ENGINEERING FIRM BUILDS MODELS QUICKLY WITH PARAGEN

Bill Dennison, chief engineer for ATDAS

A thriving engineering service company is having remarkable success with a pair of Algor products designed to help build finite element models quickly. Advanced technology Design & Analytical Services, Inc. (ATDAS) is applying both the Paragen library of models and the Paragen Programming Kit to reduce the time required to develop models for its wide-ranging design practice.

Bill Dennison, chief engineer of ATDAS, has been a particularly skillful user of the Algor Paragen library, which provides ready-to-use models for Algor finite element software. More recently, Dennison has begun to use the Paragen Programmer's Kit to add his own models to those already in the Paragen library. The only technical background the kit requires, aside from fundamental engineering skills, is knowledge of a compiled programming language, Fortran, C, Pascal, or Compiled Basic, for example.

Past and Present

"Today's personal computers provide small companies with the means to perform detailed analysis of designs," Bill notes. "Algor helps make this all possible by investing time and money in developing good software at a price everyone can afford."

"However, even though using Algor's impressive pre-processors cuts the time it takes design engineers to do complex modeling, ATDAS is always trying to find a way to further speed the design process. That's why Paragen's library of basic shapes for modeling is perfect. The simple shapes can be merged for assembly into a complete model in a fraction of the time it would take to build the model from scratch."

When Algor created the Paragen Programmer's Kit, Dennison was pleased because it gave him the opportunity to use his programming skills to add his own models to those already in the Paragen library. Dennison has many years' experience using Mainframes for finite element analysis (FEA) of structures, but his chief complaint was that it took too much time to model a system having a discontinuity (such as a pressure vessel with bosses or complex bearing support structures for aircraft engines).

Dennison claims Paragen and his Paragen Programmer's Kit have made FEA modeling a "breeze". He writes new programs in Basic, then complies them in Quick Basic for use in Paragen.

Dennison has 35 years' experience in the design and analyses of aircraft gas turbine engines, large structures for industrial engines, and high-speed rotor systems. In his last eight years at Pratt & Whitney Aircraft, he was involved in developing advanced engine concepts including prop propulsion systems for speeds of Mach 0.8.

When Dennison started his consulting career with ATDAS, he purchased Algor's PC-based FEA system. "I was impressed by the people at Algor and the reasonable price of the FEA software modules. Based on my experience with Algor to date, I made the right choice," Bill explains.

Paragen in Practice

Dennison has extensive experience in rotating parts. This experience has included studying distortion effects at bearing support locations in rotating rings that support blades. Because distortions shorten bearing life, studying them is important. "Paragen made it easy for me to model turbomachinery bearing support structures," he explains. "These structures consist of a bearing housing supported by a number of aerodynamic fairings that pass radially outward and connect to the rings, thus stiffening the annular ducts."

"Structures of this type are designed for stiffness to satisfy rotor critical speed requirements. Additionally, they must carry rotor loads and endure the thermal cycling stresses of start and stop operations."

"Modeling these structures for FEA would have been extremely time consuming if it hadn't been for the simple building block modeling programs that I wrote with the Paragen Programmer's Kit.

"To begin, the flanged sections of the inner and outer ring were modeled by a ring program in which the segment's angle is variable. The program also addressed meshing provisions for adding axial stiffening ribs or bosses."

"Next, the cylindrical portion of the rings was obtained using a similar program. Here a single curved arc with angular divisions was generated for each axial station matching the mesh coordinates of the strut. The files for all the lines were merged in Algor's SuperDraw II to form the beginning of the cylinder. By adding lines to connect the line divisions and mirroring the resulting image, a cylinder case was created."

"The flanged rings were then merged with the cylinder to form a ring segment having openings whose coordinates coincided with the mesh of the strut. The modeling process was repeated for the remaining segment.

"Minimum weight is a major design goal for aircraft engines, therefore parts usually are designed to be hollow. However, there are exceptions. The aerodynamically shaped struts require solid material at the leading and trailing edges to provide axial stiffness, similar to an "I" beam, and hard point for load transfer into the segment flanges. This makes it necessary to model a strut composed of both brick and shell elements.

"I started with SuperDraw II to draw the aerodynamic outline. I changed the color of the lines that would eventually form the brick elements and made a second copy of this file. Using the 'filter' to delete lines, it was easy to obtain a file for the outline of the bricks and another for the shells. I used the Copy:Join commands in SuperDraw II to create 3-D files for each strut element.

"The majority of the structure was composed of shell elements therefore these were assembled first by merging them in SuperDraw II and then processing this assembly through the linker. The brick files were then processed through the linker. The Substruct program was used to form the entire segment assembly."