# References

## Books

$\displaystyle \clubsuit$ D. Zwillinger, Handbook of Differential Equations, Third Edition, Academic Press, 1998. ISBN-10: 0127843965. ISBN-13: 978-0127843964. UF library QA371.Z88 1989, 2 copies, one for in-library use. Google books Amazon.com

$\displaystyle \clubsuit$ L. Lapidus & G.F. Pinder, Numerical solution of partial differential equations in science and engineering, Wiley, 1982. Google books Amazon.com UF Library Q172 .L36 1982

$\displaystyle \clubsuit$ A.P.S. Selvadurai, Partial Differential Equations in Mechanics 1: Fundamentals, Laplace's Equation, Diffusion Equation, Wave Equation, Springer, 2000. ISBN-10: 3540672834. ISBN-13: 978-3540672838. Google books UF library QA805 .S45 2000 Amazon.com

$\displaystyle \clubsuit$ A.N. Kolmogorov & S.V. Fomin, Introductory Real Analysis, Dover, 1975. Google books Amazon.com Not a major reference for this course; only for concept of linear operators.

$\displaystyle \clubsuit$ M. Abramowitz & I. Stegun, Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables, New York: Dover Publications, 1972. Read online, Download Wikipedia

$\displaystyle \clubsuit$ P.M. Morse & H. Feshbach, Methods of mathematical physics, McGraw-Hill, 1953. Two volumes. Google books Amazon.com UF library QC20.M6

$\displaystyle \clubsuit$ Additional references

J.W.S. Rayleigh, The theory of sound, Macmillan, London, Vol.1 1877, Vol.2 1878 (free pdf files), from Gallica, French National Library.

## Web references

$\displaystyle \spadesuit$ Partial differential equation in Scholarpedia. Written many well-known, famous experts (some are Nobel laureates, Fields medalists, etc.) and reviewed by experts; Scholarpedia is highly reliable, unlike Wikipedia. I became aware of Scholarpedia from an e-mail entry in NA Digest, Vol.8, No.6, 8 Feb 2009 by one of the authors of the Scholarpedia article Partial differential equation.

$\displaystyle \spadesuit$ EqWorld, The World of Mathematical Equations. It is a good idea to verify the sources, as the site is not responsible for accuracy and correctness; see Rights and obligations of contributors and website administration.

$\displaystyle \spadesuit$ Partial differential equations, wikipedia Be careful; always verify the sources.

$\displaystyle \spadesuit$ Integrals: Lists of integrals (Wikipedia). David de Bierens de Haan, Nouvelles Tables d'Inte'grales De'finies (Engels, Leiden, 1862).

# General nonlinear PDEs

Lapidus & Pinder 1982, p.1.

# Order

Lapidus & Pinder 1982, p.2.

# Linearity

## Definition

Selvadurai 2000, p.74. More general discussion, lecture.

Kolmogorov & Fomin, p.123, linear functionals.

## Linear PDEs

Lapidus & Pinder 1982, p.2 for linear first-order PDEs. General case, lecture.

## Quasilinear PDEs

Lapidus & Pinder 1982, p.2 for quasilinear first-order PDEs. General case, lecture.

## Nonlinear PDEs

Lapidus & Pinder 1982, p.2 for nonlinear first-order PDEs. General case, lecture.

# Second order PDEs : From general to particular

I decided to abandon this order of presentation (from general to particular), but rather present the material from particular to general, since it would be less abstract to students, who would be more comfortable to be anchored in what they already knew (or at least heard of), and then learn to generalize to concepts that are new to them.

So go directly to Alternative presentation from particular to general.

# Second-order PDEs : Alternative presentation, from particular to general

## PDEs linear in all orders (more particular)

### Constant coefficients

#### Two independent variables

##### Nonlinear transformation of coordinates
###### Curvilinear coordinates, separation of variables (1)

Curvilinear coordinates: Google search Wolfram Wikipedia

Laplacian in different curvilinear coordinates: Zwillinger 1998, p.187

$\displaystyle {\rm div}( {\rm grad} \, u ) = \nabla \cdot ( \nabla u ) = \nabla^2 u = \Delta u = u_{xx} + u_{yy} = u_{rr} + \frac{1}{r} u_r + \frac{1}{r^2} u_{\theta \theta}$

$\displaystyle {\rm div}( {\rm grad} \, u ) = u_{rr} + \frac{1}{r} u_r + \frac{1}{r^2} u_{\theta \theta} + u_{zz}$

$\displaystyle {\rm div}( {\rm grad} \, u ) = u_{rr} + \frac{2}{r} u_r + \frac{1}{r^2} u_{\theta \theta} + \frac{1}{r^2 {\rm tan} \theta} u_\theta + \frac{1}{r^2 {\rm sin}^2 \theta} u_\psi$

Two methods to obtain the above results

Application: Heat conduction problem (Laplace equation) Selvadurai 2000, p.195.

• in a cylinder
• in a section of an annulus domain
##### Equation for conics in 2-D

Conics (Wikipedia)

### First-order linear PDEs for classification of 2nd order PDEs

EqWorld, exact solution for some 1st-order PDEs

#### Method of characteristics (1)

from Wikipedia

Scott Sara's tutorial, Burger's equation, Java animation.

## General nonlinear, 2nd order PDEs (even more general)

### Two independent variables

Heat conductivity dependence on temperature, from a recent talk (Feb 2009) by Simon Phillpot, Materials Science and Engineering, University of Florida.

Power law (Wikipedia)

For diamond:

$\displaystyle \kappa \approx 0.4 \, W/Km$ at $\displaystyle T = 1 ^\circ K$

$\displaystyle \kappa \approx 1000 \, W/Km$ at $\displaystyle T \approx 10.7 ^\circ K$

$\displaystyle a \approx \frac { \log(1000) - \log(0.4) } { \log(10.7) - \log(1)} \approx 3.39$
$\displaystyle \log(\kappa) = a \log(T) + \log(b) \Longrightarrow \kappa(T) = b \, T^a$
$\displaystyle \log(\kappa) = 3.39 \log(T) + \log(0.4) \Longrightarrow \kappa(T) = 0.4 \, T^{3.39} \, W / Km \ {\rm for} \ T \in \left[ 1^\circ K , 10.7^\circ K \right]$

# Wave equation

## One-dimensional case: Exact solution

### Applications

#### String vibration

J.W.S. Rayleigh, The theory of sound, Macmillan, London, Vol.1 1877, Vol.2 1878 (free pdf files), from Gallica, French National Library.

# Method of characteristics revisited (2)

from Wikipedia

Scott Sara's tutorial, Burger's equation, Java animation.

# Separation of variables (2)

Zwillinger 1998, p.441

## Laplace equation (linear elliptic PDE)

### Polar coordinates

See applications in Section Curvilinear coordinates, separation of variables (1).

#### Fluid mechanics application

Fluid between rotating cylinders. F.M. White, Fluid mechanics, McGraw-Hill, 2006. Google book, p.276 Amazon.com

Divergence in polar coordinates: F.M. White, p.230

Cartesian coordinates $\displaystyle (x,y) = (x_1 , x_2)$, and basis vectors $\displaystyle \{ \mathbf i , \mathbf j \} = \{ \mathbf e_x , \mathbf e_y \} = \{ \mathbf e_1 , \mathbf e_2 \}$

Polar coordinates $\displaystyle (r, \theta) = (\overline x_1 , \overline x_2)$, and basis vectors $\displaystyle \{ \overline \mathbf i , \overline \mathbf j \} = \{ \mathbf e_r , \mathbf e_\theta \} = \{ \overline \mathbf e_1 , \overline \mathbf e_2 \}$ such that

$\displaystyle \overline \mathbf e_i := \frac {\partial P} {\partial \overline x_i}$

where $\displaystyle P$ represents the position vector of point $\displaystyle P$. Note that in general

$\displaystyle \parallel \overline \mathbf e_i \parallel \ne 1$

Consider a vector $\displaystyle \mathbf v$ such that: $\displaystyle \mathbf v = v_i \mathbf e_i = \overline v_i \overline \mathbf e_i = v_r \mathbf e_r + v_\theta \mathbf e_\theta$

Divergence:

$\displaystyle {\rm div} \, \mathbf v = \frac {\partial v_i} {\partial x_i} = \frac {1} {r} \frac {\partial} {\partial r} \left( r \frac {\partial v_r} {\partial r} \right) + \frac {\partial v_\theta} {\partial \theta}$

Compare this expression of the divergence in polar coordinates to that in F.M. White, p.230, Eq.(4.8): What is the difference? Explanation? See lecture notes.

## Unsteady heat equation (linear parabolic PDE)

### Polar coordinates, Bessel functions

Zwillinger 1998, p.442

Bessel (or cylindrical) functions: First kind, second kind, also known as "cylindrical harmonics". Wikipedia Mathworld

M. Abramowitz & I. Stegun, Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables, New York: Dover Publications, 1972. Read online, Download Wikipedia. Bessel functions starting p.358. Integral representations, p.360.

## General linear homogeneous PDEs

Zwillinger 1998, p.441

## Some special nonlinear PDEs

Zwillinger 1998, p.444

## Wave equation (linear hyperbolic PDE) with sinusoidal time dependence

1-D case: Morse & Feshbach, p.125.

2-D, 3-D cases.

### Solution for Helmholtz equation

#### Two-D case

Morse & Feshbach, p.498.

Moore & Spencer, Fields theory for engineers, D. Van Nostrand, 1961.

#### Three-D case, Stackel determinant

Morse & Feshbach, p.508.

Moore & Spencer, Fields theory for engineers, D. Van Nostrand, 1961.

# Conformal mappings: Special method for Laplace equation

Zwillinger 1998, p.399.

## Functions of complex variables

Complex analysis (Wikipedia)

### Schwartz-Christoffel transformation

Zwillinger 1998, p.399.

J.H. Mathew & R.W. Howell, The Schwarz-Christoffel Transformation, Cal State Fullerton, 2006.

### Joukowsky (Zhukovsky) transformation

J.H. Mathew & R.W. Howell, Joukowsky airfoil, Cal State Fullerton, 2006.

$\displaystyle w = F(z) = z + \frac{c^2}{z}$

with $\displaystyle c$ being a constant, and $\displaystyle w$ and $\displaystyle z$ are complex variables:

$\displaystyle w = \xi + i \eta \ , \ {\rm and} \ z = x + i y$

# Nondimensionalization, dimensionless PDEs

## Scaling: Crumpling of thin shells

"Thin naturally curved shells arise on a range of length scales: from nanometer-sized viruses (1) to carbon nanotubes (2), from the micrometer-sized cell wall (3) to bubbles with colloidal armor (4), and from architectural domes (5) to the megameterscale earths crust (6). ... our everyday experience playing with thin flat and curved sheets of similar materials such as sheets of plastic suggests that the natural geometry of the surface dominates its mechanical response: a surface with positive Gauss curvature (e.g., an empty plastic bottle) has a qualitatively different response from that of a surface that is either flat (e.g., a plastic sheet) or has negative Gauss curvature." Vaziri & Mahadevan (2008)