However, load ramping will not work in all cases, or may be inefficient. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. This case is generally difficult, or impossible, to solve since this material property is non-smooth. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. listed if standards is not an option). New Stationary Engineer jobs added daily. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Name: actdep_int1, Your email address will not be published. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Check the solver log to see if the continuation method is backtracking. 140K views 8 years ago COMSOL Multiphysics Tutorial for Beginners Please note that an updated version of the content in this video can be found in the Modeling Workflow video in the COMSOL. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. In a previous blog entry, we introduced meshing considerations for linear static problems. 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. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Function: / Failed to evaluate expression. The other low-level default settings within the Stationary Solver are chosen for robustness. Thanks for contributing an answer to Stack Overflow! See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. 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. Acidity of alcohols and basicity of amines. Hi Alexis, Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. 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 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. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. Iterative , Direct . The default Initial Values for the unknowns in most physics interfaces are zero. If it does so, use a finer increment in that range. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) The segregated approach, on the other hand, solves sets of unknowns separately. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. listed if standards is not an option). Most multiphysics problems are nonlinear. 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. Understanding the Fully Coupled vs. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Hence Comsol solved for the stationary solution at different points of time. 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. The fully coupled and segregated approaches are discussed below. 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. - Feature: Stationary Solver 1 (sol1/s1) Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. - Function: ^ Failed to evaluate variable. November 11, 2013. Note: there is no way to couple this field with the time dependent nature of this physics. Create the time-dependent step or study. 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. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. (Frequency Domain should be the last step) Not the answer you're looking for? If one particular material is missing one property, that material will also be highlighted with a red cross over that material icon in the Model Builder. Why is there a voltage on my HDMI and coaxial cables? To switch between these solver types, go to the Stationary Solver node within the Study sequence. The difference between the phonemes /p/ and /b/ in Japanese. I am trying to solve the coupling between a waveguide and a microring resonator. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Connect and share knowledge within a single location that is structured and easy to search. This involves a systematic reduction in the model complexity. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary model. Get notified about new Stationary Engineer jobs in Brea, California, United States. Communication over the phone, in person, and through email was very easy. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. First, it is physically intuitive, often matching how one would perform an experiment. 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 - 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. $130,000.00. Therefore, it is recommended to use Adaptive Mesh Refinement which will automatically refine the mesh only in regions where it is needed, and coarsen the mesh elsewhere. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. The advantages of the continuation method are two-fold. The other low-level default settings within the Stationary Solver are chosen for robustness. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. thanks for reply 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. 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. It may also reveal that the model itself is ill-posed in some way. With respect to any nonlinearities, replace them by a reasonable linearized term. Not entering required material parameters. My comment is perhaps a bit nave but it seems to me that you could simply deactivate the term of the background field equation but keep its connexion to the solid to get what you want. 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. 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. 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. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Then use this file to provide the initial conditions in time dependent model. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. Your internet explorer is in compatibility mode and may not be displaying the website correctly. "After the incident", I started to be more careful not to trip over things. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Perhaps this approach could be adapted to represent your model. For example, if there is a temperature-dependent material property such as: 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. 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. - Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. "I chose this print shop based off yelp reviews and was very happy with the outcome! If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Check the solver log to see if the continuation method is backtracking. 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. 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. listed if standards is not an option). I am following the same model as Comsol provide us on the web. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. 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. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Stationary (time-invariant) models with nonlinearities may converge very slowly. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. 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. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Contact COMSOL at Bangalore on their telephone: +9180 25323003. That is, they are tuned to achieve convergence in as many cases as possible. Could you expand a little bit more why the coupling is impossible? In our previous blog entry, we introduced the Fully Coupled and the Segregated algorithms used for solving steady-state multiphysics problems in COMSOL. For example, in an Electric Currents problem, you may want to consider a system of materials including a good conductor such as copper (with an electric conductivity of ~6e7 S/m) and an insulative material such as glass (which can have electric conductivity of ~1e-14 S/m.) Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. They worked with me. What are people saying about cards & stationery in Brea, CA? 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 it does so, use a finer increment in that range. Perhaps this approach could be adapted to represent your model. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. 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. That is, start by first solving a model with a small, but non-zero, load. 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. Use this parameter to modify the nonlinearity expressions in the model. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. 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. 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. The fully coupled and segregated approaches are discussed below. 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. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. It is sometimes necessary to manually scale the dependent variables. 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. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Hi Jason, Stationary (time-invariant) models with nonlinearities may converge very slowly. To switch between these solver types, go to the Stationary Solver node within the Study sequence. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Please dont hesitate to post comments below or send emails to us if you experience any other problems. Linear solvers. Can I tell police to wait and call a lawyer when served with a search warrant? This case is generally difficult, or impossible, to solve since this material property is non-smooth. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. 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. listed if standards is not an option). replace it with the expression: 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 These are some cards & stationery with a large number of reviews in Brea, CA. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. This guide applies solely to nonlinear stationary models. - I am solving a linear stationary finite element model but the software is not solving. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. 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. COMSOL makes every reasonable effort to verify the information you view on this page. 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. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Your Discussion has gone 30 days without a reply. Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. Click the link in the email we sent to to verify your email address and activate your job alert. . However, it is usually not possible to know this ahead of time. COMSOL does not assume any legal liability for the accuracy of the data disclosed. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: 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. 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. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. The default Initial Values for the unknowns in most physics interfaces are zero. However, if a lower-level change has been manually made to the solver settings, the software will not automatically use the correct default solver. 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. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. This is relatively expensive to do, but will lead to the most robust convergence. This algorithm was also useful for understanding what happens near a failure load. The solver settings are stored at Study > Solver Configurations > Solution. 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, 2023 by COMSOL. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: As a second example, when solving for Electric Currents, do not model perfect electrical insulators as materials with zero conductivity, instead, omit the domain from the model and use the Electric Insulation boundary condition. Here we introduce a more robust approach to solving nonlinear problems. COMSOL makes every reasonable effort to verify the information you view on this page. COMSOL does not assume any legal liability for the accuracy of the data disclosed. 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. The advantages of the continuation method are two-fold. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Find detailed information on Office Supplies, Stationery, and Gift Retailers companies in Brea, California, United States of America, including financial statements, sales and marketing contacts, top competitors, and firmographic insights. See Knowledge Base 1240: Manually Setting the Scaling of Variables. 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. With respect to any nonlinearities, replace them by a reasonable linearized term. Check the solver log to see if the continuation method is backtracking. Required fields are marked *. $140,000.00, $120,000.00 Studysteps might be listed in wrong order: Not assigning materials to all the domains. Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. 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. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Multiscale Modeling in High-Frequency Electromagnetics. The coupling terms between the different groups are thus neglected. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. The coupling terms between the different groups are thus neglected. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. 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 case is generally difficult, or impossible, to solve since this material property is non-smooth. Multiphysics problems are often nonlinear. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. Sign in to create your job alert for Stationary Engineer jobs in Brea, California, United States. The technique of load ramping is not always reasonable for all problems. Have you taken a look at this blog post? Review the model setup to resolve these. 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. What version of COMSOL are you using? Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Understanding the Fully Coupled vs. Comsol help video number 2: Solving a laminar flow problem in a slit.. We use COMSOL Multiphysics for solving distributed optimal control of un-steady Burgers equation without constraints and with pointwise control constraints.
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