Structural Health Monitoring of Offshore Buoyant Leg Storage and Regasification Platform: Experimental Investigations
14 Jun 2018-Journal of Marine Science and Application (Harbin Engineering University)-Vol. 17, Iss: 1, pp 87-100
TL;DR: This study concludes that implementation of structural health monitoring (SHM) to offshore platforms ensures safe operability and structural integrity, and proposes a novel scheme of deploying wireless sensor network for this purpose.
Abstract: Offshore platforms are of high strategic importance, whose preventive maintenance is on top priority. Buoyant Leg Storage and Regasification Platforms (BLSRP) are special of its kind as they handle LNG storage and processing, which are highly hazardous. Implementation of structural health monitoring (SHM) to offshore platforms ensures safe operability and structural integrity. Prospective damages on the offshore platforms under rare events can be readily identified by deploying dense array of sensors. A novel scheme of deploying wireless sensor network is experimentally investigated on an offshore BLSRP, including postulated failure modes that arise from tether failure. Response of the scaled model under wave loads is acquired by both wired and wireless sensors to validate the proposed scheme. Proposed wireless sensor network is used to trigger alert monitoring to communicate the unwarranted response of the deck and buoyant legs under the postulated failure modes. SHM triggers the alert mechanisms on exceedance of the measured data with that of the preset threshold values; alert mechanisms used in the present study include email alert and message pop-up to the validated user accounts. Presented study is a prima facie of SHM application to offshore platforms, successfully demonstrated in lab scale.
TL;DR: In this article, the structural health monitoring of a 10MW multibody FOWT whose tower is supported by a platform consisting of two rigid-body tanks connected by 12 tendons is investigated for the first time.
Abstract: The structural health monitoring of a Floating Offshore Wind Turbine (FOWT) tendons, taking into account the comprehensive damage diagnosis problem of damage detection, damaged tendon identification and damage precise quantification under varying environmental and operating conditions (EOCs), is investigated for the first time. The study examines a new concept of a 10 MW multibody FOWT whose tower is supported by a platform consisting of two rigid-body tanks connected by 12 tendons. Normal and the most severe EOCs from a site located in the northern coast of Scotland, are selected for the simulation of the FOWT structure under constant current but varying wind and wave conditions. Dynamic responses of the platform under different damage states are obtained based on the simulated FOWT. The damage scenarios are modelled via stiffness reduction (%) at the tendon's connection point to the platform's upper tank. Damage diagnosis is achieved via an advanced method, the Functional Model Based Method, that is formulated to operate using a single response signal and stochastic Functional Models representing the structural dynamics under the effects of varying EOCs and any magnitude of the considered damages. Due to the robustness and high number of the existing tendons, the effects of considered damages on the FOWT dynamics are minor and overlapped by the effects of the varying EOCs, indicating a highly challenging damage diagnosis problem. Very good damage detection results are obtained with the damage detection almost faultless and with no false alarms. Accurate damaged tendon identification is achieved for the 95% of the considered test cases, while the mean error in damage quantification is approximately equal to 4% using measurements from just a single accelerometer within a very limited frequency bandwidth of [0–5] Hz.
TL;DR: The results show that effective, reliable and very quick damaged tendon diagnosis is achieved via FMBM using the multibody FOWT platform’s dynamics under damaged tendons.
Abstract: The problem of damaged tendon diagnosis (damage detection, damaged tendon identification and damage precise quantification) in a new multibody offshore platform supporting a 10 MW Floating Offshore Wind Turbine (FOWT) is investigated for the first time in this study. Successful operation of the multibody FOWT depends on the integrity of its tendons connecting the upper and lower tanks of the platform. Thus, early diagnosis of the damaged tendons is of high importance and it is achieved through a vibration-based methodology. Damage detection is accomplished based on the detection of changes in the vibration response power spectral density, while damaged tendon identification and damage precise quantification are accomplished through the Functional Model Based Method (FMBM). The FMBM is appropriately formulated in this study to operate with only vibration response signals. The employed vibration responses under healthy and damaged states of the FOWT platform are obtained from a numerical model describing the platform’s dynamics. Each examined damage scenario corresponds to the reduced stiffness at the connection point of a single tendon to the platform’s upper tank. Subtle damages corresponding to a stiffness reduction of [10–25] %, have minor effects on the platform’s dynamics due to the tendons’ high strength, while damages corresponding to a stiffness reduction of [10–85] % on different tendons have similar effects on the dynamics, thus leading to an overall highly challenging diagnosis problem. The use of a single underwater accelerometer as well as a low and limited frequency bandwidth of surge acceleration signals, is explored. The results show that effective, reliable and very quick damaged tendon diagnosis is achieved via FMBM using the multibody FOWT platform’s dynamics under damaged tendons.
TL;DR: In this article , a robust methodology for long-term offshore structural health monitoring (SHM) using the Global Navigation Satellite Systems (GNSS) is presented, which relies on recently developed regional reference frames and single-receiver phase-ambiguity-fixed Precise Point Positioning techniques.
Abstract: This article presents a robust methodology for long-term offshore structural health monitoring (SHM) using the Global Navigation Satellite Systems (GNSS). The methodology relies on recently developed regional reference frames and single-receiver phase-ambiguity-fixed Precise Point Positioning techniques. The stable Gulf of Mexico Reference Frame 2020 (GOM20) provides a robust and consistent reference system for long-term offshore SHM in the Gulf of Mexico (GOM). Continuous GNSS observations (DEV1, 2010–2020) on a fixed platform in the Eugene Island 330 oil field are used to illustrate the methodology. The platform was installed in 1982 in 82-m water about 130 km away from the Mississippi Delta coastline. The major monitoring items include horizontal movements, seafloor subsidence, structure submergence, and seasonal oscillations. The stand-alone GNSS monitoring achieves 3- to 4-mm root-mean-square accuracy in the horizontal direction and 7 mm in the vertical direction for daily positions in the GOM region. According to this study, the GNSS antenna (DEV1) has moved 6 cm toward the northeast with respect to GOM20 since 2010; the ongoing structure submergence rate in the Eugene Island 330 oil field area is approximately 15 mm/year, a combination of seafloor subsidence (12 mm/year) and sea-level rise (2.6 mm/year) with respect to GOM20. The submergence in the future 40 years (2021–2060) would be greater than 0.6 m, likely between 0.8 and 1.0 m, but is unlikely to exceed 1.3 m. The peak-to-trough amplitudes of the seasonal movements at the top of the platform are below 5 mm in all three directions, comparable with the seasonal movements recorded by onshore GNSS in the Louisiana coastal region. The methodology introduced in this article can be applied to SHM in other offshore regions where stable regional reference frames are available.
TL;DR: Technical challenges that must be addressed if SHM is to gain wider application are discussed in a general manner and the historical overview and summarizing the SPR paradigm are provided.
Abstract: This introduction begins with a brief history of SHM technology development. Recent research has begun to recognise that a productive approach to the Structural Health Monitoring (SHM) problem is to regard it as one of statistical pattern recognition (SPR); a paradigm addressing the problem in such a way is described in detail herein as it forms the basis for the organisation of this book. In the process of providing the historical overview and summarising the SPR paradigm, the subsequent chapters in this book are cited in an effort to show how they fit into this overview of SHM. In the conclusions are stated a number of technical challenges that the authors believe must be addressed if SHM is to gain wider acceptance.
TL;DR: The motivations for and recent history of SHM applications to various forms of civil infrastructure are described, the present state-of-the-art and future developments in terms of instrumentation, data acquisition, communication systems and data mining and presentation procedures for diagnosis of infrastructural ‘health’ are discussed.
