Effects of Weather Routing on Maximum Vertical Bending Moment in a Ship Taking Account of Wave-Induced Vibrations

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Kazuhiro Iijima ◽  
Rika Ueda ◽  
Hitoi Tamaru ◽  
Masahiko Fujikubo
Keyword(s):  
North Atlantic Ocean ◽  
Meteorological Data ◽  
Bending Moment ◽  
Simulation Method ◽  
Extreme Value ◽  
Operational Parameters ◽  
Wave Condition ◽  
Weather Routing ◽  
Wave Induced ◽  
Vertical Bending Moment

In this paper, the effect of weather routing and ship operations on the extreme vertical bending moment (VBM) in a 6000TEU class large container ship which is operated in North Atlantic Ocean is addressed. A direct time-domain nonlinear response simulation method taking account of the wave-induced vibrations is combined with a voyage simulation based on 10 years of meteorological data in the area. The probability distribution of the ship's operational parameters conditional upon the meteorological conditions is considered. It is clarified that the most severe wave condition with the significant wave height over 16 m in the area may not be encountered by the ship due to the weather routing and the extreme value is determined mostly by the wave condition much milder than the most severe in the area. It is also found out that the ship speed assumed in the most contributing sea state strongly affects the extreme value of the total VBM. It is explained by the fact that the wave-induced vibrations in the ship tend to be excited at faster speed.

Load Combination for Fatigue Analysis of Ship Structures

2004 ◽  
Author(s):  
Yung S. Shin ◽  
Booki Kim ◽  
Alexander J. Fyfe
Keyword(s):  
Bending Moment ◽  
Linear Summation ◽  
Load Combination ◽  
Longitudinal Stiffeners ◽  
Stress Components ◽  
Tank Pressure ◽  
Wave Induced ◽  
Vertical Bending Moment ◽  
Oil Tanker

A methodology for calculating the correlation factors to combine the long-term dynamic stress components of ship structure from various loads in seas is presented. The methodology is based on a theory of a stationary ergodic narrow-banded Gaussian process. The total combined stress in short-tem sea states is expressed by linear summation of the component stresses with the corresponding combination factors. This expression is proven to be mathematically exact when applied to a single random sea. The long-term total stress is similarly expressed by linear summation of component stresses with appropriate combination factors. The stress components considered here are due to wave-induced vertical bending moment, wave-induced horizontal bending moment, external wave pressure and internal tank pressure. For application, the stress combination factors are calculated for longitudinal stiffeners in cargo and ballast tanks of a crude oil tanker at midship section. It is found that the combination factors strongly depend on wave heading and period in the short-term sea states. It is also found that the combination factors are not sensitive to the selected probability of exceedance level of the stress in the long-term sense.

Steep Wave Effects on Wave Induced Vertical Bending Moment Using a 3D Numerical Wave Tank

2017 ◽  
Author(s):  
Shivaji Ganesan Thirunaavukarasu ◽  
Debabrata Sen ◽  
Yogendra Parihar
Keyword(s):  
Comparative Study ◽  
Incident Wave ◽  
Bending Moment ◽  
Wave Steepness ◽  
Numerical Wave Tank ◽  
Wave Tank ◽  
Strip Theory ◽  
Numerical Wave ◽  
Wave Induced ◽  
Vertical Bending Moment

This paper presents a detail comparative study on wave induced vertical bending moment (VBM) between linear and approximate nonlinear calculations using a 3D numerical wave tank (NWT) method. The developed numerical approach is in time domain where the ambient incident waves can be defined by any suitable wave theory. Certain justifying approximations employed in the solution of the interaction hydrodynamics (diffraction and radiation) enabling the NWT to generate stable long duration time histories of all parameters of interest. This is an extension of our earlier works towards the development of a practical NWT based solution for wave-structure interactions [1]. After a brief outline of the implemented numerical details, a comprehensive validation and verification of vertical shear force (VSF) and bending moment RAOs computed using the linearized version of the NWT against the usual linear results of strip theory and 3D panel codes are presented. Next we undertake the comparative study between the fully linear and approximate nonlinear versions of the present code for different incident wave steepness. In the approximate nonlinear formulation, the ambient incident wave is defined by the full nonlinear numerical wave model based on Fourier approximation method which can generate very steep steady periodic nonlinear waves up to the near wave breaking limit. The nonlinearities associated with the incident Froude Krylov and hydrostatic restoring forces/moments are exact up to the instantaneous wetted surface at the displaced location, but the hydrodynamic diffraction and radiation effects are linearized around the mean wetted surface. The standard S175 container hull is considered for the comparative studies because of its geometric nonlinearities. Numerical simulations are performed for four different wave lengths with increasing wave steepness. It is observed that the computed wave induced VBM amidships from the approximate nonlinear results can be almost 30% higher compared to the results from a purely linear solution, which can be a critical issue from the safety point. Significant higher harmonics are also observed in the approximate nonlinear results which at some times may be responsible for exciting the undesirable whipping/springing responses.

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.

Experimental and Numerical Study of Wave-Induced Load Effects of Open Ships in Oblique Seas

2011 ◽  
Vol 55 (02) ◽  
pp. 100-123 ◽  
Author(s):  
Suji Zhu ◽  
Mingkang Wu ◽  
Torgeir Moan
Keyword(s):  
Shear Force ◽  
Numerical Study ◽  
Bending Moment ◽  
Vertical Shear ◽  
Torsional Moment ◽  
Numerical Predictions ◽  
Load Effects ◽  
Computer Codes ◽  
Wave Induced ◽  
Vertical Bending Moment

Open ships inherently possess low torsional rigidity because of their open deck structural configuration. Some of the structural failures for open ships are caused by wave-induced torsional moment in combination with other load components in oblique seas. Relatively few experimental results about horizontal bending and torsional moments in oblique seas have been published, however. Further, test data for vertical shear force and vertical bending moment in oblique seas are quite scarce. A backbone model has been recently tested by the Center for Ships and Ocean Structures (CeSOS) in the towing tank and ocean basin at the Marine Technology Center. The model consists of 15 box-shaped segments, in addition to bow and stern segments, which are interconnected by an aluminum beam on the top. Model tests in oblique seas without forward speed were first carried out to provide basic comparisons. Tests in head and oblique seas with speeds were then conducted in regular waves. Irregular wave tests were also carried out to assess the spectral responses and peak distributions of cross-sectional load effects. Load effects at 7 longitudinal positions were measured through strain gauges, including vertical shear force (VSF), vertical bending moment (VBM), horizontal bending moment (HBM), and torsional moment (TM). The motivation of this paper is to perform a benchmark study by comparing numerical predictions of different computer codes with these test results. The uncertainties in the experiments and the computer codes are discussed, and conclusions are presented at the end of this paper.

Coupled Simulation Between Fast and Hydro-Structural Code for a Flexible FOWT Considering Blade Pitch Control Malfunction

2016 ◽  
Author(s):  
Sharath Srinivasamurthy ◽  
Kazuhiro Iijima ◽  
Yasunori Nihei ◽  
Naoyuki Hara
Keyword(s):  
Wind Turbine ◽  
Bending Moment ◽  
Simulation Method ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Time Duration ◽  
Scaled Model ◽  
Onshore Wind ◽  
Pitch Control ◽  
Vertical Bending Moment

In this research, a coupled numerical simulation method for a Floating Offshore Wind Turbine (FOWT) is developed. Flexibility of the platform and blade pitch control malfunction can be accounted for by the proposed method. The numerical method is validated qualitatively against a series of scaled model experiment and further simulations are carried out to predict the structural load due to the abrupt failure of blade pitch control system. The influence of blade pitch malfunction for a FOWT is confirmed by utilizing a SPAR and a semi-submersible type floaters and compared against onshore wind turbine case. The behavior and tendency for combined effect of wind and wave is compared and the tool developed is validated. It is found that the abrupt change of the rotor thrust induces the tower flexible modes for the onshore case while almost rigid body motions are the dominant for the floater cases with almost no excitation of the flexible vibration mode. The maximum bending moment after malfunction is almost comparable among the onshore and floating cases however it is observed that the time duration during which the vertical bending moment takes the largest value is different.

