05.1 geometry tutorial

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Tutorial

copyright LMS International 2013 1/15

In this tutorial the capabilities of the LMS Test.Lab Geometry workbench will be explored. We will start with some background on working with geometry. After the theory we will create the simple model of a brake rotor prior to modal testing. We will continue with a more complex model with more components. We will finish with some other Geometry functions. Overview 1 Some background ..................................................................................................................... 2

1.1 Nodes, lines and surfaces ................................................................................................... 2 1.2 Coordinate systems .............................................................................................................. 2

2 The rotor disc: a simple geometry ........................................................................................ 3 2.1 How to start? ......................................................................................................................... 3 2.2 The geometry of a disc ......................................................................................................... 4

3 A more complex geometry .................................................................................................... 10 3.1 Component creation ........................................................................................................... 11 3.2 Node locations .................................................................................................................... 11 3.3 Adding lines and surfaces.................................................................................................. 12

4 Other Geometry Options ....................................................................................................... 13 4.1 Importing geometry ............................................................................................................. 13 4.2 Copying and Moving Components ................................................................................... 14 4.3 The slaves Minor Worksheet ............................................................................................. 15

Prerequisites

brake rotor, ruler, test stand, bungee / tubing LMS Test.Lab Desktop and LMS Test.Lab Geometry license The excel file InnerRing.xls

Category: LMS Test.Lab Structures Modal Testing & Analysis

Topic: Create a geometry model for the test


1 Some background

1.1 Nodes, lines and surfaces

The LMS Test.Lab Geometry add-in allows you to build a 3D representation of the structure under test. This type of representation is called a wire frame model. It is comprised of nodes (defined by their position and orientation) and lines connecting the nodes. Nodes on the wire frame model define the points where measurements will be taken on the structure. The definition of each node contains not only the location of that point, but also a nodal coordinate system. The importance of the nodal coordinate system is that it is interpreted by the LMS Test.Lab modal analysis and ODS / Time Animation workbook to define the measurement orientation at that point. This means that even on a highly complex structure, the data will be measured in a `natural' sense for the various nodes.

These nodes can be combined together into groups to form components. The use of components simplifies the definition of a large and complicated structure by splitting it into logical parts. These components can also be turned ON / OFF during geometry creation and result animations. When lines have been defined between the nodes, the wire frame model can be visualized in the display windows. Opaque surfaces can be added to the model by the use of quadrangles and triangles. This improves the visualization of the model by obscuring hidden lines and provides surface representation in the Geometry display.

1.2 Coordinate systems

Such a 3D representation is defined in a certain coordinate system. In general a Cartesian coordinate system is used, but cylindrical and spherical coordinate systems exist also.


2 The rotor disc: a simple geometry

2.1 How to start?

There are two ways to open the Geometry workbench. You can start Geometry in a standalone workbench or Add-In Geometry to another workbench such as Desktop, Impact Testing, Spectral Testing, etc.

Start up the geometry workbook Open a new project and save it under the specific name DiscBrakeImpact, since

we are going to use this geometry for the impact measurements.

The Geometry workbench has three worksheets as displayed here: The Geometry Worksheet consists of several minor worksheets:

Legend: Components:

create separate components which are logical entity used to group nodes.

Nodes: create nodes which are basic geometry element in the wire frame model.

Lines: create the connections between nodes.

Surfaces: create triangular or quadrangular drawn between nodes to assist in viewing the geometry (optional).

Slaves: create Master / Slave degrees of freedom. Defining a slave node is similar to apply a type of constraint to the geometry since the mode shape movement of a slave DOF is related to the one of the corresponding master DOF.

Mesh area: automatically create meshes for acoustic measurements (microphone and acoustic intensity probes). This is not covered in this structural testing course tutorial.


2.2 The geometry of a disc

Well start with the 3D model of a disc that can be used later for impact hammer testing or shaker testing in modal analysis. We will define 32 geometry points for the outer ring that will be used in the measurements.

