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Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. This doesn't seem to me the most elegant of methods, since I am essentially solving a stationary solution using a time dependent listed if standards is not an option). Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. If your matrix is singular than no solver in the world can solve Ax=B. Why is there a voltage on my HDMI and coaxial cables? Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. They deal with COMSOL package and train users. What are some highly rated cards & stationery in Brea, CA? Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. The fully coupled and segregated approaches are discussed below. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. 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. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. 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. However, if a lower-level change has been manually made to the solver settings, the software will not automatically use the correct default solver. This case is generally difficult, or impossible, to solve since this material property is non-smooth. 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. Such problems must solved in the time domain. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. replace it with the expression: For example, in a Solid Mechanics (wherein the software is solving for the displacement field within the solid) applying two opposite and equal Boundary Load conditions on a part is not sufficient to define the displacement. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: In such cases, see if one material (or the other) can be omitted from the analysis completely. Have you taken a look at this blog post? This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) I personally liked emailing them the file, ", "This flower shop is the best! Full text of the 'Sri Mahalakshmi Dhyanam & Stotram'. Hello, Using the first order optimality. 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. Here we introduce a more robust approach to solving nonlinear problems. Stationary Solver Iterative Direct . Wish you all the best. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 However, it is usually not possible to know this ahead of time. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. 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. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. 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. Connect and share knowledge within a single location that is structured and easy to search. 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. Not entering required material parameters. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. - Function: ^ Failed to evaluate variable. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. Hi ! listed if standards is not an option). 3 Replies, Please login with a confirmed email address before reporting spam. 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. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. I use comsol multiphysics 5.2a and . 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. The settings controlling the predictor type. Common Mistakes: Not assigning materials to all the domains. 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. COMSOL Error for Initial Values(RF Module) 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. - Your internet explorer is in compatibility mode and may not be displaying the website correctly. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. To switch between these solver types, go to the Stationary Solver node within the Study sequence. 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. The segregated approach, on the other hand, solves sets of unknowns separately. 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. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. The coupling terms between the different groups are thus neglected. The Fully Coupled solution approach, with the Plot While Solving enabled. Not the answer you're looking for? k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . See Knowledge Base 1240: Manually Setting the Scaling of Variables. In this blog post we introduce the two classes of algorithms that are used in COMSOL to solve systems of linear equations that arise when solving any finite element problem. Understanding the Fully Coupled vs. How can I use it? Feature: Stationary Solver 1 (sol1/s1)" . document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. The advantages of the continuation method are two-fold. To learn more, see our tips on writing great answers. Why do many companies reject expired SSL certificates as bugs in bug bounties? COMSOL Blog Series on COMSOL Multiphysics Solvers Set initial conditions in the physics to the appropriate dependent model variable names rather than the default 0. About the Stationary Solver - COMSOL Multiphysics What are people saying about cards & stationery in Brea, CA? In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems. Consult your product manuals for complete trademark details. 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. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. 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, Galleria dei Modelli e delle App di Simulazione, 2023 da COMSOL. Name: actdep_int1, Your email address will not be published. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) 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. Why? Improving Convergence of Nonlinear Stationary Models - COMSOL Unknown function or operator. Not meshing all the domains. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. - The settings controlling the predictor type. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. It may also reveal that the model itself is ill-posed in some way. Common Mistakes: Not assigning materials to all the domains. Your internet explorer is in compatibility mode and may not be displaying the website correctly. With respect to any nonlinearities, replace them by a reasonable linearized term. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Understanding stationary and time dependent solver COMSOL Multiphysics Do you also know how to solve this problem: using stationary solution as the initial conditions in time dependent model, How Intuit democratizes AI development across teams through reusability. Alternatively, delete and re-create the study. Trying to understand how to get this basic Fourier Series. 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. P&S: COMSOL Design Tool for Photonic Devices. If so, see: Knowledgebase 1030: Error: "Out of memory". Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. 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. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Multiscale Modeling in High-Frequency Electromagnetics. However, it is usually not possible to know this ahead of time. Cooling and Solidification of Metal. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Different physics have different default solvers. 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. They are usually called comp1.u, comp1.v, and comp1.w though. Improving Convergence of Nonlinear Stationary Models - Informazioni I am following the same model as Comsol provide us on the web. 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. That is, start by first solving a model with a small, but non-zero, load. If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. This case is generally difficult, or impossible, to solve since this material property is non-smooth. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Common Errors in Comsol - P&S: COMSOL Design Tool for Photonic Devices Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. The other low-level default settings within the Stationary Solver are chosen for robustness. A linear finite element model is one in which all of the material properties, loads, boundary conditions, etc are constant with respect to the solution, and the governing partial differential equations are themselves linear. An example would be a linear static structural model of an aluminum beverage can. 