Hexahedral Dominant AutoMesh Generator
Navy STTR 2020.A  Topic N20AT004
NAVAIR  Ms. Donna Attick donna.attick@navy.mil
Opens: January 14, 2020  Closes: February 12, 2020 (8:00 PM ET)
N20AT004

TITLE: Hexahedral Dominant AutoMesh Generator

TECHNOLOGY AREA(S): Air
Platform, Ground/Sea Vehicles, Weapons
ACQUISITION PROGRAM: NAE
Chief Technology Office
OBJECTIVE: Develop an
automated interactive mesh generator using predominately Hexahedral Finite
Elements to support finite element analysis of naval aviation structural
components and weapons systems.
DESCRIPTION: The U.S.
Navy is accelerating its development of solutions to meet Fleet needs. As part
of this urgent need, this STTR topic provides the potential to develop several
advantages to the U.S. Navy. First, the use of hexahedral elements in finite
element processing is far more efficient than tetrahedral elements, providing
more accurate solutions, faster. Second, the use of an automated hexahedral
dominant mesh generator will decrease the time spent meshing and speed the
overall development of a solution. Currently, automated mesh generators use
tetrahedral elements for finite element analysis. This approach is
computationally intensive, because, in order to increase accuracy in the
current system, there is a need for more tetrahedral elements resulting in
increased hardware requirements or longer meshing and solution times.
Much of today’s solid finite element analysis is performed with tetrahedral
elements. Tetrahedral elements, poorly formulated mathematically, require a
high element density to obtain answers to conform to classical analysis and
benchmark solutions. Using large numbers of finite elements increases the
computational burden on the computer by n2 for a fully stored stiffness matrix.
Hexahedral elements are wellformulated showing superior performance in bending
and torsion [Ref. 1]. Fewer hexahedral elements would be needed to achieve the
same level of accuracy as a model built with tetrahedral elements. A hexahedral
automated mesh generation requires specific geometric conditions.
A software is sought to analyze the geometry and create hexahedral mapable
domains, with optional user interaction. The optional interaction should
include (but not be limited to) providing options to the user to subdivide the
geometry, optimize the number of hexahedral elements, and where necessary, use
other elements to create a complete mesh for the user to apply boundary
conditions. A graphical user interface (GUI) must allow for user inputs for
variable mesh density/element size, type of elements, order of elements, and
enforcement of topology. Ideally, the software would provide an interactive
environment for the user to create the mesh and geometric conditions desired
before applying boundary conditions. The software should be able to run on most
major operating systems; Windows 10 is preferred. Software should be able to
run on machine with 4gigabytes of random access memory using Intel i5 or
equivalent central processing units (CPU). Inputs to the software should
include, but not be limited to, generic geometry formats (e.g., Standard for
the Exchange of Product model data (STEP), Initial Graphics Exchange
Specification (IGES), Parasolids, ACIS, and Stereolithography (STL)). Outputs
from the software should be compatible with major preprocessing software
packages (e.g., FeMap, Patran, Hypermesh). This output should include NASA
Structural Analysis (NASTRAN) compatibility with the option to be human
readable.
PHASE I: Design a
geometric decomposition algorithm on basic shapes. Basic shapes include
spheres, cones, annular rings, plates with circular holes in them, and plates
with “flagpoles” extending from them. Holes and like interior features should
have elements feature aligned at their interior and in an annular ring around
them.
Demonstrate the feasibility of the algorithm. Ensure that the software design
creates the mesh using predominantly highquality featurealigned hexahedral
elements, paying particular attention to the exterior boundary, using
transition and tetrahedral elements to accommodate the remainder of the
shape(s) and result in a fully meshed component. A featurealigned element has
a face parallel to the local external boundary of the geometric entity
containing it, and adjacent faces that are as perpendicular to that face as is
allowable by the geometric definition of that component. For example, not all
faces can be orthogonal and perpendicular to a sharp corner such as the tip of
a cone.
Quality metrics should be as defined in Reference 4, with the addition that all
faces of the hex shall be mapable to a regular quadrilateral, i.e., no twisted
or degenerate faces, no “bowtie” faces.
Use the metrics for hexahedral elements as summarized in Reference 4.
The Phase I effort will include prototype plans to be developed under the Phase
II.
PHASE II: Fully develop
and demonstrate capability by importing various formats of computeraided drawing
(CAD) data to include, but not be limited to, STEP, IGES, Parasolid, STL, and
ACIS. Show the geometric decomposition algorithm on Navyprovided CAD data.
Develop the GUI to allow for geometric editing of the part to support
hexahedral elements, provide optimal solutions, and allow users to mesh
components manually.
PHASE III DUAL USE
APPLICATIONS: Perform final development and testing, and demonstrate usage with
other Finite Element Preprocessing software packages. Import finalized mesh
for preprocessing with boundary/initial conditions.
Using hexahedral meshing is one of the most mathematically efficient methods of
discretizing geometry. Automotive, Aerospace, Nuclear, and Consumer Electronic
industries will benefit from the following:
Improved solution run times/faster delivery of products.
Improved efficiency: use of CPUs, company’s tech refresh cycle can be less
frequent.
Improved efficiency: use of CPUs, company’s overall power consumption will
decrease.
REFERENCES:
1. Sjaardama, G.,
Benzley, S. E., Perry, E., Merkley, K. and Clark, K. “A Comparison of All
Hexagonal and All Tetrahedral Finite Element Meshes for Elastic and
Elastoplastic Analysis.” Brigham Young University: Provo, UT and Sandia
National Laboratories: Albuquerque, NM., January 1995.https://www.researchgate.net/publication/267259986_A_Comparison_of_All_Hexagonal_and_All_Tetrahedral_Finite_Element_Meshes_for_Elastic_and_ElastoPlastic_Analysis
2. Owens, S. J., Canann,
S. A. and Saigal, S. “Pyramid Elements for Maintaining Tetrahedra to Hexahedra
Conformability.” Sandia National Laboratories: Albuquerque, NM; Siemens:
Austin, TX; and New Jersey Institute of Technology, January 1997. https://www.researchgate.net/publication/243766119_Pyramid_Elements_for_Maintaining_Tetrahedra_to_Hexahedra_Conformability
3. Meyers, R. J.,
Tautges, T. J. and Tuchinsky, P. M. “The "HexTet" HexDominant
Meshing Algorithm as Implemented in CUBIT.” Sandia National Laboratories:
Albuquerque, NM and Argonne National Laboratory, January 1998. https://www.researchgate.net/publication/221561722_The_HexTet_HexDominant_Meshing_Algorithm_as_Implemented_in_CUBIT
4. Cubit 15.3 User Documentation, Metrics for Hexahedral Elements. https://cubit.sandia.gov/public/15.3/help_manual/WebHelp/mesh_generation/mesh_quality_assessment/hexahedral_metrics.htm
KEYWORDS: Hexahedral
Meshing; Finite Element; Automated; CAD; Preprocessing; Computational
Efficiency
