Provided by:
felt_3.06-9_i386 
NAME
felt - finite element problem description file format
DESCRIPTION
The felt(4fe) file format is used by the programs of the finite element
package, felt(1fe), velvet(1fe), and burlap(1fe) to describe a finite
element problem. The file is human readable and consists of a
friendly, intuitive syntax rather than a table of numbers. Syntactic
and semantic errors are detected and reported assuring that only valid
problem descriptions are used. In general white space is unimportant,
arbitrary numeric expressions may be used, and case of keywords is
unimportant. As per standard convention, boldface items represent
keywords, italicized items represent the syntax of the grammar, and
items in brackets are optional. The file syntax is shown below.
[ problem-description ]
[ analysis-parameters ]
[ object-definitions ]
[ appearance-description ]
end
Problem description
The problem-description section specifies the problem title and the
number of nodes and elements in the problem. If this section is not
specified then the problem will be unnamed and is assumed to contain
zero nodes and zero elements. This section may be absent for example
in defaults files which define objects but do not specify an actual
problem instance. The format for a problem-description is given below.
problem description
[ title = string ]
[ nodes = integer ]
[ elements = integer ]
[ analysis = static | transient | modal | static-thermal|
transient-thermal| spectral ]
If the title is missing then the problem is unnamed. If nodes or
elements is missing then none of that type of object are expected. The
assignments can occur in any order and can even be repeated with the
last assignment being used.
Analysis parameters
The analysis-parameters section defines any parameters for a specific
type of analysis. Currently, this section is used only if the analysis
mode is transient. The format of the analysis-parameters section is
given below.
analysis parameters
[ alpha = expression ]
[ beta = expression ]
[ gamma = expression ]
[ step = expression ]
[ start = expression ]
[ stop = expression ]
[ Rm = expression ]
[ Rk = expression ]
[ nodes = [ node-list ] ]
[ dofs = [ dof-list ] ]
[ mass-mode = lumped | consistent ]
The alpha, beta, andgamma parameters are used in numerical integration
schemes (transient and transient-thermal analysis). start, stop, and
step define the range of time or frequency interest for transient or
spectral analyses. In transient analyses, start is meaningless and
duration and dt can be used as aliases for stop and step, respectively.
Rk and Rm are global Rayleigh (stiffness and mass) damping
proportionality constants. The node-list is a comma or white space
separated list of node numbers that are of interest in the analysis.
Similarly, the dof-list is a list of the degrees of freedom (Tx, Ty,
Tz, Rx, Ry, and Rz) that are of interest.
An object-definition section defines objects of a specified type.
Objects include nodes, elements, materials, constraints, forces, and
distributed loads. Each of these types of objects is discussed below.
Multiple object-definition sections are allowed and the sections may
occur in any order.
Nodes
Nodes are points in cartesian space to which elements are attached. A
node must have a constraint and may have an optional force. A node is
identified by a natural number. The syntax is as follows:
nodes
node-definitions
where a node-definition takes the following form:
node-number
[ x = expression ]
[ y = expression ]
[ z = expression ]
[ constraint = constraint-name ]
[ force = force-name ]
[ mass = expression ]
The node-number starts the definition. Each node must have a unique
number. If a cartesian coordinate is not given then the coordinate of
the previous node is used. Similarly, if no constraint is given then
the constraint applied to the previous node is used. As above, the
assignments can appear in any order and any number of times. As
indicated above, some objects are identified by their name and some by
their number. Elements and nodes have numbers while materials, forces,
loads, and constraints have names.
Elements
Elements are linear, planar, or solid objects which are attached to
nodes. Each element must have a material and may have optional loads.
Furthermore, each element has a type, or definition. Like nodes,
elements are identified by a unique natural number. Elements of
specific type are defined with the following syntax:
element-type elements
element-definition
where an element-type is one of the following:
spring
truss
beam
beam3d
CSTPlaneStrain
CSTPlaneStress
iso2d_PlaneStrain
iso2d_PlaneStress
quad_PlaneStrain
quad_PlaneStress
timoshenko
htk
brick
ctg
rod
and an element-definition has the following form:
element-number
nodes = [ node-list ]
[ material = material-name ]
[ load = load-name-list ]
The element-number starts the definition. Each element must have a
unique number. If no material is given then the material applied to
the previous element is used. The load-name-list is a list of up to
three loads to apply to the element. The node-list is a comma or white
space separated list of node numbers. Each type of element requires a
certain of nodes and in some cases a special "null node" which is
numbered zero may be used to indicate a gap or filler in the list.
Materials
Elements are made of a type of material. Each material has a name and
certain physical properties not all of which may be used by any one
element. The syntax for defining materials is as follows:
material properties
material-definitions
where material-definition has the following form:
material-name
[ color = string ] # color for velvet
[ E = expression ] # Young’s modulus
[ Ix = expression ] # moment of inertia about x-x axis
[ Iy = expression ] # moment of inertia about y-y axis
[ Iz = expression ] # moment of inertia about z-z axis
[ A = expression ] # cross-sectional area
[ J = expression ] # polar moment of inertia
[ G = expression ] # bulk (shear) modulus
[ t = expression ] # thickness
[ rho = expression ] # density
[ nu = expression ] # Poisson’s ratio
[ kappa = expression ] # shear force correction
[ Rk = expression ] # Rayleigh damping coefficient (K)
[ Rm = expression ] # Rayleigh damping coefficient (M)
[ Kx = expression ] # thermal conductivity in the x-direction
[ Ky = expression ] # thermal conductivity in the y-direction
[ Ky = expression ] # thermal conductivity in the z-direction
[ c = expression ] # heat capacitance
The material-name starts the definition. If an attribute of a material
is not specified then that attribute is zero. The assignments may
occur in any order. The color specifies the color to use in drawing
the material within velvet, and is ignored by other applications.
Constraints
Constraints are applied to nodes to indicate about which axes a node
can move. The syntax for defining a constraint is as follows:
constraints
constraint-definitions
where constraint-definition has the following form:
constraint-name
[ color = string ] # color for velvet
[ tx = c | u | expression ] # boundary translation along x axis
[ ty = c | u | expression ] # boundary translation along y axis
[ tz = c | u | expression ] # boundary translation along z axis
[ rx = c | u | expression | h ] # boundary rotation about x axis
[ ry = c | u | expression | h ] # boundary rotation about y axis
[ rz = c | u | expression | h ] # boundary rotation about z axis
[ itx = expression ] # initial displacement along x axis
[ ity = expression ] # initial displacement along y axis
[ itz = expression ] # initial displacement along z axis
[ irx = expression ] # initial rotation about x axis
[ iry = expression ] # initial rotation about y axis
[ irz = expression ] # initial rotation about z axis
[ vx = expression ] # initial velocity along x axis
[ vy = expression ] # initial velocity along y axis
[ vz = expression ] # initial velocity along z axis
[ ax = expression ] # initial accel. along x axis
[ ay = expression ] # initial accel. along y axis
[ az = expression ] # initial accel. along z axis
The constraint-name starts the definition. A value of c for a boundary
condition indicates that the axis is constrained; a value of u
indicates that the axis is unconstrained. An expression indicates a
displacement (non-zero) boundary condition and may contain the t
variable for time varying boundary conditions in transient analysis
problems. The initial dislacement, velocity and acceleration
specifications are only used in transient problems. A value of h for a
rotational boundary condition indicates a hinge. By default, all axes
are unconstrained. The color specifies the color to use in drawing the
constraint within velvet, and is ignored by other applications.
Forces
Forces, or point loads, may be applied to nodes. The syntax for a
force definition is as follows:
forces
force-definitions
where a force-definition has the following form:
force-name
[ color = string ] # color for velvet
[ Fx = expression ] # force along x axis
[ Fy = expression ] # force along y axis
[ Fz = expression ] # force along z axis
[ Mx = expression ] # moment about x axis
[ My = expression ] # moment about y axis
[ Mz = expression ] # moment about z axis
[ Sfx = expression ] # frequency-domain spectra of force
along x axis
[ Sfy = expression ] # frequency-domain spectra of force
along y axis
[ Sfz = expression ] # frequency-domain spectra of force
along z axis
[ Smx = expression ] # frequency-domain spectra of moment
about x axis
[ Smy = expression ] # frequency-domain spectra of moment
about y axis
[ Smz = expression ] # frequency-domain spectra of moment
about z axis
The force-name starts the definition. If the force or moment is not
specified then it is assumed to be zero. The expressions for forces
may be time-varying. Time-varying expressions include the single
variable t to represent the current time in the solution of a dynamic
problem or consist of a list of discrete (time, value) pairs.
Frequency varying expressions for spectra can also use w to represent
the independent variable (radial frequency). The color specifies the
color to use in drawing the force within velvet, and is ignored by
other applications.
Loads
Distributed loads, or loads for short, are applied to elements. The
syntax for a defining a distributed load is as follows:
distributed loads
load-definitions
where a load-definition has the following form:
load-name
[ color = string ] # color for velvet
[ direction = dir ] # direction
[ values = pair-list ] # local nodes and magnitudes
The load-name starts the definition. The dir is one of LocalX, LocalY,
LocalZ (local coordinate system), GlobalX, GlobalY, GlobalZ (global
coordinate system), parallel, or perpendicular. The pair-list is a
sequence of pairs. A pair is a node number and an expression enclosed
in parentheses. The node number refers to the position within the
element rather than referring to an actual node. The color specifies
the color to use in drawing the load within velvet, and is ignored by
other applications.
Appearance Description
The appearance-description section is used by velvet to describe the
appearance of a problem. This section is currently not used by felt.
The appearance includes the state of the drawing area and any tool
figures. This section consists of two subsections, the canvas-
configuration section and the figure-list section. The canvas-
configuration section has the following syntax.
canvas configuration
canvas-parameters
where a canvas-parameter has the following form:
[ node-numbers = boolean ] # node numbering
[ element-numbers = boolean ] # element numbering
[ snap = boolean ] # snap grid status
[ grid = boolean ] # visible grid status
[ snap-size = expression ] # snap grid size
[ grid-size = expression ] # visible grid size
[ node-color = color-name ] # node color
[ element-color = color-name ] # element color
[ label-font = font-name ] # labeling font
[ tool-color = color-name ] # tool figure color
[ tool-font = font-name ] # text figure font
[ x-min = expression ] # x-axis minimum
[ x-max = expression ] # x-axis maximum
[ y-min = expression ] # y-axis minimum
[ y-max = expression ] # y-axis maximum
[ x-pos = expression ] # x position of drawing area
[ y-pos = expression ] # y position of drawing area
[ width = expression ] # width of viewport window
[ height = expression ] # height of viewport window
[ scale = expression ] # scale of drawing area
A boolean is either true or false. A color-name is the name of a valid
X11 color. Similarly, a font-name is the name of a valid X11 font.
The last five parameters are probably not very meaningful to the user.
The figure-list section has the following syntax.
figure list
figure-definitions
where a figure-definition has the following form:
figure-type
[ x = expression ] # x coordinate
[ y = expression ] # y coordinate
[ width = expression ] # width
[ height = expression ] # height
[ start = expression ] # starting angle
[ length = expression ] # arc length
[ text = name ] # text string
[ color = name ] # color
[ font = name ] # text font
[ points = [ point-list ] ] # line points
The figure-type starts the definition and is one of rectangle,
polyline, text, or arc. Note that not all properties have meaning for
all figures. Any unneeded property is ignored. If a color or font
property is not given then the previous property is used. The point-
list is a list of (x-coordinate, y-coordinate) pairs.
Expressions
An expression can be either constant or time-varying. As discussed
above, time-varying expressions contain the variable t or consist of a
list of discrete (time, value) pairs. If a time-varying expression is
given where a constant expression is expected, the expression is
evaluated at time zero. An expression has one of the following forms,
where all operators have the precedences and associativities given to
them in the C programming language.
expression ? expression : expression # in-line conditional
expression || expression # logical or
expression && expression # logical and
expression | expression # integer inclusive or
expression ^ expression # integer exclusive or
expression & expression # integer and
expression == expression # equality
expression != expression # inequality
expression < expression # less than
expression > expression # greater than
expression <= expression # less than or equal
expression >= expression # greater than or equal
expression << expression # integer shift left
expression >> expression # integer shift right
expression + expression # addition
expression - expression # subtraction
expression * expression # multiplication
expression / expression # division
expression % expression # integer remainder
- expression # arithmetic negation
! expression # logical negation
~ expression # integer bitwise negation
( expression ) # enforce precedence
sin ( expression ) # sine
cos ( expression ) # cosine
tan ( expression ) # tangent
pow ( expression , expression ) # power (exponentiation)
exp ( expression ) # exponential
log ( expression ) # natural logarithm
log10 ( expression ) # base-10 logarithm
sqrt ( expression ) # square root
hypot ( expression , expression ) # Euclidean distance
floor ( expression ) # floor
ceil ( expression ) # ceiling
fmod ( expression , expression ) # floating point remainder
fabs ( expression ) # absolute value
number # literal value
t # current time
Finally, a discretely valued expression has the following syntax, where
the optional + indicates that the list represents one cycle of an
infinite waveform.
( expression â€â€™,â€â€™ expression ) ... [ + ]
AUTHOR
The felt file format was developed by Jason I. Gobat (jgobat@mit.edu)
and Darren C. Atkinson (atkinson@ucsd.edu).
SEE ALSO
corduroy(1fe), felt(1fe), velvet(1fe), xfelt(1fe), corduroy(4fe).