Nastran In-CAD 101: Element Types | Autodesk Virtual Academy

good morning everyone and welcome to today's Autodesk Virtual Academy session I'm Nigel and byuk application engineer here at Khateeb and your host for today and all days today I'm joined by Nikhil Venkat so he's an application engineer here on our team mainly working with our post sales team doing a lot of data management stuff but where he really shines is in simulation both in you know mechanical simulation and CFD right but today we're gonna be going into an asteroid and CAD if you don't already know those of you who do have the product design and manufacturing collection already own that random CAD so that might be a tool that you know you might have access to but you don't have it installed yet if you wonder if you do have it or not you have some questions on how to get that on your machine definitely reach out to us let us know and I'll make sure that I get one of my teammates excuse me to help you get that on your system as soon as possible today Nikhil is going to be talking about element types in that writing Kent so one of the options in any finite element software just about any finite element software are the types of elements you use I'm gonna kill is gonna go over the different types of elements what kind of use cases you use them for and just how to get the most accurate results by using you know the right elements at the right time so first of all I just want to talk about myself a little bit I am an applications engineer here at Eve I have I'm the newest member of the team here so I won't even here a few weeks I'm from Bangalore India India Silicon Valley and I in 2014 I moved to Florida to pursue a master's degree at the University of Florida Jeff so nobody gets us confused with that other school I'm new to Qatif but I have been in the industry for a while about a couple years um my focus has been simulation throughout and I'm a certified ordered a simulation expert so this actually mentioned we're gonna talk about element type strain a strain and CAD and this is just a quick outline just a little bit of an introduction on what element types what elements are in general why we need them we use them the types of different elements that we have in a strand a seanandkat how the program perceives these elements and puts them together into what they call idealize ations and then we'll do a couple of quick demonstrations and then wrap that up with a summary and a quick Q&A session now most of us are aware of the traditional product development process marketing designing testing validation production the concept of simulation in in general is meant to shorten the testing phase it allows you to explore design options early in the design cycle before expensive prototypes are created and tested now in order to create and calculate and compute displacements and stresses and strains or any other results that that may be of interest the FE a process the finite element analysis process can be used to obtain these desired results so the process begins by breaking down your CAD model into small building blocks into a series of finite elements and these as you can see here are the elements now these known as Shannon cats gonna take this CAD geometry for you and it can create a mesh a mesh is just an interlocking of these elements a mesh for you now these elements are connected to each other at at points called nodes and it is at these nodes that note that loads and constraints of any kind whether they be structural or thermal it's at these nodes that they get applied now why is there such a big focus on on elements and mesh why is the type of mesh and the size of mesh important now this little plot shows the effect of the mesh on the von mises stress had an area of stress concentration mash number three is consider has considerably more elements than mesh number one and as we can see the change in the value in the actual final result is sizable because especially between mesh one when you look from mesh 1 to mesh 3 it's almost double and this is because the number of points that are present to one represent the geometry into to calculate these results at these points a stress concentration these areas of stress concentration has greatly increased from mesh one to mesh three now in general as a general rule of thumb a higher element count is gonna need to create a solution accuracy in most problems however refining the mesh beyond a certain point leads to very small if any King isn't solution this convergence is one of the primary means of actually verifying the results of an FAA study and we'll we'll look at that in in short you can control the mesh to lead the convergence by reducing the element size and in conjunction monitoring the changes in the results now models with certain complex elements tend to converge with smaller element count than than others but the time and resources associated with these complex problems may sometimes be prohibitive so most FAA studies at the end of the day require us the analyst to strike fine balance between analysis time the cost to run the analysis and the desired accuracy now let's look at the different types of finite elements that we have in Nastran and CAD now the simplest element is a line made of two nodes we have that it's called a 1d element there are three types of line elements supported by an Astra and can buzz beams and pipes and you can also have an axial preload on the is on these elements now to define the geometry of cross-section for a beam element is gonna require several several properties several cross sectional properties now the input this this data you can either put that in from empirical data of what recommended is that you use the inbuilt element library which has a lot of preset standard sizes that you can just pick and it's it's going to populate every property that's that you need for you [Music] to the elements are typically surface elements with triangle or quadrilateral shapes as their basic shapes anyway these surface elements can have either regular shapes or irregular shapes in the model itself and the they're often used for 2d elasticity problems since they account for plane stress and plane strain now the product of main the fundamental property of a shell element is the actual thickness you can sign this thickness property to geometric surfaces a geometric solids depending on what your model requires now 3d elements of solid elements are usually used to mesh volumes most 3d solid elements only account for translational displacements and this is something to keep in mind so the choice of element is very important when using solid elements the geometry is entirely described by the geometry of the CAD model now nasha in CAD has tetrahedral elements used a toroidal elements and there are two types of those linear and parabolic linear tetrahedron tetrahedrons are mathematically stiff so it's best to use these only for trench studies where the absolute results are not nearly as important as the relative changes in the results parabolic elements are much more suitable and much better general-purpose elements that can be used for most of most applications now Nashville in CAD terms the mesh itself as an idealization so essentially this comes from the fact that we are idealizing the geometry to look like these preset standard elements now for those of you that may have used the software we actually have we can set up different kinds of elements and different materials doing completely different things performing differently in the same model and you just have to create a different idealization for for each type right so for a complex model for example it can have solid elements it could have an area that that requires shell elements and it could have components that require beam elements so you can use all of these in conjunction and the idea is to be able to convert the 3d CAD model into the best possible finite element mesh let's jump into the actual program real quick right so this is a simple railing really simple simple analysis now this was created using in met the frame generators so this comes in this i-beam idealizations are automatically created for us but if we didn't want to create a new one you go into idealizations select your type of elements so for this we're gonna use line elements so you can select beam pipe let's say power for this one select a material and if the o material doesn't show up here you can always add it to the list oops you always add it to the list by selecting a material here [Music] so for this one if we consider let's say being one then we see that this this this structure is represented by a bar element and the reason we're using a bar element instead of beam element is that we're not subjecting this to actual bending so beam elements are allowed to bend bar bar elements typically are not now for this particular instance this was used this was created using frame generator the properties come in from inventor so all your cross-section property is already in here but if you didn't have that if you didn't have those properties to begin with then you can select cross-section and you have different kinds of dimensions different shapes that you can use different channels so you will have to put in put in these properties so I do have an analysis setup already now our mesh settings here we're going to use an absolute mesh size of 1 we're going to use parabolic elements because as we discussed these are good general-purpose elements now I can also go into settings mess with the tolerances on here so let's just say I use the tolerance of 0.01 I can't generate mesh and you'll see those different colors so if I just hit my actual model this is our mesh of bars and beam elements and the colors here represent the colors they correlate with the colors in your idealizations so mesh is quite fine loads are applied on the nodes constraints as well so that's all we we need we can also add one more load of you like that's going to be gravitational force so FY o minus three hundred and eighty six point four right so this here shows you let gravity is acting as well so we get to learn now NASA in can also is really really quick at solving problems now these notice how your results are in terms of bar stresses not necessarily himself in terms of one meeting stresses solid one we see stresses but this actually behaves now as a series of bars and beams now the next model that I have is this little channel here so I'm going to jump into an Astra and Kevin if you new to the program itself and the way you would get in from inventor is it's an environment within inventor so just go into the environments tab no open a stranded cat so I'm gonna use a linear static model for this as well and notice we don't have an idealization here so sometimes that can happen so we want to create one right now this is a really thin element it's a really thin component rather so we want to make sure we use shell elements and this is when you would use them when you have a thin-walled component that needs a thickness but you don't necessarily want to be modeling that as a as a solid so I can select associated geometry and select different components of the geometry in case I want different elements but if I don't select this then these settings are going to be applied to everything to the complete geometry so I want to use a thickness of 0.125 inches and this is just gonna be a standard thickness okay notice I didn't select a material here so I'm just going to pick something simple alloy steel net so there we go so amitiel populates here and we can we can now select back in the drop-down menu now we're going in to actually set this up so it's going to be fairly simple I won't be selecting edges it's those two holes there I also want us I want to apply constraints on this end as well I want to constrain the motion of of these edges and make sure that the only way it's constrained is that it cannot translate in the y-direction I'm also gonna apply loads to the same three edges same side of it it's gonna be enforced motion actually so I'm just going to displace this upwards by 0.01 inches so now then we can go ahead create a standard mesh a default mesh because and the way we you verify whether your mesh is OK or not is you look at these areas of high stress concentration right this doesn't look like a particularly good mesh because the elements that we have here doesn't exactly represent don't exactly represent a circle so instead we can go into our mesh settings I'm gonna change my element size to something smaller 0.10 and just an update that mesh okay that's slightly better now you have all of our information then so we should be good to run and just keep note to that I know it seems pretty self-explanatory but the more elements you have the smaller you make those elements the longer it's gonna take to calculate this so you could get like infinitesimally small but your computer might not be a huge fan of that the cool thing is is we're actually running in CAD right now on some laptops we're not even running on like super-powerful desktops so just note that even our not super stellar laptops can run simulation like this so you don't necessarily need a supercomputer anymore to be