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Found 15 results

  1. Dear all, As for now it is impossible to extract contact forces in implicit dynamic analysis using CONTF. However, FORCE/ELFORCE (elemental force) is still available. Is there a way to extract the temporal contact forces using FORCE on shell elements which may be in frictional contact some time during the analysis? Thank you, Amir
  2. Hello, i need some help because i cant find any solution to my problem. I've a Project where i have to work with dynamic stiffness (pbusht element) of a structure and want to see the Eigenvalues and normal modes of my structure. To get into the theory i set up a simple model: A CBUSH element with a pbush property and with a 1D Mass (m=1kg) on top and a BC on the bottom. I specified in pbusht property with elastic stiffness of K=100 (N/mm) and a loss factor of GE=0.3 Then i did an normal mode analysis and i know that the "Damping is neglected" (see link (1)) and i have just my K=100. The solution of my normal mode analysis is a normal mode frequency of omega = 50,33 Hz. This is correct, because the formula for free, undamped oscillations is f = sqrt(k/m)/2PI = sqrt(100 N/mm / 0,001 tonnen) / 2PI = 50,33 Hz (i use N, mm, tons as units) Now i want to include the damping, so i use the complex eigenvalue analysis. In theory i learned that for free, undamped oscillations with the damping factor D<1 the cycle frequency omega_d = omega * sqrt(1-D²). Because of the relation that 2*D = tan(phi) = GE i can fill in the my loss factor of GE=0.3. Then i got my omega_d = 49.76 Hz. This is also logically, because for D<1 the oscillations of damped systems are always slower than the ones of the undamped system. ...so omega_d < omega is okay. Now i did the complex eigenvalue analysis (just defined a load collector EIGC card and connected it to the CMETHOD of the complex eigenvalue load step (of course the SPC and EIGRL card to the SPC and Method(Struct) too like i did for the normal modes). The result of the simulation is a frequency of 50,88 Hz and a loss factor of 0,2935. Now i'm confused - first: why is my loss factor not 0,3? Yes, its just a little difference but its a really simple model - in the normal modes analysis the eigenfreqency was also exact to 5 decimal places. But okay, maybe some numeric accuracy. But i definitely do not understand the frequency of 50,88 Hz. Where is the mistake? Its higher than before whats definitely wrong in theory and not my calculated value. Anyone got some ideas? I already thank you Regards Rene (1) https://altairhyperworks.com/hwhelp/Altair/2019/help/os/topics/solvers/os/analysis_normal_modes_r.htm?zoom_highlightsub=eigra (2) https://altairhyperworks.com/hwhelp/Altair/2019/help/os/topics/solvers/os/analysis_complex_eigenvalue_r.htm CBUSH.hm modal_complex.fem modal_complex.h3d modal_normal.fem modal_normal.h3d
  3. Hello, I work on a suspension construction. I have done done a static analysis due to vehicle mass (I managed to do both linear and lgdisp nonlinear). However, I also need to perform a dynamic analyis due to riding over an obstacle and I have encountered few problems with the simulations: 1) As an excitation I use a displacement of a triangular shape (picture below). It works fine for the direct transient (linear), however, when performing nonlinear direct transient (with and without LGDISP on) the excitation is not as I intend it to be (second picture). The plots show the displacement in the Y direction in nodes where the displacement is applied in the model. The actual input load data is a triangle as in the first picture. Therefore, I do not understand why when performing nonlinear transient the displacement starts to increase before it is larger than 0 in the input data. There should not be any loading applied before 0.100 s and when changing to nonlinear analysis somehow there is a loading. Also the system does not go back to the zero position. 2) the second problem is that when i use nonlinear direct transient the simulations calculates without any problem but when turning on the LGDISP option I encounter convergence problems: *** ERROR # 4966 *** Minimum time increment reached, analysis aborted. I tried changing the minimum time increment but it does not help. I use TSTEPNL and NLADAPT setup. What options should I change so that the convergence problems does not happen? Thank you very much in advance for any help.
  4. Hello everyone, I would like to learn the duty of "clearance" in PCONT card. In Hypermesh help it says: "Prescribed initial gap opening between master and slave, irrespective of the actual distance between the nodes."; but that does not explain anything for me. Could anybody tell me in a detailed way, what happens when i use clearance section in PCONT card for contacts. Thanks in advance.
  5. Hi, The problem consists of a connecting rod submitted to axial loads which define the phases of admission (traction) and combustion (compression). I am trying to run the following optimization:  2 load steps : Traction Compression 2 responses : Volume Compliance 1 constraint : 60% Volume 1 objective : Minimize compliance I managed to run a direct transient analysis for the two separate load cases. I tried running a topology optimization for one of the load cases but an error occured with the following message: *** ERROR # 557 *** DRESP1 2 is not referenced from within a static or an MBD SUBCASE. This type of response must be specified from within a static or an MBD SUBCASE. This error occurs in DESOBJ 2. I would like to know: How can I create alternating load steps to simulate the traction and compression phases If it is possible to run an optimization with these dynamic loads Thank you !
  6. Hello, I would like to know how to create a macro (script) using OptiStruct and HyperStudy for dynamic analysis (modal, harmonic and transient) of a free cantilever beam 1D. How to create / import geometry, put materials and properties, meshing, put loads and run the analysis. Thank you
  7. Hello, I'd like to know if there's a way to conclude/cut-off an on-going iteration before it reaches the subcase termination time? I'm running a geometric non-linear explicit dynamic subcase. I want to base this iteration cut-off criteria once the rigid wall reaction force reaches a specific value...This should speed-up my topology optimization considerably... If not then, is there a way to define a constrain on the rigidwall reaction force ? I'm referring to the reaction force that we read from the "T01" file... Thanks !!
  8. I would like to determine the maximum stress that each individual component experiences during a crash simulation however, when I try to do this in post processing I can only analyze one component at a time or the maximum stress across several components but not each one individually. Ideally I am looking to plot several graphs (one for each component) of the maximum dynamic stress against time. Is this possible without putting each new graph + component on a separate page. Further to this I would then like to evaluate this stress value to the material yield point, is there a way of looking up this information on hyperview / extracting it from the .out or .rad file and inserting it into a note on the graph?
  9. I want to perform Dynamic Stress analysis on a structure undergoing high magnitude and high frequency loads please suggest me some tutorial and viedos thank you
  10. How to perform simulation (Nastran) on a system by applying a sinusoidal load of 0.1g which swept from 10-50 Hz which varies at rate of 1Hz/min ??? How to use the Time domain in solver deck? In Modal Frequency Response i don't use varying rate (1 Hz/min) . So please let me know how to apply the time here.....!!!
  11. General Applications The starting point for most applications should be the steady state Spalart-Allmaras model. For most industrial applications, this model provides sufficient accuracy. For applications involving massive separation, the DES model may be used if a higher level of accuracy is required. Unsteady Simulations For the simulation of unsteady flows, users have the option of unsteady RANS (URANS), DES, or LES. Depending on the goal of the simulation, different turbulence models may be used. If the unsteadiness in the flow is driven by some type of thermal transient, then the use of URANS (i.e. the Spalart-Allmaras model in unsteady mode) is typically sufficient. If the unsteadiness is due to large scale separation and bluff body vortex shedding, the DES model or LES model should be used. For cases where small scale turbulent structure is of interest, the Dynamic LES model should be used.
  12. Hello, Good Afternoon. I have a model to which I need to apply a base excitation. I am basically trying to simulate a forced vibration case wherein I have 2 load cases, which are as follows:- · LC1: 5 – 10 Hz : ±8 mm (Constant displacement) · LC2: 10–500 Hz : ±18 m/sec2 (Const. Acceleration) I am doing it with the FREQUENCY RESPONSE (MODAL) LOAD STEP. I have used all the standard cards that are required for such an analysis like SPCD, RLOAD, DLOAD, FREQ, TABLED1 etc. Let's say I am exciting my model in the X direction, I have checked DOF1(scaled to 1) and unchecked all other DOF's. But the results seem to directly vary with that scale factor which it should but aren't matching with my benchmark results.When i use TABRAND1 instead of TABLED1 i get satisfactory results but I am not sure if I am supposed to do so. I am yet to establish the correct methodology for this sort of forced vibration cases. Could you please help me out.
  13. Hello all ! This is my first post here, I'm a student doing my master thesis in Mechanical engineering. Here is my issue, I successfully did the tutorial in order to realize dynamic explicit analysis with the "full car" model available in Hypermesh database and also the " Example 51 - Optimization in RADIOSS for B-Pillar (Thickness optimization) " in order to understand how the ESL method works. The next step is to optimize the car crash box using he ESL method, my aim is to optimize the component called " COMP-PSHELL_1 " by Thickness optimization. I wrote the .radopt file but I encountered an issue with the .fem file. See below the error, I was not able to solve the issue. *** See next message about line 14864 from file: fullcarv5.fem "CONTACT,3,3,0,3" *** ERROR # 1000 *** in the input data: Incorrect data in field # 4. See attached the .radopt, the engine/stater file and the .fem file Thanks for your help ! Aub N. fullcarv5.fem fullcarv5.radopt fullcarv5_0000.rad fullcarv5_0001.rad
  14. Hello everybody, my question is, what yields more stress static or dynamic (transient) analysis? According to what I could know up til now, it is dynamic analysis in which the stress values are expected to be higher in case of the static analysis. It it always likely to happen that stress values will be higher in case of the transient analysis if I perform both analyses for the same structure? Please guide.
  15. Hi I have a connecting rod that is subjected to two loads, Tensile (Admission phase) and Compression (Combustion phase). Both loads have TLOAD2 as their card image and hence each of them have their own loadstep. When observing the results, i would like to see both loadsteps one after another eg: t1 : Combustion , t2 : Admission, t3 : Combustion , t4 : Admission...... I have derived both results together but it showed me the combustion results first then after t500 only it will show admission. Is there anyway to correct this? Regards.
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