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2012
An analytical approach to torsion of thin-walled beams of open section with one plane of symmetry is considered. The theory of torsion of thin-walled beams of open section with influence of shear, based on the classical Vlasov's theory of thin-walled beams of open section, as well as the Umansky's theory for closed-open sections, is applied. The general transverse loads act in the beam walls, reduced to the moments of torsion with respect to the principal pole (torsion/shear centre) only. The beam will be subjected to torsion with influence of shear with respect to the principal pole and in addition to bending due to shear in the horizontal plane trough the principal pole. The obtained analytical expressions for displacements are applied in the analysis of displacements of the modern container ship hull girder subjected to torsion, as well as in the parametric analysis of simple U sections. Comparisons with the finite element method by applying shell elements are provided.
2013
Container ships with wide hatch openings are thin walled open sections and have low torsional stiffness. Hence response arising from torsional loads is significant and subsequently the torsional analysis of container ship is necessary. Using the ANSYS software, the progressive collapse behaviour of a typical container vessel under torsion was analysed. The effect of torsional moment on the ultimate strength of ship hull subjected to design vertical shear force was also determined. Full hull between the bulkheads was modeled with fully restrained warping displacement at the unloaded end. When pure torsion is applied, the hull corner regions are typically the most highly stressed areas, which may collapse. Thus, scantlings of the hull corner region should be sufficient for ship hulls with large deck openings. The ultimate strength based safety factor under pure torsion for the vessel, is 4.5, which is reduced by 30% when subjected to design vertical shear force also.
In this paper a new methodology (numerical and experimental) proposed to analyze the ship hull torsion is treated. The torsion analysis is performed on a scale model (1:50) of a container ship, made of composite material. The outline of the section is considered as a polygonal one. The material is orthotropic. For a straight line portion of cross section outline is corresponding a longitudinal strip plate. Due to the torsion of the thin walled beam, in the strip plate, the stretching-compression, bending and shearing occur. The strip plate is treated as an Euler-Bernoulli plate. The stiffness matrix of the macro-element is obtained by assembling the stiffness matrices of the strips. The results obtained from numerical and from experimental analysis are presented.
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.
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.
Marine Structures, 2014
The hull girder moment capacity of a very large crude oil carrier (VLCC) called Energy Concentration (EC), for which many benchmark studies have been carried out using the simple progressive collapse method (SPCM), is predicted. In this study, three approaches are used to represent the load-shortening behavior, socalled average compressive strength, of a stiffened panel, comprising the hull section: 1) kinematic displacement theory (KDT); 2) nonlinear finite element analysis (FEA); and 3) simple formulas in the common structural rule (CSR) for tankers. Loadshortening curves for various kinds of stiffened panels in EC are compared for five different scenarios with variations of loadshortening approaches and initial imperfections. In order to verify the effect of load-shortening on the prediction accuracy of the hull girder moment-carrying capacity, load-shortening curves are imported into an SPCM-based in-house program called Ultimate Moment Analysis of Damaged Ships (UMADS). Comparison of the hull girder ultimate strength for general heeling conditions, including hogging and sagging conditions, reveals that the loadshortening curves significantly affect the hull girder momentcarrying capacities. Based on our comparison of these capacities with other benchmark results, it is concluded that nonlinear FEA provided the most conservative results, KDT provided the second most conservative results, and the CSR formulas predicted the upper bound.
Brodogradnja
Original scientifi c paper Very large container ships are rather fl exible due to the large deck openings. Therefore, hydroelastic stress analysis is required as a basis for a reliable structural design. In the early design stage, the coupling of the beam model with a 3D hydrodynamic model is rational and preferable. The calculation is performed using the modal superposition method, so natural hull modes have to be determined in a reliable way. Therefore, the advanced thin-walled girder theory, which takes the infl uence of shear on both bending and torsion into account, is applied for calculating the hull fl exural and torsional stiffness properties. A characteristic of very large container ships is the quite short engine room, whose closed structure behaves as an open hold structure with increased torsional stiffness due to the deck effect. The paper deals with the calculation of its effective torsional stiffness parameters by utilizing the energy balance approach. Also, estimation of distortion of transverse bulkheads, as a result of torsion and warping, is given. The procedure is checked by the 3D FEM analysis of a ship-like pontoon. Such a modifi ed beam model of the engine room structure can be included in the general beam model of a ship hull for the need of hydroelastic analysis, where only a few fi rst natural frequencies and mode shapes are required. For practical use in the preliminary design stage of ship structures, the simplicity of the beam model presents an advantage over 3D FEM models.
EPI International Journal of Engineering
The strength of transversal structure of the ship has a great effect on the safety of ship. Shipswill experience conditions that affect the strength of the ships structure. A deck-container ships are the ships that all container are loaded on deck such as MV. Khendaga Nusantara series ships. The transversal strength of the ships is loaded mainly by the weight of cargolaying on deck.. This research aims to determine the transverse strength of a deck-container ship due to the all container loads on deck. The research was done by usingfinite element method throughmodeling transverse ship structure, the simulation is conducted by varying the amount and lay-out of containers on dec). The loads appliedto the model are side loads, bottomloads, and deck loads in according to BKI rules. The results shows that the stress that occurred in the web frame was 140,63 N/mm2due to the placement of the entire container on the deck(full loading). For ship structure response, a deformation of 2,86 mm o...
