Masahiko Fujikubo

• Osaka University

In order to clarify and visualize the real state of the structural performances of ships in operation and establish a more optimal, data-driven framework for ship design, construction and operation, an industry-academia joint R&D project on the digital twin for ship structures (DTSS) was conducted in Japan. This paper presents the major achievement...

A novel safety monitoring method for ship structure in waves by using real-time response measurements is proposed. In the method, the structural responses, such as the vertical and horizontal bending moments, at unmeasured points can be estimated by the Wave profile Kalman Filter (WKF) method using the ship response measurements and the transfer fu...

Full-scale hull monitoring is a direct way to ensure the structural integrity of the ship during actual operation. Typically, multiple strain sensors are installed on structural members of several cross-sections. The greater the number of sensors, the more accurate the monitoring is, but the more costly to install and maintain them. This paper prop...

A simple estimation method for ultimate strength of curved plates under axial compression is proposed. Existing estimation methods are mostly empirical based on plastic correction of elastic buckling strength or curve fitting the results of test or nonlinear finite element analysis (NLFEA). For more rational design, it is important to develop a met...

This paper presents a method for estimating the sectional loads along ship hull girder in real-time by combining a Kalman filtering algorithm and a mode superposition method, as part of digital twining system. The developed method is applied to a full-scale measurement on an 8600 TEU container ship and the strain signal at several locations is used...

In this paper, a Kalman filter technique for identifying the wave time histories encountered by a ship is developed and verified in a series of tank tests. The method inversely analyzes the wave time histories from the measured response. A series of irregular wave tests using a flexible ship model made of acrylic resin was conducted at the Actual S...

Longitudinal bending strength is the most fundamental strength of ship hull girders, and longitudinal bending moment acting on hull girders should be accurately monitored to ensure structural safety during ship operations. The longitudinal bending moment classified into still-water bending moment and wave-induced bending moment. This study proposes...

This paper presents a benchmark study on the ultimate limit state analysis of a stiffened plate structure subjected to uniaxial compressive loads, initiated and coordinated by the ISSC 2022 technical committee III.1-Ultimate Strength. The overall objective of the benchmark is to establish predictions of the buckling collapse and ultimate strength o...

This paper presents a benchmark study on the ultimate limit state analysis of a stiffened plate structure subjected to uniaxial compressive loads, initiated and coordinated by the ISSC 2022 technical committee III.1-Ultimate Strength. The overall objective of the benchmark is to establish predictions of the buckling collapse and ultimate strength o...

Smith’s method has been widely used for the progressive collapse analysis of a ship’s hull girder under longitudinal bending. In the Smith’s method, a hull girder’s cross section is divided into the plate and stiffened-panel elements which are given a priori an average stress-average strain relationship under uniaxial tension/compression considerin...

This paper is the second of the two companion papers dealing with the buckling strength of a non-spherical tank in the partially filled condition, which is one of the severest loading conditions in terms of the buckling design of Moss-type LNG tanks. A method to estimate the reduction factor of the elastic buckling strength due to initial shape imp...

Buckling strength of a non-spherical tank in the partially filled condition, which is one of the severest loading conditions in terms of the buckling design of Moss-type LNG tanks, is investigated both experimentally and theoretically. As the first part of the study, an axisymmetric loading condition for an upright tank position is considered. The...

The estimation of buckling strength of plates and stiffeners as a basic component of ship structures is very important to evaluate her safety. As for plates, recent classification rules consider the compressive ultimate strength, which is beyond elastic buckling strength, as their buckling criteria because the elastic bucking strength of plates lik...

The fatigue strength of a drill pipe is a critical factor governing the performance of drillings. Substantial research has been conducted related to fatigue evaluation and various factors that have an effect on fatigue. However, earlier studies have expressed concerns over the use of fatigue curves obtained from full scale tests and stress response...

In Part 1 study, a time-domain collapse analysis method of ship hull girder was developed and named FE-Smith method. Hull girder was treated as elastoplastic beam model and Smith’s method was used for collapse analysis of cross sections. A concept of average stress-average plastic strain relationship was introduced so that nonlinear collapse behavi...

This paper is the second of two companion papers concerning the ultimate hull girder strength of container ships subjected to combined hogging moment and bottom local loads. The nonlinear finite element analysis in Part 1 has shown that local bending deformation of a double bottom due to bottom lateral loads significantly decreases the ultimate hog...

