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To switch between these solver types, go to the Stationary Solver node within the Study sequence. However, it is usually not possible to know this ahead of time. Reply . If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. November 11, 2013. However, if a lower-level change has been manually made to the solver settings, the software will not automatically use the correct default solver. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. 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 fully coupled and segregated approaches are discussed below. 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. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. With respect to any nonlinearities, replace them by a reasonable linearized term. They worked with me. Is it possible to rotate a window 90 degrees if it has the same length and width? First, it is physically intuitive, often matching how one would perform an experiment. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Here, we will examine techniques for accelerating the convergence of these two methods. She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. That is, start by first solving a model with a small, but non-zero, load. Such a large difference in the materials properties can be challenging. I highly recommend this flower shop. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. COMSOL makes every reasonable effort to verify the information you view on this page. - A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. 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. 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. 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. Note: there is no way to couple this field with the time dependent nature of this physics. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. In such cases, see if one material (or the other) can be omitted from the analysis completely. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. . There will always already be either a Segregated or Fully Coupled feature beneath this. This guide applies solely to nonlinear stationary models. comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. Comsol help video number 2: Solving a laminar flow problem in a slit.. What did people search for similar to stationary stores in Brea, CA? This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. 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. Have you taken a look at this blog post? SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version listed if standards is not an option). 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. Function: / Failed to evaluate expression. Communication over the phone, in person, and through email was very easy. If your matrix is singular than no solver in the world can solve Ax=B. Hi Jason, I am following the same model as Comsol provide us on the web. listed if standards is not an option). Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. Required fields are marked *. Review the model setup to resolve these. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. It may also reveal that the model itself is ill-posed in some way. How do/should administrators estimate the cost of producing an online introductory mathematics class? Note the star symbol on the Solution feature. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Note: there is no way to couple this . 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. With respect to any nonlinearities, replace them by a reasonable linearized term. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. They are usually called comp1.u, comp1.v, and comp1.w though. "After the incident", I started to be more careful not to trip over things. 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 many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. 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. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. Wrong ordering of study steps. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Could you expand a little bit more why the coupling is impossible? Such problems must solved in the time domain. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. 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. Get notified about new Stationary Engineer jobs in Brea, California, United States. The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! Changes to these low-level settings from the defaults will usually be quite model- and case-specific. That is, they are tuned to achieve convergence in as many cases as possible. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Not meshing all the domains. Alle Rechte vorbehalten. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. 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 is a review for cards & stationery in Brea, CA: "Love this store!!! You can unsubscribe from these emails at any time. What is the purpose of non-series Shimano components? $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 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. To start a new discussion with a link back to this one, click here. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Such problems must solved in the time domain. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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. In the COMSOL Multiphysics software, this step of the modeling workflow is made. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. thanks for reply If it does so, use a finer increment in that range. Stationary (time-invariant) models with nonlinearities may converge very slowly. 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 settings controlling the predictor type. Hello guys. 3. 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. Set initial conditions in the physics to the appropriate dependent model variable names rather than the default 0. If you see this, right-click on the Solution feature and select Reset Solver to Default. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. This guide applies solely to nonlinear stationary models. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. With respect to any nonlinearities, replace them by a reasonable linearized term. . If you are unsure if your problem is linear and stationary, look at the Log. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. 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. 3 Replies, Please login with a confirmed email address before reporting spam. Direct Iterative , Direct . 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. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Your Discussion has gone 30 days without a reply. That is, they are tuned to achieve convergence in as many cases as possible. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Tutti i diritti sono riservati. Any trademarks referenced in this document are the property of their respective owners. Using the first order optimality. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. What version of COMSOL are you using? If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. 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. - Function: ^ Failed to evaluate variable. However, load ramping will not work in all cases, or may be inefficient. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. 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. replace it with the expression: 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. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. 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. Making statements based on opinion; back them up with references or personal experience. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 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. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) The default Initial Values for the unknowns in most physics interfaces are zero. rev2023.3.3.43278. The objective here is to simplify the model to a state where the model will solve, with linear approximations. Any trademarks referenced in this document are the property of their respective owners. If you have both as steps in the same study, then solve that study. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. 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. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. 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.) 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. 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. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. 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. 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. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. I am trying to solve the coupling between a waveguide and a microring resonator. This consent may be withdrawn. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. Alternatively, delete and re-create the study. 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. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Thanks, Andres. 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 the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. How can I use it? You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version $140,000.00, $120,000.00 (Frequency Domain should be the last step) Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems. Posted Sep 9, 2020, 1:44 p.m. EDT Not entering required material parameters. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Have you taken a look at this [blog post](https://www.comsol.com/blogs/modeling-fluid-structure-interaction-in-multibody-mechanisms/)? This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. 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. This algorithm was also useful for understanding what happens near a failure load. 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. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. That is, they are tuned to achieve convergence in as many cases as possible. 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.