Penalty methods are easier to program, but suffer from numerical instability: the ideal penalty is infinite, but then you. If any one of them could work , then it would be sufficient to me. 2. just to fine-tune all solution parameters, it is better to use a linear mesh (linear discretization both for displacement and contact pressure) at the beginning. I tried to use your suggestion "penalty method". The number of increments may need to be quite large, and you will want to monitor at what values of the ramping factor there is slow convergence of the solver. Quality Factor of Axisymmetric Resonators in COMSOL M. Imran Cheema, and Andrew G. Kirk 1 1 . All the best, Best wishes! Jay. I am using comsol 4.2 to simulate a contact problem. If you have a specific problem, please post much more details, so I can better understand your problem. 'Penalty, Dynamic' is selected as the contact method. --, Hi Remi, Your internet explorer is in compatibility mode and may not be displaying the website correctly. We will leave this thread up for historical purposes but will lock the thread for further comments. so please if you have any idea that could help let me know. The penalty factor is gradually increased up to its full value, which is used in the iteration after the one where the specified number of iterations with relaxation have been reached. Right now I have no idea what cause convergence problems. Nagi Elabbasi Veryst Engineering Veryst Engineering, Dear Nagi, 4. define a parametric solver to fine-tune the load step (use a small parameter-step if the convergence does not appear). I am looking for simulate the assembly process among perturbed parts (clamping, fastening and releasing). If one part is significantly stiffer than the others, its deflections will be relatively negligible, and it can often be considered as rigid. There are three contact constraint enforcement methods available in Abaqus/Standard : The direct method attempts to strictly enforce a given pressure-overclosure behavior per constraint, without approximation or use of augmentation iterations. Regards. Marjan, Hi Pasquale & Marjan Make sure to create at least a contact pair before. Have you set your constraints in a good way? It is hard to think about your problem without seeing the model. I hope at least I can give you some idea. Then remove the contact pressure variable from the solve for list in the solver manager. A single Contact feature can be applied to all Contact Pair definitions at once. 1- what do you call solver manager? Using a penalty function for contact problem is good alternative of the augmented Lagrangian method available in the structural mechanics module. Is that what did you mean? All the best, There are many reasons why contact problems do not converge. If your geometry contains parts that are adjacent to each other, that have mating boundaries, the finalization method should be set to Form Assembly with the Create Pairs of pair type Contact Pair selected. The default COMSOL expression in front of Pn has two components. Then below the solid mechanics main icon, there is the contact icon, if you click you will find again discritization. I consider every aspects you guys posted here. Penalty contact adds stiff springs (penalty factor) between the contacting surfaces that are only active when the surfaces overlap. As in your model the three domains are still in contact in the un-deformed configuration, you should set a small initial contact pressure (say 1e-3). I have set the stiffness value equal to the young's modulus (I have assumed an isotropic elastic material). This will be easier to solve than the case of domains with only applied loads, forces, and Contact conditions, but that are otherwise unconstrained. Thank you! You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version The magnitude of this spring constant is initially set at a very high value, high enough such that the deformations are negligible due to the initially applied loads. If it did not converged, change the contact discritization to 1. [QUOTE] December 3, 2018. I mean that you can solve any kind of multiphysic problem. In some cases, this approach can result in faster computations and provide smoother convergence when compared to the Augmented Lagrangian method. A pioneer in chemistry, sanitary engineering, and human ecology, Ellen Swallow Richards paved the way for women in science. It helps the solver to converge better in case that you introduce a small pressure in contact area. The cylinder is passing through the slab because the applied cylinder displacement is too big for one step. I am modeling a transient contact problem using the penalty method instead of the augmented Lagrangian method. The contacting boundaries should be meshed finely enough to give good resolution of the contacting area. listed if standards is not an option). There is good COMSOL documentation on the penalty contact method in the Contact Analysis of a Snap Hook Using a Penalty Formulation page. Guidance of manual tuning of the Penalty Factor is in Knowledge Base entry However, manual tuning of the Penalty Factor should only be done after all of the other recommendations in this Knowledgebase. Pasquale, Pasquale: I also implemented parametric sweep for solving. If it is possible to reformulate your problem such that there is some initial constraint on all domains, do so. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version I am modeling a transient contact problem using the penalty method instead of the augmented Lagrangian method. If you have to modify the solver sequence, this separate segregated group should still be kept, and solved for after the displacements. The model is attached below. If it is expected that there will be little sliding between the contacting boundaries (such as in a shrink fit or when two parts are bolted together) then go to the Contact Pair > Advanced settings, and change the Mapping method to Initial Configuration. In some cases, this approach can result in faster computations and provide smoother convergence when compared to the Augmented Lagrangian method. : "perturbed" parts are like-real parts which may come from forming processes and are used in automobile applications. the scale of dependent variables for example. sensor model with tissue_upper and lower jack.mph, sensor model with tissue_simplyfied model.mph, Methods for Dealing with Numerical Issues in Constraint Enforcement, Finding contact stress at the interface of contact pair, How to Evaluate Gear Mesh Stiffness in a Multibody Dynamics Model. I made my best to use mechanical properties in simulation similar to the properties of the real components, including the friction constants even. The default COMSOL expression in front of Pn has two components. I understand how it is used in the augmented Lagrangian method. When using the augmented Lagrangian formulation, it is necessary to manually scale the variables in a contact problem. However, I am still struggling with this model. Yajuan, Hi everybody, Veryst Engineering, Nagi, Where is the contact pressure variable and also I can't find the Lagrangian solver option in order to deselect it. I would start by examining the error message that COMSOL reports. May be it is just because visualize problem, but it looks like two domains penetrate each other. I also would recommend that you attach your model. In general it is possible to simulate your problem with Comsol . [/QUOTE] Good luck COMSOL document says "A contact pair is a pair that define boundaries where the parts may come into contact but cannot penetrate each other under deformation for modeling of structural contact and multiphysics contact." But there is penetration. honestly do not know what to do with the model, and I have very important dead line in two weeks. The Penalty method must be used when modeling adhesion. Did anyone have solve this kind of problem? I am looking for simulate the assembly process among perturbed parts (clamping, fastening and releasing). I have search the documentation but can not find anywhere where it defines the solid.hmin_dst variable. I have applied your procedure on a 2D example and it seems to work very well. This should not be changed. 3. solve the problem with the time-dependent solver. . The lower penalty usually leads to faster convergence, but more interpenetration between the surfaces, which is a deviation from the exact contact constraints. I consider every aspects you guys posted here. In the contact node under solid mechanics, the expression for penalty factor was not evaluating. Structural Mechanics listed if standards is not an option). Dear Comsol users, I noticed that for decohesive settings tag, there is a parameter called shape factor when multi-linear seperation is selected. I am programming a Matlab-Comsol automatic application. If the "Viscous only" on the Penalty factor control node is changed to be "User . COMSOL Blog. Thanks You do not need to start with the two objects not in contact. and similarly in any other directions that need to be restrained. The Penalty method is relatively less accurate, but more robust and will require less solver tuning, making it preferable for multiphysics problems and time-dependent models. That was a good point. I would rather rely on what is written in front of Pn but just multiply it by a constant like (1/3). Version 3.5a Discussion Closed This discussion was created more than 6 months ago and has been closed. Ahmad, Hi Marjan and , Pasquale . Click on solid mechanics. The destination boundary of the contact pair must be meshed finer than the source boundary, by at least a factor of two. Hello Remi, The moment had arrived when Burnley, a team struggling to get a foothold at the wrong end I know the ugmented Lagrangian method and the penalty method are different. As long as your mesh is not moving, use extension instead of parametric sweep. This contact algorithm is based on the penalty factor formulation related to the penetration of the solid parts in contact. In your application you can do this just by observing that the model has a symmetric wrt the middle plane (have a look to the attached modified model). However, I am still struggling with this model. It is a good idea to scale this expression up or down based on two factors: (i) ease of convergence and (ii) solution accuracy. But in my case one of the two contact surfaces was a static, stiff, perfect plane so defining the force equation was trivial. However I am still new with the comsol and I hope that I didn't do any stupid mistakes in building the models. If you are solving a stationary (steady-state) model, you will want to ramp the prescribed displacements, loads, and stiffnesses of any spring foundations during the solution. I am really sorry for the late replay. 