The Monocoque Tank Analysis Spreadsheet System (MONTASS) computer program is an integrated software system that incorporates Microsoft Excel worksheet software and Visual BASIC software. MONTASS was developed to enable rapid analysis and preliminary design of structural domes and truncated sections of cones.

MONTASS performs both design and analysis functions by (1) calculating the minimum skin thicknesses needed to enable analyzed and/or designed components to withstand design temperatures and loads (as in a proof test), and then (2) running stress and buckling analyses under operational temperatures and loads. Although MONTASS was developed to analyze monocoque propellant tanks, it can also be used to analyze nonpressurized conical structures.

MONTASS can be run easily from a user-friendly, three-page interface worksheet that controls a propellant-tank-analysis software subsystem. Two other visible worksheets present information on properties of materials as functions of temperature and a table of stored fluids and densities. The user can customize the data on both of these worksheets. The MONTASS system also includes six component worksheets and two Visual BASIC functions that are ordinarily hidden from view but can easily be viewed by following directions given on the interface sheet.

Design and analysis inputs include shapes and sizes, minimum allowable skin thicknesses (constraints imposed by manufacturing or fracture mechanics), properties of fluids, safety factors, a choice of the max principle or the von Mises failure criterion, loads, and temperatures. Properties of materials are interpolated from the data base for the input temperatures specified by the user. The user can also choose to design a dome with either a constant or a tapered skin-thickness distribution.

The primary design data products from MONTASS are internal volumes, skin thicknesses, and a summary of masses. Using these data, MONTASS then performs a stress analysis for all components and a buckling analysis for truncated section of a cone. Analysis load sets can include bending moments, axial forces, ullage pressures, hydrostatic pressures, longitudinal acceleration, and rotations. Analysis data products from MONTASS are a summary of radial and vertical deflections, material-failure margins of safety for all components, and buckling margins of safety for the truncated section of a cone. If the analysis has shown that a tank can be expected to fail in buckling, then MONTASS also calculates the pressure needed to stabilize the tank.

Stand-alone components are included in MONTASS to provide users the option to run the MONTASS computational tools without using the interface that is integral to the MONTASS system. An additional Excel worksheet calculates the skin thickness of a monocoque cylinder that yields the same moment of inertia as that of a cylinder of a given thickness reinforced with integral T stiffeners.

MONTASS was developed as a Microsoft Excel v5.0a workbook program on a Power Macintosh computer. MONTASS has also been implemented on '486- and '586-class personal computers using Microsoft Excel v7.0a for Windows 95. The standard distribution medium for MONTASS is a 3.5-in. (8.89-cm), 1.44MB diskette in MS-DOS format. Power Macintosh computers can read MS-DOS-format diskettes; however, a Macintosh-formatted diskette can be made available if necessary. The documentation is available on the spreadsheets only. MONTASS was developed in 1996. The program is a copyrighted work with all copyright vested in NASA.

This program was written by P. L. Luz of Marshall Space Flight Center.

Inquiries concerning this program should be addressed to Larry Gagliano at the Center Software Release Authority at Marshall Space Flight Center (telephone 205-544-7175). MFS-31223

NASA Tech Briefs Magazine

This article first appeared in the February, 2000 issue of NASA Tech Briefs Magazine.

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