This paper is the first of two companion papers concerning the ultimate hull girder strength of container ships subjected to combined hogging moment and bottom local loads. In the midship part of container ships, upward bottom local loads are usually larger than the downward ones. This leads to the increase of biaxial compression in the outer botto...

In recent years, container ships become larger and larger to increase the transport efficiency. The torsional rigidity of a container ship is lower than other type of ships, because the container ship has the large deck opening and large flare structure. Therefore, it is important to calculate the longitudinal ultimate strength with considering the...

The scientific drilling vessel Chikyu is performing Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), a challenging deep drilling activity, for scientific purpose. We faced difficulty to drill deep during past NanTroSEIZE operations due to unstable sediments and insufficient cutting removal. Non-Stop Driller concept is, therefore, applied fo...

The aim of the present study is to obtain the ultimate strength and load response of a single side shell panel of a bulk carrier under longitudinal thrust and out-of-plane pressure. Time-domain analysis using nonlinear strip method and a whole ship finite element analysis are performed to calculate the pressure and stress responses of the side shel...

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 bas...

This paper addresses development of a mathematical model which describes the behavior of an elasto-plastic beam afloat on water surface. The mathematical model is valid for predicting the collapse of a Very Large Floating Structure (VLFS) subjected to extreme wave-induced vertical bending moment. It is a follow-up of the previous work in which the...

In this study, for the stiffened panels subjected to the in-plane cyclic compression loads, the two followings are clarified. One is a generating process of the cumulative buckling deformation at panel parts of stiffened panels. The other is the effect of the cumulative buckling deformation on the ultimate strength of stiffened panels. To clarify t...

A method of time-domain collapse analysis of ship hull girder considering the interaction between elastoplastic deformation and hydrostatic/dynamic forces is developed. Ship hull girder is longitudinally divided by conventional beam elements, and progressive collapse behavior of cross sections is simulated by Smith method considering material yield...

A very large floating structure (VLFS) may undergo buckling and yielding under rare and extreme waves. Then, the cross section of the VLFS collapses completely. The evaluation of the consequence of collapse is critical in view of the risk analysis. In this paper, the parametric dependencies of the collapse extent of a VLFS under extreme vertical be...

This paper addresses collapse behaviour of Very Large Floating Structure (VLFS) under extreme vertical bending moment. The study is performed as part of risk analysis to evaluate the consequence of a rare collapse event. Elastic and plastic deformation of VLFS develops under the extreme vertical bending moment while the deformation interacts with t...

This paper is the third followed by the two companion papers dealing with ultimate longitudinal strength analysis of container ships considering effects of bottom local loads. The major causes of reduction of ultimate hull girder strength due to local loads were discussed based on the finite element analysis of a hold model in the Part 1. The exten...

A method of estimating elastic buckling strength of a non-spherical tank intended for the use in LNG carriers is presented. Partially filled condition that causes combined meridional tension and circumferential compression is considered. Analytical expression of pre-buckling stress distributions is derived based on membrane shell theory. These stre...

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 20k...

Scientific drilling vessel Chikyu faced drill pipe failure during offshore commissioning of drilling control and instrumentation system upgrade work. The failure occurred with cyclic bending stress which was enough low to prevent fatigue failure according to S-N curve obtained from full-scale fatigue tests. Material tests and observation of a remai...

This chapter deals with the most important strength of ship structure: the ultimate longitudinal strength. At the beginning, early research works are reviewed related to the ultimate hull girder strength including strength tests using existing ships. Then, the progressive collapse of hull girder in bending is briefly explained in relation to the de...

This chapter deals with buckling/plastic collapse behavior and the ultimate strength of structural members and systems, some of which are not the main structural members.

This chapter deals with buckling/plastic collapse behavior and the ultimate strength of stiffened plates subjected to various loads. At the beginning, it is explained how the stiffener affects on buckling behavior and buckling strength. Buckling/plastic collapse behavior and the ultimate strength of stiffened plate under longitudinal thrust are exp...

This chapter deals with the fundamental theory and method for the analysis of buckling/plastic collapse behavior of rectangular plates and stiffened plates subjected to combined in-plane loads. First, based on the fundamentals in the bucking collapse behavior of plates and stiffened plate under various loading conditions, the deflection modes that...

Ship and ship-like floating structures are constructed by welding and the structural members and systems are accompanied by initial imperfections such as welding residual stress and initial deflection/distortion produced by welding. In general, such initial imperfections affect the strength and the stiffness of structural members and systems. From...

