Drilling holes in Finite Element meshes

AG Geometrische Algorithmen
Prof. Dr. Georg Umlauf

Diplomarbeit

Development and validation of a robust and fully automated algorithm for drilling holes in FE-meshes

Motivation:
Finite Element Modeling (FEM) is a widely accepted technique in design departments of car manufactures for daily analysis of noise, vibration and durability problems with car bodies and fully assembled vehicles. It basically comes down to discretizing the CAD (Computer Aided Design) models into many small elements approximating the geometry and assign properties to those elements. Different element types are used such as triangular and quadrangle shell elements for thin plate structures, beam elements and 3D solid elements. Figures 1 and 2 give an illustration of a CAD and related FE model of a front subframe of a car.

Beam, shell and solid meshers are available on the market which generate the FE mesh (nodes and elements) from a CAD model. Changes of the CAD model require repeating the meshing step, which might be a tedious and time-intensive process for complex shapes.

Therefore, in practice, not each design change/iteration is implemented on the CAD model. Engineers often prefer to directly modify the FE model for what-if analysis. Also, in some cases, only the FE model is available. So, it is of crucial importance that design engineers are able to locally modify the mesh, e.g. for connecting items such as battery, headlamps, brake booster, etc. with bolted connections. This requires drilling holes in the meshes.

Figure 1: CAD model

Figure 2: FE model

Objective:
Objective of this thesis is to develop a fully automated and robust algorithm as well as a software prototype that allows drilling holes in industrial meshes of vehicle structures, preserving high quality of the mesh (measured through a series of mesh quality indicators) and a minimal amount of additionally added elements of a user-specified size.

Questions:

Georg Umlauf, Raum 36-236, TU Kaiserslautern, umlauf@informatik.uni-kl.de.
Luc Hermans, Product Development Manager, CAE division, LMS, Leuven, Belgium.

More Details:

As input, the user specifies the center, the diameter, the number of equally spaced nodes surrounding the hole and the number of rows of quad elements surrounding the hole (see Figure 3 and 4).

Figure 3: Specificatin of the hole

Figure 4: Examples of drilled holes in a mesh

Generating the hole requires deleting existing elements, positioning new elements and stitching those to remaining elements of the FE model. In this process, it is very important that the element quality criteria are fully meet (e.g. for quad elements, the ratio of the longest diagonal over the smallest diagonal should not exceed 2, …). In case the hole can not be automatically drilled, clear diagnostic messages need to be given to the user.

The developed “hole drilling” algorithm needs to be translated into a stand-alone C++ program (possibly using shareware libraries such as e.g. OpenMesh) which reads the mesh from a simple ASCI file as well as the specifications for the holes, drills the holes and writes out a new ASCI file with a diagnostics file for those failing. The algorithm needs to be validated on several industrial vehicle models that will be provided by LMS.

The thesis will be carried out in 4 steps in close collaboration with LMS, recognized leader of predictive technologies for the critical functional disciplines such as structural integrity, acoustics, durability, and dynamic motion simulations.

The first month will be spent on-site LMS Kaiserslautern to learn more about the FE modeling ,the problem to address and industrial applications.
In the next 2 to 3 months, the algorithm and C++ program needs to be developed at University of Kaiserslautern. Regular follow-up meetings with LMS will be set up.
Months 4, 5 are focusing on validating the developed algorithm on different industrial cases and tuning the algorithm where needed. This work will be mainly carried on-site LMS Kaiserslautern.
The last month is devoted to writing the thesis (by preference, in English).

Details on LMS

LMS is the fastest-growing provider of solutions that integrate functional performance engineering into the digital development pipeline. We provide the testing systems, multidisciplinary virtual prototyping software, engineering services and collaborative engineering tools that enable our customers to turn product refinement and superior process efficiency to their strategic competitive advantage.

Through our technology, software, and people, LMS has become the partner of choice for Fortune 500 companies in the automotive, aerospace, and other advanced manufacturing industries around the world.

LMS is the recognized leader of predictive technologies for the critical functional disciplines such as structural integrity, acoustics, durability, and dynamic motion simulations. Our integrated range of solutions can handle the most sophisticated of modeling situations: the operating dynamics of high performance engines with flexing parts and clashing springs, the fatigue life of spot-welded bodies subject to multiple loads, the sound field inside a car as mount stiffnesses are varied... They use patented technologies. They are unrivalled in their accuracy. They are also very fast: seamless integration with the CAD model, automated meshing, efficient algorithms and parallel processing mean that individual simulations can often be set up and completed in hours. This means that virtual models can be tested and refined at the component, sub-assembly, and full system levels early enough in the design process to make a real difference.

More details on LMS can be found on www.lmsintl.com

Last modified: 10th February 2005