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Simon Križnik

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Everything posted by Simon Križnik

  1. Simon Križnik


    Using the Gapmin value of 1.5 will not produce contact from the start of simulation because there is no initial penetration at this distance. Try to increase this value and check the resulting penetrations with tool > penetration check. Igap=1000 is a constant gap equal to Gapmin. It is more computationally efficient, but does no take into account the thickness of parts in contact Igap=1,2,3 are variable gap which is computed for each impact as the sum of the master element gap (gm) and the slave node gap (gs). If Igap=1, variable gap is computed as: max[Gapmin,(gs+gm)]max[Gapmin,(gs+gm)] If Igap=2, variable gap is computed as: max{Gapmin,min[Fscalegap⋅(gs+gm),Gapmax]}max{Gapmin,min[Fscalegap⋅(gs+gm),Gapmax]} If Igap=3, variable gap is computed as: max{Gapmin,min[Fscalegap⋅(gs+gm),%mesh_size⋅(gs_l+gm_l),Gapmax]}max{Gapmin,min[Fscalegap⋅(gs+gm),%mesh_size⋅(gs_l+gm_l),Gapmax]} The problem with type 7 interface is it can't handle edge to edge contacts due to Edge to Edge Impact Locking (refer to User Guide). This is a possible reason why the computation crashes and it can be corrected with type 11 interface.
  2. Simon Križnik


