Numerical Modeling - Science method

Akila Dulanjalee Wijethunge Can you share your Abaqus models (.inp format)?

Please check, that you extract data at the right location

Make sure, that the steel does not yield

try to validate your input data - you can use differential equation solver for this => check my matlab files

have a look at the phd thesis of Roman Sedlmair from KIT Germany

Influence coefficients are used in numerical simulations to determine how much influence a given node or point in the domain has on other nodes or points. These coefficients are often calculated based on the nodes' relative positions and the system's physical laws, such as the heat equation or Navier-Stokes equations for fluid dynamics.

As you've noticed, one common issue with influence coefficients is handling the boundaries or corners of the domain. In many cases, the influence coefficients near the boundaries will differ from those in the interior because the boundary conditions affect the system's behaviour.

One way to handle this is by using different formulas or methods to calculate the influence coefficients near the boundaries and interior. For example, you might calculate the first row of the influence coefficient matrix using x1 and y1 for the corners, and then use a different method for the interior points.

Another potential issue is that some numerical methods assume periodic boundary conditions, meaning that the system wraps around from one domain edge to the other. As you've described, this can result in 'continued influence' on the other edge of the domain. If your system doesn't have periodic boundary conditions, you might need to use a different method that properly handles the actual boundary conditions of your system.

It's hard to give more detailed advice without knowing the specifics of your system and the method you're using. However, I hope this gives you a starting point for understanding and resolving your issues.

Hi Amir,

I checked your input file and it seems that you are using MC material def. for your soil. So, my guess was that the strain concentration is caused by discontinuity in the material behavior. Your soil block is pulling the infinite region and since it is less deformable, you get the stress concentration and plasticity in the interface region. But I tried to run your input file and in fact, the plasticity already occurred during the static step.

So, there are 2 concerns here from my pov:

1. The way you create the model. First, there is no infinite elements in the bottom of the soil. I understand what you are trying to simulate but by modelling it this way, you have no representation of the static and dynamic behavior in the vertical direction.

2. The geostatic state is missing. As you know, the soil behavior is governed by its confining stress. And it is paramount in nonlinear soil simulation. In your static step, you apply the gravity loading to the soil but there is no predefined stress in the soil. This yields incorrect nonlinear behavior because the soil strength is underestimated. Any deformation beyond this point would be considered invalid. If you are unfamiliar with this, please check the abaqus manual regarding geostatic step.

So, for your model, I recommend to apply the infinite elements surrounding the main study area. You can imagine the interface to be like a half-ellipsoid. The interface here is the line between regular and infinite elements.

And then apply the correct geostatic step. I know it can be a challenge to implement a geostatic step on a model with irregular surface. How I usually solve it is by having a preliminary geostatic computation. In this preliminary model, I apply the geostatic computation while applying fixed boundary condition to all soil (finite) region and record the reaction forces. These reactions are then used as input in the true geostatic step in the main model to stabilize the result. I don't know whether you want to go this far, so I'll stop with the details.

Cheers and good luck with the model.

Are you asking how to make your particles a helix/spiral shape? First, before doing that, I recommend running simulations that will just use the effective properties that your helices should give. That will let you explore device ideas without needed the complexity and inefficiency of having to resolve the spirals in your grid. Second, you will want to create a small simulation of a helix to retrieve the effective properties. This is usually called homogenization or parameter retrieval. Third, if you need to, move on to your more complicated 3D simulation.

That still leaves the question of how to build a helix in a 3D grid. One way you can do this is to create the helix in a CAD software such as SolidWorks or Blender. You can export that model as an STL file, which is just a surface mesh that MATLAB (or whatever software you are using) can import. From there, there are codes available that can import those STL files and "voxelize" them into a 3D array. If you are using MATLAB, search the MathWorks website for "voxelize" and you will find multiple solutions. Once you have that, you can create copies of the spiral in your FDTD grid. This approach will let you import even more complicated shapes relatively easily. Alternatively, you can create the spiral directly in your grid. I would do this by creating a array that has a list of points along the center of your spiral. From there, you can calculate what points your FDTD grid should be assigned to that spiral by calculating their distance to the points on the spiral. If they are within a certain distance, assign the material properties of your spiral. Otherwise, assign the material properties of whatever medium the spirals are residing in.

