Science topic

Finite Element Analysis - Science topic

A computer based method of simulating or analyzing the behavior of structures or components.
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I am analyzing RC beam under elevated temperature using heat transfer approach. The temperature is applied uniformly over the entire surface. I have also defined Amplitude and thermal interaction.
There is no variation in nodal temperature.
Is there any issue in modelling?
#FEM #ABAQUS #heattransfer
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Martin Veidt Thankyou for the help. I just found that I was applying temperature as boundary condition instead of load.
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I'm researching the best software to do FEA for hose construction based on elastomers (rubber) and metal cords. In the past we used MSC but wondering if ANSYS have been updated their tools/software to produce better results for complex elastomer/metal part composition.
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Kindly check Ansys Composite PrepPost (ACP).
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I am currently testing a basic design for my research topic with a hollow cylinder.
The displacement was set as 0 on one end as a fix support and -5 in Y direction on another end.
The reaction solution i had is different from in Ansys Mechanical and i believe that the result generated from APDL was wrong.
The last screenshot is the result from APDL using .cbd file from Workbench mechanical
The result is still incorrect comparing to the result from Workbench Mechanical.
What is my mistakes here or any suggestion ?
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Please select all the nodes.
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Anybody knows how to change the density of materiel during a deformation process in a specific strain range, for example (when strain raise from 0.1 to 0.2) using VUMAT ABAQUS subroutine?
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Martin Veidt : Thank you for your comment, but there is no density dimension in the VUSDFLD subroutine nor Strain.
Based on what dimension density can be changed or assumed?
Can you please explain a bit specifically?
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Hi,
I am modelling a beam reinforced with GFRP bars on ATENA 2D. The experimental and analytical load-deflection behaviours are in agreement with each other however, my FE model terminates 10 KN before the experimental load due to stress concentration near to loading plate. I tried to avoid it by increasing the plate's surface area but it didn't work. Please guide me on how to prevent stress concentration.
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I presume, you are using concrete with GFRP on the bottom face to avoid tensile failures. Which material model is used for concrete ? There is a large stiffness contrast at the interface of concrete and loading plate. Given the choice, I would for coarse mesh at the loading place, and surrounding concrete. Another way is to provide graded stiffness at this interface. This is by increasing the E value of concrete layers, at top most face, and reducing by 10% to 25% based on mesh size. This shold give smooth stress flow from loading plate to concrete, and analysis may not terminate. Try and give feedback.
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Hi All,
I am going to model oxide layer growth on metal and I have referred the following paper;
Z. Wang, J.-L. Grosseau-Poussard, B. Panicaud, and C. Labergère, “Finite Element Analysis of Stress Evolution During the High-Temperature Oxidation of Ni30cr+ Cr2O3 Systems,” Journal of Alloys and Compounds, vol. 904, p. 164094, May 2022, doi: 10.1016/j.jallcom.2022.164094.
The model consists of the 3D cube (20x20x20μm) and up to 18μm a metal layer existed. Then 18 to 20μm is an air layer that facilitates oxide layer growth. The system is starting with the initial 25oC and the temperature has increased up to 900oC within 30 minutes. Then the system is kept for 10 hours at 900oC and the temperature has decreased to 25oC. During only the isothermal step, the oxide layer has grown according to an exponential function.
This simulation was done on ABAQUS User Material (UMAT) subroutine. Further, the first author told me (in a couple of email conversations) that he used the air layer's Young's Modulus low value and set STRESS and STRAIN zero to prevent impact on the system behaviour within every increment. As the paper, the sole objective of the air layer is to provide space for the oxide layer growth.
My question is how to set STRESS and STRAIN zero in every increment through a UMAT?
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Thanks Martin Veidt and Christian Willberg for immediate responses.
I tried it 2 to 5 and then increased up to 50 MPa too. Still failed the simulation with excessive distortion in the selected region. When I am increasing the value up to 5000MPa, there was the same scenario, but number of distorted regions tends to decrease. It is important that, this model has no applicable load. Thermal stress, Viscoplastic stress, and oxide growth stress (only for the oxide layer) are available.
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Dear,
Please, how to use ABAQUS ''SWELLING'' option with Law as ''Input''. I have inserted a range of values for ''Strain rate'' and corresponding Field variable 1 - see attached screenshot file as pdf.
But when I run the job in ABAQUS it ONLY read the first value of the table (first row - as highlighted in the attached file) and ABAQUS doesn't read any other value for 'Strain rate' and 'Field 1'?
Please, can I use ONLY the tabular data (multiple values of Strain rate and corresponding Field 1) without using the subroutine USDFLD?
Many thanks for your support and time.
Best regards,
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I didn't work on this model, sorry.
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I have the following questions regarding vibration-based damage detection of a cantilever beam:
1-What is the purpose of discretizing the cantilever beam by finite element technique?
2-Do the number of discretized elements and their length affect the modal analysis( healthy and damaged natural frequency, mode shapes)?
3- Why do the biggest changes in natural frequency happened when the damage occurred near the fixed end and became smaller if the damage occurred far away from its fixed end?
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The reduction in stiffness will be high if the defect/crack is present in regions of high stress. In a cantilever beam, the maximum stress occurs at the fixed end. Therefore, if the defect/crack is near the free end you can expect a greater reduction in the natural frequency from that of an undamaged beam as compared to when the defect/crack is present elsewhere. You can find a discussion on the same in my research article. I have attached it below for your perusal.
Hope it helps.
Regards,
Jatin
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Hello,
I am doing an impact analysis in Abaqus/Explicit (as shown in image 1) using Johnson-Holmquist (JH-2) material model for brittle materials. I am expecting to get the simulation as like image 2 where the particle rebounded after the impact. But instead, I am getting something like image 3 where the particle is penetrating the substrate. Any ideas why this is happening? The only material parameter change is the strain rate coefficient (C) in JH-2 model, For image 2 it is 1, for image 3 it is 0.007
I appreciate any suggestions you can provide.
Thank you.
Regards,
Arif.
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Hello Martin,
Thank you for your input!
I checked my material definition and interaction. I have applied a general contact algorithm (explicit) between the particle and substrate. The contact properties are a friction coefficient of 0.5, pressure overclosure as hard contact, and specified a heat generation of 0.9.
