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Internal balance calibration and uncertainty estimation using Monte Carlo simulation

- Bidgood, Peter Mark

Authors: Bidgood, Peter Mark
Date: 2014-03-18
Subjects: Wind tunnel balances - Calibration - Simulation methods , Monte Carlo method
Type: Thesis
Identifier: uj:4379 , http://hdl.handle.net/10210/9728
Description: D.Ing. (Mechanical Engineering) , The most common data sought during a wind tunnel test program are the forces and moments acting on an airframe, (or any other test article). The most common source of this data is the internal strain gauge balance. Balances are six degree of freedom force transducers that are required to be of small size and of high strength and stiffness. They are required to deliver the highest possible levels of accuracy and reliability. There is a focus in both the USA and in Europe to improve the performance of balances through collaborative research. This effort is aimed at materials, design, sensors, electronics calibration systems and calibration analysis methods. Recent developments in the use of statistical methods, including modern design of experiments, have resulted in improved balance calibration models. Research focus on the calibration of six component balances has moved to the determination of the uncertainty of measurements obtained in the wind tunnel. The application of conventional statistically-based approaches to the determination of the uncertainty of a balance measurement is proving problematical, and to some extent an impasse has been reached. The impasse is caused by the rapid expansion of the problem size when standard uncertainty determination approaches are used in a six-degree of freedom system that includes multiple least squares regression and iterative matrix solutions. This thesis describes how the uncertainty of loads reported by a six component balance can be obtained by applying a direct simulation of the end-to-end data flow of a balance, from calibration through to installation, using a Monte Carlo Simulation. It is postulated that knowledge of the error propagated into the test environment through the balance will influence the choice of calibration model, and that an improved model, compared to that determined by statistical methods without this knowledge, will be obtained. Statistical approaches to the determination of a balance calibration model are driven by obtaining the best curve-fit statistics possible. This is done by adding as many coefficients to the modelling polynomial as can be statistically defended. This thesis shows that the propagated error will significantly influence the choice of polynomial coefficients. In order to do this a Performance Weighted Efficiency (PWE) parameter is defined. The PWE is a combination of the curve-fit statistic, (the back calculated error for the chosen polynomial), a value representing the overall prediction interval for the model(CI_rand), and a value representing the overall total propagated uncertainty of loads reported by the installed balance...
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An investigation into the relationship between performance and product/supply chain alignment in the clothing and textile industry in Gauteng, South Africa

- Chiromo, Forbes

Authors: Chiromo, Forbes
Date: 2018
Subjects: Clothing trade - South Africa - Gauteng - Management , Textile industry - South Africa - Gauteng - Management , Business logistics - South Africa - Gauteng
Language: English
Type: Doctoral (Thesis)
Identifier: http://hdl.handle.net/10210/293746 , uj:31947
Description: D.Phil. (Mechanical Engineering) , Abstract: This study investigated the relationship between performance and product/supply chain alignment in the clothing and textile industry in the Gauteng Province of South Africa. It was conducted to validate Stavrulaki and Davis’s (2010) framework that unequivocally claims that companies that perform well are those aligned with supply chains. The framework integrates product characteristics, supply chain processes (production and logistics) and strategic focus required to source raw material, produce the products and deliver finished products to customers. It builds on design-to-order, assemble-to-order, make-to-order and build-to-stock supply chains. The study was cross-sectional, empirical, quantitative, non-experimental and pre-structured. It was guided by clear and specific research questions, a clear conceptual framework, a pre-planned design, clear data collection and a thorough data analysis process. The sample frame for this study was comprised of clothing and textile companies in the manufacturing segment. Raw material suppliers and retailers were excluded. A non-probability purposeful sample was drawn from clothing and textile companies operating in the Gauteng. The data were collected through a self-administered questionnaire comprised of closed questions. The analysis was conducted using IBM SPSS statistics version 22. The statistical methods used to capture and analyse the data included descriptive statistical analysis, factor analysis, reliability testing (Cronbach’s alpha) and the Mann-Whitney U test. Besides describing the influence of product/supply chain alignment on company performance, the study explained how and why the alignment influenced performance in the sector. The performance analysis section collected findings on product characteristics, supply chain characteristics, product/supply chain alignment, factor analysis and reliability tests. Since the researcher used a purposeful sampling technique, the two supply chain groupings (one with product/supply chain alignment and the other without) were compared on the basis of non-parametric tests. This study used the Spearman Rank Order correlation to determine the magnitude of performance ranked position of one performance measure relative to the ranked performance position of the other performance factors...
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Binary image features designed towards vision-based localization and environment mapping from micro aerial vehicle (MAV) captured images