Abstract: Structural health monitoring (SHM) is a term increasingly used in the last decade to describe a range of systems implemented on full-scale civil infrastructures and whose purposes are to assist and inform operators about continued 'fitness for purpose' of structures under gradual or sudden changes to their state, to learn about either or both of the load and response mechanisms. Arguably, various forms of SHM have been employed in civil infrastructure for at least half a century, but it is only in the last decade or two that computer-based systems are being designed for the purpose of assisting owners/operators of ageing infrastructure with timely information for their continued safe and economic operation. This paper describes the motivations for and recent history of SHM applications to various forms of civil infrastructure and provides case studies on specific types of structure. It ends with a discussion of the present state-of-the-art and future developments in terms of instrumentation, data acquisition, communication systems and data mining and presentation procedures for diagnosis of infrastructural 'health'.
•01 Jan 1998
TL;DR: A structural monitoring system comprises a plurality of modular, battery powered data acquisition devices which transmit structural information to a central data collection and analysis device over a wireless data link.
Abstract: A structural monitoring system comprises a plurality of modular, battery powered data acquisition devices which transmit structural information to a central data collection and analysis device over a wireless data link. The data acquisition devices each comprise mechanical vibration sensors, data acquisition circuitry, a digital wireless transmitter, and a battery for providing electrical power to the device. The central data collection device comprises a digital wireless receiver that receives data sent from the data acquisition devices, and a microprocessor for processing the data. A more powerful computer may be interfaced with the central device to provide more sophisticated analysis after a natural hazard or other extreme event. A methodology for operating the monitoring system is also disclosed.
TL;DR: The purpose of this paper is showcase successful VBM applications and to make the case that VBM does provide valuable information in real world applications when used appropriately and without unrealistic expectations.
Abstract: Structural health monitoring (SHM) is a relatively new paradigm for civil infrastructure stakeholders including operators, consultants and contractors which has in the last two decades witnessed an acceleration of academic and applied research in related areas such as sensing technology, system identification, data mining and condition assessment. SHM has a wide range of applications including, but not limited to, diagnostic and prognostic capabilities. However, when it comes to practical applications, stakeholders usually need answers to basic and pragmatic questions about in-service performance, maintenance and management of a structure which the technological advances are slow to address. Typical among the mismatch of expectation and capability is the topic of vibration-based monitoring (VBM), which is a subset of SHM. On the one hand there is abundant reporting of exercises using vibration data to locate damage in highly controlled laboratory conditions or in numerical simulations, while the real test of a reliable and cost effective technology is operation on a commercial basis. Such commercial applications are hard to identify, with the vast majority of implementations dealing with data collection and checking against parameter limits. In addition there persists an unhelpful association between VBM and ‘damage detection’ among some civil infrastructure stakeholders in UK and North America, due to unsuccessful transfer of technology from the laboratory to the field, and this has resulted in unhealthy industry scepticism which hinders acceptance of successful technologies. Hence the purpose of this paper is showcase successful VBM applications and to make the case that VBM does provide valuable information in real world applications when used appropriately and without unrealistic expectations.
TL;DR: A newly designed integrated wireless monitoring system that supports real-time data acquisition from multiple wireless sensing units that has been fabricated, assembled, and validated in both laboratory tests and in a large-scale field test conducted upon the Geumdang Bridge in Icheon, South Korea.
Abstract: Structural health monitoring (SHM) has become an important research problem which has the potential to monitor and ensure the performance and safety of civil structures. Traditional wire-based SHM systems require significant time and cost for cable installation. With the recent advances in wireless communication technology, wireless SHM systems have emerged as a promising alternative solution for rapid, accurate and low-cost structural monitoring. This paper presents a newly designed integrated wireless monitoring system that supports real-time data acquisition from multiple wireless sensing units. The selected wireless transceiver consumes relatively low power and supports long-distance peer-to-peer communication. In addition to hardware, embedded multithreaded software is also designed as an integral component of the proposed wireless monitoring system. A direct result of the multithreaded software paradigm is a wireless sensing unit capable of simultaneous data collection, data interrogation and wirele...