If you have both as steps in the same study, then solve that study. The technique of load ramping is not always reasonable for all problems. 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. 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. Comsol help video number 2: Solving a laminar flow problem in a slit.. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Mesh Name: actdep_int1, Your email address will not be published. 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. What are some highly rated cards & stationery in Brea, CA? COMSOL does not assume any legal liability for the accuracy of the data disclosed. 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. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Understanding the Fully Coupled vs. Not assigning proper boundary conditions: Especially if you have ports. How do/should administrators estimate the cost of producing an online introductory mathematics class? That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. 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. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. Such problems must solved in the time domain. 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. 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. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. For the Nozomi from Shinagawa to Osaka, say on a Saturday afternoon, would tickets/seats typically be available - or would you need to book? 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. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. - The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. 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. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. If you are unsure if your problem is linear and stationary, look at the Log. The continuation method will again backtrack and try intermediate values of the ramping parameter, thus giving you the nearest approximation to the abrupt transition that is solvable. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. The fully coupled and segregated approaches are discussed below. 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. I highly recommend this flower shop. However, it is usually not possible to know this ahead of time. 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. Asking for help, clarification, or responding to other answers. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. 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. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. This case is generally difficult, or impossible, to solve since this material property is non-smooth. The other low-level default settings within the Stationary Solver are chosen for robustness. You can unsubscribe from these emails at any time. The solver settings are stored at Study > Solver Configurations > Solution. 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. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Reply . 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. 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. 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. In such cases, see if one material (or the other) can be omitted from the analysis completely. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. Consult your product manuals for complete trademark details. The technique of load ramping is not always reasonable for all problems. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Not entering required material parameters. P&S: COMSOL Design Tool for Photonic Devices. These are some highly rated cards & stationery in Brea, CA: What are some cards & stationery with a large number of reviews in Brea, CA? The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. 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. Find centralized, trusted content and collaborate around the technologies you use most. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Cooling and Solidification of Metal. Review the model setup to resolve these. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. 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. 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. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. 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. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) 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. 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. 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. 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. First, it is physically intuitive, often matching how one would perform an experiment. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. I am solving a linear stationary finite element model but the software is not solving. What did people search for similar to stationary stores in Brea, CA? It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. 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. 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. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. - Feature: Stationary Solver 1 (sol1/s1) If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. This involves a systematic reduction in the model complexity. This is relatively expensive to do, but will lead to the most robust convergence. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) there is no defined multiphysics for it as I know, I have a standing accoustic wave and a flow in the background but I don't see their connection. The continuation method will again backtrack and try intermediate values of the ramping parameter, thus giving you the nearest approximation to the abrupt transition that is solvable. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Hence Comsol solved for the stationary solution at different points of time. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. COMSOL makes every reasonable effort to verify the information you view on this page. To switch between these solver types, go to the Stationary Solver node within the Study sequence. 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. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. Using the first order optimality. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Hello, 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. In the COMSOL Multiphysics software, this step of the modeling workflow is made. (Frequency Domain should be the last step) k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Again, introduce a Global Parameter that gets ramped from exactly zero to one. 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. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. It's brand new in the hmart plaza and I wish it was open back when I would hangout in the plaza after school (although they would have taken all my allowance money! An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: For example, if there is a temperature-dependent material property such as: The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Not entering required material parameters. Your internet explorer is in compatibility mode and may not be displaying the website correctly. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. The coupling terms between the different groups are thus neglected. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. Tutti i diritti sono riservati. The Fully Coupled solution approach, with the Plot While Solving enabled. To start a new discussion with a link back to this one, click here. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Consult your product manuals for complete trademark details. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. What are people saying about cards & stationery in Brea, CA? 3. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) Learn how your comment data is processed. Any trademarks referenced in this document are the property of their respective owners. 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 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. That is, they are tuned to achieve convergence in as many cases as possible. - the incident has nothing to do with me; can I use this this way? This approach is known as a Continuation Method with a Constant predictor. Function: / Failed to evaluate expression. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. "I chose this print shop based off yelp reviews and was very happy with the outcome! 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 Computational Fluid Dynamics (CFD), API thanks for reply This guide applies solely to nonlinear stationary models. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. 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. 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. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. 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. These can be used alone, or in combination with other interfaces. It may also reveal that the model itself is ill-posed in some way. These are some cards & stationery with a large number of reviews in Brea, CA. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. What sort of strategies would a medieval military use against a fantasy giant? Popular answers (1) This problem generally occurs when there is some mistake in the physics or study section or wrong selection of the mesh size. Stationary (time-invariant) models with nonlinearities may converge very slowly. Segregated approach and Direct vs. Here we introduce a more robust approach to solving nonlinear problems. Some models are numerically ill-conditioned due to the setup. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. Not assigning proper boundary conditions: Especially if you have ports. 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. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Linear solvers. So far, weve learned how to mesh and solve linear and nonlinear single-physics finite element problems, but have not yet considered what happens when there are multiple different interdependent physics being solved within the same domain. Not the answer you're looking for? Most multiphysics problems are nonlinear. That is, start by first solving a model with a small, but non-zero, load. 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. The advantages of the continuation method are two-fold. Discussion Closed This discussion was created more than 6 months ago and has been closed. For example, if there is a temperature-dependent material property such as: Note: there is no way to couple this . Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. Cooling and Solidification of Metal. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. 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. 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. Use this parameter to modify the nonlinearity expressions in the model. Click the link in the email we sent to to verify your email address and activate your job alert. (I am begginer in comsol) Thank you. 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. Hi Jason, This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. The continuation method will again backtrack and try intermediate values of the ramping parameter, thus giving you the nearest approximation to the abrupt transition that is solvable. Thanks for contributing an answer to Stack Overflow! Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. $130,000.00. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Use this parameter to modify the nonlinearity expressions in the model. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. This approach is known as a Continuation Method with a Constant predictor. Common Mistakes: Not assigning materials to all the domains. 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. It is also possible to manually refine the mesh. - 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. However, it is usually not possible to know this ahead of time. The technique of load ramping is not always reasonable for all problems. listed if standards is not an option). The other low-level default settings within the Stationary Solver are chosen for robustness. My comment is perhaps a bit nave but it seems to me that you could simply deactivate the \frac{\partial \cdot}{\partial t} term of the background field equation but keep its connexion to the solid to get what you want. The settings controlling the predictor type. 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. Get email updates for new Stationary Engineer jobs in Brea, California, United States. If it does so, use a finer increment in that range. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! 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. Save this information to a file. 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. To switch between these solver types, go to the Stationary Solver node within the Study sequence. The advantages of the continuation method are two-fold. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. The other low-level default settings within the Stationary Solver are chosen for robustness. I personally liked emailing them the file, ", "This flower shop is the best! Get notified about new Stationary Engineer jobs in Brea, California, United States. . Making statements based on opinion; back them up with references or personal experience.

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