You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Alternatively, delete and re-create the study. 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. Again, introduce a Global Parameter that gets ramped from exactly zero to one. However, it is usually not possible to know this ahead of time. This case is generally difficult, or impossible, to solve since this material property is non-smooth. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Stationary (time-invariant) models with nonlinearities may converge very slowly. The default Initial Values for the unknowns in most physics interfaces are zero. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Thanks, Andres. Not assigning proper boundary conditions: Especially if you have ports. Stationary Solver Iterative Direct . Hi ! 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. Does anyone know what should cause this problem? P&S: COMSOL Design Tool for Photonic Devices. We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. This involves a systematic reduction in the model complexity. listed if standards is not an option). There will always already be either a Segregated or Fully Coupled feature beneath this. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Wish you all the best. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. 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. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) 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. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Learn how your comment data is processed. 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. - Feature: Stationary Solver 1 (sol1/s1) Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. Have you taken a look at this [blog post](https://www.comsol.com/blogs/modeling-fluid-structure-interaction-in-multibody-mechanisms/)? - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Save my name, email, and website in this browser for the next time I comment. Can I tell police to wait and call a lawyer when served with a search warrant? Mesh Also, keep in mind that a linear stationary model should solve regardless of how coarse the mesh is (albeit to a low accuracy) so you can always start with as coarse a mesh as possible, and refine the mesh (See also: Knowledgebase 1030: Performing a Mesh Refinement Study. This involves a systematic reduction in the model complexity. If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. 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. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. The Fully Coupled solution approach, with the Plot While Solving enabled. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Stationary in the COMSOL Multiphysics Programming Reference Manual Damped Newton Methods The nonlinear solver uses an affine invariant form of the damped Newton method as described in Ref. Again, introduce a Global Parameter that gets ramped from exactly zero to one. 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. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Different physics have different default solvers. The coupling terms between the different groups are thus neglected. thanks for reply As we saw in Load Ramping of Nonlinear Problems, we can use the continuation method to ramp the loads on a problem up from an unloaded case where we know the solution. 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. Such problems must solved in the time domain. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. In such cases, see if one material (or the other) can be omitted from the analysis completely. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. This guide applies solely to nonlinear stationary models. Comsol help video number 2: Solving a laminar flow problem in a slit.. Here, we will examine techniques for accelerating the convergence of these two methods. 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. 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. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. 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. 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. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. How can I check before my flight that the cloud separation requirements in VFR flight rules are met? This case is generally difficult, or impossible, to solve since this material property is non-smooth. Today's top 351 Stationary Engineer jobs in Brea, California, United States. The technique of load ramping is not always reasonable for all problems. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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. Some models are numerically ill-conditioned due to the setup. See Knowledge Base 1240: Manually Setting the Scaling of Variables. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. 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. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). 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. Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble Leverage your professional network, and get hired. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. What version of COMSOL are you using? In the COMSOL Multiphysics software, this step of the modeling workflow is made. The problem is that when I run my model this message appear: Undefined value found. 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. This approach is known as a Continuation Method with a Constant predictor. Hi Jason, Such problems must solved in the time domain. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) I am trying to solve the coupling between a waveguide and a microring resonator. Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. Segregated approach and Direct vs. Iterative linear solvers, Time dependent function and stationary study, Combining Adaptive Mesh Refinement with Data Filtering, What to do when a linear stationary model is not solving, Galleria dei Modelli e delle App di Simulazione, 2023 da COMSOL. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. COMSOL makes every reasonable effort to verify the information you view on this page. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. 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. 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 the star symbol on the Solution feature. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. With respect to any nonlinearities, replace them by a reasonable linearized term. The coupling terms between the different groups are thus neglected. What sort of strategies would a medieval military use against a fantasy giant? Create the time-dependent step or 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. Repeat this for every nonlinearity of the model. These are some cards & stationery with a large number of reviews in Brea, CA. 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. 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. She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. COMSOL makes every reasonable effort to verify the information you view on this page. Screenshot showing a Solver Configuration that has been altered. The advantages of the continuation method are two-fold. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. Tutti i diritti sono riservati. Get email updates for new Stationary Engineer jobs in Brea, California, United States. How do/should administrators estimate the cost of producing an online introductory mathematics class? Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. COMSOL does not assume any legal liability for the accuracy of the data disclosed. If you have both as steps in the same study, then solve that study. The segregated approach, on the other hand, solves sets of unknowns separately. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. 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. COMSOL 22.9K subscribers Adding a study to your simulation is necessary in order to solve your problem. Making statements based on opinion; back them up with references or personal experience. How can I use it? Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. 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. 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. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. Your internet explorer is in compatibility mode and may not be displaying the website correctly. To start a new discussion with a link back to this one, click here. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version If your matrix is singular than no solver in the world can solve Ax=B. 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. It is also possible to manually refine the mesh. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). 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 you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. They worked with me. Could you expand a little bit more why the coupling is impossible? Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) Click the link in the email we sent to to verify your email address and activate your job alert. 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 This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. To learn more, see our tips on writing great answers. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Your internet explorer is in compatibility mode and may not be displaying the website correctly. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version - Your internet explorer is in compatibility mode and may not be displaying the website correctly. Wrong ordering of study steps. 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. The fully coupled and segregated approaches are discussed below. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. The settings controlling the predictor type. rev2023.3.3.43278. The difference between the phonemes /p/ and /b/ in Japanese. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. The advantages of the continuation method are two-fold. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) (Frequency Domain should be the last step). The fully coupled and segregated approaches are discussed below. 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. The default Initial Values for the unknowns in most physics interfaces are zero. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. Hence Comsol solved for the stationary solution at different points of time. 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. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. The other low-level default settings within the Stationary Solver are chosen for robustness. The settings controlling the predictor type. The algorithm is, generally speaking, a Newton's method approach. 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. However, it is usually not possible to know this ahead of time. 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. They deal with COMSOL package and train users. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. 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. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. 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. 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. Consult your product manuals for complete trademark details. Understanding the Fully Coupled vs. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. Hi Jason, If you are unsure if your problem is linear and stationary, look at the Log. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. To start a new discussion with a link back to this one, click here. Thanks for contributing an answer to Stack Overflow! Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. so many cute little stationary items , hair". 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.) 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. If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Common Mistakes: Not assigning materials to all the domains. To switch between these solver types, go to the Stationary Solver node within the Study sequence. $140,000.00, $120,000.00 If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. However, if a lower-level change has been manually made to the solver settings, the software will not automatically use the correct default solver. 0 Replies, Please login with a confirmed email address before reporting spam. If it does so, use a finer increment in that range. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. To switch between these solver types, go to the Stationary Solver node within the Study sequence. What are some highly rated cards & stationery in Brea, CA? $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 It may also reveal that the model itself is ill-posed in some way. First, it is physically intuitive, often matching how one would perform an experiment. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. 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. Direct PARDISO Solver , PARDISO . Connect and share knowledge within a single location that is structured and easy to search. Use this parameter to modify the nonlinearity expressions in the model. To switch between these solver types, go to the Stationary Solver node within the Study sequence. 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. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. See Knowledge Base 1240: Manually Setting the Scaling of Variables. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. 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. 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. The algorithm is, generally speaking, a Newton's method approach. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. 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.
How Did Teresa Meet Eddie Brucks,
Articles S
