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Experimental test setups and simulations in skiing mechanics
KTH, Strukturmekanik.ORCID iD: 0000-0001-5234-6554
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Product testing and development are essential parts in sports and for the athletes in their quest to reach the podium. Manufacturers of sports equipment often use basic test methods which do not test the equipment in a sports specific way. Much of the equipment used by world-class athletes is chosen based only on subjective tests and the athletes’ feelings. One short term aim was therefore to develop test methods for objective tests of sports equipment that also tested the equipment in a sports  specific  way.  Another  aim  was  to  integrate  mechanics  and  simulations  to  enhance  the understanding of the test results. The more long term aims are to contribute to increased theoretical knowledge regarding test methods for sports equipment and to contribute to the development of test  methods  to  create  new  and  better  sports  equipment.  Experimental  tests  combined  with simulations  can  give  valuable  information  to  improve  the  performance  and  safety  of  sports equipment. Three studies dealt with the issue of objective yet sport specific test methods for sports equipment. The main methodological advancement is the modification of established test methods together  with  conventional  mechanics  calculations.  New  test  devices  and  methodologies  are proposed for alpine ski helmets and cross-country ski poles. Suggestions are given for improved test setups as well as theoretical simulation are introduced for glide tests of skis. The results show how sport   specific   test   methodologies   together   with   theoretical   calculations   can   improve   the objectiveness and relevance when testing sports equipment. However, the collected and used data require high precision to obtain high accuracy in the simulations. High data accuracy can be an issue in field measurements but also due to manufacturers not disclosing key material data. Still, the used methods  and  calculations  in  this  thesis  produce  relevant  and  reliable  results  which  can  be implemented to accurate evaluations of different sports equipment. Even though it has not been a first priority aim in this work, the results from the alpine helmet study have been used by helmet manufacturers to design new helmets with increased safety properties. This further show how an objective and sport specific test approach together with theoretical simulation can improve sports equipment and in the longer perspective, also the athletes’ performances.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2014. , p. v, 31
Keywords [en]
sports equipment, test methods, sports mechanics, alpine skiing, cross-country skiing, poles, helmets, glide, performance
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:du-32262OAI: oai:DiVA.org:du-32262DiVA, id: diva2:1414929
Presentation
2014-04-29, Sal D3, Lindstedtsvägen 5, KTH, 13:15 (English)
Opponent
Supervisors
Available from: 2020-03-16 Created: 2020-03-16 Last updated: 2020-03-16Bibliographically approved
List of papers
1. Repeated low impacts in alpine ski helmets
Open this publication in new window or tab >>Repeated low impacts in alpine ski helmets
2013 (English)In: Sports Technology, ISSN 1934-6182, E-ISSN 1934-6190, Vol. 6, no 1, p. 43-52Article in journal (Refereed) Published
Abstract [en]

Alpine ski race helmets are subjected to multiple impacts during a race caused by the skiers hitting the gates on their way down the course. This study investigated the difference between expanded polystyrene (EPS) and expanded polypropylene (EPP) cores in alpine ski race helmets when subjected to repetitive violence, caused by alpine slalom gates. A special test rig was developed where a rotating slalom pole impacted the helmets with a velocity of 13.3 m·s− 1. All helmets (six EPS and six EPP) were attached to a headform, monitored with a triaxial accelerometer at the center of mass. Each helmet sustained 1000 impacts and acceleration data were collected around every 200 impacts. No significant differences were observed between the first hit and after 1000 hits for either the EPS or the EPP helmets. However, the total group mean acceleration and mean peak acceleration were 15% and 16% higher, respectively, for the EPS series compared with the EPP series. Also, all EPS helmets showed cracked cores after 1000 impacts compared with 1 cracked EPP core. Findings suggest that EPP cores might be more suitable for absorbing multiple low impacts caused by alpine gates and that repeated violence is a relevant parameter to consider when constructing alpine ski race helmets.

Keywords
alpine skiing, head acceleration, multiple impacts
National Category
Other Mechanical Engineering Sport and Fitness Sciences
Identifiers
urn:nbn:se:du-32279 (URN)10.1080/19346182.2012.744413 (DOI)2-s2.0-84893933854 (Scopus ID)
Available from: 2012-11-23 Created: 2020-03-16 Last updated: 2020-03-16Bibliographically approved
2. Testing method for objective evaluation of cross-country ski poles
Open this publication in new window or tab >>Testing method for objective evaluation of cross-country ski poles
2013 (English)In: Sports Engineering, Vol. 16, no 4, p. 255-264Article in journal (Refereed) Published
Abstract [en]

The aim of the study was to develop an objective classification method for cross-country ski poles. A test device was designed to expose different pole models to maximal loading and impact tests. A load cell measured the axial forces in the pole shafts, and a laser distance meter measured shaft deflection when a load was applied via the wrist strap. In the loading tests, each shaft reached a plateau where no more force could be transferred. This maximal force transfer (MFT) value was a characteristic measure for flexural rigidity and thereby also strength. The developed test method enables a loading that is more similar to real-life skiing than a standard three-point bending test. Results show that the introduction of shaft indices for buckling strength is beneficial for comparison purposes. The MFT is a relevant parameter used in the characterization of poles. © 2013 International Sports Engineering Association.

Keywords
Bending, Buckling, Force transfer, Impact
National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:du-32284 (URN)10.1007/s12283-013-0139-6 (DOI)2-s2.0-84888024383 (Scopus ID)
Available from: 2016-09-26 Created: 2020-03-16 Last updated: 2020-03-16Bibliographically approved
3. Validation of test setup to evaluate glide performance in skis
Open this publication in new window or tab >>Validation of test setup to evaluate glide performance in skis
2014 (English)In: Sports Technology, ISSN 1934-6182, E-ISSN 1934-6190, Vol. 7, no 1-2, p. 89-97Article in journal (Refereed) Published
Abstract [en]

Although today's ski waxing chemicals and micro-machining techniques of the ski base are highly sophisticated, objective procedures for testing and verification of the results have not yet been developed and evaluation is based on comparison of subjective experience. The purpose of the present study was thus to compare different setups for testing the glide of cross-country skis. Two differently waxed ski pairs were tested for glide inside a ski tunnel. Inertial measurement units (IMUs) were attached to each ski; instantaneous velocities monitored by three different speed-traps; the velocities during the acceleration phase determined by Doppler radar. Kinetic, potential and total energy, giving the energy dissipation, were calculated for four representative trials during the acceleration phase. No reliable data were obtained from the IMUs due to high drift. The mean maximal velocity for the two ski pairs were 6.97, s = 0.09 and 6.70, s = 0.09 m·s − 1, respectively. Higher differences between the skis were identified during the retardation phase compared to the acceleration phase. The mean difference between the velocities determined by the speed-trap and Doppler radar was 0.6, s = 1%, demonstrating that the latter provides accurate data for evaluation of gliding characteristics and performance. However, theoretical confirmation of the friction coefficient, on the basis of data provided by Doppler radar and energy calculations requires exact measurements of the inclination and topography of the track in question.

Place, publisher, year, edition, pages
Routledge, 2014
Keywords
alpine, cross-country, friction, skiing, snow, wax
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:du-32296 (URN)10.1080/19346182.2014.968164 (DOI)2-s2.0-84938955462 (Scopus ID)
Available from: 2015-11-16 Created: 2020-03-16 Last updated: 2020-03-16Bibliographically approved

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3334353637383936 of 56
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