A Method for Experimentally Determining Rotational Mobilities

Abstract

Mobility functions involving rotational velocities and moment excitations must be determined for the prediction of the responses of certain types of structures in dynamic analyses. Previous investigators have approached the difficult task of experimentally measuring such mobilities with the use of special fixturing attached I am also grateful to Professor Emmett A. Witmer of the Department of Aeronautics and Astronautics for his aid in connection with the method of finite differences. Many thanks go to fellow student Charles Gedney for his pointers on the operation of the Acoustics and Vibration Laboratory minicomputer; to Dr. Richard Dedong of Cambridge Collaborative, Inc. for sharing some of his vibration testing experience; and to Mary Toscano for her diligence in the typing of this thesis. I owe a debt of gratitude to my employer, Westinghouse Electric Corporation, for having awarded me a B.G. Lamme Graduate Scholarship enabling me to pursue a course of study in vibration and acoustics at MIT. I am especially thankful to my wife, Jerry, and to our daughters, Julia and Allison, for the encouragement they gave me and the many hours of family time they sacrificed throughout the year of my studies at MIT.

Estimation of Rotational Degrees of Freedom by EMA and FEM Mode Shapes

“…4b), three accelerometers along x direction and three along y direction are placed at a relative distance of 20 mm. These measurements allow to calculate by central finite difference the derivative of the flexural acceleration [2,3], which provide an estimate of rotational accelerations around x and y axes.…”

“…Several techniques have been devised to estimate rotational FRFs from measurement of translational FRFs: they range from the use of T-blocks [1] to the use of finite differences [2,3]. Other techniques are aimed at directly obtaining rotational FRFs using particular transducers [4].…”

Development of a Rotation Transducer Based on Bimorph PZTS

“…Rotations can be also obtained by finite difference schemes applied to measured translations [4,5]. Although these methods proved to be efficient when selected correction algorithms are applied to the measured translations, they were in fact efficiently applied only to one-dimensional systems.…”

“…10 shows a perfect linear behaviour for curvatures ranging from 0 to 0:015 m À1 : Beyond this value a clear non-linear behaviour was observed. 4. RESULTS By using the mentioned PZTs, we checked several measurement configurations, provided the required calibration and performed curvature measurements on a number of points along a beam, from which rotations at different points were identified by interpolation techniques.…”

Application of Hybrid Frequency Domain Substructuring for Modelling an Automotive Engine Suspension

“…This would mean that unless the effect of boundary moments can be ignored (e.g., when both components are connected to each other by spherical hinges), we would not be able to compute a correct system FRF-matrix. If rdof related FRFs appear to be significant, and these FRFs cannot be measured directly, a number of methods is available to approximate them from measured translational data (Sattinger, 1980;O'Callahan et al, 1985). Errors in the experimentally derived FRFs due to offset errors in the position of the accelerometers.…”