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Estimation of wave run-up has been of increasing concern for offshore wind structures and a critical aspect for designers. The highly nonlinear phenomenon makes the study difficult. That is the reason for the very few design rules and experimental data available to estimate it. Actual wave run-up is greater than commonly predicted. The goal of this research is to benchmark the theoretical formulations with the results of the physical model tests performed by Deltares in the field of crest elevation, run-up, forces and pressures. The laboratory reproduced in a wave tank (75 m length; 8.7 m width; 1 m depth; and a 1:60 scale, with Froude similarity) an offshore power converter platform located at intermediate water depths (25⁻43.80 m) in the Southern North Sea, designed by the Norwegian company Aibel. The purpose of this research is to offer a preliminary design guide for wave run⁻up using theoretical expressions both for cylinders and gravity based structures (GBS), leaning on the cited laboratory tests to validate the results obtained by such theoretical models.

The quantity and location of offshore platforms are of great significance for marine oil spill monitoring and offshore oil-gas development. In the past, multiphase medium- and low-resolution optical or radar images have been used to remove the interference of ship targets based on the static position of a platform to extract the offshore platform, resulting in large demands and high image data costs. According to the difference in shape between offshore platforms (not elongated) and ships (elongated shapes) in SAR (synthetic aperture radar) images, this paper proposes an automatic extraction method for offshore platforms in single SAR images based on a dual-step-modified model. First, the two-parameter CFAR (constant false alarm rate) algorithm was used to detect the possible offshore platform targets; then, the Hough transform was introduced to detect and eliminate ship targets with linear structures. Finally, the final offshore platform was obtained. Experiments were carried out in four study areas in the Beibu Gulf basin and the Pearl River estuary basin in the northern South China Sea. The results show that the method has a good extraction effect in the above research area, and the extraction accuracy rate of offshore platforms is 86.75%. A single SAR image can obtain satisfactory extraction results, which greatly saves on image data cost.

Grouted connections are frequently used as structural detail of offshore wind turbines and platforms for the load transferring connection between piles and support structure. At latticed substructures this connection is commonly located at mudline. However, a potential influence of the surrounding water on the connection’s fatigue behaviour was neglected in earlier tests and consequential design methods. Herein described experimental investigations at small and large-scale fatigue tests in submerged conditions showed a significant reduction of endurable load cycles. In addition, the water impact caused varied damage mechanism in the connection. [ABSTRACT FROM AUTHOR]

Copyright of China Petroleum Machinery is the property of China Petroleum Machinery Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of China Petroleum Machinery is the property of China Petroleum Machinery Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The purpose of the present paper is to develop a simple methodology for seismic life cycle cost (LCC) estimation for a steel jacket offshore platform structure. This methodology accounts for accuracy of LCC modelling as well as simplicity of application. Accuracy is maintained through incorporating the effect of aleatory and epistemic uncertainties in the LCC estimation framework. Simplicity is achieved by using equivalent single-degree-of-freedom (ESDOF) system instead of the full structure and by eliminating full incremental dynamic analysis and fragility analysis. Instead, an approximate fragility curve and a localised incremental dynamic analysis curve are used along with a probabilistic simple closed-form solution for loss estimation. In the design of model structures, different bracing systems are used for the seismic design of the offshore platform, such as conventional and buckling-restrained braces. The proposed LCC methodology is validated through comparison with the results from a more rigorous method. It is found that even though the proposed methodology results in a slightly different solution compared to the reference method, the method can be used as an efficient tool for preliminary LCC evaluation of structures. [ABSTRACT FROM AUTHOR]

