stationary solver comsol

Multiscale Modeling in High-Frequency Electromagnetics. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Note: there is no way to couple this field with the time dependent nature of this physics. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: 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. Have you taken a look at this blog post? 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. 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 the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. Not assigning proper boundary conditions: Especially if you have ports. Not assigning proper boundary conditions: Especially if you have ports. In this posting, we introduce the idea of ramping the nonlinearities in the problem to improve convergence. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Could you expand a little bit more why the coupling is impossible? This algorithm was also useful for understanding what happens near a failure load. I am following the same model as Comsol provide us on the web. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. 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. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Consult your product manuals for complete trademark details. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. - the incident has nothing to do with me; can I use this this way? Understanding the Fully Coupled vs. 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. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Note the star symbol on the Solution feature. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. Your internet explorer is in compatibility mode and may not be displaying the website correctly. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: 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. Reply . You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version See Knowledge Base 1240: Manually Setting the Scaling of Variables. Screenshot showing a Solver Configuration that has been altered. Here, we will examine techniques for accelerating the convergence of these two methods. - Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). The other low-level default settings within the Stationary Solver are chosen for robustness. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. The settings controlling the predictor type. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . 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. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. There will always already be either a Segregated or Fully Coupled feature beneath this. This information is presented in the context of a very simple 1D finite element problem, and builds upon our previous entry on Solving Linear Static Finite Element Models. This involves a systematic reduction in the model complexity. For example, if there is a temperature-dependent material property such as: Studysteps might be listed in wrong order: Not assigning materials to all the domains. 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. I use comsol multiphysics 5.2a and . Multiphysics problems are often nonlinear. This involves a systematic reduction in the model complexity. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. 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. 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 guide applies solely to nonlinear stationary models. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. 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. 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. 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. We have also introduced meshing considerations for linear static problems, as well as how to identify singularities and what to do about them when meshing. 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. This guide applies solely to nonlinear stationary models. Your Discussion has gone 30 days without a reply. 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. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. 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 is enabled by default when using the Auxiliary sweep study extension, as shown below. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. 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. 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. 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. "After the incident", I started to be more careful not to trip over things. There will always already be either a Segregated or Fully Coupled feature beneath this. First, it is physically intuitive, often matching how one would perform an experiment. 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. I'm trying to model a solid that's moving through a steady background field in a background flow, I want to take into account the effect of movement of the solid after each time step so I have to use stationary solver after each time step in order to see how field has changed after solid moved. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. The problem is that when I run my model this message appear: Undefined value found. 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. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) (I am begginer in comsol) Thank you. rev2023.3.3.43278. 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. 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. It is also possible to manually refine the mesh. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. 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. 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. 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. listed if standards is not an option). By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). I personally liked emailing them the file, ", "This flower shop is the best! Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. 3. 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. Wrong ordering of study steps. replace it with the expression: If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. If it does so, use a finer increment in that range. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. You can unsubscribe from these emails at any time. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Common Mistakes: Not assigning materials to all the domains. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. 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. 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. Different physics have different default solvers. $130,000.00. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. 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. That is, they are tuned to achieve convergence in as many cases as possible. GCRO-DR is a method for Krylov subspace recycling. -Detail: NaN or Inf found when solving linear system using SOR. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 Mesh 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. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. This involves a systematic reduction in the model complexity. The settings controlling the predictor type. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Your internet explorer is in compatibility mode and may not be displaying the website correctly. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. Leverage your professional network, and get hired. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. New Stationary Engineer jobs added daily. 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. This is a review for cards & stationery in Brea, CA: "Love this store!!! The default Initial Values for the unknowns in most physics interfaces are zero. Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble Computational Fluid Dynamics (CFD), API The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. However, it is usually not possible to know this ahead of time. listed if standards is not an option). Find centralized, trusted content and collaborate around the technologies you use most. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version That is, start by first solving a model with a small, but non-zero, load. COMSOL makes every reasonable effort to verify the information you view on this page. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. 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. Stationary (time-invariant) models with nonlinearities may converge very slowly. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. 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. 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.) These can be used alone, or in combination with other interfaces. 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. What did people search for similar to stationary stores in Brea, CA? That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. It may also reveal that the model itself is ill-posed in some way. 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. The coupling terms between the different groups are thus neglected. Direct PARDISO Solver , PARDISO . Asking for help, clarification, or responding to other answers. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 They worked with me. 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. 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. - Feature: Stationary Solver 1 (sol1/s1)Failed to find a 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. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) You can write the discrete form of the equations as f(U) = 0, where f(U) is the residual vector and U is the solution vector. I'm trying to model a solid that's moving through a steady background field in a background flow, I want to take into account the effect of movement of the solid after each time step so I have to use stationary solver after each time step in order to see how field has changed after solid moved. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. The technique of load ramping is not always reasonable for all problems. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Stationary (time-invariant) models with nonlinearities may converge very slowly. Hello, If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. (Frequency Domain should be the last step) Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. For example, in a Solid Mechanics (wherein the software is solving for the displacement field within the solid) applying two opposite and equal Boundary Load conditions on a part is not sufficient to define the displacement. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings).