Eigenvalues of a string with fixed ends and a mass in the middle

In summary, the eigenvalues of a string with fixed ends and a mass in the middle represent the possible frequencies at which the string can vibrate. These eigenvalues are determined by the length, tension, and mass of the string, and can be found by solving the eigenvalue equation for the string's boundary conditions. The lowest eigenvalue, known as the fundamental frequency, corresponds to the string's natural frequency of vibration. Higher eigenvalues represent harmonics of the fundamental frequency, and each eigenvalue has a corresponding eigenvector that describes the shape of the string at that frequency.
  • #1
Frank93
4
0
Hi there. First of all, sorry for my bad english. I ´m trying to solve next exercise, from Vibrations and Waves in Continuos Mechanical Systems (Hagedorn, DasGupta): Determine the eigenfrequencies and mode-shapes of transverse vibration of a taut string with fixed ends and a discrete mass in the middle.

I set next wave equation:

T * ∂^2 Y/ ∂^2 X = ( ρ + m*δ(x-L/2) ) * ∂^2 Y/ ∂^2 t

where
T: tension, ρ: lineal density of the string, m: mass of the particle in the middle of the string, δ: Dirac delta, L: length of the string, and the boundary conditions are Y(0,t)=0 and Y(L,t)=0.


I don`t know how to continue this, because to determine the eigenvalues, I need the wave equation, but it isn`t the usual Y(x,t) = [A*Cos(k*x)+B*Sin(k*x)]*[C*Cos(w*t)+D*Sin(w*t)]. How can I solve this differntial equation? Or another way to solve this?
 
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  • #2
  • #3
Thank you drvrm!
 

1. What is the physical significance of eigenvalues in this scenario?

The eigenvalues represent the possible frequencies at which the string can vibrate with fixed ends and a mass in the middle. These frequencies are determined by the material properties and dimensions of the string, and can be used to predict the behavior of the string in different situations.

2. How do the eigenvalues change if the mass in the middle is varied?

The eigenvalues will change depending on the mass of the object in the middle of the string. As the mass increases, the eigenvalues will decrease, meaning the string will vibrate at lower frequencies. This relationship between mass and eigenvalues can be explained by the equation for frequency: f = (1/2π)√(T/μ), where T is the tension in the string and μ is the mass per unit length.

3. Can the eigenvalues be calculated mathematically?

Yes, the eigenvalues can be calculated using the wave equation for a string with fixed ends and a mass in the middle. This equation takes into account the tension, length, and mass of the string to determine the possible frequencies of vibration.

4. How do the eigenvalues of a string with fixed ends and a mass in the middle compare to those of a string with only fixed ends?

The eigenvalues of a string with fixed ends and a mass in the middle will be lower than those of a string with only fixed ends. This is because the added mass in the middle reduces the tension in the string, causing it to vibrate at lower frequencies.

5. Can the eigenvalues be used to determine the natural frequencies of a vibrating string?

Yes, the eigenvalues can be used to determine the natural frequencies of a vibrating string. The natural frequencies are the frequencies at which the string will vibrate without any external force acting on it. By calculating the eigenvalues, we can determine these frequencies and predict the behavior of the string in different situations.

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