Connecting Flexible Bodies to Your Model
Once you have your flexible body imported into Adams View, you need to make it part of your model by attaching it to rigid bodies or other flexible bodies and applying forces to it as appropriate. You can also replace existing rigid bodies with flexible bodies.
Learn more about how to make flexible bodies essential components of your model:
About Connecting Flexible Bodies
When you initially create a flexible body from a Modal Neutral File (MNF) or an MD DB file (*.MASTER), Adams Flex places the flexible body at the global coordinate system origin. The flexible body is not attached to any other part in your model nor are its movements constrained.
Using any of the features of Adams View, you can connect the flexible body to elements in your model, apply forces to it, and attach points and markers to it. There are some limitations, however, and these are explained in Limitations on Applying Elements to Flexible Bodies.
As you connect flexible and rigid bodies, you will often find it useful to create dummy parts, called massless links, to help you create your model. Also, the connection of some modeling elements is only supported through massless links so Adams View often creates massless links between the bodies to facilitate the creation of the model. For more information, see Using Massless Links.
If you haven't already done so, you may want to go through the first tutorial, Integrating Flexible Bodies into Your Adams Model, of Getting Started Using Adams Flex, to get some ideas for how to connect flexible and rigid bodies.
Limitations on Applying Elements to Flexible Bodies
Currently, there are a few limitations to the elements you can use with flexible bodies. Most of these limitations are based on the version of Adams Solver that you are using, either the FORTRAN or C++ version. Most of the limitations are removed if you use Adams Solver (C++) as the solver executable. Learn more about Solver versions.
Learn more about the limitations:
Flexible Connector Limitations in Adams Solver (FORTRAN)
The following Adams View flexible connectors have not been implemented for use with flexible bodies in Adams Solver (FORTRAN):
■Torsion spring (Rotational spring-damper elements)
In each case, the flexible connectors can indirectly act on the flexible body through a dummy part, called a massless link. If one of these elements is connected directly to the flexible body, Adams Solver (FORTRAN) automatically introduces a massless link for you. Learn about Using Massless Links.
Force Limitations in Adams Solver (FORTRAN)
Like the rotational spring damper, you cannot directly attach a rotational Single-component force to a flexible body in Adams Solver (FORTRAN). You need to use a masslink to connect the force to the flexible body. Learn about using massless links.
You cannot apply the following forces to a flexible body when the flexible body is the reaction body:
Again, you can avoid this limitation by attaching massless links to your flexible body, which makes the massless link the reaction body. It is important, however, to understand the consequences of making the massless link the reaction body. For example, consider a rigid sphere rolling on a flexible surface. Ideally, you would model the contact using a force vector element with the I marker on the bottom of the sphere and a floating marker on the flexible surface. Because a point of contact on a flexible body must be a set of nodes determined a priori, you cannot define a floating marker on a flexible body. Therefore, the flexible body cannot be the reaction body.
As a workaround, assume that you attach a massless link on some remote location on the flexible surface and define the floating marker on the massless link. Adams Solver would simulate the model without difficulty, but the effect you modeled is now different from the one you intended to model. Rather than modeling a point force sliding over the flexible surface, you modeled a varying point torque acting on the flexible surface at the location of the massless link. For this reason, Adams Solver does not automatically introduce a massless link like it does when attaching an unsupported force to a flexible body.
When the flexible body has a large number of modes (more than 40), the computational cost can be considerable. In these cases, you will find it more expedient to attach a massless link at the location of the flexible body marker so that the function expression depends on part states rather than the higher number of flexible body states.
You should also note that whenever a function expression associated with a force element, including those listed above and single-component forces, refers to a marker on a flexible body, it establishes a functional dependency on all the state variables of the flexible body. For example, if you use a DX function to define the force on the flexible body, you would establish the dependency.
Joint Limitations in Adams Solver (FORTRAN)
You cannot directly connect the following joints to a flexible body when using Adams Solver (FORTRAN):
■Joints, such as the translational joint or an inplane joint primitive, because the point of contact on a flexible body must be well defined. You can eliminate the joint limitation by attaching the joint to a massless link, the same as you would when applying vector forces. You will also, however, have the same consequences. For more information on using massless links with forces, see Force Limitations in Adams Solver (FORTRAN). If you do not use a massless link and attach either a translational or inplane joint primitive directly to your flexible body, Adams Solver (FORTRAN) automatically inserts one for you.
■Joints that are being driven by motion generators. For example, a revolute joint can be attached to a flexible body when no motion generator is attached to it but not when a motion generator is acting on the revolute joint. Again, to circumvent this limitation, Adams Solver (FORTRAN) introduces a massless link between the joint and flexible body.
Supported Forces and Joints
The following tables list the forces and joints that you can apply directly to flexible bodies.
For the features that you cannot directly apply to flexible bodies, see the workarounds listed in Limitations on Applying Elements to Flexible Bodies.
The force: | Is supported in Adams Solver (FORTRAN) | Is supported in Adams Solver (C++) |
|---|---|---|
ACCGRAV | Yes | Yes |
BEAM | No | Yes |
BUSHING | No | Yes |
CONTACT | Yes* | Yes* |
FIELD | No | Yes |
FRICTION | SPHERICAL, CYLINDRICAL, UNIVERSAL, HOOKE, REVOLUTE | SPHERICAL, CYLIDRICAL, UNIVERSAL, HOOKE, TRANSLATION, REVOLUTE |
GFORCE | Yes** | Yes |
MFORCE | Yes | Yes |
NFORCE | Yes | No |
TRANSLATIONAL SFORCE | Yes | Yes |
ROTATIONAL SFORCE | No | Yes |
TRANSLATIONAL SPRINGDAMPER | Yes | Yes |
ROTATIONAL SPRINGDAMPER | No | Yes |
VFORCE | Yes** | Yes |
VTORQUE | Yes** | Yes |
* For Adams Solver (FORTRAN), only point-to-plane and point-to-curve contacts are supported, where the point is on the flexible body. Adams Solver (FORTRAN) can only treat one point per CONTACT statement. Adams Solver (C++) can treat multiple points per CONTACT statement. From Adams MD R3, general Flexible to Flexible, Flexible to Rigid Contact is supported in Adams Solver (C++).
** For Adams Solver (FORTRAN) the floating marker cannot be on a flexible body, and the reaction force cannot act on a flexible body. There are no restrictions for Adams Solver (C++).
Joints Supported
The joint: | Is supported in Adams Solver (FORTRAN) | Is supported in Adams Solver (C++) |
|---|---|---|
CONVEL | No | Yes |
CYLINDRICAL | No | Yes |
FIXED | Yes | Yes |
HOOKE | Yes | Yes |
PLANAR | No | Yes |
RACKPIN | No | Yes |
REVOLUTE | Yes | Yes |
SCREW | No | Yes |
SPHERICAL | Yes | Yes |
TRANSLATIONAL | No | Yes |
UNIVERSAL | Yes | Yes |
GEAR | No | Yes |
COUPLER | No | Yes |
CVCV | No | No |
MOTION | No | Yes |
PTCV | No | No |
UCON | No | No |
JPRIM | ATPOINT, ORIENTATION, PARALLEL_AXES, PERPENDICULAR | ATPOINT, ORIENTATION, PARALLEL_AXES, PERPENDICULAR, INLINE, INPLANE |
Using Massless Links
A massless link, also called a dummy part, is a link with zero or an insignificant amount of both mass and inertia. A massless link is not actually part of your model but facilitates the creation of a model so it behaves like your physical mechanism. It allows you to indirectly connect forces and joints to your flexible body, which are not supported.
You can either:
Automatic Massless Link Creation in Adams Solver (FORTRAN)
When Adams Solver (FORTRAN) detects either:
■An unsupported force or joint on a flexible body (see Limitations on Applying Elements to Flexible Bodies)
■A marker on the flexible body, which is not coincident with a node (see Configuration 2: Position and Attachment Nodes are Not Coincident)
It automatically introduces a massless link between the unsupported element and the flexible body. The massless link is attached to the flexible body with a fixed joint. Neither the kinematic results of the massless link or the reaction forces at the joint will be available.
Creating Massless Links Manually
To create a massless link, you can simply remove the geometry of a link since, by default, Adams View determines the mass of a part using its geometry. If you want to keep the link geometry in your model display to help remind you that there is a massless link in your model, you may want to edit the link to set its mass and inertia properties to zero.
Note: | A massless link cannot contribute Degrees of freedom to your model. Therefore, a massless link should always be connected to another mass-bearing element using a fixed joint. |
To create a massless link:
1. Create a link between parts, as desired.
2. Do one of the following:
■Delete the link's geometry.
■Display the link's Modify Body dialog box. Set Category to Mass Properties and set Define Mass by to User Input. In the Mass and Moments of inertia text boxes, enter 0.
3. Select OK.
Adding Markers to Flexible Bodies
You can add markers to your flexible body in the same way you add them to parts so that you can apply operating loads, attach other Adams elements, or measure a response. Adding markers to flexible bodies requires specifying both the location of the marker, as well as the nodes to which it is attached. This is a fundamental difference between specifying a marker on a flexible body and specifying a marker on a part. Moreover, the position of a marker on a flexible body is treated independently from the nodes to which it is attached. For example, the position of the marker does not need to be coincident with a node.
Joint forces and applied loads are applied at the marker position and then distributed onto the flexible body at the attachment points you specify. How the loads are distributed depends on the marker configuration. For example, the offset behaves like rigid lever on a marker which is not coincident with its attachment node. That is, a force applied to the marker is transferred to the node as a force-moment pair.
Because the location of a marker is independent of how it is attached to the flexible body, there are three general marker configurations, which are described below. Of the three configurations, Adams Solver (FORTRAN) only directly supports markers whose position and attachment node are coincident. Adams Solver (FORTRAN) indirectly supports markers that are not coincident with their attachment node by automatically introducing a massless link (see Using Massless Links). Adams Solver (FORTRAN) does not support markers attached to multiple nodes. All marker configurations are directly supported in Adams Solver (C++). (Learn more about Adams Solver versions.)
Because Adams Solver (FORTRAN) is the default solver for Adams View, when you create a marker in Adams View, the marker is always positioned at a node. To obtain one of the other alternative configurations using Adams View, first create a marker whose position is coincident with its attachment point and then modify it.
Configuration 1: Position and Attachment Node are Coincident
This is the default marker configuration that Adams View creates and the only one that Adams Solver (FORTRAN) supports. This configuration is suitable for creating measures and applying concentrated point loads at the attachment node.
To create a marker whose position and attachment node are coincident:
1. Click the Bodies tab. From the Construction container, select Marker tool
.
. (Classic Interface) From the Geometric Modeling tool stack of the Main toolbox, select the Marker tool 
.
. 2. In the marker construction container, select Add to Part.
3. Following the instructions in the status bar, select the flexible body to which the marker will be attached. Then, click the node closest to the position you want to place node.
Adams View positions the marker at the closest node and attaches the marker to the same node.
Configuration 2: Position and Attachment Node are not Coincident
It is often necessary to add a marker to a flexible body where there is no node. For example, you may need to connect two flexible bodies whose nodes are not coincident or apply a force at a location offset from a node.
A similar marker configuration which is compatible with the Adams Solver (FORTRAN) can be obtained using massless links. The massless link is attached to the flexible body at the desired attachment node using a fix joint. Subsequently, a marker is attached to the massless link at the desired position. For more information about massless links, see Using Massless Links.
To create a marker whose position is offset from its attachment node:
1. First create a marker which is positioned at the node you wish to attach it to following the steps in Configuration 1: Position and Attachment Node are Coincident.
Now modify the marker.
2. Right-click the marker you just created, and then select Modify.
The Marker Modify dialog box appears.
3. In the Location text box, enter the desired position of the marker. You can either type in the coordinates directly; or right-click the Location text box, select Pick Location, and then click the desired location with the mouse.
4. Select OK.
Adams View issues a warning indicating that the model is only compatible with the Adams Solver (C++). In addition, a white leader line from the attachment node to the marker icon appears.
To create a marker whose position is offset from its attachment node using massless links:
1. Create a massless link near where you want to position the marker. For more information about massless links, see Using Massless Links.
2. Fix the massless link to the desired attachment point by first selecting, Connectors tab → Joints container → Fixed Joint tool
(Classic Interface) Fix the massless link to the desired attachment point by first selecting the Fixed Joint tool 
from the Joint tool stack on the Main toolbox.
from the Joint tool stack on the Main toolbox. 3. In the construction container, select the method 2 Body 1 Location.
4. Following the instructions in the status bar, select the massless link you just created and then the flexible body to which you want to attach it. Finally, select the node to which you want to attach the massless link.
Adams View creates a fix joint between the massless link and flexible body.
5. Create a marker on the massless link at the desired position by first selecting, Bodies tab → Construction container → Marker tool.
. (Classic Interface) Create a marker on the massless link at the desired position by first selecting the Marker tool from the Geometric Modeling tool stack on the Main toolbox.
from the Geometric Modeling tool stack on the Main toolbox. 6. In the marker construction container, select Add to Part.
7. Following the instructions in the status bar, select the massless link, and then select the desired location.
Adams View creates a marker on the massless link. The behavior of this marker is identical to one which was added directly to the flexible body but offset from its attachment node.
Configuration 3: Attached to Multiple Nodes
Point forces, applied force acting at single point on a flexible body, are idealized representations of concentrated distributed forces. Point forces typically give rise to large stress gradients that may not be present in the physical structure. A more meaningful result is often obtained by distributing the force over a small patch on the flexible body. This can be accomplished by introducing a rigid element spider web in the finite element discretization or introducing a marker that is attached to multiple nodes. A force applied to the marker is then distributed to the attachment nodes.
To create a marker attached to multiple nodes:
1. First create a marker which is positioned at one of the nodes you wish to attach it to following the steps in Configuration 1: Position and Attachment Node are Coincident.
Now modify the marker.
2. Right-click the marker you just created, and then select Modify.
The Marker Modify dialog box appears.
3. In the Location text box, enter the desired position of the marker.
You can either type in the coordinates directly; or right-click the Location text box, select Pick Location, and then click the desired location with the mouse.
4. In the text box to the right of Snap, enter a comma-separated list of attachment nodes, or right-click the text box, select Pick FlexBody Node, and then click the desired attachment nodes with the mouse.
5. Select OK.
Adams View issues a warning indicating that the model is only compatible with Adams Solver (C++). In addition, white leader lines from all the attachment nodes to the marker icon appear.