4.2 Gravity-Driven Flow Regime Characterization
169
Fig. 4.4 Particle velocity field at t 1 and t 2 : a t = 72.4s; b t = 72.5s; c t = 82.6s; d t = 82.7s
impulse) for t 2 = 82.6s, respectively. For pre-impulse states (Fig. 4.4a, c), large
velocity vectors exist inside the bed, which indicate a sudden change of large-scale
distribution structure of particles inside the bed. The mechanisms can be explained
as follows:
• When the particles are being removed at the bottom, the structure of local forces
may change slightly and depart from the local force equilibrium. But, its influence
is fist restricted within a local region, because it needs time for the effect of force
change to be spread out to another part. The degree of force structure change is so
slight that it does not meet the power threshold to affect the entire global distribution
structure of particles. In other words, a large-scale structure of force or particle
distributions is maintained, though its strength may be gradually attenuated. The
forthcoming change of the large-scale structure is delayed, but the degree of the
large-scale instability is increasing;
• As time progresses, particles are removed continuously. The force structures and
the base at the bottom for supporting the upside particles become weaker. At
169
Fig. 4.4 Particle velocity field at t 1 and t 2 : a t = 72.4s; b t = 72.5s; c t = 82.6s; d t = 82.7s
impulse) for t 2 = 82.6s, respectively. For pre-impulse states (Fig. 4.4a, c), large
velocity vectors exist inside the bed, which indicate a sudden change of large-scale
distribution structure of particles inside the bed. The mechanisms can be explained
as follows:
• When the particles are being removed at the bottom, the structure of local forces
may change slightly and depart from the local force equilibrium. But, its influence
is fist restricted within a local region, because it needs time for the effect of force
change to be spread out to another part. The degree of force structure change is so
slight that it does not meet the power threshold to affect the entire global distribution
structure of particles. In other words, a large-scale structure of force or particle
distributions is maintained, though its strength may be gradually attenuated. The
forthcoming change of the large-scale structure is delayed, but the degree of the
large-scale instability is increasing;
• As time progresses, particles are removed continuously. The force structures and
the base at the bottom for supporting the upside particles become weaker. At