NASA Engineering Directorate Reduces Time Required to Perform Engineering Calculations by a Factor of 5-10

The Engineering Directorate of the National Aeronautics and Space Administration's Lewis Research Center, located in Cleveland, Ohio, is responsible for providing design services for the rest of the 4000-employee operation. A few years ago, no task was as common within the directorate as reaching for a reference manual or handbook, searching through it to find a section that applies to the task at hand, selecting a series of formulas, generating equations and then solving them with a calculator. Recently, NASA engineers have discovered a way to dramatically reduce the time required to solve these every day problems while increasing accuracy and improving the documentation quality at the same time. A software package called The Desktop Engineer was purchased from Desktop Engineering, Woodcliff Lake, New Jersey. This package, described as a "computerized engineering handbook", incorporates solutions to over 5000 structural/mechanical engineering equations found in over 100 reference books. Now, technicians simply select the type of problem using a graphical user interface then enter the required parameters in response to prompts. Input is automatically verified by the program. The computerized handbook also makes it possible to modify a parameter and to quickly determine new results.

A common task of the Engineering Directorate is designing rakes and probes that sense temperature and pressure while extending from the body of the spacecraft. Normally the critical design parameters include sizing the bodies of cylindrical probes for aerodynamic loads and, in many situations, also determining their ability to resist vibrational loads induced during launching. In the past, the problem would be attacked by looking up the proper formulas in a handbook such as Roark & Young's "Formula for Stress and Strain" with hand calculations. On the average, 10 different iterations were required to find an appropriate design which took about two hours. Now, the calculations are performed in far less time using the flat plate and Beam modules of DE/CAASE. The engineer first uses the Geometric Section Property module to calculate the moment of inertia of the cross-section, then enters the cross-section, length of the probe, material and aerodynamic loading into the beam module. In configurations where the probe consists of a hollow airfoil, the arbitrary assembly solution of The Desktop Engineer or hand calculations is used to determine the moment. The Desktop Engineer then generates the solution. The time required to enter the data and solve the problem is several minutes for the first iteration and less than a minute for subsequent ones. Selection time is actually less than 10 seconds. Total time required for the typical solution requiring 10 iterations is about 10 minutes -- less than 10% of the time previously required.

The output provided by the program includes the bending moment at the root as well as the deflection, forces, reaction and stress. The program also provides printed documentation of all calculations which are required for our records. This analysis is sufficient for all but the most critical applications such as cases where the probe is mounted directly in front of a jet engine and thus runs the risk of damaging the engine if it should fail. In these situations, the probe is still designed as described above but after this process is completed a verification analysis is performed using MSC/NASTRAN (The MacNeal-Schwendler Corporation, Los Angeles, California). The finite element analysis typically takes one to two weeks for a single iteration therefore optimizing the design with The Desktop Engineer before using MSC/NASTRAN is critical to avoiding costly delays. In some applications, the computerized handbook is used for vibration qualification of rakes and probes. The probe is simulated as a beam and vibration loading is applied as a side load while geometry and wall thickness are sized appropriately. The program also calculates natural frequency and mode shapes. In the most critical situations, dynamic finite element analysis is used to verify vibrational performance, however, for the vast majority of cases The Desktop Engineer has been shown to provide sufficient accuracy.

A wide variety of larger components used in space experiments are designed in an analogous manner. The Desktop Engineer is used to size structural components such as housings, brackets, mechanisms, etc. A recent example is a fuel dispensing mechanism in which a stepping motor drives a syringe through a drive screw. The program was used to design the aluminum housing based on static loads due to the weight of the structure itself and vibrational bending loads experienced during launch. The housing consists of four identical cantilever legs attached to a base. All the legs are identical so only one needed to be analyzed. This type of problem was also previously analyzed with hand calculations based on Roark and Young. The four iterations which are typically required took about 40 minutes using manual methods. The problem described was analyzed, as are nearly all similar ones, with The Desktop Engineer using the Beam module in three or four minutes. The actual solution time was less than 5 seconds. In this case, verification with finite element analysis was not required but it is sometimes performed as a verification step if particular hazards are involved. In the early phases of using The Desktop Engineer, the analysis was also performed using a handbook as a verification tool. A wide variety of examples have shown almost perfect correlation.

One of the more unusual projects which was designed with the computerized engineering handbook is a linear inflatable seal which is used in a wind tunnel. This is basically an opening which can be used to traverse an instrumentation probe for testing without incurring any leakage. The Lewis Research Center Engineering Directorate has built a prototype of the device and used the computerized handbook to design the pressure test hardware, which was optimized in several iterations. Hand calculations would have taken five or six times longer than The Desktop Engineer. The inflatable seal device is featured in the November 1992 issue of NASA Tech Briefs.The Desktop Engineer is basically a computerized handbook of solutions to over 5000 structural/mechanical engineering equations found in over 100 reference books. It includes 37 modules grouped into the following categories: geometric and material properties; beams and columns; rings, arches and frames; plates, shells, and pressure vessels; cables and springs; natural frequencies; dynamics and stresses; miscellaneous; user defined modules; and utilities. Modules are self-prompting to help the user find section properties, displacement, forces, stresses, etc. The Desktop Engineer also includes a material property database and a unit conversion utility. Once the problem is defined, the program will perform the necessary calculations and solutions to provide the required output. The program operates using MS-DOS using the Windows environment and user interface as well as UNIX.