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Inspired by the local resonance mechanism, a resonant periodic structure (RS) constructed by an array of periodic floating oscillators is proposed for enhancing surface water wave attenuation. A hybrid frequency domain method is introduced for solving the linear or nonlinear initial-boundary value mixing problem. The numerical results show that the RS has a superior suppression effect on the propagation of waves in comparison with the Bragg periodic structure (BS) of the same scale. The incoming waves across the spectrum are substantially reduced by RS through the inverse propagation of radiation waves induced by the wave-driven oscillators. Furthermore, to achieve a better attenuation effect, a nonlinear resonant periodic structure which the periodic oscillators are integrated with the nonlinear stiffness mechanism (NSM) is proposed based on the idea of reducing equivalent stiffness. The motions of oscillators are regulated by the NSM, and the attenuation effect is further improved due to the modified radiation wave. The concept and results presented herein may provide forward-looking technical guidance for future coastal protection. [ABSTRACT FROM AUTHOR]

Subsea systems for oil exploitation and renewable offshore energy generally employ cables, hoses, risers, umbilical and power energy cables, mooring lines, among other slender components. From the global modeling perspective, all such "lines" can be well represented by classes of structural models according to phenomena of interest for each analysis—eg.: bending/torsion and/or tension/compression loads. In this context, one is frequently interested in static and dynamic effects. Moreover, geometric nonlinearities, hydrodynamic loads and contact with the seabed can play an important role. The present work proposes a general and robust numerical methodology able to establish and analyze complete offshore systems, composed of numerous lines attached to a floating unit. Catenary, lazy-wave, vertical, or other geometric configurations can be considered for each line. The initial guess for the system configuration is produced by a set of analytical solutions, considering a multi-segment extensible catenary formulation. This is implemented into an in-house numerical finite element framework, which models and solves the statics and dynamics of the system. We employ geometrically exact beam and truss models, handling all external loads of interest and contact interactions with the seabed. Case studies following the proposed methodology are exemplified, discussing details on modeling aspects, such as comparing results with other tools/methodologies. [ABSTRACT FROM AUTHOR]

Jacket structures play an ever-increasing role in meeting the world's burgeoning energy demand by providing support structure for exploiting offshore wind energy and oil and gas resources. Many of these structures are past their design lifetimes, and thus may have suffered significant degradation, highlighting the importance of investigating their earthquake response in seismically active regions. This study investigates the seismic performance of a typical offshore jacket platform, denoted as baseline structure, as well as four versions with two longer (25% and 50% larger) and two shorter (25% and 50% smaller) natural vibration periods accounting for two levels of degradation and retrofit effects on structural performance. For each case, eleven ensembles of ground motions compatible with the site's seismic hazard are selected using the generalized conditional intensity measure methodology. The loading uncertainty is incorporated in the performance assessment procedure via probabilistic seismic demand analysis and the demand hazard is quantified. The results provide valuable information regarding reliability of these structures both at design stage and during service life, which can aid decision-making around rehabilitation of older platforms, the suitability of reusing obsolete platforms beyond service lifetime, and risk-based design of new platforms. [ABSTRACT FROM AUTHOR]

Offshore structures are deployed extensively to harvest marine resources. Due to the harsh marine environments and heavy-duty working conditions, the risks associated with failure due to scour are high, and the need for accurate prediction of these risks is increasing. Often, pipelines and cables are critical elements of subsea energy transportation and telecommunication, and they are highly susceptible to scour-induced failure. The scour around spheres is relevant to the offshore industry as a simplified three-dimensional representation of subsea structures. This paper presents a numerical study, using FLOW-3D HYDRO, of the scour around on-bottom cylinders and spheres. Whereas most published research investigated scour around stationary solid objects, this paper presents numerical results of a more challenging case of scour around sagging cylinders and spheres. The model was validated against published experimental and numerical results. The scour depth was found to increase with the decrease of the sagging velocity of the solid object. For sagging horizontal cylinders, the scour depth reaches a plateau of 1.1 times the cylinder diameter when the dimensionless sagging velocity is smaller than 0.094. For sagging spheres, the maximum scour depth reaches 0.37 times the sphere diameter when the dimensionless sagging velocity is reduced to 0.0103. The findings provide guidelines for future research on more complicated interactions between flow, solid objects, and the seabed, accounting for the deformation of infrastructure over time. Practical Applications: This paper concerns the flow, sediment transport, and scour around horizontal cylinders and spheres undergoing slow downward motion, which resembles the sagging of on-bottom infrastructure under the influence of gravity and bed erosion. Offshore structures are deployed extensively to harvest marine resources. Pipelines and cables are critical subsea infrastructures that are susceptible to scour-induced failure. Spherical objects are commonplace in the offshore industry, so a sphere can be deemed as an idealized three-dimensional body. This paper provides detailed FLOW-3D simulations and developed empirical relationships between the dimensionless scour depth and dimensionless sagging speed. Most previous research considered only the scour around fixed objects, so this paper provides a novel addition to the existing knowledge on the scour phenomenon. The computational methods established in this study are useful for simulating more-complicated scenarios. The findings provide guidelines for more-realistic predictions of scour and for the design of scour mitigation measures. [ABSTRACT FROM AUTHOR]

This article describes a new method for the design of rectangular foundations in cohesionless soil subject to a combination of vertical and horizontal loads, overturning moments, and torsional moments. It can be seen as a supplement to the general bearing capacity equation in which possible torsional effects of horizontal loads are not included. Torsional effects have had an increasing interest and are common in the design of offshore structures, but onshore structures, such as wind turbines and masts, may also be subject to torsional loads, which can have a substantial effect on the design. The method, which is suitable for hand calculations, applies an equation proposed by Finnie and Morgan for a Tresca material and it is shown that this equation can be used for cohesionless soil for the design of rectangular footings subject to vertical and horizontal forces, overturning moments, and torsional moments. The new method has been compared with those of DNV (DNV: global quality assurance and risk management company in the maritime industry) "Recommendations on offshore soil mechanics and geotechnical engineering" and it is shown that it produces results that are considerably more advantageous than the DNV method. In addition, comparisons have been made with results produced by OptumG3 software, and it is shown that the method leads to safe design. Charts and equations suitable for practical design have been prepared and the equations have been implemented into a computer program, which can be obtained at no cost by contacting the first author. [ABSTRACT FROM AUTHOR]

