Category "Tips & Tricks"

In the FEA solver world, users come across multiple numerical schemes to solve the formulated stiffness matrix of the problem. The most popular ones among all are the implicit and explicit solvers. In Abaqus terminology they are called a standard solver and explicit solver respectively. Each of these schemes has its own merits and demerits and this blog post compares these two schemes based on several parameters.

For ease of understanding, I am avoiding the use of long and complicated mathematical equations in this post. 😉

        Implicit Scheme

From an application perspective, this scheme is primarily used for static problems that do not exhibit severe discontinuities. Let’s take an example of the simplest problem: Linear static in which any physical situation can be mathematically formulated as:

[K]{x}={F}

Here K is the stiffness matrix, x is the displacement vector and F is the load vector. The size of the matrix and vectors can vary depending on the dimensionality of the problem. For example, K can be a 6×6 matrix for a 3D continuum problem or a 3×3 matrix for a 2D structural problem. The composition of K is primarily governed by material properties. F primarily includes forces and moments at each node of the mesh. Now, to solve the above equation for x, matrix K should be inverted or inversed. After inversion, we get a displacement solution used to compute other variables, such as strains, stresses, and reaction forces.

[M]d2{x}/dt2+[C]d{x}/dt+[K]{x}={F}

The Implicit scheme is applicable to dynamic problems as well. In the above equation, M is mass matrix, C is damping matrix and the rest are as usual. This equation is defined in real time. Backward Euler time integration is used to discretize this equation in which the state of a system at a given time increment depends on the state of the system at later time increment. K matrix inversion takes place in a dynamic scenario as well because the objective is still to solve for x. Abaqus standard solver uses three different approaches to solve implicit dynamic problems: quasi static, moderate dissipation or transient fidelity. Each method is recommended for specific types of non-linear dynamic behavior. For example, the quasi static method works well in problems with severe damping.

Merits of this scheme

  • For linear problems, in which K is a constant, implicit scheme provides solution in a single increment.
  • For non-linear problems, in which K is a function of x, thereby making it necessary to solve problem in multiple increments for sake of accuracy, size of each increment can be considerably large as this scheme is unconditionally stable.

Due to these reasons, implicit scheme is preferred to simulate linear/non-linear static problems that are slow or moderate in nature with respect to time.

Demerits of this scheme […]

In today’s post, I would like to focus on Functional Modeling.

Plastic Part

I’ve always wondered why this workbench never really caught on. Speaking purely from an FM1 trigram standpoint, it comes with the MCE add-on that most people who have PLM Express have added on to their CAC (CAC+MCE).

CAC+MCE

FM1 gets you the Functional Modeling Part Workbench.

Functional Modeling Part Workbench

First let’s talk about what it was created for, which is plastic parts or parts with draft, because it could also be used for core-cavity type parts like castings. This workbench is very unique in that you do not necessarily model in a particular sequence order like you would in the Part Design workbench. Modeling in the Part Design workbench is what we would call traditional feature modeling, i.e. create a sketch then make a pad, then add some dress up features like draft, fillets, then shell it out, etc.

Feature Based Modeling

There is nothing at all wrong with modeling this way – in fact, it is how most of this work is done today! Now let’s look at what we call Functional modeling which looks at a shape and incorporates a behavior for a specific requirement. […]

Siemens PLM‘s robust FEA solver NX Nastran is offered in multiple flavors. At first, it is associated with multiple graphical user interfaces, and the right choice depends on the user’s existing inventory as well as technical resources available. There are three options to explore:

  • Basic designer-friendly solution: In this bundle, basic NX Nastran capabilities are embedded in the NX CAD environment. The environment also offers stress and frequency solution wizards that provide direction to the user throughout the workflow. This solution is primarily meant for designers who wish to perform initial FEA inquiry on simple models. Advanced solver and meshing functionalities are not available.
  • Advanced solution for analysts: This solution offers more features with more complexity, so it is not meant for novice users and requires prior understanding of FEA technology. There are two separate GUIs associated with this type of NX Nastran.
  • NX CAE based solver: This is a dedicated pre/post processor for FEA modeling that has its own look and feel. It looks different from NX CAD but it is tightly coupled with NX CAD in terms of associativity – hence any updates in the CAD model are quickly updated in the FEA model as well through synchronous technology. If required, it is possible to associate this solution with Siemens Teamcenter for simulation process management.
  • FEMAP based solver: This is yet another dedicated PC based pre/post processor from Siemens with its own look and feel. FEMAP offers a CAD neutral and solver neutral FEA environment. It is tightly coupled with the NX Nastran solver but it is also possible to generate input decks for Abaqus, ANSYS, LS-Dyna, Sinda, etc.

This explains all the possible GUI offerings for NX Nastran. Now let’s have a look at what functionalities are available within the NX Nastran solver. Veteran Nastran users know very well that various physics-based solver features of Nastran are called solution sequences and each one of those is associated with a number.

  • Solution sequence 101: This is the most popular sequence of Nastran family. It primarily offers linear static functionalities to model linear materials, including directional materials such as composites for small deformation problems. Basic contact features such as GAP elements are also included. This sequence is widely used in T&M and aerospace verticals.
  • Solution sequence 103: This is yet another popular solution sequence that extracts natural frequencies of parts and assemblies. Multiple algorithms are available for frequency extraction such as AMS and Lancoz. This sequence serves as a precursor for full-blown dynamics analysis in Nastran.
  • Solution sequence 105: This sequence offers linear buckling at the part and assembly level. A typical output is buckling factor as well as buckling eigen vector. The buckling factor is a single numerical value which is a measure of buckling force. Eigen vectors predicts the buckling shape of the structure.
  • Solution sequence 106: This sequence introduces basic non-linear static capabilities in the solution and Nastran 101 is a prerequisite for this sequence. It supports large deformations, metal plasticity as well as hyper elasticity. Large sliding contact is also available but it is preferable to limit the contact modeling to 2D models only; it is tedious to define contact between 3D surfaces in this sequence.
  • Solution sequences 108,109,111,112: All these solution sequences are used to model dynamic response of structure in which inertia as well as unbalanced forces and accelerations are taken into consideration. These solution sequences are very robust, which makes Nastran the first choice dynamic solver in the aerospace world. Sequences 108 and 111 are frequency-based, which means that inputs/outputs are provided in a frequency range specified by the user. The solution scheme can be either direct or modal. Sequences 109 and 112 are transient or time-based which means inputs/outputs are provided as a function of time and scheme can be either direct or modal.
  • Solution sequences 153, 159: These are thermal simulation sequences: 153 is steady state and 159 is transient. Each one of these takes thermal loads such as heat flux as inputs and provides temperature contours as outputs. They do not include fluid flow but can be used in conjunction with NX flow solver to simulate conjugate heat transfer flow problems.
  • Solution sequence 200: This is a structural optimizer that includes topology and shape optimization modules for linear models. An optimization solver is not an FEA solver, but works in parallel with the FEA solver at each optimization iteration, hence sequence 101 is a prerequisite for NX Nastran optimization. Topology and shape optimizations often have different objectives; topology optimization is primarily used in lightweight design saving material costs while shape optimization is used for stress homogenization and hot spot elimination.

Questions? Thoughts? Leave a comment and let me know.

Today we will continue our series on the hidden intelligence of CATIA V5.  It is important to note that I am using a standard Classic HD2 license for this series In my last post, we discussed building a catalog of parts based on a single part that has a spreadsheet that drives the parameters with part numbers.  What about features?  If CATIA V5 is powerful enough to generate entire parts based on parameters, shouldn’t it also be able to be able to generate repetitive features? For instance, take a boss feature that appears on the B-Side of a plastic part. As a leader, I would not be interested in paying my designer his rates to keep repeatedly modeling a feature that may only change slightly throughout the backside! Model smarter: make once, use many times.

