AEROSPACE ENGINEERING IS MADE EASY WITH ALGOR SOFTWARE

Algor software was used to create and analyze the model of this bulkhead which separates the hot and cool air in a commercial jet.

The way parts and products are tested and engineered is evolving rapidly in the aerospace industry. As a basic tool for engineering analysis, finite element analysis (FEA) software has emerged as the fundamental tool for analysis and has become more flexible and easier to use over the years.

Before FEA, engineers primarily used rough hand calculations and then tested parts through destructive testing of several prototypes, which was time-consuming and costly. FEA enables mechanical engineers to test many prototypes and investigate design changes on the computer to understand how they will perform under the extreme conditions of everyday flight: turbulence, frigid temperatures, hot exhausts, vibration and forces.

FEA Aids Aerospace Industry

Formerly FEA software was difficult to operate, and even more difficult to fit into the total design and manufacturing process. But a new generation of FEA software not only overcomes these obstacles, it also more readily accommodates the way the aerospace industry tends to do business.

"It's typical for large and small aerospace companies to contract with an outside equipment supplier or original equipment manufacturer (OEM) to design and manufacture parts. The OEM then contracts with an engineering consultant to help improve the design and analyze the part," said David Dearth, president at Applied Analysis & Technology, an engineering consulting firm based in Huntington Beach, California which specializes in computer analysis and design. The company designs products for a variety of industries including aerospace (commercial, military and satellite), medical, computer peripherals, fossil fuel and nuclear power plants, and general manufacturing. Applied Analysis & Technology also provides expert witness testimony services.

The company's engineers are exposed to a diverse array of industries, products, manufacturing procedures and tools for analysis and design. "Engineering analysis needs to be provided all along the chain of vendors in the aerospace industry. Engineers from each company use a variety of FEA and CAD software. They may prefer that the FEA results be given in a particular FEA software or in one different from what we like to use. In addition, we receive models in a variety of computer-aided design and manufacturing (CAD/CAM) software formats, and we must be able to transform these models into an FEA-ready format," reports Dearth.

Easy to Use

Engineers at Applied Analysis & Technology have working knowledge of virtually all of the CAD and FEA software products on the market today. For several years, Dearth has used Algor FEA software to analyze and engineer aerospace parts because of the relative ease with which it can fit in with other computer-aided engineering products. "Algor is more hands-on intuitive and overall the easiest-to-use FEA software that I have tried. And with Algor's open architecture, it is easy to export and import Algor models to any other FEA software or to virtually any CAD system," said Dearth.

In one instance, Dearth used Algor software to perform a transient heat transfer analysis on an engine duct assembly of a high performance jet. This assembly supports the duct that carries exhaust from the engine and is a typical design found on many high performance jet engine exhaust systems. The design drawing was originally created using AutoCAD, a popular CAD software. Upon receiving the design from the contracting company, Dearth easily transformed the CAD design geometry into Algor's format to begin the finite element analysis of the duct.

CAD solid modelers typically create models with triangular elements like those presented here.

Engineers perform FEA by breaking a computer-generated CAD model down into tiny pieces called finite elements. A CAD solid model is sometimes in the shape of three-dimensional triangles called tetrahedrons. These tetrahedrons vary in size and are fairly large.

A solid mesh of regularly shaped eight-node bricks created by Algor's Houdini software from a CAD solid model. Most engineers agree that eight-node bricks are the fastest and most accurate method for FEA.

To perform FEA, the model must be substantially transformed so that it is broken down into the finite elements. These elements should be regular in size and shape and can either be in the shape of cubes, called hexahedrons, or tetrahedrons. Most engineers and current research both indicate that hexahedrons produce faster, more accurate results.

Once the model is in this FEA-ready format, the computer analyzes the part by making computations on each of the small finite elements. These computations are based on engineering theory. By analyzing each of these small parts, engineers can locate potential problem areas of the design and make the appropriate changes. The computer can also study how a part will react during operation by simulating various real-world environments.

