composite, and all -steel bridges, mainly according to experimental studies. Bridge-borne noise is attracting increasing attention because of its low-frequency noise characteristics. This results in a bridge-borne noise source, which occurs in addition to the main noise source (i.e., wheel–rail interactions). Many of these networks require elevated bridges. The predicted directivity patterns of second- and third-order modes are dominated by the drag noise component and peak in the direction near the rotational plane.In recent years, there has been rapid growth of Chinese rail transit networks. For the first-order mode, the predicted directivity exhibits a forward-leaning characteristic, which is in good agreement with the experimental result. Theoretically, the leading order thrust noise is found to peak along the rotation axis and plummet in the rotational plane. It is found that the modal directivity of interaction noise for CR fans is more complicated than that for conventional fans. To extract the interaction tones from the measured acoustic data, the Vold-Kalman filter is applied, with which the influences of broadband noise are excluded. Modal directivities of lower-order interaction tones are investigated with the derived formula as an application example, which is generally validated by the experimental results. The derived formula is intended to enhance the understanding of the interaction noise mechanisms and help devise noise control methods in CR fans. It is demonstrated that the conventional stator-rotor interaction noise problem is a special case of the present model, whereas the rotor-stator case is not. In the formulation, blade section misalignments leading to blade sweep and lean are considered. The interaction noise radiated from contra- rotating (CR) fans is theoretically characterized, focusing on the unsteady lift force caused by aerodynamic interaction between the front and rear rotors.
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