To do this successfully, you must address a few things – the first being how it may change. Of course you may not anticipate all changes, but a good rule of thumb is to try to model with maximum flexibility (big slabs for surfaces, overbuild everything, pay close attention to design intent) and do not use B-reps for your design. Avoid creating and building off of features CATIA builds, meaning whenever possible build your own and pick only from the tree to link to them.  The second issue to address is – what are going to be the parametric numerical inputs to drive the design? See my first post in this series on how to set these up.  i.e. Draft Angle, Wall thickness, Outer Diameter, etc.

Finally, what are going to be the geometric inputs to drive the design?  i.e. Location point, Pull Line, Slide Line, Mating Surface, etc.  A good rule of thumb here is to limit these features to as few as possible that are needed to get the job done. Sometimes it may be beneficial to sketch all this out on paper before you build it; I suggest gathering input from all the possible parties to help you in your definition.

In the example below, I have constructed a boss. Let’s review what I did. […]

PDF Publishing

‘Nuff said.

*and there was much rejoicing*

Well, maybe I could add a little more detail. It has long been known that the PDF is the currency of visual data exchange. All too often, I work with users and organizations that have to print PDFs outside of Vault, creating an uncontrolled document. If you were using the item master (discussed by my colleague here), you could attach it to the item; however, keeping it up to date is still going to be a manual process.

Now, thanks to the #1 most requested feature being implemented, that will no longer be an issue. Vault will now publish PDFs as part of your release process (as part of a transition action in a lifecycle change). This file will be categorized differently than the native CAD file, or even the DWF visualization file. The new category is called “Design Representation,” which can then be assigned its own set of rules, properties, and lifecycles.

As of this release, we have the ability to publish 2D file formats: DWG and IDW; that means either AutoCAD based files or Inventor drawings can be published to PDF. At some point, Autodesk may need to add the 3D PDF generation that was added to Inventor recently – which, by the by, could be used to publish all of the new Model Based Definition (MBD) annotations Inventor 2018 has added. I suspect we could see 3D publishing in the next release, or even a mid-year “R2” release (if there is an “R2;” who knows at this point).

Questions, comments, and celebrations welcome.

This is Part 3 in my series on the hidden intelligence of CATIA V5. To quickly recap what we have already talked about, in my first post I discussed the importance of setting up and using parameters and formulas to capture your design intent and quickly modify things that you know are likely to change. We took those principles a bit farther in my second post and discussed the value of building a design table in those situations when you may have a design with parameters that will vary and that you want to use many times. In that case you could see that we had our rectangular tubing part and could modify its wall thickness, height, and width to make several iterations of basically any size of tubing one would ever need! You would simply keeping doing a Save as… and placing those parts in your working directory to be added into an assembly at some time (I assume).

This methodology would work fine, but today I want to focus on a very cool spin on this theory by building a catalog of your most commonly used parts which are similar enough to be captured in a single model. Using our tubing model, and picking up where we left off, we have a spreadsheet that defines the parameters that change. All we would need to do to build a catalog of each iteration of the design table is add a column to the spreadsheet named PartNumber just as I have it with no spaces in the name and then associate that to the ‘Part Number’ intrinsic parameter that is created automatically when you being a model.

Let’s get started.  I will open both the model and the spreadsheet, edit the spreadsheet with the column, and then add in some part numbers.

Part numbers added

When you save the file, the field should appear in CATIA when you click on the Associations tab. […]

When working with our customers, from time to time, we’ll get questions on why they see unexpected results in some of their searches. This typically happens when they search without wildcards (I’ll explain later). In this blog post, I hope to shed some light on what can be a confusing experience for some Vault users.

The search engine in Vault operates on a on a general computer science principle called general Tokenization. This process essentially chops up the indexed properties into chunks called tokens. When a user searches in Vault (either quick search or advanced find), the search engine will attempt to match the tokens in the search string to the tokens in the appropriate properties.  Before going further, I’ll explain how Vault does the slicing and dicing.

First, there are three categories of characters (for our purposes, at least); alpha [a-z, A-Z], numeric [0-9], and special [#^$, blank space, etc.].  Vault will parse the string and sniff out groups of characters belonging to a category.  For instance, ABC123$@# would be tokenized into 3 individual tokens:

  • ABC
  • 123
  • $@#

Again, what happened is that Vault saw the first character, A, and understood it to be an alpha character. Vault then asked “Is the next character an alpha, too?” to which the answer was yes, so the token became AB. C was then added to the initial token, as it too was an alpha character.  However, the answer was “No”, when it came to the character 1.  Vault finished its first token and began the next one, now that it sensed a different category of character. Vault continued this line of questioning with the subsequent characters.

Another example might be a file name like SS Bearing Plate-6×6.ipt. Here, we have 8 tokens:

  • SS
  • Bearing
  • Plate
  • 6
  • x
  • 6
  • ipt

Now, you may have caught the missing period. Vault will only tokenize six special characters – all others are ignored. These special special characters (sorry, had to do it) are:

  • $ (dollar sign)
  • – (dash)
  • _ (underscore)
  • @ (at symbol)
  • + (plus)
  • # (octothorpe, aka number sign)

So now where do the unexpected results come in? This usually happens when an incomplete token is used without wild cards. For example, a user wants to find a specific mounting bracket. This user then types in “mount,” expecting that to be enough. In our hypothetical Vault environment, the results would return “Fan mount.ipt” but not “Mounting bracket.ipt” like they intended. Why? Remember that Vault is trying to match exact tokens (again, without wild cards).

If the user had entered mount*, the results would return the expected “Mounting bracket.ipt” as the user intended.

Moral of the story?  Always use wild cards…always.  No, really, all the time.  For everything.

One of the first things I typically discuss with customers concerning file management is the relationship between files in their engineering data.  This is especially the case when working with data from 3D CAD systems like Autodesk Inventor. When you have Assemblies, parts, drawings, and presentations all with linked file relationships, it can be extremely challenging to manage this data without a tool that understands and maintains all the file links.  Simply renaming a single file can cause all sorts of problems if done in Windows Explorer.  Here are some of the areas where file relationships matter.

  1. Part, Assy, Drawing – As previously mentioned, 3D CAD data can be a challenge to manage.  Simply understanding where a file is used (or linked) can be tremendously helpful.
    vault-where-used

    “Where Used” within Autodesk Vault

  2. Copy Design – There is a “copy design” tool in Autodesk Vault that can make it much easier to reuse existing designs in the creation of variants based on the original.  This also reduces the amount of duplicate data in Vault because so much more is reused rather than recreated.
  3. Renaming – In many workflows, files are initially created using descriptive filenames.  These files then need to be renamed once a design is approved and will go into production.  With Inventor data, renaming files in Windows Explorer will break the links between parts, assemblies, and drawings. The files then have to be manually relinked, which can become extremely troublesome if a file was used by more than one assembly without knowing it.  When someone opened up the other assembly, the file would be missing and very difficult to locate.  Vault simply fixes all the file references whenever a file is renamed so this isn’t a problem.
  4. Moving – Files that are moved in Windows Explorer can cause the same problems as renaming, but usually because of the way Inventor uses project files. Using Autodesk Vault with a single Vault type project file eliminates many of the challenges in moving files to more relevant or common locations.
  5. Attachments – Attachments in Vault can also be tracked.  One example might be a design specification document that might apply to a whole class of components.  The design spec can be attached to the relevant designs.  If the design spec document changes, you can simply do a “where used” from it to see which files will be impacted by the specification change.

This is a second look at the hidden intelligence of CATIA V5. Our topic today will focus on the creation and use of design tables. As I talked about in my last blog post, parameters and formulas can be used to drive your design from the specification tree based on your design intent. We will continue on using the rectangular tubing part and build several variations of that tubing that can be driven from a spreadsheet.

