# Simon Križnik

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1. ## Pin hinge and torsion spring

Hi Prakash, there is rotational stiffness definition for both type 8 and 13 spring. This creates a torsion spring with free angle the same as initial angle. However, I am looking for the rotational spring which is preloaded at the initial time step and tends to open towards free angle, that is different form the initial angle.
2. ## Pin hinge and torsion spring

Hi Mrt, I did not yet solve the torsion spring in hinge connector. The procedure to create kjoint is descibed in https://forum.altairhyperworks.com/index.php?/topic/14759-kinematic-constraints/&tab=comments#comment-39258 There is also a youtube video about kjoint2:
3. ## tension only 1D element

Thanks for suggestions, I will use one degree of freedom spring element (TYPE4) with nonlinearity defined through force-displacement curve.
4. ## tension only 1D element

Hi Mrt, thanks for your input. My observation is if the force or displacement is applied coaxial to the truss/beam elements they will not buckle in compression, since FEA does not model material or geometry imperfections that would buckle the structure in reality.
5. ## tension only 1D element

Hi, how to set up tension only (no compression, bending and torsion) 1D element in Radioss? I have tried with truss and spring elements. However, truss elements have axial compression stiffness and there is discrepancy in the plots, possibly because of geometric non-linearity. compression (truss in blue, spring in red color) tension spring_truss.hm
6. ## Pin hinge and torsion spring

Hi, thanks for the hint. How to model torsion spring (similar to Motionview): -Produces a moment between two bodies that is a function of the relative angular displacement and the relative angular velocity between the two bodies. -Free Angle specify the angular displacement produced when a torque is applied to the linear torsion spring.
7. ## Pin hinge and torsion spring

Hi, what is the procedure to define pin hinge with torsion spring in Radioss with similar functionality as in Motionsolve? In the file attached bellow I have modeled continuous pin (piano) hinge through type 2 contact with spotflag=4. This works great except there is no option to define small translational compliance (play in the hinge) or joint friction. The other option is to define the hinge through Kjoint2 spring, which requires rigid body on adjacent elements that adds artificial stiffness. How can torsion spring with rotational stiffness, damping, free angle and preload be added on pin joints? pin & torsion.hm
8. ## fatal error #8004

Hi, my observations is the same: this error only comes up when ESLM optimization is run with pattern repetition.
9. ## fatal error #8004

Hi, the optimization has stress constraint in DSIZE card. The same error happens when optimizing for minmax compliance subject to volume fraction constraint. ERROR _ 8004_minmax comliance.hm
10. ## fatal error #8004

Hi, the same error # 8004 occured when free-size ESL optimization is run with pattern repetition. Error termination happens after first outer loop, just after updated master CMS flex file is generated. The message from out file is: ERROR # 8004.hm
11. ## Transfer models between Hypermesh and Motionview

Hi, what is the procedure to transfer MBD models created in Hypermesh to Motionview and vice versa?
12. ## Polar array system/assembly

Hi, sorry for the inconvenience. Please find the requested files attached bellow. I am using version 2017.2. Is there a way to orient & position flexible bodies? Regards, Ivan polar_graphic.h3d polar.fem
13. ## Polar array system/assembly

Hi Praful, thanks for your response. The described approach only seems to works for primitive graphic entities and is not applicable to the model I have shared (containing imported CAD graphics). As a workaround, on import CAD dialogue there is a Locator points option to later position, orient and scale CAD graphics in Location tab on the graphics panel. The main drawback with this approach is it can only locate one graphic at a time so it can not be used efficiently for systems/assemblies.
14. ## Polar array system/assembly

Hi, I need help modeling polar array (rotational symmetry) using system/assembly. When instancing the sub-systems they stay at their original position and orientation. There is an option System translation, but no rotation. The 4 sectors needs to be attached to central polygon as well as to adjacent sector. Is there a way to automatically align subsystems with attachments? polar_array.mdl SECTOR.mdl
15. ## rigid body mechanism

Hi George, thanks for the tip. I will try to simulate with flexible body in Motionsolve.
16. ## rigid body mechanism

Hi, Is it possible to simulate a rigid body mechanism similar to rigid MBD? Bodies and joints have to be perfectly rigid to avoid jamming/binding closed kinematic chain mechanisms. Attached is the sample containing RBODY elements connected through revolute Kjoint2, which is defined with stiffness so there is some unwanted compliance. Any ideas or workarounds to carry out kinematic studies in Radioss? rigid_body_mechanism.hm
17. ## Multi point Constraint

Thank you for the tip, however I am unable to properly apply this workaround. The reason is this model probably needs node to node constraints like MPC. Could you please look into the files?
18. ## Multi point Constraint

Hi, I would also like to know how to create MPC in Radioss user profile to model cyclic symmetry. An example using this type of kinematic constraint would be appreciated.
19. ## imposed displacement between two nodes with skew/frame

Hi George, I have tried with Isolid=17, which eliminates horglassing, but the run stil terminates with negative volume. There is also the problem with contact type 3 stiffness between soft (rubber) and hard (wood) parts. Attached are excerpts form Radioss User Guide 2017 which discusses such situations. To get the stiffnes ratio of hard over soft material the Young's or bulk modulus is required, but I only have ogden material parameters. I have also unsuccessfully tried type 5 interface with arbitrary contact stiffness scale factor of 170. planestrain_hinge_convolute.hm
20. ## imposed displacement between two nodes with skew/frame

Thanks George, it does work with SKEW/MOV2. I have some more queries: 1. Which control cards should be requested to output contact forces/pressures and strains for quad elements in 2D plane strain analysis? 2. The run terminates with: There is also a lot of hourglassing. The property for hyperelastic material are exactly the same as in Example 42 - Rubber Ring: Crush and Slide. Can you suggest some solution? 3. What are recommended shell property settings for nearly incompressible hyperelastic materials in 3D analysis?
21. ## imposed displacement between two nodes with skew/frame

Hi, I have already checked that thread about frame/skew, but I am still confused. You can check the sample I am trying to solve. I have set up imposed displacement, but it is not responding as required. If you delete the imposed diplacement you will get desired behaviour which is provided by spring (darker blue). I would like to get the same response with imposed displacement to have control over relative distance throughout simulation (prescibed by curve function). planestrain_hinge.hm
22. ## imposed displacement between two nodes with skew/frame

I am trying to set up imposed displacement between two nodes with moving skew or frame (not sure which should be used). Coordinate system of imposed displacement should be aligned between those two nodes and updated throught simulation. The function curve is defined so the distance between nodes should be gradually reduced. The required behaviour is similar to pretensioned spring but with prescribed displacements throughout simulation.
23. ## quasi static test

Hi Roy, quasi-static simulation could be done using Rayleigh damping, kinetic or dynamic relaxation (see Example 16). This way the dynamic effects (inertia forces, vibrations) are neutrailzed so the simulation run time could be reduced. To control the number of steps I suggest using imposed displacements (instead of velocity) and matching the Time History or animation output intervals with test data points.
24. ## Radioss optimization to minimize compliance

Hi, thanks for update. I would also like to know how to setup radopt syntax so optimization parameters (DOPTPRM) and shres ouput requests are passed down with /BULK to OptiStruct deck during design optimization. The following had no influence on the run: /BULK/IO/1 OUTPUT,SHRES,ALL /BULK/DATA/2 DOPTPRM,DESMAX,200,DISCRETE,4.0
25. ## Radioss optimization to minimize compliance

Hi, a gentle reminder: is there anything I can help you with to resolve this query?
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