Condition Monitoring of Tidal Stream Turbines Under, Dissertation Example

The finite limit of fossil fuels (oil, coal, natural gas) mandate the necessity of developing and implementing renewable sources for energy use. Tidal streams offer a viable alternative by harnessing the kinetic power of the ocean currents into a hydrokinetic energy system, sustainable and environmentally conscious. Marine turbines are installed on the ocean floor with the turbine blades in horizontal configuration allowing the stream currents flow to rotate them, powering a generator like wind turbines. Tidal turbines work in the harsh environment of ocean forces and corrosive seawater, therefore the importance of maintenance and condition monitoring (CM) is vital to the success and uninterrupted production of energy. This research will examine and analyze tidal turbine systems condition monitoring (CM) by investigating the available philosophies to determine the most appropriate utilization to increase reliability, reduce failures, and lower costs of offshore maintenance and inspection.

Introduction

Coal, oil, and natural gas are the predominate energy resources used throughout the world. Unfortunately, the supply is finite and non-renewable as it takes 100 million years or more for dead plants and animals to decompose, compress, and evolve into fossil fuels. Development of renewable and/or sustainable sources of energy is imperative for Earth and its inhabitants. Current research includes utilizing nuclear, wind, and ocean settings to capture the raw power each create through their natural processes and functions. Nuclear energy, while affording plentiful “clean” generation of electricity, creates hazardous waste and environmental damage rendering the process unsafe for man and earth. Wind power is abundant, but the process requires vast wind farms for energy harnessing while the predictability of wind patterns is chaotic at best. Ocean or Tidal energy offers an energy resource that is renewable and environmentally safe while ocean and tidal currents are relatively calculable.

Tidal stream energy

The finite nature and continued price escalation of coal, oil, and natural gas coupled with their devastation to the environment have directly led to search for alternative renewable energy for investment and production. Tidal stream energy is one type of sustainable energy that can decrease the dependence on fossil fuels while being a resource available to nearly every nation on the globe. Fossil fuel burning, and its usage impacts global warming through sea levels rising, increased temperatures on the land and sea, and with changing weather patterns occurring across the earth. The continuation of fossil fuels for energy resources is impractical, cost prohibitive, and environmentally dangerous, thus, development and implementation of sustainable sources for energy generation to reduce and eventually replace carbon-based materials for energy production.

Tidal Stream Energy is the capturing of the power created by the water movements and flow produced by gravitational effects generated between the earth, sun, and moon. These forces combine in pulling and pushing the tidal streams in predictable currents in all bodies of water. The exploiting of tidal streams for power generation into electricity involves installing tidal turbines in strategic locations across the ocean floor using the movement of the current to flow across the turbine blades causing their rotation and thus converting the tidal streams power into a source of renewable electricity.

Stressors behind tidal energy

There are several reasons for the necessity of tidal stream energy development with the main driver being the EU directives set forth as targets the UK Government must achieve to reduce green-house emissions. The following is a summation of the UK government policies agreed to with the EU coalition government on future energy generation targets:

1. 80% reduction in greenhouse gas emissions by 2050;
2. 15% of the UK’s energy demand must come from renewable sources by 2020;
3. Nuclear power stations to be generating electricity by 2019;
4. Funding for a 4-year Carbon Capture and Storage research, development, and innovation programme;
5. £110 billion investment in the UK electricity market to ensure an affordable supply of electricity while meeting climate change targets.

However, the recent UK elections in 2015 changed the balance of power in the parliament to the conservative party which has moved away from “green” policies. Their efforts have shifted to fracking and sending more funding to North Sea oil and gas fields, while the effects of Brexit are just coming into play.

UK tidal resource potential

The UK has an enormous potential of tidal stream resource due to its geographic location and length of its coastline. In 2010/2011, the UK’s estimated tidal potential, as determined by the Carbon Trust, indicates sites and project areas such as Strangford Lough, Severn estuary, and the Eastern Irish sea. These and other sites are studied for their tidal wave and current energy

Tidal stream energy fructification

Problems with Tidal energy becoming “the” viable replacement for fossil fuels centers around the hesitancy of the industry regarding the operation and maintenance of marine turbines. As compared to wind power, the environment of tidal currents is corrosive and caustic as the salinity of seawater can quickly erode the metal components comprising the turbine systems used to convert tidal power into electricity. Thus, the need for effective and proactive condition monitoring and equipment maintenance must be developed in conjunction with the tidal stream systems.

Tidal stream energy and this project

A key problem with tidal energy centers on the maintenance of the tidal turbines and the ability to detect faults within the turbine before the system fails. Being located offshore, it is imperative that early fault detection is fast and reliable, so maintenance and repair takes place quickly, thus limiting the operational down time. Condition Monitoring (CM), the active monitoring and servicing of various parts or the entire machine, is needed throughout the offshore energy industry. CM techniques are widely used across many industries particularly in the monitoring of machine tools for wear and tear as well as in high-rick industries like aerospace for active monitoring and maintenance of airplanes and space vehicles. In fact, in high-risk industries condition monitoring is essential for safety and optimized operation of parts and machinery.

As tidal turbines are in remote areas, active monitoring of all aspects of the turbines is crucial to minimize costs and maintenance time. Faults to the turbines cannot be checked via usual methods like a visual inspection due to their offshore location and under water. Thus, monitoring systems using sensors for offsite access and ease is imperative. Condition monitoring methodology for tidal turbines includes a plethora of techniques developed and researched by industry researchers and academics. Certain pieces of the machinery (turbine) require different monitoring tactics. For example, the hydraulic system should use pressure monitoring, oil debris analysis, and pump’s motor MCSA while turbine blades require strain and performance monitoring. The nacelle must have leakage detection, the Yaw system must be watched for pressure and performance issues, and the gearbox must be monitored for torque measurements, oil debris and vibration analysis. The remaining components of the turbine should all be closely followed for condition monitoring.

