Nonlinear Dynamic Analysis of Jack-Up Platforms Exposed to Extreme Random Waves

2012 ◽  
Author(s):  
Jalal Mirzadehniasar ◽  
Mehrdad Kimiaei ◽  
Mark J. Cassidy
Keyword(s):  
Dynamic Response ◽  
Dynamic Analysis ◽  
Time Domain ◽  
Nonlinear Dynamic ◽  
Spectral Composition ◽  
Random Time ◽  
Offshore Platforms ◽  
Wave Loading ◽  
Nonlinear Dynamic Response ◽  
Jack Up

Deterministic waves with uniquely specified parameters remains widely used in the analysis of offshore platforms, even though the random nature of the sea-state is one of the main uncertainties in loading. The response of dynamically sensitive and highly redundant structures is significantly changed when random wave loading is considered. Therefore, to more confidently simulate wave loads, all of the randomness of water surface should be taken into account. Load history also plays an important role in the nonlinear dynamic response of structures. Accordingly, an appropriate way to consider these effects is dynamic analysis of offshore platforms using random time-domain generation of the sea surface over a long period of time. However, in general, this method is very complex and time consuming. Constrained NewWave theory is an alternative method that can effectively simulate many hours of random time domain simulation for wave loading but in a more computationally efficient manner. It takes a NewWave — a deterministic wave of predetermined height that accounts for the spectral composition of the sea — and constrains it within a random background. In this paper, both the singular NewWave and multiple constrained NewWaves are employed to simulate random sea-states in order to investigate the nonlinear dynamic response and collapse mechanisms of a jack-up platform subjected to extreme waves. Different assumptions of the behavior of the jack-up spudcan-soil interaction are considered.

Nonlinear Dynamic Response of a Compliant Tower Under the Effect of Steady and Unsteady Sea States

2017 ◽  
Author(s):  
Konstantinos Chatziioannou ◽  
Vanessa Katsardi ◽  
Apostolos Koukouselis ◽  
Euripidis Mistakidis
Keyword(s):  
Structural Analysis ◽  
Dynamic Response ◽  
Deep Water ◽  
Nonlinear Dynamic ◽  
Wave Theory ◽  
Random Wave ◽  
Wave Loading ◽  
Nonlinear Dynamic Response ◽  
Steady Wave ◽  
Compliant Tower

The purpose of this work is to highlight the importance of considering the actual nonlinear dynamic response for the analysis and design of fixed deep water platforms. The paper highlights the necessity of applying dynamic analysis through the comparison with the results obtained by the authors by applying static nonlinear analysis on the structure under examination. The example treated in the context of the present paper is a compliant tower, set-up in deep water. Nonlinearities are considered both for the calculation of the wave loadings and the structural analysis. The wave loading is based on linear random wave theory and comparisons are provided with the steady wave theories, Airy and Stokes 5th. The former solution is based on the most probable shape of a large linear wave on a given sea-state; the auto-correlation function of the underlying spectrum. On the other hand, in the field of structural analysis, two cases are considered for comparison, static analysis and time history dynamic analysis. For both types of analysis, two sub-cases are considered, a case in which geometric nonlinearity and nonlinearities related to the modelling of the soil are considered and a case in which the corresponding linear theories are employed (reference cases). The structural calculations were performed using the well-known structural analysis software SAP2000, which was enhanced by a special programming interface that was developed to calculate the wave loading and to directly apply the generated loads on the structural members. The results show that the consideration of the particle velocities associated with the linear random wave theory in the wave loading lead to significant differences with respect to the steady wave theories in terms of the displacements and stresses of the structure. Moreover, irrespectively of the adopted wave theory, the nonlinear analyses lead to significant discrepancies with respect to the linear ones. This is mainly associated with the nonlinear properties of the soil. Another source of discrepancies between the results of static and dynamic analyses stems from the change of the effective natural frequency of the structure when nonlinearities are considered.

Nonlinear Dynamic Behavior of Fixed Jacket-Type Offshore Platforms Subjected to Simultaneously Acting Wave and Earthquake Loads

2004 ◽  
Author(s):  
A. K. Etemad ◽  
A. R. M. Gharabaghi ◽  
M. R. Chenaghlou
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Dynamic Response ◽  
Dynamic Behavior ◽  
Persian Gulf ◽  
Nonlinear Dynamic ◽  
Longitudinal Component ◽  
Offshore Platforms ◽  
Nonlinear Dynamic Response ◽  
Earthquake Loads

The nonlinear dynamic response of jacket-type offshore platform (which has been installed in Persian Gulf) under simultaneously wave and earthquake loads is conducted. The interaction between soil and piles is modeled by Konagai-Nogami model. The structure is modeled by finite element method. The analyses include models with the longitudinal component of earthquake and wave in the same direction and in different directions. The results indicate that when the longitudinal component of earthquake and wave are in the same direction, wave may reduce the response of studied platform and when they are in different directions, in some cases there is an increase in the response of platform.

Nonlinear Dynamic Response and Buckling of Damaged Composite Pipes Under Radial Impact

2006 ◽  
Author(s):  
Wenyong Tang ◽  
Tianlin Wang ◽  
Shengkun Zhang
Keyword(s):  
Dynamic Response ◽  
Shear Deformation ◽  
Nonlinear Dynamic ◽  
Shear Deformation Theory ◽  
Nonlinear Dynamic Response ◽  
Nonlinear Dynamic Equations ◽  
Geometric Deformation ◽  
Initial Geometric Imperfections ◽  
Set Up ◽  
Composite Pipes

In this paper, the nonlinear dynamic response and buckling of damaged composite pipes under radial impact is investigated. A model involving initial geometric deformation, delamination and sub-layer matrix damage is set up for theoretical analysis. Based on the first order shear deformation theory, the nonlinear dynamic equations of the composite pipe considering transverse shear deformation and initial geometric imperfections are obtained by Hamilton’s theory and solved by a semi-analytical finite difference method. The effects of damage on the dynamic response and buckling of composite pipes are discussed.

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