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. To switch between these solver types, go to the Stationary Solver node within the Study sequence. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. if I want to do an adaptive mesh refinement, I get this error. This guide applies solely to nonlinear stationary models. Troubleshooting for 3D trusses, if anyone's out there. : r/COMSOL - reddit It is sometimes necessary to manually scale the dependent variables. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) Load ramping and nonlinearity ramping can be used in combination, but start with only one or a few of the loads or nonlinearities being ramped. Wrong ordering of study steps. $140,000.00, $120,000.00 In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Top 10 Best Stationary in Brea, CA - October 2022 - Yelp The segregated approach, on the other hand, solves sets of unknowns separately. 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. Multiphysics problems are often nonlinear. Most multiphysics problems are nonlinear. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. It may also reveal that the model itself is ill-posed in some way. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. "I chose this print shop based off yelp reviews and was very happy with the outcome! Not entering required material parameters. The default Initial Values for the unknowns in most physics interfaces are zero. 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. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). As a rough rule of thumb, once the aspect ratio between the largest characteristic dimension to the smallest approaches 100:1, you might start to run into issues and should look to alternative ways of posing the problem, especially in a 3D model. First, it is physically intuitive, often matching how one would perform an experiment. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Hello, Again, introduce a Global Parameter that gets ramped from exactly zero to one. 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Any trademarks referenced in this document are the property of their respective owners. Review the model setup to resolve these. Common Mistakes: Not assigning materials to all the domains. $130,000.00. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 The Auxiliary Sweep can be used to implement ramping of any Global Parameter. comsol - using stationary solution as the initial conditions in time I highly recommend this flower shop. Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. That is, they are tuned to achieve convergence in as many cases as possible. This consent may be withdrawn. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). replace it with the expression: Tutti i diritti sono riservati. 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. November 11, 2013. COMSOL does not assume any legal liability for the accuracy of the data disclosed. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. Your Discussion has gone 30 days without a reply. Sign in to create your job alert for Stationary Engineer jobs in Brea, California, United States. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Load ramping and nonlinearity ramping can be used in combination, but start with only one or a few of the loads or nonlinearities being ramped. GCRO-DR is a method for Krylov subspace recycling. 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. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown 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. Thanks for contributing an answer to Stack Overflow! k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) There will always already be either a Segregated or Fully Coupled feature beneath this. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. 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. Check the solver log to see if the continuation method is backtracking. The technique of load ramping is not always reasonable for all problems. COMSOL Error for Initial Values(RF Module) Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. These are some highly rated cards & stationery in Brea, CA: What are some cards & stationery with a large number of reviews in Brea, CA? If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. 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 segregated approach, on the other hand, solves sets of unknowns separately. Multiphysics problems are often nonlinear. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. Iterative - COMSOL Multiphysics Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. 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. Perhaps this approach could be adapted to represent your model. Hi Jason, 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. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. 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. That is, start by first solving a model with a small, but non-zero, load. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 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. Wish you all the best. I am trying to solve the coupling between a waveguide and a microring resonator. To switch between these solver types, go to the Stationary Solver node within the Study sequence. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. thanks for reply I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary model. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. COMSOL makes every reasonable effort to verify the information you view on this page. Studysteps might be listed in wrong order: Not assigning materials to all the domains. 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. 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 "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). 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. Stationary Solver Iterative Direct . 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. In such cases, see if one material (or the other) can be omitted from the analysis completely. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. This doesn't seem to me the most elegant of methods, since I am essentially solving a stationary solution using a time dependent A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. COMSOL makes every reasonable effort to verify the information you view on this page. That is, they are tuned to achieve convergence in as many cases as possible. Such a large difference in the materials properties can be challenging. 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. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. 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. That is, they are tuned to achieve convergence in as many cases as possible. This is relatively expensive to do, but will lead to the most robust convergence. If it does so, use a finer increment in that range. Mesh 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. 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. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. This approach is known as a Continuation Method with a Constant predictor. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. With respect to any nonlinearities, replace them by a reasonable linearized term. By default, the COMSOL Multiphysics software determines these values heuristically depending on the physics as, for example, the specified initial values or a solution from an earlier study step. Linear solvers. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the - COMSOL COMSOL does not assume any legal liability for the accuracy of the data disclosed. 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. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. 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. rev2023.3.3.43278. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. 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