Mats Tinnsten

Skiing economy and efficiency in recreational and elite cross-country skiers

Abstract Ainegren, M, Carlsson, P, Tinnsten, M, and Laaksonen, MS. Skiing economy and efficiency in recreational and elite cross-country skiers. J Strength Cond Res 27(5): 1239–1252, 2013—The purpose of this study was to investigate and compare skiing economy and gross efficiency in cross-country skiers of different performance levels, ages and genders; male recreational skiers and elite senior and junior cross-country skiers of both genders. The skiers performed tests involving roller skiing on a treadmill using the gear 3 and diagonal stride techniques. The elite cross-country skiers were found to have better skiing economy and higher gross efficiency (5–18%) compared with the recreational skiers (p < 0.05) and the senior elite had better economy and higher efficiency (4–5%) than their junior counterparts (p < 0.05), whereas no differences could be found between the genders. Also, large ranges in economy and gross efficiency were found in all groups. It was concluded that, in addition to V[Combining Dot Above]O2peak, skiing economy and gross efficiency have a great influence on the differences in performance times between recreational and junior and senior elite cross-country skiers, as well as between individual skiers within the different categories. Thus, we recommend cross-country skiers at all performance levels to test not only V[Combining Dot Above]O2peak, but also skiing economy and efficiency.

Optimization of acoustic response

The expression “acoustic optimization” can be applied to numerous different disciplines within the field of acoustics. From seismic waves, sound in the atmosphere through bioacoustic, psychoacoustics, and room and theater acoustics over shock and vibration in mechanical structures. This paper deals with the latter. Sound generated by vibrating structures is often called noise which is to be minimized. However, not all vibrating structures produce noise, for example the violin is also a vibrating structure that in most peoples opinion produces sound called music. In the case of the violin, great effort is made not to minimize but to optimize the sound, i.e. to get the “right” sound out of the structure. Acoustic optimization within this discipline involves automatic changes of structural design variables to obtain minimum or specified sound in specified regions inside or outside the structure. Examples of problem formulations and some theoretical considerations in the field of acoustic optimization in connection with vibrating mechanical structures will be pointed out. Four simple test cases are included as numerical examples of the method proposed.

Combined finite element and multibody musculoskeletal investigation of a fractured clavicle with reconstruction plate

This paper addresses the evaluation of clavicle fixation devices, by means of computational models. The aim was to develop a method for comparison of stress distribution in various fixation devices, to determine whether the use of multibody musculoskeletal input in such model is applicable and to report the approach. The focus was on realistic loading and the motivation for the work is that the treatment can be enhanced by a better understanding of the loading of the clavicle and fixation device. The method can be used to confirm the strength of customised plates, for optimisation of new plates and to complement experimental studies. A finite element (FE) mesh of the clavicle geometry was created from computed tomography data and imported into the FE solver where the model was subjected to muscle forces and other boundary conditions from a multibody musculoskeletal model performing a typical activity of daily life. A reconstruction plate and screws were also imported into the model. The combination models returned stresses and displacements of plausible magnitudes in all included parts and the result, upon further development and validation, may serve as a design guideline for improved clavicle fixation.

Dirt absorption on the ski running surface - quantification and influence on the gliding ability

We propose a thesis that minimising dirt on the running surface of skis improves the surface glide. Waxing usually improves the gliding ability of skis in the short term. But how does waxing affect pollution absorption in the long term? In this study a number of skis with a transparent base and a white background were treated by steel scraping and with different glide waxes. The gliding ability of waxed and unwaxed skis, the sliding surface whiteness and the hydrophobicity were tested and documented. Tests were performed before and after the skis had been used for different distances. It was observed that all the waxed skis (regardless of the wax used) absorbed more dirt than unwaxed, and as a result all waxed skis lose their glide ability sooner than unwaxed (freshly scraped) skis in wet snow conditions.

Numerical Simulation of Cross Country Skiing

A program for numerical simulation of a whole ski race, from start to finish, is developed in MATLAB. The track is modelled by a set of cubical splines in two dimensions and can be used to simulate a track in a closed loop or with the start and finish at different locations. The forces considered in the simulations are gravitational force, normal force between snow and skis, drag force from the wind, frictional force between snow and ski and driving force from the skier. The differential equations of motion are solved from start to finish with the Runge–Kutta method. Different wind situations during the race can be modelled, as well as different glide conditions on different parts of the track. It is also possible to vary the available power during the race. The simulation programs output is the total time of the race, together with the forces and speed during different parts of the race and intermediate times at selected points. Some preliminary simulations are also presented.

OPTIMIZATION OF DRYING SCHEDULES ADAPTED FOR A MIXTURE OF BOARDS WITH DISTRIBUTION OF SAPWOOD AND HEARTWOOD

ABSTRACT A distributed optimization model for wood drying with several different boards simultaneously is presented. Optimization is performed with a gradient-based program. During optimization, convex subproblems are created and transformed to the dual problem and solved. Arbitrary outtakes and board dimensions are possible, as well as different material data and distribution of sapwood and heartwood. It is also possible to optimize drying schedules where drying of boards with variations in environmental conditions is simulated. A two-dimensional orthotropic drying model is used in the moisture transport and structural analysis, where the variation in radial and tangential directions are considered. The influence of temperature and moisture content on material data and mechanical properties is also taken into account. The drying schedules achieved are optimized to minimize drying time for a representative mixture of boards. A numerical example is presented where the drying schedule is optimized for two boards with different outtakes and distributions of sapwood and heartwood. Optimization is performed with two computers in a network. Drying starts from the fibre saturation point in these simulations.

Essential ski characteristics for cross-country skis performance

Winner or trail hog? Much depends on the ski characteristics. The manufacturing of skis is a complicated process involving several materials and different process steps. This gives as a result that every ski obtains unique characteristics such as span curve and bending stiffness etc. For high performance skiers as the member of the Swedish ski team the importance of equal characteristics of each ski in a pair is vital. The process of matching skis to a pair is the process of finding two individual skis with the most similar characteristics. This is traditionally done by hand with simpler equipment. Our measurement system is developed for faster and more accurate ski characteristics assessment. The characteristics do impose the overall performance of the ski. It produces the span curve with very high accuracy and gives a good representation of the pressure distribution over the full length of the ski. The measured characteristics could, in our opinion, also be used in selecting skis for different weather and track conditions. The ski measurement system has been used by the Swedish cross-country team during the last 2,5 years which have resulted in a faster and more accurate matching of skis. In collaboration with the Swedish ski team have also an investigation concerning correlation between ski characteristics and weather and track conditions has been initiated with some preliminary results already obtained.

The relationship between the type of machining of the ski running surface and its wettability and capillary drag

This paper considers the mechanically treated dry ski running-surface. The difference in the shear wettability of ski running-surfaces treated using different types of machining was studied by measuring the advanced and receding contact angles on two different ski base materials. The hypotheses regarding relationship between the shear wettability and the capillary drag of ski running-surface have been presented. The study found that ski running-surfaces with a lower roughness (e.g. flattened by a steel drum or sliced) have a lower wettability factor and seem to be more effective in reducing capillary drag under homogenous wetting conditions.

Hot Glide Wax Treatment and the Hardness of the Ski Running Surface

In the cross country skiing community, hot wax treatment of the ski running surface (SRS) is used in order to influence the surface hardness of the skis in relation to the hardness of the snow crystals. This is discussed in a number of scientific papers and recommended in almost every ski waxing manual. The general idea is to decrease (soften) the surface hardness by the use of a soft glide wax treatment for wet snow conditions and to increase (harden) the hardness of the surface by a hard (synthetic) glide wax treatment for cold, dry snow conditions. The question is; does the hot glide wax treatment of the ski running surface influence the surface hardness? And if so, in what way?

Optimization of a violin top with a combined laminate and honeycomb model of the wood material

Summary Stochastic optimization with the simulated annealing method (SA) is performed on a violin top made of Norway spruce (Picea Abies). A numerical example is presented which shows that it is possible, through changes in thickness variables, to compensate for changes in vibration properties caused by a variation in the material parameters in the top. A material model is also presented for the blank which considers the influence of density variations in the annual rings, the cellular structure of wood and reinforcement from the wood rays.