Double Hull Research Articles

Study on the Impact of Crashworthiness Materials on the Crashworthiness Capacity of Double Hull Ship

Improving the crashworthiness of ship is an important guarantee for ship security. To fill different materials in the shipboard structure or attach fender devices outside the shipboard are important measures that can improve the crashworthiness of ship. They are boiled down to the use of crashworthiness materials, and the impact of crashworthiness materials on the double side ship is classified as the changes of shipboard structure elastic modulus, and then this paper carries out an analysis of the impact of the changes of various parts’ elastic modulus of the shipboard structure on the crashworthiness of ship, and the computing result shows that to lay crashworthiness materials on the sheet metal can improve the structure crashworthiness before the rupture occurs, some useful conclusions about the material impact on the crashworthiness of ship are obtained.

補強材のレイアウトを考慮した船体構造最適化に関する研究

The optimization of the ship structure with design variables of the plate thickness and the shape of stiffener is a popular study filed. But, the optimization of the structure with the design valuables of the number and the position of stiffners are necessary for obtaining a better optimal solution. Therefore, the optimization with theses design valuables is performed in this paper. The optimization with theses design variables needs a lengthy calculation time because recreating FEM models and re-analyzing must be performed. In order to overcome this problem, the calculation method for evaluation of the strength of structures without recreating FEM models and the method of reducing calculation amount of FEM are proposed. There is another problem in optimization part. Since the number of stiffeners is changed the number of design variables may vary during an optimization process. In order to solve this problem, an effective optimization method for this problem is proposed. The structure which imitate a double hull part of oil tanker is selected for target of optimization. These proposed methods are applied to this optimization model and their effectiveness an verified.

Blast loading of underwater targets – A study through Explosion Bulge Test experiments

Contemporary nuclear submarines are built with double hulls which enhance the protection against explosive attacks. As the two hulls are separated by a distance (stand off), blast loading on the inner hull diminishes significantly. Thus, warheads fitted to underwater weapons with limited quantity of explosive become ineffective. In the present study, an attempt is made to quantify the enhanced protection to the underwater vessels due to double hull construction, through Explosion Bulge Test (EBT) experiments. Four different cases of air back up, water back up, partial water back up and free flood water back up are studied in the EBTs. The extent of reduction in damage to the double hulled vessel under various modes of back up are studied and discussed in this paper. Through these experiments, it is established that there is a significant reduction in damage from 22.5 to 63% to the hull when compared to air back up depending on different test conditions of water back up. The response of double hull to proximity explosion with air and water back up is simulated using a Finite Element (FE) model and compared.

Design of controller for mobile robot in welding process of shipbuilding engineering

Abstract The present study describes the development of control hardware and software for a mobile welding robot. This robot is able to move and perform welding tasks in a double hull structure. The control hardware consists of a main controller and a welding machine controller. Control software consists of four layers. Each layer consists of modules. Suitable combinations of modules enable the control software to perform the required tasks. Control software is developed using C programming under QNX operating system. For the modularizing architecture of control software, we designed control software with four layers: Task Manager, Task Planner, Actions for Task, and Task Executer. The embedded controller and control software was applied to the mobile welding robot for successful execution of the required tasks. For evaluate this imbedded controller and control software, the field tests are conducted, it is confirmed that the developed imbedded controller of mobile welding robot for shipyard is well designed and implemented.

Time-Dependent Ultimate Strength Performance of Corroded FPSOs

Recently, various types of offshore structures are built and constructed to fulfil the high demand of ocean exploration especially in oil and gas industry. In this regards, the deep-water area is becoming more and more important field for exploration activity. Floating production storage and offloading (FPSO) is one of the popular structures used to exploit the sources of oil and gas in subsea area. Basically, FPSO is exposed to ocean environment and thus faces age-related problems such as corrosion damage. In the present study, the time-dependent effect of corrosion wastage on the ultimate limit state-based structural safety assessments of three FPSOs was performed. An empirical time-dependent corrosion wastage model, which was obtained using real corrosion measurement database, was adopted to predict the progress of corrosion damages. Ultimate strengths of stiffened panels and hull girders for converted FPSOs (single hull type and double hull type) were compared with a new-built FPSO. Important insights obtained from the present study were documented.

