Search

In offshore jacket structures, the stress within the chord thickness of tubular joints arises from both membrane and bending stresses. The Degree of Bending (DoB)—the ratio of bending stress to the total stress—is key to evaluating these joints' fatigue resistance. This study delves into the DoB in tubular X-joints reinforced with fiber-reinforced polymer (FRP) subjected to in-plane bending moment. It begins by validating finite element (FE) analysis accuracy through comparison with existing theoretical and experimental evidence. Following this, the analysis of 166 joints was conducted to examine how variations in FRP characteristics (such as type, layer count, and layout) and the joints' dimensionless geometric factors influence the DoB and its ratio in reinforced joints compared to their unreinforced counterparts. Findings indicate that FRP layers enhance fatigue resistance by lowering hot spot stresses on the chord's inner and outer surfaces and elevating the DoB value by up to 26.16%. Consequently, the study introduces a parametric formula for calculating the DoB in FRP-reinforced tubular X-joints under an in-plane bending moment. This development is significant, as there was no existing parametric formula for determining DoB in FRP-reinforced joints. The proposed formula stands out for its high determination coefficient and minimal error, effectively addressing a notable gap in the field. • The Degree of Bending (DoB) evaluation in FRP-reinforced tubular X-joints under in-plane bending (IPB) is conducted. • 166 finite element models are analyzed for parametric investigation. • The influence of FRP characteristics and geometric factors on the DoB is investigated. • A parametric formula is introduced to calculate the DoB in FRP-reinforced tubular X-joints subjected to IPB moment. [ABSTRACT FROM AUTHOR]

In deep-sea mining operations, the mining riser is the most fragile and technologically demanding segment of the entire system. It is crucial to investigate the dynamic response and fatigue characteristics of mining risers to elucidate their motion patterns and fatigue mechanisms. In this study, we examine the vibration behavior of the deep-sea mining riser using the time-domain finite element method under various sea conditions and estimate the fatigue life of the mining riser based on the Miner-Palmgren damage rule. Results indicate that the significant wave height and peak period of irregular waves significantly influence the dynamic response characteristics and fatigue damage properties of the riser. The axial displacement, rotation angle, bending moment, effective tension, and von Mises stress of the riser are maximized and minimized at the top and bottom, respectively, whereas the lateral displacement shows the opposite trend. In general, the axial displacement exhibits a more complex pattern than the lateral displacement, and the maximum fatigue damage is predominantly concentrated in the middle and upper sections of the riser. • Dynamic behaviors of a deep-sea mining riser under various sea conditions are investigated. • The axial compared with lateral displacements of the riser demonstrate a more intricate pattern of behavior. • The motion trajectory and frequency of the buffer station of the mining riser are ascertained. • The dynamic stress levels and fatigue distribution along the mining riser affected by the irregular waves are given. [ABSTRACT FROM AUTHOR]

Design codes and recommended practices for geotechnical structures generally include some conservatism to take into account any possible source of uncertainty, with conservative design being generally accepted as safe. Such approaches are not appropriate for offshore wind turbines where both over-and-under designs would result in a sub-optimal performance in terms of structural dynamics. The soil surrounding wind turbines is a main contributor to their stiffness, it is also one of the major sources of uncertainty, which makes an accurate prediction of the structural dynamics a rather difficult task. Monitoring data on wind turbines can provide useful insight into their real in-situ behaviour, allowing designers to examine the validity of design assumptions further. In this paper, the bending moments of five monitored wind turbine monopiles are back analysed, using 3D FEM and 1D beam–column models in which the soil is modelled according to API RP2 GEO recommendations, and the rule-based PISA reaction curves. It is found that despite the efforts to get an as accurate soil response as possible, the monitored bending moments are overestimated by the 3D FEM models at some locations, reflecting a mismatch between the simulated and monitored wind turbine monopiles. The possible effect of scour protection is highlighted. The API-based 1D beam–column models overestimate bending moments, rotations, and displacements and underestimate the wind turbine stiffness, while the PISA models are able to give satisfactory results. • Five site-specific wind turbine models are established. The calibration of advanced soil constitutive models is presented. • Bending moments on five wind turbines are computed using both 3D and 1D models and are compared to the monitoring data. • A clear mismatch is shown between the simulated and the monitored bending moments. • One of the possible reasons for this mismatch is the missing contribution of the scour protection in the simulations. • The API RP2 GEO recommendations overpredict the wind turbine's bending moments, rotations and displacements. [ABSTRACT FROM AUTHOR]

The assessment of the ultimate strength of hull girders constitutes a critical safeguard for the structural integrity and safety of maritime vessels. Beyond the traditional approach of assessing the static ultimate strength of hull girders in a one-time analysis, incorporating an evaluation of the ultimate strength under cyclic bending moments provides a more precise representation of the operational realities faced by vessels in service. This approach accounts for the repetitive loading cycles that ships encounter, thereby offering a more accurate reflection of their structural integrity under actual loading conditions. When subjected to cyclic bending moments of varying amplitudes, the hull girder may either achieve an elastic shakedown condition or experience progressive plastic accumulation. The nonlinear finite element approach is employed to evaluate the ultimate strength of a bulk carrier girder subjected to monotonic/cyclic bending moments. Initial deformations and residual stresses, intrinsic to the welding manufacturing process, are fundamental parameters incorporated into the finite element analysis framework. Building upon this foundation, the study conducts a detailed investigation into the elastic shakedown and plastic accumulation behaviors of the hull girder under various cyclic loading amplitudes. The findings reveals that the bulk carrier hull girder's ultimate strength will be weakened by the welding residual stress, and the extent of this weakening is most noticeable while the hull girder is sagging. At its maximum, the bulk carrier hull girder's ultimate strength is 8.22% less. When considering both of the initial deformation and welding residual stresses, the bulk carrier hull girder exhibits the widest elastic shakedown interval. Under the influence of extreme cyclic bending moments, the bulk carrier hull girder ultimately fractures as a result of the ongoing accumulation of plastic deformation. • The effects of varying levels of welding initial deformation and residual stress on ultimate strength of a bulk carrier hull girder was studied. • The static one-time analysis, the characteristics of elastic shakedown and plastic accumulation under cyclic bending moments was considered. • The fracture failure location of a bulk carrier hull girder was identified under extreme cyclic bending moments. [ABSTRACT FROM AUTHOR]

