Abstract
In the given chapter, free vibrations of different nonlinear mechanical systems with one-degree-of-freedom, two-degree-of-freedom, and multiple-degree-of-freedoms are reviewed with the emphasis on the vibratory regimes which could go over into the aperiodic motions under certain conditions. Such unfavorable and even dangerous regimes of vibrations resulting in the irreversible process of energy exchange from its one type to another type are discussed in detail. The solutions describing such processes are found analytically in terms of functions, which are in frequent use in the theory of solitons.
Keywords
- soliton-like solution
- nonlinear mechanical systems
- free vibrations
- method of multiple time scales
- suspension bridge
1. Introduction
It is known [1] that the periodical transfer of energy from one type to another is made possible during vibrational processes occurring in nonlinear mechanical systems. This phenomenon is called
Investigations on the energy exchange originate from the chapter [4], wherein the authors studied small nonlinear vibrations of a two-degree-of-freedom (2dof) system consisting of a load suspended on a linearly elastic spring and executing pendulum vibrations and vibrations along the spring’s axis in the same vertical plane. In spite of the apparent simplicity of that system, it realistically explains some phenomena occurring during vibrations of more complex nonlinear systems and in particular describes all types of energy exchange from pendulum vibratory motions into oscillatory motions along the spring’s axis, and vice versa: the periodic and aperiodic energy interchange, as well as stationary regimes during which the energy exchange is absent.
The energy-exchange mechanism in a similar nonlinear 2dof system has been studied in [5, 6]. The system was made up of two loads, one of which was suspended on a linearly elastic spring and executed vertical vibrations, and the other was suspended on an unstretched rod and executed pendulum vibrations in the same vertical plane. Reviews devoted to nonlinear vibrations of 2dof systems can be found in [2, 3].
However, the energy transfer is observed during free vibrations of different nonlinear mechanical systems: possessing one-degree-of-freedom (1dof), two- (2dof), and more degrees-of-freedom (multiple-dof), and as well as having infinite number of degrees-of-freedom (deformable solids).
The majority of papers devoted to the dynamic behavior of suspension-combined systems studies free nonlinear vibrations of suspension bridges with a thin-walled stiffening girder [7, 8, 9, 10, 11]. Different dynamic loads (wind, seismic excitation, moving loads, etc.) after the completion of acting on a suspended structure setup prolonged free nonlinear vibrations of this structure, in so doing both vertical and flexural-torsional vibrations could be excited. One of the most unfavorable nonlinear effects, which is observed in suspension systems during free vibrations, is just the “energy exchange” from one type of vibratory motions into the other under the conditions of the internal resonance.
The intensity and frequency of energy exchange between strongly coupled modes essentially depend on an absolute level of the initial amplitudes [7, 8, 11, 12] which is governed by the value of the initial mechanical energy of the system.
However, the qualitative character of the energy exchange is dependent on the relative level of initial amplitudes which is independent of the system’s initial energy and is defined as the ratio of the initial amplitudes of the two interacting modes [9]. It has been found in [9] that in accordance with a value of that level, three types of an energy-exchange mechanism exist
Solutions describing the one-sided energy transfer occurring in mechanical systems we shall call as
In this chapter, it is shown that solutions of such a type exist both in 1dof systems and in systems possessing two- and more degrees-of-freedom.
2. A one-degree-of-freedom system
The phenomenon of energy transfer, when one type of the energy completely and irreversibly goes into another type of the energy as time passes, can be observed on such a simple object as a mathematical pendulum (Figure 1).
In order to demonstrate this, let us consider the expression for the total mechanical energy of the mathematical pendulum which is combined from the kinetic energy
and the potential energy (Figure 1)
and has the form
where an overdot denotes a time derivative,
Rewrite Eq. (3) in the dimensionless form
where
Consider the case of motion of the mathematical pendulum when its energy
or
Dividing the variables in Eq. (5b), integrating separately the right and left parts of the relationship obtained, and considering that
or
Differentiating Eq. (6b) over
Reference to Eqs. (6) and (7) shows that if the mathematical pendulum begins its motion from the extreme low position, then at
If one represents the phase trajectories of the pendulum motion on the phase plane
3. A two-degree-of-freedom system
3.1. Governing equations
Now, consider a 2dof system presented in Figure 3. The kinetic
where
Applying Lagrange equations of the second kind [15]
and considering Eq. (8), the system’s equations of motion in the dimensionless form within an accuracy of the values of the second order of smallness with respect to
where
Suppose that the linear natural frequency
or the linear natural frequency
It is said that the system is being under the conditions of
For analyzing nonlinear vibrations of the systems subjected to the internal resonance (10), assume that the amplitudes of vibrations are small but finite values and weakly vary with time. Then, perturbation technique could be used to construct the solution of the set of Eq. (9), and, particularly, the method of multiple time scales [16].