1. when handling contact pairs, the weak of constraint could make the solution not so stable (the stiffness matrix becomes ill-conditioned). If that doesnt provide any clues then try disabling contact and checking that the model otherwise works. contact length, Comsol evaluated it as 7.22mm while the analytical solution gave 7.16mm, that is a May be it is just because visualize problem, but it looks like two domains penetrate each other. It works well. Thanks again :). Using the parameter RampFactor that ranges linearly from 0 to 1, a spring foundation with spring constant kz in the Z-direction can be introduced where, kz = k0*(1-RampFactor)*2^(-RampFactor*10). In the augmented Lagrangian method, the expression of "pn" is "E_smsld/hmin_cp1_smsld*min(1e-3*5^auglagiter,1)". Ahmad, Hi everyone 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. cause I even tried different conditions but it still do not work. I mean it is very sensitive to the problem definition e.g. The Structural Mechanics Module User's Guide > Structural Mechanics Modeling > Contact Modeling section. If you apply the displacement gradually (over 3 steps) using a Parametric Sweep with values 0.1, 0.5 and 1.0 times the full displacement it works. Would you please help me to find it? This means that you should assure that all domains have all rigid motions avoided. go to physics>boundary settings>pairs>contact>"pn". Finally deselect the augmented lagrangian solver option in the solver parameters (stationary page). But I am wondering that did the contact normal penalty factor only affect the penalty method but not the augmented Lagrangian method. Structural Mechanics if you can, please attach your model so we can see better your settings. When using the augmented Lagrangian formulation, the default solver configuration uses a segregated approach where the contact pressures (and friction forces, if friction is included) are solved in a separate Lumped step. This is where the overclosure/contact formulation comes into play. But there is penetration. Thanks alot. If the parts have a similar stiffness, set concave parts as source and convex parts as destination. The ramping of applied loads and displacements should begin from a value very close to zero, at which there is negligible, or even no, contact and should ramp up linearly to the maximum value. Hi Kevin, parameters, initial contact pressure and penalty factor, . Pasquale, Hi Dear Ahmad, Use more increments when the convergence is slow. Then remove the contact pressure variable from the solve for list in the solver manager. I have a model that contains an elastic beam that when deflected comes in contact with two different hyperelastic materials one on each side. The mapping between the source and destination boundaries will be computed only once, based upon the initial positions of the domains, which leads to faster and more stable convergence. If the initial overlap is too much convergence may be a problem, but you have them initially forming a line contact which is fine. Comsol Offices Contact us using the details below. Veryst Engineering. This affects the shape function and convergence as well. Many Thanks Remi Magnard. In COMSOL Multiphysics, there are two possible methods for solving contact problems: the penalty method and the augmented Lagrangian method. The mesh on the boundaries of the deformable domains will need to be fine enough to give a good resolution of the contact patch and stress state. This method (penalty function) is a bit less accurate than the augmented Lagrangian one as it allow penetration between the elastic body but it is also much more stable. Why does it have . Happy Birthday, Ellen Swallow Richards. It is used for both the penalty method and the augmented Lagrangian method, but its interpretation differs: This is described very nicely in the Structural Mechanics User's Guide. Structural contact modeling is a highly non-linear problem. Suggested Products Download the application files Warning: MUMPS allocation factor increased, Methods for Dealing with Numerical Issues in Constraint Enforcement. The iterative solver will require less memory, but convergence is usually much slower. The COMSOL discussion forum covers a wide variety of simulation topics. I am trying to model a contact problem into structural module application. Thus, question are: is there a way to solve the contact problem without calculate the pressure field at the coontact interface? Solution Number: 1292 Applies to: COMSOL Model Manager, COMSOL Multiphysics, COMSOL Server Versions: All versions. Setting contact pair, meshing and solver setting looks fine, but why convergence strat oscillation up to very high value or down low finally not converge with current setting up??? The scaling of the contact pressure is used when checking the convergence, so if a too high value is used, there is a risk that the results are not correct. The brief introduction is that: The upper two domains are solid, the lower two domains are also solid and the intermediate domain is fluid. Using weak constrains for the moving object, I mean for source sometimes helps alot. It works almost fine for me to choose the order of discritization of displacement 4 and the order of contact pressure discritization 1. A PML can be treated as an anisotropic ab-1 Excerpt from the Proceedings of the COMSOL Conference 2010 Boston. In Comsol, the displacement discritization should not have higher order than pressure one. Yours, How can I set the penalty factor value when the lagrangian solver is disabled? The iteration part was also a big question mark that now is clear. If the contacting parts are in contact at the start of the simulation, then Speed is the preferred setting. Use the default suggested direct solver rather than the iterative solver whenever possible. Introduce first a Global Parameter, such as RampFactor that multiplies all displacements, loads and stiffnesses. What does the expreesion mean? Are you checking the box of