Comparing Dynamic and Kinematic Simulations in MotionView and MotionSolve

Welcome to the Multibody Dynamics for Automotive Applications using MotionView and MotionSolve blog series! In this chapter, we analyze the key differences between kinematic and dynamic simulations using a four-bar mechanism in MotionView software. By switching between these simulation types, we can observe how forces influence motion and how constraints affect system behavior in vehicle dynamics simulation. 

Understanding Kinematic vs. Dynamic Simulations 

• Dynamic Simulation – The motion is influenced by external forces such as applied torques, gravity, and compliance. The solver calculates the resulting motion based on Newtonian mechanics. 
• Kinematic Simulation – Motion is fully dictated by prescribed constraints. The solver forces the system to follow a predefined motion, ignoring external forces such as torque, damping, and inertia. 

To illustrate these differences, we first perform a dynamic simulation and then switch to a kinematic simulation by modifying the model parameters. 

Switching to a Kinematic Model 

• Deactivate Driving Torque – Right-click on the applied Driving Torque and select Deactivate. 
• Reactivate Motion Input – Right-click on Motion 1 and select Activate. 
• Verify the Degree of Freedom – Go to Tools > Check Model and confirm that the system now has zero degrees of freedom, indicating a fully constrained kinematic model. 
• Run the Kinematic Analysis – Save the model and execute the kinematic simulation.

Observing the Differences 

Dynamic Simulation Results 

• The BYSTOP torque applied earlier prevents full rotation and causes a bounce-back effect. 
• The mechanism responds naturally to forces, with constraints acting dynamically.

Kinematic Simulation Results 

• Despite the BYSTOP torque, the small bar completes a full revolution because the motion constraint dictates the movement. 
• Unlike the dynamic simulation, the torque constraint is ignored, and the mechanism continues rotating without restrictions. 

This comparison highlights the fundamental difference: 

• In dynamic simulations, forces influence motion and constraints restrict movement. 
• In kinematic simulations, motion is enforced regardless of external forces. 

Practical Applications in Multibody Dynamics 

Understanding these differences is crucial for automotive dynamics analysis. Engineers use dynamic simulations when evaluating: 

• Vehicle suspension behavior under real driving conditions. 
• Powertrain motion considering applied torques. 
• Crash simulations where force responses matter. 

On the other hand, kinematic simulations are useful for: 

• Verifying motion feasibility in automotive engineering simulation. 
• Testing mechanical linkages without considering mass and inertia effects. 
• Checking interference issues in vehicle system modeling. 

Conclusion 

This exercise demonstrates the importance of selecting the right simulation approach in multibody dynamics analysis. While dynamic models offer realism, kinematic models provide controlled testing environments. In MotionView certification courses and MotionSolve online training, engineers learn when to apply each technique for multibody dynamics in automotive applications. 

Stay tuned for more insights on multibody simulation software, and continue exploring MotionView tutorials for beginners to enhance your understanding of automotive dynamics fundamentals! 

This blog is part of our ongoing Multibody Dynamics blog series. If you missed the previous posts, check them out here.  

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