Post-Ultimate Strength Behavior of Very Large Floating Structure Subjected to Extreme Wave Loads

2012 ◽  
Author(s):  
Kazuhiro Iijima ◽  
Masahiko Fujikubo
Keyword(s):  
Ultimate Strength ◽  
Cross Section ◽  
Simple Formula ◽  
Bending Moment ◽  
Wave Loads ◽  
Extreme Wave ◽  
Floating Structure ◽  
Strength Behavior ◽  
Wave Induced ◽  
Vertical Bending Moment

In this paper, post-ultimate strength behavior of VLFS to extreme wave-induced loads is investigated. A mathematical model to describe the post-ultimate strength behavior of VLFS is developed taking the hydroelasticity into account. The whole VLFS is modeled by two beams on an elastic foundation connected via a nonliner rotational spring assuming that VLFS collapses amidship under severe bending moment. The model is solved numerically by using FEM. It is shown that the extent of collapse of VLFS is smaller than that of ship structures for given amplitude of vertical bending moment on condition that the structures have the same cross section and the same moment-displacement relationship. A simple formula to represent the extent of collapse of VLFS is derived. Its efficacy is shown.

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.

Response Based Identification of Critical Wave Scenarios

2012 ◽  
Author(s):  
Günther F. Clauss ◽  
Marco Klein ◽  
Carlos Guedes Soares ◽  
Nuno Fonseca
Keyword(s):  
Linear Method ◽  
Bending Moment ◽  
Extreme Wave ◽  
Offshore Structure ◽  
Sea State ◽  
Worst Case ◽  
Strip Theory ◽  
Wave Conditions ◽  
Vertical Bending Moment ◽  
Method Approach

In the last years the identification and investigation of critical wave sequences regarding offshore structure responses became one of the main topics in the ocean engineering community. Thereby the area of interest covers the entire field of application spectra at sea — from efficient and economic offshore operations in moderate sea states to reliability as well as survival in extreme wave conditions. For most cases, the focus lies on limiting criteria for the design, such as maximum global loads, maximum relative motions between two or more vessels or maximum accelerations, at which the floating structure has to operate or to survive. These criteria are typically combined with a limiting characteristic sea state (Hs, Tp) or a rogue wave. For the investigation of offshore structures as well as the identification of critical wave sequences, different approaches are available — most of them are based on linear transfer functions as it is an efficient procedure for the fast holistic evaluation. But, for some cases the linear method approach implies uncertainties due to nonlinear response behavior, in particular in extreme wave conditions. This paper presents an approach to these challenges, a response based optimization tool for critical wave sequence detection. This tool, which has been successfully introduced for the evaluation of the applicability of a multi-body system based on the linear method approach, is adjusted to a nonlinear task — the vertical bending moment of a chemical tanker in extreme wave conditions. Therefore a nonlinear strip theory solver is introduced into the optimization routine to capture the nonlinear effects on the vertical bending moment due to steep waves acting on large bow flares. The goal of the procedure is to find a worst case wave sequence for a certain critical sea state. This includes intensive numerical investigation as well as model test validation.

Experimental Assessment of Form Based Approach for Predicting Extreme Value Distribution of Hull Girder Bending Moment in a Ship

2019 ◽  
Author(s):  
Tomoki Takami ◽  
Yusuke Komoriyama ◽  
Takahiro Ando ◽  
Kazuhiro Iijima
Keyword(s):  
Estimation Method ◽  
Bending Moment ◽  
Extreme Value Distribution ◽  
Irregular Waves ◽  
Extreme Wave ◽  
Scaled Model ◽  
Element Analysis ◽  
Hull Girder ◽  
Reliability Method ◽  
Wave Induced

Abstract This paper describes a series of towing tank tests using a scaled model of a recent container ship for validating the First Order Reliability Method (FORM) based approach to predict the maximum response. The FORM based approach is adopted in conjunction with the nonlinear strip method as an estimation method for the most probable wave episodes (MPWEs) leading to the given extreme wave-induced vertical bending moments (VBMs). Tank tests under the pre-determined MPWEs are conducted to evaluate the extreme wave-induced VBMs. Numerical simulations based on the coupled Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) are also conducted and are compared with the test results under the MPWEs. Furthermore, to estimate the extreme VBM statistics, tank tests under random irregular waves are conducted. A series of validations of the probability of exceedances (PoEs) of the VBM evaluated from the FORM based approach is carried out. The effect of hydroelastic (whipping) vibrations on the extreme VBM statistics are finally discussed.

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.

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.

Improvement of Wave Loads Estimation From Spatial Pressure Distribution on Ship Hull

2019 ◽  
Author(s):  
Kurniawan T. Waskito ◽  
Masashi Kashiwagi
Keyword(s):  
Pressure Distribution ◽  
Pressure Sensors ◽  
Estimation Method ◽  
Bending Moment ◽  
Ship Hull ◽  
Accurate Estimation ◽  
Wave Loads ◽  
Local Pressure ◽  
Shipbuilding Industry ◽  
Vertical Bending Moment

Abstract In modern shipbuilding industry, merchant ships tend to increase in size. Accurate prediction of the vertical bending moment in large-maplitude waves has become important for structural design. For establishment of an accurate estimation method, more detailed local hydrodynamic quantities such as the spatial pressure distribution on the whole ship hull surface should be checked. For that purpose, the experiment has been conducted by means of Fiber Bragg Grating (FBG) sensing technology. Using the measured local pressure distribution by only sticking the FBG pressure sensors onto the hull surface, we can evaluate the wave loads; which may lead to establishment of a new evaluation method for the wave loads without using a segmented model. We confirm favorable agreement of the pressure distribution between measurement and computation by Rankine Panel Method (RPM). Furthermore, the vertical bending moment computed at some transverse sections shows favorable agreement between measured and computed results.

Experimental and numerical analysis of ultimate strength of inland catamaran subjected to vertical bending moment

2019 ◽  
Vol 188 ◽  
pp. 106320 ◽  
Author(s):  
Shuangxi Xu ◽  
Bin Liu ◽  
Y. Garbatov ◽  
Weiguo Wu ◽  
C. Guedes Soares
Keyword(s):  
Numerical Analysis ◽  
Ultimate Strength ◽  
Bending Moment ◽  
Vertical Bending Moment

scholarly journals Study on ultimate strength of ship’s hull considering cross section and beam finite element.

2018 ◽  
Vol 177 ◽  
pp. 01030
Author(s):  
Muhammad Zubair Muis Alie ◽  
Juswan ◽  
Wahyuddin ◽  
Taufiqur Rachman
Keyword(s):  
Finite Element ◽  
Ultimate Strength ◽  
Cross Section ◽  
Bending Moment ◽  
Bulk Carrier ◽  
Longitudinal Bending ◽  
The Cross ◽  
The One ◽  
Double Hull ◽  
Oil Tanker

The objective of the present research is to study the ultimate strength of ship’s hull considering cross section and beam finite element under longitudinal bending. The single hull bulk carrier and double hull oil tanker are taken to be analysed. The one-frame space of ship is considered in the calculation. The cross section of ship’s hull is divided into element composed plate and stiffened plate. The cross section is assumed to be remained plane and the simply supported is imposed to both side of the cross section. The longitudinal bending moment is applied to the cross section for hogging and sagging condition. The Smith’s method is adopted and implemented into the in-house program of the cross section and beam finite element to calculate the ultimate strength of ship’s hull. The result of the ultimate strength for hogging and sagging condition obtained by considering the cross section and beam finite element is compared with one another.

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