Offshore Engineering Research Articles

Research on the quality control strategy of marine engineering based on big data technology

Abstract The research of quality control strategy of marine engineering using big data technology is to better promote the enterprise to reduce cost and increase efficiency. In this paper, starting from the project quality control system, a quality control risk evaluation model is constructed based on hierarchical analysis and fuzzy comprehensive evaluation by means of the fuzzy comprehensive evaluation of affiliation degree. For the model constructed based on AHP-FCR in this paper, experimental analysis of quality control influencing factors and fuzzy comprehensive evaluation examples were conducted by establishing indicators. From the influence factors, the severity of engineering personnel risk and engineering machine risk are 19.289 and 20.216, respectively, both of which are significant levels of influence. From the fuzzy comprehensive evaluation, 49.09% of the experts voted that the level of quality control risk of S Company’s offshore engineering module oilfield construction project is now low and in an acceptable state. It can be concluded that the AHP-FCR model with big data technology can realize the quality control risk assessment of offshore engineering and also provides theoretical support for companies to solve the risk.

Lateral bearing characteristics of subsea wellhead assembly in the hydrate trial production engineering

Conductor and suction anchor are the key equipment providing bearing capacity in the field of deep-water drilling or offshore engineering, which have the advantages of high operation efficiency and short construction period. In order to drill a horizontal well in the shallow hydrate reservoir in the deep water, the suction anchor wellhead assembly is employed to undertake the main vertical bearing capacity in the second round of hydrate trial production project, so as to reduce the conductor running depth and heighten the kick-off point position. However, the deformation law of the deep-water suction anchor wellhead assembly under the moving load of the riser is not clear, and it is necessary to understand the lateral bearing characteristics to guide the design of its structural scheme. Based on 3D solid finite element method, the solid finite element model of the suction anchor wellhead assembly is established. In the model, the seabed soil is divided into seven layers, the contact between the wellhead assembly and the soil is simulated, and the vertical load and bending moment are applied to the wellhead node to simulate the riser movement when working in the deep water. The lateral bearing stability of conventional wellhead assembly and suction anchor wellhead assembly under the influence of wellhead load is discussed. The analysis results show that the bending moment is the main factor affecting the lateral deformation of the wellhead string; the anti-bending performance from increasing the outer conductor diameter is better than that from increasing the conductor wall thickness; for the subsea wellhead, the suction anchor obviously improves the lateral bearing capacity and reduces the lateral deformation. The conduct of the suction anchor wellhead assembly still needs to be lowered to a certain depth that below the maximum disturbed depth to ensure the lateral bearing stability, Thus, a method for the minimum conductor running depth for the suction anchor wellhead assembly is developed. The field implementations show that compared with the first round of hydrate trial production project, the conductor running depth is increased by 9.42 m, and there is no risk of wellhead overturning during the trial production. The method for determining the minimum conductor running depth in this paper is feasible and will still play an important role in the subsequent hydrate exploration and development.

Flow-induced vibration fatigue damage of two unequal-diameter flexible cylinders in side-by-side and tandem arrangements

Flow-induced vibrations (FIVs) are the indispensable factor causing the fatigue damage and failure for multi-cylindrical structures in offshore engineering. Mutual interferences between unequal-diameter cylinders complicate the fatigue behaviors. In this paper, an experiment was conducted on two flexible cylinders with a diameter ratio d/D of 0.5 (d and D denote the diameter of small and large cylinders) in uniform flow to investigate their fatigue damage characteristics. Two typical arrangements of side-by-side arrangement and tandem arrangement with a center-to-center spacing ratio P/d = 6.0 (P refers to the center-to-center distance between two cylinders) were examined. The results indicate that the fatigue damage is considerably affected by the arrangement and the diameter ratio. For the side-by-side arrangement, the small cylinder suffers from more serious fatigue damage in the CF direction due to the continuous impingement of the stable biased gap flow. However, the fatigue of the large cylinder is insensitive to the presence of the small cylinder. In a tandem arrangement, the wake shielding effect of the large cylinder located upstream is pronounced, resulting in a significant alleviation in the fatigue damage of the small cylinder. The wake inhibitory effect of the large cylinder is more prominent compared with that of two identical cylinders. The upstream large cylinder behaves analogously to the isolated cylinder. However, its CF fatigue damage is restrained in a few cases of 16.28 ≤ Vr ≤ 18.79 because the vortex shedding frequency is suppressed by the downstream small cylinder. On the other hand, when the small cylinder is located upstream, the wake shielding effect somewhat reduces the IL vibration of the large cylinder. The upstream small cylinder in this unequal-diameter experiment undergoes similar fatigue damage to the cylinder in the equal-diameter experiment.