2.2.1 Component Creation

In the first minor worksheet Components, one or more components can be created. You can do this by typing a component name in the table and by clicking Accept Table (in the upper right). By default, the coordinate system is Cartesian and the color of the component is orange. You can change the color by clicking on the box under the column Color and selecting another one. You can also change the coordinate system by choosing another field of the drop down menu in the Coord System column.

Create a red disc component with cylindrical coordinates and red color. Note that the spelling and case (capital or lower case letters) is important.

Notice that a component disc is created in the Geometry in the left after the table is accepted. The table is not accepted and saved until you press the Accept Table button. Note: if LMS Cada-X Modal Analysis is being used, it has a limitation that all components must be less than four characters. Please follow this rule if you are exporting data to Cada-X for analysis. Test.Lab processing workbooks do not have this limitation In the upper right corner you can also find the Table Options. Here you can customize the table options (turn on/off the columns that are shown):

Position - defines a component translation from the global coordinate system. Orientation - defines a component rotation from the global coordinate system. Show Units and Labels - displays the label for the degree of freedom and its unit.

Play with these options and Accept Table to accept the created components when

done.


2.2.2 Node locations

After one or more components have been created, the node locations have to be specified. This can be done in the Nodes minor worksheet.

Go to the Nodes minor worksheet Highlight the component disc in the Navigator window on the left and add the 16

nodes in cylindrical coordinates (r, theta and Z). Also mark the points on the structure!!! You can copy / paste cells and patterns to expedite entering these r, Theta, Z values.

If your units are English Units (in), go to Tools Options Units, change the Active Unit System and restart the software as suggested.

After filling in the Names and the coordinates of the points, again click on the Accept Table button.

The full Name of the first node will become disc:1 and the points are shown in the Geometry Display. When measuring data, the Point ID as specified in Channel Setup must be exactly this Full Name, otherwise there is not a mapping between the geometry and the measurements. In addition to the Point ID, the Direction will be required, Note: if LMS Cada-X Modal Analysis is being used, it also has a limitation that all node names have to be less than four characters (e.g. 9999). LMS Test.Lab does have this limitation


In the Nodes table, the following Table Options can be set:

Local / Global coordinates defines if the point coordinates are defined with respect to the global coordinate system or the local coordinate system of the component. This option is used

when the geometry is more complex and consists of more than one component. Read only - makes the table read only (not editable) until the flag is turned off. Show position shows the X, Y and Z / r, theta and Z / r, theta and phi location of node. Show orientation shows the local coordinate system at this node (Euler angles). Show units and labels - toggles ON or OFF the label and unit for the degrees of freedom. Show full node names - after the table is refreshed includes component and node number.

Switch between local and global coordinates to see the cylindrical coordinates in the

global Cartesian axis system; then switch again to local coordinates. 2.2.3 Adding Lines

To add the lines or wire frame geometry, select the Lines minor worksheet from the Geometry Workbook flow diagram. There are two ways to add lines to the geometry: Per default, the check box Add Lines in Display on top of the table is selected. This option

allows you to use the first way of adding lines which is also the easiest. In the Geometry display, select a starting point. Then, move the cursor in the display: you can see a line drawn between the starting point and the current position of the cursor. By clicking on a second point, the line between the selected point and the starting point is defined. The cursor can be moved now to the next point: the line will now be drawn between the last selected point and the current cursor position. Clicking the last point again (so double click!) ends the line at the last selected point.

The [Backspace] key deletes the current line to be added.


If the option Add Lines in Display is not selected, the table becomes white and you can type manually the nodes at the beginning and the end of each line. This way is rather used as a way to change some lines than to add them all.

