stationary solver comsol

If so, see: Knowledgebase 1030: Error: "Out of memory". The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. rev2023.3.3.43278. If you are unsure if your problem is linear and stationary, look at the Log. The difference between the phonemes /p/ and /b/ in Japanese. Again, introduce a Global Parameter that gets ramped from exactly zero to one. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. . Hence Comsol solved for the stationary solution at different points of time. 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. 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. They are usually called comp1.u, comp1.v, and comp1.w though. 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. 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. 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 can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. There will also be a red cross over the Materials branch icon. What is the purpose of non-series Shimano components? Specify Material Properties in COMSOL Multiphysics (3/8) 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. The technique of load ramping is not always reasonable for all problems. 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. However, it is usually not possible to know this ahead of time. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). If you see this, right-click on the Solution feature and select Reset Solver to Default. 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. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. 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. 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. This case is generally difficult, or impossible, to solve since this material property is non-smooth. What did people search for similar to stationary stores in Brea, CA? Thanks for contributing an answer to Stack Overflow! The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). The default Initial Values for the unknowns in most physics interfaces are zero. Why doesn't iterative solver converge in COMSOL? - ResearchGate Hello guys. See Knowledge Base 1240: Manually Setting the Scaling of Variables. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. Alternatively, delete and re-create the study. Cecilia M. came from the backroom to help me and went out of her way to help me even though I had not called before going into the store. 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. Understanding stationary and time dependent solver COMSOL Multiphysics It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. Use this parameter to modify the nonlinearity expressions in the model. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Trying to understand how to get this basic Fourier Series. Iterative , Direct . These are some cards & stationery with a large number of reviews in Brea, CA. Feature: Stationary Solver 1 (sol1/s1)" . Discussion Closed This discussion was created more than 6 months ago and has been closed. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. The coupling terms between the different groups are thus neglected. - It may also reveal that the model itself is ill-posed in some way. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. COMSOL makes every reasonable effort to verify the information you view on this page. Solver . If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. There will always already be either a Segregated or Fully Coupled feature beneath this. The fully coupled and segregated approaches are discussed below. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. COMSOL makes every reasonable effort to verify the information you view on this page. That is, they are tuned to achieve convergence in as many cases as possible. 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. 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, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. That is, start by first solving a model with a small, but non-zero, load. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. - Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. Here we introduce a more robust approach to solving nonlinear problems. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. With respect to any nonlinearities, replace them by a reasonable linearized term. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. In this case, it would likely be reasonable to treat the insulative material as a perfect insulator, omit it from the analysis, and use the Electric Insulation boundary condition instead of modeling those domains. About the Stationary Solver The following background information about the Stationary Solver discusses these topics: Damped Newton Methods, Termination Criterion for the Fully Coupled and Segregated Attribute Nodes, Linear Solvers versus Nonlinear Solvers, and Pseudo Time Stepping. I am solving a linear stationary finite element model but the software is not solving. 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. The default Initial Values for the unknowns in most physics interfaces are zero. The settings controlling the predictor type. 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. If it does so, use a finer increment in that range. It is sometimes necessary to manually scale the dependent variables. Consult your product manuals for complete trademark details. 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. 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. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. This guide applies solely to nonlinear stationary models. Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. 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. If some, or all, of the needed materials properties needed by the physics interfaces are not defined, the model will generate an error at runtime. This guide applies solely to nonlinear stationary models. What sort of strategies would a medieval military use against a fantasy giant? Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Note: there is no way to couple this . Stationary Solver Iterative Direct . 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. 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. It is sometimes necessary to manually scale the dependent variables. To switch between these solver types, go to the Stationary Solver node within the Study sequence. This consent may be withdrawn. (Frequency Domain should be the last step) Not entering required material parameters. $140,000.00, $120,000.00 Linear solvers. Screenshot showing a Solver Configuration that has been altered. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Is it possible to rotate a window 90 degrees if it has the same length and width? To start a new discussion with a link back to this one, click here. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Stationary (time-invariant) models with nonlinearities may converge very slowly. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. (COMSOL Multiphysics) : Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble 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. - 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. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. The advantages of the continuation method are two-fold. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. 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. Then use this file to provide the initial conditions in time dependent model. Get email updates for new Stationary Engineer jobs in Brea, California, United States. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Posted 26 set 2019, 11:57 GMT-4 There will always already be either a Segregated or Fully Coupled feature beneath this. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Create the time-dependent step or study. Common Mistakes: Not assigning materials to all the domains. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. Here, we will examine techniques for accelerating the convergence of these two methods. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Troubleshooting for 3D trusses, if anyone's out there. : r/COMSOL - reddit comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. 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. COMSOL does not assume any legal liability for the accuracy of the data disclosed. For example, if there is a temperature-dependent material property such as: Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. Not assigning proper boundary conditions: Especially if you have ports. Making statements based on opinion; back them up with references or personal experience. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. This case is generally difficult, or impossible, to solve since this material property is non-smooth. This is relatively expensive to do, but will lead to the most robust convergence. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 The conditions on the geometric aspect ratio are relatively more strict. 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. Minimising the environmental effects of my dyson brain. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Reply . Check the solver log to see if the continuation method is backtracking. In the COMSOL Multiphysics software, this step of the modeling workflow is made. 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. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. 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. Could you expand a little bit more why the coupling is impossible? 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. Direct Iterative , Direct . Solve the stationary study then the time dependent study. Multiphysics problems are often nonlinear. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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 is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Wrong ordering of study steps. The coupling terms between the different groups are thus neglected. Such problems must solved in the time domain. (Frequency Domain should be the last step) Can I tell police to wait and call a lawyer when served with a search warrant? The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. 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. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. The other low-level default settings within the Stationary Solver are chosen for robustness. It may also reveal that the model itself is ill-posed in some way. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) The technique of load ramping is not always reasonable for all problems. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. What are some highly rated cards & stationery in Brea, CA? From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. This is relatively expensive to do, but will lead to the most robust convergence. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Your internet explorer is in compatibility mode and may not be displaying the website correctly. Your Discussion has gone 30 days without a reply. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. Mesh Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. First, it is physically intuitive, often matching how one would perform an experiment. The segregated approach, on the other hand, solves sets of unknowns separately. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. See Knowledge Base 1240: Manually Setting the Scaling of Variables. With respect to any nonlinearities, replace them by a reasonable linearized term. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Cooling and Solidification of Metal. 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. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Not entering required material parameters. L'objectif de notre prsent travail se repose sur l'tude par simulation numrique du comportement de bton au jeune ge sous des conditions svres de temprature pendant les premires 24h aprs. 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. 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. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. How can I use it? 140K views 8 years ago COMSOL Multiphysics Tutorial for Beginners Please note that an updated version of the content in this video can be found in the Modeling Workflow video in the COMSOL. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. Common Study Step Settings - COMSOL Multiphysics See Knowledge Base 1240: Manually Setting the Scaling of Variables. Wrong ordering of study steps. 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. 3 Replies, Please login with a confirmed email address before reporting spam.

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