Jérôme De Lauzon

Evaluation of structural design of ultra large container vessel

The trend in modern sea transportation is building of ever larger container vessels, which require application of different numerical tools according to the relevant methodologies, in order to achieve their reliable structural design. The aim of this paper is to review direct strength assessment procedure based on long-term hydro-structure calculations including whipping and springing. As illustrative example, ultra large container ship with a capacity of 19000 TEU is selected and her structural design is evaluated both for fatigue and extreme response, respectively. Mathematical model is based on coupling of the 3D potential flow hydrodynamic model with the 3D FEM structural model. The general hydro-structure code HOMER, developed in Classification Society Bureau Veritas (BV) is used. Stress RAOs of selected structural details are obtained for full scatted diagram by the top-down procedure, and further used to assess their fatigue lives. Linear long term analysis is performed to define most contributing sea state to the vertical bending moment (VMB). Whipping response is computed on so called increased design sea state in time domain. Ultimate bending capacity was determined by nonlinear finite element analysis. Finally, extreme VBM is determined, and ultimate strength check according to the BV Rule Note NR583 was done.

Structural Reliability Analysis Applied on Steel Ships for Rule Partial Safety Factors Calibration

Ultimate strength assessments in current IACS Common Structural Rules (CSR) are determined by a limited number of constant partial safety factors (PSF). These coefficients are inherited from the previous Common Structural Rules for Oil Tankers, and were determined using a structural reliability analysis (SRA) based on a limited number ship. The authors decided to lead a more comprehensive structural reliability analysis to propose and discuss a new set of rule formulations. A literature review is carried out in order to determine an extensive database of virtual ships covering the whole range of existing ships with a few representative parameters. SRA is applied for ultimate strength assessment on this database. Uncertainties are modeled by a set of probability distributions applied to each characteristic quantity (still water bending moment, wave bending moment and capacity) and a Second Order Reliability Method (SORM) is used to target the ultimate capacity corresponding to a given failure probability for each ship. A set of several PSF formulations are then derived from these results using both Working Stress Design (WSD) and Load and Resistance Factor Design (LRFD) approaches. These formulations are then discussed to get an optimum between simplicity and accuracy of the results.

Structural Design Of Ultra Large Ships Based On Direct Calculation Approach

This paper presents a project of a composite trimaran structure, designed and built for the purpose of competing at the Hydro Contest 2016 competition at Geneva Lake. Concept of the contest is to raise the awareness of tomorrow’s engineers, industrialists, opinion leaders and the general public of what is at stake with regard to energy efficiency in the sea transportation of goods and passengers, as well as to be the laboratory of tomorrow’s boats, particularly enabling the most innovative ideas to be developed in collaboration with the industrial partners. Designed boats must have technological innovations enabling them to achieve the most efficient use of energy. Therefore, the goal was to design and construct lightweight structure, within a simple closed rules, with a satisfactory stiffens and strength as well as to strive for more efficient transport, which means higher speed with minimal energy consumption. An analysis of project variants was made with regard to the hull shape, material and technology of the fabrication, and for the adopted variant a computer structure model was developed and the FEA was carried out. The structure is divided into three main sections analyzed individually: hulls, front wing and rear wing along with rudder. Calculation was made for the worst load case, i.e. mass transfer, while wings were analyzed at the highest advancing speed. The boat has structurally met all requirements since there were no structural problems in testing and competing.The trend in modern sea transportation is building of ever larger ships, which require application of different direct calculation methodologies and numerical tools to achieve their reliable structural design. This is particularly emphasized in case of ultra large container ships (ULCS), but also other ship types like bulk carriers or large LNG ships belong to this category. In this context some classification societies have developed guidelines for performing direct calculations and for that purpose there are several hydro-structure tools available around the world, mainly relying on the same theoretical assumptions, but having incorporated different numerical procedures. Such tools are mostly based on the application of the 3D potential flow theoretical models coupled with the 3D FEM structural models. This paper illustrates application of general hydro-structure tool HOMER (BV) in the assessment of ship structural response in waves. An outline of the numerical procedure based on the modal approach is given together with basic software description. Application case is 19000 TEU ULCS built in South Korean shipyard Hyundai Heavy Industries. Extensive hydroelastic analyses of the ship are performed, and here some representative results for fatigue response with linear springing influence are listed.

Non Linear Wave Loading of the 3D FE Structural Model of Floating Bodies

Different numerical methods exist to treat the non-linear wave body interaction problem. These methods go from very complex CFD simulations (VoF, SPH…) to simpler potential flow based methods. Within the potential flow methods, different types of numerical approaches also exist, going from very complex fully nonlinear time domain methods to simpler hybrid frequency-time domain methods. In this paper, only the hybrid frequency-time domain potential flow methods are of concern.The basic principle of these methods is to use the linear frequency domain data and transfer them to the time domain (Cummings-1962, Ogilvie-1964) using the inverse Fourier transforms. Once in the time domain, all kind of nonlinearities can be added on top of the linear solution. This method showed to be very computationally efficient for global behavior of the floating bodies. However, in the context of the body structural response, it is not trivial to make the load transfer from the 3D hydrodynamic panel model to 3DFE model of the structure. One of the main problems concerns the radiation part of the potential which comes into the play through the well-known convolution integral of the impulse response functions. Within the hydro-structure interaction problem which is of concern here, the straightforward application of the Cummings principles leads to the convolution integral for every pressure point (either on hydrodynamic or structural mesh) which can lead to very expensive numerical simulations.Previous study by Tuitman, Sireta, Malenica and Bosman (2009) proposed the use of the fast Fourier transform (FFT) to compute the radiated wave loads at each point of the structural model, as a post-processing of the seakeeping calculations.In this way the CPU time is significantly reduced but the slight unbalancing of the 3DFE model remains. In this paper, we propose the direct use of the local radiated pressure impulse response functions and we show that a good numerical implementation of such method can result in acceptable CPU time with perfect balance of the 3DFE model.Copyright