nominally

ironman2012

Senior Member
Hi,

Guidance magnets located on both sides along the entire length of the vehicle keep the vehicle laterally on the track. Electronic systems guarantee that the clearance remains constant (nominally 10 mm).

(This comes from an article about Principle of Maglev and I didn't find its origin. Here is a Chinese website about it.)

Does "nominally" here mean "so-called"?

• ScalloperFan

New Member
Nominally generally implies that the value is the official measurement, but not always would be in reality. So here, perhaps guidelines enforce a 10mm clearance, but it varies.

Packard

Senior Member
You can buy certain products with a "nominal" dimension which will differ from the "actual" dimensions.

Lumber is classic. 2" x 4" lumber (nominal) has an actual dimension of 1½" x 3½".

For lumber, they measure the wood while it is "wet" and then they put it in a kiln to dry it and it shrinks. It is sort of like the quarter pound hamburgers (pre-cooked weight). The burger you eat is much smaller.

They are "calling" this dimension "10mm" but the actual measured dimension will be more or less.

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AnythingGoes

Senior Member
In this context, the nominal measurement is the mean clearance. It will vary from 10 cm by some amount, but the mean of a large enough set of repeated measurements will be 10 cm.

manfy

Senior Member
In this context, the nominal measurement is the mean clearance. It will vary from 10 cm by some amount, but the mean of a large enough set of repeated measurements will be 10 cm.
Right -- but that's only the "static" clearance based on manufacturing and assembly tolerances.

On top of that you have the potential change in clearance when the train is in operation. I suppose there will be immense lateral forces when a 30 ton carriage goes around bends with a speed of 500 km/h. That's a lot of kinetic energy trying to resist a change of direction!
Since the carriages are floating in a magnetic field - vertically and horizontally - the electronic control system will change the current, thus the strength of the magnetic field, of those magnets to counteract those lateral and centrifugal forces and to ensure that the train stays away from the guide rail to avoid collision with the magnets on the carriage. The overall clearance, i.e. static and dynamic clearance, between magnets and guide rails is designed to be 10mm - the nominal or targeted clearance.

AnythingGoes

Senior Member
I see I misread the OP. It's 10 mm, not cm.

Anyway, the way I read it, 10 mm is the intended clearance while operating. Lateral forces will change it, but it has to remain greater than 0 mm.

kentix

Senior Member
Yes, the targeted, ideal clearance is 10 mm. While the train is in operation the actual number will vary based on the exact current conditions, but the control system always tries to return it to the 10 mm clearance that it's designed to operate at under ideal conditions.

How far it can vary from 10 mm without causing problems the passage doesn't say. Maybe it can go as low as 7 or 5 or 3 or maybe only to 9. This passage doesn't tell us.

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Packard

Senior Member
The image helps me understand clearance issue.

manfy

Senior Member
Anyway, the way I read it, 10 mm is the intended clearance while operating. Lateral forces will change it, but it has to remain greater than 0 mm.
10 mm is impressively small for a structure that may be hundreds of kilometres long, especially considering thermal expansion/contraction and ground movement.
I certainly wouldn't want to be on a Maglev train when an earthquake hits, not even a minor one!

Packard

Senior Member
It is advertised as "frictionless" travel. So "0 mm" would doubtless involve friction.