Team ASSNL: Approximation and stability of nonlinear systems (headed by Abdelhak CHIKHAOUI)
Study of stability using the optimal derivative
Approximation of nonlinear systems
Cooperation : Université Béchar, I.R.D- Bondy (France), Université Bordeaux II
It was realized long ago that most of the phenomena of mathematical physics are nonlinear case, the most famous being the Boltzmann equation in static mechanics, the Navier-Stokes equations of fluid mechanics (equations are Moreover, an approximation of the Boltzmann equation), the equations of Von Karman flat plates with large displacements, etc. ....
However, before the possibility of using systematic-and almost «trivial» computers to compute approximate solutions of the system state, accurate results could generally be obtained in the linear case.
Some physical problems can be modeled directly (ie without approximation) by linear equations: the case of the neutron transport equation in particular. Other phenomena may be deducted from the "true" nonlinear systems is neglecting certain terms (which is valid in certain situations: "small" movements, movements, movements "slow").
Our team offers a method that has given his evidence through a large number of results (doctoral theses, Magisters, Publications .....).
Our goal is to use the optimal derivation developed by Arino, Benouaz (1995-1996-2001) and supplemented by Bohner, Benouaz (2007-2009-2011) for approximation and study the stability of certain classes of function non-linear, in order to test this method and demonstrate its capabilities.
Validation of the method through:
PhD thesis: they will be facing several nonlinear models Energetic.
Develop a user-friendly software to popularize the method.
An example of application of this method for the detection of bifurcations is presented as follows:
It presents a comparison with the continuation software Auto 2000.
Bifurcation diagram obtained using the simulation code Auto 2000
Bifurcation diagram showing the variation of the L2 norm depending on the parameter a (gain) solid solution stable, dotted unstable solution, PB pitchfork bifurcation, HB: Hopf bifurcation, PD: Bifurcation to split time. Information from the qualitative analysis conducted using the optimal derivation applied to bifurcation points are indicated by arrows circled red on the diagram
Different types of points and symbols encountered in the bifurcation diagram for the execution of software auto2000 are defined according to the following parameters:
TY: Abbreviation of the name of the type of solution
TY: Number of solution
BR: Number of branches
PT: Number of points
LAB: Label Solution
TY LAB meaning
BP 1 bifurcation point
HB 3 Hopf bifurcation
7 PD period doubling bifurcation to
EP 9 beginning and end of normal execution
PRM (1) is the parameter for continuation, here U (1), U (2), and U (3) are x, y, z.