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. This approach is known as a Continuation Method with a Constant predictor. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Posted Sep 9, 2020, 1:44 p.m. EDT Not assigning proper boundary conditions: Especially if you have ports. 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. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 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. 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. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. -Detail: NaN or Inf found when solving linear system using SOR. Could you expand a little bit more why the coupling is impossible? Can someone help me fix the COMSOL error below? | ResearchGate The Auxiliary Sweep can be used to implement ramping of any Global Parameter. If it does so, use a finer increment in that range. listed if standards is not an option). 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. The default Initial Values for the unknowns in most physics interfaces are zero. COMSOL makes every reasonable effort to verify the information you view on this page. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Is there a way to use the stationary solution obtained in Comsol 4.2 as the initial conditions in a time dependent model? Get email updates for new Stationary Engineer jobs in Brea, California, United States. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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. Function: / Failed to evaluate expression. About the Stationary Solver - COMSOL Multiphysics 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. Hi Jason, I am solving a linear stationary finite element model but the software is not solving. 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. For example, in an Electric Currents problem, you may want to consider a system of materials including a good conductor such as copper (with an electric conductivity of ~6e7 S/m) and an insulative material such as glass (which can have electric conductivity of ~1e-14 S/m.) 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 guide applies solely to nonlinear stationary models. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) Get notified about new Stationary Engineer jobs in Brea, California, United States. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Here, we will examine techniques for accelerating the convergence of these two methods. 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. 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! Acidity of alcohols and basicity of amines. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Mesh Top 10 Best Stationary Stores in Brea, CA - December 2022 - Yelp Such a large difference in the materials properties can be challenging. Such problems must solved in the time domain. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. 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. Discussion Closed This discussion was created more than 6 months ago and has been closed. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. Sign in to create your job alert for Stationary Engineer jobs in Brea, California, United States. Understanding the Fully Coupled vs. ", "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. 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. To switch between these solver types, go to the Stationary Solver node within the Study sequence. What version of COMSOL are you using? These are some cards & stationery with a large number of reviews in Brea, CA. The default Initial Values for the unknowns in most physics interfaces are zero. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. This is relatively expensive to do, but will lead to the most robust convergence. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Asking for help, clarification, or responding to other answers. Today's top 351 Stationary Engineer jobs in Brea, California, United States. If it does so, use a finer increment in that range. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Linear solvers. Review the model setup to resolve these. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. To switch between these solver types, go to the Stationary Solver node within the Study sequence. Multiphysics problems are often nonlinear. COMSOL does not assume any legal liability for the accuracy of the data disclosed. That is: It is also possible to compute the derivative of the solution with respect to the continuation parameter and use that derivative (evaluated at the iteration) to compute a new initial value: where is the stepsize of the continuation parameter. Not assigning proper boundary conditions: Especially if you have ports. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. There will also be a red cross over the Materials branch icon. 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. Again, introduce a Global Parameter that gets ramped from exactly zero to one. Also, keep in mind that a linear stationary model should solve regardless of how coarse the mesh is (albeit to a low accuracy) so you can always start with as coarse a mesh as possible, and refine the mesh (See also: Knowledgebase 1030: Performing a Mesh Refinement Study. This is a review for cards & stationery in Brea, CA: "Love this store!!! This is relatively expensive to do, but will lead to the most robust convergence. There will always already be either a Segregated or Fully Coupled feature beneath this. She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. The advantages of the continuation method are two-fold. replace it with the expression: Second, the continuation method will automatically take smaller load increments if a solution cannot be found. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. That is, they are tuned to achieve convergence in as many cases as possible. 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. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. That is, start by first solving a model with a small, but non-zero, load. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Solve the stationary study then the time dependent study. The technique of load ramping is not always reasonable for all problems. Can I tell police to wait and call a lawyer when served with a search warrant? In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. . Any trademarks referenced in this document are the property of their respective owners. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Computational Fluid Dynamics (CFD), API 351 Stationary Engineer jobs in Brea, California, United States (15 new) if I want to do an adaptive mesh refinement, I get this error. 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. - Feature: Stationary Solver 1 (sol1/s1) The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. Perhaps this approach could be adapted to represent your model. Common Study Step Settings - COMSOL Multiphysics In this posting, we introduce the idea of ramping the nonlinearities in the problem to improve convergence. The Fully Coupled solution approach, with the Plot While Solving enabled. COMSOL does not assume any legal liability for the accuracy of the data disclosed. That is, they are tuned to achieve convergence in as many cases as possible. 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. Comsol help video number 2: Solving a laminar flow problem in a slit.. 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. If you have both as steps in the same study, then solve that study. This involves a systematic reduction in the model complexity. That is, start by first solving a model with a small, but non-zero, load. It is sometimes necessary to manually scale the dependent variables. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Tutti i diritti sono riservati. 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. As a second example, when solving for Electric Currents, do not model perfect electrical insulators as materials with zero conductivity, instead, omit the domain from the model and use the Electric Insulation boundary condition. 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.