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Grass waves. Presented by Bulanchuk Pavel. Build a theory of grass waves excitation. Structure. Features Models : А) Independent cones B ) C ollisions C ) T hick grass Details of “Thick grass” Demonstration. Features. 2 types of waves: “quick small waves” and “slow big waves”
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Grass waves Presented by BulanchukPavel
Structure • Features • Models: А) Independent cones B) Collisions C)Thick grass • Details of “Thick grass” • Demonstration
Features • 2 types of waves: “quick small waves” and “slow big waves” • Weak wind → only quick waves
Independent cones(quick waves) • Waves - a consequence of heterogeneity of air flow (turbulence) • Disturbances propagate at the speed of wind
Collisions • Cones collide→disturbances propagate • Problem: quick dying-out
Thick grass • The higher the blade above the rest → → The stronger it is bend → → The grass starts to sway→ → effect of self-oscillations
Thick grass: theory • 1D model • Stable wind • Grass surface is described by
Thick grass: theory • Linear approximation Wind elasticity fading
Thick grass: theory • Dispersion law:
Thick grass: theory • Disturbance will exponentially rise if
Dispersion law No waves
Conclusion • Slow and fast waves • Self-oscillations in constant wind • Critical wind velocity
Experiment Artificial Real
Thick grass: analysis • Phase speed: • Group speed:
