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Dear members,
I am trying to predict temperature distribution in laser melting process using FEM. It is a 3D transient heat conduction problem.
I have modelled it without considering phase change at the melting temperature of metal, but I am not able to understand how to incorporate the phase change, particularly how to handle the nonlinearities associated with the phase change (the latent heat, enthalpy as well as heat conductivity might not be continuous at the point of phase transition)?
Please provide some resources or any kind of help will be helpful.
Sincerely,
Ravi Varma
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Hello Mr. Simon Smith
Yes I am modelling heat transfer only by conduction, just to keep the FE implementation simple. I will add other heat-transfer phenomenon later once I completely understand the conduction, FE formulation, and the coding part.
Thank you for the answer.
Best regards,
Ravi
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Hello everyone,
I've written a rather simple linear elastic UMAT for orthotropic materials. I found that my output stresses are different from stresses should be.
For example:
In my model, I set a max load of 25 MPa and min load of 2.5 MPa (aka cyclic load ratio R=0.1). In my UMAT a wrote a line "write(*,*) "stress(2)=", stress(2) " to see how applied load matches outputs. I expect see alternation of 25 and 2.5 (when increment time=0.5), but I see the following:
stress(2)=0 - okay, initial step
...
stress(2)=-25 - okay
...
stress(2)=-49.99 ????
...
stress(2)=-2.5 - okay
...
stress(2)=-19.99 ????
then everything repeats
But in ABAQUS visualization stresses are as I set, 25 2.5 ...
Have you seen something similar? I'm bit confused, don't understand how it works.
If you have any ideas what can be wrong, let me know.
I have attached the UMAT subroutine file and inp file. Thank you.
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I found the answer. The problem was that I manipulated with stresses after the calculation of the ddsdde and a stress vector. I solved the problem by putting the stress vector calculation at the end of the subroutine. In other words, "the correct stresses" are at the beginning.
If you have similar issues, let me know.
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Greetings to all.
I am new to UMAT in Abaqus and want to create UMAT for "shell" elements for an isotropic and anisotropic material, can anyone suggest any reference material, book, or website link which can help me.
Thank You
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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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I am New to MDS simulation which software will be open source and free tutorial available for beginners?
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Hi,
I have a little bit of MDS experience in 3 different software, so my opinion is based on these three:
1) Rich learning resources and analysis modules: Amber simulation engine
2) Beginner-friendly, good learning resources, and free: Gromacs
3) Pythonic and reasonable beginner-friendly but scarce analysis modules: OpenMM
In the case of Amber, the simulation engine is not free, while the rest of the resources are free, and its learning curve is steep. The various input files are difficult to understand in the beginning. However, Its analysis module contains almost everything. Plus, managing multiple trajectories/topologies during analysis is very easy.
Gromacs is easy to learn, however, the analysis module is not as rich compared to Amber. If you can somehow learn MDAnalysis (a python based MD analysis suite), then you can do almost everything required to analyze the trajectories.
For openMM, it is more suitable to develop and test new theories and force fields, however, you can run simulations using this.
There are other tools as well, like NAMD, CHARMm, etc but I don't have any experience in them, so I cannot comment.
Good luck.
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Dear ABAQUS users,
I want to make a three-dimensional model of the three-point bending simulation!
What do you think is the best element to use in ABAQUS for this problem? C3D8R - C3D8 - C3D20R - C3D20 - C3D8I
Can you please tell me about the advantages and disadvantages for each element or send me a reference for that!
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Three-dimensional (3D) eight-node solid C3D8 elements for concrete &
T3D2 elements for reinforcement are adequate to get the damage mechanism on the type of testing.
For a 4-point bending test, a numerical verification of CDPM in ABAQUS based on experimental results can be found here:
Bests,
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I couldn't find any example or useful info online. Can anyone familiar with altair help me with it?
Basicly, I want to study the optimized parameters of a I-beam under given BC and max stress/strain.
I have created the beam using HyperBeam standard I-section and assign PROD properties to the component. Now, I am stuck here. I want to link the desvar in size optimziation to the dimensions of I-beam parameters. How do I do this?
Thank in advance for any help!
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Can you share your finite element model?
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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 Researchers:
I need help, please if someone knows how to, o can, help me, I'll really appreciate it
I am trying to solve a model of a Medium voltage Energy Cable. So I need to solve for the Temperature Distribution across the whole 2D cross section (my model is a 2-D Model).
I have two direct questions :
(first image) I am trying to use the coupled Joule Heating Multiphysics. This is the "Electromagnetic Heating (emh1)" section.
1. My first question is : Do I have to ad a domian of "Heat Source", or I don't need to add this Boundary Condition ?
And if so, on the "Heat Source" section is it correct to select "General Source" and then: "Volumetric loss density, electromagnetic (ec) for the "Qo" ? (as is shown in the first image attached).
