stationary solver comsol

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. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Your internet explorer is in compatibility mode and may not be displaying the website correctly. That is, they are tuned to achieve convergence in as many cases as possible. 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. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. "After the incident", I started to be more careful not to trip over things. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. To switch between these solver types, go to the Stationary Solver node within the Study sequence. 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. The Fully Coupled solution approach, with the Plot While Solving enabled. 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. Computational Fluid Dynamics (CFD), API This is relatively expensive to do, but will lead to the most robust convergence. 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 segregated approach, on the other hand, solves sets of unknowns separately. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Review the model setup to resolve these. Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble If so, see: Knowledgebase 1030: Error: "Out of memory". Why? You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. . If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 The default Initial Values for the unknowns in most physics interfaces are zero. The advantages of the continuation method are two-fold. 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. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie 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. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. The other low-level default settings within the Stationary Solver are chosen for robustness. The segregated approach, on the other hand, solves sets of unknowns separately. 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. Multiphysics problems are often nonlinear. For example, if there is a temperature-dependent material property such as: Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: 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. Any trademarks referenced in this document are the property of their respective owners. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. 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. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) COMSOL makes every reasonable effort to verify the information you view on this page. . COMSOL 22.9K subscribers Adding a study to your simulation is necessary in order to solve your problem. What is the purpose of non-series Shimano components? Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. Note: there is no way to couple this . Check the solver log to see if the continuation method is backtracking. 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. They worked with me. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version It is also possible to manually refine the mesh. Get email updates for new Stationary Engineer jobs in Brea, California, United States. 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. Please dont hesitate to post comments below or send emails to us if you experience any other problems. Leverage your professional network, and get hired. 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. I personally liked emailing them the file, ", "This flower shop is the best! The issue here has do with the iterative algorithm used to solve nonlinear stationary models. The settings controlling the predictor type. rev2023.3.3.43278. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. 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 Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. The default Initial Values for the unknowns in most physics interfaces are zero. Multiscale Modeling in High-Frequency Electromagnetics. It may also reveal that the model itself is ill-posed in some way. - An example would be a linear static structural model of an aluminum beverage can. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. 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. $140,000.00, $120,000.00 Could you expand a little bit more why the coupling is impossible? Use this parameter to modify the nonlinearity expressions in the model. Click the link in the email we sent to to verify your email address and activate your job alert. COMSOL does not assume any legal liability for the accuracy of the data disclosed. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. 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. Hello guys. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 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. 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. If you are unsure if your problem is linear and stationary, look at the Log. This is relatively expensive to do, but will lead to the most robust convergence. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. To switch between these solver types, go to the Stationary Solver node within the Study sequence. If your matrix is singular than no solver in the world can solve Ax=B. Segregated approach and Direct vs. It is also possible to manually refine the mesh. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) There are also cases when an extremely poor quality mesh leads to an ill-conditioned problem, This issue often arises in combination with, and as a consequence of, geometries that have extreme aspect ratios. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) This case is generally difficult, or impossible, to solve since this material property is non-smooth. Create the time-dependent step or study. It is sometimes necessary to manually scale the dependent variables. This guide applies solely to nonlinear stationary models. 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. Save this information to a file. There will always already be either a Segregated or Fully Coupled feature beneath this. How can I check before my flight that the cloud separation requirements in VFR flight rules are met? Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. 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. However, it is usually not possible to know this ahead of time. 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. 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. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Again, introduce a Global Parameter that gets ramped from exactly zero to one. The coupling terms between the different groups are thus neglected. ", "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. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. 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. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. Cooling and Solidification of Metal. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a 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. Multiphysics problems are often nonlinear. It is sometimes necessary to manually scale the dependent variables. The coupling terms between the different groups are thus neglected. The coupling terms between the different groups are thus neglected. How can I use it? Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. 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. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. 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. Feature: Stationary Solver 1 (sol1/s1)" . The default Initial Values for the unknowns in most physics interfaces are zero. 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. The other low-level default settings within the Stationary Solver are chosen for robustness. Not meshing all the domains. The objective here is to simplify the model to a state where the model will solve, with linear approximations. We use COMSOL Multiphysics for solving distributed optimal control of un-steady Burgers equation without constraints and with pointwise control constraints. 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. 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. 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. 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. Any trademarks referenced in this document are the property of their respective owners. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. This algorithm was also useful for understanding what happens near a failure load. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. 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. Wrong ordering of study steps. How do/should administrators estimate the cost of producing an online introductory mathematics class? 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. This doesn't seem to me the most elegant of methods, since I am essentially solving a stationary solution using a time dependent In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. There will always already be either a Segregated or Fully Coupled feature beneath this. It may also reveal that the model itself is ill-posed in some way. 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. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. Your Discussion has gone 30 days without a reply. 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. 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. Such problems must solved in the time domain. Some models are numerically ill-conditioned due to the setup. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. 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. 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. This involves a systematic reduction in the model complexity. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. Why do many companies reject expired SSL certificates as bugs in bug bounties? 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. 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. 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. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. 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. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. To learn more, see our tips on writing great answers. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Does anyone know what should cause this problem? 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. 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. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. - Function: ^ Failed to evaluate variable. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. 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. However, load ramping will not work in all cases, or may be inefficient. The segregated approach, on the other hand, solves sets of unknowns separately. 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. Hi ! This involves a systematic reduction in the model complexity. so many cute little stationary items , hair". You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version These can be used alone, or in combination with other interfaces. replace it with the expression: Hence Comsol solved for the stationary solution at different points of time. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. In this posting, we introduce the idea of ramping the nonlinearities in the problem to improve convergence. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. 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.) COMSOL does not assume any legal liability for the accuracy of the data disclosed. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. 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. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. 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. I use comsol multiphysics 5.2a and . Discussion Closed This discussion was created more than 6 months ago and has been closed. 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. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Note the star symbol on the Solution feature. Hello, The technique of load ramping is not always reasonable for all problems. listed if standards is not an option). (I am begginer in comsol) Thank you. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. Different physics have different default solvers. replace it with the expression: 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. 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. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Not entering required material parameters. (Frequency Domain should be the last step). Check the solver log to see if the continuation method is backtracking. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. $130,000.00. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. 0 Replies, Please login with a confirmed email address before reporting spam. Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2, Simulation of effect of heated resistance on temperature distribution in laminar flow, COMSOL: Diffusion in Transport of Diluted Species Produces Unphysical Results. Direct PARDISO Solver , PARDISO . In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values.