A ship is an obvious example of a relatively large and complex engineering system, and in most cases the vessel itself is a part of an even larger system which influences with its behaviour, shape and the economics involved in all the processes involved in building and maintaining such a complex system. The ship consists of several subsystems, each essential to the whole system such as the
propulsion subsystem, and the cargo handling subsystem. The structure of the ship can be regarded as a subsystem providing physical means whereby other subsystems are integrated into
the whole and given adequate protection and suitable foundation for their operation. In general terms the design of an engineering system may be defined as “The formulation of an accurate model of the system in order to analyze its response-internal and external-to its environment, and the use of an optimization method to determine the system characteristics that will best achieve a specified objective, while also fulfilling certain prescribed constraints on the system characteristics and the system response.”
RATIONALLY-BASED STRUCTURAL DESIGN
The ever increasing demand for more efficient marine transport has lead engineers in that field to consider a number of significant changes in ship sizes, types and production methods over the
last 40 years. Different types of vessels have appeared attempting to meet the demands of the shipping industry. The growing number of factors which give rise to this process of change The
need for protection against pollution, new trade patterns that emerge, new types of cargos and the need to safely transport any type that might be considered dangerous, increasing numbers in
production lines of standard ship designs and their consequent development to achieve a higher degree of efficiency and the development of structures in vehicles for the extraction of ocean
resources, require scientific, powerful and versatile methods for structural design. One can say that we are at present in the midst of a progressive and gradual but profound change in the
philosophy and practice of ship structural design.
Based on individual ship designer and shipyard experience and ship performance, in the past ship structural design had been mostly empirical based on the structural designers’ accumulated
experience This approach lead eventually to the publication of structural design codes, or “rules” as they are referred to in the industry, published by various ship classification societies.
These “manuals” of ship structural design provided a simplified and care-free method for the determination of a ship’s structural dimensions. This procedure provided a time and cost
effective method for design offices and simplified classification and approval process at the same time. The method unfortunately has several disadvantages including the inability to handle
the large number of complex modes of structural failure, the possibility of unsuitable results in regard to the specific goals of the ship owner or the particular purpose or economic environment
that the ship is required to operate in and the inability to distinguish between structural adequacy and over adequacy leading to increased cost and steel weight in a structure. Most
important though is the large number of simplifying assumptions included which bound such design process within certain limits.
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