Marine Structures最新文献

As the main component of semi-submersible platforms, the deck-column structure is inevitably subjected to severe wave impacts in extreme ocean environments. The wave impact pressure and its time integral, impact pressure impulse, play an important role in the structural design, especially for the analysis of dynamic response. To investigate the characteristics of impact pressure and pressure impulse, wave impact tests on a square column with overhanging deck were carried out under a series of regular waves. Wavelet denoising technique and empirical mode decomposition (EMD) method were employed to remove the noise interference and the dynamic amplification effect from raw data. Considering the stochastic feature, statistical analysis of pressure impulse was performed based on generalized extreme value (GEV) and two-parameter Weibull distribution models. The results show the strong variability of the wave pressure impulse and the necessity of statistical analysis even in regular waves. The peak impact pressure is more sensitive to the variation of initial air gap and column incline angle than the pressure impulse. The probability distribution of extreme pressure impulse agrees well with the GEV distribution and is mainly distinguished by the shape parameter. Furthermore, the probability distribution of extreme pressure impulse is significantly affected by the initial air gap, and the effect is also related to wave parameters. The present research reveals the probability distribution of wave pressure impulse in regular waves and lays a foundation for the statistical analysis of pressure impulse in irregular waves.

This work extends an existing seakeeping tool (OceanWave3D-seakeeping) to allow for the efficient and accurate evaluation of the hydroelastic response of large flexible ships sailing in waves. OceanWave3D-seakeeping solves the linearized potential flow problem using high-order finite differences on overlapping curvilinear body-fitted grids. Generalized modes are introduced to capture the flexural responses at both zero and non-zero forward speed, but we focus on the zero speed case here. The implementation of the hydroelastic solution is validated against experimental measurements and reference numerical solutions for three test cases. The ship girder is approximated by an Euler–Bernoulli beam, so only elastic bending deformation is considered and sheer effects are neglected. Some controversy has long existed in the literature about the correct form of the linearized hydrostatic stiffness terms for flexible modes, with Newman (1994) and Malenica and Bigot (2020) arriving at different forms. We provide here a complete derivation of both forms (including the gravitational terms) and demonstrate the equivalence of the buoyancy terms for pure elastic motions.

With the increasing number of ships navigating in polar regions, collisions between ships and sea ice are inevitable. The cabin noise problem caused by ship-ice collisions is significantly different from that of ships navigating in open water, and it seriously affects the comfort and safety of shipboard personnel. To explore the transient cabin noise response caused by ship-ice collisions, this paper performs numerical studies of the ice load, compares the ice resistance values of experimental and empirical formulas through the ship-ice-water‒air coupled collision method, and gives the sound source load excitation. Then, in the frequency domain acoustic analysis, the acoustic response of the typical cabin noise under icebreaking excitation and coupling excitation is calculated by using the acoustic-structure coupling analysis model and statistical energy analysis model, respectively. The effect of ship transient cabin noise on personnel comfort is analyzed according to the standard of ship noise. The results show that the transient cabin noise is scattered from the collision position to the stern at a certain angle and decays along the length, width, and superstructure of the ship as the frequency increases. The transient cabin noise under coupled excitation shows an M-shape distribution in the ship ranges. The icebreaking excitation mainly affects the transient cabin noise within 1000 Hz, with strong nonlinearity at a low-frequency band. The sound source excitation has a more obvious effect on the cabin noise in the middle-high frequency bands. The A-weighted sound pressure level of transient cabin noise in accommodation cabins and wheel houses during icebreaking operations of polar ships exceeds 5–20 dB(A) of the standard limit, which seriously affects the comfort of people on board. The research results of this paper can provide a reference for the study of ship-ice collision-induced transient cabin noise and the formulation of relevant standards.

