Building Flex Body Models - Kxcad.net

10
Adams/Flex
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.
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:
• Let Adams/Solver create a massless link for you
• Create one yourself
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 (seeConfiguration 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.