Second-Order Superharmonic Wave Loading on Jack-Up Platforms

2001 ◽  
Vol 127 (6) ◽  
pp. 319-326 ◽  
Author(s):  
C. Y. Liaw ◽  
T. Naik ◽  
C. G. Koh
Keyword(s):  
Second Order ◽  
Wave Loading ◽  
Jack Up

Fundamentals concerning wave loading on offshore structures

1986 ◽  
Vol 173 ◽  
pp. 667-681 ◽  
Author(s):  
James Lighthill
Keyword(s):  
Fluid Mechanics ◽  
Natural Frequency ◽  
Potential Flow ◽  
Vortex Flow ◽  
Offshore Structures ◽  
Second Order ◽  
Mechanics Of Solids ◽  
Wave Loading ◽  
Velocity Fluctuations ◽  
Substantial Body

This article is aimed at relating a certain substantial body of established material concerning wave loading on offshore structures to fundamental principles of mechanics of solids and of fluids and to important results by G. I. Taylor (1928a,b). The object is to make some key parts within a rather specialised field accessible to the general fluid-mechanics reader.The article is concerned primarily to develop the ideas which validate a separation of hydrodynamic loadings into vortex-flow forces and potential-flow forces; and to clarify, as Taylor (1928b) first did, the major role played by components of the potential-flow forces which are of the second order in the amplitude of ambient velocity fluctuations. Recent methods for calculating these forces have proved increasingly important for modes of motion of structures (such as tension-leg platforms) of very low natural frequency.

Extreme Response Predictions for Jack-Up Units in Second Order Stochastic Waves by FORM

2007 ◽  
Author(s):  
Jo̸rgen Juncher Jensen
Keyword(s):  
Second Order ◽  
Sea State ◽  
First Order ◽  
Reliability Method ◽  
Extreme Response ◽  
Stochastic Waves ◽  
Short Time ◽  
Wave Induced ◽  
Jack Up ◽  
Operational Time

The aim of the present paper is to advocate for a very effective stochastic procedure, based on the First Order Reliability Method (FORM), for extreme value predictions related to wave induced loads. All kinds of non-linearities can be included, as the procedure makes use of short time-domain simulations of the response in question. The procedure will be illustrated with a jack-up rig where second order stochastic waves are included in the analysis. The result is the probability of overturning as function of sea state and operational time.

Interaction of a Second-Order Solitary Wave With a Vertical Permeable Plane Breakwater

2004 ◽  
Author(s):  
A. Basmat
Keyword(s):  
Solitary Wave ◽  
Water Waves ◽  
Boussinesq Equations ◽  
Second Order ◽  
Wave Loading ◽  
Coastal Structures ◽  
Transformation Techniques ◽  
Incident Plane ◽  
Impermeable Wall ◽  
Plane Barrier

The purpose of this paper is to develop mathematical models to investigate the interaction between long non-linear water waves and dissipative/absorbing coastal structures. The diffraction of a plane second-order solitary wave at a vertical permeable plane barrier standing in front of an impermeable wall, with calculation of the second-order wave loading is investigated. An incident plane second-order solitary wave is the Laitone solution of Boussinesq equations. The analytical solution is obtained by means of a small parameter development and Fourier transformation techniques. Computational results were performed using the software MATHEMATICA version 4.0.1.0.

Probabilistic Models Applicable to the Short-Term Extreme Response Analysis of Jack-Up Platforms

2003 ◽  
Vol 125 (4) ◽  
pp. 249-263 ◽  
Author(s):  
M. J. Cassidy ◽  
G. T. Houlsby ◽  
R. Eatock Taylor
Keyword(s):  
Probabilistic Models ◽  
Probability Distributions ◽  
Response Analysis ◽  
Wave Loading ◽  
Physical Processes ◽  
Short Term ◽  
Analysis Techniques ◽  
Extreme Response ◽  
Increasing Demand ◽  
Jack Up

There is a steadily increasing demand for the use of jack-up units in deeper water and harsher conditions. Confidence in their use in these environments requires jack-up analysis techniques to reflect accurately the physical processes occurring. However, nearly all analyses are deterministic in nature and do not account for the inherent variability in governing parameters and models. In this paper, probabilistic models are used to develop an understanding of the response behavior of jack-ups, with particular emphasis placed on the extreme deck displacement due to a short-term event. Variables within the structural, foundation and wave loading models are assigned probability distributions and their influence on the response statistics is quantified using a response surface methodology.