2. And second. On the "Electric Current (ecs)" physics. Do I have to use the domain "Terminal" or the domain "External Current Density" ?? I have a fixed value dor the voltage in the problem, and I also know the electric resistance of my Cable
Does anyone know How to solve this ?
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What you need to do is to couple the "Magnetic Fields" interphase (not the "Electric Currents" interphase) with the "Heat Transfer in Solids" Interphase, through the Multiphysics "Electromagnetic Heating".
And then you should be able to couple all the phenomena correctly.
Regards !
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I am trying to analyse a large structure with multiple loading scenarios (independent - different loading directions), while considering geometric non-linearity. Using different steps is not sufficient, since each step starts off with the geometry shaped as it was at the end of the previous step.
I tried creating a dummy step just to deactivate all the loads from the previous step, but the non-linearity causes some distortion to remain even without any loads.
One obvious solution is to run each step in a separate analysis, but the model is quite large and the input file processing takes about about as much time as it takes the solver to solve a step, which would immediately double the time required to obtain the entire solution and there would also be redundant information in the result files (mesh data repeated in each result file). So creating a separate analysis for each step is something that I am trying to avoid for the moment.
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Nils Wagner Here's a sample job that I created, which should be enough to understand the situation. There are 3 steps with loads (Step-1, Step-2 & Step-3) and 2 dummy steps (Step-1_D & Step-2_D) which only exist to deactivate the loads from the previous step.
This is not the actual model that I am working on, since I don't think I am at a liberty to share that. But the problem is exactly the same. Here the loading is in 3 different directions, which need to be evaluated independently of each other. To save on computation time, I am trying to do them as different Steps in the same analysis rather than create a separate analysis for each direction, but it does not seem to be working out very well so far.
Please let me know if you would like any more details.
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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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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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I want to do FEM analysis on cold extrusion.
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hi every body i will appreciate that if you introduce me screw design software
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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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Hello everyone,
I found in some papers that the bolt joint can be conveniently modeled using the thin layer element which has been integrated into many commercial FE packages.
In the tutorial Modeling the dynamics of mechanical joints (S. Bogradet al, 2011, MSSP), the authors have given a simple example (see Fig. 20 and Table 4 in section 3.5 of the attached PDF); however, it was completed in MSC. Nastran with which I am not familiar. I wonder if similar treatment can be done in COMSOL?
My final goal is to simulate how the pretension of the bolts affects the dampings of different vibration modes and I think the thin layer element based method can be a possible solution. If anyone has ever done or seen similar simulations before? COMSOL based tutorial will be of great help.
Thank you so much for reading and I appreciate your help.
Best regards,
Hao
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If you use the Structural Mechanics module, you can find the Thin Elastic Layer and many other option to be used in your 3D simulation.
Regards
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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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I'd like to draw a simple model on Plaxis LE designer but I did not find any guideline video that could help me to design it.
The model sample I attached. Please I hope any one can help me as fast as you can
Thanks
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Nesrine El Houari Thank you but already check the manual and did not mention it
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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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Hello Researchers,
I am using Gauss Quadrature for numerical integration to obtain the stiffness and mass matrices for a plate element in my FEM code. We know that both these matrices are symmetric. However, I find that due to numerical integration the stiffness and mass matrix turns out to be asymmetric.
Kindly note that the asymmetry is not by any means large. The result of the subtraction of a symmetric matrix from its transpose is a null or zero matrix. If I subtract the stiffness and mass matrix from their respective transposes, the resulting matrix has all the non-diagonal terms of the order 10 to the power of -8 and all diagonal terms are zero (maybe for most cases it can be considered as a zero matrix).
At the point of writing this question, I am suspecting that this discrepancy (i.e asymmetry of the mass and stiffness matrices) is due to the finite precision arithmetic of floating-point numbers. (need your thoughts on whether my suspicions are true)
The end result of not having symmetric stiffness and mass matrices is that the 'eig' function in MATLAB gives incorrect eigenvectors although the eigenvalues are correct.
I would like to know if anyone has encountered such issues and how was it resolved.
I am also attaching a couple of links related to finite precision arithmetic errors below for your reference:
Thank you,
Jatin Poojary
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yes, your diagnosis seems correct since the difference is of order of 1e-8. in computers, no floating point number can be represented exactly. therefore, it's common to use some epsilon value is used to avoid it. alternatively, when writing from scratch, only upper or lower diagonal is saved in the memory for a symmetric array to avoid such issues.
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I am using abaqus to model geosynthetic encased stone column (wished in-place). I am new to abaqus so how should I model geosynthetics in 3D and 2D (solid or shell or wire ) and can I get an idea about what type of interaction should I apply in between soil- geosynthetics and geosynthetic-stone column ( in 2D and 3D ).
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Embedded beam element or shell element
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Hello friends
Nowadays I am trying to use Code_Aster to simulate CABLE . I want to know how to add a force like this F=0.5*velocity^2 on selected nodes?
