Hydroelastic Effects Research Articles

Global Responses Analysis of Submerged Floating Tunnel Considering Hydroelasticity Effects

To investigate the applicability and differences in wave loads and the dynamic response calculation principles for SFT on an entire-length scale, two numerical models of entire-length SFT with identical dimensions and parameters were established. These models are employed by a 3D diffraction method based on rigid-body assumptions, the potential flow theory and the Dummy-Connection-Mass (DCM) method based on the lumped mass method and Morison equation while considering hydroelasticity effects. The applicability of the potential flow theory and Morison equation for wave load calculation of SFT is presented along with the differences in their dynamic response calculation, which aim to explore the impact on SFT dynamic responses considering hydroelasticity by comparing the numerical calculation results. Furthermore, a comparison between free-end boundary and fixed-end boundary models, established using the DCM method, is conducted to examine the reasonableness of the commonly adopted free-end boundary condition.

Fluid–structure interaction analysis of curved wedges entering into water

The water entry of wedges with curvature differs significantly from that of linear wedges, which have been fully investigated and formulated. The safety and integrity of structures prompt an urgent investigation into the mechanism by which the curvature affects slamming loads and structural responses during water entry. This study examines the slamming force characteristics, pressure distributions, fluid jet evolutions, and structural response behaviors of two-dimensional curved wedge sections, considering five different curvatures and two panel thicknesses. A two-way coupling fluid–structure interaction (FSI) solver has been proposed within an open-source framework. The FSI solver was validated against published literature to ensure its high-fidelity. The small deadrise angle results in a more complicated time-domain characteristics for the slamming pressure, with a gradual transition from a single peak to a double peak. The half-peak pressure duration time were defined, and the quantitative results reveal that the hydroelastic effect of the linear wedge is significantly higher than the curved wedges. When considering the geometric curvature, the elastic wedges do not consistently reduce the peak slamming pressure and lengthen the pulse time. Additionally, large deformations generated by the panel vibrations alter the evolutionary pattern of the fluid jet. In contrast to the linear wedge, the structural responses of the curved wedges show distinctive two-stage behaviors.

A coupled smoothed particle hydrodynamics–peridynamics model for two-dimensional hydroelastic water entry

In this paper, a numerical model coupling the smoothed particle hydrodynamics (SPH) with peridynamics (PD) is developed to solve the problem of the hydroelastic water entry. By combining the geometric nonlinear peridynamics with the weakly compressible SPH, the proposed model can efficiently simulate the nonlinear deformation of the structure and the deformation of a fluid free surface. The transmission of information between the fluid and solid phases is implemented by a dummy particle boundary treatment method. By simulating benchmark tests, the ability of the proposed model to solve nonlinear fluid–structure coupling problems is verified. In order to improve the computational efficiency, the graphics processing unit parallel acceleration scheme is applied to the SPH-PD model. Compared with the serial scheme, the speedup effect of the parallel scheme in large-scale computation is verified. As an application of the numerical model, the water entry of the flexible panel at a constant entry velocity is studied. The mechanism of hydroelastic effect is explained by analyzing the variations in the fluid pressure field, slamming force, and panel deformation during water entry. In addition, the influences of plate rigidity, impact velocity, and deadrise angle on the hydroelastic effect are investigated.

Hydroelasticity effects induced by a single cavitation bubble collapse

To investigate hydroelasticity effects on a single cavitation bubble dynamic, a focused laser was used to generate the bubble in water near a flexible aluminium foil fixed to a specimen holder with a circular aperture to allow the foil to vibrate. The bubble was generated below the foil's center. A laser-based optical sensor measured the displacement at the center of the foil. Simultaneously, a high-speed camera monitored the bubble's dynamics to correlate it with the foil's displacement. By directly measuring the foil's displacements, we provided building block missing in previous investigations. We found that a key difference between bubble dynamics near a rigid and an elastic structure was that, at relative wall distances larger or equal to unity, the bubble did not collapse on the elastic foil. The bubble's dynamics caused dominant foil displacements during its first growth (after plasma seeding) and during its subsequent collapse. Foil displacements during the bubble's first collapse were about twice as large as those during its growth phase. For lower relative wall distances, the induced foil displacements were significant until the bubble's third collapse. At larger relative wall distances, the bubble did not collapse on the elastic foil and, thus, it did not induce erosion. However, it caused foil vibrations and, therefore, may contribute to the foil's structural fatigue damage. Our study postulates that the cavitation may not be erosive, however it can induce impulsive loads causing vibrations and thereby fatigue damage of nearby structures.

A Comprehensive Analysis of Structural Alternatives and Local Opening for a 2000 TEU Green Methanol-Powered Container Vessel

In the context of global trade and environmental concerns, this research focuses on examining the influence of the principal dimensions of a container feeder vessel whose propulsion has been modified to operate with green methanol. Methanol emerges as a sustainable marine fuel, reducing emissions and dependence on fossil fuels. The study comprehensively examines the structural challenges posed by container ships, with a particular focus on torsional stresses and hydroelasticity effects. A significant novelty of this study is the inclusion of a comparative structural analysis evaluating how changes in the vessel’s main dimensions impact its structural response. This analysis sheds some light on crucial insights into the effects of structural modifications required for accommodating these changes, ensuring the structural strength of these vessels. The research also underscores the impact of permanent and transient springing and whipping phenomena on fatigue damage. The study’s significance lies in its role in the ongoing transition to sustainable maritime transportation, as it not only examines structural challenges but also provides solutions for achieving an optimal structural configuration in this new era of environmental responsibility.

CFD-FEM simulation of water entry of aluminium flat stiffened plate structure considering the effects of hydroelasticity

In this paper, the slamming loads and structural response of an aluminium flat stiffened-plate structure during calm water entry considering the hydroelasticity effects are studied by a partitioned CFD-FEM two-way coupled method. The target structure is simplified as one segment of an idealized ship grillage structure, comprising flat plate and stiffeners. The typical numerical results are analyzed such as vertical displacement, velocity, acceleration, impact loads, and structural stress of the flexible flat bottom grillage structure considering the hydroelasticity effect and air cushion effect in different free fall height conditions. Drop test results of the same structure and other existing numerical simulation data by both coupled and uncoupled solutions in the literature are used for comparison with the present numerical simulation results. This study provides a practical means to simulate the slamming behaviour and structural response of ship structures, which is useful for predicting ship hull stiffened panel loads and related structural design.

Hydroelastic response of Froude scaled stiffened steel panels exposed to design-critical wave slamming

Stiffened steel panels of offshore ocean structures may experience violent wave impacts which needs to be accounted for in design. The slamming pressures are often measured in scaled wave tank tests and imposed on finite element models to obtain local structural responses. These responses are sometimes high, which has raised the question if hydroelastic effects are properly accounted for. One way to address the uncertainty of hydroelasticity, is to carry out hydroelastic model tests and compare measurements statistically with FEA calculations. This paper presents the hydroelastic model tests required for this type of comparison. Approximate elastic panels representing Froude scaled stiffened steel panels were 3D printed, validated, and then installed in a vertical column in a wave tank. The elastic panels were exposed to design critical wave slamming during irregular wave conditions relevant for the North Atlantic. Two different elastic panels were tested, one strong and one weak panel. The hydroelastic response of the elastic panels are reported in detail and shows that the panel responds with a limited set of frequencies. In most cases the strain time series of the stiffeners and girders obtain its maximum value during the first half period of vibration. Furthermore, the vibration of the panels generally show strong decay after the time of maximum strain. The extreme strains fit reasonably well with the Gumbel distribution. Furthermore, the variability of the extreme strains, measured as the coefficient of variation (COV), is comparable to the variability of slamming pressures from literature, for the strong elastic panel, but is found to be reduced significantly for the weak elastic panel.

Assessing the efficiency of a distensible-tube wave attenuator at three different scales considering aero and hydro-elastic effects

A water-filled floating distensible tube connected to a forward-bent oscillating water column is here considered in the context of harnessing energy from sea waves. Based on wave-tank experiments conducted at three different scales, under intermediate and deep-water incident regular waves of small and finite amplitudes, the present study addresses important aspects that determine the energy capture-width of the system. The comparison between the results obtained at the three scales reveals non-linear and aero-hydroelastic scale effects inherent in modelling the device. The following issues are also tackled: (i) the occurrence of various working modes of the floating tube and their contribution to its performance; (ii) the compressibility of the airflow through the orifice power take-off system; (iii) the viscous-effects associated with the Reynolds and Keulegan-Carpenter numbers. The parameters that govern the system's efficiency are the tube's length, the OWC natural period and the bulge wave tuning period. The system becomes very efficient not only at the OWC resonance, but also when the incident wavelength is equal to or twice the tube's length. Video frames further provide evidence of the relationship between the tube's working modes and its performance. An iterative algorithm based on Buckingham's formula, with an empirical expansibility factor, provides adequate estimates of the compressible flow through the power take-off. Viscous losses closely related to the Reynolds and Keulegan-Carpenter numbers are found to be important even for waves with moderate steepness. Finally, the experiments suggest that a single distensible-tube system in open sea has a maximum capture-width of no more than 2 tube-diameters.