- Cronje, Jaco

Authors: Cronje, Jaco
Date: 2012-10-24
Subjects: Binary image , Micro aerial vehicle captured images , Remote sensing - Data processing , Micro air vehicles , Mobile geographic information systems , Imaging systems
Type: Thesis
Identifier: http://ujcontent.uj.ac.za8080/10210/387081 , uj:10415 , http://hdl.handle.net/10210/7881
Description: M.Phil. , This work proposes a fast local image feature detector and descriptor that is im- plementable on a GPU. The BFROST feature detector is the first published GPU implementation of the popular FAST detector. A simple but novel method of feature orientation estimation which can be calculated in constant time is proposed. The robustness and reliability of the orientation estimation is validated against rotation invariant descriptors such as SIFT and SURF. Furthermore, the BFROST feature descriptor is robust to noise, scalable, rotation invariant, fast to compute in parallel and maintains low memory usage. It is demonstrated that BFROST is usable in real-time applications such as vision-based localization and mapping of images captured from micro aerial platforms.
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The design and development of a platform type wind tunnel balance with optical fibre bragg grating sensors

- De Ponte, Jules David

Authors: De Ponte, Jules David
Date: 2015
Subjects: Wind-pressure , Wind tunnel balances , Wind tunnels - Design and construction , Strain gages
Language: English
Type: Masters (Thesis)
Identifier: http://hdl.handle.net/10210/56142 , uj:16335
Description: Abstract: The requirements which a wind tunnel balance must meet are becoming increasingly stringent. The wind tunnel testing community is calling for balances which; offer higher resolution, are stiffer, are immune to electro-magnetic interference (EMI) and provide compensation for thermal effects. It is proposed that in order to meet these requirements, balance design philosophy needs to be further expanded to include different manufacturing methods, materials and sensor technology. This study investigates the design and development of a six component wind tunnel platform balance incorporating Optical fibre Bragg grating (OFBG) sensors. Under an applied load, conventional balances measure strain at the surface of a material, by means of a foil strain gauge. For this reason, sections of material in the balance are purposely made thin, in order for the strain in that section to be sufficiently high to offer adequate resolution. This may compromise the stiffness of the balance. A platform balance is designed which incorporates OFBG sensors using the two-groove method of strain measurement. The optical fibres are spanned between two probes. One probe protrudes from the metric end of the balance, the other protrudes from the fixed end. Under an applied load, the gap between the two protrusions will change, which will induce a strain in the fibre Bragg grating spanning it. This strain in the fibre Bragg grating will cause the Bragg wavelength to shift proportionally to the magnitude of the strain in the fibre. Therefore, the balance is designed around the idea of measuring displacements within the structure of the balance. This displacement is comparatively larger than the deformation at the surface of a material. Therefore, strain induced in the fibre spanning the gap would be larger than the strain at the surface of the material. The balance to which these fibres are bonded can be made stiffer, while still offering a comparable relative resolution. The two-groove method uses two fibres to measure one load component. Each fibre is part of a pair for strain measurement. Each fibre Bragg grating has a different reference Bragg wavelength. These are spanned across two separate gaps. The balance has been designed such that, under an applied load, one fibre of a strain measurement pair experiences a tensile strain, and the other experiences a compressive strain. The final output is determined by calculating the change in difference between the two fibres’ respective Bragg wavelengths. This method compensates for unwanted force and thermal interactions... , M.Ing. (Mechanical Engineering Science)
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Theoretical limits to risk management models : model risk

