Torsion and Shear Stresses in Ships

2014

Pronounced shear loading of the significant intensity can induce occurrence of the shear buckling and eventually lead to the shear collapse of the hull girder structural elements loaded in shear, if acting shear load surpasses their ultimate shear load capacity. Therefore, consideration of the stiffened plate shear load capacity can represent a relevant aspect and important structural adequacy criterion in analysis and synthesis of the ship structures. Since the contemporary ultimate shear load capacity formulations are based on correction of the calculated elastic shear buckling critical stress, this paper investigates various possible approaches to inhibition of the elastic shear buckling and identifies the most effective one. Based on relevant theoretical aspects and results of the performed finite element method analyses of the considered problem, a formulation for determination of the critical shear stress for the appropriately stiffened plates is proposed.

2018

The course is intended to develop the student’s knowledge of ship structures. The focus is on various types of intact structural behavior, building upon concepts from mechanics of materials and statics. Changes to 2018 edition: • Updated Topic 1 – with ship structural features included • Updated Topic 2 – new discussion of approach to structural design • New Topic 11 – discussion of use of tables and superposition • New beam tables in Appendix 4 • Energy Methods moved to Appendix 7

electronic form only:: NE

Large deck openings of ultra large container ships reduce their torsional stiffness considerably and hydroelastic analysis for reliable structural design becomes an imperative. In the early design stage the beam model coupled with 3D hydrodynamic model is a rational choice. The modal superposition method is ordinary used for solving this complex problem. The advanced thin-walled girder theory, with shear influence on both bending and torsion, is applied for calculation of dry natural modes. It is shown that relatively short engine room structure of large container ships behaves as the open hold structure with increased torsional stiffness due to deck effect. Warping discontinuity at the joint of the closed and open segments is compensated by induced distortion. The effective torsional stiffness parameters based on an energy balance approach are determined. Estimation of distortion of transverse bulkheads, as a result of torsion and warping, is given. The procedure is illustrated in the case of a ship-like pontoon and checked by 3D FEM analysis. The obtained results encourage incorporation of the modified beam model of the short engine room structure in general beam model of ship hull for the need of hydroelastic analysis, where only the first few natural modes are of interest.

Ocean Engineering, 2017

This work is focused on experimental investigation of the hull girder loads on an intact and damaged naval ship DTMB 5415 at zero speed. The experimental campaign was carried out in head and beam regular waves at the University of Strathclyde. The effect of the use of moorings in the model experimental setup was investigated in the context of loads assessment, and the moorings are shown to influence the measured hull girder loads at some wave frequency compared to the free drift case. Therefore the tests in beam seas are performed with free drifting model while the moored model setup was adopted for head seas. The results for ship motions are compared with those from a previous campaign giving an insight into repeatability and uncertainty of measurements. The roll decay of the ship in both intact and damaged conditions is analysed and the linear and quadratic extinction coefficients for the model and the ship scale are reported and detailed discussion on intact-versus-damaged ship roll damping behaviour is given. The results for the hull girder loads are presented for intact and damaged ship. An investigation of the nonlinear effects due to wave height variation in the range wave height to wave length from 1/50 to 1/22 on shear force and bending moment was carried out for a range of wave lengths to ship length ratios from 0.8 to 1.4. The results of the extensive campaign are compared against similar experimental studies forming a benchmark for validation of numerical methods. Keywords: 5415 DTMB model, wave loads on intact and damaged ship; nonlinear responses; experimental shear force and bending moments assessment, roll decay, equivalent linear roll extinction coefficient NOMENCLATURE A -wave amplitude, m B OA -beam over all, m B WL -beam at waterline, m C B -block coefficient C M -midship section coefficient C P -prismatic coefficient D -depth, m g -acceleration of gravity, 9.80665 m/s 2 GM -transversal metacentric height, m H -wave height, m HBM -horizontal bending moment, Nm HSF -horizontal shear force, N H/λ W -ratio between wave height and wave length k -wave number, 2π/λ W KG -vertical position of the centre of gravity, from BL, m KM -vertical position of the metacentre, from BL, m k XX -radius of gyration with respect to x axis, m,

