Abstract
The shakedown analysis process of an offshore structure having elastic-plastic material presented. The finite element model of the structure has been developed first, and then a simple method has been applied for shakedown analysis using matrix tool. Simplifying the relationships together with applying the theory concepts of shakedown analysis is one of the characteristics of the presented method for practical problems. Here, shakedown analysis formulation discussed in four steps. First, the Morison equation adopted for converting the velocity and acceleration terms into resultant forces and it extended to consider arbitrary orientations of the structural members. Then the loads due to the waves have been calculated and they have been converted to specific repeating cyclic loads on the structure nodes. In the second step, the finite element model of the structure has been developed and considered under nodal loads resulted from the specific combined wave loads. Thirdly, the shakedown multiplier has been calculated using shakedown static theorem based upon the stress domain governing the problem. Finally, in the fourth step, a graph has been developed indicating the critical sea waves domain that cause the structure shakedown. The formulation has been applied for two types of offshore structures to verify the concept employed and its analytical capabilities.
Highlights
Many structural components operate under complex variable or cyclic loading [4, 9, 10, 12]
Acceleration, a y is known, the force resulted from the Occurring Shakedown: Based upon the static shakedown theorems [13], the offshore structure shakedown will happen if the plastic strains increase after the first cycle of a specific load combination due to the waves such that in any cycle loading, P(t), the behavior of the structure is still elastic
A simple finite element model with pipe type elements have been used for analyzing the structure frames of the offshore structure
Summary
Many structural components operate under complex variable or cyclic loading [4, 9, 10, 12]. Acceleration, ax , and vertical component of Shakedown Analysis of an Offshore StructureS acceleration, a y is known, the force resulted from the Occurring Shakedown: Based upon the static shakedown theorems [13], the offshore structure shakedown will happen if the plastic strains increase after the first cycle of a specific load combination due to the waves such that in any cycle loading, P(t) , the behavior of the structure is still elastic. This can be stated by the following relationship. The component of the velocity of the water perpendicular to the cylinder axis, V, can be found using the following relationship [14]
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