V.2 No 1

91

Bend effect on vibration pattern

fig3.gif (7882 bytes)

Fig. 3. The vibration patterns in a homogeneous semi-finite elastic line having a bend with the angle alphacut.gif (839 bytes) = 32o at the 17th line element, with respect to the external force inclination angle psi.gif (848 bytes) to the axis x. The line parameters: s = 100 N/m; m = 0,01 kg; F0 = 1 N; omegacut.gif (838 bytes) = 110 sec-1

 

As was supposed, the difference between the x- and y-components is only the value of projections of external force amplitude, and the solutions before and after the bend do not differ. None the less, the vibration patterns within the indicated regions will differ. In Fig. 3 the typical pattern is shown dependently on the external force inclination angle psi.gif (848 bytes) at the positive angles alphacut.gif (839 bytes), and in Fig. 4 – at the negative alphacut.gif (839 bytes).

fig4.gif (8678 bytes)

Fig. 4. The vibration patterns in a homogeneous semi-finite elastic line having a bend with the angle alphacut.gif (839 bytes) = - 32o at the 17th line element, with respect to the external force inclination angle psi.gif (848 bytes) to the axis x. The line parameters: s = 100 N/m; m = 0,01 kg; F0 = 1 N; omegacut.gif (838 bytes) = 110 sec-1

In Fig. 5 the diagrams of typical vibrations in the lines with positive and negative bend angles are shown dependently on the external force momentary phase tetabig14cut.gif (856 bytes) = omegacut.gif (838 bytes)t + ficut.gif (844 bytes)0 . As we can see from the construction, in the region before the bend in all the diagrams the inclined waves propagate. The inclination value equals to the angle of an external force inclination to the axis x. During the vibration process all elements move elliptically, in full correspondence with the multiple experimental facts (see, e.g., [13, pp. 300–301]). In the after-bend region, with positive alphacut.gif (839 bytes) we see the decreasing amplitude of a longitudinal component, and vice versa with negative alphacut.gif (839 bytes). At the same time, with the positive alphacut.gif (839 bytes) the slop of wave front grows with growing psi.gif (848 bytes), and with the negative alphacut.gif (839 bytes) it diminishes with growing  psi.gif (848 bytes).

fig5.gif (8523 bytes)

Fig. 5. The vibration patterns in a homogeneous semi-finite elastic line having the bend angle alphacut.gif (839 bytes) at the 17th line element, with respect to the external force momentary phase tetabig14cut.gif (856 bytes) = omegacut.gif (838 bytes)t + ficut.gif (844 bytes)0  at the external force inclination angle psi.gif (848 bytes) = 40o to the axis x. The line parameters: s = 100 N/m; m = 0,01 kg; F0 = 1 N; omegacut.gif (838 bytes) = 110 sec-1

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