A method is presented to estimate the ultimate moment based on a simplified approach to represent the behavior of stiffened plate columns. The assessment of the strength of a very large crude carrier is performed and compared with the moment at failure in hogging estimated by other methods applied to the same case. The proposed method allows the prediction of the degradation of the strength due to corrosion and residual stresses. It also allows the evaluation of the strength of the hull at several heeling conditions. Finally, an analysis of the efficiency of the high tensile steel is carried out. * The elements into which the cross section is subdivided are considered to act and behave independently. 60 MARCH 1996 0022-4502/96/4001-0060$00.45/0 JOURNAL OF SHIP RESEARCH

Volume 2: Structures, Safety and Reliability, 2008

Many modern ships, particularly large containerships, are characterized by extreme bow flare, large stern overhang, and low torsional rigidity due to an open deck structural configuration. Software package GL ShipLoad was developed as an aid to assess the structural integrity of such ships. This software tool became the standard method to generate rule based loads for a global strength finite element analysis of sea going displacement ships. It efficiently generates loads based on first principles. A graphical user interface facilitates the convenient application of ship and cargo masses to the finite element model and aids in the selection of relevant design wave situations. User defined selection criteria, such as maximum values of rule based bending moments, shear forces, or torsional moments, specify which waves have to be chosen for the global strength analysis. This approach yields a reduced number of balanced load cases that are sufficient to dimension the hull structure. To adequately simulate roll motion, additional roll angles are analyzed that simulate realistic distributions of torsional moments over the ship length. A strength analysis of a typical post-panamax containership demonstrated the load generation procedure. First, efficiently modeled mass items were grouped into reusable assembled masses for the ship at hydrostatic equilibrium. Second, regular design wave scenarios were estimated, and hydrodynamic pressures for a large number of regular waves were computed. Third, a reduced number of relevant wave situations were automatically selected, and balanced hydrostatic, hydrodynamic, and inertia loads were applied to the finite element model. Enforced roll angles were found to contribute significantly to the initial torsional moment in the fore holds. Finally, based on a locally refined FE submodel of the hatch corners in way of the ship's fore hold, a fatigue analysis was performed to assess effects of critical loading under enforced roll angles.

Journal of ETA Maritime Science, 2021

Construction profiles in different shapes such as bulb flats, tees, channels, and angles are widely used in the shipbuilding industry. During the ship construction process, these conventional profiles are joined to the plates as stiffeners and are dimensioned according to class rules. This article investigates the structural performance of a novel construction profile, the so-called TP profile, that can be used in the hull construction of ships and of which form is inspired by the human bone geometry. The cross-sectional area and the weight of the TP profile are designed to be equal to those of the conventional HP profile and commercial T profile. Strength performances of these profiles are compared via analytical and numerical analyses. The plate joint profiles are modeled under various loading and boundary conditions and the finite element method is used for the calculation of stress components and deflections. The TP profile has a high potential to be used in the shipbuilding industry.

Due to the limited enclosed area, container ships with large openings in deck are subject to torsional failure as well as bending failure. Specifically, both moments contribute measurably to the ultimate strength in the scenario of ships travelling in oblique seas. This paper focuses on the ultimate strength of container ship subject to combined moments of bending and torsion, and the modelling scope is limited to the longitudinal structures between two adjacent frame girders to reduce the calculation cost. The limit state of failure for a 3100 TEU container ship is derived through Minimum Square Error (MSE) technique based on a series of Nonlinear Finite Element Analysis (NFEA). On the other hand, corrosion takes place in the life cycle of container ships, resulting in degradation of structural strength. Thus, corrosion effects with uncertainty on ultimate strength regarding to pure bending moments, pure torsional moments and combination of both are studied, which can be a useful reference for the scheduled maintenance of container ships.