During the construction of an offshore wind turbine (OWT) system, the lifting of the wind turbine blade requires setting up of jacks near preinstalled foundations, which could impact the existing adjacent foundations. To explore the movement characteristics of preinstalled caissons induced by the installation of rectangular footings, this study performs large deformation numerical analyses to quantify these influences. A numerical model is generated and validated against existing testing data in terms of penetration resistance of rectangular footings and soil deformation around the structure. An extensive parametric study is then conducted to quantify the influences of caisson aspect ratio, vertical distance between caisson and two rectangular footings, spacing between two rectangular footings, soil strength, the rectangular footing area, and roughness. It is found that the normalized distance between the caisson and the rectangular footing as well as the caisson aspect ratio play important roles in the movement of the adjacent caisson, with rotational angles of 0.05–0.9°, while the rest factors have limited impacts. Based on numerical results, empirical design formulae are proposed for estimating the maximum inclination angle of the caisson which can be used for engineering application. [ABSTRACT FROM AUTHOR]

This paper reviews the state-of-the-art progress of research into corrosion fatigue on marine structures, both theoretical and experimental. This includes corrosion fatigue life prediction models/methods, load-environment interaction/coupling test methods, accelerated corrosion methods in corrosion fatigue testing, fatigue crack measurement, and corrosion fatigue life assessment in the whole life period. To date, some theoretical models and methods for predicting the corrosion fatigue life of metallic materials or structures have been proposed and applied. Meanwhile, load-environment interaction/coupling testing on metallic material specimens has been maturely developed and widely applied. Some newly developed corrosion fatigue theoretical and experimental methods, based on data-driven machine learning and at-sea monitoring, have received preliminary application. This review of accelerated corrosion methods, fatigue crack measurement methods, and corrosion fatigue life assessment for marine structures in the whole-life period has been undertaken by extensive reference to relevant studies conducted worldwide. Challenges and recommendations for further developing and improving corrosion fatigue assessment methods and test techniques are also reported and discussed. [ABSTRACT FROM AUTHOR]

The fracture mechanism and macro-properties of SVSAC were studied using a novel test system combined with numerical simulations, which included three-point bending beam tests, the digital image correlation (DIC) technique, scanning electron microscopy (SEM), and ABAQUS analyses. In total, 9 groups and 36 specimens were fabricated by considering two critical parameters: initial notch-to-depth ratios (a0/h) and concrete mix components (seawater and volcanic scoria coarse aggregate (VSCA)). Changes in fracture parameters, such as the load-crack mouth opening displacement curve (P-CMOD), load-crack tip opening displacement curve (P-CTOD), and fracture energy (Gf), were obtained. The typical double-K fracture parameters (i.e., initial fracture toughness ( K IC ini ) and unstable fracture toughness ( K IC un )) and tension-softening (σ-CTOD) curve were analyzed. The test results showed that the initial cracking load (Pini), Gf, and characteristic length (Lch) of the SVSAC increased with decreasing a0/h. Compared with the ordinary concrete (OC) specimen, the P-CMOD and P-CTOD curves of the specimen changed after using seawater and VSCA. The evolution of the crack propagation length was obtained through the DIC technique, indicating cracks appeared earlier and the fracture properties of specimen decreased after using VSCA. Generally, the K IC un and K IC ini of SVSAC were 36.17% and 8.55% lower than those of the OC specimen, respectively, whereas the effects of a0/h were negligible. The reductions in Pini, Gf, and Lch of the specimen using VSCA were 10.94%, 32.66%, and 60.39%, respectively; however, seawater efficiently decreased the negative effect of VSCA on the fracture before the cracking width approached 0.1 mm. Furthermore, the effects of specimen characteristics on the fracture mechanism were also studied through numerical simulations, indicating the size of the beam changed the fracture toughness. Finally, theoretical models of the double-K fracture toughness and the σ-CTOD relations were proposed, which could prompt their application in marine structures. [ABSTRACT FROM AUTHOR]

Offshore Triceratops are classified as form-dominant structures possessing the novelty of counteracting the lateral loads with material strength and geometric form. The deck is supported by the buoyant legs, which are positioned on the seabed using taut-moored tethers. Ball joints connect the legs with the deck and help partially isolate the deck to remain horizontal under waves and wind. While offshore structures commonly have tubular legs, the current study investigates Triceratops with elliptical legs under the postulated failure of tethers. Detailed dynamic analysis under postulated failure conditions is carried out using ANSYS AQWA, while the LIBRIUM analysis is used to obtain the equilibrium position of the platform under intact and postulated failure conditions. Results show that under postulated failure conditions, the peaks of the power spectral density function of the pitch response are seen closer to its natural frequency and the input wave frequency. Ball joints restrain this rotation from transferring to the deck, conforming to one of the advantages of its existence. The fatigue life of tethers calculated for different load cases under intact and postulated failure conditions helps understand the stability conditions of the platform. [ABSTRACT FROM AUTHOR]

This study investigates the mechanical properties of hybrid composites composed of web kapok fibers and fiberglass reinforced with epoxy for potential application in the marine industry. The web kapok fibers were carefully processed using a carding technique to ensure better alignment and consistency. Various composite configurations were produced, and extensive mechanical testing was conducted, including flexural, tensile, and impact tests. The results revealed that the presence of two web kapok fiber layers within the composite significantly increased flexural strength and flexural modulus compared to pure fiberglass laminates. However, a single layer of web kapok fabrics exhibited the highest tensile strength, although it decreased with additional layers. The impact strength of these hybrid composites also showed promising results, especially when compared to raw fiberglass composites. Moreover, these composites exhibited improved resistance to water absorption and corrosion, making them potentially suitable for marine applications. This research highlights the potential of web kapok/fiberglass hybrid composites as an eco-friendly alternative for marine engineering, with implications for reduced environmental impact and sustainable technology in the industry. [ABSTRACT FROM AUTHOR]

Steel-coped beams are used in industrial structures to accommodate a cluster of water mains, fire hydrants, power cables and telecommunication wires. The coped regions restrict the ultimate capacity and cause unfavorable failure modes. The current study investigates the structural assessment of the coped section in offshore topsides while their use enhances operational safety for drilling and production. The structural evaluation is done through 2D digital image correlation (DIC) experiments to quantify the influence of various cope geometries. The DIC technique illustrated the strain and deformation measurements under different loading conditions for different coped geometry. The primary failure mode observed in local web buckling is characterized by noticeable lateral displacement and the development of buckling lines over the coped web. Studies showed the influence of the cope depth on the load-carrying capacity and buckling processes for different cope geometries. The results of the DIC analysis are strongly aligned with experimental data and finite element numerical results, suggesting this technique to the structural assessment of coped section. [ABSTRACT FROM AUTHOR]

