This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. It is sometimes necessary to manually scale the dependent variables. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. 3. listed if standards is not an option). The algorithm is, generally speaking, a Newton's method approach. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. This is relatively expensive to do, but will lead to the most robust convergence. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. This involves a systematic reduction in the model complexity. Consult your product manuals for complete trademark details. Using the first order optimality. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Segregated approach and Direct vs. Have you taken a look at this [blog post](https://www.comsol.com/blogs/modeling-fluid-structure-interaction-in-multibody-mechanisms/)? Multiphysics problems are often nonlinear. In our previous blog entry, we introduced the Fully Coupled and the Segregated algorithms used for solving steady-state multiphysics problems in COMSOL. For example, in an Electric Currents problem, you may want to consider a system of materials including a good conductor such as copper (with an electric conductivity of ~6e7 S/m) and an insulative material such as glass (which can have electric conductivity of ~1e-14 S/m.) Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Not assigning proper boundary conditions: Especially if you have ports. Such problems must solved in the time domain. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. This involves a systematic reduction in the model complexity. The advantages of the continuation method are two-fold. Here we introduce a more robust approach to solving nonlinear problems. Any trademarks referenced in this document are the property of their respective owners. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? Check the solver log to see if the continuation method is backtracking. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. 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. Save my name, email, and website in this browser for the next time I comment. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. 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. Not meshing all the domains. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. For example, if there is a temperature-dependent material property such as: This doesn't seem to me the most elegant of methods, since I am essentially solving a stationary solution using a time dependent Multiphysics problems are often nonlinear. 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. Not entering required material parameters. The solver settings are stored at Study > Solver Configurations > Solution. As a rough rule of thumb, once the aspect ratio between the largest characteristic dimension to the smallest approaches 100:1, you might start to run into issues and should look to alternative ways of posing the problem, especially in a 3D model. Posted 26 set 2019, 11:57 GMT-4 How can I use it? Please dont hesitate to post comments below or send emails to us if you experience any other problems. GCRO-DR is a method for Krylov subspace recycling. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. 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 segregated approach, on the other hand, solves sets of unknowns separately. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. The coupling terms between the different groups are thus neglected. 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. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. replace it with the expression: COMSOL 22.9K subscribers Adding a study to your simulation is necessary in order to solve your problem. There will always already be either a Segregated or Fully Coupled feature beneath this. I use comsol multiphysics 5.2a and . replace it with the expression: - Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Not the answer you're looking for? Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Name: actdep_int1, Your email address will not be published. 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. The Fully Coupled solution approach, with the Plot While Solving enabled. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. COMSOL makes every reasonable effort to verify the information you view on this page. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. This approach is known as a Continuation Method with a Constant predictor. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. However, it is usually not possible to know this ahead of time. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. listed if standards is not an option). Perhaps this approach could be adapted to represent your model. November 11, 2013. Why is there a voltage on my HDMI and coaxial cables? comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Note: there is no way to couple this field with the time dependent nature of this physics. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Hence Comsol solved for the stationary solution at different points of time. In this page, we will be sharing some common errors that might occur in Comsol and their solutions. Comsol help video number 2: Solving a laminar flow problem in a slit.. 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. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. Contact COMSOL at Bangalore on their telephone: +9180 25323003. 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 I want to do an adaptive mesh refinement, I get this error. They are usually called comp1.u, comp1.v, and comp1.w though. In this case, it would likely be reasonable to treat the insulative material as a perfect insulator, omit it from the analysis, and use the Electric Insulation boundary condition instead of modeling those domains. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. This guide applies solely to nonlinear stationary models. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. 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. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. 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. Again, introduce a Global Parameter that gets ramped from exactly zero to one. Direct Iterative , Direct . That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Different physics have different default solvers. 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. In a previous blog entry, we introduced meshing considerations for linear static problems. If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. That is, they are tuned to achieve convergence in as many cases as possible. 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. 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. Such problems must solved in the time domain. 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? With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Sign in to create your job alert for Stationary Engineer jobs in Brea, California, United States. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. Does anyone know what should cause this problem? 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version -Detail: NaN or Inf found when solving linear system using SOR. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 The advantages of the continuation method are two-fold. To learn more, see our tips on writing great answers. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. 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. Asking for help, clarification, or responding to other answers. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). 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. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 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. 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. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . 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. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. 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. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. 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. Solve the stationary study then the time dependent study. Use this parameter to modify the nonlinearity expressions in 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. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. The settings controlling the predictor type. See Knowledge Base 1240: Manually Setting the Scaling of Variables. It is sometimes necessary to manually scale the dependent variables. Required fields are marked *. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. Function: / Failed to evaluate expression. I am trying to solve the coupling between a waveguide and a microring resonator. Repeat this for every nonlinearity of the model. 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.
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