A Review of Test Protocols for Assessing Coating Performance of Water Ballast Tank Coatings

Concerns on corrosion and effective coating protection of double hull tankers and bulk carriers in service have been raised especially in water ballast tanks (WBTs). Test protocols/methodologies specifically that which is incorporated in the International Maritime Organisation (IMO), Performance Standard for Protective Coatings for Dedicated Sea Water ballast tanks (PSPC) are being used to assess and evaluate the performance of the coatings for type approval prior to their application in WBTs. However, some of the type approved coatings may be applied as very thick films to less than ideally prepared steel substrates in the WBT. As such films experience hygrothermal cycling from operating and environmental conditions, they become embrittled which may ultimately result in cracking. This embrittlement of the coatings is identified as an undesirable feature in the PSPC but is not mentioned in the test protocols within it. There is therefore renewed industrial research aimed at understanding this issue in order to eliminate cracking and achieve the intended coating lifespan of 15 years in good condition. This paper will critically review test protocols currently used for assessing and evaluating coating performance, particularly the IMO PSPC.

Ultimate strength performance of tankers associated with industry corrosion addition practices

In the ship and offshore structure design, age-related problems such as corrosion damage, local denting, and fatigue damage are important factors to be considered in building a reliable structure as they have a significant influence on the residual structural capacity. In shipping, corrosion addition methods are widely adopted in structural design to prevent structural capacity degradation. The present study focuses on the historical trend of corrosion addition rules for ship structural design and investigates their effects on the ultimate strength performance such as hull girder and stiffened panel of double hull oil tankers. Three types of rules based on corrosion addition models, namely historic corrosion rules (pre-CSR), Common Structural Rules (CSR), and harmonised Common Structural Rules (CSRH) are considered and compared with two other corrosion models namely UGS model, suggested by the Union of Greek Shipowners (UGS), and Time-Dependent Corrosion Wastage Model (TDCWM). To identify the general trend in the effects of corrosion damage on the ultimate longitudinal strength performance, the corrosion addition rules are applied to four representative sizes of double hull oil tankers namely Panamax, Aframax, Suezmax, and VLCC. The results are helpful in understanding the trend of corrosion additions for tanker structures.

극지환경을 고려한 선체보강판 구조의 최종강도 평가

Environmental changes, especially global climate change, are creating new routes to reduce a shipping service distance in Arctic area. The Arctic routes are shorter than 60% of existing ways Panama or Suez canal). For this reason, ship owners prefer to navigate in Arctic area and a transportation of goods though the Arctic area is increasing. But the low temperature in Arctic condition changes the material properties. Especially, the material will be brittle and strength will increase. And an ultimate strength analysis of ship stiffened panels is changed depending on temperatures. In present study, the ultimate strength analysis of stiffened panels in double hull oil tankers is performed under various low temperatures with the material properties obtained by tensile coupon test. The analytical method as named ALPS/ULSAP was used for analysis method and 6 kinds of temperature (20, 0, -20, -40, -60 and <TEX>$-80^{\circ}C$</TEX>) were considered to investigate the effect of Arctic conditions.

