Open Access Repository

Determination of motion characteristics of a floating body with respect to the variations in degrees of freedom: an analytical study

Das, SK, Das, SN and Sahoo, PK 2008 , 'Determination of motion characteristics of a floating body with respect to the variations in degrees of freedom: an analytical study' , Ships and Offshore Structures, vol. 3, no. 3 , pp. 255-262 , doi:

[img] PDF
SAOS-196-final...pdf | Request a copy
Full text restricted


The paper investigates the motion response of a floating body under the action of small amplitude regular waves and
determines the influence of uncoupled as well as coupled systems through an analytical approach. The governing equations
of motion describing the overall balance between the wave-exciting force with the linear form of inertial, damping and
restoring forces are transformed into frequency domain by applying Laplace transform technique. The closed-form solution
is sought for three specific cases: (i) Case I: when only the roll motion is considered, (ii) Case II: when coupled roll and yaw
motions are considered and (iii) Case III: when coupled sway, roll and yaw are considered. To get an insight, we consider
a floating body of displacement 19,190 tonnes under the action of beam waves with wave frequencies 0.56 and 0.74 rad/s.
The analytical result indicates that roll amplitude increases with the increase of vessel speed for the case of single degree
of freedom. All three motions show harmonic behaviour and attain dynamic equilibrium for time t > 100 s. Model result
indicates that the reduction in degrees of freedom enhances phase lag and exhibits artificial increase in amplitude for roll.
The importance of this study lies in terms of obtaining closed-form solution for a linear system while evaluating damping
factor and critical encountering frequency for uncoupled and coupled motions.

Item Type: Article
Authors/Creators:Das, SK and Das, SN and Sahoo, PK
Keywords: sway; roll; yaw; restoring force; Froude-Kryloff force; Laplace transform
Journal or Publication Title: Ships and Offshore Structures
ISSN: 1744-5302
DOI / ID Number:
Additional Information:

The definitive version is available online at

Item Statistics: View statistics for this item

Actions (login required)

Item Control Page Item Control Page