International Marine Energy Journal

From test site to flume: replication and quantification of tidal turbine blade fatigue loads in turbulent flows

2022-10-12T17:06:53+01:00

In this paper experiments were performed on an instrumented 1/20^th scale turbine using static grids to generate turbulent flows in a circulating water flume and also at a small-scale tidal test site. Fatigue Damage Equivalent Loads (FDEL’s) were calculated to allow cross comparison between different cases. The results of this research demonstrate that a wide range of turbulent flow conditions can be generated using varying geometry grids, locating the turbine at varying distances downstream. It is possible in the laboratory to closely replicate flow conditions from a real tidal site with corresponding replication of measured fatigue loads. There was a 5-fold increase in fatigue damage acting on the turbine at the tidal test site compared to the typical low turbulence laboratory case. It was also found that the increase in fatigue damage due to increasing turbine rotational speed was only 10% of that due to increasing ambient turbulence thus the ambient flow conditions are critical in determining fatigue loading. This work found that exact replication of turbulent characteristics was not required to match fatigue damage loads between the flume and real site, but a relatively close match was sufficient.

A Rapidly Deployable Wave Energy Converter for Seawater Desalination in Disaster Response

2024-10-07T17:26:58+01:00

In the current operational landscape, there are no commercial-off-the-shelf (COTS) solutions capable of turning wave power into clean water on a small scale and expedited timeline. Available wave-powered installations and desalination plants are mostly large infrastructure projects that leverage economies of scale. This is typically the result of economic drivers – the availability and price of electrical power and clean water. However, natural disasters often strike where clean water is scarce and local infrastructure is unable to respond quickly, which drives an urgent need for clean water in locations far from these installations. Here, we present the design, modelling, and initial performance of a compact Wave-Energy-Converter (WEC) powering a reverse osmosis desalination system; a simple technical solution that provides clean water on a small scale (~1,000 Liters per day) and is quickly deployable in disaster zones.

Performance of a Multibody Point Absorber with a Damper Plate in Irregular Waves

2025-08-14T08:06:01+01:00

Wave energy converters (WECs) behave differently when operating in irregular waves than in regular waves. Although numerous studies have described WEC dynamics in regular waves, the ocean experiences irregular waves, making it essential to evaluate the performance under such conditions. A multibody WEC has mixed motion, adding complexity to system dynamics. In this study, a multibody floating-point absorber WEC equipped with a damper plate was designed and tested for irregular wave conditions in a wave basin at IIT Madras. The wave conditions varied, with significant wave heights ranging from 0.15 to 0.23 m and peak periods from 1 to 2.5 s. Hydrodynamic coefficients such as the Response Amplitude Operator (RAO), excitation force, radiation damping, and added mass were computed using the panel method. A multibody dynamics solver was used to calculate the power absorption. Additionally, a new buoy configuration with a deeper draft was designed and compared with the buoy equipped with a damper plate. The point absorber with a damper plate achieved a maximum power output of 14.05 W at Hs = 0.23 m and TP = 2.5 s. The highest absorption efficiency was 48.2% at Hs = 0.20 m and TP = 2.5 s.

Modeling analysis of the mean flow velocity ahead of a rotating tidal turbine

2025-06-03T01:58:15+01:00

This paper presents a novel method for modeling the mean radial velocity component ahead of a rotating tidal turbine. Firstly, it examines a recent hybrid model designed to reconstruct the three-dimensional mean axial flow field in front of an operating turbine under various flow conditions (uniform, shear) and rotational speeds (thrust turbine coefficient). Subsequently, based on the continuity equation and the axial velocity reconstruction on a meshgrid, a new turbine induction model is proposed to model the mean velocity component. The model is validated against experimental data under both uniform and shear flow conditions, showing excellent agreement between the modeling and experimental results, with minor discrepancies near the blade tips. The proposed method provides a useful tool to evaluate the induction impact of the angle of attack of the blade while considering the characteristics of the incoming average flow field.

A Global Design Search of a Shrouded Tidal Current Turbine by Meta-model Assisted Genetic Algorithms

2025-03-11T14:50:18+00:00

This study was conducted to investigate the effect of geometry on the performance of a shrouded tidal turbine. When the hub radius and taper change, with a fixed shroud radius, the inlet area changes from the inlet to the turbine, and according to the continuity equation, the axial velocity will also change. This inlet velocity, influences the output torque by a factor of for the power coefficient. A global search optimization system was used to search for the optimal geometry. 13 impeller design parameters and 5 shroud casing design parameters were considered for optimization. To reduce the simulation cost, an artificial neural network (ANN) was applied as the meta-model of the RANS solver. Multi-objectives of a power coefficient at different tip speed ratios were applied to provide a function of the wide operating range of the turbine. The proposed optimized turbine design exhibits a high output shaft power at low tip-speed ratio. Increasing the hub radius caused a strong velocity gradient at the turbine inlet. Hence, achieving smooth blade loading from the hub to the shroud for the baseline is difficult. However, this inlet axial velocity distortion decreased in the optimal geometry, attaining smooth blade loading from the hub to the shroud. This results in higher torque output hence higher values in the optimal geometry. From the sensitivity analysis of the design parameters with , there is a good global correlation between the axial velocity upstream of the turbine and the . A strong circumferential velocity occurs in the optimal diffuser, causing a centrifugal force at the shroud tip, suppressing the diffuser's flow separation. This improves the pressure recovery and performance of the optimal design.

Optimal Parameter Assessment of Linear PTO System for Improved Wave Energy Efficiency

2025-04-15T15:38:48+01:00

Developing efficient wave energy converters (WECs) tailored to their deployment sites is crucial for economically harvesting power from ocean waves. A key aspect of evaluating WEC performance is the estimation of the power take-off (PTO) parameters. Optimizing the PTO devices to perform effectively in sea states with varying wave amplitude, direction, and frequency is a major challenge. Most previous studies typically use a constant damping coefficient for power calculation across different wave conditions. This approach may lead to inconsistent device performance due to the variations in PTO damping with changing wave characteristics. The analysis of optimal parameters and the maximum power extraction of a PTO system offers a theoretical foundation for efficient energy utilization.
This study investigates how the damping coefficient affects the behavior of a wave energy device under various regular wave conditions. It includes the numerical modelling of a heaving wave energy device with a linear PTO system and assessing the optimal damping coefficients and buoy velocity for maximum power absorption in different wave conditions. The optimum value of PTO damping at the system's natural frequency is estimated and compared to the PTO damping which results in maximum power generation. The study outlines the development of an effective PTO configuration for the wave energy converter model. The results revealed that different wave conditions notably influenced the damping coefficient.

Influence of fish scale bionic structure on energy performance of a tidal current turbine

2025-10-13T14:44:49+01:00

The hydrodynamic performance of the tidal current turbine impeller is crucial for converting energy into electricity as it is considered the core component of the tidal current energy capture device. The morphology of fish epidermis is firstly analyzed in this paper based on the invention ideas of the unique structure of animal skin. Its biological characteristics are extracted, and basic characteristic coupling elements are obtained. The bionic structure design technique was utilized to establish a hydraulic system for surface-changeable tidal current turbine blades that will improve the effectiveness of energy capture for entire tip speed ratio conditions. The bionic structure's impact on the energy characteristics of the tidal current turbine was compared through the completion of the three-dimensional turbulent flow calculation using numerical simulation methods. By analyzing the distribution of shear stress on the blade surface, the velocity and pressure field near the blade surface, the mechanism was revealed that the bionic structure improves energy capture efficiency at low tip speed ratio conditions.

Numerical and Experimental Investigation of Float Shape Effects on Single-Heaving Wave Energy Converter Performance

2025-09-22T11:10:30+01:00

This study presents a geometric design procedure for the buoy of a single-body wave energy converter (WEC) based on specific incident wave characteristics, utilizing both numerical and experimental analyses. It explores how float shape influences hydrodynamic performance and the power absorption through a single degree of freedom in heave motion. To compare the dynamics of different floats under identical conditions, specific criteria were established. Using ANSYS AQWA for numerical modelling, two new float shapes (an asymmetric cylindrical wedge, HW, and an axisymmetric cone, CH) were designed to match the natural frequency and mass of a conventional hemispherical bottom (HB) float. Once these requirements were met, HW and CH floats were manufactured for further experimental analysis. The study investigates how variations in float shape, notably the slope of the model surface at the waterline, affect hydrodynamic parameters, response and subsequently impact WEC model power absorption. Results highlight the importance of radiation damping on power absorption and emphasize the need to select appropriate power take-off (PTO) damping. Moreover, selecting the optimal float shape and PTO damping can significantly enhance the power absorption.