stationary solver comsol

Wish you all the best. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. 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. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. If you try to solve such a model, there will be an error at runtime that will provide information about the variable name and where it is being called. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. 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. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. In our previous blog entry, we introduced the Fully Coupled and the Segregated algorithms used for solving steady-state multiphysics problems in COMSOL. Review the model setup to resolve these. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. For the Nozomi from Shinagawa to Osaka, say on a Saturday afternoon, would tickets/seats typically be available - or would you need to book? 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. 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. Not entering required material parameters. Consult your product manuals for complete trademark details. I am solving a linear stationary finite element model but the software is not solving. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. 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. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. 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. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. 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. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Any trademarks referenced in this document are the property of their respective owners. The Automatic predictor setting will use the constant predictor when a segregated solution approach is being used, and use the linear predictor when the fully coupled approach is used. The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! There will always already be either a Segregated or Fully Coupled feature beneath this. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. 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. 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. What version of COMSOL are you using? Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Different physics have different default solvers. See Knowledge Base 1240: Manually Setting the Scaling of Variables. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Stationary (time-invariant) models with nonlinearities may converge very slowly. 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. 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. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. The difference between the phonemes /p/ and /b/ in Japanese. $130,000.00. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. 3 Replies, Please login with a confirmed email address before reporting spam. However, it is usually not possible to know this ahead of time. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) 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. 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. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. 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. Tutti i diritti sono riservati. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Any trademarks referenced in this document are the property of their respective owners. The advantages of the continuation method are two-fold. 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. This guide applies solely to nonlinear stationary models. Few days back i was also facing this problem in . For example, if there is a temperature-dependent material property such as: If you see this, right-click on the Solution feature and select Reset Solver to Default. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Wrong ordering of study steps. These can be used alone, or in combination with other interfaces. Note: there is no way to couple this . However, it is usually not possible to know this ahead of time. We use COMSOL Multiphysics for solving distributed optimal control of un-steady Burgers equation without constraints and with pointwise control constraints. Then use this file to provide the initial conditions in time dependent model. The Fully Coupled solution approach, with the Plot While Solving enabled. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. The conditions on the geometric aspect ratio are relatively more strict. Thanks for contributing an answer to Stack Overflow! listed if standards is not an option). That is, start by first solving a model with a small, but non-zero, load. Repeat this for every nonlinearity of the model. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. so many cute little stationary items , hair". Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. There will always already be either a Segregated or Fully Coupled feature beneath this. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. The Fully Coupled solution approach, with the Plot While Solving enabled. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Not assigning proper boundary conditions: Especially if you have ports. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. In this posting, we introduce the idea of ramping the nonlinearities in the problem to improve convergence. Common Mistakes: Not assigning materials to all the domains. Here, we will examine techniques for accelerating the convergence of these two methods. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. This algorithm was also useful for understanding what happens near a failure load. Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Not meshing all the domains. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. Alternatively, delete and re-create the study. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. 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. Hi Jason, With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. thanks for reply 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. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Some models are numerically ill-conditioned due to the setup. - the incident has nothing to do with me; can I use this this way? Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. The nature of simulating nature: A Q&A with IBM Quantum researcher Dr. Jamie We've added a "Necessary cookies only" option to the cookie consent popup. 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. Save this information to a file. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. This doesn't seem to me the most elegant of methods, since I am essentially solving a stationary solution using a time dependent Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Not the answer you're looking for? Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. 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. For example, in a Solid Mechanics (wherein the software is solving for the displacement field within the solid) applying two opposite and equal Boundary Load conditions on a part is not sufficient to define the displacement. 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. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. (I am begginer in comsol) Thank you. 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. 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. Minimising the environmental effects of my dyson brain. Solver . If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. 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. P&S: COMSOL Design Tool for Photonic Devices. 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. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Can I tell police to wait and call a lawyer when served with a search warrant? The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. 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. There will also be a red cross over the Materials branch icon. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. Stationary Solver Iterative Direct . 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. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Click the link in the email we sent to to verify your email address and activate your job alert. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. The other low-level default settings within the Stationary Solver are chosen for robustness. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Consult your product manuals for complete trademark details. Use this parameter to modify the nonlinearity expressions in the model. 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. 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. Linear solvers. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: That is, they are tuned to achieve convergence in as many cases as possible. rev2023.3.3.43278. Have you taken a look at this blog post? Version 5.3 Not meshing all the domains. The algorithm is, generally speaking, a Newton's method approach. Multiphysics problems are often nonlinear. Required fields are marked *. 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. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. Solve the stationary study then the time dependent study. To switch between these solver types, go to the Stationary Solver node within the Study sequence. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. If you are unsure if your problem is linear and stationary, look at the Log. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. 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. That is, they are tuned to achieve convergence in as many cases as possible. First, it is physically intuitive, often matching how one would perform an experiment. if I want to do an adaptive mesh refinement, I get this error. If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. First, it is physically intuitive, often matching how one would perform an experiment. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. 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. See Knowledge Base 1240: Manually Setting the Scaling of Variables. This involves a systematic reduction in the model complexity. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Note: there is no way to couple this field with the time dependent nature of this physics. Could you expand a little bit more why the coupling is impossible? What are people saying about cards & stationery in Brea, CA? Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Perhaps this approach could be adapted to represent your 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. Posted Sep 9, 2020, 1:44 p.m. EDT Your internet explorer is in compatibility mode and may not be displaying the website correctly. The settings controlling the predictor type. listed if standards is not an option). Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. COMSOL does not assume any legal liability for the accuracy of the data disclosed. 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. This is a review for cards & stationery in Brea, CA: "Love this store!!! Any trademarks referenced in this document are the property of their respective owners. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Reply . That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. Understanding the Fully Coupled vs. In such cases, see if one material (or the other) can be omitted from the analysis completely. ", "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. It is also possible to manually refine the mesh. That is, they are tuned to achieve convergence in as many cases as possible. 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. If it does so, use a finer increment in that range. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) - Again, introduce a Global Parameter that gets ramped from exactly zero to one. 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. Such problems must solved in the time domain. They are usually called comp1.u, comp1.v, and comp1.w though. Sign in to create your job alert for 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. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). Cooling and Solidification of Metal. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 - 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. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. 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.

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