Regards,
Arif
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Hello everybody
Hope you’re doing great
Assume I have two material properties MATERIAL1 and MATERIAL2. I start my model with MATERIAL1 and calculate each element’s (von misses) stress and if any element’s stress exceeds N MPA I change its material to MATERIAL2 and continue till all the elements’ materials
are altered to MATERIAL2.
For this purpose:
Do you suggest Abaqus scripting by the following method:
1. Run the job
2. Write elements’ stresses to an .odb file
3. Check the elements’ stresses by reading the .odb file and change the desired elements’ material to MATERIAL2
4. Run the next job
5. Continue the above-mentioned loop by a script till all the elements’ materials change to MATERIAL2
Or
Do you suggest running a job and implementing Abaqus subroutines (USFLD etc)?
1. Which method is applicable?
2. What are the cons and pros of each one?
Thanks for your precious points.
Best regards,
Yunus.
PS: Let’s say the real model has 1000 elements or more and 5 different material properties to describe a small gap bone healing process.
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Hi Yunus Rezvanifar,
The best way to do this is to use a subroutine. If the ABAQUS has your material equations, it’s easier to use the USDFLD; otherwise, use the UMAT subroutine. Check the links below. They are articles that can help you write the UMAT subroutine.
Best wishes.
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Hello everyone
Hope you're doing great.
I'm trying to learn and implement Abaqus subroutines (particularly USFLD) and am struggling with the following Abaqus terms' meanings and applications:
1. field variables
2. material point (and material point quantities)
would please help me out here with the definitions and examples of the above-mentioned terms since I haven't found any useful website links online.
Best regards,
Yunus.
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Field variables in abaqus are quantities that are used to perform calculations when running user subroutines. They do not describe a specific
physical quantity but are often used to describe solution dependent material properties.
Integration points are referred as material points to distinguish between the
Langragian and Eulerian approach.
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Hello everybody How can a three-dimensional FE analysis of a threaded screw (inserted into a material with an insertion torque) be substituted with an axisymmetric analysis of the same problem? Please kindly share good references' links if are available. Best regards, Yunus.
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it all depends on the objective of the analysis: if the bolt has only to be modeled to include the effect of its pretension, the axisymmetric option seems reasonable. If the goal is to analyse the screw, a 3D model is obviously necessary.
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Dear Researcher,
Suppose there is two concentric hollow cylinder and by some metal forming process the inner cylinder is plastically fitted with the outer cylinder in such a way that there is sufficient contact pressure is generated between the two cylinder interface and they are plastically shrink fitted.
Now this assembly place in a high temperature and high pressure environment and due to creep there is decrease in contact pressure.
Can anybody suggest me how to modelled this whole process in COMSOL so that we can find out the decrease in contact pressure with time.
I also have to modelled that if there is a very small hole (gap) at the interface of two cylinder then how the diameter of this hole is changes with time?
If someone using other FEA software or code then please suggest?
Thanks for your valuable suggestions.
Shyam Kishor
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For that thing you may try the following (but again in ANSYS, I hope similar options will be available in COMSOL):
1. Plot the radial deformation of nodes at the interface near the cavity in time history postprocessor it will show at what time point (or load step) diameter of cavity starts increasing.
2. If you are interested in understanding any leak through that cavity, contact pressure zero or contact status open may be used as the indication of the same.
Regards
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Dear Researcher,
Here I attached a model in which two rectangles are compressed to each other by giving some displacement to the bottom rectangle and keeping the upper one fixed. There is a sufficient contact pressure generated at the interface in step 1 of the study (stationary). In step 2 (time-dependent), I analyze the effect of creep on this contact pressure and find that the contact pressure decreases with time, and the results are promising. Now I have to model a small hole at the interface (which will be deformed in step1), and in step2, I want to analyze the change in shape ( relaxation in deformed shape) of this hole with time(creep).
In this part, I am facing many errors in the simulation in terms of taking the initial values for step 2 from the step1.
Failed to find consistent initial values.
Iteration for finding elasto-plastic strain variables did not converge.
I am highly thankful for your valuable suggestions.
Thanks,
Shyam
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Thanks, Jigneshkumar for sharing these two links,I will go through it.
Actually what main problem I am facing in my model is that it is a two-step study, and the problem is that in step 2 (time-dependent) the initial value is not taken by step1 (stationary). I tried many things but in this linking of two steps, it is showing errors.
Thanks
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I want to know the best software and procedures to use in finite element analysis of flexible concrete
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I could only provide you some general hints since I am not a specialist in this domain.
1) Could you check literature on the Voronoi model. I am aware that a professor at Ohio State University by name Dr. Siddharth Ghosh works in this domain.
2) Alternately, you could do limited physical uniaxial component level compression and shear tests to understand the stress-strain / load-deflection properties of the test coupon. You could assume the tensile strength as a small number or zero. You could do this for various ratios of asphalt to binder, and various sizes of asphalt, so that you have a reasonable level of characterization. Alternately, there could be literature out there with these results. Temperature would play a significant role. The structure would be brittle under cold conditions and visco-elastic as the temperature increases. You could suitably create a rheological model. Your results depend on the operating temperature. If the material characterization is available (either through aforementioned experiments or literature), you could model the structure as a non-homogenous and anisotropic model with temperature dependent material properties. If there are steel rebars, that could also be modeled, or alternately I believe there is a method called as "the smear technique" for modeling concrete with rebars. This technique should be quite established.
You could use any FE package of choice and do the analysis. Initially you could work on simple compression and shear FE models to ensure that your results match with literature or experiments at coupon level.
3) You could also check commercial packages (or write to them) if they have any readymade constitutive relationship for asphalt. You could try Abaqus, ANSYS, MSC Marc, Altair, etc. I just googled "Finite element analysis asphalt" and it throws up some interesting literature.
My answer is quite generic, but at this moment this is the best I could think of.
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What are some good options for defining the constitutive elastic-plastic relation in FEM analysis? Are there any resources for stress-strain curves/data or JC parameters.
