Offshore Platforms Subjected to Wave Forcesby Bulent A. Ovunc, Univ of Southwestern Louisiana, Lafayette, LA, USA,
Abstract: The dynamic analyses of offshore platforms are mostly based on the lumped mass matrix method in the frequency domain. Although the approximations involved in the lumped mass matrix method are negligible for most of the regular frameworks in comparison with the continuous mass matrix method, heavy gravitational loads on the upper decks, wave forces and effects of member axial force and soil-structure interaction may warrant the use of continuous mass matrix method. The dynamic shape functions include, beside the member characteristics, the member axial force and if the member is embedded in soil, the soil characteristics with their real distribution over the members. The dynamic member stiffness matrices are very much dependent on the ratio of member to soil characteristics. The nature of the dynamic member stiffness matrices change entirely, passing through a transition stage. The wave forces are considered as the dynamic loads. Cnoidal or Airy or Stokes wave profile is assumed depending on the length and the height of the wave and the depth of the water. The differential equations of motion are written on an inifinitesimal element of the member, then integrated over the length of the member in order to determine the equivalent nodal forces and moments.
Subject Headings: Soil dynamics | Matrix (mathematics) | Dynamic loads | Wave forces | Soil properties | Soil structures | Equations of motion | Axial forces
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