Fatigue Assessment for Ship Structure Acted on Non-Linear Wave Loads

2007 ◽  
Vol 353-358 ◽  
pp. 2786-2789
Author(s):  
Chao He Chen
Keyword(s):  
Fatigue Damage ◽  
Bending Moment ◽  
Linear Wave ◽  
Wave Loads ◽  
Ship Structure ◽  
Random Seas ◽  
Non Linear ◽  
Bow Flare ◽  
Short Term Prediction ◽  
The Given

Efficient methods are described here to predict the fatigue damage of ship structure due to nonlinear wave loads that are produced in random seas. Firstly the effects of the non-linear waveinduced bending moment on the fatigue damage of ship structure with very large bow flare are presented in short-term prediction by the method of spectrum analysis. Then, the fatigue damage is estimated and analyzed in the given environment of long-term.

Full-Scale Measurements on Hull Response of a Large-Container Ship in Service

2006 ◽  
Author(s):  
Kenichiro Miyahara ◽  
Ryuju Miyake ◽  
Norikazu Abe ◽  
Atsushi Kumano ◽  
Masanobu Toyoda ◽  
...  
Keyword(s):  
High Harmonic ◽  
Bending Moment ◽  
Full Scale ◽  
Linear Wave ◽  
Container Ship ◽  
Wave Loads ◽  
Non Linear ◽  
Large Container ◽  
Probability Density Distributions

In order to investigate hull responses of post-Panamax container ships in the actual sea, full-scale measurements on hull responses of a post-Panamax container ship in service were conducted. In linear wave domain, the probability density distributions of hull responses obtained by full-scale measurements were compared with the Rayleigh distributions to check on the range of the applicability, and comparisons with the long-term distributions of the longitudinal stress obtained by full-scale measurements and the direct structural analyses based on the wave loads analyzed by using the linear 3D Rankine source method were made to verify the accuracy. In non-linear wave domain, the measured longitudinal stresses showed the asymmetry of vertical bending moment. The long-term distributions of hull responses, which have the high harmonic components, obtained by full-scale measurements were compared with the numerical results analyzed by using non-linear methods to investigate the non-linearity on hull responses of container ship.

Frequency Versus Time Domain Fatigue Analysis of a Semisubmersible Wind Turbine Tower

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Marit I. Kvittem ◽  
Torgeir Moan
Keyword(s):  
Wind Turbine ◽  
Fatigue Damage ◽  
Time Domain ◽  
Low Frequency ◽  
Bending Moment ◽  
Good Representation ◽  
Bending Moments ◽  
Wave Loads ◽  
Flexible Mode ◽  
Standard Deviations

The current paper deals with a study of a semisubmersible wind turbine (WT), where short-term tower base bending moments and tower fatigue damage were estimated by a frequency domain (FD) method. Both a rigid structure assumption and a generalized degree-of-freedom (DOF) model for including the first flexible mode of the turbine tower were investigated. First, response to wind and wave loads was considered separately, then superposition was used to find the response to combined wind and wave loading. The bending moments and fatigue damage obtained by these methods were compared to results from a fully coupled, nonlinear time domain (TD) analysis. In this study a three column, catenary moored semisubmersible with the NREL 5 MW turbine mounted on one of the columns was modeled. The model was inspired by the WindFloat concept. The TD simulation tool used was Simo-Riflex-AeroDyn from Marintek and CeSOS. The FD method gave a good representation of the tower base bending moment histories for wave-only analyses, for the moderate sea states considered in these analyses. With the assumption that the structure is completely rigid, bending moments were underestimated, but including excitation of the elastic tower and blades, improved the results. The wind-induced low-frequency bending moments were not captured very well, which presumably comes from a combination of nonlinear effects being lost in the linearization of the thrust force and that the aerodynamic damping model was derived for a fixed turbine. Nevertheless, standard deviations of the bending moments were still reasonable. The FD model captured the combined wind and wave analyses quite well when a generalized coordinates model for wind excitation of the first bending mode of the turbine was included. The FD fatigue damage predictions were underestimated by 0–60%, corresponding to discrepancies in standard deviations of stress in the order of 0–20%.

