School of Engineering, University of Waikato, Hamilton, New Zealand. mtwilson@waikato.ac.nz|School of Engineering, University of Waikato, Hamilton, New Zealand. mtwilson@waikato.ac.nz|School of Engineering, University of Waikato, Hamilton, New Zealand. mtwilson@waikato.ac.nz|School of Engineering, University of Waikato, Hamilton, New Zealand. mtwilson@waikato.ac.nz