And how can people add a triangle distributed force on a moving cable whose coordinate is changing with time .
Thanks for your help in advance.
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if you have a time-dept simulation, you can create a multiplyiting function with LIST_REEL and DEFI_FONC.
Franco
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Hi,
I have an experimental tensile curve. This is the engineering stress strain curve right?
I have then converted it to a true plastic strain curve using Abaqus material conversion. Using these values, I have run a tensile simulation.
However, the results that I have obtained seem to replicate more of the true stress strain curve and not the experimental curve.
The load is displacement based where it is pulled by 32 mm which reflects accordingly to the experiment.
I have plotted misses stress vs LE11.(logarithmic strain along x direction ).
The peak stress in the experiment is 50 MPa while the peak stress for the true stress strain is 70 MPa.
I have attached my results below.
From the simulation, I am getting 70 MPa also which is not representative of the experiment.
Is this how its supposed to be or am I skipping something?
Thanks in advance for your help!!
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If you plot stress/strain of an element (if that is what you are doing), you will always recover the curve you entered for your material behaviour. Doing this will not serve as any kind of verification of your model.
If you want to compare to experiment, you need to do the same thing as in the experiment: Calculate the distance between two points and the total force on the part, that will give you a true force-displacement curve which you can compare directly to your experiment.
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I'm trying to reduce a 3d printer extruder vibration. When the extruder starts to move, vibrates that decrease printing quality. How can I reduce the vibration? I need a procedure to solve the problem using FEM methods like Abaqus. The procedure should contain an optimization method.
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Reduce the printing speed; examine the Z-axis level; the machine may need a complete calibration; and inspect the mechanical components that hold the extruder.
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Hi,
When I open up Abaqus CAE, I am supposed to see the message area in the lower half of the window below the viewport. But in my system, I am not finding the "Message area" and "Kernal Command Line Interface". The screenshot is attached herewith.
Can anyone guide me where to find it?
Also, in the above link, it is given that the command line area is usually hidden, and we need to click the 3 arrows to get it. But in my case, I am not even finding the 3 arrows.
Please help.
Thanks in advance.
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Hi,
I am currently struggling to virtually ream an acetabulum from a segmented hemipelvis. This is required for an implantation of an uncemented cup. As my analysis involves FEA (ABAQUS), I am currently performing the virtual reaming using a sphere. I am currently applying a boolean subtraction operation in ABAQUS to remove the cortical bone (and expose the subchondral bone) by positioning the sphere on the Centre of Rotation of the Hip.
Nevertheless, I seem to get rid of more than desired trabecular bone. Thus, my uncemented cup doesn't seem to have contact with the reamed acetabulum unless the cup is deepened, which leads me to the next question of How to virtually implant an uncemented cup in an already reamed acetabulum?
I have reviewed some literature and some researchers seemed to have used a step in ABAQUS where they perform a displacement control until the uncemented cup is overhanged(certain level of contact is achieved). I haven't used this FEA technique before, so any comments about this is widely appreicated.
I hope I was able to explain myself and this questions aren't too technical to be answered.
Thanks!
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Interesting question. Following.
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Hello everyone,
Hope you are doing great.
I am using coupled temperature-displacement step and coupled temperature-displacement elements as well. I need to use UMAT to model plasticity behavior and fracture. In every run I do, It takes 5-10 days to finish the simulation. I don't know if this is normal for my case study or something is missing?
Usually, I run my job by writing these lines:
---------------------------------------------------------------
abaqus job=xxx.inp user=yyy.for cpus=12 standard_parallel=solver int
OR
abaqus job=xxx.inp user=yyy.for cpus=12
---------------------------------------------------------------
Another thing I'm not sure about is my step setting, which is as follow:
---------------------------------------------------------------
*Step, name=Step-1, nlgeom=NO, extrapolation=NO, inc=1000000, unsymm=NO
*Coupled Temperature-displacement, creep=none, steady state
0.002, 1, 1e-10, 0.002
*Solution Technique, type=SEPARATED
*Controls, reset
*Controls, parameters=time incrementation
5000, 5000, 5000, 5000, 5000, 5000, , , , ,
--------------------------------------------------------------
I appreciate any help you can provide.
Mojtaba Ab
#Abaqus #fem #FE_Analysis #FEM_Simulation #Plasticity #Fracture #Elastic #Simulation
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Abaqus has two different option in order to make you simulation faster.
1- use multiple processors which you currently use
2- use GPGPU acceleration , which uses the GPU (For example CUDA Core in Nvidia Graphic)
I suggest you if its possible and If you have PC with high GPU core , run your model with GPU.
In Abaqus Job Manager this option is available.
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I have seen many research papers many people have worked on different software but I am unable to conclude that which is best for research purpose.
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Dear Fahad:
ABAQUS/ LS-DYNA are very good for blast impact analysis.
