Experimental measurement and simplified prediction of T-foil performance for monohull dinghies

The rise in interest in large foiling yachts, such as those in the America’s Cup, has spurred a corresponding interest in foiling applications in monohull sailing dinghies, both for boats designed specifically for foiling, and through retro-fit foil kits. The present study considers the assessment of foil systems for such boats, and specifically the prediction of the necessary foil performance of T-foils with flaps. The main lifting foil for a moth dinghy with flap was tested at full-scale in a towing tank at a range of speeds, trim angles and flap angles, and immersions, to measure vertical and lift and drag. Results are then compared with two simplified models typical of those utilized in Velocity Prediction Programs for preliminary design. The first model uses section lift and drag data obtained using the well-known XFOIL code allied to a simple correction for 3D effects while the second model deploys a numerical lifting line theory in conjunction with section data. A number of practical conclusions are drawn regarding the set-up and sailing of foiling dinghies with flapped T-foils. Results show that whilst the simple and rapid models typically used in basic VPPs may not accurately represent the relationships between angle of attack / flap angle with lift and drag, the predicted relation between lift and drag is reasonably accurate in most cases

Assessing the impact of membrane deformations on wing sail performance

The aim of this research is to quantify the membrane deformations and their impact on performance for a ribbed wing sail. A 1m x 0.8m rectangular planform NACA0012 foil was designed to replicate a single section of a wing-sail. Two foils were manufactured based on this geometry, one out of solid foam and one using a rib and membrane structure. These were tested in the R.J. Mitchell closed return 3.6 m x 2.5 m wind tunnel at the University of Southampton. Their aerodynamic performance was assessed over a range of angles of attack using a six-component force balance showing the overall performance of the membrane wing was reduced by between 5-11% depending on the analysis conducted. A stereo camera system was used to perform Digital Image Correlation (DIC) in order to quantify the full field deformation of the membrane wing structure whilst under aerodynamic load. This showed membrane deformations of up to 15% of the section thickness. The experimental membrane displacements were then used to create a deformed wing sail geometry, removing the effect of foil bend and twist, allowing a CFD investigation of the impact of membrane deformations alone. This indicated that the static membrane deformations resulted in a decrease in performance of up to 1.3% compared to the rigid aerofoil

An investigation into the effect of ventilation, bulbs and flow turbulence on lifting T foil performance

Flapped lifting T foils are a key part of modern high-performance craft due to their ability to reduce wetted surface area and hence drag at high speed. The performance of these foils is significantly affected when ventilated. Ventilation on a T-foil normally leads to a dramatic and uncontrolled loss of lift and overall vessel drag increment due to the hull coming into contact with the water surface. Limited research of ventilated T foils has been published due to challenges associated with reproducing ventilations in a relatively low-speed tow tank environment. The current study looks into the performance of a Waszp rudder fitted with modifications. The position of the horizontal foil relative to the vertical strut was varied as was the flow turbulence around the vertical strut using a turbulence stimulating wire. Towing test of the modified Waszp rudder was carried out at the Kelvin Hydrodynamics Laboratory of University of Strathclyde. Results were compared against the original Waszp T-foil. Experimental testing results shows how the foil can be modified to the T foil performance. It also shows changes in the characteristics in the ventilated cavity when the foil is operating in fully ventilated flow. A new method capable of stimulating foil ventilation repeatably was developed utilizing turbulence wire which can potentially enable more T-foil ventilation-related experimental studies in the future

Retrofitting leading-edge tubercles onto a sailing dinghy hydrofoil using 3D printing technology

Inspired by the flippers of Humpback whales, many recent engineering studies focus on how lifting foils can benefit from leading-edge tubercles. Contributing to the ongoing research of this biomimetic concept, the study presented investigates if the main lifting foil of a Moth sailing dinghy could benefit from the implementation of a serrated leading-edge. To do so, 3D printed tubercles were retrofitted to the centreboard T-foil of a Moth dinghy that was subsequently tested in the Kelvin Hydrodynamics Laboratory towing tank at the University of Strathclyde in Glasgow. The results of these full-scale tests showed improvements for the lower Reynolds number range, but large disadvantages for higher speeds. Despite being generally unable to improve the foil’s performance, it was still successfully shown, how 3D printing can be used as simple, effective, and cost-friendly tool to be used to assess model variations or modifications in tank testing

The effect of the addition of tubercles on the performance of Moth-T-foil

Tubercles have proven, in the nature (e.g., the humpback whale) as well as in engineering (e.g., rudders, wind and tidal turbine blades, propellers, etc.), to be an efficient device to control the flow and to delay stall. This study focusses on the implementation of tubercles on the main lifting foil of a moth sailing dinghy. To do so, a "Bladerider" flapped T-foil with and without tubercles was tested in the Kelvin Hydrodynamics Laboratory in Glasgow, at a range of speeds, angles of attack, flap angles but also immersions. The results of these full-scale tow-tests, including the lift and drag data of the bare foil, are presented in this paper. The measurement data was used to investigate the effect of the addition of tubercles on the performance of a T-foil

Structural integrity analysis of containers lost at sea using finite element method

Unlike traditional transportation, container transportation is a relatively new logistics transportation mode. Shipping containers lost at sea have raised safety concerns. In this study, finite element analysis of containers subjected to hydrostatic pressure, using commercial software ANSYS APDL was performed. A computer model that can reasonably predict the state of an ISO cargo shipping container was developed. The von Mises stress distribution of the container was determined and the yield strength was adopted as the failure criterion. Numerical investigations showed that the conventional ship container cannot withstand hydrostatic pressure in deep water conditions. A strengthened container option was considered for the container to retain its structural integrity in water conditions

Wave energy extraction for an array of dual-oscillating wave surge converter with different layouts

Array configuration of oscillating wave surge converter (OWSC) devices in nearshore is a preferable option for realizing a cost-balance of extracting wave energy and reducing installation expense due to closer installed place to coastline. The goal of the present work is to assess energy extraction of an array of dual-OWSC system with different layout schemes in comparison with an isolated OWSC, which can be regarded as a guideline for multi-array configuration in realistic wave farm. The coupled three-dimensional (3-D) hydrodynamic model is established based on the potential flow theory with fully nonlinear boundary condition in time domain. A non-dimensional approach is conducted to focusing on the accurate effects of multi-body interaction, wave nonlinearity, wave resonance, mechanical damping, layout scheme and oblique incidence as optimization design. For a front-back array system, wave resonance in dual-module gap enhances significantly the energy extraction of the front OWSC but does not contribute much to that of the back OWSC. Furthermore, wave resonance in wide gap has a positive effect on the capture efficiency in large wave periods. An in-line array system has a beneficial performance in small wave periods, while a staggered array system realizes more energy extraction in resonance region. A strong wave disturbance between flap sides of an in-line and staggered system, leads to the increase of energy extraction for the back OWSC with imposing small incident wave heading. Therefore, the combination of multi-triple-array OWSC with different gap distances will provide a desirable configuration which is independent on oblique wave conditions

Performance characteristics and parametric analysis of a novel multi-purpose platform combining a moonpool-type floating breakwater and an array of wave energy converters

