Malcolm A. Cutchins

Damping phenomena in a wire rope vibration isolation system

A study of the dynamic characteristics of a wire rope vibration isolation system constructed with helical isolators is presented. Emphasis is placed on the analytical modeling of damping mechanisms in the system. An experimental investigation is described in which the static stiffness curve, hysteresis curves, phase trajectories and frequency response curves were obtained. A semi-empirical model having non-linear stiffness, nth-power velocity damping and variable Coulomb friction damping is developed, and results are compared to experimental data. Conclusions about dynamic phenomena in the wire rope system are made on the basis of the experimental and semi-empirical results.

The effect of an arbitrarily located mass on the longitudinal vibrations of a bar

Abstract For a bar/mass assembly the vibrational effect of the mass, assumed slender in comparison with the length dimension of the bar to which it is centrally attached, is investigated for various mass positions and various mass ratios. The investigation is limited to harmonic disturbances in line with the bar and symmetry of the mass with respect to the bar centerline. The general transcendental equation is derived from which the natural frequencies may be found. The eigenfunctions describing the mode shapes are also derived. A general relationship for the ratio of the inertial force acting on the attached mass to the magnitude of a harmonic end force is developed. Some comparisons with experimental results are given which verify the derived closed form solutions. In these experiments a two foot long, 1 2 inch diameter steel bar with an attached steel block was used, with various accelerometer arrangements and an electrodynamic shaker.

Investigation of dynamic characteristics of an elastic wing model by using corrections of mass and stiffness matrices

The effects of theoretical changes in mass and stiffness matrices on the dynamic characteristics of a model wing are considered. The NASTRAN computer code is utilized to find theoretical mass and stiffness matrices with their corresponding natural frequencies and mode shapes. The dynamic response is then calculated by using theoretical mass and stiffness matrices and theoretical modal data. Experimentally measured mode shapes and natural frequencies are used to improve the stiffness and mass matrices. The resulting improved stiffness and mass matrices are further used to calculate again the dynamic response for the model. Analysis of the computational results and experimental data show that the improved theoretical model represents the experimental model better than the original theoretical model. Other means of improving the theoretical model are summarized.

COMPARISON OF METHODS FOR MODAL TESTING OF A SPACE STATION ELEMENT SIMULATOR

Verification of a dynamic model of a constrained structure requires a modal survey test of the physical structure and subsequent modification of the model to obtain the best agreement possible with test data. Constrained-boundary or fixed-base testing has historically been the most common approach for verifying constrained mathematical models, since the boundary conditions of the test article are designed to match the actual constraints in service. However, there are difficulties involved with fixed-base testing, in some cases making the approach impractical. This paper addresses some of those difficulties, and some successes, related to testing the Space Station TestBed Calibration Beam. It also includes an emphasis on the Residual Flexibility Approach.

MULTIDISCIPLINARY MATHEMATICAL MODELING WITH ADVANCED SIMULATION LANGUAGES

Abstract The increasingly important role of computer languages with powerful instructions for simulating complex mathematical operations is emphasized. Features of the Advanced Continuous Simulation Language (ACSL) are described and several examples of its use in a research and an educational environment are given. Trends toward increased hardware and software capabilities are discussed, many of them enabling us to build mathematical models on computers at increasingly sophisticated, yet more conversational, levels.

A high-rate granular material dispensing mechanism

Abstract A high-rate granule handling device is described 2 . The keys to the success of the device are three suction nozzles and a granule separation scheme. The three nozzles are arranged so that three-row seeding from an aircraft can be accomplished at near 3000 seeds/min per nozzle, or near 9000 seeds/min for the mechanism. The seeds, or granules, are 3/16-in.-diam. near-spheres when coated in a water-soluble clay coating, and emphasis is on the high-rate handling problems of the granular seeds. A theoretical analysis for predicting the exit velocites of the granules as they leave the nozzle is summarized. Good agreement with experiment is obtained. Tests and development of the device are described.