Double-hulled Ship Research Articles

A multiscale DEM\u2013FEM coupled approach for the investigation of granules as crash-absorber in ship building

This paper covers a numerical analysis of a novel approach to increasing the crashworthiness of double hull ships. As proposed in Schöttelndreyer (Füllstoffe in der Konstruktion: ein Konzept zur Verstärkung vonSchiffsseitenhüllen, Technische Uni-versitt Hamburg, Hamburg, 2015), it involves the usage of granular materials in the cavity of the double hull ship. For the modeling of this problem, the discrete element method (DEM) is used for the granules while the finite element method is used for the ship’s structure. In order to account for the structural damage caused by collision, a gradient-enhanced ductile damage model is implemented. In addition to avoid locking, an enhanced strain-based formulation is used. For large-scale problems such as the one in the current study, modeling of all granules with realistic size can be computationally expensive. A two-scale model based on the work of Wellmann and Wriggers (Comput Methods Appl Mech Eng 205:46–58, 2012) is applied—and the region of significant localization is modeled with the DEM, while a continuum model is used for the other regions. The coupling of both discretization schemes is based on the Arlequin method. Numerical homogenization is used to estimate the material parameters of the continuum region with the granules. This involves the usage of meshless interpolation functions for the projection of particle displacement and stress onto a background mesh. Later, the volume-averaged stress and strain within the representative volume element is used to estimate the material parameters. At the end, the results from the combined numerical model are compared with the results from the experiments given in Woitzik and Düster (Ships Offshore Struct 1–12, 2020). This validates both the accuracy of the numerical model and the proposed idea of increasing the crashworthiness of double hull vessels with the granular materials.

Simplified contact-based segment expansion (CBSE) method for assessment of crashworthiness of double-hulled ship structure

ABSTRACT A commonly assumed ship-to-ship collision scenario is a rigid ship bow hitting the side of a ship perpendicularly. A bulbous bow has a slender shape overall but a rounded end, while a stem has a sharp horizontal edge but a gently sloping body. It was found from numerical simulations that the stem collision induces horizontal shear failure on side shell as soon as the stem contacts with the side shell. Also, progressive deformation was observed only at the lower part of side shell as the contact extended downward. Based on the present research, a simplified method for the stem collision case, named a contact-based segment-expansion (CBSE) method, herein is proposed. This method reflects the progressive collapse of side shell and considers the strain energy absorbed by the boundary girders. The validity of the method was verified from the numerical simulations in terms of energy-absorption capacity of the double-hulled structure.

Simplified buckling-and-contact-based expansion method for assessment of crashworthiness of double-hulled ship structure

Ship-to-ship collision events can have severe consequences such as loss of life and environmental degradation. For this reason, modern ship designs are required to incorporate a double-hulled structure to prevent inner-hull damage from such events. Using the experimental or numerical method to analyze the crashworthiness of double-hulled ship structures entails much effort, for which reason neither method is easy to adopt at the early design stage. In this paper, an existing simplified method called Ito's method is improved by a new buckling-and-contact-based expansion method. This method can be applied to double-hulled-structure or outer-hull-local-rupture failure mode. The perpendicular bow-to-side collision scenario is assumed for a conservative estimation of damage to a double-hulled structure. The method was verified in the present study by numerical ship collision simulations of several cases. The results for the buckling-and-contact-based expansion method and numerical simulation were similar for a blunt shape of striking body but different for a sharp shape.

Modelling and experimental testing of expanded granules as crash‐absorber for double hull ships

AbstractIn this contribution, expanded glass granules are investigated, which will be used to increase the crashworthiness in ship construction. Therefore, an experimental setup is presented. This setup represents a simplified side hull structure of a double hull ship. The empty space between the double hull structure can be filled with the granular material which acts as crash absorber.The described experiment will be used to validate the finite element simulation of the penetration of the double hull with the bulbous bow. To model the granules the Mohr‐Coulomb material model is taken advantage of. Based on the experimental data the suitability of the Mohr‐Coulomb model will be discussed.

