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Chris Coker

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Chris Coker last won the day on August 2 2019

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  1. you should not have to change the sign on the coupler ratio on each simulation task, unless you are running a closed look event (like a lane change), and NOT using the advanced driver. Even then, the sign should not matter, but the overall magnitude is used for the bicycle model inside the controller. If you are doing this with the "Altair driver" then the ratio (for the driver model) is taken are of automatically. FYI, if you run a front suspension event (like K&C) that steers the wheels, and you see the steering wheel steer to the left, but the road wheels steering to the right, then that's how you identify a need to change the coupler sign. Can you provide more information about which wizard library you are using? Best, Chris
  2. Hi- You are correct. Simply change the sign on the coupler in the steering rack. Usually, engineers will build separate half-car models first, and verify that the models are running correctly before assembling a full vehicle model. It's much easier to catch modeling errors like this. Also, if you modified the steering hard points, it's likely the value of the coupler will also need to change (and not just the sign). The overall steering ratio needs to be set for the vehicle. Chris
  3. 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.
  4. 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.
  5. 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.
  6. 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
  7. 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.
  8. 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
  9. 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
  10. 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
  11. 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.
  12. 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
  13. 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
  14. 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.
  15. 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.
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