SELF |
50 |
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S.B. Karavashkin, O.N.
Karavashkina |
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2. The method to find the
exact analytical solution In Fig.
1 there is presented the studied semi-finite 1D elastic system with lumped masses M
and elastic constraints sg on whose start the harmonic force F(t)
acts. As it was said in the introduction, the first and the last elements of its
subsystems are connected rigidly. Before
we begin studying the system as a whole, consider a separate subsystem under some harmonic
force Fi(t) acting on its start. This line consisting of n
masses connected by constraints having stiffness ss is shown in Fig. 2a.
It is easy to see that this system can be presented by an equivalent diagram shown in Fig.
2b, where the rigid constraint is substituted by the second force acting on the end of
elastic line. Note that such substitution is possible because the subsystem is perfectly
symmetrical and the end elements are rigidly connected. In case of a heterogeneous
subsystem or imperfectly rigid constraints of the end elements, the subsystem with its
main system can be conveniently considered as a heterogeneous line. It naturally requires
another technique being surplus for the present problem, so we will use the equivalent
diagram, Fig. 2b. |
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To find the exact analytical solution for the diagram
shown in Fig. 2b, conveniently use the results obtained in [22] for a homogeneous finite
elastic line on whose interior element an harmonic force F(t) acts. In [22]
three solutions were presented for forced vibrations according to the
relationship between the parameter s = (2m/4ss)1/2 and the unity. This
regularity has the following form: for the periodical regime, s < 1 |
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(1) |
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for the
aperiodical regime, s > 1 |
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(2) |
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and for
the critical regime, s = 1 |
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(3) |
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where s
= arcsin s ; s
= (2m/4ss)1/2 ; s+
= s
+ (s2
- 1)1/2
; s
- = s
- (s2
- 1)1/2 ; k
is the number of element to which the external force is applied; p is the studied
line element number and p is the momentary displacement of the pth
element of subsystem. |
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