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2019, IOP Conference Series: Materials Science and Engineering
The paper presents the method for calculating the strength of the ship vessel on the longitudinal wave, based on the modern theory of the beam and computer mathematics. It consists of two parts, which are the determination of hydrodynamic loads on the hull during the passage of a wave and the calculation of the stress-strain state caused by the ship vessel as a beam. The main feature of the technique is that the loads and deflection are considered simultaneously, which was made possible by computer mathematics. The developed method allows; increasing the accuracy of calculations of ship hulls for durability, has a relatively low cost, and does not require expensive software.
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.
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,
Volume 2: Structures, Safety and Reliability, 2011
To rationally assess the consequence of a ship collapse, it is necessary to know the post-ultimate strength behavior of the hull girder including the global deformation and motions under wave-induced extreme loads. In the foregoing research, the authors proposed a numerical analysis system to predict the collapse behavior in waves including the postultimate strength behavior. In this paper, an analytical solution to describe the post-ultimate strength behavior is proposed. The primary objective of the present research is to clarify the parametric dependencies of the severity of the collapse in a rational manner. The parameters may include those related to load-carrying capacity and those related to the extreme loads. By comparing the numerical results and the present results, the analytical solution is shown to be effective. Some important parameters to predict the severity of the collapse are derived based on the analytical solution.
Journal of Marine Science and Application, 2012
Experimental investigations into the collapse behavior of a box-shape hull girder subjected to extreme wave-induced loads are presented. The experiment was performed using a scaled model in a tank. In the middle of the scaled model, sacrificial specimens with circular pillar and trough shapes which respectively show different bending moment-displacement characteristics were mounted to compare the dynamic collapse characteristics of the hull girder in waves. The specimens were designed by using finite element (FE)-analysis. Prior to the tank tests, static four-point-bending tests were conducted to detect the load-carrying capacity of the hull girder. It was shown that the load-carrying capacity of a ship including reduction of the capacity after the ultimate strength can be reproduced experimentally by employing the trough type specimens. Tank tests using these specimens were performed under a focused wave in which the hull girder collapses under once and repetitive focused waves. It was shown from the multiple collapse tests that the increase rate of collapse becomes higher once the load-carrying capacity enters the reduction path while the increase rate is lower before reaching the ultimate strength.
Up to date rule based methods used for the prediction of wave-induced loads, have been proven to be reasonably adequate with problems arising dealt by relying on empirical rules supported by service experience. However, with the increasing market demands for more slender, higher speed open deck ocean going carriers and the continuously updated unconventional multi-hull designs, industry has noticed the advantage of assessing the usefulness and applicability of alternative load prediction tools in ship design.
… Workshop" Advanced Ship …, 2009
The paper presents an approach to determine the global load effects induced on ship structures by abnormal, freak, or episodic waves. It refers to the present procedure of determining extreme values of wave-induced responses, including the recent advances of adopting time series of wave elevation as reference design conditions to calculate the wave-induced structural loads on ships in heavy weather. It is shown how this procedure can be extended to account for abnormal or episodic waves. Reference is made to what is presently known about abnormal or freak waves, showing that although it is possible to determine the loads induced by these waves in floating and fixed structures, the present knowledge about the probability of occurrence of these waves is not enough to allow a wave design criterion to be defined in a way consistent with the present probabilistic approaches. However, it is suggested that at the present stage of knowledge it is possible to determine the loads induced by abnormal waves similar to ones that have been measured at various ocean locations and that are thus realistic; a method is described to perform such calculations. Although this information cannot replace the wave-induced loads calculated with the presently established procedures, it can serve as guidance for the design. An application example is presented of a containership subjected to a wave trace that includes an episodic wave that was measured during a severe storm in Central North Sea. The measured wave time history is modified in order to investigate the influence of the wave steepness on the induced vertical motions and loads. The loads induced by the abnormal wave are compared for the first time with extreme values from long-term distributions.
Ships and Offshore Structures, 2012
A computational tool was applied based on a two dimensional linear method to predict the hydrodynamic loads for damaged ships. Experimental tests on a ship model have also been carried out to predict the hydrodynamic loads in various design conditions. The results of the theoretical method and experimental tests are compared to validate the theoretical method. The extreme waveinduced loads have been calculated by short term prediction. For the loads in intact condition, the prediction with duration of 20 years at sea state 5 is used, while for loads in damaged conditions the prediction in 96 hours exposure time at sea 3 is used. The maximum values of the most probable extreme amplitudes of dynamic wave induced loads in damaged conditions are much less than those in intact condition because of the reduced time. An opening could change the distribution of not only stillwater bending moment but also wave-induced bending moment. It is observed that although some cross sections are not structurally damaged, the total loads acting on these cross sections after damage may be increased dramatically compared to the original design load in intact condition.
Marine Structures, 2004
This paper describes a coupled beam method, which estimates elastic response in the longitudinal bending of a passenger ship with a large multi-deck superstructure. The method can be applied during an early project stage, when detailed three-dimensional finite element modelling is not yet possible. The theory is based on the assumption that each deck in the superstructure and also the main hull can be considered as a thin-walled beam. These beams are coupled to adjacent beams with springs modelling vertical and shear stiffness. The shear effect in the side and deck structures is included with options for large openings. As a result, the method allows for the calculation of the normal stresses and vertical deflections in the arbitrary location of the hull girder. Average longitudinal displacements of deck structures and shear stresses in the side structures can be estimated as well. Simplified structures were analysed in order to validate the coupled beam method against the three-dimensional finite element method. r
2013
Direct Strength Analyses are meant for evaluating the yield strength and buckling strength using net dimensions of primary strength members of the container carrier. The paper deals about the automation of direct strength analysis procedure using ANSYS. The stresses at different locations are calculated due to internal cargo load, ballast load, and the external hydrodynamic sea pressure for specific load cases. The still water bending moment (SWBM) has been picked from loading manuals. The wave bending moments (WBM) are calculated from JBP Rules. The effects of SWBM & WBM are applied to the structure with proper load combination factor and local hull girder moment correction. The results are extracted using general post-processor of ANSYS for checking yielding, buckling and ultimate strength. The overall safety of the vessel is checked.