Best regards,
S M
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I want my ABAQUS script to read values from excel (these values will be used to create the FE Model). After the analysis, I want to extract the results (for example, maximum displacement) and save it in another excel file.
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Excel is not a file format. The spreadsheet can simply be saved/exported as csv or tsv which can be used as any other normal file in any script.
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After meshing, I want to create a set comprising of all the nodes on a particular surface of a part (in my case, the top surface of a hollow cylinder). I successfully created the node set in the GUI but for a parametric study, I will be considering many different cylinders. So I want to generalize using a python script.
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Mesh size is not a parameter in my study.
Regards
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I wrote a subroutine VDLOAD for dynamic explicit analysis in ABAQUS. The load is spatially distributed as well as varying with time. The subroutine VDLOAD works fine. But the load has two horizontal and vertical components (component1 and component2).
Horizontal component of load = 1*value
Vertical component of load = 0.75*value
Value is defined in the VDLOAD subroutine.
I know that the magnitude data entered in the editor (Attached figure) are passed into the user subroutine in an Abaqus/Standard analysis but are ignored in an Abaqus/Explicit analysis (Abaqus/CAE User’s Guide(6.14) section 16.9.8).
How to model these two components of the load by VDLOAD?
I would be grateful if you guided me through this.
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Reza Pourshab Could you please share how did you implement time variation of load? I am struggling with that...
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Dear Researchers :
I will appreciate if someone can give me some help with this issue
I already have my 2D-model of a Power Energy Cable in COMSOL Multiphysics.
But so far I haven't been able to model the Heat Transfer and Temperature Distribution in the Cable due to the Joule Effect.
The Cable works under a DeltaV = 25 000 kV, has a Longitude of 1 m , its dimensions are given, as well as the material properties.
But I don't know how to stablish this condition in the model under the 'Heat Transfer in Solids' physics
I also selected the 'Joule Electromagnetic Heating' effect to include into my model, but I cannot solve the Temperature correctly.
How do I have to consider this condition? What Boundary Condition (or Domain Condition) do I have to use on the model ?
Thak you for any help !
Regards ! :)
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Hi,
You may get some useful information from the following paper:
Solution of a coupled inverse heat conduction–radiation problem for the study of radiation effects on the transient hot wire measurements
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Dear Researchers, I ask for help;
This is in COMSOL Muliphysics ver.5.6
I am tryring to solve a model of an Energy Power Cable which is burried in the soil, is a 2D model
I choose to couple the phenomena of: -Electrostatics, -Electric Currents and -Heat Transfer in Solids (this last one is coupled using the 'Electromagnetic Heating' sub-module within the AC/DC module).
I already could solve the Electric Potential and the Electric Field (both, E and D) distribution,
But as much as I tried, I cannot understand how to solve correctly the Heat Transfer part of the model
The coupled phenomenon of Heat Transfer is due to the Joule Effect, due to the Electric Current/Voltage passing across the conductor.
When I solve for the Temperature Distribution I get :
- All the model is at the same temperature
- The value of the Temperature is negative, and
- This value is x10^18 K
Defenitevely something is wrong, very likely with the boundary condition of the Heat Source I'am trying to stablish.
It could be an evident-to detect mistake, but I cannot understand it
I am attaching the pictures
The first one is of the view 100% zoomed out, to see the complete geometry (I am including the seccion of the soil in my model),
and the second image is the view zoomed in of the geometry of the Cable
Please, does any know, and can help me, Why I cannot solve this model correctly ?
I will really appreciate it,
Best Regards !
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I see, I did find the imput for the Volumetric loss density, electromagnetic (ec)
But, when I fix the Heat Source with this source, I got no Temperature (see attached image please)
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Dear all,
Does anyone ever run site response analysis using Abaqus? Please upload some examples for reffrence.
I did but the results are very strange. I think I have problem with how to assign boudary conditions. I use tie constrain for lateral boudary and dashpot for base boudary.
Thank in advance all.
(my model is attached below)
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Hi,not yet, can you help me?
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No matter if I chose topology or shape optimization tasks (or whether they are condition-based or general) I can not see any thermally related variable to select as my design responses for heat transfer related optimization. All variables are all structural parameters (see the picture).
Does Abaqus Tosca work with heat transfer analysis at all? If it does how design responses can be defined as variables like temperature, conduction, etc.?
If you have experience performing thermal optimization using Abaqus optimization module your share of experience will be much appreciated.
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I received an official answer from SIMULIA as follows:
". . . The thermal optimization is not documented and not supported directly in Abaqus\CAE. Thus, you have directly to edit the parameter file for Tosca for adding the thermal optimization commands and then execute Tosca directly using an additional license. . . . "
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I need to model a delamination started from the pick of a transverse crack, how can I model it without using the cohesive zone ( I can't use it due to the lack of properties)
Thank you.
