Tilted Electrodes on Composite Rotor Eliminate Axial Strain
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Solution Overview
Problem
The design of electrostatic generator/motor rotor electrodes on the outer surface of a fiber composite rotor faces challenges due to high centrifugal forces, leading to axial contraction and potential failure from metal fatigue or adhesive bond failure, as the rotor expands and contracts.
Innovation Solution
The electrodes are mounted at a slight tilt angle to eliminate axial contraction and expansion effects, and an elastomeric backing layer is used to manage tensional stresses, with the specific tipping angle calculated to be 25 degrees for a S-glass/epoxy composite, and the electrodes can be formed as planar stacks of thin metal wires or aluminum foil strips with rounded edges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the electrodes are mounted aligned with the axis on the outer surface of the rotor, then the electrode configuration is simple and easy to manufacture, but the electrodes experience axial compression from Poisson Ratio effects that leads to buckling, metal fatigue, or adhesive bond failure
Solution Approach 1:
The patent applies asymmetry by mounting the foil electrodes at a specific non-zero angle (beta) relative to the radial direction, rather than aligned with the axis. This asymmetric mounting angle transforms the stress distribution so that the electrodes experience tensional stresses parallel to their length instead of axial compression, preventing buckling and adhesive failure while maintaining manufacturing feasibility
Solution Approach 2:
The patent changes the mounting angle parameter (beta) of the electrodes relative to the radial direction. By optimizing this angular parameter, the design transforms the stress state from compressive to tensile, eliminating the harmful axial compression effects caused by Poisson Ratio during rotor spin-up and spin-down cycles
2Power
If the rotor operates at high speeds to achieve high power output, then the power generation capability increases, but the centrifugal forces cause significant axial contraction and circumferential expansion that distorts the electrodes
Solution Approach 1:
The asymmetric mounting angle beta compensates for the geometric distortion caused by high-speed rotation. The specific angle transforms the coupled axial-circumferential deformation into a stress state that tensions the electrodes parallel to their length, maintaining their geometric stability and preventing distortion even at high centrifugal forces
Solution Approach 2:
By changing the mounting angle parameter beta, the patent transforms the electrode response to centrifugal forces. The optimized angle ensures that during high-speed operation, the electrodes experience beneficial tensile stresses rather than harmful compressive stresses, maintaining their structural integrity and geometric stability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration prevents buckling and adhesive failure, ensuring the electrodes remain stable and functional over decades-long operation by eliminating axial strain and managing stress within acceptable limits, thus enhancing the durability and reliability of the EMB system.
Implementation Method 1
the centrifugal radial acceleration force is of order 200,000 g. As a result of that force, the outer radius of the rotor will expand of order 2 to 3 centimeters
Implementation Method 2
as predicted by the value of the Poisson Ratio for the composite, it will contract in axial length by a comparable amount
Implementation Method 3
If the foil conducting strips are mounted with a slight tilt in angle, the electrodes will experience no axial contraction or expansion effects as the rotor spins up or slows down
Data Source
AI summary
Electrostatic generator electrodes mounted on the outer surface of a fiber-composite rotor. The conducting strips are mounted with a slight tilt in angle such that the electrodes will experience no tension or compression effects as the rotor spins up or slows down. The compression would come about from effects associated with the Poisson Ratio. This change can eliminate any metal fatigue or loss of bonding that might have arisen if the electrodes were to be aligned with the axis.