Prescreening of Ocean Environment for Predicting Extreme Tension Loads on Offshore Structures

2015 ◽  
Author(s):  
DH Lim ◽  
◽  
Y Kim ◽  
T Kim ◽  
◽  
...  
Keyword(s):  
Offshore Structures ◽  
Ocean Environment

Analysis and Design of Offshore Pile Foundation

2014 ◽  
Vol 891-892 ◽  
pp. 17-23 ◽  
Author(s):  
Sudip Basack
Keyword(s):  
Pile Foundation ◽  
Complex Loading ◽  
Offshore Structures ◽  
Laboratory Model ◽  
Element Analysis ◽  
Analysis And Design ◽  
Theoretical Investigations ◽  
Experimental Laboratory ◽  
Combined Action ◽  
Ocean Environment

The ocean environment necessitates the pile foundation supporting the offshore structures to be designed against cyclic load, moments and torques initiated by a combined action of waves, wind, tides, currents, etc. Such a complex loading condition induces progressive degradation in the pile-soil interactive performance introducing significant reduction in bearing capacity with increased settlement and displacements. The Author has carried out extensive experimental (laboratory model tests) and theoretical investigations (boundary element analysis) to study the salient features of this degradation and developed a design methodology for offshore pile foundation. The works conducted and the major conclusions drawn are highlighted in this paper.

Probabilistic Modelling of Extreme Offshore Structural Response due to Random Wave Loading

2013 ◽  
Author(s):  
Y. Wang ◽  
H. Mallahzadeh ◽  
M. K. Abu Husain ◽  
N. I. Mohd Zaki ◽  
G. Najafian
Keyword(s):  
Extreme Values ◽  
Structural Response ◽  
Offshore Structures ◽  
Random Wave ◽  
Wave Loading ◽  
Empirical Distributions ◽  
Generalized Pareto ◽  
Economical Design ◽  
Ocean Environment ◽  
Extreme Responses

Offshore structures are exposed to random wave loading in the ocean environment and hence the probability distribution of the extreme values of their response to wave loading is required for their safe and economical design. This paper investigates the suitability of the Gumbel, the Generalized Extreme Value (GEV), and the Generalized Pareto (GP) distributions for modelling of extreme responses by comparing them with empirical distributions derived from extensive Monte Carlo time simulations. It will be shown that none of these distributions can model the extreme values adequately but that a mixed distribution consisting of both GEV and GP distributions seems to be capable of modelling the extreme responses with very good accuracy.

An Efficient Monte Carlo Simulation Technique for Derivation of the Probability Distribution of the Extreme Values of Offshore Structural Response

2010 ◽  
Author(s):  
M. K. Abu Husain ◽  
G. Najafian
Keyword(s):  
Probability Distribution ◽  
Extreme Values ◽  
Structural Response ◽  
Offshore Structures ◽  
Simulation Technique ◽  
Random Wave ◽  
Wave Loading ◽  
Sampling Variability ◽  
Monte Carlo Simulation Technique ◽  
Ocean Environment

Offshore structures are exposed to random wave loading in the ocean environment and hence the probability distribution of the extreme values of their response to wave loading is required for their safe and economical design. To this end, the conventional simulation technique (CTS) is frequently used for predicting the probability distribution of the extreme values of response. However, this technique suffers from excessive sampling variability and hence a large number of simulated response extreme values (hundreds of simulated response records) are required to reduce the sampling variability to acceptable levels. In this paper, a more efficient version of the time simulation technique (ETS) is introduced to derive the probability distribution of response extreme values from a much smaller sample of simulated extreme values.

Offshore Hydrodynamics

1993 ◽  
Vol 115 (1) ◽  
pp. 2-5 ◽  
Author(s):  
T. Sarpkaya
Keyword(s):  
Dynamic Response ◽  
Materials Science ◽  
Offshore Structures ◽  
Research Issues ◽  
Offshore Engineering ◽  
Air Water Interface ◽  
Research Problems ◽  
Fundamental Research ◽  
Ocean Environment

In this paper, we present several applied as well as fundamental research problems related to the future needs of the offshore engineering. The paper starts out with a detailed discussion of the current uncertainties and constraints. Then, specific research issues on environmental input conditions, on the role of computational fluid dynamics, and on damping and dynamic response are presented. It is suggested that an appreciation of the input parameters, acquisition of extensive data to properly characterize the ocean environment, development of new methods and tools to acquire relevant data, extensive use of the computational methods, basic/applied research on the dynamic response and damping of structures, use of new materials, science-and-technology transfer from sister disciplines (e.g., aerospace industry, keeping in mind the complexities brought about by the presence of the air-water interface), and other related research will significantly enhance our ability to design and build a variety of safer and economical offshore structures in deeper waters as well as over marginal fields in the next few decades. This herculean effort will require several decades of complementary experimental, numerical and analytical studies of ocean-structure interaction which will serve to elucidate the basic as well as applied fluid mechanics phenomena relevant to the offshore mechanics.

