Search Results (38)

Following successful applications in inland water bodies, floating photovoltaics (FPV) developers are now targeting offshore sites. This advancement requires numerical tools that can quantify the hydrodynamic performance of large-scale FPV farms. The existing wave-diffraction solver DIFFRAC was extended to simulate the response of a large number of interconnected floating objects on a supercomputer. The applicability is demonstrated by simulating a 2 MWp offshore solar farm, consisting of 3660 FPV modules moored inside a protective ring of 32 interconnected floating breakwaters (FBWs). The FPV motions and loads on FPV connectors in regular and irregular waves are compared to a reference case without FBW protection. Results show an average reduction in axial FPV connector loads in the setup with FBW ring, but local load enhancements occur due to dynamic amplifications of horizontal FPV module motions. Vertical loads and overturning moments onto FPV connectors are globally reduced by up to 50% in steep irregular seas but are locally enhanced due to standing waves that develop inside the ring. The insights of the hydrodynamic behaviour lead to recommendations for improving the farm configuration to further reduce fatigue and survival loads onto FPV modules and connectors. Full article

A variety of Offshore Floating Photovoltaics (OFPVs) applications rely on the capacity of their floating support structures displacing in the shape of surface waves to reduce extreme wave-induced loads exerted on their floating-mooring system. This wave-adaptive displacement behaviour is typically realized through two principal design approaches, either by employing slender and continuously deformable structures composed of highly elastic materials or by decomposing the structure into multiple floating rigid pontoons interconnected via flexible connectors. The hydrodynamic behaviour of these structures is commonly analyzed in the literature using potential flow theory, to characterize wave loading, whereas in order to deploy such OFPV prototypes in realistic marine environments, a high-fidelity numerical fluid–structure interaction model is required. Thus, a versatile three-dimensional numerical scheme is herein presented that is capable of handling non-linear fluid-flexible structure interactions for Very Flexible Floating Structures (VFFSs): Multibody Dynamics (MBD) for modularized floating structures and floating-mooring line interactions. In the present study, this is achieved by employing the Smoothed Particles Hydrodynamics (SPH) fluid model of DualSPHysics, coupled both with the MBD module of Project Chrono and the MoorDyn+ lumped-mass mooring model. The SPH-MBD coupling enables modelling of large and geometrically non-linear displacements of VFFS within an Applied Element Method (AEM) plate formulation, as well as rigid body dynamics of modularized configurations. Meanwhile, the SPH-MoorDyn+ captures the fully coupled three-dimensional response of floating-mooring and floating-floating dynamics, as it is employed to model both moorings and flexible interconnectors between bodies. The coupled SPH-based numerical scheme is herein validated against physical experiments, capturing the hydroelastic response of VFFS, rigid body hydrodynamics, mooring line dynamics, and flexible connector behaviour under wave loading. The demonstrated numerical methodology represents the first validated Computational Fluid Dynamics (CFD) application of moored VFFS in three-dimensional domains, while its robustness is further confirmed using modular floating systems, enabling OFPV engineers to comparatively assess these two types of wave-adaptive designs in a unified numerical framework. Full article

Accurate extraction of building features from remotely sensed data is essential for supporting research and applications in urban planning, land management, transportation infrastructure development, and disaster monitoring. Despite the prominence of deep learning as the state-of-the-art (SOTA) methodology for building extraction, substantial challenges remain, largely stemming from the diversity of building structures and the complexity of background features. To mitigate these issues, this study introduces DeepSwinLite, a lightweight architecture based on the Swin Transformer, designed to extract building footprints from very high-resolution (VHR) imagery. The model integrates a novel local-global attention module to enhance the interpretation of objects across varying spatial resolutions and facilitate effective information exchange between different feature abstraction levels. It comprises three modules: multi-scale feature aggregation (MSFA), improving recognition across varying object sizes; multi-level feature pyramid (MLFP), fusing detailed and semantic features; and AuxHead, providing auxiliary supervision to stabilize and enhance learning. Experimental evaluations on the Massachusetts and WHU Building Datasets reveal the superior performance of DeepSwinLite architecture when compared to existing SOTA models. On the Massachusetts dataset, the model attained an OA of 92.54% and an IoU of 77.94%, while on the WHU dataset, it achieved an OA of 98.32% and an IoU of 92.02%. Following the correction of errors identified in the Massachusetts ground truth and iterative enhancement, the model’s performance further improved, reaching 94.63% OA and 79.86% IoU. A key advantage of the DeepSwinLite model is its computational efficiency, requiring fewer floating-point operations (FLOPs) and parameters compared to other SOTA models. This efficiency makes the model particularly suitable for deployment in mobile and resource-constrained systems. Full article

Due to their unique structural configuration, Very Large Floating Structures (VLFS) exhibit significant hydroelastic responses during their motion in the water. These responses, which are a result of the interaction between the structure and the waves, can lead to undesirable vibrations and deformations, potentially compromising the stability and performance of the VLFS. Reducing the hydroelastic response in VLFS has become a critical research focus for scholars worldwide. In the field of marine engineering, various methods are employed to address this issue, with the use of porous structures being one of the most effective solutions. These porous structures help to dissipate the energy of propagating waves, thereby reducing the magnitude of hydroelastic responses. This paper introduces a multi-layer porous plate structure designed to mitigate the hydroelastic response of horizontally moored VLFS. The proposed structure consists of multiple layers of porous plates strategically arranged to optimize the dissipation of wave energy. To evaluate the performance of this structure, a series of physical model tests were conducted, focusing on the hydrodynamic behavior of the VLFS with the multi-layer porous plate structure. The experimental results indicate that within a specific wavelength range, the properly configured multi-layer porous plate structure can significantly reduce the hydroelastic response of the VLFS. This reduction is especially noticeable in the attenuation of wave-induced forces, leading to a decrease in the structural vibrations and enhancing the stability of the floating system. The findings demonstrate that this innovative design can provide a reliable method for improving the performance of VLFS in challenging marine environments. Full article

This review provides the recent advancements in nonlinear sea ice modeling for hydroelastic analysis of ice-covered channels and their interaction with floating structures. It surveys theoretical, experimental, and numerical methodologies used to analyze complex coupled sea ice–structure interactions. The paper discusses governing fluid domain solutions, fluid–ice interaction mechanisms, and ice–structure (ship) contact models, alongside experimental techniques and various numerical models. While significant progress has been made, particularly with coupled approaches validated by experimental data, challenges remain in full-scale validation and accurately representing ice properties and dynamic interactions. Findings highlight the increasing importance of understanding sea ice interactions, particularly in the context of climate change, Arctic transportation, and the development of very large floating structures. This review serves as a crucial resource for advancing safe and sustainable Arctic and offshore engineering. Full article

Very large floating structures (VLFSs) typically employ a modular design approach to mitigate significant hydroelastic loads. A mooring system is commonly employed to maintain the position and heading of a VLFS against the forces of waves, wind, and currents, while a connector is utilized to restrict the relative motion among the modules. In this paper, we propose a comprehensive connector model based on elastic beam theory. The aim is to establish a unified mathematical model that accommodates various types of flexible connectors by adjusting the specific stiffness and damping parameters. To assess the effectiveness of the model, numerical and experimental studies are conducted on a VLFS composed of three rigid bodies connected in a series by multiple flexible connectors. The results obtained demonstrate that the general connector model is reasonable and can be applied to different types of connectors, thereby facilitating an analysis of the influence of the mechanical properties of the connectors on the motion response of the VLFS. Full article

For automatic fabric defect detection with deep learning, diverse textures and defect forms are often required for a large training set. However, the computation cost of convolution neural networks (CNNs)-based models is very high. This research proposed an involution-enabled Faster R-CNN network by using the bottleneck structure of the residual network. The involution has two advantages over convolution: first, it can capture a larger range of receptive fields in the spatial dimension; then, parameters are shared in the channel dimension to reduce information redundancy, thus reducing parameters and computation. The detection performance is evaluated by Params, floating-point operations per second (FLOPs), and average precision (AP) in the collected dataset containing 6308 defective fabric images. The experiment results demonstrate that the proposed involution-based network achieves a lighter model, with Params reduced to 31.21 M and FLOPs decreased to 176.19 G, compared to the Faster R-CNN’s 41.14 M Params and 206.68 G FLOPs. Additionally, it slightly improves the detection effect of large defects, increasing the AP value from 50.5% to 51.1%. The findings of this research could offer a promising solution for efficient fabric defect detection in practical textile manufacturing. Full article

