UTILITY READ Mode Filename

The UTILITY READ command allows the user to read information into the database from an external file, or to read a batch command file.

Mode	Filename	Comments
GEOMETRY	Name	Reads a file containing archived FEMGEN geometry
		data. If no file name is given the user will be prompted
		for one. The user will also be prompted to give a
		model name to be used when recording the geometry data
		in the FEMGV database index. (See notes 1 and 2).
		If the name of an existing model is provided, then the
		archived geometry will be appended to a host model (See note 3) ,
		otherwise a new model is created.
VIEWDATA	Name	Reads a file containing FEMVIEW topology and results
		data in the format specified in Appendix B of the User
		Manual Appendices. If no file name is given the user will
		be prompted for one.

IGES	Name	Reads geometry data from a IGES (Version 5.2) format file and
		translates it to geometry for a FEMGEN model. If no file name
		is given the user will be prompted for one. (See note 4).
PATRAN	Name	Reads geometry data from a PATRAN Neutral format file and
		translates it to geometry for a FEMGEN model. If no file name
		is given the user will be prompted for one. (See note 5).
DXF	Name	Reads geometry data from a DXF format file and translates it to
		geometry for a FEMGEN model. If no file name is given the
		user will be prompted for one.
BATCH	[Name]	Reads commands from the file specified. Where no file name
		is given a default name will be used; on most systems this is
		`fgvbatch.bat'. The special character `@' may be used in place
		of the command UTILITY READ BATCH.
Program	[Name]	Reads a results file created by the specified Finite Element
		program and either generates a new FEMVIEW model or appends
		results to an existing FEMVIEW model. This command is
		only supported for those FEMVIEW interface programs that
		are linked in as part of the FEMGV executable.

Note 1: Reading FEMGEN archived data
The UTILITY READ GEOMETRY command can be used to read either a FEMGEN coded archive file written via the UTILITY WRITE GEOMETRY command at the model index level or a FEMGEN standard archive file written via the UTILITY WRITE ARCHIVE command from within FEMGEN. Both file formats are essentially FEMGEN command files and will comprise all the commands required to regenerate the model (except the mesh). However, the coded archive format is considerably quicker to read and process.

The user will be asked if graphics output and command logging is to be suppressed during the read in order to further speed up processing of the archive file. If the 'fast read' option is selected then program control passes to FEMGEN , the archive file is read silently and, after completion, program control returns to the model index level.

Note that FEMGEN command files can be also be read by the user entering FEMGEN with a new model name and using the UTILITY READ BATCH command. However, no 'fast read' option is available in this case.

Note 2: Mesh information
When an archive file is read, it will be necessary to use MESH GENERATE to create the mesh. Note that offsets to node and element numbering (created with MESHING OPTIONS NODE or ELEMENT) are not transferred via the archive file.

Note 3: Naming convention for append to a host model
The name that is assigned (in the host model) to a newly created entity will contain the default alpha part for entities of that type, unless CONSTRUCT NAME has been used in the host model prior to the append. The numeric part of the name will be incremented from the highest numeric value encountered in the host model for names with the relevant alpha part. This will preclude potential naming conflicts. The 'fast read' option is available for a model append.

Note 4: Reading an IGES file
Geometry data from an IGES file can be read and translated into FEMGEN geometry by using the command UTILITY READ IGES. The user will be prompted to give a new model name and model description to be used when recording the data in the FEMGV database index. The user will also be prompted for the model tolerance and points which differ by less than this tolerance will be merged by the interface. The default for the tolerance is the tolerance value read from the IGES file or 0.1% of the maximum dimension if no IGES tolerance exists. The program will then scan the IGES file and list the IGES entities that can be processed. The user is prompted to specify (on a single line) which of these entities are required, the default being that all entities will be processed.

Where spline lines or spline surfaces exist, the user is asked to specify if the program is to look for any IGES splines that could be represented as straight lines or arcs. When this conversion is requested, the user will be prompted for a conversion tolerance to be used. The default for the tolerance is the same as the tolerance given above. Converting relevant spline lines to straight lines or arcs can lead to simpler line definitions, smaller databases and faster execution times, due to the creation of fewer points. If the user does not request this conversion then all IGES spline lines will be transferred as FEMGEN curves. The user will be prompted for the number of points to be used when generating FEMGEN spline lines. The default number of points is 5 which is generally found to be sufficient. More points will give a better curve fit but will increase both model size and processing time.

