by Barry Koren
At CWI two new PhD-projects are focusing on future energy production: one on controlled nuclear fusion and one on wind energy.
Energy is of vital importance to human life in the modern world. We need it for primary necessities such as food, water, clothes and heating, as well as for transport, cooling, lighting, ICT, and so on. Energy consumption is proportional to living standard, which - on average - is increasing worldwide. At the same time, the world’s population is increasing. Our fossil fuel resources are becoming scarcer and, at the same time, combustion of those resources is believed to be leading to unacceptable climate change and concomitant flooding risks in many of the world’s lowland areas. The relevance of research on sources of energy to replace fossil fuels is evident.
Both CWI’s PhD-projects make full use of numerical simulations, because experiments are either technically impossible or too expensive. Numerical mathematics can also be fruitfully used in future optimizations of both energy sources. The two PhD projects are fine examples of research for which computational science is indispensable.
Controlled nuclear fusion
Currently in France, the International Thermonuclear Experimental Reactor (ITER, Figure 1) is under construction. True to its name, ITER is an international project, involving the EU, the USA, China, Russia, Japan, South Korea and India. It is expected to become operational around 2025, and is hoped to reach a power output-over-input ratio of 10; ITER's deuterium-tritium plasma will not yet be self-burning. To magnetically confine the plasma, ITER uses the tokamak concept. ITER's tokamak plasma will be in the so-called H-mode, which implies steep density gradients near the outer edge of the plasma and yields an enhanced plasma confinement. A consequent challenge is the possible occurrence of instabilities at the plasma's outer edge: edge localized modes (ELMs). ELMs, which show some resemblance to solar flares, may damage and finally ruin the expensive tokamak walls.
Figure 2: Artist’s impression of ITER. Source: http://www.fusie-energie.nl
In February 2009, Willem Haverkort started his PhD research at CWI, funded by the FOM Institute for Plasma Physics Rijnhuizen. The research goal is to investigate ITER ELMs by the further development and application of computational tools. In the first phase of the project, a study is being made of tokamak plasma equilibria in the presence of toroidal flow, using the generalized Grad-Shafranov equation. For these equilibrium studies, the existing FINESSE and PHOENIX software are extensively used, with FINESSE being extended for ITER's specific H-mode conditions. In the second phase, full, unsteady magnetohydrodynamic simulations will be made of the ITER plasma in H-mode. Here also, use will be made of existing software. A full MHD code will be coupled to FINESSE, and numerical extensions that appear to be necessary for ITER will be made. The software to be developed in this project is intended to be finally included in software for integrated ITER modelling and simulation.
A significant portion of the future energy needs of the Netherlands is to be produced by wind farms in the North Sea. A wind farm is a large set of coupled wind turbines, positioned in a matrix form. The advantages of wind farms as compared to sets of individual wind turbines are their smaller occupation of space and their lower construction and maintenance costs. The disadvantage is a reduced average power output per wind turbine. Designing wind farms involves creating, positioning and controlling each turbine such that the energy production of the wind farm as a whole is maximal, its maintenance cost minimal and its life time maximal. Two mathematical challenges are that these objectives are conflicting, and that the situation is complicated by the uncertainty in wind. State-of-the-art stochastic, multi-objective optimization techniques are required to meet these objectives. Further, a good physical understanding of wind-farm wake aerodynamics is crucial. Whereas for controlled nuclear fusion most experimental research is technically impossible, in wind-farm aerodynamics it is not. Nevertheless, wind-farm experiments have the disadvantage of being expensive at full scale, and involving upscaling difficulties at reduced scale. In fact, computational research is proving to be indispensable here as well.
In October 2008, funded by the Energy Research Centre of the Netherlands (ECN), Benjamin Sanderse started his PhD research, at both CWI and ECN, to develop a state-of-the-art computational method for simulating wind-farm wake aerodynamics. Proper turbulence modelling and accurate and efficient numerical simulation of the multiscale flow features are major research challenges in this project. We are opting for Large-Eddy Simulation to treat turbulence. The numerical methods to be developed and applied will preserve specific mathematical properties of the continuous equations.
CWI, The Netherlands
Tel: +31 205924114