adams電子教程adams2012培訓(xùn)用的英文版

1、SECTION 24 MENDED PRACTICESWHAT IS IN THIS SECTIONGeneral Approach to ModelingModeling Practices: PartsModeling Practices: ConstraintsModeling Practices: Compliant ConnectionsModeling Practices: Run-time FunctionsDebugging TipsDocumentationGENERAL APPROACH TO MODELINGCrawl-walk-runTry to understand

2、the mechanism from a physical standpoint.Use building blocks of concepts that have worked in the past.Add enhancements to the model while testing periodically.Build kinematic models before building dynamic models.Use motions to check models before applying forces.Use motions which start with zero ve

3、locity.Verify enhancements to a complex model on a simpler model first.MODELING PRACTICES: PARTSGeometry associativity errorsGeometry may be added to the wrong part.Mass propertiesUsing imported CAD-created geometry (IGES, STL, and so on) can yield inaccurate mass properties.Ensure inertia matrix is

4、 realistic.Use aggregate mass for a quick check of system mass and inertia.Use the Table Editor to do a quick check and potentially fix individual part masses and inertia.Small part mass and inertia lead to unrealistically high frequencies.Initial velocitiesCheck to see that part initial velocities

5、are consistent (look in the .out file).MODELING PRACTICES: PARTS (CONT.)Dummy partsWhenever possible, avoid using them.If absolutely needed, constrain all six DOF and assign a mass of 0.0 (not 1e-20).Design configurationBuild a model close to assembled position.Build a model close to a stable equili

6、brium position, if possible.MODELING PRACTICES: CONSTRAINTSFixed jointsNot needed, since two or more parts can be combined or merged into a single part.An extra part with a fixed joint adds unnecessary equations to your system.When locking a part to ground, enormous torque may develop due to large m

7、oment arms.If absolutely needed, then add fixed joints at the center-of-mass (cm) location of lightest part.If locking a part to ground, consider assigning a very large mass/inertia to it so it can behave like ground.MODELING PRACTICES: CONSTRAINTS (CONT.)Universal jointsWhen a universal joint is at

8、 90, you get a singular matrix.MotionMotion elements should only be functions of time.Note: Avoid redundant constraints.MODELING PRACTICES: COMPLIANT CONNECTIONSSpring dampersEnsure that the marker endpoints (DM(I,J) are never superimposed.Watch out for springs with very stiff spring constants.Watch

9、 out for springs with no damping.BushingsWatch out for bushings with large rotations.MODELING PRACTICES: RUN-TIME FUNCTIONSFunction BuilderAssists in building functions.Assists in function verification.Has function plot capability.VelocityMake sure velocities are correct in force expressions. For ex

10、ample, in the damping function: -c*VX(i, j, j, _), the fourth term is missing.SplinesApproximate forces with smooth, continuous splines.Extend the range of spline data beyond the range of need.Cubic splines (CUBSPL) work better on motions than Akima.Akima splines (AKISPL) work better on forces than

11、Cubic.The Akima interpolation method is faster and can be defined as a surface, but its derivatives are generally discontinuous.MODELING PRACTICES: RUN-TIME FUNCTIONS (CONT.)IMPACTs/BISTOPsDo not use 1.0 for exponent on IMPACT or BISTOP functions (should always be greater than 1.0)Models with IMPACT

12、s/BISTOPs should have slight penetration in design position when doing statics.MeasuresSet up measures of your run-time functions.Set up measures of components of your run-time functions.Ensure that your function will not divide by zero.MODELING PRACTICES: RUN-TIME FUNCTIONS (CONT.)ContactsDo not us

13、e 1.0 for exponent on IMPACT or BISTOP functions (should always be greater than 1.0).Models with contacts should have slight penetration in design position when doing statics.TiresModels with tires should have slight penetration in model position when doing statics.If only rear tires penetrate, the

14、static position could be a “handstand.”MODELING PRACTICES: RUN-TIME FUNCTIONS (CONT.)UnitsUse consistent units throughout the model (time, mass, stiffness, damping, and so on).Choose units (mass, force, time, and so on) that do not require using very large or very small numbers.Be wary when your mod

15、el contains numbers like 1e+23 or 1e-20.Use appropriate unitswhen modeling large models such as an aircraft landing on a runway, length units of millimeters may not be appropriate. Conversely, when modeling small models such as a power window switch (made up of small moving parts), using length unit

16、s of meters may not be appropriate.Use reasonable time unitshigh frequencies may be better modeled with time units of milliseconds rather than seconds.GravityCheck magnitude and direction.Check for multiple gravity elements.DEBUGGING TIPSModel verifyLists number of moving parts, number of each type

17、of constraint.Lists Grueblers count and actual DOF count.Lists redundant constraints.Reports misaligned forces/force elements, joints, and so on.Helps identify and eliminate causes for input warning (dont ignore).Model topologyText or graphical model topology.Table Editor provides spreadsheet-like o

18、verview of model content.DEBUGGING TIPSIcon FeedbackBroken icon in design configuration probably means incorrectly defined joint or force.Table EditorConvenient way to inspect and modify models (particularly large ones).Interactive SimulationBy default is turned on.DEBUGGING TIPS (CONT.)Model displa

19、y updateAs Adams/Solver performs the simulation, you have the option to get immediate graphical feedback of the simulation at every:Output stepIntegration stepIterationIcons visible during simulationThis may help you monitor behavior of model components.DEBUGGING TIPS (CONT.)SubroutinesCheck for the

20、ir existence.While debugging a model, eliminate user subroutines so that they are not the source of the error.GravityTurning gravity off can accentuate modeling errors and make debugging easier.DEBUGGING TIPS (CONT.)StaticsWhen applicable, perform an initial static simulation first.If static solutio

21、n fails:Turn on Model display update = at every iteration to provide additional insight.Identify and eliminate the undesired static configurationthere could be more than one static configuration and Adams/Solver could be finding the undesired one.Check to see if there are any floating parts.Check th

22、e signs of applied forces.Experiment with Alimit/Tlimit/Maxit/Stability.Check if impacts are initially in contact; if not, they should be.Running an initial dynamic simulation can help you determine why the model is not finding static equilibrium.DEBUGGING TIPS (CONT.)DynamicsIf integrator fails to

23、start-up:Check sign and magnitude of forces.Look at accelerations to understand what is happening.Perform initial static analysis first.Try a quasi-static simulation.Try changing integrator parameter - HINIT.Try a different integrator.If integrator fails in the middle of a simulation:Look at animation and plots until failure, to understand simulation.Decrease integrator parameter - HMAX.Do not let the integrator step over important events.Short duration events, such as an impulse can