AWS Ocean Energy work in the renewable marine energy sector and have developed an innovative floating wave energy convertor. Their ambition is to develop reliable, affordable and operable offshore power stations. 4c engineers have contributed at every stage of the device development.

AWS – Technology Demonstrator

The Business Need

As part of the development programme for the AWS-III wave energy convertor, it was determined that a large scale technology demonstrator and test rig of the absorber subsystem was required, to be deployed in a marine environment.

The Project

The technology demonstrator consists of a floating concrete caisson, upon which the absorber subsystem, process air pipework and PTO container are mounted. Our engineers were involved at every stage of design, construction, assembly and operation.

Our Activities and Deliverables

Our engineers delivered the design of the complete test rig, including the following elements:

Determination of subsystem requirements
Concept generation and selection
Detailed design of saddle structure (see box)
Detailed design of process air system (see box)
Preparation of CAD models and drawings for fabrication
Design and commissioning of control instrumentation and remote data logging systems
Supplier selection and engagement throughout design process to ensure a final product fit for manufacture and purpose
Project management of installation, commissioning & testing phases of work, including logistics and lifting plans for test rig assembly

The Benefits

Installed and operational at its site in Scapa Flow, the test rig provides a platform for the following activities necessary for the AWS-III development programme:

Long-term durability testing of diaphragm material
Confirmation of feasibility of AWS-III concept at large scale
Measurement of diaphragm position and motions to inform FEA load studies and diaphragm geometry development activities
Monitoring of process parameters for system optimisation and to inform numerical models of system

Detailed Engineering Design - Absorber Saddle

The absorber subsystem consists of a flexible air-water interface (AWI, or “diaphragm”) and a supporting structure or “saddle”. The saddle consists of a large fabricated steel structure, which provides support to the diaphragm, and transfers wave loading back to the hull structure of the wave energy convertor (WEC). It also provides the attachment and sealing point for the diaphragm, the connection to the process air system, and a platform for the mounting of instrumentation.

The saddle surface is a complex formed 3D shape with a supporting structure of major and minor stiffeners. Our engineers undertook engineering design of this system from concept through to a detailed CAD package for fabrication. The total fabricated mass of the saddle was around 12 tonnes and measured 9 x 4.5 x 1.5 m. It was designed to withstand sea states of Hs = 3.0 m, taking into account wave slam events as experienced in scale model trials.

Our engineers delivered the design of the saddle subsystem, including the following elements:

Generation of complex 3D saddle geometry determined by hydrostatic load and diaphragm tension
Investigation and cost analysis of suitable materials and manufacturing methods
Derivation of hydrodynamic and structural loads using Morison’s equation and scale tank test results
Detailed design of saddle structure, including:
- Structural hard points and interface to supporting frame
- Scantling/stiffener layout and specification
- Lifting points
- Air system connection and de-watering system
- Flange joint around perimeter for connection and sealing of diaphragm
- Instrumentation ports (laser displacement sensors, water level sensors)
FEA of main structure and diaphragm connection details
Preparation of CAD models and drawings for fabrication
Supplier selection and engagement throughout design process to ensure a final product fit for manufacture and purpose

Detailed Engineering Design - Process Air System

The process air system consists of a collection of components including ductwork, adjustable pipe stands, valves and valve stands, and a water-trap sump with water sensors. This system connects the flow of air from the absorber to a plenum chamber contained within the concrete caisson which forms the project’s base platform, and provides the means by which air can be routed through a power take-off unit.

Our engineers delivered detailed engineering design of these components from concept through to a comprehensive package of manufacturing drawings. These components have now been fabricated, and assembled at the test site at Lyness, Orkney.

Our engineers undertook design of a variety of items, including the following:

Layout of process air system
Design of process air pipework and connections, including instrumentation ports
Specification of valves and actuators
Assessment of structural and wind loadings
Detailed design of adjustable pipe and valve stands
Specification of chemical anchor solutions for attachment of components to deck of concrete caisson
FEA work to determine resistance of structural members
Preparation of manufacturing drawings