One approach involves the collection of various pieces of data, whether raw or signaling, processed quickly as faults are not easily detected from crude information. This project will focus on the signal processing portion of Condition Monitoring of tidal turbines, paying close attention to the research conducted by Cardiff University and CMERG.

Current Cardiff University and CMERG research

CMERG, a subsidiary, and Cardiff University have conducted in-depth research concerning various issues with the production and collection of marine energy including the evaluation of tidal resource areas, flow (including directionality and force) and its effect on the performance and reliability of using Computational Fluid Dynamics (CFD). Additionally, both facilities are researching condition monitoring of tidal turbines and signal processing usage for effective fault detection. At the University of Liverpool, work has completed using a test flume to assess tidal turbine blade faults and developing early detection. This was accomplished with using blade set-ups where three were at optimal settings of identical angles of 6 degrees each and the fourth blade set-up with an offset of 15 degrees to simulate a fault. A support mounted strain gauge measured values of thrust while analyzing this data for trends, patterns, and fluctuations to assess potential fault detection. This work will be extensively reviewed in the case study stage which is included in appendix A.

The work at other research institutions and independent companies developing condition monitoring for tidal turbines near completion, but the commercial studies are guarded through copyrighting and competition limitations. Academics like Merigaud and Ringwood have reviewed the condition monitoring challenges for wave and tidal projects and allude to lack of failure data, the number of different turbine designs, and a lack of industrial incentive as primary reasons for the progression of tidal turbine condition monitoring. The research performed at Cardiff University by CMERG and other institutions across the globe will mitigate these barriers, aiding in the continued progress of tidal technology.

Project architecture

This project will review the signal processing methodologies for fault detection of tidal turbine blades in realistic flow conditions. The data for this research is derived from a tow tank simulation in Rome and flume testing at the University of Liverpool. Matlab will be used to process the raw data for interpretation and analysis. As this project focuses on the signal processing portion of the condition monitoring of tidal turbines, a literature review is included assessing different signal processing methodologies associated with rotating machinery and tidal turbines. A detailed methodology will follow the literature review will show the approach taken to processing the data and the various tools employed on Matlab. The results are then shown for the different techniques used and a discussion of the key findings will be detailed. The conclusions drawn from this research will include outlaying the next steps for potential development in condition monitoring of tidal turbines.

References

Allan, G. et al. 2011. Levelized costs of Wave and Tidal energy in the UK: Cost competitiveness and the importance of “banded” Renewables Obligation Certificates, Energy Policies, 39(2011). P. 23-39. Doi: 10.1016/j.enpol.2010.08.029.

Allmark, M. et al. 2015. Tidal Stream Turbine Blade Fault Diagnosis Using Time-Frequency Analysis. Proceedings of the 11^th European Wave and Tidal Energy Conference EWTEC2015, Nantes, France, 6-11 September 2015, pp. 1-10.

Allsop, S. et al., 2017. Hydrodynamic analysis of a ducted, open centre tidal stream turbine using blade element momentum theory, Ocean Engineering, 141(2017), pp. 531-542. Doi: 10.1016/j.oceaneng.2017.06.040.

Carrington, D., 2015. What does Cameron’s election win mean for the environment? [Online] Available at: https://www.theguardian.com/environment/damian-carrington-blog/2015/may/08/what-does-camerons-election-win-mean-for-the-environment. [Accessed 20 April 2018].

Chen, L. & Lam, W., 2015. A review of survivability and remedial actions of tidal current turbines. Renewable and Sustainable Energy Reviews, 43(2015), pp. 891-900. doi: 10.1016/j.rser.2014.11.071.

Chernin, L. & Val, V.D., 2017. Probabilistic prediction of cavitation on rotor blades of tidal stream turbines. Renewable Energy, 113(2017), pp. 688-696. doi: 10.1016/j.renene.2017.06.037.

Grosvenor, R., 2016. Flume data presentation. Cardiff: Cardiff University.

Grosvenor, R. et al., 2014. Performance and condition monitoring of tidal stream turbines. Proceedings of the 2^nd European Conference of the Prognostics and Health Management Society. Nantes, 8-10 July 2014.

Grosvenor, R. et al., 2017. An Assessment of Structure-Based Sensors in the Condition Monitoring of Tidal Stream Turbines. Proceedings of the 2017 Twelfth International Conference on Ecological Vehicles and Renewable Energies (EVER). Monte-Carlo 11-13 April 2017.

Grosvenor, R. et al., 2014. Fast and robust milling cutter tool breakage detection within a distributed microcontroller-based condition monitoring system. 27^th International Congress of Condition Monitoring and Diagnostic Engineering. Brisbane, 16-19 September 2014.

Liu, P. & Veitch, B., 2012. Design and optimization for strength and integrity of tidal turbine rotor blades. Energy, 46(2012), pp. 393-404. doi: 10.1016/j.energy.2012.08.011.

Marnoch, J. (2016). What Should a Condition Monitoring System Look like for a Tidal Turbine? 6th International Conference on Ocean Energy. Edinburgh, Scotland, UK. https://tethys.pnnl.gov/sites/default/files/publications/Marnoch-2016-ICOE.pdf.