Frequency-dependent attenuation of directional transmission asymmetry in coupled rotating systems

Vibration transmission in rotating machinery is typically interpreted through localized spectral responses associated with component-level faults. In mechanically coupled assemblies, however, defect-induced excitation propagates through interconnected structural paths, potentially producing asymmetric dynamic interactions between components. The directional characteristics and frequency evolution of such interactions remain insufficiently quantified. This study experimentally investigates the frequency-dependent attenuation of directional transmission asymmetry in a coupled rotating drivetrain under controlled fault conditions. A reciprocal transmission framework is formulated using defect-induced amplitude increments measured at paired components. Directional transmission coefficients are defined, and an asymmetry ratio is introduced to quantify the imbalance between forward and reverse excitation propagation. Experiments conducted over the 10–50 Hz excitation range across four mechanically distinct bidirectional transmission paths reveal a consistent monotonic reduction of the asymmetry ratio with increasing frequency. In all cases, the evolution is accurately described by an exponential attenuation model of the form R ij (ω) = 1+C ij exp(−kω). While the initial asymmetry magnitudes C ij depend on local interface characteristics and excitation mechanisms, the identified convergence coefficients k remain confined to a narrow interval across all transmission paths. This limited dispersion indicates that the attenuation rate of directional dominance is governed predominantly by the global dynamic structure of the coupled assembly rather than by localized contact effects. The results reveal a systematic transition from directionally biased transmission in the low-frequency regime to progressively balanced dynamic interaction at higher frequencies. The proposed formulation provides a compact and experimentally supported representation of frequency-controlled directional attenuation and offers a system-level interpretation of vibration propagation in coupled rotating systems.