In this chapter, buckling/plastic collapse behavior is explained for rectangular plate subjected to combined loads. At the beginning, the influence of loading sequence is examined under combined longitudinal thrust and lateral pressure, and the influence is hardly found. Then, influence of lateral pressure on buckling strength is examined, and empi...

There exist some formulas to evaluate the ultimate strength of stiffened plates specified in common structural rules (CSRs). Some of them have theoretical background but some of them no background. This chapter deals with such rule formulas.

This chapter is divided into three parts: (1) what is buckling/plastic collapse of members and systems in ship and ship-like floating structures; (2) a short historical review of the research works related to the subject of this textbook; and (3) the concrete contents of this textbook.

For modeling floating offshore wind turbine (FOWT) structure, it is questionable whether to consider the flexibility of the main floater while it is almost common to account for the flexibility of the tower and blades. Most of the numerical simulation tools developed consider the floater to be a rigid body and flexibility of floating structure is n...

Elastic-plastic behavior analysis methodology for a flexible FOWT is developed adopting a coupled simulation code which considers the flexibility of the floater and malfunction of blade pitch control. This paper proposes a simulation method for predicting the structural response of FOWTs when subjected to blade pitch control malfunction. The struct...

Buckling and Ultimate Strength of Ship and Ship-like Floating Structures provides an integrated state-of-the-art evaluation of ship structure mechanics including buckling, plastic failure, ultimate strength, and ultimate bending moments. For the design of any industrial product, it is necessary to understand the fundamentals in the failure behavior...

When heavy cargos such as ore are loaded on bulk carrier, they are usually loaded only in cargo holds of an odd number, which is called alternate heavy loading condition. Under such situation, double bottom structure is subjected to local bending, and this reduces the ultimate hull girder strength in hogging. In this paper, a simple method is propo...

This paper addresses collapse behavior of Very Large Floating Structure (VLFS) under large wave loads, as part of risk analysis. In predicting the consequence of collapse, the deformation of VLFS consisting of elastic and plastic ones under the large load event must be addressed. The deformation interacts with the fluid around it. Therefore, hydro-...

The evaluation of the maximum load-carrying capacity of structures is an essential issue in determining their safety. Only if the prediction of the ultimate strength is ensured, their probability of survival in extreme load conditions can be estimated. Particularly for safe dimensioning of ship structures, the determination of structural strength a...

Ultimate strength of the hull girder of containerships became a significant issue in the last years in view of recent accidents and related investigations. Actually, larger and larger ships were put into service and still are designed and built. Recognizing such an issue, investigations were carried out and led to the issuance of a specific longitu...

A ship hull is regarded as a box girder structure consisting of plates and stiffeners. When the ship hull is subjected to excessive longitudinal bending moment, buckling and yielding of plates and stiffeners take place progressively and the ultimate strength of the cross-section is attained. The ultimate longitudinal bending strength is one of the...

In this study, FE modeling method for the buckling/ultimate strength analysis of a continuous stiffened panel under combined shear and thrust is proposed. In order to validate the proposed method, shear buckling collapse tests of a stiffened panel and FEM analysis are carried out. As the result of these, it is confirmed that the buckling collapse b...

Recent progress in the development and application of the ISUM plate element is highlighted with a particular focus on its application to the progressive collapse analysis of a ship hull structure. The plate element is characterized by idealized shape functions for defection based on buckling collapse mode and a simple procedure for element formula...

The purpose of this research is to clarify the effect of bottom local loads on the hull girder collapse behavior of large container ship (8000TEU class) A 1/2+1+1/2 hold model of container ship is analyzed using implicit finite element method. The results reveal two major causes of reduction of hull girder ultimate strength due to local loads. One...

When using large models, building a comprehensive finite element (FE) numerical model able to simulate the portion of a containership whose extension in length is sufficient to properly evaluate combined loading effects is rather time consuming, and assigning proper boundary conditions representing the distribution of actual forces and moments on t...

The objective of this study is to propose an analysis method of ultimate hull girder strength under combined bending and torsion. The hull girder is modelled by a series of thin-walled linear beam elements composed of plate and stiffened panel elements and their average stress–average strain relationships under axial loads considering the effect of...

