Accession Number : ADA092475


Title :   Time-Domain Method for Computing Forces and Moments Acting on Three Dimensional Surface-Piercing Ship Hulls with Forward Speed.


Descriptive Note : Final rept. 15 Dec 77-30 Sep 80,


Corporate Author : SCIENCE APPLICATIONS INC LA JOLLA CA


Personal Author(s) : Chapman,Richard B


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a092475.pdf


Report Date : Sep 1980


Pagination or Media Count : 40


Abstract : A time-domain simulation method for computing forces and moments acting on an arbitrary surface-piercing three-dimensional ship hull is presented. Arbitrary motions can be prescribed and are assumed to be sufficiently small so that the linearized method is valid. Forward speed effects are included under the assumption that the disturbance generated by forward motion is also small and interactions with the flow generated by the prescribed motions are of second order. The hull is represented by a set of quadrilateral surface panels in a body-fixed system, while the free surface is represented by its spectral coordinates in a space-fixed rectangular system. Small time steps are used to advance the flow. This time-domain computation can also be applied to compute linearized seakeeping responses in the frequency domain. For each degree of freedom, a unit step function is applied to the velocity. The resulting impulsive forces and moments and the computed time histories of these forces and moments after the step in velocity can then be combined to compute the added mass and damping forces and moments in the frequency domain. Wave-excited forces can be computed by similar method. As a check on the computer program, the added mass and damping of a semi-submerged sphere oscillating in heave were computed numerically. The results show good agreement with analytic mass and damping coefficients for a fairly coarse representation of the hull and free surface. (Author)


Descriptors :   *FINITE ELEMENT ANALYSIS , *MARINE ENGINEERING , *SHIP HULLS , VELOCITY , COMPUTERIZED SIMULATION , COMPUTATIONS , MASS , SHIP MOTION , NUMERICAL ANALYSIS , DAMPING , MOTION , MOMENTS , THREE DIMENSIONAL , RESPONSE , COEFFICIENTS , COORDINATES , LINEARITY , DYNAMIC LOADS , SEAKEEPING , HYDRODYNAMICS , SEMISUBMERGED


Subject Categories : Numerical Mathematics
      Marine Engineering


Distribution Statement : APPROVED FOR PUBLIC RELEASE