1,720,958 research outputs found
Performance sports engineering: improving knowledge of human underwater undulatory swimming
No full textUnderwater Undulatory Swimming (UUS), performed fully submerged following a dive or push from the wall in swimming, can be exploited to gain a competitive advantage in races. Athletes can travel underwater for up to 30 % of the race while performing an undulatory motion, benefitting from a reduction of resistive forces. The undulatory motion consists of a wave which propagates along the body, from the fingertips to the toes. As this wave moves along the body its amplitude increases, accelerating the fluid downstream to generate propulsive forces which propel the swimmer forward. This swimming technique mimics the locomotion of marine mammals. This collaborative presentation highlights the work undertaken during two closely related UK Sports Institute funded PhD projects. The kinematic data acquisition process using three-dimensional optoelectronic motion capture will be presented, along with the joint centre reconstruction methods. A novel two-dimensional implicit-LES computational fluid dynamics methodology will also be introduced. Examples of applications given by the speakers will include an estimation of error within the kinematic capture domain, the efficacy of training practices in UUS skill development, and a case study on the impact of kinematic modification on UUS force generation of a regional-level swimmer
Dataset supporting the University of Southampton Doctoral Thesis: "Assessing the performance of underwater undulatory swimming techniques with computational fluid dynamics"
No full textThe dataset contains anonymised results from the simulation used during the research for the thesis.
5 folders:
1 - Body Data: relative segment lengths, total bodylength and segment thickness for every athlete.
2 - Data-Kinematics: Lists all of the Fourier coefficient for all the kinematic trials.
3 - Non modified Kinematics: Simulation outputs for the simulations first presented in the Chapter 5 of the thesis (this data is also used in chapters 6, 7 and 8).
4 - Case Study - Athlete 1: Results from the simulation used for section 7.2 of the thesis.
5 - Case Study - Athlete 5: Results from the simulation used for section 8.4 of the thesis.
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Assessing the performance of underwater undulatory swimming techniques with computational fluid dynamics
No full textUnderwater Undulatory Swimming (UUS) is of a major importance in modern competitive swimming. This technique follows a dive or a push off the wall. It consists in reproducing the way of locomotion of marine mammals: a wave travels along the body of a swimmer, from the fingers to the toes, accelerating the flow in its vicinity, and thus propelling them forward. Understanding ways to maximise performance of such a technique is essential to give the leading edge to an athlete. Past studies have looked at ways to maximise swimming speed or ways to observe the flow in the wake and in the vicinity of an athlete (e.g. Computational Fluid Dynamics (CFD), Particle Image Velocimetry). These studies often overlooked real race conditions and did not consider when UUS is not performed at maximum effort or when UUS is performed in over-speed (i.e. greater velocities than an athlete can maintain). In order to study both these aspects, the need for fast computation in order to estimate hydrodynamic forces in various configurations arose. It appeared that a methodology using an immersed boundary method with unsteady implicit-LES applied to UUS could provide fast and reliable simulations. With the combination of an accurate kinematics gathering methodology using optoelectronic motion capture and such computations, it was possible to estimate, with acceptable precision, the fluid forces, the instantaneous swimming velocity and deceleration trends of a large number of kinematics data (58 in total). Three short studies applying the methodology developed ensued. The first one consisted in observing a sample of seven swimmers performing UUS at different instructed pace (maximum effort, 100 m pace and 200 m pace). Two groups of athletes were identified and separated regarding the way they adapted their swimming motion to the pace. The first group, in order to reduce their swimming speed, simply reduced their movement frequency while keeping a similar technique form. The second group modified their undulation wavelength significantly when performing UUS at slower paces. The implicit-LES simulations provided useful information to understand how the fluid forces were affected by the change of technique. The second study proposed two possible approaches for modifications of UUS techniques: increasing or reducing an athlete's body segments angular range of motion, or forcing a linear wave propagation along the body. A case study showing insight on how these modifications could affect performance of a university level athlete was undertaken. Results provided by simulations with modified kinematics show insights on the potential direction of training for this athlete in order to maximise their UUS speed. A third and final study observed how quickly various UUS techniques decelerate during the over-speed phases of underwater swimming. It shows the potential benefits of taking advantage of a slower deceleration phase. Additionally, a case study where kinematics of an elite swimmer were modified and inputted in the CFD methodology provides insight on the potential role of the knee flexion on deceleration performance
Error assessment of a three-dimensional underwater motion capture methodology
No full textMotion analysis technology is used in various settings to assess human kinematics. Assessing human movement underwater presents many challenges, making it important to understand measurement error associated with the setup and calibration of the system ensuring accuracy in resulting kinematics. This study assessed the accuracy across the entire domain of a submerged motion capture methodology. Six Qualisys cameras created an underwater capture volume of 6.9 × 2.1 × 2.1 m3. Average error levels were acceptable in four uncertainty trials (<± 5 mm error). By selecting an area of interest that excluded areas with low accuracy near domain borders, measurement error reduced by up to 0.13 mm, up to 1.27 mm lower than outside this area. Interpolated error indicated that intracyclic measurement error may alter measured kinematics by up to 13.80 mm, with error greater than 5 mm affecting over 50% of the kick cycle. Investigating error levels across the domain can inform researchers whether a recalibration is necessary or help to identify areas where high error levels would affect kinematics. This study highlights the need to investigate error levels across a motion capture domain, particularly when this is a large volume, to ensure results obtained from investigations are reliable
Dataset to support the paper 'Error assessment of a three dimensional underwater motion capture methodology'
No full textThis data supports the publication 'Error Assessment of a Three Dimensional Underwater Motion Capture Methodology' in a currently unspecified journal.
Provided are the coordinate data for the calibrated volume (CalibrationCoordinates.csv) and coordinate data for all related trials (SystematicSectioning.csv, SystematicLength.csv, RandomOne.csv, and RandomTwo.csv).</span
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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