Nowadays, natural load excitation cannot detect all modal problems when testing vibration responses of offshore platforms. To overcome this issue, the present paper proposes a novel method to detect structural damages of offshore platforms based on grouping modal strain energy. This method divides the unit modal strain energy into axial tension-compression and bending. It may not only expand known modals and overcome the incomplete modal parameters under natural load excitation, but also could estimate the damage locations based on low-order modal parameters. The proposed method was verified by numerical simulations. Based on simulations on different damage conditions of a jacket offshore platform, damage locations could be determined accurately through comprehensive analysis of grouping modal strain energy distribution. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Architecture & Civil Engineering is the property of Chang'an Daxue Zazhishe and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We study a delayed fuzzy $H_{\infty }$ control problem for an offshore platform under external wave forces. First, by considering perturbations of the masses of the platform and an active mass damper, a Takagi–Sugeno fuzzy model is established. Then, by introducing time delays into the control channel, a delayed fuzzy state feedback $H_{\infty }$ controller is designed. Simulation results show that the delayed fuzzy state feedback $H_{\infty }$ controller can reduce vibration amplitudes of the offshore platform and can save control cost significantly. [ABSTRACT FROM AUTHOR]

Structural intensity approach is introduced to study the crack detection for offshore platform in the paper. The Line Spring Model (LSM) of surface crack is proposed based on plate crack structure, and thus the relationship between the additional angle, displacement and crack relative depth is achieved. Besides, the concept of appended structure-borne sound intensity is introduced. The expression of appended structural intensity for crack damage is derived. By observing the input energy, distribution, transmission and vibration performance of structure intensity, evidence is provided for detection of crack location. Vibration analysis is conducted on the whole platform under multi environment load. Using the structural intensity approach, the crack is detected on the key point easily. Moreover, the K-shape welded pipe point is detected using structural intensity approach, and the crack can be detected accurately. Therefore, development structural intensity approach would be extremely useful to spread out technologies that can be applied for offshore platform crack detection accurately. [ABSTRACT FROM AUTHOR]

Natural gas explosion of offshore platform is prone to cause accidental disaster such as platform collapse and casualties etc. Real-time natural gas explosion consequence reconstruction is essential to support a quick accidental emergency response planning to prevent the accidental escalation to disaster. The widely-used CFD is computationally intensive and thereby has a significant delay. Machine/deep learning-based models offer a potential real-time alternative, which however are not able to quantify the uncertainty of spatial overpressure prediction. This study aims to propose a hybrid deep learning probability model to real-time predict spatial explosion overpressure of offshore platform by using sparsely-observed overpressures. In this hybrid model, Variational Bayesian inference is incorporated into deep learning backbone. Both natural gas explosion experimental and numerical modeling of offshore platform are conducted to construct the benchmark dataset. By using this benchmark dataset, sensitivity analysis of Monte Carlo sampling number N , drop probability p on model's performance is also conducted. The results demonstrated our model exhibits high accuracy with R 2 = 0.955 and real-time capability with inference time of 2.9s. Compared to the state-of-the-art model, the additional uncertainty estimation improves the accuracy and robustness of spatial overpressure prediction, which contributes to the reliable explosion accidental emergency decision-making. Overall, this study provides a reliable alternative for constructing digital twin emergency management system to effectively manage natural gas explosion risk of offshore platforms. • Deep learning probability model for real-time natural gas explosion prediction of offshore platforms. • Model correlates spatial explosion overpressure with sparsely-observed overpressures. • Uncertainty information ensures reliable guidance for emergency decision-makings. [ABSTRACT FROM AUTHOR]

Herrn Univ. Prof. Dr.-Ing. Gerhard Hanswille zur Vollendung seines 65. Lebensjahres gewidmet Grout-Verbindungen sind ein häufig eingesetztes Konstruktionsdetail in Offshore-Windenergieanlagen und -Plattformen. Sie stellen eine lastabtragende Verbindung zwischen gerammten Pfählen und Tragstruktur her. Bei aufgelösten Unterstrukturen befindet sich diese Verbindung üblicherweise unter Wasser. Ein möglicher Wassereinfluss auf das Ermüdungsverhalten des Konstruktionsdetails wurde in früheren Versuchen und den daraus abgeleiteten Bemessungsverfahren nicht berücksichtigt. Die in dieser Veröffentlichung beschriebenen versuchsgestützten Untersuchungen zeigen an klein- und großskaligen Versuchskörpern eine deutliche Reduktion der Lebensdauer bei Ermüdungsbeanspruchung unter Wasser gegenüber trockenen Umgebungsbedingungen. Neben einer Beeinflussung der Lebensdauer verändert das umgebende Wasser auftretende Schadensmechanismen in der Verbindung. On the fatigue behaviour of grouted connections at varied ambient conditions. Grouted connections are a frequently used structural detail of offshore wind turbines and platforms for the load transferring connection between piles and support structure. At latticed substructures this connection is commonly located at mudline. However, a potential influence of the surrounding water on the connection's fatigue behaviour was neglected in earlier tests and consequential design methods. Herein described experimental investigations at small and large-scale fatigue tests in submerged conditions, showed a significant reduction of endurable load cycles. In addition, the water impact caused varied damage mechanism in the connection. [ABSTRACT FROM AUTHOR]

