By Robert Powell
Off-highway equipment challenges manufacturers to find new ways to reduce product noise. In addition to improving performance, efficiency and value in new designs, manufacturers are also expected to offer products that meet local noise regulations, reduce community disturbance, minimize operator fatigue, and ease jobsite communication.
A new process for accomplishing these goals more efficiently was presented at NoiseCON-2016 in a paper co-authored by Vermeer (https://www.vermeer.com/NA/en/N/equipment/directional_drills_utility_ins...) and Exa. In this study, titled “Total Noise Analysis of a Directional Drill,” simulation was used to help the team redesign the system for reduced noise levels while preserving cooling airflow performance. The team studied the design of horizontal directional drills used in utility applications to place underground cables with minimal disruption to the neighborhood. Total radiated noise from this machine includes contributions from the cooling fan, engine, exhaust and hydraulic systems.
The above figure from the paper illustrates the exterior of the baseline design, showing openings for cooling air, the engine exhaust stack, and the operator seat position. Openings not only serve to cool the product, but also to attenuate noise from underhood sources with help from acoustic insulation and louvers.
To simulate the Total Noise of the drill in Exa PowerFLOW, noise from the cooling fan was directly simulated while contributions from other noise sources were modeled using “virtual speakers” as a mean to realistically reproduce – in the simulation – the same sound field observed in the physical test. These speakers were tuned in separate PowerFLOW acoustic simulations to reproduce component noise – like diesel combustion, valve impacts, pump fluid pulsations, and other vibrations – all at the levels provided by the components’ suppliers or by the manufacturer. Acoustic radiation from all of the different noise sources were then combined with the fan noise in a baseline design run, with underhood absorption modeled as Acoustic Porous Media (APM) in the solver. Along with radiated noise, simulation results calculated air flow and cooling system performance. Analysis of these results was then used to optimize the design, which was re-verified using simulation, manufactured, and validated with physical experiment.
The figure below summarizes the improvement achieved in radiated sound power level (SWL, in decibels, was reduced by 4.3 dBA), with experiments confirming that the noise reduction predicted (4.7 dBA) was indeed achieved. The paper concluded that the total noise of the directional drill was accurately simulated in a short turnaround time while considering noise sources including engine, exhaust, cooling fan and other underhood components. What’s more, a new design was proposed based on the total noise analysis and subsequently tested – confirming that noise was effectively reduced. Finally, simulation was shown to be accurate when validated against physical experiments: overall A-weighted sound power levels were within 0.3 dB of tested results and overall A-weighted sound pressure levels of most microphones were within 2 dB.
These results have significant implications to improve time to market, boost product performance, reduce development costs, and of course yield quieter jobsites – all of which could positively impact heavy vehicle equipment manufacturers, according to the study: “This method has drastically reduced the duration of the product design cycle and has improved performance while minimizing manufacturing costs, all important criteria for these practices to be accepted in industry.”
J. Wu, R. Powell, A. Hermetet, C. Shue and S. Gangel, “Total Noise Analysis of a Directional Drill,” NoiseCON-16, Providence, Rhode Island, USA, June 13-15, 2016.