Marine Structures最新文献

The vertical lowering of subsea equipment is one of the most used installation methods. Consisting of the lowering of the equipment by using a cable connected to a crane located on a support vessel, this method is usually more straightforward than others. However, the vertical stiffness of the system depends on the cable's length, meaning that the natural frequency of vertical motions will vary along the lowering of the equipment. At some water depths, the natural frequency will be close to the typical wave frequency of the region, which will lead to a dynamic amplification of these motions, which can lead to the slackness of the cable, that is, there will be zero tension on the cable. The lack of stiffness due to the slackness means that the equipment's submerged weight will be responsible for bringing the equipment downwards, leading subsequently to higher tension peaks usually known as snap loads. The current recommendation by the classification societies is to avoid installing under environmental conditions when slackness occurs. However, based on the understanding of the nonlinear anatomy when the cable is slack, the present work shows that it would be possible to increase the operation window.

This paper focuses on investigating the fatigue crack growth (FCG) characteristics and residual fatigue life of tubular T-joints which are prone to suffer fatigue damage at the brace and chord intersections under multi-axial stress. Static and fatigue loading tests are performed to investigate the FCG behaviors of tubular T-joints, combining beach marking technique. The evolution of FCG characteristics is studied during the crack growth, convergence and wall penetration through an efficient co-simulation system that established using the multi-scale modeling technique. Fracture morphology analysis is conducted to gain insight into the FCG behaviors combining the scanning electron microscope (SEM) observation. Results indicate that multiple cracks initiate at the crown regions and subsequently evolve circumferentially around the weldments in a doubly-curved shape towards wall-thickness. Interaction effects between adjacent cracks extend the fatigue life along the outer surface, attributed to the premature exposure of converged crack front and the induced variation of stress intensify factor (SIF) distribution along the crack front. The dominant failure mode of tubular T-joints is characterized by an opening mode crack, with the contribution of anti-plane shear mode crack gradually increasing as structural symmetry diminishes. The established co-simulation system shows advantage in capturing the FCG behavior, predicting the fatigue life and characterizing the FCG characteristics with a good balancing of simulation efficiency and calculation accuracy.

As typical metal thin-walled structure, bellows are used widely in various engineering fields, especially in storage and transportation of floating liquefied natural gas (FLNG) system on the sea. While the shapes of the bellows are relatively complex with the characteristics of geometric nonlinearity in the structure, it is quite challenging to calculate basic mechanical properties of the bellows accurately through theoretical analysis. Concurrently, both numerical simulation and experiments also require high computational and economic cost. Given the typical one-dimensional periodicity of the structure of U-shaped bellows, novel implementation of asymptotic homogenization (NIAH) method was secondary developed in finite element software and unit-cell model of the whole structure with periodic boundary conditions was established, realizing equivalent analysis of the overall mechanical properties of the bellows accurately and efficiently. By comparing the NIAH equivalent results with the fine finite element model results, it was found that the relative error was within 3.00 % and the calculation cost was reduced by 40 times. Compared with the experimental results, the error of NIAH equivalent results was also less than 6.00 %, which verified the accuracy and high efficiency of the NIAH equivalent method. Furthermore, the influence of unit-cell model with different structural sizes on the prediction accuracy of the NIAH equivalent stiffness results of the bellows was also discussed. This study provides a new effective method for the design and analysis of the structure of bellows.

Ship structures are referred to as plated and/or welded structures. Plates are sequentially welded using a high-temperature heat source to assemble the overall ship. The heat source used in the sequential welding inevitably generates imperfections in the ship structure, e.g., welding-induced deformation. Predicting welding-induced deformation is a critical task in design and control management at a shipyard, and much research has focused on the inherent strain method among possible efficient numerical methods. However, determining the inherent strain requires the synchronisation of all strain terms as a function of time and welding uncertainty because the welding position depends on the human worker. The present study thus derives time-dependent terms for inherent strain of the overall welding process and includes the welding position and cooling method in the function of the heat transfer coefficient. The inherent strain is derived through the detailed analysis of the overall welding process in terms of the application and utilisation, and it is simulated and reviewed for the erection of the hull block of a container ship and an LNG carrier. The inherent strain is expected to be used as a simple form of strain in the further study of various large welded structures and materials and in research on welding parameters.

This Part 3 of the paper series on jack-up model tests describes the model test design and selected results for transit conditions. As part of the summary for the paper series, uncertainty analysis for the entire jack-up model tests was also conducted and presented. Operating scenarios were simulated, covering jack-up model with legs extended above the hull as well as legs partially submerged into the water. Soft moorings were used to provide horizontal restraint onto the jack-up model. Long-crested waves without and with co-linear uniform current were used throughout the tests, with current meant to simulate sea-keeping and wet towing conditions. Reduced motions in surge and pitch were observed for the jack-up with legs partially submerged into the water, demonstrating additional damping to be gained, but at the expense of increased towing drag forces. Additional measurements in terms of bending moment at the leg-to-hull connection as well as shear forces on the starboard leg were also compared. Uncertainty analysis was conducted for the entire jack-up model test to quantify the errors and confidence level of the presented results.

This study provides a clear insight into the dynamic response of rectangular plates subjected to repeated impacts using experimental and numerical methods. Repeated impacts are performed on the mild steel plates with a length-to-width ratio of 3, which can be regarded as scaled-down ship plates. During the experiments, both fracture and pseudo-shakedown phenomena are observed, occurring under relatively high and low impact velocities, respectively. By thoroughly analysing various parameters related to the dynamic response, including the plate deformation, contact force, rebound velocity of the impactor, and dissipated energy ratio, among others, the study effectively characterizes the behaviour of plates under repeated impacts. Numerical simulations are conducted and a detailed comparison between the numerical and experimental results is carried out, accompanied by a careful analysis of the discrepancies between them. The numerical simulations exhibit a qualitative capability to predict the dynamic response of plates subjected to repeated impacts. The ‘failure displacement’ proposed by the authors is verified against the experimental results. Moreover, the threshold impact velocity for the pseudo-shakedown occurrence is unveiled by numerical simulations.

