Sort by
The reliability of pre-deformation to control lateral buckling of pipelines: An evaluation based on observed embedment trends

Pre-deformation of a pipeline into a continuous sinusoidal wave-like form has been shown to be effective at controlling lateral buckling of subsea pipelines due to a substantially lower axial stiffness and the limiting of maximum strain at any location. This paper explores the feasibility and reliability of using such an approach, with an existing operating pipeline, which was installed using zero-radius bend (ZRB) initiator structures, used for comparison. Survey data of the pipeline profile and seabed bathymetry are adopted along with the pipe-soil interaction (PSI) inputs from the original design allowing a like-for-like comparison of the two approaches to management of lateral buckling. The comparison shows that, for the assumptions made in the numerical modelling, use of a pre-deformed pipeline results in lower strain than using ZRBs. Furthermore, the performance of the pre-deformed pipeline is robust, and shown to be unaffected by uncertainties in horizontal out-of-straightness, PSI input and seabed features. This study shows that pre-deformed pipelines can be an effective alternative for controlling the lateral buckling of subsea pipelines, which eliminates the need for buckle initiation structures to be installed along the pipeline route. This provides impetus for further work on installation methodologies to create the required level of pre-deformation.

Open Access Just Published
Relevant
A unified cross-series marine propeller design method based on machine learning

Propeller design diagrams, like Bp-δ diagram, are widely applied in ship propeller design. However, different propeller series use various selection approaches, so comparisons between designs are only possible after individual candidates are chosen.This paper proposes a unified approach based on machine learning to allow efficient comparison and facilitate the selection of the optimal propeller amongst the available propeller series. The process starts by compiling propeller series data to generate a comprehensive dataset on propeller performance. This dataset is then used to train an Artificial Neural Network (ANN) model, which accurately predicts open-water propeller performance. Optimization techniques are applied to maximize propeller efficiency based on the specific needs of the vessel, while ensuring compliance with cavitation and noise constraints for safety. The model's accuracy is validated using data from the KRISO Container Ship (KCS), demonstrating the prediction's reliability. The method is then applied to select both open and ducted propellers for a variety of ship types to meet specific operational requirements. Ultimately, the optimized results are ranked by efficiency, offering an organized set of options for selecting the most suitable propeller. This approach eliminates the need for manual dataset correlation, significantly improving the efficacy of generating an outperforming initial design.

Open Access Just Published
Relevant
Numerical and experimental study on the mechanism of added resistance in stepped moonpool under different waves

To study the additional resistance effect of the moonpool during the navigation of the drilling vessel, this paper explores the variation of the drilling vessel resistance under different waves based on a model test and numerical simulation. The difference between the model test and the numerical simulation results is compared, and the mechanism of the added resistance of the moonpool under different waves is revealed. The results show that the technology of numerical simulation is able to accurately simulate the navigation resistance of the drilling vessel in waves. The numerical simulation results closely correspond to the experiment results, and the error range can be controlled within 10%. In the components of the total resistance of the hull, pressure resistance plays a dominant role when the drilling vessel sails in waves. The pressure resistance accounts for about 60%–70% of the total resistance, while the friction resistance accounts for about 30%–40% of the total resistance. At low speed, the average resistance reduction rate of the dissipative equipment is 4.4%; under the condition of medium speed, it is 7.5%; at high speed, it is 9.6%; and the resistance reduction efficiency of the dissipative equipment increases with the increase in speed. The dissipative equipment partially suppresses the eddy's action stage and prevents eddy shedding from entering and directly hitting the back wall, thereby reducing the moonpool's additional pressure resistance. The research results can provide a reference for energy savings and emission reductions in drilling vessels.

Just Published
Relevant
Directional wave spectrum estimation through onboard measurement data utilizing B-spline basis functions

The utilization of digital twin technology, which integrates real-world measurement data with a digital representation of the vessel, is garnering increasing attention within the realm of structural integrity management. Due to limitations in sensor deployment on ships, the integration of the digital twin framework, which merges measurement data with the ship's digital design model, becomes crucial for ensuring the effectiveness of structural integrity management. This investigation introduces a methodological approach for estimating localized responses at unmeasured locations, leveraging both measurement and design datasets. To approximate the response at unobserved sites, the directional wave spectrum is initially determined utilizing the least squares method, thereby, minimizing the disparity between the estimated and measured response spectra. The methodology notably incorporates cubic B-spline interpolation specifically to smooth the directional wave spectrum deployed on the heading-frequency domain. This deliberate choice of employing cubic B-spline interpolation underscores the emphasis on achieving a refined and continuous representation of the directional wave spectrum, thus enhancing the accuracy and reliability of the estimation process. To validate the proposed methodology, synthetic pseudo-measurement data derived from the wave spectrum and RAO of a 13,000 TEU container ship are employed. Subsequently, the directional wave spectrum is estimated utilizing the pseudo-measurement data, and the estimated directional wave spectrum, in conjunction with the Response Amplitude Operator (RAO), is harnessed to approximate the response spectrum at the location where sensors are not installed.

