50 results on '"Boje, Edward"'
Search Results
2. Quantitative Feedback Theory design of valve position control for co-ordinated superheater control of main steam temperatures of power plant boilers
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Polton, Cheriska and Boje, Edward
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- 2020
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3. Shutter delay estimation for a low-cost stand-alone visual tracking system
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Pretorius, Arnold and Boje, Edward
- Published
- 2017
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4. Representation of simulation errors in single step methods using state dependent noise
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Boje Edward
- Subjects
Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
The local error of single step methods is modelled as a function of the state derivative multiplied by bias and zero-mean white noise terms. The deterministic Taylor series expansion of the local error depends on the state derivative meaning that the local error magnitude is zero in steady state and grows with the rate of change of the state vector. The stochastic model of the local error may include a constant, “catch-all” noise term. A continuous time extension of the local error model is developed and this allows the original continuous time state differential equation to be represented by a combination of the simulation method and a stochastic term. This continuous time stochastic differential equation model can be used to study the propagation of the simulation error in Monte Carlo experiments, for step size control, or for propagating the mean and variance. This simulation error model can be embedded into continuous-discrete state estimation algorithms. Two illustrative examples are included to highlight the application of the approach.
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- 2021
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5. Discrete Kalman filter based on quasi steady state modelling in the delta-domain
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Boje, Edward
- Published
- 2014
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6. Dry-out point estimation in once through boilers
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Boje, Edward
- Published
- 2009
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7. A refinement approach to the multivariable tracking error problem.
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Pretorius, Arnold and Boje, Edward
- Subjects
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BENCHMARK problems (Computer science) , *CONSTRAINED optimization , *FEEDFORWARD neural networks , *ITERATIVE learning control , *ARTIFICIAL satellite tracking , *CONSERVATISM , *ROBUST control - Abstract
This article presents a new refinement design routine aimed at solving the robust multivariable tracking error problem with reduced conservatism. The prevailing multivariable quantitative feedback theory (QFT) approach is to implicitly overbound the model‐error tracking set frequency response in magnitude using the triangle inequality, with the intention of arriving at a set of univariate design constraints that independently describe the feedback controller solution space. While this method is effective in the low‐frequency range (where the loop gain tends to be large), the mid‐ to high‐frequency design regions (where diagonal dominance is not possible in general) suffers from arbitrarily large design conservatism. This inhibits minimum gain‐phase solutions and necessitates undesirable over‐design in the frequency band that can contribute to large, expensive control action. The proposed method follows a refinement approach that makes use of information from an a priori feedback control design. In this way, the tracking error problem is reposed as a differential design, and gain‐phase information from the previous iteration can be captured to reduce the conservatism imposed when applying the triangle inequality. Additionally, a constrained optimization routine is used to select a prototype feedforward filter that can relax the constraint set, thereby increasing the accessible solution space of the diagonal feedback controller. Finally, a nondiagonal, multivariable feedforward filter bound generation routine is defined that relies on existence conditions and is free of induced design conservatism. The viability of this design methodology is demonstrated on two benchmark problems of varying complexity, in order to demonstrate the widespread efficacy. [ABSTRACT FROM AUTHOR]
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- 2022
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8. Approximations for state estimation in a plane using two two-axis accelerometers
- Author
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Boje, Edward
- Published
- 2008
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9. Implicit quasi-steady-state approximation and application to a power plant evaporator
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Eitelberg, Eduard and Boje, Edward
- Subjects
Electric power-plants -- Equipment and supplies ,Power plants -- Equipment and supplies ,Steam-boilers -- Design and construction ,Approximation theory -- Methods ,Control systems -- Design and construction ,Engineering and manufacturing industries ,Science and technology - Abstract
Construction of reduced order models using the conventional quasi-steady-state (QSS) or singular perturbation approach may not yield good low frequency approximations, especially if there is not a distinct time scale separation into slow and fast subsystems. An implicit QSS technique is proposed for general nonlinear models. The resulting reduced order model is accurate to first order in the perturbation parameter and its linearization is accurate to first order in frequency. An example is included showing the application of the proposed method to model reduction on a power plant evaporator. [DOI: 10.1115/1.2397153] Keywords: implicit quasi-steady state, model reduction, stiff systems, singular perturbation, power plant boiler, once through steam generator
- Published
- 2007
10. SQUARING DOWN DESIGN FOR OVER-ACTUATED SYSTEMS IN MULTIVARIABLE QFT
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Boje, Edward
- Published
- 2005
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11. Water circulation control during once-through boiler start-up
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Eitelberg, Eduard and Boje, Edward
- Published
- 2004
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12. Algorithm for calculating MIMO QFT tracking bounds
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Boje, Edward
- Subjects
Mathematics -- Models ,Engineering and manufacturing industries ,Science and technology - Abstract
An algorithm for calculating design bounds in multivariable quantitative feedback theory (QFT) tracking design is presented. The algorithm solves the problem of trade-off between on- and off-diagonal constraints.
- Published
- 2004
13. A complementary quantitative feedback theory solution to the 2 × 2 tracking error problem.
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Pretorius, Arnold and Boje, Edward
- Subjects
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PSYCHOLOGICAL feedback , *ROBUST control - Abstract
Summary: This article presents a solution to the 2 × 2 multivariable tracking error problem. Current quantitative feedback theory methods commonly employ plant‐inverting splittings in order to arrive at an approximately decoupled design on the feedback control elements. This results in suitable design regions in the high‐gain, low‐frequency range, but can result in conservative design at and above the gain‐crossover frequency, resulting in overdesigned feedback controllers. Our method aims to reduce this conservatism by supplementing a plant‐inverting design with a non‐plant‐inverting design, which tends to perform well at higher frequencies. Decoupling the design of the controller elements is facilitated by making use of appropriate existence conditions. The union of the two resulting design regions then describes a larger solution space, and by enlarging the admissible design regions for the feedback controller, lower gain feedback controller design at all design frequencies of interest may be possible. A benchmarking example is presented, showing the viability of the proposed method. [ABSTRACT FROM AUTHOR]
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- 2020
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14. Teaching Automation at the University of Natal
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Boje, Edward and Petrick, Martin
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- 2000
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15. Robust plant by plant control design using model‐error tracking sets.
