The Fully Coupled solution approach, with the Plot While Solving enabled. 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. Acidity of alcohols and basicity of amines. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 First, it is physically intuitive, often matching how one would perform an experiment. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. Mesh Leverage your professional network, and get hired. 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. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. The problem is that when I run my model this message appear: Undefined value found. Sign in to create your job alert for Stationary Engineer jobs in Brea, California, United States. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. With respect to any nonlinearities, replace them by a reasonable linearized term. There will also be a red cross over the Materials branch icon. 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. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. (Frequency Domain should be the last step). 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 can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. That is, they are tuned to achieve convergence in as many cases as possible. 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. To start a new discussion with a link back to this one, click here. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) In this posting, we introduce the idea of ramping the nonlinearities in the problem to improve convergence. Minimising the environmental effects of my dyson brain. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. 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. Understanding the Fully Coupled vs. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. 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. 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. That is, start by first solving a model with a small, but non-zero, load. Tutti i diritti sono riservati. There will always already be either a Segregated or Fully Coupled feature beneath this. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. 0 Replies, Please login with a confirmed email address before reporting spam. To switch between these solver types, go to the Stationary Solver node within the Study sequence. See Knowledge Base 1240: Manually Setting the Scaling of Variables. 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. This involves a systematic reduction in the model complexity. The solver settings are stored at Study > Solver Configurations > Solution. See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. Thanks, Andres. Required fields are marked *. Understanding the Fully Coupled vs. Save my name, email, and website in this browser for the next time I comment. Such a large difference in the materials properties can be challenging. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Solve the stationary study then the time dependent study. You can unsubscribe from these emails at any time. Any trademarks referenced in this document are the property of their respective owners. The coupling terms between the different groups are thus neglected. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. 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 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. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. That is, they are tuned to achieve convergence in as many cases as possible. 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. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. To switch between these solver types, go to the Stationary Solver node within the Study sequence. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. However, it is usually not possible to know this ahead of time. 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. For example, if there is a temperature-dependent material property such as: COMSOL 22.9K subscribers Adding a study to your simulation is necessary in order to solve your problem. Repeat this for every nonlinearity of the model. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. The other low-level default settings within the Stationary Solver are chosen for robustness. The advantages of the continuation method are two-fold. With respect to any nonlinearities, replace them by a reasonable linearized term. 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. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. 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. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. The algorithm is, generally speaking, a Newton's method approach. 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. listed if standards is not an option). This case is generally difficult, or impossible, to solve since this material property is non-smooth. 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. COMSOL does not assume any legal liability for the accuracy of the data disclosed. 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. Not assigning proper boundary conditions: Especially if you have ports. L'objectif de notre prsent travail se repose sur l'tude par simulation numrique du comportement de bton au jeune ge sous des conditions svres de temprature pendant les premires 24h aprs. 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. 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. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). Hello, In such cases, see if one material (or the other) can be omitted from the analysis completely. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. It is also possible to manually refine the mesh. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Tutti i diritti sono riservati. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Use this parameter to modify the nonlinearity expressions in the model. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Different physics have different default solvers. Is it possible to rotate a window 90 degrees if it has the same length and width? Hi Jason, Get notified about new Stationary Engineer jobs in Brea, California, United States. The technique of load ramping is not always reasonable for all problems. replace it with the expression: COMSOL makes every reasonable effort to verify the information you view on this page. 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. Any trademarks referenced in this document are the property of their respective owners. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one.