Since it became possible to store spline surfaces in FEMGEN the processing of IGES type 128 surfaces now involves creating a surface and a NURB surface shape, which are associated together with a MESHING SHAPE command. This leads to a more accurate reflection of the original CAD model; but this extra information in the shape - control points and possibly also knots and weights leads to larger databases and slower display and meshing times in FEMGENUsers are now given three new options to control this. Since many CAD surfaces are actually planar, cylindrical or conical, users can select to try to convert NURB surface shapes which are planes, cones or cylinders within the tolerance.

Alternatively, users may wish not to recover the spline surface shape data at all, and simply represent the surface using a blend of the boundary lines. They will have smaller databases and faster display and meshing times, at the cost of more simplified surface interiors.

The interface will always check for and remove duplicate points. By default, the program will also check before creating each line that the line does not already exist. This is very useful if the model contains surfaces or is known to contain a lot of duplication.

However, if the IGES file contains only lines or the user has not requested that surfaces be transferred, then it can be quicker to read the IGES file without checking for duplicate lines and then to remove any duplicate lines with the CONSTRUCT MERGE.

While the data is being processed, diagnostic messages will be printed to the screen indicating how far the interface has progressed in the translation process. After the data has been processed a summary will be given of the FEMGEN geometric entities created.

The following IGES entities are recognised and mapped to FEMGEN entities as indicated:

IGES entity	Type	FEMGEN entity generated
100	Circular arc	An arc. If the IGES arc is $\geq 180^{\circ}$ it is split
		into arcs $< 180^{\circ}$ which are then placed in set.
102	Composite curve	Processed as part of IGES 144 entities.
104	Conics	An IGES conic can be either an ellipse, a
		parabola or a hyperbola. Ellipses will be
		transferred to FEMGEN as arcs with different
		radii, while parabolae and hyperbolae will be
		simply approximated as straight lines.
106	Poly line	A poly line defined from a list if nodes exist in
		the IGES file.

IGES entity	Type	FEMGEN entity generated
110	Straight line	A straight line.
112	Parametric spline	If the IGES spline line is less than 4 line
	line	segments then each segment will be a spline line.
		Otherwise a single spline line will be fitted
		through each point defining the IGES spline.
		In FEMGEN each spline lines will have a start
		and end point and a set containing spline points.
114	Parametric spline	A single spline surface will be created for
	surface	each of the segments 'ij' patches.
120	Surface of revolution	A single spline surface will be generated
		together with a FEMGEN surface shape. This
		IGES entity type is the result of sweeping a line
		about an axis between two angles, and is
		supported when the swept line is a straight
		line, an arc or a NURB curve.
122	Tabulated cylinder	A single spline surface will be generated
		together with a FEMGEN surface shape. This
		IGES entity type is the result of sweeping a line,
		using a translation. As for the IGES type 120,
		it is supported when the swept line is a straight
		line, an arc or a NURB curve.
124	Transformation	Geometric entities referencing transformations
		will be transformed into the global system.
126	Rational B-spline	A single spline line will be fitted, using the
	curves	FEMGEN curve shape entity.
128	Rational B-spline	A single spline surface will be generated,
	surfaces	together with a FEMGEN surface shape entity.
142	Curve on a parametric	Processed as part of IGES 144 entities.
	surface
144	Trimmed Surface	A FEMGEN surface (and where the IGES
		base surface is type 128, 120 or 122 a
		corresponding surface shape entity), will
		be generated for each type 144. The type
		of the FEMGEN surface will be a REGION
		if it is bounded by more than 4 lines or
		if it has any holes. Otherwise it will be
		made into a 3 or 4 sided surface. All
		boundaries must be closed and
		non-intersecting, all holes must be contained
		within the outer boundary.

In order that a mesh may be created from entities created, lines are allocated the default number of divisions (as set by MESHING DIVISION DEFAULT) and element types are allocated according to the highest entity type in the final model. Consequently, if surfaces exist in the FEMGEN model then these will be allocated surface elements and the lines will not be given an element type.

The geometry created is stored as a FEMGEN model (named `IGTEST' in this case) and the commands required to create an identical FEMGEN model are written to the history file.

There are a number of FEMGV resources that can be used to customise the behaviour of the interface, they are listed below:

Resource name	Notes
and (default)
Femsys.*.IGES.IGES_Nshape	By default, surface shapes are generated for IGES type
(TRUE)	128 even when the shape is closed. Users can optionally
	select not to generate NURB surface shapes for types
	128 if they are closed by setting IGES_Nshape to FALSE.
Femsys.*.IGES.IGES_Debug	Users can make the IGES translator write a table
(FALSE)	summarising the translation to the history file by
	setting IGES_Debug to TRUE. The table includes an entry
	for all entities processed in the IGES file, giving the
	name of the corresponding FEMGEN part together with
	information on how parts are related. By default, this is
	disabled as it can significantly increase the size of the
	history file.

Resource name	Notes
and (default)
Femsys.*.IGES_GAPS	By default, the program will try to fill in gaps in loops
(FALSE)	which ought to be closed. Sometimes this can have some
	unwanted effects; especially where points used in the
	construction of other parts, for example points defining
	shapes or centre points get moved. Users can specify not
	to fill in gaps (ie keep the gaps) by setting IGES_GAPS
	to true. When deciding whether to fill in gaps, a critical
	gap size is used. This is controlled by the next resource
	IGES_Gtol.
Femsys.*.IGES_Gtol	By default gaps less than 3*model tolerance will be closed
(3*model tol.)	(provided IGES_GAPS is FALSE). If users wish to specify
	the maximum gap size to be closed, they can do so by
	setting IGES_Gtol. For example IGES_Gtol : 0.77
	specifies that all gaps up to size 0.77 will be closed.
Femsys.*.MESH.ALG_DLY	By default, all regions (IGES type 144) will have the
(FALSE)	automatic quad meshing algorithm called PAVING attached.
	If it is intended to use tetrahedral meshing, users may
	prefer to select the automatic triangulation algorithm
	called DELAUNAY by setting ALG_DLY to TRUE.

Note 5: Reading a PATRAN Neutral file
Geometry data from a PATRAN Neutral file can be read and translated into FEMGEN using UTILITY READ PATRAN. The format of the PATRAN Neutral file (from PATRAN 2.0 or later) is described in section 29 of the Patran Manual.

The user is prompted for the name of the PATRAN Neutral file, a model name and a description.

All lines in PATRAN are defined as spline lines and to avoid unnecessarily large databases the user can request that the interface try to transfer lines as straight lines or arcs where possible. The tolerance supplied by the user is used to determine whether the end tangents of the splines are sufficiently similar for the lines to be considered as straight or whether points evaluated on the spline are within tolerance of the arc. In a similar way, users are given the option of detecting which surface shapes could be represented as planes within the tolerance. The default value for the tolerance is 1% of the maximum model diagonal (as calculated from the point locations).

In FEMGEN all material, physical, loading and constraint data are attached to the model geometry. In PATRAN they are generally attached directly to the elements and nodes in the mesh. Because of this, loading and constraint information is not transferred. Material and Physical property definitions are transferred (Entity types 3 and 4), but are not attached to the model geometry.

The interface is primarily intended for the transfer of geometric data, and will convert the following PATRAN entity types :

PATRAN entity	Type	FEMGEN entity generated
31	Grid Point	A Point.
32	Line	A Straight or a Spline line depending on
		the values of the end tangents. Spline
		lines will refer to a FEMGEN curve
		shape.
33	Patch	A Surface created from boundary lines,
		and referring to an underlying surface
		shape describing its curvature.
34	Hyperpatch	A Body created from 5 or 6 patches.
47	Trimmed Patch	A surface shape entity describing the
		curvature of the underlying base
		surface, and a set of lines describing the
		outer boundary and each of any inner
		boundaries. Where there are holes or
		more than 3 or 4 lines in the outer
		boundary the surface will be of type
		REGION; and otherwise simply 3 or 4
		sided. All boundaries must be closed
		and non-intersecting. All holes must be
		contained in the outer boundary.
		Currently, PATRAN trimmed patches
		containing holes must have only one
		outer boundary.

PATRAN entity	Type	FEMGEN information generated
42	GFEG : Line	Mesh divisions and bias along a line.
43	GFEG : Patch	Mesh divisions and bias along lines in a
		surface.
44	GFEG : Hyperpatch	Mesh divisions and bias along lines in a
		body.
45	CFEG : Line	Element types for lines.
45	CFEG : Patch	Element types for surfaces.
45	CFEG : Hyperpatch	Element types for bodies.