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.
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.
… Workshop" Advanced Ship …, 2009
International Journal of Naval Architecture and Ocean Engineering, 2014
Some results on the hydroelasticity of ultra large container ships related to the beam structural model and restoring stiffness achieved within EU FP7 Project TULCS are summarized. An advanced thin-walled girder theory based on the modified Timoshenko beam theory for flexural vibrations with analogical extension to the torsional problem, is used for formulation of the beam finite element for analysis of coupled horizontal and torsional ship hull vibrations. Special attention is paid to the contribution of transverse bulkheads to the open hull stiffness, as well as to the reduced stiffness of the relatively short engine room structure. In addition two definitions of the restoring stiffness are considered: consistent one, which includes hydrostatic and gravity properties, and unified one with geometric stiffness as structural contribution via calm water stress field. Both formulations are worked out by employing the finite element concept. Complete hydroelastic response of a ULCS is performed by coupling 1D structural model and 3D hydrodynamic model as well as for 3D structural and 3D hydrodynamic model. Also, fatigue of structural elements exposed to high stress concentration is considered.
Ships and Offshore Structures, 2015
The objective of this study is to propose an analysis method of ultimate hull girder strength under combined bending and torsion. The hull girder is modelled by a series of thin-walled beam elements and the average stress-average strain relationship of plate and stiffened panel elements under axial loads considering the effect of shear stress is implemented in the beam elements. First, a torsional moment is applied to the beam model for a whole model within the elastic range. Then, the ultimate bending strength of cross-sections is calculated applying Smith's method to beam elements considering the warping and shear stresses. The proposed simplified method is applied to the progressive collapse tests of scale models under combined loads. On the other hand, nonlinear explicit finite element method (FEM) is adopted for the analysis of the test models. The effectiveness of the simplified method is discussed comparing with the results of experiments and FEM analysis.
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.
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
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
MATEC Web of Conferences
The objective of the present research is to study the ultimate strength of ship's hull considering cross section and beam finite element under longitudinal bending. The single hull bulk carrier and double hull oil tanker are taken to be analysed. The one-frame space of ship is considered in the calculation. The cross section of ship's hull is divided into element composed plate and stiffened plate. The cross section is assumed to be remained plane and the simply supported is imposed to both side of the cross section. The longitudinal bending moment is applied to the cross section for hogging and sagging condition. The Smith's method is adopted and implemented into the in-house program of the cross section and beam finite element to calculate the ultimate strength of ship's hull. The result of the ultimate strength for hogging and sagging condition obtained by considering the cross section and beam finite element is compared with one another.
Hydroelasticity in Marine …, 2009
This paper deals with the methodology of hydroelastic analysis, based on mathematical model, which includes structural, hydrostatic and hydrodynamic submodels. The modal superposition method is used, and ship natural modes are determined by the sophisticated beam model based on the advanced thin-walled girder theory, which takes shear influence on torsion into account as novelty, as well as the stiffness contribution of transverse bulkheads in quite a reliable way. Moreover, the complete and consistent restoring stiffness, which satisfies the ship equilibrium, is derived. The mathematical model is checked by model test of a flexible barge. Application of the developed numerical procedure is illustrated in the case of a very large container ship. 1D FEM model is verified by correlating dry natural vibrations with those obtained by 3D FEM model.
2011
Increase in global ship transport induces building of Ultra Large Container Ships (ULCS), which have a capacity up to 14000 TEU with length up to 400 m, without changes of the operational requirements (speed around 27 knots). Natural frequencies of such ships can fall into the range of encounter frequencies in an ordinary sea spectrum. Present Classification Rules for ship design and construction don't cover such conditions completely and hydroelastic analysis of ULCS seems to be the appropriate solution for analysis of their response in waves. This paper deals with numerical procedure for ship hydroelastic analysis with particular emphasis on improvements of the present beam structural model. The structural model represents a constitutive part of hydroelastic mathematical model and generally it can be formulated either as 1D FEM or 3D FEM model. For the preliminary design stage hydroelastic model derived by coupling 1D FEM structural model and 3D BEM hydrodynamic one seems to be an appropriate choice. Within the paper the importance of hydroelastic approach and methodology of hydroelastic analysis are elaborated. Further on, structural model based on advanced beam theory is described in details. The improvements include taking into account shear influence on torsion, contribution of bulkheads to hull stiffness as well as determination of effective stiffness of engine room structure. Along with that, hydrodynamic and hydrostatic models are presented in a condensed form. Numerical example, which includes complete hydroelastic analysis of a large container ship, is also added. In this case, validation of 1D FEM model is checked by correlation analysis with the vibration response of the fine 3D FEM model. The procedure related to determination of engine room effective stiffness is checked by 3D FEM analysis of ship-like pontoon which has been made according to the considered ship characteristics.
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