Dracos Vassalos

Physical modelling and similitude of marine structures

This review paper is aimed at providing information on and at explaining the appropriate use of models in the design of marine structures. Emphasis is placed on the derivation of scaling laws and on limitations of accuracy. Similitude, dimensional analysis and the use of governing equations in model experiment scaling are explained before addressing the modelling of some common ocean engineering tests.

Risk-Based Ship Design

This chapter aims to present an overview of risk-based design developments over the recent past and to attempt to demonstrate that substantial pre-requisite scientific and technological developments are in place for Risk-Based Design to be fully implemented in the maritime industry. To elucidate the realisation of the risk-based ship design concept through application, a variety of examples at basic and holistic levels using RoPax and cruise liners are presented and discussed in the second part of the present chapter.

A NUMERICAL METHOD FOR PREDICTING SNAP LOADING OF MARINE CABLES

A numerical approach for predicting the snap loading of marine cables operating in alternating taut-slack conditions is presented. The modelling is based upon the lumped-mass-and-spring method with modifications to take into account the bilinear axial stiffness of the cable. The resulting governing equations are integrated in the time domain using the modified Euler method. Numerical examples are given and comparisons of the numerical results and the experimental results available are made which demonstrate the validity of the present method.

Study on side structure resistance to ship-ship collisions

Abstract Double hull (DH) tankers may be more effective than single hull (SH) tankers in pollution prevention because they have a second barrier, the inner skin, to oil outflow in the event of side damage. The actual effect of DHs calls for quantitative study. This paper presents a comparative study on the side structure resistance to collisions. A DH Aframax tanker and an SH Aframax tanker of similar size were selected for the study. The two vessels were assumed to be struck by a same bulbous bow in different locations and angles. The bow was assumed to be rigid and different non-linear materials and contact models were considered for the struck tankers based on the original designs. The DH tanker was found to be superior to the SH tanker in relation to resistance to side structural damage. Finally, by using the simulation results, the distribution of damage extents for DH tankers is proposed based on the historical damage extents, which are mainly for SH tankers.

Dynamics of small-sagged taut-slack marine cables

The snap tension of small-sagged marine cables operating in alternating taut-slack conditions is considered in this paper. The marine cable is suspended at the two ends on the same level. One of the two ends is fixed, while the other is subjected to horizontal excitation. A single non-linear equation of vertical motion of the cable is derived and solved by the Galerkin method. It is found that only the symmetric modes with respect to the mid-span need to be considered. Numerical examples are given and comparisons are made between numerical and experimental results which help to demonstrate the validity of the present method.

Risk evaluation for RoPax vessels

The paper presents the results of a recent risk evaluation study for roll‐on‐roll‐off passenger (RoPax) vessels, carried out as part of the activities of the SAFEDOR Integrated Project. The objective of the study was to investigate hazards and their causes during RoPax operation and to quantify, to the extent possible, their frequencies and consequences. A previous study on the safety assessment of RoPax vessels sailing in north‐west European waters, covering the period until 1994, was used as the basis in putting together a high‐level risk model for the current study. All scenarios are presented in the form of event trees, quantification of which is made on the basis of worldwide accident experience (from 1994 to 2004), relevant past studies, and judgement. The study estimates the risk of loss of life among passengers and crew (by calculating for each scenario the individual risk and the potential loss of life and by plotting the corresponding F–N curves) and compares them with current risk acceptance criteria.

Application of 3D parallel SPH to ship sloshing and flooding

Smoothed particles dynamics scheme is applied in sloshing and flooding problems in this paper. New solid boundary condition is used to simulate complex geometry. Parallelization of SPH scheme is carried out using MPI standard which makes 3D simulation acceptable. The numerical solutions obtained have been compared with both experimental results and other numerical solutions.

GOALDS - goal based damage ship stability and safety standards

The new probabilistic damaged stability regulations for dry cargo and passenger ships (SOLAS 2009), which entered into force on January 1, 2009, represent a major step forward in achieving an improved safety standard through the rationalisation and harmonization of damaged stability requirements. There are, however, serious concerns regarding the adopted formulation for the calculation of the survival probability of passenger ships, particularly for ROPAX and large cruise vessels. The present paper outlines the objectives, the methodology of work and main results of the EU-funded FP7 project GOALDS (Goal Based Damaged Stability, 2009-2012), which aims to address the above shortcomings by state-of-the-art scientific methods and by formulating a rational, goal-based regulatory framework, properly accounting for the damage stability properties of passenger ships and the risk of people onboard.

Managing the exchange of engineering product data to support through life ship design

Abstract An approach for managing the exchange of engineering product data between geographically distributed designers and analysts using a heterogeneous tool set for the through-life design of a ship is described. The approach was developed within a pan-European maritime project called VRShips-ROPAX 2000 that demonstrated how information technology could be integrated into the design process. This paper describes the development of a common model containing neutral ship product data through a bottom-up consideration of the requirements of the tools to be integrated, as well as a top-down consideration of the data requirements for through life design. This common model was supported within an Integrated Design Environment (IDE) that co-ordinated design activity distributed across Europe. The IDE ensured that the users were provided with the right data in the right form at the right time to do the right task, i.e., that the design activity was timely and appropriate. The strengths and weaknesses of the approach are highlighted.

A semi-analytic treatment of three-dimensional statics of marine cables

A semi-analytic approach is presented in this paper which is capable of predicting the static performance of marine cables. The solution is derived as a function of only three parameters which can be solved numerically by implementing different kinds of boundary conditions. The efficiency and accuracy of the method permit quick parametric studies for optimal selection of the system particulars which is undoubtedly useful for preliminary design. A number of numerical examples demonstrates the validity of the approach adopted.