I am sure there are plenty of other ways to do this. If you are interested, I dedicated almost all of Chapter 1 to describing techniques for building geometries into arrays for simulation using the finite-difference method. I do not specifcally talk about spirals, but you may find some of that chapter very helpful. Here is a link to the book website:

Hope this helps!!

Hi guys,

Can anyone help me to understand, how shall i simulate the isotropic confining pressure in PFC3D using the wall servo command for triaxial testing in soil?

Dear friend Xuan Yangru

Modeling permafrost degradation under the action of preferential flow can be a complex process and requires a good understanding of the physics involved in the system. The dual permeability model and lattice Boltzmann models are commonly used to model preferential flow in permafrost. The following steps can be taken to consider the prediction of permafrost degradation under the action of preferential flow:

Matlab is a powerful tool that can be used for numerical modeling. It has various built-in functions and toolboxes that can be used to model permafrost degradation. Some toolboxes that can be used for this purpose include the Partial Differential Equation Toolbox, the Optimization Toolbox, and the Image Processing Toolbox.

Basically you have an initial kinetic energy at impact. The strain energy and energy in plastic deformation if any must equal the initial kinetic energy minus any final kinetic energy. If you cannot find plastic part of the stress-strain curve experimentally, the best guess stress is constant between the yield point and ultimate breaking point or is straight line.

Softwares like Abaqus or Plaxis are good modeling software. Yet there are good packages for MATLAB and Python as well.

I'd like to @Genick-Bar-Meir mention, that you shouldn't forget about the FEM and experimental results are not exact themselves. First you have to estimate errors in FEM analysis and experimental research and after try to find suitable norm - its my opinion. Good luck

Did you try installing the latest service pack of the DHI MIKE software? There are also some hotfixes on their website.

https://www.mikepoweredbydhi.com/download/hotfixes-2014/mike21-150108?ref={8F7B09EA-2EFB-4EDC-A1BD-E03E7C8E4427ù

Son ich ngo Yes definitely I will try this way also.

虞军辉 junhui yu here I've attached the screenshot, in laminar flow conditions I can't be able to add roughness value on boundary conditions.

This is probably related to the calculation of the mesh elements when the ST module is activated, which means that you should check the resolution of the mesh in the near shore areas and try to decrease it.

Benslafa Nacera thanks a lot. I will check it out.

By the way... the model builder (Build3D) and particle tracker (PTRAX) I wrote (at the web link above) works with FDM, FEM, and FVM models (several different element shapes too).

The acceleration you'll get will depend on interaction with the impact surface; i.e. a hard surface will result in higher acceleration due to shorter interaction time. In other words, you need to consider the time to zero velocity from the 4m/s impact (the deceleration). Above 100g seems high for impacting wood but conversely a metal on metal impact could results in much higher accelerations.

I'd be concerned your measurement results in a factor 10 difference. Maybe check the sensitivites of the accelerometers are correct in the data acquisition, a factor 10 out would explain the measurement difference; this could also come from a mistake between m/s2 and g values for sensitivity in the data acq.

Dear Sandy J. Chaaban,

You can find the files you are looking for and the tutorials with them in the links below:

Best wishes.

Aditya Kumar Mishra replication is tough though i do agree with the expert comments above that physical replication like visualization is a must one of the important criteria I feel is to To assess applicability one must always specify the requirements along with exact what attribute of a previous results of interest.

Hi

It is highly recommended. Calibration of sediment transport model is as important as hydrodynamic one which can make sure and prove the model works well.

Hi everybody,

I am facing the same problem Lei was back in 2017 with this illegal geometry error message, but I am using FLAC3D. Does anyone know any command in FLAC3D similar to rezone? Or any technical paper like Navead's one but related to same problem in 3D?

Thanks!

Hello Amirhossein Haghighat. The type of univariable pre-screening of candidate predictors you are describing is a recipe for producing an overfitted model. See Frank Harrell's Author Checklist (link below), and look especially under the following headings:

There are much better alternatives you could take a look at--e.g., LASSO (2nd link below). If you indicate what software you use, someone may be able to give more detailed advice or resources. HTH.

