A review on environmental load identification and structural health monitoring of offshore structures

Committee Mandate Concern for the structural longevity of ship, offshore and other marine structures. This shall include diagnosis and prognosis of structural health, prevention of structural failures such as corrosion and fatigue, and structural rehabilitation. The focus shall be on methodologies translating monitoring data into operational and life-cycle management advice. The research and development in passive, latent and active systems including their sensors and actuators shall be addressed. Introduction 1.1 Background & Mandate The ISSC Committee V.7 on structural longevity of ship, offshore and other marine structures have been looking into all aspects related to the diagnosis and prognosis of structural health, prevention of structural failures such as corrosion and fatigue, while also considering the work performed on lifecycle management and maintenance aspects over the last 4 years. The latter refer to also incorporating approaches and techniques associated to the development of software and hardware tools for the inspection and monitoring of ship and offshore structures. In this Committee’s report, particular emphasis has been placed on the elaboration of the available studies and most recent developments with regards to inspection and monitoring and offshore structures longevity methods and applications, expanding on the previous Committee work (ISSC, 2018). Moreover, when delivering the mandate of this work, the authors have acknowledged that potential overlaps may occur with regards to Committee III.1 Ultimate Strength, Committee III.2 Fatigue and Fracture, Committee IV.2 Design methods and Committee V.4 Offshore Renewable Energy. In this respect, all efforts have been made in order to minimize the overlap of work while if any of such similarities exist, this is done in the spirit of complementarity supporting the structural longevity of ship, offshore and any other marine structures as presented in this Committee’s mandate. 1.2 Report content The present report consists of six chapters. Each chapter provides thorough critical examination of the available literature while useful conclusions and recommendations for future direction are provided at the end of the Committee report. In this respect, following an introductory chapter that provides an overview on the Committee’s mandate and brief summary of the report content, Chapter 2 investigates the lifecycle assessment and management for structural longevity approaches and tools, considering the particular areas of lifecycle assessment and maintenance management. Data-driven maintenance and relevant approaches such as digital twin applications, iFEM, and reliability-based research efforts are covered as well. In Chapter 3, the trends and developments in inspection and monitoring techniques to improve the structural longevity of ship and offshore structures are highlighted. These concepts are complemented by the examination of hull monitoring systems, remote and autonomous testing and sensors applications for structural monitoring; the employment of artificial intelligence (AI) applications and cloud-based data acquisition and management systems. Chapter 4 specifically considers the models and applications developed in relation to offshore structures updating the work performed in the previous ISSC committee report. The review looks into the aspects of deterioration mechanisms (corrosion, crack growth, erosion and wear), mechanical limit states, implementation of methods and procedures for safe operation and aspects of risk-based integrity management of offshore structures. Furthermore, Chapter 5 explores the available literature with regards to the ships and offshore structural longevity methods and examples. In particular covering the aspects of prediction of longevity, failure modes contributing to longevity assessment and also presenting a more detailed case of a polar supply and research vessel. Finally, Chapter 6 summarises the concluding remarks of the structural longevity report and offers a number of recommendations and directions for future research and applications related to ship, offshore and other marine structures.

In order to investigate the interaction between offshore structure and base ground subjected to seismic and ice loads, a substructure on-line dynamic testing system was developed. A dynamic response analysis by computer and a pseudo-dynamic loading test which obtains the restoring force of material experimentally are combined by a computer on-line data processing system. The analyses were carried out on an offshore gravity structure based on sand seabed subjected to ice load and earthquake motion by this method. Residual deformation of base ground were observed because of development of pore water pressure in the sand layer due to cyclic loads induced by drifting floe and earthquake. As a result, unique response behaviour of base ground and structure was observed in the present study. Introduction On April 12, 1986, the Molikpaq deployed in the Canadian Beaufort Sea suffered dynamic force induced by drifting floe1), 2). Although ice loading was considered as a quasi-static situation, much of the ice loading of the Molikpaq at significant load levels had been associated with cyclic, dynamic loading. Development of pore pressure was measured by piezometer installed in the sandfill core in it. This led to a research effort on the stability of base ground underneath the offshore structures in ice-sea. The similar platforms are constructed in Okhotsk near Sakhalin. In this area, not only ice load but also seimic force should be considered in practical design. For the purpose of investigating the interaction between offshore structure and base ground subjected to ice load and seismic forces, a substructure on-line dynamic testing system was developed in this study by combining the response analysis with the simple shear tests on real soil elements. In the present method, a computer analysis of dynamic response and a pseudo-dynamic loading test were combined with a computer on-line data processing system3). With this system, which was devised to analyze the overall response behaviour, the simple shear tests were adopted only for a few layers beneath the structure demonstrating complicated properties of restoring forces, while numerical models ware applied to the remaining layers of ground and super-structure. The analyses were carried out on an offshore gravity structure in ice sea based on sand seabed by this method. The ice load which was calculated by KARNA-NKK model4) was applied in order to simulate the given penetration speed of drifting floe against structure. At the same time, earthquake motion was input from the bottom of base ground. Degradation and residual shear deformation of base ground were observed because of developing pore water pressure in the sand layer due to cyclic loads induced by drifting floe and earthquake. Stress Condition in Soil Element beneath Offshore Structure The stress condition and behaviour of soil elements beneath the offshore structure which are expected during earthquake are shown in Fig. 1 and Table 1. The overburden stress Ðv' and earth pressure at rest Ðh' exist on the planes perpendicular to them before earthquake. When the earthquake happens, cyclic shear stresses exert on the both planes.

Damage detection of offshore jacket structures using structural vibration measurements: Application of a new hybrid machine learning method

This paper deals with state of the art in structural health monitoring (SHM) methods in offshore and marine structures. Most SHM methods have been developed for onshore infrastructures. Few studies are available to implement SHM technologies in offshore and marine structures. This paper aims to fill this gap and highlight the challenges in implementing SHM methods in offshore and marine structures. The present work categorises the available techniques for establishing SHM models in oil rigs, offshore wind turbine structures, subsea systems, vessels, pipelines and so on. Additionally, the capabilities of proposed ideas in recent publications are classified into three main categories: model-based methods, vibration-based methods and digital twin methods. Recently developed novel signal processing and machine learning algorithms are reviewed and their abilities are discussed. Developed methods in vision-based and population-based approaches are also presented and discussed. The aim of this paper is to provide guidelines for selecting and establishing SHM in offshore and marine structures.

Emerging Trends in Numerical Predictive Technologies in Offshore and Marine Engineering

The ISO 19900 series of international standards comprises different levels of standards, ISO 19900 giving General Requirements for offshore structures, ISO 19901 giving Specific Requirements for various aspects of offshore structures that have relevance to different types of offshore structure (in several parts), and then a series of standards giving requirements for the different generic types of offshore structure. Of this last category, three have now been published; ISO 19902 for Fixed Steel Offshore Structures, ISO 19903 for Fixed Concrete Offshore Structures, and ISO 19904-1 for Floating Offshore Structures. The development of these three International Standards is described in this paper, which gives details of the scope, provenance, key features, contents, and organization of each of the three standards. ISO 19902 is a development of API RP2A LRFD, but in the preparation of the International Standard a number of research and Development Joint Industry Projects (JIPs) were commissioned, and the enhanced knowledge from these projects, together with knowledge and experience from the offshore operating areas around the world, have been incorporated. ISO 19903 is a new and somewhat different standard, as it deals with the entire task of engineering a concrete offshore platform facility, with mechanical systems, etc., rather than just the detailed design of its concrete members. To a large extent the standard relies on the existence of national or regional standards for design of concrete structures that can be safely used in an offshore concrete structure, as such structures can range from quite simple to really sophisticated structures. ISO 19904-1 is a new standard entirely. It is based partly on API RP 2FPS, which was developed in the same timeframe, but includes concepts taken and harmonized from North Sea practice represented by then HSE and NPD guidelines and from class rules. Some text was written specifically for this standard, particularly the clause on structural integrity monitoring and various sub clauses elsewhere that represent lessons learned in from industry experience during the period in which the standard was written.

