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. 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 is relatively expensive to do, but will lead to the most robust convergence. 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. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. 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. Not the answer you're looking for? k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) As we saw in Load Ramping of Nonlinear Problems, we can use the continuation method to ramp the loads on a problem up from an unloaded case where we know the solution. 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. An example would be a linear static structural model of an aluminum beverage can. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. 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. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Your internet explorer is in compatibility mode and may not be displaying the website correctly. This approach is known as a Continuation Method with a Constant predictor. 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. It may also reveal that the model itself is ill-posed in some way. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Minimising the environmental effects of my dyson brain. 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. In a previous blog entry, we introduced meshing considerations for linear static problems. Trying to understand how to get this basic Fourier Series. 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. Check the solver log to see if the continuation method is backtracking. 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. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Get email updates for new 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. Also, keep in mind that a linear stationary model should solve regardless of how coarse the mesh is (albeit to a low accuracy) so you can always start with as coarse a mesh as possible, and refine the mesh (See also: Knowledgebase 1030: Performing a Mesh Refinement Study. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Solve the stationary study then the time dependent study. The conditions on the geometric aspect ratio are relatively more strict. 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. Again, introduce a Global Parameter that gets ramped from exactly zero to one. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Wrong ordering of study steps. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another.
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. For example, if ramping P over values of: 0.2,0.4,0.6,0.8,1.0 the nonlinear solver may fail to converge for a value of 0.8. The 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. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. What is \newluafunction? $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 If so, see: Knowledgebase 1030: Error: "Out of memory". Different physics have different default solvers. 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. 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. See Knowledge Base 1240: Manually Setting the Scaling of Variables. In this posting, we introduce the idea of ramping the nonlinearities in the problem to improve convergence. 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.) Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. To switch between these solver types, go to the Stationary Solver node within the Study sequence. 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. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. I have searched all over comsol forum to fix this stationary solver configuration and still doesn't work because I don't know the logic behind the solver system. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. Name: actdep_int1, Your email address will not be published. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: 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. Iterative , Direct . Alle Rechte vorbehalten. 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. Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. The other low-level default settings within the Stationary Solver are chosen for robustness. Required fields are marked *. Consult your product manuals for complete trademark details. Segregated approach and Direct vs. There will always already be either a Segregated or Fully Coupled feature beneath this. In our previous blog entry, we introduced the Fully Coupled and the Segregated algorithms used for solving steady-state multiphysics problems in COMSOL. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Is there a way to use the stationary solution obtained in Comsol 4.2 as the initial conditions in a time dependent model? Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. (Frequency Domain should be the last step). This guide applies solely to nonlinear stationary models. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. 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. 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. $140,000.00, $120,000.00 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. What are people saying about cards & stationery in Brea, CA? Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble Find centralized, trusted content and collaborate around the technologies you use most. replace it with the expression: 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. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. 0 Replies, Please login with a confirmed email address before reporting spam. Few days back i was also facing this problem in . First, it is physically intuitive, often matching how one would perform an experiment. What did people search for similar to stationary stores in Brea, CA? They are usually called comp1.u, comp1.v, and comp1.w though. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Why? Such problems must solved in the time domain. The following are possible reasons why a linear stationary model will fail to solve, along with resolutions: The combination of the constraints and boundary conditions must be sufficient to define a unique solution to the problem, in terms of the field variables being solved. . It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. This guide applies solely to nonlinear stationary models. Your email address will not be published. First, it is physically intuitive, often matching how one would perform an experiment. 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. In this page, we will be sharing some common errors that might occur in Comsol and their solutions. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. If it does so, use a finer increment in that range. Segregated approach and Direct vs. Iterative linear solvers, Time dependent function and stationary study, Combining Adaptive Mesh Refinement with Data Filtering, What to do when a linear stationary model is not solving, Galleria dei Modelli e delle App di Simulazione, 2023 da COMSOL. For example, if there is a temperature-dependent material property such as: COMSOL does not assume any legal liability for the accuracy of the data disclosed. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Sign in to create your job alert for Stationary Engineer jobs in Brea, California, United States. Stationary (time-invariant) models with nonlinearities may converge very slowly. This approach is known as a Continuation Method with a Constant predictor. Most multiphysics problems are nonlinear. 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. Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2, Simulation of effect of heated resistance on temperature distribution in laminar flow, COMSOL: Diffusion in Transport of Diluted Species Produces Unphysical Results. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. 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. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Hello, Please dont hesitate to post comments below or send emails to us if you experience any other problems. Have you taken a look at this [blog post](https://www.comsol.com/blogs/modeling-fluid-structure-interaction-in-multibody-mechanisms/)? Second, the continuation method will automatically take smaller load increments if a solution cannot be found. - the incident has nothing to do with me; can I use this this way? replace it with the expression: This information is presented in the context of a very simple 1D finite element problem, and builds upon our previous entry on Solving Linear Static Finite Element Models. 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. Perhaps this approach could be adapted to represent your model. listed if standards is not an option). Your internet explorer is in compatibility mode and may not be displaying the website correctly. These are some cards & stationery with a large number of reviews in Brea, CA. Direct Iterative , Direct . Tutti i diritti sono riservati. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. listed if standards is not an option). This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. Hence Comsol solved for the stationary solution at different points of time. $130,000.00. Linear solvers. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. Any trademarks referenced in this document are the property of their respective owners. This guide applies solely to nonlinear stationary models. 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. The objective here is to simplify the model to a state where the model will solve, with linear approximations. The other low-level default settings within the Stationary Solver are chosen for robustness. To switch between these solver types, go to the Stationary Solver node within the Study sequence. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Check the solver log to see if the continuation method is backtracking. This involves a systematic reduction in the model complexity. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. 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. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. replace it with the expression: Not assigning proper boundary conditions: Especially if you have ports. 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 also possible to manually refine the mesh. Note: there is no way to couple this field with the time dependent nature of this physics. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. You can unsubscribe from these emails at any time. 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. The default Initial Values for the unknowns in most physics interfaces are zero. It is sometimes necessary to manually scale the dependent variables. Here we introduce a more robust approach to solving nonlinear problems. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? In the extreme case, suppose one wants to model an instantaneous change in properties, such as: I am trying to solve the coupling between a waveguide and a microring resonator. Hi ! listed if standards is not an option). 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. Feature: Stationary Solver 1 (sol1/s1)" . Such problems must solved in the time domain. P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. It is sometimes necessary to manually scale the dependent variables. The solver settings are stored at Study > Solver Configurations > Solution. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. thanks for reply 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. I personally liked emailing them the file, ", "This flower shop is the best! If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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 approach is used by default for most 1D, 2D, and 2D-axisymmetric models. 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. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Not entering required material parameters. 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. About the Stationary Solver The following background information about the Stationary Solver discusses these topics: Damped Newton Methods, Termination Criterion for the Fully Coupled and Segregated Attribute Nodes, Linear Solvers versus Nonlinear Solvers, and Pseudo Time Stepping. . 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. However, it is usually not possible to know this ahead of time. The coupling terms between the different groups are thus neglected. 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. 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. - Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. 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, start by first solving a model with a small, but non-zero, load. Comsol help video number 2: Solving a laminar flow problem in a slit.. Cooling and Solidification of Metal. 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. Repeat this for every nonlinearity of the model. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. The settings controlling the predictor type. Multiphysics problems are often nonlinear. Your internet explorer is in compatibility mode and may not be displaying the website correctly. She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. If you see this, right-click on the Solution feature and select Reset Solver to Default. Thanks for contributing an answer to Stack Overflow! The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Click the link in the email we sent to to verify your email address and activate your job alert. 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. (Frequency Domain should be the last step) Here, we will examine techniques for accelerating the convergence of these two methods. However, it is usually not possible to know this ahead of time. The other low-level default settings within the Stationary Solver are chosen for robustness. Communication over the phone, in person, and through email was very easy. Why do many companies reject expired SSL certificates as bugs in bug bounties? These are some highly rated cards & stationery in Brea, CA: What are some cards & stationery with a large number of reviews in Brea, CA? 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. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. COMSOL makes every reasonable effort to verify the information you view on this page. 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. The technique of load ramping is not always reasonable for all problems. It may also reveal that the model itself is ill-posed in some way. Most multiphysics problems are nonlinear. Any trademarks referenced in this document are the property of their respective owners. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. Get notified about new Stationary Engineer jobs in Brea, California, United States. 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. comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. 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. Hi Jason,
The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. I highly recommend this flower shop. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields.
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