Deformations on the ship sections during fabrication: cause and remedies

During fabrication process, material deformations are likely to occur due to various factors such as heat during steel cutting, welding induced deformations, lifting and turning of ship sections, temporary stiffening and other possible modifications of ship sections. Lifting induced deformations is one of the major causes of deformations that highly affect the production cost and quality. The aim of this thesis is to outline the main causes of deformations that occur in ship sections during fabrication and to analyse in detail the lifting and turning operations of one ship section using the Finite Element Method (FEM). A strength check using the FEM has been performed on the selected ship section to investigate the deformations and stresses in two different cases with three different loading conditions. First, the section has been analysed without temporary stiffening in three load scenarios: lifting before turning, worst-case scenario during turning and lifting after turning. Similarly, the second case study has been analysed but with the temporary stiffening added according to the lifting plan. Various influencing parameters that determine the lifting plan has been investigated such as the sling angle which directly affects the deformation characteristics. It is observed that the addition of temporary stiffening is essential to minimize the deformations and to maintain the stress levels below the yield point.

Propulsion simulation on fully appended ship model

This study presents the numerical investigation for the flow around the propeller of the ONR Tumblehome combatant in open water and for the flow around the same ship in the case of self-propulsion with actuator disk method. Computational Fluid Dynamics based on RANS-VOF solver have been used in order to analyse the flow. The free surface treatment is multi-phase flow approach, incompressible and nonmiscible flow phases are modelled through the use of conservation equations for each volume fraction of phase. Accuracy involves close attention to the physical modelling, particularly the effects of turbulence, as well as the numerical discretization.

Experimental model tests to improve a tanker resistance performance

The ship resistance is one of the most important hydrodynamics performances, being related to the contractual ship speed. The experimental model tests can be used to measure and improve the resistance performance. In this paper, the possibility of using the experimental techniques in order to improve a tanker model resistance is demonstrated, based on a bulbous bow modelling solution. In this context, the results obtained in the Towing Tank of the Naval Architecture Faculty of “Dunarea de Jos” University of Galati, related to a tanker model resistance with and without bulbous bow are presented. The bulbous bow form was realised based on the hydrodynamics principles adapted to the bow forms of the tanker. In the case of the bulbous bow solution, a significant reduction of over 8% of the tanker model resistance was obtained, in the design speed domain.

On seakeeping capabilities evaluation of a large off-shore barge

Usual specially designed barges are involved in the off-shore operations that have to be evaluated by several criteria, inclusive of the seakeeping capabilities. The paper includes a comparative seakeeping study of two constructive versions for a large off-shore barge with a length of 189 m, having different breadths 40 m and 50 m. Both constructive versions are on the full cargo 23000 t condition. The seakeeping analyses are done with our own software DYN-OSC, developed by linear potential Lewis’s strip theory. The seakeeping studies are done in oblique irregular waves with a maximum height of 12 m and for the off-shore barge maximum operation speed of 7 knots. The results of this comparative study reveal the differences in the seakeeping operation capabilities for the two off-shore barge constructive versions.

Ship concept for cleaning the navigable inland water of floating debris

Rivers like the Danube crossing many countries gather floating debris. These countless times block locks, access roads to ports, access walkways on the berths of passenger ships and more. The paper presents the studies carried out in order to design a ship for the collection of these floating debris. Several variants have been chosen, of which one will be presented that is optimal from the point of view of the propulsion installation and especially of the wave front that it produces during the operation of waste collection and navigation to the place of unloading. In order to optimize the shapes of the ship, the NUMECA calculation program was used. It provides important data on the wavefront produced by the ship.

Numerical investigations of the free surface flow around a surface piercing hydrofoil

Starting with January 2013, naval architects faces new challenges, as all ships greater than 400 tons must comply with energy efficiency index (MPEC 62, 2011). From ship hydrodynamics point of view one handy solution is using Energy Saving Devices (ESD), with the main purpose to improve the flow parameters entering the propeller. For ballast loading condition the ESD may intersect the free surface disturbing and complicating the flow due to free surface /boundary layer interaction, turbulence and breaking wave effects that coexist and which are not completely clarified so far. Therefore, a free surface flow around a NACA 0012 surface piercing hydrofoil is numerically investigated and the results are compared to experimental results obtained in the Towing Tank of the Naval Architecture Faculty, “Dunarea de Jos” University of Galati. The comparison includes drag and free surface elevation on hydrofoil surface together with numerical uncertainty.

Propulsion performances study for a chemical tank

The design of a propulsion system for each ship must take into consideration a large number of factors. Some important factors that will lead to obtaining an efficient propulsion system are: the integration of a large number of elements in a functional space, selection of suitable components, the efficiency assessment taking into account functional safety and comfort criteria for crew and passengers. Considering the factors listed above, the analysis and design of the propulsion system for a chemical tank was performed. To choose the optimal components, the propulsion performance for this ship was analysed using 4 different engines. The operation of the propeller behind the ship has an effect on both the structure of the ship and the navigation conditions of the crew on board. Ttherefore, in the last part of the paper will be presented the effect of the operation of the propeller chosen for the chemical tank. In this sense, the surface forces induced by the propeller that appear in the stern vault will also be a center of interest in this work.

Ship resistance performances assessment for a containership

The present work is focused on ship resistance performances assessment for a given capacity containership. Starting from the main dimensions of a parent ship, other ten hull forms have been generated using DELFTship free program. For each case, the hydrodynamic ship resistance has been calculated using an inhouse code. The objective was to modified some geometrical parameters to obtain shapes of the hull that would provide the least resistance at the required transport capacity. The results obtained will be used in a future analysis related to the impact of hull forms improvements and ship resistance reduction on the propulsive performance and CO2 emissions per transport work.

Oscillating water column plant

This article is describing the way of construction and operation of an oscillating water column system in order to recover as much as possible from the waves energy. The oscillating water column plant is used for the production of electrical energy by tidal currents, and it is currently the most widespread and economical method for the conversion of wave motion. The environmental impact of these infrastructures remains very low: no emissions of gas or any waste during their operation. In addition, the swell is a formidable source of energy.

Evaluation of the vertical strenght of a 3000 tdw barge using the equivalent beam approach

For the preliminary design stage, the evaluation of vertical strength is mandatory for the preliminary scantling of the structure. This paper presents the evaluation of the vertical sectional efforts by equivalent beam approach, using the 3D-CAD lines plan of a 3000 tdw barge and mass diagram. For numerical analysis the own program P_QSW is used, for sagging and hogging wave condition, ship headings 0 and 45o, wave height max. 1.2 m. The vertical sectional efforts are compared with the maximum bending moment and shearing force prescribed by the classification societies for the 3000 tdw preliminary vertical strength assessment.