Added Mass of Sphere Starting Upward Near Floor

by Wallis S. Hamilton, (F.ASCE), Prof. of Civ. Engrg.; Northwestern Univ., Evanston, Ill.,
Gerald L. Courtney, Soils Engr.; Nevada Testing Lab., Las Vegas, Nev.,

Serial Information: Journal of the Engineering Mechanics Division, 1977, Vol. 103, Issue 1, Pg. 79-97

Document Type: Journal Paper


A method for suddenly releasing a buoyant sphere under water and measuring its acceleration was used to get experimental added-mass coefficients a short time after release. To show the effect of a plane boundary, the sphere was released zero to six diameters above a rigid floor. By definition the fluid force on an accelerating object may be divided into two parts — that due to viscosity and that which would occur if the fluid had no viscosity. A work-energy method applied to the boundary layers developing on the sphere and floor gave the viscous force at the instant the acceleration was measured. When this was subtracted from the known total force, the resulting experimental added-mass coefficients ranged from 0.83 (sphere very close to floor) to 0.50 (six diameters away). For the same set of starting positions, potential flow calculations gave coefficients from 0.8030 to 0.5000.

Subject Headings: Spheres | Floors | Viscosity | Buoyancy | Domain boundary | Terminology and definition | Boundary layers | Professional societies

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