Development of a Low-Cost 6 DOF Brick Tracking System for Use in Advanced Gas-Cooled Reactor Model Tests

This paper presents the design of a low-cost, compact instrumentation system to enable six degree of freedom motion tracking of acetal bricks within an experimental model of a cracked Advanced Gas-Cooled Reactor (AGR) core. The system comprises optical and inertial sensors and capitalises on the advantages offered by data fusion techniques. The optical system tracks LED indicators, allowing a brick to be accurately located even in cluttered images. The LED positions are identified using a geometrical correspondence algorithm, which was optimised to be computationally efficient for shallow movements, and complex camera distortions are corrected using a versatile Incident Ray-Tracking calibration. Then, a Perspective-Ray-based Scaled Orthographic projection with Iteration (PRSOI) algorithm is applied to each LED position to determine the six degree of freedom pose. Results from experiments show that the system achieves a low Root Mean Squared (RMS) error of 0.2296 mm in x, 0.3943 mm in y, and 0.0703 mm in z. Although providing an accurate measurement solution, the optical tracking system has a low sample rate and requires the line of sight to be maintained throughout each test. To increase the robustness, accuracy, and sampling frequency of the system, the optical system can be augmented with an Inertial Measurement Unit (IMU). This paper presents a method to integrate the optical system and IMU data by accurately timestamping data from each set of sensors and aligning the two coordinate axes. Once miniaturised, the developed system will be used to track smaller components within the AGR models that cannot be tracked with current instrumentation, expanding reactor core modelling capabilities

Exploring interactions between a human rhythmic jumper and an oscillating structure using experimental force-displacement analysis

Human rhythmic jumping is known to induce significant vibrations of civil structures, such as grandstands and footbridges. This has been known to introduce maintenance and serviceability concerns. The dynamic interaction between rhythmic human jumping on an oscillating surface is extremely complex due to both non-smooth, loss of contact, nonlinearities and geometric frequency dependant nonlinearity of the legs. This makes it particularly difficult to successfully characterise. A timber beam was constructed and instrumented to investigate these human-structure dynamic interactions. This was designed to simulate a cantilever tier of a grandstand, with similar natural frequency and damping ratio to the full-scale structure and with a similar mass ratio of a single human to the beam as for a crowd to the full-scale structure. Measurements of accelerations and displacements of both the jumper and beam, and of the contact force between them, were acquired. Testing was performed over a large range of prescribed jumping frequencies above and below the structure's natural frequency. Force-displacement curves of each test subject, during the contact phase of rhythmic jumping, and their evolution over all jumping frequencies tested are studied. Least squares system identification was utilised to identify the apparent leg spring stiffness conceptualised as a piece-wise linear spring-mass model. The coefficients are observed to be highly sensitive to jumping frequency. Comparative analysis between rhythmic jumping on stationary and oscillating surfaces is performed to draw conclusions on the influence of surface configuration on a jumper's mechanics. Important differences in jumping dynamics are observed indicating different nonlinear models are required to successfully characterise human rhythmic jumping for the two loading scenarios

A mathematical framework for evaluation of column shape profiles for an advanced gas-cooled reactor core model subject to seismic excitation

The safe shutdown of Advanced Gas-cooled Reactor (AGR) nuclear power stations in response to a seismic event is vital to their safety case. The tubular graphite bricks used to moderate the neutrons within an AGR core are arranged in columns whose bores provide channels for either fuel or control rods. Earthquake-induced distortion of the channels could impede the insertion of the control rods and compromise the safe shut-down, maintenance and servicing of the reactor. This paper presents a mathematical framework, utilising Euler mechanics, to evaluate the column shape displacement profiles of fuel and control rod channels within a state-of-the-art quarter-sized physical model of an AGR core when subjected to seismic loading. The data obtained from sensors installed within the model bricks, and configured to monitor interface displacements, are used to infer the global behaviour of a multi-stacked brick column subject to seismic excitation. Directly measured displacements of the top of the brick columns, obtained using a motion capture vision system, are compared with the displacements calculated using the framework presented, verifying the validity of the procedure. Statistical analysis is employed to quantify and characterise the performance of the Euler mechanics method. For multiple model build configurations, which represent different brick-cracking scenarios in an aged core, the Pearson correlation factor between the direct and indirect measurements is evaluated for the top of the column displacements giving an average value of 0.96 in the direction of the input motion. This shows that good agreement is achieved for the column shape displacement time-histories. The seismic responses are shown to be significantly larger in amplitude in the presence of large numbers of cracked bricks