"To perform our analysis of the duct assembly, we simulated the temperature conditions that the duct experiences during operation," said Dearth. "We started by placing the computer model of the duct at room temperature, 80 degrees Fahrenheit. Then we subjected the model to a rapid increase in temperature to 1,500 degrees Fahrenheit for 60 seconds. This drastic leap in temperature is representative of the fiery blast from the jet exhaust that the duct assembly would experience during engine start-up field usage," said Dearth.

Shown here is the design of an engine duct assembly on a high performance jet. The model was originally created using AutoCAD software and was then automatically transformed into Algor format.

Computer Simulation Saves Time and Money

After the 60 second simulated blast, engineers investigated the response of the computer model of the duct assembly as its temperature returned to room temperature. The overall purpose of the analysis was to find out whether or not the duct would weaken due to the high temperatures from the jet exhaust. When the engineers performed the analysis, the results indicated that the part, made of a heat-treated alloy called Inconel, should not weaken below acceptable limits. In fact, the results indicated that the assembly's design could be modified to reduce its size and weight.

"Because this simulation involved extreme temperatures, the cost of facilities that would physically test each design modification would have been exorbitant. To build a new prototype each time we change the design and then physically test each new model could eventually cost tens of thousands of dollars," said Dearth. "The computer simulations generated by Algor software enabled us to analyze many designs at a fraction of the cost and select the optimal design to be physically tested."

Other Aerospace Applications

Applied Analysis & Technology has also used Algor software to analyze a bulkhead in a commercial jet engine. This particular bulkhead serves as a barrier separating the cooling air from the warmer air between engine compartments. Engineers created the bulkhead's geometry using Algor software to perform a modal analysis. A modal analysis, also called a vibration or resonant vibration study, analyzes a design to estimate where natural frequencies occur. A natural frequency is a vibration that will cause the part to have a large change from its original shape if driven by an outside force at this particular frequency. If the natural frequency occurs within or near the range of operation of the jet engine, this vibration could potentially interfere with the engine's performance or shorten the life of the part. Since the bulkhead must keep the two air compartments separate, it has to fit tightly between the other engine components. If the excess vibration causes the bulkhead to move too much, it may allow air to flow through where it shouldn't.

A modal analysis also helps to determine if the life span of the part will be affected by vibration. Too much vibration can shorten the life of the part. Jet engine parts can weaken because of another form of vibration called acoustic fatigue, which occurs when a part is continuously exposed to vibrating pressure waves. "We ran the modal analysis to ensure that the bulkhead would not experience unnecessary vibration response during operation," said Dearth. "Algor's modal analyses software indicated that the part should not vibrate beyond acceptable limits."

Model Changes Made Easy

It is inevitable that different types of engineering software will be used when solving the aerospace problem in the aerospace industry, since a number of companies participate in the design of just one part. The OEM creates the three-dimensional model design using CAD software. Another company performs the analysis using FEA software. And the contracting aerospace company may want the results in another FEA format.

"Even in the simplest of circumstances, aerospace engineers will need to change the format of a model numerous times," said Michael L. Bussler, president of Algor, Inc. "In the past, to make a quality conversion from one format, engineers would have to do it by hand. The process to convert a file is not only time-consuming but is subject to human error. Both factors can raise the cost of a project."

Algor recently introduced a product called Houdini, which makes model conversion automatic. Houdini software is an interface, which automatically changes the format of the model. Houdini has 113 interface options which enable aerospace engineers to integrate completely their CAD and FEA models. Houdini's conversions include:

• From one CAD software package to another
• From one FEA software package to another
• From any CAD software package to any FEA software package
• From any FEA software package to any CAD software package

"Since Houdini automatically transforms a model from one format to another, I can easily integrate all of my models without sacrificing the quality of the model," said Dearth. "With the proliferation of CAD and FEA software on the market today, Houdini is an important tool for all engineers in the aerospace industry," said Dearth.