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Found 20 results

  1. I am doing a linear buckling analysis of a pressure hull for a school project in optistruct and I have a question about the buckling mode(mag) results. To my understanding this contour should be the normalized eigenvector plot (maximum vector value should be 1 then normalized from there https://forum.altair.com/topic/14296-linear-buckling-analysis/) but what I don't understand is why certain modes in my analysis produce results with max values of less than one or greater than one. Why does this occur? Does it have any mathematical significance that I should be accounting for? Is it an indication of a model problem? See example picture below. I even tried the OS-T 1040 3D buckling analysis tutorial model and extended it out a few extra modes and some of those modes do that same. Any help or guidance would be appreciated
  2. Hello, I am trying to do a linear buckling analysis on a telescopic mast of 12m. The assembly has a blend of 1D, 2D & 3D elements followed by contacts. Anyways i have taken care of all the parameters like element quality, free edges, T connections etc. As usual, I carried out a FREE-FREE Analysis first followed by MODAL & then a STATIC Analysis (Gravity Loading). All the rigid body modes have been eliminated and my modal frequency are as follows 0.676, 0.677, 6.75, 6.78, 19.53, 19.70, 39.55, 39.71, 45.30, 59.39. I don't know why the modal frequency fetched such initial low values and how to interpret the intermediate frequencies occurring in pairs? The Static Analysis results are also satisfactory with a max displacement of 0.235 mm (Mag) and stress of 11.34 MPa.The stress flow pattern is also satisfactory. Now when I simulate a linear buckling analysis I get this error: ERROR 165- Gram-Schmidt reorthogonalization did not converge. This is caused by ill-conditioning of the shifted matrix in Lanczos run. I have gone through a few other posts in this forum which said to remove rigid body modes, but i don't have any rigid body modes as such. And it is quite evident from the static analysis that my model is well connected and contacts are acting. Could you please let me know how to resolve this issue? Thank you.
  3. Hello, I'm trying to perform a linear buckling analysis on a hemisphere subjected to external pressure and constrained at the base. Running the analysis, in the .out file I find: *** INFORMATION # 3454 MPC constraints for subcase 2 will be enforced with lagrange multipliers. Could you please explain what does it mean? Thank you so much for your kindess Enrico
  4. Hello All, I created simple cylindrical shell with a hole at the center and i wanna make this shell stiffer by adding ribs on its surface thus i need to perform topography optimization in order to get ribs configuration and i did as you can see in attached picture. But after i added ribs(stiffeners) to base model and run it under the linear buckling loading , i came up with less critical load than i got from the model without any ribs so i am confused now how it could be possible. I picked objective is to minimize response which was "buckling" is there anyone knows what could be the correct objective to get correct ribs configuration? Aim is to make more stiffener structure under the linear buckling loading.
  5. Hello I want to analyse the post buckling behaviour of an arched plate (SHELL Elements) with GNA (Geometric nonlinear analysis, implicit). The model is attached. In another forum (RADIOSS) a similar case was presented, with an pdf file attached, discribing a similar problem : I am not able to reproduce the results (should be look like this: I tried different parameters for shell thickness, force size, starting load increment size and solver options (Arc, RIKS,...). Sometimes I get nothing at all, sometimes only results up to point A (s. picture above). How can I get post buckling results? Thank you PlateTest.fem
  6. Dear, I am trying to preform a buckling analysis of a composite sandwich material. But the Auto-SPC limits the DOF's of the composite skins, so that buckling can not happen in correct way. When the Auto-SPC is dissabled, the solver gives the error which states that the DOF's of these elements should be limited, because they have no stiffness in that direction. This is true, due to the material and property assignment (Mat 8, and PCOMPP) which does not provide stiffness in the 3th direction. Is there a work around? I also did a dynamic test (Radioss) where the specimen does not buckle according to the first mode. Test to be replicated: Optistruct First mode Faulty result due to Auto SPC RADIOSS Result Model : Eigenvalue_Bucke_2.hm
  7. Hi, I'm working on a spherical Vacuum vessel (external pressure > internal pressure) using an isogrid structure. I made a shell model with sphere skin and additional ribs to have more stiffness and avoid buckling. Now, I'd like to perform a free-size optimization, to see if there are particular shapes and thickness distributions that minimize the mass of the system. I tried different optimization sets (min mass + constraints on buck, min compl + constr on buckling and mass), but every optimization ends with "Unfeasible design", with very large violations of buckling constraint. Could you give some hints? Thank you so much Enrico
  8. Hello, I am trying to run topology optimization on rod elements. The optimization response would be buckling. I have two questions: 1) I am not clear about the upper and lower constraints for buckling response. Are they buckling load factors? What should I consider to define such constraint for buckling? 2) During the analysis and optimization, I am supposed to keep the length to diameter ratio greater than or equal to 10. How can I implement this as a constraint? Thank you in advance, Muge Candogan
  9. Hi Harsh2610, Can you share the complete model for calculation? I want to study how to do a bulking analysis for a bottle. Thank you Roy
  10. hello, I need your help to solve a problem on linear buckling topology optimization I am doing topology optimization for linear buckling case of simply supported I-section beam (slenderness ratio-120) having compressive axial load. Beam is made up of shell elements. I have given base thickness 3mm and my design space thickness 6mm. I have considered two cases I-case Objective- minimization of compliance Constraints- buckling and volume fraction (0.4) problem- Infeasible design , I am getting negative buckling eigenvalues and it violates my buckling constraints (lower bound=1). ( direction of my load cannot be reversed). I am applying load which are having magnitude below buckling load factor. II- case objective –minmax –objref-(minimizing the maximum buckling eigenvalue) constraints- volume fraction. Problem- In second case I am getting positive eigen value but my volume fraction become so less in 4th and 5th iterations (10^-2) .therefore I am not getting any topology Also I have applied Topology optimization with minimum member size and 2-plane symmetry constraints in both cases. i am attaching *.out file. Results are not satisfying , could you please help me out. II-case.out I case.out
  11. I am trying to optimize a wing box with all components set with composite laminates. The objective is to minimize the weight, the buckling factor should be bigger than 1. However, sometimes the iteration shows that there are no buckling modes found. How this happens? What is this mean? And it seems that the iteration goes to a wrong direction when it can't find the buckling mode.
  12. Attached is a Hypermesh deck of a structure whose mass I’m trying to minimize. The structure has a square shaped core covered on the top and bottom by composite facesheets. Shell elements have been used for modeling. The size of the square and the thickness of its wall determine the buckling characteristics of the facesheets. I’ve modeled using a square of side 6mm and its wall thickness is 1.5 mm (shown in the snapshot below). By varying the size of this square and changing the wall thickness, I’m looking to minimse the mass, the constraint being that the buckling factor must always be greater than 1. Could you please help me achieve my objective? Thanks, Kushal Agarwal. square_foam_opti.hm
  13. Hello, I am trying to use the optimization techniques in Inspire to model a tower which is subjected to a compressive load at the top. Every time I run the optimization for maximizing stiffness in the program, the final results in the design space are always vertical columns. Is there a way to specify some buckling constraints in the model? Thanks!
