Department of Mechanical and Mechatronic Engineering

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Browsing Department of Mechanical and Mechatronic Engineering by Subject "Actuators"

Now showing 1 - 4 of 4
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    Augmentation of the actuator-disk method for low-pressure axial flow fan simulation.
    (Stellenbosch : Stellenbosch University, 2024-02) Venter, AJ; Owen, Michael ; Muiyser, Jacques; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Actuator-disk rotor models are an invaluable simulation tool for cost-effective turbomachinery simulation. Actuator-disk models implicitly represent turbomachine rotors as momentum sources where the source term magnitude is determined from classical two-dimensional blade-element theory (BET) force calculations. Actuator-disk models accordingly require appropriate lift and drag coefficients as input to complete the force calculations. Conventional actuator-disk models utilize standard two-dimensional airfoil coefficient data, but this limits the accuracy of the models to only a small operating window where the bulk of the flow over the rotor itself is principally two-dimensional. This, consequently, limits the application of traditional actuator-disk models in industrial system analyses where complex flow environments prevail. This study considers the particular example of low-pressure axial flow fans, widely applied in thermoelectric air-cooled condenser (ACC) systems. ACCs are a key water-conservative cooling solution to the thermoelectric power industry, yet their operation is beset by inefficiencies and corresponding high operating costs. Given the scale of ACC systems, numerical investigations are forced to rely on simplified implicit fan models like actuator-disk rotor models, which provide limited approximations of actual ACC fan performance over a wide range of flow conditions. Expanding the usable window of actuator-disk axial fan models is therefore vital to providing an enhanced capacity to robustly analyse and ultimately improve ACC systems (and other industrial cooling fan systems alike). To realize this enhanced analysis capability, a new means of appropriately defining the actuator-disk model input coefficient data is required. The input coefficient data needs to appropriately reflect actual fan blade behaviour in a three-dimensional rotating context. Physical fan blade behaviour, however, has not been comprehensively investigated, and the multi-dimensional effects of rotation and blade solidity remain somewhat obscure. This study therefore sets out to define generalizable axial fan behaviour and to use the newly acquired insight to fabricate new coefficient formulations. This study constitutes a numerical analysis in which two low-pressure axial flow fans are both explicitly (full, solid rotating fan geometry) and implicitly simulated. Novel insights into generalizable aerodynamic behaviour of axial flow fans at off design operating conditions are presented and key details on the underlying phenomena are uncovered. Furthermore, this study rigorously explores the feasible potential of the actuator-disk method for axial flow fan simulation and ultimately proposes its revised coefficient formulation. The augmented actuator-disk method (AADM) is shown to more accurately simulate axial fan performance compared to existing model variants, and to resolve flow fields that are more representative of the physical case – an important feature for ACC and other industrial heat exchanger system analyses. Over a wide range of axisymmetric operating conditions (and across both considered fan types), the AADM is shown to approximate reference static pressure rise results with a maximum error of 10%, shaft power results within 8% and blade force magnitudes within 10%, thus offering a marked improvement in comprehensive accuracy relative to existing models.
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    The development of a system that emulates percussion to detect the borders of the liver
    (Stellenbosch : University of Stellenbosch, 2009-03) Rauch, Hanz Frederick; Scheffer, C.; Van Rooyen, G-J.; University of Stellenbosch. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    Percussion is a centuries old bedside diagnostic technique that is used to diagnose various conditions of the thorax and abdomen, among these, abnormalities of the liver. The physician taps the patient’s skin in the area of interest to determine the qualities or presence of the underlying tissue or organ, by listening to the generated sound. The research contained in this thesis views percussion as a system identification method which uses an impulse response to identify the underlying system. A design employing an electromagnetic actuator as input pulse generator and accelerometer as impulse response recorder was motivated and built. Tests were performed on volunteers and the recorded signals were analysed to find methods of identifying the presence of the liver from these signals. The analyses matched signals to models or simply extracted signal features and matched these model parameters or signal features to the presence of the liver. Matching was done using statistical pattern recognition methods and the true presence of the liver was established using MR images. Features extracted from test data could not be matched to the presence of the liver with sufficient confidence which led to the conclusion that either the test, apparatus or analysis was flawed. The lack of success compelled a further test on a mock-up of the problem – a silicone model with an anomaly representing the organ under test. Results from these tests showed that signals should be measured further from the actuator and the approach followed during this test could lead to the successful location of the anomaly and discrimination between subtle differences in the consistency thereof. It is concluded that further research should aim to first validate percussion as performed by the physician and increase complexity in a phased manner, validating results and apparatus at each step. The approach followed was perhaps too bold in light of the lack of fundamental understanding of percussion and the underlying mechanisms.
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    An electric actuator selection aid for low cost automation
    (Stellenbosch : University of Stellenbosch, 2008-03) Egbuna, C. Chukwudi; Basson, A. H.; University of Stellenbosch. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    Low Cost Automation (LCA) is of immense importance to industry, and even more so for small scale industries. In implementing LCA determining cost effective and efficient actuator alternatives present challenges for design engineers. Most often decisions are experiential or entirely based on manufacturer recommendations. Experience based decisions are most often biased with respect to the engineers’ knowledge. Similarly, manufacturer recommendations are restricted to their own products and are as such also biased. Either way, sub-optimum drive alternatives may sometimes be chosen. This demonstrates the need for making better informed decisions based on more than experience and what is available for use. This thesis reports the development of an electric actuator selection procedure and aid for use in the early layout design phase. It provides readily accessible information on technically viable actuator options. Experiential knowledge of experts in the field, commercial information, as well as data obtained from experimentation was used in its development. Being orientated towards LCA, the procedure has been targeted at the application of electric motors and their associated control technologies but can be extended to hydraulic, pneumatic and other actuators. In achieving a wider applicability of the selection aid, a generic set of actuator properties descriptive of most actuators was formulated. An AC drives control evaluation was conducted for developing the selection procedure and aid. It provided a means to validate some selection aid rules associated with actuator controllability. Quantitative data on speed and positioning accuracies of common AC three phase motors and their associated inverter technologies were the targeted results of the experimentation.
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    A framework for the design of soft pneumatic actuators using computational tools.
    (Stellenbosch : Stellenbosch University, 2024-02) Ligthart, Philip Frederik; Venter, MP; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Soft pneumatic actuators o er significant potential for advanced robotics due to their application versatility as a result of their material compliance. Their widespread adoption is, however, hindered by the difficulty in designing them. This thesis explores the development of a hierarchical design framework for soft pneumatic actuators by leveraging designer intuition and computational tools. The framework integrates finite element analysis, meta-modelling, optimisation, and parallel computing techniques to efficiently design soft pneumatic actuators. By dividing the design process into distinct hierarchical levels, the framework simplifies the complexities associated with soft robot design. In demonstrating the framework's effectiveness, two case studies are presented. The design of a bending actuator and the design of asymmetrical motion actuators. These studies not only validate the framework but also showcase its versatility and adaptability in creating diverse actuator designs. In both design case studies, good-performing actuators are designed through the framework. Further emphasising the framework's capabilities is the use of meta-models, such as radial basis functions and neural networks, which significantly enhance the design process. These meta-models, developed through various strategies, demonstrate the potential for reusability and the efficient leveraging of finite element analyses which is otherwise computationally prohibitive.