3.2. Method of solution
An approximate solution of Eq. (9) can be represented by an expansion in terms of different time scales limiting by the values of the third order of smallness in
where
Substituting Eq. (11) into Eq. (9), considering that
and equating the coefficients of like powers of
to order
to order
The solution of Eq. (12) could be sought in the form
where
3.2.1. The case of a two-to-one internal resonance
Substituting Eq. (15) into the right-hand sides of Eq. (13) yields
where
The functions
Multiply Eq. (17a) by
Representing the functions
we can rewrite the set of four differential equations as
where an overdot denotes differentiation with respect to
Eliminating the value
where
Introducing a new function
and substituting Eq. (21) in Eq. (19a), we have
where
Doubling both sides of Eq. (19d) and subtracting from the net relationship Eq. (19c) with due account for Eq. (21) and
we obtain
Putting
and substituting Eq. (24) into Eqs. (22) and (23), we are led to the equation
Separating the variables in Eq. (25) and integrating the equation obtained yield
or
where
Finely, let us eliminate the value
Separating the variables in Eq. (27) and integrating the net expression, we obtain implicitly the desired function
where
The integral in Eq. (28) can be transformed into an incomplete integral of the first kind, which is tabulated in [17].
At
and the second magnitude
Considering Eq. (29), the solutions of Eq. (28) may be written in the following form:
the first solution
or
and the second solution
or
Solutions (30b) and (31b) at
In the first solution, the process of energy transfer occurs over an infinitely large time interval, which resembles the phenomenon of the transfer of the kinetic energy into potential one, which is described by the soliton-like solution (6b) for the mathematical pendulum.
In the second solution, the process of energy transfer occurs during a finite instant of the time from 0 till
According to our classification, both of them are the soliton-like solutions. At
Physically speaking, this solution kink is responsible to the one-sided energy exchange when the energy of the pendulum vibration completely transforms with time into the energy of the vertical vibrations which energy was equal to zero at the initial moment of time, so the pendulum vibrations give way to the vertical vibrations.
In order to understand the physical meaning of the first integral (26b), let us introduce into consideration the phase plane
Writing the equation of a streamline of the phase fluid
Streamlines constructed according to the relationship
at different magnitudes of
3.2.2. The case of a one-to-one internal resonance
To construct the solution in the case of a one-to-one internal resonance (10b), it will suffice to restrict consideration to the terms of the order of
The resonance (10b) is weaker than (10a), since in order to eliminate circular terms arising in the second approximation, it would suffice to consider the functions
where overdots denote differentiation with respect to
The two first integrals of the system (35) have the following form:
in so doing
where
and the rest of the values have the same meaning as in the abovementioned case (10a).
Streamlines constructed according to Eq. (37) at different magnitudes of
On the boundary lines of these zones (separatrixes), the value
where the sign “+” fits to the initial magnitudes
The upper branch of the separatrix describes the partial irreversible energy transfer from the vertical vibrations to the pendulum vibrations, but the lower branch, on the contrary, is in compliance with partial irreversible transfer of the energy of the pendulum vibrations to the energy of the vertical vibrations.
The points with coordinates
4. System with an infinite number of degrees-of-freedom
Similar solutions corresponding to the one-sided energy interchange could be obtained for more complex nonlinear systems that describe dynamic behavior of real structures, as an example, for systems with an infinite number of degree-of-freedom. Among such systems are suspension bridges, the scheme of one of them is shown in Figure 6.
The suspension bridge scheme presents a bisymmetrical thin-walled stiffening girder, which is connected with two suspended cables by virtue of vertical suspensions. The cables are thrown over the pilons and are tensioned by anchor mechanisms. The suspensions are considered as inextensible and uniformly distributed along the stiffening girder. The cables are parabolic, and the contour of the girder’s cross section is undeformable. The cross section
It is known for suspension bridges [8] that some natural modes belonging to different types of vibrations could be coupled with each other, that is, the excitation of one natural mode gives rise to another one. Two modes interact more often than not, although the possibility for the interaction of a greater number of modes is not ruled out.
If only two modes predominate in the vibrational process, namely the vertical
where
The resolving system of equations in a dimensionless form is written as [7, 8]
where the coefficients
An approximate solution of Eq. (40) for small but finite amplitudes could be written as an expansion in terms of different time scales in the following form [16]:
The number of the independent time scales needed depends on the order to which the expansion is carried out. Here,
Substituting Eq. (41) into Eq. (40) and equating the coefficients of like powers of
where and are unknown complex functions, and
Substituting Eq. (42) into the set of equations obtained on the first step and using the second step to eliminate secular terms, as well as representing the functions
where
Representing
The solution to Eq. (44) has the form
where
In the case of the one-to-one internal resonance (10b), we seek the solution in the form of Eq. (42) also. Using the procedure for the elimination of secular terms, we obtain the following set of equations:
where
Representing
The solution to Eq. (47) has the form
where
Eliminating the variable
where
4.1. Soliton-like solutions
As examples, the nonlinear free vibrations of the Golden Gate Bridge in San Francisco are considered. All geometrical data, as well as natural frequency spectra and mode shapes for this one of the most beautiful suspension bridges, are available in [19].
It can be shown that under the relationship among the natural frequencies
Under the relationships among the natural frequencies,
where
In the first case of Eq. (50), the coefficients
In the second case of Eq. (50), the analytical solution corresponding to the separatrix
The solutions obtained may be interpreted on the phase plane
The analysis of the phase portraits in terms of the variables
Note that soliton-like solutions could be found also in an analytical form for the case of free damped vibrations of a suspension bridge, when damping features of the system are described by ordinary first-order time derivative [21] or defined by a fractional derivative with a fractional parameter (the order of the fractional derivative) changing from zero to one [22].
5. Conclusions
From the review presented, the following conclusions could be deduced. In all considered vibratory systems—1dof, 2dof, and multi-dof—under certain conditions, there exist solutions that describe irreversible processes of energy transfer from its one type to another. Such solutions are called
On the phase plane, these solutions correspond to streamlines which separate closed lines of phase fluid flow from nonclosed ones. These lines are called
Since soliton-like solution may describe unfavorable vibratory regimes of real mechanical systems, then they should be investigated systematically by virtue of mathematical models of these systems, in order to avoid, wherever possible, such dangerous vibratory regimes when designing and constructing real structures. A thorough analysis of internal resonances in thin plates and cylindrical shells could be found in [23, 24] and [25, 26], respectively.
Soliton-like solutions in the cases of combinational internal resonances for systems with an infinite number of degrees-of-freedom, when more than two natural modes of vibration are coupled, could be found in sight as well, and such examples for nonlinear plates and cylindrical shells are presented in [27, 28] respectively.
Acknowledgments
The research described in this publication was made possible in part by the Ministry of Education and Science of the Russian Federation under Project # 9.5138.2017/8.9.
References
- 1.
Mandel’shtam L. Lecture Notes on Theory of Vibrations (in Russian). Moscow: Nauka; 1972 - 2.
Nayfeh AH, Balachandran B. Modal interactions in dynamical and structural systems. Applied Mechanics Reviews. 1989; 42 :175-201 - 3.
Sado D. Energy transfer in two-degree-of-freedom vibrating systems—A survey. Mechanika Teoretyczna i Stosowana. 1993; 31 :151-173 - 4.
Vitt AA, Gorelik GA. Vibrations of an elastic pendulum as an example of vibrations of two parametrically coupled linear systems (in Russian). Journal of Technical Physics. 1933; 2–3 :294-307 - 5.
Sado D. Analysis of vibration of two-degree of freedom system with inertial coupling. Machine Dynamics Problems. 1984; 1 :67-77 - 6.
Shitikova MV. Modelling of free nonlinear vibrational processes in suspension bridges by a two-mass system (in Russian). In: Advanced Methods of Static and Dynamic Analysis of Structures 1. Voronezh: Voronezh Civil Engineering Institute; 1992. pp. 147-153 - 7.
Abdel-Ghaffar AM, Rubin LI. Nonlinear free vibrations of suspension bridges: Theory and application. ASCE Journal of Engineering Mechanics. 1983; 109 :313-345 - 8.