The deformation caused by waves and current in an aquatic environment significantly impacts the remaining volume of a net cage. Its fluctuations in magnitude could pose a potential threat to the well-being of cultivated species. There is a critical need for a simple, cost-effective solution to monitor cage deformation in real-time. This study proposes a depth-based method, utilizing just two depth meters attached to the cages floating collar and tube sinker, to estimate the remaining volume. Compared to the experimental measurements from previous studies, this method demonstrates satisfactory accuracies. Under current-only and waves-current conditions, the estimation differences are around 11.6% and 23%, respectively. In contrast, when compared to commonly used volume-based methods, the differences are approximately 1.8% and 9.5%. Despite a tendency for overestimation when the mean cross-sectional area deviates from the original top or bottom area of the cage, this method remains a feasible alternative. Its practicality highlights its potential as an efficient means of monitoring cage deformation. [ABSTRACT FROM AUTHOR]

In addressing the active control challenges of marine structures in ocean waves, a coupling model is proposed combining computational fluid dynamics (CFD) and deep reinforcement learning (DRL). Following the Markov decision process (MDP), the proposed DRL-CFD model treats the wave fields and simplified marine structures as the environment and the agent, respectively. The CFD component utilizes the PIMPLE algorithm to solve the Navier–Stokes equations, in which the free surface is reconstructed using the volume of fluid method. The DRL component utilizes the Soft Actor-Critic algorithm to realize the MDP between marine structures and the wave fields. Three simulation cases with different control purposes are conducted to show the effectiveness of the DRL–CFD coupling model, including the active controls for wave energy absorption, attenuation, and structure heave compensation. Comparative analyses with passive (resistive) control are performed, demonstrating the advantages of the DRL–CFD coupling model. The results confirm that the proposed coupling model enables the marine structure to observe the wave environment and generate effective active control strategies for different purposes. This suggests that the model has the potential to address various active control challenges of marine structures in ocean waves, while being capable of environmental sensing and handling multiple tasks simultaneously. [ABSTRACT FROM AUTHOR]

A submerged flexible breakwater can be used to control waves in shallow water as an advanced alternative to traditional rigid submerged structures. Submerged flexible breakwaters not only cost less to build than conventional submerged breakwaters but also allow ships and marine life to bypass them if they are deep enough. These marine structures decrease the intensity of the shock wave and prevent standing waves from forming. We present a solution for transmission/reflection using a series of submerged identical elastic scatterers. Scattering and transfer matrices will be used to compute the transmission and reflection coefficients for N-submerged elastic scatterers. The behavior of the transmission for different values of physical parameters such as submergence depth, length of the scatterer, the gap between two successive scatterers, stiffness of the scatterer, and the number of submerged elastic scatterers is given. In doing so, we can achieve the frequencies and the incident amplitudes at which these submerged elastic scatterers can be effectively used as breakwaters in water of finite depth. We have looked at the transmission and reflection behaviors for a range of physical parameter values, such as the submergence depth, the length of the scatterer, the spacing between successive scatterers, the stiffness of the elastic scatterer, and the number of scatterers over a wide frequency range. We have given a spectrum of frequencies for which, given certain values of physical parameters, we can achieve zero transmission. Furthermore, even at high frequencies, we have demonstrated an incidence amplitude range for which zero propagation of transmission is feasible. [ABSTRACT FROM AUTHOR]

The present study illustrates an experimental investigation of flow hydrodynamics in the vicinity of a submerged circular pier across various submergence levels under only current and wave–current combined flow conditions. The instantaneous velocity data are collected using particle image velocimetry for three distinct frequencies of waves to determine the influence of wave superimposition on the current-induced turbulence parameters. The distribution of phase averaged turbulence quantities, such as mean velocities, Reynolds shear stress, turbulent kinetic energy, flow patterns, and vorticity analysis by Q-criterion, are presented. The results provide insight into the impacts of wave frequency and submergence ratio on the formation of horseshoe vortices, trailing vortex, and reverse flow zones. From the results it is observed that a decrease in the submergence level of the structure causes the formation of strong horseshoe vortices and reverse flow zones in the absence of waves. Also, an increase in wave frequency intensifies the turbulence kinetic energy at the upstream of the pier and eddy generation behind the pier. The present findings highlight the effects of pier submergence and wave characteristics, such as frequency, wave height, and wave period, on flow patterns and turbulent flow characteristics and aid in the design of marine structures. Furthermore, experimental data serve as a valuable resource for validating theoretical or mathematical models related to combined wave–current environments. [ABSTRACT FROM AUTHOR]

This study examines the performance of a data-driven model in predicting the motions and loads of a floating power system (FPS) in various irregular waves, considering nonlinear wave–structure–mooring interactions. A surrogate model, constructed using a long short-term memory network, is trained and tested on robust datasets obtained from physical tank tests. The model's accuracy is initially validated through the temporal responses of the moored FPS and the associated extreme events. Its effectiveness is further assessed under varying random sea states, including different peak periods and wave steepness. A detailed harmonic analysis of extreme events indicates that while the model accurately captures the linear components of FPS's motions, it tends to underpredict higher-order harmonics, especially for pitch motions and mooring line tensions. Our results highlight the potential of data-driven models in marine applications, offering substantial computational savings for complex physical problems and the possibility of creating digital twins of real offshore structures. However, their limitations in capturing extreme events and higher-order nonlinearities must be carefully addressed when applying this methodology in strongly nonlinear sea states. [ABSTRACT FROM AUTHOR]

Considering that marine structures are frequently subjected to the combined effects of waves and currents, the wave–current coupling environment largely determines the structural load and the surrounding water–air mixed flow, which is a typical feature of offshore structures, such as ships and offshore platforms. This study focuses on the interaction between a horizontal cylinder and a free surface in a wave–current nonlinear coupled environment using numerical simulations. The numerical method is based on the incompressible Navier–Stokes equation, with the volume-of-fluid method used to capture the free surface. Based on the second-order Stokes wave theory, we studied the impact of wave height and steepness on the cylinder force, vorticity field, free-surface deformation, and spatial–temporal distribution characteristics of entrainment bubbles. The results showed that the wave height and wave steepness have opposite effects on the root mean square (RMS) value of the force and influence the amplitude and period of the force curve. The stretching of the negative vortex led to varying degrees of double-frequency oscillation modes in the force curves. The main sources of bubbles in the wake are the breaking of the free surface and the entrainment caused by the cylinder vortex, and the bubbles caused by the former account for the majority. Compared with the wave height, an increase in wave steepness can cause a more severe interface breaking, resulting in more entrainment bubbles. [ABSTRACT FROM AUTHOR]

