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When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. Learn how your comment data is processed. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. If it is not clear that any of the above strategies are working, it is useful to take a more general approach to verifying the general validity of the model. The other low-level default settings within the Stationary Solver are chosen for robustness. This involves a systematic reduction in the model complexity. Mesh The advantages of the continuation method are two-fold. What are people saying about cards & stationery in Brea, CA? (Frequency Domain should be the last step). Use this parameter to modify the nonlinearity expressions in the model. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Posted 26 set 2019, 11:57 GMT-4 There will always already be either a Segregated or Fully Coupled feature beneath this. Not the answer you're looking for? Solve the stationary study then the time dependent study. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Segregated approach and Direct vs. This is relatively expensive to do, but will lead to the most robust convergence. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) The fully coupled and segregated approaches are discussed below. 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. - Feature: Stationary Solver 1 (sol1/s1) 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. "After the incident", I started to be more careful not to trip over things. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version I use comsol multiphysics 5.2a and . Such a large difference in the materials properties can be challenging. Check the solver log to see if the continuation method is backtracking. Your internet explorer is in compatibility mode and may not be displaying the website correctly. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. I am solving a linear stationary finite element model but the software is not solving. Could you expand a little bit more why the coupling is impossible? In this page, we will be sharing some common errors that might occur in Comsol and their solutions. 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. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. $130,000.00. They worked with me. Function: / Failed to evaluate expression. With respect to any nonlinearities, replace them by a reasonable linearized term. Have you taken a look at this blog post? This case is generally difficult, or impossible, to solve since this material property is non-smooth. Use this parameter to modify the nonlinearity expressions in the model. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? If one particular material is missing one property, that material will also be highlighted with a red cross over that material icon in the Model Builder. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. 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. Not assigning proper boundary conditions: Especially if you have ports. Tutti i diritti sono riservati. Contact COMSOL at Bangalore on their telephone: +9180 25323003. Why? View the Settings window for the Materials branch to get a list of all domains with undefined materials and add a material to those domains. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) 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. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). However, it is usually not possible to know this ahead of time. Understanding the Fully Coupled vs. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Here, we will examine techniques for accelerating the convergence of these two methods. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. If you are unsure if your problem is linear and stationary, look at the Log. That is, they are tuned to achieve convergence in as many cases as possible. It may also reveal that the model itself is ill-posed in some way. Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble Segregated approach and Direct vs. 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. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. There will also be a red cross over the Materials branch icon. This is a review for cards & stationery in Brea, CA: "Love this store!!! 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. This approach is known as a Continuation Method with a Constant predictor. Then use this file to provide the initial conditions in time dependent model. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Multiscale Modeling in High-Frequency Electromagnetics. Save this information to a file. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. COMSOL does not assume any legal liability for the accuracy of the data disclosed. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. The coupling terms between the different groups are thus neglected. For more details, see: Performing a Mesh Refinement Study, Mesh refinement may often need to be combined with load or nonlinearity ramping and may require a set of studies, first starting with a relatively coarse mesh for nonlinearity ramping, refining the mesh, and the ramping further on the refined mesh. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. I personally liked emailing them the file, ", "This flower shop is the best! Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Perhaps this approach could be adapted to represent your model. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. 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. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Most multiphysics problems are nonlinear. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. New Stationary Engineer jobs added daily. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Knowledgebase 1260: What to do when a linear stationary model is not solving, Knowledge Base 1240: Manually Setting the Scaling of Variables, What to do when a linear stationary model is not solving, Knowledge Base 1254: Controlling the Time Dependent solver timesteps, 2023 by COMSOL. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. What did people search for similar to stationary stores in Brea, CA? A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. (I am begginer in comsol) Thank you. 140K views 8 years ago COMSOL Multiphysics Tutorial for Beginners Please note that an updated version of the content in this video can be found in the Modeling Workflow video in the COMSOL. The default Initial Values for the unknowns in most physics interfaces are zero. Stationary (time-invariant) models with nonlinearities may converge very slowly. there is no defined multiphysics for it as I know, I have a standing accoustic wave and a flow in the background but I don't see their connection. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. These are some highly rated cards & stationery in Brea, CA: What are some cards & stationery with a large number of reviews in Brea, CA? thanks for reply Repeat this for every nonlinearity of the model. rev2023.3.3.43278. Repeat this for every nonlinearity of the model. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. 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. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. First, it is physically intuitive, often matching how one would perform an experiment. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Discussion Closed This discussion was created more than 6 months ago and has been closed. If it does so, use a finer increment in that range. 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. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. Consult your product manuals for complete trademark details. If you try to solve such a model, there will be an error at runtime that will provide information about the variable name and where it is being called. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. With respect to any nonlinearities, replace them by a reasonable linearized term. If you see this, right-click on the Solution feature and select Reset Solver to Default. 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. 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. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. With respect to any nonlinearities, replace them by a reasonable linearized term. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. 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. In this case, it would likely be reasonable to treat the insulative material as a perfect insulator, omit it from the analysis, and use the Electric Insulation boundary condition instead of modeling those domains. However, it is usually not possible to know this ahead of time. This approach is known as a Continuation Method with a Constant predictor. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. - Function: ^ Failed to evaluate variable. 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! That is, they are tuned to achieve convergence in as many cases as possible. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. My comment is perhaps a bit nave but it seems to me that you could simply deactivate the \frac{\partial \cdot}{\partial t} term of the background field equation but keep its connexion to the solid to get what you want. 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version About the Stationary Solver The following background information about the Stationary Solver discusses these topics: Damped Newton Methods, Termination Criterion for the Fully Coupled and Segregated Attribute Nodes, Linear Solvers versus Nonlinear Solvers, and Pseudo Time Stepping. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. This algorithm was also useful for understanding what happens near a failure load. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Hi Jason, The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! What are some highly rated cards & stationery in Brea, CA? This involves a systematic reduction in the model complexity. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Stationary (time-invariant) models with nonlinearities may converge very slowly. COMSOL does not assume any legal liability for the accuracy of the data disclosed. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. It is also possible to manually refine the mesh. The nature of simulating nature: A Q&A with IBM Quantum researcher Dr. Jamie We've added a "Necessary cookies only" option to the cookie consent popup. We have also introduced meshing considerations for linear static problems, as well as how to identify singularities and what to do about them when meshing. Hi Alexis, The continuation method will again backtrack and try intermediate values of the ramping parameter, thus giving you the nearest approximation to the abrupt transition that is solvable. 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. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. If this was solved using the Solid Mechanics physics interface the thin walls of the container would need to be explicitly modeled, but the wall thickness is much smaller than the overall can dimensions. Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems. Can I tell police to wait and call a lawyer when served with a search warrant? 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. 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. 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. Studysteps might be listed in wrong order: Not assigning materials to all the domains. Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. To switch between these solver types, go to the Stationary Solver node within the Study sequence. 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. Tutti i diritti sono riservati. Again, introduce a Global Parameter that gets ramped from exactly zero to one. 3. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. Such problems must solved in the time domain. How can I use it? ", "Absolutely the best place to shop for flowers and greenery, I spent an hour just looking around for fun prior to purchasing a bouquet, they have the best customer service people all over the place and it's a huge place", "Recently came in here to pick up 45 chocolate Seegars (cigars) for a dinner banquet in honor of my baby nephew. Wish you all the best. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. -Detail: NaN or Inf found when solving linear system using SOR. Linear solvers. 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. This case is generally difficult, or impossible, to solve since this material property is non-smooth. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Understanding the Fully Coupled vs. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary model. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Today's top 351 Stationary Engineer jobs in Brea, California, United States. The settings controlling the predictor type. There are also cases when an extremely poor quality mesh leads to an ill-conditioned problem, This issue often arises in combination with, and as a consequence of, geometries that have extreme aspect ratios. SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. Name: actdep_int1, Your email address will not be published. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. If the model is very large, and if you do not have very much memory in your computer, you may get an error message regarding memory. Hi Jason, Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. 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. In our previous blog entry, we introduced the Fully Coupled and the Segregated algorithms used for solving steady-state multiphysics problems in COMSOL. As a rough rule of thumb, once the aspect ratio between the largest characteristic dimension to the smallest approaches 100:1, you might start to run into issues and should look to alternative ways of posing the problem, especially in a 3D model. However, load ramping will not work in all cases, or may be inefficient. It is sometimes necessary to manually scale the dependent variables. listed if standards is not an option). Direct Iterative , Direct . replace it with the expression: The issue here has do with the iterative algorithm used to solve nonlinear stationary models. The algorithm is, generally speaking, a Newton's method approach. This is relatively expensive to do, but will lead to the most robust convergence. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. COMSOL makes every reasonable effort to verify the information you view on this page. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. Screenshot showing a Solver Configuration that has been altered. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. Your Discussion has gone 30 days without a reply. Linear solvers.