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Dobór sprężyny głównej wibroizolatora kwazizerowej sztywności

100%

Ćwik R.

tom z. 7

387-392

W pracy przedstawiono zasadę doboru prostoliniowej sztywności sprężyny głównej wibroizolatora kwazizerowej sztywności . Za podstawę doboru sprężyny głównej przyjęto odkształcenia dynamiczne mostu suwnicy wywołane naciągiem sztywnych lin, na których podnoszony jest ładunek.

In the paper there is presented the principle of selecting the rectilinear stiffness of the main spring of avibroinsulator with quasi-zero stiffness . The selection of the main spring is influenced by dynamic strains of the crane bridge which are caused by the tension of stiff ropes while lifting some load.

Application of force-length curve for determination of leg stiffness during a vertical jump

84%

Struzik A. , Zawadzki J.

Acta of Bioengineering and Biomechanics

2016

tom Vol. 18, no. 2

163--171

Purpose: The aim of this study was to present the methodology for estimation of a leg stiffness during a countermovement jump. The question was asked whether leg stiffness in the countermovement and take-off phases are similar to each other as demonstrated in previous reports. It was also examined whether the stiffness in left lower limb is similar to the one in right lower limb. Methods: The research was conducted on 35 basketball players. Each participant performed three countermovement jumps with arm swing to the maximum height. Measurements employed a Kistlerforce plate and a BTS SMART system for motion analysis. Leg stiffness (understood as an inclination of the curve of ground reaction forces vs. length) was computed for these parts of countermovement and take-off phases where its value was relatively constant and F(∆l) relationship was similar to linear. Results: Mean value (±SD) of total stiffness of both lower limbs in the countermovement phase was 7.1 ± 2.3 kN/m, whereas this value in the take-off phase was 7.5 ± 1 kN/m. No statistically significant differences were found between the leg stiffness in the countermovement and the take-off phases. No statistically significant differences were found during the comparison of the stiffness in the right and left lower limb. Conclusions: The calculation methodology allows us to estimate the value of leg stiffness based on the actual shape of F(∆l) curve rather than on extreme values of ∆F and ∆l. Despite different tasks of the countermovement and the take-off phases, leg stiffness in these phases is very similar. Leg stiffness during a single vertical jump maintains a relatively constant value in the parts with a small value of acceleration.