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A linear finite element model is one in which all of the material properties, loads, boundary conditions, etc are constant with respect to the solution, and the governing partial differential equations are themselves linear. 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. 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 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. I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary model. The coupling terms between the different groups are thus neglected. 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 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. 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. If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. 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. 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 segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. My comment is perhaps a bit nave but it seems to me that you could simply deactivate the term of the background field equation but keep its connexion to the solid to get what you want. Could you expand a little bit more why the coupling is impossible? Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? 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. 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. 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. 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. 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. -Detail: NaN or Inf found when solving linear system using SOR. The coupling terms between the different groups are thus neglected. In the COMSOL Multiphysics software, this step of the modeling workflow is made. Discussion Closed This discussion was created more than 6 months ago and has been closed. The problem is that when I run my model this message appear: Undefined value found. 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. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. If you have both as steps in the same study, then solve that study. 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. This approach is known as a Continuation Method with a Constant predictor. I am solving a linear stationary finite element model but the software is not solving. 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. What did people search for similar to stationary stores in Brea, CA? That is, start by first solving a model with a small, but non-zero, load. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. It may also reveal that the model itself is ill-posed in some way. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. 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 difference between the phonemes /p/ and /b/ in Japanese. To learn more, see our tips on writing great answers. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Consult your product manuals for complete trademark details. COMSOL makes every reasonable effort to verify the information you view on this page. It is also possible to manually refine the mesh. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. . Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. How can I check before my flight that the cloud separation requirements in VFR flight rules are met? Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. listed if standards is not an option). Not entering required material parameters. 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. listed if standards is not an option). COMSOL does not assume any legal liability for the accuracy of the data disclosed. 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. For example, if there is a temperature-dependent material property such as: 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. 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. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. COMSOL makes every reasonable effort to verify the information you view on this page. The algorithm is, generally speaking, a Newton's method approach. Solve the stationary study then the time dependent study. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Direct Iterative , Direct . 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. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. How do/should administrators estimate the cost of producing an online introductory mathematics class? This is relatively expensive to do, but will lead to the most robust convergence. Required fields are marked *. Multiphysics problems are often nonlinear. I highly recommend this flower shop. 3 Replies, Please login with a confirmed email address before reporting spam. The default Initial Values for the unknowns in most physics interfaces are zero. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Consult your product manuals for complete trademark details. You can unsubscribe from these emails at any time. Note: there is no way to couple this field with the time dependent nature of this physics. For example, if there is a temperature-dependent material property such as: Why? listed if standards is not an option). P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. Save this information to a file. Find centralized, trusted content and collaborate around the technologies you use most. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. 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. It is sometimes necessary to manually scale the dependent variables. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. For the Nozomi from Shinagawa to Osaka, say on a Saturday afternoon, would tickets/seats typically be available - or would you need to book? 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. rev2023.3.3.43278. As part of our solver blog series we have discussed solving nonlinear static finite element problems, load ramping for improving convergence of nonlinear problems, and nonlinearity ramping for improving convergence of nonlinear problems. Hence Comsol solved for the stationary solution at different points of time. Hello, Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. 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. 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. First, it is physically intuitive, often matching how one would perform an experiment. In this posting, we introduce the idea of ramping the nonlinearities in the problem to improve convergence. We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. COMSOL does not assume any legal liability for the accuracy of the data disclosed. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. The other low-level default settings within the Stationary Solver are chosen for robustness. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. 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. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. To switch between these solver types, go to the Stationary Solver node within the Study sequence. Review the model setup to resolve these. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems. Posted Sep 9, 2020, 1:44 p.m. EDT If so, see: Knowledgebase 1030: Error: "Out of memory". 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. 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. Thanks, Andres. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Such problems must solved in the time domain. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Click the link in the email we sent to to verify your email address and activate your job alert. Learn how your comment data is processed. How can I use it? If one particular material is missing one property, that material will also be highlighted with a red cross over that material icon in the Model Builder. Asking for help, clarification, or responding to other answers. Alternatively, delete and re-create the study. 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. Any trademarks referenced in this document are the property of their respective owners. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. If it does so, use a finer increment in that range. Today's top 351 Stationary Engineer jobs in Brea, California, United States. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) 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. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: The fully coupled and segregated approaches are discussed below. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. I use comsol multiphysics 5.2a and . Consult your product manuals for complete trademark details. If it does so, use a finer increment in that range. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). Not assigning proper boundary conditions: Especially if you have ports. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! See Knowledge Base 1240: Manually Setting the Scaling of Variables. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Your internet explorer is in compatibility mode and may not be displaying the website correctly. . The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. If you are unsure if your problem is linear and stationary, look at the Log. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used.