A reliability-based design and optimization strategy using a novel MPP searching method for maritime engineering structures

PurposeIn order to solve the problems faced by First Order Reliability Method (FORM) and First Order Saddlepoint Approximation (FOSA) in structural reliability optimization, this paper aims to propose a new Reliability-based Design Optimization (RBDO) strategy for offshore engineering structures based on Original Probabilistic Model (OPM) decoupling strategy. The application of this innovative technique to other maritime structures has the potential to substantially improve their design process by optimizing cost and enhancing structural reliability.Design/methodology/approachIn the strategy proposed by this paper, sequential optimization and reliability assessment method and surrogate model are used to improve the efficiency for solving RBDO. The strategy is applied to the analysis of two marine engineering structure cases of ship cargo hold structure and frame ring of underwater skirt pile gripper. The effectiveness of the method is proved by comparing the original design and the optimized results.FindingsIn this paper, the proposed new RBDO strategy is used to optimize the design of the ship cargo hold structure and the frame ring of the underwater skirt pile gripper. According to the results obtained, compared with the original design, the structure of optimization design has better reliability and stability, and reduces the risk of failure. This optimization can also better balance the relationship between performance and cost. Therefore, it is recommended for related RBDO problems in the field of marine engineering.Originality/valueIn view of the limitations of FORM and FOSA that may produce multiple MPPs for a single performance function, the new RBDO strategy proposed in this study provides valuable insights and robust methods for the optimization design of offshore engineering structures. It emphasizes the importance of combining advanced MPP search technology and integrating SORA and surrogate models to achieve more economical and reliable design.

Bearing behaviors and design method of laterally loaded batter pile groups (BPGs) in sand

In recent years, the batter pile groups (BPGs) are increasingly used in offshore engineering; however, the optimal and economic design of BPGs is still poorly understood. Therefore, in this study, the lateral bearing behaviors of a typical 2 × 2 BPG in sand are comprehensively investigated by experimental and numerical methods. Firstly, a 1-g scale model test was carried out to study the effect of pile inclination on the responses of BPGs under lateral loads. Secondly, a total of 44 finite element (FE) models considering various conditions are utilized to reveal the lateral load bearing mechanism of BPGs, and the influence of design indicators on the lateral bearing capacity (Hu) of BPGs is thoroughly studied through a parametric study. Finally, an empirical design method is proposed based on 32 numerical model results to predict the bearing ratio (γ) as well as the lateral bearing capacity of BPGs in sand. The results show that, as the batter angle (θ) becomes larger, the lateral bearing capacity increases, and the maximum bending moments of both front-row piles (FRPs) and rear-row piles (RRPs) decrease, which means the shadowing effect on the RRPs is also reduced. With the increasing of batter angle (θ), the improvement effect of the pile length on the lateral bearing capacity becomes more significant, and the enhancement effects of the pile diameter and the relative density of sand on the lateral bearing capacity are decreased. The conclusions derived from this study can provide guidance for the design of BGPs in practice.

