On the Assessment of Extreme Wave-Induced Bending Moment of a Ship by FORM and Reduced Order Method Based on Coupled CFD and FEA

Author(s):  
Tomoki Takami ◽  
Shohei Ozeki ◽  
Kazuhiro Iijima
Author(s):  
Tomoki Takami ◽  
Yusuke Komoriyama ◽  
Takahiro Ando ◽  
Kazuhiro Iijima

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.


Author(s):  
Kazuhiro Iijima ◽  
Masahiko Fujikubo

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.


Author(s):  
Xuan Chen ◽  
Dongyun Lin

This paper tackles the issue of global stabilization for a class of delayed switched inertial neural networks (SINN). Distinct from the frequently employed reduced-order technique, this paper studies SINN directly through non-reduced order method. By constructing a novel Lyapunov functional and using Barbalat Lemma, sufficient conditions for the global asymptotic stabilization issue and global exponential stabilization issue of the considered SINN are established. Numerical simulations further confirm the feasibility of the main results. The comparative research shows that global stabilization results of this paper complement and improve some existing work.


Author(s):  
Yung S. Shin ◽  
Booki Kim ◽  
Alexander J. Fyfe

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.


1994 ◽  
Vol 31 (04) ◽  
pp. 315-326
Author(s):  
John B. Woodward ◽  
Michael G. Parsons ◽  
Armin W. Troesch

A dry bulk carrier, a tanker, and a containership—taken as typical of ships trading to U.S. ports—are analyzed for possible hazards caused by emptying and refilling ballast tanks at sea. Using hydrostatic data furnished by the shipowners, hull bending moments and stabilities are investigated to find the tank-emptying operations that produce the greatest changes in those parameters. As should be expected, bending moment changes do not exceed allowable stillwater values. Changes in GM are insignificant. The worst hydrostatic cases serve as a guide to conditions that should be analyzed in rough water. The University of Michigan SHIPMO program shows that in waves of 10-ft significant height wave-induced bending moments and shears are far below the design values published by the American Bureau of Shipping. On the other hand, in waves of 20-ft significant height, the maximum wave heights that occur occasionally can cause moments or shears that exceed design values. For the 20-ft case, both linear and nonlinear versions of SHIPMO are used.


1972 ◽  
Vol 9 (02) ◽  
pp. 173-194
Author(s):  
Dan Hoffman

The recent advent of the large tanker and bulk carrier has promoted the requirements for more detailed structural analysis of a ship and the reevaluation of theories for calculating the static, quasistatic and dynamic loads. The paper begins with discussion of the methods available to determine the various types of loads expected, their phase relationship, and ways of superimposing them. It then proceeds to the treatment of sea loads based on theoretical and experimental data, and techniques of determining the ship response in a seaway are discussed. The response to regular waves is reviewed with special reference to the determination of pressure distribution on the hull. Statistical ship response, immediate and cumulative over the life of the ship, is demonstrated in relation to the prediction of long-term bending moment trends, and the distribution of the extremes is discussed. Special loading conditions are described with special emphasis on the transverse pressure distribution, dynamic effects due to motion of liquid cargo in tanks, shipping of green water, wave-induced vibrations, slamming pressures and whipping stresses due to various causes. The paper treats the above subjects in a broad manner and no attempt to illustrate the theory in detail is made.


1981 ◽  
Vol 25 (04) ◽  
pp. 243-251
Author(s):  
J. Juncher Jensen ◽  
P. Terndrup Pedersen

This paper presents some results concerning the vertical response of two different ships sailing in regular and irregular waves. One ship is a containership with a relatively small block coefficient and with some bow flare while the other ship is a tanker with a large block coefficient. The wave-induced loads are calculated using a second-order strip theory, derived by a perturbational procedure in which the linear part is identical to the usual strip theory. The additional quadratic terms are determined by taking into account the nonlinearities of the exiting waves, the nonvertical sides of the ship, and, finally, the variations of the hydrodynamic forces during the vertical motion of the ship. The flexibility of the hull is also taken into account. The numerical results show that for the containership a substantial increase in bending moments and shear forces is caused by the quadratic terms. The results also show that for both ships the effect of the hull flexibility (springing) is a fair increase of the variance of the wave-induced midship bending moment. For the tanker the springing is due mainly to exciting forces which are linear with respect to wave heights whereas for the containership the nonlinear exciting forces are of importance.


2020 ◽  
Vol 129 ◽  
pp. 392-402
Author(s):  
Shanshan Chen ◽  
Haijun Jiang ◽  
Binglong Lu ◽  
Zhiyong Yu ◽  
Liang Li

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