Investigations into soccer aerodynamics via trajectory analysis and dust experiments

We present a summary of our investigations into the aerodynamics of soccer balls (association footballs). Using a ball launcher and high-speed cameras, we are able to determine drag and lift coefficients using trajectory analysis. Advantages of this approach over wind tunnels include studying balls in flight without a support rod, which may influence aerodynamic studies in wind tunnels, and the ability to determine lift coefficients in regions inaccessible by many wind tunnels. We have found lift coefficients for spin parameters between 0 and 1 and Reynolds numbers between 130,000 and 300,000. Launching a ball into a dust cloud allows for the study of boundary-layer separation, again without the need of a support rod, which is needed for wind-tunnel studies. We have found boundary-layer separation angles in and around the drag crisis. Anomalous behavior is seen just past the drag crisis. © 2012 Published by Elsevier Ltd

An evaluation of dexterity and cutaneous sensibility tests for use with medical gloves

© 2015 Institution of Mechanical Engineers.The ability of selected dexterity and cutaneous sensibility tests to measure the effect of medical glove properties (material, fit, and number of layers) on manual performance was analyzed. Manual performance testing of gloves to-date has focused on thicker gloves where the effects are more obvious. However, clinicians have reported dissatisfaction with some medical gloves and a perceived detriment to performance of new materials compared to latex. Three tests (Purdue Pegboard Test, Crawford Small Parts Dexterity Test, and Semmes-Weinstein Monofilaments) were performed by 18 subjects in five hand conditions (ungloved; best-fitting, loose-fitting and a double layer of latex examination gloves; best-fitting vinyl gloves). Tests were performed in the ungloved condition first, and the order of the gloved tests was randomized. Learning behavior was also measured. The Purdue test showed a significant effect of hand condition, but no differences between latex and vinyl. No significant effect of hand condition was found in the Crawford "Pins and Collars" test, but the "Screws" test showed promising discrimination between glove types. The Monofilaments test showed a significant effect of hand condition on cutaneous sensibility, particularly a reduction when "double-gloving," but no significant differences between glove types. Existing tests show some ability to measure the effect of gloves and their properties on manual performance but are not comprehensive and require further validation. In order to fully describe the effects of medical gloves on manual performance, further tests should be designed with greater resolution and that better replicate clinical manual tasks

Boot-insole effects on comfort and plantar loading at the heel and fifth metatarsal during running and turning in soccer

Plantar loading may influence comfort, performance and injury risk in soccer boots. This study investigated the effect of cleat configuration and insole cushioning levels on perception of comfort and in-shoe plantar pressures at the heel and fifth metatarsal head region. Nine soccer academy players (age 15.7 ± 1.6 years; height 1.80 ± 0.40 m; body mass 71.9 ± 6.1 kg) took part in the study. Two boot models (8 and 6 cleats) and two insoles (Poron and Poron/gel) provided four footwear combinations assessed using pressure insoles during running and 180° turning. Mechanical and comfort perception tests differentiated boot and insole conditions. During biomechanical testing, the Poron insole generally provided lower peak pressures than the Poron/gel insole, particularly during the braking step of the turn. The boot model did not independently influence peak pressures at the fifth metatarsal, and had minimal influence on heel loads. Specific boot-insole combinations performed differently (P < 0.05). The 8-cleat boot and the Poron insole performed best biomechanically and perceptually, but the combined condition did not. Inclusion of kinematic data and improved control of the turning technique are recommended to strengthen future research. The mechanical, perception and biomechanical results highlight the need for a multi-faceted approach in the assessment of footwear

Rubber friction and the effect of shape

Contrary to the classic laws of friction, rubber friction is not independent of shape. The friction of three shapes of the same rubber compound sliding over a dry-rough surface was measured. The three shapes had the same nominal contact area but different sliding direction-lengths and widths. Frictional differences were found between all three shapes at sliding speeds of 10 mm/s and 0.5 mm/s. The effect of frictional heating and other friction mechanisms that cause these differences are evaluated and discussed

The influence of gravimetric moisture content on studded shoe–surface interactions in soccer

It is desirable for the studs of a soccer shoe to penetrate the sport surface and provide the player with sufficient traction when accelerating. Mechanical tests are often used to measure the traction of shoe–surface combinations. Mechanical testing offers a repeatable measure of shoe–surface traction, eliminating the inherent uncertainties that exist when human participant testing is employed, and are hence used to directly compare the performance of shoe–surface combinations. However, the influence specific surface characteristics has on traction is often overlooked. Examining the influence of surface characteristics on mechanical test results improves the understanding of the traction mechanisms at the shoe–surface interface. This allows footwear developers to make informed decisions on the design of studded outsoles. The aim of this paper is to understand the effect gravimetric moisture content has on the tribological mechanisms at play during stud–surface interaction. This study investigates the relationships between: the gravimetric moisture content of a natural sand-based soccer surface; surface stiffness measured via a bespoke impact test device; and surface traction measured via a bespoke mechanical test device. Regression analysis revealed that surface stiffness decreases linearly with increased gravimetric moisture content (p = 0.04). Traction was found to initially increase and then decrease with gravimetric moisture content. It was observed that: a surface of low moisture content provides low stud penetration and therefore reduced traction; a surface of high moisture content provides high stud penetration but also reduced traction due to a lubricating effect; and surfaces with moisture content in between the two extremes provide increased traction. In this study a standard commercially available stud was used and other studs may provide slightly different results. The results provide insight into the traction mechanisms at the stud–surface interface which are described in the paper. The variation between traction measurements shows the influence gravimetric moisture content will have on player performance. This highlights the requirement to understand surface conditions prior to making comparative shoe–surface traction studies and the importance of using a studded outsole that is appropriate to the surface condition during play

The influence of tennis court surfaces on player perceptions and biomechanical response.

This study aimed to examine player perceptions and biomechanical responses to tennis surfaces and to evaluate the influence of prior clay court experience. Two groups with different clay experiences (experience group, n = 5 and low-experience group, n = 5) performed a 180° turning movement. Three-dimensional ankle and knee movements (50 Hz), plantar pressure of the turning step (100 Hz) and perception data (visual analogue scale questionnaire) were collected for two tennis courts (acrylic and clay). Greater initial knee flexion (acrylic 20. 8 ± 11.2° and clay 32.5 ± 9.4°) and a more upright position were reported on the clay compared to the acrylic court (P < 0.05). This suggests adaptations to increase player stability on clay. Greater hallux pressures and lower midfoot pressures were observed on the clay court, allowing for sliding whilst providing grip at the forefoot. Players with prior clay court experience exhibited later peak knee flexion compared to those with low experience. All participants perceived the differences in surface properties between courts and thus responded appropriately to these differences. The level of previous clay court experience did not influence players' perceptions of the surfaces; however, those with greater clay court experience may reduce injury risk as a result of reduced loading through later peak knee flexion

The development of a new artificial model of a finger for assessing transmitted vibrations.

Prolonged exposure of the hand to tool-induced vibrations is associated with the occurrence of conditions such as vibration white finger. This study involves the development of a new artificial model that approximates both loading and vibration behaviour of the human finger. The layered system uses polypropylene "bones", encased in a cylinder of low modulus, room-temperature curing silicone gel (to replicate subcutaneous tissues), with an outer layer of latex (to replicate the dermis and epidermis). A protocol for manufacture was developed and dynamic mechanical analysis was carried out on a range of gels in order to choose a range close to the mechanical properties of the human finger. The load-deflection behaviour under quasi-static loading was obtained using an indenter. The indentation measurements were then compared with a set of validation data obtained from human participant testing under the same conditions. A 2-D FE model of the finger was also used to assess vibration responses using existing parameters for a human finger and those obtained from the tested materials. Vibration analysis was conducted under swept sinusoidal excitations ranging from 10 to 400Hz whilst the FE finger model was pressed 6mm toward the handle. Results were found to compare well. This synthetic test-bed and protocol can now be used in future experiments for assessing finger-transmitted vibrations. For instance, it can aid in assessing anti-vibration glove materials without the need for human subjects and provide consistent control of test parameters such as grip force

The effect of normal load force and roughness on the dynamic traction developed at the shoe-surface interface in tennis

During tennis-specific movements, such as accelerating and side stepping, the dynamic traction provided by the shoe-surface combination plays an important role in the injury risk and performance of the player. Acrylic hard court tennis surfaces have been reported to have increased injury occurrence, partly caused by increased traction that developed at the shoe-surface interface. Often mechanical test methods used for the testing and categorisation of playing surfaces do not tend to simulate loads occurring during participation on the surface, and thus are unlikely to predict the human response to the surface. A traction testing device, discussed in this paper, has been used to mechanically measure the dynamic traction force between the shoe and the surface under a range of normal loading conditions that are relevant to real-life play. Acrylic hard court tennis surfaces generally have a rough surface topography, due to their sand and acrylic paint mixed top coating. Surface micro-roughness will influence the friction mechanisms present during viscoelastic contacts, as found in footwear-surface interactions. This paper aims to further understand the influence micro-roughness and normal force has on the dynamic traction that develops at the shoe-surface interface on acrylic hard court tennis surfaces. The micro-roughness and traction of a controlled set of acrylic hard court tennis surfaces have been measured. The relationships between micro-roughness, normal force, and traction force are discussed. © 2013 The Author(s)

Controlled peel testing of a model tissue for diseased aorta

In this study, we examine the effect of collagenase, elastase and glutaraldehyde treatments on the response of porcine aorta to controlled peel testing. Specifically, the effects on the tissue׳s resistance to dissection, as quantified by critical energy release rate, are investigated. We further explore the utility of these treatments in creating model tissues whose properties emulate those of certain diseased tissues. Such model tissues would find application in, for example, development and physical testing of new endovascular devices. Controlled peel testing of fresh and treated aortic specimens was performed with a tensile testing apparatus. The resulting reaction force profiles and critical energy release rates were compared across sample classes. It was found that collagenase digestion significantly decreases resistance to peeling, elastase digestion has almost no effect, and glutaraldehyde significantly increases resistance. The implications of these findings for understanding mechanisms of disease-associated biomechanical changes, and for the creation of model tissues that emulate these changes are explored