Designing a ship hull to keep the hydrodynamic performance meet the requirements is an indispensable step in the ship's preliminary design. However, in the traditional design process, the design workload is labor-intensive and time-consuming due to the need to estimate a large number of design schemes. To address this issue, this work developed a Neural Network Proxy Model (NNPM) to assist the hydrodynamic resistance prediction for the ship hull design process. The data used in the NNPM construction was supported by two Computational Fluid Dynamic (CFD) methods with different fidelity where the low-fidelity one for tuning and pre-training, and the high-fidelity one for fine-training. To mitigate the risk of overfitting stemming from disparities in data volumes, the parameter freezing strategy is adopted during the high-fidelity dataset-based fine-training. The results obtained from validation numerical experiments indicated that the NNPM exhibited a forecast error of less than 1% when compared to the high-fidelity CFD method. Importantly, this high accuracy is achieved while maintaining a low construction workload, demonstrating the potential of Artificial Intelligence (AI) to predict the hydrodynamic load of hulls in the ship's preliminary design, which can further advance the artificial intelligence-assisted design (AIAD) technology for various marine structures. [ABSTRACT FROM AUTHOR]

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Monopiles serve as the foundational support for offshore wind turbines and are constructed as large, hollow, and rigid steel pipes. Given their offshore installation, these foundations experience cyclic lateral forces from wind and waves. This paper focuses on investigating the cyclic lateral capacity of monopiles through experimental and numerical analysis. The study examines varying factors such as slenderness (L/D) ratios of 2, 4, and 6, load amplitudes (ξb) of 40%, 30%, and 20%, and different densities of sand (RD) at 35%, 55%, and 75%. One-way cyclic loading at a frequency of 0.25 Hz was applied during the experiments using a pneumatic cylinder setup to the model piles. Numerical analysis was conducted on the prototype piles using PLAXIS 3D finite element software. The analysis utilised a hypoplastic model with an intergranular strain concept as the constitutive model. The model was validated against the experimental results of MLD2/LA40/RD55 and exhibited similar behaviour. The experimental findings indicate an initial 40% increase in stiffness during the first 10 cycles, leading to a higher accumulation of displacement. However, as the number of cycles increased, the rate of stiffness increase decreased due to soil getting dispersed around the pile, resulting in an increased rate of accumulated displacement. This behaviour was observed across various L/D ratios, load amplitudes, and soil densities. Additionally, an increase in load amplitude and L/D ratio, as well as a decrease in soil density, resulted in higher accumulated displacement and reduced stiffness. [ABSTRACT FROM AUTHOR]

Reliability‐based design optimization (RBDO) traditionally relies primarily on high‐fidelity and computationally expensive simulations to search for and evaluate design solutions. However, significant disparities could emerge for complex nonlinear behavior that are challenging for numerical modeling. In contrast to mitigating the impact of inaccurate numerical modeling through optimization algorithms, laboratory experiments realistically capture the complex nonlinear behavior of structures or their components. Real‐time hybrid simulation (RTHS) is widely considered as an efficient and cost‐effective technique for integrating numerical modeling with experimental testing for structural response evaluation. This study proposes an innovative framework that utilizes RTHS for the performance assessment of candidate designs to enable RBDO of structures subjected to pulse‐like ground motions. RTHS tests are conducted to physically evaluate structural responses through realistically replicating complex nonlinear behavior of experimental substructures. This study introduces a novel penalty function‐based efficient global optimization (P‐EGO) method to minimize the required number of laboratory tests through surrogating the response quantities of interest derived from RTHS. The proposed framework is experimentally evaluated for design optimization of a two‐story four‐bay steel moment‐resisting frame with self‐centering viscous dampers subjected to pulse‐like ground motions. The results demonstrate innovative application of RTHS in dynamic optimal design to account for uncertainties. It offers an effective and efficient alternative for traditional RBDO through pure computational simulation, particularly when structural components pose challenges for numerical modeling. [ABSTRACT FROM AUTHOR]

Base‐isolated hospitals are frequently preferred to fixed‐base ones because of their improved seismic structural performance. Despite this, the question remains open on the advisability of using this modern seismic protection technology in preference to other conventional solutions, on the grounds of a holistic approach based on limiting non‐structural damage as well as continuity of service to the community in the aftermath of an earthquake. Two full‐scale four‐storey (fixed‐base) and three‐storey (base‐isolated) hospital buildings have been recently built and subjected to three‐dimensional shaking table tests at the National Research Institute for Earth Science and Disaster Prevention (Japan), with particular attention to evaluating and classifying functionality of non‐structural components and vital medical equipment. A two‐phase experimental campaign was carried out considering two earthquakes scaled at different intensity levels and applied along the horizontal and vertical directions. The current study aims to provide results of a numerical structural and non‐structural blind prediction of these hospital settings. A homemade numerical code is developed to account for lumped plasticity modelling of steel frame members and variability of the friction coefficient of spherical sliding bearings. Moreover, three non‐structural components are modelled in the fixed‐base structure: that is, elastic single degree of freedom systems representing two tanks filled with sand at the top floor; elastic beam elements for piping at the third floor; five‐element macro‐model for the in‐plane‐out‐of‐plane nonlinear response of partition walls at the first floor. The identification of predominant vibration periods of the fixed‐base structure is carried out using a homemade numerical code based on the continuous wavelet transforms in combination with the complex Morlet wavelet. Finally, the sliding and rocking motion of three items of medical equipment (i.e., incubator at third floor, dialysis machine at second floor and surgical bed at first floor) are analysed by means of a homemade numerical code, considering acceleration time histories of selected structural nodes of the fixed‐base structure. [ABSTRACT FROM AUTHOR]

In this article, we examine the influence of bolt threads on the tensile rupture strength of the net section corresponding to single-bolt double-lap connections in pultruded materials made of dicyclopentadiene-based unsaturated polyester resin reinforced with E-glass fibers in the forms of roving, continuous-strand mats and triaxial fabrics that incorporate chopped strand mats and plies oriented in the 45∘ , 90∘ , and −45∘ directions with respect to the longitudinal direction (i.e., roving direction). Thirty-six single-bolt double-lap connection tests were carried out on plates in which the bolt-hole diameter to plate width ratios were 0.5, 0.6, and 0.75. All these connection tests incorporated finger-tight A307 zinc-coated bolts fully threaded in one case and partially threaded in another case. The results from these experiments revealed that bolt threads in contact with the bolt-hole surface influence the tensile resistance of the net section. This influence is evident as the bolt-hole diameter to plate width ratio decreases. Analysis of our findings highlights a notable discrepancy: current design guidelines in both the United States and Europe can considerably underestimate the net section tensile rupture strength of single-bolt connections made from pultruded materials with an offaxis reinforcement scheme. Recommended design guidelines that can be adopted by practicing engineers are proposed. [ABSTRACT FROM AUTHOR]