Experimental evaluation of phase and velocity control for a cyclorotor wave energy converter

The research presented in the paper is dedicated to the analysis of the 3D experimental testing results of a 1:20 scale prototype LiftWEC cyclorotor wave energy converter (WEC). The scaled prototype was built and tested in the Hydraulic and Offshore Engineering wave Tank (HOET) by Ecole Centrale Nantes (ECN) in 2022. The analysis is conducted using the analytical control-oriented point-vortex model. The presented research covers a range of tests, with particular focus on cases where positive mechanical power generation has been recorded. The analysis of such cases is important, in highlighting the conditions needed for optimum energy conversion, for future development of cyclorotor WEC technology. The study also reviews the results of tests where the rotor rotational speed is varied within each period of monochromatic waves. This is the first experimental test of such a control strategy for cyclorotor WECs.

Evaluation of Spectral Wave Models Physics as Applied to a 100‐Year Southern Hemisphere Extra‐Tropical Cyclone Sea State

AbstractExtreme significant wave height estimates, and their probability of exceedance, are fundamental offshore and coastal engineering design parameters. These estimates are characterized by uncertainty due to an incomplete understanding of the atmosphere‐ocean energy and momentum exchanges during intense storms. This particularly affects extreme wave statistics of ocean regions exposed to large and frequent synoptic disturbances such as Extra‐Tropical Cyclones (ETCs). In this work, we assessed the performance of global phase‐averaged spectral wave models in representing the 1 in 100‐year sea state generated by a Southern Ocean ETC in April 2021. We collected in situ and remote sensing observations, from the storm generation region to its decaying phase and the impact on South‐East Australian coastlines. We compared the observations with a suite of reanalysis and hindcast global wave model data sets. While comparing well for wind speed up to 20 m/s, the models presented differences in solving the air‐sea momentum exchange between the atmosphere and the ocean for wind speed velocities between 20 and 35 m/s, which are a distinctive characteristic of ETCs. Despite marked differences in the storm generation region, the models converged to a similar representation of the swell systems impacting the South‐East Australian coastlines, as demonstrated by a comparison with deep‐water buoy observations close to the coastlines. Furthermore, we found that the energy of the ERA5 reanalysis, which assimilates satellite wave height measurements is quickly dispersed and, as such, of little advantage in representing the 9.9 m significant wave heights that impacted the South‐East Australian coastlines on 10 April 2021.

Experimental study on characteristics of liquid dynamics in a cylindrical water tank under harmonic excitation

AbstractAs the offshore engineering industry continued to develop, issues such as damage to storage structures due to liquid shaking became increasingly prevalent. This paper explored the dynamic response of liquid within a rigid cylindrical water tank subjected to harmonic excitation through vibration table tests, analyses, and numerical simulations. Using the Laplace equation and the Bessel function of the first kind, the analytical formula of liquid dynamic response was derived. A numerical model was established by ANSYS software to verify the accuracy of the analytical solution. At the same time, the response characteristics of hydrodynamic pressure and liquid level wave height were studied by vibration table tests. In this experiment, a rigid cylindrical water tank with varying depths of liquid was subjected to harmonic excitations utilizing a vibration table. In most cases, the experimental results agreed well with the analytical formula. However, under conditions of relatively severe liquid sloshing, there was a discrepancy in peak values between the experiment and the analytical formula. The experimental data indicated that both the hydrodynamic pressure and liquid level wave height increase with an increase in harmonic excitation frequency and amplitude.

Statistical characteristics of sea surface waves derived from buoy measurements in the eastern Guangdong offshore water

The wave characteristics of the eastern Guangdong offshore water were quantified based on 1-year wave observations at a water depth of 60 m. This study statistically analyzed the observed wave characteristics and quantified the variations of the wave parameters and spectrum due to Super Typhoon Mangkhut. Results showed that the dominant and strong wave directions in the northeastern South China Sea were north-eastern and eastern, respectively. The average significant wave height was in the range of 0.7–2.4 m. During Super Typhoon Mangkhut, the maximum wave height and period were 11.3 m and 10–12 s, respectively, and peak spectral density mainly varied between 0.06 and 0.1 Hz. Results of this study can provide a basis for offshore engineering design and are of great significance for marine forecasting and disaster prevention and reduction.

