The lively discussion that followed Dr Lotz's presentation focused primarily on wheel/rail rolling noise: mechanisms for noise generation, the relative importance of the wheel and the rail as sources of noise, means for control of the noise, etc. The report paraphrases, as faithfully as possible, the comments of all participants. The writer's opinions are confined to a brief section at the end.
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DISCUSSION R. Lotz (U.S. Department of Transportation (U.S. DOT)) opened the discussion by stating he hoped to provoke discussion with a number of questions such as the following.
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Does anyone have an explanation for the very low noise levels measured by Bender and Hecklt on the Berlin U-Bahn at grade? 2. How quiet can a rail system be? Is there a lower limit to the noise? 3. How closely can you expect to estimate train noise from data on another system? B. Hemsworth (British Rail (BR)) described a number of measurements performed by BR that showed that rail vibration alone could not account for the wayside noise observed during passage of a train on welded rail. These data, he claimed, showed the rail to be an insignificant source of rolling noise.
C. Stanworth (BR) described an SNCF (French National Railways) experiment that compared the noise produced by similar rolling stock when equipped with solid webbed wheels and spoked wheels. There was no difference in the noise levels produced by the rolling stock when equipped with each of the two types of wheels. These tests indicate either that spoked wheels are an ineffective means for reducing noise from the wheel or that the wheel itself is an insignificanfsource of noise.
Stanworth went on to describe additional tests performed by the SNCF with a coach on a roller test bed. The wheels were spun by the rollers, and noise was measured as the wheels were progressively screened. The tests indicated that most of the noise was coming from near the point of contact between the wheel and the roller.
B. Hemsworth (BR) reported data that showed that peaks can be discerned in the wayside noise spectra from the passage of BR trains. These peaks occur at frequencies that can be associated with the resonant frequencies of BR wheels. These observations indicate that the wheel may be a significant contributor to rolling noise, at least on BR rolling stock. P. J. Remington (Bolt Beranek and Newman Inc. (BBN)) reviewed briefly the work performed by BBN for the U.S. DOT on the mechanisms for the generation of wheel/rail rolling t E. K. Bender and M