The overall objective of this study was to develop a biological early warning system (Mosselmonitor®) on offshore platform to detect critical environmental situations. The experiment was conducted on oil off-shore platform called Rospo Mare B. This structure is located in the area in front of Molise coast line (Italy, Adriatic Sea), characterized by a depth of about 77 m and a bathymetry between 65 and 80 m. The Mosselmonitor® works with eight mussels connected via specific sensors to PC for recording opening values of valves. A probe was installed inside the instrument to daily control of water pH, dissolved oxygen, salinity and temperature. Water samples are weekly analyzed for heavy metals, organochlorine pesticide and suspended matter. During the entire observation period, closure alarms were predominantly detected (99.9%) and a decrease of 65% in alarms maximum duration was recorded from the fifth week. During the first month, none changes in water physicochemical parameters were observed so that affect the bivalves behavior. The only chemical parameter steadily detected in water was copper; its average concentrations were of 10 ppb. Detected alarms were not comparable to those recorded in the first month: this observation could be explained considering that mussels will be adapted to copper constant presence. [ABSTRACT FROM AUTHOR]

Quasi static push-over analysis is widely utilized to evaluate nonlinear behavior and ultimate capacity of offshore platforms against environmental wave loading. In reality the forces imparted by the waves traversing the structure, are dynamic loads. If these lateral dynamic loads are to be used in push over analysis, they can provide a more precise estimation of the maximum load that can be resisted by the structure compared to the value derived using quasi static approach. Other parameters that have effect on determination of the ultimate capacity of platforms are the platform structural configuration and its supporting conditions. In this paper, a comprehensive technique within a dynamic push-over analysis for jacket offshore platforms is provided. In the analyses performed herein, the ultimate capacity of a sample platform with two bracing configuration, and with different supporting conditions has been evaluated by using static and dynamic push-over analysis.

A challenging problem in structural health monitoring systems is the requirement of a systematic, effective method for damage localisation and assessment severity of structures, based on vibration data measured by sensors. To address this issue, a novel technique, referred to as damage estimator with modal parameters of structure before and after damage, is applied to detect the location and estimate the severity of existing damage of complex structures. Specifically, a series of experimental tests using a scaled offshore platform model of a 4-story jacket type has been conducted to verify the efficiency of proposed approach, with white noise excitations applied to the top plate of test model. For 6 scenarios of damage conditions simulated by bolt adjustment in the 3rd layer, vibration-based impulse data are induced by an impact hammer and recorded to analyse the variations of modal parameters. Upon the investigation, the results highlight that damage estimator is capable of tracking damage orientation and severity longitudinally, using data from only the fundamental mode shape before and after damage. However, detection accuracy declines considerably for small-scale damages.

The purpose of structural health monitoring (SHM) is to detect damage as early as possible. To this end, damage-sensitive features (DSFs) must be evaluated to achieve the objectives. Researchers have developed numerous features. However, some gaps remain in the literature for feature selection; thus, conducting research that collects, evaluates, and suggests suitable DSFs are deemed essential. Consequently, this article seeks to identify effective DSFs and damage diagnosis recommendations. Seven categories are examined for output-only DSFs: 1) statistical features, 2) spectral function features, 3) modal property-based features, 4) entropy-based features, 5) transmissibility function (TF), 6) time series models, and 7) vibration parameter features. The sensitivity of DSFs to noise is also investigated. Three types of offshore platforms subjected to ambient loads are modeled in SAP2000. For each model, nine damage scenarios with three types of damage (cross-section area, moment of inertia, and pinned connection) are considered. The results of this study include a comparison of the performance of categories and features, efficient features for identifying the damage occurrence, and efficient features for locating the damage in noise-free and noisy conditions. Finally, suggestions are made for effective damage diagnosis. • This research covers a significant gap in the SHM literature, particularly for offshore platforms. • A comprehensive analysis of seven categories of output-only damage-sensitive features (DSFs) for damage detection is presented. • Three types of damage are considered: reduction of the cross-section area, the moment of inertia, pinned connection with severity ranging from 5% to 50%, and ambient loads such as waves, currents, and winds. • Suggestions are made concerning sensitive and efficient DSFs for damage detection. In addition, the noise sensitivity of various categories and features for noise conditions is investigated. • Several recommendations and observations on damage diagnosis are presented. [ABSTRACT FROM AUTHOR]

Among offshore platform structures, multi-planar tubular joints are usually in the most dangerous positions and generate fatigue cracks the earliest. In this study, DX-joints were regarded as the research object, and finite element method was adopted to conduct systematic research on the fatigue properties of multi-planar tubular joint welds. Axial, in-plane bending moment, and out-of-plane bending moment loads were applied to explore the stress distribution along the weld path and the hotspot location under different load conditions. Results indicated that the hotspot stress (HSS) location of DX-joints changed with the variation in the combined stress ratio. Through HSS analysis, cracks were prefabricated at the hotspot location of DX-joints to analyze the change rule of the stress intensity factor (SIF). The influence of different loads, crack lengths, and crack depths on SIF was studied to estimate the growth trend of the weld crack and its dominance. The findings can provide theoretical guidance for fatigue damage and safety assessment of offshore platforms. [ABSTRACT FROM AUTHOR]

Prototype monitoring techniques play an important role in the safety guarantee of mooring systems in marine engineering. In general, the complexities of harsh ocean environmental conditions bring difficulties to the traditional monitoring methods of application, implementation and maintenance. Large amounts of existing mooring systems still lack valid monitoring strategies. In this paper, an underwater monitoring method which may be used to achieve the mechanical responses of a multi-point catenary mooring system, is present. A novel self-contained assembled water depth-inclination (D-I) sensor is designed and manufactured. Several advanced technologies, such as standalone, low power consumption and synchronism, are considered to satisfy the long-term implementation requirements with low cost during the design process. The design scheme of the water resistance barrel and installation clamp, which satisfies the diver installation, are also provided in the paper. An on-site test has previously been carried out on a production semisubmersible platform in the South China Sea. The prototype data analyses, including the D-I value in the time domain (including the data recorded during the mooring retraction and release process) and spectral characteristics, are presented to reveal the accuracy, feasibility and stability of the sensor in terms of fitting for the prototype monitoring of catenary mooring systems, especially for in-service aging platforms. [ABSTRACT FROM AUTHOR]

The vibration reduction device for the offshore platform truss structure has exposed to long term high-energy ultraviolet light and salt spray radiation, the traditional viscoelastic damping technology is easy to aging and failure, and its operational lifetime is limited. The semi‑active particle damping technology has the advantages of high temperature resistance, anti‑aging and so on, at the same time it is also able to adapt the changes of external complex load. The coupling simulation algorithm was used in this paper to study on vibration reduction performance of semi-active particle damping technology for the offshore platform truss structure. The control strategy, simulation algorithm and key parameters of semi-active particle damping are investigated to analyze the vibration reduction effect of the offshore platform truss structure with semi‑active particle damper. The results have shown that the semi-active particle damping has a better effect of vibration reduction compared with the passive particle damping. In addition, the control strategy in different frequency bands has different vibration reduction effects to the system; and the simulation has a good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

This article introduces a new technology about a rod pumping in the offshore platform according to the demand of offshore heavy oil thermal recovery and the production of stripper well, analyzes the research status of hydraulic pumping unit at home and abroad, and designs a new kind of miniature hydraulic pumping unit with long-stroke, low pumping speed and compact structure to resolve the problem of space limitation. The article also describes the whole structure and the working principle of this pumping unit, determines the choice of stroke and rate of the pumping unit, and establishes mathematical models based on the polished rod loads. A new composite hydraulic cylinder with a special structure was designed by combining the hydraulic cylinder with the energy accumulator. This composite hydraulic cylinder is applied on land, and the model prototype runs smoothly, which indicates that the whole structure design of the pumping unit is reasonable and the control strategy is correct. [ABSTRACT FROM AUTHOR]

Copyright of Oil Drilling & Production Technology / Shiyou Zuancai Gongyi is the property of Shiyou Zuancai Gongyi Bianjibu and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper is concerned with adaptive integral sliding mode control (AISMC) based on a wavelet kernel support vector machine for offshore steel jacket platform subject to nonlinear wave-excited force and parameter perturbations. The sliding mode control technique is combined with adaptive control algorithm and wavelet support vector machine to achieve the desired attenuation on the wave-induced vibration and to limit the displacement of offshore platforms. In this method, wavelet kernel support vector machine is used to establish the adaptive controller and an on-line learning rule for the weighting vector and bias is derived. The most important feature of the proposed control strategy is its inherent robustness and its ability to handle the nonlinear behavior of the offshore platform. By means of this control scheme the performance of the AISMC has been improved. The performance of the proposed control strategy is compared with some existing control schemes. It is demonstrated that the proposed control scheme in this paper is more effective in improving the control performance of the offshore platform. This controller is designed based on solving a set of linear matrix inequalities. It has been illustrated through simulation results that the proposed control scheme is effective in improving the control performance of offshore platforms. [ABSTRACT FROM AUTHOR]

At present, trawl fishing as a traditional method is widely used in shellfish harvesting at home and abroad. However, using this method to catch the scallops has many disadvantages, such as huge energy consumption, high labor intensity, and poor fishing efficiency, which have become the key questions to restrict the sustainable development of marine fishing industry. Therefore, it’s very worth researching alternative scallop fishing equipment to meet the requirements of green development. The offshore scallop capture equipment is made up of platform deck, floating body and mooring, which is a kind of floating offshore engineering structure. This equipment occupies multiple functions, such as fishing, sorting, refining, storage and so on. Winch motors (ground net machine and anchor winch), cargo winch, generator unit, scallop separator, working cabin, accommodation and diesel generator were installed on the platform, and solar power as the source of power. In addition, to keep the scallops fresh and achieve the purpose of saving space, 2 shellfish purification storage networks were also set below the platform. Compared with the trawl fishing, it would substantially reduce energy consumption, realize precision fishing, raise fishing efficiency, and decrease the cost of purification. In this paper, based on the comparative methods, the technologic and economic parameters and the economic assessment indices were selected for the establishment of the technical and economic evaluation model, which was to investigate the economy of offshore scallops capture working platform. Firstly, the platform trawling engine power, the platform span, the hauls of platform anchored one time, the lateral movement time of platform anchored one time, the trawling speed of platform and the total construction cost of platform were selected as the technologic and economic parameters. Secondly, the capture fuel consumption per unit area, the unit cost of fishing and the capture efficiency were selected as the economic assessment indices. Next, the technical and economic evaluation model was established according to the technologic and economic parameters and the economic assessment indices. At last, based on this model, the economic calculation of fishing methods including fishing vessels and scallops capture working platform was carried out by using the comparative method. The results showed that when the platform trawling engine power was 400-470 kW, the platform span was 0.5-3.0 km, the lateral movement time of platform anchored one time was less than 2 h, the trawling speed of platform was beyond 1.4 kn, the total construction cost of platform was less than 27.5 million yuan, the scallops capture working platform project had more advantages over the fishing method of fishing vessels. Meanwhile, from these data, it was concluded that the haul of platform anchored one time was not very sensitive to the effect of scallops capture working platform project. The offshore scallops capture working platform conformed the policy of energy saving and emission reduction that was in line with the national “Twelfth Five-Year Plan”. By further experimental verification, the analysis model and method can provide the economic theory reference for the fundamental changes in fisheries production mode in China. [ABSTRACT FROM AUTHOR]