EPI International Journal of Engineering, 2018

The location of the beam and the deck girder of the ship can be effect on it is strength especially for the longitudinal strength due to the vertical wave bending moment. The objective of this study is to know the structural response of the ship due to vertical bending moment load on hogging and sagging conditions. The analysis is carried out by using Finite Element Method so-called ANSYS TM. The results shows that the stress occurring on the ship model with deck beam above the deck plate is larger than the ship model with deck beam under the deck plate. When the load with the variated of 0.2 x moment of vertical moment load, there is an increase of stress that occurs both on the deck area about 12% while on the bottom area about 0.98%. This study also conducted a stress comparison by using analysis methods with analytical methods. The results show that by the Stress differences that occur in the structure with the longitudinal deck beam and deck girder above are 14.1% on the deck and 7.1 on the bottom. Whereas in the structure with deck longitudinal deck eam and deck girder under there is a difference of 5.7% on the deck area and 3.5% in the bottom area of the ship. The stress that occur in both models have a difference that is not too far away and still under the permisible stress by the classification society so that both can be applied to the construction of a tanker.

2017

The paper presents basic knowledge about Finite Element Method including the modeling method of ship structures. Numerical modeling methods were also shortly described. A ship hull and an upper works is typical thin-wallded structure. Modeling method of plates (typical 2-D elements) with stiffeners (1-D elements) is presented in details. In the part II of the article the practical example of Ro-Ro ship's deck analyses was performed with using Patran-Nastran software (MSC Software). The most common and dangerous risks and errors occurring in the process of ship structure modeling were discussed.

Journal of Ship Research

A method is presented to estimate the ultimate moment based on a simplified approach to represent the behavior of stiffened plate columns. The assessment of the strength of a very large crude carrier is performed and compared with the moment at failure in hogging estimated by other methods applied to the same case. The proposed method allows the prediction of the degradation of the strength due to corrosion and residual stresses. It also allows the evaluation of the strength of the hull at several heeling conditions. Finally, an analysis of the efficiency of the high tensile steel is carried out. * The elements into which the cross section is subdivided are considered to act and behave independently. 60 MARCH 1996 0022-4502/96/4001-0060$00.45/0 JOURNAL OF SHIP RESEARCH

Mathematical Problems in Engineering, 2012

A new methodology based on a macroelement model proposed for torsional behaviour of the ship hull made of composite material is proposed in this paper. A computer program has been developed for the elastic analysis of linear torsion. The results are compared with the FEM-based licensed soft COSMOS/M results and measurements on the scale simplified model of a container ship, made of composite materials.

Ships and Offshore Structures

This paper presents a new methodology to determine the design values of wave-induced hull girder loads acting on ships. The method is based on probabilistic approaches associated with selected scenarios that represent possible events in terms of the ship's functionality, operation and environment. As illustrative examples, the method is used to determine the design values of wave-induced vertical bending moments for as-built ships (a VLCC class tanker, a 9,300 TEU containership and a 22,000 TEU containership) and a hypothetical 25,000 TEU containership. The probabilities of exceedance for wave loads acting on ships are discussed in association with the design load values determined from classification society rules. It is found that both the class rule method and the present method are in good agreement for the considered example ships. The present methodology can of course be applied to determine other components of design wave loads such as horizontal bending moments and torsional moments.

Marine Structures, 1995

Explicit fatigue analysis of welded structures is mostly based on the stress range philosophy, which implies that high residual stresses from the welding process are always present. The structural analysis for the design of ships will normally consider only some of the largest quasi-static loads that the s~ip will experience in its lifetime. The effects of the high frequency loads responsible for fatigue damage are not described and analysed, as is done in most civil engineering and offshore applications. Ship structural details are designed to sustain fatigue loading by an implicit method where long term experience has selected successful design. This study shows that residual stresses are frequently redistributed in cut-outs and openings of tanker webframes and that the resulting residual stress conditions are predictable. Different assumptions of the initial residual stress fieM are made and redistribution due to sea loads is studied with non-linear finite element analysis (FEA ). Examples chosen for the investigation are flame cut edges in a conventional tanker webframe. It is shown that during each voyage local yielding will occur at the most fatigue-sensitive notches in the studied webframe. High stress ranges will cause considerable redistribution of the initial residual stress field. Locations with high tensile as well as compressive mean stresses can be detected. For cut-outs, geometrical optimisation by variation of the curvature is made possible. A reduction of damage is demonstrated for a specific notch in the studied webframe by a Palmgren-&Iiner damage calculation. A comparison of different approaches to calculate the damage has also been made showing significant differences.

… Workshop" Advanced Ship …, 2009