5003 Lectures - Faculty of Engineering and Applied Science

E5003 - Ship Structures I 9
© C.G. Daley
plane, everywhere in the universe, always!) the
force acts in both ways. This powerful idea is the
key to following what happens in a structure.
Structural Design
The process of ship structural design varies
depending on the specific issues. Structural design
occurs after the mission is set and a general
arrangement is determined. The general
arrangement allows us to determine both the
environmental loads and the distribution of
hull/outfit/cargo weights. The establishment of
scantlings (structural dimensions) is iterative. We
assume that a preliminary set of dimensions is
settled upon from experience or by other choice.
The loads will cause a set of responses (stresses,
deflections). The response criteria are then
compared to the responses. For any inadequacies
we modify the structural dimensions and repeat
the response analysis. When all responses are
satisfactory, we are finished.
In cases where we wish to satisfy additional
constraints (cost, performance..) we add checks for
these items after we have checked the structural
response. Again we loop until we have met the
constraints, and reached optimal values for some
measure.
As stated above, the structural design can only
occur after the overall vessel concept and
arrangement is set, which is done during the
preliminary design stage. The structural design
itself is a process that is comparable to the overall
design. Just as the vessels has a mission and a
concept to satisfy that mission, so too does the
structure have a mission and concept to satisfy the
mission. Prior to deciding on the structural sizes
(scantlings) , the designer must decide on the
overall structural concept and arrangement. In
rule based design (Classification Society rules), the
loads and response criteria have been combined
into standard scantling requirements formulae.