BUD3D Analysis and Design Package

BUD3D Analysis and Design package is a general Finite Element modeling and analysis package, consisting in Femwin4.1 which is a pre-post processing interface between the Bud3D-Swept, BUD's Finite Element Analysis code, and TireMesh for pre-processing. For post-processing purpose, several programs can be used such as Ansys of FEMAP. TireMesh has also some post-processing features which can be used successfully in almost every stress strain visualization.

Femwin is an interface between the components of the package and also has the feature to export several types of files for external FEA programs (Ansys, FEMAP).

BUD3D Swept is the core of the BUD3D Analysis and Design package.
It allows computations for very large strains and displacements as shown. The convergence of the algorithm is very much improved by the highly optimized total lagrangian framework used (possibility to restart the computations with different materials, with completely different boundary conditions, with new types of loads and even with new elements).

The elements used are robust low order elements (brick, wedge, membrane and calendared ply "rebar" elements). The problem is not only set up in r, teta, z coordinates but the resolution itself is carried out in the above coordinate system. A large experience has been accumulated in using such a method over the years (never published).

One of the important advantages of the methodology results from the rim contact algorithm. The special contact algorithm converges very fast and is very robust. The foot print contact algorithm is of similar kind. Any friction law can be introduced.

Presently, the program uses a library of static material laws: Hyperelastic and elastic (isotrope/orthotrope bimodulus) with prestrains and prestresses. Again additional material laws can be easily implemented at request. A rubber viscoelasticity material law is available as a module taken from an other code.

The main advantage of the proposed approach results from the possibilities of modeling the full production cycle of the air-spring. Very important prestrains and prestresses can thus be determined.

TireMesh is a general finite element modeling program. Describing the features of BudMesh2D is not the purpose of this help. You can find additional informations about BudMesh2D in the software package's help.

Overview of BUD3D Design and Analysis Process

The basic procedure for any tire or airspring modeling is the same. The most important rule to remember with all analysis procedures is to start with as simple a model as possible and add detail if required. In practice this means that you should initially:

• Omit less significant parts or features in an assembly
  
• Simplify geometric representations
  
• Use a coarse element mesh
  
• Check solution results using basic calculations
  

Once you are confident that the initial model is reasonable then add detail and use a finer mesh if necessary. The basic modeling process is as follows:

• step 1 : Geometry modeling/import
  
• step 2 : 2D mesh , input of the materials, loads, boundary conditions, contact (BudMesh2D)
  
• step 3 : input of the master cards, 3D topology, load curves (Femwin)
  
• step 4 : finite element computation (Bud3D-swept).
  
• step 5 : generation of the post processing ansys files for Ansys 5.x (Femwin)
  
• step 6 : post-processing (Ansys 5.x)

Air-spring/tire manufacturers have to study special complexities related to how their products interact with the fittings and/or the soil. Furthermore, the industry is regulated by exacting standards and requirements. As a result, these companies spend much time running tests to ensure product integrity, safety, and effectiveness.

While testing can never be eliminated, it can be significantly reduced via the proper use of finite element techniques. Any reduction in early testing provides a sizable return later in the product development cycle. One way to do this is to perform virtual laboratory testing, which provides opportunities for innovation and gains in saving money and time on real testing.

Simulations can provide a depth of understanding that is not possible with testing alone. Not all product behavior can be seen or measured via testing, and important information about performance might be missed otherwise. Virtual prototypes can provide that information. At any point in the model, an engineer can observe the phenomena from any angle, and combine information in unique ways to provide knowledge about a system and its behavior.

Several videos have been constructed starting from the results of a full closed air-spring including extreme loading cases. Most of the features presented are not available using the traditional codes on the market. Special model not reproduced here is built near the bead region in contact with the fittings. These models are all 3D ones. They include ply/bead composites, inner/outer liner and steel/rubber auxiliary spring.

There is a possibility in modeling of gas filled cavities by automatically updating the volume dependent cavity pressure as the cavity volume change. Applications for this feature include the modeling of air-springs, tires, etc undergoing large deformation.

One aspect of this feature is that the cavity pressure can be directly applied to the structural elements forming the cavity boundary. Thus, if the cavity is completely surrounded by structural elements, no additional elements are required to model the cavity boundary. The general treatment of the fluid inside the cavity follows the CLAPEYRON law. Several loading schemes are available including reservoirs.

The most advanced part is the modeling of textile composites. Using only the traditionally measured data such as cord modulus and ply descriptions, the code generates automatically the necessary material and finite element input. All this input is made very concise/compact and is automated (for easy product optimization). Automatic adaptive mesh is available in addition to the native WINDOWS user-friendly preprocessor generated one.

To help further, the computations are auto-convergent even in the difficult extreme cases where other codes don't converge.

As an example the following files are presented (you can download the entire package zipped from this link):

Rebar (~ cord) 'vector' stresses (REBAR) for the inner/outer plies,

VON MISES stress (MISES),

Strain energy (ENERGY),

TRESCA engineering strain (TRESCA),

Displacements (DISP)

In the video files, in the left corner, one can find the axis-system allowing understanding how the model is set up. Also in parenthesis is given the highest displacement value computed. Below one finds the type of contours shown...in some cases the stress 'vectors'. In the left upper corner one can find the code name used and the type of model selected. For rebars the ply/material number (starting from 3 to 6) is given here. I addition the run information is printed out. All these computed items are very important for the designer (explanations are given during the TRAINING in particular about the unit systems used).

Further in conclusion the input and output data is presented in a new tabular easy to understand very compact 'data basis' form. Thus one can interpolate/extrapolate and compute/filter different indexes used by the designer. A very large organized data basis exists to help him. Also much information can be gained from the assembly held together by its parts and the auxiliary spring and performing like the actual product without modeling simplifications and assumptions leading to errors. The applications also include complex manufacturing steps that must be modeled in order to assemble a suspension system/tire-wheel and then actuate it to investigate its function. These factors are critical to understanding the functions of these products.

All these computed items are very important for the designer, further in conclusion the input and output data is presented in a new tabular easy to understand very compact 'data basis' form.

Full Agreement of Test and BUD3D-OFFICE computational lateral ‘load-deflection' airspring results at extreme loading. Thus one can interpolate/extrapolate and compute/filter different indexes used by the designer. A very large organized data basis exist to help him. Very much information can be gained from the assembly held together by its parts and the auxiliary spring and performing like the actual product without modeling simplifications and assumptions leading to errors.

It is possible to get a good idea of the computation accuracy (shown below) using different theta mesh refinements. For instance by an appropriate extrapolation method on gets the optimal result values as delta-theta goes to zero.

Load-deflection for 7(yellow),14(green),24(blue) and28(violet) meridians (airspring with auxiliary spring under lateral load)

Different convergence parameters = function (full ‘lateral' loading) (airspring with auxiliary spring under lateral load)

The applications also include complex manufacturing steps that must be modeled in order to assemble a suspension system/tire-wheel and then actuate it to investigate its function. These factors are critical to understanding the functions of these products.