Stress Combination for Fatigue Analysis of Ship Structures

2004 ◽  
Vol 127 (2) ◽  
pp. 175-181 ◽  
Author(s):  
Yung S. Shin ◽  
Booki Kim ◽  
Alexander J. Fyfe
Keyword(s):  
Bending Moment ◽  
Short Term ◽  
Linear Summation ◽  
Longitudinal Stiffeners ◽  
Stress Components ◽  
Tank Pressure ◽  
Wave Induced ◽  
Vertical Bending Moment ◽  
Oil Tanker

A methodology for calculating the correlation factors to combine the long-term dynamic stress components of ship structure from various loads in seas is presented. The proposed methodology is valid for a stationary ergodic narrow-banded Gaussian process. The total combined stress in short-term sea states is expressed by linear summation of the component stresses with the corresponding combination factors. This expression is proven to be mathematically exact when applied to a single random sea. The long-term total stress is similarly expressed by linear summation of component stresses with appropriate combination factors. The stress components considered here are due to wave-induced vertical bending moment, wave-induced horizontal bending moment, external wave pressure, and internal tank pressure. For application, the stress combination factors are calculated for longitudinal stiffeners in midship cargo and ballast tanks of a crude oil tanker. It is found that the combination factors strongly depend on wave heading and period in the short-term sea states. It is also found that the combination factors are not sensitive to the selected probability of exceedance level of the stress in the long-term sense.

Numerical Investigation Into Uncertainty of Wave-Induced Vibration of Large Container Ships due to Ship Operation

2017 ◽  
Author(s):  
Kazuhiro Iijima ◽  
Rika Ueda ◽  
Masahiko Fujikubo
Keyword(s):  
Time Series ◽  
Bending Moment ◽  
Forward Speed ◽  
Sea State ◽  
Large Container ◽  
Hydroelastic Response ◽  
Wave Induced ◽  
Ship Operation ◽  
Vertical Bending Moment ◽  
Ship Speed

A series of seakeeping simulations accounting for the wave-induced vibration is performed on three large container ships with different sizes. Time series of bodily motions, accelerations and stress due to vertical bending moment are calculated for the three ships navigating in a short-term sea state. Ship forward speed is varied from 0 knot to 20knots to investigate the sensitivity of the hydroelastic response to the change of the speed. Statistical analysis is made over the time series results, and the results are compared in terms of significant value. The uncertainty of the wave-induced vibration with respect to the ship speed is evaluated for the respective ships. It is found out that the increase rate of pitch motion, accelerations and stress to the increase of the ships’ forward speed is different from each other. It is further observed that the acceleration and vertical bending moment increase is less prominent for the largest ship.

Uncertainties of Climate Modeling and Effects on Wave Induced Bending Moment

2014 ◽  
Author(s):  
Erik Vanem ◽  
Elzbieta M. Bitner-Gregersen ◽  
Lars Ingolf Eide ◽  
Luca Garrè ◽  
Peter Friis Hansen
Keyword(s):  
Climate Change ◽  
North Atlantic Ocean ◽  
Bending Moment ◽  
Wave Climate ◽  
Potential Effect ◽  
Analytical Models ◽  
Climate Projections ◽  
Operational Experience ◽  
Safety Level ◽  
Wave Induced

Ocean going ships are exposed to the environmental forces from waves and wind and the expected environmental loads over the life cycle of the ship need to be taken into account in the design. Classification societies have, by gathering historical observations of met-ocean conditions, developed rules based on semi-analytical models for response and strength, empirically modified to obtain agreement with observations. The safety level of existing ship structures is thus, to a large extent, defined by failure statistics and proven by successful operational experience. The fundamental assumption behind this practice is that observed data are stationary and ergodic. Because of climate change this no longer holds, however, and within a climate change perspective, the historic data will not represent a valid met-ocean description of future conditions. Therefore, the effect of climate change needs to be considered in ship design and operations. Even though there is general agreement among the majority of the world’s leading climate scientists that the world is experiencing climate change, there are still large uncertainties related to any climate projections and this uncertainty must also be taken into consideration. In this paper, the potential effect of climate change on the ocean wave climate is investigated and the possible impacts on safety of ships are demonstrated using the wave induced bending moment as an example. In particular, projections of the wave climate for a location in the North Atlantic Ocean will be analyzed and related uncertainties will be presented. The results will be discussed in the perspective of a risk-based framework for climate change adaptation, which is adopted in order to evaluate different design options.

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