To start a new discussion with a link back to this one, click here. That is, start by first solving a model with a small, but non-zero, load. -Detail: NaN or Inf found when solving linear system using SOR. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. The other low-level default settings within the Stationary Solver are chosen for robustness. Solving such models in a stationary sense should simply require solving a single (large) system of linear equations and should always be solvable, but there are cases when the software will fail to find a solution. Your internet explorer is in compatibility mode and may not be displaying the website correctly. If some, or all, of the needed materials properties needed by the physics interfaces are not defined, the model will generate an error at runtime. She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. That is: Even if the forces on a part are opposite and equal, this is not sufficient information to say where the part is, so you must add some other condition, such as as Fixed Constraint to constrain displacement.
Could you expand a little bit more why the coupling is impossible? The following are possible reasons why a linear stationary model will fail to solve, along with resolutions: The combination of the constraints and boundary conditions must be sufficient to define a unique solution to the problem, in terms of the field variables being solved. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases.
It is also possible to manually refine the mesh.
Troubleshooting for 3D trusses, if anyone's out there. : r/COMSOL - reddit Your Discussion has gone 30 days without a reply. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Note that while COMSOL employees may participate in the discussion forum, COMSOL software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team. In that case, the continuation method will automatically backtrack and try to solve for intermediate values in the range of 0.6 through 0.8. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary model. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. That is, start by first solving a model with a small, but non-zero, load. The difference between the phonemes /p/ and /b/ in Japanese. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. - That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model.
Top 10 Best Stationary in Brea, CA - October 2022 - Yelp However, it is usually not possible to know this ahead of time. At a value of P=0 the above expression is linear, and at a value of P=1 the expression is equal to the original nonlinear expression. Again, introduce a Global Parameter that gets ramped from exactly zero to one.
It is sometimes necessary to manually scale the dependent variables. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. COMSOL does not assume any legal liability for the accuracy of the data disclosed. The segregated approach, on the other hand, solves sets of unknowns separately. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. The Fully Coupled solution approach, with the Plot While Solving enabled. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 listed if standards is not an option).
Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Extending this logic, if one wants to solve for any arbitrary load on a nonlinear system, it makes sense to solve a sequence of intermediate problems with gradually increasing load values and using the solutions from each previous step as the initial condition for the next step. Reply . If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Therefore, it is recommended to use Adaptive Mesh Refinement which will automatically refine the mesh only in regions where it is needed, and coarsen the mesh elsewhere. I am solving a linear stationary finite element model but the software is not solving.
comsol - using stationary solution as the initial conditions in time This approach is known as a Continuation Method with a Constant predictor. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: The settings controlling the predictor type. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. Could you expand a little bit more why the coupling is impossible? Direct Iterative , Direct . The algorithm is, generally speaking, a Newton's method approach. At a value of P=0 the above expression is linear, and at a value of P=1 the expression is equal to the original nonlinear expression. Consult your product manuals for complete trademark details. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) This case is generally difficult, or impossible, to solve since this material property is non-smooth. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. To start a new discussion with a link back to this one, click here. Therefore, it is recommended to use Adaptive Mesh Refinement which will automatically refine the mesh only in regions where it is needed, and coarsen the mesh elsewhere.
Does anyone know how to solve error in stationary solver in COMSOL Linear solvers. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below.
Office Supplies, Stationery, and Gift Retailers Companies in Brea Why is there a voltage on my HDMI and coaxial cables? For example, if ramping P over values of: 0.2,0.4,0.6,0.8,1.0 the nonlinear solver may fail to converge for a value of 0.8. Get notified about new Stationary Engineer jobs in Brea, California, United States. Within either of these features, it can also be helpful to enable the Results While Solving option, as shown in the screenshot below, to visualize the iterations being taken during the solution. listed if standards is not an option). First, it is physically intuitive, often matching how one would perform an experiment. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) thanks for reply
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Specify Material Properties in COMSOL Multiphysics (3/8) Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. It is quite rare that changing these settings is superior to using a combination of the other techniques in this Knowledgebase, although it is possible to tune these settings to reduce solution time and memory requirements, once a model is already converging. Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. Thanks, Andres. The technique of load ramping is not always reasonable for all problems. Within either of these features, it can also be helpful to enable the Results While Solving option, as shown in the screenshot below, to visualize the iterations being taken during the solution. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. COMSOL does not assume any legal liability for the accuracy of the data disclosed. if I want to do an adaptive mesh refinement, I get this error. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. This involves a systematic reduction in the model complexity. This guide applies solely to nonlinear stationary models. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. You can write the discrete form of the equations as f(U) = 0, where f(U) is the residual vector and U is the solution vector. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. An example would be a linear static structural model of an aluminum beverage can. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. In such cases, see if one material (or the other) can be omitted from the analysis completely. At low flow speeds the flow solution will be time invariant, but at higher flow rates there will be vortex shedding, a time-varying change in the flow field behind the cylinder. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. This approach is known as a Continuation Method with a Constant predictor. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. November 11, 2013. See Knowledge Base 1240: Manually Setting the Scaling of Variables. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Stationary (time-invariant) models with nonlinearities may converge very slowly. As we saw in Load Ramping of Nonlinear Problems, we can use the continuation method to ramp the loads on a problem up from an unloaded case where we know the solution. thanks for reply Your internet explorer is in compatibility mode and may not be displaying the website correctly. The Automatic predictor setting will use the constant predictor when a segregated solution approach is being used, and use the linear predictor when the fully coupled approach is used. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Set initial conditions in the physics to the appropriate dependent model variable names rather than the default 0. Use this parameter to modify the nonlinearity expressions in the model. These are some highly rated cards & stationery in Brea, CA: What are some cards & stationery with a large number of reviews in Brea, CA? Required fields are marked *. With sufficient simplification, a model can be reduced to a linear problem, and if this simplified model does not converge, see: What to do when a linear stationary model is not solving. Wrong ordering of study steps. It's brand new in the hmart plaza and I wish it was open back when I would hangout in the plaza after school (although they would have taken all my allowance money! Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. (Frequency Domain should be the last step).
P&S: COMSOL Design Tool for Photonic Devices - ETH Z Alle Rechte vorbehalten. The objective here is to simplify the model to a state where the model will solve, with linear approximations. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model.
Improving Convergence of Nonlinear Stationary Models - COMSOL If you try to enter a variable that is undefined, the automatic syntax highlighting will identify this as you enter it, and it is best practice to resolve this immediately. Hence Comsol solved for the stationary solution at different points of time. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Learn how your comment data is processed. However, it is usually not possible to know this ahead of time. The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! This consent may be withdrawn. L'objectif de notre prsent travail se repose sur l'tude par simulation numrique du comportement de bton au jeune ge sous des conditions svres de temprature pendant les premires 24h aprs. Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . Any trademarks referenced in this document are the property of their respective owners.
Improving Convergence of Nonlinear Stationary Models - Informazioni In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. I'm trying to model a solid that's moving through a steady background field in a background flow, I want to take into account the effect of movement of the solid after each time step so I have to use stationary solver after each time step in order to see how field has changed after solid moved. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. My comment is perhaps a bit nave but it seems to me that you could simply deactivate the term of the background field equation but keep its connexion to the solid to get what you want. The technique of load ramping is not always reasonable for all problems. - Discussion Closed This discussion was created more than 6 months ago and has been closed. Consult your product manuals for complete trademark details.
Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Using the first order optimality. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Hi Alexis,
listed if standards is not an option). Function: / Failed to evaluate expression. With sufficient simplification, a model can be reduced to a linear problem, and if this simplified model does not converge, see: What to do when a linear stationary model is not solving. What version of COMSOL are you using? To learn more, see our tips on writing great answers. For example, if there is a temperature-dependent material property such as:
How to solve "Undefined material property 'sigma - ResearchGate Common Mistakes: Not assigning materials to all the domains. The segregated approach, on the other hand, solves sets of unknowns separately. COMSOL makes every reasonable effort to verify the information you view on this page. Stationary Solver Iterative Direct . The software then computes an initial solution and from there it iteratively re-computes the solution, taking into account how these intermediate solutions affect the nonlinearities. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. Can I tell police to wait and call a lawyer when served with a search warrant? The default Initial Values for the unknowns in most physics interfaces are zero. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. One can say that, in general, if the loads on a nonlinear system are zero, the system will be at rest; that is, the solution will be zero. Sometimes, reducing the model complexity can be quite challenging and it can be better to start from as simple a case as possible and gradually increase the complexity. There will always already be either a Segregated or Fully Coupled feature beneath this. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. I personally liked emailing them the file, ", "This flower shop is the best! A nonlinearity can be introduced into the model either in the governing equation, or by making any of the material properties, loads, or boundary conditions dependent upon the solution. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is:
Alternatively, delete and re-create the study. This approach is known as a Continuation Method with a Constant predictor. Your internet explorer is in compatibility mode and may not be displaying the website correctly. The latter method is known as the Continuation Method with a Linear predictor, and is controlled within the Study Configurations as shown in the screenshot below. In that case, the continuation method will automatically backtrack and try to solve for intermediate values in the range of 0.6 through 0.8. Perhaps this approach could be adapted to represent your model. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. Cooling and Solidification of Metal. If all of the above approaches have been tried and you are certain that the problem itself is well-posed, consider that the nonlinear problem may not, in fact, have a stationary (time-invariant) solution. There will always already be either a Segregated or Fully Coupled feature beneath this. Not assigning proper boundary conditions: Especially if you have ports. For example, if there is a temperature-dependent material property such as: Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. If you have both as steps in the same study, then solve that study. Assuming a well-posed problem, the solver may converge slowly (or not at all) if the initial values are poor, if the nonlinear solver is not able to approach the solution via repeated iterations, or if the mesh is not fine enough to resolve the spatial variations in the solution. Review the model setup to resolve these. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings).
Improving Convergence of Nonlinear Stationary Models - COMSOL In this posting, we introduce the idea of ramping the nonlinearities in the problem to improve convergence. At low flow speeds the flow solution will be time invariant, but at higher flow rates there will be vortex shedding, a time-varying change in the flow field behind the cylinder. In particular, choosing an improper initial condition or setting up a problem without a solution will simply cause the nonlinear solver to continue iterating without converging.
- Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. In this post, we will delve deeper into how to choose an appropriate mesh to start your mesh convergence studies for linear static finite element problems. This algorithm was also useful for understanding what happens near a failure load. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. Solver . Does anyone know what should cause this problem? (I am begginer in comsol) Thank you. Have you taken a look at this [blog post](https://www.comsol.com/blogs/modeling-fluid-structure-interaction-in-multibody-mechanisms/)? Within either of these features, it can also be helpful to enable the Results While Solving option, as shown in the screenshot below, to visualize the iterations being taken during the solution. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. A nonlinearity can be introduced into the model either in the governing equation, or by making any of the material properties, loads, or boundary conditions dependent upon the solution. Wish you all the best. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. By providing your email address, you consent to receive emails from COMSOL AB and its affiliates about the COMSOL Blog, and agree that COMSOL may process your information according to its Privacy Policy. Linear solvers. COMSOL makes every reasonable effort to verify the information you view on this page. Note: there is no way to couple this field with the time dependent nature of this physics.
Why doesn't iterative solver converge in COMSOL? - ResearchGate This involves a systematic reduction in the model complexity. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. I use comsol multiphysics 5.2a and . This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Multiscale Modeling in High-Frequency Electromagnetics. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Your internet explorer is in compatibility mode and may not be displaying the website correctly.
Common Study Step Settings - COMSOL Multiphysics For example, if ramping P over values of: 0.2,0.4,0.6,0.8,1.0 the nonlinear solver may fail to converge for a value of 0.8. Therefore, it is recommended to use Adaptive Mesh Refinement which will automatically refine the mesh only in regions where it is needed, and coarsen the mesh elsewhere. Check the solver log to see if the continuation method is backtracking.
The Iterative Solvers - COMSOL Multiphysics With respect to multiphysics couplings, rather than solving the problem using a fully coupled approach (the default) solve the problem sequentially, with one physics being solved after another. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. Load ramping and nonlinearity ramping can be used in combination, but start with only one or a few of the loads or nonlinearities being ramped. Create the time-dependent step or study. Comsol help video number 2: Solving a laminar flow problem in a slit.. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. It may also reveal that the model itself is ill-posed in some way. Hi Jason,
Extending this logic, if one wants to solve for any arbitrary load on a nonlinear system, it makes sense to solve a sequence of intermediate problems with gradually increasing load values and using the solutions from each previous step as the initial condition for the next step. listed if standards is not an option). How can I check before my flight that the cloud separation requirements in VFR flight rules are met? Sometimes, reducing the model complexity can be quite challenging and it can be better to start from as simple a case as possible and gradually increase the complexity. . The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another.
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