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For high-speed trains, the dominant noise source is aerodynamic noise, so underframe noise protection is insufficient. On conventional lines, you would need to empty the bottom corner of the loading gauge, which includes stuff like safety equipment, walkways (in particular in tunnels) and simple platforms on un-refurbished stations.

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Mon Oct 1st, 2012 at 04:31:24 PM EST
[ Parent ]
Two further notes on shrouds covering the running gear.

Such shrouds a long history running back to the streamlined steam locos of the 1930s. But historically, the shrouds have been removed more often than not for a reason unrelated to aerodynamics and noise: accessibility for maintenance.

The second issue is that even for high-speed trains where the maintenance difficulty may be an acceptable trade-off, the limitation is that parts of the bogie can protrude beyond the outer envelope of the carbody in curves. If the bogie shroud has to bump out significantly, then it will be a noise source itself. Of course, for normal-gauge vehicles, protruding bogie parts in curves are more likely the narrower the carbody, thus it is easier to design a bogie-shrouded high-speed train for Japan or China than continental Europe, and it is virtually impossible for Britain.

Now for some real-world examples:

  • A number of newer full-width Shinkensen types have end bogie shrouds (Series 500, Series 700, Series 800), and the two newest also partial (N700 Series) or complete (E5 Series) shrouds on the rest of the bogies. The narrower E6 Series has full bogie shrouds too, but unlike those of the E6, they protrude compared to the rest of the underframe.
  • China's CRH380A (developed on the basis of the E2 Series Shinkansen) and CRH380B (based on the Siemens Velaro) have rounded semi-shrouds on all bogies (covering the top and the outer end of the wheels only). In contrast, the narrower 500+km/h test train, which is based on the CRH380A, has a wider cut-out and some bogie parts protruding even on straight track.
  • The Bombardier Zefiro 380 (which shall run in China as CRH380D) have been originally designed (when 380 km/h was the goal) with complete bogie shrouds that protrude slightly, but now receive a partial shroud covering most of the wheels (but leaving the yaw damper accessible).
  • The Frecciarossa 1000 are to receive near-complete but protruding shrouds on the end bogies (also see the photo of the mock-up in the diary).
  • Alstom AGVs (like NTV's .Italos) have partial covers for the end bogies, which protrude, but are interesting for being an integral part of the aerodynamic design.
  • The other Spanish maker, CAF, is testing its new Oaris high-speed train. Like the Zefiro 380, this had first designs with complete shrouds on end bogies, but the prototype has only a partial shroud on photos shot during testing.


*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Mon Oct 1st, 2012 at 05:43:15 PM EST
[ Parent ]
Thank you very much; very informative!

I suppose the one good thing about all this--from the U.S. viewpoint--is that there appears to be a "last mover" advantage. Given that we have no high speed rail at all, and are building it from scratch, complications like this can be handled more easily..

by asdf on Mon Oct 1st, 2012 at 07:57:29 PM EST
[ Parent ]
Since US systems are to be connected to the existing conventional network, too, existing loading gauges should be the determining factor, again. However, those are closer in width to the Shinkansen and Chinese loading gauges, so an E5-Series-ish look is possible.

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Tue Oct 2nd, 2012 at 05:54:10 AM EST
[ Parent ]

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