It may also reveal that the model itself is ill-posed in some way. Tutti i diritti sono riservati. Get notified about new Stationary Engineer jobs in Brea, California, United States. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. I highly recommend this flower shop. Today's top 351 Stationary Engineer jobs in Brea, California, United States. replace it with the expression: You can unsubscribe from these emails at any time. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. Use this parameter to modify the nonlinearity expressions in the model. Have you taken a look at this blog post? With respect to any nonlinearities, replace them by a reasonable linearized term. 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. COMSOL makes every reasonable effort to verify the information you view on this page. Consult your product manuals for complete trademark details. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Repeat this for every nonlinearity of the model. 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. There will also be a red cross over the Materials branch icon. Not entering required material parameters. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. 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. 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. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. - Function: ^ Failed to evaluate variable. Could you expand a little bit more why the coupling is impossible? The advantages of the continuation method are two-fold. The technique of load ramping is not always reasonable for all problems. listed if standards is not an option). Why do many companies reject expired SSL certificates as bugs in bug bounties? Trying to understand how to get this basic Fourier Series. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. 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.) 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. 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. If you are unsure if your problem is linear and stationary, look at the Log. What did people search for similar to stationary stores in Brea, CA? If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. 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. Version 5.3 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. COMSOL does not assume any legal liability for the accuracy of the data disclosed. if I want to do an adaptive mesh refinement, I get this error. Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . See Knowledge Base 1240: Manually Setting the Scaling of Variables. 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. That is, they are tuned to achieve convergence in as many cases as possible. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. How do/should administrators estimate the cost of producing an online introductory mathematics class? To learn more, see our tips on writing great answers. I am trying to solve the coupling between a waveguide and a microring resonator. If it does so, use a finer increment in that range. It is also possible to manually refine the mesh. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. 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. Save my name, email, and website in this browser for the next time I comment. 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. Note the star symbol on the Solution feature. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Note: there is no way to couple this . Name: actdep_int1, Your email address will not be published. To start a new discussion with a link back to this one, click here. Such problems must solved in the time domain. This is relatively expensive to do, but will lead to the most robust convergence. 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. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. 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. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Linear solvers. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. With respect to any nonlinearities, replace them by a reasonable linearized term. Cooling and Solidification of Metal. They deal with COMSOL package and train users. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Not entering required material parameters. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. 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 also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). 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. I am solving a linear stationary finite element model but the software is not solving. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. The default Initial Values for the unknowns in most physics interfaces are zero. 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. Communication over the phone, in person, and through email was very easy. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. In a previous blog entry, we introduced meshing considerations for linear static problems. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. 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. These can be used alone, or in combination with other interfaces. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. 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. New Stationary Engineer jobs added daily. Hence Comsol solved for the stationary solution at different points of time. 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 such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Solving such models in a stationary sense should simply require solving a single (large) system of linear equations and should always be solvable, but there are cases when the software will fail to find a solution. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. 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. Any trademarks referenced in this document are the property of their respective owners. The problem is that when I run my model this message appear: Undefined value found. I personally liked emailing them the file, ", "This flower shop is the best! A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. That is, start by first solving a model with a small, but non-zero, load. If you have both as steps in the same study, then solve that study. What is the purpose of non-series Shimano components? It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. 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. They are usually called comp1.u, comp1.v, and comp1.w though. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. This guide applies solely to nonlinear stationary models. 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. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: 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. 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. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) 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. Stationary (time-invariant) models with nonlinearities may converge very slowly. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. The advantages of the continuation method are two-fold. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. The segregated approach, on the other hand, solves sets of unknowns separately. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). With respect to any nonlinearities, replace them by a reasonable linearized term. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. The advantages of the continuation method are two-fold. This case is generally difficult, or impossible, to solve since this material property is non-smooth. Multiscale Modeling in High-Frequency Electromagnetics. For example, if there is a temperature-dependent material property such as: This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. Stationary in the COMSOL Multiphysics Programming Reference Manual Damped Newton Methods The nonlinear solver uses an affine invariant form of the damped Newton method as described in Ref. The objective here is to simplify the model to a state where the model will solve, with linear approximations. Asking for help, clarification, or responding to other answers. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 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. 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. Set initial conditions in the physics to the appropriate dependent model variable names rather than the default 0. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. The algorithm is, generally speaking, a Newton's method approach. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Discussion Closed This discussion was created more than 6 months ago and has been closed. 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. Wish you all the best. The technique of load ramping is not always reasonable for all problems. 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. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. The algorithm is, generally speaking, a Newton's method approach. The default Initial Values for the unknowns in most physics interfaces are zero. This approach is known as a Continuation Method with a Constant predictor. 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.
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