NUMERICAL STUDY ON THE INTERACTION BETWEEN PERIODIC WAVES AND A FLEXIBLE WALL

Coastal structures were usually considered as stiff in the majority of studies related to wave structure interaction I n certain situations, such as impulsive wave loading on flexible breakwaters, ship hulls, tank walls hydroelasticity can be of importance for both wave dynamics and structural responses Akrish et al. (2018) showed that hydroelastic effects can either relax or amplify the hydrodynamic characteristics (i.e., wave run up and force) and structural oscillations in a deformable cantilever wal l interacting with an incident wave group. For flexible coastal defenses, Huang and Li (2022) showed that an elastic horizontal plate breakwater can exhibit a better performance of wave damping than a rigid one. Sree et al. (2021) experimentally investigated a submerged horizontal viscoelastic plate under surface waves. They reported a complete cutoff of the wave energy with the flexible plate. However, the hydroelasticity of a steep fronted structure in nonlinear progressive waves was not yet studied in a de tailed manner , which requires advanced numerical methods for modelling the nonlinear interaction between the fluid and the solid with finite deformations. The present study focus es on the hydroelastic behavior of a flexible vertical wall in nonlinear periodic waves with different wave periods (or frequencies )). The effects of the structural stiffness on the wave evolution and the structural deformation are investigated with a fully coupled wave structure interaction model.

Hydroelastic effects on the vertical bending moment of a container ship in head and oblique seas

Large-sized ships like Ultra large container ships (ULCS) experience severe hydroelastic vibrations like springing and whipping. This study numerically investigates the performance of a time domain method to assess the effect of structural vibration in calculating of vertical bending load of an ULCS. The proposed 2-D body nonlinear time-domain numerical method comprises a seakeeping solver based on potential flow theory and a structural solver based on Timoshenko beam theory. The simulations are carried out in the head and oblique waves for various forward speed conditions. The solver captures the effects of high-order springing and whipping in vertical bending. The numerical method identifies the whipping effect based on the slamming associated with the relative motion of the ship. The vertical bending moment is calculated in both regular and irregular waves, and the results are compared with the experimental results. The statistical evaluations of available results for irregular waves are carried out and presented. The numerical results are in good agreement with the experimental ones for most of the analyzed cases.

Hydroelasticity analysis of a vessel-shaped fish cage under incident, diffraction and radiation wave fields

Vessel-shaped fish cages are promising large aquaculture structures developed in recent years, with an overall length of nearly 400 m. In this paper, a coupled hydroelasticity model of a vessel-shaped fish cage is used to calculate the motion and structural response in the time domain. First, the floating body of the cage is discretized into a multimodule system to calculate the frequency-domain hydrodynamic loads. Then, the multimodule system is connected by equivalent elastic beams to consider the hydroelastic behavior in the time domain. The hydrodynamic loads of the multimodule system are transformed from the frequency-domain loads. Moreover, based on the velocity field transfer functions and the motion of the multimodule system, coupling wave fields considering incident, diffraction and radiation waves are built and used to calculate the loads on the net and steel frame. By iterating the motion response of the multimodule system and the hydrodynamic loads on the net and steel frame in the time domain, the balanced hydroelasticity response of the whole cage is finally obtained. The results show that the hydroelasticity effects have a significant influence on the vertical displacement and cross-sectional load effects of the vessel-shaped fish cage.

Slamming loads and responses on a non-prismatic stiffened aluminium wedge: Part I. Experimental study

Hydroelastic slamming is a phenomenon that occurs when there is a fully coupled interaction between the water surface and a deformable structure, and it has a significant effect on the local and global loads of the structure during high impact velocities in rough seas. Estimating the simultaneous structural responses caused by hydrodynamic loads during high impact water entry is a challenging task. This article, which is Part I of a two-part companion paper, deals with the experimental studies of the impact-induced loads and structural responses of a three-dimensional non-prismatic aluminium wedge with stiffened panel during free-fall water entry. Two different plates were considered on the bottom of the wedge in order to study the influence of flexural rigidity on hydroelastic slamming. A description of the experimental conditions, including the geometry of the wedge, material properties, and the test plan is provided. The effects of water impact velocity, deadrise angle, mass of the wedge, and bending stiffness on the slamming pressures and structural responses are discussed in detail. It is shown that the maximum strain and deformation occur during the partially wetted phase of the slamming problem. The study concludes that the hydroelasticity effects on slamming responses generally increase at lower deadrise angles and higher impact velocities. The importance of FSI simulation is assessed using a hydroelasticity factor (RF), which is found to have a significant effect on the unstiffened bottom for all impact velocities studied. For a stiffened bottom panel, hydroelasticity is only significant at high impact velocities.

