Hydroelastic Response Research Articles

Effect of a floating permeable plate on the hydroelastic response of a very large floating structure

The effectiveness of a floating porous plate for mitigating the wave-induced structural response of a very large floating structure is investigated using the eigenfunction expansion method. The analysis is based on the assumption of a small-amplitude structural response of the very large floating structure and the linearized theory of water waves with the assumption that the elastic plate is floating freely on the free surface. The elastic plate is modeled using thin plate theory, and the wave past the porous plate is based on the assumptions of the generalized porous wavemaker theory. The horizontal plate reflects and dissipates a major part of the wave energy, which in turn reduces the wave-induced structural response of the structure. Wave reflection and dissipation increase in an oscillatory manner with an increase in the wavenumber associated with the incident wave, and a complementary trend is observed in the wave transmission, with the oscillatory trend diminishing for higher values of structural porosity. When the distance between the porous plate and floating elastic plate is an integer multiple of half the wavelength, a certain periodic oscillatory pattern occurs in the wave reflection, with complementary patterns being observed in the wave transmission and dissipation. The amplitude of the periodic oscillatory pattern in the wave reflection reduces with an increase in the length of the porous plate of moderate porosity. Moreover, the wave energy reflection and dissipation are greater in case of short compared with long waves for a floating porous plate of larger length. The elastic plate deflection and free surface elevation on the lee side of the floating elastic plate attenuate with an increase in the length of the porous plate for a moderate value of the structural porosity. The reflection coefficient and forces acting on the plate follow a similar pattern with variation of the distance between the porous plate and large floating structure, whilst the shear force and strain acting on the floating structure are complementary to the wave reflection and forces acting on the porous plate.

Hydroelastic responses of a 3-module VLFS in the waves influenced by complicated geographic environment

During the Very Large Floating Structure (VLFS) is deployed not far from the shore line or near the island, the ocean waves and hydroelastic responses of VLFS could be greatly influenced by the complicated geographic environment, particularly for the depth-varying seabed. Firstly, the extreme wave parameters of different recurrence periods at the deployed location are solved by the numerical simulations of wave evolution and propagation in an archipelagic water field using the third-generation wave model. The numerical results are compared with the data from the on-site measurement and model test in a shallow water wave basin. Secondly, one hydroelastic numerical coupled model of the floating structure responding to the waves in shallow water with a specified seabed profile is proposed and validated by comparing with the model test results. Finally, based on the above model, the hydroelastic responses of the VLFS in the waves influenced by complicated geographic environment are obtained. It is concluded that the wave statistics experiences obviously changes when propagating and approaching towards the island; meanwhile, the complicated seabed profile has an apparent influence on the hydroelastic responses of the VLFS.

A direct coupling analysis method of hydroelastic responses of VLFS in complicated ocean geographical environment

In this paper a direct coupling analysis method (DCAM) of hydroelastic responses of a very large floating structures (VLFS) in complicated geographical environment is presented. In this method the three-dimensional hydroelasticity theory of floating bodies is combined with the shallow water wave theory, to allow for proper description of the influence of uneven seabed and sheltering effect of islands on the hydroelastic responses of a VLFS deployed near island and reefs in shallow sea. This method and the numerical procedures were verified and validated by comparison between the predictions and the model test results of a 3-module VLFS and an 8-module VLFS in two simulated shallow sea regions with different seabed topography.

Fluid-structure interaction of a large ice sheet in waves

With global warming, the ice-covered areas in the Arctic are being transformed into open water. This provides increased impetuses for extensive maritime activities and attracts research interests in sea ice modelling. In the polar region, ice sheets can be several kilometres long and subjected to the effects of ocean waves. As its thickness to length ratio is very small, the wave response of such a large ice sheet, known as its hydroelastic response, is dominated by an elastic deformation rather than rigid body motions. In the past 25 years, sea ice hydroelasticity has been widely studied by theoretical models; however, recent experiments indicate that the ideal assumptions used for these theoretical models can cause considerable inaccuracies. This work proposes a numerical approach based on OpenFOAM to simulate the hydroelastic wave-ice interaction, with the Navier-Stokes equations describing the fluid domain, the St. Venant Kirchhoff solid model governing the ice deformation and a coupling scheme to achieve the fluid-structure interaction. Following validation against experiments, the proposed model has been shown capable of capturing phenomena that have not been included in current theoretical models. In particular, the developed model shows the capability to predict overwash, which is a ubiquitous polar phenomenon reported to be a key gap. The present model has the potential to be used to study wave-ice behaviours and the coupled wave-ice effect on marine structures.

Hydroelastic response of three-layered beam resting on winkler foundation

The hydroelastic oscillations problem of the sandwich beam resting on elastic foundation and interacting with the pulsating fluid layer was investigated. The three-layered beam with an incompressible lightweight filler was considered. The broken normal hypothesis for the three-layered beam and the model of viscous incompressible fluid, as well as Winkler model for elastic foundation, was chosen to study hyroelastic problem. A mathematical model of the considered mechanical system consists of dynamic equations of the three-layered beam with incompressible lightweight filler and the Navier-Stokes equations with continuity equation for the pulsating viscous fluid layer. The no-slip conditions and pressure coincidence at the edges with the given pressure into edges cavities were selected as boundary ones. The plane problem of hydroelastic beam bending oscillations for the regime of steady harmonic ones were considered. The solution of the hydroelastic problem was carried out by the perturbations method using proposed small parameters of the hydroelastic problem. As a result, the laws of three-layered beam elastic deflections and the hydrodynamic parameters of pulsating viscous fluid layer were obtained.

Fluid exciting force due to flutter and rotor-stator interactions in axial flow turbines

In recent years, the size and the speed of axial flow type hydraulic turbines have been continuously increased, leading to an increase of the fluid exciting forces due to rotor-stator interactions in hydraulic machines featuring both rotor and stator. In addition, the use of composite material for the blades of large hydraulic machines is increasingly investigated. Such flexible and lightweight hydrofoils can however easily experience self-excited vibration such as flutter effect. Fluid exciting forces generated in hydraulic machines might cause resonance, fatigue of the blade and finally damage. This paper aims to evaluate fluid exciting forces produced by rotor-stator interactions in axial flow turbines and the hydro-elastic response to the flutter of a flexible hydrofoil. To evaluate fluid exciting forces due to rotor-stator interactions, experiments are carried out using a closed-loop water channel featuring an axial flow turbine. The pressure distribution on the blade surface and the influence of axial distance between rotor and stator on the pressure fluctuations amplitude on the blade surface are investigated. A good agreement between experimental and numerical values is found. Regarding the flutter effect, FSI (Fluid Structure Interaction) simulation of one hydrofoil coupling RANS (Reynolds-averaged Navier–Stokes equations) and FEM (Finite Element Method) simulation is carried out to study the three-dimensional behaviour of the flutter.

Study of the Prediction of Fatigue Damage Considering the Hydro-elastic Response of a Very Large Ore Carrier (VLOC)

Study of the Prediction of Fatigue Damage Considering the Hydro-elastic Response of a Very Large Ore Carrier (VLOC)

Extracting energy while reducing hydroelastic responses of VLFS using a modular raft wec-type attachment

This paper presents the use of a modular raft Wave Energy Converter (WEC)-type attachment at the fore edge of a rectangular Very Large Floating Structure (VLFS) for extracting wave energy while reducing hydroelastic responses of the VLFS under wave action. The proposed modular attachment comprises multiple independent auxiliary pontoons (i.e. modules) that are connected to the fore edge of the VLFS with hinges and linear Power Take-Off (PTO) systems. For the hydroelastic analysis, the auxiliary pontoons and the VLFS are modelled by using the Mindlin plate theory while the linear wave theory is used for modelling the fluid motion. The analysis is performed in the frequency domain using the hybrid Finite Element-Boundary Element (FE-BE) method. Parametric studies are carried out to investigate the effects of pontoon length, PTO damping coefficient, gap between auxiliary pontoons, and incident wave angle on the power capture factor as well as reductions in the hydroelastic responses of the VLFS with the modular attachment. It is found that in oblique waves, the modular attachment comprising multiple narrow pontoons outperforms the corresponding rigid attachment that consists of a single wide pontoon with respect to the power capture factor and the reduction in the deflection of the VLFS. In addition, it is possible to have a considerable gap between pontoons without significantly compromising the effectiveness of the modular attachment.

Viscous fluid–structure interaction response of composite hydrofoils

Composite materials are increasingly used in hydrodynamic lifting surfaces due to their higher specific strength and favorable fatigue properties. A set of parametric studies are performed to investigate the influence of fiber orientation on the vibration characteristics and load-dependent bend-twist coupled behavior of composite hydrofoils in viscous flow. A 3-D Reynolds-averaged Navier–Stokes (RANS) solver is coupled with a 3-D finite-element method (FEM) to predict the fluid–structure response of cantilevered composite hydrofoils made of unidirectional carbon fiber reinforced polymer (CFRP). Fiber orientation changes the modal characteristics of composite hydrofoils, as well as the hydroelastic response. The bending-up and nose-down material bend-twist coupling leads to lower hydrodynamic load coefficients with increasing flow speed, as well as delayed separation, stall, and static divergence. The opposite trend is observed when the fiber orientation results in a bending-up and nose-up material bend-twist coupling. Material failure index contours show that the fiber orientation affects the location of failure. These parametric studies provide guidance for future design and optimization of composite hydrodynamic lifting surfaces.

Water influence as internal fluid in polymer pipes on the hydro-elastic response of structure

Water influence as internal fluid in polymer pipes on the hydro-elastic response of structure

Water influence as internal fluid in polymer pipes on the Hydro-elastic response of structure

This articles presents hydro-elastic response of surrounded carbon nanotubes (CNTs) armed pipes as functionally graded (FG) with internal fluid. The elastic foundation is simulated by orthotropic temperature-dependent Pasternak model. Shell Flugge model is utilised for modelling of pipe. Utilising principal of Hamilton, the motion final equations are obtained. A numerical approach is utilised for deriving the critical velocity of fluid. The influences of different variables of CNTs volume fraction, elastic foundation and geometrical variables are presented. Outcomes revel that reinforcing the pipe by CNTs lead to higher critical velocity of fluid.

Optimization of modular raft WEC-type attachment to VLFS and module connections for maximum reduction in hydroelastic response and wave energy production

This paper presents optimization of modular raft WEC-type attachment to VLFS and connections between floating modules of the VLFS for regular and irregular waves. The modular raft WEC-type attachment consists of multiple independent auxiliary pontoons connected to the fore edge of the VLFS with hinges and linear Power Take-Off (PTO) systems. The two objectives of the optimization are to maximize the reduction in hydroelastic response of VLFS and the power capture factor. The optimization process is proposed by using differential evolution (DE) algorithm. A numerical analysis framework based on finite element-boundary element (FE-BE) method is presented for determining the power capture factor as well as the hydroelastic response reduction for regular and irregular waves. The proposed optimization process is used to investigate the effects of the design variables, including PTO damping coefficient, pontoon length, the number of connections and connection stiffness, on the trade-off curve (i.e. Pareto front). In addition, the maximum power capture factor and hydroelastic response reduction are examined for various regular and irregular waves.

A simplified method to estimate the hydroelastic responses of VLFS in the inhomogeneous waves

For the very large floating structure (VLFS) which is deployed near seashore, islands and reefs, the encounter wave conditions will become extremely complex. The influences of the inhomogeneous incident waves (multi-directions, different wave height) should be taken into account, particularly in extreme typhoon wave environment. Therefore, the traditional methods with homogeneous wave inputs cannot be applied in this type of hydroelasticity analysis of VLFS. A simplified method and its corresponding software THAFTS-IHIW were established to estimate the hydroelastic responses of VLFS in the inhomogeneous waves. The accuracy of the simplified method was verified by model test results, and an application of this simplified method for the hydroelastic analysis of the 8-module VLFS in the Typhoon ‘Kalmaegi’ was presented in this paper. Some useful conclusions are obtained, which can provide a reference for the analysis of dynamic responses, design and construction of the floating bodies near seashores and islands.

The Effects of Moving Load on the Hydroelastic Response of a Very Large Floating Structure

The hydroelastic response of a very large floating structure in regular waves suffering an external moving point load is considered. The linearized velocity potential theory is adopted to describe the fluid flow. To take into account the coupled effects of the structure deformation and fluid motion, the structure is divided into multiple segments and connected by an elastic beam. Then through adding a stiffness matrix arising from the elastic beam into the multiple bodies coupled motion equations, the hydroelastic response is considered. By applying the Fourier transform to the obtained frequency domain coefficients, the motion equation is transformed into the time domain and the external point load is further considered. The accuracy and effectiveness of the proposed method are verified through the comparison with experimental results. Finally, extensive results are provided, and the effects of the moving point load on the hydroelastic response of the very large floating structure are investigated in detail.

Effect of a Submerged Porous Plate on the Hydroelastic Response of a Very Large Floating Structure

Scattering of oblique flexural-gravity waves by a submerged porous plate in a finite water depth is investigated under the assumptions of linearized surface waves and small-amplitude structural response. The study is carried out using eigenfunction expansions and the corresponding orthogonal mode-coupling relations associated with flexural-gravity waves in uniform water depth. The characteristics of the roots of the complex dispersion relation are examined using the principle of counting argument and contour plot. Characteristics of the flexural-gravity waves are studied by assuming both the floating elastic plate and the submerged porous plate are infinitely extended in horizontal directions. The effectiveness of the submerged porous structure on the reflection, transmission, and dissipation coefficients is analyzed for various wave and structural parameters.

Time-Domain Hydro-Elastic Analysis of a SFT (Submerged Floating Tunnel) with Mooring Lines under Extreme Wave and Seismic Excitations

Global dynamic analysis of a 700-m-long SFT section considered in the South Sea of Korea is carried out for survival random wave and seismic excitations. To solve the tunnel-mooring coupled hydro-elastic responses, in-house time-domain-simulation computer program is developed. The hydro-elastic equation of motion for the tunnel and mooring is based on rod-theory-based finite element formulation with Galerkin method with fully coupled full matrix. The dummy-connection-mass method is devised to conveniently connect objects and mooring lines with linear and rotational springs. Hydrodynamic forces on a submerged floating tunnel (SFT) are evaluated by the modified Morison equation for a moving object so that the hydrodynamic forces by wave or seismic excitations can be computed at its instantaneous positions at every time step. In the case of seabed earthquake, both the dynamic effect transferred through mooring lines and the seawater-fluctuation-induced seaquake effect are considered. For validation purposes, the hydro-elastic analysis results by the developed numerical simulation code is compared with those by a commercial program, OrcaFlex, which shows excellent agreement between them. For the given design condition, extreme storm waves cause higher hydro-elastic responses and mooring tensions than those of the severe seismic case.

Investigation on Ship Hydroelastic Vibrational Responses in Waves

The hydroelastic vibrational responses of a large ship sailing in regular and irregular head waves are investigated numerically and experimentally. A 3D time-domain nonlinear hydroelastic mathematical model is established in which the hydrostatic restoring forces and incident wave forces are calculated on the instantaneous wetted hull surface to consider nonlinear effects of the rigid motion and elastic deformation of the hull in harsh waves. Radiation and diffraction wave forces are computed on the mean wetted surface based on the 3D frequency-domain potential flow theory. The slamming loads are calculated by momentum theory and integrated into the hydrodynamic forces. The 1D Timoshenko beam theory is adopted to model the vibrational structural response and is fully coupled with the presented hydrodynamic theory in time-domain to generate the hydroelastic equation of motion. Moreover, self-propelled segmented model tests were conducted in a laboratory wave tank to experimentally investigate the hydroelastic responses of a target ship in regular and irregular head seas. The numerical and experimental results are systemically compared and analyzed, and the established hydroelastic analysis model turns out to be reliable and effective in the prediction of ship hydroelastic responses in waves.

A Time-Domain Method for Hydroelasticity of a Curved Floating Bridge in Inhomogeneous Waves

This paper presents a time-domain hydroelastic analysis method for bridges supported by floating pontoons in inhomogeneous wave conditions. The inhomogeneous wave effect is accounted for by adopting different wave spectra over different regions along the structure, then the time history of inhomogeneous first-order wave excitation forces on the floating pontoons can be obtained. The frequency-domain hydrodynamic coefficients are transformed into the time-domain hydroelastic model using Cummins' equations. The linear hydroelastic responses of a curved floating bridge with end supports, subjected to irregular waves with spatially varying significant wave heights and peak periods, are investigated. Moreover, sensitive analyses are performed to study the effects of the inhomogeneity on the hydroelastic responses. The primary results indicate that the inhomogeneity of the waves has a significant effect on the dynamic responses of the floating bridge.

Nonlinear time-domain hydroelastic analysis for a container ship in regular and irregular head waves by the Rankine panel method

ABSTRACTThis work presents a nonlinear time-domain numerical study on the hydroelastic phenomena in regular and irregular head waves based on the Rankine panel method. Firstly, a numerical damping beach approach is applied to satisfy the radiation condition and the velocity potential is solved. Secondly, a three-dimensional nonlinear time-domain hydroelastic method is proposed, and the hydroelastic method is generalised to the irregular wave problem in which the influence from the various incident wave frequencies is considered by adopting time-domain convolution theory and memory function. Thirdly, segmented model tests of a 15,000-TEU container ship are performed. A testing system is designed and the measured results are analysed. Finally, load responses of the container ship in regular and irregular waves are predicted. From the comparison between experimental measurements and numerical results, it is confirmed that the present concept for dealing with nonlinear hydroelastic responses is reliable and accurate.

Measurement and prediction of cavitating flow-induced vibrations

The objective of this paper is to investigate the unsteady cavitation behaviors and the corresponding cavitating flow-induced vibrations. Results are presented for the modified NACA66 hydrofoils made of stainless steel and POM Polyacetate respectively at Re = 6.0×105 for various cavitation regimes. The high-speed camera and the single point laser Doppler vibrometer (LDV) are used to observe the transient cavitating flow patterns and measure the vibration velocities. The results showed that the vibration amplitude increases dramatically for the cloud cavitation due to the development of large-scale cloud cavity. The main flow-induced frequencies, which are in accordance with the cavity shedding frequency, decrease with the decrease of the cavitation number. As for the effect of the hydroelastic response on the vibration behavior, the lift coefficient for the POM Polyacetate hydrofoil fluctuates more significantly with a larger mean value than that for the stainless steel hydrofoil. Compared with the vaporous cavity along the suction side of the stainless steel hydrofoil, the cavity for POM Polyacetate hydrofoil appears to be fragmentized. The main vibration frequencies for the POM Polyacetate hydrofoil are larger than that for the stainless steel hydrofoil, with the chaotic hydroelastic response with high frequency.