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.

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.

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.

Calculation of Horizontal Sectional Loads and Torsional Moment

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Vladimir Shigunov ◽  
Alexander von Graefe ◽  
Ould el Moctar
Keyword(s):  
Free Surface ◽  
Shear Force ◽  
Three Dimensional ◽  
Bending Moment ◽  
Green Functions ◽  
Container Ship ◽  
Horizontal Shear ◽  
Torsional Moment ◽  
Oblique Waves ◽  
Rankine Source

Horizontal sectional loads (horizontal shear force and horizontal bending moment) and torsional moment are more difficult to predict with potential flow methods than vertical loads, especially in stern-quartering waves. Accurate computation of torsional moment is especially important for large modern container ships. The three-dimensional (3D) seakeeping code GL Rankine has been applied previously to the computation of vertical loads in head, following and oblique waves; this paper addresses horizontal loads and torsional moment in oblique waves at various forward speeds for a modern container ship. The results obtained with the Rankine source-patch method are compared with the computations using zero-speed free-surface Green functions and with model experiments.

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.

A TECHNIQUE OF PANELS CUTTING FOR MODIFICATION OF HULL GEOMETRY HYDRODYNAMIC MODELS

2021 ◽  
Vol 162 (A2) ◽  
Author(s):  
H Jafaryeganeh ◽  
C Guedes Soares
Keyword(s):  
Case Studies ◽  
The Body ◽  
Vertical Shear ◽  
Vertical Load ◽  
Load Prediction ◽  
Shear Forces ◽  
Hydrodynamic Models ◽  
Initial Mesh ◽  
Load Effects ◽  
Wave Induced

A panel cutting technique is developed for automatic modification of an initial mesh of a ship hull used for hydrodynamic computations leading to improved meshes for the prediction of wave induced vertical load effects. The technique can provide a model with divided panels in any defined position regardless of the initial discretization of the body. The applications of the provided technique include panel distinction and division in predetermined positions, generation of finer mesh based on the initial coarser model of meshes and improvement of vertical load prediction in predetermined positions. The method is applied for case studies of a barge, shuttle tanker and frigate to depict various applications. Finally, the hydrostatic and hydrodynamic vertical shear forces are calculated for two models of initial and modified panels of well-known frigate 5415. The results are compared for the sections alongside the ship and accuracy of load integration is shown for predetermined sections.

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.

Sign in / Sign up

Export Citation Format

Share Document