If it does so, use a finer increment in that range. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. so many cute little stationary items , hair". Communication over the phone, in person, and through email was very easy. Consult your product manuals for complete trademark details. If you are unsure if your problem is linear and stationary, look at the Log. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Required fields are marked *. This involves a systematic reduction in the model complexity. Here we introduce a more robust approach to solving nonlinear problems. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. 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. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. Full text of the 'Sri Mahalakshmi Dhyanam & Stotram'. This guide applies solely to nonlinear stationary models. 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. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. That is, they are tuned to achieve convergence in as many cases as possible. . That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. First, it is physically intuitive, often matching how one would perform an experiment. 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 default Initial Values for the unknowns in most physics interfaces are zero. Wrong ordering of study steps. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. 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. Contact COMSOL at Bangalore on their telephone: +9180 25323003. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) I use comsol multiphysics 5.2a and . This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. 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. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. With respect to any nonlinearities, replace them by a reasonable linearized term. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). See Knowledge Base 1240: Manually Setting the Scaling of Variables. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. 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. 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. 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. Could you expand a little bit more why the coupling is impossible? 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. There will always already be either a Segregated or Fully Coupled feature beneath this. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. The settings controlling the predictor type. This approach is known as a Continuation Method with a Constant predictor. Cooling and Solidification of Metal. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Leverage your professional network, and get hired. 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. Use this parameter to modify the nonlinearity expressions in the model. This case is generally difficult, or impossible, to solve since this material property is non-smooth. See Knowledge Base 1240: Manually Setting the Scaling of Variables. This approach is known as a Continuation Method with a Constant predictor. Your email address will not be published. The conditions on the geometric aspect ratio are relatively more strict. 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. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. 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! The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. To switch between these solver types, go to the Stationary Solver node within the Study sequence. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Iterative , Direct . Consult your product manuals for complete trademark details. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Is it possible to rotate a window 90 degrees if it has the same length and width? 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.) 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. 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. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Save my name, email, and website in this browser for the next time I comment. Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble It is sometimes necessary to manually scale the dependent variables. Unknown function or operator. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. Note the star symbol on the Solution feature. 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. Wish you all the best. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. For the Nozomi from Shinagawa to Osaka, say on a Saturday afternoon, would tickets/seats typically be available - or would you need to book? Save this information to a file. 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. 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. COMSOL does not assume any legal liability for the accuracy of the data disclosed. 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. - Function: ^ Failed to evaluate variable. 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. 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. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. What are people saying about cards & stationery in Brea, CA? 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. rev2023.3.3.43278. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Any trademarks referenced in this document are the property of their respective owners. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. This approach is known as a Continuation Method with a Constant predictor. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. Perhaps this approach could be adapted to represent your model. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. 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. See Knowledge Base 1240: Manually Setting the Scaling of Variables. In the COMSOL Multiphysics software, this step of the modeling workflow is made. These are some cards & stationery with a large number of reviews in Brea, CA. COMSOL does not assume any legal liability for the accuracy of the data disclosed. The Automatic predictor setting will use the constant predictor when a segregated solution approach is being used, and use the linear predictor when the fully coupled approach is used. If 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. 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. For example, if there is a temperature-dependent material property such as: The advantages of the continuation method are two-fold. To start a new discussion with a link back to this one, click here. Hi Alexis,
A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Note: there is no way to couple this field with the time dependent nature of this physics. 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. 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. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. Have you taken a look at this [blog post](https://www.comsol.com/blogs/modeling-fluid-structure-interaction-in-multibody-mechanisms/)? The other low-level default settings within the Stationary Solver are chosen for robustness. My comment is perhaps a bit nave but it seems to me that you could simply deactivate the \frac{\partial \cdot}{\partial t} term of the background field equation but keep its connexion to the solid to get what you want. The other low-level default settings within the Stationary Solver are chosen for robustness. Discussion Closed This discussion was created more than 6 months ago and has been closed. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: If so, see: Knowledgebase 1030: Error: "Out of memory". Repeat this for every nonlinearity 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. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. In this page, we will be sharing some common errors that might occur in Comsol and their solutions. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. Get email updates for new Stationary Engineer jobs in Brea, California, United States. 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. 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. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Name: actdep_int1, Your email address will not be published. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. Asking for help, clarification, or responding to other answers. Today's top 351 Stationary Engineer jobs in Brea, California, United States. New Stationary Engineer jobs added daily. That is, start by first solving a model with a small, but non-zero, load. 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. Different physics have different default solvers. 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. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. - the incident has nothing to do with me; can I use this this way? Why is there a voltage on my HDMI and coaxial cables? 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. These can be used alone, or in combination with other interfaces. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. 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. 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. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). - Feature: Stationary Solver 1 (sol1/s1) The settings controlling the predictor type. If it does so, use a finer increment in that range. What sort of strategies would a medieval military use against a fantasy giant? 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. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Hello guys. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. 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. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Not entering required material parameters. This case is generally difficult, or impossible, to solve since this material property is non-smooth. Can I tell police to wait and call a lawyer when served with a search warrant? Some models are numerically ill-conditioned due to the setup. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Computational Fluid Dynamics (CFD), API 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. This doesn't seem to me the most elegant of methods, since I am essentially solving a stationary solution using a time dependent COMSOL does not assume any legal liability for the accuracy of the data disclosed. However, it is usually not possible to know this ahead of time. 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. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. The technique of load ramping is not always reasonable for all 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. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. With respect to any nonlinearities, replace them by a reasonable linearized term. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. 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. Repeat this for every nonlinearity of the model. Tutti i diritti sono riservati. It is sometimes necessary to manually scale the dependent variables. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. 3 Replies, Please login with a confirmed email address before reporting spam. 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. The algorithm is, generally speaking, a Newton's method approach. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. This case is generally difficult, or impossible, to solve since this material property is non-smooth. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. 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. Review the model setup to resolve these. Trying to understand how to get this basic Fourier Series. listed if standards is not an option). For example, if there is a temperature-dependent material property such as: Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. listed if standards is not an option). Acidity of alcohols and basicity of amines. if I want to do an adaptive mesh refinement, I get this error. Few days back i was also facing this problem in . (I am begginer in comsol) Thank you. Minimising the environmental effects of my dyson brain. The default Initial Values for the unknowns in most physics interfaces are zero. 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. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Alle Rechte vorbehalten. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. What did people search for similar to stationary stores in Brea, CA? Check the solver log to see if the continuation method is backtracking. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. In our previous blog entry, we introduced the Fully Coupled and the Segregated algorithms used for solving steady-state multiphysics problems in COMSOL. Cooling and Solidification of Metal. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Check the solver log to see if the continuation method is backtracking. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. 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. 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. 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. 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. Again, introduce a Global Parameter that gets ramped from exactly zero to one. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. 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. 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.