Offshore Compliant Platforms

Analysis, Design, and Experimental Studies

Srinivasan Chandrasekaran, R. Nagavinothini

• Publisher: Wiley-ASME Press Series
• Year: 2020
• Print ISBN: 9781119669777
• eBook ISBN: 9781119669807
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

A guide to the analysis and design of compliant offshore structures that highlights a new generation of platforms

Offshore Compliant Platforms provides an authoritative guideto the analysis and design of compliant offshore structures and puts the focus on a new generation of platforms such as: triceratops, Buoyant Leg Storage and Regasification platforms. Whilst the authors – noted experts on the topic – include basic information on the conceptual development of conventional platforms, the book presents detailed descriptions of the design and development of new deep-water platforms.

The book describes the preliminary design of triceratops in ultra-deep waters and presents a detailed analysis of environmental loads that are inherent in offshore locations such as wave, wind and current. The new methodology for the dynamic analysis of triceratops under ice loads, predominantly in ice-covered regions, is also examined with detailed parametric studies. In addition, the book covers the structural geometry and the various methods of analysis for assessing the performance of any other similar offshore platform under the special loads. A discussion of the fatigue analysis and service life prediction is also included. This important book:

• Includes the analysis and design of compliant offshore structures with a focus on a new generation of platforms

• Examines the preliminary design of triceratops in ultra-deep waters

• Covers an analysis of environmental loads that are inherent in offshore locations such as wave, wind and current

• Reviews the structural geometry and various methods of analysis for assessing the performance of any other similar offshore platform under special loads

• Discusses fatigue analysis and service life prediction

Written for engineers and researchers across engineering including civil, mechanical, structural, offshore, ocean and naval architecture, Offshore Compliant Platforms fills the need for a guide to new offshore platforms that provides an understanding of the behaviour of these structures under different loading conditions.

1
Common Compliant Platforms

Summary

This chapter presents details of the structural geometry of compliant offshore platforms while emphasizing the design and development of these platforms rather than of fixed platforms. Details of investigations carried out on the response control of a tension leg platform (TLP) and an articulated tower are presented. This chapter also presents various control strategies that are commonly deployed for response control of structures subjected to lateral loads while presenting detailed applications of tuned mass dampers (TMDs) in offshore structures. Experimental investigations and numerical analyses, reported by R. Ranjani (2015, “Response Control of Tension Leg Platform Using Tuned Mass Damper,” PhD thesis, IIT Madras, India) and Prof. Deepak Kumar (Dept. of Ocean Engineering, IIT Madras, India) are sincerely acknowledged by the authors.

1.1 Introduction

While it is a common understanding that structural forms are conceived to counteract the applied loads acting on them, it may not be completely true in the context of offshore structures. This is due to the basic fact that offshore structures are designed to alleviate the encountered environmental loads based on their geometric form and not by the strength of the materials and structural properties based on the cross‐section of the members. On the other hand, offshore structures are essentially form‐dominant. Therefore, rigid‐supported structural systems, which are conventionally good to transfer the applied loads to the foundations, are not attractive candidates for offshore structures. A few factors that influence the choice of the geometric form of offshore structures are a structural form with a stable configuration, and a geometric form with low installation, fabrication, and decommissioning costs; that leads to lower capital expenditures (CAPEX) and a higher return on investment (ROI). The result is an earlier start for production and greater mobility, and a platform that requires the least intervention so that uninterrupted production can take place.

Offshore structures are grouped as fixed, compliant, and floating types, based on the boundary conditions of their station‐keeping characteristics. Fixed platforms are further categorized as jacket platforms, gravity platforms, and jack‐up rigs. Compliant platforms are further categorized as guyed towers, articulated towers, and tension leg platform (TLPs). Floating platforms are further categorized as semi‐submersibles, floating production units (FPUs), floating storage and offloading (FSO), floating production storage and offloading (FPSO), and spar. While fixed platforms are designed to remain insensitive to lateral loads that arise from waves, wind, currents, and earthquakes, these platforms are expected to resist the encountered loads using both their material strength and structural redundancy. A strength‐based design approach is more popular for use when designing such platforms, as they exhibit very low displacement under lateral loads. These structural forms are also stable due to their massive weight, which is an advantageous design factor. However, with regard to the other factors that influence the choice of the structural forms of offshore structures, as explained earlier, fixed platforms are least preferred for deepwater construction. Table 1.1 shows a list of fixed platforms constructed worldwide (Srinivasan Chandrasekaran 2017).

It is interesting to note that offshore engineers gradually realized that restricting the motion of the platform by making it fixed to the seabed was not necessary. Instead, conceptual developments were focused on flexible structural forms and gave birth to compliant structures....

Table of contents

• Cover
• Table of Contents
• List of Figures
• List of Tables
• Foreword by Professor Purnendu K. Das
• Foreword by Dr. Atmanand N.D.
• Series Preface
• Preface
• 1 Common Compliant Platforms
• 2 Buoyant Leg Storage and Regasification Platforms
• 3 New‐Generation Platforms: Offshore Triceratops
• 4 Triceratops Under Special Loads
• 5 Offshore Triceratops: Recent Advanced Applications
• Model Exam Paper 1
• References
• Index
• End User License Agreement