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Holding a tune with SOLIDWORKS Simulation

Monday February 6, 2017 at 11:33am

Holding A Tune with SOLIDWORKS Simulation

In this blog we’re going to have a look at modelling a simplified guitar string and seeing the effect of stretching the geometry, in the way of using a prescribed displacement, has on the first natural frequency of the guitar string using a SOLIDWORKS Frequency Simulation.

We’re going to assume that the guitar string is 0.6m long, has a cross section diameter of 0.5mm and is made from Alloy Steel, which has the material properties:

·         Poisson’s ratio: 0.28

·         Elastic Modulus: 2.1x1011 N/m2

·         Density: 7700 Kg/m3

The setup being used in this study is a solid mesh (as beam meshes do not allow the Prescribed Displacement External Load) of curvature based, high quality elements of default size. One end is fixed (which therefore has all 6 Degrees of Freedom fixed), whilst the other has a prescribed displacement normal to the end face of the guitar string, with the other two translation directions fixed.

In this study we’re going to look at the first natural frequencies using displacements in the Z-direction of 1 to 10mm in increments of 1mm. To do this we’re going to use a Design Study. To start this design study we first need a variable, which in this case is the Prescribed Displacement. So by editing the Prescribed Displacement in the frequency study, going to the Z-translation, clicking the dropdown arrow and selecting link value, we will be able to create a variable.

The pop up window will be empty as we will not have created any variables yet. Clicking on “Edit/Define..” opens up a new pop up window which allows us to create the simulation variable we require.

Using the settings from the screengrab above we can then hit “Apply” and “Ok” which will close the pop up window and take us to the previous pop up. In this window we just need to select the variable we created, in this case it is called “Displacement” and then hit “Ok”. Once this is done, the variable is now linked to the Prescribed Displacement in the frequency study which we can then alter in the Design Study. The value box for the Z-translation will now have turned grey to indicate that it is linked. To create the study simply right click on the frequency study just above the Status Bar and select “Create New Design Study”

Going into the Design Study 1 tab we can then create our Design Study. In the variables we are going to select “Displacement” from the drop down menu, using “Range with Step” option going from 1mm to 10mm with 1mm steps. In the Constraints options we’re going to select “Add Sensor…” from the drop down menu and create a sensor which will get the value for the first natural frequency value.

And we will then set this Constraint, “Frequency1”, to Monitor only. All we need to do now is clear the optimization checkbox by the Run button and hit Run. This will automatically run all 10 simulations for us and give us the results.

Therefore, as we tighten the guitar string and increase its length, the natural frequency increases. This blog was done on a simplified guitar string, but in reality guitar strings increase in length and diameter. Using the design study, creating a few more variables and linking them to the model you would be able to test all 6 real guitar strings and see how much you have to tighten it to get the correct frequency out. The setup of the geometry, frequency study and design study all took under 10 minutes with another 5-10 minute run time. This really quick simulation has given us a lot of data which you wouldn’t be able to work out any other way than real life testing, which takes a lot longer!

By Chris Boyles


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