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For example I want to model a sandwich composites and I have modelled bi-woven composites in TexGen which I want to import in Abaqus for FE analysis where in the core of the sandwich has to be modelled and I should be able to give interactions between the core and face sheets.
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Maybe this topic will be of some help:
Best regards
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Hi,
I am doing analysis for Reinforced concrete sandwich panel subjected to blast load.After submission, the job aborted due to this error Truss Element 1 has zero length
Need your help.
Thanks.
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Dear.
I suppose you worked on Ansys.
Zero length problem happened when you wrongly click on the same node twice (in link element).
Go to select entities > elements > by attributes > check the element number > delete it.
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I need to simulate a Hyper Velocity Impact upon a sensible plate. I would like to split the simulation in two: firstly simulating the part of the plate near the impact (which is subjected to extreme deformation) in Autodyn, exploiting the SPH method; then starting from the results obtained in Autodyn I will conduct the analysis FE involving the rest of sensible plate.
Thus, I need to know how to use the results of Autodyn (in term of displacements/forces/pressures...) directly as the input of FE analysis, which I will do as a "simple " transient structural analysis, to reduce significantly the computational time.
Thank you for your help!
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Thank you for the advice Michele Raucci.
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I have modeled a flexible multi-body system in Abaqus and I wish to let Abaqus/Explicit solver simulate the system under some actuator loads. Description of simulation steps is as follows:
At the end of "each time-step", some selected results of the simulation (eg. displacements of bodies) are extracted and fed into a MATLAB program to compute the new actuator force which in turn is used as new actuator input for Abaqus simulation.
So after each time-step, Abaqus/Explicit pauses and waits for MATLAB program to run and then receives new inputs for actuators and resumes the simulation for the next time-step.
Attached is a snapshot from ANSYS brochure showing the exact simulation setup where I can insert my FE model into a control loop within SIMULINK editor. I want to know the ways I could do the same thing with Abaqus. Any help would be greatly appreciated.
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Here is the summary of the methods that can be used to implement a control system in Abaqus. I will provide a detailed discussion of these approaches in a separate pdf file.
Abaqus uses UAMP subroutine as a built-in solution to model control engineering aspects of the system.
At the beginning of each 'increment', Abaqus provides UAMP subroutine with 'sensor' data (defined in .inp file). Upon receiving this new data, UAMP applies the control law (through one the methods discussed in the following) and returns updated 'amplitude' to abaqus analysis.
1. If the control function can be implemented in FORTRAN, no third-party software is required for your control application.
2. In this method matlab controller function is exported as an executable file (.exe) which is called by FORTRAN 'system' function along with its input arguments in UAMP subroutine. Controller is designed to write its output in a file which is shared by Abaqus and MATLAB. Abaqus reads the file, updates 'amplitude' and resumes the analysis. (Note that MATLAB standalone executable files are slow. This issue is also discussed in MATLAB forums)
3. In this method a local server is established which acts as an interface between MATLAB and FORTRAN code. using cURL command in UAMP subroutine, a POST request is sent to localhost where MATLAB is constantly listening to for new incoming requests. Upon receiving this new request, MATLAB runs controller function and writes its results in a files shared by Abaqus and MATLAB. Abaqus reads the file, updates 'amplitude' and resumes the analysis.
Third method is a reasonably effective method for MATALB/Abaqus co-simulation.
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I am trying to estimate the thermal stresses that develop during the sintering of yittria stabilized zirconia (YSZ) cylindrical pellet containing Gd2O3 sphere, from room temperature to 1500oC with a heating rate of 10oC/min and holding time of 20 min, using the heat transfer in solids interface, solid mechanics interface, and coefficient form PDE interface.
Problem description and simulation files are attached for your reference
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📷hi Qusai, could you please walk me through , how you have implemented the stress eq. 1 in your model.
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Hey guys,
I am attempting to model the installation of a helical pile into sand using Abaqus CAE (explicit). I am using a CEL model with a rigid pile and Eulerian sand part.
Every time I run the job, the sand part 'explodes' and has very large deformations. I have attempted to rectify this problem via the following trials:
-assigning cohesion to the sand;
-applying a pressure to the sand;
-beginning the installation with the pile already penetrated into the sand part.
Through an exhaustive trial-and-error process, I found that I have solved the exploding sand problem by changing the 'hard' normal contact interaction to a 'linear' contact interaction. However now, the history outputs show no plasticity/plastic deformation! This is kindof important as I am interested in finding the installation disturbance effects of screw-pile installation.
Is anyone aware of what I can do to accurately/realistically model the installation disturbance effects of a screw-pile being installed into sand? I am happy to provide any more information as needed.
Thanks!
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Dear @Harrison stamoudis,
You can assume a cohesion of 0.01kPa for sand as an aparent cohesion.
Feel free to get in touch with me.
Cheers,
Ali Ahmadi
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Hello all!
