stationary solver comsol

That is, they are tuned to achieve convergence in as many cases as possible. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. The coupling terms between the different groups are thus neglected. Hi Jason, Not meshing all the domains. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. 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. We use COMSOL Multiphysics for solving distributed optimal control of un-steady Burgers equation without constraints and with pointwise control constraints. Posted Sep 9, 2020, 1:44 p.m. EDT That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. The Fully Coupled solution approach, with the Plot While Solving enabled. 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. It may also reveal that the model itself is ill-posed in some way. The coupling terms between the different groups are thus neglected. Is it possible to rotate a window 90 degrees if it has the same length and width? 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. It is sometimes necessary to manually scale the dependent variables. This is relatively expensive to do, but will lead to the most robust convergence. COMSOL makes every reasonable effort to verify the information you view on this page. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. 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. Solve the stationary study then the time dependent study. I personally liked emailing them the file, ", "This flower shop is the best! This solver is automatically used when a Stationary or Frequency Domain study is added to the model. 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 Fully Coupled solution approach, with the Plot While Solving enabled. This guide applies solely to nonlinear stationary models. Not assigning proper boundary conditions: Especially if you have ports. Consult your product manuals for complete trademark details. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model 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. 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 objective here is to simplify the model to a state where the model will solve, with linear approximations. Screenshot showing a Solver Configuration that has been altered. 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. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. Not assigning proper boundary conditions: Especially if you have ports. However, it is usually not possible to know this ahead of time. listed if standards is not an option). From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. Hence Comsol solved for the stationary solution at different points of time. listed if standards is not an option). Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. thanks for reply Stationary (time-invariant) models with nonlinearities may converge very slowly. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Computational Fluid Dynamics (CFD), API $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. 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. Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble 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. 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. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Find centralized, trusted content and collaborate around the technologies you use most. Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. 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. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Why? 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 you have both as steps in the same study, then solve that study. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Cecilia M. came from the backroom to help me and went out of her way to help me even though I had not called before going into the store. Discussion Closed This discussion was created more than 6 months ago and has been closed. Making statements based on opinion; back them up with references or personal experience. 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. - Cooling and Solidification of Metal. 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. Then use this file to provide the initial conditions in time dependent model. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. Stationary (time-invariant) models with nonlinearities may converge very slowly. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 Trying to understand how to get this basic Fourier Series. Comsol help video number 2: Solving a laminar flow problem in a slit.. 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. Why is there a voltage on my HDMI and coaxial cables? 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. It is also possible to manually refine the mesh. 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. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. (Frequency Domain should be the last step) P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. Save my name, email, and website in this browser for the next time I comment. That is, start by first solving a model with a small, but non-zero, load. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Your internet explorer is in compatibility mode and may not be displaying the website correctly. This case is generally difficult, or impossible, to solve since this material property is non-smooth. Thanks for contributing an answer to Stack Overflow! By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. Check the solver log to see if the continuation method is backtracking. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. This approach is known as a Continuation Method with a Constant predictor. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Use this parameter to modify the nonlinearity expressions in the model. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. 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. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Check the solver log to see if the continuation method is backtracking. 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. To switch between these solver types, go to the Stationary Solver node within the Study sequence. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. 3 Replies, Please login with a confirmed email address before reporting spam. 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. So far, weve learned how to mesh and solve linear and nonlinear single-physics finite element problems, but have not yet considered what happens when there are multiple different interdependent physics being solved within the same domain. Such problems must solved in the time domain. What is \newluafunction? k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Function: / Failed to evaluate expression. Again, introduce a Global Parameter that gets ramped from exactly zero to one. 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. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. This case is generally difficult, or impossible, to solve since this material property is non-smooth. 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. Perhaps this approach could be adapted to represent your model. $130,000.00. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. This involves a systematic reduction in the model complexity. 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. If it does so, use a finer increment in that range. COMSOL makes every reasonable effort to verify the information you view on this page. "I chose this print shop based off yelp reviews and was very happy with the outcome! This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. 