scholarly journals Predictions of Ship Extreme Hydroelastic Load Responses in Harsh Irregular Waves and Hull Girder Ultimate Strength Assessment

2019 ◽  
Vol 9 (2) ◽  
pp. 240 ◽  
Author(s):  
Jialong Jiao ◽  
Yong Jiang ◽  
Hao Zhang ◽  
Chengjun Li ◽  
Chaohe Chen
Keyword(s):  
Ultimate Strength ◽  
Time Domain ◽  
Three Dimensional ◽  
Direct Calculation ◽  
Wave Force ◽  
Irregular Waves ◽  
Restoring Force ◽  
Strength Assessment ◽  
Hull Girder ◽  
Rule Approach

In this paper, the hydroelastic motion and load responses of a large flexible ship sailing in irregular seaways are predicted and the hull girder ultimate strength is subsequently evaluated. A three-dimensional time-domain nonlinear hydroelasticity theory is developed where the included nonlinearities are those arising from incident wave force, hydrostatic restoring force and slamming loads. The hull girder structure is simplified as a slender Timoshenko beam and fully coupled with the hydrodynamic model in a time domain. Segmented model towing-tank tests are then conducted to validate the proposed hydroelasticity theory. In addition, short-term and long-term predictions of ship responses in irregular seaways are conducted with the help of the developed hydroelastic code in order to determine the extreme design loads. Finally, a simplified strength-check equation is proposed, which will provide significant reference and convenience for ship design and evaluation. The hull girder ultimate strength is assessed by both the improved Rule approach and direct calculation.

Automated Assessment of Ultimate Hull Girder Strength

2003 ◽  
Vol 125 (3) ◽  
pp. 211-218 ◽  
Author(s):  
M. J. Smith ◽  
N. G. Pegg
Keyword(s):  
Ultimate Strength ◽  
Progressive Collapse ◽  
Three Dimensional ◽  
Strength Analysis ◽  
Cross Sectional ◽  
Strength Assessment ◽  
Hull Girder ◽  
Single User Interface ◽  
Interaction Curves ◽  
The Uk

An automated approach to ultimate hull girder strength assessment using DRDC’s ultimate strength analysis suite (ULTSAS) is described. The analysis suite improves the ability to perform rapid ultimate strength assessments by providing access to UK and Canadian analysis codes and databases under a single user interface. The interface also allows for automatic cross-sectional model generation from three-dimensional ship finite element models with the MGDSA program. The main features of the ULTSAS system are described, including cross-sectional modelling, and the use of load-shortening curve databases. The paper also provides a review of the progressive collapse method for determining ultimate strength, which is now used in both the UK and Canadian analysis codes. Two numerical approaches are described, one based on curvature incrementing and the other on moment incrementing. It is shown that the moment incrementing procedure produces more accurate bi-axial interaction curves in some instances. Results are obtained for two damage configurations of the HALIFAX class frigate.

Time-Domain Hydroelasticity Theory of Ships Responding to Waves

1997 ◽  
Vol 41 (04) ◽  
pp. 286-300
Author(s):  
Jinzhu Xia ◽  
Zhaohui Wang
Keyword(s):  
Time Domain ◽  
Separation Of Variables ◽  
Mathematical Formulation ◽  
Rigid Motion ◽  
Surface Flow ◽  
Slender Body ◽  
Irregular Waves ◽  
Restoring Force ◽  
Slender Body Theory ◽  
Body Theory

A time-domain linear theory of fluid-structure interaction between floating structures and the incident waves is presented. The structure is assumed to be elastic and represented by general separation of variables, whereas the fluid is described as an initial boundary value problem of potential free surface flow. The general interface boundary condition is used in the mathematical formulation of the fluid motion around the flexible structure. The general time-domain theory is simplified to a slender-body theory for the analysis of wave-induced global responses of monohull ships. The structure is represented by a nonuniform beam, while the generalized hydrodynamic coefficients can be obtained from two-dimensional potential flow theory. The linear slender body theory is generalized to treat the nonlinear loading effects of rigid motion and structural response of ships traveling in rough seas. The nonlinear hydrostatic restoring force and hydrodynamic momentum action are considered. A numerical solution is presented for the slender body theory. Numerical examples are given for two ship cases with different geometry features, a warship hull and the S175 containership with two different bow flare forms. The predicted results include linear and nonlinear rigid motions and structural responses of ships advancing in regular and irregular waves. The results clearly demonstrate the importance and the magnitude of nonlinear effects in ship motions and internal forces. Numerical calculations are compared with experimental results of rigid and elastic material ship model tests. Good agreement is obtained.

Design Loads Used for Direct Strength Assessment of Merchant Ship Structures

2004 ◽  
Author(s):  
Tingyao Zhu ◽  
Toshiyuki Shigemi
Keyword(s):  
Irregular Waves ◽  
Estimation Methods ◽  
Regular Waves ◽  
Bulk Carrier ◽  
Ship Structures ◽  
Strength Assessment ◽  
Hull Girder ◽  
Merchant Ship ◽  
Bulk Carriers ◽  
Design Loads

This paper summarizes the results of extensive research on the design loads used for strength assessment of merchant ship structures such as tankers, bulk carriers and container ships. The main aim of the research was to develop practical estimation methods of design loads having rational technical backgrounds acting on primary structural members of tankers, bulk carriers and container ships. During this study: 1) The design sea states that closely resemble the actual sea states which are considered as the most severe for hull structures are proposed. 2) The practical estimation methods of the design sea states are proposed by parametric studies using the results of series calculation of representative merchant ships. 3) The practical estimation methods of design regular waves resulting in the same level of stresses with that induced in irregular waves under the design sea states are proposed. 4) The practical estimation methods of the design loads such as ship motions, accelerations, hull-girder bending moments and hydrodynamic pressures that are induced under design regular waves are briefly introduced. The findings in this study have been summarized and implemented in the new design standards for tanker, bulk carrier and container ship structures. (Guidelines for Tanker Structures, 2001, Nippon Kaiji Kyokai. Guidelines for Bulk Carrier Structures, 2002, Nippon Kaiji Kyokai. Guidelines for container Carrier Structures, 2003, Nippon Kaiji Kyokai.)

scholarly journals Fatigue Strength Assessment of Trimaran Cross-Deck Structure Based on Spectral and Simplified Fatigue Method

2019 ◽  
Vol 2019 ◽  
pp. 1-13
Author(s):  
Chunbo Zhen ◽  
Tianlin Wang ◽  
Pengyao Yu ◽  
Liang Feng
Keyword(s):  
Transfer Functions ◽  
Three Dimensional ◽  
Stress Transfer ◽  
Direct Calculation ◽  
Fatigue Behaviour ◽  
Fatigue Analysis ◽  
Fe Analysis ◽  
Linear Potential ◽  
Wave Loads ◽  
Strength Assessment

In order to investigate the fatigue behaviour of trimaran cross-deck structural details, the spectral and simplified fatigue analysis approaches are proposed. In spectral fatigue approach, three-dimensional (3D) linear potential flow theory and global FE analysis are used for wave loads and stress transfer functions calculation; the stochastic spectral fatigue analysis is carried out considering the weighted wave headings factors. In simplified fatigue approach, based on the direct calculation procedure of LR rules, the evaluation of simplified fatigue loads and loading conditions are presented, and the stress ranges are obtained by global finite element (FE) analysis. Then the fatigue lives of a few hot spots are computed to demonstrate the application of the proposed method. The result shows that the method given in this paper has a good applicability. This study offers methodology for the fatigue analysis of trimaran cross-deck structure, which may be regarded as helpful references for structural design of these types of ships.

