Marine Structures

Based on the statistics published by corrosion researches of Ohio State University of
America (RPI), one ton steel is destroyed due to corrosion per seconds. The
investigation of each of factors involved in materials corrosion under environmental
conditions of sea water is very difficult. Each of the researches conducted on
materials corrosion in sea water only were conducted from one view and one type of
corrosion on one or some materials. The present study had a general summary
regarding the general failures in marine environments.

At present ships are designed to satisfy the minimum requirements for safety. And history shows that this practice does not suffice, and nor is it sustainable. A new paradigm is needed. This thesis aims to contribute in that respect by proposing a design method that should move ship safety beyond the minimum requirements as much as possible and as long as it is economically sound. The thesis focuses mostly on environmental safety in the event of accidents such as collisions and grounding. A special feature is the consideration of maritime stakeholder preferences regarding safety and profitability. This is an underlying element in all the analysis performed and conclusions reached.
This design method features new approaches in multi-objective optimization of ship structures and in advanced decision making for design selection. The multi-objective optimization is based on evolutionary algorithms, more precisely the genetic algorithm (GA) with advanced treatment of design constraints and objectives. Through the approach of vectorization, the GA becomes not only more efficient, but also more flexible in use, bearing in mind the complexity and demands of accident analysis for optimization. The decision making is established on the concepts of Game Theory, resulting in a new criterion for design selection, the Competitive Optimum, based on the maximal concurrent satisfaction of stakeholder preferences.
The proposed design method is intended in particular for ship structural design projects, permitting the definition of hull structural scantlings, or even hull topology if desired. The approaches to multi-objective optimization and design selection that are introduced possess a wider basis of application, and are extensible to other fields in maritime safety and naval architecture.
The results of the thesis provide several relevant conclusions with an impact on practical naval architecture. For example, i) by increasing ship crashworthiness, significant risk reduction can be attained, ii) raising safety is economically justified if the benefits to the public are considered alongside those of the industry, and iii) the crashworthiness of ships can be controlled effectively with conventional double-bottom and double-sided structures.

The primary aim of the present study is to investigate the collision resistance and residual strength of single side skin (SSS) and double side skin (DSS) bulk carriers subject to collision damage. The impact dynamics analyses were conducted using ANSYS LS-DYNA for the evaluation resistance forces, energy absorption and penetration depth for various collision scenarios. The struck vessels of Capsize SSS and DSS designs were assumed to be entirely standstill and the striking vessels of an Aframax-type oil tanker with different bulbous bow shapes were modeled as rigid bodies. The findings were compared, where possible, with existing analytical tools. Residual strength calculations on SSS and DSS vessels were computed corresponding to all considered collision damage scenarios. Traditional Smith's method was applied with the average stress — average strain relationships of elements based on derived semi - analytically. The effect of corrosion was also evaluated by Joint Bulker Project (JBP) Rules on the influence of plate and stiffener thickness. The safety of the vessels was determined as a ratio of the ultimate hull girder strength to bending moment in damaged condition. Finally, results and insights derived from the present work are summarized.

Oil pollution into the concrete composed materials, leads to decrease the compressive strength of the constructed structure. In the present study, effect of using a natural pozzolan named Zeolite on concrete structures was tested in different marine conditions. A fixed amount of oil equal to 2% of sand weight was added as the pollution into the concrete composed materials. Natural Zeolite was added into the concrete instead of cement to the mix design with weight percentages of 10, 15 and 20. After preparing and curing, concrete specimens were placed into the three different conditions: fresh water, tidal, and sea water environments. Results of compressive strength tests showed that replacement of natural Zeolite instead of cement significantly increased compressive strength in comparison with control specimens, in all environments. Adding 20% natural Zeolite increased the compressive strength to its highest values about 60-85% higher than control specimens.