Korteweg–de Vries equation
In mathematics, the Korteweg–de Vries equation (KdV equation for short) is a mathematical model of waves on shallow water surfaces. It is particularly notable as the prototypical example of an exactly solvable model, that is, a non-linear partial differential equation whose solutions can be exactly and precisely specified. KdV can be solved by means of the inverse scattering transform. The mathematical theory behind the KdV equation is rich and interesting, and, in the broad sense, is a topic of active mathematical research. The KdV equation was first introduced by Boussinesq (1877, footnote on page 360) and rediscovered by Diederik Korteweg and Gustav de Vries (1895).
with ∂x and ∂t denoting partial derivatives with respect to x and t.
The constant 6 in front of the last term is conventional but of no great significance: multiplying t, x, and by constants can be used to make the coefficients of any of the three terms equal to any given non-zero constants.
Consider solutions in which a fixed wave form (given by f(X)) maintains its shape as it travels to the right at phase speed c. Such a solution is given by (x,t) = f(x − ct − a) = f(X). Substituting it into the KdV equation gives the ordinary differential equation
or, integrating with respect to X,
where A is a constant of integration. Interpreting the independent variable X above as a virtual time variable, this means f satisfies Newton's equation of motion in a cubic potential. If parameters are adjusted so that the potential function V(X) has local maximum at X = 0, there is a solution in which f(X) starts at this point at 'virtual time' −∞, eventually slides down to the local minimum, then back up the other side, reaching an equal height, then reverses direction, ending up at the local maximum again at time ∞. In other words, f(X) approaches 0 as X → ±∞. This is the characteristic shape of the solitary wave solution.
More precisely, the solution is
Integrals of motion
where the polynomials Pn are defined recursively by
The first few integrals of motion are:
- the mass
- the momentum
- the energy
Only the odd-numbered terms P(2n+1) result in non-trivial (meaning non-zero) integrals of motion (Dingemans 1997, p. 733).
The KdV equation
can be reformulated as the Lax equation
with L a Sturm–Liouville operator:
and this accounts for the infinite number of first integrals of the KdV equation. (Lax 1968)
Least action principle
The Korteweg–de Vries equation
with defined by
It can be shown that any sufficiently fast decaying smooth solution will eventually split into a finite superposition of solitons travelling to the right plus a decaying dispersive part travelling to the left. This was first observed by Zabusky & Kruskal (1965) and can be rigorously proven using the nonlinear steepest descent analysis for oscillatory Riemann–Hilbert problems.
The history of the KdV equation started with experiments by John Scott Russell in 1834, followed by theoretical investigations by Lord Rayleigh and Joseph Boussinesq around 1870 and, finally, Korteweg and De Vries in 1895.
The KdV equation was not studied much after this until Zabusky & Kruskal (1965), discovered numerically that its solutions seemed to decompose at large times into a collection of "solitons": well separated solitary waves. Moreover the solitons seems to be almost unaffected in shape by passing through each other (though this could cause a change in their position). They also made the connection to earlier numerical experiments by Fermi, Pasta, and Ulam by showing that the KdV equation was the continuum limit of the FPU system. Development of the analytic solution by means of the inverse scattering transform was done in 1967 by Gardner, Greene, Kruskal and Miura.
Applications and connections
The KdV equation has several connections to physical problems. In addition to being the governing equation of the string in the Fermi–Pasta–Ulam problem in the continuum limit, it approximately describes the evolution of long, one-dimensional waves in many physical settings, including:
- shallow-water waves with weakly non-linear restoring forces,
- long internal waves in a density-stratified ocean,
- ion acoustic waves in a plasma,
- acoustic waves on a crystal lattice.
Many different variations of the KdV equations have been studied. Some are listed in the following table.
|Korteweg–de Vries (KdV)|
|KdV (Lax 7th) Darvishi, Kheybari & Khani (2007)|
|KdV (modified modified)|
|KdV (variable coefficients)|
|Korteweg–de Vries–Burgers equation|
- Benjamin–Bona–Mahony equation
- Boussinesq approximation (water waves)
- Cnoidal wave
- Dispersion (water waves)
- Dispersionless equation
- Kadomtsev–Petviashvili equation
- Novikov–Veselov equation
- Ursell number
- Vector soliton
- Darrigol, O. (2005), Worlds of Flow: A History of Hydrodynamics from the Bernoullis to Prandtl, Oxford University Press, p. 84, ISBN 9780198568438
- See e.g. Newell, Alan C. (1985), Solitons in mathematics and physics, SIAM, ISBN 0-89871-196-7, p. 6. Or Lax (1968), without the factor 6.
- Alexander F. Vakakis (31 January 2002). Normal Modes and Localization in Nonlinear Systems. Springer. pp. 105–108. ISBN 978-0-7923-7010-9. Retrieved 27 October 2012.
- See e.g. Grunert & Teschl (2009)
- Gardner, C.S.; Greene, J.M.; Kruskal, M.D.; Miura, R.M (1967), "Method for solving the Korteweg–de Vries equation", Physical Review Letters 19 (19): 1095–1097, Bibcode:1967PhRvL..19.1095G, doi:10.1103/PhysRevLett.19.1095.
- Dauxois, Thierry; Peyrard, Michel (2006), Physics of Solitons, Cambridge University Press, ISBN 0-521-85421-0
- Boussinesq, J. (1877), Essai sur la theorie des eaux courantes, Memoires presentes par divers savants ` l’Acad. des Sci. Inst. Nat. France, XXIII, pp. 1–680
- de Jager, E.M. (2006). "On the origin of the Korteweg–de Vries equation". arXiv:math/0602661v1 [math.HO].
- Dingemans, M.W. (1997), Water wave propagation over uneven bottoms, Advanced Series on Ocean Engineering 13, World Scientific, Singapore, ISBN 981-02-0427-2, 2 Parts, 967 pages
- Drazin, P. G. (1983), Solitons, London Mathematical Society Lecture Note Series 85, Cambridge: Cambridge University Press, pp. viii+136, ISBN 0-521-27422-2, MR 0716135
- Grunert, Katrin; Teschl, Gerald (2009), "Long-Time Asymptotics for the Korteweg-de Vries Equation via Nonlinear Steepest Descent", Math. Phys. Anal. Geom. 12 (3): 287–324, arXiv:0807.5041, Bibcode:2009MPAG...12..287G, doi:10.1007/s11040-009-9062-2
- Kappeler, Thomas; Pöschel, Jürgen (2003), KdV & KAM, Ergebnisse der Mathematik und ihrer Grenzgebiete. 3. Folge. A Series of Modern Surveys in Mathematics [Results in Mathematics and Related Areas. 3rd Series. A Series of Modern Surveys in Mathematics] 45, Berlin, New York: Springer-Verlag, ISBN 978-3-540-02234-3, MR 1997070
- Korteweg, D. J.; de Vries, G. (1895), "On the Change of Form of Long Waves Advancing in a Rectangular Canal, and on a New Type of Long Stationary Waves", Philosophical Magazine 39 (240): 422–443, doi:10.1080/14786449508620739
- Lax, P. (1968), "Integrals of nonlinear equations of evolution and solitary waves", Comm. Pure Applied Math. 21 (5): 467–490, doi:10.1002/cpa.3160210503
- Miles, John W. (1981), "The Korteweg–De Vries equation: A historical essay", Journal of Fluid Mechanics 106: 131–147, Bibcode:1981JFM...106..131M, doi:10.1017/S0022112081001559.
- Miura, Robert M.; Gardner, Clifford S.; Kruskal, Martin D. (1968), "Korteweg–de Vries equation and generalizations. II. Existence of conservation laws and constants of motion", J. Mathematical Phys. 9 (8): 1204–1209, Bibcode:1968JMP.....9.1204M, doi:10.1063/1.1664701, MR 0252826
- Takhtadzhyan, L.A. (2001), "K/k055800", in Hazewinkel, Michiel, Encyclopedia of Mathematics, Springer, ISBN 978-1-55608-010-4
- Zabusky, N. J.; Kruskal, M. D. (1965), "Interaction of "Solitons" in a Collisionless Plasma and the Recurrence of Initial States", Phys. Rev. Lett. 15 (6): 240–243, Bibcode:1965PhRvL..15..240Z, doi:10.1103/PhysRevLett.15.240
|Wikimedia Commons has media related to Korteweg–de Vries equation.|
- Korteweg–de Vries equation at EqWorld: The World of Mathematical Equations.
- Korteweg–de Vries equation at NEQwiki, the nonlinear equations encyclopedia.
- Cylindrical Korteweg–de Vries equation at EqWorld: The World of Mathematical Equations.
- Modified Korteweg–de Vries equation at EqWorld: The World of Mathematical Equations.
- Modified Korteweg–de Vries equation at NEQwiki, the nonlinear equations encyclopedia.
- Weisstein, Eric W., "Korteweg–deVries Equation", MathWorld.
- Derivation of the Korteweg–de Vries equation for a narrow canal.
- Three Solitons Solution of KdV Equation – 
- Three Solitons (unstable) Solution of KdV Equation – 
- Mathematical aspects of equations of Korteweg–de Vries type are discussed on the Dispersive PDE Wiki.
- Solitons from the Korteweg–de Vries Equation by S. M. Blinder, The Wolfram Demonstrations Project.
- Solitons & Nonlinear Wave Equations