Unsteady forces on spheres during free-surface water entry
We present a study of the forces during free-surface water entry of spheres of varying masses, diameters, and surface treatments. Previous studies have shown that the formation of a subsurface air cavity by a falling sphere is conditional upon impact speed and surface treatment. This study focuses o...
| Main Authors: | , , |
|---|---|
| Other Authors: | |
| Format: | Article |
| Language: | en_US |
| Published: |
Cambridge University Press
2013
|
| Online Access: | http://hdl.handle.net/1721.1/80816 https://orcid.org/0000-0003-3223-7400 |
| _version_ | 1826202961910431744 |
|---|---|
| author | Truscott, Tadd T. Epps, Brenden P. Techet, Alexandra H. |
| author2 | Massachusetts Institute of Technology. Department of Mechanical Engineering |
| author_facet | Massachusetts Institute of Technology. Department of Mechanical Engineering Truscott, Tadd T. Epps, Brenden P. Techet, Alexandra H. |
| author_sort | Truscott, Tadd T. |
| collection | MIT |
| description | We present a study of the forces during free-surface water entry of spheres of varying masses, diameters, and surface treatments. Previous studies have shown that the formation of a subsurface air cavity by a falling sphere is conditional upon impact speed and surface treatment. This study focuses on the forces experienced by the sphere in both cavity-forming and non-cavity-forming cases. Unsteady force estimates require accurate determination of the deceleration for both high and low mass ratios, especially as inertial and hydrodynamic effects approach equality. Using high-speed imaging, high-speed particle image velocimetry, and numerical simulation, we examine the nature of the forces in each case. The effect of mass ratio is shown, where a lighter sphere undergoes larger decelerations and more dramatic trajectory changes. In the non-cavity-forming cases, the forces are modulated by the growth and shedding of a strong, ring-like vortex structure. In the cavity-forming cases, little vorticity is shed by the sphere, and the forces are modulated by the unsteady pressure required for the opening and closing of the air cavity. A data-driven boundary-element-type method is developed to accurately describe the unsteady forces using cavity shape data from experiments. |
| first_indexed | 2024-09-23T12:28:37Z |
| format | Article |
| id | mit-1721.1/80816 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T12:28:37Z |
| publishDate | 2013 |
| publisher | Cambridge University Press |
| record_format | dspace |
| spelling | mit-1721.1/808162022-09-28T08:04:42Z Unsteady forces on spheres during free-surface water entry Truscott, Tadd T. Epps, Brenden P. Techet, Alexandra H. Massachusetts Institute of Technology. Department of Mechanical Engineering Epps, Brenden P. Techet, Alexandra H. We present a study of the forces during free-surface water entry of spheres of varying masses, diameters, and surface treatments. Previous studies have shown that the formation of a subsurface air cavity by a falling sphere is conditional upon impact speed and surface treatment. This study focuses on the forces experienced by the sphere in both cavity-forming and non-cavity-forming cases. Unsteady force estimates require accurate determination of the deceleration for both high and low mass ratios, especially as inertial and hydrodynamic effects approach equality. Using high-speed imaging, high-speed particle image velocimetry, and numerical simulation, we examine the nature of the forces in each case. The effect of mass ratio is shown, where a lighter sphere undergoes larger decelerations and more dramatic trajectory changes. In the non-cavity-forming cases, the forces are modulated by the growth and shedding of a strong, ring-like vortex structure. In the cavity-forming cases, little vorticity is shed by the sphere, and the forces are modulated by the unsteady pressure required for the opening and closing of the air cavity. A data-driven boundary-element-type method is developed to accurately describe the unsteady forces using cavity shape data from experiments. United States. Office of Naval Research (Laboratory Initiative Grant N00014-06-1-0445) 2013-09-20T12:03:29Z 2013-09-20T12:03:29Z 2012-07 2011-04 Article http://purl.org/eprint/type/JournalArticle 0022-1120 1469-7645 http://hdl.handle.net/1721.1/80816 Truscott, Tadd T., Brenden P. Epps, and Alexandra H. Techet. Unsteady Forces on Spheres During Free-surface Water Entry. Journal of Fluid Mechanics 704 (August 2, 2012): 173-210. © Cambridge University Press 2012 https://orcid.org/0000-0003-3223-7400 en_US http://dx.doi.org/10.1017/jfm.2012.232 Journal of Fluid Mechanics Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf Cambridge University Press MIT web domain |
| spellingShingle | Truscott, Tadd T. Epps, Brenden P. Techet, Alexandra H. Unsteady forces on spheres during free-surface water entry |
| title | Unsteady forces on spheres during free-surface water entry |
| title_full | Unsteady forces on spheres during free-surface water entry |
| title_fullStr | Unsteady forces on spheres during free-surface water entry |
| title_full_unstemmed | Unsteady forces on spheres during free-surface water entry |
| title_short | Unsteady forces on spheres during free-surface water entry |
| title_sort | unsteady forces on spheres during free surface water entry |
| url | http://hdl.handle.net/1721.1/80816 https://orcid.org/0000-0003-3223-7400 |
| work_keys_str_mv | AT truscotttaddt unsteadyforcesonspheresduringfreesurfacewaterentry AT eppsbrendenp unsteadyforcesonspheresduringfreesurfacewaterentry AT techetalexandrah unsteadyforcesonspheresduringfreesurfacewaterentry |