Accurate and reliable prediction of the maximum pile bending moment of soil-pile-superstructure system (SPSS) in liquefiable soils is essential for the seismic design. The maximum pile bending moment can be obtained using experiments that consider only a limited number of factors or time-consuming finite element simulations. The study aims to develop a machine learning-based model for predicting the maximum pile bending moment of SPSS in liquefiable soils. To train the model, a large number of three-dimensional finite element models considering soil and structural uncertainties are dynamically analyzed under different ground motions. In addition, six machine learning regression algorithms are used to develop the predictive model: multiple linear regression (MLR), lasso regression (Lasso), decision tree (DT), random forest (RF), gradient boosting decision tree (GBDT), and extreme gradient boosting (XGBoost). The results show that the XGBoost prediction model has the highest prediction accuracy. The ground motion features (especially peak ground velocity, PGV) have the greatest effect than soil- and structure-related features on the maximum pile bending moment of SPSS in liquefiable soils. • A finite element model verified is used to establish the database. • Six ML methods are developed to predict the maximum pile bending moment. • XGBoost is found to perform the best in both accuracy and overfitting. • Ground motion features are more important than soil and structure-related features. [ABSTRACT FROM AUTHOR]

Frequent and intense internal solitary waves (ISWs) and ISW packets pose serious threats to the in-service safety of deep-water risers in the South China Sea. In this study, a deep-water steel catenary riser (SCR) under multiple ISWs was investigated along with the dynamic characteristics of the touchdown zone (TDZ), including displacements, pipe-soil interactions, tensions, and bending moments. A nonlinear numerical model was developed with a novel vector form intrinsic finite element method and improved pipe-soil interaction model that considers soil stiffness degradation and trench formation. The ISW flow velocity field was solved using the mixed Korteweg-de Vries (mKdV) equation and the hydrodynamic forces were determined using Morison's equation. The effects of the ISW amplitudes, riser configurations, seabed stiffnesses, and pipe-soil models on the structural dynamic responses were investigated. The results showed that the ISW packets rapidly increased the penetration depth of the TDZ. Trench formation changes the bending moment response of the TDZ in subsequent ISWs, increasing the response of the front section and decreasing the response of the latter section. However, its effect on the riser tension is limited. The steel lazy wave riser (SLWR) has significantly larger displacement and bending moment responses in the TDZ than SCR because of the different riser tension and configuration. Different pipe-soil interaction models exert a significant influence on the penetration depth and the variation of the bending moment in the TDZ. • Dynamic analysis of SCRs under multiple ISWs considering soil stiffness degradation and trench formation. • A nonlinear numerical model based on Vector form intrinsic finite elements and an improved pipe-soil interaction model. • Quantitative analysis of displacements, pipe-soil interactions, tensions, and bending moments of the touchdown zone. • Impact analysis of ISW amplitudes, seabed stiffnesses, pipe-soil models, and riser configurations. [ABSTRACT FROM AUTHOR]

The objective of this study is to assess the ultimate strength of box girder using equivalent single layer (ESL) approach. Box girders, composed of stiffened panels, are subjected to a four-point bending load for the ultimate strength analysis. The results of ESL were validated using FEM and experiments. Modeling of ESL includes a single plate with the same stiffness as the actual stiffened panel topology, as opposed to traditional FEM modeling and test specimen, where the stiffener is explicitly modeled. For ESL approach, VUGENS subroutine in Abaqus software is used to define the non-linear stiffness properties. Material and geometric non-linearities were considered during simulations. The ESL stiffness matrix was derived from unit cell simulations under six loading conditions. In this case, a unit cell is a periodic structure that represents the entire stiffened panel model. Contact interaction is utilized to simulate the controlled movement of a hollow cylinder contacting a box girder, a precise modeling approach essential for comprehensive analysis. The explicit dynamic analysis is used to allow the large deformation and non-linear material behavior on stiffened panels. The effect of initial imperfection, residual stress, and stiffener slenderness on the ultimate strength was studied. The ultimate strength of a box girder is determined by its maximum bending moment. According to the results, the ESL model achieves results similar to the traditional FEM model and experiment. The accuracy of ESL to FEM in the ultimate strength assessment varies depending on the magnitude of residual stress and initial imperfection applied to the stiffened panel. [Display omitted] • The ultimate strength of box girder under bending load using equivalent single layer approach is analyzed. • VUGENS subroutine is invoked for explicit analysis in Abaqus. • Material and geometric non-linearities were considered. • The effect of initial imperfection, residual stress, and stiffener slenderness on the ultimate strength is investigated. [ABSTRACT FROM AUTHOR]

With the development of offshore wind power energy, the monopile-wheel composite foundation has attracted wide attentions from scholars as an innovative foundation for offshore wind turbines (OWTs). And in offshore engineering, the local scouring usually tends to weaken the bearing capacity by moving surrounding soil till even become a non-negligible reason for some engineering disasters. To explore this effect of local scour qualitatively and quantitatively, the scouring morphology of the monopile-friction wheel composite foundations under unidirectional flow are obtained by means of CFD. Then, a 3D finite element model is developed to estimate the bearing behaviors and deformation characteristics with the consideration of various scouring conditions. Both internal forces and failure envelopes under H-T combined loads are also obtained through numerical analysis. The results reveal that key scouring parameters significantly affect the bearing capacity and envelopes shrinkage of the composite foundation. In particular, the scouring depth has the greatest effect on lateral and torsional bearing behaviors of 15%–32% and 24%–58%, respectively, followed successively by the scouring angle and extent. And the loading point height has a noticeable impact on the lateral resistance of the composite foundation. The findings provide valuable insights into understanding the load bearing behaviors of composite foundations and their practical application in engineering. • Through CFD, the morphology of monopile-wheel composite foundations under unidirectional flow is simulated and the morphology is simplified to evaluate the local scour. • Through numerical simulations, the influence of key scouring parameters and different loading point heights on the bearing capacity for the monopile-friction wheel composite foundation is obtained. • The distribution of the bending moment and torque along the monopile is explored, taking into consideration different parameters. • The failure envelopes for the composite foundations under H - T combined loads with the consideration of key scouring parameters are also obtained. [ABSTRACT FROM AUTHOR]