Vortex-induced vibration will occur due to the vortex shedding around the marine towing cable during the towing movement, which will further affect the acquisition efficiency of the marine seismic exploration system. Suppression device is widely used to suppress the VIV response of the marine slenderness structures. In order to investigate the passive suppression mechanism on the marine towing cable, a numerical VIV model is proposed to predict the VIV response of marine towing cable with buoyancy modules. The steady-state and VIV characteristics of marine towing cable with different coverage, layout and slenderness ratio are studied firstly. The parameters have a nonlinear relationship with the VIV response of cable and excessive arrangement of buoyancy module will enlarge the vibration displacement. Where to install a limited number of suppression devices is a challenge for practical engineering. Genetic algorithm is introduced to solve the optimization problem of the suppression device arrangements in this paper. The suppression device arrangement of towing cable will evolve in the direction of decreasing cable VIV displacement until reaching the optimal arrangement. The proposed method is demonstrated by comparing with some typical working conditions. It turns out that the proposed method can perform the optimization design of the suppression device arrangement efficiently. The VIV displacement of cable can be reduced obviously through the optimization design.

This paper proposes a novel data-driven framework for scour detection around offshore wind turbines (OWTs), where damage features are derived from wind and wave-induced acceleration signals collected along the tower. A numerical model of the NREL 5 MW wind turbine, which considers aerodynamic and hydrodynamic loading with soil-structure interaction (SSI) and servo-dynamics, is developed. The model is used to simulate the acceleration responses along the tower for a healthy structure, and a structure affected by progressive scour. A data segmentation process is initially performed on the collected data, which is followed by a feature selection scheme based on the analysis-of-variance (ANOVA) algorithm, to eliminate irrelevant characteristics from the time domain feature set of responses. The proposed framework consists of two main components: (a) offline training, and (b) real-time classification. The acceleration responses collected from the healthy structure and the structure subjected to three different damage scenarios (different scour depths) and under various load conditions, are used in the offline training mode. The selected feature vector from the feature extraction process is used as input to a Naive Bayes classifier (NBC) algorithm to train the model. In the real-time classification, a prediction of the scour depth affecting the structure is performed using a new dataset simulated from unseen load cases and scour conditions of the OWT. The results show that the model trained in the offline stage can predict the scour depth in the real-time monitoring stage with performance measures over approximately 94%.

Active vibration isolation (AVI) is a state-of-the-art technique used to attenuate vibration and noise of the underwater vehicle's power machinery. In certain operational conditions, the pre-installed actuator in AVI system may be redundant, and only a subset of them is required for effective vibration suppression. Therefore, optimization of the actuator configuration is necessary. However, the installation position of the actuators is fixed during the design stage, and only the on/off status of the actuators is adjustable. Additionally, the structural complexity of the practical system poses challenges to the conventional state-space-equation-based optimization methods. In this paper, an optimization strategy based on frequency response functions (FRFs) is proposed to optimize the on/off status of the actuators. The optimization problem of actuator status is formulated as an 0–1 nonlinear programming, which can be solved by teaching-learning based optimization (TLBO), a heuristic algorithm. Simulation and experimental results demonstrate that the proposed optimization strategy can effectively determine the optimal actuator configuration under specific disturbance conditions, with only a subset of the actuators being activated to achieve sufficient vibration suppression.

Ship collision accidents occur frequently and developing rapid prediction methods for structural crashworthiness analysis is of crucial importance in the design phase. This paper proposed a new analytical method to rapidly evaluate side structural responses impacted by a rigid raked bow in right-angle ship collisions with large indentation. Numerical simulations were carried out to help identify and understand the mechanisms of structural deformation of primary structural members. The side structure is divided into different key components and a new analytical model for evaluating the hull shell plating and stiffeners under large indentation subjected to lateral impact was developed. The model considered the shell plating deformation in three different phases, denting, ruptured and tearing phase. Different formulas were derived to cover the analysis from minor deflection to large indentation. Combined with other existing formulas for stiffened decks under in-plane loads, an integrated method was proposed to predict the total resistance and energy dissipation of the side structure. The newly developed method innovatively considered the coupling effects and interactions between various structural members in the collision analysis by dynamically correcting some parameters theoretically. The newly developed method was verified against numerical simulations of full-scale ship collisions through five typical scenarios and good accuracy was achieved. The newly developed method is valuable for use in the preliminary design phase, especially for severe collision scenarios.

