Application of functional analysis to oscillatory ship model testing

1973 ◽  
Vol 332 (1588) ◽  
pp. 37-49 ◽  
Keyword(s):  
Functional Analysis ◽  
Time History ◽  
Model Testing ◽  
Ship Model ◽  
Fluid Forces ◽  
General Acceptance ◽  
History Effects ◽  
Interpretation Of Results

The need for data relating to fluid forces and moments has led to general acceptance of oscillatory testing of ship models. Although the technique is well established, certain problems still attend the interpretation of results. The nature of the difficulties is explained and they are elucidated by making allowance for time history effects, using functional analysis. Allowance for these effects in this way also establishes that certain results which have hitherto been assumed to require nonlinear representations are in fact capable of very accurate linear specification.

Directional stability analysis of a ship allowing for time history effects of the flow

1973 ◽  
Vol 335 (1602) ◽  
pp. 341-354 ◽  
Keyword(s):  
Functional Analysis ◽  
Characteristic Equation ◽  
Time History ◽  
Stability Criteria ◽  
Fluid Forces ◽  
Stability And Control ◽  
Directional Stability ◽  
Characteristic Roots ◽  
History Effects ◽  
And Control

By means of a functional analysis, the assumption of instantaneous fluid forces or (quasisteady flow) may be relaxed. It is shown how time-history effects are incorporated into the hydrodynamic representation to determine the directional stability and control of a ship. A method of analysis is presented which indicates that the characteristic equation describing the directional stability may have more characteristic roots and more stability criteria than that which the usual ‘instantaneous’ theory predicts. By introducing a suitable feedback device this characteristic equation may be suitably modified to give the desired ship response.

On modal analysis of ship strength

1974 ◽  
Vol 341 (1624) ◽  
pp. 121-134 ◽  
Keyword(s):  
Rigid Body ◽  
Structural Dynamics ◽  
Model Test ◽  
Time History ◽  
Body Motion ◽  
Strength Analysis ◽  
Fluid Forces ◽  
History Effects ◽  
Orthogonality Relations ◽  
First Time

An approach is formulated by which structural dynamics of ships may be analysed in a linear modal form. By employing the principal modes of the ship in vacuo , simple orthogonality relations can be retained without dependence on the necessarily approximate techniques used to estimate fluid forces. It is also possible to identify modal contributions to mass, damping and stiffness for the hull and for the hydrodynamic actions separately. Those contributions of hydrodynamic origin may depend significantly on time history effects which can be measured by means of a model test; these effects can be admitted into the ship strength analysis, it is believed for the first time. It is shown how existing modal theories of ship strength and theories of seakeeping (i. e. of ‘rigid body’ motion in a seaway) fit into this more general analysis.

Multiple Resonances, Responses, and Parametric Instabilities in Offshore Structures

1988 ◽  
Vol 32 (04) ◽  
pp. 285-296
Author(s):  
Xiong-Jian Wu ◽  
Yigong Wang ◽  
W. G. Price
Keyword(s):  
Mathematical Model ◽  
Time History ◽  
Offshore Structures ◽  
Offshore Structure ◽  
Fluid Forces ◽  
History Effects ◽  
Free Decay ◽  
Parametric Instabilities ◽  
The Mathematical Model ◽  
Approach Time

Based on a functional analysis approach, time history effects are introduced into the representation of the fluid forces associated with offshore structures operating at shallow draft, shallow submergence and/or having a multihull construction, etc. A general linear theory is developed illustrating the pattern of behavior expected in the structure when performing a free decay motion or a forced motion excited by sinusoidal waves. It is shown that even in a simple one-degree-of-freedom mathematical model describing the behavior of an offshore structure, multiple natural frequencies and resonances may be exhibited in the responses. These features are examined and the investigation extended to assess the possibility of multiple parametric instabilities arising in the motions. For this purpose, the mathematical model is slightly modified to include a specific sinusoidal time-dependent term—as is common in a Mathieu type analysis—and conditions determined allowing motion instabilities to occur. This is confirmed by simple numerical examples.

The uses of functional analysis in ship dynamics

1973 ◽  
Vol 332 (1588) ◽  
pp. 23-35 ◽  
Keyword(s):  
Volterra Series ◽  
Time History ◽  
Slow Motion ◽  
Ship Motions ◽  
Fluid Forces ◽  
Stability And Control ◽  
History Effects ◽  
Planar Motion Mechanism ◽  
Calm Water ◽  
And Control

Generally speaking, linear theory is unsatisfactory for the analysis of ship manoeuvres. The reason for this probably lies in the representation of fluid forces and moments, which are normally specified (on the basis of quasi-steady flow) by ‘slow motion derivatives’. Fluid forces and moments are at best represented only very crudely even though they play a dominant part in ship motions. It is known that time history effects must exist, in that the flow conditions at some instant cannot uniquely determine the flow forces and moments at that instant. Failure to allow for this is probably the major potential source of weakness in most techniques of analysing ship motion. A method is shown by which the effects of time history may be allowed for when specifying fluid force or moment. The specification, which is in terms of a Volterra series, has an approximate linear form. The standing of slow motion derivatives is examined in the light of this improved linear specification. There is no evident major obstacle to the application of the new approach to any of the branches of hydrodynamics conventionally studied in naval architecture, e. g. resistance in waves, use of the planar motion mechanism for model testing, directional stability and control (in calm water or in waves and on the surface or submerged).

Ship Model Testing

2016 ◽  
Author(s):  
Richard A. Royce
Keyword(s):  
Model Testing ◽  
Ship Model

Transient Fluid Forces on a Rigid Circular Cylinder Subjected to Small Amplitude Motions

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Cédric Leblond ◽  
Vincent Melot ◽  
Jean-François Sigrist ◽  
Christian Lainé ◽  
Bruno Auvity ◽  
...  
Keyword(s):  
Circular Cylinder ◽  
Compressible Fluid ◽  
Small Amplitude ◽  
Fluid Model ◽  
The Body ◽  
Analytical Models ◽  
Fluid Forces ◽  
History Effects ◽  
Perturbation Problem ◽  
Dimensional Boundary

The present paper treats the transient fluid forces experienced by a rigid circular cylinder moving along a radial line in a fluid initially at rest. The body is subjected to a rapid displacement of relatively small amplitude in relation to its radius. Both infinite and cylindrically confined fluid domains are considered. Furthermore, non-negligible amplitude motions of the inner cylinder, and viscous and compressible fluid effects are addressed, successively. Different analytical methods and models are used to tackle each of these issues. For motions of non-negligible amplitude of the inner cylinder, a potential flow is assumed and the model, formulated as a two-dimensional boundary perturbation problem, is solved using a regular expansion up to second order. Subsequently, viscous and compressible effects are handled by assuming infinitesimal amplitude motions. The viscous fluid forces are formulated by solving a singular perturbation problem of the first order. Compressible fluid forces are then determined from the wave equation. A nonlinear formulation is obtained for the non-negligible amplitude motion. The viscous and compressible fluid forces, formulated in terms of convolution products, are linked to fluid history effects induced by wave propagation phenomena in the fluid domain. These models are expressed with dimensionless parameters and illustrated for a specific motion imposed on the inner cylinder. The different analytical models permit coverage of a broad range of motions. Hence, for a given geometry and imposed displacement, the appropriate fluid model can be identified and the resulting fluid forces rapidly estimated. The limits of these formulations are also discussed.

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