Ship propulsion shafting is inevitably subject to various uncertainties during navigation. Uncertain numerical models can reflect the dynamic behaviour of the shafting more accurately, enabling the dynamic alignment. This review investigates the progress of research on two type of uncertainty modelling methods, stochastic finite element and nonparametric modelling, in the dynamic alignment of shafting. First, the development of the alignment of ship propulsion shaft systems is outlined, and the calculation methods are summarised according to different alignment principles in two directions: static and dynamic. Second, the uncertainties affecting the ship propulsion shafting are distinguished, and the corresponding modelling methods are applied. i.e., stochastic finite element methods for data uncertainty and nonparametric modelling methods for nonparametric uncertainty. Both the methods are discussed detailedly, including the basic principles, constraints, advantages, and limitations. Then, propulsion shafting dynamic characteristics, such as bearing loads, bending moments, and bending angles, are described under various uncertainties. Additionally, the root mean square value of vibration at the bearing seat and the spectral and natural characteristics will be analysed to determine the uncertainty of the shafting. Finally, the development of both methods for the alignment of ship propulsion shafting is described, as well as the future research directions. • This paper provides an overview of ship propulsion shafting alignment technology development and limitations. • The uncertainties affecting the shafting are distinguished, and the corresponding modelling methods are applied. • This paper describes how SFEM and non-parametric modeling methods can be used to shafting alignment. • Recommended future directions for ship propulsion shaft alignment. [ABSTRACT FROM AUTHOR]

Floater structural flexibility plays a significant role in accurate predictions of global dynamic responses of floating wind turbines (FWTs), especially for ultra-large wind turbines with increasing size and cost-effective floater design. The conventional analysis of FWTs often considers the floater as one rigid body, which cannot capture the correct resonant responses of the floater (especially the column that supports the tower). In this paper, a new approach where the floater is divided into multiple rigid bodies connected by flexible beams is developed for advanced modelling of flexible floaters in combination with coupled time-domain simulations. The hydrostatic and hydrodynmaic loads on each body from a one-body hydrodynamic analysis, together with gravitational loads and inertial loads, are implemented in the beam-based finite element model of the floater to carry out a time-domain analysis. The proposed approach is used to compare the responses of a 15-MW semi-submersible FWT considering a rigid and a flexible floater. The inclusion of floater flexibility reduces the tower natural frequency. It leads to larger bending moment amplitudes at the tower base close to the tower bending natural frequency, particularly in only-wind, irregular wave and wind-wave conditions, but smaller dynamic responses in regular wave conditions. • A new approach to model the floater flexibility of floating wind turbine. • Global dynamic responses are compared under the rigid and flexible floater. • The tower bending natural frequency is decreased for the flexible floater. • The floater flexibility significantly affects the responses around the tower bending natural frequency. [ABSTRACT FROM AUTHOR]

As important equipment for deep-sea oil and gas development, risers are subjected not only to external ocean environmental loads but also to internal drilling pipe contact collisions. In this study, a dynamic analysis model of the riser system considering the contact collision of drill pipe in drilling operation is established. Moreover, the contact stiffness method is used to describe the contact collision force between the drill pipe and riser. The model is discretized using the finite element method and solved using the Newmark-β method. The dynamic characteristics of the riser under the action of the marine environment and drilling conditions are analyzed. In addition, the corresponding safety protection measures are put forward for the contact collision between the drill pipe and riser. The results show that the collision force between drill pipe and riser is the largest in the initial period, and the contact form is gradually stable. The distribution of the collision force is basically consistent with that of the bending moment, and the collision force and collision probability are the largest near the water surface and at the flexible joint of the bottom end, which is easy to cause column wear failure. The collision force and collision probability of the drill pipe and riser increase with the increase of platform offset and sea current velocity but decrease with the increase of top tension and bit pressure. The increase of the top tension and the increase of the platform offset will reduce the contact area between the drill pipe and the riser. • The dynamic analysis model of the riser system considering the contact collision of drill pipe is established. • The contact stiffness method is used to describe the contact collision force between the drill pipe and riser. • The distribution characteristics of the contact load between drill pipe and riser are mastered. • The collision mechanical properties under different working conditions are discussed. • The contact load near the water surface and the flexible joint of the bottom end is larger. [ABSTRACT FROM AUTHOR]

Effective and convenient prediction of the peak displacement of piles under collision conditions facilitates the design framework preparation and pile damage evaluation. Hence, an energy-based method was proposed to predict the peak displacement of the widely used steel casing composite (SCC) piles under impact loading. The pile deformation energy was first calculated based on its deformation characteristics and the relationship between the sectional bending moment and curvature. The pile deformation energy and pile–soil energy distribution ratio were then employed to determine the relationship between the total absorbed impact energy and pile head displacement, which was represented by curves. The peak pile displacement under lateral impact loading was finally obtained by interpolating the absorbed impact energy curves. By conducting sectional analysis of the pile considering the strain rate effects and using a structural pushover procedure, the peak pile head displacements for various collision cases were predicted with reasonable accuracy. The effectiveness and reliability of the proposed method were verified by comparing its results with those of previous reduced-scale impact tests and validated full-scale finite element models. • An energy-based method was proposed to predict the peak displacement of the SCC pile under lateral collision. • The proposed method required only impact energy input, sectional analysis, and pushover procedure. • The deformation and energy distribution characteristics of piles under static and impact loading were similar. • The SCC piles had two deformation forms: a single plastic hinge and a double plastic hinge. • Pile deformation energy was derived from its deformed shapes and the sectional bending moment–curvature relationship. [ABSTRACT FROM AUTHOR]

