Multiphysics problems are often nonlinear. listed if standards is not an option). This guide applies solely to nonlinear stationary models. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. 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. What is \newluafunction? A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. 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. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Top 10 Best Stationary Stores in Brea, CA - December 2022 - Yelp You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. In this posting, we introduce the idea of ramping the nonlinearities in the problem to improve convergence. Check the solver log to see if the continuation method is backtracking. 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. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. If it does so, use a finer increment in that range. Not meshing all the domains. It is also possible to manually refine the mesh. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. However, it is usually not possible to know this ahead of time. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Note: there is no way to couple this field with the time dependent nature of this physics. COMSOL makes every reasonable effort to verify the information you view on this page. 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. - Here, we will examine techniques for accelerating the convergence of these two methods. Alternatively, delete and re-create the study. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Posted 26 set 2019, 11:57 GMT-4 3. [COMSOL_Users] output of stationary solver as input to time-dependent Could you expand a little bit more why the coupling is impossible? They are usually called comp1.u, comp1.v, and comp1.w though. 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. Understanding stationary and time dependent solver COMSOL Multiphysics The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Cooling and Solidification of Metal. If you define this nonlinearity ramping such that the first case (P=0) is a purely linear problem, then you are guaranteed to get a solution for this first step in the ramping. 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. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. 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. Then use this file to provide the initial conditions in time dependent model. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? The technique of load ramping is not always reasonable for all problems. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. It is sometimes necessary to manually scale the dependent variables. The Fully Coupled solution approach, with the Plot While Solving enabled. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. What are people saying about cards & stationery in Brea, CA? If you have both as steps in the same study, then solve that study. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. 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. Stationary Solver - COMSOL Multiphysics Trying to understand how to get this basic Fourier Series. 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. If it does so, use a finer increment in that range. Improving Convergence of Nonlinear Stationary Models - Informazioni Repeat this for every nonlinearity of the model. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) 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. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) The idea behind the GCRO-DR method is to retain the subspace determined while solving previous systems and use it to reduce the cost of solving the next system. Function: / Failed to evaluate expression. Thanks for contributing an answer to Stack Overflow! I have searched all over comsol forum to fix this stationary solver configuration and still doesn't work because I don't know the logic behind the solver system. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. 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. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. See Knowledge Base 1240: Manually Setting the Scaling of Variables. 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. The advantages of the continuation method are two-fold. Unknown function or operator. (I am begginer in comsol) Thank you. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version However, load ramping will not work in all cases, or may be inefficient. When the difference in the computed solutions between successive iterations is sufficiently small, or when the residual is sufficiently small, the problem is considered converged to within the specified tolerance. Get email updates for new Stationary Engineer jobs in Brea, California, United States. It may also reveal that the model itself is ill-posed in some way. 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. Stationary (time-invariant) models with nonlinearities may converge very slowly. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. (Frequency Domain should be the last step) It may also reveal that the model itself is ill-posed in some way. Repeat this for every nonlinearity of the model. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. Most multiphysics problems are nonlinear. This case is generally difficult, or impossible, to solve since this material property is non-smooth. Why? Please dont hesitate to post comments below or send emails to us if you experience any other problems. Your email address will not be published. As part of our solver blog series we have discussed solving nonlinear static finite element problems, load ramping for improving convergence of nonlinear problems, and nonlinearity ramping for improving convergence of nonlinear problems. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. 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. When the difference in the computed solutions between successive iterations is sufficiently small, or when the residual is sufficiently small, the problem is considered converged to within the specified tolerance. Name: actdep_int1, Your email address will not be published. Again, introduce a Global Parameter that gets ramped from exactly zero to one. Top 10 Best Stationary in Brea, CA - October 2022 - Yelp With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Why doesn't iterative solver converge in COMSOL? - ResearchGate Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. 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. An example would be a linear static structural model of an aluminum beverage can. Repeat this for every nonlinearity of the model. By default, the COMSOL Multiphysics software determines these values heuristically depending on the physics as, for example, the specified initial values or a solution from an earlier study step. listed if standards is not an option). This solver is automatically used when a Stationary or Frequency Domain study is added to the model. Such problems must solved in the time domain. First, it is physically intuitive, often matching how one would perform an experiment. - To switch between these solver types, go to the Stationary Solver node within the Study sequence. In such cases, see if one material (or the other) can be omitted from the analysis completely. Can I tell police to wait and call a lawyer when served with a search warrant? Your internet explorer is in compatibility mode and may not be displaying the website correctly. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. This involves a systematic reduction in the model complexity. I am solving a linear stationary finite element model but the software is not solving. It is also possible to manually refine the mesh. However, it is usually not possible to know this ahead of time. Your internet explorer is in compatibility mode and may not be displaying the website correctly. There will always already be either a Segregated or Fully Coupled feature beneath this. This involves a systematic reduction in the model complexity. The Fully Coupled solution approach, with the Plot While Solving enabled. 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. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. Find centralized, trusted content and collaborate around the technologies you use most. November 11, 2013. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) First, it is physically intuitive, often matching how one would perform an experiment. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) 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. See Knowledge Base 1240: Manually Setting the Scaling of Variables. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. Minimising the environmental effects of my dyson brain. The fully coupled and segregated approaches are discussed below. 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. -Detail: NaN or Inf found when solving linear system using SOR. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. This consent may be withdrawn. Consult your product manuals for complete trademark details. Can someone help me fix the COMSOL error below? | ResearchGate Learn how your comment data is processed. Direct Iterative , Direct . There will always already be either a Segregated or Fully Coupled feature beneath this. The segregated approach, on the other hand, solves sets of unknowns separately. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Connect and share knowledge within a single location that is structured and easy to search. The segregated approach, on the other hand, solves sets of unknowns separately. Your Discussion has gone 30 days without a reply. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Common Mistakes: Not assigning materials to all the domains. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). listed if standards is not an option). About the Stationary Solver - COMSOL Multiphysics An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Is it possible to rotate a window 90 degrees if it has the same length and width? Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. Click the link in the email we sent to to verify your email address and activate your job alert. - Why do many companies reject expired SSL certificates as bugs in bug bounties? k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Note the star symbol on the Solution feature. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. 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. What is the purpose of non-series Shimano components? Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. 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. 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. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. listed if standards is not an option). That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. If you see this, right-click on the Solution feature and select Reset Solver to Default. Does anyone know what should cause this problem? Multiphysics problems are often nonlinear. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version The issue here has do with the iterative algorithm used to solve nonlinear stationary models. listed if standards is not an option). 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. 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. When the difference in the computed solutions between successive iterations is sufficiently small, or when the residual is sufficiently small, the problem is considered converged to within the specified tolerance. COMSOL does not assume any legal liability for the accuracy of the data disclosed. How to solve "Feature: Stationary Solver 1 (sol1/s1) Attempt - COMSOL The difference between the phonemes /p/ and /b/ in Japanese. Wrong ordering of study steps. Mesh To switch between these solver types, go to the Stationary Solver node within the Study sequence. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. The algorithm is, generally speaking, a Newton's method approach. Cooling and Solidification of Metal. Not meshing all the domains. 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. - Function: ^ Failed to evaluate variable. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. 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. 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. This involves a systematic reduction in the model complexity. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. Linear solvers. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. New Stationary Engineer jobs added daily. The settings controlling the predictor type. 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. GCRO-DR is a method for Krylov subspace recycling. Common Errors in Comsol - P&S: COMSOL Design Tool for Photonic Devices numeric (each ports needs their ownboundary mode analysis in the study if they are numerically defined)Wave excitation: on/off(input/output), - Feature: Stationary Solver 1 (sol1/s1) Division by zero. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. Specify Material Properties in COMSOL Multiphysics (3/8) You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version The default Initial Values for the unknowns in most physics interfaces are zero.