stationary solver comsol

The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. I highly recommend this flower shop. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version (COMSOL Multiphysics) : 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. It is also possible to manually refine the mesh. Using the first order optimality. Office Supplies, Stationery, and Gift Retailers Companies in Brea Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Linear solvers. 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. To learn more, see our tips on writing great answers. Any trademarks referenced in this document are the property of their respective owners. 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. This involves a systematic reduction in the model complexity. listed if standards is not an option). That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. The technique of load ramping is not always reasonable for all problems. It's brand new in the hmart plaza and I wish it was open back when I would hangout in the plaza after school (although they would have taken all my allowance money! Minimising the environmental effects of my dyson brain. The following are possible reasons why a linear stationary model will fail to solve, along with resolutions: The combination of the constraints and boundary conditions must be sufficient to define a unique solution to the problem, in terms of the field variables being solved. Why do many companies reject expired SSL certificates as bugs in bug bounties? This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. Studysteps might be listed in wrong order: Not assigning materials to all the domains. 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. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. (Frequency Domain should be the last step) 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. Here we introduce a more robust approach to solving nonlinear problems. 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. 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. Improving Convergence of Nonlinear Stationary Models - COMSOL 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. Your Discussion has gone 30 days without a reply. Is it possible to rotate a window 90 degrees if it has the same length and width? Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. It may also reveal that the model itself is ill-posed in some way. I am following the same model as Comsol provide us on the web. If you try to enter a variable that is undefined, the automatic syntax highlighting will identify this as you enter it, and it is best practice to resolve this immediately. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. 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. replace it with the expression: P&S: COMSOL Design Tool for Photonic Devices - ETH Z The coupling terms between the different groups are thus neglected. If it does so, use a finer increment in that range. These are some highly rated cards & stationery in Brea, CA: What are some cards & stationery with a large number of reviews in Brea, CA? Alternatively, delete and re-create the study. Contact COMSOL at Bangalore on their telephone: +9180 25323003. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. - Feature: Stationary Solver 1 (sol1/s1) replace it with the expression: Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. Such a large difference in the materials properties can be challenging. The nature of simulating nature: A Q&A with IBM Quantum researcher Dr. Jamie We've added a "Necessary cookies only" option to the cookie consent popup. An example would be a linear static structural model of an aluminum beverage can. This is relatively expensive to do, but will lead to the most robust convergence. $140,000.00, $120,000.00 This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Reviews on Stationary in Brea, CA - Mievic, Typo, Tokyo Japanese Lifestyle, Fancy, Posh Paper, Morning Glory, Velvet Fox Designs, Barnes & Noble, Michaels, Select Graphics & Printing A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. 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. P&S: COMSOL Design Tool for Photonic Devices. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Check the solver log to see if the continuation method is backtracking. thanks for reply 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. However, it is usually not possible to know this ahead of time. Save my name, email, and website in this browser for the next time I comment. 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. There will always already be either a Segregated or Fully Coupled feature beneath this. 3. How to Add a Study to Your Simulation in COMSOL Multiphysics Such problems must solved in the time domain. 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. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Iterative - COMSOL Multiphysics We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. listed if standards is not an option). 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. The objective here is to simplify the model to a state where the model will solve, with linear approximations. 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. Stationary Solver Iterative Direct . This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Not meshing all the domains. 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. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 Check the solver log to see if the continuation method is backtracking. 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. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. 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. Specify Material Properties in COMSOL Multiphysics (3/8) 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. 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. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. 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. To start a new discussion with a link back to this one, click here. Cooling and Solidification of Metal. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. If it does so, use a finer increment in that range. Does anyone know what should cause this problem? However, it is usually not possible to know this ahead of time. This algorithm was also useful for understanding what happens near a failure load. Why doesn't iterative solver converge in COMSOL? - ResearchGate The issue here has do with the iterative algorithm used to solve nonlinear stationary models. Stationary (time-invariant) models with nonlinearities may converge very slowly. 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. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. Segregated approach and Direct vs. Connect and share knowledge within a single location that is structured and easy to search. 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. This is relatively expensive to do, but will lead to the most robust convergence. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. About the Stationary Solver - COMSOL Multiphysics COMSOL does not assume any legal liability for the accuracy of the data disclosed. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. In this posting, we introduce the idea of ramping the nonlinearities in the problem to improve convergence. 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. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. How can I check before my flight that the cloud separation requirements in VFR flight rules are met? Solve the stationary study then the time dependent study. Stationary (time-invariant) models with nonlinearities may converge very slowly. 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. Review the model setup to resolve these. 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. They worked with me. If you are unsure if your problem is linear and stationary, look at the Log. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. The segregated approach, on the other hand, solves sets of unknowns separately. How to solve "Feature: Stationary Solver 1 (sol1/s1) Attempt - COMSOL In the COMSOL Multiphysics software, this step of the modeling workflow is made. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. 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. COMSOL Blog Series on COMSOL Multiphysics Solvers 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. 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. Not entering required material parameters. 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. -Detail: NaN or Inf found when solving linear system using SOR. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). 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. The algorithm is, generally speaking, a Newton's method approach. The technique of load ramping is not always reasonable for all problems. 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.) To start a new discussion with a link back to this one, click here. 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. They are usually called comp1.u, comp1.v, and comp1.w though. This guide applies solely to nonlinear stationary models. 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. Trying to understand how to get this basic Fourier Series. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: 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 solution approach, with the Plot While Solving enabled. 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. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) The issue here has do with the iterative algorithm used to solve nonlinear stationary models. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. COMSOL makes every reasonable effort to verify the information you view on this page. What are people saying about cards & stationery in Brea, CA? 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 Auxiliary Sweep can be used to implement ramping of any Global Parameter. Cooling and Solidification of Metal. 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. This involves a systematic reduction in the model complexity. How to solve "Undefined material property 'sigma - ResearchGate Not assigning proper boundary conditions: Especially if you have ports. See Knowledge Base 1240: Manually Setting the Scaling of Variables. Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2, Simulation of effect of heated resistance on temperature distribution in laminar flow, COMSOL: Diffusion in Transport of Diluted Species Produces Unphysical Results. Improving Convergence of Nonlinear Stationary Models - Informazioni 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. 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. This case is generally difficult, or impossible, to solve since this material property is non-smooth. 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. 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. November 11, 2013. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). 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. It is sometimes necessary to manually scale the dependent variables. Save this information to a file. The solver settings are stored at Study > Solver Configurations > Solution. This involves a systematic reduction in the model complexity. What is the purpose of non-series Shimano components? SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. 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. Multiphysics problems are often nonlinear. 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. New Stationary Engineer jobs added daily. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. How can I use it? Wrong ordering of study steps. 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. 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. comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. - Function: ^ Failed to evaluate variable. 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, 2023 by COMSOL. Again, introduce a Global Parameter that gets ramped from exactly zero to one. Leverage your professional network, and get hired. Some models are numerically ill-conditioned due to the setup. I am trying to solve the coupling between a waveguide and a microring resonator. 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. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. The default Initial Values for the unknowns in most physics interfaces are zero. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. listed if standards is not an option). That is, they are tuned to achieve convergence in as many cases as possible. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 Your internet explorer is in compatibility mode and may not be displaying the website correctly. Use this parameter to modify the nonlinearity expressions in the model. It is sometimes necessary to manually scale the dependent variables. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Any trademarks referenced in this document are the property of their respective owners. Is there a way to use the stationary solution obtained in Comsol 4.2 as the initial conditions in a time dependent model? The algorithm is, generally speaking, a Newton's method approach. Segregated approach and Direct vs. Hi ! 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. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. Making statements based on opinion; back them up with references or personal experience. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 351 Stationary Engineer jobs in Brea, California, United States (15 new) Direct Iterative , Direct . If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving.