To start a new discussion with a link back to this one, click here. I dont know if this page dates back to v3.5A. If the contacting parts are in contact at the start of the simulation, then Speed is the preferred setting. so please if you have any idea that could help let me know. and the sensor has a softer silicone rubber in his structure under the beam. Please of course feel free to open new threads and refer back to this if needed. It is hard to think about your problem without seeing the model. the model with extra layers resemble the experimental test where the extra layers work as two jacks one to be a substrate to the sensor and the other push the tissue against the sensor. Also, the contact pressure penalty factor in penalty method is interpreted as the stiffness of a distributed spring connecting two contact boundaries. Hi Pasquale I am programming a Matlab-Comsol automatic application. This affects the shape function and convergence as well. Also, I need to have the solution up to 5N loading, which means according to the model that I upload I have either to extend the para up to 5, or to replace the loading boundary condition in y axis with (- (16.67/568)*para) [N/mm^2]. Best regards listed if standards is not an option). 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. sorber [3] in which the diagonal . The penalty method is not described at all. 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. 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. Penalty Method The default penalty method is rather simple and robust method to introduce the contact condition. Contact problems with friction should always be solved incrementally using a parametric or time dependent solver since the development of friction forces is history dependent. The rigid part should be the source in the Contact Pair. It is a good idea to scale this expression up or down based on two factors: (i) ease of convergence and (ii) solution accuracy. problem with contact pair-penalty factor setting. "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." Happy Birthday, Ellen Swallow Richards. I am programming a Matlab-Comsol automatic application. Posted Jun 24, 2009, 8:50 a.m. GMT+2 Where is the Contact normal penalty factor expression located? Good luck Hello everyone, How does COMSOL use the penalty factor when the penalty method is being used? Ahmad, Hi Ahmad, The mesh is also far to coarse, COMSOL does not assume any legal liability for the accuracy of the data disclosed. The default is 0.005. There is good COMSOL documentation on the penalty contact method in the Contact Analysis of a Snap Hook Using a Penalty Formulation page. My guess is that on contact, the stress changes . By using Matlab a "perturbed" geometry is generated, by using a morphing mesh approach. Thanks again But there is penetration. I have a model that contains an elastic beam that when deflected comes in contact with two different hyperelastic materials one on each side. 1. when handling contact pairs, the weak of constraint could make the solution not so stable (the stiffness matrix becomes ill-conditioned). Sat in the stand at Turf Moor (Burnley FC) watching a Premiership football match on a freezing December afternoon. . If one part is significantly stiffer than the others, its deflections will be relatively negligible, and it can often be considered as rigid. --, Hi Remi, Any help would be greatly appreciated! Any advices will be helpful and appreciate! Concerning about constraints before in contact between two parts, I already test each part is fully constraint or not. : "perturbed" parts are like-real parts which may come from forming processes and are used in automobile applications. [/QUOTE], Hi Sharon, 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. Ahmad, Hi Marjan and , Pasquale Penalty contact adds stiff springs (penalty factor) between the contacting surfaces that are only active when the surfaces overlap. Posted May 21, 2013, 9:28 p.m. GMT+2 This article contains guidance for solving models that include structural contact, and the procedures that should be followed to achieve a converged solution. Below the material icon, you have main solid mechanics (where there is sound waves and). listed if standards is not an option). Then you can try reducing the nonlinearity of the model (temporarily) by applying a smaller load, removing or reducing friction if you have any. Thanks again :). In COMSOL Multiphysics, there are two possible methods for solving contact problems: the penalty method and the augmented Lagrangian method. Add a Contact feature within the Solid Mechanics interface. Marjan. Thanks for your attention! When using the augmented Lagrangian formulation, it is necessary to manually scale the variables in a contact problem. Why does it have . a penalty term to suppress the false solutions, a well known problem in nite element formu- . The fillet radius can be very small, and that surface will need to be meshed quite finely. The destination boundary of the contact pair must be meshed finer than the source boundary, by at least a factor of two. Hello Remi, Would you please help me to find it? A pioneer in chemistry, sanitary engineering, and human ecology, Ellen Swallow Richards paved the way for women in science. Dear Comsol users, I noticed that for decohesive settings tag, there is a parameter called shape factor when multi-linear seperation is selected. 