A Impact considerations

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The discussion centers on the dynamics of a vertical spring-mass system, particularly during the collision phase when the mass re-engages with the spring. Key points include the need to consider impact forces and whether additional considerations are necessary for modeling these interactions, especially in a finite element analysis (FEA) context. The conversation highlights that the spring is assumed to be massless, which influences the behavior of forces during impact. Participants debate whether an impulse occurs upon collision, noting that while there may not be an instantaneous change in momentum, there can be a sudden change in force or acceleration. Overall, the interaction between the mass and the spring presents complexities that require careful consideration in mathematical modeling.
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Impact considerations with differential equations with event handling
Hi guys

I am not going to go into detail with the problem at hand just an outline. Let’s assume a spring mass system where the system acts in the vertical. The equations are simple to derive and event handling on Julia can help with decoupling the system where the mass and spring are no longer in contact. At that point the mass will move vertically up and then come down to collide with the spring again.

When the collision occurs, do extra co desperations need to be defined to account for the impact forces? My reason for the question is that in an FEA environment I do t believe anything further is considered
 
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Is the spring massless?
 
Mishal0488 said:
When the collision occurs, do extra co desperations need to be defined to account for the impact forces?
What do you mean by 'impact forces'? There is only one contact force between spring and mass.

How that contact force looks like on impact depends on whether the spring is massless or has inertia. With inertia you get longitudal waves propagating in the spring.
 
Spring is massless. By impact forces I am implying moment the spring and mass connect again, the mass will have an acceleration which will obviously cause an impulse in the system. Should that vbs taken care naturally by the direction equations or does it need to have special considerations
 
Mishal0488 said:
Spring is massless. By impact forces I am implying moment the spring and mass connect again, the mass will have an acceleration which will obviously cause an impulse in the system.
Why do you think there will be an impulse? We are talking about an interaction between a mass and a massless spring. There is no instantaneous change of momentum.

Depending on the exact arrangement, there may be an instantaneous change in force. Or an instantaneous change in the rate of change of force.

Consider, for example, a captive spring that is under compression but is restrained against expansion. Suppose the spring is held upright under a falling mass. The mass arrives at the position of the spring. Prior to its arrival, it is in free fall, accelerating downward due to gravity. After arrival, the mass is deflecting the spring and is immediately subject to a finite and increasing non-zero supporting force from the spring. The vertical acceleration of the mass has instantly changed. This is a point of discontinuity for the differential equations describing the motion.

Or consider a spring that is relaxed. It is not restrained against expansion. This spring is held upright under a falling mass. The mass arrives at the position of the spring. Prior to its arrival, it is in free fall, accelerating downward due to gravity. After arrival, the mass is deflecting the spring and is immediately subject to a zero but increasing supporting force from the spring. The vertical acceleration of the mass has not changed. However, the rate of change of its vertical acceleration has instantly changed. This is a point of discontinuity for the differential equations describing the motion.
 
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