Just Published
Relevant
Structure design and ultimate strength envelope of a modular carbon fiber-reinforced polymer (CFRP) laminate tube box on a 5000 ft deep-sea ultra large unmanned underwater vehicle

Deep-sea tube box is a crucial and basic structural component of various deep-sea equipment such as deep-sea submarine and unmanned underwater vehicles. The deep-sea ultra large unmanned underwater vehicle (ULUUV) is the most representative one of them. Tube boxes are the basic modular members on the ULUUV, which are widely used as the load-bearing hull in torpedo launch, load transportation, pipeline protection and etc. Due to the extremely harsh operation condition, deep-sea tube box simultaneously suffers extremely high lateral water pressure and tremendous axial compression induced by water pressure. Considering the strict requirements for lightweight, high strength, and corrosion resistance of deep-sea tube boxes, carbon fiber-reinforced polymers (CFRP) have become the most potential choice for the construction materials of future deep-sea tube box. Thus, the aim of this paper is to make a structure design of a deep-sea CFRP tube box which can operate at the water depth of 5000 ft. In this paper, a detailed design process of the deep-sea CFRP tube box was introduced, including geometrical configuration, critical buckling load prediction method, FE modeling technique and experimental validation. Corresponding to 5 ply schemes, 495 cases of FE analyses were performed to obtain the ultimate strength envelopes of the CFRP tube box subjected to combined axial compression and external lateral water pressure. Based on the obtained results, the best ply scheme for the deep-sea CFRP tube box was figured out. This paper could provide design method and data references for deep-sea CFRP structures which are subjected to combined loads.

Just Published
Relevant
Effects of transverse loading on the ultimate strength prediction of stiffened panels under biaxial loads: Potential improvements to the IACS rule formulation

The current International Association of Classification Societies (IACS) rule for designing stiffened panels was found in Wang et al. (2024) to conservatively predict the ultimate strength of panels when transverse loads predominate. This conservatism arises from the overestimation of bending moments acting on stiffeners by directly applying the beam analogy in both longitudinal and transverse directions in the rule formulation when evaluating stiffener yielding.To address this issue, this paper applies the orthotropic plate theory to calculate bending moments experienced by the stiffeners of panels under biaxial loads. Orthotropic properties are derived from equivalent sectional areas and moments of inertia. The predicted bending moments are validated through comparisons with numerical simulations. The effects of boundary conditions and deflection patterns with varying numbers of half-waves are discussed. Based on the analytical results, a modification of the IACS rule formulation is proposed by introducing a correction factor to account for transverse loading effects in the bending moment calculations. The factor is a function of the ratio between longitudinal and transverse loading.The modified IACS rule formulation is verified through numerical simulations of aluminium panels using ABAQUS and comparisons with results from existing literature on steel stiffened panels under various biaxial loading conditions. The modified rule formulation shows improved accuracy in predicting the ultimate strength of stiffened panels, particularly in cases with dominating transverse loads. The modified IACS rule formulation can be useful for more reliable and cost-effective design of ships and offshore structures.

Open Access Just Published
Relevant
Deep analysis of power regulation on fatigue loads and platform motion in floating wind turbines

The fatigue loads experienced by components and the motion of the platform in floating wind turbines are likely influenced by their operation within a limited power state; however, the corresponding effects remain inadequately understood. This study investigates a 5 MW semi-submersible floating wind turbine, aiming to provide a comprehensive analysis of fatigue loads on critical components and platform motion under various power regulation modes. To achieve this objective, we employed the NREL 5 MW semi-submersible wind turbine model, generated three-dimensional wind fields using TurbSim, and conducted dynamic simulations with OpenFAST, utilizing MLife software for post-processing of fatigue load analysis. We assessed the fatigue loads of four key components—the blade root, tower base, drivetrain, and mooring cables—alongside the platform motion under varying generator speeds, yaw angles, and active power levels. Additionally, correlation analysis was performed to explore the relationship between component fatigue loads and platform motion under different yaw conditions. The results demonstrate that both generator speed and yaw angle significantly influence fatigue loads and platform motion, while the effect of active power appears to be relatively minor. Specifically, an increase in generator speed markedly elevates fatigue loads on the blade root and drivetrain, while concurrently reducing loads on the tower base and certain mooring lines. The analysis further reveals that, under various yaw angles, the fatigue loads on symmetrically positioned mooring cables exhibit a symmetric response, impacting fatigue damage in the blade root and tower base moments. Moreover, the relationship between maximum horizontal platform displacement and fatigue loads varies. The findings of this study provide critical insights into the operational optimization of floating wind turbines.

Just Published
Relevant