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. Understanding the Fully Coupled vs. GCRO-DR is a method for Krylov subspace recycling. In this page, we will be sharing some common errors that might occur in Comsol and their solutions. However, it is usually not possible to know this ahead of time. It is also possible to manually refine the mesh. The fully coupled and segregated approaches are discussed below. listed if standards is not an option). "After the incident", I started to be more careful not to trip over things. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. This case is generally difficult, or impossible, to solve since this material property is non-smooth. 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. To start a new discussion with a link back to this one, click here. The settings controlling the predictor type. 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. 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. This approach is known as a Continuation Method with a Constant predictor. 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. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Posted 26 set 2019, 11:57 GMT-4 I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary model. Here we introduce a more robust approach to solving nonlinear problems. 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 such cases, use the same continuation method, but instead ramp the nonlinearities in the model. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. There will always already be either a Segregated or Fully Coupled feature beneath this. Minimising the environmental effects of my dyson brain. 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. If you are unsure if your problem is linear and stationary, look at the Log. 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. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. 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. Could you expand a little bit more why the coupling is impossible? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. 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. 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. 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. See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. 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. For the Nozomi from Shinagawa to Osaka, say on a Saturday afternoon, would tickets/seats typically be available - or would you need to book? Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. These can be used alone, or in combination with other interfaces. 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. Asking for help, clarification, or responding to other answers. 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.) I highly recommend this flower shop. Perhaps this approach could be adapted to represent your model. There will also be a red cross over the Materials branch icon. COMSOL does not assume any legal liability for the accuracy of the data disclosed. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. The algorithm is, generally speaking, a Newton's method approach. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) Common Mistakes: Not assigning materials to all the domains. 0 Replies, Please login with a confirmed email address before reporting spam. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. That is, start by first solving a model with a small, but non-zero, load. rev2023.3.3.43278. Any trademarks referenced in this document are the property of their respective owners. Not the answer you're looking for? Mesh 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. Feature: Stationary Solver 1 (sol1/s1)" . Multiphysics problems are often nonlinear. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. For example, if there is a temperature-dependent material property such as: Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. 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. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. Note: there is no way to couple this . In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. 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. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. How can I use it? As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Segregated approach and Direct vs. Set initial conditions in the physics to the appropriate dependent model variable names rather than the default 0. 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. 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. How can I check before my flight that the cloud separation requirements in VFR flight rules are met? 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. 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. 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 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. Solver . Not entering required material parameters. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Can I tell police to wait and call a lawyer when served with a search warrant? 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. That is, they are tuned to achieve convergence in as many cases as possible. COMSOL 22.9K subscribers Adding a study to your simulation is necessary in order to solve your problem. Multiphysics problems are often nonlinear. 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. To switch between these solver types, go to the Stationary Solver node within the Study sequence. It is sometimes necessary to manually scale the dependent variables. As we saw previously in the blog entry on Solving Nonlinear Static Finite Element Problems, not all nonlinear problems will be solvable via the damped Newton-Raphson method. 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. Review the model setup to resolve these. Acidity of alcohols and basicity of amines. - the incident has nothing to do with me; can I use this this way? However, it is usually not possible to know this ahead of time. Please dont hesitate to post comments below or send emails to us if you experience any other problems. Linear solvers. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. 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. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. Full text of the 'Sri Mahalakshmi Dhyanam & Stotram'. 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. replace it with the expression: Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. I am trying to solve the coupling between a waveguide and a microring resonator. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. 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. 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. Your email address will not be published. She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. In such cases, see if one material (or the other) can be omitted from the analysis completely. How do/should administrators estimate the cost of producing an online introductory mathematics class? Stationary Solver Iterative Direct . If it does so, use a finer increment in that range. Studysteps might be listed in wrong order: Not assigning materials to all the domains. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Contact COMSOL at Bangalore on their telephone: +9180 25323003. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. They are usually called comp1.u, comp1.v, and comp1.w though. They deal with COMSOL package and train users. Wrong ordering of study steps. What are some highly rated cards & stationery in Brea, CA? 3. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. These are some cards & stationery with a large number of reviews in Brea, CA.