Rotatable Variable-Stiffness Magnetic Spring for Linear Resonance Tuning
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Solution Overview
Problem
Current wave energy converters (WECs) face challenges in achieving high efficiency and reliability due to limited force density and mechanical reliability issues, particularly with hydraulic and electromechanical generators, and the difficulty in creating a linear spring force-to-displacement relationship in magnetic springs.
Innovation Solution
A variable stiffness magnetic spring with a rotatable and translatable magnetic component configuration, allowing for adjustable spring constant, high force density, and long stroke length, enabling a highly linear force-to-displacement relationship across a majority of the stroke length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If hydraulic PTOs are used to achieve high force density, then force density is improved, but reliability deteriorates due to leakage hazards and maintenance requirements
Solution Approach 1:
The patent replaces hydraulic mechanical systems with a magnetic spring system that uses magnetic field interactions instead of hydraulic fluid and mechanical contact. The magnetic spring generates restoring force through magnetic attraction/repulsion between permanent magnets, eliminating hydraulic fluid leakage hazards and mechanical contact wear, thereby achieving both high force density and improved reliability
Solution Approach 2:
The patent employs adjustable stiffness magnetic springs where the spring constant can be varied by changing the magnetic configuration (e.g., air gap distance, magnet orientation). This allows optimization of the restoring force characteristics to match varying wave conditions, maintaining high force density while improving reliability through contactless operation
2Force
If electromechanical generators with mechanical gearing are used, then force density is improved, but reliability deteriorates due to mechanical contact between parts
Solution Approach 1:
The patent eliminates mechanical gearing by using a magnetic spring system where permanent magnets create the restoring force through magnetic field interactions. This contactless mechanism removes mechanical contact between parts, eliminating wear and reliability issues associated with mechanical gearing while maintaining high force density
3Reliability
If direct-drive electromagnetic generators are used to improve reliability, then reliability is improved, but force density deteriorates due to current density and magnetic saturation constraints
Solution Approach 1:
The patent uses adjustable stiffness magnetic springs that can be configured to provide optimal restoring force characteristics for different operating conditions. By adjusting the magnetic configuration (air gap, magnet strength, arrangement), the system achieves high force density without the current density and magnetic saturation constraints that limit direct-drive electromagnetic generators
Solution Approach 2:
The patent implements variable stiffness magnetic springs where the spring constant can be dynamically adjusted by changing the magnetic configuration. This allows the system to adapt to varying wave conditions and maintain optimal force density across different operating regimes, overcoming the fixed performance constraints of direct-drive generators
4Reliability
If magnetic springs are used to improve reliability, then reliability is improved, but the ability to create a linear spring force-to-displacement relationship deteriorates
Solution Approach 1:
The patent employs adjustable stiffness magnetic springs where the spring constant and force-displacement characteristics can be tuned by modifying the magnetic configuration. This allows optimization of the linearity of the force-to-displacement relationship while maintaining the reliability benefits of contactless magnetic operation
Solution Approach 2:
The patent implements variable stiffness magnetic springs that can be adjusted to provide linear force-displacement characteristics over the required operating range. By dynamically or statically adjusting the magnetic configuration, the system achieves both linearity and reliability
5Power
If WECs are designed to operate at resonance to maximize power extraction, then power extraction is improved, but adaptability deteriorates because the narrow frequency range limits operation under varying wave conditions
Solution Approach 1:
The patent implements adjustable stiffness magnetic springs where the spring constant can be varied to match the natural frequency of the WEC system to the prevailing wave frequency. This dynamic adjustment capability allows the system to maintain resonance and maximize power extraction across a broad range of wave conditions, simultaneously achieving high power extraction and adaptability
Solution Approach 2:
The patent uses variable stiffness magnetic springs that allow continuous adjustment of the system's natural frequency by changing the magnetic spring constant. This enables the WEC to track varying wave frequencies and maintain optimal power extraction under different sea states, resolving the contradiction between resonance operation and adaptability
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
The magnetic spring enhances the efficiency and reliability of WECs by providing adjustable stiffness, allowing continuous operation at resonance, reducing energy conversion costs, and increasing power extraction, while maintaining long-term mechanical reliability.
Implementation Method 1
The magnetic spring relies only on magnetic field interaction, and no current excitation
Implementation Method 2
very high magnetic force densities can be achieved
Data Source
AI summary
This disclosure presents a new type of variable stiffness magnetic spring, which can have a highly linear translational force characteristic. The variable stiffness is achieved through the rotation of a central magnet. Both positive and negative spring constants can be created. Using an analytic-based field analysis modelling technique, the operating principle and linearity characteristics of the adjustable magnetic spring are studied. The use of a magnetic spring with an adjustable negative spring constant could enable an ocean generator to continuously operate in a resonant state, thereby greatly increasing its power generation capability. The described variable stiffness spring could also be useful in other energy harvesting applications, robotic actuator applications, and/or other applications.