Browsing by Author "Van der Merwe, Johan"
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- ItemContinued development of a joint-type knee wear simulator(Stellenbosch : Stellenbosch University, 2012-03) Van der Merwe, Johan; Scheffer, C.; Muller, C.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical & Mechatronic Engineering.ENGLISH ABSTRACT: This thesis is concerned with the continued development of the Stellenbosch University joint-type knee wear simulator. Initially, information regarding simulators from the literature and commercial entities was collected to provide a knowledge base for current and future work. To further the design of the simulator itself, electronic hardware and software subsystems was developed and evaluated during experimental testing procedures. National Instruments’ cDAQ 9174 data acquisition unit was deemed inadequate for real-time inputoutput control, though proved sufficient for signal capturing purposes in conjunction with LabView software. Furthermore, the various servo-pneumatic sub-circuits’ individual ability to conform to the ISO 14243 series standards’ protocol led to the estimation of measurable performance criteria and the application to a single circuit for illustration. The anterior/posterior actuation circuit in question demonstrated adequate performance for the cases where the piston’s rod was respectively fixed and free to move. In-silico modelling and identification of the relevant servo-pneumatic components then commenced, with the valve and cylinder chamber models yielding adequate estimates of the recorded data. The identified quasi-static friction model proved sensitive to transient effects present within the system, resulting in performance deterioration of the integrated model. Sufficiently accounting for these effects would result in the emergence of the sub-circuit’s model as an invaluable tool in terms of control system development, prediction of the simulator’s behaviour and subsequent design recommendations. Future work therefore concerns improvement, identification and integration of the various sub-circuit models to fully exploit the aforementioned advantages.
- ItemDevelopment of a patient-specific unicompartmental knee replacement(Stellenbosch : Stellenbosch University, 2018-03) Van der Merwe, Johan; Van den Heever, David Jacobus; Stellenbosch University. Faculty of Engineering, Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: Patient-specific Unicompartmental Knee Replacements (UKRs) could potentially restore an Osteoarthritic (OA) knee closer to its pre-pathological state than off-the-shelf products. Nevertheless, the current state-of-the-art is still heavily reliant on a technician's interpretation and skill in order to reproduce healthy geometries. This dissertation therefore focused on developing a reliable, semi-automated approach to implant design. Inter-patient variability and inter- and intra-observer agreement and reliability was studied for a set of landmarks defined on the distal femur and proximal tibia. This provided necessary input to downstream processes. The variation in a populations' knees was captured by Statistical Shape Models (SSMs), and the subsequent use of a Graphical User Interface (GUI) was investigated to incorporate local constraints as part of sparse SSM estimation. These estimates formed the base of the implants' femoral components, and together with matching metal-backed, motion-guided tibial components were created using automated B-spline parametrisations. Sixteen unseen knees were used as test candidates and it was found that the resulting condyle estimations were sufficiently accurate, while the generated implant components matched normal knee anatomy. Both the GUI-based estimation and the automated design process showed good repeatability. The implant design presented here is ready for pre-clinical testing and evaluation.
- ItemFiat Lux : navigating chaos through sensing leadership(Pieter de Waal Neethling Trust, 2018) Van der Merwe, JohanThis article provides an overview of change management strategies described in business science. From the distinctions made, it becomes clear that change is all-pervasive and the result of complex interactions within and between the internal and external environments of organizations and communities. Complexity theory is subsequently considered as a better vantage point from where a response to change may be informed. The leadership style to correspond to this new reading of change needs to be that of “transcending leadership” where sensing and sense-making skills are honed to sense emerging meaning in organizations, in interpersonal relationships and through intrapersonal reflection. Instead of “making” change happen, the new leadership “lets” things happen, sensing the connections between emerging events in the context and creating a level of readiness to find the potential meaning in what may usually have been perceived as mere chaos. The creation narrative and a new reading of chaos as possibility provide Judeo-Christian sources of spirituality in this regard. Other Biblical narratives are cited to show in which way different change management frameworks can be applied to the respective narratives, but also how sensing and sense-making remain the common leadership attributes in successfully navigated change.
- ItemParametric mandible reconstruction plate(Southern African Institute for Industrial Engineering, 2020) Giddy, Brett; Van der Merwe, JohanENGLISH ABSTRACT: This study investigated the feasibility of a parametric mandible reconstruction plate in order to reduce surgical lead time, improve fit, and reduce residual stresses. The parametric plates were generated on the basis of simulated cephalometric measurements. A finite element analysis and a reconstruction plate/mandible fit test were performed on several combinations to determine whether the parametric plate provided a suitable alternative to conventional reconstruction plates in terms of fit and structural performance. The results indicated that the parametric plate is structurally superior to a conventional plate. The comparison test indicated that the parametric plate provides a reasonable approximation of mandible geometry.