'Penalty, Dynamic' is selected as the contact method. The iteration part was also a big question mark that now is clear. However the discritization of displacement is always higher. We will leave this thread up for historical purposes but will lock the thread for further comments. If you needed any clarification about the model components please let me know. I completely agree with the previous post. Nagi Elabbasi COMSOL document says For your application, I think you have to: 1. define contact pair2. Penalty methods are easier to program, but suffer from numerical instability: the ideal penalty is infinite, but then you. hi, 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. 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. Adjust it to linear. All contact pairs, both manually and automatically created, are defined at: Component > Definitions > Contact Pairs. Prodotti consigliati Scarica i file del modello How does COMSOL Multiphysics handle complex-valued numbers and problems in the frequency domain? 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. Thanks for the quick replay. Your internet explorer is in compatibility mode and may not be displaying the website correctly. May be it is just because visualize problem, but it looks like two domains penetrate each other. Where is the contact pressure variable and also I can't find the Lagrangian solver option in order to deselect it. As you suggest, the penalty method is more stable than the lagrange one and thus the automatic procedure may be performed with few problems by using a penalty function. I also would recommend that you attach your model. the scale of dependent variables for example. If you have to modify the solver sequence, this separate segregated group should still be kept, and solved for after the displacements. It works well. I'd like to solve the contact problem without calculating the pressure at contact pair interface (I have disabled the augmented lagrangian solver). Using a penalty function for contact problem is good alternative of the augmented Lagrangian method available in the structural mechanics module. and similarly in any other directions that need to be restrained. This contact algorithm is based on the penalty factor formulation related to the penetration of the solid parts in contact. Hello, Remi! Hi dear Sungho, But in my case one of the two contact surfaces was a static, stiff, perfect plane so defining the force equation was trivial. where k is a stiffness constant in the order of the stiffness of the material. listed if standards is not an option). In parametric sweep for every parameter the solver solves the problem from beginning but in extension, the previous results is the answer for next step. I changed pairs to contact pair, but still have penetration. As you suggest, the penalty method is more stable than the lagrange one and thus the automatic procedure may be performed with few problems by using a penalty function. Discussion Closed This discussion was created more than 6 months ago and has been closed. 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. If you must model a domain that is initially unconstrained, add a Spring Foundation feature to these unconstrained, deformable, domains (or to the boundaries of these domains.) To use such a method in COMSOL you just need to replace the Contact normal penalty factor expression in the contact pair by the following expression : k/h No matter how I change the contact parameters (i.e. I am not quite sure if what I found and change is the one that you meant. I am modeling a transient contact problem using the penalty method instead of the augmented Lagrangian method. If you have a specific problem, please post much more details, so I can better understand your problem. Solution Number: 1292 Applies to: COMSOL Model Manager, COMSOL Multiphysics, COMSOL Server Versions: All versions. Please someone answer me and correct the error, i'm new of software. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version I know the ugmented Lagrangian method and the penalty method are different. I also am trying to simulate contact between stent device and blood vessel. In this way you are modifing the default boundary constraint equation. I am using comsol 4.2 to simulate a contact problem. I am trying to get what exactly u meant by the order of the discritization and where I can change it. Ahamad, Hi Ahmad, Have you set your constraints in a good way? Discussion Locked This discussion was locked by a forum moderator. Thanks again How can I set the penalty factor value when the lagrangian solver is disabled? I find it also useful in some problems to remove the iteration part of the expression (min(1e-3*5^segiter, 1)). [QUOTE] The model is attached below. During her career, she developed standards for water quality and. . Within the Contact Pair definition, choose the stiffer part as the source. Kindly, find attached two models of my work. thanks for your fast reply! This will automatically create Contact Pairs between mating boundaries of objects. Marjan. For example, the screenshot below shows RampFactor starting at a value of 0.001 and then increasing from 0.1 to 1 in increments of 0.1. Use the Swap source and destination button for this. Ahmad, Hi everyone The lower penalty usually leads to faster convergence, but more interpenetration between the surfaces, which is a deviation from the exact contact constraints. Friction usually only causes minor local effects, and friction coefficients are difficult to obtain with any accuracy, so this simplification is practically justified. In some cases, this approach can result in faster computations and provide smoother convergence when compared to the Augmented Lagrangian method. This is described very nicely in the Structural Mechanics User's Guide. Pasquale: I didn't look at your file. I have set the stiffness value equal to the young's modulus (I have assumed an isotropic elastic material). Note: This discussion is about an older version of the COMSOLMultiphysics software. 3 Replies, Please login with a confirmed email address before reporting spam. In the help file, it said:"Note that in the augmented Lagrangian method, the value of the penalty factor does not affect the accuracy of the final solutin, like it does in the penalty method". 2009 ., 02:50 GMT-4 Structural Mechanics & Thermal Stresses 27 Replies Contact Pressure evaluation in a contact mechanics problem. I hope at least I can give you some idea. Sorry again I am really new to the 4.1 version of the software. Posted 24 . Ahmad Atieh, hi, 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. 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. Good luck 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. When using the augmented Lagrangian formulation there is a Penalty Factor that controls how hard the interface surface is during the iterations, but does not directly affect the converged results. Thanks alot. honestly do not know what to do with the model, and I have very important dead line in two weeks. I made my best to use mechanical properties in simulation similar to the properties of the real components, including the friction constants even. Posted Nov 16, 2012, 4:13 p.m. EST Could not obtain license for COMSOL Multiphysics GUI. P.S. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version The penalty method is a stiff approximation of hard contact. The second part of the Pn expression (min(1e-3*5^segiter, 1)) is an iteration dependent term that reduces the severity of the contact condition by using a lower penalty parameter in the first few iterations . 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 . There are many reasons why contact problems do not converge. However, once I included the denpendence of the expansion rate on the stress, the contact part of the problem simply could not converge. Any help will be appreciated. For example the contact pair model is very sensitive to meshing. And the contact surfaces are defined as contact pairs. Pasquale Quality Factor of Axisymmetric Resonators in COMSOL M. Imran Cheema, and Andrew G. Kirk 1 1 . Thus, question are: is there a way to solve the contact problem without calculate the pressure field at the coontact interface? Have you try to use conact pair in an analysis with two types of physics? As long as your mesh is not moving, use extension instead of parametric sweep. MEMS & Nanotechnology, Piezoelectric Devices, Geometry, Modeling Tools & Definitions, Structural Mechanics, Understanding the Different Elements of Gear Modeling, Analyzing Reverse Electrodialysis Units with Multiphysics Modeling. Use the default suggested direct solver rather than the iterative solver whenever possible. Yours, Any trademarks referenced in this document are the property of their respective owners. Until now I didn't get any good results, all case I got convergence errors. As surfaces come in and out of contact, load paths and stress states will abruptly change. It is better to have a Prescribed Displacement constraint on all domains that will come into contact in the model. I mean it is very sensitive to the problem definition e.g. Hoping this help, regards. Structural Mechanics You do not need to start with the two objects not in contact. I tried to use your suggestion "penalty method". Build & Customize Your Car With Ultra Wheel Car Builder! I think all this is due to the penalty factor assignment. I understand how it is used in the augmented Lagrangian method. 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). To start a new discussion with a link back to this one, click here. [QUOTE] par Bridget Paulus. I am trying to find where I can play with the linear mesh (linear discretization both for displacement and contact pressure) at the beginning.
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