Applied Ocean Research最新文献

Monopile is a popular choice in the foundation supporting offshore wind turbines (OWTs), with local scour significantly impacting their lateral responses. Macro-element model, which encapsulates the response between the monopile and the surrounding seabed soils into a force-displacement relation, has been extensively developed to describe offshore foundations. However, such kind of models specifically targeting monopiles subjected to lateral loading in local scour remain underdeveloped. This work proposes a macro-element model with a succinct hyperbolic hardening relation for laterally loaded monopiles in local scour conditions, using the evolutionary polynomial regression (EPR) machine learning technique for easy and optimal design. First, the finite element model is verified and extended to generate force-displacement responses considering the monopile geometries, soil characteristics, and local scour geometries. These results are then utilised to determine the optimal hyperbolic hardening relation of the macro-element model. Next, the EPR technique is employed to determine the relationship between the hyperbolic hardening relation parameters and the influencing factors. Finally, the macro-element model is successfully evaluated by comparing with measurements from centrifuge tests and numerical solutions by finite element analysis, demonstrating its applicability in practical design and the ability to reproduce FEA results with a significant reduction in computational cost.

The study uses linearized water wave theory to examine the role of detuned frequency on Bragg scattering of surface gravity waves over an array of bottom-standing submerged sinusoidal patches. Explicit formulae for reflection and transmission coefficients are derived using the matrix transfer method in the case of an array of patches, with each patch having a finite number of ripples. Bragg resonance occurs in the case of more than two patches beyond a certain cutoff frequency corresponding to supercritical detuning, while a monotonic increasing trend is observed below the cut-off frequency which is referred to as subcritical detuning. The number of sub-harmonic peaks between two consecutive harmonic peaks is one less than the number of patches. As the number of patches grows, so does the number of zero reflections, while the number of sub-harmonic peaks is invariant with the number of ripples within a patch. The corrugated length of the submerged sinusoidal patches and the resonator length determine the highly resonating/wave trapping features of wave reflection within the resonator and the corrugated patches. The time-domain simulation of surface displacement reveals the scattering and splitting of wave pulses over the submerged patches.

This work aims to determine the wave conditions that generate maximum surge response excited predominantly by second-order difference frequency forces. Standard narrow-band wave conditions have random phase components and obtaining the maximum surge response requires long sea-state durations to cover all combinations and correspondingly long computation times using second-order diffraction–radiation models. Multiple 3-hour random sea-states are typically used to evaluate the expected extreme response. The maximum force may be obtained by shifting phases to be equal between component pairs with a frequency difference equal to the structure’s surge natural frequency. However, this work shows that such an approach gives a highly transient force and the lightly damped surge displacement response does not approach a representative maximum value. The larger motion responses may be achieved by sequential wave groups and here we use a genetic algorithm to optimise the phase distribution to give more regular low-frequency excitation in relatively short sea-state durations, less than 1 h. This is demonstrated with a one degree-of-freedom Fourier model. The method is applied to a lightly-moored spar substructure and compared with an experimentally validated standard six degree-of-freedom time domain model (Orcaflex) showing satisfactory agreement.

This study endeavors to realize the concurrent utilization of marine soft clay (MSC) and industrial waste, specifically calcium carbide residue (CCR) and fly ash (FA), through a series of experimental investigations. The optimal ratio between CCR and FA, as well as the efficacy of the composite agent (CF–1), were examined, and an empirical equation associating the unconfined compressive strength (q_u) of stabilized MSC was developed through unconfined compressive strength (UCS) tests. Microscopic analyses, including X–ray diffraction (XRD), scanning electron microscopy (SEM), and energy–dispersive spectroscopy (EDS), were employed to unveil the intrinsic mechanisms underlying CF–1 stabilized MSC. Subsequently, the suitability of CF–1 solidified MSC as a roadbed filler was ascertained through laboratory tests. Results revealed the optimum CCR:FA ratio for CF–1 to be 4:1, demonstrating superior curing effects compared to individual components such as Portland cement (PC), CCR, and FA, with commendable environmental and economic benefits. The developed empirical equation exhibited effectiveness in predicting the q_u of CF–1 solidified MSC under varying curing dates (T) and dosages (W_g) conditions. Characterization through XRD, SEM, and EDS identified the primary products formed within the stabilized MSC matrix with CF–1 as comprising calcium–silicate–hydrate (C–S–H) gel, calcium–aluminate–hydrate (C–A–H) gel, and a minor amount of calcite. As T and W_g increased, the reduction in pores between soil particles enhanced the structural integrity and macro–strength of the cured MSC. The failure pattern of CF–1–solidified MSC elementary samples depended on the CF–1 dosage and curing duration. The solidification mechanism of CF–1 on MSC involved pozzolanic, ion exchange, and carbonation reactions. CF–1 solidified MSC satisfied all the specified requirements for roadbed filler in the relevant code, demonstrating substantial potential for in–situ solidification projects involving MSC.

The pipe-in-pipe (PIP) system, with good structural resistance and favourable thermal insulation capacity, has been extensively applied in oil and natural gas exploitation in deep waters. In the present paper, a simplified equivalent numerical model of the PIP system for deepwater J-lay operation was developed to evaluate the dynamic response of the outer pipe and the inner pipe under the combined hydrodynamic load and pipelay vessel motion by the software OrcaFlex. The comparison of mechanical responses between the present equivalent model and other available PIP models was performed to verify its reasonability. Considering vessel motion, pipe-soil interaction, wave and current, the dynamic behaviour of the outer and inner pipes was evaluated on aspects of the bending moment, effective tension, equivalent stress and strain. After that, the influences of key geometric parameters on the dynamic behaviour of PIP systems were systematically studied, including the diameter-to-thickness ratios of the outer pipe and inner pipe as well as the core thickness. The findings would provide good guidance for the structural design and the installation analysis of PIP systems using the deepwater J-lay operation.