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11:30   Hydrodynamics of swimming Chair: Stephan Odenwald 11:30 20 mins OPTIMIZE PROPULSION IN SWIMMING Josje van Houwelingen Abstract: The goal of this research is threefold with the main objective to develop a system to visualize the flow around a human swimmer in practice. Since the experimental setup will be build in the swimming pool several challenges had to be tackled varying from tracer particles, light exposure, data transfer from cameras to computer and the underwater environment. Finally the setup consist out of a bubble system placed at the bottom of the swimming pool and a camera array of six cameras in underwater casing placed on the side of the swimming pool. This camera array is used to get some in depth information using a so called map shift algorithm in the post processing of the images to focus artificially on several planes of interest. The evenly spread bubbles of about 3 mm in diameter act as tracer particles. Because of their size they will not follow the flow exactly, but as a start this type of visualization can be used to obtain some qualitative information about the formation of the large vortices in the flow field around the swimmer. In addition to this visualization system, work is done on the hydrodynamics of the hand of a swimmer. Several other studies have been assigned to this topic. In the past most work was related to finding drag coefficients in all kind of orientations. Nowadays the experiments and simulations get more advanced and the unsteady flow development around a moving hand is studied in more detail (e.g. vortex formation and shedding). Although done in the past, the effect of finger spacing is tested using simulations and wind tunnel experiments. Hopefully a definite answer can be given on what causes the beneficial effects of a small finger spread. Other work in this research is related to applying auditory pacing in swimming. 11:50 20 mins PATTERNS OF FLOW PRESSURE DUE TO HAND-WATER-INTERACTION OF SKILLED BREASTSTROKE SWIMMERS – A PRELIMINARY STUDY Bodo E. Ungerechts, Daniel Cesarini, Maria Hamann, Yvonne Ritter, Sven Weidner, Tim Haldorn, Thomas Hermann Abstract: Self-induced aquatic propulsion is an effect of interaction of the limbs and water mass (LWI) which change the energy-density per volume and the momentum of water mass, simultaneously. The change of volumetric energy-density of water can be measured via pressure tap probes detecting static pressure of unsteady flow via pressure sensors. The data of elite breaststroke swimmers wearing gloves with pressure taps on both sides of the hands were presented as pressure difference per hand (p-diff) in real-time in a split screen video together with the hand action. The purpose of this preliminary study was to check a) the stability of the setup including the data collection under pool condition with various swimmers and b) to answer coaches’ questions concerning the relation of peak pdiff-data and hand action. Among others it is shown that p-diff(max) coincides with a) deepest hand penetration at the end of the inward sweep of the hands and b) max body acceleration during hand action, shortly before max body velocity occurs. 12:10 20 mins MUSKULOSKELETAL MODELLING IN SPORTS Evaluation of different software tools with focus on swimming Janna Brit Langholz, Gunnar Westman, Magnus Karlsteen Abstract: Previous swim start measurements at Chalmers University of Technology involved electromyography (EMG) in order to get an overall picture of the muscle activation pattern during the swim start applying the nowadays most common start dive techniques of competitive swimming events - differently weighted track starts from the OMEGA OSB11 starting block. In order to fully evaluate sports performance trainers may facilitate additional tools, like videography and force plates, to be able to underpin the feedback given to the athletes. However, the output of the different tools are often complicated and lengthy to handle or understand. Therefore it would be valuable to find an easily applicable tool to visualize biomechanical data. Feedback to athletes based on scientifically measured variables would then ideally be more efficient and effective. This paper evaluates three different software tools regarding musculoskeletal modelling and simulation: OpenSim, BoB and AnyBody. The software package SWUM was also analyzed as it is currently the only tool that can model forces and buoyancy during swimming. It is intended to investigate whether the properties of the different software packages allow the data import from various sports analysis modalities and enable quick, meaningful and unambiguous processing and presentation of the data. It has been found that OpenSim is a great tool for academic projects as it is freely available and provides a big pool of users and papers available to support the user with additional knowledge. BoB is the most straight-forward tool so it might be most appropriate for biomechanical teaching and applications where a fast analysis is required. AnyBody has the most sophisticated model which can be adjusted to the user’s demands in great detail and is favorable for investigations with focus on the interaction between the body and the environment or a detailed medical analysis. Great potential lies in the further development and usage of SWUM as its basic interface with valuable outputs and simulations as well as an illustrative interface to AnyBody might allow for advancements in swim training.