It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. Thanks, Andres. That is, they are tuned to achieve convergence in as many cases as possible. That is, they are tuned to achieve convergence in as many cases as possible. Computational Fluid Dynamics (CFD), API k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) However, it is usually not possible to know this ahead of time. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. 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. She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. - Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. Specify Material Properties in COMSOL Multiphysics (3/8) Your Discussion has gone 30 days without a reply. Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. listed if standards is not an option). The problem is that when I run my model this message appear: Undefined value found. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. Not assigning proper boundary conditions: Especially if you have ports. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. Comsol help video number 2: Solving a laminar flow problem in a slit.. 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 stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. Direct PARDISO Solver , PARDISO . 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. This involves a systematic reduction in the model complexity. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. 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. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. 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. 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. COMSOL does not assume any legal liability for the accuracy of the data disclosed. The objective here is to simplify the model to a state where the model will solve, with linear approximations. 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. listed if standards is not an option). Posted 26 set 2019, 11:57 GMT-4 In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? Please dont hesitate to post comments below or send emails to us if you experience any other problems. Improving Convergence of Nonlinear Stationary Models - Informazioni The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Can I tell police to wait and call a lawyer when served with a search warrant? 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. As we saw previously in the blog entry on Solving Nonlinear Static Finite Element Problems, not all nonlinear problems will be solvable via the damped Newton-Raphson method. Cooling and Solidification of Metal. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Again, introduce a Global Parameter that gets ramped from exactly zero to one. I use comsol multiphysics 5.2a and . Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. This guide applies solely to nonlinear stationary models. 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. Here we introduce a more robust approach to solving nonlinear problems. 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 Asking for help, clarification, or responding to other answers. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. Not assigning proper boundary conditions: Especially if you have ports. 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. 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. Consult your product manuals for complete trademark details. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. 351 Stationary Engineer jobs in Brea, California, United States (15 new) Could you expand a little bit more why the coupling is impossible? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Get notified about new Stationary Engineer jobs in Brea, California, United States. 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. (COMSOL Multiphysics) : To switch between these solver types, go to the Stationary Solver node within the Study sequence. Wish you all the best. 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. If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. The fully coupled and segregated approaches are discussed below. Acidity of alcohols and basicity of amines. This involves a systematic reduction in the model complexity. This is relatively expensive to do, but will lead to the most robust convergence. 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. I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary model. First, it is physically intuitive, often matching how one would perform an experiment. First, it is physically intuitive, often matching how one would perform an experiment. "After the incident", I started to be more careful not to trip over things. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). 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. How do/should administrators estimate the cost of producing an online introductory mathematics class? If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Such a large difference in the materials properties can be challenging. Perhaps this approach could be adapted to represent your model. Improving Convergence of Nonlinear Stationary Models - COMSOL Not entering required material parameters. 3. 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. 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. Click the link in the email we sent to to verify your email address and activate your job alert. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Such problems must solved in the time domain. 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. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. 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. However, it is usually not possible to know this ahead of time. 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. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) Few days back i was also facing this problem in . Name: actdep_int1, Your email address will not be published. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Multiphysics problems are often nonlinear. In the COMSOL Multiphysics software, this step of the modeling workflow is made. COMSOL makes every reasonable effort to verify the information you view on this page. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Tutti i diritti sono riservati. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Stationary Solver Iterative Direct . 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. COMSOL Blog Series on COMSOL Multiphysics Solvers COMSOL makes every reasonable effort to verify the information you view on this page. 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. Troubleshooting for 3D trusses, if anyone's out there. : r/COMSOL - reddit Hi Alexis, You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version The objective here is to simplify the model to a state where the model will solve, with linear approximations. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Improving Convergence of Nonlinear Stationary Models - COMSOL 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. The coupling terms between the different groups are thus neglected. Communication over the phone, in person, and through email was very easy. The advantages of the continuation method are two-fold. 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. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. 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 is also possible to manually refine the mesh. The segregated approach, on the other hand, solves sets of unknowns separately. 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. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. In this post, we will delve deeper into how to choose an appropriate mesh to start your mesh convergence studies for linear static finite element problems. P&S: COMSOL Design Tool for Photonic Devices. Not meshing all the domains. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. COMSOL makes every reasonable effort to verify the information you view on this page. Not entering required material parameters. - 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. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version They worked with me. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. Hi Jason, Stationary Solver - COMSOL Multiphysics Any trademarks referenced in this document are the property of their respective owners. [COMSOL_Users] output of stationary solver as input to time-dependent In this page, we will be sharing some common errors that might occur in Comsol and their solutions. The Fully Coupled solution approach, with the Plot While Solving enabled. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 Can someone help me fix the COMSOL error below? | ResearchGate 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. Minimising the environmental effects of my dyson brain. These are some cards & stationery with a large number of reviews in Brea, CA. Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. Function: / Failed to evaluate expression. An example would be a linear static structural model of an aluminum beverage can. This involves a systematic reduction in the model complexity. Iterative - COMSOL Multiphysics The coupling terms between the different groups are thus neglected. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. 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. It may also reveal that the model itself is ill-posed in some way. What is \newluafunction? This is relatively expensive to do, but will lead to the most robust convergence. Top 10 Best Stationary Stores in Brea, CA - December 2022 - Yelp 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 memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. As we saw in Load Ramping of Nonlinear Problems, we can use the continuation method to ramp the loads on a problem up from an unloaded case where we know the solution. This case is generally difficult, or impossible, to solve since this material property is non-smooth. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. 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. Why is there a voltage on my HDMI and coaxial cables? With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Multiphysics problems are often nonlinear. 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. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. Common Mistakes: Not assigning materials to all the domains. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Learn how your comment data is processed. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. By providing your email address, you consent to receive emails from COMSOL AB and its affiliates about the COMSOL Blog, and agree that COMSOL may process your information according to its Privacy Policy. (I am begginer in comsol) Thank you. The Iterative Solvers - COMSOL Multiphysics What version of COMSOL are you using? You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version . Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. Common Errors in Comsol - P&S: COMSOL Design Tool for Photonic Devices That is, they are tuned to achieve convergence in as many cases as possible. Studysteps might be listed in wrong order: Not assigning materials to all the domains. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. These are some highly rated cards & stationery in Brea, CA: What are some cards & stationery with a large number of reviews in Brea, CA? Consult your product manuals for complete trademark details. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Screenshot showing a Solver Configuration that has been altered. Stationary (time-invariant) models with nonlinearities may converge very slowly. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: For example, if there is a temperature-dependent material property such as: You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. Here, we will examine techniques for accelerating the convergence of these two methods. Does anyone know what should cause this problem? Stationary (time-invariant) models with nonlinearities may converge very slowly. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Using the first order optimality. 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. rev2023.3.3.43278. I am following the same model as Comsol provide us on the web. 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. Hi Jason, (Frequency Domain should be the last step). In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. 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. COMSOL makes every reasonable effort to verify the information you view on this page. 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. Segregated approach and Direct vs. Any trademarks referenced in this document are the property of their respective owners. It is sometimes necessary to manually scale the dependent variables. Multiphysics problems are often nonlinear. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. Repeat this for every nonlinearity of the model. Any trademarks referenced in this document are the property of their respective owners. Hi ! With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). Any trademarks referenced in this document are the property of their respective owners. See Knowledge Base 1240: Manually Setting the Scaling of Variables. Tutti i diritti sono riservati. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. thanks for reply k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach.

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