tochnog1

Usage

Overview

tochnog is a free finite-element program.

The finite element method is “a general discretization procedure of continuum problems posed by mathematically defined statements.” [O.C. Zienkiewicz & R.L. Taylor. Finite Element Method, 5th ed, sect 1.1. 2000.] tochnog implements one-, two- or three-dimensional, or axi-symmetrical computational domains, each consisting of finite elements connected at nodes; but (unlike as in common finite element programs) with all fields assumed to be continuous over the domain. Such continuity gives a more diffuse but at the same time a more stable numerical scheme, with the further advantage that all fields are stored not in integration points but in the nodes themselves, leading to a relatively easy implementation of remeshing and refining techniques. Only first order in time equations are solved; time derivatives are approximated with Euler backward time discretization.

tochnog accepts format-free input; reports results over points, lines, quadrilaterals, etc., as well as at nodes; outputs suitably for plotting; provides springs, trusses and 2D beams in addition to isoparametric elements; implements tools to generate and refine model meshes; reports accuracy by residue and error estimate; analyzes interactions between fluids and solids, and also contact with and without friction; frames Lagrangian, Eulerian and AEL calculations; simulates statically, quasi-statically or dynamically; and significantly parallelizes its calculations to take advantage of parallel processing when available.

For thermal analysis, tochnog evolves the energy balance equation. For fluids, the Stokes and Navier-Stokes. For solid elasticity, the isotropy and transverse isotropy. For solid elastoplasticity, the von Mises, Mohr-Coulomb and Gurson. For solid hypoplasticity, the von Wolfersdorf, cohesion, intergranular strain, and pressure-dependent initial void ratio. Also for solids, the damage, thermal stress, hypoelasticity, viscoelasticity, viscoplasticity and viscosity. For ground water flow, the storage equation. For general wave phenomena, the wave equation.

tochnog is an extensive numerical free-software package whose operation extends far beyond that which a mere man page can document. The TOCHNOG User's Manual and other documents found in /usr/share/doc/tochnog/ give complete instructions on tochnog's use.

Invocation

If the input-file name given on the command line contains no “.” dot, then the standard tochnog input filename extension “.dat” is implicitly appended to it (for example, “problem” is interpreted as “problem.dat”). If omitted, input-file defaults to “tn.dat”.

It is usual to redirect tochnog's output rather than to let it stream to the terminal. For example,

$ tochnog tn.dat >tn.out

Options

The instructions given in input-file control tochnog. The tochnog command itself accepts no command-line options. See the documentation in /usr/share/doc/tochnog/ for further information.

Files

tn.dat

the default input file

tn.run

the runtime input file

tn.log

the calculation message log

tn.dat, et al.

output files in various formats, suitable for plotting

tn.dbs

the state database, containing full calculation state data, including nodes, elements, solution fields, etc.

tn.dvd

the step-by-step record of the evolution over time of the model's unknown variables

tn.tmp

a scratch file (do not use this name yourself)

tn.out

conventionally, the file to which tochnog's stdout is redirected (but the user controls this as described under INVOCATION above)

/usr/share/doc/tochnog/

reference documents including the TOCHNOG User's Manual (on a Debian system, found only when the tochnog-doc package is also installed)