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Pretorius, Arnold and Boje, Edward
- Subjects
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FACTORY design & construction , *PLANTING , *MAXIMUM power point trackers - Abstract
Summary: This paper presents a method for designing a robust two‐degree‐of‐freedom control scheme, capable of satisfying multiple model‐error specifications on a plant by plant basis. Traditional quantitative feedback theory methods generally use a single model‐error or above‐below magnitude tracking specification, which can result in overdesign for plants located away from the bounding conditions. The performance specifications are also generally hand‐tuned, or iteratively adjusted to keep the underlying time‐domain signals within permissible levels. Our method aims to perform a model‐error design on a per‐plant basis, such that each plant's corresponding model tracking has equal weighting given the plant's inherent feedback requirements and capability. The quantitative feedback theory method allows this per‐plant approach to be undertaken with ease. Additionally, sufficiently low‐order model specifications are designed using simple optimisation, which take into account performance limiting effects, such as non‐minimum phase behaviour and signal constraints. A worked example is presented, showing the viability and transparency of the proposed method. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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16. Optimal LED-based illumination control via distributed convex optimization
- Author
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Aslam, Muhammad, Hermans, R.M., Pandharipande, A., Lazar, M., Boje, Edward, Xia, Xiaohua, Smart Buildings and Cities, Control Systems, Control of high-precision mechatronic systems, Constrained Control of Complex Systems, and Dynamic Networks: Data-Driven Modeling and Control
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Engineering ,Linear programming ,Computational complexity theory ,business.industry ,Illuminance ,Control engineering ,Energy consumption ,Rate of convergence ,Control theory ,Convex optimization ,SDG 7 - Affordable and Clean Energy ,business ,Energy (signal processing) ,SDG 7 – Betaalbare en schone energie - Abstract
Achieving illumination and energy consumption targets is essential in indoor lighting design. The provision of localized illumination to occupants, and the utilization of natural light and energy-efficient light-emitting diode (LED) luminaires can help meet both objectives. Localized illumination control schemes require suitable coordination mechanisms to obtain luminaire dimming levels that achieve the desired illuminance levels and reduce energy costs. This paper presents several distributed optimal LED-based illumination control schemes that provide localized illuminance to occupants. The lighting system consists of multiple LED-based luminaires, each of which has a controller that can process information locally and communicate with nearby controllers. The illuminance requirements and energy costs for the lighting system are expressed as a linear programming problem. This optimization problem is solved, in a distributed manner, across the network of controllers using local communication amongst the controllers. State-of-the-art distributed optimization methods, based on accelerated first-order methods, are applied to parallelize the computational tasks among multiple controllers. Important practical aspects such as the rate of convergence, computational complexity, and communication requirements are investigated via simulations.
- Published
- 2014
17. On the Conical Motion of a Two-Degree-of-Freedom Tail Inspired by the Cheetah.
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Patel, Amir and Boje, Edward
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ROBOTS , *CHEETAH , *TAILS , *DEGREES of freedom , *ROBOTICS - Abstract
An actuated tail can impart large angular impulse over short time spans, but swinging in a plane results in inevitable tail angle saturation. Cheetahs (Acinonyx jubatus) are observed swinging the tail in a cone during turns
[1] , and this paper develops a simplified two-degree-of-freedom (pitch and roll) rigid tail model to investigate this motion. Trajectory optimization and experiments on a robotic platform confirm the observed cone motion as a useful solution to roll stabilization. These results are relevant to the understanding of tail motions in biomechanics and bioinspired tailed robots. [ABSTRACT FROM PUBLISHER]- Published
- 2015
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18. Brachiating power line inspection robot.
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Patel, Javaad and Boje, Edward
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- 2014
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19. Modelling and control of a power supply for a power line inspection robot.
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Boje, Edward
- Published
- 2014
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20. Approximate models for continuous-time linear systems with sampling jitter
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Boje, Edward
- Published
- 2005
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21. Computer Vision-Based Classification of Flow Regime and Vapor Quality in Vertical Two-Phase Flow.
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Kadish, Shai, Schmid, David, Son, Jarryd, and Boje, Edward
- Subjects
TWO-phase flow ,DEEP learning ,GASES ,ONLINE databases ,VAPORS ,COMPUTER vision - Abstract
This paper presents a method to classify flow regime and vapor quality in vertical two-phase (vapor-liquid) flow, using a video of the flow as the input; this represents the first high-performing and entirely camera image-based method for the classification of a vertical flow regime (which is effective across a wide range of regimes) and the first image-based tool for estimating vapor quality. The approach makes use of computer vision techniques and deep learning to train a convolutional neural network (CNN), which is used for individual frame classification and image feature extraction, and a deep long short-term memory (LSTM) network, used to capture temporal information present in a sequence of image feature sets and to make a final vapor quality or flow regime classification. This novel architecture for two-phase flow studies achieves accurate flow regime and vapor quality classifications in a practical application to two-phase CO
2 flow in vertical tubes, based on offline data and an online prototype implementation, developed as a proof of concept for the use of these models within a feedback control loop. The use of automatically selected image features, produced by a CNN architecture in three distinct tasks comprising flow-image classification, flow-regime classification, and vapor quality prediction, confirms that these features are robust and useful, and offer a viable alternative to manually extracting image features for image-based flow studies. The successful application of the LSTM network reveals the significance of temporal information for image-based studies of two-phase flow. [ABSTRACT FROM AUTHOR]- Published
- 2022
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22. Quantitative feedback design for systems with probabilistic parameterizations.
- Author
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Boje, Edward
- Published
- 2007
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23. Augmented Kalman Filtering for a Superheated Steam Header System.
- Author
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Boje, Edward and Eitelberg, Eduard
- Subjects
KALMAN filtering ,DISTRIBUTED parameter systems ,SUPERHEATED steam - Abstract
This paper examines the distributed parameter model of a main steam header system and simplifies it to retain only the significant dynamics of the pipe wall temperature and quasisteady-state behavior of the steam in the headers. An augmented linear optimal filter is developed for estimating the steam and pipe wall temperatures along the interconnected main steam headers, between the superheater outlet and the turbine. The filter algorithm is illustrated using data from a power plant. [ABSTRACT FROM AUTHOR]
- Published
- 2003
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24. Non-diagonal controllers in MIMO quantitative feedback design.
