On Tuesday we posted on what I thought were the 10 coolest features in ANSYS Mechanical for R15. Now it is time to take a good look at ANSYS Mechanical APDL, or MAPDL (classic ANSYS, black window ANSYS, or my favorite: ANSYS). The developers have been very busy and added a lot of useful features, and there are a large number of “Oh Yes!” capabilities in this release that different groups of users will be very excited about. For this posting though, we are going to stay focused on the things that impact larger groups of users and/or expand capability in the code. As always, you can learn more by attending one of the many upcoming ANSYS webinars or reading the release notes in the help.
1: Rezoning Enhancements and Additions
This is my favorite change in R15, a mix of some improvements and some new capabilities. The whole idea of rezoning is that when you have a part that sees a large amount deformation, the mesh often gets very distorted. It often gets so distorted that the elements are no longer accurate and crazy strains are calculated and the element literally blows up. Or it turns inside out and generates an error in the solver.
Rezoning has been around for a while but at this release some holes are plugged and some big advances are made. The first change was a hole plug, you can now rezone areas that contain surface effect (SURF153/154) elements. It is very common to have that type of load on highly distorted geometry, so this is welcomed.
The next change was adding mesh splitting for 3D tetrahedral elements. This is used for manual rezoning with the REMESH command. It was available before with 2D elements. The 2D example from the manual shows it best:
The advantage of this approach is that the subsequent stress field that is placed upon the new mesh is already accurate at the nodes that existed for the original mesh, and are fairly accurately interpolated for the new nodes. When you read in a completely new mesh, you have to interpolate the stress field and then iterate till the stresses are accurate. This approach can be much faster.
The third and best addition is Automatic Rezoning or Mesh Nonlinear Adaptivity. This process is completely automatic and does not require the user interaction that rezoning does. Both splitting and remeshing are used. You can turn remeshing on based upon position, energy levels, or contact conditions.
Here is an example from the user manual:
And here is an example that ANSYS, Inc. is showing on the new :
2: Bolt Thread Modeling
Modeling bolt threads. Classic newby mistake right? They model threads on 37 bolts and then try and set up contact on all of them. Never goes well does it. ANSYS MAPDL has had a bolt modeling capability for some time that allows you to simulate a bolt as a cylinder with preload and everything. But what that approximation missed was the fact that the contact is at an angle that is not normal to the cylinder surface.
At R15 you can now specify your thread geometry and the contact algorithm will calculate the proper normal and contact pattern for the contact forces. Much more efficient. There is a great example in the Technology Demonstration Guide, Section 39, showing all three approaches: model the threads in the mesh, use the new contact threads, or just bond the threaded area.
Needless to say we will be doing an in-depth posting on this one in the future.
3: Mode-Superposition for Harmonic Analysis of Cyclic Structures
I started my career in turbomachinary and from day one, one of the holy grails was to be able to do a harmonic analysis using blade pressure loads from a CFD run: getting the actual stresses in the blades caused by the varying aerodynamic load as they spun around and dealt with variations caused by passing frequencies and resonance in the flow itself. It was always doable as a full 360 model on both the CFD and structural side. And you could have done it using the full method for a few releases. But now we can use cyclic symmetry and mode-superposition.
The ANSYS MAPDL side of things is released in R15. You can take your complex loading info from CFD and apply that as a load on your blades using the new /MAP pre-processor (see below), a bit of a pain to do in the past. The other big change was making it all work with modal-superposition. The grail is almost complete.
4: Arc Length
This is one of those things buried in the code that the user really doesn’t have to do anything to benefit from. If you are not familiar with the method, it is an approach used on non-linear problems using the Newton-Raphson method. Most solves use other methods, but for things like non-linear buckling it is a better method. Check out 14.12 in the Theory Reference for the math and all that.
The bottom line at R15 is that they changed the algorithm to use the Crisfield Method and to avoid Driftback. What it means to you the user is those nasty non-linear buckling problems that always seem to have a hard time converging, or that require really small steps to converge, should converge now or converge faster.
5: Mode Selection
This is another one of those advanced options that users of other solvers have been asking for in the past. When you do a modal analysis that produces a ton of modes, you often want to ignore the majority of them and focus on the few modes that are strong or that get excited. In the past you could specify a range only, and only one range. At R15 you can now select which modes to use in modal-superposition analysis. You can decide which modes to use based on the modal effective mass, the mode coefficient, or the DDAM Procedure. Or, if you have your own criteria, you can use APDL to create a table that specifies a 1 for keep, and a 0 for toss. Very handy.
6: Acoustics Enhancements
This is really not one new feature, but an overall continuation of adding functionality to the acoustics capability in ANSYS MAPDL. For decades, this capability was not really focused on advanced acoustic modeling. But over the last couple of releases we have seen added functionality that put the functionality on a par with specialty acoustics codes.
The key enhancements at R15 are:
- Frequency-dependent acoustic material properties
- Surface impedance can be frequency-dependent
- A new boundary layer impedance (BLI) model is available for visco-thermo fluids modeling
- A wider range of units are now supported for acoustics, including support for user defined units (/UNITS)
- Many enhancements for coupling acoustics with CFD for FSI
- New postprocessing commands for calculating acoustics specific information like sound power level, A-weighted sound pressure level (dBA), and return loss, and transmission loss, amongst others.
7: Shape Memory on Beam, Shell and Plane Strain
For whatever reason shape memory alloys have always fascinated me, and being able to simulate them accurately is very important for those that use the material in their products. Development has been adding more and more functionality in this area for many releases. The material has two unique properties: it is super elastic and it has a memory effect.
With R15 development rounds out the capabilities with full support for beam and shell elements, adding the memory behavior. This is important, and warrants top 10 status for me, because many of the geometries we have worked on that use Nitinol (the most common shape memory alloy) are made with wires. In the past you had to model them in 3D, now we can use beams. Faster, more accurate, etc…
8: RSTMAC to Experimental Data
Something we should all be doing more is comparing our FEA results to experimental data. One excuse we often use is that it is too hard to compare the data from a vib test to our modal analysis results. Well, that is no longer to. The RSTMAC command has been modified to not only compare to ANSYS result files, but to also read the old Universal file format for results. Yipee!
Why that format? Because back in the days when SDRC was SDRC and IDEAS was their prep/post tool, they had some awesome result comparison tools. So a lot of test software out there writes to the file that IDEAS read, the Universal file. If your software does not write to a Universal file, the key info you need is in the user manual: Basic Analysis Guide, section 184.108.40.206. and here is a link to some documentation on it.
9: Mapping Processor
It has been a long time since ANSYS, Inc. has added a new processor to ANSYS Mechanical APDL. /PREP7, /SOLVE, /POST26. So it was kind of cool to see that they are creating a new mapping processor called /MAP that will be a place for you to do load mapping. At this initial release, it maps surface pressures as a point cloud from a CFD model onto your mechanical model.
Under the hood it is actually just the algorithms used in the *MOPER APDL function. But now it is exposed in through its own set of commands so that users don’t have to script their load mapping. And it supports imaginary loading for that fancy cyclic-symmetry stuff some of us need to do. As you can imagine, this needs its own article, but here are the high points:
- Enter the processor with /MAP
- Your model must have surface effect elements (SURF154) elements paved onto the outside of where you want the pressures.
- Specify the nodes you want to map the pressures on to with the TARGET command
- You can provide pressures in a variety of formats (specified with the FTYPE command):
- CFX Transient Blade Row format is made by CFX and contains real and imaginary terms
- The standard output file from ANSYS CFDPost
- A fixed format file that has x, y, z, and pressure, and yes, you can specify the actual format in FORTRAN using the READ command
- And of course the trusty comma delimited file format: x, y, z, pressure.
- The READ command specifies some other parameters and reads in the point based pressure data.
- They have given us a PLGEOM command to view the target nodes and the point cloud on top of each other so you can see if things are aligned
- A whole slew of /PREP7 like commands to edit and move your point cloud data. Basically they are treated as nodes and you manipulate them like nodes. They are just nodes with a pressure assigned to them.
- When everything is good, use MAP to actually do the interpolation.
- View the results with PLMAP
- When you are happy, save the pressures as SFE commands using WRITEMAP
There is no GUI interface for this yet. It was put into place to support some advanced FSI modeling of turbomachinery, but it benefits all users. We hope to see more in this new module in future releases. Here is an example we were playing with at PADT:
10: Performance Enhancements, Including GPU Stuff
Last but certainly not least are the enhancements to solver performance that we have come to expect. New compilers, optimized code, and new hardware all come together to deliver better bang for your ANSYS buck. There is a ton in there, all documented in section 2.3.1 of the ANSYS, Inc. Release Notes part of the help. The highlights are:
- The sparse solver now has some sophisticated error detection for handling singular or near singular matrices. This should keep you from solving poorly constrained models, or models with really messed up elements. Do note, some models that ran in the past, maybe with a warning, will now not solve. This is a good thing since the matrices are not good
- Better domain decomposition for distributed ANSYS, especially for larger core counts.
- The subspace method has been added for solving modal analysis. It is well suited for larger problems and runs well distributed.
- Switching to the new Intel compiler has resulted in a 30% faster solve time on some problems when using Sandy Bridge Intel processors.
- Harmonic analyses solves using the full method have been improved, resulting into up to 40% improvements in solve time.
- The Intel Xeon Phi coprocessor is now supported – we have no data yet on the performance but will try and get some as soon as we can
- The latest NVIDIA Kepler GPU’s are now supported and the sparse solver has been improved again to take advanged of the Kepler GPU’s.
The hard part for me in writing this posting was picking the top 10. There are a lot of significant enhancements but few are world changing. Most improve existing technologies, provide functionality for a subset of users, or fill a hole in capability. Taken as a whole though, they show ANSYS, Inc.’s strong commitment to core technology: new elements, new material models, faster solves, expanded advanced capability, etc…
The end result is giving greater power to the user through greater depth and breadth. And in the end, isn’t this why we use ANSYS Mechanical APDL in the first place – the incredible breadth and depth of capability it offers? Scrolling back up through the images you have to admit, this is some pretty cool stuff.