164 results for Hann, C.E.

  • Vertical Wind Tunnel for Prediction of Rocket Flight Dynamics

    Bryson, H.; Sültrop, H.P.; Buchanan, G.; Hann, C.E.; Snowdon, M.; Rao, A.; Slee, A.; Fanning, K.; Wright, D.; McVicar, J.; Clark, B.; Harris, G.; Chen, X.Q. (2016)

    Journal Articles
    University of Canterbury Library

    A customized vertical wind tunnel has been built by the University of Canterbury Rocketry group (UC Rocketry). This wind tunnel has been critical for the success of UC Rocketry as it allows the optimization of avionics and control systems before flight. This paper outlines the construction of the wind tunnel and includes an analysis of flow quality including swirl. A minimal modelling methodology for roll dynamics is developed that can extrapolate wind tunnel behavior at low wind speeds to much higher velocities encountered during flight. The models were shown to capture the roll flight dynamics in two rocket launches with mean roll angle errors varying from 0.26 to 1.5 across the flight data. The identified model parameters showed consistent and predictable variations over both wind tunnel tests and flight, including canard–fin interaction behavior. These results demonstrate that the vertical wind tunnel is an important tool for the modelling and control of sounding rockets.

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  • Minimal Models to Capture the Dynamics of a Rotary Unmanned Aerial Vehicle

    Choi, R.L.W.; Hann, C.E.; Chen, X. (2014)

    Journal Articles
    University of Canterbury Library

    This paper presents a method for characterising the primary dynamics of a rotary unmanned aerial vehicle. Based on first principles and basic aerodynamics, a mathematical model which explains the rigid body dynamics of a model-scale helicopter is developed. This model is reduced to three simplified decoupled models of attitude dynamics. Empirical test data is collected from a field experiment with significant wind disturbances. The method worked accurately on both uncoupled and fully coupled attitude models. An integral based parameter identification method is presented to identify the unknown intrinsic helicopter parameters as well as model of wind disturbance. An extended Kalman filter system identification method and common nonlinear regression are used for comparison. The EKF was found to be highly dependent on the initial states, so is not suitable for this application which contains significant disturbance and modelling errors. Nonlinear regression proved to be sufficiently accurate but computationally expensive. The proposed integral based parameter identification method was shown to be fast and accurate and is well suited to this application.

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  • Validation of subject-specific cardiovascular system models from porcine measurements

    Revie, J.A.; Stevenson, D.J.; Chase, J.G.; Hann, C.E.; Lambermont, B.C.; Ghuysen, A.; Kolh, P.; Shaw, G.M.; Heldmann, S.; Desaive, T. (2013)

    Journal Articles
    University of Canterbury Library

    A previously validated mathematical model of the cardiovascular system (CVS) is made subject-specific using an iterative, proportional gain-based identification method. Prior works utilised a complete set of experimentally measured data that is not clinically typical or applicable. In this paper, parameters are identified using proportional gain-based control and a minimal, clinically available set of measurements. The new method makes use of several intermediary steps through identification of smaller compartmental models of CVS to reduce the number of parameters identified simultaneously and increase the convergence stability of the method. This new, clinically relevant, minimal measurement approach is validated using a porcine model of acute pulmonary embolism (APE).

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  • Real-time integral based structural health monitoring

    Singh-Levett, I.; Chase, J.G.; Hann, C.E.; Deam, B.L. (2006)

    Conference Contributions - Published
    University of Canterbury Library

    An algorithm has been developed to provide real-time structural health monitoring during earthquake events. For a given input ground acceleration the algorithm matches the Bouc-Wen hysteresis model to structural response data using piecewise least squares fitting. The methodology identifies pre-yield and post-yield stiff-ness, elastic and plastic components of displacement and final residual displacement. This approach is particularly useful for rapid assessment of structural safety by owners or civil defense authorities. The algorithm is tested with simulated response data using the El Centro and Kobe earthquake records. Using simulated data for a two degree of freedom shear building model, the algorithm captures stiffness to within 2% of the real value and permanent deflection to within 5% when significant non-linear response occurs. This is achieved with acceleration data sampled at 1KHz and displacement data sampled at 10Hz

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  • Boundary element methods in elastography: a first explorative study

    Berger, H-U.; Hann, C.E.; Chase, J.G.; Broughton, R.L.; Van Houten, E.E.W. (2007)

    Conference Contributions - Published
    University of Canterbury Library

    http://spiedigitallibrary.aip.org/dbt/dbt.jsp?KEY=PSISDG&Volume=6511&Issue=1&bproc=symp&scode=MI07 to find paper and front matter etc.

