stationary solver comsolstationary solver comsol
(Frequency Domain should be the last step). The advantages of the continuation method are two-fold. 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. These can be used alone, or in combination with other interfaces. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. 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. Use a manually defined mesh to avoid elements with extreme aspect ratios and perform a mesh refinement study, as described here: Performing a Mesh Refinement Study, For problems that are ill-conditioned, using a direct solver is often called for. This involves a systematic reduction in the model complexity. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. November 11, 2013. 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. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. Direct PARDISO Solver , PARDISO . Reviews on Stationary in Brea, CA - Mievic, Typo, Tokyo Japanese Lifestyle, Fancy, Posh Paper, Morning Glory, Velvet Fox Designs, Barnes & Noble, Michaels, Select Graphics & Printing replace it with the expression: Studysteps might be listed in wrong order: Not assigning materials to all the domains. Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. 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. Comsol help video number 2: Solving a laminar flow problem in a slit.. Function: / Failed to evaluate expression. New Stationary Engineer jobs added daily. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. The other low-level default settings within the Stationary Solver are chosen for robustness. - You can write the discrete form of the equations as f(U) = 0, where f(U) is the residual vector and U is the solution vector. 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. For example, in Solid Mechanics, if the Poisson Ratio set to 0.5, then the model will not solve, as this value in incompatible with the theory of linear elasticity. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: That is, they are tuned to achieve convergence in as many cases as possible. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. This guide applies solely to nonlinear stationary models. 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. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. With respect to any nonlinearities, replace them by a reasonable linearized term. listed if standards is not an option). Changes to these low-level settings from the defaults will usually be quite model- and case-specific. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. 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. listed if standards is not an option). There will always already be either a Segregated or Fully Coupled feature beneath this. 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. See Knowledge Base 1240: Manually Setting the Scaling of Variables. - Feature: Stationary Solver 1 (sol1/s1) Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Use this parameter to modify the nonlinearity expressions in the model. comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. They are usually called comp1.u, comp1.v, and comp1.w though. 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. We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. Trying to understand how to get this basic Fourier Series. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Few days back i was also facing this problem in . 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. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Making statements based on opinion; back them up with references or personal experience. 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 following the same model as Comsol provide us on the web. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Some models are numerically ill-conditioned due to the setup. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Such problems must solved in the time domain. To learn more, see our tips on writing great answers. Iterative , Direct . How can I use it? The solver settings are stored at Study > Solver Configurations > Solution. Wrong ordering of study steps. However, if a lower-level change has been manually made to the solver settings, the software will not automatically use the correct default solver. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. 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. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Stationary in the COMSOL Multiphysics Programming Reference Manual Damped Newton Methods The nonlinear solver uses an affine invariant form of the damped Newton method as described in Ref. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Tutti i diritti sono riservati. To switch between these solver types, go to the Stationary Solver node within the Study sequence. COMSOL makes every reasonable effort to verify the information you view on this page. The problem is that when I run my model this message appear: Undefined value found. For example, if there is a temperature-dependent material property such as: 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. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. I personally liked emailing them the file, ", "This flower shop is the best! 0 Replies, Please login with a confirmed email address before reporting spam. SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Understanding the Fully Coupled vs. This algorithm was also useful for understanding what happens near a failure load. 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. 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. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. 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. 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. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. This case is generally difficult, or impossible, to solve since this material property is non-smooth. Multiphysics problems are often nonlinear. In this posting, we introduce the idea of ramping the nonlinearities in the problem to improve convergence. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. listed if standards is not an option). Not assigning proper boundary conditions: Especially if you have ports. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Common Mistakes: Not assigning materials to all the domains. In a previous blog entry, we introduced meshing considerations for linear static problems. This doesn't seem to me the most elegant of methods, since I am essentially solving a stationary solution using a time dependent 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. Not assigning proper boundary conditions: Especially if you have ports. 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. For example, if there is a temperature-dependent material property such as: 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. Use this parameter to modify the nonlinearity expressions in the model. 3 Replies, Please login with a confirmed email address before reporting spam. If you see this, right-click on the Solution feature and select Reset Solver to Default. 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. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. 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. If you have both as steps in the same study, then solve that study. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. 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. The objective here is to simplify the model to a state where the model will solve, with linear approximations. 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. The advantages of the continuation method are two-fold. 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 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. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Why is there a voltage on my HDMI and coaxial cables? Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Why do many companies reject expired SSL certificates as bugs in bug bounties? The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! However, it is usually not possible to know this ahead of time. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. 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. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. Alternatively, delete and re-create the study. 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. See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. The technique of load ramping is not always reasonable for all problems. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. COMSOL makes every reasonable effort to verify the information you view on this page. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Check the solver log to see if the continuation method is backtracking. This consent may be withdrawn. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 The objective here is to simplify the model to a state where the model will solve, with linear approximations. Solver . The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. We use COMSOL Multiphysics for solving distributed optimal control of un-steady Burgers equation without constraints and with pointwise control constraints. 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. Today's top 351 Stationary Engineer jobs in Brea, California, United States. Not entering required material parameters. COMSOL does not assume any legal liability for the accuracy of the data disclosed. The coupling terms between the different groups are thus neglected. Create the time-dependent step or study. 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. Is it possible to rotate a window 90 degrees if it has the same length and width? For the Nozomi from Shinagawa to Osaka, say on a Saturday afternoon, would tickets/seats typically be available - or would you need to book? This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Cooling and Solidification of Metal. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. Again, introduce a Global Parameter that gets ramped from exactly zero to one. 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. That is, they are tuned to achieve convergence in as many cases as possible. Segregated approach and Direct vs. Stationary (time-invariant) models with nonlinearities may converge very slowly. In this page, we will be sharing some common errors that might occur in Comsol and their solutions. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) To switch between these solver types, go to the Stationary Solver node within the Study sequence. Find centralized, trusted content and collaborate around the technologies you use most. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. Thanks, Andres. The Fully Coupled solution approach, with the Plot While Solving enabled. This involves a systematic reduction in the model complexity. Solve the stationary study then the time dependent study. How can I check before my flight that the cloud separation requirements in VFR flight rules are met? Cooling and Solidification of Metal. 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. There will also be a red cross over the Materials branch icon. Segregated approach and Direct vs. Iterative linear solvers, Time dependent function and stationary study, Combining Adaptive Mesh Refinement with Data Filtering, What to do when a linear stationary model is not solving, Galleria dei Modelli e delle App di Simulazione, 2023 da COMSOL. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. listed if standards is not an option). With respect to any nonlinearities, replace them by a reasonable linearized term. rev2023.3.3.43278. That is: Even if the forces on a part are opposite and equal, this is not sufficient information to say where the part is, so you must add some other condition, such as as Fixed Constraint to constrain displacement. 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. Hello, When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Note: there is no way to couple this field with the time dependent nature of this physics. Get notified about new Stationary Engineer jobs in Brea, California, United States. 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. Multiscale Modeling in High-Frequency Electromagnetics. Using the first order optimality. Consult your product manuals for complete trademark details. What version of COMSOL are you using? Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. 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. COMSOL does not assume any legal liability for the accuracy of the data disclosed. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. It is sometimes necessary to manually scale the dependent variables. Discussion Closed This discussion was created more than 6 months ago and has been closed. Review the model setup to resolve these. 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. Any trademarks referenced in this document are the property of their respective owners. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. The default Initial Values for the unknowns in most physics interfaces are zero. - The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. This information is presented in the context of a very simple 1D finite element problem, and builds upon our previous entry on Solving Linear Static Finite Element Models. 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. This approach is known as a Continuation Method with a Constant predictor. - Function: ^ Failed to evaluate variable. 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. 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. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 Cooling and Solidification of Metal. That is, start by first solving a model with a small, but non-zero, load. 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. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Posted 26 set 2019, 11:57 GMT-4 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 Auxiliary Sweep can be used to implement ramping of any Global Parameter. Stationary (time-invariant) models with nonlinearities may converge very slowly. It is also possible to manually refine the mesh. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. COMSOL 22.9K subscribers Adding a study to your simulation is necessary in order to solve your problem. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. What are people saying about cards & stationery in Brea, CA? This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. The conditions on the geometric aspect ratio are relatively more strict. 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. 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. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. - 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. 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. With respect to any nonlinearities, replace them by a reasonable linearized term. 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. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. These are some cards & stationery with a large number of reviews in Brea, CA. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. (I am begginer in comsol) Thank you. See Knowledge Base 1240: Manually Setting the Scaling of Variables. Contact COMSOL at Bangalore on their telephone: +9180 25323003. 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. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. 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. 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.
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