Determination of global design loads for large high-speed catamarans

2002 ◽  
Vol 216 (1) ◽  
pp. 79-94
Author(s):  
S E Heggelund ◽  
T Moan ◽  
S Oma
Keyword(s):  
High Speed ◽  
Bending Moment ◽  
Wave Loads ◽  
Strip Theory ◽  
Non Linear ◽  
Design Loads ◽  
Linear Effects ◽  
Operational Criteria ◽  
Vertical Bending Moment

Methods for calculation of design loads for high-speed vessels are investigated. The influence of operational restrictions on design loads is emphasized. Relevant operational criteria for high-speed displacement vessels are discussed. Procedures and criteria for numerical calculation of operational limits are incomplete and should be further investigated. Operational limits and design loads for a 60 m catamaran are calculated on the basis of linear strip theory. Non-linear effects on design loads are assessed from calculations in regular waves. Simplified formulae commonly used by classification societies for prediction of operational limits seem to over-predict the reduction of motions and wave loads at reduced speed. When operational limits typically given by the shipmaster or the operator are used, the design loads found by direct calculations are comparable with design loads given by classification societies. For vertical bending moment and torsion, the use of active foils is found to increase the linear loads. Owing to reduced motions, the foils reduce the non-linear loads and hence the total loads. The effect of non-linear horizontal loads is not investigated but can be important for transverse bending moment.

Non-linear wave loads and ship responses by a time-domain strip theory

1998 ◽  
Vol 11 (3) ◽  
pp. 101-123 ◽  
Author(s):  
Jinzhu Xia ◽  
Zhaohui Wang ◽  
J.Juncher Jensen
Keyword(s):  
Time Domain ◽  
Linear Wave ◽  
Wave Loads ◽  
Strip Theory ◽  
Non Linear

Estimation of hull girder vertical bending moments including non-linear and flexibility effects using closed form expressions

2009 ◽  
Vol 223 (3) ◽  
pp. 377-390 ◽  
Author(s):  
P T Pedersen ◽  
J J Jensen
Keyword(s):  
Closed Form ◽  
Linear Response ◽  
Bending Moment ◽  
Phase Lag ◽  
Bending Moments ◽  
Hull Girder ◽  
Strip Theory ◽  
Non Linear ◽  
Bow Flare ◽  
Wave Induced

A simple but rational procedure for prediction of extreme wave-induced hull girder bending moment in slender mono-hull displacement vessels is presented. The procedure takes into account main ship hull characteristics such as length, breadth, draught, block coefficient, bow flare coefficient, forward speed, and hull flexibility. The wave-induced loads are evaluated for specific operational profiles. Non-linearity in the wave bending moment is modelled using results derived from a second-order strip theory and water entry solutions for wedge-type sections. Hence, bow flare slamming is accounted for through a momentum type of approach. The stochastic properties of this non-linear response are calculated through a monotonic Hermite transformation. In addition, the impulse loading attributable to, for example, bottom slamming or a rapid change in bow flare is included using a modal expansion in the two lowest vertical vibration modes. These whipping vibrations are added to the wave frequency non-linear response, taking into account the rise time of the impulse response as well as the phase lag between the occurrence of the maximum non-linear load and the maximum impulse load. Previous results for the sagging bending moment are validated by comparison with fully non-linear strip theory calculations and supplemented with new closed form results for the hogging bending moment. Focus is on the extreme hull girder hogging bending moment. Owing to the few input parameters, this procedure can be used to estimate the wave-induced bending moments at the conceptual design phase. Another application area is for novel single-hull ship types not presently covered by the rules of the classification societies. As one application example the container ship MSC Napoli is considered. Further validations are needed, however, in order to select proper values of the parameters entering the analytical form of the slamming impulse.

Numerical and Experimental Investigation on Nonlinear Cyclic Collapse Response of Ship Model in Regular Waves

2020 ◽  
Vol 143 (4) ◽  
Author(s):  
Weiqin Liu ◽  
Yu Huang ◽  
Ye Li ◽  
Xuemin Song ◽  
Fangyi Wei ◽  
...  
Keyword(s):  
Ultimate Strength ◽  
Nonlinear Dynamic ◽  
Dynamic Strength ◽  
Bending Moment ◽  
Bending Test ◽  
Wave Loads ◽  
Nonlinear Simulation ◽  
Ship Structure ◽  
Ship Model ◽  
Element Method

