Sound Radiation Analysis of a Longwall Cutting Drum

Operators of longwall mining systems experience sound levels of 93–105 dB(A) and receive noise exposures that place them at risk of noise-induced hearing loss. To address the problem, the National Institute for Occupational Safety and Health (NIOSH*) Office of Mine Safety and Health Research (OMSHR) has conducted research to develop engineering noise controls for longwall systems. In previous field surveys, the sound radiated by the cutting drums was identified as a major hazard, especially considering their close proximity to the operators. Cutting drums are complex structures consisting of curved metal pieces welded together, and NIOSH has used modeling and simulation to characterize the acoustic properties of this structure. Based on a finite element (FE) model of the drum, the boundary element method (BEM) was used to predict the sound radiated from the vibrating drum due to an excitation force applied to one of the cutting bits. Simulations were used to examine the following with respect to the radiated sound power: (1) the ramifications of adding the welds to the model rather than assuming direct attachment between the metal components; (2) the effect of weld stiffness; (3) the relative contributions of the vanes and the cylindrical part of the drum; and (4) the sensitivity to the direction of the applied force. Parametric studies have shown that including the weld in the finite element model has a significant effect on the predicted sound power level, while varying the weld Young’s modulus by 20% does not radically change the sound radiation. Panel contribution analysis indicates that the vanes contribute much more to the total sound power level, as compared to the cylindrical part of the drum. Consequently, it is expected that damping treatments would be most effective at controlling noise radiation if applied to the vanes rather than to the cylindrical portion. Finally, case study results show that the sound power levels are most sensitive to the tangential and bending forces above 500 Hz. For frequencies below 500 Hz, the sound power level is most sensitive to axial and bending forces.