NAMEstardis-input - thermal system description for stardis(1)
stardis-input is the format used by the stardis(1) program to describe a thermal system. It relies on a line-based ad-hoc syntax.
A thermal system is composed of lines of text, each one describing either a medium (solid or fluid) frontier, a boundary (limit condition or connection between two media), or the scale of the geometry. In the medium or boundary cases, description lines include a list of file names that constitute the limit or boundary. The current version of stardis only accepts triangle mesh geometry files in STL format. If a scale is specified, it defines the scaling factor to apply to the geometry to have it expressed in meters (e.g. 1e-3 if the geometry is in mm).
A medium limit or a boundary description can be split accross files and a single file or description line can describe more than one frontier (more than one connex region). The main semantic constraint on descriptions is that any enclosure must be defined by a single description line, to ensure that any part in the system is made from a single medium.
Finally, description lines can be submitted to the stardis(1) program in any order and can be split accross more than one file, through multiple use of option -M.
Any physical quantity involved in descriptions is expected in the International System of Units (second, metre, kilogram, kelvin, watt, joule); the same applies to stardis(1) outputs as described in stardis-output(5).
However, the geometry provided to stardis(1) can be described in any unit, multiple of meters or not, as long as the scaling factor is provided.
TINIT VS TIMPOSED
Media's descriptions, either solids or fluids, include two possible temperatures: initial and imposed. If imposed temperature is set (that is not "UNKNOWN"), initial temperature must be defined at the same value. As a consequence, one cannot define a medium with an imposed temperature that changes at t=0.
In what follows, some lines end in \. This is used as a convenience to continue a description next line. However, this trick cannot be used in actual description files and actual description lines must be kept single-line. Also, text appearing between quote marks has to be used verbatim in the input, except the quote characters. Finally, text introduced by the # character in descriptions, when not verbatim, is a comment and is not part of the description.
<thermal-system> ::= <description-lines> [ <scaling-factor> ] <description-lines> ::= <description-line> [ <description-lines> ] <description-line> ::= [ <medium-frontier> ] [ <comment> ] | [ <medium-boundary> ] [ <comment> ] | [ <media-connection> ] [ <comment> ] <scaling-factor> ::= "SCALE" <scaling_factor> [ <comment> ] ------------------------------------- <medium-frontier> ::= <solid-frontier> | <fluid-frontier> <medium-boundary> ::= <t-bound-for-solid> | <t-bound-for-fluid> | <h-bound-for-solid> | <h-bound-for-fluid> | <f-bound-for-solid> <media-connection> ::= <solid-fluid-connect> <comment> ::= "#" Any text introduced by the # character <scaling_factor> ::= REAL # scaling factor to apply to the geometry # in ]0 INF) <solid-frontier> ::= "SOLID" <medium-name> <lambda> <rho> <cp> <delta> \ <initial-temperature> <imposed-temperature> \ <volumic-power> <triangle-sides> <fluid-frontier> ::= "FLUID" <medium-name> <rho> <cp> \ <initial-temperature> <imposed-temperature> \ <triangle-sides> <t-bound-for-solid> ::= "T_BOUNDARY_FOR_SOLID" <bound-name> <temperature> \ <triangles> <t-bound-for-fluid> ::= "T_BOUNDARY_FOR_FLUID" <bound-name> <temperature> \ <emissivity> <specular-fraction> <hc> <triangles> <h-bound-for-solid> ::= "H_BOUNDARY_FOR_SOLID" <bound-name> <emissivity> \ <specular-fraction> <hc> <outside-temperature> \ <triangles> <h-bound-for-fluid> ::= "H_BOUNDARY_FOR_FLUID" <bound-name> <emissivity> \ <specular-fraction> <hc> <outside-temperature> \ <triangles> <f-bound-for-solid> ::= "F_BOUNDARY_FOR_SOLID" <bound-name> <flux> <triangles> <solid-fluid-connect> ::= "SOLID_FLUID_CONNECTION" <bound-name> <emissivity> \ <specular-fraction> <hc> <triangles> ------------------------------------- <medium-name> ::= STRING # no space allowed <lambda> ::= REAL # conductivity in W/(m.K); in ]0, INF) <rho> ::= REAL # volumic mass,in kg/m3; in ]0, INF) <cp> ::= REAL # capacity, in J/(kg.K) or kg.m2/(s2.K) # in ]0, INF) <delta> ::= "AUTO" # delta is automatically set to V/6A (V and A # being respectively the solid volume and its # boundary area) | REAL # delta*scaling_factor in m; in [0, INF) <initial-temperature> ::= REAL # in K; in [0, INF) <imposed-temperature> ::= "UNKNOWN" # temperature has to be solved | REAL # in K; in [0, INF) <outside-temperature> ::= REAL # in K; in [0, INF) <volumic-power> ::= REAL # in W/m3; in (-INF , INF) <triangle-sides> ::= <side-specifier> <file-name> [ <triangle-sides> ] <bound-name> ::= STRING # no space allowed <emissivity> ::= REAL # in [0, 1] <specular-fraction> ::= REAL # in [0, 1] <hc> ::= REAL # in W/(m2.K); in [0, INF) <flux> ::= REAL # in W/m2; in (-INF , INF) <triangles> ::= <file-name> [ <triangles> ] ------------------------------------- <side-specifier> ::= "FRONT" | "BACK" | "BOTH" <file-name> ::= STRING # no space allowed
Side descriptions in side specifiers rely on the following convention: we first consider the direct triangle's normal (right-hand rule), then we define the BACK side of a triangle to be the side this normal comes out from. That means that a closed set of triangles with normals pointing outside should be used with the FRONT side specifier to describe inside medium.
Names, either file names, medium names or boundary names, are a sequence of one or ore ASCII characters, including numbers and special characters like . _ - as one may consider using in standard file names, without any spacing either escaped or not. Names are case-sensitive anf two different description lines, either in the same description file or from different description files, cannot use the same name.
Define a solid named Cube with a h boundary. The cube geometry is read from the file cube.stl and the solid medium properties are lambda=0.1, rho=25, cp=2. The numerical parameter delta, that is used for solid conductive walks, is 0.05. The initial temperature of the cube is 0°K and its volumic power is 0. The boundary properties are emisivity=0, specular-fraction=0, h=10 and external-temperature = 100°K.
SOLID Cube 0.1 25 2 0.05 0 0 FRONT cube.stl H_BOUNDARY_FOR_SOLID HdT 0 0 10 100 cube.stl