Resolved CFD-DEM Simulation of Free Settling of Polyhedral Particles with Various Orientations: Insights Provided by Oscillation Behavior in Quiescent Liquid

Particle settling is the process by which particulates move toward the bottom of a liquid, which can affect the sediment transport and energy balance of marine systems. However, the deficiency in understanding the resolved fluid–particle interactions with complex boundaries in the settling process awaits resolution. This study employs a hybrid approach that combines computational fluid dynamics (CFD) with the discrete element method (DEM) to fully simulate the free-settling behavior of polyhedral particles in water. The accuracy of the method is verified by comparing numerical results with experimental data of ellipsoidal particle settling. Two series of tests with horizontal and vertical particle release directions are established to investigate the effects of particle shape features, such as the aspect ratio (AR) and corner (C), on the particles’ mechanical behavior and hydrodynamic characteristics. The results demonstrate that particle shape exerts a substantial influence on fluid resistance, rotational motion, and fluid disturbance throughout the settling process. The maximum velocities in vertically released cases are roughly 1.2–1.3 times greater than those in horizontally released cases. The study highlights the potency of the resolved CFD-DEM method as a robust technique for comprehending fluid–particle phenomena within the marine geotechnical engineering, including sedimentation and erosion of seabed sediments.

Sea Floor Characterization by Multiples’ Amplitudes in Monochannel Surveys

The lithological characterization of the seafloor is key information for offshore engineering, especially when it comes to pier and platform design. Undetected shallow gas pockets may cause the collapse of heavy platforms for hydrocarbon production. Unconsolidated sediments are not ideal for the basement of wind farms for electric power production. Drilling and coring can be used for local sampling, but continuous profiles or even areal coverage are far more preferable. High-resolution seismic profiles are successfully used when ports are not too busy, but otherwise, single-channel systems must be used. We show in this paper that even these simpler systems can be used to estimate parameters such as the acoustic impedance of shallow sediments directly beneath the seafloor. We exploit the amplitude decay of the multiple reflections between the seafloor and the surface, which does not depend on the source energy. If the offset between source and receiver is not too small, we can estimate the shallow P velocity and, via acoustic impedance, also the rock density.

On the development of a generalized atmospheric boundary layer velocity profile for offshore engineering applications considering wind–wave interaction

Within industrial standards, effects due to wind–wave interaction on the marine atmospheric boundary layer (ABL) may be included via the Charnock sea-surface roughness parameter for open-sea and near-coastal waters. This roughness parameter does not accommodate the wide variety of wave states possible, nor does it modify the ABL to include speed-up effects resulting from an undulating wave profile. In an attempt to provide an updated definition of the general ABL profile for offshore wind engineering applications, an experimental and numerical study is performed to assess the interaction of the ABL on a fixed wave geometry. By extracting the mean velocity field during the wind–wave interaction, bespoke values of the velocity profile power exponent and wind risk factor can be obtained. A range of wave heights and wave lengths are considered from which a Kriging surrogate model is trained to supply the relevant wind profile parameters depending on the wave state. These newly garnered parameters enable the practitioner to define a reference wind velocity, and then adjust the velocity profile characteristics to contain the influence of the wave. This approach provides a new inlet velocity condition that can be used within computational wind engineering investigations without the need to explicitly model the wave surface, as well as flexibility in specifying the underlying wave conditions. Application of the re-calibrated velocity profile shows that wind forces are significantly greater throughout an offshore wind turbine (OWT) swept blade area when large (H= 15 m) and small (H= 1.5 m) wave heights are compared.

