That is, start by first solving a model with a small, but non-zero, load. The fully coupled and segregated approaches are discussed below. Use this parameter to modify the nonlinearity expressions in the model. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Direct PARDISO Solver , PARDISO . The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. 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. What are some highly rated cards & stationery in Brea, CA? This is relatively expensive to do, but will lead to the most robust convergence. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. Improving Convergence of Nonlinear Stationary Models - Informazioni Different physics have different default solvers. comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. The advantages of the continuation method are two-fold. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. The objective here is to simplify the model to a state where the model will solve, with linear approximations. rev2023.3.3.43278. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. 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. thanks for reply Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. The objective here is to simplify the model to a state where the model will solve, with linear approximations. This case is generally difficult, or impossible, to solve since this material property is non-smooth. Hello guys. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. Save this information to a file. 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. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. 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. Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . 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. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. 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. 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. Consult your product manuals for complete trademark details. The advantages of the continuation method are two-fold. I personally liked emailing them the file, ", "This flower shop is the best! Multiphysics problems are often nonlinear. Iterative , Direct . 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. Does anyone know what should cause this problem? 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. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. There will always already be either a Segregated or Fully Coupled feature beneath this. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Top 10 Best Stationary in Brea, CA - October 2022 - Yelp COMSOL makes every reasonable effort to verify the information you view on this page. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Not entering required material parameters. Not assigning proper boundary conditions: Especially if you have ports. 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. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. 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. If you are unsure if your problem is linear and stationary, look at the Log. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. The Fully Coupled solution approach, with the Plot While Solving enabled. Contact COMSOL at Bangalore on their telephone: +9180 25323003. Consult your product manuals for complete trademark details. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Is there a way to use the stationary solution obtained in Comsol 4.2 as the initial conditions in a time dependent model? Any trademarks referenced in this document are the property of their respective owners. Have you taken a look at this blog post? The fully coupled and segregated approaches are discussed below. 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, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. listed if standards is not an option). Is it possible to rotate a window 90 degrees if it has the same length and width? Common Errors in Comsol - P&S: COMSOL Design Tool for Photonic Devices "After the incident", I started to be more careful not to trip over things. 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: Iterative - COMSOL Multiphysics This approach is known as a Continuation Method with a Constant predictor. 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. Improving Convergence of Nonlinear Stationary Models - COMSOL 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. Such a large difference in the materials properties can be challenging. In a previous blog entry, we introduced meshing considerations for linear static problems. COMSOL does not assume any legal liability for the accuracy of the data disclosed. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) 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 Iterative Solvers - COMSOL Multiphysics In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. Full text of the 'Sri Mahalakshmi Dhyanam & Stotram'. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) replace it with the expression: k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) What version of COMSOL are you using? However, it is usually not possible to know this ahead of time. If it does so, use a finer increment in that range. 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. 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 Solver Iterative Direct . 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. replace it with the expression: 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]) To learn more, see our tips on writing great answers. 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. 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. Discussion Closed This discussion was created more than 6 months ago and has been closed. "I chose this print shop based off yelp reviews and was very happy with the outcome! 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. thanks for reply However, if a lower-level change has been manually made to the solver settings, the software will not automatically use the correct default solver. 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. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Not entering required material parameters. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Solving for laminar flow using Comsol - YouTube -Detail: NaN or Inf found when solving linear system using SOR. COMSOL 22.9K subscribers Adding a study to your simulation is necessary in order to solve your problem. We use COMSOL Multiphysics for solving distributed optimal control of un-steady Burgers equation without constraints and with pointwise control constraints. 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. 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. For example, if there is a temperature-dependent material property such as: The coupling terms between the different groups are thus neglected. Could you expand a little bit more why the coupling is impossible? In such cases, see if one material (or the other) can be omitted from the analysis completely. With respect to any nonlinearities, replace them by a reasonable linearized term. 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. 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. This case is generally difficult, or impossible, to solve since this material property is non-smooth. 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. 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. The objective here is to simplify the model to a state where the model will solve, with linear approximations. Solve the stationary study then the time dependent study. Not meshing all the domains. Office Supplies, Stationery, and Gift Retailers Companies in Brea $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 Top 10 Best Stationary Stores in Brea, CA - December 2022 - Yelp You can unsubscribe from these emails at any time. . The default Initial Values for the unknowns in most physics interfaces are zero. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 Screenshot showing a Solver Configuration that has been altered. Segregated approach and Direct vs. How to Add a Study to Your Simulation in COMSOL Multiphysics That is, start by first solving a model with a small, but non-zero, load. What is the purpose of non-series Shimano components? Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Perhaps this approach could be adapted to represent your model. Making statements based on opinion; back them up with references or personal experience. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. 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. COMSOL does not assume any legal liability for the accuracy of the data disclosed. 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. 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 technique of load ramping is not always reasonable for all problems. 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. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. 0 Replies, Please login with a confirmed email address before reporting spam. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. What is \newluafunction? See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. 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. If it does so, use a finer increment in that range. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the - COMSOL First, it is physically intuitive, often matching how one would perform an experiment. Click the link in the email we sent to to verify your email address and activate your job alert. Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. 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. New Stationary Engineer jobs added daily. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Stationary (time-invariant) models with nonlinearities may converge very slowly. 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 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. The other low-level default settings within the Stationary Solver are chosen for robustness. Consult your product manuals for complete trademark details. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Why doesn't iterative solver converge in COMSOL? - ResearchGate Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. However, load ramping will not work in all cases, or may be inefficient. Not meshing all the domains. Not assigning proper boundary conditions: Especially if you have ports. Note the star symbol on the Solution feature. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Does anyone know how to solve error in stationary solver in COMSOL I highly recommend this flower shop. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Wrong ordering of study steps. I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary model. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. 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. These can be used alone, or in combination with other interfaces. The segregated approach, on the other hand, solves sets of unknowns separately.