- Dos Santos, Marco Paulo Ferreira

Authors: Dos Santos, Marco Paulo Ferreira
Date: 2015-10-07
Subjects: Risk management , Risk perception , Business planning
Type: Thesis
Identifier: uj:14260 , http://hdl.handle.net/10210/14712
Description: M.Ing. (Engineering Management) , This mini-dissertation provides an overview of enterprise risk management and its components, while focusing on risk analysis and risk models. Since all entities face uncertainty with respect to the aspects that they interact with, enterprise risk management aims to maximize value to stakeholders. One of the tools used in the risk assessment component of enterprise risk management is a quantitative assessment technique called risk modelling. Risk modelling allows various risks to be evaluated by observing their effects on simulation outputs. Decision making under uncertainty has become heavily reliant on risk models, resulting in more complex models being formulated and utilized. As such, the risks associated with the modelling of risks are becoming increasingly more pervasive in risk management and whose effects are just as severe (if not more so, due to their lack of awareness). A more in depth examination of model risk is performed and discussed in order to highlight its lack of awareness, extent and implications, and theoretical limits in risk modelling. Using this background information, the analysis of models used in literature for pricing in telecommunications wireless mesh networks is conducted in order to evaluate their model risks. This analysis shows that very few publications acknowledge the shortcomings of their models, let alone evaluate or discuss them in any way. Further, this analysis shows that some of the models and their assumptions produce pointless results. A simple investigation of the risks associated with their models would have produced results that are more conclusive and substantiatable, and with less flaws. Although the model risk analysis has been performed on models that simulate certain billing aspects of telecommunication wireless mesh networks, the model risk a alysiscan just as easily be performed on any other models or risk models. The aim of this mini-dissertation is to provide an overview of model risk and its impact, and also highlight the importance of including the management of model risk in the enterprise risk management process.
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Benchmarking a neural network forecaster against statistical measures

- Herman, Hilde

Authors: Herman, Hilde
Date: 2014-09-16
Subjects: Forecasting - Data processing , Neural networks (Computer science) , Artificial intelligence , Benchmarking (Management)
Type: Thesis
Identifier: uj:12312 , http://hdl.handle.net/10210/12098
Description: M.Ing. (Mechanical Engineering) , The combination of non-linear signal processing and financial market forecasting is a relatively new field of research. This dissertation concerns the forecasting of shares quoted on the Johannesburg Stock Exchange by using Artificial Neural Networks, and does so by comparing neural network results with established statistical results. The share price rise or fall are predicted as well as buy, sell and hold signals and compared to Time Series model and Moving Average Convergence Divergence results. The dissertation will show that artificial neural networks predict the share price rise or fall with less error than statistical models and yielded the highest profit when forecasting buy, sell and hold signals for a particular share.
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Contribution to spectrum management in the dynamic spectrum utilization

- Mavungu, Masiala

Authors: Mavungu, Masiala
Date: 2017
Subjects: Stochastic control theory , Dynamic programming , Stochastic models
Language: English
Type: Doctoral (Thesis)
Identifier: http://hdl.handle.net/10210/242822 , uj:25058
Description: D.Phil. (Engineering Management) , Abstract: This thesis deals with computation of pricing policies to maximize the profit of a Telecommunication Regulator using Dynamic Spectrum Utilization Technology. In order to improve the spectrum utilization, a Telecommunication Regulator suggests the migration from Static to Dynamic Spectrum Utilization. Some studies were conducted to analyze the dynamic spectrum utilization models and architectures and then obtain all the necessary informations on the interactions between the spectrum owner and the spectrum users and the interactions between spectrum users accessing spectrum. Game Theory was used to rigorously analyze such interactions and then a Stochastic Differential Stackelberg Game model was developed. Stochastic Optimal Control Theory was used to investigate the obtained Game Theory model. By considering price as a stochastic control variable, numerical and computational pricing strategies were computed to approximate the pricing policy maximizing the Telecommunication Regulator profit under certain hypothesis. Since, the Telecommunication Regulator must always dream big, to manage the interactions between the spectrum scarcity and the demand increase from users, to deal with the fact that demand may be superior to supply, auction was suggested and investigated. Some optimal auction design and optimal bidding strategies were presented...
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The effect of surface finish on fatigue life of aluminium alloy during uniaxial fatigue loading

- McDuling, Christoffel Petrus

Authors: McDuling, Christoffel Petrus
Date: 2018
Subjects: Aluminum alloys - Fatigue , Aluminum alloys - Mechanical properties , Aluminum alloys - Testing
Language: English
Type: Masters (Thesis)
Identifier: http://hdl.handle.net/10210/297340 , uj:32413
Description: Abstract: In this study the effects of surface finish on the fatigue life of 7449-T7651 aluminium alloy were evaluated as a result of different surface roughness conditions polished in the longitudinal direction of the specimens. The efficiency of the boundary parameters of surface roughness as well as the surface roughness techniques was also investigated. The surface roughness and residual stress were characterized using contact profilometry and x-ray diffraction techniques respectively. The 7449-T7651 aluminium alloy round specimens were subjected to uniaxial constant amplitude cyclic loading using a R-ratio of 0.1. Load controlled high cycle fatigue testing was carried out at both low and high amplitudes covering four surface roughness conditions. The decrease in peak alternating stress from 360 MPa to 320 MPa showed a significant increase in fatigue life, however at 360 MPa the effect of surface roughness and residual stress on fatigue life was unfounded mainly due to the effect of adequate plastic strain amplitude which reduces the crack initiation process and increase the crack growth process in relation to total fatigue life. Test results of the specimens, tested at 320 MPa indicated that a decrease of surface roughness resulted in an increase in the fatigue life. The test results further showed that a surface roughness more than 0.2 μm Ra has a detrimental effect on fatigue life and below 0.2 μm Ra the roughness effect on fatigue life is less evident mainly because of lower external surface and residual stress concentrations. The effectiveness of the arithmetic mean roughness (Ra) and the mean peak-to-valley height (Rz) was found to be questionable in order to accurately detect the maximum valley depth on the surface layer where microcrack nucleation is most likely to initiate. The roughness measurements covering a small localized area of the total surface in the longitudinal direction of the specimen was found to be inadequate and not representative enough for the use of semi-empirical fatigue life assessment methods in order to calculate the surface stress concentration factor Kt, which require the asperity root radius ρ of the surface topography. Traditional stylus-based methods were not sensitive enough and it is advisable to use optical methods like white light interferometry or perhaps tomography for surface topography measurement which is significantly more accurate at 0.1nm resolution. For the purpose of determining the effect of the surface layer on the fatigue crack initiation process it is recommended that residual stress measurement to be conducted after final polishing and should represent the full circumference of the gauge section of round specimens. , M.Tech. (Mechanical Engineering)
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Direction control of an underactuated snake robot using amplitude modulation

- Moloi, Brian Lehlohonolo

Authors: Moloi, Brian Lehlohonolo
Date: 2017
Subjects: Robots - Control systems , Autononous robots , Amplitude modulation , Robotics
Language: English
Type: Masters (Thesis)
Identifier: http://hdl.handle.net/10210/242281 , uj:24985
Description: M.Ing. (Mechanical Engineering) , Abstract: This dissertation presents the solution to the direction control problem of an underactuated snake robot using the amplitude modulation method. The amplitude modulation method allows for the control of the joint relative angles during the serpentine movement to produce friction forces that propel the snake robot to the desired path. In this dissertation, the snake robot equations of motion derived from the Euler-Lagrange method utilizing the joint relative angles as the generalized coordinates to decouple the equations into actuated and unactuated equations. The partial feedback linearization technique transformed the equations of motion into the control affine nonlinear system, where geometric control techniques proved the controllability of the snake robot subjected to the Coulomb friction law represented by an arctangent function. The solutions to the equations of motion calculated from the Mathematica software for a given control law showed the state space evolution of the snake robot performing the serpentine gait. In the simulation results (without the direction control), the snake robot moved forward after few seconds from starting and its direction changed. The change in direction was due to the approximated Coulomb friction law considered using the arctangent function. This resulted in zero friction forces at the beginning, zero propelling force, and thus the snake robot did not move for some time. However, at this point, the joint angles changed according to the control law employed and the direction of the robot changed. Consequently, the snake robot was unable to track the desired straight path due to the change in direction at the beginning. Furthermore, the dissertation considered the solution to the direction control problem using the amplitude modulation and the joint offset angle controllers. In the simulation results, both controllers stabilize the snake robot to its desired path. The direction control based on controlling the head angle determined from the line-of-sight guidance law. The guidance law allowed for the derivation of the desired head angle to track a given path. The implementation of the line-of-sight guidance law caused a difference (error) between the actual head angle and the desired head angle at the start of motion, where the snake robot was unable to track the desired path for some time for both direction controllers. For amplitude modulation, this error forced the tail link to...
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A foreground and background region segmentation approach to facial recognition identification photographs

- Mopaka, Papatso Ronald

Authors: Mopaka, Papatso Ronald
Date: 2015
Language: English
Type: Masters (Thesis)
Identifier: http://hdl.handle.net/10210/226677 , uj:22924
Description: M.Phil. (Electrical and Electronic Engineering) , Abstract: Identi_cation photos of human faces are required to meet a standard set by the ISO/ICAO organizations, for quality or for visibility since identi_cation photos are a type of biometric used mainly for access control. Some of the quality constraints that need to be met are the uniformity of the background, that there should not be more than one face on the photograph, that no shadows appear behind the person or on their face etc. The _rst step to be taken before developing an automatic system which will be able to detect whether all of these constraints have been compliant with is to _rstly know the structure of an image, that is the system needs to know where the person in the image is situated (hair, face/skin, torso and background). This can potentially be solved by segmentation of the di_erent regions of the person in the image. In this dissertation a region based segmen- tation using several methods available in image segmentation litera- ture is proposed to segment the person from the background. The results obtained showed the capability to segment facial images irre- spective of background illumination levels, texture and variation in size. These results are displayed in the dissertation of how the al- gorithm performed. It was observed that the algorithm performed better on uniform background facial images compared to other back- ground types. The other background types also performed well, but not as good as facial images with uniform background.
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Retention of engineering students in a South African higher education institutions

- Mouchou Tchamdjeu, Rosine

Authors: Mouchou Tchamdjeu, Rosine
Date: 2018
Subjects: College dropouts - Prevention , Engineering students
Language: English
Type: Masters (Thesis)
Identifier: http://hdl.handle.net/10210/293902 , uj:31967
Description: Abstract: Recently, a greater emphasis has been placed on the retention of male and female engineering students in higher education institutions in South Africa. Ralston (2013) states that the retention of engineering students contributes to the goal of increasing the number of engineers in the workforce. Engineering programs in South Africa have been working to improve the student retention rates for many years, (Ogude et al., 2012). Presently, most South African universities are committed to the retention of students by ensuring that the students remain in the system and work through the system to the end. The aim of this study was to gain insight into the retention of female students, which has remained a point of concern in the engineering sector, in order to investigate the need to improve the retention of engineering students in a South African higher education institution. To achieve this aim, the study assesses the available retention strategies, examines the driving factors and evaluates the barriers, to the improvement of the retention rates of engineering technology students. The data used in this study was derived from primary and secondary sources. The secondary source was collected via a detailed review of the relevant literature. The primary source was collected through a questionnaire administered to respondents. Findings revealed that female engineering students were better retained than male Industrial Engineering Technology students, in comparison to students in programmes such as mechanical engineering technology. The significance of this study resides in that the researcher intends to raise awareness on the challenges associated with the improvement of the retention rates for undergraduate National Diploma (NDip) and Bachelor of Engineering Technology (BET) students at the University of Johannesburg (UJ) in South Africa. The study will add to the body of knowledge on the effectiveness of initiatives aimed at improving the retention of engineering students in a South African institutions. , M.Tech. (Industrial Engineering Technology)
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Accurately scaled 3-D scene reconstruction using a moving monocular camera and a single-point depth sensor

- Reginald Leonard Masher

Authors: Reginald Leonard Masher
Date: 2019
Subjects: Three-dimensional imaging , Three-dimensional display systems , Computer graphics , Cameras
Language: English
Type: Masters (Thesis)
Identifier: http://hdl.handle.net/10210/437693 , uj:38014
Description: Abstract: A 3-D reconstruction produced using only a single camera and Structure from Motion (SfM) is always up to scale i.e. without real world dimensions. Real-world dimensions are necessary for many applications that require 3-D reconstruction since decisions are made based on the accuracy of the reconstruction and the estimated camera poses. Current solutions to the absence of scale require prior knowledge of or access to the imaged environment in order to provide absolute scale to a reconstruction. It is often necessary to obtain a 3-D reconstruction of an inaccessible or unknown enviroment. This research proposes the use of a basic SfM pipeline for 3-D reconstruction with a single camera while augmenting the camera with a depth measurement for each image by way of a laser point marker. The marker is identiﬁed in the image and projected such that its location is determined as the point with highest point density along the projection in the up to scale reconstruction. The known distance to this point provides a scale factor that can be applied to the up to scale reconstruction. The results obtained show that the proposed augmentation does provide better scale accuracy. The SfM pipeline has room for improvement especially in terms of two-view geometry and structure estimations. A proof of concept is achieved that may open the door to improved algorithms for more demanding applications. , M.Ing. (Electrical and Electronic Engineering)
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