Fatigue damages of an offshore wind turbine (OWT) would be caused by long-term wind and wave loads, necessitating the importance of fatigue life analysis to ensure the in-service behaviors of OWT. This study evaluates the fatigue damage and predicts the fatigue life of OWT considering full-directional wind inflow under the coupling effects of non-Gaussian wind field and wave. The forces and bending moments are assessed in three types of the wind field, i.e., Gaussian, softening non-Gaussian, and hardening non-Gaussian, according to the Kaimal spectrum by using OpenFAST. The dynamic responses of OWT are implemented by a three-dimensional finite element model (FEM) established by ABAQUS. The fatigue life is assessed in the tower base section and the pile of OWT under different loading combinations. Results show that the crack initiation life is greatly affected by the non-Gaussian wind field, while the crack propagation life is not that sensitive. The fatigue life of OWT under a full-directional wind inflow is approximately three times longer than that under a single-directional wind inflow. It is recommended to consider full-directional wind inflow in the non-Gaussian wind field for OWT design. • It is found that the crack initiation life is greatly affected by the non-Gaussian wind field. • The fatigue life of OWT under a full-directional wind inflow is longer than that under a single-directional wind inflow. • It is recommended to consider full-directional wind inflow in the non-Gaussian wind field for OWT design. [ABSTRACT FROM AUTHOR]

The ship shaft alignment is crucial to achieve a high-performance propulsion system. This alignment is carried out, still in drydock, by adjusting the bearings' offsets. However, there are numerous available combinations sets of vertical offsets which results in good alignment final condition. Defining an optimum set of vertical displacements is costing shipyards a valuable time. Therefore, this work proposes the use of machine learning algorithms to predict if a given set of offsets, following the mandatory rules in force, should be implemented or not. In this manner, this paper presents a case study where a finite element model of an Anchor Handling Tug Supply (AHTS) vessel' shaft line was assembled in order to obtain the bearings reactions, shaft line deflections, shear forces, bending moments and, finally, the influence coefficients matrix (ICM). Those data were used to feed machine learning (ML) models based on four different algorithms, namely, K-Nearest-Neighbors, Extremely Randomized Trees, Random Forest and Gradient Boosting in order to solve multiclass classification problems concerning the offset's set to be applied in the alignment of the shaft line. Results showed that the Gradient Boosting and Random Forest algorithms presented the best results, achieving up to 98.1% of precision in one of the 36 scenarios tested, and an average precision above 96.0%. Such results corroborated with the authors' proposal to implement ML techniques as a way to speed up the currently very time-consuming shaft alignment process. • Machine learning algorithms applied in ships shafting system alignment. • Techniques to predict if the bearings' offsets return an aligned shaft system. • Machine learning classification models applied in shaft alignment. • Influence coefficients matrix verifying the shaft system alignment. • Stiffness method calculating bearings reactions. [ABSTRACT FROM AUTHOR]

Numerical investigation is conducted in this paper on both intact and dented seamless metallic pipelines (diameter-to-thickness ratio D / t around 21), deploying nonlinear finite element method (FEM). A full numerical model is developed, capable of predicting the residual ultimate strength of pipes in terms of bending capacity ( M c r ) and critical curvature ( κ c r ). The simulation results are validated through test results by using the measured material properties and specimen geometry. An extensive parametric investigation is conducted on the influences of material anisotropy, initial imperfection, friction of the test set-up and dent parameters. It is found that the structural response is quite sensitive to the frictions that have been introduced by the test configuration. For a pipe with a considerable dent size, the effect of manufacturing induced initial imperfection is insignificant and can be neglected in the FEM simulation. The material yield stress in the pipe longitudinal direction dominates the bending capacity of structures. In the end, formulas are proposed to predict the residual ultimate strength of dented metallic pipes under pure bending moment, which can be used for practical purposes. A satisfying fit is obtained through the comparison between the formulas and FEM methods. [ABSTRACT FROM AUTHOR]

The piled-raft foundation is usually adopted to support the offshore structures. In the present study, a large piled-raft has been simulated numerically through 3-D finite element modeling. The objective of the present study was to investigate the effect of pile spacing, pile length, pile diameter and raft-soil stiffness ratio on the settlement, load-sharing, bending moments, and shear force behavior of large piled-raft foundation. The results indicated that with increase in pile spacing up to the 5 to 6 times of the pile diameter, both average settlement ratio and differential settlement ratio decreased effectively and thereafter it increased gradually. Raft with smaller raft-soil stiffness ratio and larger pile group to raft width ratio observed to be effective in decreasing the average settlement ratio. The load-sharing ratio decreased with increase in pile spacing whereas; it increased with increase in pile length. With increase in pile spacing, bending moment ratio increased and as the length of pile increased bending moment ratio decreased up to pile group to raft width ratio of 0.6 and thereafter it increased. [ABSTRACT FROM AUTHOR]

This paper proposes design principles of a new concept prismatic pressure vessel that is primarily constructed of plane surfaces. These principles were compared with those of conventional pressure vessel which is primarily constructed of revolutionary surfaces. Considering structural characteristics of prismatic pressure vessel, membrane force and bending moment were calculated individually. Formulas including maximum bending moment and membrane force effects were illustrated by applying Levy's method and superposition method. For total stress at the plate of the pressure vessel, membrane force effects obtained from the shear loads of adjacent plates were included to enable to get more accurate solutions. The proposed simplified formulas for prismatic pressure vessel were suggested so that they can be applied for all dimensions and thicknesses. Case studies were conducted to verify the formulas by comparing with FEM results. By providing an overview of the stress relations of a non-stiffened type prismatic pressure vessel, the design principle of a prismatic pressure vessel shows distinctive concept to the conventional cylindrical pressure vessel. The membrane force effect studied in this research will be useful in the design of larger pressure vessels that require stiffeners. [ABSTRACT FROM AUTHOR]

This paper proposed a new three-dimensional numerical model of the integral vertical transport system (VTS) in deep-sea mining using the vector form intrinsic finite element (VFIFE) method. The method shows great advantages in solving complex dynamic behavior problems of VTS with large differences in mechanical properties and strong geometric nonlinearity. The governing equations are established according to Newton's second law and solved in the time domain by the central difference method. The simulation program for predicting the nonlinear dynamic behavior of VTS is developed with MATLAB and verified with the results of relevant literature. Then, a parameter sensitivity analysis is conducted to investigate the influences of the amplitude and period of the top vessel motion, current velocity, internal flow velocity and buffer mass on the VTS dynamic characteristics. The results show that the heave motions of the vessel are the most adverse motion state to the rigid pipe stress. The influence of the internal flow velocity on the system tension is significantly greater than the bending moment. The rigid pipe, which exhibits a higher sensitivity to each parameter than the flexible pipe, is the weakest area that needs more attention in the design. • A new 3D model of the integral deep-sea mining system including the rigid pipe, buffer and flexible pipe is established. • Calculate the dynamic response of the deep-sea mining pipe by applying the vector form intrinsic finite element method. • The dynamics of the system was analyzed by considering the internal and external flow effects. [ABSTRACT FROM AUTHOR]