Journal of Marine Science and Technology, 2011
Dynamic collapse behavior of a ship's hull girder in waves is investigated; post-ultimate strength behavior is the focus. Firstly, a simulation method is proposed. Assuming that a plastic hinge is formed during the collapse of the hull girder, the whole ship is modeled as two rigid bodies connected amidship via a nonlinear rotational spring. The post-ultimate strength behavior, such as the reduction of load carrying capacity due to buckling and yielding, is reflected in the model. Hydrodynamic loads are evaluated by using nonlinear strip theory to account for the effect of large plastic deformations on the loads. A scaled model for validation of the simulation is designed and fabricated. Then a series of tank tests is conducted using the scaled model to validate the simulation results. Postultimate strength behavior characteristics in waves are clarified by using the numerical and tank test results. It is shown that the hull girder collapses rapidly after reaching ultimate strength, and then the plastic deformation grows until unloading starts at the collapsed section. Finally, several parametric dependencies of the extent of the collapse behavior are discussed based on a series of the simulations.
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.
2011
The study presents an experimental investigation to obtain motion and load measurements of an intact and damaged frigate model in waves. The experimental measurements will show the changes in motion and hull girder loading when a ship hull is damaged and form benchmarking data.
Transactions-Society of …, 2003
The European cooperative research project WAVELOADS investigated use of a linear frequency-domain numerical technique and developed a nonlinear time-domain numerical technique to predict wave-induced global loads for a high-speed ferry and round-bilge fast monohull. For the frequency-domain technique, besides adding viscous effects, an advanced software module was developed to evaluate hydrodynamic influence coefficients, whereby forward speed effects were fully accounted for. The procedure relied on the Fourier-Kochin free-surface forward-speed Green function method that promised to provide a solid mathematical basis for obtaining robust and computationally efficient predictions. Incorporation of this module into two existing frequency-domain panel codes resulted in accurate predictions of wave-induced global response for a slender Wigley hull advancing in regular head waves at high forward speed. However, for the reference ships, predictions deviated excessively from experimental data because numerical inaccuracies could not be resolved. Therefore, subsequent frequency-domain computations were performed on the basis of the so-called encounter-frequency approach. To validate the numerical techniques and to specify limits of application, numerical predictions were compared to experimental data obtained from systematic model tests. For ship speeds corresponding to Froude numbers up to about 0.4, this encounter-frequency approach produced accurate predictions, albeit only in waves of small steepness. To obtain long-term design values in a realistic seaway consisting of finite amplitude waves, linearly computed loads were corrected for nonlinear effects. As a practical demonstration, a statistical analysis yielded long-term (design) values of wave-induced midship vertical bending moments for the high-speed ferry. In sagging, the resulting bending moment deviated by five percent from classification society rule values; in hogging, by thirteen percent.
25th ATTC, …, 1998
In 1996, the 22 nd ITTC formed a Specialist Committee on Ship Stability. There were two main mandates given to this committee. The first was to examine the techniques for carrying out model experiments used to investigate the capsize of intact and damaged ships and provide guidelines for carrying out these experiments. The second was to assess the methods available for numerical simulations of the capsize of intact and damaged ships.
In this paper, we compute and study motions and loads on a catamaran hull with forward speed, based on a strip theory method in which the sectional hydrodynamic properties are determined using a source-distribution or so-called Frank close-fit method. Two alternative schemes for this double-hull problem have been used for the computations of the sectional properties. Comparative results with available experimental data on the sectional hydrodynamic properties and ship motions are shown, followed by presentation and study of various modes of important structural loads on a catamaran hull. Results are discussed in comparison with available experimental data. It is found that while results follow the general trend with the results reported in some of the available studies, wide scatter still exists among the results. The two schemes used here also do not produce consistent results over the speed range. This suggests that further work is necessary before reliable tool for wave-induced l...
Ocean Engineering, 2016
The aim of this paper is to critically assess the methods used for the evaluation of wave-induced loads on ships examining analytical, numerical and experimental approaches. The paper focuses on conventional ocean going vessels and loads originating from steady state and transient excitations, namely slamming, sloshing and green water, for the latter, and including extreme or rogue waves, as well as the more occasional loads following damage. The advantages and disadvantages of the relatively simpler potential flow approaches against the more time consuming CFD methods are discussed with reference to accuracy, modelling nonlinear effects, ease of modelling and of coupling with structural assessment procedures, suitability for long term response prediction and suitability for integration within design and operational decision making. The paper also assesses the uncertainties involved in predicting wave-induced loads and the probabilistic approaches used for the evaluation of long term response and fatigue analysis. The current design practice is reviewed and the role of numerical prediction methods within the classification framework and goal based design approach discussed. Finally the suitability of current developments in prediction methods to meet the needs of the industry and future challenges is assessed.
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.
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.
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