COMSOL does not assume any legal liability for the accuracy of the data disclosed. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. However, load ramping will not work in all cases, or may be inefficient. Note the star symbol on the Solution feature. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Check the solver log to see if the continuation method is backtracking. Again, introduce a Global Parameter that gets ramped from exactly zero to one. 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. What did people search for similar to stationary stores in Brea, CA? If you see this, right-click on the Solution feature and select Reset Solver to Default. Communication over the phone, in person, and through email was very easy. However, it is usually not possible to know this ahead of time. Find detailed information on Office Supplies, Stationery, and Gift Retailers companies in Brea, California, United States of America, including financial statements, sales and marketing contacts, top competitors, and firmographic insights. Stationary (time-invariant) models with nonlinearities may converge very slowly. 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. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) 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. Have you taken a look at this blog post? That is, they are tuned to achieve convergence in as many cases as possible. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. 3. The fully coupled and segregated approaches are discussed below. Posted 26 set 2019, 11:57 GMT-4 In this page, we will be sharing some common errors that might occur in Comsol and their solutions. If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. It may also reveal that the model itself is ill-posed in some way. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Check the solver log to see if the continuation method is backtracking. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. listed if standards is not an option). This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Comsol help video number 2: Solving a laminar flow problem in a slit.. Your internet explorer is in compatibility mode and may not be displaying the website correctly. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. 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. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. The algorithm is, generally speaking, a Newton's method approach. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. In a previous blog entry, we introduced meshing considerations for linear static problems. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Not meshing all the domains. GCRO-DR is a method for Krylov subspace recycling. Have you taken a look at this [blog post](https://www.comsol.com/blogs/modeling-fluid-structure-interaction-in-multibody-mechanisms/)? Hello guys. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. 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. Tutti i diritti sono riservati. That is, they are tuned to achieve convergence in as many cases as possible. 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 advantages of the continuation method are two-fold. Note that while COMSOL employees may participate in the discussion forum, COMSOL software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. 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. 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. replace it with the expression: Hi Jason, The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. COMSOL does not assume any legal liability for the accuracy of the data disclosed. It may also reveal that the model itself is ill-posed in some way. What is \newluafunction? Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. 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. Consult your product manuals for complete trademark details. This is relatively expensive to do, but will lead to the most robust convergence. I use comsol multiphysics 5.2a and . Here we introduce a more robust approach to solving nonlinear problems. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Wrong ordering of study steps. (I am begginer in comsol) Thank you. Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems. The Fully Coupled solution approach, with the Plot While Solving enabled. 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. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) 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. We use COMSOL Multiphysics for solving distributed optimal control of un-steady Burgers equation without constraints and with pointwise control constraints. 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. Function: / Failed to evaluate expression. Connect and share knowledge within a single location that is structured and easy to search. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. The other low-level default settings within the Stationary Solver are chosen for robustness. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. To switch between these solver types, go to the Stationary Solver node within the Study sequence. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Learn how your comment data is processed. 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 objective here is to simplify the model to a state where the model will solve, with linear approximations. Repeat this for every nonlinearity of the model. The settings controlling the predictor type. Could you expand a little bit more why the coupling is impossible? 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. listed if standards is not an option). 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. comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Save my name, email, and website in this browser for the next time I comment. Making statements based on opinion; back them up with references or personal experience. Different physics have different default solvers. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. In such cases, see if one material (or the other) can be omitted from the analysis completely. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). There will always already be either a Segregated or Fully Coupled feature beneath this. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 Most multiphysics problems are nonlinear. This guide applies solely to nonlinear stationary models. 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. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Stationary Solver Iterative Direct . P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) COMSOL makes every reasonable effort to verify the information you view on this page. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. It is also possible to manually refine the mesh. 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. Acidity of alcohols and basicity of amines. This is relatively expensive to do, but will lead to the most robust convergence. Again, introduce a Global Parameter that gets ramped from exactly zero to one. What are some highly rated cards & stationery in Brea, CA? 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. Segregated approach and Direct vs. Segregated approach and Direct vs. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. . 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.) First, it is physically intuitive, often matching how one would perform an experiment. Not entering required material parameters. 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. Reply . 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. Create the time-dependent step or study. Any trademarks referenced in this document are the property of their respective owners. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. The fully coupled and segregated approaches are discussed below. replace it with the expression: Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. These are some highly rated cards & stationery in Brea, CA: What are some cards & stationery with a large number of reviews in Brea, CA? In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. 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. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. It is sometimes necessary to manually scale the dependent variables. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. 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. Your Discussion has gone 30 days without a reply. Leverage your professional network, and get hired. This is relatively expensive to do, but will lead to the most robust convergence. They are usually called comp1.u, comp1.v, and comp1.w though. 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. Not assigning proper boundary conditions: Especially if you have ports. Multiphysics problems are often nonlinear. 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version These are some cards & stationery with a large number of reviews in Brea, CA. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. 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. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. First, it is physically intuitive, often matching how one would perform an experiment. As we saw previously in the blog entry on Solving Nonlinear Static Finite Element Problems, not all nonlinear problems will be solvable via the damped Newton-Raphson method. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. I am following the same model as Comsol provide us on the web. 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. "After the incident", I started to be more careful not to trip over things. 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! The default Initial Values for the unknowns in most physics interfaces are zero. COMSOL makes every reasonable effort to verify the information you view on this page. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Is it possible to rotate a window 90 degrees if it has the same length and width? Unknown function or operator. I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary model. If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. 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. The coupling terms between the different groups are thus neglected. Using the first order optimality. Hence Comsol solved for the stationary solution at different points of time. This guide applies solely to nonlinear stationary models. 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. Sign in to create your job alert for Stationary Engineer jobs in Brea, California, United States. The Fully Coupled solution approach, with the Plot While Solving enabled. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. thanks for reply This solver is automatically used when a Stationary or Frequency Domain study is added to the model. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. Not meshing all the domains. Why? The continuation method will again backtrack and try intermediate values of the ramping parameter, thus giving you the nearest approximation to the abrupt transition that is solvable. If it does so, use a finer increment in that range. P&S: COMSOL Design Tool for Photonic Devices. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Use this parameter to modify the nonlinearity expressions in the model. She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. Your internet explorer is in compatibility mode and may not be displaying the website correctly. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. 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. Thanks for contributing an answer to Stack Overflow! The continuation method will again backtrack and try intermediate values of the ramping parameter, thus giving you the nearest approximation to the abrupt transition that is solvable. Version 5.3 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. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. This approach is known as a Continuation Method with a Constant predictor. The fully coupled and segregated approaches are discussed below. 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. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Can I tell police to wait and call a lawyer when served with a search warrant? 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. so many cute little stationary items , hair". As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. $140,000.00, $120,000.00 Does anyone know what should cause this problem? With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. I am solving a linear stationary finite element model but the software is not solving. Thanks, Andres. 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. 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. This algorithm was also useful for understanding what happens near a failure load. Direct Iterative , Direct . How can I use it? (Frequency Domain should be the last step) document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. If one particular material is missing one property, that material will also be highlighted with a red cross over that material icon in the Model Builder. 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. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. Then use this file to provide the initial conditions in time dependent model. Trying to understand how to get this basic Fourier Series. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. To start a new discussion with a link back to this one, click here. - Could you expand a little bit more why the coupling is impossible? That is, start by first solving a model with a small, but non-zero, load. 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. To start a new discussion with a link back to this one, click here. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Therefore, an initial value of zero is almost always reasonable if a very small load is applied. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. If you are unsure if your problem is linear and stationary, look at the Log. 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. 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. Multiphysics problems are often nonlinear. An example would be a linear static structural model of an aluminum beverage can. The technique of load ramping is not always reasonable for all problems. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. Discussion Closed This discussion was created more than 6 months ago and has been closed.
Jen Beattie Husband, Articles S