able to run advanced the analysis yeah so that was a pretty even though we had a fairly fine element mesh that didn't take very long to run so that sounds actually really powerful in that sense I can also solve a bunch of different element types problem types so just as with the 1d elements where our results were all in terms of bars bar stress and bar one is his person bar displacements he'll be looking at the shell itself so depending on the type of elements you use here the assumptions you make are going to be different because this is clearly an approximation of the actual physical problem that you're required to solve so depending on on what kind of problem you're solving what elements you use the assumptions you make will have to be different and those assumptions will have to be factored in to your final results as well now one of the things that I did want to show you here is is invisible and one other thing that I wanted to show you was the actual mesh conversion factor now we know this is a good mesh because if you look at the mesh convergence error the highest the maximum error here is about 0.4% so that's okay for for an first solution error so this is how this is your preliminary way to verify and validate your results from a simulation as as you look at the mesh and you see if there's anything you can do to actually improve upon the accuracy of those solutions my last model that I have who you guys is a solid model this is really simple it's just it's a regular beam with a hole through one end of it the loading end of it so again this is already in national intent and this is how the problem comes into nash fanon CAD from your CAD software especially for solids typically an idealization gets created automatically cool hold aspire pavetta real quick um while he's doing that all that's there a couple of questions while the kill blew up as a veteran could double kill but uh since our a couple of questions here can we import assemblies for analysis yes you can't import anything from an inventor for analysis just curious as to what you need to bring in if it's the whole assembly per se and then the second one is there's an Astra in CAD make use of multi-core capability the kill cancer that in about five seconds while you're hitting the open on this file multi-core capability yes and no that's the five-second answer there you go okay that's gonna require much deeper discussion definitely so Ian if you definitely want to talk a little bit about that being able to use multi core capabilities on your CPUs definitely reach out to us we can take care of that sona kills got this guy open almost awesome and so the kill mentioned earlier that if you open your inventor and then you hit that environments tab and then you hit Natura and Kent from there if you don't have natural in CAD in that list it could be one of two things it could be you haven't installed it in which case you need to install it or it's not the Adhan is not loaded and essentially you just go into your add-ins there's big list of checkboxes and then you just make sure you hit the check box for an Astra in CAD so that gets loaded okay so thanks for answering those questions yep so this is how it comes in I mean click it now so thank goodness for that but this is how it comes in a solid idealization gets treated automatically and if you don't have a material already set up in Inventor then it comes in as you noted so you only have to go in and change that material but if you yeah if you do have an inverter see you assigned 6061 aluminum to that in Inventor in your modeling environment it'll bring it over which is like kind of awesome yeah so for this I'm just going to choose a me to you I will take 6061 aluminum because Nigel seems to like that so and the color here is just to represent your actual mesh so there's a really simple problem just a very simple bending problem so our big fix this end apply a load on this end say - 5,000 and - just represents that it's in the negative y-direction and I'm going to create generate a mesh so look at my settings I think I can reduce the element size a little bit turn that to 1.5 generate that make sure yet right now no matter what I do though if you look actually let's make this more visible right so if you notice this still doesn't accurately represent the geometry the actual geometry the meshes they seem to be nodes inside the soul which is not what we want so when you have areas of stress concentration like this one you want to one of the settings that you want to turn on is go to Mir in into your mesh settings hit the Settings button and project mid side nodes just check that box hit OK and generate the mesh again and that suddenly looks a lot better now so I didn't change anything else but when you have these these areas you know holes fill it you want to make sure sharp corners you want to make sure that you turn on project mid side nodes it's just a quick quick tip thing so recipe looks good should be good to run all right so this the profile looks exactly like what you would expect and again when you look at your final results all of your results are with respect to an actual volume so these all solid stresses and solid strains and saw the displacements definitely yeah I know we went over elements today but something equally as important if not more important than elements are the meshes they're kind of intertwined and related you know elements comprise your mesh so they're kind of intertwined in that sense I feel like doing a mesh a VA might be super important because just being able to refine the mesh in a proper way without getting too crazy in terms of like element number be very valuable so if anyone thinks that that is super valuable as much as I do definitely make note of that in things like the survey and the questions and we can make sure to prioritize something like that I know that when I first started doing simulation I think what is that almost like six or seven years ago I'll just like I've got a really awesome computer let me just make the mesh size infinitesimally small and run this thing for like 16 hours and then you get a you get an answer that's maybe like 0.5% better than the one that took you 30 minutes it's not worth it so definitely something to keep note of where to stop refining your mesh yeah well point you kind of hit that barrier of could you feedback convergence yeah so definitely keep that in mind go ahead to kill yeah and now some of these these settings in here right the mesh settings they will require much much deeper discussion so what amid side notes for example what's the difference between linear and parabolic element orders that's probably beyond the scope of this particular ABA but please reach out to us and we can have that that discussion definitely the mesh table the mesh table is I'm a fan I'm a big fan this is awesome especially if you have assembly the mesh table is awesome because you can you can edit your your meshes and your different kinds of elements and everything inside this one table and keep updating yep per each different solids if of multi use and multi body it's like assemblies the big makes it a lot easier yeah so definitely so jump straight back in here so just to summarize real quick elements in mesh affect the accuracy of of your FPS solution that one of the things that you actually have a lot of control over so you need to make sure you choosing right elements meshing it correctly to actually get to an accurate final solution nasara in CAD contains several element types that are suitable and useful for most industrial applications there's some which you know Nastran can go above and beyond in trying to predict so it's it's definitely very powerful and very robust now just a couple of couple of things to keep in mind if you are using elements already you are running analyses you want to make sure you use linear order elements for nonlinear structural analyses and it's a little hard to remember the track and keep this in mind when you're running nonlinear analyses because most of the time you're likely to a plane obtain more accurate solutions with a fine mesh of linear elements than with a coarse quadratic quadratic mesh even though the quadratic element is presumably supposed to be much more robust and much more powerful it's it's useful for certain applications but not for nonlinear structural analyses now the thing to keep in mind is when you you when you have a years of high con stress concentration high defamations you want to make sure you use quadratic elements because they tend to perform better than linear elements now again all of these you know rules of thumb and ticks and trips come with their own specific caveats but as a general rule these will be applicable so can the software analyzed non-homogeneous non isotropic materials things like composites yes the short answer is yes yes another question is can the solver be ported to run on multiple stations no I believe that is a negatory something on the roadmap is to be able to run this thing on the cloud yeah I know that's on Autodesk's roadmap I don't know when or how soon something like that is gonna come out information yeah once we do get that information that's definitely something we'll let everybody know because running CFD in the cloud is like the coolest thing ever all right this is a great question from Jake what are the main differences between master and in CAD and the built-in stress analysis tool in something like your better professional so in meta Pro is very basic it can only do linear static analysis and structural analysis you can only do linear static and modal analysis Nash fine in cat on the other hand can do a lot of stuff and one of the big ones is tell these different things like inventor has invented stress analysis has still these options so it's definitely a lot more powerful than inventor even though it sits inside mentors looks a little bit like inventor it's infinitely more powerful than inventor stress analysis definitely and in regards to in cat versus inventor the big one that I always hear is thermal people are always saying can I own thermal and inventor analysis and people used to have to get things like simulation mechanical but now that's not the case you can do some thermal analysis in nashua and CAD directly into inventor it's a great question too from Ian how can we locally refine a mesh so that's when we get into things in the mesh settings themselves yep so local refinement is right here the mesh control button so if say you wanted to use let's say you want to refine the mesh along this edge you select this edge change the element size use the number of elements whatever you want so I think it was 1.5 to begin with so I can make this 0.5 if I want to hit OK and then I can I'll have to regenerate the mesh but that's how you would do it locally yeah the other ways to do it is to make this a multi body solid yeah and then to Jim to apply a different mesh setting to that body so you would have like part one there and then you might have part two you yeah that's maybe a small cylinder around that hole yeah and then you would apply a different mesh settings to that cylinder maybe make them smaller it really depends localizing your mesh where you want to do it and there's a couple ways to do it and Nikhil showed one I mentioned another way there's probably like ten more ways to do it exactly so definitely if you have any questions about that in the future reach out to us just real quick before we end today master and CAD is literally in Kent that's why they aim cats on the end of the name - I think Kent was developed a number of years ago and they're not exactly by NASA so so it does it does come from a reputable source and it's something you can trust as you can see like that was pretty easy for Nikhil to do it's not crazy you don't need to be a full-blown analyst to be able to run some of these simulations and we like you know we like to think about that as people in the design process run analyses that aren't necessarily like that final super analysis but just to be able to get your designs better earlier right so if you're in the whole design process you're making multiple iterations of your design being able to do simple testing and something like mashra and CAD or even you know I'm done a professional some other simulation in there could help you get to a better spot so with that again thank you everybody for joining us today for for today's honor this Virtual Academy in the kill thank you for joining us both as like a team both as on Autodesk Virtual Academy today it's definitely really really thank you all for attending

Channel: KETIV Technologies

Views: 13,894

Keywords: autodesk, autodesk inventor, inventor, inventor 2018, autodesk nastran incad, simulation, help with simulation, fea model, help with fea model, finite elements, engineering, inventor simulation, computer aided design, computer aided engineering, how to nastran inCAD, how to nastran in-CAD, how to simulation, advanced simulation, thermal simulation, linear simulation, akn_include, nastran, nastran incad, nastran in-cad, in-cad simulation, ketiv academy, ketiv autodesk academy

Id: acqkxBsV_Fw

Length: 35min 31sec (2131 seconds)

Published: Thu Mar 01 2018