scholarly journals Method for Prediction of Extreme Wave Loads Based on Ship Operability Analysis Using Hindcast Wave Database

2021 ◽  
Vol 9 (9) ◽  
pp. 1002
Author(s):  
Tamara Petranović ◽  
Antonio Mikulić ◽  
Marko Katalinić ◽  
Maro Ćorak ◽  
Joško Parunov
Keyword(s):  
Transfer Functions ◽  
Extreme Values ◽  
Bending Moment ◽  
Ship Motions ◽  
Bending Moments ◽  
Wave Loads ◽  
Extreme Wave ◽  
Short Term ◽  
Passenger Ship ◽  
Limiting Values

The method for the prediction of extreme vertical wave bending moments on a passenger ship based on the hindcast database along the shipping route is presented. Operability analysis is performed to identify sea states when the ship is not able to normally operate and which are likely to be avoided. Closed-form expressions are used for the calculation of transfer functions of ship motions and loads. Multiple operability criteria are used and compared to the corresponding limiting values. The most probable extreme wave bending moments for the short-term sea states at discrete locations along the shipping route are calculated, and annual maximum extreme values are determined. Gumbel probability distribution is then fitted to the annual extreme values, and wave bending moments corresponding to a return period of 20 years are determined for discrete locations. The system reliability approach is used to calculate combined extreme vertical wave bending moment along the shipping route. The method is employed on the example of a passenger ship sailing across the Adriatic Sea (Split, Croatia, to Ancona, Italy). The contribution of the study is the method for the extreme values of wave loads using the hindcast wave database and accounting for ship operational restrictions.

Probabilistic Load Combination Factors of Wave and Whipping Bending Moments

2015 ◽  
Vol 59 (01) ◽  
pp. 11-30
Author(s):  
Maro Corak ◽  
Joško Parunov ◽  
C. Guedes Soares
Keyword(s):  
Extreme Values ◽  
Bending Moment ◽  
Practical Method ◽  
Time Instant ◽  
Regression Equations ◽  
Bending Moments ◽  
Short Term ◽  
Load Combination ◽  
Combination Methods ◽  
Probabilistic Load

Extreme values of wave and whipping bending moments are important in structural design of large containerships. Since the extreme values of these two, partially correlated processes do not occur at the same time instant and even at the same environmental conditions, it is necessary to combine them by using probabilistic load combination methods. The correlation analysis between wave and whipping bending moments is performed and a practical method for calculation of the most probable load combination factor between considered bending moments is presented. Short-term load combination factors are calculated by reconstruction of the signal from the frequency domain solution. Results are validated by comparison with model test data of the 9400-TEU containership for various sea states and speeds and heading angles. Practical regression equations for estimation of the most probable short-term load combination factor are formulated. Regression equations are then used in the computation of the long-term distribution of combined bending moment. The procedure is demonstrated on the example of the two large containerships.

Analysis of Design Wave Loads on an FPSO Accounting for Abnormal Waves

2005 ◽  
Vol 128 (3) ◽  
pp. 241-247 ◽  
Author(s):  
C. Guedes Soares ◽  
Nuno Fonseca ◽  
Ricardo Pascoal ◽  
Guenther F. Clauss ◽  
Christian E. Schmittner ◽  
...  
Keyword(s):  
Transfer Functions ◽  
Prediction Method ◽  
Bending Moment ◽  
Rogue Waves ◽  
Wave Loads ◽  
Short Term ◽  
Operational Lifetime ◽  
Standard Linear ◽  
Long Term Prediction ◽  
Vertical Bending Moment

The paper presents an analysis of structural design wave loads on an FPSO. The vertical bending moment at midship induced by rogue waves are compared with rule values. The loads induced by deterministic rogue waves were both measured in a seakeeping tank and calculated by an advanced time domain method. Two procedures are used to calculate the expected extreme vertical bending moment during the operational lifetime of the ship. The first one relies on a standard linear long term prediction method, which results from the summation of short term distribution of maxima weighted by their probability of occurrence. The short term stationary seastates are represented by energy spectra and the ship responses by linear transfer functions. The second one is a generalization of the former and it accounts for the nonlinearity of the vertical bending moment, by using nonlinear transfer functions of the bending moment sagging peaks which depend of the wave height.