Abstract Large ocean waves with large wave height may destroy the ship’s structure, whereas it is difficult to predict the nonlinear dynamic strength in the large waves. In this study, we used a nonlinear simulation based on boundary element method (BEM)-finite element method (FEM) and a collapse experiment of ship model to study dynamic ultimate strength and dynamic course of collapse of ship structure, the collapse test was performed in regular tank wave. Besides, a simulation method for nonlinear dynamic ship strength was proposed to predict and compare the results of collapse test. A collapsed model consisting of a plastic hinge and two ship strips is designed. Subsequently, we performed the nonlinear simulation of the ultimate strength of ship model induced by tank wave. Wave loads were calculated following potential theory and BEM. Next, ship structural FEM model was modeled, the ship pressure was transferred to ship wet surface elements, and inertia force was exerted as well. Finally, the nonlinear dynamic strength calculation of ship model was performed in accordance with nonlinear FEM. A four-point-bending test adopted displacement controlling method was designed to obtain the hysteresis characteristic of the elastoplastic hinge. Hysteretic test and simulation analysis was performed to determine post-ultimate bending moment. Time-domain computational results including rotation angle history and vertical bending moment are close to collapse test results so that the two methods are verified. This study verifies that structural nonlinearities of ship structure induced by wave loads could be predicted.

Non-linear electrostatic plasma waves

1972 ◽  
Vol 7 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Hans Schamel
Keyword(s):  
Debye Length ◽  
Trapped Ions ◽  
Linear Wave ◽  
Ion Acoustic Wave ◽  
Non Linear ◽  
Unknown Distribution Function ◽  
The One ◽  
Image Position ◽  
The Given ◽  
Electrostatic Plasma Waves

A solution of the one-dimensional time-independent Vlasov–Poisson system, including the condition of no net current, is constructed for a large class of electric potential functions φ(x), including periodic and solitary waves, as well as monotonic transitions. Displaced Maxwell distributions for the free particles, and an unshifted Maxwell distribution for the trapped ions, are used. The condition of positiveness of the unknown distribution function for the trapped electrons (which can be split into two parts, one depending solely on the chosen wave, the other on the given distributions) is examined. It is shown, for a non-linear wavethat this condition plays no rôle when the thickness l of the wave considerably exceeds the Debye length λD(l ≫ λD). If, however, l lies in the neighbourhood of λD(l ≳ λD), there exist limits for the free parameters. The smallest thickness lmin results if the Mach number M lies in the range 1 > M > 2 and the electronion—temperature ratio θ = Te/Ti exceeds 10. This confirms the view that the wave is a steepened ion-acoustic wave. lmin decreases with decreasing amplitude ϕmax of the wave and decreasing number of trapped ions, but does not lie below the Debye length as long as the wave is non-linear. In the linear case, the condition of positiveness imposes no restrictions.

Long-Term Fatigue Damage of Ship Structures Under Nonlinear Wave Loads

2002 ◽  
Vol 39 (02) ◽  
pp. 95-104
Author(s):  
Xue KangGu ◽  
Torgeir Moan
Keyword(s):  
Fatigue Damage ◽  
Nonlinear Wave ◽  
Direct Analysis ◽  
Linear Wave ◽  
Wave Loads ◽  
Ship Structures ◽  
Hull Girder ◽  
Structural Fatigue ◽  
Large Container

Fatigue is a principal mode of failure in ship structures, especially when high tensile steels are applied. Although significant efforts have been made to predict fatigue damage, there are still uncertainties existing, e.g., in the stress histories that cause fatigue. This paper addresses estimation of fatigue damage in ships under wave loads, with an emphasis on containerships, which have large bow flare and low hull girder rigidity. Linear and nonlinear wave-induced loads as well as dynamic effects due to hull flexibility, i.e., whipping, are researched. With the direct analysis method of fatigue, the nature of the wave loading, hull rigidity, structural damping, stress range counting algorithm and SN curve on structural fatigue damage are investigated. In long-term fatigue damage estimates, the influence of different sea environments is numerically analyzed. The importance of nonlinearity of wave loads and especially the whipping on the structural fatigue damage is demonstrated by calculation for a large container vessel with large flare and lowest natural frequency of 0.749 Hz. Depending upon sea environments and SN curves used in long-term predictions, the fatigue damage based on nonlinear wave loads (excluding whipping) is 10–100% larger than that due to linear wave loads; the fatigue damage based on nonlinear combined loads (including whipping) may be 1–9 times larger than that of steady-state nonlinear wave loads.

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