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So there is a simple beam element on which I was experimenting, trying to find answers to the questions: What is the difference between body load on a constrained assembly (bolted onto a baseplate) and direct nodal load on the constrains? Is there any of these setups that is close to Large Mass Method?
I got some very interesting findings that need explanation. I bolded out the questions that need an answer. Please find the simulation details in the attached images!
Findings:
- Free-free setups have many orders of magnitude lower response to the same unit acceleration load than fixed-free setups. Is this explainable physically, or is it only a simulation gimmick because of mode participation factors (99.99...% factor for rigid-body mode)?
- Also, when nodal acceleration is applied, if rigid-body mode is included, the response is the same as when omitted. Why? (.f06 was checked and it really uses the selected modes) And also if rigid-body mode is omitted from the body acceleration load type, the response is the same (whereas, when rigid-body mode is included, I got unit response because rigid-body mode dominates). Why?
- Enforced acceleration on one end of the free-free beam resulted in a fixed-free modal response. So I'm guessing enforced motion works like a fixed constraint in the modal analysis, then in the Frequency Response it works like a load. Is this statement true?
- In the fixed-free setups, nodal and body load types resulted in similar responses at the eigenfrequencies, but showed differences elsewhere. Why? Also, nodal load goes to unit response at 0Hz while body load goes to 0 response at 0Hz. Why?
Sidenote: I also made a reference run with SOL108 Direct Freq. Response with the fixed-free nodal load setup without damping, and got of course similar result to SOL111 same setup.
Thank you if anyone can answer my questions! The 'Help' of NX was not very helpful :(
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I am currently solving a static structural problem using ansys. I have given all the inputs but stress is not transmitting across the body. I have attached the files and I am bit new to ansys. Please guide me through the problem.
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It is not true that stress is not transmitting across the body. The results show a max von Mises stress of 1694 MPa, which is a sign of very localised stress singularity, perhaps at a sharp notch or edge. Such a high max value in the color band makes your whole body appear in blue color. Simply change the maximum scale value in your color band (e.g. 500 MPa).
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I wanted to add a stiffener to the rectangular plate by considering the maximum deflection node to the nearest minimum deflection node.
I can add the stiffener by considering the maximum deflection node (coordinates) to the minimum deflection node (coordinates), but it is not the nearest one.
Could anybody tell me how can I get the nearest minimum deflection nodes???
Odb Abaqus script for maximum and minimum deflection nodes but not nearest
stepframe = odb.steps['Step-1'].frames[-1]
displacement = stepframe.fieldOutputs['U']
field=displacement.getScalarField(componentLabel='U3')
maxp = max([(g.data,g.nodeLabel) for g in field.values ])
minp = min([(g.nodeLabel) for g in field.values])
nodel_label_01=minp
nodel_label = maxp[1]
coordinate = f.nodes[nodel_label].coordinates
coordinate_01 =f. nodes[nodel_label_01].coordinates
Maximum_deflection = maxp[0]
p_1 = coordinate[0]
t_1 = coordinate[1]
g_1= coordinate_01[0]
w_1= coordinate_01[1]
Min_2_x.append(g_1)
Min_2_y.append(w_1)
Max_2_x.append(p_1)
Max_2_y.append(t_1)
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Can you share your Abaqus model (.inp)?
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I am modelling a L-shaped shear wall in ABAQUS for my project. I have applied a cyclic loading on top surface of my specimen. I have extracted the "base shear vs drift data" (and obtained a backbone envelope curve from the hysteresis). Apart from this load-deflection curve I wish to determine time and position when first cracking and crushing of concrete starts. And the same for the yielding of rebars. Can anyone help me with this ?
Some people here have suggested to plot ALLPD vs time (for whole model) and note down the time when curve becomes non-zero, that's when cracking of concrete has initiated. What's the logic behind that? And what about crushing of concrete and yielding of rebars?
Note: There are many rebars, so practically impossible to compare all rebar nodes time history to determine the first yielding point.
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Hello,
First, you need to know what your damage initiation criterion is? After completing your job, select the damage initiation criterion from the Field Output dialog box. Check the frames and legend. Find out when the first point value is greater than one. You can read the time from the step time. To find the point location, select the Contour from the options menu, then go to the Limits tab, and toggle on the Show location to observe the location of the point.
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Hello everyone,
I have a question regarding FEA analysis in bones.
I scanned a bone with a microCT device, and the result is pretty neat. To translate the data into the polygonal mesh topologized for FEA in Abaqus or Inventor, I have to segment the CT-stack (correct me if I'm wrong, I've just started to scratch the surface of this topic). Is there a "easy" way to segment the cortical bone and the trabecular bone as separated elements? If I understood correctly, to obtain a more confident result in FEA, these two tissues should be present in the final mesh...
Thanks to everyone eager to help :)
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Hi Filippo,
There is different software you could use to obtain a 3D model from a stack of CT images. If you have a license you could use Avizo for instance or if you look for a free alternative there is 3D Slicer. Some software can directly create a tetrahedral mesh (the last version of Avizo for instance) but other will export a surface mesh (made of triangles) that you will have to transform into a volumetric mesh afterward. You can indeed segment separately cortical and trabecular bone to obtain more precise FE models, here is an exemple on sabertooths: Figueirido & al 2018 Distinct Predatory Behaviors in Scimitar- and Dirk-Toothed Sabertooth Cats but some recent papers don't make the difference between those two and as it sounds you don't have any experience with segmentation or FEA maybe it would be better to start with simpler models. If you really want to pursue in that direction there is indeed some automatic tools in different segmentation software allowing you to segment a few slices of your stack and apply the threshold to your whole stack. As you have microCT images the cortical and trabecular bone should appear quite different on the images and this should be feasible. This is a bit complicated to answer in more details as I don't know which licenses you have or what your CT data look like but I hope that helped!
Best,
Narimane
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In the case of simulation of an iterative process (Let's say we have 30 iterations) in which elements' material properties need to be changed after each iteration based on the results (eg. strain field) of the previous iteration, which method is preferred and why?
linking Abaqus & MATLAB or Abaqus scripting and UMAT subroutines.
Regards,
Yunus.
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In this case, I highly recommend you use ABAQUS scripting. Because it's more convenient than linking ABAQUS with Matlab, and your run time decreases significantly. In this regard, I suggest you use Micro Manger in ABAQUS to write an ABAQUS script.
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I've been having some issues with abaqus lately. After the last windows 10 update my Abaqus for student isn't working correctly. The response time is very high, I'm not even able to draw something because I click on some tool and the program is delayed one minute or more. I tried to look for some tutorial to fix it, but I didn't find it. Someone can help me?
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Hi ,
You could face this issue due to many reasons, if you have any third party security software or when the components responsible for the installation of Window Update are corrupt. I would suggest you to follow the steps given below.
Method 1: Run the Windows Update troubleshooter.
Follow these steps to run Windows Update troubleshooter.
1.Press Windows key + W and type troubleshooting.
2.Select Troubleshooting.
3.Select View all on the top left corner.
4.Run Windows update troubleshooter.
Move to next method if issues persists.
Method 2: Temporarily disable third party security software.
If you have installed any third party security software like antivirus program/firewall, they can interfere with the download. I would suggest you to temporarily disable and check if you are able to download the update.
Method 3: Reset Windows Update Components.
I would suggest you to Reset Windows Update Components and try installing the update by placing the computer in Clean Boot.
Reset Windows Update Components
Note: This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base. How to back up and restore the registry in Windows:
You can follow the steps given in the link below for reference.
Troubleshooting problems with installing updates
(All articles are applicable for Windows 10 also)
Hope it helps
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Most of the researchers concerned with analytical study or numerical study use ANSYS for the FE Modeling. The awareness about NASTRAN is low. What may be the reason and Why?
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NASTRAN is a solver and it is used as processor so you cannot compare Ansys and Nastran. Every FEA package has its own pros and cons. Ansys being a very user friendly software it is widely used in academic institutions and in few companies. Aerospace industry mainly use Hyper mesh for meshing work and Patran to preprocess the stress analysis work. Hope this helps
Regards
Paul Vizhalil
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I am looking for an open-source finite element analysis library for Python programming language.
I want to develop my own finite element software in the specific study and also for my academic studies. Please share your opinions about the various free FEM library for python with your experience.
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Have a look at FEniCS, which is a very powerful library running in all OSes via docker. In Ubuntu you can install the packages directly. Writing the code is in Python, but actually the package wraps it into a C++ and solves very efficiently. All codes are ready for parallel computation. Basically, you write the weak form, what you want to solve, hence, you can use linear or nonlinear material equations without any problem. I use it for multiphysics computations and can only recommend to begin with it.
The community is very helpful as well, if you cannot use a feature or not working as expected, have a look in this blog
I may recommend their tutorial to learn the basics
and also this book in more advanced use of FEniCS in continuum mechanics
This book has an older version of the code, please have a look for the changes in the Errata to this book in my web site
Have fun!
Emek
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I simulated a pile embedded in sand soil. The pile was subjected to lateral and vertical forces. The model was aborted. I have printed the "Job Diagnostic" to present the causes of the aborted model. The problem occurred because of the nodes at the contact surfaces between the soil and pile. Some nodes were overclosure, and others separated, as presented in the figure below. How can I solve this problem?
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Good afternoon! If the model solution stops, it is desirable to check the boundary conditions, it is also possible to increase the size of the computational grid. The pile is usually monolithic and the moment of inertia is evenly distributed.
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Hello,
I am studying the performance of 2 wing models (with the same size, constraints, loading and material properties but different material distribution) using Nastran. Wing A is lighter and 24% stiffer than wing B and that is demonstrated in the static analysis (under a distributed load on the top skin).
The two wings have about the same fundamental frequency (34.25Hz and 34Hz). Using the relationship f=sqrt(K/m), the difference between the two frequencies should be significant.
Also, the divergence analysis yields exactly the same displacement for the two wings.
Does any one know what could be causing such results? why the divergence displacement is not smaller for wing A (since it is stiffer) and its frequency is not much higher than wing B?
Thank you in advance for your input.
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Rossana Fernandes Can you share the two Nastran models (.bdf)?
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I am running a model of concrete SOLID65 with LINK (bar) elements.
I have attached below my material properties and failure criteria.
The model has not converged yet.
Any tips on how to make the model converge?
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The answer to your question could be pages. I will suggest few things assuming the definitions of the material models and boundary conditions replicate the given specimens in the test (in case you are trying to validate your model with experimental results).
0- Apply displacement rather than forces.
1- Turn off the force convergence criteria and only keep the displacement.
2- Exclude the extra displacement shapes for SOLID65 (Keyopt 1).
3- Use finer mesh as SOLID65 is mesh dependent.
4- Use bond-slip relation by employing COMBIN39 element.
NOTE: check the value of uniaxial tensile strength as it seems too small for the given concrete strength. You may use ACI or any other code to find that value.
Let me know.
Good luck.
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We're trying to perform a finite element analysis (FEA) simulation on the application of force to the skin of a human limb. In order to set up the simulation we are in need of damping coefficients for two of the layers - skin and fat. We've searched for but cannot find separate values for those two tissue types. Can anyone point us to references for these?
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I do not think you will find a specific value for the damping as it depends on the type of skin, thickness, and age of the human. Furthermore, the skin itself will have a varied damping value for the same person from one spot to another (due to the boundary conditions).
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Numerical simulation in Ansys was done on a full model made of 3D printed ABS plastic sample.
Material model used for simulation was extracted from a tensile test that was run on a 3D printed 100% infill (full volume) specimen.
While comparing experimental results and simulation results it was found that Force- elongation (displacement) diagram printed form numerical simulation is having large deviation from the experimental results, while stress strain diagram is in agreement with experimental results.
I have tried using large deflection and have got very similar results.
The diagrams are attached below, orange lines are experimental results, and blue lines are simulation results.
Can anyone help with suggestions why there is such large difference between experimental and simulation results and only in force-displacement diagram while stress-strain diagram has good agreement between experimental and numerical results? Why simulation results only have linear trend while I did include Multilinear isotropic hardening model?
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What you mean by " I have applied displacement on a surface"
why you aren't applied load and record the displacement ?
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Hello,
I have question regarding the use of Abaqus.
