AM  Vol.8 No.5 , May 2017
Distribution Free Waves in Viscoelastic Wedge with an Arbitrary Angle Tops
Abstract
In work questions of distribution of waves in a viscoelastic wedge with any corner of top is considered. The elastic cylinder with a radial crack is a wedge corner. The regional task for system of the differential equations in private derivatives is decided by means of a method of straight lines that allows using a method of orthogonal prorace.

1. Introduction

The problems of the propagation of viscoelastic waves in extended laminate and layers of variable thickness are considered in [1] [2] [3] . In these papers, the boundaries in the formation of the structure of the wave field, as a spectrum of Eigen frequencies and Eigen modes, are revealed in a series for simple problems (for unchanged boundaries), and the boundary change is consistently accompanied by increasing difficulties. We also consider the occurrence of local singularities in wave fields.

In this paper, in contrast to the above, the propagation of waves along the z axis in an infinite viscoelastic cylinder with a radial crack is considered, which is a wedge with some angle | φ | < 180 ..

2. Statement of the Problem and Methods of Solution

The basic equations of motion of a deformable cylinder (with a radius R) with a longitudinal crack, which at φ = | φ 0 | < 180 , Case describes a wedge. They are given with three groups of relations. The system of equations of motion of a wedge in a cylindrical coordinate system ( r , φ , z ) it takes the form

ρ u r d t 2 = σ r r d r + σ r r σ r φ r + 1 r σ r φ φ + σ r z z ; ρ 2 u φ t 2 = 1 r σ φ φ φ + 2 σ r φ r + σ r φ r + σ z φ z , ρ 2 u z t 2 = σ z z z + σ r z r + σ z z r + 1 r σ z φ φ . (1)

Here

ε r r = u r r ; ε z z = u z z ; ε φ φ = 1 r u r φ + u r r ; } ) T , i = 1 , N ¯ (11)

Central differences (10), (11) are used for internal straight lines ( 1 < i < N ), the left and right differences (10), (11) allow us to take into account the boundary conditions for φ. In the first case, the derivative of φ on the right sides of Equation (8) can be expressed by the formulas [4] :

1 < i < N

w i , φ = ( w i + 1 w i 1 ) / 2 Δ ; u i , φ = ( u i + 1 u i 1 ) / 2 Δ ; v i , φ = ( v i + 1 v i 1 ) / 2 Δ ; (12)

τ φ i , φ = ( τ φ ( i + 1 ) τ φ ( i 1 ) ) / 2 Δ ; σ φ i , φ = a ( σ i + 1 σ i 1 ) / 2 Δ + b r [ ( v i + 1 2 v i + v i 1 ) / Δ 2 + w i , φ ] + c k u i , φ ;

B i = ( u i + 1 2 u i + u i 1 ) / Δ 2 / k k v i , φ .

Boundary conditions at φ = φ 0 2 is taken into account in the equations cor-

responding to the straight lines i = 1 .

For the main unknowns that do not enter into the boundary conditions, wi, vi, ui use the right difference (10):

i = 1 :

w i , φ = ( 3 w 1 + 4 w 2 w 3 ) / 2 Δ ; v i , φ = ( 3 v 1 + 4 v 2 v 3 ) / 2 Δ ; u i , φ = ( 3 u 1 + 4 u 2 u 3 ) / 2 Δ . (13)

For a variables τ φ using central difference

τ φ i , φ ( τ φ 0 τ φ 2 ) / 2 Δ = τ φ 2 / 2 Δ (14)

The first and third of the conditions (9,c) are taken into account when approximating the derivatives of the function sj, B by j

σ φ 1 , φ = ( σ φ 2 σ φ 0 ) / 2 Δ = σ φ 2 / 2 Δ = ( a σ r 2 + b r [ ( v 3 v 1 ) / 2 Δ + w 2 ] c k u 2 ) / 2 Δ

B 1 , φ ( B 2 B 0 ) / 2 Δ = B 2 / 2 Δ = [ ( u 3 u 1 ) / 2 Δ / r k v 2 ] / 2 Δ .

Similarly, derivatives for the straight line with the number i = N, taking into

account the boundary conditions at φ = φ 0 2 . The only difference is the replace-

ment of the right finite difference left:

i = N :

w i , φ = ( 3 w N 4 w N 1 + w N 2 ) / 2 Δ ; v i , φ = ( 3 v N 4 v N 1 + v N + 1 ) / 2 Δ ; u i , φ = ( 3 u N 4 u N 1 + u N + 1 ) / 2 Δ ; (15)

τ φ i , φ = τ φ ( N 1 ) / 2 Δ ; σ i , φ = ( a σ N 1 + b r [ ( v N v N 2 ) / 2 Δ + w N 1 ] + c k u N 1 ) / 2 Δ = σ N 1 2 Δ

B i , φ = [ ( u N u N 2 ) / 2 Δ / r k v N 1 ] / 2 Δ = B N 1 2 Δ .

