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 involves a systematic reduction in the model complexity. 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. - 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. 3. However, if a lower-level change has been manually made to the solver settings, the software will not automatically use the correct default solver. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Could you expand a little bit more why the coupling is impossible? Stationary (time-invariant) models with nonlinearities may converge very slowly. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. This doesn't seem to me the most elegant of methods, since I am essentially solving a stationary solution using a time dependent In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Is it possible to rotate a window 90 degrees if it has the same length and width? Review the model setup to resolve these. Understanding the Fully Coupled vs. Therefore, an initial value of zero is almost always reasonable if a very small load is applied.
Improving Convergence of Nonlinear Stationary Models - COMSOL "I chose this print shop based off yelp reviews and was very happy with the outcome! It is also possible to manually refine the mesh. 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. 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. Use this parameter to modify the nonlinearity expressions in the model. Linear solvers. Your Discussion has gone 30 days without a reply. 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. If you see this, right-click on the Solution feature and select Reset Solver to Default. Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. Wrong ordering of study steps. I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary model. For example, if there is a temperature-dependent material property such as: Hello guys. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. 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. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. Connect and share knowledge within a single location that is structured and easy to search. That is, start by first solving a model with a small, but non-zero, load. COMSOL does not assume any legal liability for the accuracy of the data disclosed. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. 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. This approach is known as a Continuation Method with a Constant predictor. P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. The default Initial Values for the unknowns in most physics interfaces are zero. GCRO-DR is a method for Krylov subspace recycling. Not the answer you're looking for? Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. I am solving a linear stationary finite element model but the software is not solving. Any trademarks referenced in this document are the property of their respective owners. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. 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. Cooling and Solidification of Metal. 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. Thanks, Andres. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. What are people saying about cards & stationery in Brea, CA? Popular answers (1) This problem generally occurs when there is some mistake in the physics or study section or wrong selection of the mesh size. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Screenshot showing a Solver Configuration that has been altered. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. ", "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. 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. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. 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 This solver is automatically used when a Stationary or Frequency Domain study is added to the model. What did people search for similar to stationary stores in Brea, CA? 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. 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. It may also reveal that the model itself is ill-posed in some way. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Again, introduce a Global Parameter that gets ramped from exactly zero to one.
- Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. The segregated approach, on the other hand, solves sets of unknowns separately.
Top 10 Best Stationary Stores in Brea, CA - December 2022 - Yelp Minimising the environmental effects of my dyson brain. The advantages of the continuation method are two-fold. Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems.
Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the - COMSOL Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Consult your product manuals for complete trademark details. 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. Different physics have different default solvers. The difference between the phonemes /p/ and /b/ in Japanese. 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. replace it with the expression: listed if standards is not an option). To start a new discussion with a link back to this one, click here. Here we introduce a more robust approach to solving nonlinear problems. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. - That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Thanks for contributing an answer to Stack Overflow! If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. - Feature: Stationary Solver 1 (sol1/s1) Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. 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. 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. That is, they are tuned to achieve convergence in as many cases as possible. if I want to do an adaptive mesh refinement, I get this error. Use this parameter to modify the nonlinearity expressions in the model. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is:
About the Stationary Solver - COMSOL Multiphysics 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. Making statements based on opinion; back them up with references or personal experience. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. How do/should administrators estimate the cost of producing an online introductory mathematics class? The objective here is to simplify the model to a state where the model will solve, with linear approximations. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Changes to these low-level settings from the defaults will usually be quite model- and case-specific.
P&S: COMSOL Design Tool for Photonic Devices - ETH Z Get notified about new Stationary Engineer jobs in Brea, California, United States. Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). COMSOL does not assume any legal liability for the accuracy of the data disclosed. In the COMSOL Multiphysics software, this step of the modeling workflow is made. This is relatively expensive to do, but will lead to the most robust convergence. It's brand new in the hmart plaza and I wish it was open back when I would hangout in the plaza after school (although they would have taken all my allowance money! Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Get email updates for new Stationary Engineer jobs in Brea, California, United States. The objective here is to simplify the model to a state where the model will solve, with linear approximations. 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. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Most multiphysics problems are nonlinear. 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. Use this parameter to modify the nonlinearity expressions in the model.
