The tetrapod jacket-supported offshore wind turbine is subjected to marine environmental loads, resulting in monotonic and cyclic lateral-compression-tension interaction behavior of the pile-soil system. Although the excellent applicability that has been demonstrated by three-dimensional numerical simulation for aiding the revelation of the mechanism of jacket foundation-soil interaction, a significant challenge remains in accurately reflecting the nonlinear stress-strain relationship and cyclic behavior of the soil, and others. Finite element numerical models are therefore established for laterally loaded tetrapod jacket pile foundations in this study, and a bounding surface model is adopted to simulate the elastoplastic characteristics and cyclic ratchet effect of the soil. Subsequently, a parametric analysis is conducted on different net spacings and aspect ratios of the jacket base-piles to investigate the pile deformation characteristics, bearing mechanisms, evolution of pile-soil interaction, and the internal force development under monotonic and cyclic conditions, respectively. The results indicate that under monotonic loading, the pile deformation pattern transitions from a flexible pile mode to a rigid rotational deformation mode as the aspect ratio decreases. Under cyclic loading, attention should be paid to the asynchronous accumulation of axial forces within the base-piles and its impact on overall bearing performance.

The quest for clean, renewable energy resources has given a global rise in offshore wind turbine (OWT) construction. As OWTs are more exposed to harsh environmental conditions, the dynamic behavior of OWTs with jacket support structures under critical loading scenarios is crucial yet least understood, which becomes more convoluted with the consideration of soil-structure interaction (SSI) effects. In addition, the seismic characteristics of such systems heavily depend on the excitation characteristics like frequency content, a feature that is still ambiguous. This research aims to examine the influence of seismic frequency contents on the dynamic characteristics and damage modes of jacket-supported OWT systems including SSI effects. The numerical model is established and validated based on a previous study, which ensures the accuracy of the numerical modeling framework. Upon validation, extensive numerical analyses are performed under earthquakes with varying frequency contents. Results reveal the relationship among the ground motion frequency, SSI, and the dynamic and damage behavior of jacket-supported OWTs, offering important insights for the improved seismic design and analysis of jacket-supported OWTs.

Offshore wind turbines (OWTs) empoly various foundation types, among which Jacket-type offshore wind turbines (JOWTs) are often used in shallow waters with challenging soil conditions due to their lattice framework foundations and multiple anchoring points. However, prolonged exposure to harsh marine environments (e.g. storms) and age-related degradation issues like corrosion, fatigue cracking, and mechanical damage increases failure risks. To address these issues, this paper introduces a Digital Healthcare Engineering (DHE) framework, which provides a proactive strategy for enhancing the safety and sustainability of JOWTs: (1) Real-time health monitoring using IoT; (2) Data transmission via advanced communication technologies; (3) Analytics and simulations using digital twins; (4) AI-powered diagnostics and recommendations; as well as (5) Predictive analysis for maintenance planning. The paper reviews recent technological advances that support each DHE module, assesses the framework's feasibility. Additionally, a prototype DHE system is proposed to enable continuous, early fault detection, and health assessment.

In the transitional waters of 30 to 90 m, jacket foundation has great application potential due to its advantages of light weight, high structural stiffness and good stability. In addition to the long-term normal wind and waves, the wind turbines will suffer from typhoons and waves in extreme bad weather. Currently, research on the dynamic response of jacket supported OWTs in clay under severe typhoons is very rare. The study develops a numerical method to calculate the dynamic response and fatigue damage of jacket supported OWTs under typhoon loads by incorporating a simplified single bounding surface model of clays. Through three-dimensional numerical analysis across various scenarios, this study investigates the dynamic response characteristics of jacket supported OWTs on clay soil. It also examines the impact of wind-wave coupling effects on the fatigue damage experienced by these structures. It was found that severe typhoons can lead to notable permanent tilting of the jacket foundation, thereby failing to meet the requirements of normal serviceability limits. The most critical nodes of the OWT are situated at the mudline of the pile foundations, followed closely by the bottom of the tower structure. The most significant fatigue damage occurs for wind-wave co-directional coupling loading along the orthogonal direction of the OWT. The research outcomes provide valuable guidance for enhancing the typhoon-resistant design of jacket supported OWTs.

For offshore platforms installed in seismically active regions, maintaining the safety of operations is an important concern. Therefore, the reliability of these structures, under earthquake ground motions, should be evaluated accurately. In this study, reliability methods are applied to determine the probability of failure of jacket platforms against extreme level earthquake (ELE), considering uncertainties in ground motions and the properties of the structure and soil. They are verified by two variance reduction Monte Carlo sampling methods to find the most efficient method in terms of both accuracy and calculation time. During the ELE event, also called strength level earthquake, structural members and foundation components are permitted to sustain localised and limited nonlinear behaviour, so a force-based criterion is utilized for the limit-state function. The results indicate that all reliability methods, except for FOSM, provide a good approximation of the probability of failure. Also, Point-fitting SORM is the most efficient method.

API-RP2EQ (2021) has recommended annual probabilities of failure for Jacket-Type Offshore Platforms (JTOPs) against earthquake events and has specified that catastrophic failure modes that can lead to environmental damage or loss of structural integrity shall not occur during an Abnormal Level Earthquake (ALE). In this study some structural and non-structural limit states are proposed for the seismic evaluation of JTOPs and a comprehensive methodology is used for evaluating the probabilities of reaching relevant limit states, considering the nonlinear dynamic behavior of JTOPs, soil-pile interaction, pipeline risers, and relevant uncertainties. Incremental Dynamic Analysis (IDA) has been carried out on finite element models of platforms, and record-to- record and epistemic uncertainties have been considered in deriving fragility curves. Results show that the slope-based limit states derived from nonlinear static pushover curves provide a fairly good estimate of the target annual probability of structural failure. They also show that a non-structural limit state associated with containment leakage of pipeline risers should also be considered in the analysis. The research provides valuable insights into probabilistic performance-based seismic assessment of steel jacket-type offshore platforms and indicates that the reserve strength coefficients recommended in the relevant standard may be too conservative.

