# Chris Coker

Moderators

55

1

1. ## Flexible Body Assign Problems

Based on the limited information provided, we really can't offer much in terms of help. The possible problems are to many to discuss here. Rather than start with a full vehicle model, you should be just the front and rear suspension separately. Using this method, you can use the half-car events to fully debug your model before going to complex full vehicle simulation. When we assemble the full vehicle model, we first run simple events, like straight line acceleration and straight line braking. If the model looks good with these events, then we run events like constant radius, and swept steer. Only when the model is fully debugged, do we look at running events like lane change.
2. ## How to deactivate / change a joint during motion

There may be others that have better answers than myself. You might try posting this on the Hypermesh, or Hypergraph forum. One "trick" is that you can load the .h3d file into Hypergraph, and plot element stresses on an element by element basis. If you load the .h3d into HyperView, you can look at the contour plots during the animation, and I believe you can also visualize the max element stress. That's the typical way it's done, based on my experience. The .plt file is an ascii based file format. You can use that file to plot with other tools.
3. ## Flexible Body Assign Problems

If there is a big force in the joint with a rigid body, then it is likely your forces are unrealistically high. When you start to use the flexbody, this results in undesired behavior. This is a common issue. The forces are unrealistic, due to some problem with the model, but it runs because the bodies are all rigid, and therefore infinitely strong. When you start to use the flexbody, it deforms a large amount due to the extremely high forces. It's also possible that your flexbody has incorrect property data, or you used incorrect units when creating it with flexprep. Look at the mass of the flexbody (in the bodies panel). Does the mass make sense? I would animate just the flexbody by itself, using HyperGraph. You can use this method to animate the mode shapes. Note: the first 6 modes in the file are rigid body modes, and can be ignored. But look at the first few modes. Is the frequency reasonable? When you animate the rest of the modes, do you see any parts that are not correctly correctly. Sometimes users will miss a connection here and there, which results in brackets not being completely attached to the rest of the structure. In summary, this should be a two step process for you: Step 1. Ensure the forces in the model are reasonable before adding the flexbody Step 2. Ensure the flexbody is reasonable.
4. ## Creating Markers and a Deformable Surface

There are two tutorials in our Help that deal with deformable surfaces: MV-1028: Modeling Point-to-Deformable-Surface (PTdSF) Higher-Pair Constraint MV-1029: Modeling Point-to-Deformable-Surface Force (PTdSforce) If you search our help just for "MV-1028" that should take you to the correct location. Chris Coker
5. ## Friction in MBD using motionsolve

Also, check the log file. If your model is purely kinematic, then you will not get forces out, therefore friction will not be applicable or calculated. Also, do not as Felipe suggested, do not rely on the default parameters for friction. You need to carefully select the correct properties, based on the dimensions of your problem.
6. ## Motorcycle flex body for fatigue analysis

These are pretty basic operations in MotionView. If you have not already, I would recommend going through some of the basic tutorials. Other than that, I'm not sure what more detail you need. Chris
7. ## How to deactivate / change a joint during motion

Hi Flo- have you tried modifying the integrator settings? Usually when a solution values, you will find a lot of text that will point you in the direction of things to try. For example tighten (or loosen) integrator tolerance. Decrease the maximum step size. Chris
8. ## Gears

Hi Lokesh- I took a look at your model, but there were not graphics included, so I couldn't test. However, your contact settings look a bit suspect to me. I would suggest looking over the section in our help "Best practices for contact modeling" Your stiffness value is likely too low, and you should use the Advanced option "find precise contact event" On the transient integrator settings, change the max step size from .01 to .001 Best, Chris
9. ## Motorcycle flex body for fatigue analysis

1. You need to type in the values for mass an inertia for each body. Also make sure you correctly define the cg location for each body. You can obtain these values from CAD data, from measuring the physical parts, or estimating them based on previous experience, or using historical data. 2. You can define a curve, that represents the displacement inputs from real world test data, and use that to define the motion, rather than using an expression.
10. ## Working procedure - find forces, export and import forces in Hypermesh and optimize the topology of a part

My background is mainly with MotionView. Now that you have successfully exported the loads, you may want to pose your question in the Hypermesh forums to get a better answer with that product. One tip when you export the loads using the Load export utility, you can specify the specific grid ID numbers you wish to apply the loads to. These should be ID's that already exist in the FE model. Kind regards, Chris
11. ## Working procedure - find forces, export and import forces in Hypermesh and optimize the topology of a part

Hi Flo- The short answer is yes. 1. First change you need to make is to your outputs. You need to create Force outputs on each Body of interest, not the joints. 2. When you run the your simulation a .meta file will be created (because you have a model with Force Outputs on Bodies) 3. Use the Load Export Utility (instructions in our help) to export the loads of interest. It will need to read in the .meta file created during the run. The utility will export loads in a tabular format, or in a format compatible with Optistruct Chris

Here is a workaround that will override the Altair Driver, get a transient analysis to run, and at least get some results out of the model, to help you for debugging purposes. The process here will insert a Transient simulation command before the Altair Driver code takes over. Step 1, open the .xml solver file written out my MotionView, and scroll to the bottom of the file. Step 2, near the end of the file, you will find commands that look like this: <UserProgramControl usrsub_param_string = "user(6454, 10901010, 30101010,32802100,32802700)" usrsub_dll_name = "msautoutils" usrsub_fnc_name = "RUN_STANDARD_CAR_MODEL" /> Step 3 - Right above this command, insert the following commands: <Simulate analysis_type = "Transient" end_time = "4" print_interval = "0.01" /> <Stop/> Step 4 - Save the file, and run the .xml through motionsolve. To do this from MotionView, you can use the "run panel" but you have to change the option from "Save and run current model" to "Run MotionSolve file" You can then point to the .xml file you just edited. If you don't change this option, MotionView will overwrite the .xml file you just edited. Step 5 - you can then animate results, which can often be helpful in diagnosing the problem with the model.
13. ## Gears

Two ways you can do this: 1. Create a displacement output on each Gear body. You will get displacements (and rotations) of the body, you could also request velocities, etc. 2. Create a displacement output for the joint that attaches the gear body.