Structural health monitoring (SHM) is a critical technology for ensuring infrastructure safety, extending their service life, and reducing their maintenance costs. With the rapid development of digital twin (DT) technology, an increasing number of studies have implemented DT in SHM systems. This study provides a detailed analysis of the role of DT in SHM through a comprehensive literature review, specifically examining its applications in damage detection, dynamic response monitoring, and maintenance management. The paper first reviews advances in DT applications across various fields, then systematically discusses how DT enhances monitoring accuracy, enables real-time performance, and supports predictive maintenance strategies in SHM. Finally, technical challenges and future research directions for DT implementation in SHM are explored. The findings highlight DT’s significant potential to improve both the efficiency and the accuracy of structural monitoring systems, while proposing innovative solutions for intelligent infrastructure management.

Structural health monitoring (SHM) has been recognized as a useful tool for safety management and risk reduction of offshore wind farms. In complex offshore environment, jacket structures of offshore wind turbines are prone to damages due to corrosion and fatigue. Effective SHM on jacket structures can substantially reduce their operation risk and costs. This work reviews the latest progress on the SHM of offshore wind jacket structures. The achievements in the structural damage identification, location, quantification, and remaining useful life (RUL) estimation are respectively introduced in detail, and existing challenges are discussed. Possible solutions to the challenges using the Digital Twin (DT) technology are put forward. The DT is able to mirror a real jacket structure into a virtual model, and Bayesian updating can refresh the virtual model parameters in real-time to keep consistency between virtual model and physical structure; then, just-in-time SHM can be carried out for jacket structures by performing damage detection, location, quantification, and RUL estimation using the virtual model. As a result, the DT may provide engineers and researchers a practicable tool for safety monitoring and risk reduction of fixed foundation offshore wind structures.

This is one of the most definitive references available on marine construction. This comprehensive book covers all major aspects of the construction process for a variety of waterborne structures, including marine, offshore, coastal, riverine, and arctic engineering structures. The late Professor Gerwick has substantially revised the previous edition of his Construction of Marine and Offshore Structures book by extensively augmenting this third edition to include recent developments in these rapidly expanding engineering fields. With the added chapters and improvements, the third edition becomes a necessary reference book for all marine and civil engineers and corporations involved in planning, building, and maintaining structures in water environments. This book is an authoritative guide because it addresses many aspects of the current state of practice in easily understandable style, presenting the most comprehensive treatment of the construction process for marine and offshore structures. The author starts with design factors and planning considerations and describes many issues affecting the building of different types of structures in a marine environment. In addition, the book includes chapters on construction and maintenance of coastal and inland waterway structures and pays special attention to recent advances for ice-resistant structures, dams and locks, and bridge foundations. A number of the latest developments in materials and techniques are also described in this new edition that should be of great interest to engineers in the oil and service industries, as well as marine construction planners, designers, and contractors. To retain the volume’s standing as a complete authoritative resource, the author has incorporated into this edition many changes related to techniques, tools, and materials that have found their way into marine and offshore engineering practice. Topics with expanded coverage include construction equipment, marine operations, steel and concrete offshore platforms, cables and flexible or rigid pipelines and risers, tubes tunnels , walls, piles, rubble-mound breakwaters, precast armor units in coasts, repairs and strengthening existing structures, and removal and salvage. The author also provides new information on novel technologies, methods, materials, liquefaction of loose sediments, scour and erosion, ultra-high-performance concrete, H-piles and high-performance steel, cracking and corrosion, and construction in remote areas. He presents an interesting insight to archaeological concerns and damage from sabotage and terrorism, since these are important elements of the construction process. For marine construction planners, designers, contractors, ocean, coastal, and marine engineers involved in constructing waterborne structures, this book describes effec-