Anirudh Singh Rana Thank you for your help, but I can't use zero flux boundary conditions on these two boundaries, the selection list suggests that these two boundaries are not suitable for the application. I‘m a new one and I have no idea about the reason, do you have any more detailed suggestions?

Regarding your question on the Nocke paper, Equation 6 is derived from the previous 5 equations. The numerical value of Equation 6 depends on the values chosen for the parameters b, d, t and D. If the system is linear, the impedance should not be dependent on sound pressure, so I am guessing that the p in the denominator should not be there.

Nowadays, a variety of pushover analysis methods have been developed, including Modal pushover, Adaptive pushover, and Cyclic pushover, in which some weaknesses of the conventional pushover method have been rectified. In the conventional pushover analysis method, the effects of cumulative growth of cracks are not considered on the reduction of strength and stiffness of RC members that occur during the earthquake or cyclic loading.

I think these papers will help you:

Dear Ali Gamra, I tested some series of triplets within this masonry project (the simulation had been done by a colleague):

In my project "CC" I did the experiments and the simulation (smeared cracking based on experimental data).

In my opinion, this should also work on your mentioned masonry project.

Nesrine El Houari Thank you but already check the manual and did not mention it

see

1-Shaking table model test and numerical analysis of a complex high-rise building

Xilin Lu, Ying Zhou, Wensheng Lu

Journal:

The Structural Design of Tall and Special Buildings

Year:

2007

2-Shaking table model test and numerical analysis of a long-span cantilevered structure

Chen, Shiming, Ge, Kang, Xue, Weichen, Lin, Yingru, Lin, Gao

Journal:

The Structural Design of Tall and Special Buildings

Year:

2018

For using piles in FLAC 3D, alot of parameters of every pile element should be determined such as bending moment and shearing force.

If you use stone columns in FLAC 3D, only some parameters of stone zone should be determined, but bending moment and shearing force of every pile element can not be obtainedobtained and the infill materials of stone columns are totally different with that for RC piles.

Best regards,,,

Thank you for your attention and your useful suggestions. John Machell Kaveh Zamani

problem solved, it was a mesh problem.

At first I generated mesh with other software and then tried to import it as a .mesh file. Everything was fine visually but there was a little problem with connectivities. MIKE needs only counterclockwise but my previous mesh generated in clockwise direction, so I changed it and model run successfully.

So if you generate a mesh and then imported it as a .mesh file in MIKE it's necessary to check element lines and make sure about connectivity directions. MIKE only accept counterclockwise.

This book isn't free until 12/21 (https://www.amazon.com/dp/B07Q5L1CHT) but the software and spreadsheets are always free (http://dudleybenton.altervista.org/software/FluidProperties.zip) I cover every significant equation of state in this book, including the strengths and weaknesses. Which to use depends on what behavior you're hoping to capture. So to answer your question, we would need more information. I have supplied many equations of state for industry, including the latest formulation for steam.

Dear Adolfo,

You can use a nonlinear interface relation for that allowing to gap to a certain extend and then build up stiffness from a certain displacement.

best regards Ab

Generally, you should compare the value of your error with the reported error by other researchers in your field. Then you can see whether you error is acceptable or not.

Due to different factors

Dear Alireza Akbari

the following tutorials can help you:

Dear Mohammed,

many journals would publish purely numerical results. Some of them are purely mathematical like SIAM Journal on Scientific Computing, some of them belong to some specific field of application like e.g. Computer Methods in Applied Mechanics and Engineering. The key point for acceptance is the scientific novelty of your paper, which means that either your simulation results use an establish simulation technique and reveal some new effect or explain other experimental results available in the literature, or that you mainly focus on some new method of computation or a new mathematical model and the computation results merely demonstrate the good properties of this new simulation strategy. In the latter case, a comparative study with some other reference results available from the open literature or from computations using commercially available software should generally also be performed and discussed.

General hint: each journal has a website with an "Aims and Scope" section, from which you can learn, whether your specific manuscript submission would be considered suitable for the journal by the editors. Often you can also see the acceptance rate and other metrics of the journal, from which one can estimate the chances of successful publication.