My goal is to make an extensive FEA of the pelvic region to investigate fracture patterns (big plans I know). To do this I would like to model the contact between the pelvis bone (E=17GPa), cartilage (E=10.25MPa) and the femur head (E=20GPa), this is where I struggle loads. In this model the hemipelvis will be fixed at the sacroiliac joint and the pubis. The loads will be applied via the Femur head.
So I decided to take a step back, to investigate the contact properties, therefor I've made a simplified the contact model (see attachment) by making a simplified box (named bot) with half a sphere (R=12), then a layer of cartilage (named kraakbeen) with outer R=12mm and inner R=10mm. and then the femur head is simplified as a sphere with R=10mm. The inner surface of the bone is tied with outer-surface of cartilage. The contact between the cartilage and the femur is supposed to be friction-less.
The FEA is done in 2 steps. The first step (step-contact) is displacement step, where the head of the femur is displaced 0.01mm to ensure contact. (displacement is placed with a BC)
The second step (step-load) is the step in which a load (same direction as the displacement) of 2500N is applied.
Preferably I would like to have the displacement-BC removed in the second step and only have a influence of the load that's applied on the femur. However my model does not solve that way.
If I continue the displacement BC into the second step, my model is able to fully solve, however the results are not correct. Since the stresses do not chance during the second step (in which 2500N) is applied. Meaning the application of the load doesnt seem to have any influence.
Can anyone help me how I correctly apply the load to the model and have proper boundary conditions of the pelvic-cartilage-femur?
Thank you.
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I propose my explanation: when you impose displacements in Step 1, the upper sphere is fully constrained, so the solver is able to converge. When, instead, you remove displacements, the sphere is not constrained anymore – in fact, you have no friction at the contact, so the sphere is not prevented to rotate (this happens also you have a vertical load because the program does not know that the sphere is in equilibrium).
If you apply displacements and, then, also the load, such a load has no effect on the lower region because the applied displacements “dominate” the sphere response; in other words, you impose a displacement that behaves like a constraint that cannot be changed by the further load in Step 2, which perhaps will only modify the stress in the upper portion of the sphere.
A final remark: your geometry can be modelled by a symmetric 3D model, or even by an axisymmetric model with a significant reduction of computational time.
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Dear Researchers,
i am using a python script for a parametric study. This script generates .odb files automatically. The problem is, that i can't open the files with ABAQUS cause the Output database created by python is too recent. Error message: "... .odb is from a more recent release of ABAQUS."
The Version of python used by my ABAQUS Version is 2.7.3.
I would be glad about any tips on how to solve this problem. Unfortunatley upgrading ABAQUS is not an Option at the moment
Thanks in advance
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I have created 44 Video Lectures for ABAQUS Python Scripting:
suitable for beginners and experts.
The corresponding Code can be found at github:
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Hello All!
Anybody knows a better way than eps(i) / dt1 to calculate strain rates in a UMAT?
I'm trying with eps / dt1 but apparently it is not giving me a proper rate-dependent result.
Thanks..
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I have three modules (in free form .f90 format) which are being called from inside of a UMAT subroutine in ABAQUS, in the following manner:
module module_A
use module_C
use module_B
....
end module_A
module module_B
use module_C
....
end module_B
module module_C
....
end module_C
subroutine UMAT(STRESS,...)
....
Here the subroutines from module_A and module_B are being called
...
end subroutine UMAT
Now, what is the appropriate format for writing these modules with UMAT subroutine? How to merge different module files into a single *.for file (free format)?
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Hello All,
I am performing finite element analysis of an hyperelastic structure in ABAQUS with the use of UMAT subroutine. The anlaysis is done in two steps:
1. In the step1, the structure is deformed by 11 mm.
2. In Step2, mesh-to-mesh solution mapping is performed. Later, the structure is further deformed by 5mm.
When performing the second step, the requirement is that the final strain energy of step 1 (ALLSE) should be considered as a start point instead of starting over from zero again. In other words, the initial strain energy should be considered from the input file.
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Dear researchers,
I am just trying to vibrate a plate with a horn (see attached figure) in one direction with ultrasonic vibrations in Abaqus. I am new to Abaqus, how can I apply an external vibration/vibrational load to surface of a plate? Harmonic analysis needs a force but can I manipulate it as a vibration? I am open to any suggestions.
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The cycle load module can completely solve this problem
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I am trying to solve 2D heat flow in the finite element Galerkin method with the discretization of 40 triangular elements. I want to solve the problem with internal heat generation node-by-node(ie linearly distributed within each element) . I want to know how to solve the heat source term with the shape functions inside the Integral. Is it through Gauss quadrature rule? if yes, please explain me how .
1.I want to know how to solve the heat source term with the shape functions inside the Integral. Is it through Gauss quadrature rule? if yes, please explain me how .
2. Since the heat source is not constant, do I need to calculate for all the elements ?  Since the triangular element has 3 nodes, does it require 3 gauss points?
Thanks and Regards,
Sunag R A.
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I simulate a pile embedded in multi-layer soil (Five Layers: 3 layers of clay, and 2 layers of sand ), subjected to earthquake (El-Centro earthquake) as solid elements by using Abaqus. Why the present curve gives a good agreement at the beginning only? How could I improve the model?
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Manar Naser Can you share your Abaqus model (.inp format)?
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I am performing a parametric study into the effects of various parameters on the size/shape of indentation in a pipeline.
For each combination of parameters, I would like to have a simplified length, width and height of the resulting indentation. I am trying to use coordinates data (from before and after the indenter strikes the pipe) taken from a node set (contained within the red box on the image) to achieve this.
I have a rough idea of how I will go about this:
  • To find dent height/depth I will find the node with the greatest y displacement
  • To find length and width I will look for nodes that are furthest from the centre (in X or Z direction) that have deformed by Xmm (to be decided), then I will measure the distance between them
How can I use MATLAB to process the coordinates data to find a L, W & H of each indentation?
There are roughly 2000 nodes. What methods/processes can I use to find the desired information, I am completely new to MATLAB and to the processing of large amounts of ABAQUS data.
