Wells Turbine In Wave Energy Conversion Using Marine Technology And Ocean Engineering

Principles behind wave energy conversion

The world has taken a keen interest in renewable energy following the detrimental side effects of using other kinds of fuels to provide energy to the industrial or residential setups. This area of study is known as wave energy or ocean engineering. The global energy production has increased greatly over the recent years. Statistics show that the production between the year 2005 and 2013 improved by about 8 percent. The ocean is a huge potential for the production of renewable energy as the power waves in the ocean are continuous round the clock. The marine wave programs have been tested in several European countries. The principle behind the wave energy conversion using the wells turbine is that of an oscillating water column. Similarly, the Bernoulli’s continuity flow principle is incorporated in the determination of the rotation of the water column to determine several mechanical and turbine dynamics and as a result of the electrical energy. There is a fixed or oscillating hollow structure that opens to the seas below to trap air. The wave action as defined by the principle tends to compress and decompress the trapped air forcing air to flow through a turbine which is connected to a generator for the production of electricity.

Different devices are used to produce such renewable energy. The devices produce sufficient work to drive electrical generators and as a result electricity is produced. The marine wave energy producers are used with respect to the water depth at which they operate. The wells turbine is a common device that is a fixed structure operating on the principle of the oscillating water column systems (Raghunathan, 1995, p 336). The turbine is installed at the shoreline or close enough to the shore. When the device is installed at the shoreline, it is easier to maintain and install. As a result, there is no need to have deep water moorings and long underwater cables running to the device and back to the mainland (Cashman, et al, n.d,. p 8). These devices can either be fully submerged in water or floating on the water. Such devices aim at taking advantage of the most powerful wave system available in deep water. Some wave energy converters are found on the mainland away from the water bodies. The operating principle behind the wells turbine is that a water column in the turbine oscillates with respect to the wave motion. The oscillation is used to drive an oscillating air column and mechanical energy is developed in the rotor effect. The turbine is referred to a low-pressure turbine. It tends to rotate continuously in a particular direction in line with the direction of the air flow. It is easier denoted as a self-rectifying air turbine (Henriques, et al., 2015 p.715). It does not require a system of non-return valves to control the movement of water.

Types of devices used in wave energy production

The wells turbine operates such that the oscillating air flow generates a unidirectional rotation of the mechanical rotor without using a rectifying valve. The wells turbine operates in two stages namely the compression stage and the suction stage (Falcao, et al., 2016. P.460). At the compression stage, the water is required to rise to a certain level in the reservoir. Several forces are involved as denoted in the equation below,

Later on, the water level drops and air is sucking into the duct. The direction of the tangential forces tends to be maintained in the two stages unlike the axial forces which reverse direction when switching from one stage to another (Ashlin, et al. 2016, p. 345). In operation, it is observed that the rotor rotates in the direction of the tangential forces or in a vertical movement stroke with no regard to the direction of airflow. The design of the oscillating water column depends on the level of sea waves in a particular region.

When compared to wind and solar power which is restricted to day time as night time the performance is low. Several studies have been carried out to compare the wind power, solar power, and the wave energy power. The wind power is measured using the cube of air speed. The wave energy is a preferred method of energy production. Several merits back up the case study. A marine or ocean wave tends to travel greater distances without significant energy losses. This ensures that the power produced acts as a very reliable renewable and efficient energy resource. The wave energy could even travel over kilometers without losing its power.

• To determine the operation of the wells turbine in wave energy conversion
• To determine the merits of the turbine over other alternatives
• To analyze the power production using wave energy conversion as compare to other renewable energy sources.
• To define the wave energy conversion technique and its sustainability.

In the design of the turbine configuration, the research seeks to obtain the best method of installation. The method should ensure that the system generates the maximum power from the waves that are obtained from the high seas or when it is installed at the shoreline. A lot of research on the design to be implemented is done to ensure that the project implements a risk averse turbine. The location of the installation at the shoreline is critically analyzed and studied to get a grip of the wave strength before implementation.

