solving stationary solver after each time step - COMSOL Multiphysics The Iterative Solvers - COMSOL Multiphysics As we saw previously in the blog entry on Solving Nonlinear Static Finite Element Problems, not all nonlinear problems will be solvable via the damped Newton-Raphson method.
[COMSOL_Users] output of stationary solver as input to time-dependent 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. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. 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. 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. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. This involves a systematic reduction in the model complexity. It is also possible to manually refine the mesh. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Alle Rechte vorbehalten. COMSOL makes every reasonable effort to verify the information you view on this page. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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! Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . Posted 26 set 2019, 11:57 GMT-4
P&S: COMSOL Design Tool for Photonic Devices - ETH Z The fully coupled and segregated approaches are discussed below. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. Cooling and Solidification of Metal. 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. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Repeat this for every nonlinearity of the model. For example, if there is a temperature-dependent material property such as: 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. Wish you all the best. listed if standards is not an option). This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Unknown function or operator. That is, start by first solving a model with a small, but non-zero, load. This case is generally difficult, or impossible, to solve since this material property is non-smooth. Stationary (time-invariant) models with nonlinearities may converge very slowly. Hello, COMSOL does not assume any legal liability for the accuracy of the data disclosed. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. Stationary (time-invariant) models with nonlinearities may converge very slowly. The objective here is to simplify the model to a state where the model will solve, with linear approximations. 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. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. This approach is known as a Continuation Method with a Constant predictor. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Screenshot showing a Solver Configuration that has been altered. 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, Galleria dei Modelli e delle App di Simulazione, 2023 da COMSOL.
The segregated approach, on the other hand, solves sets of unknowns separately. The advantages of the continuation method are two-fold. That is, start by first solving a model with a small, but non-zero, load. They worked with me. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. - Function: ^ Failed to evaluate variable. Direct PARDISO Solver , PARDISO . Segregated approach and Direct vs. What is \newluafunction? If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Please dont hesitate to post comments below or send emails to us if you experience any other problems. Note the star symbol on the Solution feature. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. 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. Save this information to a file. Discussion Closed This discussion was created more than 6 months ago and has been closed.
comsol - using stationary solution as the initial conditions in time Most multiphysics problems are nonlinear. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2).
Office Supplies, Stationery, and Gift Retailers Companies in Brea Not meshing all the domains. The settings controlling the predictor type. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is:
COMSOL Blog Series on COMSOL Multiphysics Solvers 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. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) The Auxiliary Sweep can be used to implement ramping of any Global Parameter. if I want to do an adaptive mesh refinement, I get this error. How do/should administrators estimate the cost of producing an online introductory mathematics class? I am following the same model as Comsol provide us on the web. Hello guys. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. With respect to any nonlinearities, replace them by a reasonable linearized term. Sign in to create your job alert for Stationary Engineer jobs in Brea, California, United States. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Again, introduce a Global Parameter that gets ramped from exactly zero to one. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version "I chose this print shop based off yelp reviews and was very happy with the outcome! This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. 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. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. It is also possible to manually refine the mesh. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. replace it with the expression: 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. To switch between these solver types, go to the Stationary Solver node within the Study sequence. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) 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. Check the solver log to see if the continuation method is backtracking. 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. SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. It is also possible to manually refine the mesh. Create the time-dependent step or study. Segregated approach and Direct vs.
What to do when a linear stationary model is not solving - COMSOL Click the link in the email we sent to to verify your email address and activate your job alert. In a previous blog entry, we introduced meshing considerations for linear static problems. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. The problem is that when I run my model this message appear: Undefined value found. I am solving a linear stationary finite element model but the software is not solving. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. In such cases, see if one material (or the other) can be omitted from the analysis completely. Common Mistakes: Not assigning materials to all the domains. Any trademarks referenced in this document are the property of their respective owners. Save my name, email, and website in this browser for the next time I comment. Studysteps might be listed in wrong order: Not assigning materials to all the domains. Cooling and Solidification of Metal. Reply . Note: there is no way to couple this field with the time dependent nature of this physics. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. 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. ", "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. If it does so, use a finer increment in that range. 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. 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. It may also reveal that the model itself is ill-posed in some way. As part of our solver blog series we have discussed solving nonlinear static finite element problems, load ramping for improving convergence of nonlinear problems, and nonlinearity ramping for improving convergence of nonlinear problems. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. - Not meshing all the domains. They are usually called comp1.u, comp1.v, and comp1.w though. There will always already be either a Segregated or Fully Coupled feature beneath this. 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. Not entering required material parameters. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. replace it with the expression: Using the first order optimality. With sufficient simplification, a model can be reduced to a linear problem, and if this simplified model does not converge, see: What to do when a linear stationary model is not solving. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. Wrong ordering of study steps. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Repeat this for every nonlinearity of the model. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 Why? Understanding the Fully Coupled vs. Find centralized, trusted content and collaborate around the technologies you use most.
