Static Vs Dynamic Force Analysis in Mechanism

In summary, static force analysis in mechanisms involves evaluating forces and moments under static conditions, ensuring that the system is in equilibrium without motion. This analysis focuses on the forces acting on the mechanism at rest or at constant velocity, allowing for the determination of support reactions and internal forces. In contrast, dynamic force analysis considers the effects of motion, accounting for acceleration and inertia, leading to a more complex evaluation of forces during operation. This analysis is crucial for understanding the behavior of mechanisms under varying loads and speeds, ensuring structural integrity and performance in real-world applications.
  • #1
tetris
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Homework Statement
When should static or dynamic force analysis be applied when analyzing moving mechanisms ?
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My understanding is that :
Static Force Analysis
  • carried out on objects in static or dynamic equilibrium, that is rigid bodies that are not moving or moving with zero acceleration
  • therefore, does not take into account the inertia of the object
Dynamic Force Analysis
  • carried out on objects in motion with an acceleration
  • therefore, takes into account the inertia of the object (along with the angular velocity and angular acceleration)
However, I have seen both static and dynamic force analysis applied to a moving four bar linkage. In the case where I would like to find the force applied to the coupler to move the mechanism from position A to B, would dynamic force analysis be used? Since, the velocity would not be constant, hence, it has an acceleration.

Any help is appreciated, thanks in advance.
 
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  • #2
Welcome! :smile:
It depends on what force is greater.
We are interested on how robust the joint should be to resist those forces.
We can have a light link accelerating much and rapidly, like the connecting rod of a small engine: dynamic forces are more important in that case.
 
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  • #3
Firstly, thank you for your help :smile:

In summary, it depends on the speed of the mechanism. So, for the same mechanism, if one is moving at very high speed, then dynamic analysis would be used. On the other hand, if it is moving at low speed, static analysis would be sufficient since the inertia effects are small.

However, is there a velocity or any other value threshold where dynamic analysis should be applied?
 
  • #4
tetris said:
Firstly, thank you for your help :smile:

In summary, it depends on the speed of the mechanism. So, for the same mechanism, if one is moving at very high speed, then dynamic analysis would be used. On the other hand, if it is moving at low speed, static analysis would be sufficient since the inertia effects are small.

However, is there a velocity or any other value threshold where dynamic analysis should be applied?
It depends on the accelerations of the mechanism components. There could be a mechanism with a low output velocity, but that experiences large accelerations in its components. Accelerations and mass are what generate force. It really should be taken on a case by case basis.
 
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FAQ: Static Vs Dynamic Force Analysis in Mechanism

What is the difference between static and dynamic force analysis in mechanisms?

Static force analysis deals with forces in a mechanism when it is in a state of equilibrium, meaning all forces and moments are balanced and there is no motion. Dynamic force analysis, on the other hand, considers the forces and moments in a mechanism when it is in motion, taking into account inertial forces due to acceleration and deceleration of the components.

Why is dynamic force analysis more complex than static force analysis?

Dynamic force analysis is more complex because it requires accounting for time-dependent variables such as acceleration, velocity, and inertia. This involves solving differential equations and often requires numerical methods and computer simulations. Static analysis, in contrast, only requires solving algebraic equations and does not involve time-dependent changes.

When should static force analysis be used instead of dynamic force analysis?

Static force analysis should be used when the mechanism operates at very low speeds or is in a state of equilibrium, where inertial forces can be neglected. It is also useful for initial design stages to get an approximate understanding of the forces involved. For high-speed mechanisms or those with significant acceleration, dynamic force analysis is necessary.

What are the typical applications of dynamic force analysis in mechanisms?

Dynamic force analysis is essential in applications where mechanisms operate at high speeds or undergo significant accelerations and decelerations. Examples include automotive engines, robotic arms, aerospace mechanisms, and any system where precise control and prediction of forces are critical for performance and safety.

How do engineers typically perform dynamic force analysis?

Engineers typically perform dynamic force analysis using a combination of analytical methods and computer-aided engineering (CAE) tools. They may use software like MATLAB, Simulink, or specialized dynamic analysis programs to model the mechanism, input the necessary parameters, and simulate its behavior over time. These tools can handle complex calculations and provide visualizations of the forces and motions involved.

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