CFD-FEM simulation of water entry of a wedged grillage structure into Stokes waves

The fluid-structure interaction problem and the slamming loads on a wedged grillage structure free-falling into 5th order Stokes plane progressive wave under gravity effect is investigated by a partitioned CFD-FEM two-way coupled numerical method. Verification and validation of the CFD-FEM coupled method using calm water entry results of the wedge are first conducted, which indicates that the numerical method is feasible and reliable. Then, the slamming loads and structural stresses on the wedge, considering hydroelasticity effects, are investigated during the entry on Stokes waves for different wedge-wave relative positions and are also compared with calm water results. Moreover, the influence of horizontal and rotation degree-of-freedom motions on the vertical water wave entry results is also investigated. This study provides some insights into the slamming behaviour of ship hull structure impact with sea waves, which is useful for ship hull grillage structure design and strength assessment.

Assessment of Hydrodynamic Loads on an Offshore Monopile Structure Considering Hydroelasticity Effects

Regular and irregular waves were numerically generated in a wave canal to investigate hydrodynamic loads acting on a wind turbine monopile and to predict its structural response. The monopile was implemented in the canal and modeled as a flexible structure, with the turbine blades and rotors considered as a point mass situated at the top of the monopile. Fluid–structure interaction (FSI) simulations were performed by coupling a structure solver based on a finite element method (FEM) with an unsteady Reynolds-averaged Navier–Stokes (URANS) equations solver of the finite volume method (FVM). The FSI simulations considered the two-way interaction between the deformable structure and the fluid flow. The URANS equations solver was coupled with the volume of fluid (VoF) method to account for the two-phase flow. In regular waves, numerically predicted total load coefficients occurring at the monopile’s first eigenfrequency compared favorably to experimental measurements. A deviation between calculations and measurements was observed for the total loads in irregular waves. This deviation occurred due to the smaller wave energy density of the numerically predicted irregular wave. Hydroelasticity effects increased wave-induced forces by about 6% and wave induced bending moments by about 16% in regular waves. A relatively strong whipping event was observed, which characterized the hydroelasticity response bending moment of the monopile in irregular long-crested waves. This whipping event also had a significant influence on the loads on the monopile. These investigations demonstrated the favorable use of FSI simulations to predict hydroelasticity effects on a monopile.

Hydroelastic response of concrete shells during impact on calm water

Many ocean structures located offshore are supported by large vertical concrete columns. High and steep storm waves – in the process of breaking – may induce large local slamming loads on these columns. The present work is related to the fundamental physics of the local hydroelastic shell response due to slamming.The concrete columns supporting typical offshore structures are large. The size means that full scale tests of a segment of the column is impractical and expensive. Model-scale testing in a wave tank is also challenging. Firstly, the scaling of structural properties need to adhere to the scaling laws of hydrodynamics. Secondly, the manufacturing of realistic Froude scaled elastic shell models is hard since curved shells carries loads by a combination of bending and membrane action. The challenge is to scale both the bending and membrane action properly. One part of this study shows how realistic Froude scaled elastic shells representing concrete shells can be designed.The second part of this study presents results from experimental and numerical analysis of drop tests. Numerical hydroelastic analyses of both the elastic model shells and the real concrete shells are presented. The results show that even large and thick concrete shells experience significant hydroelastic effects during slamming.The hydroelastic response of the concrete shells is dominated by only a few structural eigenmodes. This means that the calculated dynamic amplification factors, DAF, resemble those of one-degree-of-freedom mass–spring systems exposed to loads of finite duration.The structural responses are seen to significantly modify the hydrodynamic loads. This hydrodynamic load modification consists of the well-known added mass term but also a time dependent slam damping term which reduce the structural response when properly accounted for. Both terms are necessary to calculate the concrete shell response accurately.

CFD-FEM Simulation of Slamming Loads on Wedge Structure with Stiffeners Considering Hydroelasticity Effects

In this paper, both numerical and experimental methods are adopted to study the fluid–structure interaction (FSI) problem of a wedge structure with stiffeners impacted with water during the free-falling water entry process. In the numerical model, a partitioned two-way couple of CFD and FEM solvers is applied to deal with the FSI problem, where the external fluid pressure exported from the CFD simulation is used to derive the structural responses in the FEM solver, and the structural deformations are fed back into the CFD solver to deform the mesh. Moreover, a tank experiment using a steel wedge model that has the same structural properties is also conducted to compare with the numerical results. Verification and validation of the numerical results indicate that the CFD-FEM coupled method is feasible and reliable. The slamming response results by numerical simulation and experiments, including displacement, velocity, acceleration, slamming pressure, deformation, structural stresses and total forces on the wedge, accounting for hydroelasticity effects in different free falling height conditions are comprehensively analyzed and discussed.

A study into the FSI modelling of flat plate water entry and related uncertainties

This paper presents systematic comparisons of experiments against fluid structure interaction (FSI) simulations for flat water plate entry. Special focus is attributed on hydroelasticity and air trapping effects, quantification of the experimental and numerical uncertainties and the validity of modelling assumptions for the prediction of bottom slamming induced loads. Consequently, the American society of Mechanical Engineers standard for Verification and Validation is used to estimate the errors. Numerical and experimental results agree favourably. It is shown that pressures and strains may be prone to spatial effects that lead to minor deviations between experiments and simulations. High frequency vibration modes and model boundary conditions may also influence the results.

Frequency-domain approach of hydroelastic response for offshore bottom-mounted slender structure

ABSTRACT Bottom-mounted slender structures are often flexible enough to induce hydroelastic effect which could change their dynamic properties and affects the resultant response. This study presents a frequency-domain approach to characterise the hydroelastic response as well as wet dynamic characteristics for offshore bottom-mounted structure with arbitrary geometry. The boundary element method associated with Euler-Bernoulli theory is integrated and coupled. The approaches for wet fundamental period, wet damping ratio and hydroelastic response are validated against a benchmark experiment. Results show that surrounding water has obvious influence on the structural period and damping ratio, particularly on damping ratio. The distribution of added mass grows quickly with depth to about z/d = 0.2 and then gradually decreases whereas added damping mainly concentrates near free surface and drops rapidly with depth. If hydroelastic effect is not considered, it could cause considerable frequency-to-frequency errors from −26% to 52% in responses.

Frequency-domain approach of aero-hydro-elastic response for offshore bottom-mounted slender structures under wind and wave

Bottom-mounted slender structures in offshore regions, e.g., high-rising bridge pylon and monopile foundation are often flexible enough to induce considerable aero-hydro-elastic effect which could change their dynamic properties and obviously affects the resultant response against wind and free surface waves. This study presents an efficient frequency-domain approach to characterize the aero-hydro-elastic response as well as the dynamic properties for offshore bottom-mounted structure. A specific attention is drawn to the hydrodynamic mass and damping modeling. The boundary element method associated with Euler-Bernoulli theory is coupled in frequency domain to bridge the gap between the deformable boundary condition on discretized panels and the elastic structure. The quasi-stationary approach considering instantaneous structural motion is employed to calculate the aero-elastic effect. The proposed approach is well validated against a benchmark experiment. Results of a prototype structure subject to wind and wave emphasize the significant influence of aero- and hydro-elastic effect on the structural responses as well as dynamic properties, particularly on damping ratio. If the aero-hydro-elastic effect is not properly considered, it could obviously overestimate the structural responses by 6.8%–32.6%. It is necessary to investigate the aero- and hydro-elastic response in a coupled scheme, otherwise it may induce errors up to 8.5% in structural responses.

Hydroelastic analysis of Pre-Swirl Stator

This paper presents the investigation of the dynamic effects in the structural response of a Pre-Swirl Stator. The implemented model is based on the modal superposition which improves the efficiency of the hydro-structural coupling. Structural response is decomposed into a set of orthogonal dry modes which are computed in the pre-processing stage. Mode shape displacement vectors are interpolated from the structural nodes onto the fluid mesh on the selected merging interface. This allows the dynamic equation solution directly inside the fluid solver. Compared to the standard hydro-structural interaction which requires additional iterations between the structure and fluid models per time-step, this approach reduces the complexity and computational effort. Model is verified on a simplified PSS simulation setting and computational guidelines are derived. The PSS is further analysed on the realistic cases of propeller and wave loads with the hydroelastic effects included. The results suggest a negligible amount of dynamic amplification in the current PSS design.