creat creat pair at the end of Geometry? I am using the weak constraint in the properties, does that affect my model? The ramping of spring constants used for spring foundations on unconstrained domains should begin at the peak value of spring stiffness and then down to zero. Concerning a contact pressure, I suggest that you take a look at cylinder roller example in the library. Sorry again I am really new to the 4.1 version of the software. par Bridget Paulus. The model is solving, but the cylinder is passing through the slab. Suggestion de Produits Tlchargez les fichiers du modle This article contains guidance for solving models that include structural contact, and the procedures that should be followed to achieve a converged solution. How does COMSOL use the penalty factor when the penalty method is being used? Nagi Elabbasi As surfaces come in and out of contact, load paths and stress states will abruptly change. Within the Contact feature, select either the augmented Lagrangian or Penalty as the Contact Pressure Method. Penalty Method The default penalty method is rather simple and robust method to introduce the contact condition. Marjan, Hi Pasquale, Keywords: Mechanical Contact, Augmented Lagrangian method, penalty factor, Hertz contact, convergence Fabienne Pennec received the mechanical degree engineering from ENSMM, Besanon, France in 2005 and is currently pursuing the PhD . Thanks Could not obtain license for COMSOL Multiphysics GUI. 3 Replies, Please login with a confirmed email address before reporting spam. This is described very nicely in the Structural Mechanics User's Guide. 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. The higher the penalty factor the less the overlap between the surfaces (and hence more accurate solution) yet the more ill-conditioned the stiffness matrix will be. Concerning about constraints before in contact between two parts, I already test each part is fully constraint or not. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Please someone answer me and correct the error, i'm new of software. COMSOL document says The first part (solid.Eequ/solid.hmin_dst) is a geometry/material part of the same form as the E/k expression you mentioned that is automated to get good estimates for E and k. The material stiffness Solid.Eequ is automatically calculated based on the material of the destination surface, and the minimum element size solid.hmin_dst is automatically calculated also from the destination surface. COMSOL document says "A contact pair is a pair that define boundaries where the parts may come into contact but cannot penetrate each other under deformation for modeling of structural contact and multiphysics contact." But there is penetration. The numerical solvers within COMSOL Multiphysics expect some degree of smoothness to the solution, so solving such models is inherently challenging. Remi Magnard listed if standards is not an option). How does COMSOL Multiphysics handle complex-valued numbers and problems in the frequency domain? Kindly, find attached two models of my work. The convective fluid flow. Adjust it to linear. listed if standards is not an option). Sincerely, I have uploaded my file and would appreciate if you could take a quick look. [/QUOTE] I must avoid any solver-error during the automatic calculation. Thanks If you anticipate contact between any sharp corners and surfaces in the model, you should modify the geometry such that the sharp corner is replaced with a rounded boundary, a fillet. If you are solving a transient model but do not want to consider inertial effects (if you do not want to model the vibrations of the structure) then go to the Solid Mechanics interface, Structural Transient Behavior settings, and select Quasi-static, which will solve much more quickly. COMSOL makes every reasonable effort to verify the information you view on this page. Any trademarks referenced in this document are the property of their respective owners. For efficiency, include in each contact pair only those boundaries that have the possibility of coming into contact. Any help will be appreciated. Thank you, [QUOTE] Hi Ryan, The augmented Lagrangian method is more accurate, but has higher computational cost, and will require more fine-tuning to converge. Modeling friction is will often increase the computation time significantly, so if you can reasonably ignore friction, do so. How can i set Contact penality setting? Build & Customize Your Car With Ultra Wheel Car Builder! How does COMSOL use the penalty factor when the penalty method is being used? Use the Swap source and destination button for this. The peak value of spring stiffness, k0, should be chosen such that the displacement due to the full applied load is about equal to the element size of the contacting boundaries. Thanks again I have a 2D model costituited by elastomer (rectangular block) that sliding on rigid (square) pyramidal substrate; how can i estimate effective contact area of elastomer? Please of course feel free to open new threads and refer back to this if needed. I notice also that the slab is very thin, so ideally it should be defined as the destination not the source of the contact pair (since it is less stiff). If your contact simulation does involve friction, set up and solve the problem without friction first. Head Office Contact form Enter your details below and we'll get right back to you. Dear Comsol users, I noticed that for decohesive settings tag, there is a parameter called shape factor when multi-linear seperation is selected.
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