How to model a composite model with a high strain rate (explicit dynamic analysis) in ANSYS or Ls-Dyna.
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Try the suitable element that convey your material and input your stress strain data
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I am trying to predict the preload loss in a bot using the analytical relation ( Equation-(28)) given in the paper: . I am not sure How to implement the analytical relation in algorithm. The preload loss seems not to effect any parameter in the Eq-28 except sliding speed to rotational speed ratio. But that dependency of bolt can be neglected based on the assumption of Eq.28 .
It will be of great help if you could suggest something here.
Thanks!
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The torque – tension relationship is highly sensitive to normal variations in the coefficients of friction between threads and between the turning head and the surface of the joint. Refer to the following paper:
Effect of Tightening Speed on the Torque-Tension and Wear Pattern in Bolted Connections
  • Journal of Pressure Vessel Technology 129(3)
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Dear ANSYS users,
I am doing FE analysis of RC beam using ANSYS APDL VI9, where I assigned force-displacement (bond-slip) to COMBIN39 based on CEB-FIP 2010 MODEL CODE, to model the steel-concrete INTERFACE. After completion of simulation, I wish to determine the interface bond stress at each load step and the respective slip values. Kindly suggest your reply how can I find these values, so that I could draw load VS slip curves.
Thank you,
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You can plot stress history for specific element or node from time history list of commands
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Hi. I am doing non linear FE analysis using a new material beam under flexural 2 point loading using ANSYS. I have defined a bilinear material model. The solution has converged. In results I am getting good stress strain curves (as expected, i.e slope decreasing post yield). However the load displacement curves show an increase in stiffness pattern. Please help me to correct the load displacement curves.
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It will be better if you share photos of your model and both the curves...
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Hello everyone, hope all is good.
I want to analyse multi-phase fluid flow through pipe, which software is best to do so ?
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Go for Ansys CFX or COMSOL.
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Please share any Example, Tutorial or any article related to CDPM. For a 3D Pushover analysis.
Thanking in anticipation!
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If you are interested in concrete model for explicit solver (VUMAT), you can use this link to download it
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Greetings to everyone,
Our team is currently working on the development of a VUMAT code in Abaqus for composite modelling using the Puck's failure theory as damage initiation criteria. Currently we manage to develop 6 different algorithms (4 on literature and 2 of our own) to find the fracture angle of any state of stress in an accurrate and efficient manner.
My question is related to the post damage behavior. Let's assume that a material point reach the Puck's failure initiation condition for an angle of -58° in matrix compression. It is clear that the material can resist further load in matrix tension and we need to degrade the stiffness matrix and so on. However, for this post damage stresses the fracture angle needs to be set to -58° or do we need to still look for the fracture angle? It is also known that the most critical angle depends on the state of stress and if we set constant from that point on are we understimating the damage?
If you need further instructions or the question is not clear enough please let me know. I'll be glad to share more details in case they are required.
Thanks in advance for your aid and support
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Daniel Badel Torres I do not know which material model of Puck criterion you are writing a subroutine that. But, we prepared different methods for the degradation of composite material properties. In all of them(In different element types or sudden or gradual degradation of composite material properties ) the fracture path is find out by the eauations
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Is the stress throughout the thickness of the shell element the same?
I learned that transverse shear stresses are accounted for in SHELL181 but I also read that stresses in shells along the thickness are assumed to be constant in linear analysis.
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Hello,
ANSYS calculates a stress level for each layer of your shell element (depends on element type tion => see the keyopt(8) for your element type). If you have only one layer (common use), the default option is to store the three values : top, bottom, and middle.
If you use the command SHELL,TOP (default) before your PLNSOL or PLESOL command, we will have a contour plot with the top and bottom values (you don't have the same values on each side of your elements il you have a membrane stress effect). With a SHELL,MID, you will see the stress on the neutral fiber of your shell element, with the same value on the both sides.
If you use the Workbench version, these options are avaliaible interactively.
Bye,
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Hello
I want to add thermal convection load on specific area of concrete volume.
it asks for film coefficient which is a constant value but the bulk temperature has no. of values that i have as excel file.
Can i import that excel file in ANSYS APDL or can how can i add tabular data in ansys apdl?
TIA
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Hello,
If you use ANSYS APDL I don't think you can import directly an Excel file. But you can import a formatted text file, with the *VREAD command (export a csv file from Excel first, for example, be sure that each data in one column of your file use the same number of characters, and then the use of the *VREAD command is not so difficult !
Note: you will have to use the Fortran format descriptor.
Bye,
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What are the shape functions of CST triangular and Q4 rectangular element models in terms of natural coordinate system (N.C.S) with (s,t) not with (x,y) in software programs as ANSYS mechanical APDL?
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Good question
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Why does normal bending stress/flexural stress value (Sx) just direct below a concentrated load of simply supported beam which is compression stress higher than the hand calculation Exact solution (theory of beam stress) in value in ANSYS APDL with any element type (Area type) of FE modelling 2D, solid 182 or 183 quadrilateral or triangle?
  1. Compression stress in Exact solution (-4687.5 Kpa). In ANSYS (-7077.26 Kpa).
  2. Tension stress in Exact solution (4687.5 Kpa). In ANSYS (4490.11 Kpa).
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The problem is that you apply concentrated load to the beam modeled by 2D finite elements, which means that, in essence, you deal with equations of 2D theory of elasticity. In this case, according to the exact solution, stresses in the vicinity of the loaded point tend to infinity. You can see this effect by refining the mesh in your model. At some remote points, however, the FE results should agree with the solution based on the beam theory. For example, the tensile stresses at the lower surface of the beam are in good agreement.
For comparison, you could consider the beam under uniformly distributed load. The results would be more optimistic.
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I want to analysis of 2D FE modelling beams cantilever/simple support in ANSYS, then compare it with exact solutions (elementary) such as deflection or stresses, however what element types (solid 182 or 183) in ANSYS Mechanical APDL are the best and appropriate? While the results will be close?
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This is not a matter of rectangular or triangular elements, but of the geometry of the area of meshing. Both elements work well when they strive for regular shapes: an equilateral triangle or square. And as a result of deformation, they do not change the aspect ratio much.
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Usually, in COMSOL MultiPhysics, there is an option to choose the parameter value from material properties. For example, for choosing Young's modulus value E in the solid mechanics module, one can select "from material" or input the value. Here one can simply define more than 1 domain having different values of E. But if there is no such option how can I access the material property. (I have two domains with different material property value).
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Both Link180 and SOLID185 elements have 3 degrees of freedom each (translation along the x, y and z) with no rotation allowed.
But why do both behave differently under applied load?
Why does SOLID185 "BEND" although it does not have translational degrees of freedom
But LINK180 does not bend under applied loads, like it deforms down but the element itself does not bend (the element stays straight without any curving)
Finite element model.
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Simply, the two elments rely on a quite different theory. LINK is based on the beam theory (exact results) and can withstand only axial loads, whereas SOLID is a plane element that has interpolating functions (shape functions) and leads always to approximated results.
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is there sensor history output for energy ALLKE and ALLPD in abaqus 2020?
is there any one help me
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Yes, the total energy output quantities such as ALLCD, ALLIE, ALLKE, ALLKL, ALLPD, ALLSD, ALLMD are available in the ABAQUS/CAE 2020 program.
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I do not understand how to provide pinned support to the rigid bodies. ABAQUS suggests that either rotary inertia must be defined at the reference nodes or all of the rotational degrees of freedom at the reference nodes must be constrained. What I do not understand is what values of rotary inertia is to be used in this case. Is there any other way to do pinned case in ABAQUS/EXPLICIT that I am missing? Thanks!
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Hi, I am trying to create a computation model of acoustic plane wave propagation through multiple layers of fluid. What should be the appropriate boundary conditions in my fluid-fluid interface? Thank you.
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The pressure and the normal components of the velocity have to be continuous across the boundaries. See for example in Fundamentals of Acoustics by Kinsler, Frey, Coppens, and Sanders Chapter 6.
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want to make a fatigue simulation on some mechanical parts like Gears, Bearing, and gear housing. please assume 2 gears in contact.when they Are rotating under constant torque and velocity the stress in every node is unique and varies every time. I can define a signal for a node based on time stress (\Sigma (t)) of the node but I cannot do that for the millions of them. Is there any solution for this problem? I saw some tutorial videos but all of them using one or two signals and applying to all elements but I cannot do that. Stress in posision1 (X1(t),Y1(t),Z1(t)) do not change the same as posision2 (X2(t),Y2(t),Z2(t)). But in tutorial videos stress in po1 is a constant scale of po2 in every time and the scale stays constant. please help me to solve that I have many problems with that.
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I recommend you use FRANC3D for Fatigue analysis. The stress analysis from ABAQUS or ANSYS can be exported to the mentioned software.
Hope it helps!
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Hello,
I am looking for a research partner who has ample experience in the FE modelling for structural retrofitting with any commercial software and has access to it. You need to conduct series of FE modelling (in ABAQUS/ANSYS/DIANA/any platform of your choice) for retrofitted structure (beam/columns) and verify the experimental data (experiment already done). It's not a large task, once material model is verified you need to run few simulations. I am expecting article writing assistance as well.
If you are interested, please send me an email at imrosebin.muhit@uon.edu.au with your CV. Please let me know your experience regarding FE analysis.
Cheers!
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Basim Mohammed Fadhil : Please check the paper related to the preliminary findings of the project. We mentioned the outline of the project and what we want to achieve eventually.
