Guide Tour for Granular Dynamics

I have started to construct Guide Tour. Although most of content can be reachable from some place in Powder Page, they are too scattered to reach easily. Thus, I will provide beginners for granular dynamics to know what is new and interesting. Even if your results are not introduced here, please do not get angry. It may simply means that your www page is not so colorful..... As another reference, I recommned XMDA: different view on sand 

Last modified: 18 April 1997
Contents: 
  1. MIXING 
  2. FLOW 
  3. VIBRATION 
  4. FLUIDIZATION
MIXING 
Mixing is one of most important process for industry. It is usually hard to mix them uniformly. For example[*], suppose you try to mix granular material homogeneously using rotating disk whose axis is horizontal. One may think that it is easy if one can continue rotation forever, it is not the case. If disk is filled by granular matter more than half, uniform mixing can never be achieved. 
 
After here  		In these figures, disk has been filled with half by half with granular material colored differently. Mixing can occur only near surface region where avalanche take place during rotation, center part of disk can never be mixed. Even if mixing same kind of granular matter, it is not so easy as you can see here. So what about mixing different kind of granular matter? For example, different sizes, weight, and so on? As you may imagine, it is much, much more difficult. For example, spontaneous band structure and radial structure appear in rotating drums filled with binary mixture. It is also related to segregation. You can also find here or here how to mix granular matter in industry by animations. 
Granular matter flows like fluid, but do so in remarkably different way from fluid. For example, you can see here top-view of two-dimensional granular flow on a inclined funnel 
Flow 
Granular matter flows like fluid, but do so in remarkably different way from fluid. For example, you can see here top-view of two-dimensional granular flow on a inclined funnel 

 

Further infomation here. 
You can see that it flows very intermittently. It is also observed in granular flow in the vertical pipe (mpeg movies 718Kb/445Kb). 

VIBRATION  
 
After here  		Vibrating bed is recently the most attracting topics for physicists. Especially, standing surface wave is popular topics. By changing several parameters, you can see various shapes of standing waves [left]. If you magnify standing wave, you can notice that their shape is extremely non-linear[right]. 
 
After here 
Other interesting feature of vibrating bed is convection and segregation. Under strong vibration, the bed is fluidized and comes to have flow, which usually results in convection. In addition to this, there is strong size segregation where larger, thus heavyer, particle goes UP! The relation between convection and segregation is still under active investigations. 

FLUIDIZATION
 After here  		If air strongly flows  upwards into granular bed from the bottom, bed becomes fluidized. If you are a good swimmer and the bed is large enough, you may be able to swim in it! Actually speaking,  this fluidied bed totally behaves like fluid. Air bubble blown into bed goes up just like that in ordinary fluid [left]. Even stronger air flow causes spontanious bubbling [right]. It looks like nothing but Boiling water.
After here
To be continued. 
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