by

D.R. Henrie
Principal Engineer
General Electric Nuclear Energy

Among my primary responsibilities are the theoretical basis and methodology for the structural dynamic analysis performed by GE Nuclear Energy. Significant effort is directed to the methodology required for verifying the structural design and dynamic qualification of all safety related equipment (mechanic & electrical) required for the nuclear reactor steam supply system.

Some of the computational tools used in performing this function are advanced finite element codes such SAP4G07, MSC/NASTRAN, ANSYS, SUPERSAP and STARDYNE. In addition, hand calculations are frequently required to perform many other types of analysis which do not require finite element analysis because of the simplicity of the problems or the constraints on the time required to build a finite element model or for other reasons.

A few years ago, I began to use a software tool designed to automate the performance of a wide variety of engineering tasks which are typically performed with an engineering handbook and hand calculator. The Desktop Engineer, a computerized engineering handbook (Desktop Engineering, Woodcliff Lake, New Jersey) has significantly reduced the time it takes me to perform these tasks. For example, instead of spending 60 minutes to determine section properties of composite sections in control room panels and other equipment by hand, the task can be completed in less than 5 minutes using DE/CAASE. Likewise, with The Desktop Engineer one can calculate mode shapes and frequencies of simple structures in less than 10 minutes compared to the hours it used to take by hand calculation. For such problems, the time and dollar resources required using conventional mainframe finite element analysis are generally not justified.

The control panels and equipment in the control room of a nuclear power plant must be qualified to insure their structural integrity and operability. These structures contain a wide variety of complex sections which would not be practical to incorporate directly into a finite element model because they would significantly increase both modeling and solution time.

Standard procedure in the past was to calculate composite section properties from the section properties of the individual members by searching through a reference manual or handbook to find the sections that apply to the task at hand, selecting a series of formulas, generating equations and then solving them with a calculator. For a typical composite section, comprised of angles, channels, unistruts and rolled plate elements used in the corner posts of a control panel, the required calculations would include finding the neutral axis for each element, using the parallel axis theorem to find the neutral axis for the entire section, then calculating the moments of inertia, section areas and shear area properties which are needed to define the sectional properties of the composite section. This process typically took about an hour to calculate and verify for a typical composite section. With The Desktop Engineer, all that is essentially required is to enter the dimensions of the various sections -- the program calculates all the required section properties except for the shear areas which are readily determined from the composite section geometry. This typically takes less than 5 minutes.

Another area in which relatively large amounts of time were previously spent for hand calculations was in determining natural frequencies of simple systems. For more complicated structures, full blown finite element dynamic analyses are performed. However, for many problems, the time and cost involved cannot be justified for secondary structures. A good example of this situation might be a switch mounted on a bracket inside of a control panel. This problem used to take several hours to solve by hand if more than three degrees of freedom were required. With The Desktop Engineer, we simply enter dimensions and material properties and the program calculates the answers. The total process takes less than 10 minutes.

The ability to obtain results this quickly has made it possible to perform parametric studies which allow us to evaluate far more design alternatives than were previously possible. In many cases this has helped to increase the performance of our designs. Aside from time savings, another major advantage of the program is that it automatically provides complete documentation of all of the calculations that were performed. We need to document all of our work because of the inherent safety issues involved in nuclear industry. When we performed these types of calculations by hand we had to microfilm our calculation books which was both inconvenient and expensive.

The Desktop Engineer incorporates solutions to over 5000 structural/mechanical engineering equations found in over 100 reference books. In most cases, the program will do the equation substitutions, integration, and boundary condition analysis in exactly the way an engineer would solve the problem by hand. In some of the more complicated analyses, the computerized handbook uses finite elements to obtain a solution; however, the input and output format remains similar to the other modules and the user is not required to know finite element techniques. It includes 37 modules grouped into the following categories: geometric and material properties; beams and columns; rings, cables, arches and frames; plates, shells and pressure vessels; natural frequencies) user-defined modules; and miscellaneous. Modules are self-prompting to help the user find items like material properties and calculate section properties like area, moment of inertia, etc. In addition, several utility modules are included to assist the designer with complex problems. The program also has a convenient material property database and several modules that look at complex geometries and dynamic conditions.