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  • Digital Imaging Based Screening and Detection of Breast Cancer

    Chase, J.G.; Hann, C.E.; Brown, R.G.; Peters, A.; Ray, L.E. (2008)

    Conference Contributions - Published
    University of Canterbury Library

    Keynote speech

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  • Real-Time Structural Health Monitoring of a Non-linear Four Storey Steel Frame Structure

    Singh-Levett, I.; Hann, C.E.; Deam, B.L.; Mander, J.B.; Chase, J.G. (2009)

    Journal Articles
    University of Canterbury Library

    Structural health monitoring (SHM) is a means of identifying damage from structural response to environmental loads. Real-time SHM is of particular use for rapid assessment of structural safety by owners and civil defense authorities. This paper presents an algorithm for real-time SHM during earthquake events using only acceleration measurements and infrequently measured displacement motivated by global positioning system. The algorithm identifies a nonlinear baseline model including hysteretic dynamics and permanent deformation using convex integral-based fitting methods and piecewise linear least squares fitting. The methodology identifies pre and postyield stiffness, elastic and plastic components of displacement, and final residual displacement. It thus identifies key measures of damage affecting the immediate safety or use of the structure and the long-term cost of repair and retrofit. The algorithm is tested with simulated response data using the El-Centro earthquake record and with measured response data. Both data sets are based on a four-story nonlinear steel frame structure using the El-Centro ground motion record. Overall, the algorithm is shown to provide accurate indications of the existence, location, and magnitude of structural damage for nonlinear shear-type buildings. Additionally, the identified permanent displacement is a particularly useful damage measure for the construction of probabilistic fragility functions.

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  • A pointwise smooth surface stereo reconstruction algorithm without correspondences

    Brown, R.G.; Chase, J.G.; Hann, C.E. (2012)

    Journal Articles
    University of Canterbury Library

    This paper describes an algorithm for 3D reconstruction of a smooth surface with a relatively dense set of self-similar point features from two calibrated views. We bypass the usual correspondence problem by triangulating a point in space from all pairs of features satisfying the epipolar constraint. The surface is then extracted from the resulting point cloud by taking advantage of the statistical and geometric properties of the point distribution on the surface. Results are presented for computer simulations and for a laboratory experiment on a silicon gel phantom used in a breast cancer screening project.

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  • A simplified model for mitral valve dynamics

    Moorhead, K.T.; Paeme, S.; Chase, J.G.; Kolh, P.; Pierard, L.; Hann, C.E.; Dauby, P.C.; Desaive, T. (2013)

    Journal Articles
    University of Canterbury Library

    Located between the left atrium and the left ventricle, the mitral valve controls flow between these two cardiac chambers. Mitral valve dysfunction is a major cause of cardiac dysfunction and its dynamics are little known. A simple non-linear rotational spring model is developed and implemented to capture the dynamics of the mitral valve. A measured pressure difference curve was used as the input into the model, which represents an applied torque to the anatomical valve chords. A range of mechanical model hysteresis states were investigated to find a model that best matches reported animal data of chord movement during a heartbeat. The study is limited by the use of one dataset from the literature. However, results clearly highlight some physiological issues, such as the damping and chord stiffness changing within one cardiac cycle. Very good correlation was achieved between modeled and experimental valve angle with 1-10% absolute error in the best case, indicating good promise for future simulation of cardiac valvular dysfunction, such as mitral regurgitation or stenosis. In particular, the model provides a pathway to capturing these dysfunctions in terms of modeled stiffness or elastance that can be directly related to anatomical, structural defects and dysfunction.

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  • Algorithmic Processing of Pressure Waveforms to Facilitate Estimation of Cardiac Elastance

    Stevenson, D.; Revie, J.A.; Chase, J.G.; Hann, C.E.; Shaw, G.M.; Lambermont, B.; Ghuysen, A.; Kolh, P.; Desaive, T. (2012)

    Journal Articles
    University of Canterbury Library

    Background: Cardiac elastances are highly invasive to measure directly, but are clinically useful due to the amount of information embedded in them. Information about the cardiac elastance, which can be used to estimate it, can be found in the downstream pressure waveforms of the aortic pressure (Pao) and the pulmonary artery (Ppa). However these pressure waveforms are typically noisy and biased, and require processing in order to locate the specific information required for cardiac elastance estimations. This paper presents the method to algorithmically process the pressure waveforms. Methods: A shear transform is developed in order to help locate information in the pressure waveforms. This transform turns difficult to locate corners into easy to locate maximum or minimum points as well as providing error correction. Results: The method located all points on 87 out of 88 waveforms for Ppa, to within the sampling frequency. For Pao, out of 616 total points, 605 were found within 1%, 5 within 5%, 4 within 10% and 2 within 20%. Conclusions: The presented method provides a robust, accurate and dysfunction-independent way to locate points on the aortic and pulmonary artery pressure waveforms, allowing the non-invasive estimation of the left and right cardiacelastance.

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  • Structural model of the mitral valve included in a cardiovascular closed-loop model: Static and dynamic validation

    Paeme, S.; Moorhead, K.; Chase, J.G.; Lambermont, B.; Kolh, P.; Lancellotti, P.; Dauby, P.C.; Desaive, T.; Hann, C.E.; Moonen, M. (2012)

    Conference Contributions - Published
    University of Canterbury Library

    invited, 6-pages

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  • Minimal Elastographic Modeling of Breast Cancer for Model Based Tumour Detection in a Digital Image Elasto Tomography (DIET) System

    Lotz, T.; Muller, N.; Hann, C.E.; Chase, J.G. (2011)

    Conference Contributions - Published
    University of Canterbury Library

    Digital Image Elasto Tomography (DIET) is a non-invasive breast cancer screening technology that images the surface motion of a breast under harmonic mechanical actuation. A new approach capturing the dynamics and characteristics of tumor behavior is presented. A simple mechanical model of the breast is used to identify a transfer function relating the input harmonic actuation to the output surface displacements using imaging data of a silicone phantom. Areas of higher stiffness cause significant changes of damping and resonant frequencies as seen in the resulting Bode plots. A case study on a healthy and tumor silicone breast phantom shows the potential for this model-based method to clearly distinguish cancerous and healthy tissue as well as correctly predicting the tumor position.

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  • Processing aortic and pulmonary artery waveforms to derive the ventricle time-varying elastance

    Stevenson, D.; Chase, J.G.; Hann, C.E.; Revie, J.A.; Shaw, G.M.; Desaive, T.; Lambermont, B.; Ghuysen, A.; Kolh, P.; Heldmann, S. (2011)

    Conference Contributions - Published
    University of Canterbury Library

    Time-varying elastance of the ventricles is an important metric both clinically and as an input for a previously developed cardiovascular model. However, currently time-varying elastance is not normally available in an Intensive Care Unit (ICU) setting, as it is an invasive and ethically challenging metric to measure. A previous paper developed a method to map less invasive metrics to the driver function, enabling an estimate to be achieved without invasive measurements. This method requires reliable and accurate processing of the aortic and pulmonary artery pressure waveforms to locate the specific points that are required to estimate the driver function. This paper details the method by which these waveforms are processed, using a data set of five pigs induced with pulmonary embolism, and five pigs induced with septic shock (with haemofiltration), adding up to 88 waveforms (for each of aortic and pulmonary artery pressure), and 616 points in total to locate. 98.2% of all points were located to within 1% of their true value, 0.81% were between 1% and 5%, 0.65% were between 5% and 10%, the remaining 0.32% were below 20%.

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  • Pulmonary embolism diagnostics from the driver function

    Stevenson, D.J.; Revie, J.A.; Chase, J.G.; Hann, C.E.; Le Compte, A.J.; Shaw, G.M.; Lambermont, B.; Kolh, P.; Desaive, T. (2011)

    Conference Contributions - Other
    University of Canterbury Library

    Ventricular driver functions are not readily measured in the ICU, but can clearly indicate the development of pulmonary embolism (PE) otherwise difficult to diagnose. Recent work has developed accurate methods of measuring these driver functions from readily available ICU measurements. This research tests those methods by assessing the ability of these driver functions to diagnose the evolution of PE.

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  • Structural Model of the Mitral Valve Included in a Cardiovascular Closed Loop Model

    Paeme, S.; Moorhead, K.T.; Chase, J.G.; Hann, C.E.; Lambermont, B.; Kolh, P.; Moonen, M.; Lancellotti, P.; Dauby, P.C.; Desaive, T. (2011)

    Conference Contributions - Other
    University of Canterbury Library

    http://www.ncbme.ugent.be/pdf/ND2011Abstracts.pdf Page 111

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  • Model-based cardiovascular monitoring of large pore hemofiltration during endotoxic shock in pigs

    Revie, J.A.; Stevenson, D.J.; Chase, J.G.; Hann, C.E.; Le Compte, A.J.; Lambermont, B.; Ghuysen, A.; Kolh, P.; Shaw, G.M.; Desaive, T. (2011)

    Conference Contributions - Other
    University of Canterbury Library

    http://ccforum.com/supplements/notes/ccv15s1-info.pdf P116

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  • Model-based cardiovascular monitoring of acute pulmonary embolism in porcine trials

    Revie, J.A.; Stevenson, D.J.; Chase, J.G.; Hann, C.E.; Lambermont, B.; Ghuysen, A.; Kolh, P.; Shaw, G.M.; Desaive, T. (2011)

