Marine Structures最新文献

Due to the vulnerability of wharves against accidental attacks, the reinforced concrete (RC) caisson quay wall, as a widely adopted wharf form, is faced with the potential threat of underwater explosions. The present work aims to study the dynamic responses and damage modes of caisson against underwater explosions through the underwater explosion test and numerical simulations. Firstly, four shots of underwater explosion test were conducted, including two cases for different focuses, i.e., two shots of the free field underwater explosion with a charge weight of 0.2 and 1 kg respectively, and another two shots of a 1/5 reduced scale caisson specimen subjected to the underwater explosion with a charge weight of 0.2 and 1 kg successively. The underwater explosion overpressure-time histories and periods of bubble pulsation, as well as the deflection-time histories and damage modes of caisson specimen were experimentally obtained. Then, the refined finite element (FE) models were established, including the 1D model for explosion loading and the 3D model for predicting the dynamic behaviors of caisson with adopting the Coupled-Eulerian-Lagrangian algorithms and remapping technology, which were validated by comparing with the test data. Finally, the influences of explosion conditions, such as explosion standoff, depth of burst, and charge weight on the dynamic behaviors of caisson specimens were numerically discussed. It derives that, the existing calculation formulas of overpressure and period of bubble obtained from the spherical charge are also applicable to the group charge; the reflection coefficient of hydraulic RC structure is around 1.7; the bubble pulsation induced by the underwater explosion could further deteriorate the damage level of RC caisson when the blast wave has already led to an inelastic structural response. The present work could provide beneficial references for the blast-resistance evaluation and design of hydraulic RC structures against underwater explosions.

This paper describes the development of a time-domain hydroelastic numerical model for investigating the slamming and whipping loads imposed on a ship traveling at different forward speeds. The numerical model integrates a beam model, the 3-D Rankine panel model, and the 2-D modified Logvinovich model. The tilt angle of the 2-D profile in the slamming model is determined by the direction of relative velocity, which takes the forward sailing speed into account. The computational results are validated against a segmented model test of a large cruise ship. The convergence of the model with different numbers of elastic modes and slamming profiles is studied to ensure that the numerical results are stable. The main contributor to the whipping response is found to be the vibration of the first-order elastic mode. The slamming force is sensitive to the longitudinal interval of the slamming profiles, especially in the stern. The characteristics of the slamming pressure under bow flare and the whipping response at midship are also investigated. The numerical and experimental whipping responses are found to be in good agreement, and the local slamming pressure based on the slamming profile is more accurate when considering the effect of the ship's forward speed.

An acoustic emission (AE) and hybrid deep learning networks based damage source localization method for heterostructure of wind turbine blades is proposed in this paper. Firstly, comprehensive data preprocessing is performed, including AE signal denoising, feature extraction, feature selection and normalization. New training features including AE descriptors, features of time, frequency domains and spectral features are extracted. A feature selection method based on Light-GBM and correlation analysis is employed to identify relevant features for AE source localization. Subsequently, two deep learning networks, AM-BiLNN and AM-LCNN, are developed to locate the damage source in two steps. Then, numerical tests are implemented on localized structure of a wind turbine blade to verify the performance of the proposed method and the performance of the selected features and the robustness of the proposed method under noise are investigated. Furthermore, a comparative investigation between the proposed method with long short-term memory neural networks (LSTM), convolutional neural networks (CNN) and the cluster-based method is carried out to demonstrate the superiority of the proposed method. The results highlight the superiority and robustness of the proposed method. Feature selection is shown to effectively enhance coordinate localization performance.

The initial proof of concept model scale test campaign for the TetraSpar floating wind turbine substructure is presented here along with a detailed response analysis and numerical reproduction. The tests were conducted at scale 1:60 in wind and waves with the pitch-regulated DTU 10 MW wind turbine. The floater was tested in two configurations: semi-submersible and spar. The experimental setup and program is described in detail followed by system identification for natural frequencies and damping. The responses of the floater in the two configurations to hydrodynamic loading are analysed and compared. The analysis includes irregular sea states and focused wave groups at both 0° and 30° heading. The hydrodynamic damping of the floaters was quantified in decay tests, showing a clear linear and second-order component. It was observed that the semi-submersible configuration had significantly larger motion response than the spar configuration in ultimate limit state wave conditions. Emphasis is placed on the mooring loads and the tensions in the support lines for the ballasted keel. The increased ballast of the spar keel led to larger loads in these support lines. Further, second- and higher-order wave forcing were observed in responses of both configurations. A numerical model based on first-order radiation-diffraction theory, second-order Newman loads and additional Morison viscous forcing is set up. The model damping is calibrated against the measurements at each sea state. It is demonstrated that after this calibration, the model is able to reproduce the floater response and tower top accelerations with good accuracy, both in the linear range and at the natural floater frequencies, with heave in the storm sea state as the exception. The dynamic tensions in the keel lines are found to depend strongly on the lines projection to the inline wave direction. Also this behaviour is reproduced accurately by the model, although with some under-prediction in one of the lines in the rated wind sea state, which is linked to differences in the experimental pre-tension for the six lines.

This paper investigates the structural optimization of a polyhedral composite subsea pipeline (cylinder) under pressure and thermal fields. The pipeline is confined tightly and deforms inward when it is subjected to external loadings. The interface is frictionless between the pipeline and its surrounding medium. Based on the above assumptions, thin-walled shell principles, and an admissible displacement function, the potential energy of a pipeline per unit length is obtained explicitly by simplifying the radius and bending rigidity. After taking the first derivative of the potential energy, two equilibrium equations are obtained. By combining these two equations, the critical buckling pressure of the polyhedral pipeline is expressed analytically with the inclusion of the temperature effects. Then, the present analytical study is compared with other numerical and experimental results, and excellent agreements are reached. A configuration factor is defined as the buckling pressure between the polyhedral and circular pipeline. Finally, parametric studies show the configuration factor decreases with the increase of thickness-to-radius ratio, the increase of the number of sides, and the increase of the temperature variation, respectively. Therefore, a polyhedral pipeline with a low thickness-to-radius ratio is recommended in engineering practices since it may reduce the material cost.

Results

are presented of a benchmark study organised by the Marstruct Virtual Institute on motion and global wave loads on a warship model in regular waves. The aim of the study is the quantification of the uncertainty in numerical whipping predictions. Nine institutions participated in the benchmark with 6 codes, quantifying the hydroelastic responses. The seakeeping methods employed include non-linear strip theory, 3D boundary element method formulated in frequency and time domain, and computational fluid dynamics (CFD). Euler and Timoshenko beams are used for modelling the hull girder stiffness. Experimentally based methods, CFD and momentum theories are employed for calculating slamming loads. The study encompasses a comparison of wet natural frequencies of ship vertical flexural vibration, vertical ship motions, vertical wave bending moments and whipping bending moments at midships. Wave-induced and whipping responses are analysed for regular head waves of different steepness and for two ship speeds. For most comparisons, experimental results are available from previously performed and published model-scale experiments on a Canadian Patrol Frigate. Frequency-independent model error, which is commonly used for uncertainty quantification of rigid body seakeeping responses is extended to quantify uncertainties in whipping bending moments. It is found that fully coupled CFD and finite element method (FEM) provide results consistent with measurements, but such simulations are prohibitively computationally expensive and the interpretation of results can be challenging. The combination of the potential theory seakeeping method with correction based on CFD-FEM simulation for limiting number of cases is a promising alternative.

