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Found 12 results

1. ## Shape Optimization, Frequency Response Modal Analysis: Minimize dynamic Stiffness

Hello, i want to reduce the dynamic stiffness of a rubber bearing by changing the geometry. I have an approximate idea of the "optimized" geometry of this rubber bearing therefore I created morphvolumes and changed the specified area (solid elements) by translating the handles. I saved these changes as shapes which are my design variables. I know that the optimum is between the initial model and the changed model. I want to do an optimization with optistruct to find the optimum. To reduce the dynamic Stiffness i need 3 responses and an equation (dont know another way so far). The calculation of the dynamic Stiffness is simple: Cdyn = Force/Displacement. First i defined an equation with the dequation-panel: F(x,y)=x/y --> where x is the "frf force (ELFORCE)" and y the displacement (frf displacement) which are two of the three responses. The Last response is "function" which includes the dequation and the other two responses defined before. I would like to minimize the response "function" (which is the dynamic stiffness). But it's not possible to create an objective which minimizes my response "function", i get following error: *** ERROR # 1812 *** Multiple responses are assigned to the DESOBJ objective function. A MINMAX/MAXMIN objective function definition with DOBJREF should be used instead. Number of responses = 1000 1) Do you know what the maximum number of responses is? (It's an frequency response analyis from 0 Hz to 3000 Hz with an increment of 3, thats why its 1000 responses (i guess)) . I created an obj reference "dobjref" which includes the response "function", then i created MINMAX objective.This works, and i can start the optimization but here i have some questions: 2) When i define the obj reference i can choose neg and pos reference. What can i do with these references? 3) I don't really know what this minmax function does. Does it minimize the maximum value of the equation? It is not my goal to minimize only the maximum value of the equation, it's rather minimizing the area of the function. 4) Is it normal that optistruct finds a solution after 2 iterations? I have two different shapes and i would expect that it takes a lot of time and iterations to find the optimum. I guess i did something wrong or forgot sth. Sry for asking so many questions and sry for my bad english. I thank you so much in advance. Regards, Fatih Uysal
2. ## Topology Optimization with frequency constraint

Hi, I am new to Inspire. I want to perform topology optimization of a simple geometry with frequency constraint. (Attached a sample image for reference) Is there any tutorial which can help me get started? Thanks, Roshan
3. ## Frequency domain LS Dyna

Hello, I'm using hyperemsh to carry out a dynamic analysis with LS Dyna implicit solver. I'm using Hypermesh 14. I'm trying to do a frequency analysis but I can't find the keyword FREQUENCY_DOMAIN in the solver browser. The version in the LS Dyna user profile is the 8 so there should be the option for frequency domain analysis. Any ideas? Thanks, Stefano
4. ## Frequency Response Analysis

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.....!!!
5. ## Setting a load in a Direct Frequency Response Analysis

Hello, I have a doubt, and I was wondering if someone here could help. I am setting up a Direct Frequency Response Analysis, and I want to set an oscillating load. I've read the documentation and some tutorials, however, I can't find the solution. The load I want to apply is: force (time)=A+B*cos(wt) A and B are constants, and w is the angular frequency. If A=0, the proccess would be (I think): - Set a unit load in the given direction, with load type DAREA, and magnitude 1. - Set a TableD1 load collector, with a range of frequencies and y=B - Set Freqi and Rload2 load collectors, and a freq resp (direct) loadstep accordingly. (I would be grateful if someone can confirm that is correct) However, when A is not zero, I have no idea what I should do. One more thing, is there a way to view the applied load in Hyperview? If there was, I could see for myself what I am doing. EDIT: I think I found a way to do this, with the global output request OLOAD, not sure it it'll work though. Thanks for your attention, hope someone can help! Regards
6. ## Direct Transient Analysis of a Beam

Hello everyone, I'm trying to set up a direct transient analysis of the beam you see in the picture below (simplified geometry): The beam is meshed with tetra elements. On top the beam is constrained in all dof. In the middle of the beam is a hump and the mass of it has an influence on the eigenfrequency of the beam. At the lower end of the beam a periodically enforced displacement in the range of the eigenfrequency (3 kHz < f < 4 kHz) of the beam is applied. With the FE analysis I want to get information about the following questions: What is the stress at the top of the beam? Later I would like to get information about fatigue. What is the eigefrequency of the beam? What is the exact displacement of the hump in the middle of the beam when a certain displacement is applied at the lower end with its eigenfrequency? So far I've tried to adapt the tutorial "OS-T: 1310 Direct Transient Dynamic Analysis of a BracketOS" to my purposes but I have problems with applying the periodically enforced displacement. Can someone tell me what the best way is to realize this problem with optistruct? Thank you in advance Felix Link to the tutorial: https://altairhyperworks.com/hwhelp/Altair/2017/help/os/topics/solvers/direct_transient_dynamic_anlaysis_bracket_r.htm#direct_transient_dynamic_anlaysis_bracket_r
7. ## Frequency response analysis

Why do we apply a unit load using DAREA card in constraint panel when running a harmonic analysis using optistruct, and why is the load applied on the geometric center of the model ?
8. ## Unable to change EPWM Frequency

Submitted by Uzair Ahmed Mohammad on Sun, 02/19/2012 - 00:03 Hi, I am new to Vissim. I have used the example code epwm2833x.vsm. The freqency of the PWM is 3.7Khz, and the width is changing. Q: - I am unable to change this frequency (3.7 KHz). May be I am missing something? Need help. Objective is to generate a 20ms period and vary the pulswidth.
9. ## Dynamic stiffness analysis

Hi all, i need to calculate a dynamic stiffness in a frequency response analysis. The term stiffness is defined as follows: i have a structure (free from RB-modes) and i put a force load on a node in it, which must vary sinusoidal with time. The force load will deform the structure and i want to monitor the deformation of a certain node in the structure, which lies a distance away from the load point. The stiffness now is calculated as force / displacement. What i need for postprocessing is the stiffness-value described above plotted over a frequency domain for the force of about 50 Hz to 10 kHz. Is that possible in RADIOSS Bulk? How do i model the loading? Which Output requests will deliver the needed values from the Solver? Many thanks in advance
10. ## Differentiating output request between inertance, mobility and receptance

Hello, I am using Optistruct to numerically calculate some FRFs. I have test data to validate my numerical results. Measured test data is an FRF data in the form of Inertance (acceleration/force). I see that there is a big gap in frequency components' amplitudes between the measured data and numerically calculated data, though calculated and measured natural frequencies align very well. I have followed the modal frequency response tutorial and nowhere in the tutorial is it shown that we're specifically selecting the type of FRF we're wanting (e.g. inertance or mobility or receptance). GLOBAL_OUTPUT_REQUEST is used with DISPLACEMENT enabled and that makes me think that, what I am calculating in Optistruct is Receptance and not Inertance. I tried to request ACCELERATION instead of DISPLACEMENT, but ACCELERATION doesn't let me select the output node set which I used for DISPLACEMENT. How can I make sure in Optistruct that the numerical data I'm getting is inertance and not mobility (velocity/force) or receptance (displacement/force)? Best regards
11. ## Minimizing and Maximizing Frequencies with specific ranges

Hi all, I'm working on a frequency optimization problem, where I want to minimize certain modes, maximize certain modes, and maintain a single mode within a certain range. Specifically: - reduce all modes under 10,000 Hz as much as possible - maintain a single longitudinal mode between 10,000-11,000 Hz (the 'working' mode) - maximize all modes above 11,000 Hz as much as possible Basically, the goal is to create high separation between the working mode and surrounding modes. There's a few key challenges here: 1) It's difficult to know how many modes exist under 10,000 Hz as the optimization runs. For example, ignoring rigid body modes, let's say there are 6 modes to begin. If I target the 6th mode to be reduced, it is sometimes eliminated entirely as the structure changes, which results in an error because the mode no longer exists, and the analysis stops. If I target the 5th mode instead, the 6th mode may not be as effectively reduced. Is there a way to perform a modal analysis in which the search decreases in frequency (i.e. it begins at 10,000 Hz and finds the first mode under)? This would solve this issue at least, as I could always target the first mode. Or are there other options? 2) Another problem is that it's difficult to maintain the working mode within the constraints. As soon as it goes below or above the range, the analysis again stops as there is no mode in the specified range. 3) A third problem is identifying the mode in 10-11 kHz as a longitudinal mode. Although it may begin as a longitudinal mode, that can quickly change to bending or torsional as the optimization runs. In the past, I've performed a harmonic analysis to excite this mode, and then try to maximize the displacement. This tends to point the optimization towards a longitudinal mode, since it resonates with the harmonic input force and creates larger displacements. However, I'm looking for a simpler method, if there is one. Does anyone have any ideas on how to formulate this problem for OptiStruct/HyperStudy? Much appreciated! albatrossor
12. ## optistruct frequency analysis

Hello, I need some help to perform the frequency analysis using Optistruct profile in Ls-dyna as a solver. Input : Impulse excitation, A medium impact hammer with a soft tip (uniform input out of 50Hz) shall be used Impact in the fore/aft direction , next to accelerometer. Change the accelerometer orientation to lateral,and impact the it in the lateral direction. Output. Aquire data out to at least 50Hz with frequency delta as close to 0.25Hz as possible. (modal frequency in all X, Y, Z direction) How can i apply these inputs in my product, which dyna card ? any tutorial ? Please let me know if i missed some input info. Thanks a lot in advance..
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