# Simon Križnik

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1. ## Variable temperature in a BEAM

Yes, according to Learn Thermal Analysis with Altair OptiStruct ebook: Attached is an example from the ebook which I modified to include multiple heat sources (ambient & local). Note: The ambient temperature is applied with convection on the outer surface. The local temperature is imposed at one end of the tube. This approach is valid for 3D elements, but not for 1D beams. Pipe_One_Step_Transient_multiple.fem
2. ## Pretension Bolt Analysis

Hi, The following might be helpful: https://www.altair.com/resource/optistruct-section-force-output-from-pretension-bolt
3. ## Hyperstudy + Multiscale Designer

Hi, thanks for your response, but I have already found the command line for linear material export. The query is regarding non-linear (multiscale) material export. I hope the Multiscale Designer and Hyperstudy will be coupled similar to Multimech in the future versions.
4. ## Which theory is used to solve in Optistruct with PCOMPP

OptiStruct uses classical lamination theory to calculate effective stiffness and mass density of the composite shell. This is done automatically within the code using the properties of individual plies. The composite inter-laminar stress is calculated based on the first-order shear deformation laminated plate theory.
5. ## Which theory is used to solve in Optistruct with PCOMPP

Hi, according to Optistruct help (page 22): Elements.pdf
6. ## Variable temperature in a BEAM

Hi, this is a simple analysis: For more advanced thermal simulations please refer to FREE eBook: Learn Thermal Analysis with Altair OptiStruct thermal_beam.fem
7. ## Laminate and ply dimensions (surface)

Hi, to get the area of ply use tool>mass calc>elems>by ply (extended entity selection)
8. ## Shear stress in composite material: mat8 and PCOMPP

Hi, I do not think transverse shear stress can be output for plane stress elements. However, composite transverse interlaminar shear stress 1Z and 2Z can be output: transverse_shear.fem The transverse shear stress can be output for solid elements: pcompls.fem

Hi, according to Radioss help this value should be calculated:

Hi, Radioss optimization requires an additional runname.radopt file containing the optimization keywords. This file has to be created manually with any text editor taking care to follow the appropriate syntax. It is also possible to setup the optimization problem in HM (Optimization View in Model browser) but I haven't found a way to export/run the radopt solverdeck. Attached are two examples from Radioss help 51_RADIOSS_Optimization.rar Implementation.pdf RD-E_ 5101 Size Optimization of a B-Pillar.pdf RD-E_ 5102 Topology Optimization for Solids.pdf
11. ## ACCEL Card Exporting Wrong?

Hi, this is strange: both issues do not occur on my end (version 2019.1). Update to the latest version and try again. HopperCarPanel4_HC.h3d HopperCarPanel4_HC.fem
12. ## Modal Frequency response analysis

Hi, you are getting zero displacements because the output set contains 8 nodes constrained by SPC in all DOF. Only unconstrained nodes should have non-zero displacements.
13. ## fake Stress in Hyperview

Glad to help. 1. Actually the formula for nodal timestep is: Δtnodal=√2mk Where m is Nodal mass and k is Equivalent nodal stiffness Regarding units, just follow a consistent set: https://www.altairuniversity.com/wp-content/uploads/2012/04/Student_Guide_55-57.pdf For timestep calculation refer to: III_Considerations about Time-Step - Altair University You can review the nodal timestep in the starter out file. Initial Added mass estimation is also printed in starter out file: 2. %ERR= - 99% is not acceptable and means the simulation is diverging and the negative energy means it is dissipated. Energy error debugging: · Check the last animation file (written before the computation stops with option /STOP in the engine file). · Usual issue : · Imposed time step too high · Material badly defined · Elastic material with large deformation · Contact interface (stiffness, gap, contact penetrations and intersections) not correctly defined In your case the imposed timestep is too high again: see last column mass error- it should be below 2e-2 (2%), but you have 1 (100%) and 194 (19400%) mass added You may find helpful Free eBook: Introduction to Explicit Analysis with Altair RADIOSS. I have recently revised the third edition which should be available in the near future.
14. ## "Negative 2D solid volume" on some elements

Hi, If /ANALY is N2D3D ≠ 0, for example; for axisymmetrical and plane strain analysis, the elements must be defined in YZ plane and their normals have to be in the positive x-direction. Resolve the issue by 2D>composites>element normals>display/adjust/reverse
15. ## Map contact forces form Radioss to Optistruct

Glad to help. Extract the contact force vector (three components) instead of contact contour. Request contact vector output by eng/anim/vect flags CONT and PCONT. The linear interpolation rules for input files have been changed (no comma allowed, separated by space or tab, only 3 coordinate components followed by vectors components): for example: Interpolation works best when the source mesh is geometrically similar to the target mesh.
16. ## Error by Surf Cars and Line Cards

Hi, the Grnod Cards, Surf Cards and Line Cards errors are due to their Id being out of bounds. Resolve the problem by renumbering the offending entities in Mesh edititng>renumber panel (tool>renumber in Hypermesh).
17. ## Coordinate System CORD2R vs CORD3R Difference?

