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Journal of Ocean and Ship Technology
Volume 3 Number 1

ISSN: 0975-301X
Publication Year: June 2012
Pages: 1-52
Weight: 90

Comparative Analysis of the Stagger Variation Influence on the Hydrodynamic Performance of High Speed Trimaran
- K. A. Hafez

Abstract :This paper is devoted to the numerical investigation of the outriggers stagger variation influence on the hydrodynamic performance of high speed trimaran (HST). The slender body method (SBM) is used for calculating the wave-making resistance of three symmetric trimaran series moving in the vicinity of the free surface of deep water. Each trimaran series consists of 4681 configurations generated by considering 151 staggers (α), 31 separations (β) and 81 Froude numbers (Fn). In developing the three trimaran series, Wigley-st (Wigley 1934), AMECRC-09 (Bojovic 1995, and Bojovic et al 1996), and NPL-4a (Marwood et al 1969, and Bailey 1976) models are used separately for generating both the main and side hulls of each series models. A computer macro named Tri-PL© is developed from scratch for sequentially interfacing the model generator module; Maxsurf©(2011), and the resistance calculator module; Hullspeed©(2011). Thenumerical results of both Wigley-st and AMECRC-09 trimaran models are validatedagainst the available published results to benchmark Tri-PL© macro and Hullspeed©, and to rely on the analysis outcomes as well. A graph template of the SigmaPlot©(2006) is also created to visualize the significant design charts of the considered trimaran series.

Hat Stiffened Plates for Ship Building
- Manoj G. Tharian , C. G. Nandakumar

Abstract : The key interest in ship building is to design a ship having minimum weight and maximum strength. Usage of open sections like Flat bar, Angle bar, Holland Profile and Tee bar are common in ship structure. The stiffeners of closed section offer numerous advantages as much from the structural as from the economic point of view. Hat Stiffened Plate has a number of closed profile stiffeners provided along dominant direction. A representative unit cell of Hat Stiffened Plate has been selected and numerical investigations using finite element software ANSYS have been carried out to quantify the structural advantages of hat shaped stiffeners over the commonly used open section stiffeners like flat bar, angle and tee sections. Hat stiffeners can very effectively be used in the design of lighter ships.

A Study on Weld Induced Residual Stress and Distortion
- D. V. N. J. Jagannadha Rao

Abstract : Steep temperature gradients arising due to concentrated non uniform heating and cooling of welding causes residual stresses and distortion in the welded structures. Residual stresses and distortion is a perennial problem in welded fabrication. It is important to estimate the levels of residual stresses and distortion at the design stage so as to evaluate whether it is within permissible limits or need mitigation. In this work four cases of welding (three cases of submerged arc welding and one case of shielded metal arc welding) were studied and the residual stresses and distortion were computed for each case. Sequential thermo-mechanical analysis was used for computation of the temperature distribution, which subsequently was used as input for the mechanical analysis to compute resulting residual stresses and distortion. Double ellipsoidal heat flux density distribution was used to model the heat source along with element birth and death technique to consider filler metal deposition. Identical material properties were used for filler metal and base metal. The plastic strains at the liquid stage of the material were ignored in these analyses. The computed temperature distribution compared well with those of experimental thermal ones. Further the residual stress levels and distortion were calculated.

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