Mathematical Problems in Engineering

Volume 2017 (2017), Article ID 1208563, 19 pages

https://doi.org/10.1155/2017/1208563

## On Dynamical Behavior of a Friction-Induced Oscillator with 2-DOF on a Speed-Varying Traveling Belt

School of Mathematical Sciences, Shandong Normal University, Jinan 250014, China

Correspondence should be addressed to Jinjun Fan

Received 30 September 2016; Accepted 4 January 2017; Published 5 February 2017

Academic Editor: Stefano Lenci

Copyright © 2017 Jinjun Fan et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

The dynamical behavior of a friction-induced oscillator with 2-DOF on a speed-varying belt is investigated by using the flow switchability theory of discontinuous dynamical systems. The mechanical model consists of two masses and a speed-varying traveling belt. Both of the masses on the traveling belt are connected with three linear springs and three dampers and are harmonically excited. Different domains and boundaries for such system are defined according to the friction discontinuity. Based on the above domains and boundaries, the analytical conditions of the passable motions, stick motions, and grazing motions for the friction-induced oscillator are obtained mathematically. An analytical prediction of periodic motions is performed through the mapping dynamics. With appropriate mapping structure, the simulations of the stick and nonstick motions in the two-degree friction-induced oscillator are illustrated for a better understanding of the motion complexity.

#### 1. Introduction

In mechanical engineering, the friction contact between two surfaces of two bodies is an important connection and friction phenomenon widely exists. In recent years, much research effort in science and engineering has focussed on nonsmooth dynamical systems [1–11]. This problem can go back to the 30s of last century. In 1930, Hartog [1] investigated the nonstick periodic motion of the forced linear oscillator with Coulomb and viscous damping. In 1960, Levitan [2] proved the existence of periodic motions in a friction oscillator with the periodically driven base. In 1964, Filippov [3] investigated the motion in the Coulomb friction oscillator and presented differential equation theory with discontinuous right-hand sides. The investigations of such discontinuous differential equations were summarized in Filippov [4]. However, Filippov’s theory mainly focused on the existence and uniqueness of the solutions for nonsmooth dynamical systems. Such a differential equation theory with discontinuity is difficult to apply to practical problems. In 2003, Awrejcewicz and Olejnik [5] studied a two-degree-of-freedom autonomous system with friction numerically and illustrated some interesting examples of stick-slip regular and chaotic dynamics. In 2014, Pascal [6] discussed a system composed of two masses connected by linear springs: one of the masses is in contact with a rough surface and the other is also subjected to a harmonic external force. Several periodic orbits were obtained in closed form, and symmetry in space and time had been proved for some of these periodic solutions. More discussion about discontinuous system can refer to [7–11].

However, a lot of questions caused by the discontinuity (i.e., the local singularity and the motion switching on the separation boundary) were not discussed in detail. So the further investigation on discontinuous dynamical systems should be deepened and expanded. In 2005–2012, Luo [12–17] developed a general theory to define real, imaginary, sink, and source flows and to handle the local singularity and flow switchability in discontinuous dynamical systems. By using this theory, a lot of discontinuous systems were discussed (e.g., [18–20]). Luo and Gegg [18] presented the force criteria for the stick and nonstick motions for 1-DOF (degree of freedom) oscillator moving on the belt with dry friction. In 2009, Luo and Wang [19] investigated the analytical conditions for stick and nonstick motions in 2-DOF friction induced oscillator moving on two belts. Velocity and force responses for stick and nonstick motions in such system were illustrated for a better understanding of the motion complexity. Based on this improved model, which consists of two masses moving on one speed-varying traveling belt and in which the two masses are connected with three linear springs and three dampers and are exerted by two periodic excitations, nonlinear dynamics mechanism of such a 2-DOF oscillator system will be investigated.

