Successful Installation & Retrieval Trials in Real Tidal Conditions
Recent testing of the Subhub operations model in high tidal flow conditions proved its ballast system capabilities and installation and retrieval methodology with great success. QED Naval were able to install the model on the seabed safely and in a controlled manner within minutes. The model was then secured on the seabed overnight before being recovered to the surface gracefully within an equally short time period and control.
Despite onerous wind, wave and current conditions experienced during testing, the Subhub coped admirably during the installation and retrieval trials. Scaling these extreme conditions to the prototype size, based on a 4.0m diameter turbine, would be equivalent to over 2m/s or 4 knots with a significant wave heights over 1.0m
Frontal profiles of turbine blades were added to the cross beam to simulate three turbines being installed on the Subhub; the blades acting against the current presented no issues.
The Subhub Operations Model continues it fit-out and setup for the testing at Forth Estuaries Engineering’s (FEE’s) dock in Leith. An essential part of that was the “weigh-in” to check against our design calculations to ensure she is correctly ballasted for her initial trials.
The operations model is based on a 1.0m tidal turbine rotor diameter. It is designed to accommodate 3 of the heaviest tidal turbines on the market. The Operations Model has been built to the same mass proportions of the prototype so its motions will be accurately modeled.
The “Operations Model” is the 3rd in a series of models with very specific objectives. It has been developed to test the ballasting system and conduct installation/retrieval trials.
Fabrication has been completed on the operational model of the Subhub at Pentland Precision Engineering allowing QED Naval to begin the pre-testing setup of the device. The Subhub looked magnificent in the Edinburgh Sun as weeks of work culminated in a device that will be tested to the limit by QED Naval. Over the next week the team at QED will be carrying out pre-testing preparations fitting extensive instrumentation and ballast systems to gain the most out of the coming testing phase.
Project team at Pentland Precision Engineering Gordon Hardman (left) Grant Middleton (centre) and Chris Scott (right).
QED Naval is proud to welcome a new member of staff into the ranks. Aris Zavvos who has recently joined us has a Sustainable Energy Systems Master degree and a PhD in Electrical Engineering from the University of Edinburgh. Aris has been recruited as the Electrical Systems and Turbine Integration Engineer to manage the electrical design and development of the Subhub tidal turbine foundation as well as validating the instrumentation and data acquisition system during the testing stages of our first prototype.
QED Naval is delighted to announce that they have received the financial backing from Kelvin Capital and the Scottish Investment Bank this week to support the continued development of the Subhub, the tidal turbine foundation structure.
This 1st tranche of money will allow QED Naval to conduct the tank testing of 2 models of increasing scale within the world class, FloWave TT facility. These experiments will allow them to validate the current Subhub design against 3 principle objectives that include:
Verification of the design process and tools;
Provide evidence of the performance claims increased power output and;
Define the limitations from extreme loading events from combined wave and tidal forces.
It is a pleasure to announce that QED Naval have been awarded Scottish Enterprise, SMART R & D grant to support the ongoing development of the Subhub project.
This project aims to complete the validation, build and test of a large scale prototype of the Subhub. The overall goal is to demonstrate a large reduction in the cost of deployment of tidal turbines and validate the performance claims that show large gains in power output when compared with a typical tower installation.
It may be small but the new model of the Subhub prototype really seems to bring the project to life. Built using the state of the art Selective Laser Sintering (SLS), 3D printing method, to tight tolerances required for the test tank models.
The tank testing will be used to validate design analysis carried out to date using our fluid modelling CFD software from ANSYS (Fluent). Verification of the drag forces on the Subhub and the velocities in way of the duct will provide confidence to go on to build the community scale prototype, capable of generating 600kW of energy into the national grid. The prototype is scheduled to go to sea in 2015, installed at the EMEC tidal test site in Shapinsay Sound, Orkney.
A second submission to the MARINET FP7 has been made, to use the facilities at Tecnalia in Derio, Spain to test the stabililty, reliability and performance of the Power Take Off (PTO) systems to be used in the Subhub prototype testing in 2015.
After a recent training course hosted by Tecnalia and University College Cork (UCC) into the electrical control systems of marine energy converters, it was clear that work needed to done in order to optimise the power output of turbines to take advantage of the additional mechanical power generated by the Subhub. Further work is envisaged with connecting up 3 turbines as an array which all experience very different hydrodynamic loading and hence torque/rpm characteristics.
The configuration and optimal setup of the power electronics will be reviewed as part of this project. The control laws will be developed from the numerical models and scale model testing. These will then be simulated using a time response data driven by virtual tidal flow conditions on the Subhub/turbine. Finally, longer term physical testing of the control systems will be conducted on facilities at Tecnalia to provide reliability and performance data for the prototype prior to it going to sea.
QinetiQ GRC have completed the initial sizing model of the Subhub and Turbine Module using their Paramarine software. It has concluded that both the Subhub main hull and Turbine Module would pass IMO and MCA stability standards. These results surpass all expectations at this stage of the development and provides a high level of confidence in forging ahead with the feasibility study. The next stage will review the dynamics and motion characteristics of the Subhub and Turbine Module which will explore the safe operating limits of these large marine structures to realistic environmental loads.
Below is the initial stability for the Subhub in its deployment role which includes the Turbine Module. It has a massive initial stability and peaks at approximately 15 degrees and remains positively stable until 80 degree heel angle.
To provide some feeling of how stable this platform is, below, is a picture of the GZ curve including heel angles that have been imposed from 100 knot gusts. It uses a tiny fraction of its 8.0 m GZ righting arm at just over 0.1 metre. This also suggests that it performs equally well on the seabed under turbulent tidal stream conditions.
Pictured below is the Turbin Module floating on both the light ship and with the main hull section flooded. This is the condition used for the maintenance and swop over of modules and are the waterlines used to tow it back to port.
The picture below shows the Turbine Module after it has been disconnected from the Subhub platform which remains firmly anchored to the seabed with over 1000 tons of ballast holding it in position.
Below is the initial stability assessment of the Turbine Module with all the tanks full and shows that it is very stable at the surface in this condition and capable of supporting more intrusive operations on the turbines generator or electrical conditioning equipment or towed back to port.
QinetiQ GRC have just completed an assessment on the Subhub’s stability in the floating and compared it with stability standards used commonly within the marine industry. I pleased to announce that it surpassed all these standards with flying colours. Included within the assessment was a generic turbine with a payload of 150 tons elevated at approximately 25m above the Subhub main hull, not including self weight. It also included a payload of 300tons within the main hull representing all the switching gear, heat exchangers, pumps, on electrical transmission equipment.
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