Article - Issue 71, June 2017

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IN SUPPORT OF TIDAL LAGOONS

The news that the government-commissioned Hendry Review supported plans for a tidal lagoon to be built in Swansea Bay (‘Review backs plans for tidal lagoons’, Ingenia 70) is welcome.

Indeed, tidal energy is abundant around the UK and developing projects on our doorstep will foster an indigenous industry and substantial local economic growth, among other benefits. It would be short-sighted if the UK government was not supporting (or subsidising) this new technology now or in the immediate future. What is not to like about clean, renewable and, in the long term, cheap energy at our doorstep?

It has been reported that the government is hesitant to begin work on the potential pathfinder project in Swansea Bay. This could be due to the potential cost of the Swansea Bay Tidal Lagoon project, mainly the capital expenditure costs (CAPEX) of an estimated £1.3 billion. At first sight, this appears expensive for only 500 MW (megawatts). However, a tidal lagoon will have a lifetime greater than 100 years, and hence at some point in the future, the Swansea Bay Tidal Lagoon will produce energy at almost no cost as the capex will be amortised. But as the Hendry Review points out this ‘expensive now and cheap (much) later’ concept is not easy to sell.

So why is the Swansea Bay Tidal Lagoon CAPEX so high and what are the main challenges for it and other tidal lagoon projects?

First of all, the Swansea Bay Tidal Lagoon is quite small but with a long U-shaped seawall, which is probably the most expensive component of the project. More water can be stored and used for power generation in a larger enclosed area and ideally a tidal lagoon should make use of a curved coastline or a natural bay, so Swansea Bay Tidal Lagoon’s U-shape is not ideal. The lagoon’s rated capacity of 500 MW is reasonably large, but a tidal power plant does not operate 24/7. There will be holding periods to create the necessary pressure so that the amount of energy generated over the year will be 30% to 40% less than that of a traditional hydropower plant with the same rated capacity that operates at almost 24 hours a day, 365 days a year.

Secondly, and this applies to all tidal lagoons, the generation head is relatively small, typically around two to three metres. Tidal lagoons are ‘very-low-head-very-high-discharge’ hydropower plants that require big, large diameter and expensive turbines to be able to move vast amounts of water in and out of the lagoon within short periods of time. In comparison, the diameter of a 500 MW low-head (20 metres) traditional hydropower turbine is approximately five times smaller than the tidal lagoon equivalent.

Thirdly, and again all tidal lagoons will face this challenge, a traditional hydropower turbine will operate at peak efficiency almost all of the time because input parameters such as head and discharge will remain constant and the direction of flow does not change. Meanwhile, a tidal turbine will have to ‘deal with’ a variable water depth for some periods of the time (as the lagoon fills or drains), ambient currents around the turbine diffuser and, even more challenging, a reversal in flow direction approximately every six hours. For the reverse flow, turbine efficiency may not be as high as for a turbine that is optimised for unidirectional flow.

Despite the economic and technical challenges that tidal lagoons face today, their power generation could be an opportunity for the UK to harness its own, clean, renewable, safe and predictable energy. This sustainable industry could create thousands of jobs and secure (part of) the energy for future generations, as well as serving at the forefront of innovation and technology development. The Swansea Bay Tidal Lagoon could potentially become the world-leading example that the industry needs.

Professor Thorsten Stoesser
Director
Hydro-environmental Research Centre
Cardiff University

VIRTUAL AND MIXED REALITY IS TRANSFORMING CONSTRUCTION

The article on virtual reality (VR) in engineering is very timely (‘How virtual reality is changing engineering’, Ingenia 70). New technologies are transforming infrastructure and construction, and VR has a crucial role to play in conjunction with the latest innovations in sensor technologies. It is already being used for the modelling of buildings, as described in the article, but closely related mixed-reality technology can also be used to transform control of the construction process for many other types of infrastructure. This is part of the mission of the Centre for Smart Infrastructure and Construction (CSIC) at the University of Cambridge: to transform the future of infrastructure through smarter information, enabling step changes in construction practice.

CSIC collaborators working with the Construction Information Technology Laboratory at Cambridge, under the direction of Dr Ioannis Brilakis, are working with California-based company Trimble, which provides technology for the construction, geospatial and transportation industries, and with Microsoft to develop an automated inspection process for construction progress monitoring. The Automated Progress Monitoring Inspection App uses Microsoft HoloLens and multiplatform game engine Unity to create a semi-automatic inspection method that aligns the 3D as-planned model to the real world as-built environment. This app allows inspectors to bring the design model out of the office and onto the construction site. It marks the first time a 3D model of a building, a bridge or any other type of infrastructure has been taken off the screen and put onto the real structure as it is being constructed.

The HoloLens allows the wearer to walk through the construction site and automatically see what is on schedule and what is behind schedule. This advance in automation allows engineers to visualise the building information model in full scale at their offices or superimposed on the real structure at the construction site. After automatically placing the 3D model to the correct height and orientation, the user manually adjusts the model by moving it horizontally to fit the actual structure. Once the registration of the model to the real world is secured, an analysis to compare the current as-built status with the as-planned 3D model can be completed. A time attribute is added to every element and the comparison can be performed, enabling status progress to be accurately determined and recorded. This information can be used to monitor and control actual progress, improving productivity by making time- and cost-saving interventions where required.

Construction processes and completed infrastructure can be potentially transformed as this mixed-reality technology is combined with other new tools and technologies, including fibre-optic strain measurement, ultra-low power sensors, vibration energy harvesting devices, photogrammetric monitoring systems, computer vision and data management tools. Used in combination, these new technologies offer a whole-life approach to infrastructure; from design to improved and more productive construction, through to operation, maintenance and eventual decommissioning. Many of these innovations have already been tested and proved on some of the largest civil engineering projects in the UK, including Crossrail, National Grid London Power Tunnels, London Underground station upgrades, and the Staffordshire Alliance West Coast Mainline railway bridges for Network Rail. The opportunity for combining these innovations with mixed-reality technology is exciting.

As Dr Scott Steedman noted in his editorial in the same issue (‘A strategy for a digital future’, Ingenia 70), the digital revolution has opened the door for smarter infrastructure. To enable this, the need to invest in digital infrastructure across the UK cannot be overemphasised. The Building our Industrial Strategy Green Paper recognises this and highlights the importance of digital skills, where a large gap appears between the requirements of the future and the level of provision in our education system. Enhancing digital skills at all levels will be key to a successful long-term industrial strategy. STEM subjects should be given much more emphasis in primary as well as secondary schools. To exploit innovative sensor and virtual reality technologies, our future engineers will need to be fully conversant with software, computing and coding; only then we will see the huge potential for smart infrastructure and construction fully realised.

Professor Lord Robert Mair CBE FREng FRS
Centre for Smart Infrastructure and Construction
University of Cambridge

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