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Julian

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  1. Hello everyone, is it possible to calculate a Bode plot of a MBS directly in MotionView? Thank you in advance! Julian
  2. Hello everyone, I want to get a bode plot for a flexible shaft as the result of my analysis. I want to use a rotational force for the excitation and use the rotational displacement as the output. The question is, what kind of constraints do I have to apply? Can I proceed in the same way as in the Tutorial "OS-1300"? Best regards Julian
  3. Hi Prakash, I haven't fixed the problem with the rotational stiffness yet, and I'm desperately looking for some good advice. I've asked a similar, but much more detailed question here: Do you have any idea how I can fix this problem? Thank you in advance! Best regards, Julian
  4. Hello everyone, currently I have some issues with modeling a flexible shaft. I've imported a fem model of my shaft in MotionView via FlexPrep. During simulation the model definitely can bend, but it seems to have an infinite torsional stiffness. These are the material specifications I made. I chose a very soft material, so that there should definitely be some kind of torsion. The property-card just refers to the material "Gummi" and defines the shaft as "PSOLID". This is the shaft I want to use as a flexible shaft in MotionView: This is the MotionView model I've created with the flexible shaft. To import the shaft as a flexible body I've used the Flexprep-Tool. The two masses (about 20kg and 40kg) are rigid bodies and connected to the shaft with fixed joints. The shaft is mounted on two revolute joints, each at the center of one side of the shaft. The input is a sinusoidal rotational force at the center of the green mass and I measure the rotational displacement about the x-axis at the front and rear end of the shaft. I expect a phase shift between the measured angle at the input and at the output due to the elastic properties of the shaft. These are the visualised results of simulation: The shaft is definitely flexible and there also seems to be a torsion, but when I visualise the results in HyperGraph 2D, I get the following results: The upper curve is the result of the measurement at the front and rear end of the flexible shaft. It's exactly the same curve. F8 is the difference in the angular displacement at the forn and rear end, which is exactly zero. The lower curve is the result of a reference measurement with a rigid shaft. Angular displacement at the front and at the rear end are - as expected - exactly the same. Are there any additional solver options I have to activate or special things I have to consider while modelling the shaft to be able to measure a phase shift in the rotational displacement? I urgently need some good advice! Thank you in advance! Your sincerely
  5. Hi, I'm currently trying to use the FMI-Standard in order to calculate the frequency response of a mechanical System in Matlab/Simulink. This is my current approach: 1. Import a stp-file in Hypermesh, do the meshing and define a material and property (OptiStruct-Solver) 2. Export the Hypermesh-Session as fem-file 3. Create a flexible body in MotionView using FlexPrep and the fem-file from step 2 - Synthesis Type: Craig-Bampton - Cutoff type/value: 15 highest Modes - perform stress and strain recovery 4. Define a torque as input and an angular displacement at the same point as the output, by using SolverVariables and SolverArrays 5. Export the MotionSolve-Model as FMU After defining the necessary environmental variables and importing the FMU in Simulink the simulation works fine, but the frequency response isn't plausible and it seems to be independent of the chosen material in step 1. Can you imagine a possible reason for that? Thank you in advance! The problem seems to be, that the rotational stiffness is infinite, no matter which material I choose, even though the translational stiffness is not infinite. Has anyone of you experienced the same problem so far? Thank you in advance!
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