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Dear Edward,
Abaqus2Matlab is a program for the extraction of ABAQUS analysis results to MATLAB. It provides a link between ABAQUS and MATLAB, and enable you to perform postprocessing of ABAQUS results in MATLAB.
As an alternative, you can extract the displacement result and save them in an excel file. You should have a file containing coordinates and the displacement magnitude. Then, import the data into MATLAB using xlsread function.
To get the length and height, starting from the coordinate that the indenter strikes the pipe and moving in two directions, write a while loop in MATLAB, that saves the coordinate and the corresponding displacement magnitudes in a matrix, while: abs(displacement_magnitude) >= 0
Now you have the coordinates of the displaced nodes and the magnitudes of indentation at each node. the maximum value of displacement gives you the depth, and the maximum - minimum of the displaced node coordinates gives you the length of indentation.
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What is the difference between the finite element method and the hierarchical finite element method?
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There is no real difference. It is merely the choice of shape functions that differs. In a hierarchical approach the shape functions are set up such that we only add a shape function when increasing the order of the approximation (see p-FEM), while in other versions of FEM all shape functions need to be updated (IGA, SEM, etc.). Each approach has obviously some advantages and drawbacks of their own. But in principle the range of possible applications is the same.
Cheers,
Sascha
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Hello Researchers,
The FEM discretized (meshed) geometry/domain is considered stiffer than the actual geometry/domain due to the assumption of variation of the displacement within each element. This is analogous to the displacement being constrained to vary in a particular fashion within each of the elements. This results in the stiffness of the discretized domain being greater than the actual domain. As the element size decreases (or the number of elements increases), the constraint on the displacement loosens due to the smaller size of the element and hence, the smaller constraint zone. Thus, the stiffness of the meshed domain decreases and approaches that of the actual domain as the number of elements is increased.
Based on the above reasoning, the natural frequencies (on increasing the number of elements) must converge from above to the actual value (i.e. converge from higher values to the actual value).
  1. Can this be considered to be strictly true?
  2. Has any deviation from it been observed (i.e. convergence from below or lower values to the actual value) and if so how can that trend be physically explained/interpreted?
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Dear Jatin,
Not always does a finer mesh result in a more exact solution. A mesh convergence study should always be performed to guarantee the descending trend of the error as the mesh size gets smaller.
Having this verified, yes, a finer mesh reduces the stiffness of the model. Because FE approximates the the PDE solution by forcing the element into specific modes of displacement which yields a stiffer element. But as the element size decreases, the FE solution converges to the analytical solution of PDE.
Eigenvalue can be physically interpreted as how stiff the structure is in the eigenvector direction. So it follows the same pattern as stiffness.
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I'm having trouble finding an effective way to simulate a submodel in solid elements obtaining boundary conditions from a shell global model.
I've applied everything described in Abaqus user's guide and the tutorial that uses shell-to-solid submodeling on an elbow pipe.
In my case I'm applying it on a region of a sailing yacht mast, the geometry is considerably simple in terms of meshing so a good hexahedral elements mesh is obtained, having nodes present in the middle of the mast's thickness, which corresponds to the shell surface.
Despite that, I keep having an error when simulating that states "Error in job: NO VALID ELEMENT TYPES FOUND IN GLOBAL MODEL" and no further details about the error are explicited.
I've read that this type of submodeling does not allow to use 5dof's in shell elements' nodes for the global model but that is not my case.
There is very little information available regarding this technique so any help would come in great hand. Does anyone have an idea on how to solve this?
Thank you
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Useful content to understand tolerances in the link below.
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My question is that I'm wondering why my hoop stress in my composite pressure vessel is coming out to be non-constant throughout the ply layer. Wondering if it's in my composite layup or something else. Images below should show composite layup, encasture boundry conditions, and FEA Visualization of irregular hoop stress. Any help would be greatly appreciated.
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In my openion - [1] Revise boundary conditions [2] Revise input parameters & default co-ordinate axes.
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How can we know the average element size from the generated mesh? And its standard deviation? And average aspect ratio? And Jacobian ratio?
I am using Hypermesh to generate mesh and Abaqus to do FEA.
Any methods we can obtain the element statistic information?
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Hello, I have a static general simualtion, for which I hace created a specific Field Output request asking for those results (image).
However, when I check the results I don't have the option to choose these (image2)
Does anyone know why this is happening?
Thanks in advance
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Dear Ana,
Check that if your model fully supports these outputs. Make sure that the analysis type, material properties, and element type are defined in a way to produce these outputs.
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Many experimental results revealed that there is no sign of cartilage in implants' osseointegration process. Regarding the tiny gap between implant threads and surrounding bone, would the mechano-biological environment exclude endochondral ossification from the peri-implant healing process?
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Dear Yunus,
After putting some more thoughts on the question we've discussed about in regard to the osseointegration process, and based on what we know from mechanobiology of bone healing process, I speculate that we may have either endochindral or intramembraneous ossification at the existing gap between the implant's thread and its neighboring bone. I think what does matter there is the extent of micromotion, and the relative motion between the implant and bone can determine the outcome of the differentiation process.
On another note, I think there should be some difference between bone healing and osseointegration process, as the former is between the two dynamic structure, but the latter is between a dead, man-made material and a dynamic structure.
Last point: another important consideration is that to differentiate between bone remodeling and bone healing (also osseointegration) process, which unfortunately in many papers this point was not taken into account.
Let's see what other fellow researchers' thoughts are in regard to your interesting question.
Best of luck
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Hi everyone,
I am currently trying to create a contour plot(ABAQUS) of relative micromotions between two surfaces in contact. I have already developed a method for calculation of relative motions. However, I haven't been able to assign my obtained values to the nodes of the geometries that I am evaluating.
Until now, I have read that some people use subroutines to track paired nodes between two surfaces in contact and then they assign the obtained values in a form of a contour plot. Alternatively, developing a MATLAB code and creating a sort of scatter plot with the relative micromotions has also been discussed on some research works.
Nevertheless, I am trying to find a more friendly alternative that doesn't involve a developed code or the use of subroutines.
Creating a field variable from field output is not an option because the first task is to pair closest nodes between surfaces in contact, which is not possible using the operators available here.
If I need to explain myself better, I can provide more details. I will really appreciate any help on this matter.
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Suppose that there is a file of nodal relative motions composed of lines with format X, Y, Z, value. I suggest:
1. Create nodeset from nodes of contact surface.
2. In Initial step create temperature predefined field with type Mapped field using created nodeset.
3. Import XYZ Point data from the mentioned file.
4. Request nodal temperature output.
5. Visualize initial nodal temperatures.
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Is there a UMAT ?
Thanks in advance.
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Yes, when you install Ansys there is an option that asks you to install a file its name is examples.
This file has a basic USERMAT file.
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I am trying to model Slab on grade subjected to impact load in ABAQUS/Explicit. I want to connect each node of slab to ground using springs. I cannot use direct "Connect points to ground" option in springs in ABAQUS as it is valid only in ABAQUS/Standard.
What would be the best way to model springs beneath the slab and perform the dynamic analysis? (Winkler Method)
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You can use springs with connectivity type: Connect two points. The first point is a node at the bottom of the slab, the second is a ground point (should be fixed).
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Hi all,
I am trying to determine the relative motion between two surfaces in contact. Although I know how to calculate the relative motion, I don't know how to extract the paired nodes (closest nodes) of surfaces in ABAQUS when my geometry of study is undeformed.
For relative motion I will be using the following formula:
If there are contact surfaces named A and B, where there are i-th number of nodes:
X - Relative motion: square root( ( (X Deformed Node1B - X Deformed Node 1A) - (X Undeformed Node1B - X Undeformed Node 1A) )^2 )
Y - Relative motion: square root( ( (Y Deformed Node1B - Y Deformed Node 1A) - (Y Undeformed Node1B - Y Undeformed Node 1A) )^2 )
Z - Relative motion: square root( ( (Z Deformed Node1B - Z Deformed Node 1A) - (Z Undeformed Node1B - Z Undeformed Node 1A) )^2 )
Total relative motion: square root ( (X - Relative motion)^2 + (Y- Relative motion)^2 + (Z - Relative motion)^2 )
Please let me know if I can make my question more understandable or if there's more information required to make it clearer.
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In case anyone wonders how to do it, I managed it using excel (as I am not really good at writing scripts in Python).
I looked for the closest nodes (between the two surfaces) in the undeformed state by looking at the coordinates of all the nodes of interest. After identified, I obtained the row position where the data of this node was. Next, I obtained the X,Y,Z coordinates of that closest node by indexing.
Once I had those coordinates for the closest node, I also obtained the final coordinates of this node in the deformed state.
Finally, I used the formula for the relative position which I wrote on my question, and that's how I got the relative movement of one node from another one (closest in undeformed state). I repeated the process for all nodes within the surface and that allowed me to track the relative movement of one surface to the other.
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Non-linear problem on Implicit Ls-Dyna.
Unable to achieve convergence. If someone has experience in the Implicit solver of Ls-Dyna, please let me know.
Thanks in advance
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How did you solve the problem? I am also getting the same nonlinear solver failed to find equilibrium error. My analysis ran for 6 hours and then I got a termination error.
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hello how to input materials parameter for the following
elastic - plastic material
I have the following parameters only
lame constants
yield stress
hardening parameter
young modulus and poisson's ratio
I know how to input everything except lame constants
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For what kind of materials?
Linear elastic: Its 3D plot has no special meaning
It is significant for materials with anisotropic and nonlinear properties.
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please, someone can me is it way to evaluate the quality in the workbench. if not please suggest any other method to do so in ansys16.
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yes, you can do.
Skewness is one of the primary quality measures for a mesh. Skewness determines how close to ideal (i.e., equilateral or equiangular) a face or cell is.
The following table lists the range of skewness values and the corresponding cell quality.
According to the definition of skewness, a value of 0 indicates an equilateral cell (best) and a value of 1 indicates a completely degenerate cell (worst). Degenerate cells (slivers) are characterized by nodes that are nearly coplanar (colinear in 2D). Highly skewed faces and cells are unacceptable because the equations being solved assume that the cells are relatively equilateral/equiangular.
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Dear all, I have a problem with defining ZeroLenght element.
I want to connect black nodes with 4-dof (soil nodes) with green ones (intermediate nodes) with ZeroLenght element by defining p-y, t-z and q-z materials, and then connect green nodes with yellows (pile nodes with 6-dof) by equalDOF command.
Any idea for doing this correctly? I got this error:
"WARNING ZeroLength::setDomain cannot handle 3dofs at nodes in 4 d problem"
I think the problem is the fourth DOF of soil nodes that contain pore pressure of soil.
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Hi Abolfazl,
If I understand your problem right, I don't think that the number of DOF is the cause of this error. In order to define a ZeroLength element between two nodes, the location of those must be identical. So the location of green and black nodes should be the same. Then you could define p-y, t-z, and q-z materials separately. There is a term of direction in predefined ZeroLength element (-dir), in which you can define a direction for these elements. For example, if you referred to the y-direction as the number of 2, you would write 2 for the elements in the y-direction (-dir 2).
I hope this information can help you in solving the problem.
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Dear all
Please find attached the image T.jpg.
The image of the FE model attached is a hollow body with some prismatic textures on the interior surfaces. Here I need to select all the nodes at the interior surfaces of the FE model. I have tried to use:
NSEL, S, LOC, X, X1, X2
but as the body is having a certain curvature on one side, all the required nodes are not getting selected. And as the number of nodes is many i.e. above 100000, graphical picking seems to be a cumbersome task.
Please help.
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Dear all,
Probably it is too late to respond to this question. However, I wanted to put my two cents here.
Selecting interior nodes is always a challenge and simply selecting a surface and the nodes attached to a surface is not always going to work. The best way of selecting nodes is selection based on a coordinate system and a geometry referred to that coordinate system (as also suggested by
Claudio Pedrazzi
). In Mechanical (by default) you can select nodes based on a cube geometry which is related to a Cartesian coordinate system (in the background). You can developed algorithms that uses different shapes e.g. cylinder, sphere and etc. based on either Cartesian or Cylindrical coordinate systems.
I developed an ACT sometimes back that enables selecting nodes in ANSYS Mechanical based on different shapes and coordinate systems. This ACT is available in ANSYS app store right now. I put a pdf document here hat shows the ACT capabilities.
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Greetings,
We know that locking in the finite element method (FEM) is a numerical artifact due to the choice of the approximation functions. A couple of implications of locking in a static analysis can be mentioned as follows
  1. A FEM model of a beam subjected to a point load at its tip can severely underpredict the tip displacement if the FEM model is prone to shear locking.
  2. A FEM model of a beam acted upon by pure bending moment would develop spurious membrane strains if the FEM model is prone to membrane locking.
As far as modal analysis is concerned, what is the effect of the locking phenomenon on the determination of the natural frequencies and mode shapes of the system?
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Hi all
The examples I provide do increase stiffness. The first example from internal maths, the second example from autoconstraining connecting dependent RBE2 dofs to ground and the last, connecting rotational dofs to ground.
If you look at hour glass modes where element formulation provides internal resonances, there I'd say that you lose stiffness .
Connecting beams to membranes, you will likely deal with all of the above.
To elaborate on the RBE2 - a rigid beam element - using it to connect a beam (6dof) to a solid (3dofs) - you get problems with the 3 rotational dofs. If the dependent dofs are on the solid, these get constrained to ground.
The practical workaround is to add a thin shell onto the solid element and to define it using a material with zero density to avoid spurious resonances in the thin shell.
Just my 2 cents
C
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Hello everyone! I have a query regarding the Torsional constant and the Polar moment of inertia being used in Ansys workbench for a non circular cross-section .
In the Ansys help, i found that for the special case of a circular cross-sections, the torsionnal constant is equal to the polar moment of inertia and calculated by using this formula: Ixx=J=Iyy+Izz. Could any one clarify as to what formulation Ansys follows for the calculation of the Torsional constant and Polar moment of inertia of a non circular cross section.
Thank you!
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The torsional stiffness for circular cross section is indeed equal to the polar moment of inertia as the cross section is axisymmetric. But as the non-circular cross sections are not axisymmetric their cross section would bulge or warp when the shaft is twisted. If no value is entered for Ixx then ANSYS will compute the torsional stiffness (Ixx) as 'Iyy+Izz' which is correct for circular cross section but not for non-circular cross sections.
The expressions for allowable twist angle, allowable shear stress and torsional stiffness are available in literature. You can input this value in ANSYS as Ixx.
Best Regards,
Shlok
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I am working on seismic analysis of shear walls. So I am trying to calibrate CDP parameters for my further research by comparing load-Disp hysteresis (experimental and ABAQUS analysis) of U wall under cyclic loading.
For Experimental data I am referring this article:
I have attached an image showing best match (along with CDP parameters) which I could get for E=7000 MPa, which is very less than usually taken values like 25MPa. Is this normal when doing nonlinear cyclic analysis?
And how can I make my curve look similar to experimental one (there is huge difference in peak values and shape of cycles - experimental result shows narrow cycles whereas my ABAQUS analysis is resulting in wider cycles)
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In the ABAQUS program, you need to select one hysteresis models which have similarities to your experimental curve.
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Hello Researchers,
Say that I have 'p' number of variables and 'm' number of constraint equations between these variables. Therefore, I must have 'p - m' independent variables, and the remaining variables can be related to the independent ones through the constraint equations. Is there any rationale for selecting these 'p - m' independent variables from available 'p' variables?
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Bob Senyange Sir and Victor Krasnoshchekov Sir, thank you for your comments.
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I am simulating piled raft foundation subjected to seismic load (earthquake) in ABAQUS. I have modeled soil as solid elements and Mohr-Coulomb parameter. I want to know how can I apply geometric damping (silent boundary) to prevent the reflection of seismic waves?
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The simplest solution you can use in an Abaqus simulation is to place viscous dampers at the boundaries of your model as described by Lysmer and Kuhlemeyer (1969) and make sure your boundaries are not too close to the structure and foundation. This works well in the presence of a homogeneous soil profile and perpendicular/tangential waves with respect to the sides of your model. The next step would be to look at more advanced approaches such as: infinite elements, absorbing layers (e.g., CALM = Calm Absorbing Layer Method), PML (Perfectly Matched Layers) or even hybrid approaches mixing FEM and BEM formulations. However, I do not know if these methods are available in Abaqus software (perhaps using user-defined elements?) nor the particular problems that may arise when calibrating their parameters, numerical stability, etc.
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Hello everyone
When I plot elements of a FE model with node numbering and multi plots ON, I am also able to see the nodes which are of elements that are opposite/adjacent/not relevant to a particular element of interest. Is there any option in ANSYS APDL to make sure that only the nodes of a particular element is only seen and not that of another element that is adjacent or opposite to that particular element of interest?
N.B: In the attached image, I don't want to see the red-marked nodes.
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In APDL main menu, you should use Select Enitities, It s a usefull tools for selecting and unselecting everything such as node, kepoints, element and etc.
First use Select>>Entities
then use "Element", "By Num/Pick" , after that select the element you want.
After that you should use again Select>>Entities, then used "Node", "Attached to"
after that select the element. then use Plot>>Nodes.
I made an example and put it in the attached photo, I hope it is useful.
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So far world knows agile has emerged from IT/software solution projects. The methodology/ concept of agile is so highly effective that companies now want to explore its scope in managing mechanical product development.
1 biggest challenge i see before even embarking on the concept is, having an agile approach in CAD. A CAD engineer will take several days in general to modify or create a new model. Similarly, FEA/CFD will take days to iterate constraints to reach a solution. This cycle time is too big to go the agile way. How can we break down this work chain and check midway to make sure the progress is in right direction and effort will not need a redo?
Mechanical engineers are orthodox in working pattern so to say. There has been many improvisations and upgrades in CAD software but none in working style or thinking style.
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In CAD, there are ways to simplify and reduce your design time. if you use creo, there is a feature called Skelton concept, with Top-Down and Bottom-Up Design. we are using this concept to reduce the design time. every new design we make few master models, linked with family table and reference. this method reducing more than 75% of our design time. even we can have parametric drawings, no need to make separate drawing for the new design.</