Hi, the difference is in the creation process and in their behavior: the CORD2R is created by axis direction and its position is fixed in space the CORD3R is created by node reference and its position is moving according to the movement of the reference nodes System Collectors and Systems.pdf from Optistruct User's guide:
18. ## fake Stress in Hyperview

Hi, the stress on the door before the impact is because too high mass scaling is used; the imposed timestep increases the total mass by 633% (check the DM/M or mass error in engine out file), while the recommended is less than 2%. There are several other issues in your model: -the begin card declares unit system of kg m s, but material and model dimensions are consistent with tonne, mm, s. -the initial velocity of the pole is 200- if the units are m/s it means 720 km/h! The pole impact is performed at 32 km/h. -the pole is deformable with added mass applied on it. The computationally more efficient approach would be to put a rigid body on the pole and add mass to this rigid body. -there are initial contact penetrations. Remove them in Hypercrash: Quality>Check all Solver Contact Interfaces or in Hypermesh: Tool>penetration check. If penetrations are less then 1/3 of the gap the Inacti=5 or 6 can be used. -the pole could be moved closer so the impact happens sooner FR_Door_LH_98_11_19_edit.hm
19. ## Initial Von Mises stresses on motorcycle frame

Hi, the procedure to add mass: When assigning loading like initial velocity and gravity make sure to also select nodes or components of added mass.
20. ## (SOLVED) Multiscale material without shear stiffness

Hi, I am trying to model a coated fabric (architectural fabric) as a multiscale material. The homogenized linear material has in-plane shear stiffness (G12=23MPa), but the multiscale nonlinear reduced-order model has almost no shear stiffness and force is decreasing with displacement. As a workaround, I duplicate the elements and assign homogenized material with only shear stiffness to complement no stiffness of multiscale material. But the homogenized material has better test correlation than multiscale+homogenized with only shear stiffness. Any comments or suggestions would be greatly appreciated. multiscale_material.rar
21. ## Hyperstudy + Multiscale Designer

Hi, I would like to perform constituent material property calibration (tow and matrix) in Hyperstudy by coupling Multiscale Designer and Radioss models, similar to: https://www.altair.com/resource/using-radioss-hyperstudy-and-multimech-for-improved-composite-design https://www.altair-gmbh.de/resource/using-hyperstudy-and-multimech-for-advanced-composite-material-design I need to write the solver script that would generate a multiscale material model at each iteration.The Multiscale Designer graphical user interface does not show the commands that are used in the back end programs. Edit: The command lines can be found in the MDS user manual. There is a command for Homogenized Linear Material Export, but the command for multiscale material export is missing. Is this command not available or just missing in the manual?
22. ## Problem with setting of IMPVEL

Hi, there were some issues with frames and the solution is to recreate them from scratch. Note: In the method from the attached document, each floor has its own gravity acting sequentially (defined by a function). In your model there is only one gravity with respect to floor 1. drop_test_IMPVEL-edit1.hm drop_test_IMPVEL-edit1_0000.rad
23. ## Map contact forces form Radioss to Optistruct

Hi, to extract the contact forces from Radioss simulation and use them in Optistruct follow the procedure from the attached reference (page 32): Identify the time of contact force peaks by requesting /TH/INTER contact interface output block and postprocessing in Hypergraph. Define /ANIM/VECT/CONT output request and query the contact forces on nodes of interest at the time of contact force peaks in Hyperview. Export the data in csv file format. Import the contact forces in Optistruct by Analysis>forces>linear interploation>file
24. ## Topography optimisation

Hi, in topography optimization formulation make sure to define draw height (to a lesser extent minimum bead width and draw angle) so as not to violate package space of adjacent components. Since version 2019 a new GRID-based free-shape optimization with more flexible shape changes for shells and solids, enabling the nodes to move normal to the surface is available. This method would probably also allow barrier mesh option. Altair OptiStruct Grid Based Free Shape Optimization
25. ## damping in DTRAN

Glad to help. The damping effect is more pronounced at frequencies near the resonance peaks. The worst-case scenario is when the excitation frequency is near the resonant frequency and there is no damping. When you are unsure about the damping, perform a sensitivity analysis by varying structural damping in the realistic range 2-10% and observe how much the responses of interest are affected.
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