ARDS (Analysis of RotorDynamic Systems) is a public-domain computer program that simulates transient and steady-state dynamics of a rotary machine that can include as many as five interconnected flexible shafts. ARDS can be used to analyze the dynamics of such diverse machines as turbocompressors, turbopumps, gas turbines, steam turbines coupled with electric generators, power-transmission shafts, and other rotating machinery in which the flexibility of shafts is significant. Researchers at Arizona State University wrote the original version of ARDS in the FORTRAN 77 language during the early 1980s for execution on a mainframe computer. Retaining the original FORTRAN 77 language and capabilities, the code was modified into the present version, denoted ARDS-PC, for execution on personal computers. ARDS-PC is also readily convertible to a FORTRAN 90 version for personal computers.

ARDS utilizes finite-element analysis and component-mode synthesis to quickly and accurately calculate transient and steady-state rotor responses. The program includes a fourth-order Runge-Kutta integrator that uses a fixed time step specified by the user. ARDS can compute transient responses to four types of excitation: turns of entire machines about axes other than shaft axes (these turns affect rotor behavior through gyroscopic effects), variable base acceleration, variable applied forces, and suddenly applied imbalance (e.g., loss of a blade). The effects of squeeze-film dampers and dropping onto (and thus rubbing against) backup bearings and the finite stiffness of bearings (including magnetic bearings) can be included in simulations. The customary steady-state responses, including natural frequencies, critical speeds, and effect of rotor imbalance can all be calculated.

Additional functions in ARDS-PC include (1) estimating the peak response following loss of a blade without resorting to a full transient analysis; (2) calculation of sensitivity of response to input parameters; (3) formulation of optimum rotor and damper designs that are optimized in the sense that critical speeds are placed in desirable ranges or bearing loads are minimized; and (4) generation of Poincaré plots so the presence of chaotic motion can be ascertained.

ARDS-PC produces printed and plotted output. The executable code uses the full array sizes of the mainframe version and fits on a high-density floppy disc. ARDS-PC can be executed on personal computers equipped with '486 (or more capable) processors that utilize the DOS operating system with an extended memory manager.

This program was written by David P. Fleming of Glenn Research Center. For further information, access the Technical Support Package (TSP) free on-line at under the Software category.

Inquiries concerning rights for the commercial use of this invention should be addressed to

NASA Glenn Research Center
Commercial Technology Office
Attn: Steve Fedor
Mail Stop 4—8
21000 Brookpark Road
Ohio 44135.

Refer to LEW-17007.