In this paper, we discuss nonlinear motion of a buoy connected vertically to the seabed via a tensioned tether (tethered-buoy). A series of scaled model tests has been conducted and a significant nonlinear behavior of the buoy motion, sub-harmonic motion in particular, is observed. Taking account of the influence of time-varying tether tension on t...

This chapter deals with buckling/plastic collapse behavior and the ultimate strength of rectangular plate subjected to uni-axial thrust. At the beginning, elastic buckling and postbuckling behavior are explained as fundamentals. Then, elastic behavior is explained including buckling and postbuckling behavior including secondary buckling. Regarding...

This chapter deals with buckling/plastic collapse behavior and the ultimate strength of plate girders subjected to shear and bending loads as well as their combinations. More than 50 years ago Busler and Fujii conducted research works related to this issue including a series of experiments. The fundamental findings related to this issue is briefly...

This paper is the second of the two companion papers dealing with ultimate longitudinal strength analysis of container ships considering the effects of bottom local loads. The major causes of reduction of ultimate hull girder strength due to local loads were discussed based on the finite element analysis of a hold model in the Part 1. The objective...

This paper is the first of two companion papers dealing with ultimate longitudinal strength analysis of a container ship considering local loads effects. The purpose of this paper is to clarify the effect of bottom local loads on the longitudinal bending collapse behavior of a large container ship. An important problem is a bending deformation of t...

In order to investigate the influence of strength mismatching on brittle fracture strength for large heat-input welded joints, a series of tension tests was conducted using surface notched specimens. Furthermore, notched round-bar tension tests were carried out for simulated bond material (homogeneous material) which was base metal heat-treated on...

Ring stiffened cylinder is generally used as main structural members of offshore and submergible structures. In designing of such structures, it is very important to estimate the buckling strength of ring stiffened cylinder under external pressure accurately. The buckling mode of ring stiffened cylinder under external pressure can be divided into t...

The objective of this study is to propose an analysis method of ultimate hull girder strength under combined bending and torsion. The hull girder is modelled by a series of thin-walled beam elements and the average stress–average strain relationship of plate and stiffened panel elements under axial loads considering the effect of shear stress is im...

The Mega-Float project is a pontoon-type Very Large Floating Structure that was designed for deployment in protected waters such as in a large bay. It consists of a floating structure, a mooring system, and access infrastructure. While construction of a breakwater was contemplated, the existing breakwater around the site was found to be sufficient....

This paper addresses the cumulative collapse behavior of a ship hull girder under a series of extreme wave loads. It is a follow-up of the previous work done by the present authors. In the previous work, the post-ultimate strength behavior under a single extreme wave was investigated by using numerical simulations and tank tests. The reduction in t...

Abstract To ensure the safety of navigating ship, working loads and structural load-carrying capacity are two important aspects. In the present paper, a total simulation system combing load calculation and structural collapse analysis is applied to simulate progressive collapse behaviour of a single-hull Kamsarmax type bulk carrier. A three dimensi...

A series of experimental investigations on the post-ultimate strength collapse behaviour of a ship's hull girder under whipping loads are presented. It is a follow-up study of the authors based on numerical simulations. One of the important conclusions of the previous work is that given the same magnitude of the loads, the collapse extent is smalle...

The primary objective of the present paper is to obtain an irregular wave train inducing the most likely nonlinear response at an arbitrary probability level in a short term sea state. The target response includes nonlinear combined load, e.g., von Mises stress, and cumulative elasto-plastic behavior of hull girder after the ultimate strength. To t...

A series of collapse analyses is performed applying nonlinear FEM on stiffened panels subjected to longitudinal thrust. MSC.Marc is used. Numbers, types and sizes of stiffeners are varied and so slenderness ratio as well as aspect ratio of local panels partitioned by stiffeners keeping the spacing between adjacent longitudinal stiffeners the same....

FEM analysis using fine-mesh shell models has been increasingly applied to the ultimate longitudinal strength analysis of ship's hull girder. However, the cost and elapsed time necessary for FEM analyses including FE modelling are still large for the design stage. Therefore, it is a common procedure to apply the Smith's method and to evaluate appro...

The aim of this paper is to determine an appropriate configuration of the boundary conditions and geometric model to calculate the ultimate strength of a continuous stiffened panel under compressive loading in the finite element (FE) analysis. The 1+1 spans model with periodical symmetric boundary conditions is proposed to be used in the FE analysi...

