If you are unsure if your problem is linear and stationary, look at the Log. - Function: ^ Failed to evaluate variable. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Different physics have different default solvers. The Fully Coupled solution approach, with the Plot While Solving enabled.
Does anyone know how to solve error in stationary solver in COMSOL k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Segregated approach and Direct vs. It is also possible to manually refine the mesh. My comment is perhaps a bit nave but it seems to me that you could simply deactivate the \frac{\partial \cdot}{\partial t} term of the background field equation but keep its connexion to the solid to get what you want. Comsol help video number 2: Solving a laminar flow problem in a slit.. listed if standards is not an option). Such problems must solved in the time domain. It may also reveal that the model itself is ill-posed in some way. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. (I am begginer in comsol) Thank you. New Stationary Engineer jobs added daily. The objective here is to simplify the model to a state where the model will solve, with linear approximations. Consult your product manuals for complete trademark details. What did people search for similar to stationary stores in Brea, CA? However, it is usually not possible to know this ahead of time. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. Direct PARDISO Solver , PARDISO . 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. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. 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. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. Minimising the environmental effects of my dyson brain. 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. Such a large difference in the materials properties can be challenging. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. If it does so, use a finer increment in that range. 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! Leverage your professional network, and get hired. 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. 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. 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. The settings controlling the predictor type. 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. 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.) This guide applies solely to nonlinear stationary models. I use comsol multiphysics 5.2a and . ", "Absolutely the best place to shop for flowers and greenery, I spent an hour just looking around for fun prior to purchasing a bouquet, they have the best customer service people all over the place and it's a huge place", "Recently came in here to pick up 45 chocolate Seegars (cigars) for a dinner banquet in honor of my baby nephew. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 Check the solver log to see if the continuation method is backtracking. For example, if there is a temperature-dependent material property such as: To switch between these solver types, go to the Stationary Solver node within the Study sequence. 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. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge.
Office Supplies, Stationery, and Gift Retailers Companies in Brea 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. Repeat this for every nonlinearity of the model.
The Iterative Solvers - COMSOL Multiphysics As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) The Auxiliary Sweep can be used to implement ramping of any Global Parameter. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Create the time-dependent step or study. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Computational Fluid Dynamics (CFD), API Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Understanding the Fully Coupled vs. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. 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. Do you also know how to solve this problem: using stationary solution as the initial conditions in time dependent model, How Intuit democratizes AI development across teams through reusability. This doesn't seem to me the most elegant of methods, since I am essentially solving a stationary solution using a time dependent
How to solve "Undefined material property 'sigma - ResearchGate Your Discussion has gone 30 days without a reply. 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. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Please dont hesitate to post comments below or send emails to us if you experience any other problems. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. First, it is physically intuitive, often matching how one would perform an experiment. The Fully Coupled solution approach, with the Plot While Solving enabled.
[COMSOL_Users] output of stationary solver as input to time-dependent Multiphysics problems are often nonlinear. Solver . You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. As we saw in Load Ramping of Nonlinear Problems, we can use the continuation method to ramp the loads on a problem up from an unloaded case where we know the solution. The conditions on the geometric aspect ratio are relatively more strict. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Segregated approach and Direct vs. Iterative linear solvers, Time dependent function and stationary study, Combining Adaptive Mesh Refinement with Data Filtering, What to do when a linear stationary model is not solving, Galleria dei Modelli e delle App di Simulazione, 2023 da COMSOL. Not meshing all the domains. There will always already be either a Segregated or Fully Coupled feature beneath this. Save my name, email, and website in this browser for the next time I comment. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Here we introduce a more robust approach to solving nonlinear problems. 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. To switch between these solver types, go to the Stationary Solver node within the Study sequence. rev2023.3.3.43278. Hi Jason,
This is relatively expensive to do, but will lead to the most robust convergence. 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. Such problems must solved in the time domain. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. 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. Repeat this for every nonlinearity of the 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. Why? Set initial conditions in the physics to the appropriate dependent model variable names rather than the default 0. Wrong ordering of study steps. 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. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. Review the model setup to resolve these. In a previous blog entry, we introduced meshing considerations for linear static problems. 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 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. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Few days back i was also facing this problem in . Cooling and Solidification of Metal. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. The technique of load ramping is not always reasonable for all problems. However, load ramping will not work in all cases, or may be inefficient. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) 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. The technique of load ramping is not always reasonable for all problems. 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. That is, they are tuned to achieve convergence in as many cases as possible. Most multiphysics problems are nonlinear. "After the incident", I started to be more careful not to trip over things. 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. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Wish you all the best. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions.
solving stationary solver after each time step - COMSOL Multiphysics By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. See Knowledge Base 1240: Manually Setting the Scaling of Variables. The other low-level default settings within the Stationary Solver are chosen for robustness. Note: there is no way to couple this field with the time dependent nature of this physics. We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. 3. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields.
Solving for laminar flow using Comsol - YouTube Hi Alexis,
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 the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. The other low-level default settings within the Stationary Solver are chosen for robustness. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. 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. Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems. That is, start by first solving a model with a small, but non-zero, load. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions.
comsol - using stationary solution as the initial conditions in time There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. Hello, 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.
How to solve "Feature: Stationary Solver 1 (sol1/s1) Attempt - COMSOL $130,000.00. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. An example would be a linear static structural model of an aluminum beverage can.
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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. That is, they are tuned to achieve convergence in as many cases as possible. To switch between these solver types, go to the Stationary Solver node within the Study sequence. 0 Replies, Please login with a confirmed email address before reporting spam. This approach is known as a Continuation Method with a Constant predictor. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. 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. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. 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. What sort of strategies would a medieval military use against a fantasy giant? - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. P&S: COMSOL Design Tool for Photonic Devices.
Understanding stationary and time dependent solver COMSOL Multiphysics COMSOL makes every reasonable effort to verify the information you view on this page. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh.