Forcing function of falling mass

[canwesteng]

Does anyone know what the forcing function of a repeated impact is? In this case, rocks falling at the same frequency over and over. Due to the machinery, the impacts will happen at the same frequency, though the force could vary. As a worst case I have modelled it as a sine function right now, but this now has a negative force component that will lift up on the structure, which won't happen in reality.

 

[JStephen]

Small gravel off a conveyor belt- just treat like a liquid impinging on a surface.
Large rocks at uniform intervals- (sin(t)+1) to get rid of the negative, or square wave, etc. If you don't know the actual wave shape, go with the simplest.

 

[ANE91]

Periodic forcing function

 

[goutam_freelance]

You can consider it as shock loading with a half sine wave forcing function. Alternatively an impulse excitation can be assumed.

 

[HTURKAK]

p = −mv − mv = −2mv

Does anyone know what the forcing function of a repeated impact is? In this case, rocks falling at the same frequency over and over.

I do not understand if the rocks stick or say accumulate on the machine . Say does not accumulate ,
The upper bound could be calculated using the principles of particle dynamics using the momentum and impact.

- Calculate the velocity of the rock before impact. V= SQRT (2gh)
- The momentum before impact is mv and after impact −mv so , Δp = −mv − mv = −2mv ( i have copy and pasted Δδ , from internet . The greek letters together with some expressions now missing with this new forum set-up)
- If the frequency ( no. of falling rocks in one second ) is f,
- The upper bound limit for the force would be F = +2m*V*f. ( for SI units , m=kg, V= m/sec and F= Newton)

 

[canwesteng]

You can consider it as shock loading with a half sine wave forcing function. Alternatively an impulse excitation can be assumed.
View attachment 9602

Can you share the reference for this text?

 

[goutam_freelance]

Can you share the reference for this text?

I apologize for not having the book details as I have only a small part of the book. But you may have the required information in the following books.​

1.Vibration Dynamics and Control by Giancarlo Genta​

2. Vibration and Shock Handbook by Clarence W. de Silva