Study on a Time Domain Prediction Method for Wave Force: Application for a Point-Absorber WEC

2018 ◽  
Author(s):  
Qiao Li ◽  
Motohiko Murai
Keyword(s):  
Time Domain ◽  
Wave Spectrum ◽  
Time Domain Analysis ◽  
Wave Force ◽  
Domain Analysis ◽  
Irregular Waves ◽  
Floating Body ◽  
Control Force ◽  
Electric Generator ◽  
The Time Domain

There are a lot of numerical analysis for solving hydrodynamic responses of a floating body in the time domain. Most of them can give a theoretical solution in given irregular waves. It means, however, that the solution can be obtained only if the accurate irregular waves represented by the wave spectrum should be given. As we consider the actual operation, we know it is difficult to detect the accurate irregular waves instantaneously as needed accuracy in the most of the time domain analysis for feed backing the control force to the system. This paper proposes a new method to predict the practical wave force from the displacement of waves at a floating body in time domain analysis almost instantaneously. The method, that can apply to predict forces in wave energy converter with linear electric generator, helps us to choose the control force for convert more electric power in irregular waves. We confirm the algorithm and examine its effectiveness.

The Simulation of Ship Motions Using a B-Spline–Based Panel Method in Time Domain

2007 ◽  
Vol 51 (03) ◽  
pp. 267-284
Author(s):  
Ranadev Datta ◽  
Debabrata Sen
Keyword(s):  
Time Domain ◽  
Three Dimensional ◽  
Basis Functions ◽  
The Body ◽  
Irregular Waves ◽  
Ship Motions ◽  
B Spline ◽  
Head Waves ◽  
Wigley Hull ◽  
Spline Basis

In this paper, a B-spline-based higher-order method is developed for simulating three-dimensional ship motions with forward speed. The problem is formulated in time domain using a transient free surface Green function. The body geometry is defined by open uniform or nonuniform B-spline basis functions depending on the hull type, whereas the unknown field variables are described by open uniform B-spline basis functions. The collocation method is applied to discretize the integral equation and then solved for the unknown potentials and source strengths. Motion computations in head waves are carried out for three types of ship hulls: a mathematically defined Wigley hull, a typical containership (S175 hull), and a Series 60 hull. Results are obtained for regular and irregular waves and compared with available experimental and computational results. It is found that the results from the present method are in very good agreement with the published results, and in particular with experimental data. Long-duration simulations have also been carried out with an ordinary desktop PC (PIV with 512 MB RAM) to demonstrate the ability of the method to simulate motions over long periods without any visible deterioration using only modest computational resources.

A Study on Forced Vibration of Double Bottom Structure due to Whipping on an Ultra Large Container Ship

2017 ◽  
Author(s):  
Yohei Kawasaki ◽  
Tetsuo Okada ◽  
Hiroaki Kobayakawa ◽  
Ichiro Amaya ◽  
Tetsuji Miyashita ◽  
...  
Keyword(s):  
Ultimate Strength ◽  
Time Domain ◽  
Forced Vibration ◽  
Wave Frequency ◽  
Container Ship ◽  
Hull Girder ◽  
Vibratory Response ◽  
Bottom Structures ◽  
Large Container ◽  
Wave Induced

Worldwide expansion of economy has brought about prominent and rapid enlargement of container ships. Their greater beam has caused more flexible double bottom structure, giving rise to concerns about its adverse effect to the ultimate strength of hull girder. To accurately assess the ultimate strength of hull girder, it is essential to precisely grasp how the double bottom structures behave in the actual sea state, in terms of whipping and vibratory response as well as wave frequency response. In this paper, the authors investigated structural behavior of the double bottom of a 14,000 TEU ultra large container ship in long-crested irregular head seas. Firstly, time domain ship motion and wave pressure on the hull surface was obtained through numerical analysis using Rankine source method. Subsequently, the obtained loads were applied to 3-dimensional whole ship finite element model, and time domain elastic responses of all over the hull structures were analyzed using Newmark-β method in terms of both whipping and wave frequency responses. As a result, regarding the wave frequency response, it was found that maximum wave induced upward bending of the midship double bottom structures is exerted almost simultaneously with the maximum wave induced hogging hull girder bending moment. The correlation factors between the double bottom bending and the hull girder bending were about 0.94 around the midship region, and they decreased in the fore and aft region. Regarding the whipping and vibratory response, it was found that large whipping response induces forced vibration of the double bottom structures, especially in the midship region. Because of the higher natural frequencies of the double bottom structures compared with that of whipping, the double bottom structures are excited in the same phase as the hull girder whipping, resulting in superimposed longitudinal stresses in way of the bottom shell plating. From these observations, it can be concluded that the local bending behavior of the double bottom structures adversely affects the hull girder ultimate strength, both in terms of wave loads and whipping loads, and it is necessary to take sufficient care to the double bottom rigidity.

scholarly journals Hydrodynamic Simulation of the Semi-Submersible Wind Float by Investigating Mooring Systems in Irregular Waves

2020 ◽  
Vol 10 (12) ◽  
pp. 4267
Author(s):  
Yu-Hsien Lin ◽  
Cheng-Hao Yang
Keyword(s):  
Time Domain ◽  
Potential Flow ◽  
Near Field ◽  
Three Dimensional ◽  
Irregular Waves ◽  
Viscous Drag ◽  
Floating Platform ◽  
Model Based ◽  
Damping Matrix ◽  
Slow Drift

The present study aims to implement the software ANSYS AQWA to discuss the hydrodynamic analysis of the DeepCwind semi-submersible floating platform in waves based on the potential flow theory by considering the second-order wave exciting force. In this study, the linearized potential-flow hydrodynamic radiation and diffraction problems in the frequency domain were firstly solved by adopting the three-dimensional panel method. Subsequently, the hydrodynamic coefficients and wave loading data were transformed to time domain forms by the Cummins time domain equation as a system loading input. Furthermore, the quadratic transfer function (QTF) matrices with different frequencies and directions deduced based on the near field integration over the mean wetted hull surface were adopted for the calculation of slow-drift forces. In order to represent the damping in a real system for modeling potential flow without Morison’s elements, an additional quadratic damping matrix was added to capture the viscous drag. Eventually, both of the dynamic mooring model based on the lump-mass (LM) approach and the quasi-static mooring model based on the multi-segmented, quasi-static (MSQS) approach are introduced to discuss the mooring effect on the platform hydrodynamics. The effect of wave heading angles on the platform motion is considered as an influential parameter as well.

Numerical Study of Large Amplitude Ship Motion With Forward Speed in Severe Seas

2009 ◽  
Author(s):  
D. C. Hong ◽  
H. G. Sung ◽  
S. Y. Hong
Keyword(s):  
Free Surface ◽  
Time Domain ◽  
Large Amplitude ◽  
Numerical Study ◽  
Surface Condition ◽  
Three Dimensional ◽  
Ship Motion ◽  
Forward Speed ◽  
Restoring Force ◽  
Head Waves

A three-dimensional time-domain calculation method is of crucial importance in prediction of ship motion with forward speed in a severe irregular sea. The exact solution of the free surface wave–ship interaction problem is very complicated because of the extremely nonlinear boundary conditions. In this paper, an approximate body nonlinear approach based on the three-dimensional time-domain forward-speed free-surface Green function has been presented. It is a simplified version of the method known as LAMP (Lin and Yue 1990) where the exact body boundary condition is applied on the instantaneous wetted surface of the ship while free-surface condition is linearized. In the present study, the Froude-Krylov force and the hydrostatic restoring force are calculated on the instantaneous wetted surface of the ship while the forces due to the radiation and scattering potentials on the mean wetted surface. The time-domain radiation and scattering potentials have been obtained from a time invariant kernel of integral equations for the potentials. The integral equation for the radiation potential is discretized according to the second-order boundary element method (Hong and Hong. 2008). The diffraction impulse response functions of the Wigley seakeeping model are presented for various Froude numbers. A simulation of coupled heave-pitch motion of the Wigley model advancing in regular head waves of large amplitude has been carried out. Comparisons between the fully linear and the present approximate body nonlinear computations have been made at various Froude numbers.

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