Читать книгу Vibroacoustic Simulation - Alexander Peiffer - Страница 78

The Bessel functions can be approximated by a series in 2kR taking the first series term of both functions (Jacobsen, 2011)

(2.154)

This expression is valid for ka<0.5. From the imaginary part we get for the mass

(2.155)

Assuming a cylindrical volume V=πR2lc of the fluid above the piston we can calculate the length of the moving mass cylinder to be

(2.156)

meaning that at low frequencies the piston is moving a fluid layer of 0.85 times the radius acting as an inertia without radiation.