Revealing Inclusion Evolution Behaviors During Hot-Rolling Heating of EH550 Offshore Engineering Steel

Revealing Inclusion Evolution Behaviors During Hot-Rolling Heating of EH550 Offshore Engineering Steel

Effect of soil spatial variability on characteristics of depth-varying multi-support seismic motions at offshore sites

The purpose of this study is to evaluate the influence of soil spatial variability (SSV) on the simulation of depth-varying multi-support seismic motions (DMSMs) at offshore sites. Firstly, the random field theory is used to quantify the extent of SSV, and a series of random field models with different characteristics are established for an offshore site by changing the coefficient of variation (COV) and correlation distance of soil parameters. Then, the simulation approach for random ground motion transfer functions (GMTFs) and DMSMs at offshore sites are introduced. The sensitivity of each uncertain soil parameter on the offshore seismic motions is explored using the single variable method. Finally, the effects of SSV on the GMTFs and DMSMs are investigated, in which the effects of COV and correlation distance are studied in detail. The results demonstrate that SSV has a remarkable influence on the GMTFs of offshore sites, which results in a large intensity variation of DMSMs. The sensitivity analysis indicates that the soil density and shear modulus are influential factors for the horizontal components of DMSMs; except these two parameters, the Poisson’s ratio also significantly affects the vertical DMSMs. Moreover, both COV and correlation distance can lead to certain variability in the GMTFs and DMSMs, and the effect of COV is more prominent than the correlation distance. This study provides an effective approach for the simulation of DMSMs at random offshore sites, which is valuable for rational probabilistic seismic performance assessment of offshore engineering structures.

A bibliometric analysis on the relevancies of artificial neural networks (ANN) techniques in offshore engineering

A bibliometric analysis on the relevancies of artificial neural networks (ANN) techniques in offshore engineering

Study on the relationship between fractal dimension and particle fragmentation for marine coral sand under impact load

As a subsoil for many offshore structures, marine coral sand can encounter various impact loads, resulting in particle fragmentation. The "fractal theory" is an excellent method to quantify particle fragmentation. However, the relationship between the fractal dimension and relative breakage as well as its influencing factors are somewhat limited for coral sand under impact loads. Therefore, this paper systematically investigates the fractal behavior of a classic type of coral sand in the South China Sea through a series of impact load experiments. The experiment results show that the gradation curve of the coral sand under impact loading exhibits evident fractal characteristics after fragmentation, with the fractal dimension increasing with increasing fragmentation. And the ultimate fractal dimension is independent of the particle size and uniformity coefficient. Therefore, taking the ultimate fractal dimension as an ultimate state of particle fragmentation, a relative breakage index based on the relationship between the original, current, and ultimate fractal dimensions is proposed. These results can support more efficient and accurate predictions of particle fragmentation, thus promoting the safer design and construction of offshore engineering in coral sand.

Vertical vibration characteristics of an offshore end-bearing pile embedded in saturated soils

Pile foundations have increasingly been used extensively for the foundations of offshore engineering structures such as cross-sea bridges, offshore wind turbines and gas infrastructure. Meanwhile, pile integrity testing (PIT) is an important method for evaluating the safety of the pile foundation. In this study, the vertical vibration characteristics of an offshore end-bearing pile embedded in saturated soils is studied by a semi-analytical method. The upper water is assumed to be an ideal compressible fluid and the lower soil is assumed as saturated soil and satisfies Biot's theory of poroelasticity. The dynamic governing equations of the ideal compressible fluid and the saturated soil governing equations are decoupled by introducing potential functions and Helmholtz decomposition using the Laplace transform. Analytical solution for the offshore end-bearing pile vertical vibration is obtained in the frequency domain. The semi-analytical solution for an offshore pile excited by a half-sine wave in the time domain is then obtained by means of inverse Fourier transform. By downscaling the pile-water-soil model to a pile-soil model, the accuracy of the proposed solution was verified. A parametric study is conducted to investigate the influences of water depth, pile radius, soil shear modulus, soil porosity, and soil permeability on the vertical dynamic responses of offshore pile, including complex impedance, the admittance of velocity, and time domain velocity response. The results indicates that the water depth, pile size and soil properties have considerable influence on the response of offshore pile vertical vibration.