This paper considers the hydroelasticity effect in liquid slamming. A series of experiments were designed and performed in a nearly two-dimensional (2D) rectangular tanks with four elastic materials. The effect of the Young's modulus on the kinematic and dynamic characteristics of fluid-structure interaction (FSI) during flip-through impact is investigated. Furthermore, the peak values of slamming pressure, impact duration, pressure impulse and structural displacement in different cases are discussed. The hydrodynamic force of fluid acting on the sidewall is defined and compared for different cases. The results show that the Young's modulus of the sidewall plays an important role in hydroelasticity induced by liquid slamming. And a strong hydroelastic behavior could be observed when the impact occurs, especially in the case with a small Young's modulus. In addition, the artificial neural network (ANN) method is adopted to build the hydroelastic response prediction model. The relationship between Young's modulus and peak structural displacement is predicted with the model. This study could help verify and calibrate the theoretical and numerical models of the FSI problems in the sloshing tank and provide guidance on the study of hydroelastic slamming for the flexible cargo containment system.

Increased frequency and intensity of extreme events can make offshore constructions unsafe due to the rapidly shifting wind-wave pattern. The consequences of climate change are disregarded by the current performance-based design of offshore wind turbines (OWT). The Statistical Downscaling Model (SDSM) and Artificial Neural Network (ANN) algorithm are used to present a simplified approach to enable the inclusion of future climatic projections in the design of spar-floating wind turbines. A two-variable statistical equation employing an Artificial Neural Network is established for calculating wind-induced wave height for the North Sea and West Coast of India, which is a valuable parameter for the site-specific design of offshore constructions. Under the SSP2-4.5 scenario, the North Sea's most likely wind speed is anticipated to decrease by 11 %, whereas the west coast of India experiences a slight decrease in wind speed. Serviceability responses, such as tower deflection, rotation, and nacelle acceleration, are expected to rise by 8–10 %. In contrast, a decrease in these responses is projected in the North Sea due to a decrease in future wind speed and wave height. Climate change has a greater impact on shutdown conditions than on normal operations, primarily due to the pronounced shifts in extreme climate conditions.

A novel type of side structure of ship is proposed, inspired by auxetic materials with a negative Poisson's ratio, for enhancing the crashworthiness of double-hull vessels. Three different unit cells (VRE, HRE, and ARR) are designed and numerical simulation is conducted to demonstrate their resistance to collision. A comparative study on the crashworthiness of the proposed side structures and those of traditional side structures (double hull, X-core, and Y-core) is performed and a superior capability of energy absorption and collision resistance of the proposed side structures is observed. These findings demonstrated a potential for auxetic-based structures to be applied as a collision resistance structure implemented in various protective structures.

Trench and burial, as a primary and effective protection measurement for offshore pipelines from impact loads, has received much research attention recently. Previous studies were usually performed based on the assumption that the soil material was homogeneous with deterministic mechanical properties. The soil spatial variability, which is demonstrated to have significant influences on the soil capacity in marine geotechnical analysis, has not been included. This study was motivated to investigate the response of the buried pipelines subjected to the impact loads, with special address on the soil variability. Firstly, a three-dimensional random large deformation finite element analysis model was developed, which was implemented by the field variable (FV) technique to map the non-stationary random field (NSRF) into the verified Coupled Eulerian-Lagrangian (CEL) model (Hereafter referred to as FVRCEL). Then the FVRCEL model was integrated with the Monte-Carlo simulation (MCS) to obtain the statistical characteristics of the pipeline structural response. The failure mechanisms of the pipeline in the random soil with different fluctuation scales were investigated, and a parametric study was performed to identify the influential factors. Finally, the failure probability curves and surfaces were presented, providing clues for the pipeline safety design. The results revealed that in general, more than 50 % of the realized NSRF scenarios in the random analysis yielded more severe dent damage than the deterministic result, indicating that the latter would underestimate the damage degree, which was more pronounced when the increasing gradient of soil strength was high. The horizontal fluctuation scale had a remarkable influence on the pipeline damage behaviours and the corresponding statistical characteristics, of which the inner mechanisms were discussed. From the probabilistic perspective, at most an extra failure probability of 75 % would be suffered if the soil variability was ignored.