This paper presents a comprehensive on-site decision-making framework for assessing the structural integrity of a jacket-type offshore platform in the Gulf of Mexico, installed at a water depth of 50 m. Six critical analyses-(i) static operation and storm, (ii) dynamic storm, (iii) strength-level seismic, (iv) seismic ductility (pushover), (v) maximum wave resistance (pushover), and (vi) spectral fatigue-are performed using SACS V16 software to capture both linear and nonlinear interactions among the soil, piles, and superstructure. The environmental conditions include multi-directional wind, waves, currents, and seismic loads. In the static linear analyses (i, ii, and iii), the overall results confirm that the unity checks (UCs) for structural members, tubular joints, and piles remain below allowable thresholds (UC < 1.0), thus meeting API RP 2A-WSD, AISC, IMCA, and Pemex P.2.0130.01-2015 standards for different load demands. However, these three analyses also show hydrostatic collapse due to water pressure on submerged elements, which is mitigated by installing stiffening rings in the tubular components. The dynamic analyses (ii and iii) reveal how generalized mass and mass participation factors influence structural behavior by generating various vibration modes with different periods. They also include a load comparison under different damping values, selecting the most unfavorable scenario. The nonlinear analyses (iv and v) provide collapse factors (Cr = 8.53 and RSR = 2.68) that exceed the minimum requirements; these analyses pinpoint the onset of plasticization in specific elements, identify their collapse mechanism, and illustrate corresponding load-displacement curves. Finally, spectral fatigue assessments indicate that most tubular joints meet or exceed their design life, except for one joint (node 370). This joint's service life extends from 9.3 years to 27.0 years by applying a burr grinding weld-profiling technique, making it compliant with the fatigue criteria. By systematically combining linear, nonlinear, and fatigue-based analyses, the proposed framework enables robust multi-hazard verification of marine platforms. It provides operators and engineers with clear strategies for reinforcing existing structures and guiding future developments to ensure safe long-term performance.

The expansion of offshore wind farms, driven by better offshore wind conditions and fewer spatial limitations, has promoted the growth of this technology. This study focuses on the design of jacket support structures for Offshore Wind Turbines, which are suitable for deeper waters. However, the structural analysis required for designing these structures is computationally intensive due to multiple load cases and numerous checks. To reduce this computational cost, artificial-neural-network-based surrogate models capable of estimating the feasibility of a jacket structure acting as the support structure for any given wind turbine at a specific site are developed. A synthetic dataset generated through random sampling and evaluated by a structural model is utilized for training and testing the models. Two kind of models are compared: one is trained to estimate global feasibility, while the other estimates compliance with each of the structural partial requirements. Also, several assembly methods are proposed and compared. The best-performing model shows great classification metrics, with a Matthews Correlation Coefficient of 0.674, enabling an initial assessment of the structural feasibility. The low computational cost of artificial neural networks compared to structural models makes this surrogate model useful for accelerating otherwise prohibitive parametric studies or optimization processes.

Jacket foundation is typically the preferred choice for Offshore Wind Turbines (OWTs) erected in water depth varying from 40 m to 80 m. In this paper, an integrated dynamic analysis model is designed to study the coupling between aerodynamics, servodynamics, hydrodynamics, soil-structure interaction for piled jacket OWTs. The performances of the AeroDyn and ServoDyn modules are verified by FAST, showcasing their applicability under deterministic and stochastic environmental conditions. The OWT dynamic responses, especially for t-z modeling, stress-transfer mechanism and structural fatigue damage, are subsequently studied. The overall deformation of the jacket calculated by the nonlinear elastic t-z curve in the API guideline, is overwhelmed by the t-z curve formulated using bounding surface plasticity framework, due to the ignorance of the loading history effect. Accompanied by a compressed-released-recompressed stress-transfer process, the downwind tube would experience high stress level, hence necessitating more attention in the ultimate limit state design of piled jacket structure. Otherwise, the upwind tube seems to be more decisive to the fatigue limit state design of piled jacket structure, owing to severe fluctuation in structural stress caused by a tensed-released-re-tensed stress-transfer tendency.

Advances in the design process and understanding of the structural behaviour of jacket -type foundations for offshore wind turbines are fundamental to the expansion of these devices in medium -depth waters. The structural evaluation of jacket foundations is a complex and computationally expensive task because of the large number of structural elements and numerous load scenarios and requirements imposed by international standards. In this context, the soil-structure interaction is not usually incorporated into the optimisation process of these devices, assuming that the foundation flexibility does not significantly affect the supporting structure. This study investigated an approach for analysing the influence of the soil-structure interaction on the structural design. To perform a relevant analysis, an optimisation process was used to obtain feasible designs for a 10 -MW wind turbine in a specific location. To optimise and evaluate the jackets, a structural model based on static equivalent analysis of the most representative load scenarios for environmental loads was used. The obtained designs highlight the importance of considering the soil-structure interaction for evaluating the technical requirements imposed on these structures, especially in the ultimate limit states.