Quantitative Risk Assessment for Collisions Involving Double Hull Oil Tankers

In recent decades, the safety of ships at sea has become a major concern of the global maritime industries. Ships are rarely subject to severe accidents during their life cycle. Collision is one of the most hazardous accidents, with potentially serious consequences such as the loss of human life, structural damage and environmental damage, especially if large tankers, LNG and/or nuclear-powered vessels are involved. This study presents a Quantitative Risk Assessment (QRA) for double hull oil tankers that have collided with different types of ships. The methodology used to perform the QRA is based on the International Maritime Organisations' (IMO) definition of a Formal Safety Assessment (FSA). Using probabilistic approaches, ship-ship collision scenarios are randomly selected to create a representative sample of all possible scenarios. The collision frequency is then calculated for each scenario. As this is a virtual experiment, the LS-DYNA nonlinear finite element method (NLFEM) is used to predict the structural consequences of each scenario selected. In addition, the environmental consequences are estimated by calculating the size of each scenario's oil spill. To assess the economic consequences, the property and environmental damages are calculated in terms of monetary units. The total risk is then calculated as the sum of the resultant structural and environmental damages. Exceedance curves are established that can be used to define the collision design loads in association with various design criteria.

Reliability analysis of plate elements under uniaxial compression using an adaptive response surface approach

This paper presents a reliability analysis of plate elements under uniaxial compression using an adaptive response surface approach. The limit state considered is the buckling collapse failure of the plate elements computed through nonlinear finite element analysis. A response surface model based on second-order polynomials is combined with the first-order reliability method in order to compute reliability estimates at moderate computational time. An adaptive interpolation scheme combined with a Latin hypercube sampling technique is used to define the response surface model iteratively in the region of the basic random variables space that most contributes to the failure probability. Plate elements typical of the deck structure of double hull tankers with random thickness, material properties and amplitude of weld-induced initial distortions are used as case study. The uniaxial compressive load is defined considering extreme values in a reference time period of one year of operation of the ship. The effect of considering constrained or restrained boundary conditions along the longitudinal plate edges as well as corroded plate elements on the reliability analysis results is determined. Sensitivity analyses are performed to identify the relative contribution and importance of each basic random variable to the estimated reliability indices.

Experimental and numerical analysis of a tanker side panel laterally punched by a knife edge indenter

The paper presents finite element simulations of a small-scale stiffened plate specimen quasi-statically punched at the mid-span by a rigid indenter, in order to examine its energy absorbing mechanisms and fracture. The specimen, scaled from a tanker side panel, is limited by one span between the web frames and the stringers. The paper provides practical information to estimate the extent of structural damage within ship side panels during collision accidents. Moreover, the results of this investigation should have relevance to evaluate grounding scenarios in which the bottom sustains local penetration. This is possible since the structural arrangement of the double hull and the double bottom of tanker vessels is very similar. The experimentally obtained force–displacement response and shape of the deformation show good agreement with the simulations performed by the explicit LS-DYNA finite element solver. The numerical analysis includes aspects of particular relevance to the behaviour of ship structures subjected to accidental loads which could give rise to difficulties in interpreting finite element calculations. In particular, the paper comments on the material nonlinearities, the importance of specifying the precise boundary conditions and the joining details of the structure. The considerable practical importance of these aspects has been the focus of attention in previous publications of the authors which evaluate the experimental-numerical impact response of simple ship structural components, such as beams and plates. Therefore, this paper uses the definitions proposed in those references to evaluate its applicability in the scaled tanker side panel, as an example of a more complex ship structure.

The Influence of Weld Joints on the Failure Mechanism of Scaled Double Hull Structures under Collision Load in Finite Element Simulations

As a result of growing safety-related requirements in shipbuilding the design of double hulls in respect to accidents and collisions is mainly orientated on damage stability calculations. In order to increase the collision resistance and thereby the damage stability of ships the concept of an alternative stiffening system (English: plates strengthened stiffeners, German: Plattenverstärkte Profilsteifen – PVPS) invented by Röhr et al. (2008) was investigated for practical use within the scope of the project SideColl, funded by the German Federal Ministry of Economics and Technology (BMWi). A collision experiment with a scaled double hull structure is performed with the alternative stiffening system. Beside the experimental investigations numerical simulations with the finite element software LS-Dyna are conducted. With the adaption of suitable discretizations and fracture criteria in the finite element model the structural response in terms of the force-displacement curve are well predicted. Furthermore, the crack initiation and the failure mechanism are captured in good agreement with the experiment. An equivalent model for weld joints is applied to the double hull structure to reproduce the different material behavior at plastic deformations and fracture in the numerical analysis.

