The Solitary Wave Theory

The Solitary Wave Theory

The Solitary Wave Theory, have soliton-like solutions of nonlinear evolution equations describing wave process in dispersive and dissipation media [6]. A sketch of these types of waves is shown below

2.1  Soliton

A soliton [14] is a solitary wave which asymptotically preserves its shape and velocity upon nonlinear interaction with other solitary waves. Soliton has following properties

  1. They are of permanent form.
  2. They are localized within a region.
  3. They can interact with other solitons and emerge from the collision unchanged, except for a phase shift.
  4. Soliton is caused by a delicate balance between nonlinear and dispersive effects.

2.2 Travelling Wave

Travelling wave [14] can be defined as a wave in which the medium is travelling in the direction of propagation of wave. Travelling waves arises in the study of nonlinear differential equations where waves are represented by the form

u(x,t) = f(x-ct)

                                                                               Figure (2.2)-Travelling Waves

and  c is the speed of wave propagation. For c < 0 , the wave moves in the positive  direction whereas the wave moves in the negative x direction for  c < 0.

2.2.1 Types of Travelling Wave Solutions

Travelling wave solutions are of many types and they are of particular importance in solitary wave theory. Here we are going to describe six different types of travelling wave solutions with their figures.

Definition 1.1. Solitary waves [14] are localized travelling waves with constant speeds and shapes, asymptotically zero at large distance solutions. Solitons are special kind of solitary waves. The soliton solution is a spatially localized solution, hence

 

 

 

 

 

 

 

 

 

 

The KdV equation is a pioneer model for analytic bell-shaped sech²  solitary wave solutions.

Definition 1.2. Kink waves [14] are travelling waves which rise or descend from one asymptotic state to another. The Kink solution approaches a constant at infinity. The standard dissipative burgers equation

is a well-known equation that gives kink solutions where v is the viscosity coefficient.

The graphical representation of Kink wave is

 

 

 

 

 

 

 

 

 

Figure (2.4) – General Representation of Kink Waves                                           Figure (2.4) – 2D-Animation

Definition 2.19. Periodic waves [14] are travelling wave that are periodic such as cos(x-t) . The standard wave equation  gives periodic solutions. Graphical representation is given below

Figure (2.5) – General Representation of Periodic Waves                          Figure (2.5) – 2D Animation

Definition 2.20. Peakons [14] are the solitary wave solutions. In this case the travelling solutions are the smooth except for a peak at a corner of its crest. The peakons are solutions retaining their shape and speed after interacting. Peakons were investigated and classified as a periodic peakons and peakons with exponential decay. Some graphical representations of peakons are given below

Figure (2.6) – General Representation of Peakons                                Figure (2.6) – 2D Animation

Definition 2.21. Cuspons [14] are other form of solitons where solution exhibit cusps at their crests. Unlike Peakons where the derivative at the peak differs only by a sign, the derivative at the jump of a Cuspons diverges.  It is important to note that the Soliton solution u(x,t), along with its derivatives tends to zero as Cuspons were investigated and classified as periodic Cuspons and Cuspons with exponential decay.

Figure (2.7)-General Representation of Cuspons

Definition 2.22. It is new class of Soliton with compact spatial support such that each compacton is a Soliton confined to a finite core. Compactons [14] has some properties and we can describe it in one of the following ways:

  1. Compactons are Solitons with finite wavelength.
  2. Compactons are solitary waves with compact support.
  3. Compactons are Solitons free of exponential tail.
  4. Compactons are Solitons characterized by the absence of infinite wings.
  5. Compactons are robust Soliton-like solutions.

Graphical representation is given below

Figure (2.8) – General Representation of Compactons                          Figure (2.8) – 2D Animation

2.2 Some Basic Definitions of Wavelets Theory

2.2.1 History

Wavelet analysis developed in the largely mathematical literature in the 1980’s and began to be used commonly in geophysics in the 1990’s. Wavelets can be used in signal analysis, image processing and data compression. They are useful for sorting out scale information, while still maintaining some degree of time or space locality.

2.2.2 Wavelets

A wavelet [11, 16] is a wave-like oscillation that is localized in the sense that it grows from zero, reaches maximum amplitude, and then decreases back to zero amplitude again. It thus has a location where it maximizes, a characteristic oscillation period, and also a scale over which it amplifies and declines. The following figure represents Wavelets constitute a family of function constructed from dilaition

2.2.3 Types of Wavelets

According to Meyer (1993), two fundamental types of wavelets [16] can be considered,

  1. The Grossmann-Morlet time-scale wavelets
  2. The Gabor-Malvar time-frequency wavelets.

Time-scale wavelets are defined in reference to a “mother function” ψ(t)  of some real variable t .The mother function can be used to generate a whole family of wavelets by translating and scaling the mother wavelet.

Here  is the translation parameter and  is the scaling parameter. Provided that ψ(t)  is  real-valued, this collection of wavelets can be used as an orthonormal basis. If we restrict the parameters  and  to discrete values as and n,k are positive integers, we have the following family of discrete wavelets

where  forms an orthogonal basis.

2.2.4 Functions Approximation

 A function f(t) define over [0, 1) may be expanded [46] as

where in which  denotes the inner product. If the infinite series in Eq.  is truncated, then above Eq.  can be written as

It can be written as

 

where C and ψ(t) are matrices given as

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