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. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. COMSOL makes every reasonable effort to verify the information you view on this page. Save my name, email, and website in this browser for the next time I comment. The objective here is to simplify the model to a state where the model will solve, with linear approximations. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. 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. Could you expand a little bit more why the coupling is impossible? Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. As a second example, when solving for Electric Currents, do not model perfect electrical insulators as materials with zero conductivity, instead, omit the domain from the model and use the Electric Insulation boundary condition. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. 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. P&S: COMSOL Design Tool for Photonic Devices. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. What are people saying about cards & stationery in Brea, CA? . Use this parameter to modify the nonlinearity expressions in the model. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. 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. Discussion Closed This discussion was created more than 6 months ago and has been closed. 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. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: It may also reveal that the model itself is ill-posed in some way. Not entering required material parameters. COMSOL does not assume any legal liability for the accuracy of the data disclosed. The other low-level default settings within the Stationary Solver are chosen for robustness. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. 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. Check the solver log to see if the continuation method is backtracking. Use this parameter to modify the nonlinearity expressions in the model. This case is generally difficult, or impossible, to solve since this material property is non-smooth. 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. 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. Minimising the environmental effects of my dyson brain. The other low-level default settings within the Stationary Solver are chosen for robustness. 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 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. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. Studysteps might be listed in wrong order: Not assigning materials to all the domains. What is \newluafunction? That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. First, it is physically intuitive, often matching how one would perform an experiment. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. Create the time-dependent step or study. Stationary (time-invariant) models with nonlinearities may converge very slowly. Tutti i diritti sono riservati. 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. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. 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. The default Initial Values for the unknowns in most physics interfaces are zero. Perhaps this approach could be adapted to represent your model. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. 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])) This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. This information is presented in the context of a very simple 1D finite element problem, and builds upon our previous entry on Solving Linear Static Finite Element Models. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Consult your product manuals for complete trademark details. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. First, it is physically intuitive, often matching how one would perform an experiment. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. The technique of load ramping is not always reasonable for all problems. Unknown function or operator. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. If it does so, use a finer increment in that range. This involves a systematic reduction in the model complexity. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Name: actdep_int1, Your email address will not be published. This approach is known as a Continuation Method with a Constant predictor. 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. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. 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.) If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. 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. Learn how your comment data is processed. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. 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. Why is there a voltage on my HDMI and coaxial cables? Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. The objective here is to simplify the model to a state where the model will solve, with linear approximations. It is also possible to manually refine the mesh. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Such a large difference in the materials properties can be challenging. It is sometimes necessary to manually scale the dependent variables. 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. However, load ramping will not work in all cases, or may be inefficient. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. 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. If it does so, use a finer increment in that range. This guide applies solely to nonlinear stationary models. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. Segregated approach and Direct vs. In the COMSOL Multiphysics software, this step of the modeling workflow is made. 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. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. - Not entering required material parameters. For example, if there is a temperature-dependent material property such as: 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. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 Solve the stationary study then the time dependent study. Hi ! This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. That is: Even if the forces on a part are opposite and equal, this is not sufficient information to say where the part is, so you must add some other condition, such as as Fixed Constraint to constrain displacement. Making statements based on opinion; back them up with references or personal experience. Cooling and Solidification of Metal. In this posting, we introduce the idea of ramping the nonlinearities in the problem to improve convergence. P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. Solver . Your internet explorer is in compatibility mode and may not be displaying the website correctly. Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. 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. ", "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. 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. There will always already be either a Segregated or Fully Coupled feature beneath this. The settings controlling the predictor type. Common Mistakes: Not assigning materials to all the domains. Reply . 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. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Stationary (time-invariant) models with nonlinearities may converge very slowly. The other low-level default settings within the Stationary Solver are chosen for robustness. For example, if there is a temperature-dependent material property such as: The fully coupled and segregated approaches are discussed below. What are some highly rated cards & stationery in Brea, CA? For example, in Solid Mechanics, if the Poisson Ratio set to 0.5, then the model will not solve, as this value in incompatible with the theory of linear elasticity. First, it is physically intuitive, often matching how one would perform an experiment. This doesn't seem to me the most elegant of methods, since I am essentially solving a stationary solution using a time dependent 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. Tutti i diritti sono riservati. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? 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 exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Not assigning proper boundary conditions: Especially if you have ports. 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. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. 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. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. With respect to any nonlinearities, replace them by a reasonable linearized term. 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. Multiscale Modeling in High-Frequency Electromagnetics. Hi Jason, Here, we will examine techniques for accelerating the convergence of these two methods. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Thanks for contributing an answer to Stack Overflow! $140,000.00, $120,000.00 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Thanks, Andres. Version 5.3 The advantages of the continuation method are two-fold. How do/should administrators estimate the cost of producing an online introductory mathematics class? Have you taken a look at this blog post? 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. 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. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) If so, see: Knowledgebase 1030: Error: "Out of memory". Stationary Engineer Jobs in Brea, California, United States, $87,400.00 This approach is known as a Continuation Method with a Constant predictor. 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. The settings controlling the predictor type. 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. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. - I am solving a linear stationary finite element model but the software is not solving. 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 - 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. If this was solved using the Solid Mechanics physics interface the thin walls of the container would need to be explicitly modeled, but the wall thickness is much smaller than the overall can dimensions. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Find detailed information on Office Supplies, Stationery, and Gift Retailers companies in Brea, California, United States of America, including financial statements, sales and marketing contacts, top competitors, and firmographic insights. To start a new discussion with a link back to this one, click here. Function: / Failed to evaluate expression. Required fields are marked *. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Such problems must solved in the time domain. Mesh Knowledgebase 1260: What to do when a linear stationary model is not solving, Knowledge Base 1240: Manually Setting the Scaling of Variables, What to do when a linear stationary model is not solving, Knowledge Base 1254: Controlling the Time Dependent solver timesteps, Galleria dei Modelli e delle App di Simulazione, 2023 da COMSOL. Hence Comsol solved for the stationary solution at different points of time. Multiphysics problems are often nonlinear. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Linear solvers. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. COMSOL 22.9K subscribers Adding a study to your simulation is necessary in order to solve your problem. 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 guide applies solely to nonlinear stationary models. (Frequency Domain should be the last step) I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary model. It may also reveal that the model itself is ill-posed in some way. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Direct PARDISO Solver , PARDISO . From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. 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. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Then use this file to provide the initial conditions in time dependent model. I use comsol multiphysics 5.2a and . These are some cards & stationery with a large number of reviews in Brea, CA. The fully coupled and segregated approaches are discussed below. Have you taken a look at this [blog post](https://www.comsol.com/blogs/modeling-fluid-structure-interaction-in-multibody-mechanisms/)? It may also reveal that the model itself is ill-posed in some way. Stationary (time-invariant) models with nonlinearities may converge very slowly. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. See Knowledge Base 1240: Manually Setting the Scaling of Variables. Comsol help video number 2: Solving a laminar flow problem in a slit.. The Fully Coupled solution approach, with the Plot While Solving enabled. . Get notified about new Stationary Engineer jobs in Brea, California, United States. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Segregated approach and Direct vs. Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems. Not assigning proper boundary conditions: Especially if you have ports. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Multiphysics problems are often nonlinear. How can I use it? (I am begginer in comsol) Thank you. 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. The advantages of the continuation method are two-fold. This involves a systematic reduction in the model complexity. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. This is a review for cards & stationery in Brea, CA: "Love this store!!! 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. listed if standards is not an option). This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Why? - Function: ^ Failed to evaluate variable. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. See Knowledge Base 1240: Manually Setting the Scaling of Variables. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. It is also possible to manually refine the mesh. Not meshing all the domains. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). (Frequency Domain should be the last step) You can unsubscribe from these emails at any time. Linear solvers. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. This approach is known as a Continuation Method with a Constant predictor. Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. If you are unsure if your problem is linear and stationary, look at the Log. Any trademarks referenced in this document are the property of their respective owners. Hi Jason, 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. However, it is usually not possible to know this ahead of time.

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