The experiment is set up as shown in the figure below. The apparatus used are indicated on the figure as well,

• The turbine test was carried out on a test section at the exit and entry points of a bell-mouthed section.
• The piston is driven to and from the internal part of the cylinder. There are three ball screws fixed to nuts at the piston.
• Three screws are driven by a servomotor via the torque transducer. A computer control the actions of the servomotor and in turn the piston velocity develops the flow velocity.
• The performance of the experiment was evaluated and logged.

The test turbine in the experiment is attached to a generator, simulated by a servomotor. The generator section is controlled electrically. The turbine shaft angular velocity is held constant regardless of any set value. The performance is evaluated on the basis of the turbine output torque, the flow rate, the angular velocity of the blades, and the total pressure drop experienced across the turbine (Falcao, et al, 1998, p 1280). The parameters described above are denoted as,

Operating principle behind the wells turbine

The inhalation of the air or exhalation through the hollow column is measured as the flow rate. It is obtained by measuring the velocity at which the piston is moving. The value is confirmed when a pivot test is performed. The Reynolds number was approximated to 2.6*10⁵ and 0.5*10⁵ for this turbine based on the blade chord. The uncertainty on the efficiency is almost negligible and it is taken into account due to measurement errors on the physical parameters where efficiency is derived. The common speed obtained for the flow rate are

A project plan looks at a project scope and determines the relevant activities to be carried out to achieve the set objectives. The sections indicate what will be done to complete the study on the wells turbine in wave energy conversion under marine technology and ocean engineering. The project is simulated first using the inventor software to determine the design and simulate the process before implementation. A project Gantt chart is used in the project management with the aim of identifying critical processes and the duration of each process. A critical path is thereafter defined showing the least time a project can take having accomplished all the critical tasks. The researcher employs monitoring techniques to ensure that the project progress is forthcoming. The project is bound to face several uncertainties or risks. A good risk management plan goes a long way in helping a researcher deal with risks as they come. Some of the risks in running such a project include a change in the weather or climatic conditions hindering the installation of equipment at the shoreline.

The figure below shows the project plans and Gantt charts done using the MS Project Software,

Conclusions

In a nutshell, the wells turbine is a very useful tool in the wave energy conversion and it effectively operates under the oscillating water column. The study shows the performance of the wells turbine before and after using the booster turbine to revamp the performance. There are several risks associated with implementing the turbine as the oceans tend to have perilous wave power from time to time. Such power may destroy the turbine if not well harnessed. This mainly would affect the floating systems unlike the submerged systems. This project leaves room for future modification and improvement. The project seeks to bridge a gap that has been created by the limitation or scarcity of renewable energy options, some of which are easily depleted.

References

Ashlin, J.S., Sundar, V. & Sannasiraj, S.A. 2016, "Effects of bottom profile of an oscillating water column device on its hydrodynamic characteristics", , pp. 341-353.

Cashman, D.P., Sullivan, D.L.O., Egan, M.G. & Hayes, J.G. "Modelling and Analysis of an Offshore Oscillating Water Column Wave Energy Converter" , pp. 1-10.

Falcão, A.F.O., Henriques, J.C.C. & Gato, L.M.C. 2016, "Air turbine optimization for a bottom-standing oscillating-water-column wave energy converter", , pp. 459-472.

Falcao, A.F. & Justino, A.P. 1998, "OWC wave energy devices with air flow control", , pp. 1275-1295.

Henriques, J.C.C., Gomes, R.P.F., Gato, L.M.C., Falcao, A.F.O., Robles, E. & Ceballos, S. 2015, "Testing and control of a power take-off system for an oscillating water- column wave energy converter",  pp. 714-724.

Raghunathan, S. 1995, "The Wells Air Turbine For Wave Energy Conversion", vol. 31, pp. 335-386.