Sweden: Minesto Develops World’s First Simulator for Anchored Flying Underwater Vehicles

Nordic marine energy technology leader Minesto has developed a simulator to aid the development of its Deep Green marine power plant. Deep Green is the only marine power plant that is able to cost efficiently produce electricity from low velocity tidal and ocean currents.

The simulator has been developed in-house by Minesto’s own research and development department, and is in essence based on two existing open source programs: one for commercial flight simulation and one for marine vehicle simulation.

The end result is an analysis and simulation tool called HAMoS, Hydrodynamic Analysis and Motion Simulation, believed to be the first in the world to simulate the movements of a flying tethered underwater vehicle. It will be used to predict how Minesto’s marine power plant, Deep Green, moves subsea in various ocean environments and depending on the plant’s design.

Minesto’s research, development and testing staff can change a number of variables in the power plant’s design to simulate and optimize its performance. The simulator can be used to predict Deep Green’s behaviour and power performance in different real-life site conditions (i.e. the strength and direction of the currents).

Deep Green resembles a sweeping underwater kite, comprised of a wing and a turbine, which is secured to the seabed with a tether and moves with high speed in an 8-shaped path in the tidal or ocean current. Deep Green produces 100% renewable tidal energy.

“The new simulator is a very valuable tool for us as a supplement to real life sea tests since it speeds up the development of Deep Green,” said Anders Jansson, CEO, Minesto. “We can easily scale and change different variables in the simulator to predict and optimize Deep Green’s power production performance with great accuracy. It is of great commercial value to be able to estimate the cost of energy more precisely at a specific location.”

HAMoS combines CFD analysis with a flight simulator and a simulator for marine vehicles. The CFD analysis is used to calculate lift, drag and added mass acting on the body. The flight simulator is used as the main simulation platform formulating the equations of motion, it utilises both the results from CFD computations and also specific formulas for underwater motion from the marine vehicles simulator. In addition to this a tethered flying body, opposed to a free flying body, creates a computational stiff and difficult case which requires special attention.

The simulation works in five steps:

1. A parameterised CAD model is used to define the body to be simulated.

2. A potential flow CFD method calculates the hydrodynamic forces on the body.

3. The hydrodynamic forces, as a function of the body’s orientation and velocity, are fitted to polynomials with six degrees of freedom. These are combined with the non-hydrodynamic forces to obtain the global force resultant.

4. Through discrete integration the movement of the device can be obtained as a function of time.

5. The output power from the power plant is calculated from the modelled movement and performance data for the used turbine.

The simulator raises the understanding of the Deep Green power plant as it is possible to see how the kite moves and which forces the water current creates. The simulator enables Minesto to try new ideas for e.g. the geometrical shape, the flight path or the control system, and get direct feedback for the effects on the performance.

In the future, HAMoS could be used for educational purposes like training of system operators at Minesto and the company’s end customers.

[mappress]

Press release, July 1, 2013; Image: Minesto