The Influence of Alternative Wave Loading and Support Modeling Assumptions on Jack-Up Rig Response Extremes

1996 ◽  
Vol 118 (2) ◽  
pp. 109-114 ◽  
Author(s):  
L. Manuel ◽  
C. A. Cornell
Keyword(s):  
Nonlinear Models ◽  
Random Wave ◽  
Force Model ◽  
Wave Loading ◽  
Force Modeling ◽  
Hydrodynamic Damping ◽  
Extreme Response ◽  
The Absolute ◽  
Non Gaussian ◽  
Jack Up

A study is conducted of the response of a jack-up rig to random wave loading. Steady current and wind load effects are also included. The effects of varying the relative motion assumption (in the Morison equation) and of varying the bottom fixity assumptions are investigated. One “fixity” model employs nonlinear soil springs. Time domain simulations are performed using linearized as well as fully nonlinear models for the jack-up rig. Comparisons of response statistics are made for two seastates. Hydrodynamic damping causes the rms response to be lower in the relative Morison case. The absence of this source of damping in the absolute Morison force model gives rise to larger resonance/dynamic effects—this tends to “Gaussianize” the response. Hence, the relative Morison model leads to stronger non-Gaussian behavior than the absolute Morison model. This is reflected in moments as well as extremes. The different support conditions studied are seen to significantly influence extreme response estimates. In general, stiffer models predict smaller rms response estimates, but also exhibit stronger non-Gaussian behavior. The choice of the Morison force modeling assumption (i.e., the relative versus the absolute motion formulation) is seen to have at least a secondary role in influencing response moments and extremes.

Second Order Loads on LNG Terminals in Multi-Directional Sea in Water of Finite Depth

2007 ◽  
Author(s):  
Fla´via Rezende ◽  
Xin Li ◽  
Xiao-Bo Chen
Keyword(s):  
Near Field ◽  
Low Frequency ◽  
Finite Depth ◽  
Accurate Method ◽  
Second Order ◽  
Wave Loading ◽  
Storage Tanks ◽  
Offshore Area ◽  
Directional Waves ◽  
Poor Convergence

Large LNG terminals are designed to be installed in an offshore area approximate to harbors where the water is of finite depth and waves are multi-directional. The terminal can be of a barge type LNG/FRSU including accommodations, gas preconditioning and liquefied plant, a number of storage tanks and offloading facilities. It serves also as a support to moor a LNG carrier during offloading operations. In the design of such mooring system of LNG/FRSU and LNG carriers in a zone of shallow water, one key issue is the accurate simulation of low-frequency motions of the system to which the second-order wave loading is well known as the main source of excitation. The computation of second-order wave loading in multi-directional waves of finite waterdepth is considered here. New formulations obtained recently in [1] for the computation of second-order loads in mono-directional waves are extended to the case of multi-directional waves. Both the classical near-field formulation and the new middle-field formulation developed in [1] are used and numerical results are compared. Unlike the usual near-field formulation giving results of second-order loads with poor convergence, the middle-field formulation provides an accurate method for the computation of vertical components.

Approximation of Second-Order Low-Frequency Wave Loading in Multi-Directional Waves

2010 ◽  
Author(s):  
Flavia C. Rezende ◽  
Xiao-bo Chen
Keyword(s):  
Low Frequency ◽  
Second Order ◽  
Wave Loads ◽  
Wave Loading ◽  
Frequency Wave ◽  
New Developments ◽  
Directional Waves ◽  
Novel Method ◽  
The Difference ◽  
Accurate Scheme

Further to the studies by Chen & Rezende (OMAE2009) on the quadratic transfer function (QTF) of low-frequency wave loading in which the QTF is developed by the series expansion associated with the difference-frequency up to the order-Δω2, new formulations have been developed in order to take into account the effect of interactions between waves of different headings. It provides a novel method to evaluate the low-frequency second-order wave loads in a more accurate than usual order-Δω approximation (often called Newman approximation) and more efficient way comparing to the computation of complete QTF in multi-directional waves. New developments including numerical results of different components of QTF are presented here. Furthermore, the time-series reconstruction of excitation loads by quadruple sums in the motion simulation of mooring systems is analyzed and a new efficient and accurate scheme using only a triple sum is demonstrated.

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