Yours

Yury

Hi, Alireza!

I recommend checking out this paper on the use of hard and soft contact implementations through the general finite-element software, Abaqus. You can jump directly into section 7.3, which is related to your concern. Below is the link.

I hope this helps. Good luck!

This paper describes the metrics needed:

For accuracy it is MAE if predictions were found as medians of predictive density and MSE if predictions were found as means of predictive density.

For bias it is Overestimation Percentage corrected (OPc) if predictions were found as medians and ME for the means.

You can use FEW-L1 or FEW-L2 workflow depending on the way how the forecasts were obtained.

Further reading:

A couple of websites I checked include - https://www.ncei.noaa.gov/access/global-ocean-currents-database/category.html and https://oceanservice.noaa.gov/facts/find-tides-currents.html. Although I see that the second one has historic data which may provide you some climatological data, it does seem restricted to given basins around the U.S. There is also World Ocean Database which should include directional information - that site is https://www.ncei.noaa.gov/products/world-ocean-database.

Perhaps one of these will give you the information you are seeking?

Best of luck with your research.

Mary

I am familiar with C#，C，C++, and not APDL.

Hello,

The moving concentrated forces of wheel load can be applied in ABAQUS using cyclic dynamic force. Find attached the paper on similar moving load analysis of a bridge beam subjected to moving wheel load for your reference..ok all the best..

Sujeet Kumar dear sujeet

thanks for your attention, but I have doubt about that, because my purpose is to use stress-strain curve in Elastic phase Not Plastic ,I mean using plasticity option for my goal seems wrong , whats your opinion?

Interesting

According to my experience, modeling the sediment transport in Flow-3D needs a considerable time and computational efforts while the accuracy of your modeling ,depending on the geometry and boundary conditions, is about 10 to 20 percent in the best case.

Xuejian Chen

Thank you so much dear chen, could you please guide me more about fist way( using field variable in abaqus) or suggest me any video or article related to this title?

Hi,

We're in the process of validating a new method for simulating reacting flows, and have been taking it step by step, starting from scratch only recently. The model may not be of interest to you, but the test cases should :

- [1] > 1D premixed flame, 1 step, constant Cp

- [1] > 2D counterflow diffusion flame, 1 step, constant Cp

- [2] > 1D premixed flame, NASA Cp, detailed chemistry

- [2] > flame vortex interaction, 1 step

- more complex cases in subsequent publications

Refs (on RG)

[1] Y. Feng, M. Tayyab, and P. Boivin, “A lattice-boltzmann model for low-mach reactive flows,” Combustion and Flame, vol. 196, pp. 249 – 254, 2018.

[2] M. Tayyab, S. Zhao, Y. Feng, and P. Boivin, “Hybrid regularized lattice-boltzmann modelling of premixed and non-premixed combustion processes,” Combustion and Flame, vol. 211, pp. 173–184, 2020.

K. Mahesh You need a boundary layer mesh.

+1 to Konstantinos answer. I was able to solve rather sophisticated nonlinear dynamic problem with GetFEM++

As for your question, mechanical, thermal, optical and chemical reactions sounds for me as elastic operator(div \sigma=rhs; ) and many Laplace operators for temperature, concentration, etc in one equation system.

You may solve this in GetFem with your full control at each stage

if for instance your are using abaqus, the DCP is an option.

You can also use the Mander model in SAP2000 and Seismostruct

The following discussion seemingly can be found of some interest, concerning to your query:

non to my knowledge

Dear Abd Ur RAHIM Niazi ,

Assalamualaikum. As far my knowledge, you can easily model masonry wall in SeismoStruct and most convincingly you just require a student license to use SeismoStruct and no need to have a professional license with payment.

So, just get your student license and enjoy using SeismoStruct.

Dear Zmour,

It can be better in term of diffusion convection reaction. My opinion is little different, the least-squares method has better control of the streamline derivative than the SUPG.

Ashish

Dear S M Muhaiminul Islam

The two following articles might help you:

The problem I faced while using SST I need to put the value of turbulence intensity at the entrance, and if I specify it to zero then my solution does not converge.

