Corrugations

Submitted: Wednesday, Jun 25, 2003 at 22:39
ThreadID: 5659 Views:1353 Replies:7 FollowUps:0
This Thread has been Archived
Thought this explanation might make you feel better next time you replace the shocks.
There's much more to the story if you want more.

Quote:
An early attempt at explaining road corrugation is due to Relton [4],
who proposed that the underlying instability mechanism is a “relaxation
oscillation,” caused essentially by stick-slip dynamics. According to this
view, a moving wheel pushes grains ahead of it. The grains pile up in front
of the wheel and form a heap. When the heap grows large enough, the
wheel sticks momentarily, and then slips, running over the heap and leaving
it behind as a ridge. For a given uniform speed, this stick-slip process will
be fairly periodic, and so will generate equidistant ridges.

A di erent picture was provided by Mather [2], who argued that the origin
of the road instability is the bouncing motion of the wheel, caused by random
irregularities on the ground. When the bouncing occurs, the car is projected
upward along a certain angle and is airborne for a brief time. When it then
strikes the ground, the car creates a crater and the motion then repeats
itself. According to this picture, it is not the piling up of grains ahead of
the vehicle that is responsible for the instability, but the impact stress of the
vehicle on the ground. The wavelength of the resulting corrugations will be
determined by the competition between the typical distance the car flies over
the ground and the size of the crater generated by the impact stress, which
should in turn depend on the hardness of the ground and the relaxation time
of the ejected grains. Mather’s picture is similar to other surface instabilities
involving granular materials, in particular the ripple patterns in wind blown
sand [5, 6, 7, 8], where ejected grains are carried away by the wind and
land in a place far from the ejection point. In such a nonlocal model, what
sets the wavelength of the ripple is the ratio of the flux of the grains to the
appropriately scaled saltation length, i.e., the distance that an ejected grain
is carried by the wind.

Credits to Booth & Hong of Lehigh University PennsylvaniaCarpe Diem
Back Expand Un-Read 0 Moderator

Reply By: Member - Trevor - Wednesday, Jun 25, 2003 at 22:42

Wednesday, Jun 25, 2003 at 22:42
These explanations are a bit rough
AnswerID: 23526

Reply By: bruce.h (WA) - Wednesday, Jun 25, 2003 at 23:17

Wednesday, Jun 25, 2003 at 23:17
actualy ithought that they were caused by the same action that causes both waves on the ocean & sand dunes. which is combination of wind against surface tension taking into acount the gravitaional pull of the earth ,basicly the wind blows across the surface of the ground picking up sand as it goes & a combination of surface tension ,friction & gravity brings tham back down to earth creating small mounds which are exasipated by the inificant or warn shock absorbers of the vehcles that pass over the mounds
at least thats my theory
regards Bruce
AnswerID: 23529

Reply By: Member - Bob - Thursday, Jun 26, 2003 at 10:06

Thursday, Jun 26, 2003 at 10:06
My gut feeling was that it was a combination of the two effects. The bounce effect breaks up the surface in the hollow between the ridges and the rolling wheel then pushes that material forward to build up the ridge. Things like acceleration and braking increase the breakup of the hollows which would explain why corrugations sometimes seem worse near bends.
AnswerID: 23550

Reply By: phil - Thursday, Jun 26, 2003 at 10:16

Thursday, Jun 26, 2003 at 10:16
A book I was reading about the early days of transport in WA, around Carnarvon, made the comment that corrugations only started when baloon tyres replaced the narrow high pressure types.
There may be a clue there.
Phil
AnswerID: 23552

Reply By: Glenno - Thursday, Jun 26, 2003 at 22:15

Thursday, Jun 26, 2003 at 22:15
Dr Karl from Triple J / ABC has written a few articles on the subject. (See the green box on this web page below)

www.abc.net.au/science/k2/

Last time i read it i think he said it is / was one of the great unsolved mysteries.

Cheers,

Glenn.
AnswerID: 23601

Reply By: Slammin - Thursday, Jun 26, 2003 at 23:16

Thursday, Jun 26, 2003 at 23:16
A road engineer told me it was the soft layer on top being elongated by the weight of a vehicle passing over it and then trying resuming its normal state albeit with creases.
BUT remember that in most places I have seen, the corrugation covers the entire width of the road and is of similar construction for traffic in ether direction, I have also noticed that the shoulders get the same sand dune effect but the dune is smaller and closer together, I have also seen a newly graded road corrugated after strong winds and last but not least when our prevailing winds change direction the corrugations will lessen if the wind is strong.
As with everything - probably a bit of each theory as nothing in the universe is independent of any cause or reaction.
Solution - go faster!!!!!!!!!
AnswerID: 23611

Reply By: Member - Wherethehellawi - Monday, Jun 30, 2003 at 11:52

Monday, Jun 30, 2003 at 11:52
TFH (Too f$#%ing hard) to fathomRichard
AnswerID: 23834

Sponsored Links

Popular Products (13)