It is important to ensure the safe and reliable use of massive engineering structures such as offshore platforms, including all aspects of safety and design code compliance. Although routine inspection is an integral part of the safety protocol in operating and maintaining these structures, regular assessment of the effectiveness and efficiency of existing safety evaluation methods is clearly desired in view of emerging technologies for structural health monitoring of engineering structures. The recent advancement in plastic optical fibre (POF) materials and processing render POF sensors an attractive alternative to glass-based optical fibre sensors as they offer much greater being flexibility, high resistance to fracture and hence the ease in their handling and installation. In this paper, some preliminary results demonstrating the use of plastic optical fibre sensors for damage detection and structural health monitoring for offshore and marine-related applications will be summarized. In this study, POF will be used for crack detection in tubular steel specimens in conjunction with a high-resolution photon-counting optical time-domain reflectrometry (v-OTDR). Although the use of OTDR technique is an established method in the telecommunication industry, this study is new in that it is now possible, with the availability of v-OTDR and graded-index perfluorinated POF, to detect and locate the crack position in the host structure to within 10 cm accuracy or better. It will also be shown that this technique could readily be configured to monitor crack growth in steel tubular members.

Reconstruction of Unmeasured Strain Responses in Bottom-fixed Offshore Structures by Multimetric Sensor Data Fusion

The development of offshore renewable energy structures is growing at a fast pace, and their maintenance will become critical in further years. Because steel corrosion on offshore structures is one of their highest maintenance cost, researchers are working to replace steel by Fibre Reinforced Polymers (FRP), due to their immunity to corrosion. This is done in the EU H2020 funded project FIBREGY, which also seeks improving maintenance costs by incorporating Structural Health Monitoring (SHM) strategies. A critical issue in SHM is the damage detection process, which is addressed in this paper. This study aims to characterize the dynamic behaviour of an offshore windmill FRP tower, and its evolution due the presence of structural damage. This analysis will be carried out using a Finite Element Model (FEM) of the structure, and the Serial-Parallel mixing theory to characterize the material performance. A sensitivity analysis of the changes in the dynamic response of the tower (frequencies and modal shapes) produced by structural damage is carried out. This analysis will provide the optimum design variables and objective functions required by a damage detection algorithm. The algorithm is optimization based, since it converts the damage detection problem into a mathematical one, and finds the best design variables to minimize the objective function. The algorithm is also model based, as it uses the structural model to obtain the objective function for the proposed design variables. Finally, this work presents the analysis of a potential damage scenario, in order to evaluate if the damage is effectively detected.

There is a large risk of damage, triggered by harsh ocean environments, associated with offshore structures, so structural health monitoring plays an important role in preventing the occurrence of critical and global structural failure from such damage. However, obstacles, such as applicability in the field and increasing calculation costs with increasing structural complexity, remain for real-time structure monitoring offshore. Therefore, this study proposes the comparison of cosine similarity with sensor data to overcome such challenges. As the comparison target, this method uses the rate of changes of natural frequencies before and after the occurrence of various damage scenarios, including not only single but multiple damages, which are organized by the experiment technique design. The comparison method alerts to the occurrence of damage using a normalized warning index, which enables workers to manage the risk of damage. By comparison, moreover, the case most similar with the current status is directly figured out without any additional analysis between monitoring and damage identification, which renders the damage identification process simpler. Plus, the averaged rate of errors in detection is suggested to evaluate the damage level more precisely, if needed. Therefore, this method contributes to the application of real-time structural health monitoring for offshore structures by providing an approach to improve the usability of the proposed technique.

The technology of condition monitoring for wind farm operation has been used for many years, such as Supervisory control and data acquisition (SCADA). However, structural health monitoring (SHM) of the support structure is still at the research stage. In this paper an offshore structure monitoring system for the offshore wind turbine jacket structure is proposed. The major monitoring items include vibration, strain and corrosion. In addition to those corresponding sensors, other instruments are also included in the proposed system to evaluate the structural integrity of the offshore wind turbine jacket structure. A detailed description of the monitoring methods and the framework of system are provided which is expected to be applied to the real support structure in the future.

Structural health monitoring of offshore wind power structures based on genetic algorithm optimization and uncertain analytic hierarchy process