Analytical method to assess double-hull ship structures subjected to bulbous bow collision

The paper presents simplified analytical methods to assess the plastic deformation and failure of double-hull ship structures subjected to bulbous bow collision. To validate the methods, numerical simulations are conducted on double-hull tanker side structures including three frame spacings along the longitudinal direction and two stringer spacings along the vertical direction. The paper estimates the extent of damage within double-hull ship structures during minor ship-to-ship collision, where the inner hull does not participate in dissipating incident energy. In the analytical methods, the nose shape of striking bulbous bow is simplified as a hemisphere or a cylinder with hemispherical ends. This equivalence is validated against the similar numerical force-displacement responses using the actual bulbous bow and the simplified strikers. The analytical methods derive expressions to estimate the relation between the plastic deformation and the crushing force of the double-hull structures. The onset of fracture in the outer hull is evaluated by a simple formula based on experimental and theoretical analyses. Finally, the probabilistic structural absorbed energy until the rupture of specific struck ship with respect to the displacement of striking ship is assessed according to the statistical data of ship dimensions and the design principles of bulbous bow.

Investigation on the Structural Damage of a Double-Hull Ship, Part I – Ship Collision

Marine structure is designed to be able to resist various load conditions during its operational period. However, in design process, analysis of accidental loads, such collision and grounding, has not been included for both merchant ship and navy vessel. These loads are spontaneous and several remarkable casualties may occur after collision and grounding taking place. The aim of this paper is to investigate structural damage on the target ship during collision and grounding considering on failure process and damage extent. This work is divided into two parts which in the Part I, ship collision is discussed, and the Part II deals with interaction of ship structure with sea bottom in grounding. In the Part I - Ship Collision, condition of the side structure is observed, including the inner hull after impact which is considered as the key to determine safety condition of ship cargo. A passenger ship is modelled in this work and designated as the struck ship which will be struck by the striking ship in collision process. Resistance capability of the double-hull structure against side collision is evaluated. Virtual experiment is conducted by nonlinear finite element method in order to calculate several dynamic collision scenarios which are built based on physical parameter, namely target location. Based on calculation results, damage on the side hull is found to be highly influenced by relative height between two ships prior collision. Crashworthiness criteria are summarized and result tendency indicates that in the mentioned location, the striking ship produces larger tearing on the lower part of the struck ship. Contribution of each collision scenario on the resultant force is presented in later part in order to observe structural behaviour of each determined location in encountering side collision.

Investigation on the Structural Damage of a Double-Hull Ship, Part II – Grounding Impact

Possibility of marine and offshore structures to experience accidental loads has been seriously considered up to this day. Remarkable casualties on related aspects are rising demand to ensure ship safety which in this subject is observed on marine structure. Ship is an example of marine structure that may be subjected to accidental loads during its operation. The aim of this paper is to investigate damage extent of the target ship under different accidental loads, namely collision and grounding with considerations to failure process and deformation contours. This work is divided into two parts which in the Part I, ship collision is discussed, and the Part II deals with interaction of ship structure with sea bottom in grounding. In Part II - Grounding impact, evaluating tearing damage on the bottom structure is essential in estimating environmental casualties caused by oil leakage. A chemical tanker is modelled to be the target ship in a series of grounding scenarios. Condition of the structural damage and tendency of the internal energy, crushing force and structural acceleration are observed. Prediction of the tearing opening and location of the initial failure in further grounding process are also presented in this paper. Virtual experiment is conducted by nonlinear finite element method in order to calculate the defined grounding scenarios which are built based on the target location on the bottom structure. Based on calculation results, condition of the double-hull structure after grounding is found to be highly influenced by arrangement of the longitudinal members which is evidenced by the fact that these members provide higher resistance than the transverse part. Finally, influence of the indenter's position on structural responses in grounding is summarized.

Assessment of the strength of double-hull tanker side structures in minor ship collisions

The paper presents a simplified analytical method to examine the energy absorbing mechanisms of double-hull ship structures subjected to a flat edge indenter. To validate this method, a numerical simulation is conducted on a structural module derived from an experimentally scaled stiffened panel in previous work. The structural module represents one-fifth scaled double-hull tanker side structures, including three frame spacings along the longitudinal direction and two stringer spacings along the vertical direction. The paper provides practical information to estimate the extent of structural damage within double-hull tanker side structures during minor head-on collisions, where the inner hull does not participate in absorbing impact energy. The numerical definition of material nonlinearities for the selected mesh size is validated against previous experimental results. The numerical simulation describes the plastic deformation and material rupture in the double-hull structure and provides detailed information of the energy dissipated by each structural component. The simplified analytical method estimates the relation between the plastic deformation and the crushing force of the double-hull structure, giving a good agreement with the corresponding numerical force–displacement response. Moreover, the analytical method of internal mechanics is combined with a theoretical analysis of external dynamics to evaluate the energy absorption in a ship-to-ship collision. A procedure for assessing the strength of a collided ship is presented on the basis of the experiments of scaled structures.

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.

Development of a mobile robotic system for working in the double-hulled structure of a ship

Shipbuilding processes involve highly dangerous manual welding operations. Welding ship walls inside double-hulled structures presents a particularly hazardous environment for workers. This paper describes the “Rail Runner X” (RRX), a new robotic system that can move autonomously inside the walls of a double-hulled ship and automatically execute the required welding processes. The RRX robotic system is composed of a mobile platform and a welding robot consisting of a 3P3R serial manipulator. The robot is used to weld U-shaped trajectories located between two longitudinal stiffeners. The mobile platform enables traverse movements onto neighboring longitudinal stiffeners. The entire cross section of the robotic system is small enough to be placed inside the double-hulled structure via a conventional access hole from the outside shipyard floor. The overall engineering design process that led to the final robot solution developed is presented in this paper, including kinematic analysis data and experimental results for verifying the autonomous movement and welding performance.

조선에서의 이중 선체 조립을 위한 소형 용접 로봇 개발 및 적용

조선에서의 이중 선체 조립을 위한 소형 용접 로봇 개발 및 적용

Rail Running Mobile Welding Robot ‘RRX3’ for Double Hull Ship Structure

‘Seoul National University’ and ‘Daewoo Shipbuilding & Marine Engineering’ in Korea jointly developed a mobile welding robot, the ‘Rail Runner’ (RRX), which is able to freely move in both transverse and longitudinal directions, and perform welding tasks in double hull structures. Recently, RRX2, (the second version of RRX), was presented at ‘Robotics and Applications 2007'. In this paper, the design, manufacturing, and application of RRX3, the third version of RRX, is described. The moving mechanism of RRX, which is able to move freely in a double hull structure, has two functions. 1) To move in a longitudinal direction by driving wheels using longi. faces as ‘rails', and 2) To move in a transverse direction by sliding along supporting longi. faces using extension arms. The body of the RRX3 is composed of a 12-axis, 6-axis mobile platform that supports the RRX moving mechanism and a 6-axis welding robot to do the welding job. The main point in designing RRX3 is to make it capable of passing through a 600mm×800mm sized access hole, the entrance into an enclosed double hull structure. The full size of the manufactured RRX3 is 1825mm×495mm×569mm, and thus the RRX3 is able to pass through an access hole. The weight is 250kg with a 6-axis mobile platform, 6-axis welding robot, and mounted controller.

Hybrid Reliability Predictions of Single and Advanced Double-Hull Ship Structures

A hybrid approach based on the combination of the Monte Carlo simulation (MCS) technique and the first-order reliability method (FORM) is developed to quantify the small probability of failure of a hull girder under longitudinal bending. The ultimate strength (ULTSTR) bending solver, developed by the U.S. Navy, is integrated with the hybrid probabilistic analysis framework. Different from the conventional approach, where the probability distribution of the hull capacity is preassumed, the probability distribution of the ultimate bending strength is determined by propagation of the uncertainties associated with hull geometric and material property parameters into ULTSTR via a small number of Monte Carlo simulations. The FORM-based solution module is then applied in the reduced random variables space to compute the probability of failure. Both the computational efficiency and numerical accuracy of the hybrid approach are demonstrated through its application to a Navy frigate, designated Ship A. The validated hybrid approach is then applied to a Navy combatant, designated Ship B, in both its single-and double-hull configurations. The reliability results reveal the benefit in using the advanced double-hull configuration, assuming its design load is the same design load encountered by the corresponding single hull during its service life.

