Simulating Reality Blog

Parallel Computing in Marc Marc supports parallelisation of both the element loops and the equation solution. They are controlled by two different mechanisms – one of them is “free”, the other requires an additional license (or FEATURE used from MSC One tokens).  Which one is most effective for a particular analysis will be the subject of another blog entry. The following sections show the two controlling options in the Mentat GUI, and then the results of a benchmark to show the speed obtained using different solvers in combination with parallelisation. Enabling Parallel Processing There are two parts to control that are displayed in Mentat: In the flowchart below, the yellow boundary show the element loops that are affected by DDM, and the green boundary show the matrix solution phase that is controlled by solvers such as Pardiso: Alternatively, to access through the solver command line: DDM via –nps run_marc option Solver via –nthread run_marc...

Hierarchical  Structure Analysis Comparing an I-beam or box section girder with a solid beam of same dimension shows that the girder is much lighter - but just as stiff. Similarly, a sandwich panel of differing core thickness, but identical skin provides equally light – but ~40 times more stiff. It turns out that making an I-Beam girder out of lots of little girders improves the efficiency further - and most likely better able to withstand impact. This is a "hierarchical" or cellular structure. The Eiffel Tower is a classic example of a 3rd degree hierarchical structure. Even with its relatively poor quality iron, it is more resource efficient than many a modern skyscraper. An attractive manufacturing route is that of bonding of layers (laminating), forming to shape and then inflating to stiffness. The layers are not bonded everywhere: on inflation, the un-joined regions separate and form internal struts or membranes (miniature honeycomb or I-beams) where the outer layer...

Just a quick reminder on some of the limitations of Linear Elastic Analyses Linear Elastic Analyses produce wrong results (to differing and variable degrees) when: Defining ν >= 0.49 to simulate the incompressibility found in elastomers. It is easily verified that the resulting stress-strain law is singular as ν approaches 0.5. If it is attempted to enforce incompressibility in an approximate manner by using a high bulk modulus, there is not only a risk of singularity, but there is also a risk of volume locking. Special techniques have to be employed to overcome the difficulties that arise as a result of the incompressibility or near incompressibility constraint When the total elastic strain at any gauss point exceeds 5% (later blog) When the rotation of ANY element exceeds 0.5 degrees Assuming an arbitrary rigid body rotation (φ) using small displacement assumptions, then φ=0.5° gives about 1% non-physical elastic strain which limits the maximum rotation to nearer 0.05 ...

Implicit Structural Solutions   Development of the finite element method began in earnest in the middle to late 1950s for airframe and structural analysis. By the late 1950s, the key concepts of stiffness matrix and element assembly existed essentially in the form used today. NASA issued a request for proposal for the development of the finite element software NASTRAN (developed by  MSC.Software) in 1965. Steady State or Static Equilibrium (ΣF = 0) Force  = Stiffness x Displacement In actual practice, inverting the stiffness matrix to solve the system of equations for displacement is highly inefficient. MSC Nastran uses a more efficient matrix decomposition procedure rather than the matrix inversion method. It is necessary to iterate the solution to be able to solve non-linear problems (using methods such as Newton-Raphson shown below, etc.) for many real-world problems. These nonlinearities can be associated with: Contact Material Behaviour ...

TIPS MSC Nastran Notepad++ Language Filter Notepad++  As a lot of us use Notepad++ for deck editing, so colleagues have created an MSC Nastran format xml language file that can be implemented to highlight keywords, comments etc. Download the file from: userDefineLang.xml To use, simply copy to your AppData/Roaming folder typically found in: C:\Users\Name\AppData\Roaming\Notepad++ By default the filetypes are set to BDF and DAT files. Or alternatively you will find it in the Language menu under NASTRAN. There is also format for Patran PCL code as well as Patran session file format. More to come!