International Shipbuilding Progress - Volume 47, issue 450

Authors: Domnisoru, Leonard | Domnisoru, Daniela

Article Type: Research Article

Abstract: In this paper the elastic multisegmented ship model constructed at the test tank at the University of Galati, the measurement and data processing chains and the results of the experimental analysis are presented. We focused on the study of vibration phenomena: springing and whipping induced on the main vibration mode of the ship girder in the vertical plane. The necessity of this study results from the high stress level occurred on the vibration component, for the …most probable bending moment amplitudes, up to 98% from the ship oscillation component. Show more

Citation: International Shipbuilding Progress, vol. 47, no. 450, pp. 129-140, 2000

Authors: McTaggart, Kevin

Article Type: Research Article

Abstract: This paper presents a method for including appendage and viscous forces in predictions of lateral plane ship motions and sea loads in waves. Because sea loads arise from relatively small differences between large quantities, forces acting on the ship must be treated in a consistent manner for motion and sea load computations. The present implementation with strip theory correctly gives zero sea loads at the aft end of the ship. Comparisons with experiments for a narrow …stern warship model show good agreement and demonstrate the importance of appendage forces. Additional comparisons for a transom stern frigate show inferior agreement for roll and torsion, suggesting that the current treatment of appendage and viscous forces should be included in a three-dimensional ship motion and sea load program. Show more

Citation: International Shipbuilding Progress, vol. 47, no. 450, pp. 141-160, 2000

Authors: Senjanović, Ivo

Article Type: Research Article

Abstract: This paper outlines the investigation of launching ships and floating structures from a horizontal berth by a tipping table, which comprises the structure dynamics, i.e. both theory and experiments. Numerical simulation and model test of the side launching of a large tanker on even keel are analysed and a correlation study between the calculation and measurement results is performed. The advantages and limitations of this new way of launching are pointed out.

Citation: International Shipbuilding Progress, vol. 47, no. 450, pp. 161-181, 2000

Authors: Lee, Seung Keon

Article Type: Research Article

Abstract: It is common to evaluate the course-keeping quality of a ship with the use of spiral test results. But, in real situations, the spiral test is very difficult to execute, and moreover, time consuming. Therefore, if there are some alternative methods to treat the course-keeping quality of a ship, those are quite preferable in the practical fields. In this paper Zig-Zag tests and overshoot angles are simulated for various patterns of spiral curves with hysterisis loops. …Also, the relations between overshoot angles and the course-keeping qualities are discussed. Show more

Citation: International Shipbuilding Progress, vol. 47, no. 450, pp. 183-189, 2000

Authors: Sinha, Gobinda

Article Type: Research Article

Abstract: An isotropic high precision triangular stiffened shallow shell element of 36 d.o.f. are introduced to investigate the undamped free vibration behaviour of unstiffened and stiffened plates/shells supported on elastically restrained edges. In the formulation, the stiffener may take up any arbitrary orientation within the shell element, and it need not necessarily be placed along the nodal line. The consistent boundary stiffness matrix has been formulated to distribute the values of stiffness coefficients at all the nodes …of the elements on elastic boundary which ensures better accuracy to obtain the natural frequencies of the stiffened structure. A number of numerical problems on stiffened and unsiffened plates/shells have been solved and the values are compared with the available theoretical results. Results show good agreement with the compared values. A new set of results on doubly curved stiffened shell with convergence study has also been presented which will be valuable to the future investigators in this field. Show more

Citation: International Shipbuilding Progress, vol. 47, no. 450, pp. 191-214, 2000

Authors: Maerli, A. | Das, P.K. | Smith, S.N.

Article Type: Research Article

Abstract: Floating Production Storage and Off-loading (FPSO) Vessels have been chosen for an increasing number of field developments in recent years. High payload capacity, short development schedule and in-built cargo storage capacity are some important advantages that make 'Ship Shaped' FPSOs very attractive for field developers. The operation and maintenance profiles of a FPSO differ from those of a traditional merchant ship, and these differences will significantly influence the structural reliability of the vessel. This …paper presents the structural reliability analysis of the hull girder ultimate strength for a ship shaped FPSO. The ultimate strength of the hull girder was calculated using a component approach, where the behaviour of the hull is evaluated based on the behaviour of the single structural components. Three collapse conditions were investigated; failure initiated by plate compression, failure initiated by stiffener tension and failure initiated by stiffener compression. Only vertical bending moment has been considered and, the hull girder loads are divided into still water induced and wave induced components. The two loading components have been considered independent and Ferry Borges-Castenheta load combination method has been applied to obtain load combination factors for the Full Load, Partial Load (50% loaded) and Ballast condition. The distributions of the extreme values of the vertical wave bending moments (VWBM) were calculated, based on linear strip theory and a long-term formulation. The vertical mooring forces are small and they were considered to have an insignificant influence on the bending moment response. The reliability analysis was carried out using a SORM analysis. Annual reliability indices (β) and probabilities of failures were calculated for hogging and sagging conditions. The calculated β values were higher than the annual reliability indices proposed in DNV Classification Notes 30.6 for serious failures in redundant structures. This indicates that the design is safe and reliable for operation in this particular location. The sensitivity of β with respect to the different variables in the limit state function was investigated and further reliability analyses were performed based on other locations in the North Sea and various stochastic models. Some of these results are included in the paper to highlight the importance of formulating a rational failure surface equation. Show more

Citation: International Shipbuilding Progress, vol. 47, no. 450, pp. 215-225, 2000

Authors: Mandal, N.R.

Article Type: Research Article

Abstract: Cold forming of sections is an integral part of shipbuilding. It has been observed that on an average 2.8% of hull steel weight is accounted for by curvilinear welded T sections. The application of cold forming for deep T section is still very much limited due to lack of, amongst other things, proper theoretical analysis of this production problem. Cold forming of such sections might lead to web/flange weld failure, instability of web, roofing of face …plate and reduction in thickness of the web edge. A detailed analysis of all these factors has been carried out to establish a sound basis for this production problem. This simulation approach can be used either to predict the behavior of welded T sections undergoing cold forming or it can be used at the design stage as a design tool so that the required bent shape can be successfully achieved by cold forming. Full scale tests have been carried out and a good agreement between the computed and the test data has been observed. Show more

Citation: International Shipbuilding Progress, vol. 47, no. 450, pp. 227-246, 2000