Marine Structures最新文献

A comparative study between numerical modelling and experimental investigation is performed to validate the developed numerical method for simulating floating dock operations with a vessel on board. Both model-scale and full-scale experimental tests are performed on floating docks with a vessel on board, and the draughts using draught meters, floating positions and bending of the floating dock are measured. The present numerical method is proposed based on a quasi-static assumption during vessel-docking operations. A static analysis model is built to determine the static response of a floating dock under a specific ballast water distribution based on a hydrostatic force model and a Newton-Raphson method. A bending model is proposed to calculate the deflection of the floating dock along the longitudinal direction. Results of the mode-scale tests show that the draught measurements and the floating positions of the dock and vessel predicted using the present numerical method agree well with the corresponding experimental results. It proves the accuracy of the present numerical method for simulating vessel-docking operations. Moreover, a well-designed ballast plan enables successful de-ballasting operations on the model-scale dock, even in the event of one to three pump failures. The comparison of the deflection changes of the floating dock in the field test measurements further proves the accuracy of the present bending model. Therefore, the validated numerical model tested on both model-scale and full-scale docks provides a reliable foundation for creating digital twin of floating docks in shipyards.

The tendency to design high-performance ships demonstrates the importance of the trimaran and the cross-deck is of particular interest due to its exclusive structures and wave loads. Limited by the high cost of structural numerical simulation, relevant studies emphasize the effectiveness of a specific design scheme. This paper introduces the polynomial chaos expansion (PCE) and the bias-variance tradeoff to explore the statistical characteristics of the cross-deck's strength. The geometric model of a high-speed trimaran is built and the load case is designed. Samples are obtained using the Latin hypercube sampling technique and the corresponding stress response of the cross-deck is extracted by the finite element method. To overcome the limitation of sample size, the PCE is applied as a surrogate model to compute the statistical indicators of the stresses and the bias-variance tradeoff is introduced to select the hyperparameter of the PCE. The results show that the stresses at the cross-deck's corner are much higher and more sensitive to the plate thickness than those at other locations. Furthermore, the PCE is also compared with the Monte Carlo simulation to demonstrate its advantages, and it is shown that the PCE performs better under the limitation of sample size considering accuracy and convergence. The feasibility and efficiency of the PCE and bias-variance tradeoff in the statistical analysis of trimaran cross-deck structure is proved. The insights and recommendations summarized will be a useful aid for the design and optimization of the trimaran.

In ocean engineering applications, glass fiber reinforced composite materials undergo degradation over time due to various aging processes. Accurately assessing the mechanical properties of these materials as they experience aging conditions in marine environment becomes a crucial factor. Although various approaches, such as experimental, theoretical, or finite element methods (FEM), have been employed to investigate the impact of aging processes on composite materials, limited attention has been given to examining the damage of composite plates under the exposure of artificial seawater environments using the MAT162 material model. The objective of this study is to outline a methodology for identifying a group of MAT162 parameters in LS-DYNA through a unit single element analysis. S2 glass/epoxy composites were produced by vacuum assisted resin infusion method. Aging was carried out in artificial seawater environment for 4, 8 and 12 months. Tensile, through thickness tensile, compression, through thickness compression tests were performed and then the finite element modeling was conducted. Maximum strength (X_1T, X_1C, X_3T and S_FC), element eroding axial strain (E_LIMT), modulus of elasticity (E₁ = E₂, E₃), scale factor for residual compressive strength (SFFC), coefficient for strain softening property (AM) parameters were analyzed. It was determined that the proposed model for aging was in good agreement with the experimental study.

This study delves into the Local Joint Flexibility (LJF) of tubular K-joints reinforced with the collar plates under in-plane bending moments (IPBMs). 348 reinforced K-joints were simulated to analyze the impacts of the loading conditions (balanced and unbalanced moments), collar plate size (like the length and thickness) alongside the joints’ parameters (θ, γ, β, ξ) on the f_LJF and its proportionality (ψ). The research outcomes demonstrate that factors such as η, λ, and β play a significant role in determining ψ, whereas the influence of ξ, and γ on ψ appears to be negligible. Also, in the reinforced joints, the f_LJF is decreased by 77.4 % compared to the equivalent un-reinforced joint. While the role of the collar plate on the f_LJF is remarkable, the matter had not been investigated on K-joints. Therefore, following the detailed parametric study, two novel equations are proposed to safety estimate the f_LJF for such scenarios.

Given the advantages of flexible wave energy converters (FlexWECs), such as deformation-led energy harnessing and structural loading compliance, there has been a significant interest in FlexWECs in both academia and industries. To simulate the FlexWEC interaction with ocean surface waves, a 3D computational fluid-structure interaction approach is developed in this study. The fluid and solid governing equations are discretized using finite difference and finite element methods, respectively. An immersed boundary method is used to couple the two independent grid systems. A novel numerical technique is introduced to model the dielectric elastomer generator (DEG) as the power take-off (PTO). The wave energy capture performance is analysed for different PTO configurations and at various wave conditions. Based on the obtained results, the PTO damping coefficient and the relative wavelength range that maximizes the capture width ratio (CWR) are determined. The wavefield results also reveal the presence of wave-height enhancement and attenuation points around a single FlexWEC, providing potential site selection references when deploying multiple FlexWECs in an array.

