EFFECT OF FOOT POSITION ON THE COMPRESSION AND LATERAL FORCE PRODUCTION OF A PLAYER IN A RUGBY SCRUM

Knowledge of the force production of an individual player with different foot positions, and ultimately of the full pack, will provide coaches and trainers with valuable information in order to improve their team's ability to manipulate the scrum forces and moments as well as making the scrum more stable thereby improving safety. This study aimed to examine the differences in the scrum compression force and lateral force generated by an individual player during the sustained pushing phase of the scrum with parallel and nonparallel foot positions. Nineteen front row rugby players scrummed against an instrumented scrum machine with three different foot positions. The results showed that the parallel foot position produces a higher pushing force than either of the other two nonparallel conditions. It was also shown that the nonparallel conditions produces a greater lateral force than the parallel foot condition with the lateral force being directed towards the side of the front foot.

Validated leaf spring suspension models

Mathematical and computer modelling have been playing an increasingly important role in the Computer Aided Engineering (CAE) process. Simulation offers great advantages in the development and analysis phase of products and offers a faster, better and more cost effective way than using physical prototypes alone. The ever increasing demand for new and improved products in the vehicle industry has decreased the time available for the development of new vehicles, but at the same time the demands on quality, reliability and mass that are set for the vehicle are becoming ever more stringent. These requirements have lead to the investigation of procedures and methodologies such as virtual prototyping that will reduce the development time of new vehicles without inhibiting the quality of the vehicle. In order to perform effective and reliable simulations in the CAE process, accurate simulation models of the vehicle and its associated systems, subsystems and components are required. In the vehicle dynamics context simulation models of the tyres, suspension, springs, damper, etc, are needed. This study will look at creating a validated model of a leaf spring suspension system used on commercial vehicles. The primary goal set for the model is to be able to predict the forces at the points where the suspension system is attached to the vehicle chassis as the model is to be used in full vehicle durability simulations. The component which will receive a considerable amount of attention in this study is the leaf spring. Leaf springs have been used in vehicle suspensions for many years. Even though leaf springs are frequently used in practice they still hold great challenges in creating accurate mathematical models. It is needless to say that an accurate model of a leaf spring is required if accurate full vehicle models are to be created. As all simulation models in this study are required to be validated against experimental measurements a thorough experimental characterisation of the suspension system of interest, as well as two different leaf springs, are performed. In order to measure the forces between the suspension attachment points and the chassis, two six component load cells were developed, calibrated, verified and validated. This study will primarily focus on the modelling of a multi-leaf spring as well as a parabolic leaf spring. The study starts with a literature study into the various existing modelling techniques for leaf springs. A novel leaf spring model, which is based on a macro modelling view point similar to that used for modelling material behaviour, is developed. One of the modelling techniques found in the literature, i.e. neural networks, is also used to model the leaf spring. The use of neural networks is applied and some of the challenges associated with the method are indicated. The accuracy and efficiency of the physics-based elasto-plastic leaf spring model and the non physics-based neural network model are compared. The modified percentage relative error metric is compared to two other quantitative validation metrics that were identified from the literature study. It is concluded that the modified percentage relative error has certain limitations but that it is able to give an accurate and representative account of the agreement/disagreement between two periodic signals around zero. The modified percentage relative error is used to obtain the accuracies of the elasto-plastic leaf spring models and the neural network model. Both models give good results with the neural network being almost 3 times more computationally efficient. The elasto-plastic leaf spring model, for the multi-leaf spring, is further extended to model the behaviour of a parabolic leaf spring. Qualitative validation using experimental data shows that the elasto-plastic leaf spring model is able to accurately predict the vertical behaviour of both the multi-leaf spring as well as the parabolic leaf spring. The elasto-plastic leaf spring model was also combined with a method that is able to capture the effect of changes in the spring stiffness due to changes in the loaded length. Quantitative validation shows that the method proposed for accounting for the change in stiffness due to changes in the loaded length is able to capture this characteristic of the physical leaf spring. Following a systematic modelling approach the elasto-plastic multi-leaf spring model is incorporated into a model of a simplified version of the physical suspension system. The qualitative validation results from this model show that the model is able to accurately predict the forces that are transmitted from the suspension system to the chassis. The models created in this study can be used in future work and, with the addition of more detail the models, can be extended to create a model of the complete suspension system.Thesis (PhD(Eng))--University of Pretoria, 2012.Mechanical and Aeronautical Engineeringunrestricte

Suspension forces on a tri-axle air suspended semi-trailer

The aim of this study is to investigate the use of multi-body vehicle simulation models to predict the suspension forces acting on the chassis of the vehicle, in order to perform durability analyses. Traditionally, durability of vehicles is evaluated with proving ground tests. This implies that a physical prototype of the vehicle is required before its durability can be evaluated. If we were able to evaluate the durability of the vehicle without any physical part or a full prototype of the vehicle available, great cost and time savings may be gained. These possible gains have lead to the use of computer aided engineering (CAE) tools. These tools have supplemented the proving ground durability test by using historical measured data and/or predicted data from vehicle simulation models, as input to the durability analyses i.e. Finite Element Analyses (FEA). The usefulness of the historical test data is limited and many of the vehicle simulation models that are used to predict the input data, have not been validated. In this study a validated mathematical model of a 40 ton flat bed tri-axle semi-trailer, able to predict the suspension forces, is created. The validation of the full vehicle model includes correlations for displacements, velocities, accelerations and forces of various vehicle parameters. A validated mathematical model of the air springs, that includes mass transfer and flow effects for use in full vehicle dynamic simulations, is also developed. The results obtained indicate that the air spring model, integrated into the full vehicle model, is able to give relative accurate predictions of displacements, velocities, accelerations and forces of various vehicle parameters, over a discrete road event and over a rough road.Dissertation (MEng)--University of Pretoria, 2009.Mechanical and Aeronautical EngineeringUnrestricte

Biomechanical comparison between pins - polymethylmethacrylate to the “String of Pearls” interlocking plate system (SOP) to stabilize canine lumbosacral fracture-luxation

Biomechanical comparison of two internal spinal fixation techniques, applied to a surgically simulated complete spinal injury at L7-S1 was conducted. The study objective was to compare the stability provided by the two fixation techniques to the fracture-luxation.Poster presented at the University of Pretoria, Faculty of Veterinary Science Faculty Day, August 20, 2015, Pretoria, South Africa.Created in CoralDRAW X5. PDF size: 5.83 MB.ab201

Ride comfort comparison between suspension modes : input towards designing difference threshold experiments during driving

Ride comfort is an important topic for on- and off-road suspension design. Difference thresholds of whole-body vibration is important to determine perceptibility of changes in a vehicle’s dynamics. Difference thresholds can be used to guide ride comfort improvements. Difference thresholds have been estimated for vertical and multi-axial seat vibration in laboratory settings. In order to determine the applicability of these laboratory difference thresholds and/or to estimate difference thresholds during driving, it is required that changes can be made in the vehicle’s vibration that is transmitted to the occupants i.e. the stimulus. Ride comfort is quantified by the weighted vertical seat pad vibration and compared between four suspension modes of a vehicle over three roads from ten repeat runs. Significant differences in the median weighted vertical seat pad vibration were found between Mode 1 and the other three modes over Road 1 and Road 2. No significant differences were found over Road 3. The significant differences over Road 1 are in the range of the median relative difference threshold reported in literature. Over Road 2 the differences are below the reported 25th percentile relative difference thresholds. Some combinations of the suspension modes and roads result in ride comfort differences. The suspension mode and road combinations could be used to verify the applicability of available difference thresholds during driving.Paper presented to the 11th Asia-Pacific Regional Conference of the ISTVS, September 26-28, 2022.The European Union Horizon 2020 Framework Program, Marie Skłodowska-Curie actions.http://www.istvs.orghj2023Mechanical and Aeronautical Engineerin

Validation metric based on relative error

Engineers and scientists are often faced with the problem of objectively comparing time histories of measured and/or simulated data. This article presents a reliable and intuitive validation metric for use in the validation process. The proposed validation metric is able to quantify the agreement/disagreement between deterministic system response quantities of interest obtained from measurements on a physical system and predictions from a mathematical model. The validation metric is based on the relative error, and the challenges concerning the use of the relative error on periodic signals are addressed. The validation metric is compared to similar metrics and their advantages and limitations are discussed. The results show that the proposed validation metric gives a comprehensive error that is able to quantify the agreement between two periodic signals and is easily interpretable.Afrit and the Technology and Human Resources for Industry Program (THRIP) of the Department of Trade and Industry of South Africa.http://www.tandfonline.com/loi/nmcm2

Acceleration Data at Various Locations on Vehicle On Four Post Test Rig over Different Roads and at Different Tyre Pressures

<p>Dataset of acceleration data at various locations on sport utility vehicle on four post test rig over different roads and at different tyre pressures. This dataset can be used for driving comfort evaluation. </p

Methodology for developing a neural network leaf spring model

This paper describes the development of a neural network that is able to emulate the vertical force-displacement behaviour of a leaf spring. Special emphasis is placed on aspects that affect the predictive capability of a neural network such as type, structure, inputs and ability to generalise. These aspects are investigated in order to enable the effective use of it to model leaf spring behaviour. The results show that with the correct selection of inputs and network architecture, the neural network's ability to generalise can be improved and also reduce the required training data. The resulting 2-15-1 feed-forward neural network is shown to generalise well and requires minimal data to be trained. Experimental data was used to train and validate the network. The methodology followed is not limited to the application of leaf springs only but should apply to various other applications especially ones with similar nonlinear characteristics.http://www.inderscience.com/jhome.php?jcode=IJVSMT2018-06-01hj2018Mechanical and Aeronautical Engineerin

Comparative analysis of the subsidence of solid polyetheretherketone (PEEK) and 3D printed lattice titanium interbody fusion cages

Spinal interbody fusion cages are commonly used to treat various spinal conditions, but their traditional manufacturing methods have limitations in customization and fitting. With the advancement of 3D printing, it is now possible to design and manufacture interbody fusion cages with previously unachievable features and structures. Southern Medical™ is investigating the technical feasibility of 3D-printed cages based on their existing designs and exploring the new features and capabilities enabled by additive manufacturing (AM). The mechanical performance in the subsidence of the 3D-printed devices will be compared to their existing devices as one of the feasibility points for the additively manufactured implants. A gyroid structure is used as the inner lattice of the structures. To investigate the performance of the cages with the new gyroid lattices, subsidence testing according to the ASTM F2267 methods was conducted to compare existing cages to the 3D-printed cages. The 3D printed devices outperformed the PEEK counterparts with a higher test block stiffness of 0.81 kN/mm compared to 0.55 kN/mm

Single- versus double-row repair for full-thickness rotator cuff tears using suture anchors. A systematic review and meta-analysis of basic biomechanical studies

The purpose of this study was to perform a systematic review and meta-analysis comparing single- and double-row biomechanical studies to evaluate load to failure, mode of failure and gap formation.A systematic review of MEDLINE, Embase, Scopus and Google Scholar was performed from 1990 through 2016. The inclusion criteria were: documentation of ultimate load to failure, failure modes and documentation of elongation or gap formation. Studies were excluded if the study protocol did not use human specimens. Publication bias was assessed by funnel plot and Egger's test. The risk of bias was established using the Cochrane Collaboration's risk of bias tool. Heterogeneity was assessed using χ 2 and I 2 statistic.Eight studies were included. The funnel plot was asymmetric suggesting publication bias, which was confirmed by Egger's test (p\ua0=\ua00.04). The pooled estimate for load to failure demonstrated significant differences (SMD 1.228, 95% CI: 0.55-5.226, p\ua0=\ua00.006, I 2\ua0=\ua060.47%), favouring double-row repair. There were no differences for failure modes. The pooled estimate for elongation/gap formation demonstrated significant differences (SMD 0.783, 95% CI: 0.169-1.398, p\ua0=\ua00.012, I 2\ua0=\ua058.8%), favouring double-row repair.The results of this systematic review and meta-analysis suggest that double-row repair is able to tolerate a significantly greater load to failure. Gap formation was also significantly lower in the double-row repair group, but both of these findings should be interpreted with caution because of the inherent interstudy heterogeneity.Systematic review and meta-analysis