Probabilistic oil outflow: the tanker fleet in the context of risk analysis

The study of safety and environmental friendliness of tankers remains a vital concern of the shipping industry, and the analysis of risk regarding oil spillage from this type of ships is considered as a top priority item in the agenda of shipping. In this context, the paper is focused on the implementation and probabilistic formulation of regulation 23 of MAPPOL to calculate distribution and quantities of oil outflow for all major oil tanker categories such as Aframax, Suezmax, VLCC, etc. Dedicated databases for each tanker size category have been developed, checked for statistical acceptance, and utilised to obtain all necessary inputs for the calculation of oil outflow. Subsequently, numerous cargo tank configurations per tanker size were examined (for double hull vessels following regulation 19 of MARPOL), multiple scenarios were drafted, and these were put under simulation exercises to come up with oil outflow probabilistic distributions. The paper concludes with a framework for the assessment of costs for (tanker) oil spills.

Classification of Design Variables Based on Constraint Conditions and Structural Optimal Design - Application to Structural Optimal Design of Midship Section

A structure optimization of midship section is under consideration in this paper. A double hull oil tanker is selected for optimization. Since there are many design variables describing the midship section, usually, design variables are divided into some groups concerning design and manufacturing. When the classification of design variables is not proper, there is a problem that the optimal solution cannot be obtained. Classification method of design variables proposed here is intended to overcome this drawback. Influence of design variables on constraint conditions is estimated based on principal component analysis and used for classifying design variables. The classification of design variables obtained by the proposed method is different from a conventional group. Selected problems show that the proposed method can produce a better solution than the conventional method.

制約条件に対する影響度を考慮した設計変数の分類と構造最適設計

A structure optimization of mid-ship section is under consideration in this paper. A double hull oil tanker is selected for the target of optimization. Since there are many design variables in the mid-ship section, usually, design variables are divided into some groups in the viewpoints of designing and the manufacturing. When the classification of design variables is not proper, there is a problem that the optimal solution cannot be obtained. In order to overcome this drawback, a classification method of design variables is proposed here. Influences of design variables to constraint conditions are estimated based on principle component analysis and used for classifying design variables. The classification of design variables obtained by the proposed method is different from a conventional group. The selected problems by use of the proposed method are solved, and it is shown that the proposed method can give us a better solution than the conventional method.

総合的なライフサイクルリスク評価に基づいた構造最適化

Recently, structural design of a ship considering various risks in the lifecycle of the ship has become more and more important.In the committee IV.1 (Design Principle and Criteria) of the International Ship and Offshore Structural Congress (ISSC), it is discussed that sustainability of ships and marine structures should be evaluated when the structure is constructed based on assessment of "holistic risk" which includes assessment of safety, environment, social responsibility and etc. Based on the concept of holistic risk evaluation, we carried out lifecycle structural optimization of mid-ship section of a double hull tanker in this study. For the evaluation of environmental risk, the method of life cycle assessment (LCA) is introduced to evaluate the CO2 emission. Also, evaluation of environmental pollution is carried out by using oil outflow calculation shown in the MARPOL. For the evaluation of the risk of failure, we carried out structural reliability analysis of longitudinal strength of the ship. Then, we carried out the following five optimization problems, (1) Minimization of construction cost, (2) Maximization of life cycle benefit (LCB) considering the risk of oil outflow, (3) Maximization of LCB considering the risk of CO2 emission, (4) Maximization of LCB considering the risk of failure, and (5) Maximization of LCB considering the holistic risk. Finally, the optimum solutions of these five problems are compared to discuss about the advantage of the design of ship structures based on the holistic risk evaluation.