To extend the hyperbolic p-y curve model for level ground to the design of offshore piles near sandy slopes, three modifications must be incorporated: the curve framework, the ultimate soil resistance, and the initial stiffness. A new curve framework is developed, in which the displacement that determines the soil resistance is changed to the sum of the soil compression instead of the pile deflection, by considering the soil-pile-slope deformation mechanism. The ultimate soil resistance, affected by the slope angle and near-slope distance, is derived using the failure wedge (FW) model. A modified initial stiffness is obtained by considering the reduction in effective overburden pressure. The accuracy of the modified model is verified through centrifuge tests and model tests. Finally, the effects of the slope angle, near-slope distance, and soil-pile-slope deformation mechanism on the pile response and the modified model are discussed. The modified model provides practicing engineers with a simple yet comprehensive theoretical approach, without the need for additional pile tests or numerical analysis.

A mathematical model is proposed to investigate the dynamic behavior of an end-bearing pile under vertical seismic loading in a water-pile-saturated soil system. The model is based on the Euler-Bernoulli beam theory and takes into account the stress balance between pile sections, representing the pile as a one-dimensional rod. The overall response of site is divided into two components: the free-field response and the scattered-field response. The pile and soil are considered as linearly viscoelastic materials with hysteresis-based damping, while water is modeled as a linear acoustic medium. By accounting for boundary conditions involving force equilibrium and displacement continuity at the pile-soil and water-soil interfaces, an analytical solution for the system response is derived. Analytical expressions of pore water pressure and displacements are obtained, on the basis of considering water-soil interaction in both fields. A parameterization study is then conducted to evaluate the impact of key parameters on the vibration characteristics of piles in a water-pile-saturated soil system.

Bearing capacity of pile foundation is one of the important factors affecting the safe operation of the offshore wind turbines. However, due to the influence of different geological conditions, pile types and other factors, it is difficult for the existing monitoring methods to obtain the change of real constraints of the pile foundation. A statistic-based equivalent constraint position prediction method for offshore wind turbines is proposed. The method is based on the first-order displacement and first-order frequency extracting from the measured acceleration signals obtained by the accelerometers installed above the water surface, and statistical method is adopted to eliminate the influence of noise and reduce the error caused by single prediction. The most achievement of the proposed method is that the constraint of pile foundation related to bearing capacity is obtained and quantified by equivalent constraint position, and more accurate assessment of safety state of the offshore wind turbine can be achieved. To verify the reliability of proposed method, numerical model of a 4-MW monopile supported offshore wind turbine considering the pile–soil interaction is carried out. The results show that the proposed method can accurately obtain the equivalent constraint position by a combination of first-order frequency and first-order displacement. Further, the field measurement of an offshore wind turbine located in Rudong County, Jiangsu Province of China is performed. A stable prediction of equivalent constraint range from -30.86 m to -30.15 m is obtained over 43 days of the test. Therefore, the proposed method can be used to predict the change of pile foundation constraint, and is of great significance to the safety assessment of offshore wind turbines.

A simplified analytical method for analyzing the dynamic behavior of the intermittently welded stiffened plate is newly proposed.

The plate and stiffener are considered as individual beams, and the influence of the longitudinal internal shear force per unit length at the stiffener-to-plate junction of a continuously welded stiffened plate is considered. The whole span of an intermittently welded stiffened plate is divided into welded and non-welded segments. The intermittently welded stiffened plate is changed into equivalent continuously welded one, and a model for the bending vibration analysis of the intermittently welded stiffened plate is developed. The governing equation for the bending vibration analysis of the intermittently welded stiffened plate by the influence function method is formulated and a practical approach is newly developed to solve the governing equation for the bending vibration analysis of the intermittently welded stiffened plate. The numerical calculation for bending vibration analysis of the intermittently welded stiffened plate is carried out. A comparison of results from the proposed method with the finite element analysis results is carried out to demonstrate the validity of the proposed method.

Near-field underwater explosions generate complex load forms and cause destructive strikes on ships. To investigate the damage characteristics of ships under the combined effect of multiple loads, local and overall damage modes were first investigated through the combination of experimental tests and numerical simulation. Then a series of numerical simulations of full-scale ships subjected to near-field underwater explosions with different stand-off distances, equivalents, and detonation positions were carried out. The damage effects of shock wave, bubble pulsation, after flow, and water jet loads on ships were analyzed. The results show that the combined effects of different loads lead to different damage modes. Shock waves and after flow loads are the main cause of local damage and hogging damage, while pressure difference and bubble adsorption are the main reasons for the hogging damage. Finally, a criterion was proposed to determine the damage modes of ships under near-field underwater explosions.