frottement de peau

English translation: grain shear stress or grain resistance

GLOSSARY ENTRY (DERIVED FROM QUESTION BELOW)
French term or phrase:frottement de peau
English translation:grain shear stress or grain resistance
Entered by: Duncan Moncrieff

13:41 Oct 14, 2014
French to English translations [PRO]
Geology
French term or phrase: frottement de peau
The paper is about sub-marine sediments, could this be surface tension? Here's the sentence:
La formule a été adaptée pour être exprimée directement en fonction de la contrainte de frottement de peau:
It is also mentioned here:
(symbol) = la contrainte de frottement de peau en N.m-2
Anna White
United Kingdom
Local time: 17:00
grain shear stress or grain resistance
Explanation:
"Frottement de peau/frottement total :
La contrainte de frottement τ0 est classiquement décomposée en :
τ0= τ' + τ'’
avec :
. τ' : la composante du frottement de peau, qui représente le cisaillement local,
. τ'' : la composante du frottement de forme, qui représente l’effet des forces de pression, intégrées le long des formes de fond.

Seule la composante locale τ', ou contrainte effective, intervient dans le calcul des forces exercées par l’écoulement sur les grains et doit être prise en compte dans le calcul du transport solide.
L’importance relative de chacune des deux composantes dépend du régime de l’écoulement. Pour des faibles valeurs du courant, en deça du seuil de mobilité des particules, le fond est généralement plat. Lorsque le courant augmente, il y mise en mouvement des particules sédimentaires, et formation de rides de petites amplitudes puis de dunes. En présence de rides ou de dunes la composante principale du frottement est τ'', comme le montre la figure 1. "
(http://crdaln.documentation.developpement-durable.gouv.fr/do...

"La contrainte de frottement (τ0) dans un chenal possédant des formes de lit et des sédiments en suspension est déterminée par la somme de trois composantes :

τ' – la force tractrice due à la résistance des particules, ce qui représente le cisaillement local,
τ'' - la force tractrice due à la résistance provoquée par les formes du lit; elle représente l’effet des forces de pression intégrées le long des formes de fond. Elle est causée par la différence de pression entre les parties amont et aval de la dune, lesquelles provoquent une perte d’énergie de l’écoulement.
τ''' – c’est la composante associée à l’énergie dépensée pour maintenir les particules en suspension (Yalin, 1972) (Figure 73)." (http://theses.univ-lyon2.fr/documents/getpart.php?id=lyon2.2...

"Total bed shear stress τ is often divided into grain shear stress τ ,and bedform shear stress τ (Einstein and Barbarossa, 1952; Simons and Senturk, 1992; Richardson et al, 1990; Julien, 1995)." (http://www.engr.colostate.edu/~pierre/ce_old/resume/Paperspd...

"Initial experiments were conducted in a flat-bottomed flume with pebbles (median diameter slightly below 20 mm), with a view to test the validity of the methods which permit differentiation between shear stress due to grain resistance (τ″) and that due to bedform resistance (τ″). It is clearly confirmed that τ′ represents the total shear stress (τ). The method of Laursen (1958) is appropriate for evaluation of grain shear stress in the case of pebbly beds. Indeed the ratio τ′ is close to 1, except when the dimensionless flow depth (d/D50) is less than 4. A close relationship exists between the grain shear stress and the shear calculated from friction velocities." (http://onlinelibrary.wiley.com/doi/10.1002/esp.3290140606/ab...

See also:
http://sodbib.udl.es/gtb/sod/usu/$UDLG/repositorio/20340688_14707534.pdf
http://orbi.ulg.ac.be/bitstream/2268/21798/1/Geomorphology 2...
Selected response from:

Duncan Moncrieff
France
Local time: 18:00
Grading comment
Thanks for your time on this, its much appreciated.
4 KudoZ points were awarded for this answer



Summary of answers provided
5 +1skin friction
kashew
4 +2grain shear stress or grain resistance
Duncan Moncrieff
5 -2Surface tension
TommyBGoode
Summary of reference entries provided
Fluid mechanics
Anca Florescu-Mitchell

Discussion entries: 9





  

Answers


35 mins   confidence: Answerer confidence 5/5 peer agreement (net): -2
Surface tension


Explanation:
This is in reference to the forces at work. Where gravity has little effects, surface tension is the the phrase here.
Fluid mechanics is not exactly what the author is talking about here although it is related.

TommyBGoode
United Kingdom
Local time: 17:00
Native speaker of: Native in EnglishEnglish

Peer comments on this answer (and responses from the answerer)
disagree  chris collister: Surface tension is "tension superficielle": http://fr.wikipedia.org/wiki/Tension_superficielle
25 mins

disagree  Duncan Moncrieff: Right kind of idea, but it's not to do with surface tension, it's to do with grain transport.
3 hrs
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3 hrs   confidence: Answerer confidence 4/5Answerer confidence 4/5 peer agreement (net): +2
grain shear stress or grain resistance


Explanation:
"Frottement de peau/frottement total :
La contrainte de frottement τ0 est classiquement décomposée en :
τ0= τ' + τ'’
avec :
. τ' : la composante du frottement de peau, qui représente le cisaillement local,
. τ'' : la composante du frottement de forme, qui représente l’effet des forces de pression, intégrées le long des formes de fond.

Seule la composante locale τ', ou contrainte effective, intervient dans le calcul des forces exercées par l’écoulement sur les grains et doit être prise en compte dans le calcul du transport solide.
L’importance relative de chacune des deux composantes dépend du régime de l’écoulement. Pour des faibles valeurs du courant, en deça du seuil de mobilité des particules, le fond est généralement plat. Lorsque le courant augmente, il y mise en mouvement des particules sédimentaires, et formation de rides de petites amplitudes puis de dunes. En présence de rides ou de dunes la composante principale du frottement est τ'', comme le montre la figure 1. "
(http://crdaln.documentation.developpement-durable.gouv.fr/do...

"La contrainte de frottement (τ0) dans un chenal possédant des formes de lit et des sédiments en suspension est déterminée par la somme de trois composantes :

τ' – la force tractrice due à la résistance des particules, ce qui représente le cisaillement local,
τ'' - la force tractrice due à la résistance provoquée par les formes du lit; elle représente l’effet des forces de pression intégrées le long des formes de fond. Elle est causée par la différence de pression entre les parties amont et aval de la dune, lesquelles provoquent une perte d’énergie de l’écoulement.
τ''' – c’est la composante associée à l’énergie dépensée pour maintenir les particules en suspension (Yalin, 1972) (Figure 73)." (http://theses.univ-lyon2.fr/documents/getpart.php?id=lyon2.2...

"Total bed shear stress τ is often divided into grain shear stress τ ,and bedform shear stress τ (Einstein and Barbarossa, 1952; Simons and Senturk, 1992; Richardson et al, 1990; Julien, 1995)." (http://www.engr.colostate.edu/~pierre/ce_old/resume/Paperspd...

"Initial experiments were conducted in a flat-bottomed flume with pebbles (median diameter slightly below 20 mm), with a view to test the validity of the methods which permit differentiation between shear stress due to grain resistance (τ″) and that due to bedform resistance (τ″). It is clearly confirmed that τ′ represents the total shear stress (τ). The method of Laursen (1958) is appropriate for evaluation of grain shear stress in the case of pebbly beds. Indeed the ratio τ′ is close to 1, except when the dimensionless flow depth (d/D50) is less than 4. A close relationship exists between the grain shear stress and the shear calculated from friction velocities." (http://onlinelibrary.wiley.com/doi/10.1002/esp.3290140606/ab...

See also:
http://sodbib.udl.es/gtb/sod/usu/$UDLG/repositorio/20340688_14707534.pdf
http://orbi.ulg.ac.be/bitstream/2268/21798/1/Geomorphology 2...

Duncan Moncrieff
France
Local time: 18:00
Specializes in field
Native speaker of: Native in EnglishEnglish
PRO pts in category: 8
Grading comment
Thanks for your time on this, its much appreciated.

Peer comments on this answer (and responses from the answerer)
agree  merlrennes: The units are Force/area thus it is a tangential (shear) stress.
2 hrs

agree  Anca Florescu-Mitchell
2 hrs
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5 mins   confidence: Answerer confidence 5/5 peer agreement (net): +1
skin friction


Explanation:
*

--------------------------------------------------
Note added at 6 heures (2014-10-14 19:54:10 GMT)
--------------------------------------------------

http://archimer.ifremer.fr/doc/2006/publication-6306.pdf
See Résumé/Abstract.

kashew
France
Local time: 18:00
Native speaker of: Native in EnglishEnglish
PRO pts in category: 47
Notes to answerer
Asker: Many thanks for your time on this question, both explanations make sense to me so not easy!


Peer comments on this answer (and responses from the answerer)
agree  chris collister
55 mins
  -> Thanks, CC.

agree  Duncan Moncrieff: Sorry Kashew, nothing to do with skin : have a look at the refs in my answer and I think you'll agree with me./ Well, it'd help if you post your refs when you answer! Having read the article and researched the whole term, I agree with you term as well.
3 hrs
  -> I can't agree. See MY references too.

disagree  merlrennes: Skin friction is a force (measured in Newtons (N)). The term requested is "contrainte de frottement de peau". This is what is known as a stress, measured in Newtons/square metre (N/m2). It is similar to the pressure force (N) as opposed to pressure (N/m2)
17 hrs
  -> Terme ou expression en français : frottement de peau. Of course, in the context it has to be qualified.
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Reference comments


13 mins
Reference: Fluid mechanics

Reference information:
http://www.roymech.co.uk/Related/Fluids/Fluids_Drag.html

Anca Florescu-Mitchell
France
Native speaker of: Native in FrenchFrench, Native in EnglishEnglish
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