- Author
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Boje, Edward
- Published
- 2002
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25. Quantitative Feedback Design Using Forward Path Decoupling.
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Boje, Edward and Nwokah, Osita D.I.
- Subjects
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FEEDBACK control systems , *FROBENIUS algebras - Abstract
Discusses the measurement of the level of interaction in MIMO quantitative feedback design (QFT) using Perron-Frobenius root. Design approach to reduce interaction in uncertain plants via a precompensator; Application of a decentralized stability results.
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- 2001
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26. Quantitative multivariable feedback design for a turbofan engine with forward path decoupling.
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Boje, Edward and Nwokah, Osita D. I.
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- 1999
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27. Further results on Eitelberg's sampling rate design based on (1 — sT/2 ).
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BOJE, EDWARD
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- 1990
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28. Feedback controller design for plants with modes and disturbances above the sampling frequency.
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EITELBERG, EDUARD and BOJE, EDWARD
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- 1991
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29. Finding Nonconvex Hulls of QFT Templates.
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Boje, Edward
- Subjects
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NONCONVEX programming , *ALGORITHMS - Abstract
Presents an algorithm to calculate the nonconvex hull with minimum concave radius defined by the feedback system specifications. Determination of nonconvex hulls of quantitative feedback theory templates; Reduction in the computational effort required for bound calculation at a given frequency and controller phase.
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- 2000
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30. Kalman Filtering and its Application to On-Line State Estimation of a Once-Through Boiler
- Author
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Patel, Zubeida and Boje, Edward
- Subjects
Electrical Engineering - Abstract
This thesis contributes to non-linear continuous-discrete Kalman filtering of multiplex systems through the development of two main ideas, namely, integration of the unscented transforms with linearly implicit methods and incorporation of simulation errors in the state estimation problem. The newly developed techniques are then applied to the technically relevant problem of state estimation on the main components of a utility boiler. State estimators in industrial systems are used as soft-sensors in monitoring and control applications as the most cost effective and practical alternative to telemetering all variables of interest. One such example is in utility boilers where reliable and real-time data characterising its behaviour is used to detect faults and optimise performance. With respect to the state-of-the-art, state estimators display limitations in real-time applications to large-scale systems. This motivates theoretical developments in state estimation as a first part in this thesis. These developments are aimed at producing more practical and efficient algorithms in non-linear continuous discrete Kalman filtering for stiff large-scale industrial systems. This is achieved using two novel ideas. The first is to exploit the similarities between the extended and unscented Kalman filter in order to estimate the Jacobian required for linearly implicit schemes, thereby tightly coupling state propagation and continuous-time simulation. The second is to account for numerical integration error by appending a stochastic local error model to the system's stochastic differential equation. This allows for coarser integration time steps in systems that are otherwise only suited to relatively small step sizes, making the filter more computationally efficient without lowering its potential to construct accurate estimates. The second part of this thesis uses these algorithms to demonstrate the feasibility of on-line state estimation on the main components of a once-through utility power boiler that require in excess of a hundred state variables to capture its behaviour with adequate fidelity. Two separate models of the boiler are developed, a MATLAB® and a Flownex® model, comprising the economiser, evaporators, reheaters, superheaters and furnace. The mathematical MATLAB® model is better suited to real-time execution and is used in the filter. The more sophisticated model is based on a commercial thermal-hydraulic simulation environment, Flownex® , and is used to validate the mathematical modelling philosophies and construct filter observation data. After validating the performance of the filter against ground-truth data provided by the Flownex® model, the filter is demonstrated on historical plant data to illustrate its utility.
- Published
- 2022
31. Multiple Mobile Robot SLAM for collaborative mapping and exploration
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Dikoko, Boitumelo, Verrinder, Robyn, and Boje, Edward
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Map Merging ,Multi-Session Mapping ,Multiple Robot SLAM - Abstract
Over the past five decades, Autonomous Mobile Robots (AMRs) have been an active research field. Maps of high accuracy are required for AMRs to operate successfully. In addition to this, AMRs needs to localise themselves reliably relative to the map. Simultaneous Localisation and Mapping (SLAM) address the problem of both map building and robot localisation. When exploring large areas, Multi-Robot SLAM (MRSLAM) has the potential to be far more efficient and robust, while sharing the computational burden across robots. However, MRSLAM encounters issues such as difficulty in map fusion of multi-resolution maps, and unknown relative positions of the robots. This thesis describes a distributed multi-resolution map merging algorithm for MRSLAM. HectorSLAM, which is one of many single robot SLAM implementations, has demonstrated exceptional results and was selected as the basis for the MRSLAM implementation in this project. We consider the environment to be three-dimensional with the maps being constrained to a two-dimensional plane. Each robot is equipped with a laser range sensor for perception and has no information regarding the relative positioning of the other robots. The experiments were conducted both in simulation and a real-world environment. Up-to three robots were placed in the same environment with Hector-SLAM running, the local maps and localisation were then sent to a central node, which attempted to find map overlaps and merge the resulting maps. When evaluating the success of the map merging algorithm, the quality of the map from each robot was interrogated. Experiments conducted on up to three AMRs show the effectiveness of the proposed algorithms in an indoor environment.
- Published
- 2022
32. Optimisation of Rail-road Level Crossing Closing Time in a Heterogenous Railway Traffic: Towards Safety Improvement - South African Case Study
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Tshaai, Dineo Christina, Mishra, Amit, and Boje, Edward
- Subjects
Electrical Engineering - Abstract
The gravitation towards mobility-as-a service in railway transportation system can be achieved at low cost and effort using shared railway network. However, the problem with shared networks is the presence of the level crossings where railway and road traffic intersects. Thus, long waiting time is expected at the level crossings due to the increase in traffic volume and heterogeneity. Furthermore, safety and capacity can be severely compromised by long level crossing closing time. The emphasis of this study is to optimise the rail-road level crossing closing time in order to achieve improved safety and capacity in a heterogeneous railway network. It is imperative to note that rail-road level crossing system assumes the socio-technical and safety critical duality which often impedes improvement efforts. Therefore, thorough understanding of the factors with highest influence on the level crossing closing time is required. Henceforth, data analysis has been conducted on eight active rail-road level crossings found on the southern corridor of the Western Cape metro rail. The spatial, temporal and behavioural analysis was conducted to extract features with influence on the level crossing closing time. Convex optimisation with the objective to minimise the level crossing closing time is formulated taking into account identified features. Moreover, the objective function is constrained by the train's traction characteristics along the constituent segments of the rail-road level crossing, speed restriction and headway time. The results show that developed solution guarantees at most 53.2% and 62.46% reduction in the level crossing closing time for the zero and nonzero dwell time, respectively. Moreover, the correctness of the presented solution has been validated based on the time lost at the level crossing and railway traffic capacity consumption. Thus, presented solution has been proven to achieve at most 50% recovery of the time lost per train trip and at least 15% improvement in capacity under normal conditions. Additionally, 27% capacity improvement is achievable at peak times and can increase depending on the severity of the headway constraints. However, convex optimisation of the level crossing closing time still fall short in level crossing with nonzero dwell time due to the approximation of dwell time based on the anticipated rather than actual value.