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Is there any software that can provide me the stiffness matrix of a structure?I know that i can work on Abaqus or Ansys for example,but I want only the stiffness of the model without solving the final system Ax=b.Does any know how can I obtain the stiffness?Also can Gmsh provides me the stiffness file except the mesh file?
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You can use ANSYS to obtain the Stiffness matrix and Mass matrix. Please find the code below. If you carry out the modal analysis you can obtain the undeformed stiffness matrix. Hope this helps you.
!=== READ M AND K MATRICES FROM THE FULL FILE
*DMAT,K,D,IMPORT,FULL,file.full,STIFF
*DMAT,M,D,IMPORT,FULL,file.full,MASS
*PRINT,M,Mass_Matrix.txt
*PRINT,K,Stiff_Matrix.txt
! === END
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Is there any open source software that can be used to segment image data (dicom) and the segmented data can be exported as volume or mesh data for further FE analysis?
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Hi Everyone,
My attempt to use the drapability and stretching behavior of knitted composites(just fiber without matrix) in die forming. At this moment, I am only interested in the behavior of the fiber.
I ran 2 models (geometrically, constraints and interaction are identical).
Job 68-
Material model used (Steel with plasticity defined).
Results: Are converging. The behavior is as expected.
Job 69- Material model used (Carbon fiber-MAT-1 in .inp and material orientation defined based on texgen software algorithm). Added orientation by calculating the normal for each element using the node data. I have defined the material parameter based upon the property sheet from attached Hexcel-tow data.
The error I get is ratio of deformation speed is too high. I have tried a number of possibility as mentioned in this forum earlier. Any help would be highly appreciated:-)
-Sangram
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I think the mentioned error comes from element dimensions, run the simulation by default element and check the results.
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How should I create a system in ABAQUS that consists of rigid parts (parts must be connected with pins like truss systems)?
I use some techniques but I want to know other possible techniques..
Direct or tricky methods I can accept.. For instance material usage with very high elasticity, or manipulated Poisson's ratio. I can use game engine for this but I want to use Abaqus?
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Mojtaba Abdolkhani Thank you very much, I am trying today.
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In literature, Anterior longitudinal ligament (ALL), Posterior longitudinal ligament (ALL), Supraspinous Ligament (SSL), Interspinous Ligament (ISL), Intertransverse Ligament (ITL), Facet Capsular Ligament (FCL), Ligamentum flavum (LFL) ligaments are modeled with the whole lumbar vertebrae. However, I couldn't reach the exact numbers of them in the model, repectively. Do you have any information about this? Could you give me a suggestion to solve this problem?
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hi
i hope this paper can help you:
1- BIOMECHANICAL PROPERTIES OF HUMAN LUMBAR SPINE
LIGAMENTS, J.Biomechanics. Vol 25 N.o. 11, pp.1351-1356, 1992.
Kind regards
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Hello,
This is propably a primitiv question but I am trying to figure out how to implement a moment at the tip of a (for simplification) beam around the z axis. It should follow the nodal rotation in a dynamic case. When using Abaqus this is quite simple: I get a reference point in the middle of the surface (end of beam) that is supposed to rotate and couple it to the mentioned surface, with a Coupling card. Then I load the reference Point with a Moment (CLOAD)
.....
*nset, nset=end
2, 4, 6, 8, 2, 4, 6, 8, 12, 13, 14, 18, 19, 20,
*nset, nset=RP
711
*SURFACE,NAME=moment,TYPE=NODE
end,
*COUPLING,REF NODE=711,SURFACE=moment ,CONSTRAINT NAME=C1
*KINEMATIC
....
*STEP
*DYNAMIC
....
*CLOAD
RP, 6,10
*STEP END
When doing this similar in CalcuiX nothing happens for the dynamic case. I am able to do it in a static calculation though!
I also tried loading the moment on the nodes of the surface directly or just around the middle line. Also nothing happens. When loading a force though it works.
I am quite new to CalculiX and at our department nobody worked with it before.
I would really appreciate if somebody could help me and give me a hint.
Thank you very much!
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Hello,
thank you all for your answers. Sorry I did not respond to it in the last weeks.
I solved the problem a while ago. It seems like the coupling method is not the best and easiest approach in Calculix. It works, but I got strange results in dynamic simulations. A better way seems to be to work with a *rigid body. I defined the surface on which the moment is supposed to work as a rigid body with a Reference Point and a Rotational Point. The three degree of freedomes of the rotational node can than be used for the moments. This means for a moment around Y-axis you can CLOAD the second degree of Freedome of the Rotational Point. Coordinates of the Rotational Point thereby do not matter.
I now have a different issue with Calculix. When doing as told as above and running a dynamic analysis I get a lot smaller result than when calculating static. I am implementing a constant static moment, but the final result even after a long time is about a 100th smaller. If I increase the moment by 100 I get perfect results.
Does anybody have an Idea what could be the reason?
Thank you very much !
Jonas