Time-dependent residual ultimate longitudinal strength - grounding damage index (R-D) diagram

In this study, the development of the R–D diagram taking into account the time-dependent corrosion wastage effect is presented to identify the necessity of applying the time-dependent corrosion wastage on R–D diagram. The R–D (Residual strength–Damage index) diagram was proposed by Paik et al. (2012) and is an innovative method relating to safety assessment for damaged structures; its feasibility has been confirmed by a previous study concerning double hull oil tankers under grounding damage. Generally, as a result of corrosion, the structural capacity of ships and offshore structures should be decreased in parallel with the operational period. Therefore, an Aframax class double hull oil tanker that has sustained grounding damages and also corrosion with a time-dependent corrosion wastage model (13 years, 19 years and 25 years (net scantlings specified by CSR)) applied to gross (new-built) scantlings is analyzed by the ALPS/HULL progressive hull girder collapse analysis program. Based on the obtained results, the time-dependent R–D diagram is produced and compared with the original R–D diagram. Finally, for practical purposes, empirical formulas based on time-dependent R–D diagrams are proposed to evaluate the residual ultimate longitudinal strength of the corroded Aframax class double hull oil tanker under grounding damage. The proposed time-dependent R–D diagrams will be useful for assessing the first-cut safety evaluation for a ship that has sustained grounding damages under different operational periods.

The one-dimensional response of a water-filled double hull to underwater blast: Experiments and simulations

Laboratory-scale fluid–structure interaction (FSI) experiments and finite element (FE) simulations are performed to examine the one-dimensional blast response of double-walled hulls, consisting of two skins sandwiching a layer of water. Both monolithic and sandwich designs are considered for the outer skin. Experiments are conducted in a transparent shock tube which allows measurements of water cavitation and hull response by high-speed photography. Experiments and FE predictions are found in good agreement and allow concluding that the impulse imparted to double hulls by underwater explosions can be dramatically reduced by employing the sandwich construction of the outer skin; such reductions are scarcely sensitive to the thickness of the water layer.

Advanced Integrated Design Method for Fatigue Assessment of Large Elastic Ship Structures

This paper is focused on an advanced method for ship structures fatigue assessment. The ships classification societies standard rules for fatigue analysis are based on simplified procedures, with wave induced loads obtained by linear oscillation analysis (low frequency, around 0.1 Hz), or equivalent statistical wave loads. In the case of large elastic ship structures, with hull length over 150 m, the global wave induced vibration response (high frequency, around 1 Hz) becomes significant. The developed integrated method for large ships fatigue assessment includes three interlinked analyses, as follows: the hot-spot stresses evaluation by 3D finite element models, wave induced loads by short term linear and non-linear hydroelastic dynamic analysis, ship service life and fatigue assessment by damage cumulative ratio method. As testing ship, it is considered a double hull LPG Liquefied Petroleum Gas carrier, with total length 239 m, for a set of structural details with stress hot-spots. Based on the non-linear hydroelastic wave loads, the integrated method of fatigue assessment becomes more accurate, predicting for the amidships structure 14 years of ship service life, instead of over 20 years according to the rules standard approach, so that the confidence on ship structure fatigue evaluation can be increased in the design process.

Numerical simulation of solitary wave–catamaran breakwater interaction using MFCT model

In this paper, a modified flux-corrected transport method (MFCT) was developed to simulate the interaction of solitary waves with catamaran breakwater. The fluid assumed to be viscous and incompressible. The explicit version of the two-stage projection method was used to solve the time-dependent Navier–Stokes equations. For the validation of the different aspects of the model, numerical test cases were performed. Solitary waves were generated using internal wave maker. The generated waves were compared with experimental data. This comparison showed a reasonable accuracy and ability of this model for solitary wave simulation. The efficiency of a fixed double hull (catamaran) floating breakwater under surface solitary waves was considered, focusing on the effects of the immersed hull on the wave transmission and reflection characteristics. The results show that the critical point for normalized draft of catamaran breakwater is 0.4. For values less than this point, the transmission coefficient increases dramatically. For example, as this normalized draft doubles, the transmission coefficient decreases more than quintuple. Furthermore, as the normalized demi-hull spacing triplicates the transmission coefficient decreases to less than half.