Analiza awarii podczas eksploatacji podmorskich złóż ropy i gazu

Failures caused by offshore oil and gas structures operations are investigated. This work is based on the description and analysis of real case studies of accidents on offshore stationary and floating platforms; it combines foundational knowledge and current research on the latest developments in the field. It was shown that strength characteristics of offshore reinforced concrete and steel elements change during operation and cause the accumulation of defects and damages. It was established that corrosive wear, corrosion-mechanical processes, and crack-like defects are the decisive causes of element failure. It was shown that up to 60–75% of all damages to and failures of offshore engineering facilities' steel structures occur due to the corrosion-mechanical influence of an aggressive environment and force loads. This means that issues of corrosion-mechanical failure of such structures have become an industrial-scale problem. It thus allows us to draw the following conclusions: improvement of steel offshore drilling platforms (ODPs) maintenance system involves the development of new models and methods of managing the operational reliability of these structures, aimed at making decisions that take into account the crack resistance and fatigue-corrosion strength of steel ODPs in contact with the corrosive-active environment. Only on the basis of such scientifically and economically grounded models can rational strategies be shaped for carrying out revisions of the ODPs technical condition, ensuring the necessary level of their reliability during the operation period. This investigation can be very helpful to improve the design and construction of more reliable and durable offshore stationary and floating platforms.

Numerical modeling of water waves with the highly efficient and accurate Lagrangian-Eulerian stabilized collocation method (LESCM)

A novel numerical wave tank (NWT) based on the Lagrangian-Eulerian stabilized collocation method (LESCM) is constructed for modeling water waves, in which the piston-type wavemaker is employed for wave generation, and the relaxation zone technique is used for wave absorption. The LESCM is an evolution version of the particle-in-cell method. In its discretization scheme, a background mesh covering the entire tank is introduced for solving the incompressible Navier-Stokes equations by the stabilized collocation method (SCM), and the water inside is discretized by Lagrangian particles which shuttle within the Eulerian mesh. Then, the Eulerian mesh communicates with Lagrangian particles through high-order consistent reproducing kernel (RK) interpolation. Besides, the mesh is initialized at the beginning of each time step, which can avoid the reconstruction of shape functions and dramatically reduce computational efforts. Furthermore, the numerical solution of the SCM is locally and globally conserved since the SCM is a subdomain method just like the finite volume method. Moreover, the information transfer between nodes and particles satisfies the conservation property, which makes the novel NWT a fully conservative model. Several numerical examples demonstrate that the proposed NWT is highly efficient, accurate and stable, and hence can be applied to the research of coastal and offshore engineering.

Numerical Modeling of the Micromechanics Damage of an Offshore Electrical High-Voltage Phase

Due to the strong growth of offshore renewable energies, research and engineering in this field is constantly expanding. One of the centerpieces of these technologies is the high-voltage electrical cable, generally made of copper, to transport the energy produced from the offshore farm to the onshore station. The critical nature of these cables lies in the proven resistance that they must demonstrate during stays underwater for several years, even decades, in difficult environmental conditions, which begin at the handling, shipping and underground burial stage. The marine environment can lead to deformation of the copper wires well beyond the limit of proportionality and, consequently, to breakage. Copper, although being an exceptional electrical conductor, has very poor mechanical properties. The plasticity generated by the excessive deformation of copper wires affects all of the physical properties of copper. When plasticity develops, electrical transport is affected and the heat within copper increases, but care should be given to not exceed 90 °C, as this would result in the shutdown of the cable with dramatic economic consequences. The work carried out in this article, which is part of the National Project EMODI as well as the European Project FLOW-CAM, aims at studying the mechanical behavior of the phase in order to correlate the deformation levels reached to the phase geometry as well as operating mechanisms of damage which reflect the proliferation of microstructural defects within the conductor. To do this, we propose a numerical model using Abaqus. Correct description of the effects of several parameters (geometry of the phase) and plasticity development on the performance of the phase were simulated and discussed.