- Published
- 2021
33. Detailed model for robust feedback design of main steam temperatures in coal fired boilers
- Author
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Polton, Cheriska and Boje, Edward
- Subjects
Thermo-fluid model ,Valve Position Control ,Quantitative Feedback Control ,Robust Control - Abstract
Main steam temperatures play a significant role in large coal fired power plant operation. Ideally, main steam temperatures should be accurately controlled to protect the thick wall components against long term overheating and thermal stress while meeting the design conditions at the steam turbine inlet. Although high steam temperatures are beneficial for thermal efficiency, it accelerates creep damage in high temperature components which is detrimental to the life of components. Alternatively, low steam temperatures increase the moisture content at the last stage blades of the turbine, causing the blades to deteriorate and fail. Control of the outlet steam temperature according to design conditions at variable loads is maintained via a balance between heat input (flue gas temperature and mass flow rate), evaporator outlet steam mass flow and spray water. The present control philosophy accuracy of main steam temperatures at an Eskom coal fired power plant was evaluated and compared to the latest technology and control strategies. Improving and optimizing steam temperature controls ensures design efficiency while maintaining long term plant health. The level of spatial discretization applied in simplifying the real boiler for modelling purposes was approached at a relatively high level. The intention was to model normal operating conditions and certain transients such as variable heat input and load changes to see its effect on steam temperatures and to be able to evaluate the performance of different temperature control techniques. The main outcome of this project was to design a robust control system for a dynamic model of the boiler using sets of low order linear models to account for uncertainty. The main concepts, models and theories used in the development of this dissertation include: 1) A detailed thermo-fluid model developed using Flownex to have high fidelity models of the process under varying operating conditions. This model was used to test and evaluate the robust controller design. 2) System Identification in Matlab to construct mathematical models of dynamic systems from measured inputoutput data and identify linear continuous time transfer functions under all operating conditions [1]. 3) Quantitative Feedback Theory (QFT) to design controllers for an attemperator control system at various onload operating conditions. This design was used understand the engineering requirements and seeks to design fixed gain controllers that will give desired performance under all operating conditions. 4) The design of a valve position controller to increase the heat uptake in a convective pass, thereby improving efficiency: Excessive attemperation in the superheater passes is generally associated with high flue gas temperatures which decrease thermal efficiency. Therefore, robust control of the attemperation system leads to an increase in heat uptake between the flue gas and steam in the boiler, resulting in a reduction in the flue gas temperature leaving the boiler, thus improving efficiency. The robust QFT controllers were set up using the valve position control technique and were used to confirm the improvement of control performance. The theories mentioned above were used to understand the control performance under varying plant conditions using a standard cascaded arrangement. It incorporated robust control design and engineering requirements such as bandwidth, plant life, spray water and thermodynamic efficiency. The control effort allocated to each superheaterattemperator subsystem in the convective pass was designed as a multi-loop problem.
- Published
- 2021
34. Brachiating power line inspection robot: controller design and implementation
- Author
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Shongwe, Lindokuhle and Boje, Edward
- Subjects
Engineering - Abstract
The prevalence of electrical transmission networks has led to an increase in productivity and prosperity. In 2014, estimates showed that the global electric power transmission network consisted of 5.5 million circuit kilometres (Ckm) of high-voltage transmission lines with a combined capacity of 17 million mega-volt ampere. The vastness of the global transmission grid presents a significant problem for infrastructure maintenance. The high maintenance costs, coupled with challenging terrain, provide an opportunity for autonomous inspection robots. The Brachiating Power Line Inspection Robot (BPLIR) with wheels [73] is a transmission line inspection robot. The BPLIR is the focus of this research and this dissertation tackles the problem of state estimation, adaptive trajectory generation and robust control for the BPLIR. A kinematics-based Kalman Filter state estimator was designed and implemented to determine the full system state. Instrumentation used for measurement consisted of 2 Inertial Measurement Units (IMUs). The advantages of utilising IMUs is that they are less susceptible to drift, have no moving parts and are not prone to misalignment errors. The use of IMU's in the design meant that absolute angles (link angles measured with respect to earth) could be estimated, enabling the BPLIR to navigate inclined slopes. Quantitative Feedback Control theory was employed to address the issue of parameter uncertainty during operation. The operating environment of the BPLIR requires it to be robust to environmental factors such as wind disturbance and uncertainty in joint friction over time. The resulting robust control system was able to compensate for uncertain system parameters and reject disturbances in simulation. An online trajectory generator (OTG), inspired by Raibert-style reverse-time symmetry[10], fed into the control system to drive the end effector to the power line by employing brachiation. The OTG produced two trajectories; one of which was reverse time symmetrical and; another which minimised the perpendicular distance between the end gripper and the power line. Linear interpolation between the two trajectories ensured a smooth bump-less trajectory for the BPLIR to follow.
- Published
- 2021
35. Optimal state estimation for a power line inspection robot
- Author
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Soobhug, Divij and Boje, Edward
- Subjects
Electrical Engineering - Abstract
Following a paper published by E. Boje[1], this thesis discusses the design and off-line testing of different types of Kalman filters to estimate the attitude, position and velocity of a robotic platform moving along a power line. The nature of this problem limits the use of magnetometers. Magnetic field interference from the steel pylons and steel cored conductors will affect the local magnetic field. Moreover, high frequency signals from on-board power electronic drives and induced magnetic fields due to ferromagnetic components of the robot along with aliasing, quantization effects and a low signal to noise ratio make notch filtering at 50 Hz impractical. Thus, a GPS/IMU filter solution, which uses the power line curvature and horizontal direction in measurements, to constrain the robot to the line was designed. Different types of filters were implemented; The Extended Kalman filter (EKF), the Unscented Kalman filter (UKF) and the Error State Kalman filter (ErKF). Measurements were recorded and the filters were tested offline. While all the filters tracked properly, it was found that the EKF was better in computational speed completing an iteration in 87 µs, the ErKF was second best with an average time of 120 µs for one iteration and the UKF was last with an average time of 1040 µs for one iteration. Errors between the true state and estimated state for the simulation were quantified using root mean square values (RMS). The RMS values were almost the same for the EKF and ErKF with the error for the x position at 0.81 m and z position at 0.038 m. The UKF produced RMS errors of 0.79 m for x position and 0.11 m for z position. It can be seen that the UKF is slightly better for the x position but is much worse for the z position. Overall, the GPS measurement RMS values used were 4 m and 20 m for the horizontal and vertical positions respectively. Thus, the filters brought a big improvement. However, the recommended filter is the EKF as is produced comparable or better results as compared to other filters and expends the least computational effort. A state estimator was also developed for a J.Patel’s PLIR project [2], where a brachiating version of a power line robot was modeled. The brachiation mechanism was approximated to a double pendulum and kinematics based Kalman filter was designed. Simulations of EKF and UKF were made. The EKF is still recommended as its estimates are closer to the true values and its computation time is about five times faster.
- Published
- 2018
36. Modelling, estimation and control of a twin-helicopter slung load transportation system
- Author
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Reddi, Yashren and Boje, Edward
- Abstract
The development of a control system to transport and assemble cargo using two helicopters is presented in this thesis. It is more economical to use multiple lower cost helicopters in a coordinated manner to carry cargo than to use a single high performance helicopter for the transportation task. The reason for the generally higher cost of hiring high performance helicopters, is because they are not required often, and so, remain idle for most of their lifetime. Thus, using less specialised, lower performing helicopters to share the load is cheaper. Beyond just sharing the load of the cargo, the objective in this investigation is to control the attitude such that precise placement of the cargo can be made. This objective cannot be achieved using a single helicopter, unless a sophisticated tethering mechanism is developed. The installation of wind-turbine blades, powerline towers and radio masts in remote locations, are examples of where the application of this technology may be useful. The investigation of this thesis is around modelling, estimation and control of the twinhelicopter slung load transportation system. The title reflects the investigation that was required to be done to determine whether a scheme could be realisable. To test the concept, an experimental platform was developed. A small, light-weight and high performance avionics system was designed and interfaced to the helicopters. The experimentation was done indoors, and hence, the flying volume was limited. For the purpose of feedback and analysis, a motion capture system was developed to track the position and attitude of the helicopters. A high-fidelity mathematical model of a small-scale helicopter was developed. Estimation algorithms were then developed to optimally fuse the data from the instrumentation designed. The data was then used in a system identification exercise to find the parameters that capture the dynamics of the helicopter. The full constrained model of the twin-helicopter slung load dynamics was then developed. The high-fidelity multivariable, interacting system was then linearised to generate a set of uncertain plants. Unexpected resonant modes were investigated using modal analysis to understand their source. Robust controllers were designed using Quantitative Feedback Theory (QFT) for the individual helicopter attitude and altitude loops. A solution was found for the twin-helicopter load transportation system by decoupling the plant with a static pre-compensator and then designing a decentralised QFT controller for the 6 × 6 plant. The effort of this thesis is towards the (practical) realisation of a twin-helicopter aerial crane capable of attitude control; the architecture for the industrialisation of the twin-helicopter load transportation system is proposed.
- Published
- 2018
37. Sea-state interaction based dynamic model of the Liquid Robotics' Wave Glider: Modelling and control of a hybrid multi-body vessel
- Author
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Rampersadh, Gevashkar, Verrinder, Robyn, and Boje, Edward
- Subjects
Electrical Engineering - Abstract
A new class of unmanned marine research vessels makes use of wave propulsion to minimise energy requirements during voyages. Existing models of these hybrid sea-surface and underwater craft have not considered if the platform’s interaction with the immediate surrounding sea could be incorporated to allow for more accurate navigation and path planning. To this end a detailed three-dimensional model of one such vessel, the Liquid Robotics’ Wave Glider, has been developed in this study. The multi-body system is described using DenavitHartenberg parametrisation and a Lagrangian approach is used to generate the equations of motion for the body. Physical dimensions are derived from platform measurements and from the product specification sheet, hydrodynamic factors are derived from a SolidWorks model of the system, and added mass components are determined from empirical data. Finally, the dynamic model is verified for a given sea state and multiple sea states are tested to investigate the effect on the model’s performance. The developed Wave Glider model is shown to have a realistic response when hydrodynamic factors, added mass and hydrodynamic damping forces, are included and to sea states in terms of the hydrostatic restorative response. The wave-driven propulsion provided by the hydrofoils is shown to have dependence on the sea state by running the model in an open-loop simulation. Following the model validation, a control system is developed for the Wave Glider model to allow yaw attitude control of the glider using the controllable glider rudder input. The control system is generated making use of quantitative feedback theory (QFT) methods to provide robust control for the under-actuated system. The control scheme is shown to provide suitable performance for sea states that result in variable glider velocities. The model’s performance, in terms of the average velocity, is shown to have dependence on the direction of the sea state by running the model in an open-loop simulation for multiple sea states with sinusoidal waves approaching the Wave Glider model from different directions.
- Published
- 2018
38. Dual-axis tilting quadrotor aircraft: Dynamic modelling and control of dual-axis tilting quadrotor aircraft
- Author
-
Von Klemperer, Nicholas and Boje, Edward
- Subjects
Nonlinear Control, Control Allocation, Quadrotor, UAV - Abstract
This dissertation aims to apply non-zero attitude and position setpoint tracking to a quadrotor aircraft, achieved by solving the problem of a quadrotor’s inherent underactuation. The introduction of extra actuation aims to mechanically accommodate for stable tracking of non-zero state trajectories. The requirement of the project is to design, model, simulate and control a novel quadrotor platform which can articulate all six degrees of rotational and translational freedom (6-DOF) by redirecting and vectoring each propeller’s individually produced thrust. Considering the extended articulation, the proposal is to add an additional two axes (degrees) of actuation to each propeller on a traditional quadrotor frame. Each lift propeller can be independently pitched or rolled relative to the body frame. Such an adaptation, to what is an otherwise well understood aircraft, produces an over-actuated control problem. Being first and foremost a control engineering project, the focus of this work is plant model identification and control solution of the proposed aircraft design. A higher-level setpoint tracking control loop designs a generalized plant input (net forces and torques) to act on the vehicle. An allocation rule then distributes that virtual input in solving for explicit actuator servo positions and rotational propeller speeds. The dissertation is structured as follows: First a schedule of relevant existing works is reviewed in Ch:1 following an introduction to the project. Thereafter the prototype’s design is detailed in Ch:2, however only the final outcome of the design stage is presented. Following that, kinematics associated with generalized rigid body motion are derived in Ch:3 and subsequently expanded to incorporate any aerodynamic and multibody nonlinearities which may arise as a result of the aircraft’s configuration (changes). Higher-level state tracking control design is applied in Ch:4 whilst lower-level control allocation rules are then proposed in Ch:5. Next, a comprehensive simulation is constructed in Ch:6, based on the plant dynamics derived in order to test and compare the proposed controller techniques. Finally a conclusion on the design(s) proposed and results achieved is presented in Ch:7. Throughout the research, physical tests and simulations are used to corroborate proposed models or theorems. It was decided to omit flight tests of the platform due to time constraints, those aspects of the project remain open to further investigation. The subsequent embedded systems design stemming from the proposed control plant is outlined in the latter of Ch:2, Sec:2.4. Such implementations are not investigated here but design proposals are suggested. The primary outcome of the investigation is ascertaining the practicality and feasibility of such a design, most importantly whether or not the complexity of the mechanical design is an acceptable compromise for the additional degrees of control actuation introduced. Control derivations and the prototype design presented here are by no means optimal nor the most exhaustive solutions, focus is placed on the whole system and not just a single aspect of it.
- Published
- 2018
39. Sea state estimation from inertial platform data for real-time ocean wave prediction
- Author
-
Gwatiringa, Tinashe G, Boje, Edward, and Verrinder, Robyn A
- Subjects
Electrical Engineering - Abstract
Ocean observation is vital in understanding how the oceans contribute toward climate change and other effects. This is one of many undertakings requiring a persistent presence in the oceans. These maritime activities are mainly carried out on large research vessels chartered for weeks at a time, which can be extremely costly. In addition, the data obtained when using these vessels are only short snapshots of the continual processes that occur. Recently, there has been a drive toward using Unmanned Surface Vehicles (USVs) and Unmanned Underwater Vehicles (UUVs), which can be deployed at a fraction of the cost, and provide greatly improved spatio-temporal data. The wave glider (WG) is one such autonomous marine robot used for persistent ocean research and other maritime activities, and forms the focus of this study. The WG is a low power USV/UUV hybrid that harnesses wave energy for propulsion, and has a small solar- and battery-powered thruster, and a rudder for steering. Due to effects of waves, currents, and other disturbances, the platform tends to veer off its desired path. Additionally, local sea state information is not taken into consideration while manoeuvring, hence energy extraction from ocean waves is not optimal. More sophisticated navigation algorithms operating on a per-wave strategy may improve accuracy along a specified path and maximise the energy uptake from the waves. To realise these improvements requires prediction of local wave behaviour. If one can predict what the wave field will be a short time in the future, then possible control action can be taken to efficiently navigate in the environment. Inertial measurements and wave modelling have been used to improve localisation of the WG platform directly, and predict the platform’s velocity. However there is limited work in the context of WG navigation. Hence the problem this dissertation aims to solve is the estimation and subsequent prediction of local wave behaviour. This work proposes a novel approach to estimate the sea state and hence predict short-term, local wave behaviour from inertial measurements on a slow-moving marine platform such as the WG. A Kalman filtering strategy consisting of a phase-locked loop and filter based sea state estimator is used to generate local height and angle of arrival estimates. This method offers an improvement over existing Fast Fourier Transform methods as it does not require long time series data to produce results, and enables the prediction of wave behaviour a short time into the future. The ideas are tested in simulation by generating wind waves using ocean wave models such as the Pierson Moskowitz model, and dynamic a dynamic model of the WG platform. In addition, a small scale lab experiment is carried out to verify the performance of the sea-state estimator developed. Preliminary results obtained indicate that relative wave height can be estimated on-board a marine platform, using only inertial sensors.
- Published
- 2018
40. Design, modelling and control of a brachiating power line inspection robot
- Author
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Patel, Javaad and Boje, Edward
- Subjects
Power line inspection ,Brachiating robot ,Trajectory generation ,Feedback control ,Electrical Engineering - Abstract
The inspection of power lines and associated hardware is vital to ensuring the reliability of the transmission and distribution network. The repetitive nature of the inspection tasks present a unique opportunity for the introduction of robotic platforms, which offer the ability to perform more systematic and detailed inspection than traditional methods. This lends itself to improved asset management automation, cost-effectiveness and safety for the operating crew. This dissertation presents the development of a prototype industrial brachiating robot. The robot is mechanically simple and capable of dynamically negotiating obstacles by brachiating. This is an improvement over current robotic platforms, which employ slow, high power static schemes for obstacle negotiation. Mathematical models of the robot were derived to understand the underlying dynamics of the system. These models were then used in the generation of optimal trajectories, using nonlinear optimisation techniques, for brachiating past line hardware. A physical robot was designed and manufactured to validate the brachiation manoeuvre. The robot was designed following classic mechanical design principles, with emphasis on functional design and robustness. System identification was used to capture the plant uncertainty and a feedback controller was designed to track the reference trajectory allowing for energy optimal brachiation swings. Finally, the robot was tested, starting with sub-system testing and ending with testing of a brachiation manoeuvre proving the prospective viability of the robot in an industrial environment.
- Published
- 2016
41. State estimation of a cheetah spine and tail using an inertial sensor network
- Author
-
Fisher, Callen, Patel, Amir, and Boje, Edward
- Subjects
Electrical Engineering - Abstract
The cheetah (Acinonyx jubatus) is by far the most manoeuvrable and agile terrestrial animal. Little is known, in terms of biomechanics, about how it achieves these incredible feats of manoeuvrability. The transient motions of the cheetah all involve rapid flicking of its tail and flexing of its spine. The aim of the research was to develop tools (hardware and software) that can be used to gain a better understanding of the cheetah tail and spine by capturing its motion. A mechanical rig was used to simulate the tail and spine motion. This insight may inspire and aid in the design of bio-inspired robotic platforms. A previous assumption was that the tail is heavy and acts as a counter balance or rudder, yet this was never tested. Contrary to this assumption, necropsy results determined that the tail was in fact light with a relatively low inertia value. Fur from the tail was used in wind tunnel experiments to determine the drag coefficient of a cheetah tail. No researchers have actively sought to track the motion of a cheetah's spine and tail during rapid manoeuvres via placing multiple sensors on a cheetah. This requires the development of a 3D dynamic model of the spine and tail to accurately study the motion of the cheetah. A wireless sensor network was built and three different filters and state estimation algorithms were designed and validated with a mechanical rig and camera system. The sensor network consists of three sensors on the tail (base, middle and tip) as well as a hypothetical collar sensor (GPS and WiFi were not implemented).
- Published
- 2015
42. Digital Control of a Camless Engine Using Lyapunov Approach with Backward Euler Approximation
- Author
-
Theo van Niekerk, Udo Becker, Horst Harndorf, Paolo Mercorelli, Nils Werner, Xia, Xiaohua, and Boje, Edward
- Subjects
Engineering ,Control systems ,business.industry ,Lyapunov approach ,Control engineering ,Backward Euler method ,Displacement (vector) ,Euler method ,Engine control ,symbols.namesake ,Control theory ,symbols ,Digital control ,business ,Actuator ,Actuators ,Lyapunov methods - Abstract
In this paper a modelling of a hybrid actuator is proposed. The hybrid actuator consists of a piezo, a mechanical and a hydraulic ratio displacement. This paper deals with a hybrid actuator composed by a piezo, and a hydraulic part controlled using a regulator for camless engine motor applications. The discrete control law is derived using the well-known Backward Euler method. An analysis of the Backward and Forward Euler method is also presented. Simulations with real data are shown.
- Published
- 2014
43. Joint design of stochastically safe setpoints and controllers for nonlinear constrained systems by means of optimization
- Author
-
Joris Gillis, Gregory Mainland Horn, Moritz Diehl, Boje, Edward, and Xia, Xiaohua
- Subjects
Mathematical optimization ,Engineering ,business.industry ,Stability (learning theory) ,General Medicine ,Optimal control ,Setpoint ,Nonlinear system ,symbols.namesake ,Control theory ,Backup ,symbols ,Lyapunov equation ,Robust control ,business - Abstract
Implementing complex control schemes for a mechanically fragile and expensive system can be a risky undertaking. We can reduce the operational risks by a) identifying regions of state-space where the system is far from critical system bounds and exhibits natural stability, and b) designing a backup controller that keeps the system from crashing if we venture beyond those regions. We propose to maximize the safety-margin of the system's operational bounds, using a stochastic interpretation of the algebraic Lyapunov equation. This technique allows us to find optimally safe open-loop stable setpoints of the system. Next, we propose to add the parameters of a linear output feedback controller as optimization variables, such that setpoint and controller are jointly designed to yield the safest operational regimes. We demonstrate these methods on the application of rotational launch of tethered airplanes for power-generation. ispartof: pages:1637-1642 ispartof: Proceedings of the 19th IFAC World Congress vol:47 issue:3 pages:1637-1642 ispartof: World Congress of the International Federation of Automatic Control location:Cape Town, South Africa date:24 Aug - 29 Aug 2014 status: published
- Published
- 2014
44. Optimizing safety supervisors for wind turbines using barrier certificates
- Author
-
Laurijsse, M., Wisniewski, Rafal, Weiland, S., Boje, Edward, and Xia, Xiaohua
- Subjects
Wind turbines ,Safety supervisor ,Barrier certificates ,Safety analysis ,Compositional ,Fault detection ,Sum of squares - Abstract
To avoid structural damage, a wind turbine is equipped with a safety supervisor that triggers an emergency shutdown procedure in case of internal faults or large wind gusts. This paper leverages the (compositional) barrier certificate framework for the design and optimization of such a supervisor. The problem is formulated as a sum of squares problem and is solved using semi-definite programming. Both a direct and compositional approach are successfully implemented and verified for the NREL 5MW reference turbine. In conclusion, the methods derived in this paper are indeed viable for the syntheses and optimization of safety systems for future wind turbines.
- Published
- 2014
45. Dynamic positioning of a diver tracking surface platform
- Author
-
Antonio Vasilijević, Đula Nađ, Zoran Vukić, Nikola Mišković, Boje, Edward, and Xia, Xiaohua
- Subjects
Heading (navigation) ,Engineering ,business.industry ,Global Positioning System ,Dynamic positioning ,Unmanned marine vehicles ,Marine system navigation ,guidance and control ,Filter (signal processing) ,Focus (optics) ,business ,Tracking (particle physics) ,Omnidirectional antenna ,Simulation ,Field (computer science) - Abstract
This paper presents experimental results obtained on an autonomous omnidirectional surface marine platform, developed at the University of Zagreb, during two-week field trials in Murter, Croatia. We focus on results that are a part of the second phase of research on the platform that is intended to be used as a diver tracking platform. This phase includes experimental verification of the control and dynamic positioning (DP) algorithms performed in real environmental conditions, where external disturbances and sensor characteristics have significant influence on the vehicle behaviour. Specifically, we demonstrate 1) experimental results showing successful heading control of the overactuated marine platform even in cases when the platform is performing simultaneous omnidirectional motion; 2) experimental results demonstrating the quality of the DP algorithm performance, and 3) how GPS update frequency influences the quality of DP performance and the quality of the commanded control signal with the navigation filter that uses only GPS measurement and an uncoupled dynamic model of the omnidirectional marine platform.
- Published
- 2014
46. Microvia fill process boundary control
- Author
-
Tenno, Robert, Pohjoranta, Antti, Boje, Edward, and Xia, Xiaohua
- Subjects
spatially distributed systems ,monitoring ,manufacturing ,modeling - Abstract
This paper presents an exponentially stabilizing boundary control for the microvia fill process. The control accounts for the mass balance of the copper ions in the electrolyte and for the surface mass balance of the deposition-blocking additives, both modeled with a diffusion mass transfer model in a shape changing domain. With simulations based on real-world data, it is shown that by applying the control, the microvia fill process can be speeded up (in the example case by ca. 15%) without endangering product output quality
- Published
- 2014
47. Trajectory Generation for Assembly Tasks Via Bilateral Teleoperation
- Author
-
Jang Ho Cho, Rolf Johansson, M. Mahdi Ghazaei Ardakani, Anders Robertsson, Boje, Edward, and Xia, Xiaohua
- Subjects
Engineering ,Natural interaction ,business.industry ,Robotics ,Control engineering ,ComputerApplications_COMPUTERSINOTHERSYSTEMS ,Control Engineering ,Operator (computer programming) ,Control theory ,Teleoperation ,Trajectory ,Robot ,Artificial intelligence ,business ,Simulation - Abstract
in Undetermined For assembly tasks, the knowledge of both trajectory and forces are usually required. Consequently, we may use kinesthetics or teleoperation for recording human demonstrations. In order to have a more natural interaction, the operator has to be provided with a sense of touch. We propose a bilateral teleoperation system which is customized for this purpose. We introduce different coordinate frames to make the design of a 6-DOF teleoperation straightforward. Moreover, we suggest using tele-admittance, which simplifies instructing the robot. The compliance due to the slave controller allows the robot to react quickly and reduces the risk of damaging the workpiece.
- Published
- 2014
48. Model Predictive Control of Buoy Type Wave Energy Converter
- Author
-
Mahdi Teimouri Sichani, Mohsen Soltani, Mahmood Mirzaei, Boje, Edward, and Xia, Xiaohua
- Subjects
Engineering ,Buoy ,business.industry ,Electric generator ,General Medicine ,Sea state ,Optimal control ,law.invention ,Power (physics) ,Model predictive control ,Electricity generation ,Optimal operation and control of power systems ,law ,Control theory ,Control of renewable energy resources ,business ,Modeling and simulation of power systems - Abstract
The paper introduces the Wavestar wave energy converter and presents the implementation of model predictive controller that maximizes the power generation. The ocean wave power is extracted using a hydraulic electric generator which is connected to an oscillating buoy. The power generator is an additive device attached to the buoy which may include damping, stiffness or similar terms hence will affect the dynamic motion of the buoy. Therefore such a device can be seen as a closed-loop controller. The objective of the wave energy converter is to harvest as much energy from sea as possible. The straight forward solution to this maximization problem is achieved by maximizing the instantaneous range of motion of the buoy. The buoy as a single degree of freedom oscillator will undergo its maximum movements when it is in resonance with the sea state. Hence the best solution to the problem is achieved by forcing this condition. In the paper the theoretical framework for this principal is shown. The optimal controller requires information of the sea state for infinite horizon which is not applicable. Model Predictive Controllers (MPC) can have finite horizon which crosses out this requirement. This approach is then taken into account and an MPC controller is designed for a model wave energy converter and implemented on a numerical example. Further, the power outtake of this controller is compared to the optimal controller as an indicator of the performance of the designed controller.
- Published
- 2014
49. Fault Detection and Load Distribution for the Wind Farm Challenge
- Author
-
Borchersen, Anders Bech, Larsen, Jesper Abildgaard, Stoustrup, Jakob, Boje, Edward, and Xia, Xiaohua
- Subjects
wind farm ,Parameter estimation ,Wind ,fault-tolerant control ,Fault detection - Abstract
In this paper a fault detection system and a fault tolerant controller for a wind farm model is designed and tested. The wind farm model is taken from the wind farm challenge which is a public available challenge where a wind farm consisting of nine turbines is proposed. The goal of the challenge is to detect and handle different faults occurring in the individual turbines on farm level.The fault detection system is designed such that it takes advantage of the fact that within a wind farm several of the turbines will be operating under similar conditions. To enable this the turbines are grouped into several groups of similar turbines, then the turbines within each group are used to generate residuals for the turbines in the group. The generated residuals are then evaluated using dynamical cumulative sum. The designed fault detection system is cable of detecting all three fault types occurring in the model. All the detections are not within the requirement of the challenge thus room for improvement.To take advantage of the fault detection system a fault tolerant controller for the wind farm has been designed. The fault tolerant controller is a dispatch controller which is estimating the possible power at each individual turbine, using these estimates to set the reference to the turbines accordingly. The fault tolerant controller has been compared to the reference controller from the challenge. And the fault tolerant controller is better than the reference controller on all measures both under normal and faulty conditions.Thus a fault detection system and a fault tolerant controller has been designed and combined. The fault tolerant control system has then been tested and compared to the reference system and shows improvement on all measures.
- Published
- 2014
50. Quasi-steady state aerodynamics of the cheetah tail.
- Author
-
Patel A, Boje E, Fisher C, Louis L, and Lane E
- Abstract
During high-speed pursuit of prey, the cheetah (Acinonyx jubatus) has been observed to swing its tail while manoeuvring (e.g. turning or braking) but the effect of these complex motions is not well understood. This study demonstrates the potential of the cheetah's long, furry tail to impart torques and forces on the body as a result of aerodynamic effects, in addition to the well-known inertial effects. The first-order aerodynamic forces on the tail are quantified through wind tunnel testing and it is observed that the fur nearly doubles the effective frontal area of the tail without much mass penalty. Simple dynamic models provide insight into manoeuvrability via simulation of pitch, roll and yaw tail motion primitives. The inertial and quasi-steady state aerodynamic effects of tail actuation are quantified and compared by calculating the angular impulse imparted onto the cheetah's body and its shown aerodynamic effects contribute to the tail's angular impulse, especially at the highest forward velocities., Competing Interests: The authors declare no competing or financial interests., (© 2016. Published by The Company of Biologists Ltd.)
- Published
- 2016
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