Create |
This menu is for the generation of all the different possible geometrical entities. Usually, new entities are created inside the current layer (see Layers ).
Point creation |
Menu: Geometry->Create->Point
Individual points are created by entering each point in the usual way (see Point definition ). The points can then be joined together to form lines.
Caution: It is impossible to create new points joining old ones.
The Number option lets you choose the label that will be assigned to the next point created. If a point with this number already exists, the old line changes its number.
Straight line creation |
Menu: Geometry->Create->Straight line
Toolbar:
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Create line |
To create a straight line, start by entering just two points (see Point definition ), and then continue entering points in order to create more lines from the first one. Every part of the total line created is an independent line.
It is important to note that when creating lines, new points are also being created (if existing ones are not used).
The Close option joins the first point and the last point created with a straight line and finishes.
The Undo option undoes the creation of the last point (if new) and the last line. It is possible to continue undoing all the way back to the first point.
The Number option lets you choose the label that will be assigned to the next line created. If a line with this number already exists, the old line changes its number.
If Join is chosen, it is maintained for all points until No join is selected.
NURBS line creation |
Menu: Geometry->Create->NURBS line
Toolbar:
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Create NURBS line |
NURBS are non-uniform rational B-splines. They are a type of curve that can interpolate a set of points. NURBS can also be defined by their control polygon, another set of points that the curve approximates smoothly.
There are two ways of creating a NURBS line using this command, either by entering some interpolated points or entering the points that form the control polygon.
The Undo option undoes the creation of the last point; this can be done all the way back to the first point.
By default, a NURBS will be a cubic polynomial passing through all the points. However, this option can be changed by calling ByControlPts, which defines NURBS by their control polygon. This polygon is a set of points where the first and the last points match the first and last points of the curve. The rest of the points do not lie on the curve. It can be assumed that the curve approximates the points of the polygon in a smooth way. In this case, the user chooses the degree of the curve, which will be the degree of the connected polynomials that define the NURBS.
Instead of entering interpolated points, the Fitting option lets you approximate a line using a minimum squared criteria. You also have to select the degree of approximation for this curve.
When defining interpolating curves, you can choose to define the tangents to one or both ends (using the Tangents option). These tangents can be customized, in that they can either be defined by picking their direction on the screen or by considering an existing line as a tangent to the NURBS if it follows a previous curve (the option ByLine). The Next option allows only one tangent to be defined.
In this way, it is possible to create a closed NURBS by selecting the initial point as the end one and choosing one of the options 'Tangent', 'Next', or 'ByLine'.
When a NURBS has been created, all the interior points (except the first and last) are not really entity points unless they previously existed.
The Number option lets you choose the label that will be assigned to the next created line. If a line with this number already exists, its number is changed.
To enter rational weights on the curve, the Edit NURBS line/surface command (see Edit NURBS line/surface ) can be used.
Parametric line |
Menu: Geometry->Create->Parametric line
Tool to create a parametric approximated curve
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The data that must be input are the mathematical formulae of the coordinates X(t), Y(t) and Z(t), where 't' is the parameter of the curve, and its value belongs to the interval [ t0-t1 ]. The curve is created by approximation and is a NURBS (Non-Uniform Rational B-Spline) which is created with N points. In GiD these kinds of curves are cubic (order 3).
The valid mathematical funcions are all Tcl functions:
+ - * / %
abs cosh log sqrt acos double log10 srand asin exp pow tan atan floor rand tanh atan2 fmod round ceil hypot sin cos int sinh
EXAMPLE
We fill the formula bars with the expression of a conic helix.
That helix starts with radius R0 =4 and finishes with radius R1 =1, performing N=3 turns from t=0.0 to t=1.0, the height also changes from 0 to H=5.
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Polyline creation |
Menu: Geometry->Create->Polyline
Toolbar:
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Create Polyline |
A polyline is a set of at least two other lines of any type (including polylines themselves). Every line must share one or two of its endpoints with the endpoints of other lines.
There are two possible ways to create a polyline, either by selecting one line and searching the rest until a corner or end is reached, or by selecting several lines (see Entity selection ). In the case of the latter, the order of selection is not important but all of them must join each other by sharing common points.
Polylines are drawn in green to show the difference between the other lines, which are drawn in blue.
Polylines are widely used when creating 4-sided surfaces (see 4-sided surface creation ) and automatic 4-sided surfaces (see Automatic 4-sided surface creation ).
When deleting a polyline, all its lines are deleted. When exploding it (see Polyline ), the polyline will disappear and its individual lines will appear.
It is not possible to create third level polylines: one former polyline can be included inside another, but this is the limit and these two cannot be included within a further polyline.
The Number option lets you choose the label that will be assigned to the next created line. If a line with this number already exists, its number is changed.
Arc creation |
Menu: Geometry->Create->Arc
Toolbar:
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Create arc |
To create an arc you can either enter three points (By 3 points, see Point definition ) or enter a radius and the two tangent lines at the arc's ends (Fillet curves).
It is important to note that when creating an arc, new points are also being created (if existing ones are not being used).
An arc that begins and ends at the same point (i.e. where the first and third points are the same) will be created as a circle. An arc will always include the second point that is entered, though this one is only used as a reference and, if it is not an existing point, is automatically erased when the arc is created.
The Undo option undoes the creation of the last point (if it is a new one). It is possible to continue undoing all the way back to the first point.
The Fillet curves option lets you input a radius and select two lines that share one common point. An arc will then be created and the two lines will be modified to be tangent and continuous with this new arc.
To convert one arc to another one with the same center and in the same plane but with a complementary angle, the Swap arc command can be used (see Swap arc ).
NURBS surface creation |
Menu: Geometry->Create->NURBS surface
Toolbar:
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Create NURBS surface |
NURBS are non-uniform rational B-splines. They are a type of surface that is defined by its control polygon (one set of points that the surface approximates smoothly), one set of knots for the two directions u and v (a non-decreasing list of real numbers between 0 and 1) and, optionally, one set of rational weights.
To draw the isoparametric lines in u,v=0.5, check the surface drawing type option in the Preferences window.
Note: The No try planar option (found in the Contextual mouse menu) avoids the creation of a trimmed NURBS surface when lines are coplanar.
Note: To enter rational weights for the surface, use the Edit NURBS surface command (see Edit NURBS line/surface ).
Caution: When creating more than one surface in one go, it is possible that some undesired surfaces may also be created. It is necessary to check the surfaces after creation and erase the undesired ones.
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Note: This surface is an approximation to the selected points/lines, but there is no interpolation.
Parametric surface |
Menu: Geometry->Create->Parametric surface
Tool to create a parametric approximated surface
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The required input data are the mathematical formulae of the coordinates X(u,v), Y(u,v) and Z(u,v), where 'u' and 'v' are the parameters of the surface, and its value belongs to the intervals set in 'u in' and 'v in' respectively. The surface is created by approximation and is a NURBS (Non-Uniform Rational B-Spline), which is created with 'Number of points U' x 'Number of points V' points. In GiD these kinds of surfaces are cubic (order 3).
The valid mathematical funcions are all Tcl functions:
+ - * / %
abs cosh log sqrt acos double log10 srand asin exp pow tan atan floor rand tanh atan2 fmod round ceil hypot sin cos int sinh
Contact surface creation |
Menu: Geometry->Create->Contact surface
Contact surfaces are defined as being between two lines that are physically in the same place, but which have different line and point entities. From a contact surface, it is possible to generate contact elements, to be used by some calculation algorithms, which define a special contact between these two bodies.
Using contact surface entities is like a meshing specification. In this way, equal meshes will be generated for the two lines, ensuring a one-to-one relationship between nodes.
Choose the Contact surface option from the menu, and then select some lines on both bodies.
Contact elements are, by default, 4-node planar quadrilaterals. However, you can select 2-node lines for all cases (see Element type ).
The 4-node planar quadrilaterals can be converted to the 8-node or 9-node for the quadratic case.
You can also select no mesh for the contact entity. This makes it possible to have exactly the same mesh for both lines but without any additional element between them.
Surface mesh |
Menu: Geometry->Create->Surface mesh
With this option a Surface mesh can be created by selecting triangular or quadrilateral mesh elements (see Surface mesh ).
Volume creation |
Menu: Geometry->Create->Volume
Toolbar:
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Create volume |
A volume is an entity formed by a closed set of surfaces that share the lines between them.
To create a volume, some surfaces must be selected (see Entity selection ) using the By contour option. The order of selection is not important but all of them must join each other by sharing common lines and they must form a closed contour.
If there is an error and the volume is not created, a window appears with some useful information.
The Search option lets you select one surface and create one of the volumes that contains this surface.
Volumes and their surfaces are automatically orientated so that they are meshed correctly.
An additional feature allows the selection of surfaces that form the outer part of the volume as well as the ones that form the holes at the same time. In this case, GiD automatically recognizes the holes.
The Automatic 6-sided volumes option creates all possible volumes that have 6 sides (contour surfaces). It can be applied several times over the geometry and volumes are not repeated. Every new volume will be created in the current layer.
This can be useful for structured meshing (see Structured ).
Contact creation |
Menu: Geometry->Create->Contact volume
Contact volumes are defined between two surfaces that are physically in the same place but with different surfaces, lines and points. From a contact volume, it is possible to generate contact elements, to be used by some calculation algorithms, which define special contact between two bodies.
Those equivalent surfaces can be in the same location or can be separated by a movement (separated contact volume). The result will be equal meshes, ensuring a one-to-one relationship between nodes.
Choose 'contact volume' from the menu, and then select the surfaces. GiD automatically searches for possible contacts, combining the selected surfaces in pairs.
Contact elements are, by default, 8-node hexahedra or 6-node prisms (depending on the surface mesh). However, you can select 2-node lines for all cases (see Element type ).
The result elements can be also quadratic.
You can also select no mesh for the contact entity. This makes it possible to have exactly the same mesh for both surfaces but without any additional element between them.
When creating contact volumes, GiD internally checks what surfaces occupy the same location in the space and creates the contact, therefore there is no need to specify what surfaces have to be in contact. For this reason, several surfaces can be selected at once and GiD performs the contact automatically, indicating the number of contact volumes that have been generated.
One feature of GiD is the option to create 'contact separated volumes' for surfaces that are not physically in contact.
For these separated volumes, GiD internally checks whether a unique solid-rigid movement exists between two surfaces and creates the contact. There is the possibility that multiple solid-rigid movements may exist. In this situation, GiD asks for the point image of a source point to define the movement and, consequently, applies the right contact.
Object |
Menu: Geometry->Create->Object
Toolbar:
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Create object |
With this command it is possible to create the following kinds of objects:
When creating an object, GiD asks for a center and a normal. To enter the coordinates of the center you can click on the screen or select an existing point (see Point definition ). To enter the normal, GiD displays a window where you can choose one of the three axes or enter the coordinates of a point.
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The In screen button in the Enter normal window lets you manually enter the coordinates of the point which defines the normal: you can directly click on the screen or pick an existing point using the Join option in the Contextual mouse menu.
When using the commands sphere, cylinder, cone, prism or torus, the volume of the object is also created.
Automatic 4-sided surface creation |
Note: The 4-sided surface has been substituted by the NURBS surface (see NURBS surface creation ). This new entity has all the functionality of the old one.
Note: It is still possible, however, to access to this function with the Right buttons menu (see Tools ).
Inside this option, GiD creates as many 4-sided surfaces as it can find. Every new surface will be created in the current layer.
Caution: When creating more than one surface at a time, some undesired surfaces may also be created. It is necessary to check the surfaces after creation and erase the undesired ones.
4-sided surface creation |
Note: The 4-sided surface has been substituted by the NURBS surface (see NURBS surface creation ). This new entity has all the functionality of the old one.
Note: It is still possible, however, to access to this function with the Right buttons menu (see Tools ).
A 4-sided surface is an entity formed by a closed set of four lines in the space. Its mathematical definition is a bilinear Coon's surface. The surface is totally defined by the shape of the lines, with no information about the interior. This means that it will sometimes be necessary to use more surfaces to obtain a good shape definition.
To create a 4-sided surface, several lines must be selected (see Entity selection ). For the creation of a 4-sided surface defined by three lines, it is necessary to divide one of the lines into two pieces (see Divide ). The order of selection is not important, but all of them must join each other by sharing common points and they must form a closed contour. If it cannot be created, information about the endpoints is displayed in a window.
In order to make one or more lines form parts of a polyline (see Polyline creation ), select the entire polyline as one of the lines and GiD will automatically select the piece or pieces of the polyline that are required. Using this facility, non-conforming surfaces can be created. This means creating a surface by using the entire line on one side of the polyline, and creating more than one 4-sided surface by using parts of it on the other side.
When selecting more than four lines, GiD will automatically search for all the possible 4-sided surfaces that can be created with these lines. This allows the creation of many surfaces at the same time.
The Automatic button is equivalent to automatic 4-sided surface creation (see Automatic 4-sided surface creation ).
If the surfaces lie on the z=0 plane, the orientation of the surfaces will be anti-clockwise in this plane (normal vector points towards z positive). Otherwise, the orientation will be arbitrary. This can be checked with the DrawNormals command (see Normals ).
The Number option lets you choose the label that will be assigned to the next created surface. If a surface with this number already exists, the old line changes its number.
Caution: When creating more than one surface at a time, some undesired surfaces may also be created. It is necessary to check the surfaces after creation and erase the undesired ones.
Planar surface creation |
Note: The planar surface has been substituted by the NURBS surface (see NURBS surface creation ). The latter automatically detects if boundary lines lie in a plane and creates a planar NURBS.
Note: It is still possible, however, to access this function with the Right buttons menu (see Tools ).
A planar surface is an entity formed by a closed set of lines, all of them lying on the same plane. These lines must share some common endpoints.
To create a planar surface, some lines must be selected (see Entity selection ). The order of selection is not important but all of them must join each other by sharing common points and must form a closed contour. If all lines are not in the same plane the surface is not created.
It is possible to add holes to a planar surface. To do so, it is first necessary to create the outside planar surface. After this, press the Hole button and select the created surface. Then select lines that form every hole, one by one. Finish with escape (see Escape ). It is also possible to define the surface and holes at the same time, by selecting all the curves.
If the surfaces lie on the plane z=0, the orientation of the surfaces will be anti-clockwise in this plane (the normal vector points towards z positive). Otherwise, orientation will be arbitrary. This can be checked with the DrawNormals command (see Normals ).