Most of the routine work concerning the design of laterally loaded monopile foundations is conducted using simplified one-dimensional (1D) models based on p-y curves. However, many of these curves have been derived from slender piles typically used in the oil and gas industry, which behave differently than rigid monopiles used as offshore wind turbine foundations. Moreover, these curves usually represent the soil response without considering its degradation, which may significantly modify the monopile lateral response. Hence, this work proposes a numerical methodology based on the finite element method to derive suitable curves for 1D models of monopiles installed in sand. First, a three-dimensional (3D) finite element model (FEM) of the monopile and the surrounding soil was constructed. In this model, the monopile had an elastic and linear material behavior. The soil response was addressed using the Mohr-Coulomb criterion combined with three different soil stiffness degradation models. For extracting the p-y curves from the 3D FEM, a 10th-order polynomial was used to fit the bending moment profiles; consequently, an 8th-order polynomial described the soil reaction profiles. Results obtained using the proposed 3D FEM and a 1D model based on the derived p-y curves were then verified against experimental results obtained through centrifuge modeling. Furthermore, the proposed 1D model adequately matched the experimental results, especially for small displacement conditions. • Soil stiffness degradation should be considered for a proper soil modeling. • Analytical stiffness degradation models can ease the numerical soil modeling. • Good agreement between numerical and experimental results. • Numerical 1D models based on the p-y method led to fast and accurate results. • Contact modeling was found to be significant during the unloading phase. [ABSTRACT FROM AUTHOR]

Cross-sea–cable-stayed bridges located in earthquake-prone areas can be subjected to earthquakes, wave action, and other dynamic loads of potential threats during their construction and service periods. The dynamic response of a cable-stayed bridge was studied under the combined effects of earthquakes and wave flow. In this study, a cross-sea–cable-stayed bridge is investigated as a prototype. ANSYS software was used to establish a spatial finite-element model, and CFD software was used to simulate the wave loads and calculate the fluid-structure coupling. The peak displacement at each location was determined under different loading conditions during the combined action of earthquakes and waves. The displacement at the top of the tower was the largest, followed by that at the main span. However, when the wave action was severe, the peak displacements of the tower top and main span were comparable, and these two peak displacements occurred simultaneously. The internal-force-response law at the bottom of the tower tended to be consistent, and only the peak values differed. The peak change in the shear force was smaller than that in the bending moment. Earthquakes and waves had a negative effect on bridges; however, they played a dominant role. Nevertheless, the presence of waves alters the dynamic response during joint action; therefore, the effect of waves on the bridge cannot be ignored. The root-mean-square (RMS) under the joint action of earthquakes and waves was evaluated using the RMS of superimposed independent earthquakes and independent waves. However, it can be observed that the joint effect is not a simple superposition effect. Complex interactions exist between the earthquakes and waves. • Using a cross-sea cable-stayed bridge as a background, a spatial finite element model of the bridge was established by ANSYS, and wave loads were simulated by CFD software. • Investigating the dynamic response of bridge key sections under the combined action of earthquakes and waves. • Proving that the combined effects of earthquakes and waves on bridges are not a superposition of dynamic responses, but a complex coupling between earthquakes and waves. [ABSTRACT FROM AUTHOR]

During installation, catenary risers exhibit low tension in the touchdown zone (TDZ) of the seabed. Manufacturing deviations in the riser and the yaw rotation of the installation vessel may induce the unbalanced distribution of torsion. Combined with tension, loop formation may occur and lead to extreme damage. This study established a finite element model (FEM) for a steel catenary riser (SCR) using OrcaFlex software to analyze the effect of a nonlinear uneven seabed on loop formation. Four typical uneven seabed profiles, including a trench, an upheaval, a depression, and a slope, were constructed, while five key nonlinear seabed soil parameters, including mudline shear strength (S um), shear strength gradient (ρ), suction ratio (f suc), suction decay parameter (λ suc), and normalized maximum stiffness (K max) were proposed for parametric analysis to summarize the response rules of maximum tension, maximum compression and maximum bending moment of the riser loop. A specific sea area was selected for the case study to verify the applicability of the response rules. The case study also confirmed that the uneven seabed profile and nonlinear seabed soil properties had a combined effect on the riser loop, further preventing loop formation and reducing subsequent damage. • A finite element model for the catenary riser with loop formation in complex environment is established by using OrcaFlex. • The influence of seabed morphology including four typical uneven seabed profiles on the loop formation is analyzed. • The influence of nonlinear seabed soil properties including five key parameters on the loop formation is analyzed. • The applicability of the response rules and the combined effect of seabed profiles and soil properties are verified. [ABSTRACT FROM AUTHOR]

Crane, an important platform to carry and move cargo in the ports, can evidently affect the overall response of pile-supported wharf system. In many earlier analytical studies, the crane was simply represented by a lumped mass. Such modeling is unable to realistically replicate the salient response characteristics of crane-wharf interaction system. To investigate such interaction effects, a three-dimensional (3D) finite element (FE) model of a typical crane-wharf system is developed. As such, the static/dynamic response of pile-supported wharf with/without crane are systematically studied and directly compared. In addition, global sensitivity analysis is conducted to explore the effects of input parameter uncertainties on global response of crane-wharf system. From the computed results, it is shown that: (1) both the static and dynamic response are considerably dependent on the crane-wharf structure as an integral global system; (2) the bending moment and displacement of pile are more sensitive to the friction angle of soil stratum near pile tip; and (3) the interaction effect among various uncertainty parameters becomes more significant with consideration of crane. Overall, the 3D FE analysis technique and the derived insights provide a useful reference and guidance for evaluation of similar crane-wharf interaction system under static/dynamic loading conditions. • A three-dimensional finite element model of crane-wharf system is created. • Effect of crane on static and dynamic response of wharf is investigated. • Influence of input parameter uncertainty on dynamic response of wharf is evaluated. [ABSTRACT FROM AUTHOR]