Numerical simulations were generated to investigate the response of a very large floating airport to an airplane takeoff, using the set of nonlinear shallow water equations of velocity potential for water waves interacting with a floating thin plate. We have proposed two methods to reduce persistent airport vibration: reflectance reduction by decreasing the flexural rigidity in airport edge parts and amplification reduction by decreasing the still water depth partially under airport runways. First, when the flexural rigidity is uniformly decreased in an airport edge part, the reflectance of the floating body waves due to a B737 was reduced because of the multiple reflections. However, the wave reflectance for a B747 increased, depending on the conditions. A too-long edge part was not effective in reducing the wave reflectance. Conversely, when the flexural rigidity is linearly decreased in an airport edge part, the wave reflectance was reduced for both airplanes. Second, when the still water depth under an airport runway is partially reduced at the location where floating body waves are amplified, the wave heights of floating body waves tended to decrease as the still water depth in the shallower area decreased. Full article

The development of floating photovoltaic systems (FPV) for coastal and offshore locations requires a solid understanding of a design’s hydrodynamic performance through reliable methods. This study aims to extend insights into the hydrodynamic behavior of a superficial multi-body FPV system in mild and harsh wave conditions through basin tests at scale 1:10, with specific interest in the performance of hinges that interconnect the PV panels. Particular effort is put into correctly scaling the elasticity of the flexible hinges that interconnect the PV modules. Tests of a 5 × 3 FPV matrix are performed, with and without shelter, by external floating breakwater (FBW). The results show that the PV modules move horizontally in the same phase when the wave length exceeds the length of the FPV system, but shorter waves result in relative motions between modules and, for harsh seas, in hinge buckling. Relative motions suggest that axial loads are highest for the hinges that connect the center modules in the system and for normal wave incidence, while shear loads are highest on the outward hinges and for oblique incidence. The FBW reduces hinge loads as it attenuates the high-frequency wave energy that largely drives relative motions between PV modules. Full article

This paper investigates the hydroelastic responses of offshore floating solar photovoltaic farms (OFPVs). OFPVs usually occupy a large sea space in the order of hectares and structural deformation under wave action has to be taken into consideration due to their huge structural length-to-thickness ratio. The flexible deformation of the structure under hydrodynamic loading is termed the hydroelastic response. In the hydroelastic analysis of an OFPV, the diffraction and radiation of waves have to be taken into account to accurately represent the hydrodynamic loadings on the floating platform. In this study, the numerical model is first validated by comparing the eigenvalues and eigenvectors of an OFPV, obtained from the proposed numerical scheme, with their counterparts obtained from an established finite element software. This is followed by an investigation of the hydroelastic responses of various OFPVs designed in varying layout configurations. The various layout configurations are obtained by altering the floating modular units’ dimensions as well as the spacing of the OFPVs when deployed adjacent to each other. The optimal configuration that gives the best performance in terms of the overall smallest response, known as compliance, is then suggested. The results suggest that a long-ish OFPV layout has a lower hydroelastic response and that the motion could be further reduced by rearranging the layout arrangement to increase the global flexural stiffness. Full article

VLFSs (Very Large Floating Structures) are often assembled by multiple modules through connectors where the connector structure is prone to stress concentration. Therefore, the loads at the connectors have become a significant focus in VLFS design. In this paper, the FMFC (Flexible Module Flexible Connector) method, which can account for the elastic deformation of each module and the connector, is established in order to predict the coupling response of the connector and the platform. The finite element model of a dual-module transfer platform with a hinged connector is established and the modal shape characteristics of the entire structure are analyzed. The accuracy of the method is verified through a model test, where the model was scaled as 1:50. Furthermore, the RAOs (Response Amplitude Operators) of connector loads were calculated. It was found that the horizontal loads (along the x and y directions) were more sensitive to the wave direction. Furthermore, the wave direction where the maximum short-term significant value appears was not consistent with the direction of the maximum RAO. The loads response law of the VLFS with a hinged connector is summarized in this paper and provides a reference for the design of connectors. Full article

Numerical simulations were generated to investigate the response of a floating airport to airplane movement using the nonlinear shallow water equations of velocity potential for water waves interacting with a floating thin plate. First, in the 1D calculations, the airplanes were B747 and B737. At touch-and-go, when the airplane speed is closer to the water wave speed, even B737 produced large waves based on the resonance. The impacts due to both the touchdown and leaving of the airplanes generated other forward and backward waves. At landing, when the airplane speed approached the water wave speed, a forced wave was generated and amplified, with many free waves ahead. At takeoff, a wave clump, generated shortly after starting to run, propagated in front of the airplanes. Although the wave height increased from superposition with the reflected waves, the wave reflectance was reduced by lowering the flexural rigidity near the airport edge. Second, in the 2D calculations, B787 performed landing and takeoff. When the still water depth is shallower, a grid-like pattern was formed at the floating airport and appeared more remarkably in landing than in takeoff. The effective amplification occurred from a sufficient load applied when the airplane speed approached the water wave speed. Furthermore, the maximum upslope gradient beneath the airplane increased as the still water depth decreased, and it was larger in takeoff than in landing. Full article

Evaluating the structural safety and seakeeping performance of very large floating structures (VLFS) using the rigid module flexible connector (RMFC) method remains challenging due to the complexity of the coupled hydrodynamic–structural responses in this system. In this study, a coupled hydrodynamic–structural frequency–time domain model is developed based on the RMFC method employing the planar Euler–Bernoulli beam elements to investigate the dynamic responses of multi-module floating systems. To reveal the dynamic characteristics of the systems, the coupled hydrodynamic–structural responses are investigated using a frequency–time-domain numerical model with viscous correction, in which the mass and stiffness attributes of connectors are incorporated into the system. Given the effects of hydrodynamic interaction, consideration is given to the case of three modular boxes connected by flexible beams aligned in series in shallow water to validate the present model. Higher efficiency and accuracy can be found in the system using viscous correction in potential flow theory and introducing state–space model to replace the convolution terms in the Cummins equation for the time domain. Moreover, this model can be extended to a considerable number of floating modules, which provides possibilities to analyze N-module floating systems. Full article

The so-called large multi-body floating offshore structure is a new type of offshore structure with a huge and extremely flat deck area, which has a promising prospect as a floating port and also in applications in the area of marine space exploitation. Due to its unique structural form, the hydrodynamic and structural response characteristics are very complex. Specifically, due to the instantaneous position variation in the body surface, the nonlinearity of the free surface, the interactions between floating bodies, and the elastic deformation of floating bodies, the nonlinear factors are significant and cannot be neglected. For these kinds of problems, methods based on CFD-FEA (computation fluid dynamics–finite element analysis) coupling simulation have significant advantages over traditional methods. In the present paper, the hydrodynamic and structural response characteristics of a large multi-body floating offshore structure are studied using a CFD-FEA method, and the results are compared with those obtained by the potential-flow-based commercial code SESAM/WADAM, and a three-dimensional nonlinear hydroelastic analysis commercial code COMPASS-WALCS-NE. The comparison and the analysis of the results show that the CFD-FEA method presented in this study can well simulate the behavior of the hydroelastic responses of flexible floating structures and has the potential to capture complex nonlinear behaviors. Full article

This is a conference extension of the paper ‘Investigation on the mature storm cloud’s electric field using long airborne antennas’. The use of vertical antennas (including the VEDs—Vertical Electric Dipoles), lifted up by aerostats to high altitudes without being anchored to the ground, presents numerous advantages in comparison with large terrestrial VLF (Very Low Frequency) antenna structures. A slow-moving floating-earth conductor—a vertical wire antenna—is subjected to intense electrification mechanisms in the atmosphere and inside the cloud layers, producing additional risks for the transmitter and the flight train itself. The electrical potential achieved in this process is, therefore, compared with the flashover voltages over the antenna’s upper fixing point, defining the voltage margins at which the VLF transmitter is able to operate. The electrification processes are also compared to the model based on experimental data on the occurrence of corona discharges over a long, vertical wire traversing a storm cloud layer. The external electric field strength (around the antenna wire) is calculated and compared with older experimental data for storm clouds for various locations, showing the correctness of the proposed analytical electrification model, and, therefore, expanding it with the loss of the electric charge via corona. Full article