The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. Perhaps this approach could be adapted to represent your model. 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. The segregated approach, on the other hand, solves sets of unknowns separately. How can I use it? 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. What sort of strategies would a medieval military use against a fantasy giant? 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 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. Such problems must solved in the time domain. Reply . (Frequency Domain should be the last step) The settings controlling the predictor type. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. What are people saying about cards & stationery in Brea, CA? listed if standards is not an option). Any trademarks referenced in this document are the property of their respective owners. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. 140K views 8 years ago COMSOL Multiphysics Tutorial for Beginners Please note that an updated version of the content in this video can be found in the Modeling Workflow video in the COMSOL. Not assigning proper boundary conditions: Especially if you have ports. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Posted 26 set 2019, 11:57 GMT-4 The technique of load ramping is not always reasonable for all problems. Get notified about new Stationary Engineer jobs in Brea, California, United States. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Consult your product manuals for complete trademark details. Repeat this for every nonlinearity of the model. They deal with COMSOL package and train users. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. COMSOL does not assume any legal liability for the accuracy of the data disclosed. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. 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. Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. Version 5.3 Leverage your professional network, and get hired. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. View the Settings window for the Materials branch to get a list of all domains with undefined materials and add a material to those domains. Consult your product manuals for complete trademark details. This guide applies solely to nonlinear stationary models. However, it is usually not possible to know this ahead of time. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. First, it is physically intuitive, often matching how one would perform an experiment. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) Making statements based on opinion; back them up with references or personal experience. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. For example, if there is a temperature-dependent material property such as: If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. Different physics have different default solvers. Note the star symbol on the Solution feature. COMSOL 22.9K subscribers Adding a study to your simulation is necessary in order to solve your problem. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Changes to these low-level settings from the defaults will usually be quite model- and case-specific. 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. Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 Why is there a voltage on my HDMI and coaxial cables? In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Not entering required material parameters. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. 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. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. The Fully Coupled solution approach, with the Plot While Solving enabled. Repeat this for every nonlinearity of the model. COMSOL makes every reasonable effort to verify the information you view on this page. SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. 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. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. 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 approach is known as a Continuation Method with a Constant predictor. COMSOL makes every reasonable effort to verify the information you view on this page. It may also reveal that the model itself is ill-posed in some way. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. 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. The coupling terms between the different groups are thus neglected. Wrong ordering of study steps. - The issue here has do with the iterative algorithm used to solve nonlinear stationary models. In this case, it would likely be reasonable to treat the insulative material as a perfect insulator, omit it from the analysis, and use the Electric Insulation boundary condition instead of modeling those domains. Any trademarks referenced in this document are the property of their respective owners. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 GCRO-DR is a method for Krylov subspace recycling. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Hence Comsol solved for the stationary solution at different points of time. 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. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Any trademarks referenced in this document are the property of their respective owners. Again, introduce a Global Parameter that gets ramped from exactly zero to one. 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. Minimising the environmental effects of my dyson brain. Such problems must solved in the time domain. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Common Mistakes: Not assigning materials to all the domains. The difference between the phonemes /p/ and /b/ in Japanese. This is a review for cards & stationery in Brea, CA: "Love this store!!! Linear solvers. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Multiphysics problems are often nonlinear. 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. Does anyone know what should cause this problem? Such a large difference in the materials properties can be challenging. k(T,P) = 10[W/m/K]*((1-P)+P*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. 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: 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. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). 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. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Iterative , Direct . The coupling terms between the different groups are thus neglected. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. 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. To start a new discussion with a link back to this one, click here. The settings controlling the predictor type. Use this parameter to modify the nonlinearity expressions in the model. Today's top 351 Stationary Engineer jobs in Brea, California, United States. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. 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. That is, start by first solving a model with a small, but non-zero, load. I am trying to solve the coupling between a waveguide and a microring resonator. 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.