Effects of viscosity and nonlinearity on 3D flapping-foil thruster for marine applications

Papadakis, George; Filippas, E.S.; Ntouras, Dimitris; Belibassakis, Kostas

doi:10.1109/oceanse.2019.8867084

Cited by 9 publications

(10 citation statements)

References 28 publications

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“…This approach, based on the quasi-steady lifting line theory in conjunction with unsteady thin hydrofoil theory, provides a computationally efficient method to assess the performance of wave-propelled boats. For greater fidelity, 3-D boundary element methods, such as those presented in [2] and [40], may offer greater accuracy, as well as estimate ship resistance. While CFD methods (e.g., 2-D/3-D RANS and 3-D DES) may yield more accurate results capturing 3-D and free-surface boundary condition effects, these approaches require significantly greater computational resource [40]; that is, the proposed method provides a useful design tool.…”

Section: F Implementationmentioning

confidence: 99%

Forward Speed Prediction of a Free-Running Wave-Propelled Boat

Bowker

Tan

Townsend

2021

IEEE J. Oceanic Eng.

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Wave-propelled boats utilize submerged flapping foils to convert wave energy directly into propulsion. For platforms that are solely propelled using submerged flapping foils, predicting the forward speed is challenging as it is time varying and dependent on the coupled responses of the wave-induced hull motions (surge, heave, and pitch) and the foil flapping motion (driven by the waveinduced hull motions and incident wavy flow). To ascertain the free-running response of wave-propelled boats, this article presents a hybrid discrete time-domain numerical model and experimental results from a prototype wave-propelled autonomous surface vehicle (ASV) with forward and aft (tandem) flapping foils. Results from a series of free-running experiments in regular head waves, over a range of wave frequencies for three different foil locations, are presented and used to validate the numerical model. The model was found to show good agreement with the experimental results, capturing the coupled dynamics of the vessel and foils and oscillating forward speed, over a range of wave frequencies and foil locations. The model and results provide a valuable insight for the design of wave-propelled boats.

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Section: F Implementationmentioning

confidence: 99%

Forward Speed Prediction of a Free-Running Wave-Propelled Boat

Bowker

Tan

Townsend

2021

IEEE J. Oceanic Eng.

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“…Direct extensions include modelling various nonlinearities associated with large deflections and viscous effects [37,53]. Another aspect concerns the code optimization using GPGPU programming and message passing interface (MPI) techniques to significantly reduce computational time and cost, see, e.g., [13,38,44]. This step will allow three-dimensional modelling as well as shape and material optimization, supporting applications concerning realistic designs.…”

Section: Discussionmentioning

confidence: 99%

“…In that sense, lower-fidelity and cost-effective inviscid fluid flow simulations are a useful tool in the preliminary design phase of biomimetic thrusters, where emphasis is given on parametric studies, whereas high-fidelity CFD simulations, see, e.g., [37], are more computationally intensive and resource demanding compared to potential-based solvers. A direct comparison between the two approaches can be found in [38].The scope of the present work is to propose a non-linear fully coupled BEM-FEM scheme for the solution of the FSI problem of chord-wise flexible flapping foils operating as marine thrusters, including thickness and flexural rigidity profile variation. The major contribution of this work is that the developed method and software could serve, after enhancement and further validation, as a useful cost-effective tool for the preliminary design and optimum control of flexible biomimetic thrusters.…”

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confidence: 99%

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confidence: 99%

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A Non-Linear BEM–FEM Coupled Scheme for the Performance of Flexible Flapping-Foil Thrusters

Anevlavi

Filippas

Karperaki

et al. 2020

JMSE

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Recent studies indicate that nature-inspired thrusters based on flexible oscillating foils show enhanced propulsive performance. However, understanding the underlying physics of the fluid–structure interaction (FSI) is essential to improve the efficiency of existing devices and pave the way for novel energy-efficient marine thrusters. In the present work, we investigate the effect of chord-wise flexibility on the propulsive performance of flapping-foil thrusters. For this purpose, a numerical method has been developed to simulate the time-dependent structural response of the flexible foil that undergoes prescribed large general motions. The fluid flow model is based on potential theory, whereas the elastic response of the foil is approximated by means of the classical Kirchhoff–Love theory for thin plates under cylindrical bending. The fully coupled FSI problem is treated numerically with a non-linear BEM–FEM scheme. The validity of the proposed scheme is established through comparisons against existing works. The performance of the flapping-foil thrusters over a range of design parameters, including flexural rigidity, Strouhal number, heaving and pitching amplitudes is also studied. The results show a propulsive efficiency enhancement of up to 6% for such systems with moderate loss in thrust, compared to rigid foils. Finally, the present model after enhancement could serve as a useful tool in the design, assessment and control of flexible biomimetic flapping-foil thrusters.

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“…As mentioned above, in the experiment by Huxham et al [20], end-plates were used at the tips of the oscillating wing, in order make the flow around the foil more close to being two-dimensional and to increase the efficiency of the system by reducing the downwash 3D effects. In order for the present method, where no-end plates are considered in the studied configuration, to simulate the experiment, an increased value of the aspect ratio needs to be considered (see also [40]). In such a case, the present method's results can be compared with the measured data converted in the form of torque and net power output per unit span.…”

Section: Convergence and Validationmentioning

confidence: 99%

A Study of Multi-Component Oscillating-Foil Hydrokinetic Turbines with a GPU-Accelerated Boundary Element Method

Koutsogiannakis

Filippas

Belibassakis

2019

JMSE

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A biomimetic semi-activated oscillating-foil device with multiple foils in a parallel configuration is studied for the extraction of marine renewable energy. For the present investigation, an unsteady boundary element method (BEM) is used for the simulation of 3D lifting flows. For this work, the device is assumed to be submerged far from the free surface and the sea bottom. However, the geometry of the body and the initial shape of the wake are general. For the numerical simulations, a high performance in-house GPU-accelerated code (GPU-BEM) is developed. For the calculation of singular integrals, an adaptive algorithm based on the Gauss-Lobatto quadrature is used. Concerning the numerical scheme of GPU-BEM, the convergence of the method was tested, the numerical characteristics were determined and the method was validated. A parametric study of a single-foil device is presented to determine the performance characteristics of such devices. Next, twin-foil devices are investigated in parallel and staggered configurations with a phase difference between the two foils. Finally, the multiple-foil parallel configuration is compared against turbines. After enhancement and further verification, the present method is proposed for the design and control of such biomimetic devices for the extraction of energy from waves and tidal currents nearshore.Foils can also be used as devices that convert tidal stream energy to other forms, i.e., electricity. In tidal energy harvesting mode, oscillating foils operate by absorbing energy from the incident current. One of the first reports on such designs is that of reference [15], and some early experiments were conducted in 1982 [16].Oscillating foils combine a pitch motion and a heave motion. In reference [17], oscillating-foil devices are classified into three categories depending on the activation mechanism of the oscillating foil. First, there are fully activated foils, where both the pitch and heave motions are prescribed. Second, there are semi-activated foils, where the pitch motion is given as input and the heave is the response to the hydrodynamic forces. Third, there are fully passive foils, where both motions are driven by the forces acting on the foil. In the present work, we study the semi-activated oscillating foil, because this alternative is a more feasible design than the fully activated system and it provides a mechanism to actively control the operation of the foils, in contrast to the fully passive design. Also, energy extraction of both waves and current is studied by the authors in [18].Moreover, efforts have been made to map the performance of oscillating foils in the energy extraction regime, i.e., parametric studies [19][20][21]. The basic parameters of the harmonic pitching motion have been mainly investigated, through experiments or numerical simulations. In [19], the authors report a power-extraction efficiency of 36.4% for a pitching amplitude of 76.3 degrees, using the FLUENT commercial software.Various studies have shown that oscillating foils can have...

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Effects of viscosity and nonlinearity on 3D flapping-foil thruster for marine applications

Cited by 9 publications

References 28 publications

Forward Speed Prediction of a Free-Running Wave-Propelled Boat

Forward Speed Prediction of a Free-Running Wave-Propelled Boat

A Non-Linear BEM–FEM Coupled Scheme for the Performance of Flexible Flapping-Foil Thrusters

A Study of Multi-Component Oscillating-Foil Hydrokinetic Turbines with a GPU-Accelerated Boundary Element Method

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