    Conference Contributions - Other
    University of Canterbury Library

    Introduction: Diagnosis and treatment of cardiac and circulatory dysfunction can be error-prone and relies heavily on clinical intuition and experience. Model-based approaches utilising measurements available in the Intensive care unit (ICU) can provide a clearer physiological picture of a patient’s cardiovascular status to assist medical staff with diagnosis and therapy decisions. This research tests a subject-specific cardiovascular system (CVS) modelling technique on measurements from a porcine model of acute pulmonary embolism (APE). Methods: Measurements were recorded in 5 pig trials, where autologous blood clots were inserted every two hours into the jugular vein to simulate pulmonary emboli. Of these measurements only a minimal set of clinically available or inferable data were used in the identification process (aortic and pulmonary artery pressure, stroke volume, heart rate, global end diastolic volume, and mitral and tricuspid valve closure times). The CVS model was fitted to 46 sets of data taken at 30 minute intervals (t=0, 30, 60, …, 270) during the induction of APE to identify physiological model parameters and their change over time in APE. Model parameters and outputs were compared to experimentally derived metrics and measurements not used in the identification method to validate the accuracy of the model and assess its diagnostic capability. Results: Modelled mean ventricular volumes and maximum ventricular pressures matched measured values with median absolute errors of 4.3% and 4.4%, which are less than experimental measurement noise (~10%). An increase in pulmonary vascular resistance, the main hemodynamic consequence of APE, was identified in all the pigs and related well to experimental values (R=0.68). Detrimental changes in reflex responses, such as decreased right ventricular contractility, were noticed in two pigs that died during the trial, diagnosing the loss of autonomous control. Increases in the ratio of the modelled right to left ventricular end diastolic volumes, signifying the leftward shift of the intra-ventricular septum seen in APE, compared well to the clinically measured index (R=0.88). Conclusions: Subject-specific CVS models can accurately and continuously diagnose and track acute disease dependent cardiovascular changes resulting from APE using readily available measurements. Human trials are underway to clinically validate these animal trial results.

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  • Optimal Positive End-Expiratory Pressure in Mechanically Ventilated Patients: A Clinical Study

    Sundaresan, A.; Chase, J.G.; Hann, C.E.; Shaw, G.M. (2011)

    Conference Contributions - Other
    University of Canterbury Library

    The optimal level of positive end-expiratory pressure (PEEP) is still widely debated in treating acute respiratory distress syndrome (ARDS) patients. Current methods of selecting PEEP only provide a range of values and do not provide unique patient-specific solutions. Model-based methods offer a novel way of using non-invasive pressure-volume (PV) measurements to estimate patient recruitability. This paper examines the clinical viability of such models in pilot clinical trials to assist therapy, optimise patient-specific PEEP, assess the disease state and response over time.

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  • Mathematical multi-scale model of the cardiovascular system including mitral valve dynamics. Application to mitral regurgitation

    Paeme, S.; Moorhead, K.T.; Chase, J.G.; Hann, C.E.; Lambermont, B.; Kolh, P.; D’orio, V.; Moonen, M.; Lancellotti, P.; Dauby, P.C.; Desaive, T. (2011)

    Journal Articles
    University of Canterbury Library

    Background: Valve dysfunction is a common cardiovascular pathology. Despite significant clinical research, there is little formal study of how valve dysfunction affects overall circulatory dynamics. Validated models would offer the ability to better understand these dynamics and thus optimize diagnosis, as well as surgical and other interventions. Methods: A cardiovascular and circulatory system (CVS) model has already been validated in silico, and in several animal model studies. It accounts for valve dynamics using Heaviside functions to simulate a physiologically accurate “open on pressure, close on flow” law. However, it does not consider real-time valve opening dynamics and therefore does not fully capture valve dysfunction, particularly where the dysfunction involves partial closure. This research describes an updated version of this previous closed-loop CVS model that includes the progressive opening of the mitral valve, and is defined over the full cardiac cycle. Results: Simulations of the cardiovascular system with healthy mitral valve are performed, and, the global hemodynamic behaviour is studied compared with previously validated results. The error between resulting pressure-volume (PV) loops of already validated CVS model and the new CVS model that includes the progressive opening of the mitral valve is assessed and remains within typical measurement error and variability. Simulations of ischemic mitral insufficiency are also performed. Pressure-Volume loops, transmitral flow evolution and mitral valve aperture area evolution follow reported measurements in shape, amplitude and trends. Conclusions: The resulting cardiovascular system model including mitral valve dynamics provides a foundation for clinical validation and the study of valvular dysfunction in vivo. The overall models and results could readily be generalised to other cardiac valves.

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  • Development of a model-based clinical sepsis biomarker for critically ill patients

    Lin, J.; Parente, J.D.; Chase, J.G.; Shaw, G.M.; Blakemore, A.J.; LeCompte, A.J.; Pretty, C.; Razak, N.N.; Lee, D.S.; Hann, C.E.; Wang, S-H. (2011)

    Journal Articles
    University of Canterbury Library

    Invited. online 15 May 2010.

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