Plant biomass-based composites have emerged as a sustainable alternative to synthetic fillers in the maritime industry. They have gained significant attention due to their unique advantages compared to traditional synthetic fillers. These advantages include greater flexibility, environmental friendliness, biodegradability, renewability, and low density. This study provides a comprehensive evaluation of plant biomass-based composites (PBCs) within the maritime sector, focusing on their composition, treatment methods, properties, and diverse applications. It highlights the extensive use of various plant biomass components, such as stems, leaves, seeds, grass, and wood, as effective fillers for PBCs. To enhance their performance, a variety of modification techniques, both physical and chemical, have been successfully employed. Polymer-based matrices are the most commonly chosen for PBC synthesis, although metals and ceramics are also utilized. The study examines the mechanical, chemical, water absorption, thermal, electrical, and morphological properties of PBCs relevant to the maritime industry. Applications of these composites are broad and encompass the production of boats, hulls, decks, canoes, surfboards, shipping ropes, paddles, and more. The adaptability and versatility of PBCs across these applications hold the potential to enhance structural integrity, reduce maintenance costs, and improve environmental performance in the maritime industry. This research contributes to a better understanding of plant biomass-based composites' potential in the maritime sector, addressing global concerns related to climate change and resource conservation. It underscores the pivotal role of PBCs in fostering a more eco-friendly and resilient maritime industry while promoting technological advancements and operational efficiency.

Stiffeners support lateral pressure and axial load and are one of the essential members of a ship structure composed of stiffened panels. Their scantling formulae are important to ensure adequate strength against lateral pressure and for the rapid and proper initial design of hull structures. However, the current rule scantling formulae are based on the elastic beam formulation, and the effect of the simultaneous axial stress is considered differently by the rule as a coefficient for reducing the allowable stress. In this study, based on the fully plastic moment under the action of axial stress, the stiffener bending strength corresponding to the plastic hinge formation criteria (initial hinge and plastic collapse) was determined using simple theoretical formulae considering the additional lateral force induced by the axial stress on the deflected stiffener. Subsequently, the structural behaviors were investigated comprehensively by theoretical parametric studies based on various stiffener scantlings and loading combinations, which were further compared with the results of finite element analysis (FEA) based on the residual deflection criterion, thereby verifying the validity of the theoretical proposals. Consequently, by combining the findings from the theoretical and numerical investigations, the effect of the axial stress on the stiffener bending strength was expressed as closed-form coefficients. These proposed axial stress coefficients were verified to govern the actual structural behaviors well and are expected to provide a rational basis and contribute to improving rule-scantling formulae.

The jacket substructure is a critical component of the offshore wind turbine (OWT) that is the interface between the transition piece at the top and the grouted connection. This paper presents a comprehensive study on the optimization of a jacket substructure to achieve greater cost efficiency while maintain acceptable structural performance. A fast parametric finite element modelling (FEM) approach for jacket substructures was firstly proposed. The generated models took into account realistic loading conditions, including self-weight, wind load and section-dependent wave load, and soil-pile interaction. Parametric studies were conducted afterwards to investigate the trends of the mass and response of the jacket substructure with respect to the variation of geometric and sectional parameters. Optimizations of the jacket substructure were carried out using parametric optimization and numerical genetic algorithm (GA) optimization under three different optimization strategies corresponding to three groups of objective and constraint functions. The trends obtained by parametric analysis were used to guide the parameter selection in parametric optimization, while a rank-based mutation GA was established with the proposed efficient FEM embedded in as the solver to the optimization objective and constraint functions. Parametric optimization gained its advantage in computational efficiency, and the mass reduction were 6.2%, 10% and 14.8% for the three strategies respectively. GA optimization was more aggressive as the mass reductions were 16.8%, 22.3% and 34.3% for the three strategies, but was relatively more computational intense. The two proposed optimization methods and the three optimization strategies are both expected to be applied in practical engineering design of OWT jacket substructure with good optimization output and high computational efficiency.

Robotic welding has garnered significant attention in the maritime industry for its potential to enhance marine structure quality and optimize production processes. This systematic literature review aims to provide a comprehensive overview of the current state of research in robotic welding for marine applications, encompassing marine structures and production processes, following the PRISMA statement and guidelines. The review encompasses various facets, including welding techniques, processed materials, types of robotic welding, technological advancements, potential advantages, and challenges encountered when implementing robotic welding systems in the maritime sector. The results spotlight the pivotal role of gas metal arc welding (GMAW) in propelling robotic welding technology forward, while wire arc additive manufacturing (WAAM) has experienced a notable surge in popularity, signifying its potential to catalyze significant changes in maritime manufacturing processes. Notably, the predominant use of robotic welding centers on carbon steel materials. However, ongoing advancements indicate a growing diversification, with the incorporation of advanced materials like high-strength alloys on the horizon. Additionally, the utilization of 6-axis robot welding in conjunction with fully autonomous systems has emerged as a versatile and potent instrument that has revolutionized welding methodologies across various maritime research domains. Robotic welding provides a number of advantages, such as increased productivity, higher quality, adherence to industry standards, adaptation to confined and dangerous locations, and facilitation of innovative construction techniques. Nevertheless, adoption of this cutting-edge technology is not without challenges. By synthesizing the results from several investigations, this research study offers useful insights into the current knowledge gaps, emerging trends, and future prospects for the growth of robotic welding in maritime applications.