Ship Res Research Articles

The effect of sloshing on the sway motions of 2D rectangular cylinders in regular waves

In this paper, we investigated the effect of sloshing on the sway motions of two-dimensional rectangular cylinders in regular waves, bearing in mind possible applications for LNG-FPSO and LNG-FSRU. First, we carried out experiments for two models with different drafts, or the same draft but different filling ratios, in which the models were firmly connected to each other. The sway motion was measured with a noncontact video camera. This is an extension of Rognebakke and Faltinsen’s work for a single model (J Ship Res 47(3):208–221, 2003). It was found that the sway motion became small when the incident wave frequency was close to the lowest natural frequency of each model. The sway motion greatly increased when the wave frequency was higher than this frequency. The measured data were compared with numerical results obtained by a single-dominant multi-modal method; relatively good agreement was noted. However, the numerical results deviated from the experimental results near the lowest natural frequency of the smaller model, which was believed to be due to overturning waves, as observed during the experiment. Since this is out of the valid range for the single-dominant multi-modal method, other, more appropriate, methods such as the multi-dominant modal method must be applied instead.

Calculation of linear ship waves

The Sea Wave Pattern Evaluation suite of programs was originally developed to calculate far field wave elevations for thin ships but grew to encompass a raft of other tasks including calculating the complete wave field with velocity components for multihull and submerged vessels, incorporating sinkage and trim, viscous damping and finite depth effects, and measuring wave resistance and viscous resistance. It also led to investigations into waves produced by pressure distributions and planing surfaces. This article traces Sea Wave Pattern Evaluation's development, explains the mechanics of its key components, and refers to some of the results that have been produced by it. References Michell, J. H. The wave resistance of a ship , Phil Mag (5), Vol 45 (1898) 106--123. Newman, J. N. Evaluation of the wave-resistance Green function: Part 1 ---The double integral J. Ship Res. 31 (1987) 79--90. Scullen, D. C. Accurate computation of nonlinear free-surface flows , PhD Thesis, The University of Adelaide (1998). http://www.scullen.com.au Scullen, D. C. and Tuck, E. O. Sea wave pattern evaluation --- pressure distributions: Mathematical formulation , Scullen and Tuck Pty Ltd (2001). http://www.scullen.com.au Tuck, E. O., Lazauskas, L. and Scullen, D. C. Sea Wave Pattern Evaluation, Part 1 report: Primary code and test results (surface vessels) , Department of Applied Mathematics, The University of Adelaide, April 1999. http://www.scullen.com.au Tuck, E. O., Scullen, D. C. and Lazauskas, L. Sea Wave Pattern Evaluation, Part 2 report: Investigation of accuracy , Department of Applied Mathematics, The University of Adelaide, May 1999. http://www.scullen.com.au Tuck, E. O., Scullen, D. C. and Lazauskas, L. Sea Wave Pattern Evaluation, Part 3 report: Near-Field Waves , Scullen and Tuck Pty Ltd, Adelaide, January 2000. http://www.scullen.com.au Tuck, E. O., Scullen, D. C. and Lazauskas, L. Sea Wave Pattern Evaluation, Part 4 report: Extension to Multihulls and Finite Depth , Scullen and Tuck Pty Ltd, Adelaide, June 2000. http://www.scullen.com.au Tuck, E. O., Scullen, D. C. and Lazauskas, L. Sea Wave Pattern Evaluation, Part 5 progress report: Speed enhancements , Scullen and Tuck Pty Ltd (2000). http://www.scullen.com.au Tuck, E. O., Scullen, D. C. and Lazauskas, L., Sea wave pattern evaluation Part 5 report: Speed-up and Squat , Scullen and Tuck Pty Ltd (2001). http://www.scullen.com.au Tuck, E. O., Scullen, D. C. and Lazauskas, L. Sea wave pattern evaluation Submarine portfolio --- 10 knots , Scullen and Tuck Pty Ltd (2000). http://www.scullen.com.au Tuck, E. O., Scullen, D. C. and Lazauskas, L. Sea wave pattern evaluation Part 6 report: Viscosity Factors , Scullen and Tuck Pty Ltd (2002). Tuck, E. O. and Scullen, D. C. A comparison of linear and nonlinear computations of waves made by slender submerged bodies , Journal of Engineering Mathematics 42 (2002), 255-264. Wehausen, J. H. and Laitone, E. H., Surface Waves , in Handbuch der Physik, ed. Flugge W., Ch. 9. Springer--Verlag, 1962. http://coe.berkeley.edu/SurfaceWaves/

