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Abstract:
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Hat Stiffened Plates are used in composite ships and are gaining popularity in metallic ship
construction due to its high strength-to-weight ratio. Light weight structures will result in greater
payload, higher speeds, reduced fuel consumption and environmental emissions. Numerical
Investigations have been carried out using the commercial Finite Element software ANSYS 12 to
substantiate the high strength-to-weight ratio of Hat Stiffened Plates over other open section
stiffeners which are commonly used in ship building.
Analysis of stiffened plate has always been a matter of concern for the structural engineers
since it has been rather difficult to quantify the actual load sharing between stiffeners and
plating. Finite Element Method has been accepted as an efficient tool for the analysis of stiffened
plated structure. Best results using the Finite Element Method for the analysis of thin plated
structures are obtained when both the stiffeners and the plate are modeled using thin plate
elements having six degrees of freedom per node. However, one serious problem encountered
with this design and analysis process is that the generation of the finite element models for a
complex configuration is time consuming and laborious. In order to overcome these difficulties
two different methods viz., Orthotropic Plate Model and Superelement for Hat Stiffened Plate
have been suggested in the present work.
In the Orthotropic Plate Model geometric orthotropy is converted to material orthotropy
i.e., the stiffeners are smeared and they vanish from the field of analysis and the structure can be
analysed using any commercial Finite Element software which has orthotropic elements in its
element library. The Orthotropic Plate Model developed has predicted deflection, stress and
linear buckling load with sufficiently good accuracy in the case of all four edges simply
supported boundary condition. Whereas, in the case of two edges fixed and other two edges
simply supported boundary condition even though the stress has been predicted with good
accuracy there has been large variation in the deflection predicted. This variation in the
deflection predicted is because, for the Orthotropic Plate Model the rigidity is uniform throughout the plate whereas in the actual Hat Stiffened Plate the rigidity along the line of
attachment of the stiffeners to the plate is large as compared to the unsupported portion of the
plate.
The Superelement technique is a method of treating a portion of the structure as if it were a
single element even though it is made up of many individual elements. The Superelement has
predicted the deflection and in-plane stress of Hat Stiffened Plate with sufficiently good accuracy
for different boundary conditions. Formulation of Superelement for composite Hat Stiffened
Plate has also been presented in the thesis. The capability of Orthotropic Plate Model and
Superelement to handle typical boundary conditions and characteristic loads in a ship structure
has been demonstrated through numerical investigations. |