Burgers' equation or Bateman–Burgers equation is a fundamental partial differential equation occurring in various areas of applied mathematics, such as fluid mechanics, nonlinear acoustics, gas dynamics, traffic flow. The equation was first introduced by Harry Bateman in 1915 and later studied by Johannes Martinus Burgers in 1948.
For a given field and diffusion coefficient (or kinematic viscosity, as in the original fluid mechanical context) , the general form of Burgers' equation (also known as viscous Burgers' equation) in one space dimension is the dissipative system:
When the diffusion term is absent (i.e. ), Burgers' equation becomes the inviscid Burgers' equation:
which is a prototype for conservation equations that can develop discontinuities (shock waves). The previous equation is the advective form of the Burgers' equation. The conservative form is found to be more useful in numerical integration
Solution of inviscid Burgers' equation
can be constructed by the method of characteristics. The characertistic equations are
Integration of second equation tells us that is constant along the characteristic and the integration of first equation shows that the characteristics are straight lines, i.e.,
where is the point (or parameter) on the x-axis (t=0) of the x-t plane from which the characteristic curve is drawn. Since at the point, the velocity is known from the initial condition and the fact that this value is unchanged as we move along the characteristic emanating from that point, we write on that characteristic. Therefore, the trajectory of that characteristic is
Thus, the solution is given by
This is an implicit relation that determines the solution of the inviscid Burgers' equation provided characteristics don't intersect. If the characteristics do intersect, then a classical solution to the PDE does not exist and leads to the formation of shock wave. In fact, the breaking time before a shock wave can be formed is given by
Subrahmanyan Chandrasekhar provided the explicit solution in 1943 (On the decay of plane shock waves) when the initial condition is linear,i.e., , where a and b are constants. The explicit solution is
This solution is complete integral of the invisicd Burger's equation because it contains as many arbitrary constants as the number of first derivatives appearing in the equation. Explicit solutions for other relevant initial conditions are, in general, not known.
Solution of viscous Burgers' equation
which turns it into the equation
which can be integrated with respect to to obtain
where is a function that depends on boundary conditions. If identically (e.g. if the problem is to be solved on a periodic domain), then we get the diffusion equation
The diffusion equation can be solved, and the Cole-Hopf transformation inverted, to obtain the solution to the Burgers' equation:
Other forms of Burger's equation
Generalized Burger's equation
The generalized Burgers's equation extends the quasilinear convective to more generalized form, i.e.,
Stochastic Burger's equation
Added space-time noise forms a stochastic Burgers' equation
This stochastic PDE is the one-dimensional version of Kardar–Parisi–Zhang equation in a field upon substituting .
- It relates to the Navier–Stokes momentum equation with the pressure term removed Burgers Equation (PDF): here the variable is the flow speed y=u
- It arises from Westervelt equation with an assumption of strictly forward propagating waves and the use of a coordinate transformation to a retarded time frame: here the variable is the pressure
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