However, it is usually not possible to know this ahead of time. 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. Multiphysics problems are often nonlinear. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Trying to understand how to get this basic Fourier Series. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Note: there is no way to couple this . Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. 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. 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. Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. Direct PARDISO Solver , PARDISO . Second, the continuation method will automatically take smaller load increments if a solution cannot be found. These are some cards & stationery with a large number of reviews in Brea, CA. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 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 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. 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. Required fields are marked *. 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. The settings controlling the predictor type. 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. 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. It may also reveal that the model itself is ill-posed in some way. 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. 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. Not meshing all the domains. For example, if there is a temperature-dependent material property such as: Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. For example, if there is a temperature-dependent material property such as: The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. 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. There will always already be either a Segregated or Fully Coupled feature beneath this. 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. 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. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. 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. 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. 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. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. The segregated approach, on the other hand, solves sets of unknowns separately. listed if standards is not an option). It is also possible to manually refine the mesh. That is, start by first solving a model with a small, but non-zero, load. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: In a previous blog entry, we introduced meshing considerations for linear static problems. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. - the incident has nothing to do with me; can I use this this way? Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. In our previous blog entry, we introduced the Fully Coupled and the Segregated algorithms used for solving steady-state multiphysics problems in COMSOL. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. 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 See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. The advantages of the continuation method are two-fold. For example, if there is a temperature-dependent material property such as: This case is generally difficult, or impossible, to solve since this material property is non-smooth. Save my name, email, and website in this browser for the next time I comment. Consult your product manuals for complete trademark details. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. - Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. Any trademarks referenced in this document are the property of their respective owners. The coupling terms between the different groups are thus neglected. This involves a systematic reduction in the model complexity. Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. 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. 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. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Hi ! 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. First, it is physically intuitive, often matching how one would perform an experiment. replace it with the expression: 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. 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. 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. 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. With respect to any nonlinearities, replace them by a reasonable linearized term. Reply . 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. Mesh With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. This is a review for cards & stationery in Brea, CA: "Love this store!!! Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Consult your product manuals for complete trademark details. 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. Repeat this for every nonlinearity of the model. 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. Computational Fluid Dynamics (CFD), API That is, they are tuned to achieve convergence in as many cases as possible. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. 3. rev2023.3.3.43278. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. 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. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. There will always already be either a Segregated or Fully Coupled feature beneath this. Tutti i diritti sono riservati. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. Check the solver log to see if the continuation method is backtracking. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. If you are unsure if your problem is linear and stationary, look at the Log. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Cooling and Solidification of Metal. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). "I chose this print shop based off yelp reviews and was very happy with the outcome! P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. 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. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. 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 email address will not be published. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. If you see this, right-click on the Solution feature and select Reset Solver to Default. With respect to any nonlinearities, replace them by a reasonable linearized term. Solve the stationary study then the time dependent study. The segregated approach, on the other hand, solves sets of unknowns separately. To start a new discussion with a link back to this one, click here. Stationary Solver Iterative Direct . Note: there is no way to couple this field with the time dependent nature of this physics. In this posting, we introduce the idea of ramping the nonlinearities in the problem to improve convergence. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Direct Iterative , Direct . k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Hi Alexis, A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. 3 Replies, Please login with a confirmed email address before reporting spam. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. I am trying to solve the coupling between a waveguide and a microring resonator. Linear solvers. Linear solvers. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Not the answer you're looking for? 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. Here, we will examine techniques for accelerating the convergence of these two methods. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. However, it is usually not possible to know this ahead of time. COMSOL makes every reasonable effort to verify the information you view on this page. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Multiphysics problems are often nonlinear. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 Multiphysics problems are often nonlinear. 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 settings controlling the predictor type. 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. listed if standards is not an option). It is sometimes necessary to manually scale the dependent variables. The other low-level default settings within the Stationary Solver are chosen for robustness. Please dont hesitate to post comments below or send emails to us if you experience any other problems. listed if standards is not an option). Why is there a voltage on my HDMI and coaxial cables? SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Screenshot showing a Solver Configuration that has been altered. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Wrong ordering of study steps. To learn more, see our tips on writing great answers. The coupling terms between the different groups are thus neglected. (Frequency Domain should be the last step). Understanding the Fully Coupled vs. Get notified about new Stationary Engineer jobs in Brea, California, United States. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Note the star symbol on the Solution feature. See Knowledge Base 1240: Manually Setting the Scaling of Variables. 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 solver settings are stored at Study > Solver Configurations > Solution. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. Cooling and Solidification of Metal. 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. Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. What are people saying about cards & stationery in Brea, CA? That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. Alle Rechte vorbehalten. Thanks, Andres. This case is generally difficult, or impossible, to solve since this material property is non-smooth. Wish you all the best. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. Common Mistakes: Not assigning materials to all the domains. Feature: Stationary Solver 1 (sol1/s1)" . 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. I am following the same model as Comsol provide us on the web. The Fully Coupled solution approach, with the Plot While Solving enabled. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. Such problems must solved in the time domain. Discussion Closed This discussion was created more than 6 months ago and has been closed. Not assigning proper boundary conditions: Especially if you have ports. 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. Few days back i was also facing this problem in . 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. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. Segregated approach and Direct vs. As part of our solver blog series we have discussed solving nonlinear static finite element problems, load ramping for improving convergence of nonlinear problems, and nonlinearity ramping for improving convergence of nonlinear problems. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. Making statements based on opinion; back them up with references or personal experience. The difference between the phonemes /p/ and /b/ in Japanese. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. GCRO-DR is a method for Krylov subspace recycling. . This guide applies solely to nonlinear stationary models. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. listed if standards is not an option). If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: How do/should administrators estimate the cost of producing an online introductory mathematics class? The conditions on the geometric aspect ratio are relatively more strict. Any trademarks referenced in this document are the property of their respective owners. These can be used alone, or in combination with other interfaces. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. The advantages of the continuation method are two-fold. Such a large difference in the materials properties can be challenging. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. Connect and share knowledge within a single location that is structured and easy to search. How can I use it? In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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 unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Create the time-dependent step or study. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. COMSOL makes every reasonable effort to verify the information you view on this page. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases.