Fluid-like Impact
Fluid-like Impact
(OP)
This is my first time, so please be gentle.
I need to estimate the impact force acting on a conveyor system at the loading point. The system continuously receives a granular product dropped from 3' with an initial velocity of 0 ft/second (the product comes from another conveyor system). The product is typically composed of gravel sized particles. There may be some boulder sized particles weighing as much as 300 lbs in the flow sporadically. The maximum mass flow rate is 42 tons per minute.
Two questions:
1) I understand the steady-state "fluid" flow force to be approximately 1936N or 435 lbs (Force = mass flow rate [635 kg/sec]* velocity [4.24m/s given the drop]) if we assume the product is a fluid; however, is this still accurate during start-up, or is there an initial transient state with higher force?
2) How might we estimate the boulder force? Do you recommend assuming a set impulse time and average the force over this time? Should I assume a deceleration distance and kinetic energy? Should I superimpose the boulder impact force with the stead-state fluid flow force?
Any advice would be appreciated.
Thank you in advance.
I need to estimate the impact force acting on a conveyor system at the loading point. The system continuously receives a granular product dropped from 3' with an initial velocity of 0 ft/second (the product comes from another conveyor system). The product is typically composed of gravel sized particles. There may be some boulder sized particles weighing as much as 300 lbs in the flow sporadically. The maximum mass flow rate is 42 tons per minute.
Two questions:
1) I understand the steady-state "fluid" flow force to be approximately 1936N or 435 lbs (Force = mass flow rate [635 kg/sec]* velocity [4.24m/s given the drop]) if we assume the product is a fluid; however, is this still accurate during start-up, or is there an initial transient state with higher force?
2) How might we estimate the boulder force? Do you recommend assuming a set impulse time and average the force over this time? Should I assume a deceleration distance and kinetic energy? Should I superimpose the boulder impact force with the stead-state fluid flow force?
Any advice would be appreciated.
Thank you in advance.






RE: Fluid-like Impact
In your first question you mentioned the grain mimicking fluid flow so you might want to search for thrust block calculations to get some guidance on that issue. The initial startup in particular imparts a "water hammer" and whatever force they tell you to use be aware that something hitting the system like that can shake things loose in a way that might otherwise seem hard to quantify. It's certainly nothing to be trifled with.
As for your second question, well, the mechanical engineers and the dynamics gurus may have other methods, but I would calculate the kinetic energy of the bolder (i.e., .5mv^2) and set it equal to the work done on the system, force x distance, and solving for the force. This would require assuming an initial distance and refining the calculation through an interritive (sp?) process. In other words, assume a distance and calculate the force associated with it separate from the system. Then check what deflected distance that force would impart upon the system and repeat this cycle to the degree of accuracy you need. And watch your units.
RE: Fluid-like Impact
2. Have seen the use of the "strain energy" approach.
Regards,
Lyle
RE: Fluid-like Impact
Check this thread Link. With so many unknowns you should be conservative on your design unless you do on site measurement.
RE: Fluid-like Impact
RE: Fluid-like Impact
RE: Fluid-like Impact
RE: Fluid-like Impact
One thing you might consider, since you're treating it like a fluid flow is what in EE parlance is called "shot noise", which is the standard deviation of the nominal flow. If you know the particle size, you can compute the nominal number of particles per sec in the flow. The square root of that number would be representative of the standard deviation of the flow. This would at least give you some feel for the worst case of the "normal" flow.
TTFN

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