    Hi Mrt, if there are some parts initially in contact then initial penetrations should be modeled intentionally by setting: -Gapmin value bigger than physical thickness of the parts -Igap=1000 -Inacti=5 or 6 (more on Initial Penetrations in the User Guide) Because the contact occurs at shell edges it is recommended to use type 11 line contact interface in addition (or type 19 which is a combined type 7 & 11). There is a Youtube video about contacts. Please note that initial penetrations are difficult to run with time step controls (CST or AMS) because timestep drops drastically if simulation increases penetrations beyond initial penetrations handled by Inacti flag. contact.hm
  3. Hi Mickster, the default element type can be reviewed by 1D/2D/3D > elem types (the panel you posted) To change the default element type simply click on the full name or abbreviation to access other options.
  4. Hi, in the model you have shared the load is actually applied to nodes which are constrained by the rigid. The load should be applied only to the master node of the rigid. full cylind1.hm
  5. Hi SamuelIshak, Use N2D3D = 1 for /ANALY card in the Starter file and ensure that the elements are defined in YZ plane and their normals have to be in the positive X-position. Please refer Example 8 - Hopkinson Bar from the Help Menu which is an axisymmetrical analysis.
  6. Hi, the reason could be that some elements get severely distorted which is causing excessive penetration. Since you are using hyperelastic material law you should try with hyperelastic property: Try to increase the gap and use the following contact settings for type 7: Istf=4 Igap=2 Fscale_Gap=0.8 INACTI=6 Gap_min=0.1 Fric = 0.1 Iform=2 Also, there is type 11 contact, which is actually causing the error. If it is defined on the same elements as type 7 then the gap should be 0.9x the value of type 7 and if using friction then also use Iform=2.
  7. I have the same problem: when the orientation is modified by element selection in composites: material orientation panel, it affects the global orientation of the component/property. It also changes the X/Y/Z components of the reference vector in the property definition. sample_orientation.hm
  8. Hi Karthic, this error is common with inapropriate mass scaling, that is when you impose a time step which is too high. Check the mass error due to mass scaling in the .out file: in your model the mass scaling increases the system's mass by 57x. It is suggested to keep the overall mass increase bellow 2% and even then it has to be checked if mass is added to parts that are moving, which would increase the kinetic energy and therefore decrease the simulation accuracy. Short video for energy and timestep error https://altair-2.wistia.com/medias/osd349gz4k Energy error.pdf Alternatively you could try with advanced mass scaling (AMS) which does not add mass. You can find more information from Introduction to Explicit Analysis using RADIOSS – A Study Guide in Time Step Control chapter. Also recommended is 2017 Radioss user guide starting from page 30.
  9. Hi Dario Alonso, looks like composites: material orientation panel applies to the whole component/property eventhough only a few elements are selected. As a workaround assign those elements to different component/property and reorient them.
  10. Hi Karthic, 1. You can simulate a static loading more computationaly efficient by time scaling, which means applying the load more quickly than in the quasi-static experiment in order to reduce the simulation time. However, the kinetic energy should be low (5-10%) compared to the internal energy for most of simulation, to minimize the inertial effects. You can check the energy fraction in Hypergraph by plotting both energies and using Vehicle safety tools (File-Load-Preference File) to divide curves (Math-Two Curves-Divide w/Zero) 2. You can use State files to transfer the state of elements (stress, strain, etc.) between simulations. More information on State files
  11. Thanks Prakash, I am not interested in material data as such but a functioning demonstration model with fabric law 58 defined by stress-strain curves would be appreciated.
  12. Hi, this example fabric material from Radioss help was used in the previously shared model. However, the elements get deleted right at the start of simulation.
  13. Hi, can someone please provide some example model where law 58 is defined with stress-strain curves?
  14. Hi, Error id 760 is shown when there is a modelling error. Make sure that each slave node is associated with only 1 rigid body, i.e. there can be no slave nodes assigned to several rigids.
  15. Hi Prakash, yes I meant RADIOSS solver manager.
  16. Hi dragon, tires in contact with the ground under gravity would result in a contact patch over an area. There are two approaches to model such behaviour: 1. infinite rigid wal (Analysis>>Rigid walls) 2. Type 7 – ( General Purpose Interface ) a. Multi-usage impact interface, modeling contact between a master surface and a group of slave nodes. b. General purpose interface and can simulate all types of impact between a set of nodes and a master surface. A tied contact Type 2 – ( Tied Interface ) would not model the contact the most accurately. a. Tied Contacts define an interface that kinematically connects a set of slave nodes to a master surface. b. This interface is used mainly for the connections. c. It can be used to connect coarse and fine meshes, model spot-welds, rivets, etc
  17. Hi, you can open the .hm files in Hyperworks.
  18. Hi, you should remove all penetrations and intersections before running the simulation, otherwise the model could show unphysical behaviour. Check and remove manually or automatically any initial penetration in your model by using Tool>> Penetration or in Hypercrash by Quality>>Check all solver interfaces. You can go through HM-3320: Penetration tutorial in Help Menu which shows fixing penetrations. If penetrations and intersections are not resolved completely , you can use Inacti= 5 or 6.
  19. Adding DT/NODA/CST does not resolve the issue- the elements still get deleted at the start, even though there is no such message in the out file. This is strange since the imposed displacement (+ 0.1 strain) should be within stress-strain curve. Please find the model attached bellow. law58.hm
  20. Hi, the fabric law 58 is defined by stress-strain curves and parameters found in the referenece guide, which are scaled 1000x to be consistent with the tonne, mm, s unit system. However, all elements get deleted at the start of simulation with the message: -- DELETE 3N SHELL ELEMENT : 10 AT TIME : 0.9001E-05
  21. Hi, the procedure to apply pressure to shell elements: -create contact surface on shell elements (mind the normal orientation) using surfSeg card image or use SURF card image surface set -create a curve defining pressure vs. time -in BC's manager (under Utility) select type Pressure load and reference surface set/contact surface and curve
  22. You are correct- in fact the experimental testing duration was 6 minutes and the simulation duration can be reduced to 1 s for computational efficiency while keeping the kinetic energy bellow 5-10% of internal energy to ensure a quasistatic simulation. I have also tried to simulate inflatables in Radioss implicit and Optistruct, however explicit runs faster with AMS- it could also be I have not properly defined the implicit solution.
  23. Hi Mrt, thanks for your interest. Actually it is rather simple to compare curves in Hyperview; just load the data files from simulation & experiment and then offset/scale x or y components to match the curves. What I am trying to achieve is DOE and optimization of material parameters to minimize the difference (minimize the sum of squared error) between the simulation and experimental curve using Hyperstudy. Please refer to tutorials MV-3000 and MV-3010 for more details. In order to do this the solver would have to automatically adjust the simulation curve so it starts at 0 deflection at 0 force. Attached bellow is the sample experimental curve that does not match the origin of simulation curve. One possible solution would be to somehow utilize the interface sensor (which is already defined in the shared model) which triggers on initial impact the recording of time history output.
  24. Hi, I want to carry out material (law 19 and 58) parameter fitting with Hyperstudy to match results of experimental four-point bend test. The testing protocol consists of two stages: -initial inflation to prescribed pressure and positioning under gravity -four-point bend test (rigid body impactor measuring reaction force which is plotted as a function of midspan deflection). Behaviors of inflatable fabric structures often involve coupled effects from inflation pressure such as fluid-structure interactions (FSI’s), thermomechanical coupling and nonlinear constitutive responses of the materials. Because of this it is nearly impossible to predict the position after initial stage: the time and deflection are unknown when the impactor initially comes into contact with the inflatable. I will use a similar approach as in MV-3000 & 3010, where time history output curve is optimized to match the targeted experimental curve which starts form 0 force @ 0 deflection. The question is how to match the time history output with the experimental curve so the former also begins at 0 deflection? four_point_bend.hm
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