Rossikhin YA, Shitikova MV. Nonlinear free spatial vibrations of combined suspension systems. Applied Mathematics and Mechanics. 1990; 54 :825-832 - 9.
Rossikhin YA, Shitikova MV. Effect of initial conditions on the behavior of vibrational processes in a combined suspended system. Mechanics of Solids. 1991; 26 :143-154 - 10.
Rossikhin YA, Shitikova MV. Effect of viscosity on the vibrational processes in a combined suspension system. Mechanics of Solids. 1995; 30 :157-166 - 11.
Rossikhin YA, Shitikova MV. Analysis of nonlinear free vibrations of suspension bridges. Journal of Sound and Vibration. 1995; 186 :369-393 - 12.
Goldenblat II. Dynamic Stability of Structures (in Russian). Moscow: Stroy Izdat; 1948 - 13.
Dodd R, Eilbeck J, Gibbon J, Morris H. Solitons and Non-linear Wave Equations. London: Academic Press; 1982. 670 p - 14.
Filippov AT. Manifold Soliton (in Russian). “Kvant” Library Series. Moscow: Nauka; 1990. 287 p - 15.
Appell PE. Theoretical Mechanics (in Russian). Moscow: Fizmatlit; 1960. 516 p - 16.
Nayfeh AH. Perturbation Methods. New York: Wiley; 1973. 450 p - 17.
Abramowitz M, Stegan I, editors. Handbook of Mathematical Functions with Formulas, Graphs, and Tables. Washington: National Bureau of Standards; 1964. 558 p - 18.
Rossikhin YA, Shitikova MV. Analysis of nonlinear vibrations of a two-degree-of-freedom mechanical systems with damping modeled by a fractional derivative. Journal of Engineering Mathematics. 2000; 37 :343-362 - 19.
Abdel-Ghaffar AM, Scanlan RH. Ambient vibration studies of Golden Gate Bridge. I: Suspended structure. ASCE Journal of Engineering Mechanics. 1985; 111 :463-482 - 20.
Rossikhin YA, Shitikova MV. Soliton-like solution to the equations of free nonlinear vibrations of suspension bridges. In: Proceedings of the 1993 International Symposium on Nonlinear Theory and Its Applications; December 5–10, 1993; Hawaii. pp. 705-708 - 21.
Rossikhin YA, Shitikova MV. Soliton-like solutions to the nonlinear damped vibrations of a suspension bridge under an internal resonance. In: Proceedings of the 2nd European Nonlinear Oscillations Conference; September 9–13, 1996; Prague. Vol. 2, pp. 203-206 - 22.
Rossikhin YA, Shitikova MV. Application of fractional calculus for analysis of nonlinear damped vibrations of suspension bridges. Journal of Engineering Mechanics. 1998; 124 :1029-1036 - 23.
Rossikhin YA, Shitikova MV. Analysis of free non-linear vibrations of a viscoelastic plate under the conditions of different internal resonances. International Journal of Non-Linear Mechanics. 2006; 41 :313-325 - 24.
Rossikhin YA, Shitikova MV, Ngenzi JC. A new approach for studying nonlinear dynamic response of a thin plate with internal resonance in a fractional viscoelastic medium. Shock and Vibration. 2015; 2015 :795606 - 25.
Rossikhin YA, Shitikova MV. Nonlinear dynamic response of a fractionally damped cylindrical shell with a three-to-one internal resonance. Applied Mathematics and Computation. 2015; 257 :498-525 - 26.
Rossikhin YA, Shitikova MV. A new approach for studying nonlinear dynamic response of a thin fractionally damped cylindrical shell with internal resonances of the order of ε. In: Altenbach H, Mikhasev GI, editors. Shell and Membrane Theories in Mechanics and Biology: From Macro- to Nanoscale Structures. Advanced Structural Materials. Berlin-Heidelberg: Springer; 2015. Chapter 17. pp. 301-321 - 27.
Rossikhin YA, Shitikova MV, Ngenzi JC. Fractional calculus application in problems of non-linear vibrations of thin plates with combinational internal resonances. Procedia Engineering. 2016; 144 :849-858 - 28.
Rossikhin YA, Shitikova MV. Analysis of non-linear vibrations of a fractionally damped cylindrical shell under the conditions of combinational internal resonance. In: Mastorakis N et al., editors. Computational Problems in Science and Engineering. Lecture Notes in Electrical Engineering. Vol. 343. Berlin-Heidelberg: Springer; 2015. pp. 59-107