Integration of Wave Energy Converters (WECs) with floating breakwater system provides a multi-function solution to wave energy extraction and offshore infrastructural protection. The contribution of this work is to guide the optimal size and configuration of a multi-purpose platform including a moonpool-type floating breakwater and an array of heaving oscillating-buoy (OB) WECs. The investigation is performed using a developed time-domain numerical wave tank (NWT) based on the three-dimensional (3D) potential flow theory with fully nonlinear boundary conditions on transient wetted body surfaces and free surfaces. The comparison of the hydrodynamic performance among the multi-purpose platform, the isolated array WECs, and the isolated floating breakwater are examined. The internal fluid motion in the moonpools has a positive effect on the wave energy absorption of WECs, which in turn enhances the wave attenuation capacity of the floating breakwater. WECs with larger diameter have a larger water-plane area, which leads to more extracted wave energy. The wave nonlinearity reduces the optimal PTO damping value and has an adverse effect on the wave energy extraction. However, when wave nonlinearity becomes prominent, the wave attenuation capacity is improved with increasing PTO damping. For an unequal layout of moonpools, the thinner moonpools are the major contributor to wave energy extraction, especially in the short wave region. As a result of mass exchange of fluid from the moonpool to the outer domain, the multi-purpose platform indicates favorable performance of wave energy absorption. The novel floating system makes the utilization of wave energy over a wider frequency range

Energy conversion and hydrodynamic analysis of multi-degree-of-freedom wave energy converters integrated into a semi-submersible platform

The hybrid concept of multi-type wave energy converters provides viable solutions to improve the wave energy exploitation per-unit area and reduce the Levelised Cost of Electricity. In this paper, a multi-degree-of-freedom hybrid system combining an oscillating wave surge converter and two oscillating buoys, is proposed and integrated into a semi-submersible platform to be suitable for both nearshore and offshore zones. The hydrodynamic characteristics of the hybrid system is investigated by establishing a three-dimensional numerical wave tank in the context of computational fluid dynamics theory including dynamic overset grid scheme, with emphasis on its overall characteristic and respective characteristic of each device. The corresponding physical experiments are also performed to cross-check the numerical solutions, and help to further explain un-simulated phenomenons. By comparing with the single-degree-of-freedom wave energy system, the total power capture efficiency of the hybrid system increases over a broader range of wave periods due to the combination of different resonant periods. The optimal power take-off damping for the oscillating buoy and the oscillating wave surge converter decreases and is insensitive with wave height, respectively. The oscillating buoy device with larger radius and deeper draft demonstrates higher energy absorption which reduces wave loads on the platform. Both the total capture efficiency and the effective frequency bandwidth increase initially to maximum values and then decrease with increasing the geometric radius of the oscillating wave surge converter. The findings of this paper validate the feasibility of different-type wave energy converters integrated into floating platforms and show their synergy

Hydrodynamic characteristics of a hybrid oscillating water column-oscillating buoy wave energy converter integrated into a π-type floating breakwater

Combining multiple-types of Wave Energy Converters (WECs) and integrating them into in-development or pre-existing marine platforms can reduce the total Levelised Cost of Energy (LCoE) by sharing infrastructures and maintenance costs. The current study proposes an innovative multi-purpose solution by deploying an Oscillating Buoy (OB) device inside the chamber of an Oscillating Water Column (OWC) WEC integrated into a π-type floating breakwater. A fully non-linear time-domain model based on the Higher-Oder Boundary Element Method (HOBEM) is established to investigate the hydrodynamic performance of the proposed concept. The non-linear time-domain model is generalised to incorporate the OWC (aero and hydrodynamics coupling) and multi-body interaction. A series of simulations are performed to examine the hydrodynamic performance of the proposed hybrid concept. Results were compared with an isolated breakwater and an OWC-integrated breakwater, demonstrating that the proposed hybrid concept has a beneficial impact on both wave energy conversion and transmitted wave attenuation. In addition, long-period waves enter into the chamber more easily, which leads to a larger inner water motion and pressure fluctuation in the chamber. Importantly, there exists a coupled resonant motion between the OB device and the water surface in the chamber, which enhances the maximum capture efficiency and the efficiency frequency bandwidth. The asymmetric OB with a triangle-shaped bottom is found to absorb the wave energy along with the water depth more effectively. Despite the better performance, the current design does not increase the characteristic system volume and has no external moving part, making it ideal for array deployment