Getting Started Using Adams Flex MDR3

15Getting Started Using Adams/Flex

Adams/FlexGetting Started Using Adams/Flex

Getting Started Using Adams/Flex

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Welcome to Adams/Flex Adams/Flex is an add-on module to Adams products that lets you add flexible bodies to your models to achieve more realistic simulation results.

If you’ve never used Adams/Flex before, this guide is a good place to start learning about Adams/Flex. As you work through the two tutorials that we have provided, you will learn most of the basic concepts and tasks that you can perform using Adams/Flex.

Before doing these tutorials you should be familiar with the basic features of the Adams/View interface. For information about the Adams/View interface, see the guide, Getting Started Using Adams/View.

17Getting Started Using Adams/Flex

About the TutorialsThe two tutorials in this guide give you an introduction to using Adams/Flex:

• Building and Simulating a Flexible Model - The first tutorial teaches you how to integrate flexible bodies into Adams/View and attach rigid bodies to them. The tutorial also introduces you to Adams/Flex basics, such as the options that are available for setting up the modal content of flexible bodies before a simulation.

• Exchanging a Rigid Body with a Flexible Body - The second tutorial teaches you how to bring a flexible body into an existing model and replace a rigid body with the flexible body. It lets you see how easy it is to integrate the flexible body into an existing rigid model so you can gradually add complexity and realism to your model.

Note that there are additional tutorials in the guide, Using Adams/Flex, that explain many of the advanced features of Adams/Flex. They are presented in the chapters in which the advanced features are explained.


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15Building and Simulating a Flexible Model

Building and Simulating a Flexible Model


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OverviewThis tutorial explains how to create a flexible model of a cantilever link. It contains the sections:

• What This Tutorial Does

• What You’ll Create and Simulate

• Starting Adams/View and Creating a Database

• Building the Model

• Simulating the Flexible Model

• Investigating Modes

• Modifying the Modal Content

• Viewing Numeric Results


What This Tutorial DoesThis tutorial will help you learn how to investigate flexible bodies using Adams/Flex. It teaches you how to integrate a modal neutral file (MNF) into an existing modeling database to create a flexible body in Adams/View. It also explains how to build rigid bodies that attach to the flexible body and how to change the flexible body’s visual representation. Finally, it explains how to change the properties of the flexible body by disabling modes and how to examine the effect of these changes on simulation results.


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What You’ll Create and SimulateIn this tutorial, you’ll create a model of a cantilever link shown below. The cantilever link is made up of a flexible link, which you integrate into Adams/View using an MNF and a rigid body sphere. You fix one end of the link to the sphere and the other end of the link to ground. You’ll use a fixed joint to make the attachments. A fixed joint locks two parts together so that they cannot move with respect to each other. You’ll then simulate the model to see the cantilever link oscillate from the force of gravity.

Figure 0-1 Cantilever Link Model


Starting Adams/View and Creating a DatabaseYou’ll start the tutorial by running Adams/View and creating a modeling database that will contain a new model called dumbbell. You’ll also set the gravity and units for the model.

To start Adams and create your database:1. Copy the file /install_dir/flex/examples/mnf/link.mnf to your working directory. install_dir is the

directory where the Adams software is installed. If you cannot locate this directory, please see your system administrator.

2. Do either of the following depending on the platform on which you are running Adams/View:• In UNIX, type the command to start the Adams Toolbar at the command prompt, and then

press Enter. Click the Adams/View tool .• In Windows, from the Start menu, point to Programs, point to MSC.Software, point to MD

Adams R3, point to Aview, and then select Adams - View. The Adams/View main window appears.

3. In the Welcome dialog box, select Create a new model, and then assign the new model the name dumbbell.

4. Set Gravity to Earth Normal (- Global Y).5. Set Units to MKS.6. Select OK.


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Building the ModelIn this section, you’ll build a model of the cantilever link. You will build the model by:

• Creating the Flexible Link into the Database

• Adding a Fixed Joint

• Creating and Moving a Sphere

• Adding a Second Fixed Joint

Creating the Flexible Link into the DatabaseIn this section, you’ll read the modal neutral file (MNF) containing the flexible link into your model. The flexible link is defined in the file link.mnf in your working directory.

To create the flexible link:1. From the Build menu, point to Flexible Bodies, and then select Adams/Flex. The Create a

Flexible Body dialog box appears as shown below.

2. Right-click the Modal Neutral File Name text box, and then select Browse. The File Selection dialog box appears.

3. Select the file link.mnf, and then select OK. 4. Select OK.

A 0.5 meter long flexible link appears in Adams/View as shown in the following figure.

Figure 0-2 Adams/View Screen After Importing the MNF


Adding a Fixed JointNow you’ll fix one end of the flexible link to ground using a fixed joint.

To add a fixed joint:1. From the Joint tool stack of the Main toolbox, select the Fixed Joint tool .2. In the construction container of the Main toolbox, select the construction method 1 Location. 3. Place the cursor at the left end of the link. Node numbers flash on the screen as you move the

cursor. Select node 1000 for the location of the fixed joint by clicking the left mouse button when the cursor is over node 1000. Figure 3 shows the location for the fixed joint. Node 1000 is at (0,0,0).

4. If you have trouble selecting the node, try zooming in on the model by pressing either the letter w, to draw a zoom window, or the letter z, to dynamically zoom the window. The window must be active.

Figure 0-3 Location to Place Fixed Joint


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Creating and Moving a SphereNow that you’ve fixed the link to ground, you’ll create a sphere that attaches to the right end of the link. You’ll also move the sphere so its center goes through the center line of the link.

To create and move a sphere:1. From the Geometric Modeling tool stack of the Main toolbox, select the Sphere tool .2. Click the left mouse button anywhere in the screen and drag the cursor until you have a sphere

approximately 0.3 meters in diameter. (Remember that the length of the link is 0.5 meters.)3. From the Move tool stack of the Main toolbox, select the Point-to-Point tool .4. Following the instructions in the status bar, select the sphere as the object to move. Click near the

left edge of the sphere to indicate the point to move from, and then, click on node 1001 at the right end of the link to indicate the point to move to. Press the Ctrl key to use grid points or zoom in on the model to gain greater accuracy.

FLEX_BODY_1.N1000


Figure 4 shows the objects you should select to move the sphere. In the figure, the sphere is located on the left side of the link. The sphere you created could be anywhere in the screen but you still need to select the point on the sphere farthest to the left as the point to move from as illustrated in the figure. The alignment of the sphere with node 1001 does not need to be accurate. Adams/View moves the sphere so its center goes through the center line of the link.

Figure 0-4 Objects to Select to Move Sphere

Adding a Second Fixed JointYour final step in creating the cantilever link is to fix the sphere you created to the link using a fixed joint.

To add a joint:1. From the Joint tool stack of the Main toolbox, select the Fixed Joint tool .2. In the construction container of the Main toolbox, select the construction method 2 Bod - 1 Loc. 3. Select the link, the sphere, and the end of the link where it coincides with the sphere

(FLEX_BODY_1.N1001). Adams/View attaches a fixed joint as shown in the figure below.You’ll now simulate the model to see how it moves.

Figure 0-5 Sphere Connected to Flexible Link

Point to move fromPoint to move to


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Simulating the Flexible ModelIn this section, you’ll run a simulation of the cantilever link you created to see how it moves. You’ll run a one-second simulation that outputs data 100 times.

To simulate the flexible body:1. From the Main toolbox, select the Simulate tool .2. In the Simulation container in the Main toolbox, enter the following:

• In the End Time text box, enter 1 second. • In the Steps text box, enter 100.

3. Select the Simulation Start tool . You see the cantilever link oscillating because of the force of gravity as shown in the next figure.

Figure 0-6 Oscillating Cantilever Link


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Investigating ModesAdams/Flex lets you set options to help you see the deformation of the flexible body during an animation. In the next sections, you’ll change the contour color, specify a node relative to which the flexible body appears to deform, and scale the deformed mode display. There are many other options available for enhancing the visual representation of the flexible body.

• Displaying the Flexible Body Modify Dialog Box

• Adding Color Contours

• Setting the Datum Node

• Changing the Deformation Scale

Displaying the Flexible Body Modify Dialog BoxAll the changes you make to a flexible body, you make through the Flexible Body Modify dialog box. You display the dialog box just as you would any modify dialog box in Adams/View.

To display the Flexible Body Modify dialog box:1. In the Simulation container of the Main toolbox, select the Reset tool to return to modeling

mode.2. Double-click the flexible body to display the Flexible Body Modify dialog box shown in the next

figure. The figure indicates the three controls that you use to change the deformation display of a flexible body.


Adding Color ContoursIn this section, you’ll set Adams/Flex so that it changes the color of the flexible link as the link deforms to indicate the magnitude of the deformation.

By default, Adams/Flex considers the deformation to be relative to the origin of the flexible body (its local body reference frame (LBRF) or coordinate system). You’ll notice that at the start of the animation,

Specifies a node

Turns on contours

Exaggerates the amount of deformation

relative to which thebody appears to deform


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the flexible link is completely blue. As the animation runs, it changes to red to indicate where and when the maximum deformation occurred.

To change the color contour:1. From the Flexible Body Modify dialog box, set Plot Type to Contour. 2. From the Main toolbox, select the Animation tool .

3. In the Animation container on the Main toolbox, be sure that Contour Plots is selected. 4. From the Animation container, select the Play tool .

There is a short hesitation before the animation starts because Adams/View computes and scales colors based on the deformation that occurred during the simulation.

Setting the Datum NodeNow you’ll set the datum node that you want deformation color changes to appear to be relative to. As explained in the previous section, Adams/Flex considers the deformation to be relative to the origin of the flexible body (its LBRF or coordinate system) by default. In this section, you’ll change it to node 1000, which lets you see deformations relative to the nodes at the end of the link that is fixed to ground.

To change the datum node:1. In the Animation container on the Main toolbox, select the Rewind tool to reset the animation

back to its first frame.2. In the Flexible Body Modify dialog box, clear the selection of LBRF.3. In the Datum Node text box, enter 1000. 4. Select Apply or press Enter. 5. In the Animation container on the Main toolbox, select the Play tool and observe the color

scheme, which is more realistic. You’ll notice that there is a slightly longer hesitation before the animation begins because now there is the added cost of scaling deformation color relative to a datum node.

6. Select the Stop tool .

Note: If you receive the warning shown below you incorrectly selected the Animate tool on the Flexible Body Modify dialog box:

Please specify a valid mode number.

Be sure to select the Animation tool in the Main toolbox.


Changing the Deformation ScaleIn this section, you’ll exaggerate the amount the flexible body deforms so you can see deformations that might otherwise be too subtle to observe. The default scale factor is 1.

1. At the bottom of the Flexible Body Modify dialog box, move the Deformation Scale Factor slider to a value between 2 and 5.

2. In the Animation container on the Main toolbox, select the Play tool to restart the animation. Adams/Flex now exaggerates the deformations of the flexible body by the amount you requested. The flexible body also appears to be detached from the sphere and from its connection with ground. This is because the motion of a point in a flexible body is the sum of the deformation that is scaled and a rigid body motion that is not scaled.

3. In the Deformation Scale Factor text box, enter 1.0 to set the deformation scale back to 1.0. 4. Select Apply.


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Modifying the Modal ContentOne of the keys to successfully simulating flexible bodies is having the right modal content. In many cases, an MNF has more modes than you need to simulate a particular response. Using Adams/Flex, you can select the modes that you want included in the flexible body. You can disable a particular mode if it does not contribute to the overall response of a flexible body. You can also remove low influence modes if they are slowing down the simulation of your model. You can disable modes based on their mode number, frequency, or contribution of strain energy. You can also disable modes one at a time or disable a range of modes.

In this section, you’ll use the Flexible Body Modify dialog box to display the different modes in the flexible body, examine them, and then disable them based on their mode number and frequency.

• Displaying the Flexible Body Modify Dialog Box

• Disabling Individual Modes

• Disabling a Range of Modes

• Simulating the Model with Disabled Modes

Displaying the Flexible Body Modify Dialog Box

To display the Flexible Body Modify dialog box so you can modify the modal content:1. From the Main toolbox, select the Select tool to reset the model. 2. Display the Flexible Body Modify dialog box, if necessary, as explained in Displaying the

Flexible Body Modify Dialog Box.

