1 2 3 4 5

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A v a l a n c h e

D y n a m i c s

a n d

D e f e n ce

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the head-tailstructure is formed.However, thesystem size
Froude numbers forGBavalanches on 20mlong slopes
and PP avalanches on 2 m long slopes are about 1 and 10
respectively. Therefore,the head-tail structure can not be
formed yet on the slopes used in these experiments.

  1. CONCLUSIONS

    From a theoretical analysis, we found that the similarity of
    the head-tail structure relatestothe chutelength L,the
    acceleration of gravityg and the terminal velocity of the

granularavalancheon thechuteVethroughadimensionless

numberVe2 / Lg(a system size Froude number). WhenV2 /
Lg<< 1,the head-tail structure is formed.This conditione
correspondstoavalanchemotionthatisalmoststeady;
therefore,alightgranularmaterial,oralongchuteis
favorablefortheformationofthehead-tailstructure
becausealightgranularavalanchehasalowterminal
velocity.This means that a light granular material such as
styrenefoamparticlesisgoodformodelexperimentsof
avalanches on a reducedscale.REFERENCES
Hutter,K.andY.Nohguchi.1990.Similaritysolutions fora
Voellmymodelofsnowavalancheswithfinitemass.Acta
Mechanica82 , 99-127.

Ko sugi,K.,A.Sato ,O.A b e,Y.N ohguchi,Y.Yam ada,
K.Nishimura and K.Izumi (1995). Table tennis ball avalanche
experiments.ISSW'94Proceedings,636-642.

Nohguchi, Y., K. Hutter and S. B. Savage. 1989. Similarity so-
lutionsforgranularavalanchesof finite mass withvariable
bedfriction.ContinuumMechanics andThermodynamics1 ,
239-265.

Nishimura, K., Y. Nohguchi, Y. Ito and K. Kosugi. 1996. Snow
avalancheexperiments at ski jump.SubmittedtoISSW'96.

Sav age,S.B.and Y.Nohguchi.1988. Similaritysolutions for
avalanchesofgranularmaterialsdowncurvedbeds.Acta
Mechanica75 , 153-174.


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