Integral buckle arrestors are regarded as the most effective arresting devices and can be perfectly adapted to innovative sandwich pipes. In the present study, hyperbaric chamber tests were performed on reduced-scale sandwich pipe specimens equipped with integral arrestors, and the effect of interface bonding behaviour on the crossover pressure was examined. Then, numerical frameworks were proposed to replicate buckling propagating and crossing phenomena under hydrostatic pressure, with a strong consistency between measurements and predictions. A broad parametric analysis on the crossover pressure was implemented covering key material properties and geometries. After that, machine learning techniques were introduced and used for predictions of crossover pressure and arresting efficiency. Four algorithms, involving Random Forest, Multi-layer Perceptron, K-Nearest Neighbors, and Support Vector Machine, were established using a dataset comprising 248 cases with thirteen variables. Based upon an evaluation of standard statistical metrics, it is observed that RF and MLP exhibit superior prediction accuracy, whereas the prediction performance of KNN is the worst. The results show that the machine learning method provides relatively reliable predictions of crossover pressure and arresting efficiency for both flattening and flipping failure modes.

Concrete-filled steel tubes are widely applied in offshore structures, which often being exposed to aggressive ocean climate. This has recently led to the introduction of concrete-filled aluminum alloy tubular (CFAT) columns, of which aluminum alloy tube is used as a superior anti-corrosion metal material. However, limited research has led to the design of CFAT columns not being included in the current design specifications, limiting their engineering applications. Accordingly, in this paper, an experimental program including 9 CFAT specimens was launched to further investigate the compressive behavior of CFAT short columns and to clarify the confinement mechanism in such columns. The test results indicate that the ultimate capacity of CFAT short columns is improved with the increase of concrete strength or the decrease of tube diameter-to-wall thickness ratio. Based on the experimental results, the finite element model (FEM) was established, and then used to clarify the confinement mechanism of CFAT columns and investigate the effects of the salient parameters on the behavior of such columns. By comparing with the existing experimental results, the accuracy of current strength calculation formulas for CFAT columns was assessed, and the conclusion indicates that there is an unexpected deviation in the prediction results. To this end, a simplified strength prediction formula for CFAT columns was proposed, which successfully introduced a novel confinement factor that well reflects the confinement effect of the concrete core. This confinement factor considers the effects of proof stress, concrete strength, and tube diameter-to-wall thickness ratio. Finally, compared with other formulas, the proposed formula has better performance in predicting results.

A simple method for estimating the ultimate strength of rectangular plates under combined biaxial and shear loads is proposed. Although numerous studies have been conducted to predict the ultimate strength of plates, most conventional methods rely on empirical approaches that involve plastic correction of the elastic buckling strength or curve fitting through nonlinear finite element analysis (NLFEA) or experimental test results. For a more rational design of hull structures, it is important to develop an estimation method with a more theoretical basis corresponding to physical phenomena, such as post-buckling and yielding behavior, the effects of initial imperfections and material properties as well as the elastic buckling strength. Although some methods with the more theoretical basis were developed in previous studies, they often require numerical iterations such as the Newton-Raphson method to obtain load-deflection relationships. Our approach entails a thorough observation of the buckling and collapse behavior obtained from a series of NLFEA calculations, rather than merely investigating the magnitude of the ultimate strength derived from NLFEA. By applying the elastic-large deflection theory and considering the identified buckling modes, analytical solutions that describe the elastic post-buckling behaviors are derived. The ultimate strength is predicted by assessing the yield at pre-defined locations corresponding to the classified collapse modes. The proposed semi-analytical method eliminates the need for numerical iterative methods to obtain load-deflection relationships and provides a simple estimation of the ultimate strength. The accuracy of the proposed method is validated through a comparison with NLFEA results.