Behavior of Long Fatigue Cracks in Cellular Box Beam

The propagation of long cracks under constant-amplitude cyclic loading is studied in complex welded box beams made of high-strength low-alloy steel. The 8 × 1 × 0.7 m box beams were designed to simulate the cellular structure of a double-hull ship but the results of the experiments are equally applicable to other box systems such as bridges. These experiments were designed to evaluate the residual fatigue life after a significant fatigue crack has formed. After testing, residual stresses were measured on two box beams using the standardized strain-gauge hole-drilling method. The experiment results demonstrated the good crack tolerance of cellular structures. The residual life of a box beam (after a welded detail has failed) was significant. The crack-driving force was evaluated using finite-element modeling. Reasonable correlation between these large-scale tests and the fatigue crack growth rate from small compact specimens was obtained only with models that included the effects of crack closure due to residual stresses. Linear-elastic fracture mechanics proved to be sufficient to predict the behavior of long cracks in this case.

A simple formulation for predicting the ultimate strength of ships

The aim of this study is to derive a simple analytical formula for predicting the ultimate collapse strength of a single- and double-hull ship under a vertical bending moment, and also to characterize the accuracy and applicability for earlier approximate formulations. It is known that a ship hull will reach the overall collapse state if both collapse of the compression flange and yielding of the tension flange occur. Side shells in the vicinity of the compression and the tension flanges will often fail also, but the material around the final neutral axis will remain in the elastic state. Based on this observation, a credible distribution of longitudinal stresses around the hull section at the overall collapse state is assumed, and an explicit analytical equation for calculating the hull ultimate strength is obtained. A comparison between the derived formula and existing expressions is made for largescale box girder models, a one-third-scale frigate hull model, and full-scale ship hulls.

二重船殻構造モデルタンクよりの油流出-III : 貨物油物性の影響

The applicability of a method to predict the amount of oil outflow from a double hull ship with a ruptured tank bottom based on hydraulic balance inside and outside the tank is investigated for three types of test oil in addition to experimental conditions of tank sizes, tank configurations and conditions of cargo loading. The amount of oil outflow was measured using a VLCC 1/50 scale model tank with double hull under the following conditions: oil densities=810~900 Kg/m3 (15oC)m dynamic oil viscosities=3.1~100 cSt (15oC), double bottom heights=double side widths=0.2m, 0.04m, 0.06m, oil tank cross sectional areas=0.26~0.52m2, initial oil levels=0.2~0.5m, drafts=0.2~0.45m and simulated circular puncture size=71mm . The predicted amount of oil outflow is compared with the experimental data. Good agreement is shown.

Wave interference effects on a double-hull ship model, as measured by gravity dynamometer

The wave interference component of the drag of a double-hulled ship model as a function of speed and hull separation was investigated by means of a towing tank fitted with a gravity dynamometer towing system. Each hull was asymmetrical, with one flat and one curved side—an arc of a circle in plan. The results indicated smaller hull interference effects than given by the standard (parabolic) test hull results of Everest. The optimum separation ratio S L was 0.38—compared to 0.2 for Everest—while the resistance ratio R w R win = wave resistance wave resistance at ∞ separation at optimum separation was 0.87, as compared with Everest's value of 0.52. These differences were ascribed to the differences in hull shapes tested—parabolic Everest hulls would produce stronger bow and stern wave systems—but were possibly influenced by the characteristics of the gravity dynamometer system used in this study.

A Simplified Method to Analyse the Strength of Double Hulled Structures in Collision (3rd Report)

The effects of various design parameters on the strength of double hulled structures in collision were examined. At first, the scantlings and the strength characteristics of double hulls were investigated, which included double sides and double bottoms. Static destruction tests were carried out using a series of double hulled models which covered a wide strength distribution range. The validity of the simplified method to analyse the strength of double hulled structures in collision which was presented in the previous paper was confirmed by comparing the calculated results and the experimental results. Finally, choosing a double hulled ship of 100, 000 tons displacement as a standard type ship, parametric calculations were done using this method, where the side shell thickness, the transverse web thickness and the double hull breadth were taken as design parameters. It was found that the most effective method to increase the energy absorption capacity is to increase the transverse web thickness.