For a bulk carrier in alternative heavy loading condition, it is noted that the double bottom of an empty hold is subjected to both longitudinal thrust due to hull girder bending in hogging and local bending caused by high pressure loads on bottom plating. In order to examine the influence of local bending of double bottom on the ultimate hull gird...

For a bulk carrier in alternate heavy loading conditions, it is noted that the double bottom of an empty hold is subjected to both longitudinal thrust due to hull girder bending in hogging and local bending caused by high pressure loads on bottom plating. In order to examine the influence of local bending of the double bottom on the ultimate hull g...

This paper presents fracture mechanics analysis using the wavelet Galerkin method and extended finite element method. The wavelet Galerkin method is a new methodology to solve partial differential equations where scaling/wavelet functions are used as basis functions. In solid/structural analyses, the analysis domain is divided into equally spaced s...

Buckling tests for a GFRP unstiffened panel and stiffened panels with a top-hat stiffener are performed, and the fundamental buckling/fracture behavior including initiation of delamination is identified. Compressive stress in BWR layers is considered as one of the causes of the delamination, and the critical stress is derived by compressive materia...

Heat-affected zone (HAZ) of a large heat input welded joint typically found in a very large container ship is remarkably softened over a wide range. In this study, the influence of the strength mismatching on the Crack Tip Opening Displacement (CTOD) and fracture strength of such welded joints under tension is investigated both experimentally and n...

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 t...

The aim of this paper is to find out an appropriate configuration of boundary conditions and geometric model to calculate the ultimate strength of a continuous stiffened panel under uniaxial compressive loading in FE analysis. The 1+1 bays model with periodical symmetric boundary conditions is proposed to be used in FE analysis, whose results are c...

To rationally assess the consequence of a ship’s hull girder collapse, it is necessary to know the post-ultimate strength behavior of the hull girder including the global deformation and motions under extreme wave-induced loads. In the foregoing research, the authors proposed a numerical analysis system to predict the collapse behavior in waves inc...

Experimental investigations into the collapse behavior of a box-shape hull girder subjected to extreme wave-induced loads are presented. The experiment was performed using a scaled model in a tank. In the middle of the scaled model, sacrificial specimens with circular pillar and trough shapes which respectively show different bending moment-displac...

It is necessary to make clear the effect of torsional moment on the ultimate strength of the ships' hull girder for the accurate assessment of that of ultra large container ships with large deck openings. In the present study, the extension of the simplified method of progressive collapse analysis based on Smith's method is attempted to the case of...

An incremental formulation of the progressive collapse behavior of ship's hull girder with damages subjected to longitudinal bending is presented based on the Smith's method. The hull girder is modeled as a beam with asymmetric cross section subjected to biaxial bending. The explicit expression of the rotation and translation of the neutral axis du...

Dynamic collapse behavior of a ship’s hull girder in waves is investigated; post-ultimate strength behavior is the focus. Firstly, a simulation method is proposed. Assuming that a plastic hinge is formed during the collapse of the hull girder, the whole ship is modeled as two rigid bodies connected amidship via a nonlinear rotational spring. The po...

To rationally assess the consequence of a ship’s hull girder collapse, it is necessary to know the post-ultimate strength behavior of the hull girder including the global deformation and motions under wave-induced extreme loads. In the foregoing research, the authors proposed a numerical analysis system to predict the collapse behavior in waves inc...

A new approach to predicting the dynamic collapse behavior of a ship's hull girder in waves is proposed. The work is to evaluate the consequence of the collapse, which is important in evaluating the associated risk of the hull girder collapse. The progressive collapse analysis of the ship's hull could be followed by a hydro-elastoplastic response a...

Statistical analysis of the extreme wave-induced hull girder vertical bending moments in short-term sea states is conducted. A series of time-domain numerical simulations of the wave-induced hull girder vertical bending moments are performed based on nonlinear strip method to obtain peak values of the vertical bending moments. The Peaks-Over-Thresh...

In this study, the target reliability level of ships' ultimate hull girder strength is investigated by employing risk assessment. The risk can be defined as "Risk = Failure probability x Consequence." In the present case, the failure probability corresponds to the probability of hull girder collapse in bending while the consequence to a monetary lo...

Clear understanding of the collapse behaviour of container ship having large hatch openings under pure bending and pure torsion as well as combined bending and torsion is very important to ensure the safety of container ships which are now widely used all over the world. In the present paper, a series of progressive collapse analyses is performed o...