The number of straight lines can be reduced by using the ant symmetry conditions for the transverse vibrations of a plate at

φ = 0 : w = v = σ φ = 0. (16)

The corresponding difference relations that take the conditions (16) can be written in the form

i = N :

w i , φ = w N 1 / 2 Δ ; u i , φ = u N 1 / 2 Δ ; v i , φ = ( 3 v N + 4 v N 1 v N 2 ) / 2 Δ . (17)

τ φ i , φ = ( 3 τ φ N 4 τ φ ( N 1 ) + τ φ ( N 2 ) ) / 2 Δ ; σ i , φ = ( a σ N 1 + b r [ ( v N v N 2 ) / 2 Δ + w N 1 ] + c k u N 1 ) / 2 Δ = σ N 1 2 Δ

B i , φ = ( 2 u N + u N 1 ) / Δ 2 / r k v i , φ .

The resolving system of ordinary differential equations according to (8) has the form:

w i = σ i / k a ( k u i + ( w i + v i , φ ) / R ) ; v i = τ φ i + ( v i w i , φ ) / R ; u i = τ z i + k w i ; σ i = ω 2 w i + [ 2 ( ( w i + v i , φ ) / R w i ) τ φ i , φ ] / r k τ z i ; τ φ i = ω 2 v i + ( σ i , φ + 2 τ φ i ) / r k ( u i , φ / R k v i ) ; τ z i = ω 2 u i + ( B i , φ + τ z i ) / r + k ( σ i + 2 ( k u i w i ) ) . (18)

In Equation (18), the expressions for the derivatives w i , φ , v i , φ , u i , φ , τ φ i , φ , σ i , φ , B i , φ are chosen from the relations (13)-(17), depending on the boundary conditions with respect to the coordinate φ.

The free surface conditions, the equivalent conditions (9,a) and forming the boundary value problem together with the Equation (18), is obtained in the form

τ φ i = 0 , σ φ i = 0 , B i = 0 ( i = 1 , , N ) (19)

Thus, the original spectral problem (8), (9) is reduced to the canonical problem (18) and (19) by discrimination of the coordinate φ by the method of lines, for the solution of which we apply the method of orthogonal sweep.

3. Numerical Results

The results of calculations are obtained on dimensionless parameters ν = 0.25 , с / c s , R / λ , A = 0.048, β = 0.05, α = 0.1, where λ = 2 π / k is the wavelength of the wave, the density ρ = ρ / ρ 0 ( λ = ρ ( с р 2 2 с s 2 ) , μ = c s 2 ρ ) [9] [10] . For numerical realization of the problem a software tool МAPLE 9.5.

Comparisons of the obtained numerical results (without viscosity R λ ( t ) = Math_84#) with the known results [1] [3] are given in Table 1.

The limiting values of the phase velocity of the first edge mode, depending on the wedge angle at the vertex, found for a material with a Poisson’s ratio υ = 0.25 and r = R = 1 , R λ ( t ) = R μ ( t ) = 0 are given in Table 1 of Column 2. Also the results obtained in [11] for a wedge based on plates Variable thickness are given in Table 1 of column 3 (according to the theory of Kirchhoff-Love plates) and column 4 (according to the theory of Timoshenko’s plates). Column 5 corresponds to a calculation variant with three internal straight lines (N = 3) and boundary conditions (9,a), column 6 corresponds to the boundary conditions:

φ = φ 0 2 : σ φ = σ φ r = σ φ z = 0 ; φ = φ 0 2 : u r = u z = σ φ φ = 0 (20)

with the same number of straight lines. From the results, the variants of calculating variable-section plates (according to the Kirchhoff-Love and Tymoshenko theory) and the three-dimensional theory (the proposed method) show that they agree within 7% for wedge angles not exceeding 28˚ (wedge angle φ 0 28 ).

In the framework of the work described in this paper (based on the calculation procedure for a three-dimensional wedge), taking into account the viscous properties of the material R λ ( t ) = R μ ( t ) = A e β t / t 1 α , they are shown in Figure 1.

Таble 1. Comparisons of the obtained numerical results.

Figure 1. Change in real and imaginary parts of the phase velocity Fluctuations depending onк.

In Figure 1 shown the real (curves CR1, CR2) and imaginary (curves CI1, CI2) parts of the dispersion curves of the first two modes of oscillations in an infinite viscous elastic wedge with angle ( φ 0 = 45 ).

For comparison, the dependence on the wave number of the phase velocity of the first flexural mode of oscillations of a solid cylinder, founded by Pochhomer and Krie, using special functions (curve CR3) [12] [13] and curve CI3 [14] is shown in the same figure. We note the characteristic features of the curve CR3: at zero, the phase velocity is zero, and at infinity, tends to the Rayleigh wave velocity for a half-space. In the case of a viscoelastic wedge, the first mode has a cutoff frequency, and the phase velocity tends to infinity. At large wave numbers, the limiting phase velocity of this mode also coincides with the velocity of the Rayleigh wave.

4. Conclusions

Thus, unlike waveguides with a rectangular cross section in wedge-shaped waveguides with a sufficiently small wedge angle, in the analysis of the dispersion dependences of the first mode, it is permissible to use the theory of plates of variable cross section Kirchhoff-Love and Timoshenko. The established fact is explained by the phenomenon of localization of the shape of oscillations near the acute angle of the wedge, described in [3] .

Based on the results obtained, the following conclusions are drawn:

・ the results of calculating the limiting real velocity part (c = CR) of the propagation of the first mode of a wedge-shaped waveguide in the theory of changing the Kirchhoff-Love plates [10] [11] and according to the dynamic theory of elasticity differ by no more than 6% for corners of the wedge top not exceeding 28˚;

・ in the wedge-shaped waveguides, the first mode has a cut-off frequency, and the phase velocity tends to infinity.

The work was supported by the Fund for Fundamental Research F-4-14 of the Republic of Uzbekistan.

Cite this paper
Ibrahimovich, S. , Khudoyberdiyevich, T. , Sharipovich, A. and Ixtiyorovich, B. (2017) Distribution Free Waves in Viscoelastic Wedge with an Arbitrary Angle Tops. Applied Mathematics, 8, 736-745. doi: 10.4236/am.2017.85058.
References

[1]   Safarov, I.I., Akhmedov, M.Sh. and Boltaev, Z.I. (2015) Distribution of the Natural Waves of Extended Lamellar Viscoelastic Bodies of Variable Thickness. LAP, Lambert Academic Publishing, 112 р.

[2]   Safarov, I.I., Akhmedov, M.Sh. and Qilichov, O. (2016) Dynamics of Underground Hiheline from the Flowing Fluid. Lambert Academic Publishing, 345 р.

[3]   Safarov, I.I., Teshaev, M.H. and Boltaev, Z.I. (2013) Mathematical Modeling of the Wave Process in a Mechanical Waveguide with Allowance for Internal Friction. LAP, Germany, 243 p.

[4]   Godunov, S.K. (1977) On Numerical Solutions of Boundary Value Problems for Systems of Linear Ordinary Differential Equations. ELIBRARY.RU. Uspekhi Matematicheskikh Nauk, 1061, 16, 171-174.

[5]   Ilyushin, A.A. and Pobedrya, B.E. (1970) Fundamentals of the Mathematical Theory of Thermal Viscoelasticity. Science, Moscow, 280 p.

[6]   Filatov, A.R. and Sunchaliev, P.M. (1972) On Some Methods of Studying Nonlinear Problems in the Theory of Viscoelasticity. Reports of the Academy of Sciences of the USSR, 206, 201-203.

[7]   Ewing, W.M., Jardetzku, W.S. and Press, F. (1962) Elastic Waves in Layered Media. McGraw-Hill, New York.

[8]   Koltunov, M.A. (1976) Creep and Relaxation. Higher School, Moscow, 276 p.

[9]   Safarov, I.I., Akhmedov, M.Sh. and Boltaev, Z.I. (2016) Ducting in Extended Plates of Variable Thickness. Global Journal of Science Frontier Research: F Mathematics & Decision Sciences, 16, 33-66.

[10]   Bozorov, M.B., Safarov, I.I. and Shokin, Yu.I. (1966) Numerical Simulation of Oscillations of Dissipatively Homogeneous and Inhomogeneous Mechanical Systems. Siberian Branch of the Russian Academy of Sciences, Novosibirsk, 188 p.

[11]   Safarov, I.I., Akhmedov, M.Sh. and Boltaev, Z.I. (2015) Dissemination Sinusoidal Waves in of a Viscoelastic Strip. Global Journal of Science Frontier Research: F Mathematics & Decision Sciences, 15, 39-60.

[12]   Pochhammer, L. (1876) über die Fortpflanzung segechwindigkeiten schwingungen in einem unbergrawzten isotropen kreiscylinder. Y.reine und angew. Math., 81, 324-336.

[13]   Chree, C. (1886) Longitudinal Vibrations of a Corcablar Bar. The Quarterly Journal of Pure and Applied Mathematics, 21, 287-298.

[14]   Safarov, I.I., Akhmedov, M.Sh. and Boltaev, Z.I. (2016) Vibrations and Diffraction of Waves on a Cylindrical Body by a Viscoelastic Medium. Lambert Academic Publishing, Germany, 262 р.

 
 
Top