Apart from the mechanisms of ice structure interactions under various scenarios of sea ice conditions and structural configurations, the selection of probabilistic models is crucial in order to cope with the loading uncertainty. Sea ice is the primary contributor to design loads in cold regions. In many cases, ice loads present the highest magnitude. In recent years, the probabilistic study of ice thickness, ice strength coefficient, flexural strength, ice drift speed, etc., has significantly increased, corresponding to the increasing activity of offshore operations in cold regions as well as the development of instrument technology for sea ice observation. This paper reviews existing probabilistic modes of sea ice, which are used to estimate the uncertainty of ice loading with various types of offshore structures, including vertical structures, sloping structures, and stations with floating vessels. The ISO 19906 standard is employed for the probabilistic assessment of vertical and sloping structures. The interactions between ice and structures on sloping structures are considered in both the upward and downward directions. The ice resistance method is applied for station-keeping floating vessels in ice. The key parameters of sea ice properties to estimate the design loads are studied. The effect of correlation between the key parameters of ice loads is investigated. This review shows that most existing probabilistic models are proposed for the estimation of ice loading on the various types of offshore structures. [ABSTRACT FROM AUTHOR]

Synthetic ropes are increasingly favored for use in offshore systems. Accurate predictions of the coupled hydrodynamic performance and structural response of offshore structures depends on a thorough understanding of the nonlinear characteristics of fiber materials. The objective of this study is to experimentally characterize the stiffness of a polyester mooring rope for a cylindrical floating production storage and offloading system. The quasi-static stiffness of the ropes and aged ropes after installation and the dynamic stiffness in various loading conditions were computed based on sub-rope tests following the guidelines from the American Bureau of Shipping. The quasi-static stiffness curves exhibited a linear decrease in values as the logarithm of the loading period (in minutes) increased. The dynamic stiffness was, in general, much higher than the quasi-static stiffness. The dynamic stiffness under various loading conditions revealed the complexities of the mechanical properties of polyester rope. Parameters such as the mean load, load amplitude, loading period, and loading cycles all had a notable impact. More tests are required to have a better understanding of their effects. [ABSTRACT FROM AUTHOR]

Among the extreme sea scenarios, freak waves pose a serious threat to offshore structures, potentially leading to structural failure, such as mooring line failure, floater capsizing, or structural damage. In this study, we conducted a numerical investigation on the transient performance of a semi-submersible floating offshore wind turbine (FOWT) equipped with a redundant mooring system under the influence of freak waves and mooring failure. Firstly, we analyzed the dynamic responses of an intact-mooring-system FOWT under a freak wave. Next, we examined the effect of mooring failure on the transient responses. The results indicate that floater motions exhibit significant differences in the interval of freak wave crests. The impact of freak waves increases the blade tip deformation and tower root bending moment, while also affecting the tension of the mooring line and the aerodynamic performance of the wind turbine. Consecutive fracture with an interval of 20 s significantly increases surge motion and reduces output power. When mooring lines break separately with an interval of 400 s, the amplification in the responses is noticeably lower compared to consecutive fracture cases. [ABSTRACT FROM AUTHOR]

There is currently a rising interest in reusing and repurposing offshore facilities through decommissioning; however, major challenges arise, such as size, weight, sea depth, planned use, and location. This article aims to discuss the philosophy that needs to be adopted for field redevelopment, particularly when existing platforms must be preserved and integrated into new greenfield facilities. The article also discusses the concept of weight shedding during the decommissioning of offshore facilities to either extend the life of existing platforms or provide clear space for new equipment to be installed by removing unnecessary components and structures. The above aspects of decommissioning are investigated through the redevelopment of a case study of a mature offshore oil field located in shallow water. The study indicated that weight shedding presents a favourable method for decommissioning offshore installations and can effectively lower expenses, minimise environmental consequences, and optimise the use of resources. [ABSTRACT FROM AUTHOR]

Freak waves are characterized by extreme wave height, irregular wave shape, high peak energy, short duration, and formidable destructive potential, posing a significant threat to offshore structures. Therefore, analyzing dynamic responses exhibited by advanced offshore platforms such as the offshore triceratops under the influence of freak waves holds paramount importance. However, the response analysis of offshore triceratops under freak waves has not been explored so far in the literature. Hence, the present study aims to investigate the dynamics of offshore triceratops intended for ultradeep waters under the impact of freak waves. Initially, the dual superposition model was utilized to generate the freak waves, and the numerical model of the platform was developed using ANSYS AQWA. Subsequently, the dynamic response characteristics of offshore triceratops under the influence of freak waves were analyzed in the time domain. The results demonstrate the effects of freak waves on the surge, heave, and pitch responses of the deck and buoyant legs were substantial, leading to a significant increase in maximum responses and variations in mean shift and standard deviations. The innovative insights derived from this study can serve as a benchmark for validating the effective performance and design of offshore triceratops. [ABSTRACT FROM AUTHOR]

The Western Pacific region is highly vulnerable to typhoon storm surge disasters, with localized erosion posing a particularly prominent issue for coastal marine structures. The prevalence of extreme typhoon storm surges poses a significant threat to the safety of engineering projects in these areas. In this study, a parameterized wind field model with precise calculation of wind speed was employed to establish a numerical model for typhoon storm tides. Based on the Western Pacific typhoon data from 1949 to 2023, hydraulic simulations were conducted for Hangzhou Bay, Xiangshan Port, and Yueqing Bay, revealing maximum flow velocities of 4.5 m/s, 1.95 m/s, and 2.09 m/s, respectively. These velocities exceeded the maximum possible tidal flow by 0.47–1.17 m/s. Additionally, using Sun's velocity formula, the initiation flow velocities were calculated to be 1.85 m/s, 1.81 m/s, and 2.06 m/s for the aforementioned locations. Through localized erosion tests conducted around typical bridge piers and the subsequent application of similarity criteria, the maximum depth of localized erosion in the study area was determined to range from 2.16 m to 16.1 m, which corresponds to 1.1–2.3 times the scour caused by the maximum tidal flow scenario. A comparison of the erosion test results with calculations based on several formulas demonstrated that the scour prediction formula proposed by Sun exhibited the highest accuracy. This study supplements the understanding of the impact of typhoon storm surges on bridge pier erosion and provides a scientific basis for the design of bridge foundations. [ABSTRACT FROM AUTHOR]

This paper aims to study the low-velocity impact (LVI) response and compression after impact (CAI) performance of carbon/aramid hybrid woven composite laminates employed in marine structures subjected to different energy impacts. The study includes a detailed analysis of the typical LVI responses of hybrid woven composite laminates subjected to the impact with three different energies, as well as a comparative analysis of cracks and internal delamination damage within impact craters. Additionally, the influence of different impact energies on the residual compressive strength of hybrid woven composite laminate is investigated through CAI tests and a comparative analysis of internal delamination damage is also conducted. The results indicate that as the impact energy increases, the impact load and CAI strength show a decreasing trend, while impact displacement and impact dent show an increasing trend. The low-velocity impact tests revealed a range of failure modes observed in the hybrid woven composite laminates. Depending on the specific combination of fiber materials and their orientations, the laminates exhibited different failure mechanisms. Buckling failures were observed in the uppermost composite layers of laminates with intermediate modulus systems. In contrast, laminates with higher modulus systems showed early damage in the form of delamination within the top surface layers. [ABSTRACT FROM AUTHOR]

