Bidirectional torsional negative stiffness mechanism for energy balancing systems

Extreme stiffness systems due to negative stiffness elements

When an elastic object is pressed, we expect it to resist by exerting a restoring force. A reversal of this force corresponds to negative stiffness. If we combine elements with positive and negative stiffness in a composite, it is possible to achieve stiffness greater than ~or less than! that of any of the constituents. This behavior violates established bounds that tacitly assume that each pha...

Stability of Negative Stiffness Viscoelastic Systems

We analytically investigate the stability of a discrete viscoelastic system with negative stiffness elements both in the time and frequency domains. Parametric analysis was performed by tuning both the amount of negative stiffness in a standard linear solid and driving frequency. Stability conditions were derived from the analytical solutions of the differential governing equations and the Lyap...

Characterization of Torsional Stiffness in Harmonic Drive

Primarily for aerospace applications, harmonic drives (HD’s) are high-ratio, compact torque transmission systems. This mechanical transmission employs a continuous deflection wave along a non-rigid gear, the socalled ‘flexspline’, to allow gradual engagement of gear teeth. A harmonic drive also contains a wave-generator (a ball-bearing assembly with a rigid elliptical inner-race) and a circular...

Soil Structure Interaction Effects on Hysteretic Energy Demand for Stiffness Degrading Systems Built on Flexible Soil Sites

This paper aims to study the influence of soil-structure interaction on plastic energy demand spectra directly derived from the energy-balance equations of soil-shallow-foundation structure with respect to an ensemble of far-field strong ground motions obtained from Pacific Earthquake Engineering Research (PEER) database and recorded on alluvium soil. The superstructure is modeled as a single-d...

Bidirectional DC-DC Converters for Energy Storage Systems