scholarly journals Assessment of internal pressure effect, causing additional bending of the pipeline

2020 ◽  
Vol 242 ◽  
pp. 160
Author(s):  
Ramil BAKTIZIN ◽  
Rail ZARIPOV ◽  
Gennadii KOROBKOV ◽  
Radik MASALIMOV
Keyword(s):  
Internal Pressure ◽  
Pressure Effect ◽  
Extreme Values ◽  
Bending Moment ◽  
Extreme Value ◽  
Bending Moments ◽  
Temperature Stresses ◽  
Working Pressure ◽  
Trunk Pipeline ◽  
Bending Stresses

Article justifies accounting for internal pressure effect in the pipeline, causing additional bending of the pipeline. According to some scientists, there is an erroneously used concept of the equivalent longitudinal axial force (ELAF) Sx, which depends on working pressure, temperature stresses, and joint deformations of pipelines with various types of soils. However, authors of the article use ELAF Sx concept at construction of mathematical model of stress-strain state (SSS) for complex section of the trunk pipeline, and also reveal it when analyzing the results of calculating the durability and stability of the pipeline. Analysis of SSS for calculated section of the pipeline was carried out for two statements of the problem for different values of operation parameters. In the first statement, effect of internal pressure causing bending of the pipeline is taken into account, and in the second it is neglected. It is shown that due to effect of ELAF Sx at p0 = 9.0 MPa, Dt = 29 °C extreme value of bend increases by 54 %, extreme values of bending stresses from span bending moment increase by 74 %, and extreme value of bending stresses from support bending moment double with regard to corresponding SSS characteristics of the pipeline. In case of neglecting the internal pressure effect causing additional bending of the pipeline (second statement of the problem), error in calculating the extreme value of bend is 35 %, extreme value of bending stresses from span bending moments is 44 %, and extreme value of bending stresses from support bending moments is 95 %.

Experimental Study on Wave Loads of Flooded Ship

2007 ◽  
Author(s):  
B. W. Kim ◽  
D. C. Hong ◽  
S. Y. Hong ◽  
J. H. Kyoung ◽  
S. K. Cho ◽  
...  
Keyword(s):  
Model Test ◽  
Ship Motions ◽  
Test Model ◽  
Bending Moments ◽  
Wave Loads ◽  
Test Results ◽  
Ocean Engineering ◽  
Shear Forces ◽  
Engineering Research ◽  
Ship Model

This paper investigates wave loads of a flooded ship by model test. Model tests are performed in ocean engineering basin of MOERI (Maritime and Ocean Engineering Research Institute). Ship motions are measured by RODYM6D. Wave loads such as shear forces, bending moments and torsion moments are measured by ATI load cell mounted on segmented parts of the ship model. A 300 m-long barge ship with two flooded compartments is considered in model test. Responses of intact and flooded cases are compared. The test results are also compared with numerical analyses using boundary element method.

Influence of Whipping on Long-term Vertical Bending Moment

2004 ◽  
Vol 48 (04) ◽  
pp. 261-272
Author(s):  
Gro Sagli Baarholm ◽  
Jørgen Juncher Jensen
Keyword(s):  
Nonlinear Response ◽  
Extreme Values ◽  
Bending Moment ◽  
Sea Waves ◽  
Short Term ◽  
Strip Theory ◽  
Long Time ◽  
Wave Induced ◽  
Vertical Bending Moment

This paper is concerned with estimating the response value corresponding to a long return period, say 20 years. Time domain simulation is required to obtain the nonlinear response, and long time series are required to limit the statistical uncertainty in the simulations. It is crucial to introduce ways to improve the efficiency in the calculation. A method to determine the long-term extremes by considering only a few short-term sea states is applied. Long-term extreme values are estimated using a set of sea states that have a certain probability of occurrence, known as the contour line approach. Effect of whipping is included by assuming that the whipping and wave-induced responses are independent, but the effect of correlation of the long-term extreme value is also studied. Numerical calculations are performed using a nonlinear, hydroelastic strip theory as suggested by Xia et al (1998). Results are presented for the S-175 containership (ITTC 1983) in head sea waves. The analysis shows that whipping increases the vertical bending moment and that the correlation is significant.

Effect of Heavy Weather Maneuvering on the Wave-Induced Vertical Bending Moments in Ship Structures

1990 ◽  
Vol 34 (01) ◽  
pp. 60-68 ◽  
Author(s):  
C. Guedes Soares
Keyword(s):  
Wave Height ◽  
Significant Wave Height ◽  
Decision Rules ◽  
Bending Moment ◽  
Ship Motions ◽  
Bending Moments ◽  
Significant Wave ◽  
Course Changes ◽  
Wave Induced ◽  
Vertical Bending Moment

Statistical data are collected so as to quantify the probability of occurrence of voluntary course changes in heavy weather as well as their dependence on significant wave height and on ship heading. Decision rules are established about when and how to change course, on the basis of the analysis of operational data and of interviews with experienced shipmasters. A Monte Carlo simulation is performed so as to determine how an omnidirectional distribution of initial headings is changed by voluntary course changes depending on the significant wave height. Finally, the effect of the nonuniform distribution of headings on the mean wave-induced vertical bending moment is calculated. It is shown that although heavy weather maneuvering eases the ship motions, it can increase the wave-induced bending moments and thus increase the probability of structural failure.

Methods of Computing the Probability of Failure Under Extreme Values of Bending Moment

1972 ◽  
Vol 16 (02) ◽  
pp. 113-123
Author(s):  
Alaa Mansour
Keyword(s):  
Probability Density Function ◽  
Probability Density ◽  
Density Function ◽  
Extreme Values ◽  
Bending Moment ◽  
Random Variable ◽  
Probability Of Failure ◽  
Short Term ◽  
Term Analysis

Methods for predicting the probability of failure under extreme values of bending moment (primary loading only) are developed. In order to obtain an accurate estimate of the extreme values of the bending moment, order statistics are used. The wave bending moment amplitude treated as a random variable is considered to follow, in general, Weibull distribution so that the results could be used for short-term as well as long-term analysis. The probability density function of the extreme values of the wave bending moment is obtained and an estimate is made of the most probable value (that is, the mode) and other relevant statistics. The probability of exceeding a given value of wave bending moment in "n" records and during the operational lifetime of the ship is derived. Using this information, the probability of failure is obtained on the basis of an assumed normal probability density function of the resistive strength and deterministic still-water bending moment. Charts showing the relation of the parameters in a nondimensional form are presented. Examples of the use of the charts for long-term and short-term analysis for predicting extreme values of wave bending moment and the corresponding probability of failure are given.

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%.

Partial Safety Factors for Vertical Bending Loads on Containerships

1992 ◽  
Vol 114 (2) ◽  
pp. 129-136 ◽  
Author(s):  
C. O¨stergaard
Keyword(s):  
Probability Density ◽  
Reliability Analysis ◽  
Limit State ◽  
Bending Moment ◽  
Bending Moments ◽  
Wave Loads ◽  
Safety Factors ◽  
The North ◽  
Design Values ◽  
Partial Safety Factors

International design codes for seagoing steel ships of today are in the process of testing a new safety format with load factors separately multiplied with nominal (code) values of still water and wave loads. This leads to two design values of these loads, the sum of which must not exceed a design value of the strength of the ship structure, which is again a nominal (code) value of strength, this time divided by a strength factor. Such load and strength factors are generally termed partial safety factors. In the paper, vertical still water and wave bending moments of containerships are considered as loads. The partial safety factors are determined on the basis of reliability analysis, i.e., the sum of the design values of the loads will not exceed a design serviceability limit state of the ship’s structure with given probability. To enable reliability analysis, distribution density of the ship’s strength to resist bending moments is based on a stochastic interpretation of nominal (code) values used in the conventional safety format. The probability density of the still water bending moment is obtained from recently published statistical data. The probability density of the wave bending moment is calculated using advanced hydrodynamic and spectral analysis, including long-term statistics of the (North Atlantic) seaway. Reliability and related design values are estimated using the FORM algorithm with due consideration of the different repetition numbers for which the stochastic models of the two bending moments are valid. The results are presented as nonlinear regression formulas and as diagrams that specify partial safety factors related to length and beam of containerships. The nominal values of bending moments to be used with these partial safety factors are given as functions of length, beam, and block coefficient of those ships.

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