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Ice gouging is one of the main threats to the safety of the subsea pipelines buried in Arctic coastal regions. Determining the best pipeline burial depth relies on free-field ice gouging analysis and obtaining the resultant subgouge soil deformations. Therefore, improving the accuracy and efficiency of the free-field ice gouging analysis is a key demand in daily engineering practice. The pressure-induced by ice keel through the ice gouging process causes the seabed soil to undergo large localized plastic deformation, where the classical Lagrangian method confronts mesh instability challenges. Also, the conventional Mohr-Coulomb soil model is not able to account for the strain-rate dependency and strain-softening effects, which are significant in ice gouging event. In this study, free-field ice gouging in clay was simulated using a coupled Eulerian-Lagrangian approach. The strain-rate dependency and strain-softening effects were incorporated by developing a user-defined subroutine and incremental updating of the undrained shear strength in abaqus. The comparison of the model predictions with published numerical and experimental studies showed a significant improvement of accuracy. A comprehensive parametric study was also conducted to investigate the effect of various model parameters on the seabed response to ice gouging. [ABSTRACT FROM AUTHOR]

Prediction of subgouge soil deformation during an ice gouging event is a challenging design factor in Arctic subsea pipelines. An accurate assessment of ice keel-seabed interaction requires expensive model testing and large deformation finite element analysis. Proposing reliable analytical/empirical solutions needs a deep understanding of the key parameters governing the problem. In this study, dimensional analysis of subgouge soil deformations was conducted and eight dimensionless groups of parameters were identified to facilitate proposing potential new solutions. A comprehensive dataset was established for horizontal and vertical subgouge deformations in both sand and clay seabed. Using the identified dimensionless groups, linear regression (LR) models were developed to estimate the horizontal and vertical deformation. Moreover, a sensitivity analysis (SA), as well as an uncertainty analysis (UA), was carried out to identify the superior LR models and the most influential parameter group. A high range of correlation coefficient (R), Nash-Sutcliffe efficiency coefficient (NSC), and variance accounted for (VAF) along with a low range of errors was achieved for the best LR model. The results of the superior LR models were also compared with the existing empirical equations. The study showed that the shear strength parameters of the seabed soil and the ratio of gouge depth to gouge width are the governing dimensionless parameters to model the horizontal and vertical subgouge soil deformations. [ABSTRACT FROM AUTHOR]

• Iceberg draft was modeled by the generalized structure of the group method of data handling. • Iceberg width ratio and the iceberg shape factor were the most influencing inputs. • The magnitude of iceberg drafts grew by increasing the value of the iceberg width. • A GS-GMDH-based equation was presented to estimate the iceberg drafts. The iceberg draft prediction is vital to mitigate the collision risk of deep keel icebergs with the seafloor-founded infrastructures, including the subsea pipelines, wellheads, hydrocarbon loading equipment, and communication cables crossing the Arctic and subarctic areas since the drifting icebergs may gouge the ocean floor and the physical and operational integrity of the submarine structures would be threatened. In this study, the iceberg drafts were simulated using the generalized structure of the group method of data handling (GS-GMDH) algorithm for the first time. The parameters affecting the iceberg drafts were determined, and five GS-GMDH models comprising GS-GMDH 1 to GS-GMDH 5 were developed utilizing those parameters governing. A dataset comprising 161 distinct case studies measured in the most significant field investigations of iceberg characteristics was generated, and the GS-GMDH models were trained through 60 % of the data, the rest of the data (i.e., 40 %) were considered for the GS-GMDH models' validation. By defining different scenarios, the most accurate GS-GMDH model and the most important input parameters were identified. The sensitivity analysis demonstrated that the iceberg width ratio (W / H) and the iceberg shape factor (S f) were identified as the most influencing input parameters. The comparison between the performance of the premium GS-GMDH model and the group method of data handling (GMDH), artificial neural network (ANN) algorithms, and the empirical models proved that the GS-GMDH model simulated the iceberg drafts with the highest level of precision and correlation along with the lowest degree of complexity. Based on the partial derivative sensitivity analysis (PDSA), the magnitude of iceberg drafts grew by increasing the value of the iceberg width and iceberg length. Ultimately, a GS-GMDH-based equation was presented to estimate the iceberg drafts for practical applications, particularly in the early stages of iceberg management projects and engineering designs. [Display omitted] [ABSTRACT FROM AUTHOR]

The existing Steel Catenary Riser (SCR)-seabed interaction models do not account for the contribution of seawater as a key influential factor. The present study has examined the effect of SCR-seabed-seawater interaction on the trench enlargement and consequently on the fatigue performance of the SCR in the touchdown zone (TDZ). Coupled Eulerian-Lagrangian (CEL) analysis with three domains of SCR, seabed soil, and seawater were performed using ABAQUS. A parametric study was conducted to investigate the impact of seawater interaction along with incorporation of the shear strain rate and softening effects. The conventional bearing capacity approach for analysing pipe penetration into the seabed was also reviewed, and modifications were proposed to account for the effects of water entrainment into the trench. The results obtained from CEL analysis were integrated with a global SCR model to incorporate the SCR-seabed-seawater interaction effects into the fatigue analysis. The study showed that the entrainment of seawater into the trench can be coupled with SCR oscillations to further soften the seabed and erode the trench resulting in an enlarged trench profile affecting the fatigue damage in the TDZ. • SCR-seabed-seawater interaction affects the trench formation in the touchdown zone (TDZ). • Trench formation is significantly affecting the fatigue life of the SCR in the TDZ. • Existing non-linear seabed interaction models do not consider the seawater effects. • SCR-seabed-seawater interaction was incorporated into trench formation and fatigue analysis. • The study revealed the remarkable effect of the seawater in trench formation and fatigue life. [ABSTRACT FROM AUTHOR]

Abstract Fatigue response of steel catenary risers (SCR) in the touchdown zone (TDZ) is significantly affected by riser-seabed interaction. Non-linear hysteretic riser-seabed interaction models have been recently developed to simulate the SCR cyclic embedment into the seabed. Despite the advancements achieved in the prediction of non-linear hysteretic riser-seabed interaction, several inconsistencies have been recently identified in the nodal performance of some of the popular models. These limitations need to be resolved by proposing new models or improving the existing models. However, it is necessary to evaluate the influence of the identified shortcomings of the existing models on the global performance of the riser. In this paper, the influence of nodal inconsistencies observed in a popular riser-seabed interaction model on the global performance of the riser was comprehensively examined in the TDZ. The riser embedment profile, cyclic contact stress, contact stress envelop, mean shear force, cyclic bending moment, and consequently the cumulative fatigue damage was investigated. The study showed that the soil model overestimates the riser embedment and other global responses. Recommendations were made to overcome the identified shortcomings of the existing models in future developments. [ABSTRACT FROM AUTHOR]

Travelling icebergs may threaten the structural integrity of the offshore pipelines in any territories they can reach. Arctic offshore pipelines are usually buried for physical protection against ice gouging. The safe and cost-effective burial depth of these pipelines needs to be determined by accurately assessing the subgouge soil deformation and the ice keel-seabed contact forces. Layered seabed soil strata found in many geographical locations add to the complexity of assessing the ice keel-seabed interaction process. The currently used design codes have been developed for uniform soil strata-an assumption that may affect the accuracy and cost-effectiveness of the design. In this study, the significance of layered sand over clay seabed in the ice gouging process was investigated by performing large deformation finite element (LDFE) analysis using Coupled Eulerian-Lagrangian (CEL) approach. A comprehensive parametric study was conducted to assess the influence of ice gouging characteristics and soil properties on the subgouge soil deformation, the developed plastic shear strains, and the resultant ice keel reaction forces. The results showed that the seabed response to ice gouging largely depends on the soil strata, where the layers' interaction effects can alter the usual response expected from a uniform seabed. • Iceberg-pipeline interaction relies on free-field ice gouging analysis. • Layered seabed are found in Arctic offshore regions but not covered with design standards. • A model was developed for a better prediction of the ice-seabed interaction in sand over clay. • Comprehensive study was conducted to investigate the response of layered seabed to ice gouging. • The study showed the significance of the topic with recommendations for layered seabed. [ABSTRACT FROM AUTHOR]

Abstract: The subsea survey results using remote operating vehicles (ROV) show that trenches with a depth of several riser diameters can be developed underneath the steel catenary risers (SCR). Therefore, an important question in respect of the riser–seabed interaction is, how the trench formation beneath the riser affects the riser fatigue performance in the touchdown zone. A common methodology reported in literature to study the impact of trench formation on riser fatigue life is the insertion of an artificial mathematical expression of the riser profile into the seabed. This study shows that such methodology can be inconsistent and leading to contradictory results. The current paper has employed ABAQUS finite element software and coded a non-linear soil hysteretic model to automatically simulate the variable seabed stiffness and the gradual trench development through the touchdown zone. In this method, the seabed model parameters are initially adjusted to extreme values allowing trench with desired depth to be developed over a moderate number of displacement cycles of the SCR. The design wave scatter diagram is then applied, simulating a generic Spar system, after switching the model parameters to values with normal range. The paper presents the impact of trenches of different depths on the fatigue performance of SCRs in the touchdown zone. [Copyright &y& Elsevier]

Abstract: The methodologies recommended by existing codes and standards for design of steel catenary risers are considering linear springs in the seabed while it is publicly accepted that the non-linear riser-seabed interaction can have vital influence on stress variation in touchdown area and consequently fatigue performance during the cyclic motions of the riser as the latter is excited by vessel motions under environmental loads. In this study an advanced hysteretic non-linear riser-seabed interaction model has been implemented into the seabed enabling the automatic simulation of different stiffness in the seabed response through the touchdown zone and gradual embedment of riser. Then the impacts of this model on fatigue calculation procedure and fatigue performance in touchdown area has been studied. [Copyright &y& Elsevier]

Ice-induced scour is a serious challenge for the subsea pipelines in the Arctic shallow waters. Estimation of the maximum pipeline deformation and its minimum burial depth can guarantee the operational integrity of these structures in the ice-prone regions. The pipeline buried below the ice keel is still threatened by subgouge soil deformation that is extended down the ice tip due to the shear resistance of the seabed soil. Determining the subgouge soil deformations is a challenging process that needs costly experimental and numerical simulations. In this paper, an alternative and cost-effective methodology has been proposed using a robust neural network-based method titled "generalized structure of group method of data handling" (GS-GMDH) for the first time to simulate the horizontal and vertical subgouge soil deformation profiles in clay. Using the parameters governing the subgouge soil deformations, nine GS-GMDH models were defined. The premium GS-GMDH models and the most influencing input parameters comprising the soil depth and the gouge geometry were introduced by performing a sensitivity analysis. Subsequently, results of the best GS-GMDH models were compared with the classical group method of data handling (GMDH), the artificial neural network (ANN), and the empirical approaches. An uncertainty analysis showed that the GS-GMDH slightly overestimated the horizontal and underestimates the vertical subgouge soil deformations. A partial derivative sensitivity analysis (PDSA) was also performed to assess the influence of the input parameters on the subgouge soil deformations. Lastly, a set of GS-GMDH-based equations were proposed for fast estimation of the subgouge soil deformations in clay. [Display omitted] • Arctic subsea pipelines are buried for physical protection against the ice scour. • Determining the minimum burial depth needs accurate modelling of the ice-seabed interaction. • Costly analysis and experiments are usually required for assessment of the ice-seabed interaction. • An artificial intelligence model was developed to simulate the ice-seabed interaction in clay. • GS-GMDH could be an accurate and cost-effective alternative for prediction of the ice-induced subgouge deformations. [ABSTRACT FROM AUTHOR]

In ice gouging analyses, the seabed is often simplified as a uniform material domain, over-looking the potential complexities inherent in layered seabed formations, which are wide-spread in numerous Arctic regions. This study investigates the pipeline response into the distinct seabed configurations, including layered soft over stiff clay, layered stiff over soft clay, and uniformly soft and uniformly stiff compositions, to ice gouging. This was achieved through comprehensive large deformation finite element (LDFE) analysis, employing a Coupled Eulerian Lagrangian (CEL) algorithm. Incorporation of the strain-rate dependency and strain-softening effects involved the development of a user-defined subroutine and incremental update of the undrained shear strength within the Abaqus software. The pipeline is explicitly incorporated into the model, allowing for a detailed investigation of its response to ice gouging phenomena within these layered seabed scenarios. This research demonstrates that simplifying a layered seabed into a uniform can be misleading. Such an approach can lead to significant errors, potentially overestimating or underestimating pipeline response to ice gouging. By incorporating these complexities, engineers can develop more optimized designs with enhanced safety margins in Arctic environments prone to ice gouging phenomena. • Arctic subsea pipelines are buried for physical protection against the ice scour. • Determining the minimum burial depth needs accurate modelling of the ice-seabed interaction. • Layered seabed strata are not covered in design codes and recommended practices. • The effects of layered seabed on buried pipeline Response to ice gouging was investigated. • Study reveals simplifying layered seabed to uniform domain yields inaccurate prediction of pipeline response to ice gouging. [ABSTRACT FROM AUTHOR]

Subsea pipelines crossing the Arctic shallow waters are usually threatened by ice scour. A cost-effective solution to physically protect the pipeline against the ice gouging is to bury the pipeline in the seabed. Determining the minimum burial depth to minimize the construction cost and ensure pipeline integrity is a challenging design aspect. This requires proper modeling of the ice keel-soil interaction for an accurate assessment of the subgouge soil deformation and the keel reaction forces in a free field ice gouging analysis. In this study, the ice gouging process in dense sand was simulated by advanced large deformation analyses using Coupled Eulerian-Lagrangian (CEL) approach in ABAQUS/Explicit. A modified Mohr-Coulomb (MMC) model was coded into a simplified user subroutine to incorporate the effect of plastic shear strain accumulation, loading condition, density, and confining pressure on the shear strength parameters of dense sand. The MMC model captured the non-linear pre-peak hardening and post-peak softening of the dense sand that is not modeled by conventional Mohr-Coulomb (MC) model. The existing test results and numerical studies were used to verify the performance of the MMC model in ice gouging analysis. A comprehensive parametric study was conducted to investigate the effect of ice keel configuration and soil model parameters on keel reaction forces, subgouge soil deformations, and the soil berm formations. The proposed model resulted in a more accurate prediction of the seabed response to ice gouging and showed the significance of modeling the strain rate dependency of dense sand in ice gouging analysis. The proposed methodology was found to be a strong but simple framework that can be effectively used in daily engineering practice. • Arctic subsea pipelines are buried for physical protection against the ice scour. • Determining the minimum burial depth needs accurate modelling of the ice-seabed interaction. • The classical Mohr-Coulomb model does not account for non-linear features of the stress-strain response of the dense sand. • CEL analysis was conducted by using a subroutine to update the non-linear strain-dependant shear strength parameters. • The model significantly improved the simulation results and the proposed methodology was found to be an effective tool. [ABSTRACT FROM AUTHOR]