On Irregular, Nonlinear Waves in a Spread Sea

1997 ◽  
Vol 119 (1) ◽  
pp. 37-41 ◽  
Author(s):  
P. Jonathan ◽  
P. H. Taylor
Keyword(s):  
Nonlinear Waves ◽  
Three Dimensional ◽  
Nonlinear Effects ◽  
Detailed Comparison ◽  
Offshore Structures ◽  
Sea Surface ◽  
Linear Wave ◽  
Ocean Environment ◽  
Wave Nonlinearity ◽  
Good Agreement

Optimal design and reassessment of offshore structures requires a good understanding of the ocean environment. The motion of the sea surface can be viewed as a three-dimensional, nonlinear stochastic process in time. In order to characterize the wave environment adequately, we need to model its random, nonlinear, and spread nature. In this paper, we address: • the expected shape of a wave near a crest or trough, • the expected shape of the ocean surface at one point, given a crest at a different point, • an efficient method to incorporate nonlinear effects within linear wave simulations, • the magnitude of wave nonlinearity as a function of wave amplitude. Detailed comparison of theory and full-scale offshore measurements at the Shell Expro Tern platform show good agreement.

Jack-Up Site Assessment: The Voyage to an ISO

2011 ◽  
Author(s):  
Mike J. R. Hoyle ◽  
John J. Stiff ◽  
Rupert J. Hunt
Keyword(s):  
Offshore Structures ◽  
Site Assessment ◽  
Detailed Review ◽  
Technical Developments ◽  
Ocean Environment ◽  
The Many ◽  
Analytical Tools ◽  
Jack Up ◽  
Safe Working

As a mobile offshore unit, a jack-up can float, self-elevate and then impose proofing loads on the seabed to establish a safe working envelope for subsequent drilling or construction activities. Jack-up site assessment has seen significant advances over the 50 or more years that jack-ups have been deployed offshore. The advances have occurred as a result of both the improvements that have been seen in the analytical tools and also as a result of the many significant strides in our understanding of the physics of the jack-up and the ocean environment. Jack-ups, due to their semi-compliant nature, pose particularly difficult challenges to the designer and operator — more so than most offshore structures. This requires cutting edge technologies to assure that practical solutions can be reached without either too much conservatism or too little safety. These advances have often occurred, or been encouraged, as a result of the engagement of the operators hiring the jack-ups and their technical overseers such as Jan Vugts. Jan was instrumental in initiating the Shell study into jack-up site assessment that resulted in a follow-up JIP which developed the SNAME Recommend Practice. Since then ISO 19905-1 has been under development and Jan has provided both encouragement and also very detailed review comments. This paper charts the voyage from the early days of jack-up site assessment through to the development of the ISO and highlights some of the key technical developments.

scholarly journals Derivation of the Probability Distribution of Extreme Values of Offshore Structural Response by Efficient Time Simulation Method

2013 ◽  
Vol 7 (1) ◽  
pp. 261-272 ◽  
Author(s):  
M.K. Abu Husain ◽  
N.I. Mohd Zaki ◽  
G. Najafian
Keyword(s):  
Probability Distribution ◽  
Extreme Values ◽  
Structural Response ◽  
Simulation Method ◽  
Offshore Structures ◽  
Random Wave ◽  
Wave Loading ◽  
Sampling Variability ◽  
Economical Design ◽  
Ocean Environment

Offshore structures are exposed to random wave loading in the ocean environment and hence the probability distribution of the extreme values of their response to wave loading is required for their safe and economical design. To this end, the conventional simulation technique (CTS) is frequently used for predicting the probability distribution of the extreme values of response. However, this technique suffers from excessive sampling variability and hence a large num-ber of simulated response extreme values (hundreds of simulated response records) are required to reduce the sampling variability to acceptable levels. A more efficient method (ETS) was recently introduced which takes advantage of the cor-relation between the extreme values of surface elevation and their corresponding response extreme values. The method has proved to be very efficient for high-intensity sea states; however, the correlation and hence the efficiency and accura-cy of the technique reduces for sea states of lower intensity. In this paper, a more efficient version of the ETS technique is introduced which takes advantage of the correlation between the extreme values of the nonlinear response and their corre-sponding linear response values.

Efficient Derivation of the Probability Distribution of Extreme Responses due to Random Wave Loading From the Probability Distribution of Extreme Surface Elevations

2013 ◽  
Author(s):  
H. Mallahzadeh ◽  
Y. Wang ◽  
M. K. Abu Husain ◽  
N. I. Mohd Zaki ◽  
G. Najafian
Keyword(s):  
Probability Distribution ◽  
Extreme Values ◽  
Offshore Structures ◽  
Random Wave ◽  
Wave Loading ◽  
Sampling Variability ◽  
Extreme Surface ◽  
Ocean Environment ◽  
Non Gaussian ◽  
Extreme Responses

Offshore structures are exposed to random wave loading in the ocean environment and hence the probability distribution of the extreme values of their response to wave loading is required for their safe and economical design. Due to nonlinearity of the drag component of Morison’s wave loading and also due to intermittency of wave loading on members in the splash zone, the response is often non-Gaussian; therefore, simple techniques for derivation of the probability distribution of extreme responses are not available. To this end, the conventional Monte Carlo time simulation technique is frequently used for predicting the probability distribution of the extreme responses. However, this technique suffers from excessive sampling variability and hence a large number of simulated response records are required to reduce the sampling variability to acceptable levels. This paper takes advantage of the correlation between extreme responses and their corresponding extreme surface elevations to derive the probability distribution of the extreme responses accurately and efficiently, i.e. without the need for extensive simulations.

Lateral Pressure Effects on the Ultimate Strength of Plates

2015 ◽  
Author(s):  
Lei Jiang ◽  
Shengming Zhang
Keyword(s):  
Ultimate Strength ◽  
Lateral Pressure ◽  
Numerical Study ◽  
Offshore Structures ◽  
Pressure Effects ◽  
Finite Element Program ◽  
Stiffened Panels ◽  
Element Program ◽  
Ocean Environment ◽  
Ultimate Load Carrying Capacity

During the operations of ships and offshore structures in the ocean environment, these structures are subjected to combined lateral pressure and in-plane stresses. However, in today’s ship design and analysis procedures, the effects of the lateral pressure on the ultimate strength of these structures are often ignored. Previous studies have indicated that the lateral pressure could have a noticeable influence on the ultimate load carrying capacity of stiffened panels when they are subjected to combined longitudinal and transverse stresses. The purpose of this paper is to present a systematic numerical study to quantify the lateral pressure effects on the ultimate strength of plates. The sensitivity of the plate’s ultimate strength to lateral pressure is characterized as a function of the plate geometry, the pressure magnitude and the ratio of the in-plane stress components. The present numerical study is performed by using LR’s in-house nonlinear finite element program VAST and the newly development LR procedure for nonlinear structural mechanics analysis was followed. The results and findings from this study are detailed in this paper.

Efficient Derivation of the Probability Distribution of the Extreme Values of Offshore Structural Response Taking Advantage of Its Correlation With Extreme Values of Linear Response

2011 ◽  
Author(s):  
M. K. Abu Husain ◽  
G. Najafian
Keyword(s):  
Probability Distribution ◽  
Linear Response ◽  
Extreme Values ◽  
Structural Response ◽  
Offshore Structures ◽  
Random Wave ◽  
Wave Loading ◽  
Sampling Variability ◽  
Economical Design ◽  
Ocean Environment

Offshore structures are exposed to random wave loading in the ocean environment and hence the probability distribution of the extreme values of their response to wave loading is required for their safe and economical design. To this end, the conventional simulation technique (CTS) is frequently used for predicting the probability distribution of the extreme values of response. However, this technique suffers from excessive sampling variability and hence a large number of simulated response extreme values (hundreds of simulated response records) are required to reduce the sampling variability to acceptable levels. A more efficient method (ETS) was recently introduced which takes advantage of the correlation between the extreme values of surface elevation and their corresponding response extreme values. The method has proved to be very efficient for high-intensity sea states; however, the correlation and hence the efficiency and accuracy of the technique reduces for sea states of lower intensity. In this paper, a more efficient version of the ETS technique is introduced which takes advantage of the correlation between the extreme values of the nonlinear response and their corresponding linear response values.

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