Top 10 Best Stationary in Brea, CA - October 2022 - Yelp Wrong ordering of study steps. That is, they are tuned to achieve convergence in as many cases as possible. However, it is usually not possible to know this ahead of time. 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.
To start a new discussion with a link back to this one, click here. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. By providing your email address, you consent to receive emails from COMSOL AB and its affiliates about the COMSOL Blog, and agree that COMSOL may process your information according to its Privacy Policy. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. The algorithm is, generally speaking, a Newton's method approach. However, it is usually not possible to know this ahead of time. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version (Frequency Domain should be the last step) 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. 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. They deal with COMSOL package and train users. $140,000.00, $120,000.00 Here we introduce a more robust approach to solving nonlinear problems. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K])
Iterative - COMSOL Multiphysics Name: actdep_int1, Your email address will not be published. Few days back i was also facing this problem in . 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. What are people saying about cards & stationery in Brea, CA? Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. 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. listed if standards is not an option). 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. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Comsol help video number 2: Solving a laminar flow problem in a slit.. 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.
Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? 3. Hi ! 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 settings controlling the predictor type. 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. Have you taken a look at this blog post? The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. What did people search for similar to stationary stores in Brea, CA? In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. 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.
Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. 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 approach is used by default for most 1D, 2D, and 2D-axisymmetric models. - First, it is physically intuitive, often matching how one would perform an experiment. 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. The default Initial Values for the unknowns in most physics interfaces are zero.
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This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. It may also reveal that the model itself is ill-posed in some way. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Understanding the Fully Coupled vs.
Stationary Solver - COMSOL Multiphysics The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Asking for help, clarification, or responding to other answers. 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. In this post, we will delve deeper into how to choose an appropriate mesh to start your mesh convergence studies for linear static finite element problems. 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. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Why is there a voltage on my HDMI and coaxial cables? k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) 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.
Direct Iterative , Direct . (Frequency Domain should be the last step). These are some highly rated cards & stationery in Brea, CA: What are some cards & stationery with a large number of reviews in Brea, CA? This algorithm was also useful for understanding what happens near a failure load. 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. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. 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. 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. 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. This case is generally difficult, or impossible, to solve since this material property is non-smooth. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K])
Does anyone know how to solve error in stationary solver in COMSOL Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. 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. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. The technique of load ramping is not always reasonable for all problems. The idea behind the GCRO-DR method is to retain the subspace determined while solving previous systems and use it to reduce the cost of solving the next system. However, if a lower-level change has been manually made to the solver settings, the software will not automatically use the correct default solver. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Thanks for contributing an answer to Stack Overflow! This is relatively expensive to do, but will lead to the most robust convergence. This involves a systematic reduction in the model complexity. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. 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. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Consult your product manuals for complete trademark details. This guide applies solely to nonlinear stationary models. There will always already be either a Segregated or Fully Coupled feature beneath this. With respect to any nonlinearities, replace them by a reasonable linearized term. Common Mistakes: Not assigning materials to all the domains. Linear solvers. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. 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. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). 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. 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 is sometimes necessary to manually scale the dependent variables. Check the solver log to see if the continuation method is backtracking. However, load ramping will not work in all cases, or may be inefficient. The conditions on the geometric aspect ratio are relatively more strict.
How to solve "Feature: Stationary Solver 1 (sol1/s1) Attempt - COMSOL The difference between the phonemes /p/ and /b/ in Japanese. 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. 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. 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. 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. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. If it does so, use a finer increment in that range. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. It is sometimes necessary to manually scale the dependent variables. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases.