Case Study: Natural Frequency for a Mass-spring System

Using a Frequency Study with SolidWorks Simulation Professional, it is possible to calculate the Natural Frequency of a single degree of freedom (DOF) Mass-spring system.

Mass Spring.png

To calculate the natural frequency of this system, the equation below is used where k is the spring stiffness in Newtons/meter, m is the mass in kilograms, and ω is the natural frequency in radians/second.

Mass Spring Equation.png

How does this translate to SolidWorks Simulation? For this example, we can model a 1m x 1m x 1m cube with a mass density of 1000 kg/m3. For the spring, we can use the “elastic support”, with a stiffness of 100 N/m. To restrict the motion to the vertical (Y) direction only (the equation above assumes one DOF, rigid body translation in the vertical direction), we will need to add “advanced fixtures” to prevent translation in the X and Z directions.

Simulation Study Fixtures.png


Finally, we need to mesh the problem before running it. Because the geometry is simple and we’re looking for a first-order response, a high mesh density is not critical so we can go with a coarse mesh.

After running the simulation, the first natural frequency is shown to be 0.31622 rad/s. How does this compare with our hand calculations? Well, taking our previous equation we find that:

Mass Spring Equation - Expanded.png

Our answer is spot on with SolidWorks Simulation! The formula we used also gives us some insight into changing a structure’s first natural frequency. If we increase the stiffness of the structure or decrease the mass, we can raise the natural frequency. If we decrease the stiffness or increase the mass, we can lower the natural frequency.

But what about real-world assemblies and components that we want to analyze? With frequency analysis in SolidWorks Simulation, our modeled structures and assemblies behave like a complex combination of this spring-mass system. We assign materials to parts, and these materials specify a density that controls the mass; we specify an elastic modulus that controls the stiffness, and a finite-element version of the resonance equation above is performed across the entire system.


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