The present paper develops a new framework to predict the mean flow through an array of cylinders in which the flow around the array (array‐scale) and the flow around individual cylinders (element‐scale) are modeled separately using actuator disc theory and empirical drag models respectively, and then coupled through the net drag force. Applying this framework only requires knowledge of the array geometry and incident flow. The framework is validated using high‐fidelity direct numerical simulations for arrays of between 7 and 109 cylinders having different arrangements (staggered, concentric, random) and bounding shapes (circular, square) in both two‐ and three‐dimensional flows. In general, the framework outperforms existing models which require calibration and are only valid for part of the practical parameter space. The demonstrated scale separation suggests different combinations of element‐scale and array‐scale models/theories may be used for other arrangements of bluff bodies. Plain Language Summary: The temporally and spatially averaged velocity, or mean flow, within an array of cylinders is important for many practical applications including, for example, estimating the rates of sediment transport and nutrient uptake within a patch of aquatic vegetation, the hydrodynamic forces on offshore structures, and the efficiency of power generation with a turbine farm. However, a general predictive tool for mean flow is currently lacking. To develop this predictive capacity, this study uses the idea of scale separation to integrate models from different research fields, including the actuator disc theory originally developed for design of turbines and propellers, and element‐scale drag models initially proposed for aquatic vegetated flows, to develop a unifying, predictive, analytical framework to estimate the mean flow. The framework is validated using high‐fidelity direct numerical simulations of arrays of cylinders with different arrangements (staggered, concentric, random) and array shapes (square, circular). With only knowledge of the array geometry and incident flow, the framework predicts the mean flow exceptionally well across a wide range of practical flow conditions. This leads to a step‐change in our ability to predict the fraction of incoming flow passing through a porous array, hydrodynamic load on offshore structures, and sediment flux within aquatic vegetation systems when combined with bed load transport models. The framework could be an important guide for coastal and riverine restoration projects using aquatic vegetation and the design of offshore structures and turbine farms. Key Points: A predictive framework based on an idea of scale separation is proposed for the mean velocity of the flow passing through an array of cylindersThe framework is versatile, being applicable for a wide range of practically meaningful cylinder arrangements, array shapes and array flow blockagesHigh‐fidelity, three‐dimensional direct numerical simulations are employed to investigate flow through the array of cylinders and validate the new predictive framework [ABSTRACT FROM AUTHOR]

This paper presents the methodology developed for underwater measurements using electrochemical impedance spectroscopy (EIS) technique, aimed at determining the resistance of an epoxy coating applied in seawater to the legs of an oil production platform. Performing such underwater tests in an offshore environment was technically challenging. The results of measurements obtained on the platform were confronted with comparative results obtained in the laboratory, where the properties of the coating applied in water collected from the Baltic Sea (thickness, hardness, adhesion, and electrical resistance) were examined. This made it possible to conclude about the correctness of the paint coating application by divers on the legs of the platform. The single-layer epoxy coating applied by brush to the platform legs had a resistance above 10 kΩ∙cm2 and thus met the assumed minimum resistance of the protective coating cooperating with cathodic protection as the anti-corrosion protection system of the platform legs. The synergy of these two technologies ensures full protection of offshore structures against corrosion. Measurements of the potential of the platform legs confirmed this. Before painting, the potential value at a depth of 0–15 m was 310 ÷ 320 mV versus the zinc reference electrode, while after painting the potential value decreased to 220 ÷ 240 mV, which means that the effect of full cathodic protection was achieved and the platform legs were protected from corrosion. The developed methodology for underwater EIS measurements on the high seas can be applied to any underwater metal structure to assess the quality of protective coatings. [ABSTRACT FROM AUTHOR]

Marine structures are supposed to simultaneously possess high stiffness bearing high loadings and large damping dissipating dynamic energy. Structural impact protection and stiffening approach is achieved via assembling a pre-compressed negative stiffness component and linear members, which not only exhibits high initial stiffness but also dissipation capacity approaching the theoretical limit under small deformation. The effects of design parameters on the energy dissipation characteristics are investigated by the combination of quasi-static, dynamic and finite element analysis. For potential applications, the dynamic responses and vibration suppression of a representative grille structure optimized by the novel design are studied via FE simulations. [ABSTRACT FROM AUTHOR]

AbstractCurrent study presents state of the art approach to risk and reliability assessment for multivariate nonlinear dynamic systems. Specifically, novel hypersurface Gaidai risks evaluation methodology has been presented for evaluating offshore structural risks. Advocated approach being particularly suitable for offshore engineering multidimensional dynamic systems, possessing large number of critical components, that have either been physically observed/measured, or numerically modeled over a representative timelapse. Advocated Gaidai hypersurface structural risks evaluation methodology is applicable for a wide range of engineering and industrial systems. This study demonstrates that given in situ environmental conditions, it is well possible to assess accurately risks of system’s failures, damages or hazards, caused by excessive structural dynamics. Multivariate dynamic systems, possessing nonlinear cross-correlations between critical system’s components often present design challenges, when utilizing classic structural risks evaluation approaches, as those are mostly only univariate or bivariate. Dynamic offshore Jacket hot spot stresses have been utilized as an example in this reliability investigation. Modeling system’s excessive dynamics is challenging because of the non-stationarity of the system and the intricacy of fluid-structural dynamic interactions, arising from in situ wave-induced loads, influencing Jacket’s structural dynamics. Nonlinearities greatly affect structural dynamics, e.g., 2nd, 3rd, higher order effects within fluid-structural interactions. Methodology presented in this work offers a straightforward, effective, yet precise means of assessing the risks of failure or hazard for multivariate, non-stationary, non-linear dynamic offshore systems. For bivariate case, verification note has been added. [ABSTRACT FROM AUTHOR]