In this paper, a model of frictional-induced oscillator with two degrees of freedom (2-DOF) on a speed-varying belt is proposed in which multiple discontinuity boundaries exist: they are caused by the presence of friction between the mass and the belt. The model allows a simple representation of engineering applications with multiple nonsmooth characteristics as for instance friction wheels or slipping mechanisms in multiblock structures. The main goal is to study the analytical conditions of motion switching and stick motions of the oscillator on the corresponding boundaries by using the theory of discontinuous dynamical systems. Based on the discontinuity, domain partitions and boundaries will be defined and the analytical conditions of the passable motions, stick motions, and grazing motions for the friction-induced oscillator are obtained mathematically, from which it can be seen that such oscillator has more complicated and rich dynamical behaviors. An analytical condition of periodic motions is performed through the mapping dynamics. With appropriate mapping structure, the simulations of the stick and nonstick motions of the oscillator with 2-DOF are illustrated for a better understanding of the motion complexity. There are more simulations about such oscillator to be discussed in future.

#### 2. Preliminaries

For convenience, the fundamental theory on flow switchability of discontinuous dynamical systems will be presented; that is, concepts of -functions and the decision theorems of semipassable flow, sink flow, and grazing flow to a separation boundary are stated in the following, respectively (see [16, 17]).

Assume that is a bounded simply connected domain in and its boundary is a smooth surface.

Consider a dynamic system consisting of subdynamic systems in a universal domain . The universal domain is divided into accessible subdomains and the inaccessible domain . The union of all the accessible subdomains is and is the universal domain. On the th open subdomain , there is a -continuous system () in form ofThe time is and . In an accessible subdomain , the vector field with parameter vector is -continuous () in and for all time .

The flow on the boundary can be determined bywhere . With specific initial conditions, one always obtains different flows on .

Consider a dynamic system in (1) in domain which has a flow with an initial condition , and on the boundary , there is an enough smooth flow with an initial condition . For an arbitrarily small , there are two time intervals and for flow and the flow approaches the separation boundary at time , that is, , where , , and .

*Definition 1. *The -functions of the flow to the flow on the boundary are defined aswhere , , is to represent the quantity in the domain rather than on the boundary, and is a time rate of the inner product of displacement difference and the normal direction .

*Definition 2. *The th-order -functions of the domain flow to the boundary flow in the normal direction of are defined aswhere the total derivative operators are defined asFor , we have

*Definition 3. *For a discontinuous dynamical system in (1), there is a point . For an arbitrarily small , there are two time intervals and . Suppose ; iffor , then a resultant flow of two flows is a semipassable flow from domain to at point to boundary , where , .

To simplify notation usage, the symbols represent in next paragraphs.

Lemma 4. *For a discontinuous dynamical system in (1), there is a point at time between two adjacent domains . For an arbitrarily small , there are two time intervals and . Suppose , two flows and are and -continuous for time , respectively, and . The flows and at point to the boundary are semipassable from domain to if and only if * *either* *or*

*Lemma 5. For a discontinuous dynamical system in (1), there is a point at time between two adjacent domains . For an arbitrarily small , there is a time interval . Suppose . Both flows and are -continuous for time and . The flows and at point to the boundary are sink flow if and only if either or*

*Lemma 6. For a discontinuous dynamical system in (1), there is a point at time between two adjacent domains . For an arbitrarily small , there are two time intervals and . Suppose . The flows and are and -continuous for time , respectively, and . The sliding fragmentation bifurcation of the nonpassable flows and of the first kind at point switching to the passable flow on the boundary occurs if and only if *

*Lemma 7. For a discontinuous dynamical system in (1), there is a point at time between two adjacent domains . For an arbitrarily small , there are two time intervals and . Suppose . The flows and are and -continuous for time , respectively, and . The sliding bifurcation of the passable flow of and at point switching to the sink flow on the boundary occurs if and only if *

*Lemma 8. For a discontinuous dynamical system in (1), there is a point at time between two adjacent domains . For an arbitrarily small , there is a time interval . Suppose . The flow is -continuous for time , and . A flow in is tangential to the boundary if and only if either or*

*More detailed theory on the flow switchability such as the definitions or theorems about various flow passability in discontinuous dynamical systems can be referred to [16, 17].*

*3. Physical Model*

*3. Physical Model**Consider a friction-induced oscillator with two degrees of freedom on the speed-varying traveling belt, as shown in Figure 1. The system consists of two masses , which are connected with three linear springs of stiffness and three dampers of coefficient . Both of masses move on the belt with varying speed . Two periodic excitations with frequency , amplitudes , and constant forces are exerted on the two masses, respectively.*