351 Stationary Engineer jobs in Brea, California, United States (15 new) 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. To start a new discussion with a link back to this one, click here. 3 Replies, Please login with a confirmed email address before reporting spam. It may also reveal that the model itself is ill-posed in some way. Wrong ordering of study steps. 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. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Your internet explorer is in compatibility mode and may not be displaying the website correctly.
Again, introduce a Global Parameter that gets ramped from exactly zero to one. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. These can be used alone, or in combination with other interfaces. 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. 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. In a previous blog entry, we introduced meshing considerations for linear static problems.
Asking for help, clarification, or responding to other answers. (I am begginer in comsol) Thank you. Wish you all the best. I am trying to solve the coupling between a waveguide and a microring resonator. Not meshing all the domains. 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 issue here has do with the iterative algorithm used to solve nonlinear stationary models. Hi ! Have you taken a look at this blog post? This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Is there a way to use the stationary solution obtained in Comsol 4.2 as the initial conditions in a time dependent model? The default Initial Values for the unknowns in most physics interfaces are zero. 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. The solver settings are stored at Study > Solver Configurations > Solution. listed if standards is not an option). November 11, 2013. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. The technique of load ramping is not always reasonable for all problems. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Multiphysics problems are often nonlinear. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. If some, or all, of the needed materials properties needed by the physics interfaces are not defined, the model will generate an error at runtime. $130,000.00. 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. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit.
$131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. listed if standards is not an option). Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. thanks for reply Learn how your comment data is processed. replace it with the expression: If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. However, it is usually not possible to know this ahead of time. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version I use comsol multiphysics 5.2a and . 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. Repeat this for every nonlinearity of the model. What version of COMSOL are you using? 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. rev2023.3.3.43278. Solver . In our previous blog entry, we introduced the Fully Coupled and the Segregated algorithms used for solving steady-state multiphysics problems in COMSOL. The segregated approach, on the other hand, solves sets of unknowns separately. That is, they are tuned to achieve convergence in as many cases as possible. Stationary Solver Iterative Direct . Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. - Function: ^ Failed to evaluate variable. Any trademarks referenced in this document are the property of their respective owners. There will always already be either a Segregated or Fully Coupled feature beneath this. Such problems must solved in the time domain. 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. Function: / Failed to evaluate expression. 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. 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. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. However, it is usually not possible to know this ahead of time. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. This case is generally difficult, or impossible, to solve since this material property is non-smooth. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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.
How to solve "Feature: Stationary Solver 1 (sol1/s1) Attempt - COMSOL k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) The Auxiliary Sweep can be used to implement ramping of any Global Parameter. (Frequency Domain should be the last step) Hence Comsol solved for the stationary solution at different points of time. 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. Find centralized, trusted content and collaborate around the technologies you use most. Why is there a voltage on my HDMI and coaxial cables? 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. Click the link in the email we sent to to verify your email address and activate your job alert. The algorithm is, generally speaking, a Newton's method approach. Then use this file to provide the initial conditions in time dependent model. If you are unsure if your problem is linear and stationary, look at the Log.
Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. The conditions on the geometric aspect ratio are relatively more strict. . If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. P&S: COMSOL Design Tool for Photonic Devices. 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. What are some highly rated cards & stationery in Brea, CA? It is sometimes necessary to manually scale the dependent variables. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. Posted 26 set 2019, 11:57 GMT-4 Such a large difference in the materials properties can be challenging. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. listed if standards is not an option). In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. Comsol help video number 2: Solving a laminar flow problem in a slit.. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. There will also be a red cross over the Materials branch icon. The fully coupled and segregated approaches are discussed below.
Specify Material Properties in COMSOL Multiphysics (3/8) Improving Convergence of Nonlinear Stationary Models - Informazioni Cooling and Solidification of Metal. 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. Some models are numerically ill-conditioned due to the setup. The objective here is to simplify the model to a state where the model will solve, with linear approximations. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Consult your product manuals for complete trademark details. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Not assigning proper boundary conditions: Especially if you have ports. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. Name: actdep_int1, Your email address will not be published. What sort of strategies would a medieval military use against a fantasy giant? Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. The Fully Coupled solution approach, with the Plot While Solving enabled. Today's top 351 Stationary Engineer jobs in Brea, California, United States. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Repeat this for every nonlinearity of the model. What is the purpose of non-series Shimano components? 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. These are some highly rated cards & stationery in Brea, CA: What are some cards & stationery with a large number of reviews in Brea, CA? 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. 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.
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