Fine sand in motion: the influence of interstitial air

T.A.M. Homan

Research output: ThesisPhD Thesis - Research UT, graduation UTAcademic

Abstract

Sand is a granular material, and therefore it consists of individual grains arranged in a packing. The pores in-between the grains are usually filled with a fluid, in this case air. Now, is this interstitial air able to influence the behavior of the sand bed as a whole? When a ball impacts on fine, very loose sand, the interstitial air causes a pronounced change. If the bed is loose enough the ball is able to penetrate the sand and surprisingly, the final depth decreases if there is less air present in-between the grains. While the ball penetrates the bed, sand around the ball is compactified and the air in this region is compressed. Since air needs a finite amount of time to flow away it is temporarily trapped and will locally increase the pressure. If an object moves through the bed very slowly, air has ample time to move out of this compactified region and this quasi-static situation should be similar to that without air. The drag force experienced by the object for very low penetration velocities is indeed equal to the measured force at reduced ambient pressure, and much larger than the force needed to push the ball at higher velocities. The pressurized trapped air around the ball effectively reduces the drag of the sand.
LanguageEnglish
Awarding Institution
  • University of Twente
Supervisors/Advisors
  • van der Meer, Roger M., Supervisor
  • Lohse, Detlef , Advisor
Award date25 Sep 2013
Place of PublicationEnschede
Publisher
Print ISBNs978-90-365-0650-2
DOIs
Publication statusPublished - 25 Sep 2013

Fingerprint

Sand
Air
Drag
Granular materials
Fluids

Keywords

  • METIS-297538
  • IR-87237

Cite this

Homan, T.A.M.. / Fine sand in motion: the influence of interstitial air. Enschede : Universiteit Twente, 2013. 140 p.
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abstract = "Sand is a granular material, and therefore it consists of individual grains arranged in a packing. The pores in-between the grains are usually filled with a fluid, in this case air. Now, is this interstitial air able to influence the behavior of the sand bed as a whole? When a ball impacts on fine, very loose sand, the interstitial air causes a pronounced change. If the bed is loose enough the ball is able to penetrate the sand and surprisingly, the final depth decreases if there is less air present in-between the grains. While the ball penetrates the bed, sand around the ball is compactified and the air in this region is compressed. Since air needs a finite amount of time to flow away it is temporarily trapped and will locally increase the pressure. If an object moves through the bed very slowly, air has ample time to move out of this compactified region and this quasi-static situation should be similar to that without air. The drag force experienced by the object for very low penetration velocities is indeed equal to the measured force at reduced ambient pressure, and much larger than the force needed to push the ball at higher velocities. The pressurized trapped air around the ball effectively reduces the drag of the sand.",
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Fine sand in motion: the influence of interstitial air. / Homan, T.A.M.

Enschede : Universiteit Twente, 2013. 140 p.

Research output: ThesisPhD Thesis - Research UT, graduation UTAcademic

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T1 - Fine sand in motion: the influence of interstitial air

AU - Homan, T.A.M.

PY - 2013/9/25

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N2 - Sand is a granular material, and therefore it consists of individual grains arranged in a packing. The pores in-between the grains are usually filled with a fluid, in this case air. Now, is this interstitial air able to influence the behavior of the sand bed as a whole? When a ball impacts on fine, very loose sand, the interstitial air causes a pronounced change. If the bed is loose enough the ball is able to penetrate the sand and surprisingly, the final depth decreases if there is less air present in-between the grains. While the ball penetrates the bed, sand around the ball is compactified and the air in this region is compressed. Since air needs a finite amount of time to flow away it is temporarily trapped and will locally increase the pressure. If an object moves through the bed very slowly, air has ample time to move out of this compactified region and this quasi-static situation should be similar to that without air. The drag force experienced by the object for very low penetration velocities is indeed equal to the measured force at reduced ambient pressure, and much larger than the force needed to push the ball at higher velocities. The pressurized trapped air around the ball effectively reduces the drag of the sand.

AB - Sand is a granular material, and therefore it consists of individual grains arranged in a packing. The pores in-between the grains are usually filled with a fluid, in this case air. Now, is this interstitial air able to influence the behavior of the sand bed as a whole? When a ball impacts on fine, very loose sand, the interstitial air causes a pronounced change. If the bed is loose enough the ball is able to penetrate the sand and surprisingly, the final depth decreases if there is less air present in-between the grains. While the ball penetrates the bed, sand around the ball is compactified and the air in this region is compressed. Since air needs a finite amount of time to flow away it is temporarily trapped and will locally increase the pressure. If an object moves through the bed very slowly, air has ample time to move out of this compactified region and this quasi-static situation should be similar to that without air. The drag force experienced by the object for very low penetration velocities is indeed equal to the measured force at reduced ambient pressure, and much larger than the force needed to push the ball at higher velocities. The pressurized trapped air around the ball effectively reduces the drag of the sand.

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