About the Stationary Solver - COMSOL Multiphysics This case is generally difficult, or impossible, to solve since this material property is non-smooth. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) That is, start by first solving a model with a small, but non-zero, load. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. Full text of the 'Sri Mahalakshmi Dhyanam & Stotram'. 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. Not the answer you're looking for? Is it possible to rotate a window 90 degrees if it has the same length and width? With respect to any nonlinearities, replace them by a reasonable linearized term. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. (Frequency Domain should be the last step) In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. Comsol help video number 2: Solving a laminar flow problem in a slit.. Use this parameter to modify the nonlinearity expressions in the model. This is a review for cards & stationery in Brea, CA: "Love this store!!! Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems. "After the incident", I started to be more careful not to trip over things. Get email updates for new Stationary Engineer jobs in Brea, California, United States. Why is there a voltage on my HDMI and coaxial cables? An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Communication over the phone, in person, and through email was very easy. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the - COMSOL 3. Multiphysics problems are often nonlinear. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. The technique of load ramping is not always reasonable for all problems. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. In such cases, see if one material (or the other) can be omitted from the analysis completely. Stationary (time-invariant) models with nonlinearities may converge very slowly. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. Consult your product manuals for complete trademark details. Computational Fluid Dynamics (CFD), API 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. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . Trying to understand how to get this basic Fourier Series. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Thanks for contributing an answer to Stack Overflow! 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. 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. Check the solver log to see if the continuation method is backtracking. 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. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Click the link in the email we sent to to verify your email address and activate your job alert. However, if a lower-level change has been manually made to the solver settings, the software will not automatically use the correct default solver. See Knowledge Base 1240: Manually Setting the Scaling of Variables. The settings controlling the predictor type. 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. P&S: COMSOL Design Tool for Photonic Devices. What is \newluafunction? See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. However, it is usually not possible to know this ahead of time. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. 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. replace it with the expression: Your internet explorer is in compatibility mode and may not be displaying the website correctly. The objective here is to simplify the model to a state where the model will solve, with linear approximations. 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. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Popular answers (1) This problem generally occurs when there is some mistake in the physics or study section or wrong selection of the mesh size. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. listed if standards is not an option). COMSOL makes every reasonable effort to verify the information you view on this page. The objective here is to simplify the model to a state where the model will solve, with linear approximations. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. 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. Sign in to create your job alert for Stationary Engineer jobs in Brea, California, United States. To switch between these solver types, go to the Stationary Solver node within the Study sequence. 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. Could you expand a little bit more why the coupling is impossible? Can someone help me fix the COMSOL error below? | ResearchGate 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. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. Segregated approach and Direct vs. Is there a way to use the stationary solution obtained in Comsol 4.2 as the initial conditions in a time dependent model? 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. Multiscale Modeling in High-Frequency Electromagnetics. The default Initial Values for the unknowns in most physics interfaces are zero. 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. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: 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. Multiphysics problems are often nonlinear. Version 5.3 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 segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. Consult your product manuals for complete trademark details. First, it is physically intuitive, often matching how one would perform an experiment. Most multiphysics problems are nonlinear. 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. However, load ramping will not work in all cases, or may be inefficient. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. An example would be a linear static structural model of an aluminum beverage can. Why? You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Could you expand a little bit more why the coupling is impossible? If so, see: Knowledgebase 1030: Error: "Out of memory". 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 stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. The solver settings are stored at Study > Solver Configurations > 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. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) Minimising the environmental effects of my dyson brain. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. About the Stationary Solver - COMSOL Multiphysics Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. 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. We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. As we saw previously in the blog entry on Solving Nonlinear Static Finite Element Problems, not all nonlinear problems will be solvable via the damped Newton-Raphson method. Feature: Stationary Solver 1 (sol1/s1)" . 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. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. First, it is physically intuitive, often matching how one would perform an experiment. replace it with the expression: . It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. Not entering required material parameters. What sort of strategies would a medieval military use against a fantasy giant? Linear solvers. Can I tell police to wait and call a lawyer when served with a search warrant? How to solve "Undefined material property 'sigma - ResearchGate 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. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Your Discussion has gone 30 days without a reply. It is also possible to manually refine the mesh. 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. It is sometimes necessary to manually scale the dependent variables. thanks for reply 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. 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. Mesh 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. $130,000.00. Here we introduce a more robust approach to solving nonlinear problems. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. If the model is very large, and if you do not have very much memory in your computer, you may get an error message regarding memory. Iterative - COMSOL Multiphysics The conditions on the geometric aspect ratio are relatively more strict. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. 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. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. 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. 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Tutti i diritti sono riservati. 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 respect to any nonlinearities, replace them by a reasonable linearized term. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. The advantages of the continuation method are two-fold. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) The Fully Coupled solution approach, with the Plot While Solving enabled. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. How can I use it? Some models are numerically ill-conditioned due to the setup. To switch between these solver types, go to the Stationary Solver node within the Study sequence. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. 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. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. If you see this, right-click on the Solution feature and select Reset Solver to Default. I highly recommend this flower shop. 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. Name: actdep_int1, Your email address will not be published. Not assigning proper boundary conditions: Especially if you have ports. (COMSOL Multiphysics) : Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. There will always already be either a Segregated or Fully Coupled feature beneath this. Iterative , Direct . (Frequency Domain should be the last step). The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: - The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. There will also be a red cross over the Materials branch icon. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. 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 objective here is to simplify the model to a state where the model will solve, with linear approximations. Alternatively, delete and re-create the study. 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. See Knowledge Base 1240: Manually Setting the Scaling of Variables. rev2023.3.3.43278. COMSOL makes every reasonable effort to verify the information you view on this page. - Function: ^ Failed to evaluate variable. In particular, choosing an improper initial condition or setting up a problem without a solution will simply cause the nonlinear solver to continue iterating without converging. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. The algorithm is, generally speaking, a Newton's method approach. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. 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. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. Your internet explorer is in compatibility mode and may not be displaying the website correctly. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. 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. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. 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. Hence Comsol solved for the stationary solution at different points of time. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Perhaps this approach could be adapted to represent your model. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. This consent may be withdrawn. Stationary Solver Iterative Direct . 3 Replies, Please login with a confirmed email address before reporting spam. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). Troubleshooting for 3D trusses, if anyone's out there. : r/COMSOL - reddit COMSOL Blog Series on COMSOL Multiphysics Solvers Such problems must solved in the time domain. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. Stationary Solver - COMSOL Multiphysics Cooling and Solidification of Metal. For example, if there is a temperature-dependent material property such as: In our previous blog entry, we introduced the Fully Coupled and the Segregated algorithms used for solving steady-state multiphysics problems in COMSOL. What are some highly rated cards & stationery in Brea, CA? The difference between the phonemes /p/ and /b/ in Japanese. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. Today's top 351 Stationary Engineer jobs in Brea, California, United States. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. The coupling terms between the different groups are thus neglected. This is relatively expensive to do, but will lead to the most robust convergence. The segregated approach, on the other hand, solves sets of unknowns separately. The Iterative Solvers - COMSOL Multiphysics 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. 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. For example, if there is a temperature-dependent material property such as: [COMSOL_Users] output of stationary solver as input to time-dependent Not meshing all the domains. Understanding the Fully Coupled vs. Such a large difference in the materials properties can be challenging. 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. 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. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. -Detail: NaN or Inf found when solving linear system using SOR. 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. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. Check the solver log to see if the continuation method is backtracking. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field.
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