The model failed to reach a static solution, therefore it did not start the transient analysis, so, there are no results to plot. Will need to figure out the issues with the model itself. Chris
15. ## postprocess: motionview-motionsolve-PLOT

Yes, they are Torques. They are resolved in the reference frame used when you created the Output to report that force. It will default to Global if you didn't create a reference frame
16. ## How to deactivate / change a joint during motion

I took a brief look at your model. There appear to be multiple fixed joints defined constraining the two parts. This creates and kinematically over-constrained model. The demo models provided previously show show good methods. I would recommend understanding those, and trying to replicate those. Another (simpler) approach would be to create a graphic that is attached to ground, and define 3D contact between the cube and ground. Then the cube will rest of the ground due to the contact. Then you avoid some of the complex things with the templates.
17. ## Static Load Analysis force unit type

Input the loads per the unit setting in MotionView. The documentation is likely written from a perspective of a "standard" units set that is commonly used traditionally in multibody dynamics (mm, kg, s, N) Note, if you are using the static loads event from the vehicle library task wizard, you may want to check your results carefully. I think this was developed with the assumption of using N as the units of force. Not sure if it will translate correctly if using a different units system for Force. It may, but again, check your results carefully. Chris Coker
18. ## How to deactivate / change a joint during motion

Hello Flo- Sequential simulation (like what was in MV-1051) is the normal approach to setting up something like this. Another approach (still using sequential simulation) would be to use forces, rather than joints. Our MotionSolve examples library has some examples that may be of use to you. Take a look at this link: https://altairhyperworks.com/motionsolve-models/ Model MV-04 Robot Arm is probably more complicated that what you are looking for, but should work as a good source for a starting point. Regards, Chris

20. ## Motionview save file directory

Hi, You can modify your model under Tools -> Options -> Path Management. If you convert the model to use "Relative Path Names", and then keep your graphics, and .csv data in the same folder as the .mdl, then you will not have these issues. Also, you can convert the .csv data from type of "file" to "values", and the .csv will be converted to values that are stored internally. However this doesn't address the graphics, where are always externally referenced, unless you define them using graphic primitives inside MotionView.

22. ## Errors in events analysis

If you are using CAD data, and importing it into MotionView, the CG and MOI will be correctly read into MotionView. You can define it several ways, about the part CG, the vehicle CG, or the global CG, or any other location for that matter. Usually, people will define each part's mass, inertia, and CG location relative to the part, because that's how the data/CAD is defined. You don't have to calculate anything, assuming the CAD is correct. Just define your mass, CG, and inertia the way it is defined in your CAD. The tire forces should be described in our help. In general: f2 = Fx f3 = Fy f4 = Fz f6 = Tx .... It's also pretty easy to sort out the directions by plotting them, and observing the behavior of the forces using simple events.
23. ## Errors in events analysis

1. I have changed the end time to 15, yet the simulation goes on only for 6 sec. You changed the end time, not the value in the template. There is likely a templex template (assuming you are not using the Altair Driver). You can change the end time in the template, or the end time inside the Driver event. 2. I have entered the values obtained from Tools>CG\Inertia Summary>Moment of inertia into Model>Data Summary>Bodies and getting this error. Also does adding these values lead to more accurate results? The values in the CG inertia summary are used to provide you a Total values of the overall CG and inertia of the vehicle. It's getting those values from your mass properties, which you are editing in the DataSummary. You are working in a loop, editing the same numbers. The normal process works like this: 1. Mass and CG location exists for each body in the model. Update the mass and CG location for each body to match this data. 2. The CG/inertia summary provides a method to allow to sum up all of the masses and CG locations entered in step 1, and check that the overall vehicle CG and inertias are correct. Usually you will need to only update the vehicle body mass, cg, and inertia, assuming step 1 is correct.
24. ## Errors in events analysis

1. To change the end time of the simulation, you will need to edit the template. To increase the lateral acceleration, you can increase the speed of the vehicle. 2. The lane change is intended to be used with a flat road. If you need to run a non-flat road, you will need to change the road definition file. Note, some tire models are not compatible with non-flat roads, or require additional licensing depending on which tire model you are using. The Altair Driver has a path follower event that will work better for this kind of event, if you need to run something other than a lane change. 3. To change the reference frame to something other than global, when using the CG/Inertia summary, you need to be using HyperWorks version 2019 or later.
25. ## AutoBushFD Model

The error indicates there is a problem of some sort (maybe incorrectly defined properties for the graphics) As a workaround, you can try deactivating that graphic (id # 90001) that's throwing the error. The removal of the graphic will not affect the physics of the solution.
×
×
• Create New...