What you are describing is an approximate solution to Laplace's equation, which applies to inviscid flow. Viscosity is insignificant in many open channel flows such as shallow water waves. To get high school boys interested in CFD show them this... http://dudleybenton.altervista.org/projects/CFD/supergirl.gif The source code is there too, including flow over an airfoil and minivan.

Hello Navindra,

If your only goal with this simulation is to find the eigen modes/frequencies and damping, a gaussian white noise bandpass filtered to the range of your suspected natural frequencies of interest (e.g. number of floors/10 estimates f0 for buildings) will do the job without fail. The magnitude of the white noise must be sufficient to excite your structure. (usually ~0.2g suffices in my experience for buildings) I suggest using Automated FDD for OMA to ease your calculations.

I hope this helps! Good luck with your research :)

Ansuman Sahu , Regarding query no. 2 in your question,

In your code, after setting the initial temperature by TUNIF, set TIME as 0. Then start a *DO loop.

The loop should run from 1st to the last load step.

Inside the *DO loop, activate (EALIVE) the required elements sequentially. To achieve this, your element numbering should follow some ordered series in the zone where they would be sequentially activated.

Then apply your boundary conditions.

Then increase time by the time step size.

TIME_NOW=TIME_NOW+0.5 !!times step size=0.5

TIME,TIME_NOW !!set TIME to the current time

DELTIM,0.5,0,0 !!! Set min and max time steps

The solve inside the loop.

/STATUS,SOLU

SOLVE

Don't use LSWRIE/LSSOLVE. It may not work EALIVE/EKILL

Delete all loads in this step

End the loop

!!! In this way, your solution of each step would become the initial condition for the next step

Experimental results are affected by the instrumental and random errors. Numerical methods are affected by the physical model selected and the parameters belong it. For example, when you are using a turbulence model some parameters can be modified and normally you only have general recommendations for do that. On the other hand, the used mesh is another source of variations in results. The Combination of mesh, models, adaption and convergence process affect the simulation. That is the reason why is so important validate numerical results against good experimental results always be possible.

Alireza Akbari

Glad I can help, regarding why the error does not appear using Abaqus standard, I can't tell without checking the model. From what I understand, this particular type of error should appear regardless of the type of solver/step definition. If you're interested in pursuing this further, make a copy of your model with the explicit step (the one without the error) and replace the step with a general static step. If the error persists, refer to the manual.

Good luck!

Filippo Maria Denaro Thank you very much for your answer. I am solving an equation of thermal convection like dT/dt=coefficient *dT/dz

AAD% refers to Absolute average deviation.

Timothy Braun I am using MFiX for several months and I saw a Barracuda VR. But some reasons (like a budget :) ) I couldn't use a Barracuda.

Each software have different pros and cons for MPIC schemes. Firstly, MFiX is open-source and you can change everything that you want (like a user-defined-function). Also, MFiX has some different discretization schemes, solver types, etc.

Btw, Turbulent solvers are different. I'm working on turbulent case and chemical solvers these days. It seems Barracuda is beginner user friendly, but need to time for learning advanced things for MFiX.

Hi Mohammad Reza Azaddel,

By not solving the heat and flow equations in the between-the-pipes domain, you are technically considering the vacuum. However, in practice, vacuum is a relative concept: it is usually difficult to have an "absolute" vacuum. The pressure gauge may show few pascals. In this case, you may want to solve the heat/flow equations in your domain. In case it is still in continuum level (you can calculate the Knudsen number to decide), you can model the "natural convection" occurring between the two tubes. If so, you can model it in Fluent using Boussinesq model or ideal gas.

I think you should go with Matlab.

Simply amazing. Python too. Take a look at BASEMENT is an easier software but could help!

If simulation of water surface is essential, you can apply the FLUENT or FLOW-3D models, however, if you do not want to construct the water surface, you can use the SSIIM2 model.

Dear Nischal Sehrawat, The PML mathematical implementation consists of the introduction of a modified coordinate system, where an expansion coefficient is a complex number with an evanescent imaginary part. This generalization is achieved through the substitution provided in the screenshot: