stationary solver comsol

listed if standards is not an option). It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. This is relatively expensive to do, but will lead to the most robust convergence. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. COMSOL does not assume any legal liability for the accuracy of the data disclosed. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. This algorithm was also useful for understanding what happens near a failure load. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. There will always already be either a Segregated or Fully Coupled feature beneath this. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. Your Discussion has gone 30 days without a reply. This approach is known as a Continuation Method with a Constant predictor. Not assigning proper boundary conditions: Especially if you have ports. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Name: actdep_int1, Your email address will not be published. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Stationary (time-invariant) models with nonlinearities may converge very slowly. ", "Absolutely the best place to shop for flowers and greenery, I spent an hour just looking around for fun prior to purchasing a bouquet, they have the best customer service people all over the place and it's a huge place", "Recently came in here to pick up 45 chocolate Seegars (cigars) for a dinner banquet in honor of my baby nephew. 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. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. This involves a systematic reduction in the model complexity. Repeat this for every nonlinearity of the model. If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. 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. It is sometimes necessary to manually scale the dependent variables. Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . Save my name, email, and website in this browser for the next time I comment. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. 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. It may also reveal that the model itself is ill-posed in some way. COMSOL does not assume any legal liability for the accuracy of the data disclosed. The technique of load ramping is not always reasonable for all problems. Understanding the Fully Coupled vs. 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version However, it is usually not possible to know this ahead of time. They deal with COMSOL package and train users. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. Use this parameter to modify the nonlinearity expressions in the model. Hello, Screenshot showing a Solver Configuration that has been altered. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Here, we will examine techniques for accelerating the convergence of these two methods. Hi ! I am solving a linear stationary finite element model but the software is not solving. Here we introduce a more robust approach to solving nonlinear problems. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. 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. To learn more, see our tips on writing great answers. $140,000.00, $120,000.00 With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. This is relatively expensive to do, but will lead to the most robust convergence. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? With respect to any nonlinearities, replace them by a reasonable linearized term. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. I am following the same model as Comsol provide us on the web. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Different physics have different default solvers. This is a review for cards & stationery in Brea, CA: "Love this store!!! comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. Thanks, Andres. It may also reveal that the model itself is ill-posed in some way. Such a large difference in the materials properties can be challenging. listed if standards is not an option). The issue here has do with the iterative algorithm used to solve nonlinear stationary models. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 - Connect and share knowledge within a single location that is structured and easy to search. 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. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) listed if standards is not an option). Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. 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. November 11, 2013. Wrong ordering of study steps. I personally liked emailing them the file, ", "This flower shop is the best! Contact COMSOL at Bangalore on their telephone: +9180 25323003. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. For example, if there is a temperature-dependent material property such as: That is, start by first solving a model with a small, but non-zero, load. If so, see: Knowledgebase 1030: Error: "Out of memory". 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 case is generally difficult, or impossible, to solve since this material property is non-smooth. It may also reveal that the model itself is ill-posed in some way. In the COMSOL Multiphysics software, this step of the modeling workflow is made. 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. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Most multiphysics problems are nonlinear. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. 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. The segregated approach, on the other hand, solves sets of unknowns separately. The objective here is to simplify the model to a state where the model will solve, with linear approximations. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. 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. Understanding the Fully Coupled vs. 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. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. Does anyone know what should cause this problem? 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. The default Initial Values for the unknowns in most physics interfaces are zero. An example would be a linear static structural model of an aluminum beverage can. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. 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. Hi Jason, How can I use it? k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) 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. thanks for reply 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. Again, introduce a Global Parameter that gets ramped from exactly zero to one. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. 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? The settings controlling the predictor type. 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. This approach is known as a Continuation Method with a Constant predictor. Mesh Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. 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. Then use this file to provide the initial conditions in time dependent model. To switch between these solver types, go to the Stationary Solver node within the Study sequence. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. 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. Posted 26 set 2019, 11:57 GMT-4 That is, they are tuned to achieve convergence in as many cases as possible. Some models are numerically ill-conditioned due to the setup. Asking for help, clarification, or responding to other answers. The algorithm is, generally speaking, a Newton's method approach. 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. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Use this parameter to modify the nonlinearity expressions in the model. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Again, introduce a Global Parameter that gets ramped from exactly zero to one. The difference between the phonemes /p/ and /b/ in Japanese. If your matrix is singular than no solver in the world can solve Ax=B. 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. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. It is also possible to manually refine the mesh. $130,000.00. Knowledgebase 1260: What to do when a linear stationary model is not solving, Knowledge Base 1240: Manually Setting the Scaling of Variables, What to do when a linear stationary model is not solving, Knowledge Base 1254: Controlling the Time Dependent solver timesteps. If 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. - Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Get email updates for new Stationary Engineer jobs in Brea, California, United States. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. Making statements based on opinion; back them up with references or personal experience. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Cooling and Solidification of Metal. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. 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 I highly recommend this flower shop. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) What are some highly rated cards & stationery in Brea, CA? Multiphysics problems are often nonlinear. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. 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. The conditions on the geometric aspect ratio are relatively more strict. - Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. That is, start by first solving a model with a small, but non-zero, load. 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. 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. listed if standards is not an option). Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. 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. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. Alle Rechte vorbehalten. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Note the star symbol on the Solution feature. The advantages of the continuation method are two-fold. COMSOL makes every reasonable effort to verify the information you view on this page. Hello guys. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Perhaps this approach could be adapted to represent your model. However, load ramping will not work in all cases, or may be inefficient. Use a manually defined mesh to avoid elements with extreme aspect ratios and perform a mesh refinement study, as described here: Performing a Mesh Refinement Study, For problems that are ill-conditioned, using a direct solver is often called for. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. 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. To switch between these solver types, go to the Stationary Solver node within the Study sequence. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. 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. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. 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. The settings controlling the predictor type. (Frequency Domain should be the last step) As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Linear solvers. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Communication over the phone, in person, and through email was very easy. replace it with the expression: Function: / Failed to evaluate expression. 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. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) For example, if there is a temperature-dependent material property 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. This involves a systematic reduction in the model complexity. Any trademarks referenced in this document are the property of their respective owners. Segregated approach and Direct vs. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Most multiphysics problems are nonlinear. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. For example, if there is a temperature-dependent material property such as: The coupling terms between the different groups are thus neglected. The settings controlling the predictor type. If you have both as steps in the same study, then solve that study. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. Discussion Closed This discussion was created more than 6 months ago and has been closed. If you are unsure if your problem is linear and stationary, look at the Log. It is also possible to manually refine the mesh. 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. Can I tell police to wait and call a lawyer when served with a search warrant? Not entering required material parameters. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. 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. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. 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. 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.