Added Mass and Damping of Oscillating Bodies: a fully viscous numerical approach

By LUCA BONFIGLIO, STEFANO BRIZZOLARA and CHRYSSOSTOMOS CHRYSSOSTOMIDIS

Abstract: The prediction of the motion of a ship, as a rigid body, advancing in waves is classical problem in naval architecture. The vast majority of numerical approaches calculates the forces acting on the ship hull by considering an inviscid and irrotational fluid. Unfortunately, especially for motions in the transverse plane as roll or sway, and

for particular ship hulls, viscous effect are absolutely non-negligible. The paper presents a first step toward a development of a seakeeping solution method based on fully viscous solvers to evaluate the radiation forces on the hull and hence the hydrodynamic coefficients of damping and added mass appearing in the generalized equation of motion. For the scope, the direct numerical solver of Navier Stokes equations, based on finite volume technique, is implemented and applied to the case of forced oscillation of 2D simple bodies, using the open-source libraries of OpenFOAM. The improvement against traditional potential flow based theories is evident, but in particular cases some improvements need to be done yet

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http://www.wseas.us/e-library/conferences/2012/CambridgeUSA/FLUHMABE/FLUHMABE-33.pdf

Dear Sir,

Thank you for suggestion. 

Lets assume that we conducted a vertical motion experiment in regular waves or performed 3D Cfd analysis and we have gotten harmonic forces, displacements, velocities, accelerations and all the phase lags between force and motion. The question is that how can i determine the all coefficients (like a33, a55, b33, b55 a35... so on) in linear mathematical model by using forementioned information. The answer is probably Kalman filter, but is there anyone has an application experience?

Best regards.

Normally you do two seperate experiments:

One with the ship fixed and incoming regular waves to determine the forces

One with ship oscillating in still water to determine frequency dependant added mass and damping

Viscous damping for roll and sway are more problematic, cfd could help, but it will normally be a frequency indepent damping.

Attached paper contains some references to the classic papers on frequency domain modelling of ship behavior

Conference Paper Validating the Coupling of Multibody Dynamic Simulations Wit...

Thank you Stephan. Although i didn't get my answer, the paper you recommended is very very beneficial.

Cheers.