Local scour around bridge foundations significantly impacts the stability and safety of marine structures. The development of scour holes adjacent to the pile foundations of sea-crossing bridges, influenced by tidal currents, involves multidimensional physical fields, multiscale coupling, and complex variations in marine loads. However, experimental models alone are inadequate for investigating the underlying mechanisms. Numerical simulation, a critical tool for studying local scour processes, faces the challenge of accurately modeling sediment transport, particularly under tidal flow conditions near pile foundations. To solve this challenge, this research considers the effect of reciprocating flow on sediment shear as well as its characteristic dissipation based on the immersed boundary method, introduces a reciprocating flow dissipation mechanism, and adds a momentum exchange term between the fluid and the sediment to derive a new controlling equation; a new tidal flow localized scour solver is ultimately constructed, termed TidalflowFOAM. The solver effectively simulates complex flow conditions under tidal currents, extending the modeling capabilities to more realistic three-dimensional bridge scour scenarios under combined wave and current conditions. Validation through cases reported in the literature and a series of controlled experiments, encompassing varying depths, flow velocities, and pile diameters, demonstrates the solver's proficiency in capturing post-vortex data and accurately reflecting the influence of key factors on scour depth. However, the fidelity of the simulated scour hole morphology under tidal flow conditions behind the piles requires enhancement. The proposed numerical model for tidal flow conditions has high solution accuracy and can guide practical engineering applications. [ABSTRACT FROM AUTHOR]

Breakwaters play an important role in in mitigating wave-induced damage to marine structures. However, conventional submerged breakwaters often exhibit limited wave dissipation capabilities, while floating breakwaters may lack adequate safety performance. Therefore, this study introduces a novel combined breakwater design aimed at addressing the shortcomings of both traditional types. The proposed breakwater integrates a floating structure with a trapezoidal submerged breakwater via an anchor chain connection. To evaluate its efficacy, numerical simulations of wave interactions with structures were conducted using the OpenFOAM computational fluid dynamics (CFD) software in a two-dimensional (2D) numerical flume. Dynamic mesh technology was employed to simulate the motion of the floating body, and the resulting wave loads on a box girder bridge deck positioned behind the breakwater were analyzed to assess the combined breakwater's protective capabilities and influencing factors. Analysis of wave heights and loads on the bridge deck revealed that the combined breakwater outperformed traditional submerged breakwaters in terms of wave dissipation. Furthermore, it was observed that the protective efficacy of the combined breakwater was more sensitive to variations in the size of the floating body compared to the submerged structure, and more responsive to changes in wave period than wave height. Leveraging the ability of the floating body to attenuate waves near the surface and the enhanced impact resistance provided by the combined floating and submerged structures, the proposed breakwater offers a promising approach to improving wave attenuation performance and enhancing safety for coastal infrastructure. [ABSTRACT FROM AUTHOR]

Remotely operated vehicle (ROV) is a widely used subsea vehicle in offshore oil and gas industries to assist in the development and inspection of offshore oil fields, given its agility, safety, and endurance. As the offshore industry and subsea engineering fields advance, the demands on ROV technology, particularly in terms of control accuracy and safety, have been greatly increasing. Traditional methods require ROV operators to be stationed on vessels in challenging conditions, relying on video streams that offer limited spatial information about the ROV working environment. All these factors make conventional joystick controls even harder for novices. This research aims to propose a novel approach to human-autonomy collaboration aiming to diminish the learning and operational burdens on operators. A virtual reality (VR)-based sensory augmentation and body motion teleoperation method was applied, which allows operators to teleoperate the ROV in a much more comfortable environment. An interactive user interface was developed to enable seamless engagement with the autonomous system and facilitate dynamic switching between human and autonomous controls. To assess the system, a human subject experiment was conducted to compare the performance of an inspection task between human control, full autonomy, and human autonomy teaming methods. The result indicated that our solution could enhance human understanding of the ROV work status as well as reduce human workload during operation. [ABSTRACT FROM AUTHOR]

The escalation in energy demand due to the rising population highlights the need for the transition toward sustainable power generation alternatives. In this context, floating solar photovoltaic (FPV) systems emerge as an innovative and environmentally friendly alternative, offering the dual benefits of energy generation and conservation of terrestrial resources. Based on ERA5 datasets, an in-depth analysis of the potential and efficiency of FPV systems, specifically within the Indian Exclusive Economic Zone (EEZ), is conducted in this study. Findings of this study evidence the substantial capacity of the Indian EEZ that could yield energy that is equivalent to 43 times of annual consumption by utilizing 10% of the EEZ region. A full-scale utilization of the EEZ for FPV systems could revolutionize the energy landscape, potentially generating 433 times the country's present annual energy requirements. A complete transition to such renewable energy sources within the EEZ is projected to result in an annual reduction of 595 billion metric tons in carbon emissions. [ABSTRACT FROM AUTHOR]

This paper presents empirical models for the frequency content parameters of offshore ground motions in the Japan Trench area based on the S-net dataset, comprising 6,436 recordings from 496 events. Significant variations in frequency content among shallow crustal, upper-mantle, subduction interface and subducting slab are revealed. Empirical models for To, Tavg, and Tm are proposed, considering moment magnitude, source distance, focal depth, and tectonic types. A comparative analysis with four existing land models highlights differences. Total residual results indicate that land models, based on shallow crustal datasets, tend to overestimate observed frequency content parameters in the Japan Trench area. [ABSTRACT FROM AUTHOR]

The combination of AA7075 and Ti6Al4V aluminum alloys provides an effective balance of endurance, corrosion resistance, and lightness. Some potential applications include aviation components, marine structures with anti-corrosion characteristics, surgical instruments, and athletic apparel. Therefore, the hybrid nanofluid (Hnf) consists of aluminum alloys (AA7075-Ti6Al4V), water (50%), and ethylene glycol (EG-50%) in the current analysis. The Hnf flow subject to heat radiation and Lorentz force is studied through coaxial cylinders. In addition, the flow has been observed under the impacts of homogeneous-heterogeneous (HH) chemical reaction and exponential heat source/sink. The modeled equations (continuity, momentum, HH, and heat equations) are renovated into the non-dimensional form through the similarity approach, which are further numerically computed by employing the ND-solve technique coupling with the shooting method. It can be noticed from the graphical results that the flow rate of Hnf drops with the rising effect of porosity and magnetic field parameters. The addition of AA7075-Ti6Al4V nanoparticles (NPs) also reduces the fluid temperature and velocity profile. Furthermore, the concentration distribution diminishes with the flourishing effect of HH parameters. [ABSTRACT FROM AUTHOR]

Natural accumulations of wood, as well as engineered logjams, are relevant for river ecosystems. These structures, by interacting with the flow, can lead to significant backwater effects and morphological changes. Research on engineered logjams has so far mainly relied on physical modeling, which may impede the study of different flow conditions or logjam designs and configurations. Here, a simple approach for the simulation of logjams in two-dimensional depth-averaged hydrodynamic solvers is explored, building on widely available modeling options. The effect of logjams is included by combining a local contraction and an increase in local frictional losses based on the logjam characteristics, thereby reflecting the main physical flow processes in the region near a logjam. More than 350 modeling tests were used to calibrate and validate the proposed approach. For all tests, backwater rise due to channel- and partial-spanning logjams can be estimated with ±30% prediction range. Given its simple design, the calibrated model is not universal and requires careful evaluation when applying it to different setups. Nevertheless, a clear advantage of the proposed approach is that it uses tools that can be adopted in most of the standard two-dimensional hydrodynamic solvers. [ABSTRACT FROM AUTHOR]

The conventional Mohr–Coulomb (M-C) failure criterion is commonly used in existing studies to determine the ultimate pullout capacity of plate anchors buried in cohesive-frictional soils. However, this criterion overestimates the tensile strength of these soils by assuming a linear failure envelope (in both compression and tensile regimes) within the normal-shear stress space. In this study, the ultimate pullout capacity of horizontally buried plate anchors in cohesive-frictional soils was determined, accounting for the effect of tensile strength cutoff. The study proposed a series of semianalytical solutions utilizing the kinematic horizontal slice approach and investigated the ultimate pullout capacity of four different anchor shapes, including circular, square, rectangular, and strip anchors. The impact of nonassociated flow rule on the results was also examined. It has been observed that the results obtained using the M-C failure criterion with a tension cutoff are significantly lower than those obtained using the conventional M-C failure criterion. The difference between both results increases as soil cohesive strength increases and anchor burial depth decreases. These findings clearly demonstrate that eliminating tensile strength from the strength envelope leads to a more conservative estimate of plate anchor pullout capacity. The study emphasizes changes in anchor failure surfaces for various parameter combinations and provides results that are consistent with specific solutions reported in the literature. Practical Applications: The study investigates using plate anchors to enhance the stability of both onshore and offshore structures, including transmission towers, guyed masts, chimneys, and mooring platforms. These structures often encounter significant vertical pullout forces. The research establishes a theoretical framework for calculating the ultimate vertical pullout capacity of plate anchors with various shapes (strip, rectangular, and circular) when buried in cohesive-frictional soils. A crucial aspect of this analysis involves incorporating the specified/limited value of tensile strength in cohesive-frictional soils when assessing the ultimate pullout capacity of plate anchors. This consideration is vital for ensuring a safe and conservative design, especially for structures subject to uplift forces. The findings provide valuable insights for engineers and practitioners, offering a reliable method to optimize the usage of plate anchors in the design of pullout-resistant structures. [ABSTRACT FROM AUTHOR]

The seismic response of seabed is fundamental for researching the seismic response of marine structures. The one-dimensional transient response of an unsaturated seabed was studied in this paper. An analytical solution for a special case with infinite permeability coefficients and a semianalytical solution for a general case with arbitrary permeability coefficients were developed. The advantage of this semianalytical solution is that it can compute the behavior of unsaturated soils with very low permeability coefficients. During the derivation, the boundary conditions were transformed into homogeneous boundary conditions first, and then the eigenvalues and eigenfunctions were obtained. To obtain solutions in the time domain, the eigenfunction expansion method and the precise time-step integration method were employed. Through numerical examples, the reflection and transmission characteristics of three types of compression waves at the fluid–solid interface were elucidated. The impact of permeability coefficients and water saturation on the seismic response of the seabed was investigated through parametric analysis. When the soil is nearing saturation, even a slight change in saturation can lead to a drastic alteration in the seismic response of the nearly saturated seabed. [ABSTRACT FROM AUTHOR]

Steel tubular column-to-steel beam (STCSB) connections are critical parts in offshore structures, where complex component connections and the stress concentration are of significant concern. This study conducted stress concentration tests on welded STCSB connections and subsequently developed a finite element (FE) model for the connections, with the experimental results validating the accuracy of the model. The discussion focused on the influence of parameters such as the width-to-diameter ratio of the beam to the column, the diameter-to-thickness ratio of the column, the diameter-to-thickness ratio of the column to the beam, and the height-to-thickness ratio of the beam web on the fatigue performance. The study proposed optimization methods including the addition of stiffeners and outer flange plates. The findings indicate that optimized connection configurations can effectively mitigate stress concentration in the connected areas, thereby enhancing the structural stability and fatigue life. The width-to-diameter ratio of the beam to the column and the diameter-to-thickness ratio of the column significantly affect the fatigue performance of welded STCSB connections, with an increased width-to-diameter ratio of the beam to the column or a reduced diameter-to-thickness ratio of the column leading to a substantial decrease in the maximum stress concentration factors (SCFs). The addition of stiffeners and adjustment of the outer flange plate can improve stress concentration effects in the connection area. [ABSTRACT FROM AUTHOR]

This research utilised an open-sourced smoothed particle hydrodynamics (SPH) tool to model and predict the change in wave-induced forces and motions of a free-floating bergy bits approaching a fixed structure in regular waves. Simulation parameters, including particle resolution, fluid viscosity, initial wave condition and boundary treatments, are varied, and their effect on the load imparted to the bergy bit and the structure are investigated. The predicted motions are compared with previously published physical measurements for corresponding scenarios. Both predictions and measurements showed that, in regular waves, the surge motion slowed as the bergy bit approached the structure, and the heave motion increased. For wave loading on bergy bits, the agreement with the experimental data for the root mean square (RMS) force was within 2%. The pressure and velocity fields of the wave–structure–bergy bit interactions are discussed in light of the SPH predictions. This work confirms that the SPH model can accurately capture viscosity–dominated interactions, hydrodynamic damping, and eccentric impact like phenomena and predict both the impact and hydrodynamic loads due to a bergy bit drifting in waves towards a fixed offshore structure. [ABSTRACT FROM AUTHOR]

Nonlinear soil–pile–structure interaction (SPSI) phenomena are known to play a vital role in the response of bottom-fixed marine structures. For such structures, these phenomena are commonly considered by the imposition of p-y, τ-z, and q-z springs, representing the lateral and axial shaft and axial base soil resistances, respectively. The importance of each resistance mechanism depends on the type of foundation system, with only very limited studies investigating their roles in the response of piled marine structures, such as jetties. Within this context, this study presents numerical three-dimensional pushover analysis results for two marine jetties, a smaller model with four piles and a larger model supported by twenty-four piles. SPSI effects are considered through p-y, τ-z, and q-z springs, the behaviours of which are determined by following commonly employed procedures. The structures' responses are investigated under the influence of various assumptions regarding the behaviours of springs, as well as steel plasticity. The current investigation underscores the substantial influence of the axial soil–pile interaction on the response of the jetty, particularly in terms of its failure mode. Moreover, it demonstrates the importance of incorporating p-y springs, even though the choice between their linear or nonlinear constitutive behaviour is found to be less critical. Finally, the study concludes that the behaviours of the springs significantly affect the system's ductility and the degree of steel yielding in the piles, while also highlighting the unconservative influence of neglecting SPSI phenomena. [ABSTRACT FROM AUTHOR]

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