A finite element analysis of discontinuous thin-walled beams considering nonuniform shear warping deformation

The general displacement field of thin-walled section beams considering the uniform and nonuniform shear warping deformation is proposed by using step-by-step application of St Venant's semi-inverse method. For the analysis of the general flexural-torsional response on the unsymmetrical section beams, a C 1-continuous finite element using boundary element contraction technique is formulated and applied. With Pedersen's idea G. A. Gunnlaugsson and P. T. Pedersen, Comput. Struct. 15, 691–699 (1982); P. T. Pedersen, J. Ship Res. 35, 254–264, (1991) [1, 2] for the compatibility condition of the warping discontinuity, it is verified that the developed beam model is very effective and useful in evaluating the additional deflection and stress concentration due to shear warping even for discontinuously variable section beam problems.

The spray sheets produced during vertical wedge impact and steady planing

“Added mass” theory is usually employed in a momentum analysis. In connection with the vertical impact of a wedge, Pierson noted an anomaly when it is employed in an energy analysis, because the two approaches yielded different results. This led the writer to conjecture that the “difference” might be due to the energy dissipated in the spray sheets. The analysis which follows appears to support that conjecture, in that the size of the spray sheets so calculated is the same as those of Pierson's [(1950), The penetration of a fluid surface by a wedge. Stevens Institute of Technology Report No. 381 (July) (IAS paper FF-3)] numerical calculations. The theory predicts, for both vertical wedge impact at constant vertical velocity and for the steady high speed planing of a slender prismatic hull, that half the pressure drag energy ( Du o ) appears as kinetic energy in the spray sheets, the other half being absorbed by the downward deflection of the main body of water. This does not agree with the conclusions drawn from the experimental work of Latorre and Tamiya [(1975), An experimental technique for studying the planing boat spray. Proceedings of the Fourteenth International Towing Tank Conference, Ottawa, Canada, Vol. 4, pp. 562–571] and Latorre [(1983), Study of prismatic planing model spray and resistance components. J. Ship Res. 27, 187–196]. Nor does it agree with two-dimensional planing theory [summarized in ch. 3 of Payne [(1988), Design of High-speed Boats, Volume I: Planing. Fishergate, Inc., Annapolis, Maryland]] where all the energy appears in the spray sheet at very high Froude numbers. But the equal division of energy into spray and water deflection for slender surfaces was predicted for a high speed slender planing surface by both Wagner [(1932), Uber Stoss-und Gleitvorgänge an der Oberfläche von Flüssig-keiten.

Radiation and diffraction of water waves by a submerged sphere at forward speed

A submerged sphere advancing in regular deep-water waves at constant forward speed is analysed by linearized potential theory. A distribution of sources over the surface of the sphere is expanded into a series of Legendre functions, by extension of the method used by Farell ( J . Ship Res . 17, 1 (1973)) in analysing the wave resistance on a submerged spheroid. The equations governing the velocity potential are satisfied by use of the appropriate Green function and by choosing the coefficients in the series of Legendre functions such that the body surface condition is satisfied. Numerical results are obtained for the wave resistance, hydrodynamic coefficients and exciting forces on the sphere. Some theoretical aspects of a body advancing in waves are also discussed. The far-field equation of Newman ( J . Ship Res . 5, 44 (1961)) for calculation of the damping coefficients is extended, and a similar equation for the exciting forces is derived.

Vibration analysis of laminated composites

This study presents a macromechanical analysis of vibration of laminated composites within the concept of the effective stiffnesses of composites. The laminated composite may possess arbitrary number of matrix and reinforcing layers, each with a distinct but uniform thickness, curvature, and mechanical properties. Starting with a linearized displacement field for each constituent layer and using an unconstrained, dynamic variational principle due to the author [J. Ship Res. 23, 115–122 (1979)], the set of two-dimensional governing equations of the prestressed laminated composite is systematically and consistently established. The continuity of tractions and displacements at the interfaces is maintained, and all the effects of transverse shear and normal strains and the rotary inertia of layers are included. The governing equations accommodate all the types of small incremental motions as well as those of initial finite motions of the laminated composite. Further, special cases of interest are pointed out, and in particular, the linearized version of the governing equations is considered. Then a theorem which enumerates the sufficient conditions for its solutions is constructed by means of the logarithmic convexity arguments. [Supported by AEK Tek: 2940-3-77.]