stationary solver comsol

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 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 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. COMSOL does not assume any legal liability for the accuracy of the data disclosed. It is sometimes necessary to manually scale the dependent variables. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Repeat this for every nonlinearity of the model. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. Solve the stationary study then the time dependent study. 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. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Could you expand a little bit more why the coupling is impossible? Tutti i diritti sono riservati. It is also possible to manually refine the mesh. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. 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. Top 10 Best Stationary Stores in Brea, CA - December 2022 - Yelp What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? "After the incident", I started to be more careful not to trip over things. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) 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. The fully coupled and segregated approaches are discussed below. What did people search for similar to stationary stores in Brea, CA? Any trademarks referenced in this document are the property of their respective owners. Computational Fluid Dynamics (CFD), API They are usually called comp1.u, comp1.v, and comp1.w though. listed if standards is not an option). 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. To switch between these solver types, go to the Stationary Solver node within the Study sequence. The Iterative Solvers - COMSOL Multiphysics The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). If your matrix is singular than no solver in the world can solve Ax=B. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. Multiphysics problems are often nonlinear. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. See Knowledge Base 1240: Manually Setting the Scaling of Variables. The technique of load ramping is not always reasonable for all problems. To start a new discussion with a link back to this one, click here. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. The advantages of the continuation method are two-fold. In such cases, see if one material (or the other) can be omitted from the analysis completely. Direct Iterative , Direct . If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. For example, if there is a temperature-dependent material property such as: Is there a way to use the stationary solution obtained in Comsol 4.2 as the initial conditions in a time dependent model? 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. Is it possible to rotate a window 90 degrees if it has the same length and width? This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. The settings controlling the predictor type. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. 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. replace it with the expression: 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. 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. Hi Jason, You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) 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. About the Stationary Solver - COMSOL Multiphysics An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Multiscale Modeling in High-Frequency Electromagnetics. Again, introduce a Global Parameter that gets ramped from exactly zero to one. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. The Fully Coupled solution approach, with the Plot While Solving enabled. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Hi ! This case is generally difficult, or impossible, to solve since this material property is non-smooth. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 The objective here is to simplify the model to a state where the model will solve, with linear approximations. Any trademarks referenced in this document are the property of their respective owners. Hello guys. 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. There will also be a red cross over the Materials branch icon. 351 Stationary Engineer jobs in Brea, California, United States (15 new) Then use this file to provide the initial conditions in time dependent model. This involves a systematic reduction in the model complexity. Such problems must solved in the time domain. There will always already be either a Segregated or Fully Coupled feature beneath this. SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Discussion Closed This discussion was created more than 6 months ago and has been closed. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Minimising the environmental effects of my dyson brain. They worked with me. The segregated approach, on the other hand, solves sets of unknowns separately. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. 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. Why do many companies reject expired SSL certificates as bugs in bug bounties? The settings controlling the predictor type. Acidity of alcohols and basicity of amines. The technique of load ramping is not always reasonable for all problems. How can I use it? 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. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Alle Rechte vorbehalten. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. Note that while COMSOL employees may participate in the discussion forum, COMSOL software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. How to solve "Undefined material property 'sigma - ResearchGate 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 solver is automatically used when a Stationary or Frequency Domain study is added to the model. Common Errors in Comsol - P&S: COMSOL Design Tool for Photonic Devices The solver settings are stored at Study > Solver Configurations > Solution. 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. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. -Detail: NaN or Inf found when solving linear system using SOR. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. 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. If so, see: Knowledgebase 1030: Error: "Out of memory". [COMSOL_Users] output of stationary solver as input to time-dependent First, it is physically intuitive, often matching how one would perform an experiment. 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 issue here has do with the iterative algorithm used to solve nonlinear stationary models. 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. Save this information to a file. 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.) k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. if I want to do an adaptive mesh refinement, I get this error. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: It is sometimes necessary to manually scale the dependent variables. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. Hi Jason, $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 Note: there is no way to couple this field with the time dependent nature of this physics. Function: / Failed to evaluate expression. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. Unknown function or operator. 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. 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. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Improving Convergence of Nonlinear Stationary Models - COMSOL This is relatively expensive to do, but will lead to the most robust convergence. Specify Material Properties in COMSOL Multiphysics (3/8) This case is generally difficult, or impossible, to solve since this material property is non-smooth. Check the solver log to see if the continuation method is backtracking. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: 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. Not assigning proper boundary conditions: Especially if you have ports. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Posted Sep 9, 2020, 1:44 p.m. EDT - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. Common Study Step Settings - COMSOL Multiphysics 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. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. 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. 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. 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. 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. Studysteps might be listed in wrong order: Not assigning materials to all the domains. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Perhaps this approach could be adapted to represent your model. (I am begginer in comsol) Thank you. I have searched all over comsol forum to fix this stationary solver configuration and still doesn't work because I don't know the logic behind the solver system. Repeat this for every nonlinearity of the model. Review the model setup to resolve these. 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. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) 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. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. 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. How do/should administrators estimate the cost of producing an online introductory mathematics class? Second, the continuation method will automatically take smaller load increments if a solution cannot be found. I use comsol multiphysics 5.2a and . k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. Consult your product manuals for complete trademark details. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. It is also possible to manually refine the mesh. Set initial conditions in the physics to the appropriate dependent model variable names rather than the default 0. The default Initial Values for the unknowns in most physics interfaces are zero. If it does so, use a finer increment in that range. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) 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. 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. 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. 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. Required fields are marked *. listed if standards is not an option). Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. COMSOL does not assume any legal liability for the accuracy of the data disclosed. 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. P&S: COMSOL Design Tool for Photonic Devices - ETH Z To start a new discussion with a link back to this one, click here. 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. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. 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. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. The default Initial Values for the unknowns in most physics interfaces are zero. It is sometimes necessary to manually scale the dependent variables. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) 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. listed if standards is not an option). 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. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. Get email updates for new Stationary Engineer jobs in Brea, California, United States. Any trademarks referenced in this document are the property of their respective owners. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. This approach is known as a Continuation Method with a Constant predictor. This involves a systematic reduction in the model complexity. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps.

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