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. 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, they are tuned to achieve convergence in as many cases as possible. Not assigning proper boundary conditions: Especially if you have ports. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. In a previous blog entry, we introduced meshing considerations for linear static problems. There will always already be either a Segregated or Fully Coupled feature beneath this. Again, introduce a Global Parameter that gets ramped from exactly zero to one. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: The Fully Coupled solution approach, with the Plot While Solving enabled. Not entering required material parameters. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. Your internet explorer is in compatibility mode and may not be displaying the website correctly. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. 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. Have you taken a look at this [blog post](https://www.comsol.com/blogs/modeling-fluid-structure-interaction-in-multibody-mechanisms/)? Any trademarks referenced in this document are the property of their respective owners. Repeat this for every nonlinearity of the model. Cooling and Solidification of Metal. thanks for reply That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. - Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. They deal with COMSOL package and train users. Any trademarks referenced in this document are the property of their respective owners. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Minimising the environmental effects of my dyson brain. COMSOL makes every reasonable effort to verify the information you view on this page. This approach is known as a Continuation Method with a Constant predictor. - 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. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). COMSOL does not assume any legal liability for the accuracy of the data disclosed. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. 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. The technique of load ramping is not always reasonable for all problems. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. They are usually called comp1.u, comp1.v, and comp1.w though. Not assigning proper boundary conditions: Especially if you have ports. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Perhaps this approach could be adapted to represent your model. rev2023.3.3.43278. What sort of strategies would a medieval military use against a fantasy giant? Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. Note: there is no way to couple this . Office Supplies, Stationery, and Gift Retailers Companies in Brea 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. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). 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. If it does so, use a finer increment in that range. There will always already be either a Segregated or Fully Coupled feature beneath this. 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. Multiphysics problems are often nonlinear. If so, see: Knowledgebase 1030: Error: "Out of memory". It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. 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. That is, they are tuned to achieve convergence in as many cases as possible. 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. P&S: COMSOL Design Tool for Photonic Devices. To switch between these solver types, go to the Stationary Solver node within the Study sequence. This is relatively expensive to do, but will lead to the most robust convergence. It may also reveal that the model itself is ill-posed in some way. 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. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) 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. Feature: Stationary Solver 1 (sol1/s1)" . The segregated approach, on the other hand, solves sets of unknowns separately. 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. 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. How to Add a Study to Your Simulation in COMSOL Multiphysics thanks for reply That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Cooling and Solidification of Metal. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. - 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. This guide applies solely to nonlinear stationary models. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. 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. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. 3 Replies, Please login with a confirmed email address before reporting spam. I highly recommend this flower shop. Improving Convergence of Nonlinear Stationary Models - Informazioni This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. This involves a systematic reduction in the model complexity. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Solver . About the Stationary Solver - COMSOL Multiphysics 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. Is there a way to use the stationary solution obtained in Comsol 4.2 as the initial conditions in a time dependent model? You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version This consent may be withdrawn. These are some cards & stationery with a large number of reviews in Brea, CA. I am following the same model as Comsol provide us on the web. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. This approach is known as a Continuation Method with a Constant predictor. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Review the model setup to resolve these. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. What version of COMSOL are you using? Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. The conditions on the geometric aspect ratio are relatively more strict. This approach is known as a Continuation Method with a Constant predictor. 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. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. This case is generally difficult, or impossible, to solve since this material property is non-smooth. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) $140,000.00, $120,000.00 Specify Material Properties in COMSOL Multiphysics (3/8) As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Using the first order optimality. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. listed if standards is not an option). The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. An example would be a linear static structural model of an aluminum beverage can. Understanding the Fully Coupled vs. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Check the solver log to see if the continuation method is backtracking. Connect and share knowledge within a single location that is structured and easy to search. The default Initial Values for the unknowns in most physics interfaces are zero. It is sometimes necessary to manually scale the dependent variables. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: The coupling terms between the different groups are thus neglected. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. 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. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. What did people search for similar to stationary stores in Brea, CA? How to solve "Undefined material property 'sigma - ResearchGate 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. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. 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. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. 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. This guide applies solely to nonlinear stationary models. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Hi Jason, 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. Wish you all the best. To start a new discussion with a link back to this one, click here. However, it is usually not possible to know this ahead of time. 351 Stationary Engineer jobs in Brea, California, United States (15 new) 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. 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. How can I check before my flight that the cloud separation requirements in VFR flight rules are met? Common Errors in Comsol - P&S: COMSOL Design Tool for Photonic Devices k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Thanks, Andres. Any trademarks referenced in this document are the property of their respective owners. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Hi ! 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. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Not the answer you're looking for? 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 Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. 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. Stationary in the COMSOL Multiphysics Programming Reference Manual Damped Newton Methods The nonlinear solver uses an affine invariant form of the damped Newton method as described in Ref. Discussion Closed This discussion was created more than 6 months ago and has been closed. 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. 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. Here we introduce a more robust approach to solving nonlinear problems. The Fully Coupled solution approach, with the Plot While Solving enabled. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. COMSOL makes every reasonable effort to verify the information you view on this page. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. Again, introduce a Global Parameter that gets ramped from exactly zero to one. With respect to any nonlinearities, replace them by a reasonable linearized term. . The algorithm is, generally speaking, a Newton's method approach. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: For the Nozomi from Shinagawa to Osaka, say on a Saturday afternoon, would tickets/seats typically be available - or would you need to book? COMSOL makes every reasonable effort to verify the information you view on this page. (Frequency Domain should be the last step) Consult your product manuals for complete trademark details. 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. Name: actdep_int1, Your email address will not be published. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. 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. Top 10 Best Stationary Stores in Brea, CA - December 2022 - Yelp 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. 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. Reply . 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. comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. Here, we will examine techniques for accelerating the convergence of these two methods. 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. See Knowledge Base 1240: Manually Setting the Scaling of Variables. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. 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. Such problems must solved in the time domain. What are people saying about cards & stationery in Brea, CA? [COMSOL_Users] output of stationary solver as input to time-dependent Consult your product manuals for complete trademark details. (I am begginer in comsol) Thank you. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble The problem is that when I run my model this message appear: Undefined value found. 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. Solve the stationary study then the time dependent study. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. That is, start by first solving a model with a small, but non-zero, load. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. That is, start by first solving a model with a small, but non-zero, load. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. 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. There will always already be either a Segregated or Fully Coupled feature beneath this. The difference between the phonemes /p/ and /b/ in Japanese. Set initial conditions in the physics to the appropriate dependent model variable names rather than the default 0. November 11, 2013. 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. 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. 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. The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! You can unsubscribe from these emails at any time. 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. In this page, we will be sharing some common errors that might occur in Comsol and their solutions. Function: / Failed to evaluate expression. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version If you try to enter a variable that is undefined, the automatic syntax highlighting will identify this as you enter it, and it is best practice to resolve this immediately. Your email address will not be published. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Solving for laminar flow using Comsol - YouTube 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. - Function: ^ Failed to evaluate variable. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. This involves a systematic reduction in the model complexity. . The issue here has do with the iterative algorithm used to solve nonlinear stationary models. What are some highly rated cards & stationery in Brea, CA? It is also possible to manually refine the mesh. 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. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. If your matrix is singular than no solver in the world can solve Ax=B. The advantages of the continuation method are two-fold. Why? Check the solver log to see if the continuation method is backtracking. Why is there a voltage on my HDMI and coaxial cables? It is sometimes necessary to manually scale the dependent variables. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. The advantages of the continuation method are two-fold. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. The coupling terms between the different groups are thus neglected.