2 Flashcards
What is vortex shedding
When air passes around a tall slender building causing vortices to form in the wake of the airflow
What are vortices
Low pressure air masses the form on each side of structure.in an oscillating manner
What structures are affected by vortex shredding
Structures with low natural frequency (tall slender structures, chimneys and circular cylinders ) these are all flexible slender vertical cantilevers and problem arises Weber their frequency is close to the vortex causing resonance
Vortex shedding frequency formula
F vs = (St) (v)/d
Frequency ratios to avoid resonance
Fvs/fn< 0.5 or Fvs/ fn >2
Adaptions to prevent vortex shedding
1 helical stake, axial stats, shroud, ribboned cable, streamlined fairing I splinter
What do strakes do
Disrupt air flow and stiffer the structure
Types of silo failures
Eccentric discharge
Dooming of materials
Poor maintenance
Temperature ratcheting
Dust explosions
Eccentric discharge
When non - symmetrical loading occurs causing the wall to buckle on the side discharge
Doming of materials
If the moisture is high- and the materials cohesive a dome may form their buckling may occur in the wall of the material void space due to the weight of the dome
How is doming of materials prevented
Monitoring moisture content and cleanliness of the stored materials
What is temperature ratcheting and when is it most susceptible
When a silo is exposed to high temperatures it expands and the materials in it settle but when it cools it contracts and additional stresses are exerted on the wall if this happens repeatedly the walls could fail
Susceptible when temperature difference is very high and materials are stored for long time
