The technique of load ramping is not always reasonable for all problems. 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. 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. To start a new discussion with a link back to this one, click here. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? Click the link in the email we sent to to verify your email address and activate your job alert. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Why is there a voltage on my HDMI and coaxial cables? There will also be a red cross over the Materials branch icon. 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. - Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. What sort of strategies would a medieval military use against a fantasy giant? - Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) 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. 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. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Full text of the 'Sri Mahalakshmi Dhyanam & Stotram'. thanks for reply Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. 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. See Knowledge Base 1240: Manually Setting the Scaling of Variables. 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 unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Segregated approach and Direct vs. The algorithm is, generally speaking, a Newton's method approach. 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. 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. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. 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. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Screenshot showing a Solver Configuration that has been altered. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. If you have both as steps in the same study, then solve that study. This doesn't seem to me the most elegant of methods, since I am essentially solving a stationary solution using a time dependent 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. These are some highly rated cards & stationery in Brea, CA: What are some cards & stationery with a large number of reviews in Brea, CA? A linear finite element model is one in which all of the material properties, loads, boundary conditions, etc are constant with respect to the solution, and the governing partial differential equations are themselves linear. The advantages of the continuation method are two-fold. 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. Note: there is no way to couple this . A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. Hello guys. 3. If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. 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 stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. I am solving a linear stationary finite element model but the software is not solving. thanks for reply Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Some models are numerically ill-conditioned due to the setup. Not the answer you're looking for? Not meshing all the domains. 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. so many cute little stationary items , hair". 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. I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary model. What is the purpose of non-series Shimano components? You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version The coupling terms between the different groups are thus neglected. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. 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. Could you expand a little bit more why the coupling is impossible? Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. The objective here is to simplify the model to a state where the model will solve, with linear approximations. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Repeat this for every nonlinearity of the model. Such a large difference in the materials properties can be challenging. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Save this information to a file. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. It is also possible to manually refine the mesh. The coupling terms between the different groups are thus neglected. Create the time-dependent step or study. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. 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. - Feature: Stationary Solver 1 (sol1/s1) There will always already be either a Segregated or Fully Coupled feature beneath this. Repeat this for every nonlinearity of the model. The segregated approach, on the other hand, solves sets of unknowns separately. Check the solver log to see if the continuation method is backtracking. It is sometimes necessary to manually scale the dependent variables. 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. Discussion Closed This discussion was created more than 6 months ago and has been closed. 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. If it does so, use a finer increment in that range. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Understanding the Fully Coupled vs. There will always already be either a Segregated or Fully Coupled feature beneath this. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. listed if standards is not an option). 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. . I am trying to solve the coupling between a waveguide and a microring resonator. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. That is, start by first solving a model with a small, but non-zero, load. To learn more, see our tips on writing great answers. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. You can unsubscribe from these emails at any time. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. The objective here is to simplify the model to a state where the model will solve, with linear approximations. The default Initial Values for the unknowns in most physics interfaces are zero. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). I am following the same model as Comsol provide us on the web. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. 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. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . Is there a way to use the stationary solution obtained in Comsol 4.2 as the initial conditions in a time dependent model? Stationary (time-invariant) models with nonlinearities may converge very slowly. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. 0 Replies, Please login with a confirmed email address before reporting spam. These are some cards & stationery with a large number of reviews in Brea, CA. 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. Mesh Wish you all the best. Cooling and Solidification of Metal. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Here, we will examine techniques for accelerating the convergence of these two methods. COMSOL does not assume any legal liability for the accuracy of the data disclosed. COMSOL does not assume any legal liability for the accuracy of the data disclosed. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. 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. The advantages of the continuation method are two-fold. As a rough rule of thumb, once the aspect ratio between the largest characteristic dimension to the smallest approaches 100:1, you might start to run into issues and should look to alternative ways of posing the problem, especially in a 3D model. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Can I tell police to wait and call a lawyer when served with a search warrant? Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. The default Initial Values for the unknowns in most physics interfaces are zero. View the Settings window for the Materials branch to get a list of all domains with undefined materials and add a material to those domains. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. 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.) Any trademarks referenced in this document are the property of their respective owners. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. listed if standards is not an option). Second, the continuation method will automatically take smaller load increments if a solution cannot be found. The difference between the phonemes /p/ and /b/ in Japanese. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. Minimising the environmental effects of my dyson brain. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. That is, they are tuned to achieve convergence in as many cases as possible. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Trying to understand how to get this basic Fourier Series. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. 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. 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 This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. Discussion Closed This discussion was created more than 6 months ago and has been closed. 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. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Solve the stationary study then the time dependent study. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. 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. "After the incident", I started to be more careful not to trip over things. 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. 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. Wrong ordering of study steps. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. First, it is physically intuitive, often matching how one would perform an experiment. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. Consult your product manuals for complete trademark details. Not entering required material parameters. 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. Contact COMSOL at Bangalore on their telephone: +9180 25323003. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. To switch between these solver types, go to the Stationary Solver node within the Study sequence. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). 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. For example, if there is a temperature-dependent material property such as: Find centralized, trusted content and collaborate around the technologies you use most. 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. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. 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 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. (I am begginer in comsol) Thank you. This approach is known as a Continuation Method with a Constant predictor. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. 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. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Unknown function or operator. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 There will always already be either a Segregated or Fully Coupled feature beneath this. listed if standards is not an option). Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. Making statements based on opinion; back them up with references or personal experience. This guide applies solely to nonlinear stationary models. 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. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. COMSOL 22.9K subscribers Adding a study to your simulation is necessary in order to solve your problem. 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. If you see this, right-click on the Solution feature and select Reset Solver to Default. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. 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. The idea behind the GCRO-DR method is to retain the subspace determined while solving previous systems and use it to reduce the cost of solving the next system. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Consult your product manuals for complete trademark details. Save my name, email, and website in this browser for the next time I comment. Hence Comsol solved for the stationary solution at different points of time. What are some highly rated cards & stationery in Brea, CA? The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? Check the solver log to see if the continuation method is backtracking. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. (Frequency Domain should be the last step) 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. Get notified about new Stationary Engineer jobs in Brea, California, United States. 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. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. Reply . This is relatively expensive to do, but will lead to the most robust convergence. This is relatively expensive to do, but will lead to the most robust convergence. 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. Not assigning proper boundary conditions: Especially if you have ports. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version