The interaction between shallow pipe and soil near the subsea wellhead is an important factor in the maintenance of subsea wellhead stability. First, a seismic test was conducted. A shaking table and a shear model box were used to measure the displacement and acceleration of the model under earthquake conditions. The effects of different soil layers on the dynamic response of the pipe were compared and analyzed. Subsequently, a dynamic finite element model of shallow pipe and soil was established. The weakening effects due to earthquakes and waves were considered in the soil model. Based on Hamilton's principle, the dynamic partial differential equations for a shallow pipe were derived and discretized into finite element equations via the weighted residual method. The liquefaction process of submarine soil under seismic force and the dynamic response of shallow pipe were simulated. The simulation results were compared with those of the test, and the accuracy of the finite element model was verified. The displacement, angle, bending moment and shear force of shallow pipe were calculated and compared. The increasing process and law of soil pore pressure were analyzed. Soil liquefaction caused by earthquake has great influence on the stability of shallow pipe. • The dynamic experiment of shallow string in offshore drilling was carried out by using shear model box. • A submarine soil weakening model considering both earthquake and wave action is established. • Based on Hamilton's principle, the dynamic partial differential equations of shallow pipe are derived. [ABSTRACT FROM AUTHOR]

Corrosion is a common type of defect that causes failure of oil and gas pipelines. Pipelines often bear the combined loadings of axial compression force, bending moment and internal pressure in operation; therefore, it is of great significance to study the reliability of pipeline under different combined loadings. First, this work established a nonlinear finite element model of corroded pipeline for the typical internal corrosion defects of groove shape, and the reliability of the model and the accuracy of the finite element analysis method are verified. Then the burst pressure of pipeline under combined loadings is investigated. Second, this work established the BP network analysis and prediction model. The results of numerical simulation are used as samples to train the neural network. The prediction limit function value is output through the forward simulation function, which is compared with the objective function to judge whether the pipeline is reliable. Finally, back propagation neural network model calculated the reliability of pipeline under different working conditions combined with Monte Carlo method. The effects of load, corrosion depth, axial corrosion length, circumferential corrosion width and variation coefficient of parameters on pipeline reliability are analyzed. It is found that axial force and bending moment affect the reliability of corroded pipeline. Generally, the higher the combined loadings are, the lower the reliability is, but this law will be different due to the influence of corrosion parameters. In addition, the corrosion depth has the greatest influence on the reliability of corroded pipeline, followed by the corrosion width and the corrosion length. The coefficient of variation of corrosion depth has a great influence on the reliability of pipeline with high depth corrosion defect. These conclusions can provide references for the reliability evaluation of pipelines. • The burst failure of corroded pipeline under combined loadings is investigated. • Reliability analysis of corroded pipeline based on yield limit state. • MC and back propagation neural network are developed to calculate reliability. • The influence of various parameters on pipeline reliability is analyzed. [ABSTRACT FROM AUTHOR]

Various hybrid systems combined with several foundation elements have been proposed to improve the lateral performance of monopiles. Among them, the hybrid monopile-bucket foundation which consists of a traditional monopile and a wide-shallow bucket has received more and more attention and has been used in offshore wind pilot projects for supporting OWTs. However, deep insights into its monotonic and cyclic responses are still lacking. This study aims to understand the monotonic load-bearing, the evolution of cumulative displacement, stiffness and bending moment of the hybrid foundation in soft clay. A series of centrifuge model tests were conducted to simulate a hybrid monopile-bucket foundation and a monopile subjected to lateral monotonic and multi-stage cyclic loading. The monopile with the identical pile diameter and embedded length is used as a benchmark. The experimental results show that by the addition of the bucket, the hybrid foundation shows a 30.1% increase in ultimate capacity. Compared to the monopile, the cumulative displacement, unloading stiffness and the growth of bending moment of the hybrid foundation during cyclic can be reduced by up to 25%, 30% and 35.3%, respectively, implying the effectiveness and superiority of the hybrid foundation. Apart from the centrifuge tests, supplementary three-dimensional finite element analyses have also been performed to reveal the bearing mechanism and the sharing ratios of external load and moment carried by the single pile and the bucket of the hybrid foundation. The test and numerical results presented in this study are expected to provide design references for further practical applications of the hybrid foundations. • The monotonic and cyclic responses of the innovative hybrid foundation are investigated through a series of centrifuge tests. • The responses of the hybrid foundation are compared with those of the monopile with identical pile diameter and embedded length. • The feasibility and effectiveness of the hybrid foundation in resisting lateral load have been demonstrated. • Load-bearing mechanism of the hybrid foundation has been revealed through numerical analysis. [ABSTRACT FROM AUTHOR]

The subsea wellhead is a key equipment for offshore oil and gas development. Traditional research focuses on static stability of subsea wellhead system in which the dynamic effect is neglected. In this paper, a drilling platform/riser/wellhead/conductor fully coupled dynamic model is established to evaluate the dynamic stability of subsea wellhead system. An algorithm for solving the fully coupled dynamic model is proposed based on finite element method and Newmark integral method. A fully coupled analysis program is also developed in MATLAB to conduct the dynamic stability evaluation of subsea wellhead system based on the proposed fully coupled model and solving algorithm. Simulation results show that the maximum dynamic response of subsea wellhead system is obviously larger than static response. That is, the subsea wellhead system is likely to be unstable with dynamic loads. The depth of wellhead dynamic displacement and bending moment induced by dynamic loads reaches 32 m and 45 m under mudline, respectively. The dynamic response value appears an inflection point at a certain depth under the mud line. The subsea wellhead system vibrates in the opposite direction before and after the inflection point. • A drilling platform/riser/wellhead/conductor fully coupled dynamic model is established. • An algorithm for solving the fully coupled dynamic model is proposed. • A fully coupled analysis program is developed in MATLAB. • The subsea wellhead system is likely to be unstable with dynamic loads. • The subsea wellhead system vibrates in the opposite direction before and after the inflection point. [ABSTRACT FROM AUTHOR]

Low-cost midsize workover operation based on deepwater workover riser system is attractive. However, a comprehensive theoretical mechanical model for the complex workover riser system has not been found in present studies. In this paper, a coupled mechanical model of the workover riser system is established based on Euler-Bernoulli beam theory, hydraulic-pneumatic principles and the coupling relationship among workover risers, split tensioner system and workover platform. An analysis method for the coupled mechanical model is proposed based on the finite element method, Newmark- β method and Newton-Raphson method. A mechanical analysis program is finally developed in MATLAB and applied in mechanical property analysis of a deepwater workover riser system. It turns out that the bending moment of the workover riser system near the top part, tension ring and bottom part reaches extremes. Dynamic response envelopes of the workover riser system are obviously larger than static responses due to the dynamic excitation of wave loads and platform motions. It is also found that tension distribution ratio has obvious influence on mechanical properties of workover riser system. Mechanical response of the workover riser system decreases with TDR, whether in static or dynamic analyses. • A theoretical mechanical model of workover riser system is established. • Mechanical analysis method and program for workover riser system are developed. • Mechanical properties of workover riser system are identified. • The tension distribution ratio has obvious influence on mechanical properties of workover riser system. [ABSTRACT FROM AUTHOR]

This paper presents a Python-based scheme for simulating the hydroelastic response of very large floating structures (VLFS) under extreme conditions which are represented by focused wave groups. Applying the modal expansion method, we decouple the fluid-structure problem into a hydrodynamic problem in terms of velocity potentials for the fluid and a mechanical problem for the structure. The hydrodynamic problem is solved by the higher-order boundary element method in the frequency domain, while the structural analysis is performed by a time-domain finite element model. In order to validate the proposed scheme, numerical simulations are carried out on a scaled model of VLFS in regular and random waves. Both analytical and discrete numerical modal shape functions are used for representing the elastic deformations. The Mindlin plate theory is used for the finite element model. Extensive convergence studies of finite element model meshes, hydrodynamic model meshes and elastic mode numbers are carefully carried out. Good agreements of the vertical displacement, bending moment and shear force amplitudes of the floating plate are found between the predictions of the present model, and experimental data and numerical results in the literature for regular and random waves. The hydroelastic responses of the scaled model in focused wave groups are then investigated. A modified NewWave model is proposed to generate focused pressure in linear wave groups, and the results show the effectiveness of the proposed model. Influence of the focal position, water depth, incident wave angle, and peak spectrum frequency and bandwidth of the focused wave groups on the hydroelastic response of the plate is also studied. The proposed approach is shown promising for hydroelastic analysis for more complex VLFS in realistic sea states. • A Python-based framework has been developed for efficient hydroelastic analysis of VLFS in focused wave groups. • Coupled frequency- and time-domain approach has been employed by making use of advanced simulation tools. • Displacement, shear force and bending moment agree well with published experimental and numerical results. • Effects of various parameters on VLFS hydroelastic responses in focused waves have been extensively illustrated. [ABSTRACT FROM AUTHOR]

This paper numerically investigates the ultimate strength of sandwich box girders under vertical bending and torsion. The finite element modeling of the box girders is verified by the comparison between the test and numerical results. Seven sandwich box girders with different geometric dimensions are designed based on the prototype stiffened box girder according to the criteria of equal cross-sectional area. A series of nonlinear finite element analyses for the sandwich box girders are carried out with the prototype stiffened box girder being considered as a reference. The results show that the ultimate strength of the designed sandwich box girders is larger than that of the prototype stiffened box girder under the sagging, the maximum increase being 21.8%. With the increase of the face plate thickness and decrease of the web plate thickness, the warping stress increases in the sandwich box girders, and thus the ultimate bearing capacity is reduced. The interaction relationships of the box girders are obtained by the curve fitting method, and the effect of geometric dimensions of the sandwich deck on the safety margin is figured out. The safety margin for the prototype stiffened box girder is the lower bound of those for the sandwich box girders, which can be used to make conservative assessments of the ultimate strength under combined vertical bending and torsion. • Web plate spacing of sandwich deck has a significant effect on ultimate sagging moment. • Thinner face plate of sandwich deck will cause larger warping stress. • Effect of laser weld rotation stiffness on ultimate strength of sandwich box girders is not significant. • Safety margin for prototype stiffened box girder is the lower bound of those for sandwich box girders. [ABSTRACT FROM AUTHOR]

This paper presents the jack-up unit reinstallation loads in clay when it has to be reinstalled near an existing footprint due to a previous installation and removal. Large-deformation finite element analyses are performed by using the coupled Eulerian-Lagrangian (CEL) method. A three-leg jack-up unit model is used for the global investigation of the spudcan-footprint interactions. The novel rectangular-shaped flat-based spudcan is considered. A detailed parametric study is carried out with varying influential factors including spudcan shape, offset distance and footprint shape. The effects of these factors are evaluated based on the magnitudes of induced bending moment, horizontal force, lateral displacement and rotation. Compared to the generic conical spudcan, the novel spudcan reduces the peak horizontal force, lateral displacement and rotation by 40%. But it has a larger bending moment at the spudcan level, due to the corner effect. It is found that the bending moment at the hull level position is 800% larger than that at the spudcan level. The flat-based spudcan is effective at decreasing footprint-spudcan interactions, reducing the loads on the leg by about 30%. The critical offset distance is found to be that the spudcan center is at the edge of the footprint. • The novel spudcan with a rectangular shape and flat base is considered and investigated. • The three-legged jack-up unit model and simplified undrained shear strength contour in the footprint are considered by using the Large Deformation Finite Element method. • Response forces and soil flow pattern of the novel spudcan are compared with the generic conical spudcan and the circular flat-based spudcan. [ABSTRACT FROM AUTHOR]

Cylindrical shell is a common structural design solution in many engineering fields, such as the foundation supporting structures and buoyant column of the offshore wind turbine in the maritime sector. Operating in an ocean environment, these cylindrical shell structures need to withstand a combination of axial compression, bending moment, torsion and external pressure. This study contributes a parametric investigation for unstiffened cylindrical shells subjected to axial compression. Emphasis is placed on the ultimate strength characteristics and their relation with the initial geometric imperfection. The nonlinear finite element method is adopted by considering geometric and material nonlinearities in conjunction with an arc-length incrementation to solve the governing equilibrium equation. The numerical prediction is compared with the prevailing code-based approach, i.e. DNV, ABS, API and Eurocode. This study shows that the ultimate strength of unstiffened cylindrical shells in axial compression is highly sensitive to initial geometric imperfection. The code-based formulae appear to be overly conservative for predicting the ultimate compressive strength of cylindrical shells. • Numerical collapse test of unstiffened cylindrical shell under axial compression. • Different imperfection shapes in longitudinal and circumferential directions are analysed. • Comparison is completed between the numerical prediction and code formulae. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the results of an investigation of the effect of lateral pressure on the progressive hull collapse behaviour of a double-hull oil tanker subject to vertical bending moments in both the sagging and hogging conditions. As an illustrative example, a Suezmax-class double-hull oil tanker designed by the Common Structural Rules (CSR) method is considered. The ANSYS nonlinear finite element method (NLFEM) is employed for the progressive hull collapse analysis. The effects of lateral pressure – static (anchored condition) and dynamic (operating condition) – are investigated in both the full-load and ballast conditions. To check the accuracy of ultimate hull girder strength analysis methods, Dow''s test hull is also applied together with Suezmax class oil tanker under conditions of vertical bending moment but without lateral pressure loads. In this regards, the NLFEM method is compared with ALPS/HULL intelligent supersize finite element method (ISFEM) programs and International Association of Classification Societies (IACS) CSR method, which applies the idealized structural unit method (ISUM) (also called the Smith method). The important insights developed from the present study are documented. [Copyright &y& Elsevier]

Abstract: This work deals with the evaluation of the ultimate bending moment of two box girders subjected to different levels of corrosion degradation and experimentally tested under pure vertical bending moment. A series of nonlinear finite element analysis have been conducted. Two models of corrosion degradation have been used representing an average general corrosion thickness reduction, and the real corrosion thickness as it is measured. Based on the real corrosion measurements, experimental ultimate strength and finite element calculations, a relationship has been developed to predict the expected difference in the ultimate strength calculations based on the FE models representing the corrosion degradation as an average thickness reduction or as the real measured corrosion reduction. [Copyright &y& Elsevier]

Abstract: In this paper, the ultimate strength of open box girders with crack damage subjected to pure torque, compressive force, bending moment and combined loads is investigated using a commercial FEA program, ABAQUS. The ultimate strength reduction characteristics of the box girders due to cracking damage as a function of crack types, crack sizes and crack locations are studied. Based on the numerical results obtained from the present study, a simple model for predicting the residual ultimate strength of open box girders with crack damage under single load and combined loads is proposed. The suggested model has a simple form yet well represents the lower bounds of the reduced ultimate strength due to crack damage. [Copyright &y& Elsevier]

In order to investigate the liquefied soil pressure inposed on an individual pile of pile group, a centrifugal shake table test on a pile-supported wharf on the sloping saturated sand stratum has been designed and implemented in this study. Final test results, including processing results of free-field soil responses as well as lateral displacements at the deck, are presented and discussed in detail. Analysis of pile bending moments of pile group shows that seaside pile bottom can come under more bending moment in contrast to landside piles, and the bending moment seems greater at pile top and bottom. A simplified finite element model has been constructed for an accurate analysis of liquefied soil pressure arising from lateral soil flow, where triangular soil pressure and uniform soil pressure need to be calibrated according to the measured monotonic bending moment of piles. Furthermore, comparisons with the current distribution law were made using the experimental outcomes. Finally, for investigating the effect of pile connection point rotational stiffness, parametric studies were carried out. • Seismic behavior of the soil and pile-supported wharf in liquefiable sloping stratum is presented and analyzed. • A finite element modeling is developed to investigate liquefied flow soil pressure scenarios on the pile group. • Two force-based design guidelines from JRA and JSWA are further calibrated. • Influences of key factors on the behavior of pile-supported wharf are examined. [ABSTRACT FROM AUTHOR]

The interaction between an oceanic internal solitary wave (ISW) and a prototype submerged floating tunnel (SFT) is numerically investigated. Effect of oceanic internal solitary wave amplitude, the relative distance of the SFT to the pycnocline, cross-sectional geometry of the SFT, and the density ratio of the two fluid layers are analyzed. At a potential application site, the dynamic response of an SFT composed of a tube-joint-mooring system forced by an oceanic ISW is studied using Finite Element Method (FEM) modeling. The numerical results show that the ISW-induced force can be effectively reduced by adopting a parametric SFT cross section instead of a circle or ellipse. The influence of the relative distance of the SFT to the ISW pycnocline is crucial, and can remarkably alter the vertical force and buoyancy-weight ratio (BWR) of the SFT during ISW propagation. Large shear forces and bending moments on the SFT can occur, affecting the tension in the mooring lines, and threatening the safety and reliability of the SFT system. However, the deflections and accelerations of the SFT under the applied ISW are within structural serviceability requirements due to the low frequency of the ISW compared to the natural frequency of the SFT tube. • The mechanism of interaction between an internal solitary wave and submerged floating tunnel is revealed. • The influences of internal wave amplitude, cross-sectional shape, relative distance to the pycnocline, and fluid density ratio on the internal wave and structure interaction are quantified. • A numerical model of a prototype submerged floating tunnel composed of a coupled tube-joint-mooring system is established. • Dynamic response of the submerged floating tunnel is numerically simulated under an internal solitary wave. [ABSTRACT FROM AUTHOR]

Abstract: Three-dimensional hydroelasticity theory is used to predict the hydroelastic response of flexible floating interconnected structures. The theory is extended to take into account hinge rigid modes, which are calculated from a numerical analysis of the structure based on the finite element method. The modules and connectors are all considered to be flexible, with variable translational and rotational connector stiffness. As a special case, the response of a two-module interconnected structure with very high connector stiffness is found to compare well to experimental results for an otherwise equivalent continuous structure. This model is used to study the general characteristics of hydroelastic response in flexible floating interconnected structures, including their displacement and bending moments under various conditions. The effects of connector and module stiffness on the hydroelastic response are also studied, to provide information regarding the optimal design of such structures. [Copyright &y& Elsevier]