Design Table Icon

Most of the work has been already done, and although it is not necessary to have pre-defined parameters and formulas existing, the process is faster. We will begin by again looking at the Knowledge toolbar, this time focusing on the Design Table icon.

When the command is selected, a dialog appears asking for the name of the design table and also gives you a choice on whether or not you want to use a pre existing file or create one from the current parameter values.  The differences being whether or not you have an existing spreadsheet filled out already with all the tabulated values of what changes in each iteration of the design.

Design Table Dialog

 

In our case, to show the functionality we will choose the create with current parameter values option. Once that is decided, you choose which parameters you want to be driven by the spreadsheet.  In our case, we had some already created, so we changed the filter to User parameters, chose the values that were NOT driven by formulas (INSIDE and OUTSIDE RADII) and moved them to the inserted side by highlighting and clicking the arrow.

Parameters to Insert

At this point, we have defined that we want a spreadsheet to use columns for Height, Width, and Wall Thickness based on the current values in the model as it is at this moment. When we click OK on the dialog, it will ask us where we want to save the spreadsheet. I suggest that you do this in a place where anyone who uses the model can has at least read access to (i.e. a network drive).  Note that I can also change the type of file to a .txt if I do not have access to Excel® or any other software that can edit .xls files.

Read Access Directory

 

Once this has been defined, your design table is created, linked to your 3D model, and ready to be edited to include your alternate sizes. This is confirmed by the next dialog. To add in the other sizes, simply click on the Edit table… button and your editor (Excel or Notepad) should launch and simply fill in rows with your values.

Linked and ready to edit

Once you have edited and saved the values, you can close that software and CATIA will update based on your values.

Excel Modifications

 

CATIA Updated

Now you would just pick the value set you want and click OK for the change to appear on the screen.

File Updated

At any time, you can always go to make the changes by finding the Design Table under the Relations section of the specification tree and double-clicking on it.

Design Table under Relations

As you can see, it’s pretty easy to create a design table and drive your parametric file with multiple values. The world of CATIA V5 is all about re-use of data and capturing business intelligence we already know exists in all companies.  How can we help you? Tata Technologies has helped many companies time and again.

Stay tuned for Part 3!

 

 

 

 

 

 

Autodesk Vault offers a basic environment for change management that is more flexible and useful for more situations than people realize. The change management interface in Vault appears at first glance to only include a single rigid workflow for change, but upon further investigation you will find that it can be used more broadly.  Let’s take a look:

  1. ECR, ECO, ECN – The Vault change management environment is called “Change Order List,” but that is really misleading.  Different templates can be created for many purposes and these could include Change Request (ECR), Change Order (ECO), and Change Notice (ECN) to name just a few examples.  If using more that one type in your environment, it is common to use prefixes of ECR, ECO, etc. for each template type.
  2. Release management – The change environment can be used as a formal release mechanism as well.  This might be helpful if you want multiple people to review and approve work before it is initially released.  This gives you a location to capture everyone’s comments and thoughts related to the initial release.  A template with a REL prefix is often used for this.
  3. Simple changes – The flowchart for the change environment makes it look like it must be relatively complex, but there are options to shortcut many of the steps for those with the appropriate authority.  The “submit and force approval” and “fast track approval” make it much quicker to transact and capture simple changes.
  4. Complex changes – More complex changes will often use all the steps in the default workflow, and may even go through multiple iterative loops.  This can be done by simply rejecting the approval and re-opening the change.
  5. Simple or complex with the same basic workflow – There is only one formal workflow with the various options built in.  This can be used in many scenarios, and often with different people involved (based on the change template used).  Each change template can have a different routing.  The routing determines which people are responsible for each step in the workflow.
  6. Role of the change administrator – The change administrator is responsible for determining what happens when changes are in the “Open” state. This means someone else could create a change, but the change admin acts as the gatekeeper and determines if the change is really going to be made by submitting it to have work actually done. This means change requests, change orders, approvals, and notification can really all happen as part of the same workflow if you want to keep things simple.

change-order-status

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