Discussion Closed This discussion was created more than 6 months ago and has been closed. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Check the solver log to see if the continuation method is backtracking. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. The settings controlling the predictor type. The fully coupled and segregated approaches are discussed below. 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. Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems. The conditions on the geometric aspect ratio are relatively more strict. The algorithm is, generally speaking, a Newton's method approach. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. Comsol help video number 2: Solving a laminar flow problem in a slit.. Repeat this for every nonlinearity of the model. 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. Common Study Step Settings - COMSOL Multiphysics Such problems must solved in the time domain. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. Is there a way to use the stationary solution obtained in Comsol 4.2 as the initial conditions in a time dependent model? Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. 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 also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. 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. 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. Solver . Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. About the Stationary Solver - COMSOL Multiphysics $140,000.00, $120,000.00 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! Communication over the phone, in person, and through email was very easy. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Then use this file to provide the initial conditions in time dependent model. Segregated approach and Direct vs. 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. (I am begginer in comsol) Thank you. Have you taken a look at this [blog post](https://www.comsol.com/blogs/modeling-fluid-structure-interaction-in-multibody-mechanisms/)? If it does so, use a finer increment in that range. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. 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. 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. Leverage your professional network, and get hired. Cooling and Solidification of Metal. Different physics have different default solvers. The technique of load ramping is not always reasonable for all problems. With respect to any nonlinearities, replace them by a reasonable linearized term. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. To switch between these solver types, go to the Stationary Solver node within the Study sequence. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. 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. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: This involves a systematic reduction in the model complexity. 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. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the - COMSOL Hello guys. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version - Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. The Fully Coupled solution approach, with the Plot While Solving enabled. If your matrix is singular than no solver in the world can solve Ax=B. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. 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. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. listed if standards is not an option). 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. With respect to any nonlinearities, replace them by a reasonable linearized term. 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. Get email updates for new Stationary Engineer jobs in Brea, California, United States. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. This approach is known as a Continuation Method with a Constant predictor. In this posting, we introduce the idea of ramping the nonlinearities in the problem to improve convergence. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Have you taken a look at this blog post? Your internet explorer is in compatibility mode and may not be displaying the website correctly. They are usually called comp1.u, comp1.v, and comp1.w though. COMSOL Blog Series on COMSOL Multiphysics Solvers Why is there a voltage on my HDMI and coaxial cables? 351 Stationary Engineer jobs in Brea, California, United States (15 new) Your internet explorer is in compatibility mode and may not be displaying the website correctly. (COMSOL Multiphysics) : The other low-level default settings within the Stationary Solver are chosen for robustness. That is, start by first solving a model with a small, but non-zero, load. It is sometimes necessary to manually scale the dependent variables. listed if standards is not an option). 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. Note: there is no way to couple this field with the time dependent nature of this physics. The settings controlling the predictor type. Making statements based on opinion; back them up with references or personal experience. If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. -Detail: NaN or Inf found when solving linear system using SOR. Computational Fluid Dynamics (CFD), API You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. (Frequency Domain should be the last step) The segregated approach, on the other hand, solves sets of unknowns separately. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 comsol - using stationary solution as the initial conditions in time Again, introduce a Global Parameter that gets ramped from exactly zero to one. Most multiphysics problems are nonlinear. To start a new discussion with a link back to this one, click here. Any trademarks referenced in this document are the property of their respective owners. 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. Common Errors in Comsol - P&S: COMSOL Design Tool for Photonic Devices The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. The objective here is to simplify the model to a state where the model will solve, with linear approximations. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Improving Convergence of Nonlinear Stationary Models - COMSOL 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. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Discussion Closed This discussion was created more than 6 months ago and has been closed. The difference between the phonemes /p/ and /b/ in Japanese. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. The objective here is to simplify the model to a state where the model will solve, with linear approximations. Your Discussion has gone 30 days without a reply. replace it with the expression: Today's top 351 Stationary Engineer jobs in Brea, California, United States. Such a large difference in the materials properties can be challenging. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Why? Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Minimising the environmental effects of my dyson brain. 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. 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. Most multiphysics problems are nonlinear. 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. 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. 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 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. 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 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. 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. Screenshot showing a Solver Configuration that has been altered. so many cute little stationary items , hair". Your email address will not be published. Cooling and Solidification of Metal. Hello, 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. Function: / Failed to evaluate expression. 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 finite element mesh must be fine enough to resolve the spatial variations in the solution fields. To switch between these solver types, go to the Stationary Solver node within the Study sequence. However, it is usually not possible to know this ahead of time. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. There will always already be either a Segregated or Fully Coupled feature beneath this. The fully coupled and segregated approaches are discussed below. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. The algorithm is, generally speaking, a Newton's method approach. 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. For example, if there is a temperature-dependent material property such as: Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Wrong ordering of study steps. Please dont hesitate to post comments below or send emails to us if you experience any other problems. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. - Name: actdep_int1, Your email address will not be published. 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. The other low-level default settings within the Stationary Solver are chosen for robustness. Common Mistakes: Not assigning materials to all the domains. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. Not assigning proper boundary conditions: Especially if you have ports. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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. Contact COMSOL at Bangalore on their telephone: +9180 25323003. 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. I personally liked emailing them the file, ", "This flower shop is the best! 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. We use COMSOL Multiphysics for solving distributed optimal control of un-steady Burgers equation without constraints and with pointwise control constraints. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. 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. If it does so, use a finer increment in that range. Here, we will examine techniques for accelerating the convergence of these two methods. Use this parameter to modify the nonlinearity expressions in the model. 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. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. If so, see: Knowledgebase 1030: Error: "Out of memory". Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Use this parameter to modify the nonlinearity expressions in the model. Learn how your comment data is processed. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. listed if standards is not an option). 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. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Not assigning proper boundary conditions: Especially if you have ports. I highly recommend this flower shop. GCRO-DR is a method for Krylov subspace recycling. 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. Stationary (time-invariant) models with nonlinearities may converge very slowly. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. Thanks, Andres. listed if standards is not an option). Tutti i diritti sono riservati. . Consult your product manuals for complete trademark details. The segregated approach, on the other hand, solves sets of unknowns separately. How to solve "Undefined material property 'sigma - ResearchGate Full text of the 'Sri Mahalakshmi Dhyanam & Stotram'. 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. 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. This doesn't seem to me the most elegant of methods, since I am essentially solving a stationary solution using a time dependent See Knowledge Base 1240: Manually Setting the Scaling of Variables. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Understanding the Fully Coupled vs. (Frequency Domain should be the last step). This approach is known as a Continuation Method with a Constant predictor. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Not the answer you're looking for? Multiphysics problems are often nonlinear. solving stationary solver after each time step - COMSOL Multiphysics 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. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. 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 Sign in to create your job alert for Stationary Engineer jobs in Brea, California, United States. At low flow speeds the flow solution will be time invariant, but at higher flow rates there will be vortex shedding, a time-varying change in the flow field behind the cylinder. Review the model setup to resolve these. - Function: ^ Failed to evaluate variable. However, it is usually not possible to know this ahead of time. 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. The following are possible reasons why a linear stationary model will fail to solve, along with resolutions: The combination of the constraints and boundary conditions must be sufficient to define a unique solution to the problem, in terms of the field variables being solved. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Version 5.3 Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Stationary (time-invariant) models with nonlinearities may converge very slowly. Such problems must solved in the time domain. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. This guide applies solely to nonlinear stationary models. In the COMSOL Multiphysics software, this step of the modeling workflow is made. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. 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. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: It is sometimes necessary to manually scale the dependent variables. 0 Replies, Please login with a confirmed email address before reporting spam. if I want to do an adaptive mesh refinement, I get this error. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Note the star symbol on the Solution feature. Hi Alexis, Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. 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. 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.
