Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. 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. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. 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. If it does so, use a finer increment in that range. Repeat this for every nonlinearity of the model. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. 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. It is sometimes necessary to manually scale the dependent variables. 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. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. Required fields are marked *. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. If so, see: Knowledgebase 1030: Error: "Out of memory". Any trademarks referenced in this document are the property of their respective owners. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? That is, they are tuned to achieve convergence in as many cases as possible. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 The objective here is to simplify the model to a state where the model will solve, with linear approximations. Multiphysics problems are often nonlinear. 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. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Today's top 351 Stationary Engineer jobs in Brea, California, United States. 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. This algorithm was also useful for understanding what happens near a failure load. 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. This case is generally difficult, or impossible, to solve since this material property is non-smooth. Check the solver log to see if the continuation method is backtracking. k(T) = 10[W/m/K]*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. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. Review the model setup to resolve these. With respect to any nonlinearities, replace them by a reasonable linearized term. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. If you have both as steps in the same study, then solve that study. What are some highly rated cards & stationery in Brea, CA? Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. The difference between the phonemes /p/ and /b/ in Japanese. To learn more, see our tips on writing great answers. 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. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. Hi Jason, (Frequency Domain should be the last step) Unknown function or operator. I am trying to solve the coupling between a waveguide and a microring resonator. Cooling and Solidification of Metal. listed if standards is not an option). Hi Jason, The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. 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. These can be used alone, or in combination with other interfaces. There will always already be either a Segregated or Fully Coupled feature beneath this. P&S: COMSOL Design Tool for Photonic Devices - ETH Z Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. This involves a systematic reduction in the model complexity. 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. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 Few days back i was also facing this problem in . Your internet explorer is in compatibility mode and may not be displaying the website correctly. Use this parameter to modify the nonlinearity expressions in the model. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Solving for laminar flow using Comsol - YouTube - Feature: Stationary Solver 1 (sol1/s1) 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. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. COMSOL Error for Initial Values(RF Module) If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. - This approach is known as a Continuation Method with a Constant predictor. 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. COMSOL Blog Series on COMSOL Multiphysics Solvers The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. What sort of strategies would a medieval military use against a fantasy giant? This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. The Fully Coupled solution approach, with the Plot While Solving enabled. 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. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. If you see this, right-click on the Solution feature and select Reset Solver to Default. Multiphysics problems are often nonlinear. That is, start by first solving a model with a small, but non-zero, load. Iterative - COMSOL Multiphysics 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. COMSOL does not assume any legal liability for the accuracy of the data disclosed. ", "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. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. Again, introduce a Global Parameter that gets ramped from exactly zero to one. 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. The coupling terms between the different groups are thus neglected. Cooling and Solidification of Metal. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. Solving such models in a stationary sense should simply require solving a single (large) system of linear equations and should always be solvable, but there are cases when the software will fail to find a solution. First, it is physically intuitive, often matching how one would perform an experiment. 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. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. That is, start by first solving a model with a small, but non-zero, load. My comment is perhaps a bit nave but it seems to me that you could simply deactivate the term of the background field equation but keep its connexion to the solid to get what you want. How can I check before my flight that the cloud separation requirements in VFR flight rules are met? Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. 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. listed if standards is not an option). There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. Trying to understand how to get this basic Fourier Series. Get notified about new Stationary Engineer jobs in Brea, California, United States. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) The other low-level default settings within the Stationary Solver are chosen for robustness. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Sign in to create your job alert for Stationary Engineer jobs in Brea, California, United States. 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. 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. 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version This is relatively expensive to do, but will lead to the most robust convergence. Stationary Solver - COMSOL Multiphysics Solve the stationary study then the time dependent study. This consent may be withdrawn. P&S: COMSOL Design Tool for Photonic Devices. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Your email address will not be published. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. listed if standards is not an option). Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Have you taken a look at this [blog post](https://www.comsol.com/blogs/modeling-fluid-structure-interaction-in-multibody-mechanisms/)? Consult your product manuals for complete trademark details. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. 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 approach is used by default for most 1D, 2D, and 2D-axisymmetric models. I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary model. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. 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. 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 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.) The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. These are some highly rated cards & stationery in Brea, CA: What are some cards & stationery with a large number of reviews in Brea, CA? To switch between these solver types, go to the Stationary Solver node within the Study sequence. They are usually called comp1.u, comp1.v, and comp1.w though. What did people search for similar to stationary stores in Brea, CA? $130,000.00. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. Save my name, email, and website in this browser for the next time I comment. COMSOL makes every reasonable effort to verify the information you view on this page. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Hence Comsol solved for the stationary solution at different points of time. About the Stationary Solver - COMSOL Multiphysics . The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Such problems must solved in the time domain. 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. Could you expand a little bit more why the coupling is impossible? 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. It is sometimes necessary to manually scale the dependent variables. Not entering required material parameters. 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. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: 0 Replies, Please login with a confirmed email address before reporting spam. rev2023.3.3.43278. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version It may also reveal that the model itself is ill-posed in some way. There will always already be either a Segregated or Fully Coupled feature beneath this. To start a new discussion with a link back to this one, click here. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. The technique of load ramping is not always reasonable for all problems. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Understanding the Fully Coupled vs. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the - COMSOL If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. The Fully Coupled solution approach, with the Plot While Solving enabled. 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. Thanks for contributing an answer to Stack Overflow! This is relatively expensive to do, but will lead to the most robust convergence. Note the star symbol on the Solution feature. Segregated approach and Direct vs. The other low-level default settings within the Stationary Solver are chosen for robustness. 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. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Communication over the phone, in person, and through email was very easy. I highly recommend this flower shop. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. 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. 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. Wrong ordering of study steps. Segregated approach and Direct vs. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. Stationary (time-invariant) models with nonlinearities may converge very slowly. Computational Fluid Dynamics (CFD), API As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Improving Convergence of Nonlinear Stationary Models - COMSOL We use COMSOL Multiphysics for solving distributed optimal control of un-steady Burgers equation without constraints and with pointwise control constraints. The Iterative Solvers - COMSOL Multiphysics See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. solving stationary solver after each time step - COMSOL Multiphysics 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. Feature: Stationary Solver 1 (sol1/s1)" . Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . The objective here is to simplify the model to a state where the model will solve, with linear approximations. The advantages of the continuation method are two-fold. Note: there is no way to couple this field with the time dependent nature of this physics. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. In such cases, see if one material (or the other) can be omitted from the analysis completely. comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. This approach is known as a Continuation Method with a Constant predictor. Not entering required material parameters. Screenshot showing a Solver Configuration that has been altered. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Hello, Can I tell police to wait and call a lawyer when served with a search warrant? For example, if there is a temperature-dependent material property such as: Do you also know how to solve this problem: using stationary solution as the initial conditions in time dependent model, How Intuit democratizes AI development across teams through reusability. It may also reveal that the model itself is ill-posed in some way. Asking for help, clarification, or responding to other answers. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues.