Working with COSMOSMotion 2008

July 10th, 2008 by

When SolidWorks came out with the new revamped interface for Motion Simulation in 2008, I was both eager and skeptical at the same time. The interface looks a lot like Animator, and timelines dictate the simulation setup. However, as I tried my hand at it, I was a little disappointed at some of the functionality that seemed to have been stripped off. I was concerned about three main areas:

  1. Joint definition: You can no longer define joints manually.
  2. Contacts: 3D Contacts are the only choice in 2008 (as against both 2D and 3D contacts in 2007).
  3. Markers: This was probably what caught me by surprise since 2008 does not have markers anymore. Markers are ways to setup complex expressions in Motion in order to make a motion driver dependent on the results of another moving component (result-dependent properties). Difficult to understand at first, they become extremely useful once you understand their purpose and usage.

So I proceeded with the notion that 2008 Motion is fairly weak in these areas. However, over the past few months, I have had an opportunity to use it a little more, and I have come to realize that these three areas are addressed in the new release (just buried deep enough!!).

  1. Joint Definition: The SW mates have been enhanced to include the entire library of joints. I like this feature, but the onus is upon the user to ensure that he sets up mates correctly.
  2. Contacts: 2D contacts did not generate much data about contact forces and so forth. The only direct benefit of 2D contacts was displacement and velocity information. 3D Contacts are a much more realistic simulation of the problem. SolidWorks is right in terms of wanting to move contacts into the 3D Domain. Here, once again, the onus is upon the user to ensure that the correct impact properties are defined.  As problems get bigger, the solver might take more time to solve though.
  3. Markers: These tools are, in fact, much simpler to use now. Markers have been replaced with the ability to call a previously generated result directly into the expression property window, and define relationships to these result quantities in one step. The user does not have to look up all the FORTRAN based functions anymore to setup an expression.

FINAL VERDICT: Motion 2008 is not as bad as I originally thought it to be. It grows on you as you use it more and more. I have been pleasantly surprised with its ease of use, and the integration provided with SolidWorks mates.

Once again, way to go – SolidWorks!!

Vikram Vedantham

Simulation Product Manager 3DVision Technologies

6 Responses to “Working with COSMOSMotion 2008”

  1. Arturo says:

    Hi Vikram:
    I’ve get a little error on CosmosMotion 2008. 3DContacts don´t work for me, every time I add a 3DContact into a simulation, there is no results, but when I add them to a physical simulation, all work fine. Please send me a reply.
    Thanks

  2. Atilla Bayram says:

    Hi Sir,
    I have a question for you. How does Cosmos motion solve dynamically over closed systems?
    in over closed system, actual degrees of freedom does not equal to the freedom found with formulation.

    Thanks a lot……..

  3. Al Kovacs, Ph.D. says:

    I am a former MDI (Mechanical Dynamics, Inc) employee (1984-1994) and was the original ADAMS Q/A Specialist. I have been using ADAMS for the past 26 years and know it is the solver in COSMOS Motion.

    I can answer most of the questions people have about Motion, knowing exactly what statements ADAMS is calling to construct the corresponding .adm file. This file is a snap-shot of the Initial Conditions for the mechanical system at time = 0. It includes the rigid body system parameters.

    The holonomic constraints include JOINT/id and JPRIM/id standard or common constraints between two rigid bodies or the PART/id statements. Other joint connectors are COUPLER/id, CVCV/id, PTCV/id and the very powerful UCON/id (FORTRAN) or GCON/id (C++). However, all constraints in ADAMS are bilateral and are always on or active. If you need a unilateral (or one sided constraint) you use applied forces, such as the CONTACT/id statement that applies surface geometry using the “penulty solver method” as ADAMS searches for close encounters.

    MARKER/id’s are the geometry elements of a discrete set of DAE’s (Differential-Algebraic Equations) that define the Equations of Motion (EofM). They locate and orient a RCCS (rectangular cartesian coordinate system) in the Primary Inertial Reference Frame (PIRF) which is defined by ADAMS as PART/id, GROUND, or the ground part. The are used to measure one vector element with respect to another, such as displacement as DX(I,J,K), DY(I,J,K) or velocity as VX(I,J,K), etc. The Z axis of the K marker is important in many applications such as the spin axis of a JOINT/id, REVOLUTE, or the translation of JOINT/id, TRANSLATION. They can also be used in a rheonomic constraint MOTION/id, I=id1, J=id2, X, FUNCTION = expression which can arbitrarily move a body around based on the expression defined by application of the MARKER/ids.

    Moving CONTACT/id into 3-D domain places emphasis on the CAD surface geometry generated by the CAD tool, specifically SW. ADAMS contains graphics elements, such as a circle, an arc as part of its own way of defining a surface. These are specified in the GRAPHICS/id statement. Contact using these elements may require a planar mechanism joint connection. ADAMS limits the user to a 2-D or planar motion condition. The BOX and ELLIPISOID graphics allow ADAMS 3-D application including the surfaces generated by the CAD tool. Removal the 2-D restriction means SW is ignoring the ADAMS functional requirements and associated GRAPHICS/id 2-D arguments.

    I am currently working on a GD&T approach using ADAMS kinematics, kinetics and the variable topology that can be modeled. This is an extremely important feature that can inserted into a CAD package. Detroit automotive currently uses VSA (Variational System Analysis) which currently exists in UG and IDEAS, I believe. My method exceeds this approach and includes gravity, elasticity and all the ADAMS features not addressed by VSA. Further information can be obtained at akovacs@oceaneering.com. I can retrieve my email periodically at this location.

    Allen P. Kovacs, Ph.D.
    Part-Time Faculty
    Mechanical Engineering Dept.
    Wayne State University
    Detroit, MI

  4. jio says:

    . how to make a new material in 3d contact, exp. water??
    . how to make a plot result of firction force

  5. The material definition for the parts can be done in the Motion manager tree (very similar to editing SW material properties). However, the main function of material selection inside the 3DContact interface is to capture the effect of impact – in terms of stiffness, penetration depth and so forth. If you want to modify these material choices, you can do so by de-selecting the “Specify Material” box, and manually entering values for the elastic properties for impact or by specifying the restitution co-efficient.

    Hope this helps!!
    Vik.

  6. jio says:

    hi sir,

    i am verry happy abaout your answer, but the problem is that my material is contact between tyre and water. So i confused to fill a properties of water in cosmos motion 2008 ( friction, restrituen or elastic). do you have any suggestion. please!!

    thank
    jio UK

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