An aerial photograph looking west over the Arts Centre and Christ's College towards Hagley Park. The photograph has been captioned by BeckerFraserPhotos, "At the centre of this photo is a group of heritage stone buildings. Canterbury Museum and Christ's College were extensively earthquake strengthened prior to the EQs and re-opened to the public relatively quickly. The Arts Centre is undergoing extensive renovations. Hagley Park and the Botanic Gardens provide a richly colourful surrounding to these historic buildings".
A wreath from the Singapore Contingent lying on a table in the memorial tent at the Botanic Gardens. The tent was set up for people who wanted to make a tribute to those who lost their lives during the Canterbury earthquakes. A note on the wreath reads, "The Singapore Contingent wishes to express our deepest sympathies and condolences to the people of Christchurch, New Zealand and all who have lost their lives during the 22nd February 2011 earthquake. Our hearts and thoughts are with you. From the men and women of the Singapore Contingent assisting with rescue and relief efforts in Christchurch".
Earthquakes cause significant damage to buildings due to strong vibration of the ground. Levitating houses using magnets and electromagnets would provide a complete isolation of ground motion for protecting buildings from seismic damage. Two types of initial configuration for the electromagnet system were proposed with the same air gap (10mm) between the electromagnet and reluctance plate. Both active and passive controller are modelled to investigate the feasibility of using a vibration control system for stabilizing the magnetic system within the designed air gap (10mm) in the vertical direction. A nonlinear model for the magnetic system is derived to implement numerical simulation of structural response under the earthquake record in Christchurch Botanic Gardens on 21 February 2011. The performance of the uncontrolled and the controlled systems are compared and the optimal combination of control gains are determined for the PID active controller. Simulation results show both active PID controller with constant and nonlinear attracting force are able to provide an effective displacement control within the required air gap (+/-5mm). The maximum control force demand for the PID controller in the presence of nonlinear attracting force is 4.1kN, while the attracting force in equilibrium position is 10kN provided by the electromagnet. These results show the feasibility of levitating a house using the current electromagnet and PID controller. Finally, initial results of passive control using two permanent magnets or dampers show the structural responses can be effectively reduced and centralized to +/-1mm using a nonlinear centring barrier function.