Disabling Individual ModesThe MNF file that you read into Adams/View contains 32 modes. Some of these modes are rigid body modes, and Adams/Flex disables them by default. Because Adams/Flex supplies each flexible body with its six nonlinear rigid body degrees-of-freedom, you do not need to nor should you include rigid body modes.

In this section, you’ll view the first six modes (1 through 6), which are disabled because they are rigid body modes. You’ll also view the first mode that is enabled, mode 7, and disable it because it bends out-of-plane and is not needed for this simulation. Finally, you’ll disable other modes that do not contribute to inplane motion. You disable the modes so the simulation of your model is more efficient.

To disable modes one at a time:1. From the Flexible Body Modify dialog box, select the Next Mode tool to view the first

available mode (mode 1). The mode appears on the undeformed flexible body if the Superimpose check box is selected. The Superimpose check box controls whether the undeformed shape is superimposed on the deformed shape.


2. From the Flexible Body Modify dialog box, select the Animate tool to animate the mode. By default, Adams/View runs the animation 3 times or through 3 cycles. The mode you are currently animating is a rigid body mode and is disabled. To tell if a mode is disabled, Adams/Flex selects the Disable radio button and displays the mode’s number and frequency in parenthesis on the Flexible Body Modify dialog box.

3. Select the Next Mode tool until you reach mode 7 or, in the Mode Number text box, type 7 and press Enter. Mode 7 is the first flexural mode that bends out-of-plane and is the first enabled mode. Because the event you are modeling is inplane, you can disable this mode to improve efficiency. To view the out-of-plane mode better, look at the model from a top view by selecting T (uppercase) in the main window.

4. Select Disable to disable mode 7. The mode number and its natural frequency now appear in parentheses.

5. Change to mode 8. This is the first inplane bending mode. 6. Use the Contour, Datum Node, and Deformation Scale Factor settings to modify the

appearance of mode 8 so you can view it more easily. Ensure that mode 8 is enabled; it is critical for the motion you are trying to capture.

7. Examine the remaining mode shapes and disable them if they do not contribute to inplane motion. If in doubt, leave the modes enabled. Remember, however, that disabling modes results in more efficient simulations. Therefore, by leaving those modes that do not contribute to inplane motion enabled, you will not see significant improvements in your simulation time.

Disabling a Range of ModesIn this section, you’ll disable a range of modes by specifying to disable all modes that have a frequency of 10000Hz or higher.

To disable a range of modes:1. From the Flexible Body Modify dialog box, select range.

The Enable or Disable a Range of Modes dialog box appears. This dialog box is very useful when you have a large number of modes that you are managing. It lets you enable and disable ranges of modes by either their mode number or their frequency.


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2. From the third pull-down menu from the left, select above and enter 10000 in the text box that appears next to the pull-down menu.

3. Select OK.

Simulating the Model with Disabled ModesNow that you’ve disabled the modes in your model that do not contribute to inplane motion, run the simulation again as explained below. You should notice an improvement in simulation time.

To simulate the model:1. From the Flexible Body Modify dialog box, reset the deformation scale factor to 1, set Plot Types

to Contour, and set Datum Node to 1000.2. Select OK. 3. Now repeat the simulation as explained in Simulating the Flexible Model. Depending on how

many modes you disabled, the simulation time should decrease.

You should use caution when disabling modes, however. Once you disable a mode, the flexible body cannot take on the particular shape of the disabled mode. This is the same as applying a constraint to the model. If you were to remove all out-of-plane modes from the example, the flexible body would behave like a rigid body when responding to out-of-plane loads.


Viewing Numeric ResultsBy default, when you include a flexible body in your model, Adams/View measures specific attributes of the flexible body, as well attributes of markers and points on the flexible body. For a listing of the measures that Adams/View automatically tracks, see the Adams/Flex online help (under the Results tab), and for more information on measures, see the Adams/View online help (under the Test tab).

In this section, you’ll view the measures that Adams/View has tracked during the latest simulation in the plotting window. You’ll set the plotting window to surf so that you can quickly view each measure plotted against time without having to add pages to the plotting window.

To view plots of the measures:1. In the Main toolbox, select the PostProcessing tool .

The Adams/PostProcessor plotting window appears with no plots displayed.2. In the dashboard that appears along the bottom of the screen, set Source to Objects.3. From the Filter list, select body and then, from the Object list, select FLEX_BODY_1. 4. Select a characteristic and component of the flexible body to measure. Start by selecting CM

Position and Y to view the position of the center of mass of the flexible body over time. 5. Select Surf on the right of the dashboard.6. Continue selecting characteristics and components of the flexible body to view. You may find

interesting the translational deformation of markers on the flexible body, particularly in the y direction. Notice that the deformations are relative to the LBRF of the flexible body regardless of whether you set a different datum node.

7. When you are done, from the File menu, select Close Plot Window to return to the Adams/View main window.


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15Exchanging a Rigid Body with a Flexible Body

Exchanging a Rigid Body with a Flexible Body


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OverviewOne of the keys to successful modeling is to start gradually and add complexity to your model as you need it. We call this the crawl-walk-run approach. For example, the first time you simulate a new model, your primary concern may be its overall performance. As you refine your design, however, you can add complexity, such as the flexibility of key parts. Using Adams/Flex and Adams/View together, you can very easily add flexibility to your model after your initial design is complete, as shown in this tutorial. The tutorial also illustrates that often you cannot simulate a model until you add flexibility to it.

The tutorial contains the following sections:

• What You’ll Create

• Starting Adams/View and Importing a File

• Simulating the Rigid Fourbar

• Adding a Flexible Link

• Positioning the Flexible Link

• Reviewing Connections

• Simulating the Flexible Fourbar


What You’ll CreateIn the tutorial, you’ll import into Adams/View a command file that contains a rigid model of a fourbar. You’ll then replace one of the rigid links with a flexible link.

Until you replace the rigid link with a flexible link, Adams/Solver cannot simulate the motion of the fourbar because one of its joints (JOINT_3) is skewed by 1 degree. The skewing of the joint requires the motion of the fourbar to be out-of-plane. Because the links are rigid, however, they cannot deflect out-of-plane and, thus, the simulation fails. Adding a flexible link that bends allows the fourbar to move.

The following figure shows the fourbar model, the joint that is skewed, and the rigid link that you’ll replace with a flexible link. The flexible link that you’ll use to replace the rigid link is actually the same flexible link you used in the first tutorial to create a cantilever link.

Figure 0-1 Fourbar Model

Rigid link (PART_2)to be replaced

Joint (JOINT_3)skewed by 1 degree


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Starting Adams/View and Importing a FileYou’ll start the tutorial by running Adams/View and importing a command file to create a model called model_1.

To start Adams/View and create your database:1. Start Adams/View, if necessary, as explained in Starting Adams/View and Creating a Database.

The Adams/View main window appears.2. From the Welcome dialog box, select Import a file. 3. Select OK.

The File Import dialog box appears.4. Right-click the File to Read text box, and point to Search.5. From the shortcut menu, select the flex/examples directory

(aview_dir/../flex/examples).The Select File dialog box appears.

6. In the fourbar folder, select the file rigid.cmd, and then select OK. 7. Select OK.

A fourbar model like the one shown in the figure above appears.


Simulating the Rigid FourbarYou’ll now try to simulate the fourbar that you imported into your modeling database. You will not, however, be able to simulate it. Instead, you’ll receive an error in the message window.

To simulate the rigid fourbar:1. From the Main toolbox, select the Simulate tool .2. In the Simulation container of the Main toolbox, select the Simulation Start tool .

The simulation fails and the following error message appears:ERROR: No convergence was achieved after 25 iterations while solving for the kinematic displacements.ERROR: Simulation failure detected

3. Closely examine the model to see that the joints are misaligned making the mechanism locked and, therefore, unable to simulate. We’ve intentionally added this misalignment to highlight the impact flexibility can have on your model.


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Adding a Flexible LinkThe next step is to indicate the rigid link you want to replace and the replacement flexible link. You will use the Rigid to Flex swapping feature.

To add a flexible link:1. From the Main toolbox, select the Select tool to reset the model. 2. Select the upper link, PART_2. 3. From the Build menu, point to Flexible Bodies, and then select Rigid To Flex.

The Swap a rigid body for a flexible body dialog box appears. Notice that the Current Part text box already has the name of the link you selected.

4. Right-click the MNF File text box, and then, from the shortcut menu, point to Search. 5. From the shortcut menu, select the flex/examples/mnf directory

(aview_dir/../flex/examples/mnf).6. In the Select File dialog box, select the file link.mnf, and then select Open.

A 0.5 meter long flexible link appears in Adams/View.

Note: You may need to move the Swap a rigid body dialog box if it blocks your view of the body.


Positioning the Flexible LinkCurrently, the link is not positioned where it needs to be. There are three positioning tools available:

• Align flexible body CM with CM of current part• Launch Precision Move dialog box • Specify three point pairs to define the location and orientation

In this tutorial, you’ll use the first two.

To position the flexible link based on the center of mass (CM):In the Swap a rigid body for flexible body dialog box, select the Align Flex Body CM with CM of Current Part button.Adams/Flex moves the link so the CM of the rigid and flexible links align.Keep in mind that the finite element discretization of a solid will naturally have an inertia tensor and CM location that is slightly different than that of an analytical solid, due in large part to the facetization. Therefore, you may find that you need to make small precise adjustments to the position and/or orientation of the flexible body so it fits correctly into the rest of your model.

To position the flexible link precisely:1. In the Swap a rigid body for flexible body dialog box, select the Launch Precision Move Panel

button.The Precision Move dialog box appears, as shown in the figure below. Notice that many of the text boxes have been automatically filled in with the position and orientation of the flexible body relative to the ground coordinate system.

Figure 0-2 Precision Move Dialog Box

Values alreadyentered


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The C1, C2, and C3 text boxes display the location of the flexible body with much precision:-250.0000107801, 250.0, 0.0The A1, A2, and A3 text boxes display the angular orientation, and they appear acceptable:0.0, 0.0, 0.0

2. Clear the C1 text box, and enter the value: -250. 3. Select OK.

The location of the link has now been corrected to a higher level of position.


Reviewing ConnectionsIt is a good idea to review the connections that will be established for you between the link and the rest of the model. As part of the swapping operation, all the markers on the rigid body will be transferred to the flexible body, thereby establishing connections to the flexible body.

1. In the Swap a rigid body for a flexible body dialog box, select the Connections tab.2. Verify that Sort By is set to Marker (it is on the far right of the dialog box).

The Markers and Nodes table appears, as shown below. Notice that it has identified a list of markers on the rigid link that will be transferred to the flexible link. The Connections column identifies the names of constraints or forces that exist on the rigid body that you are replacing. The nodes on the flexible body that are nearest to the markers are listed in the Node ID column.

Figure 0-3 Marker and Nodes Table

3. Notice that the Distance column is reporting the distance between the nearest node and the rigid body marker that will be transferred to the flexible body.Because you have positioned the flexible body precisely, the connections are coincident with nodes and the distances are 0.00 for the markers (MAR_1 through MAR_4).

Note: You can display more digits of precision by entering a value in the Number of digits text box.

Distancecolumn


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The CM marker distance is nonzero because the finite element mesh was not constructed to have a node at the CM. This is a very common scenario and is not really a problem because it can be automatically moved to the nearest node by default.Keep in mind that the flexible body already has its own CM so you can safely ignore the CM marker on the rigid body and just let it move to the nearest node. To demonstrate the move/preserve feature of the dialog box, however, you will preserve the location.

4. Select the Distance cell (13.34) for the CM.5. Select the Preserve Location button.

The cell in the Move column has now been updated to loc. This means that the location of the CM marker will be preserved and it will not be moved to the nearest node when it is transferred to the flexible body.

6. Select OK.The flexible body has been swapped, the rigid body deleted, and all connections to the model have been established.


Simulating the Flexible FourbarYou’ll now simulate the fourbar using default values. The simulation will now be successful.

To simulate the rigid fourbar:1. In the Main toolbox, select the Simulate tool .2. Select the Simulation Start tool .


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Documents

Getting Started Using Adams Flex MDR3