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. 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. This guide applies solely to nonlinear stationary models. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. 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. The advantages of the continuation method are two-fold. 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. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) COMSOL makes every reasonable effort to verify the information you view on this page. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Not meshing all the domains. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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. listed if standards is not an option). Therefore, an initial value of zero is almost always reasonable if a very small load is applied. What did people search for similar to stationary stores in Brea, CA? 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. Understanding the Fully Coupled vs. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. This case is generally difficult, or impossible, to solve since this material property is non-smooth. 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 use comsol multiphysics 5.2a and . This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. It is sometimes necessary to manually scale the dependent variables. 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. Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. This guide applies solely to nonlinear stationary models. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. COMSOL does not assume any legal liability for the accuracy of the data disclosed. 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. For example, if ramping P over values of: 0.2,0.4,0.6,0.8,1.0 the nonlinear solver may fail to converge for a value of 0.8. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) The issue here has do with the iterative algorithm used to solve nonlinear stationary models. (Frequency Domain should be the last step) We use COMSOL Multiphysics for solving distributed optimal control of un-steady Burgers equation without constraints and with pointwise control constraints. 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. Perhaps this approach could be adapted to represent your model. The Fully Coupled solution approach, with the Plot While Solving enabled. 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. 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. Discussion Closed This discussion was created more than 6 months ago and has been closed. The technique of load ramping is not always reasonable for all problems. - Solver . What version of COMSOL are you using? Is it possible to rotate a window 90 degrees if it has the same length and width? 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. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Not the answer you're looking for? It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. As part of our solver blog series we have discussed solving nonlinear static finite element problems, load ramping for improving convergence of nonlinear problems, and nonlinearity ramping for improving convergence of nonlinear problems. The algorithm is, generally speaking, a Newton's method approach. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version This approach is known as a Continuation Method with a Constant predictor. There will always already be either a Segregated or Fully Coupled feature beneath this. These are some cards & stationery with a large number of reviews in Brea, CA. This involves a systematic reduction in the model complexity. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) COMSOL makes every reasonable effort to verify the information you view on this page. Iterative , Direct . This approach is known as a Continuation Method with a Constant predictor. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Your internet explorer is in compatibility mode and may not be displaying the website correctly. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Alle Rechte vorbehalten. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. 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. First, it is physically intuitive, often matching how one would perform an experiment. Wrong ordering of study steps. 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. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. (I am begginer in comsol) Thank you. Screenshot showing a Solver Configuration that has been altered. Here we introduce a more robust approach to solving nonlinear problems. In this page, we will be sharing some common errors that might occur in Comsol and their solutions. Cooling and Solidification of Metal. With respect to any nonlinearities, replace them by a reasonable linearized term. 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. Reply . 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. P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. 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. Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . The settings controlling the predictor type. In such cases, see if one material (or the other) can be omitted from the analysis completely. Note the star symbol on the Solution feature. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. Learn how your comment data is processed. What are people saying about cards & stationery in Brea, CA? In this posting, we introduce the idea of ramping the nonlinearities in the problem to improve convergence. The other low-level default settings within the Stationary Solver are chosen for robustness. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. This algorithm was also useful for understanding what happens near a failure load. 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. This doesn't seem to me the most elegant of methods, since I am essentially solving a stationary solution using a time dependent Hi ! This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). COMSOL does not assume any legal liability for the accuracy of the data disclosed. Use this parameter to modify the nonlinearity expressions in the model. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. 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. 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. The settings controlling the predictor type. Linear solvers. comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. The settings controlling the predictor type. -Detail: NaN or Inf found when solving linear system using SOR. Why do many companies reject expired SSL certificates as bugs in bug bounties? This is relatively expensive to do, but will lead to the most robust convergence. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Cooling and Solidification of Metal. I personally liked emailing them the file, ", "This flower shop is the best! Segregated approach and Direct vs. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. Thanks, Andres. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. The default Initial Values for the unknowns in most physics interfaces are zero. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. Check the solver log to see if the continuation method is backtracking. Full text of the 'Sri Mahalakshmi Dhyanam & Stotram'. COMSOL makes every reasonable effort to verify the information you view on this page. 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. It is also possible to manually refine the mesh. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Not entering required material parameters. 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. The difference between the phonemes /p/ and /b/ in Japanese. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. 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. if I want to do an adaptive mesh refinement, I get this error. 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. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. Repeat this for every nonlinearity of the model. It's brand new in the hmart plaza and I wish it was open back when I would hangout in the plaza after school (although they would have taken all my allowance money! You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 0 Replies, Please login with a confirmed email address before reporting spam. Review the model setup to resolve these. 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. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. It is also possible to manually refine the mesh. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? 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. The other low-level default settings within the Stationary Solver are chosen for robustness. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. However, it is usually not possible to know this ahead of time. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. What sort of strategies would a medieval military use against a fantasy giant? Wrong ordering of study steps. Connect and share knowledge within a single location that is structured and easy to search. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Communication over the phone, in person, and through email was very easy. Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Save my name, email, and website in this browser for the next time I comment. Tutti i diritti sono riservati. Create the time-dependent step or study. That is: Even if the forces on a part are opposite and equal, this is not sufficient information to say where the part is, so you must add some other condition, such as as Fixed Constraint to constrain displacement. rev2023.3.3.43278. In the COMSOL Multiphysics software, this step of the modeling workflow is made. See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. I am solving a linear stationary finite element model but the software is not solving. Save this information to a file. 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.
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