Biharmonic equation
= Biharmonic equation
{title2=$\nabla^4f=0$}
The <biharmonic equation> is $\nabla^4f=0$, where the <biharmonic operator> is the square of the <Laplacian>. In planar <Stokes flow>, taking the curl of the momentum equation and using a <Cartesian streamfunction> produces this equation. Its decaying spatial <Fourier series> modes have form $(A+By)e^{-|k|y}e^{ikx}$.