  14. Hello, i have a Problem with a buckling Analyse: There is a Aluminium Piece with three bores. In each bare there is a RBE3 with Loads and moments in every direction (xyz). The model is fixed by PARAM AutoSPC=YES and INREL=-2. The question is: How much plastic Deformation will be left after the load is being applied and than decreased to 0... I tried it with two Non-Linear quasi-static loadsteps and MATS1 Material as a table. The Analysis is runing until 50-60% of the load is reached and than gives this error: *** ERROR # 4965 *** Maximum number of time increment cutbacks reached, analysis aborted. It appears because 5 approaches to correct the foregone load increment. It seems, that the plastic Deformation starts at that Point and it expands extremly fast: Starting load increment 88 Current increment 9.8192E-008 Subcase 6 Load step: 5.5889E-01 -------------------------------------------------------------------------------- Nonlinear Error Measures Gap and Contact Element Status Maximum Iter Avg. U EUI EPI EWI Open Closed Stick Slip Frozen Plststrn -------------------------------------------------------------------------------- 1 5.97E-03 1.00E-03 2.31E-05 3.12E-08 0 0 0 0 0 5.93E-02 2 2.80E-03 1.46E+00 2.85E-01 8.33E-01 0 0 0 0 0 3.91E-02 3 3.85E-03 3.40E-01 1.19E-01 7.60E-02 0 0 0 0 0 9.51E-02 4 7.48E-03 1.24E+00 5.51E+00 6.39E+00 0 0 0 0 0 2.22E+00 5 1.34E-02 7.32E-01 5.55E+02 5.23E+02 0 0 0 0 0 7.95E+00 Adjusting load increment 88 (correction #1), Current increment 2.4548E-008 Subcase 6 Load step: 5.5889E-01 -------------------------------------------------------------------------------- Nonlinear Error Measures Gap and Contact Element Status Maximum Iter Avg. U EUI EPI EWI Open Closed Stick Slip Frozen Plststrn -------------------------------------------------------------------------------- 1 5.97E-03 1.00E-03 2.31E-05 3.12E-08 0 0 0 0 0 5.93E-02 2 2.80E-03 1.46E+00 2.85E-01 8.33E-01 0 0 0 0 0 3.91E-02 3 3.85E-03 3.40E-01 1.19E-01 7.60E-02 0 0 0 0 0 9.51E-02 4 7.49E-03 1.24E+00 5.51E+00 6.39E+00 0 0 0 0 0 2.23E+00 5 9.59E-03 7.22E-01 1.96E+03 1.27E+03 0 0 0 0 0 8.26E+00 Adjusting load increment 88 (correction #2), Current increment 6.1370E-009 Subcase 6 Load step: 5.5889E-01 -------------------------------------------------------------------------------- Nonlinear Error Measures Gap and Contact Element Status Maximum Iter Avg. U EUI EPI EWI Open Closed Stick Slip Frozen Plststrn -------------------------------------------------------------------------------- 1 5.97E-03 1.00E-03 2.31E-05 3.12E-08 0 0 0 0 0 5.93E-02 2 2.80E-03 1.46E+00 2.85E-01 8.33E-01 0 0 0 0 0 3.91E-02 3 3.85E-03 3.40E-01 1.19E-01 7.60E-02 0 0 0 0 0 9.51E-02 4 7.49E-03 1.23E+00 5.51E+00 6.38E+00 0 0 0 0 0 2.23E+00 5 9.73E-03 7.17E-01 1.02E+03 7.05E+02 0 0 0 0 0 7.19E+00 Adjusting load increment 88 (correction #3), Current increment 1.5343E-009 Subcase 6 Load step: 5.5889E-01 -------------------------------------------------------------------------------- Nonlinear Error Measures Gap and Contact Element Status Maximum Iter Avg. U EUI EPI EWI Open Closed Stick Slip Frozen Plststrn -------------------------------------------------------------------------------- 1 5.97E-03 1.00E-03 2.31E-05 3.12E-08 0 0 0 0 0 5.93E-02 2 2.80E-03 1.46E+00 2.85E-01 8.33E-01 0 0 0 0 0 3.91E-02 3 3.85E-03 3.40E-01 1.19E-01 7.60E-02 0 0 0 0 0 9.51E-02 4 7.49E-03 1.23E+00 5.51E+00 6.38E+00 0 0 0 0 0 2.23E+00 5 9.78E-03 7.18E-01 2.99E+03 2.15E+03 0 0 0 0 0 8.65E+00 Adjusting load increment 88 (correction #4), Current increment 3.8356E-010 Subcase 6 Load step: 5.5889E-01 -------------------------------------------------------------------------------- Nonlinear Error Measures Gap and Contact Element Status Maximum Iter Avg. U EUI EPI EWI Open Closed Stick Slip Frozen Plststrn -------------------------------------------------------------------------------- 1 5.97E-03 1.00E-03 2.31E-05 3.12E-08 0 0 0 0 0 5.93E-02 2 2.80E-03 1.46E+00 2.85E-01 8.33E-01 0 0 0 0 0 3.91E-02 3 3.85E-03 3.40E-01 1.19E-01 7.60E-02 0 0 0 0 0 9.51E-02 4 7.50E-03 1.23E+00 5.51E+00 6.38E+00 0 0 0 0 0 2.23E+00 5 9.79E-03 7.18E-01 5.96E+02 4.02E+02 0 0 0 0 0 6.46E+00 Adjusting load increment 88 (correction #5), Current increment 9.5891E-011 Subcase 6 Load step: 5.5889E-01 -------------------------------------------------------------------------------- Nonlinear Error Measures Gap and Contact Element Status Maximum Iter Avg. U EUI EPI EWI Open Closed Stick Slip Frozen Plststrn -------------------------------------------------------------------------------- 1 5.97E-03 1.00E-03 2.31E-05 3.12E-08 0 0 0 0 0 5.93E-02 2 2.80E-03 1.46E+00 2.85E-01 8.33E-01 0 0 0 0 0 3.91E-02 3 3.85E-03 3.40E-01 1.19E-01 7.60E-02 0 0 0 0 0 9.51E-02 4 7.50E-03 1.23E+00 5.51E+00 6.38E+00 0 0 0 0 0 2.23E+00 5 9.80E-03 7.18E-01 5.47E+02 4.05E+02 0 0 0 0 0 6.67E+00 *** ERROR # 4965 *** Maximum number of time increment cutbacks reached, analysis aborted. Saved the last (NOT-CONVERGED!) iteration for diagnostics. *** Nonlinear solution failed to converge for Subcase 6 *** NONLINEAR ITERATION SUMMARY FOR Subcase 7 Continuing nonlinear solution from Subcase 6 Subcase 6 did not converge - cannot continue. Saved the last (NOT-CONVERGED!) iteration for diagnostics. Maximum Plastic Strain at 6,67mm in itteration 5, that is way to high... Does someone already had this Problem or some advice for this sort of buckling analyse? Thank You and best regards HyperName
  15. Doing an analysis of a small plastic part in Inspire. No issues getting the static analysis to run, but when I try buckling modes I get "Analysis Error 165", anyone come across this and know how to solve? Thanks Chris W
  16. hello sir, i created a plate in optistruct, meshed it with only quads, assigned material and property. created load collectors spc,load and buckling with buckling card image as eigrl and remaining with no card image. created forces and constraints and also load steps with linear static analysis spc and load, for buckling analysis method struct,spc and staticsubcase. and then carried analysis, am getting error 14, please help, forgive me if its a silly doubt thankyou
  17. Hello at all, i made an analysis of a wireframe of a formula student car and created some loadcases for buckling. In HyperView there are some negative and some positive magnitudes for F (for buckling mode 4). I´m quite sure that this is the factor λ. So i thought if λ>0 (positiv) there is no buckling and if λ<0 (negativ) then there is buckling. Now i noticed, in every case where are the negative magnitudes, then a tension rod is buckling or deforming and when there is a positive magnitude then a pressure bar is buckling. I thought only rods/bars under pressure can buckle. My problem is to interpret these cases. Could it be that the buckling of a tension rod is a kind of neckling??? And when it is a kind of neckling, how to give an interpretation of the buckling? Why are tension rods are deforming in my buckling analysis? I hope you can help me. Regards, Rizzo
  18. Dears, When optimising using the Minimum Mass Method, is Inspire taking the buckling phenomena into account, or is it purely optimising for yield stress? Thanks! Gilbert
  19. Dear Community, I would like to present you a possible bug I found in Hypermesh 2017 when it creates the input file for optistruct including a buckling analysis (due to limited time, I have not checked if the same problem appears with other analyses). Please find attached an example and refer to the example for the description below. When you try to create the Optistruct file to run (for analysis only, -optskip), Hypermesh creates the following subcase card for buckling: SUBCASE12345678 LABEL Linear Buckling ANALYSIS BUCK SPC = 1 METHOD(STRUCTURE) = 3 STATSUB(BUCKLING) = 1 The first row is missing a space and the solver gives you the following error if the space is not added manually: *** ERROR # 1461 *** in the input data: Card "LOAD" is not allowed for this subcase type. The problem seems to be present only if the loadstep ID is made by 8 digits. I hope this will be helpful to somebody. Regards, Alessandro buckling_issue.hm
  20. Hello, I am trying to run linear buckling analysis on a structure that I created in HyperWorks. I am getting a very accurate critical buckling load result when I apply a load of 100 N. However I get a Gram-Schmidt Reorthogonalization error when: 1) The applied load is 1000 N or 10 N (I tried multiple times, I am getting an error if the load is different than 100 N) 2) When I scale the geometry to cm's. (The model consists of nodes 10 mm apart from each other, connected with rod elements. The total length is 200 mm, the total height is 20 mm) What could be the reason for getting this error? I am confused as the error occurs both when I increase and decrease the load. Thanks, Muge Candogan
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