![]() For us, dangling under gravity is close enough to approximate free-free analysis in Elmer. A free-free part in real life would be floating in space not subject to a gravity. The case we will analyze is called free-free, where the object is not rigidly held at all. (It is also slightly higher because the tension has been increased a little bit). The note is mainly higher because its length is shorter. When you pluck the string again you hear a higher note. When you press the sting onto the neck of the guitar you shorten the length of string that can vibrate. When pluck a guitar string you hear a certain not. How you hold something changes which frequencies can be excited. I’ll examine these factors in depth below. ![]() I assume my model is very close to the real life part.īased on my previous work, I’m using 2nd order tetrahedral elements, which gave answers accurate to within 2% of predicted hand calculations in my previous post, Calculating the Vibration Frequency of a Cantilevered Beam.ģ-5) Boundary Conditions, Mesh Density, ad Material Properties My model used average measured dimensions. 1 mm, thicknesses in the forks of the prong only varied by +/. I measured my tuning fork with some vernier calipers, accurate to 0. ![]() Material Properties – Is your material correct?.Mesh density – Is the mesh fine enough to give you an accurate answer?.Boundary Conditions – Is the way you’re holding the part in the model the same as the way you’re holding it in real life?.Element types – Did you use elements which will give you an accurate answer?.Geometry – Is your CAD model accurate vs the real part?.When you’re making a model of a part a number of inputs impact your answer. Hardware: Ruler + Vernier Calipers (to measure the tuning fork).Hardware: Microphone/headset microphone (allows you to record audio when you hit tuning fork in real life, I could also have used a cell phone).Software: Audacity (audio analysis/recording, analyzes the frequencies in an audio file).Software: Libreoffice/Excel (spreadsheet, conversion of FEA eignevalues into frequencies).Compare the calculated to actual results.Ping test the part in real life to find the actual frequencies.Import mesh into Elmer (Finite Element Analysis (FEA) software), solve for frequencies in Elmer.So I bought a tuning fork off and compared the Elmer analytical frequencies to the real life free-free frequencies. I’ve shown that Elmer accurately calculates a cantilevered beam’s lowest natural frequency, but I wanted to test Elmer on a real part.
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