After you have changed something, click on Accept Table to save the changes. Go to the Lines minor worksheet Connect the 16 nodes of the disc by clicking on the start point and double clicking on

the end point

If you made a mistake during the line definition and you want to delete a line, first select the line and click then on the Delete button upper right. There are two ways to select a line: By selecting a row in the table; the line according to that row becomes light green. In the

table the shift and control keys can be used to select more than one row. By deselecting first the option Add Lines in Display and then by clicking on a line in the

Geometry Display, the row according to that line will be selected. In this mode, you can press and hold your middle mouse button down as your drag an area in the display. All lines in that area are selected.

2.2.4 Adding surfaces

If you would also like surfaces drawn on your geometry to aid in visualization, click on the Surfaces minor worksheet. Surfaces can be added as triangles or quads following a procedure close to the one used to add lines.

First, check the box corresponding to the shape of the surface element you want to add: Triangles or Quadrangles.

Click consecutively on 3 nodes to place a triangular surface on it. Click consecutively on 4 nodes to place a quadrangular surface on it. Make sure you click on the 4 nodes in a clockwise or anti-

clockwise order. If you connect the nodes in a mixed order, the surface will be folded.

To delete the last surface while adding them, use the [Backspace] key.


Deleting or selecting a particular surface works in the same fashion as the deletion or selection of lines in the Lines minor worksheet: either you select a row in the table, or uncheck the Add Triangles or Quadrangles button to be able to select a surface with the mouse cursor.

Go to the Surfaces minor worksheet and select the option Add Quadrangles in

Display. Add surfaces between the points.

2.2.5 Geometry Display Features

In the upper left of the geometry display are the two model manipulation icons. The default left mouse action is to rotate the geometry. The first icon is to translate the model while the second is to enlarge or decrease the model size in the display. To use, press one of the buttons with the left mouse button, hold the button down and move your mouse Right clicking in the Geometry Display can change the settings of the display: Most of the options are straightforward. More information on options that are less obvious can be found in the help and especially in the section The Geometry display menu. The help button can be found in the upper right of the window. Following, you can see a brief description of the main options in this menu: Model:

various parts of the geometry can be toggled ON or OFF.

Selection: various parts of the geometry can be selected or deselected. Selectable elements of the deformed model will be highlighted when the mouse passes over them. Clicking on these selectable elements will select them. You can also select more than one element at the same time by left clicking on them while pressing the Shift key or dragging the mouse over the model with the middle mouse button depressed.

Fit Model: fits the model to the screen

Views: the standard isometric, top, front or side views can be selected.

Visual Extensions: some useful display parameters such as extending the views along a given plane or showing the origin may be used.


Component Visualization: Component visibility and location can be modified as while as importing a texture for each component.

Display Size: Display can be maximized and restored

Copy to Clipboard: copies the geometry picture to the clipboard thus making it available for pasting into other applications.

Options: Allows the user to set Background, Visual Extensions, Marker and Model options.

Two last things to show: In the upper right corner of the Geometry workbook is the Pane Header selection menu. This

dropdown menu allows you to select between the Upper/Lower and Left/Right views of your data.

Between the different panels, you can grab the separator bar and pull to change the panels size.


3 A more complex geometry

Now we are going to make the geometry of the rotor disc a little bit more complex by adding also the internal face of the disc as a separate component. We will also show that you can copy geometry data from Microsoft Excel. Go to the Nodes minor worksheet and select in the left the disc component. Open the excel file InnerRing.xls in Excel and copy and paste the node locations from

the inner ring of the disc. Press the [Accept] button to finish. Copy and paste also the lines and surfaces. Make sure first to deselect the options

Add Lines and Add Triangles/Quadrangles so that the table becomes editable and press the [Accept] button to finish.

You should then see that the geometry has now two different rings at two different heights, that are linked together with lines and surface.

This is the geometry with the 48 nodes that that we will use in the impact testing and shaker testing tutorials. Make sure you save your project at this time We will now some additional features to demonstrate the software but the additions wont be used in later exercises. So, dont be surprised if we dont save or use the following steps. They are for demonstration only.


3.1 Component creation

Now we will create a second component:

Fill in a name for the second component ( e.g. int_face) on the Components minor. Choose the type of local coordinate system: Cartesian, cylindrical or spherical. For

the disc, if we put sensors on the surface, it is easier to define the radius and the angle of the sensor position than to find out what the X and Y coordinates are in a Cartesian coordinate system, so we will use a cylindrical coordinate system.

Define the positions and orientations of the component coordinate systems. The coordinate system of the internal face will be shifted by -2cm in the Z-direction compared to the global coordinate system. Press Accept Table

3.2 Node locations

We continue our geometry in the Nodes minor worksheet. Since the points of the internal face have the same location as the points of the disc (except the Z coordinate is different but the component itself is already shifted), we can just copy the coordinates of the disc to the internal face points. Go to the Nodes minor worksheet and select the component disc on the left

side Copy the first 16 coordinates and names of the points Select the component int_face and paste the coordinates and names Accept the Table


3.3 Adding lines and surfaces

After we have defined the points, we can add lines and surfaces. This is the same as for the simple geometry, which was explained before in 2.2.3 and 2.2.4. Add the lines in the Lines minor worksheet, use the component visualization to

remove the other components from the display to increase the ease of use. You may need to turn ON the Add Lines in Display toggle.

Add the surfaces in the Surfaces minor worksheet You should obtain the following result after you use component visualization to

make both components visible. Delete the component int_face since we will not use it right now

Now your project is ready for testing, analysis and animation. Make sure that your data is named corresponding to the geometry. If your geometry full name is disc:1 for node 1, then your data channel must have a Point name of disc:1. The mapping between the geometry node (through component and node number) and the channel Point name (through Point and direction) must be exact in order for the geometry to be animated. This needs to be done to ensure the software knows which point to animate for each piece of data that is acquired.


4 Other Geometry Options

There are also some options to import geometry from another project, so that you dont have to make the same geometry again. In the lower left corner of the Geometry workbook you can find the next menu:

4.1 Importing geometry

Open a new project and save it as dummy project. In the Geometry worksheet, browse trough the Navigator (My computer) to the

DiscBrakeImpact project and highlight the geometry Press the Import Geometry button to import the geometry into the currently open

project. You will get this message:

Press Yes The imported geometry will replace the current geometry

Remark: In this manner, data can be imported from another LMS Test.lab, Cada-X, Pimento, Universal file For more information about this topic, see the FAQ about data drivers.


4.2 Copying and Moving Components 4.2.1 Copy

Highlight the disc component in the Navigator window on the left side of the

geometry worksheet Press Duplicate / Import Component The new component is created

4.2.2 Move

Highlight the new component that will be moved in the Navigator window Press the Move Component button so that a small window will pop up

Move the component 2 cm in the Z direction, resulting in the following geometry:


4.3 The slaves Minor Worksheet

Slave nodes are always associated with one or more master nodes. Defining such node combinations for certain directions applies a type of constraint to the geometry since the mode shape movement of a slave DOF is related to that of the master DOF. These master/slave combinations are useful for completing a mode shape, such as those for animation purposes or structural modification enhancements. It is a mechanism whereby you can compute more complete mode shapes from a limited number of measurements. When more than 1 master node is defined, a linear interpolation is used between the master nodes, according to the line or plane that connects them. If needed the slave node has first to be projected onto this line or plane.

Go to the Slaves minor worksheet The first node you have to select is the Slave (it turns blue) The next one to four nodes are the Masters (they turn red) Press Accept (on top of the table) when done

Note that this is easier, if your geometry is not red and blue Since the rotor disc is not very complex and it is possible to measure all points, it is not really necessary to define slave nodes. However you can still try to define some slave nodes just for practicing.

Make disc:1 a slave node of disc:2, disc:5 and disc:29

Then click on the Accept button. In the table a row is added:

Notice you can also specify the directions of the slaves degrees of freedom. Now you can select the row and press the [Delete]-button.

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